This article is a review of the electrical properties of the insulating media at cryogenic temperatures especially at liquid helium temperature. In general, the dielectric strength increases and the losses owing to the conduction current or the dielectric loss decrease as the temperature decreases.
Although the vacuum withstands fairly high voltages, prebreakdown currents produce losses and the support spacers are necessary for the mechanical support of the conductors.
Cryogenic liquids or gases have low dielectric strength in comparison with the vacuum or the solids, and the support spacers are also necessary. The dielectric losses, however, are low except under high electric fields.
Solids at cryogenic temperature have good dielectric strength, but the dielectric losses produce the heat loads to the refrigeration system. The matching of the thermal contraction with the metals is also required.
