Breakdown Characteristics and Size Effect in Sub-Cooled Liquid Nitrogen

We systematically investigated and discussed the ac breakdown (BD) characteristics and mechanisms of liquid nitrogen (LN2) for different pressures (0.1-0.3 MPa) and temperatures (65-77 K) under quasi-uniform electric field (field utilization factor zeta = 0.986-0.674). The BD strength (E-B) in sub-cooled LN2 (SLN2) was analyzed and discussed in terms of size effect, taking account of the stressed liquid volume (SLV) with the electric field distribution in SLN2. We also included the other reseachers' data on BD characteristics of LN2, and extended the evaluation by applying the concept of alpha % SLY (SLV with the electric field strength higher than the decisive electric field factor (alpha) of the highest electric field strength). As the result, we found that E-B with the 50 % probability decreased linearly with the increase in alpha % SLY on a universal line, i.e. E-B = 78.4 x (alpha % SLY) (-1/8.15), irrespective of the pressure and temperature of LN2.