A novel measurement technique for power transformer faults using spectral comparison technique

Abstract

The paper proposes a new measurement technique for detecting tr:insformer faults. A specially designed transient current detection device is used to capture the fault generated high frequency current transients. The device tuncd to a special band of high frequency is connected to the transformer through the CTs at both high and IOW voltage sides of the transformer. The captured transient signals a1 both ends of the transformer are then compared, with pai~ticularly emphasis on the high frequency Characteristics iii the frequency domain; the internal f a u k is discriininaied from the external fault by spectral comparison. The high frequency modelling of the transformer is incorporated into the simulation. The simulation aklo involves the inodelling of the faults between any turn and the earth andl between any two turns of the transformer windings.

A new technique for transformer protection based on transient detection

“…1 shows the basic arrangement of this technique. As shown, the signals and from the low voltage side of the CT, and from the high voltage side of the CT are first combined to form a composite signals [5] by which the background noise is effectively removed. The three phase current quantities are converted into two modal (mode 2 and 3) signals by the modal mixing circuit.…”

“…The criterion to discriminate between internal and external faults is essentially the same as that given in reference [5]; a comparison between the levels of the operate and restraint signals will determine whether a fault is within the protected zone: trip or alarm no operation…”

“…In fact, at sufficiently high frequencies, the behavior of the transformer becomes dominated by its capacitance. Thus to evaluate the high frequency behavior of the transformer, particularly under fault conditions, the shunt capacitances were added to the model [5].…”