A method to decide the switching instants of controlled switching circuit breaker for shunt reactors

This paper describes a method which determines the operating instants of the circuit breaker for controlled switching of shunt reactors independent of the network configuration, in order to reduce overvoltages and inrush currents. Some other previous papers offered the favorable instants for both isolated and directly earthed neutral case, but not for the earthed neutral through a reactor. The proposed method in this paper is based on two facts. First, the instant of a maximum voltage between contacts of the circuit breaker(CB) is the optimum point for closing to minimize the inrush current. And secondly, both the minimum arcing time of the CB and the current interruption instant of each poles should be considered as the reference for the opening instant. The performance of the proposed method was verified by the results of simulation studies using the electromagnetic transients program(EMTP). The behaviors of CB treated in the simulation involve the rate of decay of dielectric strength between contacts and the scatter of the operating time. Especially, the results of EMTP show that the closing and opening instants of the second one among the three poles shift continuously with the ratio of the impedance of a shunt reactor to that of the neutral reactor in the range of 30 phase angle, respectively. And also the maximum scatter of the CB closing time to ensure the inrush current of less than a certain level can be provided.