Transient Characteristics of the Vacuum Circuit Breaker Cut off the No-Load Distribution Transformer in 10 kV Large Current Grounding System

The removal of the no-load transformer by the vacuum circuit breaker is one of the most serious cases of operating overvoltage during its operation. The paper analyzes and studies the transient characteristics of the operating over-voltage generated by the vacuum circuit breaker of the 10 kV large-current grounding system cutting off the no-load distribution transformer. First, by establishing a single-equal value analysis circuit in this case, the specific expression of the highest intercepting overvoltage generated after the no-load transformer is opened is derived. Then the corresponding simulation waveform is established based on the ATP simulation software, and the correctness of the established model is verified according to the consistency of the calculation result and the simulation result under certain circumstance. Finally, we studied the transient characteristics of the corresponding operating overvoltage in this system under three different conditions. The research results show that:no matter when the no-load transformer is disconnected at the same time, the maximum overvoltage multiples of its low-voltage side are slightly higher than that of its high-voltage side; when the current change slope of the phase of the circuit breaker is negative and the intercept value is positive(including zero), the operating overvoltage values of the transformer's high and low voltage sides reach the maximum value at its negative peak value, and vice versa;the three-phase opening of the vacuum circuit breaker in different periods will have a more serious adverse effect on the safe and stable operation of the system; compared with the Yyn0 type transformer is opened, the first phase and the neutral point of the system have to withstand a lower voltage level when the Ynyn0 type transformer is opened. The above research conclusions can provide a theoretical basis of practical engineering applications.