The Ageing of Electrical Insulation at Cryogenic Temperatures

This paper presents some theoretical and experimental evidence that, under certain conditions, the transient voltage characteristics of electrical insulation impregnated with liquid nitrogen become the limiting factor in determining the normal operating stress. The life of the insulation is assumed to obey the well known life equation: (stress)n x time = conatant. It will be shown that the operating stress will depend upon the switching and lightning impulse strengths of the insulation, if the exponent n is above a critical value.