Internal failure analysis of transformer windings

This paper presents internal failure analysis of transformer windings based on the characteristic of winding impedance in the frequency domain. Two winding samples are selected to test. The simple equivalent circuit of the transformer winding is investigated and proposed. The two windings under test have 76 turns with different length. An iron core is either inserted or not inserted inside a winding in the test to investigate the effect of the iron core. Turn to turn short circuit on the windings is considered as internal failure in this paper. The simulated turn to turn short on the model is carried out in the experiment to observe impedance characteristic in the frequency domain. A number and position of short turns are varied to observe characteristics of impedances The impedance of the models of the transformer windings are measured by a spectrum analyzer in a wide frequency range upto 2 MHz. From the test results, it is investigated that a resonance frequency of the transformer model is depended on a number and position of short turns. From the investigation, it has high possibility that the characteristic can be used for analysis of internal failures occurring in a transformer.