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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