Statistical analysis of area and volume effects on breakdown voltage in liquid nitrogen using Weibull distribution

We measured breakdown voltage in liquid nitrogen (LN₂) with sphere to plane electrode and coaxial cylindrical electrode configurations, and discussed them with stressed electrode area (SEA) and/or stressed liquid volume (SLV). We also carried out statistical analysis of the results using Weibull distribution to examine the area and volume effects on breakdown voltage in LN₂. The dc and ac breakdown strength in LN₂ decreased to 1/4~1/5 with increasing the SSEA (statistical stressed electrode area) and SSLV (statistical stressed liquid volume). These results permitted us to confirm that the area and volume effects definitely determined the dc and ac breakdown strength in LN₂. Next, Weibull shape parameter m for sphere to plane and coaxial cylindrical electrodes were estimated to be about 6~8 and 11~13, respectively. The results of the Weibull statistics were compared with the conventional concept of the SEA or SLV. Consequently, SSEA or SSLV was found to be nearly equal to 80~85% of SEA or SLV. This result indicates that at least 80~85% of the maximum electric field strength should be considered for the insulation design in LN₂ when the area and volume effects are involved