Frequency Response Analysis to recognize inductance variation in transformer due to internal short circuit

Transformer diagnosis methods have been introduced and employed to recognize transformer internal defects since many years ago. In terms of mechanical defects in transformers, turn to turn and disc to disc short circuits in transformer windings are considered as one of the main problems in transformer active part. On the other hand, Frequency Response Analysis (FRA) is considered as a robust, sensitive and high accurate method to identify transformer mechanical defects. This study has concentrated on self-inductance variation recognition due to an internal short circuit in transformer using FRA signature. A single phase 11/0.25 kV, 25 kVA transformer has been taken as test object. Frequency response of the test object was recorded for open circuit and short circuit situations. Frequency response alteration in low frequencies caused by short circuit is interpreted through mathematical calculations. Frequency response trace deviation is employed to recognize self-inductance changes due to the internal short circuit.