Liquid Nitrogen-Impregnated Tape Insulation for Cryoresistive Cable

An investigation into the effects of hydrostatic pressure and tape thickness on the ac breakdown strengths and discharge inception stresses for various lapped dielectrics impregnated with liquid nitrogen is described. Dielectric losses are given for composite dielectrics measured at a temperature of 77.3 K and a pressure of 1.7 × 1055 N/m2 (10 psig). Analysis of the results shows that discharges occur in gas bubbles in the butt gaps of the lapped tapes and that increase in the hydrostatic pressure applied to the system increases the discharge inception stress. This suppression of discharges can also lead to an increase in the breakdown strengths of the dielectrics studied.