Located in the fastest growing area of Southern California Edison’s (SCE; Rosemead, California, U.S.) coverage area, the Mountainview Power Project is well on its way to generating 1054 MW of electricity. In February 2004, SCE exercised its option to buy the Mountainview Power Co. LLC, which will be a natural gas-fired combined cycle generation facility located on 21.8 hectares (54 acres) of an existing San Bernardino power plant in Redlands, California, located in San Bernardino County. This move is part of the utility’s plan to generate 1054 MW of electricity in 2006—enough to power one million homes.

The new facility will include two power blocks. Each block consists of two combustion turbine generators (CTGs), GE model 7FA, with a nominal gross output of 160 MW. The turbines feed exhaust gases to a heat recovery steam generator (HRSG). Steam from each power block’s two HRSG is fed to one steam generator (STG), GE model D11S (207FA), with a nominal gross output of 210 MW for that power block (total of two STGs for the facility). The CTGs will operate in the base load mode with the STGs operating in sliding pressure mode. Power will be generated at 18-kV in the CTGs and STGs and stepped up through main transformers to the grid at 220-kV.

The 230-kV Installation

Under a US$2 million lump-sum agreement with the prime contractor, Bechtel Power Corp. (San Francisco, California), the principal contractor for Mountainview Power Co., InfraSource (Media, Pennsylvania, U.S.) agreed to design, procure, construct and install four circuits of 230-kV, three-phase cross-linked polyethylene (XLPE) cable between the new switchyard and the main transformer. Each circuit consists of a 230-kV, three-phase 2500 kcmil XLPE cable. Each phase is approximately 274-m (900-ft) long and is installed in an underground 15-cm (6-inch) PVC duct. The cable selected has a 2500 kcmil copper sheath and a 50 mil polyethylene jacket. The cable along with NKT FEV 245-kV terminations were supplied by Forte Power Systems (Helfin, Alabama, U.S.), a Southwire Co. Cable pulling, installation and termination services were done by EHV Power Corp. (Gormley, Ontario, Canada) with Forte oversight.

Black & Veatch (Overland Park, Kansas, U.S.) was subcontracted to design for the spacing, depth and encasement of the PVC ducts to accommodate the ampacity requirements. Poor soil thermal characteristics and the existence of several obstacles in the duct bank pathway were also a challenge. In some places, the duct bank had to go over existing low-voltage power and control duct banks, whereas in others it had to go under existing duct banks and a 91-cm (36-inch) diameter HDPE storm water discharge pipe.

Lab Tests

The PVC ducts were encased in thermal concrete and topped with 0.9 m (3 ft) of flowable thermal backfill (FTB). To achieve the desired conductivity, lab tests were performed to determine the right mix proportion for local aggregates, fly ash, sand and cement used in the concrete and FTB. l