Hiromichi Kawano

Behavior of inhomogeneous high-temperature SF/sub 6/ gas in a gas circuit breaker

The purpose of the present paper is to show the dielectric characteristics of inhomogeneous hot SF/sub 6/ gas in a gas circuit breaker (GCB) experimentally. High-temperature and low-density SF/sub 6/ gas generated by a heavy current interruption is distributed inhomogeneously in the grounded tank, and can strongly threaten the dielectric capability of the GCB. Few studies, however, have been carried out on the dielectric characteristics of the inhomogeneous hot gas. Using small gap discharges, the hot gas behavior of a GCB model, having breakdown or no breakdown, was investigated. The temperature of the hot gas flowing through the exhaust tube was estimated from the sparking voltage of the small gap installed in the exhaust tube. It was also found that there was very little or no effect on breakdown voltages of the cool gas in the breakdown paths. This suggests that the breakdown voltage of inhomogeneous hot gas could be obtained as the applied voltage at which the electrical field strength equals E/sub crit/ of local hot gas at the location concerned.

Effect of high-frequency currents on interrupting performance of GCBs

With electric power systems, it is shown by calculations that as the transmission voltage rises, high-frequency components contained in the fault current could remain until current interruption. This paper describes the influence of high-frequency current on the thermal and dielectric performance of a gas circuit breaker (GCB) by analyzing arc and hot gas flow. It has been proved that the model used for interruption tests simulating high-frequency components has sufficient performance for practical application. >

Real-Time Numerical Analysis on Insulation Capability Improvement of Compact Gas Circuit Breaker

In order to avoid a ground fault during a large current interruption, the effect of roughness pattern inside the exhaust tube on the rapid cooling of high temperature SF6 exhaust gas has been clarified in detail. In this study, large-eddy simulation of compressible turbulent flow under the realistic inlet conditions related to the available experimental data has been carried out. It is shown that introducing roughness pattern on the inner wall of exhaust tube is very effective for the improvement of insulation capability due to the enhanced active mixing and the flowing in of cold ambient gas from the tube exit. Finally, the computed temperature on the inner wall of exhaust tube shows a good qualitative agreement with the experimental data especially for the rough surface just after the applied transient recovery voltage.

Numerical Simulation of Unsteady Behavior of Rotary Arc Plasma under Magnetic Field

We are currently developing a time-dependent, three-dimensional computational magneto-plasma-dynamics (MPD) code for simulating a rotary gas circuit breaker utilizing an external applied magnetic field. In order to test the computational code under development, we have conducted the numerical simulation of arc plasma in a cylindricalshaped chamber filled with SF6 gas in the presence of externally applied magnetic field. The present paper describes details of the MPD model in the computational code, and also shows numerical simulation results.

Time-dependent Magnetohydrodynamic Simulation of SF6 Rotary-arc Plasma with Consideration of Electromotive Force

We have carried out time-dependent three-dimensional magnetohydrodynamic numerical simulations of rotary arc plasma in a simple chamber filled with SF6 or CO2 gas under an externally applied magnetic field. In the numerical simulations for both the gas conditions, the arc current and the strength of applied magnetic field are set to DC 2 kA and 1.2 T, respectively. In this paper we show that the rotation of arc plasma induced by applying the magnetic field increases the arc voltage and the gas pressure in the chamber, and also these phenomena with applying the magnetic field are much clearly observed in CO2 gas than SF6 gas. Furthermore, we show from the numerical simulations of rotary arc plasma in SF6 gas that the rotational speed of arc plasma becomes slow by accounting for the electromotive force induced by the MHD interaction, but the induced electromotive force has only a little influence on the arc voltage and the gas pressure in the chamber.

Analytic method using laplace transform for a modified TRV of a circuit breaker

When circuit parameters are known, it is easy to calculate the modified transient recovery voltage (TRV) with resister breaking or MOSA operating by numerical simulations. But, when the TRV is only known, it is very difficult to calculate the modified TRV by numerical simulations. This paper shows the theoretical analytic method of the modified TRV at such a circuit impedance modification as breaking with parallel resister or MOSA operating. A TRV can be calculated by injecting a current from circuit breaker terminals to back impedance. TRV and injected current wave shapes can be expressed with a group of ramp waveforms in Laplace domain. By using our analytic method, the back impedance can be easily derived in the Laplace domain from the TRV and injected current waveforms. As a result, it is shown that the modified TRV at circuit impedance modification can be calculated. Moreover, the same method can be used to calculate the TRV that is reduced by asymmetrical current breaking.

Analytic Method of the Modified TRV of Circuit Breaker with Circuit Variation by Laplace Transform

When circuit parameters are known, it is easy to calculate the modified transient recovery voltage (TRV) with resister breaking or MOSA (Metal-oxide Surge Arrester) operating by numerical simulations. But, when the TRV is only known, it is very difficult to calculate the modified TRV by numerical simulations. This paper shows the theoretical analytic method of the modified TRV at such a circuit impedance modification as breaking with parallel resister or MOSA operating.A TRV can be calculated by injecting a current from circuit breaker terminals to back impedance. TRV and injected current wave shapes can be expressed with a group of ramp waveforms in Laplace domain. By using our analytic method, the back impedance can be easily derived in the Laplace domain from the TRV and injected current waveforms. As a result, it is shown that the modified TRV at circuit impedance modification can be calculated.