Upgrade 138kV Underground Circuit From Polk to Garrott Substations ERCOT RPG Meeting January 13, 2012 1.

Upgrade 138kV Underground Circuit From Polk to Garrott Substations

ERCOT RPG Meeting

January 13, 2012

1

Scope

• Upgrade capacity from 247 MVA to 480 MVA

• Parallel existing circuit (no new circuit)

• Follow existing route

• Loop into Midtown substation

• Utilize DTS technology

• Install fiber optic circuit protection

2

Circuit Route

• Downtown Houston

• 12,300 feet

• New parallel cable follows same route

3

Midtown

Challenges

• Downtown city streets

• Parallel utilities

• Crossing utilities

• METRO light rail

• NBA Season

• Paving ordinance

• Permits

4

Project Engineering

• Utilize current cable technology

• XLPE insulated– Ready domestic supply– Available craftsmen

• CNP had successful installations with these materials on other projects

• 20’ to 24’ depth

• Final permits recv’d 11/2010

5

Construction Plan

• 6,000 ft. horizontal directional drill

• 6,300 ft. guided bore 400 – 500 ft. sections

• Broke ground 12/2010

6

Planned Grout Tests

• Two 80 ft. mockups (rehearsal)

• One 500 ft. test

• One 460 ft. re-test

• Goal: prove no voids

7

Test Grout Results

• Good grout suspension

• Successful grouting of 80 ft. mockups

• Large voids in 500 ft. test section

• Revised spacer design

• 460 ft. retest successful

8

Project Delay

• Inspection revealed unacceptable ductbank segments

– Grout intrusion• Must resolve for cable installation

• Conduit source plant changed

• Schedule delay

• Installed in new section

– More grout intrusion

• Reviewed

– Process

– Material

• Schedule delay

9

Project Continuation

• New conduit supplier

• Contractor required to rebuild or repair bad segments– Rebuild

• Push out whole segments

• Install new casing and conduits

• Establish a procedure

– Repair• Excavate/shore to bad area

• Point repair

• Successful grouted sections

• Projected energization date: 4/26/2012

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