Life Expectancy of Liquid - Nitrogen Taped Cable Insulation

Tests are described on lapped taped cable models impregnated with liquid nitrogen to investigate discharge activity and insulation life. A number of polymeric materials are discussed with an emphasis on high density polyethylene. For all the polymers a life expectancy-stress relationship of the form tEn = constant is obtained. The exponent n is seen to be strohgly dependent on the pressure of the impregnant. The effect of tape thickness is also discussed. Variation in the rate of rise of the applied voltage for polyethylene tape does not affect the life expectancy, provided the initial high discharges are withstood. The application of the experimental results to cable design is discussed.