Significance of Tank Current Measurement During Short Circuit Testing of Power Transformer

Transformers are very costly equipment, when failure of the transformer happens, it affects the power supply and cost of repair is too excessive. During system operation transformers faces electrical, mechanical and thermal stresses. One of the critical situation during the short-circuits is which produces high currents in the transformer windings and hence high radial and axial forces in the windings. Transformers are specified and designed to withstand the effects of limited duration short-circuits at their terminals. Generally, Transformers undergoes various quality assurance checks, in which one of the main quality assurance checks is demonstration of ability to withstand short circuit test. Short-circuit tests are destructive test if the clamping system is not capable of sustaining the forces, it will cause permanent winding deformation, damage of core may occur. This paper will explain the importance of ability to withstand short circuit test and possible causes of failure due to short circuit forces during short circuit testing. This paper also explains the significance of tank current measurement and its evaluation with case studies. The result shows that if there is any tank current during short circuit test, it is the indication of some abnormality inside the transformer.