Impedance algorithm for protection of power transformers

A new impedance algorithm to protect power transformer is presented in this paper. The algorithm is based on three currents and three voltages measured at each side of the transformer. An edge detection technique using fast Fourier transform (FFT) provides inputs for an impedance scheme to properly detect and isolate faults within the transformer protection zone. The magnitudes of the current and voltage phasors on the high-voltage (HV) side of the transformer are compared to the low-voltage (LV) side magnitudes for detection and classification of faults. This algorithm has been tested with and without generation on the LV side of transformer and it has been compensated for weak power infeed on the LV side and for the fault resistance effect. Faults at 95% of the winding have been successfully identified on both sides of the power transformer in less than six cycles of the fundamental frequency.