A new relaying principle for power transformer protection using transient comparison technique

This paper proposes a new technique for transformer fault detection. The technique is concerned with the detection of the fault generated high frequency current transients through a specially designed relay unit. The relay, tuned to a band of high frequencies, is connected to the transformer through CTs on both the high and low voltage sides of the transformer. When a fault is detected, the transient currents from both ends of CTs are extracted by the detector; the differential and average currents between the two ends are then calculated. The spectral energies of these current signals are then extracted to produce the operate and restraint signals; a comparison between the levels of the two signals will determine whether the fault is internal or external to the protected zone