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 SFRA 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 SFRA 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.

► SFRA measurements were made on a real transformer windings damaged by low level interturn faults.
► The method was proved to be sensitive in detecting faults even down to 0.2% shorted turns along the winding.
► A method which assures sufficient sensitivity and reproducibility of the SFRA measurements was explained.
► Some signatures attained to interturn faults were extracted in order to obtain diagnosis criteria.
► The interpretation of the SFRA results was promoted by complementary statistical indicators.