Measurement of Dielectric Breakdown Properties in High Temperature CO₂ Gas Heated by Tandem-Coil Coupled Thermal Plasmas

In the present report, the dependence of the dielectric property of hot CO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gas heated by ICTP on gas temperature was studied. To understand such dielectric properties in high temperature insulation gases is important for determining the success or failure of current interruption in new gas circuit breakers (GCB). To experimentally obtain the dielectric properties, we are proposing a unique method for generating high temperature gas field by a tandem type of inductively coupled thermal plasmas (Tandem-ICTP), consisting of the two coils arranged vertically in series. The gas temperature of heated CO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gas was estimated from spectroscopy results, applying the Boltzmann plot method and the electromagnetic thermofluid simulation. To measure breakdown voltage (BDV) of the hot CO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gas, the DC voltage of 1 kV/s was applied for the gas electrodes at a gap length of 1 mm. As a result, the BDV for the gap was about 165.1 V under the gas temperature of approximately 6200 K, while it was about 707.2 V under the gas temperature of approximately 3900 K. From the measured BDV and critical electric field calculated by two-term expansion of Boltzmann equation, it was found that the dissociation reactions of CO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> molecules into O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> and CO is dominant on the dielectric strength.