Abstract
Vacuum circuit breakers (VCB) are commonly used in active mechanical direct current circuit breakers (DC CBs) to accomplish the interruption of the fault current. The post-arc current phenomenon of a VCB is related to the dielectric recovery process of the VCB. Thus, we performed experiments to investigate the influence on the post-arc current by taking the electrode separation, breaking current, and interruption of the bi-directional current with the injecting high frequency current in a fixed direction into account. To be in accordance with the practical interruption duty, the breaking current in the experiment ranges from 500 A to 20 kA. At the same time, the di/dt at current zero (CZ) varies between 200 and 1100 A/μs. The experiment results reveal that the peak value of the post-arc current in an active DC circuit breaker can reach more than 100 A with high di/dt at CZ. It is found that with a longer electrode separation, not only the residual charge increases but also the post-arc current increases. The arcing current before CZ can influence the post-arc current but the effective duration before CZ is short. This duration is the memory time and it is derived from the experiment results. The influence of the breaking current and interruption of the bi-directional current with the injecting current in a fixed direction are dependent on the relation of the current commutation time with the memory time.
Highlights
Active mechanical direct current circuit breakers (DC CBs) based on the principle of active current injection was proposed and verified by experiments in the early 1970s.1 until recent years, accompanied with the prospering evolution in the voltage sourced converter (VSC) based high voltage DC (HVDC) power transmission technologies, the application of DC CBs is becoming one of the key issues in the construction of a DC power grid.2 The active mechanical DC CB takes advantage of fast breaking, large breaking capacity and low cost
The active mechanical HVDC CBs with the highest rating values are those installed in the Zhangbei ±500 kV DC transmission project in China, where the breakers are required to suppress the 25 kA fault current in 3 ms
We summarized the potential factors that may influence the post-arc current in a Vacuum circuit breakers (VCB) from the former experiments6,11,12,14–16,18,19,23 and simulation works
Summary
Active mechanical direct current circuit breakers (DC CBs) based on the principle of active current injection was proposed and verified by experiments in the early 1970s.1 until recent years, accompanied with the prospering evolution in the voltage sourced converter (VSC) based high voltage DC (HVDC) power transmission technologies, the application of DC CBs is becoming one of the key issues in the construction of a DC power grid. The active mechanical DC CB takes advantage of fast breaking, large breaking capacity and low cost. We will report our experimental investigations on the post-arc current phenomena of the VCB in an active mechanical DC CB. Based on the experiment results, we give analysis on how the electrode separation (d), di/dt at CZ as well as du/dt after CZ, and the breaking current (Isc) influence the post-arc current. The experiment is aimed to find out how different factors influence the post-arc current of the VCB applied in the forced current zero interruption. The commutation current ic starts to rise and is injected into the VCB in the opposite direction of iVCB. The post-arc current is measured by using the M coil, and the transient interruption voltage (TIV) is measured with a P6015A probe. The slope of the first segment of the envelope is defined as the investigated du/dt or the rise of the rate of ITIV (RRITIV)
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