Abstract
In this paper, the breaking process of the vacuum circuit breakers is briefly described, and the main factors that influence the post-arc process are analyzed. Based on the detachable vacuum interrupter, the experimental platform of AC breaking is built, and the experiments of the post-arc current measurement and cathode spot observation are completed. The voltage and current during the period of current zero are measured, and the images of cathode spots during the arcing process are obtained. The experimental results show that at the same frequency, the post-arc current Ipac and the post-arc charge Qpac increase with the increase in didtcz(didt at current zero). Under the same conditions of didtcz, Ipac and Qpac decrease with the increase in frequency, but both are unchanged with frequency when the frequency is high enough. With the increase in current frequency, the distribution diameter of cathode spots decreases under the condition of the same didtcz value. According to the characteristics of cathode spot distribution, the metal vapor density under different conditions is calculated. Comparing the calculation results of metal vapor with the experimental results of post-arc current, the concept of metal vapor ionization is put forward. An ionization process of metal vapor after the current zero crossing occurs. The ionization of metal vapor will cause an increase in the number of electrons after the current zero crossing, which affects Ipac, Qpac, and sheath growth.
Highlights
Vacuum circuit breakers (VCBs) are widely used in the field of power transmission and distribution due to their excellent arc extinguishing performance, and they are mainly used to interrupt the fault current of the power system.[1,2,3,4] In the process of current breaking, the state of gap in VCBs will change after current zero from the wellconducting state of the high-current plasma to the isolating state of the cold gap.[5,6] There is residual plasma between arc gaps after current zero
The ions and electrons are emitted from the cathode and move to the anode, which is shown in Fig. 2(a), and the voltage across the gap is arc voltage
In order to obtain the characteristics of the vacuum arc near current zero crossing under different current conditions, the current frequency in the experiment is selected from 860 Hz to 8800 Hz, f 1⁄4 p1ffiffiffiffiffiffiffiffi ; (2)
Summary
Vacuum circuit breakers (VCBs) are widely used in the field of power transmission and distribution due to their excellent arc extinguishing performance, and they are mainly used to interrupt the fault current of the power system.[1,2,3,4] In the process of current breaking, the state of gap in VCBs will change after current zero from the wellconducting state of the high-current plasma to the isolating state of the cold gap.[5,6] There is residual plasma between arc gaps after current zero. There have been numerous research studies on post-arc current.[10,11,12,13] The research studies on the post-arc current mainly focus on power frequency current breaking (50 Hz),[14–18] the characteristics of which are long arcing time and low ddticz(ddti at current zero crossing). They focus on the introduction of the measurement of post-arc current and a brief description of the post-arc current waveform. The ionization of metal vapor will cause an increase in the number of electrons after the current zero crossing, which affects Ipac, Qpac and sheath growth
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