Comparative Study of Fault Detection Methods Based on Time Domain RMS Calculation

This paper compares the performance of the cosine filter method and the second-order generalized-integrator (SOGI) method in calculating RMS voltage and current for detecting faults in power systems. The theoretical analysis shows that the SOGI method requires less number of samples to update the voltage or current rms value and therefore can track the system dynamics faster than the cosine filter method. This property benefits the SOGI to quickly detect the changes or disturbances when the power system experiences an event such as a fault, capacitor switching, or transformer energizing. The simulation results from various scenarios on a power system show that the SOGI is able to activate the protection system more quickly compared to the conventional cosine filter method. The time response difference between two methods is more significant if the power system is operated at a low frequency, i.e. 10 Hz. The SOGI method, in addition, shows its excellency in differentiating between faults and other events. The voltage/current rms value from the SOGI output in case of capacitor switching or transformer energizing events does not pass the threshold, and thus the system protection is not triggered. The SOGI performance shows that this method can be a promising candidate for fault detection in system protection.