Detection of interdisc fault in the windings of power transformer wavelet approach

One of the tests carried out on power transformer winding insulation after assembly is the low voltage impulse test, for assessment of the integrity of its winding insulation. The existing transfer function method used for diagnosis lacks sensitivity in detecting minor faults. Hence, a new approach using wavelets is developed to analyze the recorded neutral current waveforms to identify the existence of fault. Comparison of recorded neutral currents is a standard technique used for the detection of fault in the power transformer winding insulation during Impulse test. Any shift in the waveforms indicate fault in the windings. Hence, proper analysis of neutral current waveforms is necessary to assess the condition of insulation of transformer winding. In order to carry out wave shape analysis, a 61MVA, 11.5/230kV generator transformer is considered and faults are created in the discs of High Voltage windings at particular locations. Noise inherent in the neutral current during recordings was isolated using Daubachies wavelet and the de-noised signals were also analyzed using Daubachies wavelet for identification of fault in the winding.