Dielectric Loss and Voltage Breakdown in Liquid Nitrogen and Hydrogen

Cryogenic liquids have unusual physical properties. At low-voltage stress the dielectric loss in the cryogenic liquid is so small that it can not be accurately measured. As the voltage stress is increased, the dissipation factor increases to the order of 0.002, which is higher than for many conventional dielectric liquids. Both the voltage and the time of application influence the dielectric loss. Voltage breakdown is relatively high in both liquid hydrogen and liquid nitrogen. When pressure is increased somewhat at constant temperature to eliminate boiling, the electric strength is increased significantly. When the pressure is increased still further, the electric strength of the cryogenic liquid shows little or no additional increase. Cryogenic liquids have potential use as dielectrics in cable and other types of electrical apparatus. Studies of their dielectric prop-properties may improve the basic understanding of dielectric performance also.