CALCULATION OF THE DC COMPONENT FREQUENCY IN FAULT CURRENTS BY IMPEDANCE FUNCTION

The time constant of the DC component of fault currents is highly needed in the analysis of the performance of protection systems (e.g.) circuit breakers, relays and current transformers). Conventional method uses the impedance seen from the faulted point in power frequency, and related the time constant to the real and imaginary parts of it . In this paper a new approach is presented which is practically an easy method for calculating the above mentioned time constant . the method is based on network equivalencing according to impedance function. The obtained results show very good accuracy in comparison with complete transient analysis results (by EMTP). In addition, the error of the conventional method is presented.