Extending the Life of Power Cables - Energy Association of ...

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Extending the Life of Power Cables - Energy Association of ...

Extending the Life of Power

Cables

Orange & Rockland Utilities, Inc.

a Subsidiary of Consolidated Edison, Inc.

Wayne A. Banker

Energy Association of Pennsylvania

September 25, 2012

1


Company Overview

P I K E

S U L L I V A N

SUSSEX

P A S S A I C

O R A N G E

R O C K L A N D

B E R G E N

Pennsylvania

New

York

New

Jersey

Electric Service Territory

Orange and Rockland

Rockland Electric Company

Pike County Light & Power 2


System Statistics

• Approximate 300,000 electrical customers served.

• Approximately 75,000 (25%) customers are served

from underground systems.

• Distribution system is predominantly overhead

facilities configured as open-loop circuits

– Underground Facilities are primarily URD, with

substation exits, highway crossings and large

business/industrial parks making up the remainder

• Total service area is approximately 1,350 square

miles.

3


Underground Primary Cable

A – Stranded or solid

conductor

B – Semi-conducting

shield

C – HMWPE, TRXLPE, EPR,

or other insulation

D - Insulation shield

E – Copper concentric

neutral

F – Outer jacket


Conductor Designs for Insulated

Cables

• Stranding increases:

– flexibility

– diameter for the same

metal area

– resistance for the same

metal area

• Material

– Aluminum

– Copper

• Function

– Carry Current

3.5% larger

Solid Conductor

Compact

Stranded Conductor

Concentric Round or Compressed

14% to 11% larger


Insulated Conductor

Insulation is put on a

conductor to save space

– Air insulation is replaced with a

better insulation

– Typical insulations include:

• HMWPE, XLPE, & EPR


Insulation Thickness

Cables are voltage rated phase to phase

based on a grounded WYE three phase

system unless stated

– Thus, unless otherwise noted, the insulation

thickness is designed for a voltage equal to the

cable voltage rating divided by 1.732

– For a 15kV cable the insulation thickness is

designed for; 15 kV/1.732 = 8.66 kV

Cables used on other systems must be selected

accordingly

– Typical thickness for 15kV – 100% level –175mils &

133% level –220mils

– Typical thickness for 35kV – 100% level –345mils


HMWPE – High Molecular Weight

Polyethylene

• Seemed impervious to moisture

• Higher AC breakdown strength

• Superior dielectric properties

• Expected 50 plus years life

• Reduced insulation thickness

• Loose Industry Standards


XLPE – Crosslinked Polyethylene

• Gained favor in late 1960’s

• Higher mechanical strength

• Higher operating temperature

• Higher AC breakdown strength

• Reduced insulation to 175 mils


EPR – Ethylene Propylene Rubber

• Long service life

• Better flexibility

• Less expansion during heating

• Better properties at high temperature

• More resistance to discharge


Initiatives to Implement Cable

Programs

• 1980’s - rising URD cable failures

• Infancy failures

• Poor specifications allowed cables to be installed

that were rejected by others

• Increased fault repair backlog and loss of loops

• Ineffective repair and replacement program

11


Program History

• 1985 - Changed Cable Specification to EPR and

Standardized Sizes and Accessories

• 1986 – Added Jacketing

• 1980’s – Pioneered rehabilitation through R&D

projects

• 1990 – Committed to Rehabilitation/Rebuild

Process

12


URD Cable History

• HMWPE Cables

– Used from 1967 - 1977

– 15 kV Cables - 175 mils

• XLPE Cables

– Used from 1978 - 1985

– 15 kV Cables - 220 mils & 35 kV Cables - 345 mils

• EPR Cables

– Used from 1986 to the Present

– 15 kV Cables - 175 mils & 35 kV Cables - 345 mils

13


Installed Cable Footage

Miles Installed

2000

1800

1600

1400

1200

1000

800

600

400

200

0

743

742

262

Years

HMWPE

XLPE

EPR

1800

702

561

14


URD Cable Failures

160

140

120

100

80

60

40

20

0

HMWPE

18.3 % of system

1967 - 1978

XLPE

22.9 % of system

1978 - 1985

86 87 88 89 90 91

92 93 94 95 96 97

98 99 00 01 02 03

04 05 06 07 08 09

10 11

EPR

58.8 % of system

1985 - present

15


Cable Failure Rates

Failures per 100 miles

22.00

18.00

14.00

10.00

6.00

2.00

-2.00

1988

18.46

9.33

3.50

0.00

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

Years

2001

2002

2003

2004

2005

2006

HMWPE Failure Rate

XLPE Failure Rate

EPR Failure Rate

Total Failure Rate

2007

2008

2009

6.95

2.85

1.93

0.00

2010

2011

16


Electric Breakdown

• Failure of a material due to the application of a voltage

stress

• Electric breakdown occurs when the applied voltage can no

longer be maintained across the material in a stable

fashion without excessive flow of current and physical

disruption


Types of Electric Breakdown

• Thermal

– Occurs when the rate of heating exceeds the rate of

cooling by thermal transfer and thermal runaway

occurs under voltage stress

• Discharge – Induced Breakdown

– Occurs when electrical discharges occur on the

surface or in voids of electrical insulation. Ionization

causes slow degradation – Corona or partial

discharges occur – Electrical Trees Form

18


Cable Failure Modes - Water Treeing

• Water Trees – Produced at

Insulation Voids

– Requirements to Initiate Growth

• Water vapor

• Electrical stress

• Time - Slow Growth – May Take

Several Years

– May Propagate Into “Electric

Trees” Especially In The Presence

of DC, Surges, & Impulses Typical Vented Water Tree

19


Cable Failure Modes (Cont.)

Water Tree Photo


Cable Failure Modes - Electrical

Treeing

• Electrical Trees

– Much Faster Growth

– May Propagate Fully Through Insulation

– Cable May Fail Within Hours of Formation

Typical Electric Tree

21


Cable Failures

30

25

20

15

10

5

0

Lightning Activity vs. Cable Failures

Time (Months)

Faults

Lightning

800

700

600

500

400

300

200

100

0

Lightning Incidents

22


Cable Rehab Repairs Water Trees

As silicone fluid diffuses it fills Voids and Trees.

– Absorbs water and expands into trees and voids

– Retards formation of new “water trees”.

– In many cases increases dielectric to greater

than new condition

23


Cable Rehab Provided by Utilx Corp.

• O&R was part of the original R&D Project on Cable

Rehab with Dow Corning.

• O&R has Utilized Utilx for over 25 years

• Utilx – CableCURE Injection Technology

– 90 million feet of cable injected

– 99% of cables remain failure free

– 20 year warranty

24


Cable Rehab Procedure

• De-energize, test & ground cable

section

• Remove old elbow or stress cone

• Test condition of the concentric

neutral wires and determine if there

are splices in cable section utilizing a

high resolution Time -Domain

Reflectometer

• Condition of neutral must be within

50% predetermined range - If not,

section is replaced

• Install new injection elbow

25


Cable Rehab Procedure (continued)

• With nitrogen gas, perform a flow test at 20 psi. Flow test

must be above 30 cc

• If test is good and no splices in section. Inject cable with

fluid up to 100 psi

26


Cable Rehab Procedure (continued)

• With a splice section, draw 10 inches of vacuum at the

collector end, then inject at 18 psi

• Injection Steps:

– Flush with Alcohol

– Inject Fluid

– Collect 2” of discharge in collector bottle or until clean fluid

• Cable sizes #2 & 1/0 stranded - Cable must be soaked at 8

psi for 60 days

• For 4/0 cables there is no soak period

• After soak period, canisters and tubing are removed and

elbows are capped

27


Subdivision Statistics Evaluation

• Subdivision Density (# cust.)

• Interruption Frequency (cust. affected/cust.

served - SAIFI)

• Average Subdivision Interruption (# cust.

hrs./cust. served - CAIDI)

• Average Outage Duration (# cust. hrs./ cust.

affected - SAIDI)

• Number of Interruptions

• Age of Cable System

28


Fault Tracking Process

Transformer

Pad 78/78

Smith Road

Transformer

Pad 84/00


Transformer

Pad 78/78

Failure Occurs

Cable Failure

Smith Road

Transformer

Pad 84/00


Underground

Equipment Failure Report

Log # Date Off Grid # Man Hours

NY-97035 7/13/97 78/78 to 84/00 6.0

Cable Conductor Insulation Type Voltage Class

4/0 Al. 175 mil HMWPE 15 kV

Defective Part System

Cable Direct Buried


Cable Fault Log

Log #

Location

Wire

Type

NY-97034 10/20 - 34/99 1/0 Al

XLP

NY-97035 78/78 - 84/00 4/0 Al

HMWPE

NY-97036 45/50 - 60/87 #2 Al

HMWPE

Street

Address

Jones

Rd

Smith

Rd

Lincoln

St.

Occurred

Repaired

7/01/97 8/15/97

7/13/97 12/10/97

7/25/97 10/28/97


Underground

Outage History Report

U/G Code: I33

Date Off Cause Type Time Off Time On Hours

7/13/97 Equip. Failure 23:44 01:53 2:09

Weather Cause Location

Clear 78/78 -84/00

Smith Road

Bad Section of 4/0 Primary

Fuse Out: 56268/39851 40K

Customers Effected Customer Hours

17 36.55


Comparing Failure Data to

Manageable Assets

• Compartmentalize the area to be evaluated

– Subdivision or protected branch

– By date of installation

– By poor performing cable feeding

• New cable

• Priority customers


Subdivision Statistics Evaluation

• Subdivision Density (# cust./mile of cable)

• Interruption Frequency (cust. affected/cust.

served - SAIFI)

• Average Subdivision Interruption (# cust.

hrs./cust. served - CAIDI)

• Average Outage Duration (# cust. hrs./ cust.

affected - SAIDI)

• Number of Interruptions

• Age of Cable System


U/G Subdivision Priority Rating

System

2 or more interruptions within 36 months

Primary problems only

U/G Intr Intr Cust Cust U/G Count Cust Hrs Cst Aff Aff/Int Priority

Subdivision % Affect % Sub % Hours % per % Rating

Mean Mean Count Mean Mean Int Mean

Mountainview 7 223 1,036 993 839 615 6,167 1,302 148 444 959

Bon-Aire 12 383 586 562 2,037 1,493 2,431 513 49 147 809

Ramapo Ridge 12 383 765 733 365 267 4,054 856 64 191 709

County Club L 3 96 494 474 579 424 2,703 571 165 495 526

Ramapo Ridge 3 96 440 422 705 517 2,111 446 147 440 488

36


Other Factors For Consideration

• Overhead system

reliability

• Recent multiple failures

• Joint trench partner

rebuild plans

• Voltage or protection

problems

• Municipal road plans

• Political issues

• Flexibility in Prioritizing

the Workload

– Monitoring Cable

Failures Monthly

– Customer Issues

– Monthly Internal Service

Reliability Meetings

– Contractor and Workload

Planning

37


Typical Recommendations

• Retrofit of riser poles with riser class MOVs

• Installation of underground open point elbow

MOVs

• Replacement of submersible with padmount

transformers

• Padmounted switching/fusing installations

• Additional fault indicator applications

• Primary cable rehabilitation

• Cable replacement

• Radial primary spur to a loop configuration

38


Radial Fed URD Subdivision


After Cable Rebuild Project


Rehab/Rebuild URD Subdivision

Cable Section with Two Sources Radial URD Section

Completed URD Subdivision

Cable Treated with Silicone Fluid

Rebuilt into a Loop Configuration


Rebuild – Rehab Decision Analysis

• Rehab $ 10 -15 / cable foot

• Rebuild $ 35 - 55 / trench foot

• Decision to Rebuild vs. Rehab

– 15kV HWMPE or XLPE only

– Rebuild verses Rehab costs

• Two (usually) or three (no) phases in a trench

– Long express run

– Existing known multiple splice sections

– Probability of neutral loss (> 50%)

– No Radials due to outage requirements

42


Cable Miles

Cable Miles Upgraded

250

200

150

100

50

0

Total Cumulative Rebuilt Miles

Total Cumulative Rehab. Miles

Years

43


URD Cable Failure Rates / Dollars Spent

Millions of Dollars

$3.00

$2.50

$2.00

$1.50

$1.00

$0.50

$0.00

23.08

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

$1.23

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

Years

Rehab($)

Rebuild($)

Ave Spending($)/Yr

Failure Rate

25

20

15

10

9.8

5

0

Failures/100 Miles

44


Rehab Benefits

• Cost savings

Life extension (guaranteed 20 years)

• Data indicates much longer time frame

• No excavation

• Customer acceptance

45


Cable Rehab Effectiveness

• Cable Rehab is a cost effective approach for

controlling and reducing cable failures

• Accessory replacement is a positive integral

part of the process

• A cable rehab program must be combined with

a cable rebuild program

• To date there have been few failures on

silicone treated cable

46


Questions ???

Thank You

47

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