Research on Improvement of “Manual Zero Crossing” Breaking Technology Under Medium Voltage and High Current Operating Conditions

The “manual zero crossing” breaking technology is an effective technical solution to solve the current breaking problem in medium and high voltage DC power systems. Under short-circuit conditions, the arc current is too high, usually above 20kA. On the one hand, the reverse pulse current injected during the forced commutation process leads to a very high current drop rate in the vacuum arc chamber, with a drop rate of about - 300A/µ s near the zero crossing of the arc current, and an initial transient recovery voltage transient of about -6kV after the zero crossing of the current. Vacuum circuit breakers often experience heavy breakdown after the arc current crosses zero, leading to disconnection failure. In response to this issue, this article proposes improvement measures from two aspects: reducing the voltage rise rate and current rise rate of the vacuum arc chamber. In the vacuum arc chamber series diode scheme, when the vacuum circuit breaker experiences arc reignition after the arc current crosses zero, the vacuum arc will cross zero again and extinguish the arc with the reverse blocking of the diode; And during the reverse blocking period of the diode, due to the blocking of the main circuit current of the DC system by the diode, energy is prevented from continuing to be injected into the vacuum arc gap, providing sufficient “zero rest” time for the vacuum arc and reducing the rate of voltage rise; The scheme of series connection of saturated reactors in vacuum arc chambers, with the continuous transfer of current, reduces the current in the vacuum circuit breaker to a small value before zero, and the saturated reactor exits the saturation state. The equivalent inductance rapidly increases, effectively slowing down the commutation process and generating a low current change rate range before the vacuum circuit breaker extinguishes. Reduce the initial plasma concentration in the vacuum gap after the arc and improve the recovery process of the medium after the arc. Two schemes can ensure reliable arc extinguishing of the vacuum arc chamber at two oscillation zero crossing points, improving the reliability of the vacuum circuit breaker in breaking large DC currents.