StudyoftheCharacteristics and Field performanceofa novelPTFE - siliconegelhigh voltage insulation system

Thecomposite insulation consisting ofPTFEfilm layers withinterstitial silicone gel, emerging asanewanddry alternative ofhighvoltage insulation structure hasbeenvery successfully usedforover15years indrytypecapacitance- graded coreinsulation ofhighvoltage equipments. This includes wallbushings, current transformers andcable terminals. Thiscomposite insulation structure isfoundin particular tohaveexcellent partial discharge performance with theunique characteristic ofself-attenuating wheninoperation, sometimes down to non-detectable levels. Numerous observations aredescribed fromearly field-testing, laboratory testing anddissection analysis. Theconsistency ofthe phenomenon, evenafter 15years ofoperation isconfirmed. Simulation experiments were ableto reproduce the characteristic anddemonstrate that thelevel ofvoltage applied, thestructure design andthepresence ofsilicone gelgovern the self-attenuation. Thispaper, after reviewing overall field performance, proposes amechanism showing that theinitial partial discharge helps toraise thebreakdown voltage ofthe capacitor elements, thusreducing theonsetoffurther discharges.