Effects of voltage on dielectric breakdown characteristics in gaps partially immersed in liquid nitrogen

Non-uniform field gaps partially immersed in liquid coolants are essential components in any cryogenic or superconducting apparatus. We have investigated the dc, ac and impulse dielectric breakdown characteristics of non-uniform field gaps partially immersed in liquid nitrogen together with those completely immersed in liquid or cryogenic gaseous nitrogen. It is found that the Sumoto effect appears for dc and ac voltages and the breakdown characteristics of the gaps partially immersed in liquid nitrogen are strongly influenced by the appearance of the Sumoto effect which depends on the applied voltage waveforms.