Application of the Impulse Response of Transformer Winding for Detection of Internal Turn-to-Turn Short Circuits

Several techniques are currently used to monitor internal defects in power transformers. These are very useful for reducing failure rates and extending the service life of transformers. One of the most sensitive techniques is the frequency response analysis method that injects a swept frequency ac signal into the transformer winding and analyses differences between the measured output signal and a benchmark reference signal. This paper applies the impulse voltage method for the diagnosis of turn-to-turn short circuit faults inside a transformer winding. The input signals are a set of impulse voltages of different shapes instead of the standard ac signals of variable frequency. The merits of this method compared with the standard swept frequency method are a shorter time for testing and for signal analysis. The output results are processed to produce a frequency response plot of the winding. Measurement results on a small test transformer show that the plots are closely similar to those obtained using the swept frequency method. In this initial study, impulse voltages are used to emulate the naturally occurring transients in power systems such as switching events and tap changer operations. The sensitivity of the method is verified by applying statistical techniques to interpret the measured frequency response in different frequency bands.