A deformation fault of the lower-voltage winding in a 220 k V transformer

which was found in routine tests

is described in this paper. First

according to the results from the short-circuit impedance test and the winding deformation test

different degrees of deformation fault of low-voltage windings were deduced. Then considering the historic chromatograms of the transformer

which were obtained after every shock of short-circuit current

and the diagnostic result

the cause of the deformation fault was due to the shock of short-circuit current at low-voltage side and the cumulative effect of winding deformation. Disintegration inspection revealed that different degrees of deformation and overheating happened in the low-voltage winding

verifying the correctness of the results from diagnosis and tests. As a result

the routine tests helped to prevent a latent failure of the transformer. In addition

some suggestions are offered for routine maintenance and overhaul of transformers.