Impact of Winding Joint to the Failure of Distribution Transformers : A Field Study

Winding joints are the crucial part of a Distribution Transformer (DT) and improper joint affects the performance of DT by generating local hot-spot, which arise due to the increase in contact resistance. In this field study, two failed 25 kVA DTs and 22 HV coils of 25 kVA DTs were analyzed by measuring the contact resistances of winding joints. The correlation between the degradation of winding joints and the failure pattern of DTs has been investigated. The observations and measurements show a direct relationship between the failure of DTs and the degradation of winding joints. The higher and unstable contact resistance of the winding joint results in more damage in the corresponding coil due to increased temperature.