Development of 500-kV AC cable employing laminar insulation of other than conventional cellulosic paper. Final report

Abstract

Results are presented of an investigation to develop a 500 kV ac laminar dielectric power cable and joint having insulation with lower losses than conventional cellulosic paper insulation. Background information is presented on proposed low-loss synthetic and composite synthetic/cellulosic paper insulations and experiments covering a period of 20 years. Two types of insulations were chosen from these studies: fibrous polypropylene paper tape and cellulosic paper-polypropylene film-cellulosic paper composite paper (PPP). Extensive testing of hand-wrapped cable models fabricated with each type of tape served to eliminate from further consideration the fibrous polypropylene paper tape. Cable model tests indicate that the PPP tape is satisfactory for insulation in 500 kV ac cable, that oil impregnants now used in conventional cellulosic paper insulated cables are unsuitable for both types of the above insulation, but that silicone oil with an additive is satisfactory for PPP tapes. Laboratory data taken on three full-size factory-made prototype pipe-type cables and on a prototype joint indicate PPP insulation is suitable for 500 kV ac operation. Four final pipe-type cables having conventional moisture seal were manufactured for possible future field testing. The dielectric loss of the final cables is 1/5 that of conventional cellulosic paper insulated cables. The estimatedmore » installed cost per MVA-mile of the PPP insulated cable, neglecting the cost of losses, is higher than cellulosic insulated cables impregnated with conventional mineral oil. However, the reactance necessary to compensate for the cable charging current is significantly reduced. The design of a pipe-type cable and joint developed in this project and the PPP insulation structure are suitable for self-contained oil-filled cable systems rated 500 kV ac operating at reasonably high oil pressure.« less