A Protection Scheme for Turn-to-Turn Faults in Three-Phase Two-Winding Transformers based on Wavelet Transform

Abstract

Power transformers are one of the most important equipment in the electric power systems. Turn faults between their windings are the most faults that are difficult to detect by traditional methods (differential and automatic protection) in their early stages. So This research introduce a new protection scheme to detect these faults ,quickly and accurately, and protect against them in three phase two winding transformers based on wavelet transform(WT).

In this method, Measured currents from the transformer are processed by wavelet transform which acts as a multi-level band pass filter, to extract two distinct bands of frequencies; the first band is high while the second band is relatively lower. The spectral energies of the extracted signals are then calculated to form two discriminating signals of the relay (operative and restraint). Based on the ratio between these discriminating signals the relay can distinguish the faults in early stages.

To verify the introduced method, these faults were modeled and simulated using Alternative Transient Program (ATP), then applied the proposed method. The results of the modeling and simulation showed that the proposed method is able to detect turn faults in three phase two winding transformer at early stages and protect the transformer from these faults.