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.