106 / 2024-04-12 16:19:41

Fundamental Investigation on Dielectric Recovery Characteristics of Copper Butt Electrode Space for Different Voltage Application Timings during Arc Decay Process

dielectric recovery characteristics,vacuum circuit breakers,transient recovery voltage,decay process

 In vacuum circuit breakers (VCBs), a vacuum arc is extinguished by diffusing the metal vapor generated from the electrodes. The vacuum arc discharge occurs between spiral electrodes and axial magnetic field electrode during current interruption process in the VCB. Using our experimental vacuum arc device, we have experimentally measured the dielectric recovery characteristics between the metal electrodes due to metal vapor diffusion during vacuum arc decaying process. As the current approaches the zero point, the vacuum arc gradually decays, leading to a current chopping before the current zero. After the current down to 0 A, residual plasma remains between the butt electrodes, which then gradually diffuses over time. When the dielectric recovery due to the diffusion of residual plasma is insufficient, the vacuum arc re-ignition can occur by a transient recovery voltage (TRV) application. To understand the relationship between dielectric recovery and re-ignition phenomenon during arc decay process, we constructed a circuit for quasi-TRV application and fundamentally investigated the dielectric recovery characteristics.

 This paper describes the results of dielectric recovery characteristics between the but copper electrodes after copper vacuum arc extinction. For this purpose, we constructed a system including circuits for providing and control the current and for applying an impulse-like voltage between the electrodes during vacuum arc decaying as quasi-TRV and. The experiment was carried out as follows: First, the butt electrode made of Cu in the vacuum chamber were closed to be connected, and the IGBT parallelly connected to the electrodes was turned off. Then, a direct current of 50 A was provided from a DC current source to the electrodes. The electrodes were opened, igniting, and maintaining the vacuum arc between the electrodes. Next, turning on the IGBT commutes the arc current between the electrodes to the IGBT. In this case, the vacuum arc in the inter-electrode space decays with time. After a setting delay time t_d from the start of commutation, quasi-TRV was applied to the electrodes whether the arc reignition occurs or not.

 As a result, the earlier quasi-TRV application timing makes the rise time of the voltage appearing between copper butt electrode longer with decrease in the rise rate of voltage dv/dt (kV/μs). This is because that the diffusion of metal vapor between copper butt electrode by the vacuum arc is insufficient during vacuum arc decay. It can also be seen that it took about 2 ms for the dielectric recovery between the electrodes. From the above, the residual arc plasma would exist between the electrodes for several hundred microseconds after the current zero.