Electrical breakdown of Liquid Nitrogen viewed from area & volume effects

Liquid nitrogen (LN₂) plays a crucial role in applying high temperature superconducting (HTSC) materials to the power apparatus. However limited literature is available pertaining to design of practical insulation for HTSC devices using LN₂. This study attempts to investigate the area and the volume effects on the electrical breakdown strength in LN₂ so as to obtain better design of electrical insulation for superconducting power apparatus. Measurements were made to assess the ac breakdown voltages in LN₂ utilizing sphere-plane electrode configuration. Experimental results revealed that the breakdown voltage in LN₂ did not increase monotonously but decreased partially as the sphere diameter increased at a constant gap length. The ac breakdown voltages in LN₂ were also measured for coaxial cylindrical electrode geometry to examine the area & volume effects and the breakdown voltage showed a decrease with an increase in 90% stressed electrode area (SEA) 90 and 90% stressed liquid volume (SLV) 90.