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Servomotors Used for Driving Control Valves,
the Economical Solution for Steam Turbines
Voith servomotors master the immense
forces necessary to adjust
live and extraction steam valves of
steam turbines. The steam mass
flows are controlled precisely and in
case of load shedding they are
blocked quickly and reliably.
The Voith servomotor is a compact
electro-hydraulic functional unit
providing high operational reliability
and availability. The integrated electronic
stroke control grants easy
and fast commissioning.

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Why do you still assemble your own control drive?
Voith offers your individual servomotor factory-assembled.
Voith’s servomotor – this is all you need on your parts list.
The control of steam turbines
typically requires a large variety
of com ponents, such as hydraulic,
mechanic and electronic parts, all
of which need to be independently
designed, administrated, assembled
and then commissioned.
These components are intelligently
combined within the Voith servomotor
into one compact and suitable
functional unit. The Voith servomotor
is a sophisticated and truly
economic solution.

Voith Servomotors – Fields of Application
Steam turbine for generator drive, equipped
with low-pressure servomotors SMRA 13xxx
Steam turbine for generator drive, equipped
with high-pressure servomotors SMRA 11xxx
In many fields, users already derive benefit from Voith Turbo’s
experience in controlling valves on steam turbines, be it live
steam control or extraction control. They reap the benefits
arising from the technical and economic advantages of the
Voith servomotor.
Steam turbine for generator drive, equipped
with low-pressure servomotors SMRA 51xxx
Steam turbine for generator drive, equipped
with high-pressure servomotors SMRA 41xxx
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We also offer the appropriate servomotor for your turbine
Low-pressure series:
pressure range up to 25 bar
SMRA 13xxx: Link joint at bottom SMRA 51xxx: Flanged version
SMRA 13001 SMRA 13002 SMRA 13004 SMRA 13401 SMRA 51101 SMRA 51201 SMRA 51301 SMRA 51401
The most convincing and decisive
technical features of the Voith servomotor
series:
Substantial savings
Voith servomotors allow substantial
savings in regard to design, materials
management, production and
service.
Individual solutions
Within a wide range, Voith servomotors
offer individual solutions
for existing machinery and provide
high functionality while still being
economic and reliable.
Long-time experience
The Voith’s servomotor series benefits
from many years of experience
in the area of control systems and
actuators.
Integrated electronic stroke
control
The control of steam turbines frequently
requires extensive adjustments
between the controller,
position pickup and actuator. Voith’s
servomotors have integrated electronic
stroke control, hence no
tuning is required during test run
and commissioning.

High-pressure series:
pressure range up to 160 bar
SMRA 11xxx: Hinge bearing on both sides SMRA 41xxx: Flanged version
SMRA 11012 SMRA 11011 SMRA 11023 SMRA 11024 SMRA 41111 SMRA 41201 SMRA 41301 SMRA 41401
Hysteresis-free design
The combination of mechanical and
hydraulic components commonly
creates hysteresis which could lead
to instability at critical operating
points. The virtually hysteresis-free
Voith servomotor ensures extraordinarily
high operating stability.
High control accuracy
For special applications, extreme
accuracy is required in regard to
linearity, hysteresis, reproducibility
and temperature drift. This is no
problem for the Voith servomotor.
Explosion-proof design
For applications in explosion
hazardous areas, the stroke has
historically been commonly fed back
mechanically. The explosion-proof
design of the Voith servomotor
offers continuous electronic control
and stroke feedback.
Dirt-resistant
Usually, hydraulic supply systems
on turbomachinery are only provided
with lube oil. Lube oil’s quality
just works well for the Voith
servomotor.
Emergency shutdown
Even if all auxiliary energies fail, the
trip function has to be guaranteed.
The restoring spring and the adapted
hydraulic pilot control of the
Voith servomotor are designed to
meet this requirement.
High dynamics
Load shedding of generators
require rapid closing of the valves.
The high dynamics of the servomotor
readily satisfy this requirement
without any difficulty.
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Technical data
Valid for all series
Ambient conditions
Temperature - 20 °C to + 80 °C
Degree of protection IP 65 to DIN 40 050
Explosion protection (optionally)
Hydraulic data
II 2G EEx de IIB T4, Ta = - 20 ... + 60 °C
Hydraulic fluid Mineral oil to DIN 51 524
Viscosity ISO VG 32 up to ISO VG 46 to DIN 51 519
Oil temperature
Electric data
+ 10 °C up to + 65 °C (+ 60 °C for explosion-proof design)
Supply voltage 24 VDC ± 15%
Power consumption 1 A, max. 3 A für approx. 3 s max.
Stroke set position 4 – 20 mA (for position 0% – 100%)
Stroke remote indication 4 – 20 mA (for position 0% – 100%)
Electro-magnetic compatibility
Accuracies
Basic specification EN 61 000-6-4 (emission), EN 61 000-6-2 (immunity to interference).
Emission test radio interference radiation to EN 55 011 Group 1, Class A.
Immunity test to EN 61 000-4-2, EN 61 000-4-3, EN 61 000-4-4, EN 61 000-4-6.
Linearity ± 0.15% of maximum stroke
Hysteresis 0.005% of maximum stroke
Reproducibility 0.015% of maximum stroke
Temperature drift 0.04% of maximum stroke / °C

Series
SMRA 13xxx:
Low-pressure; link joint at bottom
Type SMRA SMRA SMRA
13001 13002 13004
1) Piston spindle stroke electronically adjustable from 50 – 100 %.
2) At nominal pressure.
3) All data without consideration of tolerances and friction.
4) Fail-safe position piston spindle deliverable also in reversed form.
Design with deviating technical data possible upon request.
Subject to technical modifications.
SMRA
13401
SMRA 51xxx:
Low-pressure; flanged version
SMRA
51101
SMRA
51201
SMRA
51301
Mechanical data
Piston / spindle diameter 152 /34.9 mm 203.2 / 44.5 mm 254.6 / 50.8 mm 304.8 / 63.5 mm 110 / 28 mm 160 / 28 mm 200 / 45 mm
Maximum piston spindle stroke1) 105 mm 35 mm 203 mm 210 mm 90 mm
Closing speed full stroke < 0.4 s < 0.6 s < 0.8 s < 0.3 s
Opening speed full stroke2) < 2 s < 2 s
Spring tension at piston spindle
stroke 0 mm3) Double-acting operating cylinder, no retracting spring 1,500 N 3,000 N 5,000 N
Spring tension at maximum piston
spindle stroke3) Double-acting operating cylinder, no retracting spring 7,200 N 15,000 N 25,000 N
Opening force at piston spindle
stroke 0 mm2)3) Opening/(closing) force at maximum
piston spindle stroke2)3) 13,700 N 25,900 N 40,500 N 55,800 N 13,100 N 28,000 N 42,680 N
14,500 N 24,700 N 38,900 N 58,300 N 7,400 N 16,000 N 22,680 N
Fail-safe position piston spindle extended 4) retracted 4) extended 4) extended
H x L x W [mm] 780 x 570 x 460 800 x 640 x 390 930 x 580 x 410 1080 x 715 x 410 810 x 262 x 320 810 x 385 x 360 990 x 220 x 395
Weight
Hydraulic data
240 kg 310 kg 435 kg 520 kg 130 kg 200 kg 290 kg
Nominal pressure 8 bar 16 bar
Maximum pressure 16 bar 25 bar
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SMRA
51401
SMRA 11xxx:
High-pressure; link joint at bottom
SMRA
11012
SMRA
11011
SMRA
11023
SMRA
11024
SMRA 41xxx:
High-pressure; flanged version
SMRA
41111
SMRA
41201
SMRA
41301
SMRA
41401
250 / 50 mm 80 / 45 mm 80 / 45 mm 80 / 45 mm 110 / 50 mm 80 / 45 mm 110 / 50 mm 125 / 55 mm 160 / 63 mm
250 mm 85 mm 120 mm 200 mm 120 mm 55 mm
< 0.3 s < 0.3 s
< 3 s < 1 s < 1 s
3,000 N 15,000 N 12,500 N 5,000 N 16,000 N 25,000 N 42,000 N
9,000 N 21,800 N 25,000 N 26,500 N 13,000 N 29,000 N 39,000 N 52,000 N
97,000 N 39,900 N 42,400 N 108,000 N 75,500 N 104,000 N 121,400 N 230,000 N
91,000 N 33,100 N 29,900 N 28,400 N 94,000 N 67,500 N 91,000 N 107,400 N 219,000 N
retracted extended retracted extended
1000 x 550 x 460 969 x 513 x 363 1130 x 470 x 380 1200 x 550 x 400 985 x 460 x 340 1300 x 360 x 445 1340 x 500 x 380 1355 x 545 x 400
450 kg 170 kg 232 kg 290 kg 220 kg 400 kg 500 kg
21 bar 160 bar 160 bar
200 bar 200 bar
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Function
Process controller
Functional view servomotor SMRA 11xxx
x
-
w +
X1
-
KPU
KPD
+
X0
Control magnet
U Mag
U Hall
+24V
In order to achieve a variable steam
mass flow, the control system specifies
a position setpoint w (4 – 20 mA)
for the Voith servomotor. The electronics
integrated in the servomotor
transform this position setpoint w
into a proportional piston spindle
stroke and via a directly cou pled
valve or one connected via a lever
system into a steam mass flow.
U F
The Voith servomotor is the sophisticated and compact electrohydraulic
functional unit comprising a Voith control magnet
(VRM) with integrated positioner, hydraulic pilot control, electronic
stroke measurement (position pick up sensor) and a
hydraulic cylinder.
F Mag
Hydraulic pilot
control
T P
Live steam
The electronically measured actual
position value x is led back to the
control electronics and is made
available to the control system.
F F
Hydrauliccylinder
s
i
s
Position
pick up
sensor
Steam control valve
T Tank connection
P Oil supply terminal (input)
X0, X1 Parameters for stroke
adjustment (potentiometers)
KPU, KPD Control gains (potentiometers)
w Position nominal value
(4 – 20 mA)
x Position actual value
(4 – 20 mA)
FMag Magnetic force
FF Force for control spring
UHall Hall voltage
UMag Reference variable for
solenoid force FMag U Voltage
s Stroke
i Position pick up sensor current
signal
In order to achieve high speeds,
two-stage hydraulic pilot controls
are used in the SMRA 13xxx
double-acting servomotors. The
enormous closing speed of the
single-acting SMRA 51xxx and
SMRA 41xxx servomotors is
achieved through an additional
plate valve integrated in the
servomotor.

Voith Turbo GmbH & Co. KG
Electronic Drive Systems
Voithstr. 1
74564 Crailsheim, Germany
Tel. +49 7951 32-470
Fax +49 7951 32-605
turcon@voith.com
www.voithturbo.com/actuation-control-turbomachinery
cr 302 en, 05.2010, aik / WA, 1.500. Dimensions and illustrations without obligation. Subject to change.