Cable Rehabiliation at Oncor

Cable Rehabilitation at Oncor

by Richie Harp – Distribution Standards

Data provided by Mark Darilek – MaintenancePlanning

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

Cable Rehabilitation Overview

Rehabilitated cable

Cable repairs to facilitate futurerehabilitation

Oncor requirements for rehabilitation

Further considerations

2nd Responder process

Another technology

Amount of Rehabilitated Cable

Began in 1995

420 cbl-mi rehabilitated

8,000 cbl-mi in service – Pre-1993 cable

22,000 cbl-mi total cable

Amount of Rehabilitated Cable

URD

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

Began in 1995

405 cbl-mi rehabilitated

17,000 cbl-mi in service

2% of URD cables

Amount of Rehabilitated Cable

Feeder

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

Began in 2008

15 cbl-mi rehabilitated

3,400 cbl-mi in service

0.4% of feeder cable

Cable Repairs

Standard cable (Began purchasing in 1990)

#1/0 Al 19-Strands

Strand-filled conductors

25 kV, 260-mil TRXLPE

16-#14 AWG Concentric Neutral Wires(Full neutral)

Jacketed

Cable Repairs (Cont)

Only for cable repairs (2-ft pieces) forfuture injection

#1/0 Al 19-Strands

Strands not filled

25 kV, 260-mil TRXLPE

8-#14 AWG concentric neutral wires(1/2 neutral)

Unjacketed

On 1000-ft composite reel

Oncor Requirements forRehabilitation

Do not rehabilitate:

Cable installed in conduit

175-mil or 220-mil cable operating at14.4 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 intrench

There is a chance the cable will beconverted to 14.4 kV in the future

Oncor Requirements forRehabilitation (cont)

Other Requirements

There must be more than 25% concentricneutral remaining.

There cannot be more that one joint per100 feet of cable.

The faulted cable section must not havebeen de-energized more than six months.

Comments:

We tried to rehabilitate some open loopsthat had been de-energized for up to 2years

Very little success

We quit rehabilitating open loops thathad been de-energized for more than 6months.

More comments:

2006 and 2007 Processes

Left URD loops open after failures (directburied cables)

Only repaired cable to get customers’lights back on.

More comments:

Dec 2007 Process

Began 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 Change

Install joint to repair cable

Try to inject the cable

After the repair, if the cable is not able tobe injected, then just leave energized.

Defer replacement of the cable until thenext fault.

2nd Responder Process

System-Wide Process

Repair failures on direct buried cable (notin conduit)

Must be able to switch around to get lightsback on.

Not normally feeder exits (Only non-criticalcables)

2nd Responder Decision ProcessFlow Chart

Available by request

2nd Responder Process

1868 sections of failed cables camethrough the process since 2008

749 sections of cable were injected

1119 sections were not able to be injected

922 due to process requirements

197 not related to the process (alreadyenergized when arrived, in conduit, etc.)

2nd Responder Process –Injected/Not Injected

2nd Responder Process

12 cause codes for not being able to injectthe 1119 sections of cable

Age of fault (> 6 months)

Could not flow (Blocked strands or joints)

Inaccessible fault or joint location

Deteriorated neutral (< 25% remaining)

Previously injected, non-warranty or other

Previously injected, warranty

2nd Responder Process

12 cause codes for not being able to injectthe cable (Cont)

Corroded conductor

Number of joints (> than 1 joint per 100 ft)

Unknown

Cable is in conduit

Already energized upon arrival

Other

–These last three represent the 197.

2nd Responder Process – Causes

Another technology

Different formulations for injection fluid

Formulation tailored to operatingenvironment

Tailored more for feeder cables with higheroperating temperatures (»45°C)

No soak tanks required

Put back into service immediately afterinjection

Another technology (Cont)

Must replace all joints

Higher pressures for injection

Rehabilitated Cable That IsFailing

Feeder

URD