Cable Rehabilitation at Oncor

Cable Rehabilitation at Oncorby Richie Harp – Distribution StandardsData provided by Mark Darilek – Maintenance Planning

SWEDE 2009 – Tulsa, OK – Thursday, May 7, 2009

Cable Rehabilitation Overview

Rehabilitated cableCable repairs to facilitate future rehabilitation

Oncor requirements for rehabilitationFurther considerations2nd Responder processAnother technology

Amount of Rehabilitated Cable

Began in 1995420 cbl-mi rehabilitated8,000 cbl-mi in service – Pre-1993 cable

22,000 cbl-mi total cable

Amount of Rehabilitated Cable

URDCable size – Less than #4/0 AWG(#2 and #1/0 AWG, and minimalamount of #2/0 AWG)

Began in 1995405 cbl-mi rehabilitated17,000 cbl-mi in service2% of URD cables

Amount of Rehabilitated Cable

FeederCable size – #4/0 AWG and larger (up to 1000 kcmil)

Began in 200815 cbl-mi rehabilitated3,400 cbl-mi in service0.4% of feeder cable

Cable Repairs

Standard cable (Began purchasing in 1990)#1/0 Al 19-StrandsStrand-filled conductors25 kV, 260-mil TRXLPE16-#14 AWG Concentric Neutral Wires (Full neutral)

Jacketed

Cable Repairs (Cont)

Only for cable repairs (2-ft pieces) for future injection#1/0 Al 19-StrandsStrands not filled25 kV, 260-mil TRXLPE8-#14 AWG concentric neutral wires(1/2 neutral)

UnjacketedOn 1000-ft composite reel

Oncor Requirements for Rehabilitation

Do not rehabilitate: Cable installed in conduit 175-mil or 220-mil cable operating

at 14.4 kV Butyl rubber cable Cable with tape conductor shield Corroded concentric neutral

Do not rehabilitate cable if… Corroded center conductor Loss of insulation shield

conductivity Insulation shield with no adhesion Failures due to dig-ins or debris in

trench There is a chance the cable will be

converted to 14.4 kV in the future

Oncor Requirements for Rehabilitation (cont)

Other Requirements

There must be more than 25% concentric neutral remaining.

There cannot be more that one joint per 100 feet of cable.

The faulted cable section must not have been de-energized more than six months.

Comments:

We tried to rehabilitate some open loops that had been de-energized for up to 2 yearsVery little successWe quit rehabilitating open loops that had been de-energized for more than 6 months.

More comments:

2006 and 2007 ProcessesLeft URD loops open after failures (direct buried cables)

Only repaired cable to get customers’ lights back on.

More comments:

Dec 2007 ProcessBegan repairing failed loops again.Caught up with open loops (Feb 2009)–Inject cables or–Replace cable if not able to inject

More comments:

Dec 2008 Process ChangeInstall joint to repair cableTry to inject the cableAfter the repair, if the cable is not able to be injected, then just leave energized.

Defer replacement of the cable until the next fault.

2nd Responder Process

System-Wide ProcessRepair failures on direct buried cable (not in conduit)

Must be able to switch around to get lights back on.

Not normally feeder exits (Only non-critical cables)

2nd Responder Decision Process Flow Chart

Available by request

2nd Responder Process

1868 sections of failed cables came through the process since 2008

749 sections of cable were injected1119 sections were not able to be injected922 due to process requirements197 not related to the process (already energized when arrived, in conduit, etc.)

2nd Responder Process – Injected/Not Injected

922749 Injected

Non-Injected

2nd Responder Process

12 cause codes for not being able to inject the 1119 sections of cableAge of fault (> 6 months)Could not flow (Blocked strands or joints) Inaccessible fault or joint locationDeteriorated neutral (< 25% remaining)Previously injected, non-warranty or otherPreviously injected, warranty

2nd Responder Process

12 cause codes for not being able to inject the cable (Cont)Corroded conductorNumber of joints (> than 1 joint per 100 ft)UnknownCable is in conduitAlready energized upon arrivalOther–These last three represent the 197.

2nd Responder Process – Causes

11%

11%

20%

16%

5%18%

1%3%

1%2%

4%8%

Age of fault

Could not flow

Inaccessible fault or joint

Deteriorated neutral

Number of splices

Previously injected, non-warrantyPreviously injected,warrantyCorroded conductor

Unknown

Cable in conduit

Energized upon arrival

Other

Another technology

Different formulations for injection fluid

Formulation tailored to operating environment

Tailored more for feeder cables with higher operating temperatures (»45°C)

No soak tanks requiredPut back into service immediately after injection

Another technology (Cont)

Must replace all jointsHigher pressures for injection