Effects of Nonmetallic Particles on Discharges and Breakdown of Liquid Nitrogen

Aging of solid insulation and quenching heat of conductor in superconducting power equipment will degrade the insulation paper and generate fiber particle impurities, threatening the equipment’s safe and stable operation. In this article, the nonmetallic particles in liquid nitrogen (LN2) are analyzed during force movement in dc, ac, and compound electric fields. The discharge and breakdown characteristics of LN2 containing particles under different electrode structures, voltage forms, and particle properties are studied. The experiment results show that fiber particles have the least influence on the pin-plate electrode and breakdown voltage, and the influence of fiber particles on the plate-plate electrode and ball-ball electrode breakdown voltage is similar. The longitudinal electrode is easy to form a bridge under dc voltage, and the fiber particle concentration has a great influence on the initial discharge voltage and breakdown voltage. Particles move reciprocally in small amplitude under ac voltage and cannot form a bridge, but the insulation performance of LN2 is also weakened. Superposition voltage is more likely to cause insulation breakdown than the same value dc voltage, and the breakdown voltage is lower when the same polarity superposition than the different polarity.