Study on Insulation Capability of High Temperature Gas Via Laser-Produced Plasma

The fact that the specific heat and insulation capability of SF6 is very high compared to other gas species makes SF6 an excellent arc quenching media in gas circuit breakers. The global warming effect of SF6, however, causes strong environmental concern and the search for alternative gas insulator is in progress all over the world. The goal of our research is to find alternative gas insulator to be used as the arc quenching media in a gas circuit breaker. For that purpose, we investigate the insulation capability of various candidates of the alternative gas at high temperature of the order of 1000K or more. The study is intended to provide basic data to prevent the reignition of arc in the high temperature gas which still remains even after the arc is extinguished at the zero current point. In order to model the high temperature gas in a laboratory, we use a laser-produced plasma. The advantages of the laser-produced plasma are that we can produce the high temperature gas at any time and at any point in space in a very controlled manner. The gas properties produced by focusing a laser beam can be reproduced with a good precision. As we produce the plasma without any help of electrode, we can also distinguish the effects solely due to gas property from the effects of electrodes. The purpose of the present paper is to build and test the new experimental system to study the insulation capability of gas at the high temperature. As a test, we investigate how the flashover voltage changes at different gas temperature taking pure SF6, N2, CO2 as examples.