Westinghouse Steam Turbines for Power Generation

Westinghouse
STEAM TURBINES
FOR
POWER GENERATION
Power Systems
Marketing Training
MA-474B
August, 1976

STEAM TURBINES
FOR
POWER GENERATION
Edited By:
B. K. Flanery
Power Systems Marketing Train i ng
August , 1976
MA-474B
Copyright 1976, by Westinghouse El ectric Corporation
Pittsburgh, Pennsylvania -- All Publicati on Rights Reserved .

STEAM TURBINES
FOR
POWER GENERATION
Reference material for this text includes the steam turbine portion of
THE STEAM TU RBIN E-GENERATOR COURSE , edited by W. J . Kleponi s , presented
by Engineers of the Steam Turbine Division of Westinghouse Electric Corporation
at the Engineers' Cl ub of Philadelphia, December, 1972:
J. Davids, C. A. Meyer, G. B. Leyland, E. A. Kauranen,
T . J . Wa ll ace , G . J . S i 1 ve s tr i , J r .
Text review by the Steam Turbine Division:
R. 0. Brown , Manager
Product Planning, Steam Turbine Division
G. J. Silvestri, Jr., Fellow Engineer
Application Project s, Steam
A. Cohen
Engineering Administrative Services
W. J. Schell, Jr.
Product Service
Pittsburgh, PA
-i-

_J
STEAM TURBINES FOR POWER GENERATION
Section
2
3
4
5
6
7
8
9
10
Contents
INTRODUCTION: Industry growth, unit sizes, heat rate improvement,
the steam fl ow cycle (nucl ear and fossil), turbine
characteristics, turbine el ement designs and combina ­
tions, the steam flow path through the major components,
exhaust fl ow and maximum loading, annulus area .. . .. .
INLET VALVES AND STEAM CHEST: Stop-throttle valves, control
valves, throttling loss, area control, pressure control,
sliding pressure, part load performance, valve operation,
valve management, valve points, locus of valve points, valve
and steam chest designs and construction . . . . . . . . . .
INLET PIPING AND NOZZLE CHAMBERS: Provisions for expansion,
partial arc admission, separate nozzle chambers .. .. .. .
HIGH AND INTERMEDIATE PRESSURE TURBINE DESIGNS: Inner and
outer cylinders, blade rings, steam flow cooling, rotor cool ­
ing, thrust ba lance, separate HP and IP designs, interstage
sealing . .. ... . .. . ... . .. ... .. . ... .
REHEAT STOP AND INTERCEPTOR VALVES: Overspeed protection,
control of valves, valve design and construction .. . ..
LOW PRESSURE TURBINE DESIGNS: Inner--Outer cylinders, interstage
sealing, thermal shield, exhaust hood diffuser, solid
rotor--build up rotor (shrunk on discs), water removal provisions
............. . . . .... ... . .
TESTING AND INSPECTION: Principal types of tests, rotor
forging manufacture and inspection, heater box test . . .
BLADING: Factors affecting performance, impulse and reaction
principles, selection of type blading, sealing arrangements,
twisted and tapered blades, erosion control and moisture removal,
shrouds and lashing wires . . . ... . .
(APPENDIX: Blading Nomenclature.)
AUXILIARY SYSTEMS: Lubrication, turning gear, gland sealing
steam system, exhaust hood sprays, supervisory instruments,
rotor grounding . ...... . .. .
APPENDIX: Glossary of turbine terms
Turbine-generator rating and performance
51
77
87
113
127
137
145
195
221
225
-iii-

STEAM TURBINES
FOR
POWER GENERATION
This training course is a component of a series which studies the Westing ­
house equipment used in power plants.
It is designed to teach the design and operating characteristics of typical
Westinghouse turbines used in electric power generation systems .
Specific cases of design philosophy or features of construction may be exclusive
in a component . Their description here is intended to illustrate
the wide range of significant factors available for which you should be
alert when preparing a presentation or an evaluation . It is essential
that you study, and discuss with Division representatives, the proposal
which is specifically prepared for your project. Only in this manner can
a meaningful analysis of product features be prepared.
Important Instructions - Please Read Carefully
This traini ng course will be most effective if you follow this simple
procedure:
1.
2.
3.
4.
Go back and re-read the unit at a comfortable pace . Sto~ when
you come to a set of study questions . Do not read beyon the
point where the study questions begin without first completing
the assignment.
Review the unit and underline (preferably with a colored pen or
pencil) the points that you think are important . Also feel free
to make notes in the margins.
Complete the study quizzes by filling in the blanks, circling the
correct answer, etc. Check each answer immediately after you
comp l ete the question - they are provided on the page following
the study questions . Do not wait until you have completed the
entire quiz before you check your individual answers .
Suggested Prerequisites
The following Westinghouse Power Systems Marketing Training courses are
suggested:
Energy, Power, Thermal Cycles and Steam Generation
Steam Turbine Cycles
Turbine Control Systems ...
MA-462
MA-463
MA-465
Skim the section to be read to get a feel for the general contents.
-v-

Figure - Trend of Unit Si ze
::i:
12000
~ 11000
~
a:
UJ
a. 10000
::>
t- m
UJ
t-
c:i:
a:
~
UJ
::i:
9000
8000
\ ~~
~
"-
~
I I '~ I '
REGENERATIVE F EDHEATING
~,
"'
~
"• ...
' ~
' -" ~
..,. RE 1EATING
...........
r--......
' " ......
l"'oo-
·-
.., """"" --- ~ :::--
BfST
1~A~T ,__~
I I I 1..........- - '-'
COMBINED CYC~ES
7000
1910
1920 19~ 1940 1950 1960 1970
YEAR
Figure 2 - Overa ll Station Heat Rate
-vi -
_J

STEAM TURBINES
SECTI ON l
Introduction
Historically in the United States, the demand for electricity has
doubled every ten years . In 1970 the power industry in t he Uni ted States
produced more than l .5 trillion kilowatt- hours of electricity in a single
year. Reliable estimates indicate that by 1985 , in l es s than 15 years , annual
production will be more than 4 trillion kilowatt-hours .
The steam turbine-generator , using steam produced by burn i ng coa l, oil
or natural gas and -- more recently - - by nuclear fission, provides about
80 per cent of the nation's generating capacity . The remainder is supplied
by hydraulic (or waterwheel) turbine-generators that use t he force
of moving water, and by gas turbines and internal combustion engines.
As available sites for additional waterwheel turbine-generators become
fewer in number, the steam turbine-generator will have to provide a
still l arger percentage of the demand for electric power . For over 70
years, it has been unparalleled as an efficient, economical and reliable
source of the major portion of the electri c energy supply .
The development of larger capacity turbine-generator un i ts is a continuous
process. Such units must provide improved thermal performance,
lower equivalent capital cost and fewer parts to maintain than woul d the
application of multiple sets of smaller ratings required to obtain t he
same total capacity.
The trend of the si ze of steam turbine generator units is shown in
Figure l . The effect of power pooling and system interconnection has
caused a continuing rapid rise in unit size and this trend is expected to
continue . Current projections indicate that maximum unit sizes wi ll reach
2000 MW by 1980 .
Overall station heat rates have improved to approximately 9100 BTU/KWH
for fossil reheat units as shown in Figure 2.
Digital computer programs and analog studies aid in performi ng the
many detailed calculations required to optimize mechanical and thermo ­
dynamic des ign of new large elements. These calculations i ncluded:
l. Determination of rotor temperature gradients.
2. Accurate determination of blade frequencies of vibration and
stresses.
3. Comparison of various rot or and blade root cooling methods.
4. Establishing temperature grad ients in bl ade roots .
- 1-

5. Calculation of rotor deflections and critical speeds .
6. Determination of rotor stress distribution including t hermal
effects .
7. Establish temperature gradients and stress distribution in inner
and outer cylinders.
8. Calculate thermal performance and thrust.
Results of these studies, along with complete design layouts and investigation
of both impulse and reaction type machines, verified that at t he
performance level required and with the large volumetric flows involved,
the reaction design was more efficient. Furthermore , the KW loading per
stage is somewhat less with the reaction design reducing the blade stress
problem.
These design studies also provide nozzle chambers, blade rings, inner
cylinder, and outer cyl inder which can expand and contract without interaction.
Severe t emperature gradients are not passed from one t o the other ,
stresses are reduced, and running seal clearances are maintained in spite
of changing operati ng conditions.
The steam turbine-generator, simple in principle, is extremely complex
to engineer and manufacture . Based on the simple principle of the windmill,
it is the most basic and powerful machine known. Although its operating
principle is comparatively simple, its design has advanced to the point
where the turbine, with i ts connected electric generator , has become the
world's most efficient electric power producer .
An installed turbine-generator may be over 200 feet in length and
weigh four or five mi llion pounds . This machine has 300,000 "fits" that
cannot vary more than a few one -thousandths of an inch . When the machine
starts up, it expands up to two and a half inches from cold to hot . Steam
at a pressure of over one t on per square inch, and at a temperature five
times that of boil ing water, enters at more than 1 ,000 miles per hour, and
in less than one second, has expended its energy to the turbine blades and
is condensed in the condenser .
The increasing cost and diminishing supplies of fuel make it imperative
that we provide an efficient plant for energy conversion, both for
economic reasons and for conservation of our energy resources .
- 3-

STEAM TURBINES
SECTION l
TURBINE DESIGNS
Introducti on : Study Questions
l . The demand for electricity in the United States has doubled every
____ years .
2. The steam turbine generator , using steam produced by burning coal , oi l,
natural gas or by nuclear fission provides about (50) (80 ) (95) per
cent of the nation's generating capacity .
3. The trend of a continuing rapid rise in unit size is caused by:
a . Power pool ing.
b. Lack of ava il ability of small er unit sizes .
c . Sys t em interconnecti ons.
d. Federa l regulations.
4. Current projections indicate that maximum un i t sizes will reach 3000
MW by 1980.
True/False .
5. The (increasing) (decreasing) cost of fuel and the (increasing) (dimini
shing) supplies of fuel make it imperative that we provide :
a . An efficient plant .
b. A larger plant .
c . A smal ler plant .
-5-

STEAM TURBINES
SECTION l
TURBINE DESIGt~S
Introduction: Answers
l. 10 years.
2. 80 per cent.
3. (a) Power pooling and (c) System interconnections are both correct.
4. False. The prediction is for unit sizes of 2000 MW.
5. Increasing - diminishing - a. An efficient plant.
-7-

TANDEM COMPOUND DOUBLE FLOW
TANDEM COMPOUND QUADRUPLE FLOW
LP
LP
TANDEM COMPOUND QUADRUPLE FLOW
GENERATOR LP LP LP DP HP
~ 8
p;
TANDEM COMPOUND SEXTUPLE FLOW
Figure 3 - Arrangement of Turbine Elements
-8-

STEAM TURBINES
SECTION 1
FOSSIL FUEL TURBINES
Turbine Characteristics
Figure 3, on the fa cing page, shows typical arrangements of high pressure
(HP) , intermediate pressure (IP), and low pressure (LP) elements.
The fossil fue l t urbine units are composed, almost exclusively, of
3, 600 rpm turbine elements. These elements are tandem compound and cover a
rating range to 960 MW with potential capability to 1200 MW .
A compl ete turbine unit consists of several turbine elements or "building
blocks" connected in tandem to drive a single generator. A common arrangement
will include a hi gh pressure (HP), an i ntermediate pressure (IP)
and low pressure (LP) building bl ocks.
An al ternate arrangement provides the HP and IP elements in a single
cylinder which results in a shorter unit length and a saving of space.
HP, IP, and LP turbines may be either "single-fl ow" or "double-fl ow"
designs, depending on the volume of steam to be passed and the availability
of designs.
A single-fl ow turbine i s one in wh i ch the total vol ume of steam enters
at one end and passes through al ternating rows of rotating and stationary
blading to the exhaust .
The double-flow turbine is so designed that the steam enters at the
center and di vides, with half flowing in either direction through s imilar
sets of blading to exhausts located at each end of the turbines .
The LP turbine is normally a double-flow design, and in larger rati ngs ,
a typical turbine unit wil l consist of either two or three simi l ar LP elements.
In this arrangement , steam from the IP turbine is divided and ei ther
half or one-third of the total f l ow is taken to each LP unit .
- 9-

-----1
----,
MAIN STEAM
HOT REHEAT
I
I
I
r-------,
I
COLD REHEAT
~------
BOILER
FEEDWATER
DEAERATING
HEATER
I
~I
~I
V>
H.P.
HEATERS
I
I
•
I
I
I
I
r-i
1- ----.
I
I
I
t
BOILER FEED
PUMP AND
TURBINE DRIVE
I
t
I
I
I L __ _
I
L.P.
I
L.P.
I
t
_ __ _J
I
I
I
----1
COOLING
WATER
DA41rvs
L _ - - _ HEATER_s_ _ - - - _J
GENERATOR
I
I
I
I
I
I
+
I
I
I
I
I
I
Figure 4 - Basic Flow Diagram for Fossil-Fi red Plant
-10-

Steam Flow Cycle
Steam enters the turbi ne through stationary nozzles, which convert
some of the heat content of the steam into kinetic energy of the issuing
jet. The jet is made to act on the turbine blades, which move at high velocity.
It is vital that the blades absorb this jet energy to the greatest
possible degree , and transmit it to the turbine shaft.
Referring to Figure 4, a typical cycle of turbine and associated equipment
is shown schematical ly . Ma in steam supply from the steam generator
expands through the HP turbine el ement and returns to the steam generator
for reheating--usually to the ori ginal temperature of main steam.
In addition to improving efficiency or heat rate of the cycle, reheat
reduces moisture in steam at the turbine exhaust; and moisture is responsibl
e for erosion of bl ading and loss in blade efficiency .
Reheated steam is now returned to the IP section of the turbine and
then to the low pressure turbine. After the steam has passed through the
low pressure turbine, a major portion of its thermal energy has been con ­
verted to mechanical work in the various turbine elements, and it might be
exhausted to atmosphere .
This would be uneconomi cal, since it would be necessary to continuously
supply the boiler with treated water from an outside source, at added expense.
In addition, if a condition of vacuum or pressure below atmospheric
can be created at the exhaust of the turbine, it is possible to expand steam
further and extract more ener gy from it. Therefore, a condenser is integrated
into the cycle.
The single reheat cycl e is most used with main steam inlet pressures
from 1450 psig to 3500 psig.
The past several years has shown a major trend to 2400 psig or 3500
psig throttle pressure for un i ts rated above 400 MW . Advances in throttle
pressures and temperature are due to a need to take economic advantage of
available better material s wh ich can operate at 1000 degrees F. and higher
temperatures with resulting heat rate reduction and fuel savings .
Nearly all of the current fossil fuel fired reheat units are designed
for 1000 degrees F. temperature both at the throttle and at the reheat inlets
. However, a few have inl et conditions of 1800 psig - 950 degrees F. ;
these are intermediate duty units.
Al though turbines have been built with inlet temperatures above 1000
degrees F. , the signi f i cance of the drop back to this temperature is that
a 50 BTU heat rate improvement (1050 degrees F. vs. 1000 degrees F. ) does
not justify the premium material requirements and attendant boiler superheater
tube problems .
Doubl e-reheat can be justified only in high fuel cost areas where the
turbine can operate base l oaded most of the time . Double reheat vs . single
reheat to 1000 degrees F. offers a heat rate improvement of approximately
1 .5 per cent.
Upward trends in fuel costs will cause a more favorable evaluation of
higher main steam conditions and al so double reheat designs.
-11-

Steam Flow Cycle : Study Questions
STEAM TURBINES
SECTION l
FOSSIL FUEL TURBINES
l. In a typical fossil turbine cycle, main steam expands through the
----
turbine and returns to the steam generator for
2. Reheat improves and reduces in the steam at
the turbine exhaust.
3. After reheating, steam returns to the turbine and then to the
----
turbine and exhausts to a
4. The condensati on of the steam results in:
a . Reduced vol ume .
b. Increased volume.
c . No change in volume .
---
5. This reduction in volume produces a in the condenser and
at turbine exhaust.
------
6. This makes it possible to obtain more work from the steam and improves:
a . Plant morale .
b. Plant efficiency.
7. It also allows condensed steam to be recovered and used over again i n
the ------
8 . This is very important and economical since condensate i s distilled
water and very pure, thus highly desirable for:
a. Drinking water.
b. Laboratory use.
c. Use as feedwater to the boiler.
- 13-

9. Fossil fuel turbine units are , almost exclusi vely , (1200) (1800) (3600)
rpm turbine elements.
10. A complete turbine unit cons i sts of several turbine el ements or
------
II 11
connected i n tandem to drive a single
generator.
11. A common arrangement will include a ____ _ _ __ , an ____ _
(IP) and ---------
(LP) building bl ocks .
12. An alternate arrangement provides the HP and IP elements in a singl e
cylinder which results in :
a. A shorter unit length .
b. A saving of space.
c. Doubled efficiency.
13. HP, IP and LP turbines may be either 11 - -----
- -- 11 or
11 11
designs, depend ing on the vo l ume of steam to be
passed and the availability of designs .
14. A single-fl ow turbine is one in which the total volume of steam enters
at each end and passes through alternating rows of rotating and stationary
blading to the exhaust.
True/Fal se .
15. The double-fl ow turbine is so designed that the steam enters at the
------
and , with half flowing i n ei ther directi on
through simi lar sets of blad i ng to exhausts located at (one) (each)
end of the turbine.
16. The LP turbine is normally a design , and in
l arger ratings, a typical turbine unit will cons i st of either or
-----
similar LP elements.
-14-

17 . In this arrangement, steam from the IP t urbine is (divided) (not
divided) and either half or one-t hird of the total fl ow i s taken t o
each LP unit.
18. The singl e reheat cycle is most used .
True/ False.
19. There is a major trend to ___ ps i g or ___ psig t hrottle pressure
for units rated above 400 MW .
20 . Nearly all of the current fossil fuel fired reheat units are designed
for 1000 degrees F. temperature both at t he throttle and at t he reheat
inlets.
True/ Fal se .
21. Units with inlet conditions in the order of 1800 psig -- 950 degrees
F. are usually designed for duty.
- 15-

STEAM TURBHIES
SEC TI Of~ l
FOSSIL FUEL TURBINES
Steam Flow Cycle: Answers
l. HP (H igh Pressure) turbine - for reheating.
2. Improves effici ency - reduces moisture in steam .
4. a . Reduced volume .
5. Vacuum.
6. b. Plant efficiency.
7. Boi ler.
8. c . Use as feedwater to the boiler .
9. 3600 rpm .
10. "Building blocks . "
11. High-pressure (HP) - Intermediate pressure (IP) - Low Pressure (LP) .
12. a . A shorter unit length .
b. A savi ng of space .
13 . "Single-flow" - "double-flow."
14. False . The total volume of steam enters at one end .
15. Cente r - divides - each .
16. Double-fl ow - two or three .
17 . Divided .
18 . True .
19. 2400 psig . or 3500 psig .
20 . True .
21. Intermediate duty .
3. IP (Intermediate Pressure) turbine - LP (Low Pressure) turbine - condenser.
-17-

MAIN STEAM
--i---1
: I
I
I
FEEDWATER
I H.P.
I I
I 1 L_T __ _J
I I I
I r_ l _ __ l ____ j
11 I
~---- f --1
I
I
MOIST 1ST STA. 2ND STA.
SEPR. RH. RH .
::El
~I
Vl
,----,
I i
I
I
I
t
I
I ~
I ~
I ~
~ ~
I
I
+
I
I
I
I
I
t
I
I
I
L.P.
COOLING
WATER
GENERATOR
H.P.
HEATER
FEEDPUMP AND
TURBINE DRIVE
L.P.
HEATER S
Figure 5 - Basic Flow Diagram for Nuc l ear Plant
-1 8-

Steam Flow Cycle
STEAM TURBINES
SECTION l
NUC LEAR FUEL TURBINES
The nuclear turbine cycle is similar to the fossil-fired cycle but with
some characteristic differences, due to the lower steam pressure and temperature.
Thus, a typical nuclear turbine arrangement may consist of basic elements
as shown schematically in Figure 5, on the opposite page.
The HP element is usually a double flow design capable of passing the
l arge volume of steam required. The LP shown schemat i cally as a single element
usually comprises two or three simil ar turbines, and al l elements are
arranged in tandem on the shaft to drive a single generator .
Reheat is important in nuclear turbines since the initial temperature
of steam is the saturation temperature corresponding to the pressure (no
superheat). Without reheat, there would be 20 to 24% moisture at the turbine
exhaust, which would be detrimental to both blading and efficiency.
Here, reheat is accomplished in a combination mo isture separator-reheater
(MSR) . In the schematic diagram reheat is accomplished in two stages. To
reduce blade erosion and blade efficiency losses due to moisture , the fol~
lowing methods are employed by the various turbine suppliers:
a. Use of an external moisture separator.
b. The application of internal (blade) moisture removal devices such as
grooved rotating bl ades and moisture removal slots designed into the
cas ing. In some in stances , slots are present in hollow stationary
blade trail ing edges to draw off the large moisture droplets that
build up there.
c. Increased ax ial spacing between the stationary and rotating blades
to al l ow time for the large moisture droplets, that dribble off the
trailing edges of the stationary blades, to break up and be accelerated
to velocities comparable to that of the steam.
d. The use of steam for steam reheating. That is, add itional heat i s
added to the steam , after it has been expanded through the high
pressure element, and has passed through the moisture separator.
In a cycle with two stages of reheat steam leaving the HP turbines to
be reheated first passes through the moisture separator which mechan i cal ly
removes all moisture by multiple-vane chevrons. Steam then flows into the
first stage reheat section where it flows over tubes through which steam extracted
from the HP turbine is passed. It then flows to the second stage
- 19-

Figure 6 - Multiple Vane Chevron Separator
-20-

eheater section and over tubes containing main steam. The moisture separator
and two stages of reheating are usually incorporated in a single shell,
with suitable baffling and partitions to guide the flow of steam .
The reheated (superheated) steam flows to the LP turbine and, as in the
fossil cycle, to the condens er, through the heaters, and returns to the
steam generator as feedwater.
Turbine Characteristics - HTGR
Because the steam conditions for the helium cooled reactor (HTGR -­
High Temperature Gas-Cooled Reactor) are in the range of foss il reheat units
(2400 psig, 950 degrees F./1000 degrees F.) the turbine design and construction
features are similar to the fossi l turbi ne and utilize 3600 rpm turbine
elements.
Turbine Characteristics - PWR and BWR
Currently, the majority of water cooled reactor plants being planned
range in si ze from 800 to 1,200 MWe*. The expected average size will be
1,100 MWe, and the larger future plants are expected to be in the 1 ,300 and
1 ,500 MWe range.
The turbine des igns for light water reactor applica tions di ffer markedly
from tho se for high pressure, high tempera tu re operation. Present in~
let pressures range from 650 to 1050 psia with saturated or low superheat
steam (50 degrees F. superheat in some cases). These pressure levels put
the nuclear high pressure turbine elements in the same class as the double
flow intermed i ate pressure elements of fos si l reheat units without the hi gh
temperature design requirements. However, the volumetric requirements have
increased to the point where it is necessary to use large 1800 elements to
handle the flow .
In the development of high turbine ratings with low inlet steam conditions,
the designer must contend with two basic limitations:
1. Because of the relatively low energy content per pound of steam, the
turbine inlet and exhaust must pass large steam flows and ;
2. The prohibitively high level of moisture that would result from a
simple expansion from turbine inlet to exhaust, would cause excessive
blade erosion and reduce therma l efficiency substantially.
To provide a flow path which will pass the required volume of steam
with blade l engths avai lable, the turbine designer uses the double flow turbine,
which passes half of the total flow to each of two sets of blading.
*MWe - megawatt electric - power rating .
rated in MWt - megawatt thermal .
The nuclear steam supply system is
-21-

When there is insufficient f l ow area to pass the volume of steam , a
second or thi rd double flow element is added. The total steam flow is di ­
vided in this manner among two, four or six flow paths to match the flow
capacity of the LP turbine blading.
Exhaust Pressure--Fossil and Nuclear
Complex economic studies based on costs , cool ing water availabili ty,
etc., go i nto the f inal evaluations before the size of the exhaust end is
chosen.
If coo ling ponds or evaporative cooling towers are used, the cooling
water temperature i s generally higher than if natural bodies of water are
used . This is particularly true if dry cooling towers are utilized since
the condensing temperature is influenced by the dry-bulb air temperature
rather than the wet- bulb air temperature. This higher condensing temperature,
of course, causes a higher back pressure to the turbine which causes
a capability loss for the turbine.
The second effect of the higher back pressure is an increase in the
heat rate of the turbine which, of course , causes an increase in the fuel
cost component of power generation .
With dry coo ling there is also a large increase in plant capital cost
over that for once through cooli ng , cooling ponds and evaporative cooling
towers.
If dry cool ing is used, the effect on back pressure, heat rate and
plant capital cost is substantial and i s an important consideration for both
turbine design and economic optimization of the power station.
- 22 -

STEAM TURBINES
SECTION l
NUCLEAR TURBINES
Steam Flow Cycle: Study Questions
l. The nucl ear turbine usually consists of a ----- -
---- HP
element and one or more
------ --- LP elements.
2. Reheat is even more important in nuclear turbines since the initi al temperature
of steam i s t he
temperature corresponding to
the pressure (no ).
3. Wi thou t reheat , what would result, detri mental to both bl ad ing and effi ­
ciency?
4. Here , reheat is accompli shed in a combination mo isture ------
(MSR) .
5. To red uce the blade erosion and blade effi ciency l osses due to mo i sture ,
the fol lowing methods are employed:
a . Use of an external
b. The appl i cati on of internal (blade) mo i sture remova l dev i ces such as
- -------
designed into the cas ing.
rotating blades and mo i sture removal
In some cases, slots ar e present in hollow
blade
- - ------
bui ld up there.
edges to draw off the l arge mo ist ure dropl ets that
c. Increased ax i al spac ing between the stationary and rotati ng bl ades to
allow t ime for the l arge mo isture dropl ets, that dribble off t he
trail i ng edges of the stationary blades, to break up and be (s lowed)
(accel erated) to ve locities comparable to that of steam .
- 23 -

d. The use of steam for steam reheating; that is, additional heat is
added to the steam, after it has been partially expanded through the
high pressure element and has passed through:
a. The superheater.
b. The moisture separator.
6. After ma in steam has passed through the HP turbine, the steam then flows
to a combined moisture separator-reheater where the water is:
a. Removed.
b. Stored.
c . Evaporated.
7. The dry steam then enters the section .
8. The superheated main flow now enters the low pressure turbines and ex ­
pands to condenser pressure.
True/False
9. The steam conditions for the helium coo led reactor (HTGR) are in the
range of fossil reheat units.
True/False
10. Therefore , the turbine design and construction features are similar to
the turbine and utilize rpm turbine elements .
11. Turbine designs for light water reactor applications are similar to
those for high pressure/hi gh temperature operation.
Tr ue/False
12. The nuclear HP turbine element is in the same class as the OF-IP element
of fossil reheat units wi thout the high temperature des i gn requirements.
True/False
-24-

13. In the development of l arge nuclear turbines with low inlet steam conditions,
the desi gner must contend with two basic limi tations:
(1) Because of the relatively low energy content per pound of steam, the
turbine inlet and exhaust must
~~~~~-----------
( 2) The prohibitively high level of moisture that wou ld result from a
simpl e expansion from turbine inlet to exhaust wou ld cause ----
---------------------- -----
and
16. Th is back pressure to the turbine causes a:
( l )
(2)
14. The use of cool ing towers results in a (h igher) (lower) condens ing temperature.
15. This causes a (hi gher) (lower) back pressure to the turbine.
-25-

Steam Flow Cyc l e: Answers
STEAM TURBINES
SECTI ON 1
NUCLEAR TURBINES
1. Doubl e f l ow HP el ement - dou bl e f l ow LP el ements .
2. Saturation - superheat.
3. 20 to 24% mo i sture at turbine exhaust.
4. Separator-reheat er.
5. a. Mo i sture separator.
b. Grooved - slots.
Stationary - trailing .
c. Accelerated.
d. (b) The moisture separator.
6. a. Removed.
7. Reheat .
8. True .
9. True.
10. Foss il turbine - 3600 rpm .
11. False.
12. True.
13 . (1) Must pass large steam flows.
(2) Would cause excessive blade erosion and reduce thermal efficiency
substant ially.
14. Hi gher .
15. Hi gher.
16 . (1) Capabil i ty l oss.
(2) Increase in heat rate.
- 26-

STEAM TURBINES
SECTION 1
TURBINE DESIGNS
In the following descri ption of fossil and nuclear turbine designs,
various arrangements of turbine el ements , or building bloc ks, are illustrated.
These are typical of current designs and specific ratings are not
given since these are variable and are dependent on the length of last row
blade selected and site cond i tions specified . Frequently two or mo re configurations
of building bl ocks or blade length may be appl i ed for a single
rating and selection made on an economic basis of station cost and heat
rate performance .
-27 -

Figure 7 - Two Cy l inder Tandem Unit
Figure 8 - Two Cylinder Tandem Unit
Figure 9 - Three Cylinder Unit
~28-

STEAM TURBINES
SECTION 1
FOSSIL TURBINE DESIGNS
Two-Cyl i nder Tandem Units
A specific configuration for a two-cylinder reheat unit of approxima
tely 200 to 250 MW capacity is shown in longitudinal section, Figure 7.
This type of turbi ne is built in a double flow design with 23 in. last row
blades or with 25 in. last row blades. The main steam and reheated steam
both enter the cylinder in adjacent locations, thereby reducing the thermal
gradients along the cylinder wall to a minimum . The ma in steam enters the
cylinder through separate anchored side-mounted steam chests, flexible inlet
piping and separate nozzle chambers.
In higher ratings, general ly to about 400 MW, a simi lar two-cylinder
tandem-compound arrangement continues to look favorable from the standpoint
of overa ll efficiency versus installed cost. Figure 8 shows a typical longitudinal
section. Numerous combined high pressure-intermedi ate elements in
this capability range are in service. This arrangement may use 28 1/2 in.
or 31 in last row blades .
Three-Cylinder Tandem Units
For higher ratings, to approximately 600 MW, designs for three-cylinder
3600 rpm tandem-compound units are avai lable. Figure 9 shows a longitudinal
section of this unit which may use 25 in. last row blades or 28 1/2 in. last
row blades .
This quadruple flow exhaust configuration can be appl ied in tandem with
separate high-pressure and intermediate-pressure elements, as well as with
the comb ined HP-IP design. Combining the HP-IP element into a single casing
for these l arge ratings continues the historical industry trend toward
l arger combined elements , and represents a major advance in turbine design.
The installed length of such a unit is approximately 18 feet less than that
required by an equivalent four- cy linder design . Additional savings accrue
at inspecti on since one l ess el ement has to be dismantled.
Four- Cy l inder Tandem Units
Figure 10 is also a tandem compound four f l ow arrangement; however,
note that the high pressure and intermediate pressure elements are now in
separate cas ings, as opposed to the previous arrangements. This unit is
capable of 960 MW when 31 in. l ast row blades are employed.
Five-Cyli nder Tandem Un i ts
Another significant single-reheat 3600 rpm arrangement i s the five cylinder
sextuple-flow unit shown typically in Figure 11. This is a tandem
compound six flow arrangement with 31 in . last row blades and is capable of
providing the ratings required in the near future potential ly 1200 MW.
-29-

Figure 10 - Four Cylinder T and em Unit
Figure 11 - Five c Y 1. inder Tand em Unit .
-30-

Shaft B
Longitudinal stttion of CC2f rth«t turbine, 360C>/1800 rpm.
Figure 12 - Cross- Compound Double - Flow Uni t
Figure 13 - Cross-Compound Double Flow Unit
-31-

. ~rT1~n
Figure 14 - Cross-Compound 3600/3600 RPM , Four Element Unit
Fi gure 15 - Cross-Compound 3600/1800 RPM , Four El eme nt Un i t
-32-

Cross-Compound Units
Two element 3600/1800 rpm single reheat units are shown in Figure 12
and 13. The 3600 rpm unit combines the HP-IP elements into a single casing
as shown. The 1800 rpm double f l ow LP element can be furnished with 40
inch or 44 inch long last row blades.
Figure 14 shows longitudinal sections of a typical 3600/3600 rpm crosscompound
quadruple f l ow unit. This design couples the HP element in tandem
with a double-fl ow LP driving one generator, and a double-flow IP element
with another double-flow LP in tandem driving a second duplicate generator.
This 11 Cross-Quad 11
arrangement has been supplanted by single-shaft designs.
Figure 15 shows longitudinal sections of four element cross-compound
quadruple-flow 3600/1800 rpm units. All of the elements are of the doubleflow
arrangement.
The IP el ement i s of typical double-flow arrangement. The LP elements
have 40 inch long l ast row blades . Figure 16 is a photograph of a model of
an 870 MW unit of the type described. This type of turbine with 44 inch
long last row blades has been rated at 1070 MW, with steam conditions of
3500 psig - 1000 degrees F./1000 degrees F./ - 1. 5 inch Hg abs.
Double Reheat Designs
There are no fossil fired double reheat units on order at this time,
the last of this type being a four cylinder unit rated at 760 MW with design
steam conditions of 3334 ps ig - 1000 degrees F. / 1025 degrees/ 1050 degrees
- 1.5 inch Hg abs .
Figure 16 - Cross-Compound Four Element Unit
-33-

Figure 17 - Tandem Compound Four Flow Nuclear Unit
CONDENSATE
OUTLET
MANWAY
2NDSTAGE
REHEATING
STEAM INLET
lST STAGE
REHEATING
STEAM INLET
,,----~~r~~
STEAM TO
LP TURBINE
2ND STAGE
REHEATER
TUBE BUNDLE
MANWAY
CONDENSATE
OUTLET
lST STAGE REHEATER
TUBE BUNDLE
I
SEPARATED MOISTURE OUTLET
CHEVRON SEPARATOR VANES
Figure 18 - Moisture Separator Reheater, Two Stage
-34-

STEAM TURBINES
SECTION l
NUCLEAR TURBINE DESIGNS
The description of nuclear turbines will be confined to appl i cations
employing light-water reactors. These nuclear turbines for Pressurized
Water Reactor (PWR) and Boiling Water Reactor (BWR) are similar since the
steam conditions are in the same range . The principle differences are found
in the details of shielding and drain systems since the BWR uses a direct
cycle. The steam is radioactive, containing particles of radioactive scale,
isotopes of nitrogen, oxygen and possibly fission products from the reactor.
As has been said, the HTGR (high temperature helium-cooled reactor) uses
steam conditions equivalent to current fossil practice and, therefore, tne
turbine units are similar to the fossil designs.
Figure 17 is a cutaway view of a tandem-compound four~flow unit. Steam
from the steam generators and main steam lines enters the steam chest
through the throttle valves at either end, passes through control valves and
is admitted to the center of the high pressure turbine, dividing and flowing
to each end of the high pressure turbine where it exhausts through crossunder
piping to the MS-R (Moisture Separator-Reheater). The crossunder
pi pi ng is shown in the cutaway view .
Moisture in the steam at the HP turbine exhaust is removed by the
moisture separator portion of the MS-R (Moisture Separator-Reheater), then
heated to approximately 100 degrees F. superheat in the reheater, after
which it flows through the crossover piping to the low pressure turbines.
Moisture separator-reheaters are shown in Figure 17, two units, one on
each side of the main turbine. This cycle will be discussed i n more detail
later.
Figure 18 shows an MS-R with the moisture separator portion in tne
lower half of the shell and the reheater in the upper portion.
Figure 19 represents a longitudinal section of a three-cylinder Westinghouse
turbine which may use 40 inch last row blades or 44 inch last row
blades.
Figures 20 and 21 represent a larger four-cylinder unit also using
either 40 inch or 44 inch last row blades.
These three cylinder and four cylinder turbine designs are app li cable
in the range of 500 to 1300 MWe.
-35-

Figure 19 - Three Cylinder Nuclear Unit
Figure 20 - Four Cyl inder Nuclear Unit
- 36-

Figure 21 - Four Cyl inder Nuclear Uni t

~~~~
~~~~
Turbine Designs: Study Questions
STEAM TURBINES
SECTION l
1. Two cylinder reheat/fossil units consist of a combined element
and a low pressure element.
2. This type of turbine is generally applicable in the range of 200 to 400
MW depending on the choice of
~~~~~
3. Three cylinder tandem units consist of a combi ned HP- IP element and
LP elements.
4. This type of turbine is capable of ratings in the range of
~~~~~
MW .
5. A four-cylinder tandem unit is similar to the above except that it
utilizes (combined) (separate) HP and IP elements .
6. The five-cyl inder tandem unit with separate HP and IP elements and three
double flow LP elements has a potential capability of 1200 MW .
True/False.
7. Cross-compound units may have one 3600 rpm shaft and one 1800 rpm shaft.
True/False.
8. A typical four element cross- compound unit consists of a double flow HP,
a double flow IP on the 3600 rpm shaft and two double flow LP elements
on the 1800 rpm shaft.
True/False.
9. The principal differences found in the nuclear turbines for PWR and BWR
applications are in the details of and
~~~~~~~
10. This is due to the BWR direct cycle which causes the steam to be
-39-

11. The HTGR uses steam pressure and temperature similar to the PWR and BWR .
12. The turbine for application with HTGR is t herefore simi lar to :
a. PWR turbine.
b. BWR turbine .
c. Fossil turbine.
13 . A typ ica l turbine for PWR or BWR applicati on (s ingle fl ow) (double flow)
high pressure element and ei ther two or three low pressure elements .
- 41 -

STEAM TURBINES
SECTION 1
Turbine Designs: Answers
1. Combined HP- IP element double flow l ow pressure element .
2. Last row blades.
3. 2 LP elements.
4. 600 MW .
5. Separate HP and IP elements.
6. True.
7. True .
8. True.
9. Shiel ding and drain systems.
10. Radioactive .
11 . False .
12. c. Fossil turbine.
13 . Doub 1 e fl ow.
-43-

Governor Valvel
Throttle Valve
j-@----~--- ~~n_s~:_m __ _
I Interceptor Valve
c[>O
: r i_ --~--H_:> !._R_,;'2;~ -
I
Q9- T Steam
Stop Valve
I
1
~ I
L __ J:'----.l't"----------J
I I
I I :
L----r---J L------~~~~~----+-
+
To
Condenser
Figure 22 - Flow Through Fossil Turbine
Interceptor Valve Stop Valve
r~---~
I
I
DFLP
HP
Governor Valve Stop Valve
~ ~ Main
r-----Q»- ----Q>r st~;;
I
I
•
L---------~
I
+
To
Condenser
I I
I :
L--------'------~
To MS -RH
L---------------
From
Moisture Separator - Reheater
Figure 23 - Flow Through Nuclear Turbine
-44 -

STEAM TURBI NES
SECTI ON l
TURBINE DES IGNS
Fossil Turbine Components
A typical fossil turbine unit, shown schemati cally in Figure 22, i s made
up of a combi ned high pressure and intermediate pressure turbine, (or separate
HP and IP units) and a double-flow low pressure turbine. In the steam
chests, steam at 1000 degrees F. passes through the throttle and governor
valves and flows through the inlet piping i nto the high pressure turbine.
The steam passes through the nozzle chambers , into the nozzles, and expands
through the control stage blading. In this stage the temperature
drops from 1000 degrees to approximately 960 degrees at full load and to approximately
700 degrees at part load.
In the high pressure turbine, steam i s conta ined at very high temperatures
and pressures . Here the des i gn must deal with severe temperature differentials,
or variations in temperature, and high thermal stresses, and the
design must prevent thermal distortion and cracking.
Steam from the control stages passes through the high pressure bl ading,
and flows to the boi l er for reheating to 1000 degrees F.
Reheated steam returns to the intermediate pressure turbi ne through the
reheat pi ping and t he reheat stop and intercept valves. Here agai n, the
most serious problem i s with temperature gradients and thermal stresses.
The reheat pipes expand and contract. The reheat inlet features must be designed
in such a way that excess i ve pipe forces and moments are not transferred
to the turbine casing.
The reheated steam then flows through the intermediate pressure turbine,
where more energy is converted to work; and enters the crossover pipes to
the low pressure turbine at approximately 700 degrees F., and 200 psi a.
Nuclear Turbine Components
The nuclear turbine unit, shown schematically in Figure 23, is made up
of a double f l ow high pressure turbine and one or more double flow low pressure
turbines . In the steam chests, the steam passes through the stopthrottle
and governor valves, through the inlet pi ping into the HP turbine.
The steam flow path i s similar to the fossi l turbine except that steam
leav ing the HP turbine goes to the moisture sepa rator-reheater (MSR) before
entering the LP turbine through the reheat stop and interceptor valves.
In the MSR the moisture is first removed from the steam , restoring it to
a dry and saturated condition. Then the steam enters the r eheater section
where it is superheated . Steam then expands through the LP turbines .
-45-

As in t he fossil turbine, a criti cal design consideration is concerned
with avoiding distortion and cracking due to thermal gradients. Sections of
the turbine adjacent to one another must handle steam at different temperatures.
These sections may expand unevenl y, stresses are set up, and critica
l metal part s can distort or crack unless the desi gn provi des sufficient
flexibility in the areas where high temperature gradients exist i n the unit.
There wi ll be one or more l ow pressure turbines as required. Each of
them has two sets of blades, symmetrical about the center line. The steam
flows through the l ow pressure inlet chamber, and expands through both sets
of low pressure blades. Once again, the tempera ture grad i ents are severe :
500 to 550 degrees F. at the inlet, and approximately 100 degrees at the exhaust
end. In the low pressure turbine, too, des i gns must eliminate the
problems created by l arge temperature gradients, and provide the mos t efficient
thermodynamic and aerodynamic flow path . Steam from the last row
blades exhausts through a diffuser section into the large exhaust hoods of
the turbine.
Maximum Pe rmissible Exhaust Flow
It is significant that a considerable number of units are purchased on
the premise of capabilities equal to the "Maximum End Loading" exhaus t flow.
Cooling t ower installations are becoming more commonpl ace even i n cooler
geographic areas. If coo l ing tower s are used, the cooling water temperature
i s hi gher. Thi s higher condensing temperature, of course , causes a higher
back pressure to the turbine. Dry cooling or wet-dry cooling, when appli ed ,
wil l cause subst antially higher condenser pressure .
With higher condenser pressures, co nventional type turbine generator designs
may not be adequate. Higher exhaust pressure turbines necessi tate
high exhaust end loadi ngs if power level is to be maintained .
The max imum permissible exhaust flow is determined by the design and may
be expressed as the exhaust steam flow (lbs . per hr. ) through the l as t row
of blades or as exhaust steam fl ow per sq. f t . of exhaust annulus area . Exhaust
annulus area is f i xed by the di ameter of the drum or di sk to which the
blade is attached , the length of the last row blade , and t he cl earance between
the tip of the blade and the turbine cylinder. See Figure 24 .
Figure 24 - Exhaust Flow Area
-46 -

Higher exhaust end load i ngs wil l result from ei t her increasing t urbine
steam flow for a fi xed annulus area or reduc i ng the exhaus t annu l us area for
fi xed quantities of st eam flow .
The exhaust annul us area i s a functi on of the last row bl ade l eng th
which i s a factor affecting t he cost of the t urbi ne as wel l as t he performance
level (heat rate) . Therefore , an econom ic choice mus t be based upon
an eva luati on which incl udes the cos t of the hea t rejecti on syst em and the
capability penalties resulting from the heat rej ection system as well as the
cos t and performance level of the turbine.
-47 -

STEAM TURBINES
SECTION 1
Steam Flow Cyc l e: Study Questions
1. Steam flow through a typi cal foss i l turbine unit is first through the
steam ches t s containing the throttle (stop) and governor valves and
t hrough the i nlet pi pi ng to the HP t urbine.
True/Fa l se.
2. In the HP turbine it enters t he nozz le chambers , the nozzles, and expands
t hrough the
blad ing.
3. In the HP turbine the design must deal with:
a. severe temperature differenti als
b. variations in temperature
c. high t hermal stresses
4. Steam, after passing through the high pressure bl ading, flows to the
for
~~~~~- -~~~~~-
5. Reheated steam returns to the IP turbine through the reheat piping and
~~~~- -~~~~~~
the reheat and valves.
6. The reheat inlet features do not experience the severe temperature problems
whi ch ex i st i n the HP t urbine.
True/ False.
7. Steam leaving the IP turbine enters t he pipes and fl ows
~~~~~~to
the LP turbine.
8. The steam f l ow path through a nuclear turbine, l ight-water reactor appl i-
cation, is simil ar t o the fossil turbine except that steam leaving the
HP turbine goes to the
~~~~~~
before entering the LP t urbine through the r eheat stop and interceptor
valve .
- 48-

9. In the nuclear turbine the most severe temperature gradients are found
in the LP turbine.
True/False.
10. Nuc lear or fossil units may be purchased wi th a rating capab il ity wh i ch
requires the exhaust of the LP turbine to pass its max i mum permissi ble
design exhaus t flow.
True/Fal se.
11 . Hi gher cooling water temperature t o the condenser ca uses a (h igher)
(lower) back pressure to the turbine.
12. Hi gher exhaust pressure turbines necessitate high exhaus t end loadings.
True/False.
13. Hi gher exhaust end loadings ca n result from:
a. i ncreasi ng turbine steam flow for a fixed annulus area
b. reducing the exhaust ann ul us area for a fixed quantity of st eam flow.
14. An economic cho ice must be based on an eval uation wh ich includes:
(1) cost of the heat rejection system
(2) capability penalty resulting from the heat rejection system
(3) cost of the turbine (which may be a f unction of the exhaust area)
(4) performance level of the turbine
-49-

Steam Fl ow Cycle: Answers
1. True.
2. Control stage.
3. (a) (b) and (c) are all correct.
4. Boil er; reheati ng.
5. Reheat stop and intercept valves.
6. False.
7. Crossover pipes.
8 . Moisture separator-reheater.
9. True.
10. True .
11. Higher .
12. True.
STEAM TURBINES
SECTION 1
13. Either (a) or (b) is correct.
14. All four are correct. All should be selected.
- 50-

STEAM TURBINES
SECTION 2
INLET VALVES AND STEAM CHEST
Turbi ne Control
Control of the turbi ne speed and l oad is provided by a combination
stop-throttle valve and control valve assembly, which is placed ahead of
the HP turbine. Valves are controlled by an electro- hydraulic governing
system . This system was studied in a separate t est (MA-465) .
The stop-throttle valve prov ides positive shut-off of the steam supply
to the main turbine. The multiple control valves are arranged to open in
sequence to meet varying load requirements . The use of multiple valves
with sequential opening serves to minimize losses inherent in partial open ­
ing of the va l ve . Steam fl owi ng through a partly opened valve has its pressure
reduced without performi ng work; that is, it is "throttled."
At l ight loads the va l ve would be barely open and the steam would be
throttled to a low pressure before i t began expanding through the tur bine .
Turbi ne output wo ul d be limited not onl y by the low steam-flow rate but
al so by t he small amount of work do ne by each pound of st eam due to its l ow
pressure .
At low loads efficiency is poor because of the throttl i ng required to
l imit the steam-flow rate . As l oad increases the valve opens wi der , thrott
li ng dimi nishes and the effi ci ency improves.
The various methods of controlling the flow and load for turbine generator
units uti l ize ei ther area or pressure control or combinations of the
two .
Pressure Control (Throttling Operation)
If the steam generator delivers constant throttle pressure to the turbine
and the turbine utilizes single va l ve point operation , then the va l ves
do not vary the nozz le area but are used only to throttl e the pressure
ahead of the nozzles .
Area Control (Multi -Valve Operation)
If the steam generator delivers a constant t hrottl e pressure t o the
turbine and the turbine i s arranged with sequential governing valves , then
the acti ve nozzle area of the first turbine stage is varied by the governing
valves which contrOf-:rhe flow to groups of nozzles .
Slidi ng Pressure Operati on
If the steam generator delivers steam at a pressure which varies wi th
flow, then nozzle inlet pressure also varies with flow . Since these two
- 51 -

a:
:::>
0
I
~
~
al =
I
w
1-

factors, pressure and flow, determine the total energy ava i lable to the turbine
, these can be used to regul ate the speed and load of the turbine. With
control valve position held constant, control is by sl id ing pressure operation
of the steam generator.
Part Load Performance
A turbine should operate as efficiently as possible at al l loads. A
fossi l unit wi ll normally be a base load unit for a number of years, and
then be used in cyclic duty. For effi cient part l oad performance, especi
ally during t hose years when it will see extended cycl ic duty, sequenti al
mul ti-valve control i s used . Throttl ing operation is ineffi cient, and even
the complexity of sliding pressure operation does not afford the part load
economi cs ava il abl e with mul ti-val ve operation. In add i tion, sequential
multi-valve and throttling operation provide su perior l oad response in comparison
to sl iding pressure operation .
Nuclear turbines should be des igned for mul ti -va lve partial admission
operati on since wi th successive i nstallations on given power systems , some
nuclear units will be req uired to ope rate at reduced l oad for sufficient ly
l ong periods of time to justify partial admission des i gns .
Valve Operation and Va lve Management
A t ypi ca l large fossi l unit may have eight control valves--four in
each of the two steam chests. Since a combinati on of val ves may con t rol
steam fl ow to a common nozzle chamber, the number of "valve points" may be
less than the actual number of valves .
In operation, the throttle valves are in full open pos i t i on . The con ­
trol of steam admission to the unit is through the governor val ves . At full
load, in Figure 25 , the steam passes through the ful ly opened governor
valves with no valve throttl i ng loss (valve poi nt A) .
As load on the unit is decreased, the valve or valves controlling the
flow to only one nozzle chamber start to close. As they do , throttling
losses occur in these valves . This throttling loss, and resulting increase
in heat rate, i s illustrated by t he dotted line in area B.
When these valves go full y closed (valve poi nt C), the remainder of
the valves conti nue to admit steam to their respective nozzle chambers .
There is no throttl ing loss until the next valve begins to close . By comparison,
a singl e valve poi nt unit introduces throttling losses as soon as
it dro ps away from full load, and t he effect of thi s l oss continues to increase
as load decreases .
While multi -valve operation i s more efficient, the option of singl e
valve operation, even with its inherent l osses, is desirabl e under certain
unique conditions. During start-up of the turbine i t may be desi rable to
open all va l ves simultaneously (using throttl ing control) to assure uniform
heati ng of al l parts and minimize thermal stresses . Thi s fu l l admiss i on
(or full arc admission) optional capabi lity--Valve Management--swi tchi ng
from sequential t o singl e valve operation upon command also affords f l exibi
lity i n operating as a base l oad or cycl ic du ty machine .
- 53 -

6 HEAT RATE - BTU/ KW - HR
400
•
350
\
\
COMPARI SON
300
250
\ OF
'
VALVE POINTS
\
\
200
150
100
50
0
·~
A -
!...-"'
'
~
-.. -
"-''
45 BTU/ KW - HR
"
B
~ 5 VALVE POINTS
'· I/\ B
3VALVEPOINTS
' i-r-'S~~~\
I\ \' ~/ \
j_
---L....--- ~-. --.. ' \
""
~ ~ - j --- --
--~ ' '
40 45 50 55 60 65 70 75 80 85 90 95 100
PERCENT LOAD
Figure 26
6HEAT - BTU KW - HR
1600
1500 I I I I I
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
100
~
M UL T l-VALVE VS. SINGLE VALVE PERFORMANCE
(DRY AND SATURATED CONDITIONS)
" ,,,. PERCENTAGES
31% ~
'
'
.. ~
' "
I"-.
..
' """ "-
' "
"'"
~
INDICATE DIFFERENT IALS
IN PERFORMANCE BETWEEN MUL Tl-VALVE_
AND SINGLE VALVE OPERATION AT THE
VALVE POINTS.
~
""-..
.........
r--......
29%
--
-.............
f'..... ~ -
40 45 50 55 60 65 70 75 80 85 90 95 100
PERCENT LOAD
Figure 27
-54-

On a specific project, one turbine may have more valve points than
competitive units . For example, in the illustration, Figure 26, the West ­
inghouse fossil unit has five valve points. A competitive unit may have
three or four valve points depending upon the rating. Most European units
are single valve designs for both fossil and nuclear un i ts . In Fi gure 26 ,
the first valve point i s at 65 per cent load in both cases .
Heat rates are guaranteed on the basis of the "locus of the valve
points" (Heat Rate Curve A in Figure --a curve drawn through the valve
points) and, therefore, do not include throttling losses between valve
points. However, in actual operation (Heat Rate Curves B in Figure 26) the
throttling losses are present. The greater the number of valve points , the
lower the throttling losses in actual operation. The result is better efficiency
over the load range and better efficiency over the entire life of
the machine under cyclic operation.
In a similar manner, Figure 27 shows that in a nuclear turbine wi th
three valve points, the improvement in the turbine part-load heat rate for
multi -valve operation is substantial compa red to the unit with a single
valve point.
Typically, for a three valve point design, the l oad carried at the
primary valve point is approximately 80 per cent of unit capability . At
this load, the turbine heat rate is almost 3 per cent better than would be
obtained with a single valve point design of the same max imum capability,
as shown in Figure 27 .
-55-

Turbine Control: Study Questions
STEAM TURBINES
SECTION 2
INLET VALVES AND STEAM CHEST
l. Control of the turbine is provided by a combination
~~~~
valve and valve assembly
~~~~~~~~~- -~~~~~~~~which
i s placed ahead of the HP turbine.
2. On current designs, valves are controlled by:
a . A mechanical governing system.
b. An electro-hydrau l ic governing system .
c. A hydraulic governing system.
3. The stop-throttle valve provides positive shut-off of the steam supply
to the
4. The multiple control valves are arranged to open in sequence to meet:
a. Underwri ters' Laboratory standards .
b. Varyi ng load requirements .
c . Barometric deviations .
5. The use of multiple valves with sequential opening serves to (mi nimize)
(eliminate) l osses inherent in partial opening of a valve .
6. Flow and load for turbine generator units utilize either
7. With sequential governing va l ves the act i ve~~~~~~~~~~~
is varied .
8. If the turbine utilizes single valve point operation, then the valves
are used only to the pressure .
-57-

9. If the steam pressure delivered to the turbine varies wi th fl ow, then
valve positi on on the turbine i s hel d constant.
True/False.
10. In the above case, throttle pressure will also vary with flow and noz ­
zle inlet pressure wil l also vary. Control is by -----
- ------
operation of the steam generator.
11. With multi -valve operation the turbine speed and load is set by the
12. A partially opened valve reduces steam pressure by -------
13. A partly opened valve reduces the steam pressure before it expands in
the turbine and turbine output is limited by:
a. 1 ow steam fl ow rate
b. the sma ll amount of work done by each pound of steam due to its
lower pressure.
14. Sequential multi-valve control is necessary for efficient ---
performance.
15. Both the fossil and the nucl ea r units gain in efficiency at part load
when multi-valve operation is used.
True/ Fa 1 se.
16. A typical large fossil unit may have (4) (8) control control valves -­
(2) (4) in each of the two steam chests.
17. The number of valve points may be less than the actual number of valves
because:
18 . A typical large nuclear unit may have (3) (4) (5) valve points.
19. Valve points are those load points at which any combination of valves
are either fully opened or fully closed and there is no throttling.
True/Fal se.
-58-

20 . A heat rate curve drawn through these valve points is therefore one
which i s based on the of the
~~~~
21. The (fewer) (greater) the number of valve points, the (higher) (lower)
the throttl ing l osses in actual operation.
J
-59-

Turbine Control:
Answers
STEAM TURBINES
SECTION 2
INLET VALVES AND STEAM CHEST
1. Stop-throttle va l ve governor valve .
2. Elect ro-hydraulic
3. To the main turbine.
4. b. Varying load requirements .
5. Minimize
6. Area - pressure - combi na tions of t he two.
7. Nozzl e area.
8. Throttle.
9. True.
10. Sliding pressure.
11. Control valves.
12. Throttli ng .
13. Both (a) and (b) are correct .
14. Part load performance .
15. True .
16. 8 control valves -- 4 in each of the two steam chests .
17 . A comb ination of val ves may control steam fl ow to a common nozzle
chamber .
18. 3 valve points .
19. True.
20 . Locus of the va l ve points.
21. Fewer - higher or greater - lower .
- 61 -

Figure 28 - Cyli nde r-Moun ted Steam Ches t
Figure 29 - Combined HP-IP High Temperature Design
-62-

STEAM TURBI NES
SECTION 2
INLET VALVES AND STEAM CHEST
Design Concepts
The design of the modern steam turbine permits a more sophisticated
approach than than of a decade ago . However, comparing new designs with
other 1000 degrees F. units , even vintage 1950, a significant area of agreement
is noted. Specifically, the original Westinghouse high temperature
design concept of separating higher pressure, higher temperature parts from
the turbine casing proper has been verified in service and further improved
in current designs.
In lower temperature designs the steam chest with its stop and throttle
valves i s mounted on the turbine casing (Fi gure 28). The chest receives
steam fi rst -- it heats rapidly and expands . The temperature gradient --
or variation -- between the steam chest and cyl inder wall can be extremely
high during a cold start.
With the Westinghouse high temperature design philosophy, the combined
stop-throttle va l ve -steam chest assembl ies and the reheat stop-interceptor
valve assemblies are i solated from the cylinder and are anchored to the
foundation as shown in Figure 29. This design minimizes thermal stress during
start-up and load changing. Anchored main inlet va l ve permit station
piping stresses to be transmi tted to the foundation and not the turbine cylinder
where these stresses would enhance chances for expensive cylinder
cracking .
Figure 29 shows in detail the separation of the throttle valve-steam
chest combination from the cylinder proper, with flexible i nlet pipes conveying
the steam to separate nozzle chambers which are fl exibly attached
to the inner cyl inder. This concept has resulted in virtually trouble- free
operation of stationary parts such as inner and outer cylinders, nozzle
chambers and blade rings.
The overal l space requirements are reduced by combining the throttle
valves with the steam chest. Maintenance is facilitated by having all the
operating parts above the turbine floor . The placing of the throttle valve
in the horizontal position minimizes the tot al angle t hrough which the steam
must turn.
Throttle-Stop Valve
The pri mary function of the throttle valves is to shut off the flow of
steam to the turbine in the event of overspeeding beyond the setting of the
overspeed trip . These valves are al so used for controlling the steam flow
to the turbine during the period when the unit is being brought up to speed .
- 63 -

---- STRAINER
STEAM TO
CONTROL
VALVES
PROVISIONS
FOR
BACK-SEATING
MAIN
PLUG
VALVE
Figure 30 - Throttle-Stop Valve
SERVOMOTOR
OPERATING
MECHANISM
PLUG
TYPE
VALVE
DIFFUSER
OUTLET
Figure 31 - Control or Governing Valves
-64-

The valve is hydraulically opened and spring closed, and operates in
the horizontal position . Details of a typical val ve are shown in Figure
30 . It has an internal by-pass valve capable of opening against full boiler
pressure and will pass approximately 25 per cent of design steam flow at
full boiler pressure. The by-pass valve is designed for accurate speed
control will full admission starting (steam admitted to all nozzle chambers)
and initial loading up to 25 per cent of rated load . The main plug of the
throttl e valve is of the unba l anced design and can be opened after the speed
or load control i s transferred to the control valves. The throttle- stop
valve is designed for "back-seating" in both the open and closed positions
to reduce steam leakage to a minimum in the open position and to enable the
boiler to be ''bottled-up" for several hours shutdown with minimum loss of
pressure. A forged integral strainer prevents foreign objects from entering
the turbine . During initial operation additional fine mesh strainers are
added for extra protection. Cam-operated limit switches are provided and
are easily adjusted to operate i n any portion of the valve travel. During
normal operati on, all of the throttle val ve operating part s are completel y
out of the steam flow path .
Valve Stem Freedom Test
The turbine throttle-stop valves should be exercised at least weekly
to detect possibl e valve stem sticking . Prov i si ons are made to test close
t he va l ves from a push button test stat ion (so l enoid operated valves) or by
means of the test val ve mounted on the servomotor. The stop-throttl e
valves are tested one at a time.
Control Valve
The control valve, which may also be called a governor valve or steam
chest valve, provides the function of precisely regulating the speed and
load of the turbine by controlling the steam flow . The control valves,
shown in Figure 31 , are of the pl ug type with di ffuser outl ets . Each valve
i s loose on the stem to assure proper valve and seat alignment . The valves
are partially balanced to reduce the force required to lift them and are
opened by hyrdualic forces and closed by springs . Each control valve back
sets when it is i n the wide open position thus keeping the stem leakage to
a m1n1mum . Typical arrangements of inlet valves and steam chests are descri
bed in the fo l lowing pages .
-65-

Design Concepts: Study Questions
STEAM TURB ItlES
SECTION 2
INLET VALVES AND STEAM CHEST
l. One of the features of the Westi nghouse high temperature design philosophy
is the isolation of the inlet valve assemblies and reheat
valve assemblies from the cylinder.
True/False.
2. Isolation of the valve assemblies and anchoring them to the foundation
makes it possible to:
(l) minimize ---- from start-up and load changing
----
(2) permits station pi ping stresses to be transmitted to the
and not the
----- --------
3. The pri mary function of the throttle (s top) is to --------
in the event of overspeeding the onsetting of the overspeed trip.
4. The control valve or governor valve provides the function of precisely
regulating and of the turbine by
----------
-67-

STEAM TURBINES
SECTION 2
INLET VALVES AND STEAM CHEST
Desi gn Concepts: Answers
l. True.
2. (l ) minimize thermal stress from start-up and load changing
(2) permi ts stati on piping stresses t o be transmitted to the
foundat i on and not the turbine cyli nder.
3. Shut off the flow of steam to the turbine.
4. Speed and l oad; by controlling the steam f l ow .
- 69-

Figure 32 - Doubl e Ended Steam Chest
Figure 33 - External Bar-Li nkage St eam Chest
-70-

STEAM TURBINES
SECTION 2
INLET VALVES AND STEAM CHEST
Fossil Applications
Double Ended Steam Chest
The throttle-stop and control valve shown in Figure 32 i s designed for
units of approximately 600 MW and up, using two of these assemblies .
There are two throttle-stop valves on each steam chest assembly. The
control of the throttle valves is designed such that two valves , one in
each steam chest, operate together . This assures steam flow through each
steam chest during starting .
Each control valve is operated by an individual operating mechanism
(servomotor). The operating range of the servomotors is easily adj usted to
get any desired valve operating sequence and provide essentially a straight
line relationship between governor oil pressure and l oad or steam flow.
Valve Stem Freedom Test
One throttle-stop can be closed and re-opened without closing the control
va l ves . It is, therefore, unnecessary to close the control va l ves
during the valve stem freedom tests. Testin9 can be done with little or no
effect on the load.
External Bar Linkage
Two of the throttl e-stop and control valve arrangements shown in Figure
33 are used for units up to about 300 r1~~ capacity. There is a single
throttl e-stop valve on each steam chest . This valve is hydraulically opened
and spring closed and operates i n the horizontal position. The control
valves are partially balanced to reduce the force required to lift the valve
from its seat and thereby reduce the size of the linkage and the servomotor
(operating mechanism). The slotted valve stem links provide sequential
opening of the valves. Provisions are made in the linkage for fine adjustment
of the valve lifting sequence . Limit switches similar to the switches
on the throttle-stop val ve are provided.
Valve Stem Freedom Tests
The maximum load that can be carried with one throttle valve closed i s
approximately 75 per cent of maximum load.
-71-

Single Ended Steam Chest - Ind i vidual Servomotors
The arrangement shown in Figure 34 i s for units up to about 600 MW
capacity. There is a single throttle-stop valve on each of the two steam
chests . This valve is hydraulically opened and spring cl osed. Each control
valve is operated by an individual operating mechanism (servomotor). The
operating range of the servomotors is easily adjusted to get any desired
valve operating sequence and provide essential ly a straight line relationship
between governor oil pressure and l oad or steam flow.
Valve Stem Freedom Tests
The maximum load that can be carried with one throttle valve closed is
approximately 75 per cent of maximum l oad, therefore, before starting the
val ve stem freedom t ests it is necessary to reduce the load to approximately
75 per cent of max i mum load .
Figure 34 - Combined Stop-Throttle Va lve and Steam Chest
- 72 -

STEAM TURBINE S
SECTION 2
INLET VALVES AND STEAM CHEST
Nuclear Applicati on s
Double Ended Steam Chest
Steam is admitted to the high pressure turbine through separate nozzle
chambers, l ocated in the center of the double flow HP element, from four
individual governor valves through flexible pipe loops . Figure 35 illustrates
a typical assembly of two throttle valves and two governor valves
which are mounted on the foundation, one assembly on each side of the HP
turbine. The entire stop valve and governing valve assembly i s sl ed-mounted
and anchored to the turbine foundation above the floor line.
n
STRAINER
STEAM INLET
Figure 35 - Combined Stop-Throttle Valve and Steam Chest
-73-

Applications: Study Questions
STEAM TURBINES
SECTION 2
INLET VALVES AND STEAM CHEST
1. The doubl e-ended steam chest has two throttle-stop valves and is de -
signed for units of approximately MW and up.
2. One of these assemblies is required for each main turbine unit .
True/False.
3. The steam chest assembly with a single throttle-stop valve and an ex ­
ternal bar linkage is suitable for units of to about 300 MW capacity.
True/Fal se .
4. Slotted va l ve stem l inks provide
- -----
control valves.
------ -
of the
5. The single-ended steam chest with individual servomotors is used for
units up to about (300) (600) (900) MW capacity.
6. The valves are hydraulically (opened) (closed) and spring (opened)
(closed).
7. A typical nuclear unit utilizes two steam chest assemblies, one mounted
on each side of the unit and each containing throttle valves
and governor valves.
8. As with the fossil units, each entire assembly is --
and to the turbine foundation above the floor line.
9. Each of these valves is operated by an ind i vidual servomotor.
True/Fal se.
10. Si nce turbi ne throttle-stop val ves are fixed i n a fully-opened position
during normal operation, they should be tested regularly to detect pos -
sible
----
----
sticking.
- 75-

Application: Answers
STEAM TURBINES
SECTION 2
INLET VALVES AND ST EAM CHEST
1. 600 MW .
2. False . Two assemblies are required, one mounted on the foundation on
each side of the HP elements.
3. True.
4. Provide sequential openings.
5. 600 MW.
6. Hydraulically opened and spring closed.
7. 2 throttl e val ves; 2 governor valves.
8. sled-mounted and anchored to the turbi ne foundation.
9. True.
10. valve stem sticking.
-76-

STEAM TURBINES
SECTION 3
INLET PIPING AND NOZZLE CHAMBERS
High Temperature Inlet Pipe Seal
Inlet pipes carry steam at high temperatures and expand as they heat
up , which could cause a fracture where they join the casing . Therefore,
the piping system is made sufficiently flexi ble to reduce these reactions
on the cylinder to acceptable va l ues. The inlet pipes are connected to the
nozzl e chambers through a bell type, pressure seal arranged to permit
radial movement between the hot inlet pipes and the relatively cool inner
cylinder as shown in Figure 36. As the pipe expands, the transi tion piece
heats up along with it. But since it has room to expand , it does not overstress
the cyli nder . The ring seal prevents the high temperature steam
from escaping into the outer cylinder.
----+-- Turbine
Outer Casing
Pressure -----i--___.~
Seal Ring
--.---Turbine
Inner Casing
Nozzle --­
Chamber
--- Attachment
Flange
Figure 36 - Cross -Section of High-Temperature Inlet Pipe Seal
-77 -

....------ Steam - -4e=====rJ
Inlets
~,----- Oute r
Casing
Sea I Ring
Nozzle
~F--+---+- Chambers
Rotor
Cross-seccio n of high-cemJX'r.u u rc inlec, showing nozzle chamber;, nozzles, and l11gh pressurt impulst blading.
Figure 37 - High-Temperature Inl et, Foss il
l+-il--T---- Pressure­
-78-

Nozzle Chambers
The function of the nozzle chambers of the first stage of the high
pressure turbine is to provide partial arc admission . This is accomplished
by sequential opening of control va lves admitti ng steam only to nozzle
chambers fed by the open valves. In this way steam admi ssion i s controll ed
in 60° arcs in Figure 37 and 90° arcs in Fi gure 38 unless some va l ves are
programmed to ac t together as one va l ve . Multi-va l ve (sequential valve)
operation through individual nozzle chambers improves part l oad thermal
performance.
Und er f ull load, steam passes to the control stage through al l of the
nozzle chambers (full arc admission} , and all of them heat and expand
evenly. In this case, the expansion i s radial, or in and out . When the
turbine is being started or operating under part l oad , some inlet va l ves
will be open and some closed . Steam is admitted to onl y a few of the
chambers , and they wil l heat up unevenly . Some of the chambers expand;
others tend to stay as they are. The result is hi gh thermal stress set up
between adjacent chambers and a strong possibility of distortion or even ­
tual cracking. The cha nce of cracking i s even greater i f the nozzle chambers
are connec ted to the inner cylinder , for , with high di fferential temperatures,
the inner cyl inder and nozzle chambers expand non-uni fo rmly .
The use of separate nozzle chambers allows maximum freedom for thermal
expans i on of all stati onary parts. As a result , design clearances and
proper alignmen t are maintained during all phases of operation , thereby
ensuring a high degree of sustai ned efficiency and trouble-free operati on .
Nuclear turbine technology utilizes the same proven construction technique
of high pressure, high temperature fossi l un its. In the fossil and
nuclear designs illustrated in Figur es 37 and 38, steam en t ers t he high
pressure element through separate nozz l e chambers from indi vidual control
valves . The nozz l e chambers are flexibly welded and keyed to the inner
cylinder and are keyed to each other. They al l ow for unequal radial expansion
and eliminate t her ma l distress between the nozzle chambers and tu r bine
casings during cyclic operation. Individual nozzle chamber castings are
shown in Fi gure 39. With this arrangement, steam can be introduced into
any nozzle or set of nozzles, and the expa ns i on will not affect the others.
-79-

Figure 38 - Nuclear Nozzle Chambers
- 80-

Figure 39 - Individual Nozzle Chamber Castings
-81 -

admission
pi
~~~
STEAM TURBINES
SECTION 3
Inlet Piping and Nozzle Chambers: Study Questions
1. Inlet pipes are welded to
~~~~~~-
eces on the
outer cy l inder to prevent fractures during expansion due to heating up .
2. These pipes connect to the nozzle chambers through a be l l - type pressure
seal.
True/False.
3. This arrangemen t permi ts radial movement between the hot inlet pipes and
the relatively cool
4. The r i ng sea l prevents the high temperature steam from escaping into
t he outer cylinder.
True/Fa l se .
5. The function of the nozz l e chambers of t he first stage of the hi gh
pressure turbine is to provide
~~~~~
proved therma l performance .
for im-
6. The use of separate nozzle chambers allows maximum
~~~~~~~~~
of all stationary parts .
7. In thi s regard , nuclear turbines utilize t he same constructi on techniques
.
True/Fa l se.
8. Since the separat e nozzle chambers are f l exi bly welded and keyed to the
inner cylinder and are keyed to each other, they allow for unequal
and eliminate between
~~~~~~the
nozzle chambers and turbine casings during cyclic operation .
-83-

STEAM TURBI NES
SECTION 3
Inlet Piping and Nozzle Chamber s :
1. Flexible transition.
Answers
2. True .
3. Inner cylinder .
4. True.
5. Partial arc; part l oad.
6. Freedom for thermal expansion.
7. True .
8 . Radial expansion; thermal distress.
-85-

Figure 40 - HP-IP Reheat Turbine Element
Vie" of curbine cyhnder and blade ring, showing method of
supporting and locking lower bbde ring in posmon
Blade r1n$t of Jug" h1gh·prt'ssure, high cemptrature rnrbin(',
wuh uauonary bladtt 1n place
Figure 41 - Blade Rings
- 86-

STEAM TURBINES
SECTION 4
HP AND IP DESIGNS
High Temperature Fossil Cylinder Design
High pressure and intermediate pressure fossil turbines are con ­
structed with two separate cylinders -- an inner cylinder and an outer cylinder
. Both are designed with as high a degree of axial and radial symme ­
try as possible to reduce undesirable thermal stresses .
The HP-IP reheat element illustrated in Figure 40 uses an inner cylinder
to support the high temperature blade ring in the high pressure blade
path. This design minimizes temperature gradients across structural walls
resulting in lower thermal stress . The inner cyl i nders also act as a pres ­
sure vessel permitting thinner outer cylinder walls with a corresponding
reduction in horizontal flange size and, therefore, lower thermal stresses
during cycling operation.
After reheating, the steam expands through the intermedi ate pressure
blading and drops to approximately 650 to 700 degrees. This cooler steam
then flows between the inner and outer cylinders cutting the temperature
differential across the inner cylinder walls to moderate values. Also, the
entire outer cyl inder is kept at reduced temperature levels . This cooling
philosophy has been successful in reducing thermal distress of high tempe r­
ature stationary parts in reheat turbines.
The inner cyli nder is completely free to expand radially. Metallic
seals between blade rings and cylinder prevent leakage of steam in support
grooves . Seal r i ngs which hold running seals in place are separate from
the inner cylinder . These are spring-back seal s which improve performance
and the ability to maintain performance.
In the same way, as is shown in Figures 41 and 42 , separate blade
r i ngs are used to support the stationary blading within the cylinder. The
centerline support of the blade r ing insures alignment wh i le allowing for
differential expansion between the blade ring and cylinder. The separate
blade ring design allows freedom of expansion of the blade ring independent
of the casing reducing thermal stress and misalignment during cycl ic operation.
Again, these rings are supported at the horizontal centerline by
blocks and keyed with tongue and groove fittings for free radial expansion .
An upper plate in the cylinder cover prevents any "riding up " of the bl ade
ring. Thus, radial excursions of the cylinders due to temperature differentials
cannot affect the concentricity of the stationary blades and seals
with respect to the rotor . This high temperature design is further illustrated
in Figu res 43 and 44.
-87-

UPPER PLATE
UPPER HALF BLADE RING
CYLINDER WALL
LOWER PLATE
LOWER HALF BLADE RING
Figure 42 - Blade Ring Support
Figure 43 - Combined HP-IP High Temperature Design
-88-

Combined HP-IP E lement
High-Temperature Design
I
o::>
ID
I
Oncer c;uing cover.
Inner c.tsing CO"c,ar
Upp

HP and IP Fossil Designs:
STEAM TURBINES
SECTION 4
Study Questions
1. Separate inner and outer cylinder construction of HP and IP fossi l
turbines and a high degree of axial and radial symmetry reduces undesirable
thermal stresses.
True/ Fal se .
2. Since the inner cylinders act as a pressure ves sel, thinner outer cylinder
wall s are required since the pre ssure gradient is l ower across
the wall. Thinner wall s result in l ower -------
3. Seal rings wh i ch hold the spring- back r unn ing seals in place are integral
with the i nner cyl inder.
True/False .
4. The separate blade rings which support the stationary bl ad i ng are
---
supported to insure al ignment while allowing for
differential expansion.
5. Thus, radial excursions of the cylinders due to temperature differential s
cannot affect the concentricity of the stationary blades and sea l s wi th
respect to - -
-91-

HP and IP Fossil Designs : Answers
STEAM TURBitlES
SECTION 4
1. True.
2. Lower thermal stresses .
3. Fal se . These seals are separate to reduce thermal stresses.
4. Center-line supported.
5. With respect to the rotor .
- 93-

NOZZL E
CHAMBER
ROTOR
Figure 45 - Rotor Cool ing Arrangement in Area of
Main Steam Inlet Control Stage
INNER CA SING
INT ERMEDIAT E PRESSURE TURBINE
BLADE RING
BA LANCE
PIST ON
T'
ROT OR
COO L ER
STEAM
Figure 46 - Rotor Coo l ing Arrangement in Area of Hot Reheat Inlet
- 94 -

STEAM TURBINES
SECTION 4
HP AND IP DESIGNS
High Temperature Fossil Rotor Cooling
Lower temperature steam i s utilized to cool the rotor at both the main
inlet and the reheat inlet.
A metal 1 s tensile strength and other mechanical and physical properties
change as a function of time and temperature. Metal's reaction to a
load under elevated temperature over a long period of time--the metal 1 s
11
creep 11
characteristic--is an important factor in the design of high temperature
parts wh i ch rotate with high stresses. Rotor creep effects are
considerably reduced, and rotor life extended, if cooling steam can be used
to sweep critical areas adjacent to those locations where 1000 degree steam
is admitted. Figure 45 illustrates the rotor cooling arrangement in the
area of the main steam inlets and control stage. This configuration prevents
high temperature leakage steam from contacting the rotor body . Leak ­
age is controlled by two sets of seal strips (A) moun ted in the nozzle
block. The zone between the seal strips i s connected to the main stream
flow by a series of longitudinal holes (B) drilled through the nozzle block
and nozzle chamber. Hot steam that leaks by the upper set of seal strips
is directed through these longitudinal holes into the main stream flow and
does not contact the main body of the rotor. Leaka ge past the lower seal
stri p is prevented from contacting the rotor by the pumping action of the
inclined holes (C) through the control stage disc. Steam pumped through
these holes blankets the zone between the nozzle chambers and the rotor.
This steam is at impulse chamber temperature (approximately 930 degrees)
which is substantially l ower than the temperature of the leakage fl ow.
Rotor cooling at the intermediate turbine inlet is accompli shed by introducing
lower temperature steam which has been throttled through the balance
piston seals . A portion of this cooling steam flows into the intermediate
pressure turbine blade path between the first stationary and rotating
rows.
The remainder of the cooling steam passes through grooves in the rotor
at the bottom of the serrated root of the side entry blades. This arrangement
is illustrated in Figure 46.
This reduction in rotor temperature more than doubles the rotor creep
rupture life.
These methods of cooling will result in a maximum rotor temperature of
approx imately 930 degrees F. for units with 1000 degrees F. inlet temperature.
This is considerably lower than rotor temperatures on earlier des i gn
units.
-95-

Rotor Thrust Ba lance
When steam passes over a set of blades , it prod uces a powerful t hrust .
In a double-flow element, this poses no probl em since steam flows simu l ­
taneously in opposite directions, and the thrust i s equalized, as i l lustrated
in Figure 47 .
STEAM
THRUST FORCES
Figure 47 - Balanced Thrust
In an oppo sed or spli t flow fos sil turbine the steam passes fi rst over one
set of blades , then another in series . This causes thrust in opposi t e directions
in the high pressure and in the intermediate pressure. To illustrate
this, the steam f l ow path through the combi ned HP - IP element i n
Figure 48 i s traced. Main steam enters through inlets A (separate inlet
pipes for each nozzle group ) and passes through t he contro l stage -- B-C-0.
It f l ows around the inlet pipes in the inner cylinder and enters the
HP bl ading section at 0, exits at E, returning through pipes F t o the
boiler for reheating.
Reheated steam enters the IP section at G and the IP blading section
at H. It exi ts through the space between the inner and outer cylinders, I
and J, to the crossover pipe leading to the LP turbine.
If the design depended on balancing the thrust of the high pressure
blading against the thrust of the intermedi ate pressure blading, a build-up
of deposits in one section of the unit and not the other could cause eventual
unbalanced thrust. Even more serious , a valve malfuncti on cou ld cause
instantaneous complete thrust unbalance with resulting serious da mage to
the machine.
To minimize this thrus t force, a double flow arrangement, as described,
may be used or the turbine designer may provide areas of the rotor body of
known cross- section exposed t o known pressures which then provide a predi
ctable force to resi st or bal ance the thrust in the blade path. Such an
area generally has the con figuration of a pi ston and the forces ac ting on
it are similar to those in a pi st on engine . There i s no axial mot ion , of
-96-

G
Figure 48 - HP- IP Turbine Element
OPPOSED FLOW - BALANCED THRUST
" A " z: ''B''
"Cl+ c2 = " D"
" A" - HP BLADE PATH
Figure 49 - Thrust Balance in HP-IP Element
-97-

Fi gure 50 - Double Flow HP Turbine
Figure 51 - Double Flow IP Turbine
-98-

course, since a thrust bearing must always be provided to hold t he rotor in
its proper position in the cylinder. This provision for thrust balance may
be a "thrust piston," "dummy" or "balance piston. "
In the HP- IP element described, thrust unbalance and resulting damage
is prevented by designing HP and IP blade paths which are independently
thrust balanced by their own dummies (thrust pistons), Figure 49, opposing
the blade path. These pistons always feel the same pressure differentials
as the sections they balance.
When the turbine rating, and therefore the volume of steam, exceeds
the capabi lity of combined elements similar to that described, it becomes
neces sary to separate the high and intermediate pressure sections into
separate turbine elements which can be built for higher ratings.
If the increased rating exceeds the capabili ty of this design, then
the individual HP and IP elements are designed in a double -flow arrangement
similar to the LP turbine. This arrangement is used for ratings in the
1200 MW range.
Fi gures 50 and 51 illustrate a double flow high pressure and double
flow intermediate pressure element respectively.
In Figure 50, steam is fed to the double flow control stage. Each of
the two half capacity control stages is fed by four 90 degree nozzle chambers.
The control valves are so arranged that the valves will open in
pairs and will feed chambers that are opposite in direction (one chamber of
each stage) and diametrically opposite. The torque force on one control
stage wheel is ba l anced by an equal and opposite force on the other wheel.
This arrangement balances the partial admiss ion forces and eliminates side
deflection of the rotor. Cooling of the rotor in the area of the control
stage is accomplished in the same manner as in the combined element previously
described. Beyond the control stage, flow is completely symmetrical.
The major result of this symmetry is that the ax ial thrust of the rotor is
balanced without the need of balance pistons. Consequently, shaft leakages
are minimized and exist at the shaft ends only. Externa l balance piston
leakoff pipes are eliminated.
The intermediate pressure element, Figure 51, has steam fed through
four inlet pipes to a common inlet chamber. The hot reheat steam is prevented
from contacting the rotor by an inlet f l ow guide that bridges the
gap between the first stationary blade rows of the double flow blade path.
Steam from the high pressure turbine exhaust is fed into the zone between
the flow guide and the rotor to provide cooling i n the inlet area as de ­
scribed in connection with the combined high intermediate pressure element.
As in the case of the double f l ow high pressure element , this element is
compl etely symmetrical and is inherently thrust ba l anced .
-99-

own
~~~~-
STEAM TURBINES
SECTION 4
HP and IP Fossil Designs: Study Questions
1. The rotor i s cooled at both the main steam inlet and the reheat inlet
by use of
steam.
2. Rotor life is substantially lengthened if the rotor is cooled by using
l ower temperature steam in those areas where 1000 degrees F. steam is
admitted .
True/False
3. Since the steam pressure is higher on the inlet side of a row of blades,
a powerful force is produced in an axial direction.
True/ False.
4. In a double-flow element, steam flows simultaneously in opposite directions
and thi s force or thrust is
~~~~~~-
5. In other desi gns it i s desirable to bal ance individual sections of the
rotor independently in order to prevent damage in the event of:
a .
b.
6. The HP and IP blade paths are independently thrust balanced by their
7. These pi stons always feel the same ~~~~~~~~~~~- as the
sections they balance .
8. Larger turbine ratings have the HP and the IP sections in separate turbine
elements.
True/False.
-100-

9. For the l argest ratings , t he HP and IP elements are made in a doubl e­
fl ow confi guration with 50 per cent of t he steam flow i ng through eac h
bl ade path . Thi s construction i s used for ratings of MW to
---
MW.
10. Is rot or cooling of the separate HP and IP el ements similar to that of
t he combi ned element?
Yes
No
11 . Si nce steam fl ow through t he double-fl ow element is symmetri cal, the
--- --
of t he rotor is bal anced without the need of
-101-

HP and IP Fossil Designs: Answers
1. Lower temperature steam.
2. True.
3. True.
4. Equalized.
STEAM TURBINES
SECTION 4
5. (a) a build- up of deposits in one section of the unit and not the other
(b) a valve malfunction which coul d cause instantaneous complete thrust
unbalance.
6. Their own dummies (t hrust pistons) .
7. The same pressure differenti al s.
8. True .
9. 1000 MW to 1200 MW.
10. Yes
11 . The axial thrust; balance pistons.
-103-

EXHAUST (1) EXHAUST (1)'
Figure 52 - High Pressure Element - 1800-RPM Double-Flow Design
-104-

Nuclear High Pressure Turbine
STEAM DESIGNS
SECTION 4
HP AND IP DESIGN
A l ong itudinal section of the 1800 rpm double fl ow high pressure turbine
is shown in Figure 52. Steam is admi tted to the double flow element
through four inlet pipes, t wo in the base and t wo in the cover, connected
to fo ur separate nozzle chambers wh ich are flexibly mounted in the turbine
casing.
Separate nozzle chambers flexibly wel ded di rectly to the outer cyl ­
inder provide partial arc admission for improved part load performance .
The use of separate nozzle chambers and separate bl ade rings also al ­
l ows maximum freedom for thermal expansion of all stationary parts. As a
resul t, design clearances and proper alignment are maintained during all
phases of operation , thereby ensuring a high degree of sus t ained efficiency
and trouble-free operation. Since the nuclear steam condi tions, both pressure
and temperature are low at the inlet, no inner cylinder i s provided.
The turbine is completely symmetrica l emp loying two bl ade rings per
side. Steam exhausts through four openings in the cylinder base and two
openings in the cyl inder cover. Exhaust flow t o the MS -Rs was shown in
Figure 21 on Page 37. Thi s type of construction fol lows techniques developed
for the hi gh pressure, high temperature un i ts using fossil fuel steam
conditions.
The material of the outer cylinder, nozzle chambers and blade rings is
carbon steel as compared to chrome moly steel alloys used in the fossil
fired units at the same pressure level. Removable spring-backed segment al
seal rings are used in the blade rings to min i mi ze blade tip leakage . These
seals are illustrated in Figure 53 . Al l blade rings located in the high
moisture zones are prov ided with stainl ess steel cl adding and mo i sture removal
drainage slots as shown in Figure 54 .
-105-

Blade Rino
Rotor
Spring-Bocked
Se9mentol
Seal Rin9
Figure 53 - Sealing for HP Reaction Blading
-1 06-

CYLINDER
BLADE RING
Figure 54 - Mo isture Prot ecti on
- 107-

STEAM DESI GNS
SECTION 4
HP AND IP DESIGN
Nuclear HP Turbine:
Study Ques tions
l. Steam is admitted to the HP turbine in separate nozz l e chambers which
provide
for improved
--------------- ------
2. In this design, steam is admitted through separate -------
chambers, l ocated in the center of the
HP
elements, from (two) (four) (six) individual governor valves through
f lexible pipe loops.
3. Inner cylinder construction is used here as on the fossil units.
True/ False.
4. Separate nozzle chambers and separate blade rings allow:
a . maximum freedom for of al l stationary
parts;
b. maintenance of ----
c. mai ntenance of proper
------
5. Following techniques devel oped for the hi gh pressure, high temperature
foss i l units , the nuclear HP turbine is designed with as high a degree
of axial and radial symmetry as possible to reduce undesirable thermal
stresses .
True/False .
6. A particular consideration in nuclear design is due to the relatively
high content of the steam .
-109-

7. Moisture protection features include:
2.
----
cil itate interstage moisture remova 1 .
1. blade bores lined with ------
through the blade ring to the exhaust to fa-
-110-

STEAM DESIGNS
SECTION 4
HP AND IP DESIGN
Nuclear HP Turbine: Answers
1. Provide partial arc admission for improved part load performance.
2. Nozzle - double flow - four.
3. False. No inner cylinder is provided due to the lower temperature
level at the inlet.
4. (a) freedom for thermal expansion; (b) design clearances; (c) proper
alignment.
5. True.
6. Moisture content.
7. Stainless steel; drain holes .
-111-

Figure 55 - Fossil Reheat Stop and Interceptor Valve
-11 2-

STEAM TURBINES
SECTION 5
REHEAT STOP AND INTERCEPTOR VALVES
Fossil App l ications
The reheat stop valve and interceptor valve frequently act as back-up
va l ves to each other in the steam line entering the IP or LP turbine. See
Figure 55.
Steam returning to the turbine after reheating, enters through reheat
stop-interceptor valves. These have no governing function as did the inlet
control valves . In the event of a "trip" or shutdown of the unit, suffi ­
cient steam may be present in the HP system , including piping and reheat
section of the boiler, to cause overspeed of the turbine.
Therefore, a positive means of preventing this reheated steam from
entering the IP turbine is provided. As at the main inlet, a deg ree of redundancy
and added safety, is provided by placing the reheat stop valve
and interceptor valve in series .
The reheat stop valve can be of a design similar to the ma in stop
va l ve ; or a swing check valve which incorporates a rotating shaft design
to nullify the effects of deposits from operation and a spherical seated,
pressure sealed bushing to eliminate shaft l eakage.
The interceptor valves are generally similar to a highly balanced
control valve , or they may also be butterfly valves . The valve is opened
hydraulically and spring closed . It is surrounded by a forged type
strainer to keep foreign material from enteri ng the turbine. During initial
operation additional fine mesh strainers are used.
The interceptor val ve may be used when a temporary fault in the power
transmission line occurs. If the turbine can be protected aga inst overspeed
ing but still kept on line by rapid closing and opening of the interceptor
valves, a more stable system exists. These valves control steam flow
to t he intermed iate and low-pressure turbine elements, which in combination
generate approximately 70 percent of the total unit power . By closing the
interceptor valves, this major portion decays quickly because the stored
energy effect of the reheater i s avo ided. This valving scheme is generally
referred to as fast turbine-valve control. (See Fast Valving, MA-465).
When the i nterceptor valves close , the large reheater volume absorbs
steam flow ahead of the i nterceptor valves for several seconds . This cushioning
effect, along with possible blowing of reheater safety valves, minimizes
the transient felt by the steam supply system . (However, in the event
that reheater safety valves do open, reseating difficulties and resulting
steam leakage could cause operating probl ems.)
Typical stop and interceptor valves are shown in the following description.
-113-

Figure 56 - Reheat Stop Valve
- 11 4-

Reheat Stop Valve, Unanchored
Figure 57 - Reheat Interceptor Valve
The reheat stop valve i s of the unbalanced swing disc type and is
shown i n Figure 56.
The operating mechanism for the reheat stop valve is a two pos i t i on
hydraul ic mechanism . It is either in the wide open or closed positi on . No
manual test device is provided since the reheat stop should not be t ested
without cl osing the corresponding interceptor valve.
Interceptor Valve, Unanchored
The design of the typical interceptor valve is shown on Figure 57.
There may be two or four of these valves depending on the size of the unit.
- 115-

Figure 58 - Reheat Stop Valve-Interceptor Valve Assembly
- 11 6-

Reheat Stop-Interceptor Valves -- Anchored )
One reheat stop valve is combined with two interceptor valves as shown
in Figure 58 . Combining the valve assemblies into one unit minimizes the
overall space required. There are two of these assemblies -- one on each
side of the turbine.
features:
The combined reheat stop- interceptor valve assembly has the following
1. One reheat stop valve and two interceptor valves are combined into
one unit at the factory to minimize overall space required.
I
2. Total assembly anchored to the foundation permits hot reheat con ­
nections to be stressed to the piping code al l owable limits .
3. "Straight-through" reheat stop valve and single 90 degree turn in
interceptor valves plus diffuser constructi on of interceptor valve
outlet minimize overall pressure drop.
4. All operating parts above the turbine fl oor line readily accessi ­
ble for maintenance.
5. Total assembly with supports is mounted on a bedp late to facilitate
shipment and erection.
6. Supports are "cold sprung" at the factory, simplifying field ins
ta 11 a ti on .
- 11 7-

STEAM TURBINES
SECTION 5
REHEAT STOP AND INTERCEPTOR VALVES
Nuclear Applica t ions
Figure 59 represents a cross-sectional view of a butterfly type reheat
stop and interceptor valve as used by Westinghouse . The stop and interceptor
valves, identical in design, are placed in series in the LP turbine
inlet steam piping. These quick-closing valves provide overspeed
protection after a load rejection by limiti ng t he fl ow of steam from the
moisture separators or moisture separator-reheaters to the low pressure
turbine .
Figure 59 - Stop and Interceptor Valve
-119-

Stem Freedom Tests
STEAM TURBINES
SECTION 5
REHEAT STOP VALVES AND INTERCEPTOR VALVES
Bot h nuc l ea r and foss il i ntercep t or va l ves and reheat stop va l ves
should be exercised at least weekly to detect possible valve stem sticking .
This test can be carried out at any load , wi th neg l i gible effect on the
l oad. On units with two reheat lines , interlocks prevent testing of both
sets of valves at the same time. On units with four reheat lines , interl
ocks prevent more t han two sets of valves from being tested at one time;
however , the normal test procedure i s to test only one set of valves at a
time.
- 120-

Rehea t Stop and Interceptor Valves:
STEAM TURBINES
SECTION 5
Study Questi ons
1. Steam returning to the turbine after reheating enters through reheat
----------
val ves.
2. These (have) (have no) governing functi on as did t he inlet control
va l ves.
3. In the event of a "trip" or shutdown of the unit, sufficient steam
may be present in the HP sys tem, including pi ping and reheat section
of the boiler, to cause (underspeed) (overspeed) of the tu r bi ne.
4. Therefore a positive means of preventing this reheated steam from
entering the turbine is provided .
5. As at the main inlet, a degree of redundancy and added safety, is
provided by placing valves in series - - - - va lve
and
valve.
6. The fossil turbine reheat stop valve design may be :
a. Simi lar to the main stop valve;
b. A butterfly- type valve;
c. A swing -check va lve.
-------
7. The intercept or valve i s genera lly similar to a bal anced control valve
or may be a
valve.
- ------
8. The interceptor valve is under control.
- ------
9. It is never closed when the main contro l valves are open.
True/False.
10. The interceptor valve may be of the unanchored-type which is mounted
in steam piping.
True/Fa l se.
-121-

11. For fossil applications, the reheat stop and interceptor valves may
be of the anchored-type and the combined valve assembly includes
---
stop valve(s) and interceptor valve(s) .
12 . There are usual ly two of these assemblies -- one on either side of
the turbine.
True/Fa 1 se .
13 . The combined arrangement minimizes --------
required .
14 . The total assembl y anchored to the foundation permi ts hot reheat connections
to be stressed to the piping code allowable limits .
True/ Fa 1 se .
15. Total assembly with supports is mounted on a bedplate to faci l itate
------- -------
and
16. For nuclear applicati ons , the design of the stop and interceptor valve
i s the same and is of the type .
17. These va lves are mounted on the turbine foundation .
True/ False.
18. No additional space or major foundation support is needed .
True/Fa lse.
19 . Li ke the main stop valve , these valves are fully opened duri ng normal
operation of either fossil or nuclear units .
True/False .
20 . For thi s reason , they shou ld be exercised regularly in order to detect
possible ------ --
sticking .
-123-

STEAM TURBINES
SECTION 5
Reheat Stop and Interceptor Valves :
l. Stop- interceptor.
Answers
2. Have no.
3. Overs peed .
4. IP.
5. Reheat-stop; interceptor.
6. The valve may be either (a) or ( c).
7. Butterfl}'. valve.
8. Governor control.
9. True .
10 . True .
11 . .l_ stop valve and~ interceptor valves .
12. True .
13. minimi zes overall space required .
14. True .
15. facilitate shipment and erecti on .
16. butterfl,l'. type .
17 . False. The valves are placed in series in the LP inlet steam pi ping.
18 . True.
19 . True .
20 . valve stem sticking .
-125-

OUTER CYLINDER
INNER CYLINDER
I
---'
N
O"l
I
Figure 60 - 3600 RPM Double-Fl ow Low Pressure Turbine

Fossil Fuel Turbines
STEAM TURBINES
SECTION 6
LOW PRESSURE DESIGNS
Westinghouse follows the high temperature design philosophy in the low
pressure turbines where the potential temperature differentials are the highest
in the unit. When the steam enters the turbine inlet from the crossover
lines, the temperature is approximately 700 degrees F. When it crosses the
last row blades, its temperature is less than 100 degrees F. -- a 600-degree
drop. In spite of the moderate temperature levels, this is the largest differential
encountered in the turbine.
For this reason the low pressure turbine, illustrated in Figure 60, is
constructed with an outer cylinder, and two inner cylinders and a thermal
shield. The design provides three walls over which the temperature differential
between the inlet and the condenser is distributed. As in the high
pressure-intermediate pressure element, each stationary part is designed so
as not to impose thermal stress upon an adjacent part. Liberal seal clearances
are used for all inter-stage sealing.
This construction reduces temperature gradients and eliminates the problems
of thermal distortions of major fabrications. There is less chance of
seal rubbing and accompanying loss of efficiency. The low pressure turbine
is manufactured as a fabrication to insure uniform wall thickness for large
stationary parts minimizing thermal stresses. This construction provides a
liberal exhaust hood configuration to minimize blade excitation forces. A
low pressure rotor is shown in Figure 61 .
Figure 61 - 3600-RPM Double-Flow Low Pressure Rotor
-127-

.......
I
~
CX>
I
Figure 62 - 1800-RPM Double-Flow Low Pressure Turbine

Nuclear Fuel Turbines
Construction of the low pressure nuclear turbines for light water reactor
applications is essentially the same as that of 1800 rpm elements in
many fossil fired plants. See Figure 62 and 63. To minimize possible distortion
effects of large fabricated stationary parts on seal clearances,
the temperature drop from inlet to exhaust is taken in steps across multiple
walls, utilizing a combination of separate inner cylinders and separate
blade carriers rings. In addition, thermal shields are attached to the outside
of the inner cylinder to reduce temperature gradients that cause distortions.
The rotors are built up of alloyed discs shrunk and keyed onto
an alloy shaft.
Water is removed at extraction points and specially designed moisture
removal zones as shown in Figure 64. The effectiveness of moisture removal
was determined from a series of laboratory and field tests . Since the size
of the water droplets varies inversely with the pressure level, a greater
amount of water can be removed at the lower pressure extraction zones.
Figure 63 - 1800-RPM Double-Flow Low Pressure Rotor
-129-

Figure 64 - Moisture Remova l in Low Pressure Cyl inder Base
-130-

STEAM TURBINES
SECTION 6
Low Pressure Designs: Study Questions
l. In both nuclear and fossil low pressure units, the potential temperature
differential s are the (highest) (lowest) in t he unit.
2. For this reason, the fossil low pressure turbines are constructed with
an cylinder, and cylinders and a shield.
3. Each stationary part is designed so as not to impose thennal stress upon
adjacent part. This construction reduces
and
eliminates the problems of
of major fabrications.
4. Liberal seal clearances are used for al l interstage sea li ng and there is
is less chance of and accompanying loss of
~~~~-
5. Both the nuclear and fossil low pressure turbines are of fabricated
construction.
True/False
6. The rotor may be machined from a sol i d al l oy steel forging or may be
built up of alloyed discs shrunk and keyed onto an alloy shaft. The
solid steel forging construction is usual ly applied to~- r pm (fossil)
units . The built-up construction is usua lly applied to~- rpm
(nuc l ear) construction.
l .
Construction of the l ow pressure nuc lear turbines for light water reactor
applications is (essentially the same) (radically di fferent from)
that of l ,800 rpm el ements in many foss i l fired plants.
8. To minimize possibl e distortion effects of l arge fabricated stationary
parts on seal cl earances, the tempera ture drop from inlet to exhaust
is taken in steps across walls .
-131-

9. This method uti l izes a combination of separate --
and
separate blade
---
10. In add i t i on, therma l shields are attached to the outside of the inner
cylinder to (reduce) (i ncrease) temperature gradients that cause distortions.
11 . As stated earlier, water i s removed at ----- points and specially
des i gned
zones.
12. Si nce t he si ze of the water dropl ets varies inversely with the pressure
l evel , a greater amount of water can be removed at the:
a. Lower pressure extraction zones .
b. Hi gher pressure extract ion zones .
- 133-

Low Pressure Des igns:
l. Highest.
Answers
STEAM TURB INES
SECTION 6
2. Outer cylinder; two inner cylinders; thermal shield.
3. Reduces temperature gradients and eliminates the problems of thermal
distortions .
4. Less chance of seal rubbing and l oss of efficiency.
5. True.
6. The solid steel forging construction is usuall y applied to 3600 rpm
un i ts which wi l l normally be for fossil application. The longest, l as t
row blades may be installed on a disc which is shrunk and keyed to t he
rotor body . Discs shrunk and keyed onto an alloy shaft are usually
1800 rpm construction.
7. Essential ly the same
8. Multiple.
9. Inner cylinders - carri er rings.
10. Reduce.
11. Extraction - mo isture removal.
12. a. Lower pressure extraction zones.
-1 35-

STEAM TURBINES
SECTION 7
TESTING AND INSPECTION
Proper scientific testing procedures are not only essential for assuring
the quality of the product while i t i s being manufactured, but also are
an essential part of routine maintenance activity through the life of the
equipment to assure reliability. A number of testi ng procedures are avai l­
able to assist in the diagnosis of the condition of a part of the equipment
either during the manufacturing phase or after the equipment is in service.
Generally, testing procedures can be classified as either 11 destructive 11
or 11 non-destructive. 11 For example, the qual ity of a turbine rotor could be
tested by rotating it at an increasing rate until it exploded -- a destructive
test. As an alternate, a number of "non-destructive" test procedures
are availabl e which can be used to assist in a diagnosis of the rotor quality
without damaging it. Most of these procedures are, of course, applicable to
testing other parts of the mach ine as well as other products.
Boroscopic Examination
This test is used typically on turbine and generator rotor forgings.
These forgings genera l ly have a bore hole dri l led through the axis for this
purpose. This ho l e at the center of rotation does not appreciably affect
the strength of the forging and is actually the region which is most likely
to contain inclusions (foreign particles) and voids or discontinuities .
The bore is polished to improve the sensitivity and reliability of the inspection.
The inspection is carried out by use of a visual instrument containing
magnifying mirrors and lights which can be inserted through the
bore of the rotor forging. In addition to this visual inspection a test
using magneti c particle techniques or borosonic (u l trasonic) techn iques may
be performed . These procedures wi ll be di scussed below .
Magnetic Particle
Magnetic parti cl e inspection is a nondestructive method for detecting
cracks , seams, porosity, or lack of fus i on at or near the surface. It depends
on the magnetic properties of the materials to be tested and cannot
be used on al uminum, brass, copper, bronze, magnesium, austenitic stainless
steel or other nonmagnetic materials .
The method utilizes magnetic fields to reveal discontinuities in materials.
A magnet will attract magnetic materials onl y when it has ends or
poles . If there are no external poles, magnetic materials will not be attracted
to a magnetized material even though there are magnetic lines of
force flowing through it.
When a discontinuity or crack is present the effect is to establish
minute magnetic poles at the edge of the discontinuities. This forces some
of the mag netic lines of force out of the metal path and creates an attraction
for magnetic particles at the discontinuity.
- 137-

The surface to be examined is magnetized by means of a high-amperage
current and, with the current on, the area under investigation is dusted
with fine iron particles. A light stream of air is generally used to remove
parti cl es not affected by the magnetic field.
If there is a crack or defect in the part at or near the surface the
iron particles wil l collect at this point, outlining the defect.
Ultrasoni c Test
Ultrasonic inspection is used for the detection of surface and sub ­
surface flaws. Ul trasonic inspection methods utilize high-frequency mechanical
vibrations, usually between l and 10 megacycles. The principle
involves a controll ed and uniform beam of ultrasonic energy which is directed
by a transducer into a test material. The energy will be transmitted
with little loss (or attenuation) through a homogeneous material.
It will be either attenuated or reflected by discontinuities or defects in
the physical structure existing in a second location in the same material
or in another material. The measurements of the energy change, either by
attenuation or reflection, are the criteria employed.
Radiography
This is one of the most important and standardized non-destructive inspection
tools. The source of radiation can be either X-rays or a radioactive
isotope. In either case. the radiation proceeds in straight lines
to the object being tested . Some of the rays pass through the material
and others are absorbed depending on the thickness and density of the material
being radiographed.
Where the material being examined has a void such as gas pockets,
incomplete weld penetration, or a material of less density than the base
material such as slag, less radiation is absorbed. A greater amount of
radiation is t hen projected on to the radiographic film, recording a dark
spot corresponding to the position of the void or defect.
Film radiography thus provides a permanent, visible record of the
internal condition of a product, furnishing funda menta l information helpful
in judging material soundness or unsoundness.
Dye Penetrant Test
This procedure normally involves applying a dye by spraying or brushing
?n th~ meta l surface and al l owing it to penetrate i nto cracks and
crevices .
The surface is then cleaned by wiping with cleaner or washing with
water spray. This removes the excess penetrant from the surfaces but not
from the cracks or pores. The next step is the application of the developer,
a fine white powder suspended in a volatile solvent, which is sprayed
on the surface. As the liquid in the developer evaporates, the white
-138-

Dri ve Turbine
Thrust Bearing
and
Turning Gear
Low Temperature
Zone
Insu l ati on
Figure 65 - Multi ple-Temperature Heater Box
- 139-

powder rema1n1ng acts as a blotter by drawing t he penetrant from the
crevices and defects and spreading it over a surface above and on each side
of the defect.
This test provides an effective method for the detection of fine and
narrow discontinuiti es such as cracks, seams , porosity and laminations .
Rotor Manufacture and Inspection
Rotor shafts are received from the manufacturer as solid, rough ­
machined forgings . The ingots from which these forgings are made are
poured by the vacuum degassi ng process, the most advanced technique known
to the metals industry for producing f l awless ingots .
Many different tests are performed before the rough forging is shipped
to the Steam Turbine Division . An ultrasonic test is conducted on the
rotor forging . This test detects any flaws existing deep within the body
of the forging. In addition, magnetic particle tests are conducted t hat
will reveal the presence of flaws on and near the external and bore surfaces,
plus a complete visual inspection of the bore.
Next, a hollow drill cuts steel samples from the forging sp indle
itself -- a process called "trepanni ng . " These are selected at critical
sections, in areas of excess metal which wi ll eventually be mach ined off.
These specimens are examined and tested in creep-rupture test units. If
they do not meet rigid specifications , the forging is rejected. If the
forging passes these tests, it moves on for final machining , blading, and
ma ny more rigid inspections.
One of these tests is to determine notch sensitivity. Samples are
taken from the rotor, notches are machined in them, and they are placed
under specified loads. A furnace maintains a constant temperature around
the sample. The test shows how well the metal resists fracture at the
notch points.
After completion of manufacture, the rotor is run with its blades at
full speed and overspeed in a heater box, Figure 65, at operating temperature
that the rotor will encounter in service . The use of this facility
permits shop balancing at operating speeds and tempera tures. This facil ­
ity locates thermally unstable rotors before they are shipped to the field,
and it also min imizes the need for touch-up balance in the field during
initial operation . Finally, the rotors are installed in the completely assembled
unit for checking of fits and clearances.
-141-

STEAM TURBINES
SECTION 7
Rotor Manufacture and Inspection: Study Question s
l. Many different tests are performed on the solid, rough machined fo rging
for a turbine rotor . These include:
l . a test to detect any flaws existing deep within the body of the
forging--an
-----
test;
2. test s for the presence of flaws on or near the external or bore
surface -- a
-------
test;
3 . a complete -------inspection of the bore;
4. "Plugs" removed from the forging by the process called trepanni ng
are examined and tested in test units .
5. samples from the rotor with notches machined in them are placed
under specified load and temperature to determine --------
2. After manufacture, the bladed rotor is run at full speed and overspeed
in a heater box at operating temperatures it will experience and
service.
l. The use of this facility permits - -- at operating
-------
speeds and temperatures.
3. The thermal stabi l ity of the rotor is determined before shipment to
the field.
t rue/false
-143-

STEAM TURBINES
SECTION 7
Rotor Manufacture and Inspection: Answers
1. (1) ultrasonic test;
(2) magnetic particle test
(3) complete visua l inspection;
(4) creep-rupture test;
(5) notch sensitivity test.
2. (1) permits shop balancing
3. true
-144-

STEAM TURBINES
SECTION 8
BLADING
Factors Affecting Performance
The basic function of a steam turbine is to convert the stored thermal
energy of steam into mechanical work. This is accomplished by expansion of
the steam through stationary nozzle vanes and rotating blades. The geometry
of the nozzles and blades determines the pressure distribution throughout
the turbine and also directs and turns the steam jets so that the forces
on the blades develop a torque on the shaft.
The efficiency of the conversion of t hermal energy to mechanical energy
is a fun ction of:
1. Specific work level of the blading used;
2. Aero-dynamic qual i ty of the flow passages formed by the nozzl es
and blades;
3. Amount of steam by-passing the passages through leakage areas
formed by the necessary running clearances existing between rotating
and stationary parts;
4. Losses associ ated with transporti ng the steam to and from the turbine.
Approximately half of the fluid dynamic losses of a steam turbine occur
within the flow path and consist of losses within the blade flow passages,
internal blade path leakage losses , and separation losses caused by
discontinuities in the fl ow path.
Impulse and Reaction Bladi ng
The steam turbine takes two steps to change heat energy to mechanical
work. First, steam expands in a nozzle, discharging at high velocity. In
this way the total heat (enthalpy) of the steam partly changes to velocity
(kinetic energy -- the energy of motion) .
The force of the jet produced by this transformation in the nozzle
can be used in either of two ways.
In each case, heat energy of the steam is transformed into velocity
energy in the nozzle and then into mechani cal work.
As s hown in Figure 66, if the nozzle is free to move, the reaction
pushes against the nozzle and it travels in the direction opposite to the
jet, lifting the weight.
-145-

f Steam
R~~~~~n • • h?
w
Figure 66 - Reaction Principle
For every action there is an equal and opposite reaction -- this i s
the basis for such devices as rotating lawn sprinklers, rockets, and jet
aircraft.
The reaction principle is sometimes mi sunderstood -- the push of the
jet on air has nothing to do with the action. The force that does the
pushing is in the nozz le. If the box in Figure 66 has no nozz le opening
and is f illed wi th steam under press ure, the pressure act i ng on each wall
balances that acting on the opposite wall. Since there are no unbal anced
forces, the box remains still. However, if we make a hole in one side for
a nozzle, steam will be released in a jet and pressure in the nozzle is
less than pressure at a corresponding point on the opposi te wall . The unbalanced
force thus produced causes the box to move in a direction opposite
to the jet stream. Very simply, this is the principle of the reacti on t urbine.
In Figure 67 the nozzle is mounted on a whee l and supplied with a box
filled with steam. The reaction force rotates the wheel in a direction opposite
to the jet and useful work is available at the shaft.
Nozzle
mounted-~
on wheel
Figure 67 - Reaction Principle
-146-

If the nozzle i s fixed as in Fi gure 68 and the jet directed against a
crude blade, the jet's impulse force pushes the blade forward, lifting the
weight.
Impulse
Force
Fi gure 68 - Impulse Principle
A force i s exerted i n chang ing either the speed or direction of a body
in moti on, and the amount of force depends on the extent to whi ch speed or
directi on is changed. Th i s is illustrated in Fig ure 68 where t he jet (a
movi ng body) has its speed and direction changed by the cur ved blade and
the force moves the bucket and lifts the weight.
In Figure 69 i f we mount the curved blade on t he wheel ri m and fi x t he
nozzl e , we also obtain shaft work and have a crude but wo rkable impu l se turbine
.
······························
~~;~i~~ l ll~ l~~~~~~ ~ l ~ ~; i ·..
.........................
························
Blade
mounted
on wheel
/
Stationary
nozzle
Figure 69 - Imp ul se Principle
-147-

STEAM TURBINES
SECTION 8
Blading :
Study Questions
l . The conversion of thermal energy of steam into mechanical work is ac ­
complished by expansion of the steam through stationary
~~~~~~~
and
~~~- -~~~~~--~~~~-
2. The design of the nozzles and blades determi nes:
l .
throughout the turbine.
2. directs and turns the steam jets so that the forces on the blades
develop a
on the shaft.
3. The principle losses within the flow path are a function of:
l .
The aero-dynamic quality of the flow passages formed by the nozzle
and blades .
True/Fal se
2. The amount of steam by-passing the passages through leakage areas .
True/False
4. In a steam turbine, the steam expands in a nozzle, dischargi ng at hi gh
velocity . This ve locity -- kineti c energy the energy of motion --
is used to produce
~~~~~~
5. This energy of motion may be used in two ways :
l . If the nozzle is not fixed, the will move it in a
~~~~~direction
opposite to the jet.
2. If the nozzle is fixed and the jet is directed against a moveable
blade, the jets force pushes the blade forward .
-149-

STEAM TURBINES
SECTION 8
Blading: Answers
1. (1) nozzle vanes and rotating blades
2. (1) determines the pressure distribution (2) develop a torque on the
shaft
3. 1. True
2. True
4. mechanical work
5. (1) reaction (2) impulse
-150-

STEAM TURBINES
SECTION 8
BLADING
In an actual turbine the stationary nozzles of a reaction turbine are
made by using blade sections shaped to form nozzle walls as shown in Figure
70 . These are arranged in a ring around the shaft or rotor. In Figure 71
an adjacent set of moving blades moun ted on the turbine rotor receives
steam flow from these stationary nozzles. Some expansion occurs in both
moving and fixed blades . Figure 71 shows approx imately the same pressure
drop in both fixed and moving blades . By definition this is a 50 per cent
reaction stage and the acceleration of the steam is also divided equally
between the stationary and rotating rows. This illustration also shows how
the absolute velocity rises in the fixed blades and falls in the moving row .
This may seem to contradict the principle that expansion in a nozzle
produces increased velocity and the prior statement that acceleration of
the steam is divided equally between stationary and rotating rows . While
the absolute velocity (referred t o the earth) decreases in the moving
blades, expansion in the moving blades does boost velocity in relation to
the moving blades - - that is if we had a viewpoint on a blade - - the steam
would seem to speed up .
Fixed l Moving
Figure 70 Figure 71
Reaction Nozzle Wall (Fixed Blades) and Moving Blades
- l 51 -

111111
Stationary
Diaphragm
(Nozzles)
in
Nozzles
Steam pressure
Figure 72 - Impulse Nozzles
Figure 73 - Impulse Blading
Figure 74 - Impulse Blading
Figure 75 - Reaction Blading
- 152-

A pure impulse stage is one where the entire stage pressure drop occurs
across the stationary row and no pressure drop across the rotating
row . Thus, the acceleration of the steam takes place entirely in the stationary
row or nozzle .
Fi gure 72 shows an actual nozzle and blade relationship in a simple
impulse turbine . In Figure 73 the nozzl es , arranged in a ring at one side
to clear the blades , feed steam at an angle to bl ade travel . The crescentshaped
blades permit free entry and discharge and produce the change of
speed and directi on which gives the rotational force. This figure also
shows that steam expansion (pressure drop) occurs only in nozzles and pres ­
sure rema ins essential ly constant in blades . The velocity rises in nozzles
but falls in the bl ades.
A force is exerted in changi ng either the speed or direction of a body
in mot ion and the amount of force depends on the extent to which speed or
direction i s changed . For thi s reason , and since all of the pressure drop
occurs across the stationary row in a pure impulse stage, the steam velocity
leaving the st ationary row is quite high -- general ly twice that of t he
blade speed . In addition, since the change in direction is important in
the impulse blade to opti mi ze the energy conversi on , the t urning ang le is
quite large. This i s illustrated in Fi gure 74 .
In the case of the reaction stage, Figure 75, the pressure drop is
di vided over both the stationary and rotating row, thus the steam velocity
leaving the stationary row is lower . The steam velocity relative to the
rotating blade is also lower. A lower turning angle is required through the
rotating blade of the reaction stage t han i s required through the rotating
blade of an i mpulse stage. This is also illustrated in Fi gure 76.
-153-

Leaving A ngte
Leaving

Re lative
Aerodynamic Efficiency
-, -'* ,.
,,
-~
-----
---- ----
Reaction
Impulse
-
6
.3
6 .8
Stage Velocity Ratio: V Blade
V Steam
Figure 77 - Ve locity Compoundi ng
Figure 78 - Rel ati ve Effi ciency
Velocity Compounding -- Curtis Stage
An ideal Rateau stage i s s i mp ly the pure impul se stage previously discussed
. Rateau was one of the early builders to successfully use this type.
When the pressure drop across a Ra teau stage i s large , the steam velocity
i s relatively high and the high speed steam jet gives up only part
of its kinetic energy in the first row of moving blades . If the directi on
of the steam is reversed, the remainder of the energy can be utilized without
the necessity for a row of nozzles . Thus , in the Curtis stage the steam
jet gives up part of its energy in the first row of mov ing bl ades. Then it
passes through a row of stati onary reversing blades which redirect the steam
into the second row of moving bl ades where mos t of its remaining energy is
absorbed . The Curtis stage i s also referred to as a velocity compounded
impulse stage. This arr angement is illustrated in Figure 77.
Selection of Blading
Each type of stage has inherent advantages which must be wei ghed in
making a sel ection. Two factors must be weighed if maximum efficiency is
t he primary concern:
l. Aerodynamic losses in the fl ow passages;
2. Leakage.
The aerodynamic loss of any blade path i s a function of the amount of
turning the steam must undergo in travelling t he path. Passage eff ici ency
decreases as the flow turning angle i ncreases due t o added fri ction and
turbu lence in t he blades. The relative aerodynami c efficiency is illust
rated in Figure 78 . Velocity ratio is t he ratio of blade velocity to steam
velocity and as the velocity ratio increases , the loading per stage_decreases
. As is shown , the peak relative effi ciency of impulse type stages
is usually lower t han for reaction stages .
- 155-

Figure 79 - HP -IP Reheat Turbine Element - Impulse Design
Figure 80 - Impulse Nozzle Diaphragm
- 156-

Sealing Arrangement
The effect of leakage also plays an important role in the selection of
stage type.
Where the leakage areas become an appreciable percentage of the total
steam flow area, leakage effects will outweigh the greater aerodynamic
passage efficiency of reaction blading and one would select an i mpu lse
stage. However, where leakage areas are a small percentage of the total
steam flow area, the greater aerodynamic quality of reaction stages outweighs
the leakage losses and the reaction stage should be selected.
Impul se turbines are normally constructed with the moving blades on
wheels or discs that are shrunk on and keyed to the shaft. An alternate
constructi on shown in Figure 79, uses a sol id forging which has been ma ­
chined out to form an integral disc and shaft arrangement. Nozzles are
carried in diaphragms, Figure 80 , that have center holes through which
the shaft passes. Seals at these openings limit the steam leakage which
bypasses the nozzles. Since steam pressure drops in passing through the
fixed nozzles , the pressure is higher on the inlet side of the diaphragm
and it is important that effective seal s be maintained to minimize the
quantity of steam bypassing the turbine blades.
This construction permits arranging seals on t he shaft of the machine
on re latively small diameters. However, as turbine ratings increase, the
shaft diameter must also increase so the impulse stage no longer has the
small diameter on which to provide sealing arrangements.
-1 57-

Figure 81 - High Pressure El ement - 1800 RPM Double-Flow Design
IMPULSE CONSTRUCTION
L EAKAGE
REACTION CONSTRUCTION
RADIAL CLEARANCES
LEAKAGE
ZONE CLEARANCE
ZONE CLEARANCE
I - .OIO"- .020"
I - .030"- .040
2 - . 035'~ .045"
2 - .03o''- .04d'
Figure 82 - Comparison of Sealing
-158-

As shown in Fi gure 81, react ion turbines are usually built wi th a
ro tor machined f rom a solid forg i ng. The blades are mounted di rectly on
the rotor wh i ch increases in di ameter toward the low pressure end where
st eam vo l ume is greater. This requires that steam seals to prevent l eakage
between blade rows must be pro vided on somewhat l arger diame t ers than was
the case i n the impul se des i gn. Thus , a reacti on s t age may encounter
greater st eam leakage than t he impu l se stage across the stationary and rotati
ng bladi ng.
These sealing arrangements are illustrated in Figure 82.
Typi cal inter- st age sealing arrangemen t s are i l lustrated in Figure 84
and Fi gure 85 on the foll owing pages .
St age Type and Vol ume t r i c Fl ow
Figure 83 s hows the combined efficiency , both leakage and passage effi
ci ency, for HP elements of impul se and reaction type turbines plotted
aga inst inlet vol umet r i c f l ow i s proportional t o t he output and the inlet
st eam conditions of a turbine. At l ow volumetric flows t he i mpul se type
t urbi ne i s superi or; but, as the vol umetri c f l ow increases, the react ion
turbine becomes unquest ionab ly superi or . Wes t inghouse bui l ds impul se turbines
for l ow volumetri c flow ap pl i cations and react ion turbi nes for high
vol umetri c f l ow appli cat ions. There i s an area where the designer has a
choice of whet her to use impul se or reacti on .
EFFECT OF STAGE T YPE AND VOLUMETRIC FLOW
ON CO MBINED EFFIC IENCY
~ 98
~ 96 L----J----~1J.r:l"iJ..~kk~~~~~~~~~==~l=~t:~
!!:!
~ 94
...
"'
0
"' z
al
:a
EQU IVALENT RATING
0
0 88~-7'H-11-H-ftit----- - - 1800 PSIG,IOOO" F. - -+---1
"' >
j:: 86
"' -'
~ 8 4 W-~LJ-4L-l----~~~=l=~~~::::([~~=t:== 3500 PSIG,1000• F.~--+----<
~ "'------'-----'---'---''---'-~"-L..--'-----'---..._____._ _.__.__._...._....._.
.I .2 .3 .4 .5 .6 .7 .9 .9 1.0 2.0 3.0 4.0 5.0 6.0 7.08.09.010.0
I NLET VOLUMETRIC FLOW IN MILLION CUBIC FEET PER HOUR
, 68L(.o
Figure 83 - Stage Type and Volumetric Fl ow Effect on Combined Efficiency
-159-

Rotor
Spring-Backed
Segmental
Seal Ring
Figure 84 - Sea ling fo r HP Reac tion Bladi ng
- 160-

Rotor Disc
Figure 85 - Sealing for LP Blad ing
-161-

Blading:
Study Questions
STEAM TURBINES
SECTION 8
1. In an actual turbine the stationary nozzles of a reaction turbi ne are
made by us i ng sections shaped to form nozz l e walls .
2. Steam from these stationary nozzles is directed into an adjacent set
of moving bl ades mounted on the turbine rotor.
True/False
3. Some expansion occurs in both mov i ng and fixed blades. If approxi ­
mate ly the same pressure drop occurs i n both fixed and moving bl ades,
by definition it is a % stage.
4. In the impulse stage nozz l es feed steam at an angle to blade travel.
The crescent shaped blades permit free entry and discharge and produce
the change of and which give the rotat
ional force.
5. The impulse blade is dependent on the force exerted in changing either
speed or directi on and therefore the change in direction is important
in the impulse blade . The is quite large.
6. The reaction blade requires a (hi gher) (lower) turning angle than does
the impulse blade.
7. An ideal rateau stage is the pure stage.
~~~~-
8. In the curtis stage a row of blades is placed between
~~~~~~
two rows of rotating rateau stages.
9. Thus, where the pressure drop is large as at the inlet to the turbine,
the steam velocity is hi gh and more of the available energy can be absorbed
by the rotating blades in two rows with only reversing blades
rather than a row of nozzles.
True/False
-163-

10. The signi f i cant factors for maximum efficiency of t he blade path are:
l .
aero-dyn ami c losses in the flow passages
2. blading material
3. leakage
11 . The aero- dynami c loss i s a function of the amount of turning t he steam
must undergo in traveling the path.
True/ False
12. Leakage is an important factor in efficiency since leakage steam does
not produce usefu l work on the sha ft.
True/False
13. Impul se turbines are normally constructed with the moving blades on
----- or that are shrunk on and keyed t o the shaft.
14. Nozzles are carried in fixed diaphragms that have center holes t hrough
whi ch the shaft passes .
Seals at these openings limit the ____ _
- - - - -
which bypasses the nozz les.
15. The sealing of the shaft of the machine on relatively sma ll diame ter
provides a smaller leakage area .
However , as turbine ratings increase
the shaft di ameter must increase and the leakage area wi ll (increase)
(decrease) .
16. Si nce the bl ading in the reaction turbine i s usually mounted directly
on the rot or the sea l s will be on the l arger diameter.
Therefore, the
reaction stage may have greater leakage area and res ulting steam leakage
than the impul se stage.
True/False
17. At low volumetric flows the comb ined effi ciency, both leakage and passage
ef fi ciency , is superior fo r the type blading .
18. As volumetric f l ow increases, the turbine becomes supe-
------
ri or.
-165-

STEAM TURBINES
SECTION 8
Blading:
Answers
l. blade sections
2. true
3. 50% reaction stage
4. speed and direction
5. turning angle
6. lower turning angle is required
7. impulse stage
8. reversing blades
9. true
10. (1) and (3) are correct
11. true
12. true
13. wheels or discs
14. limit the steam leakage
15. wi 11 increase
16. true
17. impul se type
18. reacti on turbine
-167-

Figure 86 - Typical Last- Row Reaction Blades (40 Inch and 44 Inch) -
Twisted and Tapered
Nozzles Vortex flow
Moving
blades
Axial
flow
--
--
Figure 87 - Flow Illustrati on
- 168-

Factors Affecting Actual Bl ade Design
STEAM TURBINES
SECTION 8
BLADING
A typical steam turbine consists of various arrangement s of impulse
and reaction type blading . In fact , as wi l l be shown, a given turbine blade
may contain cross sections at vario us poi nts in its leng t h which illustrate
both the reacti on and impulse design. These blades are often referred t o
as "twisted and tapered," whi le t he blades with const an t section are referred
to as "parallel sided." In general, the parallel sided bl ading i s
found in the HP t urbine el ement and in the IP turbine element; the twi s ted
and tapered blading i s usua lly found i n the last few r ows of LP turbine
elements .
Twisted and Tapered Blades
The taper­
The twisted and t apered blade is illust rated in Fi gure 86.
ing of the bl ade i s due to mechanical design requirements only .
When the blade height becomes a signi ficant part of the total stage
diameter, as is normally t he case wi t h the last few rows of blading i n the
turbine, the ratio of steam and bl ade speed changes over t he length of the
bl ade . Vel ocity rati o i s the rati o of the linear ve locity of a given point
on the length of a blade t o the absolute velocity of the steam jet at en ­
trance to the blade .
Figure 87 shows a row of nozzles , t he vortex flow of t he steam leaving
the nozz les, a row of bl ades and the leaving exhaust steam. Ide ally , steam
enters the nozzles in an axial di recti on and it leaves in a circumferential
directi on , f ormi ng a vortex flow or eddy that i s contai ned by t he turbine
casing before the steam enters moving blades.
It i s characteristic of the vortex flow l eaving the nozzles that the
steam veloci ty at the inner radius is higher t han at the outer radius .
Howeve r , the linear velocity of t he blade increases with radius. Therefore,
the velocity ratio i s steadi ly increasing from root to tip.
The ideal ve l ocity ratio for a pure impu lse design wou ld be approxi ­
mate ly 0.5; whereas the ideal ratio for a pure reaction blade wou ld be
hi gher as was shown in Fi gure 78 wh i ch i s repeated on the following page.
Since the velocity ratio at the root of the blade favors the imp ul se
des i gn , it i s typical to desi gn the root of the blade for impul se f low,
equivalent to 0 per cent reaction -- no pressure drop. As we said, the
steam velocity in the ideal impulse des i gn shoul d be double the blade velocity
. The entrance ang le of the bl ade i s determi ned by the angle of approach
of the steam so that the st eam wi ll slide smoothly over the blade.
-1 69-

Figure 88 - Stellite Strips
-170-

Re lative
Aerodynamic Efficiency
.6
.i
,.
9'
~
, m;
--
~----·
·-------- Impulse
Reaction -
.6
.4
.3 .4 .5
.6
.7 .6
Stage Velocity Ratio:
V Blade
V Steam
Figure 78 - Relati ve Efficiency
At the tip of this long blade, the blade velocity is higher than the
approaching steam velocity. This means the steam approaches from a direction
almost opposite to the blade's motion . For this reason the blade section
must be twi sted in order to receive the steam smoothly .
Due to the vortex flow, the st eam pressure is higher at the tip than
at the root, and there wi ll be some pressure drop through the blade . Thus,
the conditions favor the use of a reaction blade section since the pressure
ratio is in the range suitable for reaction design and since there will be
pressure drop through the blade, there wil l be velocity increase at the
blade exit which also conforms to the reaction design. Thus , while a pure
impulse force exists at the blade root, a pure reaction force is acti ng at
the bl ade tip.
The principal factor that controls the amount of twist is the distribution
of pressure between the stationary and rotating blade . The smaller
the change in pressure between the base and tip, t he smaller the change in
velocity and thus the smaller the difference in flow angle to the rotating
blade. Relatively short blades exhibi t only a small pressure variation
along the length of the bl ade and as a result, the rotating blade inlet flow
angle vari ation becomes neg l igi bl e.
Eros i on Control and Moisture Remova l
The longer last rows of blades are fitted with stellite strips which
are silver sol dered to the leading edge, Figure 88. Stellite is a very
hard al loy -- a binary alloy of cobalt and chromium -- which is highly resistant
to erosion. In the last rows of blading in the turbine, there is
mo i sture which wou l d be qu i te erosive to the bl ade material wi t hout this
protection. This minimizes erosion in this section of the turbine and increases
blade life , maintains blade efficiency , and reduces maintenance requirements
.
-171-

Figure 89 - Moisture Removal in Low Pressure Cyl inder Base
-172-

Moisture removal and erosion control are major considerations in the
design of steam turbines appl ied with nuclear steam supply systems that
generate dry and saturated or low superheat steam. Moisture particles are
removed with the extraction steam and also at specially designed moisture
removal zones.
Increased axial spacing between stationary rotating blades also decreases
erosion . Thi s allows sufficient time for the large moisture drop ­
lets, which stream from the trailing edges of the s t ati onary bl ades, to be
broken up into smaller particles , which more easily pass thru the rotating
blades without impingement.
An additional moi sture remova l devi ce at the inlet to the last rotating
row in the l ow pressure turbine has proved particularly effective in
minimizing erosion in the bl ade tip area. This device, shown in Figure 89 ,
consists of a narrow circumferential slot just ahead of the inlet to the
tip of the l ast rotating blade. A small quantity of blade path steam flows
through this slot directly to the exhaust, and by eductor action removes a
cons iderab le amount of entrained moisture from th~ steam at the tip area.
Blading Effect on Heat Rate
It was mentioned previously that the basic function of a steam turbine
i s to convert the stored therma l energy of st eam into mechanica l work. It
was also pointed out that the conversion is on ly accomplished through control
led turning of the steam through stationary and rotating flow passages .
Thus, the physical design of the blading pl ays a most important role in
turbine performance.
Westinghouse man ufactures both impul se and reaction type turbines.
Each type is used in the area where its applicati on is most advantageous.
This provides a unique positi on to judge not only the theoretical but
practical strength and weakness of the t wo design philosophies .
Other Bl ade Features
There are other blade features which are required for mechanical or a
combination of mechanical and thermodynamic reasons. One example of a requirement
which serves a dual role is the blade shrouds il lustrated in
Fi gures 90 and 91. These shrouds supply several important functions; such
as:
1. A sealing surface to prevent steam leakage . Steam that bypasses
the blade represents a direct loss in efficiency and must be carefully
controlled.
2. Contro ls the level of stress at the base and root of a bl ade.
3. Controls the blade frequency to a limited degree. Blading design
must include consideration of the various modes of vibration which
will occur. Stress levels which wi l l result from vibrati on must
be a factor in the blade des i gn.
-1 73-

Figure 90 - Control Stage Bl ading
Figure 91
- Rateau Control Stage
-174-

In addition to shrouds, some low pressure bl ades are al so provided with
integral lashing wires which are we l ded together to provide additional frequency
control . Shrouds, as well as l ashi ng wires, may not be continuous
but are used to cause the blades to act in groups. This grouping provides
additional frequency of vibration control. Integral lashing wires Clashing
abutments) are illustrated on the last row reaction blading in Fi gure 92.
Such l ashing wires are provided on unshrouded last row blading and are primarily
mechanical means of providing frequency control and maintaining
st ress levels within design limits.
At the end of this section an appendix is included which illustrates
the principal types of blading and their nomenclature.
LASHING
_ _..._ ABUTMENTS
Figure 92 - Typical Last- Row Reaction Bl ades (40 Inch and 44 Inch) -
Twisted and Tapered
-175-

STEAM TURBINES
SECTION 8
Blade Design: Study Questions
1. Twisted and tapered blading is found in the last _____ of bl ading
in the turbine.
2. In this area of the turbine, the blade height becomes a significant part
of the total stage diameter.
True/ Fa 1 se
3. This causes the ratio of steam and blade speed to change substantially
over the length of the blade. Thi s results in characteristi cs wh i ch
favor the blade at the root and the profi le at the
tip of the bl ade.
4. Some of the functions of the blade shroud are:
1. a sealing surface to prevent steam~----
2. control the level of at the base and root of a blade .
3. contro l the blade to a limited degree .
5. In addition to shrouds , some low-pressure blades are also provided with
integral
wh ich are welded together to provide
additional frequency control.
6. Shrouds as well as l ash ing wires are continuous t o make the row of
blades a so li d unit .
True/False
7. In the hi gh moisture area of the turbine the blading is provided with
st ri ps of
---- ---
which are silver soldered to the leading
edge .
-1 76-

8. Moisture would be erosive to the blade material without the protection
of this very hard alloy.
True/False
9. Moisture removal and erosion control are more important considerations
in the (fossil) (nuclear) turbines.
-177 -

Blade Design: Answers
1 . the l as t few rows
2. True
3. i mpul se - reaction
4. 1. Leakage
2 . Stress
3. Frequency
5. integral lashing wires
6 . false
7. s te 11 i te strips
8. true
9. nuclear
STEAM TURBINES
SECTION 8
-178-

SECTION 8 - APPENDIX
BLADING NOMENCLATURE
-1 79 -

TAPERED TWISTED CURVED SIDE ENTRY BLADE
TIPEND----
EROS ION SHIELD----
RECESS----
--+-- LASHING
STUBS
AIRFOIL
LENGTH
OVERALL
LENGTH
INLETEDGE----1;
OUTLET EDGE
TOP OF PLATFORM
PLATFORM
v
INLET SIDE OF ROOT~
t
OUTLET SIDE
OF ROOT
ROOT
CONVEX SIDE OF ROOT
-181 -

STRAIGHT SIDE ENTRY IMPULSE BLADE
TOP OF TENON
.....----CHAMFER TOP OF TENON
---OUTLET EDGE
RADIUS INLET SIDE BOTTOM-----..
OF SHROUD t
t
ROOT
ROOT
SERRATIONS
---CONCAVE
---TOP OF PLATFORM
INLET SIDE OF ROOT
BASE END
-183-

PARALLEL, MACHINED,
SINGLE TEE BLADE
TAPERED, FORGED,
SINGLE TEE BLADE
TOP OF TENON
TOP OF AIRFOIL
OUTLET
EDGE
.•t---INLET
EDGE
AIRFOI L
LENGTH
CONVEX
CONCAVE
OVERALL
LENGTH
TOP OF PLATFORM
l
ROOT
... -
i-
PLATFORM
+-
SHANK
TEE
WING
RELIEF
I
WING
CONCAVE SIDE OF
ROOT
TEE CHAMFER
BASE CHAMFER
CONVEX SIDE
OF ROOT
OFF SET
CLEARANCE
BASE END
- 185-

DOUBLE TEE IMPULSE BLADE
TOP OF SHROUD------.
TOP OF TENON
TOP OF
INTEGRAL SHROUD
--- -INTEGRAL SHROUD
BOTTOM OF ___
SHROUD
_ __,
--1'-----CONVEX
\..---- - CONCAVE
-----CONCAVE PLAT FORM
RADIAL MILLED
SURFACES OF T EES
BASE END
- 187-

SIDE ENTR Y BLADING
Partially bladed rotor showing side-entry control
stage blading on through low pressure forged blades.
STEEPLES
- 189-

STEPS IN MANUFACTURE OF TW IST ED AND T APER ED BLADES
Lefc co righc : forged bar scock; rough scock before die forging; blade afcer drop forging in dies; rough blade cue
before final machin ing; fi nished blade.
-1 91-

LOW-PRESSURE EXHAUST BLADES
-193-

Figure 93 - Typica l Lubrication System
-194-

STEAM TURBINES
SECTION 9
AUXILIARY SYSTEMS
Introduction
Since a turbine consists of many parts when assembled, it must have
auxiliary systems to allow proper fun ctioning of the ma i n equipment . This
chapter describes the aux iliary systems and how they operate.
Lubrication System
A typical lubrication system is shown in Figu re 93 . This shows a lube
system which is separate from the co ntrol system. Control systems were
studied in MA-465.
Ma in Pump
The ma in pump is mou nted on the turbine sha f t and is a volute type centrifugal
pump with a l arge capacity range with very little change in discharge
head. All operating mecha ni sms are si ng le acting, that i s, they open
hydrau lically, and are cl osed by spri ngs. Thus there is no extra load imposed
on the pump when the valve operating mechanisms are sudden ly closed
following a t r i p-out or load rejection.
Beari ng Oil Pump
The ma in oil pump supplies all of the oil required for the l ubr i cation
system during normal operation and in add i tion prov ides back-up oil for the
hydrogen seal oil system of the generator. The pump supplies oil to one or
more ejectors in parallel . The ejector s pick up a quanti ty of oil from the
reservoir approximately equal to the amount of HP oil suppl i ed to the ejectors.
The lubricating oi l supply to the bearings, taken from the ejector
discharge, flows through one of two identical oil coolers to the ma i n and
thrust bearings, generator bearings, and to the turning gear . The ejector
di scharge pressure is sufficient to assure a positive supply of lubricating
oil to the bearings.
An A-C mo to r dri ven oil pump, Figure 94, is provided to supply the oil
required during st arting and for operating the un it on turning gear. Bearing
oil is used to prime the main pump. The ma in pump will overtake the
auxil iary oil pump at about 90 per cent of ma in unit speed .
Rotor Turni ng Gear
The motor driven turning gear shown in Figure 94A operates the motor at
l ow speed while the unit is being start ed or stopped. This prevents unequal
expansion or co ntraction of the rotor which cause thermal bowing of the
rotor.
-1 95-

Figure 94 - Turning Gear Oi l Pump
-196-

- I
.............._ I
CENTER ~ ltfft< ­
OF TURBINE i
I
Figure 94A - Side-Mounted Turni ng Gear
- 197-

Figure 95 - Oil Reservoir
-198-

Emergency Bearing Oil Pump
This pump is driven by a D-C motor and is the final back-up to the
bearing oil system. This pump protects the turbine in case of loss of A-C
power . It should have sufficient D-C storage battery capacity to operate
for approximately 30 mi nu tes which is the approx imate time required for a
unit to coast down from 90 per cent to O speed .
High Pressure Hydrogen Seal Oil Back- Up Pump
The application of hydrogen as a coolant for turbine generators re~
quires the use of an oi l-pressure, floating ring type of gland seal to pre~
vent gas leakage where the shaft extends through the gas t i ght housing .
Independent seal oi l systems for air and gas sides are provided in the
main generator hydrogen system. This emergency seal oil back-up pump A-C
motor driven, interconnected with the turbine oil system automatically pro~
vides continuous operation of the seal oil supply.
Automa tic Start of Pumps
The switches controlling these pumps will start the pumps on falling
pressure, but the pumps are stopped manually. The pumps remain under control
of the pressure switches and will restart should the bearing oil pres~
sure decrease to the settings of the switches. A test valve installed in
the bearing oil line to these switches permits testing the cut-i n points of
the pumps. The tests ca n be made during normal operation.
During start-u p and shut-down periods the A-C bearing oil pump and the
seal oil back-up pump supply all oil requirements for the main oil pump
suction ejector, develop a sufficient pressure to latch the overspeed trip
mechan ism, lubrication to the bearings, turning gear, and seal oi l back-up
for the generator.
As the turbine reaches normal speed, the ma in oil pump discharge pressure
exceeds and replaces discharge pressure from the auxi liary pump and
the seal oil back-up pump to become the control pressure for al l oil requirements.
Another pressure switch which is also connected to the bearing oil line
prevents the turning gear from bei ng started until the beari ng oil pressure
has r isen to a satisfactory level.
Oil Reservoir
The oil reservoir, shown in Figure 95, contains screens for removing
all fo reign matter from the oil drained back to the reservoir. The ejectors,
orifices, check valves, etc . , are all enc losed in the reservoir. Two
identical oil coolers, Fi gure 96, are provided and connected by a tandem
operated three way valve which permits either oil cooler to be used . The
cooler not in use ca n be drained and cl eaned or replaced with the unit in
operation. A vapor extractor is mou nted on the reservoir, Figure 97 . This
extractor mai ntains a slight negative pressure in the oil drain system and
oil reservoir.
-199-

Figure 96 - Oil Cooler
- - -
- - ----- --- _ ._ .... J'----- -- , -·~--- ..o.-.&...L__..i._..__
Figure 97 - Oil Vapor Extractor
-201-

STEAM TURBINES
SECTION 9
Lubricating System: Study Questions
1. The ma in oil pump, mounted on the turbine shaft, suppl ies all of the
oil required for the lubrication system during normal operation and in
addition prov ides backup oil for
oil system
of the generator.
2. The motor driven turning gear turns the turbine rotor at a low speed to
prevent:
3. An AC motor driven oil pump is provided to supply oil requ i red during
and for operati ng the unit
~~~~- -~~ ~~~~~~~~~~
4. An emergency bearing oil pump driven by a DC motor is the final back up
to the bearing oil system. true/false
5. The hydrogen cooled generator requi res the use of an oil pressure
~~~type
of gland seal.
6. An emergency back up pump (AC) (DC) motor driven is
supplied.
7. This pump interconnected with t he turbine oil system, automatically provides
of the seal oil supply .
8. The pumps which will start automati cally on falling pressure are:
a. a ma in oil pump
b. bearing oil pump
c. emergency bearing pump
d. seal oil back up pump
9. Two oil coolers are provided because one is inadequate to properly cool
the oil. true/false
- 203 -

10 . Prov i ding two oil coolers permits one oil cooler to be (drained and
cleaned) (replaced) with the unit in operation.
11. The vapor extractor mainta ins a slight negative pressure in order to:
a. remove vapor and vapor in the oi l reservoir
b. prevent the leakage of oil vapor outward to~~~~~ ~~~~~
- 205 -

Lubricating System:
Answers
STEAM TURBINES
SECTION 9
l. hydrogen seal oil .
2. Unequal expansion or contraction of the rotor can cause thermal bowing.
3. during starting , on turning gear.
4. true.
5. Floating ring.
6. seal oil-AC motor driven.
7. continuous operation.
8. b, c, and dare correct a-the main oil pump is of course shaft driven
from the turbine.
9. false.
10 . it may be either drained and cl eaned or repl aced if necessary.
11. a. remove oil vapor and any hydrogen vapor.
b. prevents the leakage of oil vapor outward to shaft seals.
- 207-

I
'~
11 ,, ~
I I I I 1 1 11
___
ll_ __ - - --- _.l.I_., __ .,.__..,.. __ ,..___ ~ - ------- .. lf
I I I I I
I I I I I
Ji~
1..---------{ : I --------...J ! L_T __ J
Valve Siem
Leakoffs
I
I
I
I
:
I
I
I
I
I
I
L- - - - - - - --"'- - - --- ---
I '
.. ------
: I
Desuperhealer l t-T/C
r--------J
I : I
1
,
J From
..i.---r-- ---T---- Main Sleom
, : Safely Head I Supply)
_L_____________ J
~'
: ~H1ohPressure
11
Safely Valve-' !- I -

STEAM TURBINES
SECTION 9
AUXILIARY SYS TEMS
Gland Sea ling Steam System
Des c ri pt i on
At points where the rotor penetrates the outer cylinders, some means
is needed to prevent leakage of air into , or steam from the cylinders. The
glands , with their labyrinth-type seal rings and the gland sealing steam
system, are designed to perform this function .
The system , shown in Figure 98 , consists of indi vidually con t rol led
diaphragm operated valves , a desuperheater section for the LP turbine
gl ands, relief valves, and a gland steam con denser.
The gland sealing steam is supplied from either t he main steam generator
or from an auxiliary source during the starting cycle .
During operation at partial loads the gland sealing steam is supplied
from the HP and IP turbine glands and from the "col d" reheat zone. As the
reheat pressure increases , the regul ator fed from the boiler (or auxiliary)
supply cl oses until all supplementary steam is finally supplied from the
"co ld" reheat zone.
Rotor Glands
As illustrated in Figure 99 , the glands contain a number of seal strips
which encircle the rotor at the ends of each outer cylinder , clearing the
rotor surface just enough to prevent co ntact during operation .
- 209-

TYPICAL ROTOR GLAND PRESSURE DISTRIBUTION
L.e TUBB. GLAND H. P. OR 1. P. TURB. GLAND
ATMO S. ATMOS.
1

On starting the turbine, and at low loads (Figure 100) the pressure at
the HP , IP, and LP exhaust is below atmospheric pressure. Sealing steam is
supplied to chamber "X", leaking past the seals into the turbi ne on one
side, and into chamber "Y" on the other. The leakage steam and air is removed
from chamber "Y" through a connection to the gland steam condenser.
When the exhaust zone pressure (HP and IP) equals zone "X" pressure, a
reversal in flow occurs across the inner seal ring . As exhaust zone pressure
increases, flow increases and the gland becomes self-seal ing (Fi gure
101). At this point, steam is discharged from zone "X" to the LP glands.
At high loads, spil lover is used.
Desuperheaters
The LP gland desuperheater lowers the temperature of the LP gland seal ­
ing steam to prevent possible distortion of the gland cases and damage to
the turbine rotor.
The desuperheater which was shown schematically in Figure 98, consists
of a reduced pipe section into which a spray nozzle has been inserted .
The superheated s team enters the desuperheater and has its velocity
increased through the reduced section of pipe. It t hen passes the spray
nozzle, which injects the cool ing water into the high velocity steam , insuring
positive atomization and reducing its temperature by evaporation .
Cooling water from the condensate pump enters the desuperheater through a
pipe to the spray nozzle located in the throat of the desuperheater.
The unit is also equipped with a desuperheater for the HP and IP
glands which protects them in the event of a temperature mismatch between
the gland steam and rotor gland area . A maximum mismatch occurs after a
turbine trip, when steam from the main boiler is used to seal the glands.
Gland Steam Condenser
The condenser maintains a sub- atmospheric pressure in the gland leakoff
system at all times. This draws the leakage steam from the glands,
condenses and removes it.
Exhaust Hood Sprays
During startup there is a possibility of exhaust hood temperatures becoming
excessive whi ch can cause cyli nder distortion and shaft misalignment.
It is not expected that there will be overheati ng of the LP exhaust
hood with no-load steam flow, low absolute condenser pressure, and the ex ­
haust hood sprays out of service. High absolute condenser pressure will
cause overheating , as will less than no-load st eam flow (at rated speed)
which would result if the unit were allowed to motori ze.
Automatically controlled exhaust hood sprays are provided which cool
the hood and maintain all owable temperatures. The use of exhaus t hood
sprays will also help to minimize the time required to start up a unit by
automatic control of the exhaust temperature.
-211-

STEAM TURBINES
SECTION 9
Gland Sealing Steam System and Exhaust Hood Sprays: Study Questions
l . The gland sealing system prevents the leakage of into or
----
from the cy linders .
2. The steam for sealing the glands i s suppl ied from the mai n boiler or
from an auxiliary source during the starting cycle.
True/False.
3. During the operation the sealing steam is supplied from some point on
the main turbine. Since adequate pressure i s required for satisfactory
sealing, the source of the steam depen ds on the turbine
----
4. A number of grooves or steps are machined in the rotor shaft at the
gl an d area . Thin meta l strips encircle the rotor at thi s point and
thus i s formed a seal .
--------
5. Since the temperature of the steam used for seali ng may be eccessive
the desuperheater lowers the temperature in order to prevent possible
of the gland cases and damage to the
----- ---------
6. The purpose of the gland steam condenser is to draw the ----
from the glands, it and remove it.
7. If a condition of hi gh absolute condenser pressure (poor vacuum) should
exi st with inadequate steam flow to properly cool the exhaus t hood, the
exhaust hood temperature may become excessive.
True/False.
8. This could cause cylinder and shaft
------- --------
9. Condensate is automatically injected by the exhaust hood sprays and
will cool the hood to allowable temperatures. The spray will also
help to required to start up the unit.
- 213-

STEAM TURBINES
SECTION 9
Gland Sealing Steam System and Exhaust Hood Sprays : Answers
1. air--steam
2. true
3. turbine 1 oad
4. step-type labyrinth seal
5. possible distortion of the gland cases and damage to the turbine rotor .
6. draw the leakage steam from the glands, and condense it.
7. true
8. cyl inder distortion and shaft misalignment
9. help to minimi ze the time required.
-214-

TURBINE SUPERVISORY INSTRUMENTS
Appropriate safeguards are a very important factor in providing safe
operation of turbines with minimum maintenance .
Supervisory instruments are provided to record the following turbine
variables: rotor eccentricity, rotor vibration, rotor position, casing and
differential expansion, speed and additive governor valve position, and turbine
metal temperatures. These instruments employ circuit miniaturization ,
fast scan rate of certain variables, and maximum reliability through use of
solid stat e devices . Furthermore, circuits can be suitably arranged for
computer scanning.
Each instrument requires a detector, some recording means, and a package
of circuits t o make the detector signal sui table for recording .
Detectors are installed in the turbo-generator structure and connected
to a terminal box on the unit.
Eccentricity Recorder
When a turbine has been sh ut down, the rotor will tend to bow due to
uneven cooling if the upper half of the casing enclosing the rotor i s at a
higher temperature than the l ower half. By rotating the rotor slowly on
turning gear, the rotor will be subjected to more uniform temperatures,
thereby minimizing bowing.
Rotor eccentricity is monitored continuously while the unit is on turning
gear, and also as it is brought to higher speeds on starting. Bowing
of the rotor will appear as vibration over 600 rpm. The recorder is
equipped with an alarm which will cl ose a contact when the eccentricity
limit is reached .
Vibration Recorder
The vibration instrument is used to measure and record vibration of a
turbine rotor at speeds above 600 rpm; below this speed, rotor runouts are
recorded as eccentricity. The vibrations are meas ured on the rotor ·near
the main bearings. Excessive vibrations serve as a warning for abnormal
and possible hazardous conditions in the turbine. The vibration recorder
is equipped with an alarm and will close a con tact when excessive vibrations
are measured at any one of the bearings .
Rotor Position Recorder
The rotor position instrument measures the relative axial position of
the turbine rotor thrust collar with respect to the thrust bearing support.
The thrust collar exerts a pressure against the thrust shoes, which are
located on both sides of the thrust collar. A small axial displacement of
the rotor occurs as the electrical load on the unit changes. Wear on the
thrust shoes results in an axial movement of the rotor, which is indicated
on this instrument. The instrument is equipped with an al arm and will close
a contact if the rotor moves beyond a predetermined distance.
- 215-

Differential Expansion Recorder
When steam is admitted to a turbine, both the rotating parts and the
casings will expand . Because of its smal ler mass , the rotor will heat
faster and therefore expand faster than the casings . Axial clearances between
the rotating and the stationary parts are provided to allow for differential
expansion in the turbine, but contact between the rotating and
st ationary parts may occur if the al l owable differential expansion limits
are exceeded.
The purpose of the differential expansion meter is to chart the relative
moti on of the rotating and stati onary parts. It gives a continuous
indi cati on of the axial clearance while the turbine is in operation. The
instrument is equipped wi th an alarm and wil l close a contact i f the limits
of axial clearances are approached. As the rotating and stationary parts
become equally heated after a transient condition, the differential expan ­
sion will decrease, resulting in larger axial clearances; the s team flow
and the temperature to the turbine can then again be changed.
Casing Expansion Recorder
As a unit is taken from its cold condition to its hot and loaded state ,
the thermal changes in the casings wil l cause it to expand. Because one end
of the unit-near the center-line of the LP turbine(s)-i s secured to the
foundation, the casing wi ll expand axially away from this anchored point.
The opposite end of the unit (the governor pedestal} is designed to move
freely along lubricated longitudinal keys . If the free end of the unit is
hampered from sliding smoot hly along the guide keys as the casings expand ,
serious damage to the unit may result.
The casing expansion meter measures the movement of the governor ped ­
estal relative to a f i xed point (the foundation). It indicates expansion
and contraction of the casi ng s during starting and stopping periods , and
for changes in load, steam temperature, etc. The rel ati ve position of the
governor pedestal, as indicated by this instrument, should be essentially
the same for similar conditions of l oad , steam conditions, vacuum, etc.
Additive Governor Valve Position Recorder
During a startup or following an inst antaneous loss of l oad , it is desirable
to have a record of rotor speed. However, when the generator i s on
the line, the speed is constant and need not be recorded. At synchronous
speed a record of governor valve position is useful, since the val ve opening
varies with the l oad on the unit.
The selection of either valve position or speed input to
is controlled by the position of the main generator breaker.
ord is maintained with the breaker open , and a valve position
the breaker closed.
the recorder
A speed recrecord
with
- 217-

Turbine Met al Temperatures
Thermocouples are installed to permit monitoring of criti cal temperatures
throughout the unit. Those usually provi ded have the following funct
ions:
A. For meas urement of turbine steam and metal temperatures for the
purpose of turbine operati on.
B. Embedded in thrust bearing shoes on each side.
c. Embedded in meta l of the main bearings.
D. For main bearing drains.
E. For the thrust bearing drains .
F. For the oil inlet and outlet of the oil coolers .
I
- 218-

Differential Expansion Recorder
When steam is admitted to a turbine, both the rotati ng parts and the
casings will expand. Because of its smaller mass , the rotor will heat
faster and therefore expand faster than the casings. Axial clearances between
the rotating and the stationary parts are provided to allow for differential
expansion in the turbine, but contact between the rotating and
stationary parts may occur if the allowab l e differential expa nsion limits
are exceeded.
The purpose of the differential expansion meter is to chart the relative
motion of the rotating and stationary parts . It gives a continuous
indi cati on of the axial clearance whi le the turbine is in operation . The
instrument is equipped with an al arm and will cl ose a contact if the limits
of axial clearances are approached. As the rotating and stati onary parts
become equal ly heated after a transient condition, the differential expansi
on will decrease, resulting in l arger axi al clearances; the steam fl ow
and the temperature to the turbine can then again be changed .
Casing Expansion Recorder
As a unit is taken from its cold condition t o its hot and loaded state ,
the therma l changes in the casings will cause it to expand . Because one end
of the unit-near the center- line of the LP turbine(s)-i s secured to the
foundation, the casing will expand axially away from this anchored point.
The opposite end of the unit (the governor pedestal) is designed to move
freely along lubricated longitudinal keys . If the free end of the unit is
hampered from sliding smoothly along the guide keys as the casings expand ,
serious damage to the unit may result.
The casing expansion meter measures the movement of the governor ped ­
estal relative to a fixed point (the foundation). It i ndicates expansion
and contraction of the casings during starting and stopping periods , and
for changes in load, steam temperature , etc . The relative position of the
governor pedestal, as indicated by this instrument, should be essentially
the same for similar conditions of load, steam conditions , vacuum, etc.
Additi ve Governor Valve Position Recorder
During a startup or following an instantaneous l oss of load , it is desirable
to have a record of rotor speed . However , when the generator is on
the l ine , the speed is constant and need not be recorded. At synchronous
speed a record of governor va lve position is useful, since the valve open ­
ing varies with the l oad on the unit.
The selection of either valve position or speed input to
is contro ll ed by the position of the mai n generator breaker.
ord is maintai ned with the breaker open , and a valve pos iti on
the breaker cl osed.
the recorder
A speed recrecord
with
-217-

Turbine Metal Temperatures
Thermocouples are installed to permit monitoring of critical temperatures
throughout the unit. Those usually provided have the fo ll owing func ­
tions:
A. For meas urement of turbine steam and metal temperatures for the
purpose of turbine operation.
B. Embedded i n thrust bearing shoes on each side.
c. Embedded in meta l of the main bearings.
D. For mai n bearing drai ns.
E. For the thrust bearing drains.
F. For the oil inlet and outlet of the oil coolers.
I
-21 8 -

ROTOR GROUNDING DEVICE
The rotor grounding device, Figure 102, is provided on turbines having
all steam-sealed glands to prevent bui l ding up of high electrostatic charges
on the turbine rotors.
Th i s device consists of brushes (4) mounted in the brush holders (2).
The brush holders are clamped on dowels (1) which are welded to the turbine
(generator end) oil seal ring. The brushes are held in contact with the
turbine rotor by the brush holder spri ngs. Any electrostatic charge built
up in the turbine rotor is carried to ground through the brushes (4) , the
oi l seal ring and the bearing pedestal housing.
~
~
A
~
A
~
A
i...)I
Figure 102 - Rotor Grounding Dev ice
-219-

GLOSSARY
TURBINE TERMS
-221-

GLOSSARY OF TURBINE TERMS*
ANNULUS AREA - The area of the last-stage annu lus.
AUSTENITE - An iron alloy having a face-centered, cubic crystal structure
characterized by high -corrosion resistance and good high-temperature
strength properties.
AVA ILABLE ENERGY - The isentropic enthalpy difference between a given initi al
condition and a known final pressure .
BINARY CYCLE - A cycle utilizing two working substances, the most common of
these being mercury and steam .
BLADES - The rotati ng vanes which convert the kinetic energy and heat energy
to work.
COMB INED CYCLE - An arrangement utilizing interconnected steam-turbi ne and
gas -turbine cycles.
CONDENSER FLANGE - The connection between the turbine and the condenser .
CONTROL VALVES - The va l ves which admit steam f rom the throttle to the nozzle
arcs of the governing stage .
CROSS-COMPOUND UNIT - Turbine-generator unit in which the various turbine
components are arranged on two or more separate shafts, each with its
own coupled el ectric generator.
CROSSOVER - A connecting pipe which conducts the steam from one turbine
section to another, usually from the intermediate pressure section to
the low pressure secti on .
DIAPHRAGM The heavy plate which carri es the turbine nozzles and prevents
steam from bypassing them in Rateau type tu r bi nes .
EXHAUST LOSS - Energy losses which occur between the last stage and the
condenser .
EXHAUST PRESSURE - The steam pressure at exit from a tu r bine section , i.e.,
high-pressure-turbine exhaust, reheat-turbine exhaust . Also used as a
synonym for condenser pressure.
EXPANSION LINE - A line drawn through the in let and exit state points of
each turbine stage on a Mo l lier diagram. Also referred to as a state
l ine .
*Revised August, 1973 .
- 222-

EXPANSION LINE END POINT - The enthalpy of steam upon completion of its
expansion through a high-pressure turbine section, reheat section, or
l ow pressure section.
EXTERNAL GLAND LEAKAGES - Gland l eakages whose effect on performance is
measurable by external means, and which are therefore normally shown on
a heat balance.
EXTRACTION STAGE - A turbine stage which has steam extracted at its exit
conditions for feedwater heating or process steam.
FERRITE - An iron alloy having a body-centered, cubic crystal structure .
Carbon steels and other low-alloy steels are basically ferritic.
GOVERNING STAGE - A stage, normally the first, which controls the flow of
steam into the turbine . Usually each segment of the first- stage nozzle
arc is directly connected to individually operated control valves .
HIGH-PRESSURE SECTION - The turbine casing into which steam from the steam
generator is first admitted. The section or sections through which the
steam passes prior to reheating.
HOOD - The structure which supports the l ow-pressure-turbine sections and
serves as a conduit connecting the turbine exhaust and the condenser.
INTERCEPTOR VALVE - The protective valves located just ahead of the point
where reheated steam is admitted to the reheat section of the turbine.
INTERMEDIATE-PRESSURE SECTION - A turbine casing receiving steam from a
higher-pressure section and exhausting to be lower-pressure section.
INTERNAL GLAND LEAKAGES - Interstage gland leakages which cannot be measured
external ly and therefore cannot be considered separately in heat-balance
calculations.
LOAD FACTOR - The ratio of unit load to rated load.
LOW-PRESSURE SECTION - A turbine casing which does not exhaus t to another
turbine component. Usual ly one which exhausts directly to a condenser.
MAXIMUM CALCULATED FLOW - The steam flow which the turbine is calculated to
pass with the control valves wide open. The maximum calculated flow is
5% greater than the maximum guaranteed fl ow and is also used as a synonym
for valves wide open (VWO) flow .
MAXIMUM GUARANTEED FLOW - The throttle f l ow required to produce the guaranteed
capability or rating.
MECHANICAL LOSS - Bearing losses, oil-pump losses, and any other losses of
a mechanical nature in a turbine-generator unit.
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MOISTURE REGION - The area of a steam-properties chart in which both the
liquid and vapor phases exist.
NONREHEAT UNIT - Turbine-generator unit with no provision for reheating.
OPTIMUM FINAL FEEDWATER TEMPERATURE - The final feedwater temperature which
gives the minimum heat rate for the specified cycle and steam conditions .
PITCH DIAMETER - The diameter of a turbine stage measured to the mid -point
of the blades .
RATED LOAD - The guaranteed rating of a turbine-generator unit.
REHEAT - The practice of removing partially expanded steam from a turbine,
resuperheating it, and then returning it to the turbine to complete its
expansion.
REHEAT PRESSURE - The pressure at which steam is removed from the turbine
for reheating. It is al so referred to as the high-pressure-section
exhaust pressure.
REHEAT SECTION - The turbine section or sections through which the steam
expands after reheating.
STAGE - The combination of a single row of stationary nozzles and a row or
rows of moving blades.
STEAM RATE - Weight flow at a specified point divided by the electrical output
of the unit.
STEAM-SEAL ING SYSTEM - The sealing arrangement which prevents the escape of
steam from the turbine gl ands and prevents the leakage of air through
them into the turbine under subatmospheri c conditions.
TANDEM-COMPOUND UNIT - Turbine-generator unit in which the various components
are arranged on a single shaft.
THROTTLE - This term usually refers to the main turbine throttle valve or
the conditions existing at that point.
TOP HEATER - The highest-pressure heater through which the feedwater flows
before entering the steam generator.
VALVE-STEM LEAKAGE - Leakages from the stem of the control valves . These
leakage flows are usually piped to low-pressure heaters.
VOLUMETRIC FLOW - Weight fl ow of steam in pounds per hour multiplied by
initial specific volume in cubic feet per pound.
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GLOSSARY
TURBINE-GENERATOR RATING AND PERFORMANCE
-225-

GLOSSARY OF
TURBINE-GENERATOR RATING AND PERFORMANCE
Turbine Rating (Al so called Turbine Nameplate)
Turbine rating is normally considered t he guaranteed capability of a turbine
at rated inl et and reheat conditions , 3.5 In. Hg Abs exhaust pressure and 3
percent makeup.
For the purpose of this glossary, a 500,000 kw turbine with steam conditions
of 2400 psig/1000 F/lOOOF is assumed . With these steam conditions, the unit
is guaranteed to produce 500,000 kw at the generator terminal s while operating
at 3.5 In. Hg Abs exhaust pressure, 3 percent makeup with all feedwater
heaters in service. In some instances, turbine ratings are specified at exhaust
and makeup conditions other than 3.5/3 .0. Also on occasion, turbine
ratings are specified with provision for steam extracted from the turbine
for purposes other than the unit' s own feedwater heating. An example may
be the requirement for extracting steam from the turbine to heat boiler combustion
air. In any case these parameters must be defined in order for a
turbine rating to be fully defined.
Throttle Flow
The throttle flow required to produce the guaranteed capability at nameplate
(or rati ng) conditions is known as the throttle flow correspond ing to guaranteed
capability.
Maximum Guaranteed Capability
Maximum guaranteed capability is the capability of the turbine while passing
throttle flow corresponding to guaranteed capabil i ty, operating at rated
inlet and reheat conditions, and assigned site exhaust and makeup conditions.
A purchaser will frequently wish to know the maximum guaranteed output of a
turbine at a condition different than t he rated exhaust pressure and make -up
conditions . For example, assume the unit i s rated at 500 ,000 kw at 3.5 In.
Hg Abs exhaust pressure and 3 percent makeup and the purchaser wishes to
know the maximum guaranteed capability at 1 .5/0 . This necessitates thermo ­
dynamic calcul ations using the throttle flow corresponding to guaranteed
capability at the new exhaust pressure and makeup conditions. The difference
between the 3.5/3.0 and 1 .5/0 maximum guaranteed capabilities will vary depend
ing upon the exhaust end l oading and method of handling the makeup in the
cyc l e . Variations in capability can be as much as 6 percent or more with
li berally sized last stage blading to as little as 3 percent or less on a
heavily l oaded exhaust end. For purposes of this example, assume the throttle
flow corresponding to guaranteed capability of the 500 mw unit i s
3,500,000 lb/hr. Calculating the performance and heat balance using this
guaranteed throttle flow, the resulting maximum guaranteed capability of
the assumed unit is 525,000 kw at 2400 psig/lOOOF/lOOOF/l .5 In. Hg Abs/0
percent makeup.
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Maximum Calculated Throttle Flow (Also cal led Design Flow)
In order to compensate for variations in manufacturing tolerances all turbines
are designed for a maximum calculated throttle flow 5 percent greater
than throttle flow corresponding to guaranteed capability (5 percent flow
margin). Therefore, the turbine selected, for example, would have a maxi ­
mum calculated throttle flow of 3,675,000 lb/hr, which is 3,500,000 lb/hr
x 1. 05.
Max i mum Cal culat ed Capability (or Valves Wide Open Capabil i ty)
Maximum calculated capability is the calculated (not guaranteed) capability
of the turbine while passing maximum calculated throttl e flow at rated inlet
conditions and assigned site exhaust and make -up conditions. The 5 percent
flow margin will generally produce about 4.5 percent addi tional kw. Thus,
the assumed 500 mw turbine will have a maximum calculated capability of
525,000 X 1 .045=548,600 kw at 2400/ l OOOF/lOOOF/l .5 In. Hg Abs/0 percent
makeup.
5 Percent Overpressure
All units (except those for nuclear application) are safe for continuous
operation at 105 percent of rated pressure with valves wide open and all
feedwater heaters in service. Such operation wil l normally increase the
flow passing ability of the unit 5 percent above its flow passing ability
at rated pressure. The accompanyi ng output gain will be about 4.5 percent.
Therefore (548 ,600 X 1 .045=573,300 kw will be the approximate maximum calcu
lated capabil ity at 2520 psig/lOOOF/lOOOF/l .5 In. Hg Abs/O percent makeup .
However, the output at 5 percent above rated pressure is not guaranteed.
Heater Out of Servi ce
All of the foregoing definiti ons are on the basis of a turbine that is not
suitable for obtaining additional capability by removing the top (highest
pressure) feedwater heater from service. Should a turbine be purchased
such that the top heater may be removed from service to gain additional capability,
the foregoing definitions change somewhat . Removal of the top
heater providing the turbine is designed for this type of service, gives a
capabil ity increase of about 4.5 percent, depending upon the cyc l e configuration
. Therefore, the unit would have a namepl ate rating of 522,500 kw
rather than 500,000 kw and woul d be priced and designed accordingly. With
such a turbine, all ratings would increase when the top heater was out of
service. The maximum guaranteed capability woul d be about 548,600 kw rather
than 525,000 kw, a maximum calculated capability of 573,000 kw instead of
548,600 kw, and a maximum calculated capability at 5 percent overpressure
of 599,100 kw rather than 573,300 kw .
With the top heater out of service, both throttle flow corresponding to
guaranteed capability and maximum calculated throttle flows are slightly
less than the flows with al l heaters in service. This is caused by a sl ight
increase in impulse or first stage pressure which reduces the flow passing
capability of the first stage nozzles.
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Heat Rate Definition
Gross cycle heat rate is defined as:
HR Gross =
WT (HT-HF) + WR (6HR)
KWG
Net cycle heat rate is defined as:
HR Net =
WT (HT-HF) + WR (6HR)
KWG-KWMFP
where:
WT
WR
=Throttle flow (lb/hr)
Reheat flow (lb/hr)
HT= Steam enthalpy at throttle (Btu/ l b)
6HR = Difference in steam enthalpy across the reheater (Btu/lb)
HF= Liquid enthalpy of final feedwater (Btu/lb)
KWG = Gross cycle kw output
KWMFP = kw requirements of main feed pump
As can be seen, the only difference between net and gross heat rate is in
the denominator of the heat rate equations. The total energy input to the
cycle is divided by the gross cycle output for a gross heat rate, and di ­
vided by the net cycle output for a net heat rate .
Why do we find two heat rate equations? Simply because boiler feed pump
work is a function of inlet pressure and fl ow . If the heat rates of one
cycle are to be compared to the heat rates of another cycle with different
inlet pressures, then the net heat rate offers a better basis for compa ri son
because it reflects the larger requirement for pump work in the cycle with
the higher inlet pressures.
It is important to recognize that the cycle net output used in turbine cycl e
heat balance calculations is not the same as station net output. The cycle
net output for turbine cycle calculations allows only for the boiler feed
pump work. The station net output allows for the additional station auxil ­
iaries such as pulverizers, conveyors, condensate and circulating water
pumps, draft fans, lighting, etc.
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Main Feed Pumps Drives
One of three method s of driving main feed pumps is generally used: (1)
electric motors, (2) aux iliary turbines, or (3) a shaft extension of the
main turbine. Occasionally a combinati on of two methods is used. It is
necessary to understand the relationship between the generator terminal output
and cyc le output.
l. Separate motor drive: The gene rator terminal output is the gross cycle
output . The net cycle output is the generator terminal output minus the
power input to the motor dri ving the main feed pump (kwMFP).
2. Shaft extension from the main unit: The generator terminal output is
the net cycle output. The gross cycle output is the generator terminal output
plus the power input to the fluid coupling driving the main feed pump
( kwMFP)'
3. Separate turbine drive: The generator terminal output is the net cycle
output. The gross cycle output is the generator terminal output plus the
( kwMFP).
For studies involving different methods of main feed pump drive, i t is sug ­
gested that the net cycle output be held constant. Therefore, the generator
terminal output would be greater for Case l than for Case 2 and 3 by the
amount of main feed pump power. For example, comparing the pump drives on
a 500,000 kw unit with steam i nl et conditions of 2400 psig, lOOOF-lOOOF, the
generator terminal outputs are listed below:
l. Separate motor drive: The generator terminal output and gross cycle
output is 510,000 kw. The net cycl e output is 500,000 kw .
2. Shaft extension from the main unit: The generator terminal output and
net cycl e output is 500,000 kw . The gross cycle output is 510,000 kw.
3. Separate turbine drive: The generator terminal output and net cycle
output is 500,000 kw. The gross cycle output is 510,000 kw .
Heat Balance Guarantees (Performance Guarantees or Contract Heat Balances)
What is meant by Heat Balance Guarantees? Some heat bal ances submitted by
manufacturers are not guaranteed and are so labeled, such as, "maximum calculated
and /or 5 percent overpressure heat balances."
A heat balance labeled "maximum guaranteed" means that the manufacturer has
guaranteed: (1) the turbine generator will produce at least the i ndicated
output at the generator terminals under the assigned cond i tions for which
the heat bal ance was calcul ated, and (2) the combined effects of turbine
efficiency including turbine valves and gland leakages, generator efficiency,
and exciter efficiency, all in good operating conditions, are suffi cient to
permit the indicated heat rate on a locus of valve point basis under the
as signed conditions for which the heat balance was calculated.
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For heat balances calculated at other load points and unless otherwise noted
on the heat balance, the manufacturer 1 s intent is to guarantee that the unit
efficiency, while in good operating condition, is sufficient to permit the
indicated heat rate on a l ocus of the valve point basis at the indicated
l oad point under the assigned conditions for which the heat bal ance was
cal cul ated.
It is important to recognize that performance guarantees apply only t o the
equipment as a unit and not to the indi vidual components.
Heat Balance Parameters
When requesting any heat balance calcul ations, it is necessary that all the
parameters be defined. In calculating the turbine-generator performance, the
generator output and heat rate will reflect variations in cycle parameters.
When comparing various alternates, erroneous results can be obtained if the
parameters are not the same for all alternates . Therefore, it is necessary
for all of the following parameters to be specifi ed when requesting heat
balance cal cul ations .
1. Steam Conditi ons:
a. Ini tial steam pressure
b. Initial steam temperature
c. Reheat st eam tempe rature
d. Exhaust pressure
2. Turbine configuration : TC2F-25 inches, TC4F-28 .5 inches , CC4F- 44
inches, etc.
3. Feedwater Heaters: (A cycle diagram is recommended)
a. Number, type (cl osed cascade, etc), location and disposition of
drains.
b. Characteristi cs including t erminal difference, drain cooler approach
or subcool ing.
c. Pressure drop fr om t urbine extracti on fl ange to heater .
d. If a specific final feedwater temperature is desired it should be
specified with a tol erance .
4. Reheater pressure drop
5. The fo l lowing additional equipment is sometimes included in the heat
balance calculations: oi l cool er, hydrogen cooler, air ejector, evaporator
for makeup, air preheater; etc . Equipment such as evaporators and air preheaters,
etc . , require extraneous extraction from the turbine . It is important
for this t ype of equi pment to be adequately descr ibed in order t o
calculate the extraneous extraction. Th i s description would incl ude approximate
extraction pressure level, the quantity of extraction steam or heat
requirement, and the dispos i tion and condition of the flow returning to the
cycle.
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6. Main Feed Pump (MFP): The location of the MFP in the feedwater cycle
and the type of MFP drive shou ld be specified. In order to ca l cu l ate the
MFP power and heat added to the feedwater cycle, the pu mp discharge pressure
and pump efficiency (or pump ~ h) must be specified. The efficiency of the
pump drive shou ld also be specified .
7. Turbine Rati ng : As pointed out in the previous section, turbi ne ­
generator units are rated at 3.5 In . Hg Abs exhaust and 3 percent makeup .
However, it is not necessary for the customer to specify this rating when
requesting heat balance calculations. Anyone of the following load or flows
at design site exhaust pressure and makeup may be specified : (a) maximum
guaranteed load or flow, (b) maximum calculated load or fl ow, (c) maximum
calculated - 5 percent overpressure load or flow. Westinghouse wil l establish
the 3.5 In . Hg Abs - 3 percent makeup rating using any one of the above specified
load or f l ows as a reference point.
An additional method of rati ng a unit is on the basis of maximum permissible
exhaust flow. Using the maximum permissible ~xhuast flow , a max i mum ca l cu ­
lated, 5 percent overpressure throttle flow is established. This maximum
calculated, 5 percent overpressure throttl e flow is then used as a reference
point to establish the maximum guaranteed load .
8. Generator Rating: The generator rating or the method of rating the gen ­
erator must be specified. In cases, such as maximum permissibl e exhaus t f l ow
un i ts, the exact load at which the generator is to be sized is not known
until the heat balance cal cul ations are made . In situations such as this it
is normal practice to request Westinghouse to rate the generator at a certain
operating condition. For example, assume the purc haser has requested performance
data on a unit rated with a max imum guaranteed load of 525,000 kw
at 1 .5 In. Hg Abs and zero percent makeup. Purchaser has requested that the
generator be rated at a 0.90 power factor at the maximum calculated, 5 percent
overpressure load. Not knowing exactly what this l oad will be, purchaser
can request Westinghouse to rate the generator as described above .
Westinghouse will make t he calculations to determine the maximum calculated,
5 percent overpressure load and apply the 0.9 P. F. to determine the generator
rating. Us ing the exampl e in the Glossary Section, a maximum guaranteed load
of 525,000 kw would result i n approximately 573,300 kw at max imum calculated
5 percent over -pressure cond ition.
The generator rating would be 573,300 kw :0.9=637,000 kva.
Maximum End-Loaded Units
The maximum permi ssible exhaust flows have been establi shed for each low
pressure turbine configuration ; these figures are publ i shed in the Westinghouse
Steam Turbine Di vision pri ce list. The t hrottle flow corresponding
to the maximum permissible exhaust flow is establ ished at those conditions
which result in the highest permis sible flow through the l ast stage bl ade .
These conditions include valves wide open, maximum permissible initial pressure
for safe continuous operation, 3.5 Hg Abs exhaust pressure , zero percent
makeup, heaters out of service where applicable , attemperation flows ,
and conti nuous air preheating requirements, etc. Air preheating steam that
-231-

is seasonal will not be included in determining the maximum throttle flow
since, when this extraction is shut off, the maximum permissible exhaust
flow would be exceeded.
The feedwater cycle and auxiliary equipment have a great effect on the rated
output of a maximum end-loaded unit . Any change in the extraction steam
will result in a change in the last-stage blade flow. Therefore, when feed ­
water heater and auxiliary equipment specifications change , the maximum cal ­
culated 5 percent overpressure throttle flow must be recalculated. If this
throttle flow changes, the max imum guaranteed load will also change .
Control Va lve Points
Large turbines are equipped with several control valves . Occasionally a
turbine is designed so that all control valves open simultaneously. This
is called a single valve point unit. The disadvantage of this type design
i s that throttling losses occur across the control valves at all loads except
when all control valves are wide open. The advantage is that single
valve point designs reduce operating stresses on the first stage blading.
However, most turbines are designed to permit sequential opening of control
valves or groups of control valves. These are called multivalve point units
and permit partial load operation at some partial load points without the
occurrence of throttling losses across the control valves . The load points
at which some control valves are fully closed are called valve points . Thus
valve points are partial load points of a mu ltivalve turbine where no throttling
losses occur across partially opened control valves.
Operation on the valve loop means operating at a load point where a control
valve or group of control valves are partially open and throttling losses
occur across the partially opened valves. This term i s derived from the
characteristic loop shape of a heat rate versus l oad curve calculated with
consideration of throttling losses across control valves.
On multivalve point turbines, heat rates are calculated on the basis of locus
of the valve points. Locus of valve point heat rate data are advantageous
from two view points. First, it simplifies calculation procedures . And
secondly, it simplifies comparison of calculated data to field test performance
data.
Exact prediction of valve point loads by a manufacturer is l imited by manu ­
facturing tolerances which can compound to influence predictions by several
per cent. Location of actual valve point loads can be easily verified during
operation. Changes in seal clearances and collection of deposits on
turbine blading during operation can also produce changes in valve point
loads amounting to several percent .
-232-

6. Mai n Feed Pump (MFP) : The location of the MFP in the feedwater cycle
and the type of MFP drive should be spec i fied. In order to calculate the
MFP power and heat added to the feedwater cycle, the pump discharge pressure
and pump efficiency (or pump 6h) must be specified . The efficiency of the
pump drive should also be spec ified.
7. Turbi ne Rating: As pointed out in the previous section, turbinegenerator
units are rated at 3.5 In . Hg Abs exhaust and 3 percent makeup .
However, it is not necessary for the customer to specify this rating when
requesting heat bal ance calculations. Anyone of the following load or flows
at design site exhaust pressure and makeup may be speci f ied : (a) maximum
guaranteed l oad or flow , (b) maximum calculated load or f low, (c) maxim um
calcul ated - 5 percent overpressure load or flow. Westi nghouse will establ i sh
the 3. 5 In. Hg Abs - 3 percent makeup rating using any one of the above spec ­
ified l oad or flows as a reference point .
An additional method of rati ng a unit is on the basis of maximum permissible
exhaust flow. Using the maximum permissibl e ~xhuast flow, a maxi mum calculated,
5 percent overpressure t hrottle flow is established. This maximum
calculated, 5 percent overpressure throttle flow is then used as a reference
point to establish the maximum guaranteed load.
8. Generator Rating: The generator rating or the method of rat ing the gen ­
erator must be speci fied . In cases, such as maximum permissible exhaust flow
units, the exact l oad at which the generator is to be si zed is not known
until t he heat balance calculations are made. In situations such as this it
is norma l practi ce to request Westinghouse to rate the generator at a certain
operating condition. For example, assume the purchaser has requested performance
data on a unit rated with a maximum guaranteed load of 52 5,000 kw
at 1 . 5 In. Hg Abs and zero percent makeup. Purchaser has requested that the
generator be rated at a 0.90 power factor at t he maxi mum ca l culated, 5 percent
overpressure load . Not knowing exactly what this load will be, purchase
r can request Westing house to rate the ge nerator as described above .
Westinghouse will make the calcul ations to determine the maximum calculated ,
5 percent overpressure load and apply the 0.9 P. F. to det ermine the generator
rating . Using the example in the Glossary Sect ion, a maximum gua ranteed l oad
of 525,000 kw would result in approxi mat ely 573 ,300 kw at maximum cal culated
5 percent over-pressure condition.
The generator rati ng would be 573,300 kw :0.9=637,000 kva .
Maximum End- Loaded Units
The ma ximum permissibl e exhaust flows have been established for each low
pressure turbine configuration; these figures are published in the Wes tinghouse
Steam Tu rbine Division price list. The t hrottl e flow corresponding
to the maximum permi ssibl e exhaust flow i s establ ished at those conditions
which result in the highest permi ssible flow through the last stage blade.
These conditions include valves wi de open, maximum permissible initial pressure
for safe continuous operati on, 3.5 Hg Abs exhaust pressure , zero percent
makeup, heaters out of servi ce where appl icable, attemperation flows ,
and continuous air preheating requirements, etc . Air preheating steam that
- 231-

is seasonal will not be included in determining t he maximum throttle flow
since , when this extraction i s shut off, the maximum permiss ible exhaust
flow would be exceeded.
The feedwater cycle and auxiliary equipment have a great effect on the rated
output of a maximum end -loaded unit. Any change i n the extraction steam
will result in a change in t he last-stage blade flow. Therefore , when feed ­
water heater and auxiliary equi pment specifications change , the maximum calculated
5 percent overpressure throttl e flow must be recalculated . If t his
throttle flow changes, the max imum guaranteed l oad wil l also change.
Control Valve Points
Large turbines are equipped with several control valves. Occasionally a
turbi ne is designed so that al l control va l ves open simu l taneously. This
i s called a single valve point unit. The disadvantage of this type design
is that throttling losses occur across the control valves at all loads except
when all control valves are wide open. The advantage is that single
valve poi nt des i gns reduce operating st resses on the first stage blading.
However, most tur bines are designed to permit sequential opening of control
val ves or groups of control valves. These are called multival ve point units
and permit partial load operation at some partial load points without the
occurrence of throttling losses across the control valves. The load points
at which some control valves are full y closed are called valve points . Thu s
valve points are partial load points of a multivalve turbine where no throttling
l osses occur across partially opened control valves .
Operation on the val ve loop means operating at a l oad point where a control
valve or group of control val ves are partially open and throttling losses
occur ac ross the partially opened valves. This term i s derived from the
characteristic l oop s hape of a heat rate versus load cu rve cal cu l ated with
consideration of throttling losses across control val ves .
On multivalve po int tu r bines, heat rates are cal cu l ated on the basis of l ocus
of the valve points. Locus of valve point heat rate data are advantageous
from two view points. Fi rst, it si mplifi es ca l cul ati on procedures . And
secondl y , it simplifies compari son of calculated data to field test pe r fo rmance
data.
Exact prediction of valve po int l oads by a manufactu rer is limited by ma nu ­
f acturing tol erances which can compound to influence predictions by several
per cent. Location of actual valve point loads can be easily verified during
operation. Changes in seal clearances and col lection of deposits on
turbine bladi ng during operation can al so produce changes in valve point
loads amou nting to several percent.
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I