Vantage to Pomona FEIS Index 34 - Laserfiche WebLink

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Vantage to Pomona Heights Chapter 2 230 kV Transmission Line Project FEIS Proposed Action and Alternatives PAGE 2-37 FIGURE 2-9 TYPICAL UNDERGROUND VAULT INSTALLATION (EPRI 2008) Underground Cable Technologies There are four basic underground cable technologies for underground circuits: • Solid Dielectric (Cross-Linked Polyethylene [XLPE]) • Gas Insulated Transmission Line (GIL) • Pipe-type (Fluid Filled or High Pressure Fluid-Filled [HPFF]) • Self-Contained Fluid Filled (SCFF) Solid Dielectric Cable The typical cable consists of a stranded copper or aluminum conductor; semi-conducting extruded conductor shield; extruded dielectric insulation; extruded semiconducting insulation shield; a lead, aluminum, copper or stainless steel sheath moisture barrier; and a protective jacket. A metallic shield, tape, or drain wire is required to carry fault current when a sheath is not used. Newer cable technology uses a high voltage extruded dielectric insulation of XLPE. Gas Insulated Transmission Line GIL technology at 230 kV and higher voltage levels has been implemented primarily within substations and not for transmission lines. GIL has been incorporated into substation designs with the length typically limited to distances less than 1,000 feet. The high cost and lack of experience with respect to longer underground transmission lines and questions of reliability are more of a concern than with other more prominent cable technologies for underground circuits. High Pressure Fluid Filled Cable HPFF cable systems are a pipe-type system where three single phase cables are located within a single steel pipe. HPFF cables use Kraft paper insulation or a laminated polypropylene paper (LPP) insulation that is impregnated with dielectric fluid to minimize the insulation breakdown under electrical stress. Since the system requires a continuous high pressure, pumping plants are required every 7 to 10 miles along the route, assuming a relatively flat topography. The pumping plants are responsible for maintaining a constant pressure on the system, but must have large reserve tanks to facilitate the expansion and contraction of the dielectric fluid as the system undergoes thermal cycling. To maintain an