On the layout of low temperature bushings for high ac voltage

Abstract

Bushings for high ac voltages may cause a noteworthy heat inleak into cryostats due to dielectric losses and heat conduction and rising at least with the square of the voltage. The overall heat inleak from the bushing insulator and other parts can be minimized for given radial dimensions by using the optimum length. Then the heat exchange with the outside at the warm flange region vanishes. To ensure a low heat input insulators with low product values of the dielectric loss factor and the heat conductivity and with a high dielectric strength should be used. At least the prospects for lowering the heat inleak by precooling with cold gas are hinted.