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Cable Rehabilitation at Oncor
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  1. Cable Rehabilitation at Oncor by Richie Harp – Distribution Standards Data provided by Mark Darilek – Maintenance Planning SWEDE 2009 – Tulsa, OK – Thursday, May 7, 2009

  2. Cable Rehabilitation Overview • Rehabilitated cable • Cable repairs to facilitate future rehabilitation • Oncor requirements for rehabilitation • Further considerations • 2nd Responder process • Another technology

  3. 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

  4. 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

  5. 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

  6. 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

  7. Cable Repairs (Cont) • Only for cable repairs (2-ft pieces) for future 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

  8. 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

  9. Oncor Requirements for Rehabilitation (cont) • 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

  10. 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.

  11. Comments: • We tried to rehabilitate some open loops that had been de-energized for up to 2 years • Very little success • We quit rehabilitating open loops that had been de-energized for more than 6 months.

  12. More comments: • 2006 and 2007 Processes • Left URD loops open after failures (direct buried cables) • Only repaired cable to get customers’ lights back on.

  13. 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

  14. 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 to be injected, then just leave energized. • Defer replacement of the cable until the next fault.

  15. 2nd Responder Process • System-Wide Process • Repair 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)

  16. 2nd Responder Decision Process Flow Chart • Available by request

  17. 2nd Responder Process • 1868 sections of failed cables came through 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 (already energized when arrived, in conduit, etc.)

  18. 2nd Responder Process – Injected/Not Injected

  19. 2nd Responder Process • 12 cause codes for not being able to inject the 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

  20. 2nd Responder Process • 12 cause codes for not being able to inject the 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.

  21. 2nd Responder Process – Causes

  22. 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 required • Put back into service immediately after injection

  23. Another technology (Cont) • Must replace all joints • Higher pressures for injection