Calculation of branch short circuit asymmetrical current considering breaking sequences

With the expansion of the scale of power grid interconnection, the grid connection is becoming more and more closely, and the grid resistance ratio is also increasing, which slows down the attenuation of the DC component of the short-circuit current, and affects the checking of the breaking capacity of the circuit breaker. At present, in practice, only the periodic component of the short circuit point is considered in checking the breaking capacity of the circuit breaker, and the short-circuit asymmetric current affected by the DC component is not considered. A method is proposed to calculate the DC component of the short circuit current flowing through the circuit breaker directly in this paper. Firstly, the fault point is divided into two parts by node splitting method, and the node impedance matrix is modified based on the branch-adding method. Then, the DC component of the short-circuit current can be obtained by using the transfer impedance obtained by the modified node impedance matrix. Finally, the maximum short-circuit asymmetric current flowing through the circuit breaker branch is calculated and compared with the symmetric component of the short-circuit point. It is suggested that the former should be used to check the breaking capacity of the circuit breaker.