Breakdown Voltage and Recovery Rate Estimation of a Supercritical Nitrogen Plasma Switch

Supercritical fluid (SCF), characterized by high pressure and high density, combines the advantages of gas and liquid: high ability of mass transfer and high heat transfer. SCF has a high potential as an electrical switching medium owing to its high breakdown strength and fast dielectric recovery capability after electrical breakdown. One other significant characteristic of SCF as insulating medium is its low impact to the environment, hence it is proposed as an ideal substitute for SF6-an extreme greenhouse gas in power system circuit breakers. In this paper, the thermodynamic characteristics of SCF are introduced by the review of references. An experimental analysis of electrical breakdown phenomena of a supercritical (SC) plasma switch with pressure up to 180 bar is presented, focusing on the breakdown voltage variation as a function of the fluid pressure, gap width of the electrodes, and fluid flow rate through the gap. A thermodynamic model for recovery rate analysis of a gas insulated switch is proposed and its feasibility is discussed. The model is used to predict the recovery rate of an SC switch.