The Impulse Characteristics of Electrical Insulation Operating at Cryogenic Temperatures

This paper reports the transient voltage breakdown characteristics of electrical insulation operating at cryogenic temperatures. Nomex®e, Tyvek® and polypropylene film/cellulose paper laminate (PPLP) specimens impregnated with liquid nitrogen (LN2) and containing cavities of known dimensions were subjected to either 1.2/50 or 250/2500 ps impulses of increasing amplitude until breakdown. The effect of repeated impulses of constant amplitude, hydrostatic pressure, cavity location, and polarity reversal were also investigated. Of the three materials examined, PPLP exhibited the highest impulse strength, but also showed deterioration with repeated impulses above 150 kV/mm.