Sweep frequency response analysis for diagnosis of low level short circuit faults on the windings of power transformers: An experimental study

This contribution is aimed at obtaining diagnosis criteria for detection of low-level short circuit faults throughout sweep frequency response analysis (SFRA) measurements on the transformer windings. Significant advantages would accrue by early detection of low level short circuit faults within the transformer, since if not quickly detected, they usually develop into more serious faults which result in irreversible damage to the transformer and the electrical network, unexpected outages and the consequential costs. A Finite Element Model (FEM) of the tested transformer has been developed to assist in justifying the modifications of the winding frequency response as a result of fault occurrence. Successful operation of the SERA method in precisely detecting interturn faults along the transformer windings, even down to a few shorted turns on the winding, is proved through a large number of experiments and measurements. Improving the interpretation of the SERA measurements needs complementary statistical indicators. The usage of correlation coefficient and spectrum deviation for comparison of the frequency responses obtained through SFRA measurements provides quantitative indicators of the fault presence on the transformer windings and also the fault severity level in the shorted turns. (c) 2012 Elsevier Ltd. All rights reserved.