Breakdown characteristics and size effect in sub-cooled liquid nitrogen

Abstract

We systematically investigated and discussed the ac breakdown (BD) characteristics and mechanisms of liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) for different pressures (0.1-0.3 MPa) and temperatures (65-77 K) under quasi-uniform electric field (field utilization factor ζ = 0.986-0.674). The BD strength (E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) in sub-cooled LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (SLN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) was analyzed and discussed in terms of size effect, taking account of the stressed liquid volume (SLV) with the electric field distribution in SLN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . We also included the other reseachers' data on BD characteristics of LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and extended the evaluation by applying the concept of α % SLV (SLV with the electric field strength higher than the decisive electric field factor (α) of the highest electric field strength). As the result, we found that E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> with the 50 % probability decreased linearly with the increase in α % SLV on a universal line, i.e. E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> = 78.4 × (α % SLV) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1/8.15</sup> , irrespective of the pressure and temperature of LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> .