Experimental Research on Cumulative Deformation of Transformer Winding Induced by Short-Circuit Current Impacts
Power transformer is one of the most important apparatus to the normal operation of power system. The main cause of winding deformation for transformers is the enormous electromagnetic force induced by the short-circuit current. Therefore, it is significant to study the winding deformation under this condition. The sweep frequency impedance (SFI) technique, a combination of frequency response analysis (FRA) and short-circuit impedance (SCI) method, contains more reliable indices to detect winding deformation accurately. In this paper, the cumulative effect of the winding deformation under repeated short-circuit current impacts is experimentally studied based on a customized power transformer. The SFI data of the transformer is acquired every time after the impact, with which the condition of the transformer winding can thus be evaluated. The disassembly results of the transformer after the whole experiments reveals that severe radial deformation and short-circuit fault within the winding have occurred. The SFI data obtained after every impact indicates that the winding condition just holds slight change with relatively small short-circuit current value in the initial stage while deteriorates irreversibly with the increased current value and test times. This finding can illustrate the cumulative tendency of winding deformation for the actual in-service transformer to some degree. For the actual transformer suffering many short-circuit current impacts in service, the deformation for its winding may initially develop slowly but in latter stage can abruptly collapse after many short-circuit current impacts, which suggests that timely overhaul on older transformers is necessary.
KeywordsCorrelation coefficient Short-circuit current Sweep frequency impedance
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