Extending analyzed frequency range in interpretation of frequency responses measured on a distribution transformer

Abstract

In the field of diagnosis of mechanical failures in power transformer’s active part, i.e., windings, leads and the core, the technique of Frequency Response Analysis (FRA) has been recently approved as the main application tool. Mechanical failures in transformer windings reflect changes on measured terminal frequency responses normally in medium frequency range, from several to hundreds of kHz, which is in fact not easy to interpret for diagnosis. The authors proposed a new method based on simulation of a lumped three-phase equivalent circuit of power transformers to interpret frequency responses effectively, but only within low frequency range. This limitation is due to the fact that, the circuit cannot reflect well physical phenomena at medium and higher frequencies. To improve the FRA performance of the proposed method at medium frequencies for transformer failure diagnosis purpose, the paper introduces an investigation on a distributed three-phase equivalent circuit of a 200 kVA 10.4/0.46 kV Yy6 distribution transformer. Result of the investigation is a simplified procedure in determination of electrical parameters associated with the distributed circuit for better simulation based FRA interpretation at medium frequencies.