Application of the inductively coupled thermal plasma (ICTP) technique was proposed for investigating plasma-quenching efficiency of various gases including the arc-quenching medium of SF6. The ICTP enables us to study fundamentally the effect of gas injection on thermal plasma without any impurities because it has no electrode. Seven kinds of gases including CO2, SF6 and environmentally benign gases (N2, O2, air, He and H2) were injected into Ar ICTP. Spectroscopic observation was carried out in order to investigate a change in the excited state of Ar atoms due to addition of these gases. Radial distributions of the radiation intensity of Ar spectral lines and the temperature of Ar ICTP were estimated. It was found that 10% CO2 addition causes a remarkable decline of the radiation intensity and temperature at any radial position, similarly to 2% SF6 addition. Two-dimensional local thermal equilibrium modelling for Ar ICTP also revealed that CO2 causes temperature decay more than the other gases of N2, O2, air, He and H2 except SF6.

A high-pressure inductively coupled thermal plasma (ICTP) system was developed; it can modulate the amplitude of the induction coil current periodically with a cycle of several hundred hertz by switching a metal-oxide semiconductor field effect transistor inverter power supply. This type of ICTP was named a 'pulse-modulated induction thermal plasma (PMITP)'. The PMITP in different gases of Ar, Ar-H 2 , Ar-N 2 and Ar-O 2 , was successfully generated at an input power of 30 kW under atmospheric pressure conditions. Shimmer current level (SCL), which is the ratio of lower to higher levels of coil current in modulation, can be reduced from 100% to 40% to sustain the Ar PMITP. The influence of SCL and diatomic molecular gas-inclusion on the PMITP behaviour was investigated. Temperature variation of PMITP was evaluated by the two-line method. The minimum value of the temperature measured during a modulation cycle proved to decrease drastically with a reduction of SCL by over 1000 K, especially with inclusion of the diatomic molecular gas, with the maximum temperature value almost unchanged. The inherent response time of the PMITP was found to have a magnitude of several milliseconds; it increases with decreasing SCL and with the inclusion of a diatomic molecular gas.

A two-dimensional hydrodynamic model for an N2 inductively coupled thermal plasma (ICTP or thermal ICP) at atmospheric pressure was developed using reaction rates without the chemical equilibrium (CE) assumption. Particle composition distribution in the N2 ICTP was derived by solving the mass conservation equations for each of the particles, considering diffusion, convection and production terms. The electrical conductivity, mass density and diffusion coefficient were calculated at each of the calculation steps with the derived particle composition distributions. Using this model, the influence of gas flow rate on chemical composition distribution was investigated. The dependence of mass flow of N atom on gas flow rate was obtained. From the result, a large deviation from CE in the distribution of the particle composition was found, especially near the wall of the ICTP.

We have calculated the multi-temperature SF6 plasma composition by two different methods. One method is based on the mass action law whereas the other method uses a kinetic chemical reaction scheme. The first approach is furthermore split up in two different calculations. One is based on the multi-temperature Saha equation and the other is based on the excitation temperature of the involved species. With respect to the electron density we conclude that the multi-temperature Saha equation results in appreciable higher number densities compared to both the kinetic scheme and the excitation-temperature-based calculations. The difference increases with decreasing gas temperature and increasing electron temperature (i.e. with increasing degree of kinetic non-equilibrium). The kinetic scheme and the excitation-temperature-based calculation yield comparable results for higher gas temperatures. In this region the excitation-temperature-based method is preferable over the kinetic method. However, for the dielectric case (i.e. lower gas temperature) we find different results at higher electron temperatures. The excitation-temperature-based calculation method requires additional modelling at this point.

The transport and thermodynamic properties of gas under contaminated conditions with Cu and PTFE vapours have been determined taking into account the new introduction of molecular particles, produced by chemical interactions between gas and impurities like CuF, , and , making in total 25 species. The main concern of this work is to predict, from the obtained material properties data, the transient behaviour of gas wall-stabilized arcs with these types of contamination that inevitably happen in gas circuit breakers during arc interruption. The results indicate that the electron density and the electrical conductivity increase with Cu vapour contamination, especially below 9000 K, due to the lower ionization potential of Cu atoms, but are almost invariant with PTFE contamination. The thermal conductivity changes only at higher admixture ratios above around 10% for both impurities. Typical increases in due to molecular dissociation have been found at temperatures around 4000 K for Cu vapour and at 3000 - 8000 K for PTFE vapour contamination. The transient behaviours of contaminated gas arcs have been analysed for step-current modulation in the wall-stabilized arcs under the condition of no gas flow. The greater value of arc conductance with Cu vapour contamination broadens the arc current channel, exposing possible disturbance of the current interruption function in gas circuit breakers. PTFE vapour contamination does not affect the arc decay process in wall-stabilized arcs significantly.