Hot spots mitigation on tank wall of a power transformer using electromagnetic shields

The presence of stray losses in the tank walls, near the low voltage cable leads, can be substantial. This usually leads to high temperatures in power transformers. This paper presents the experimental analysis of overheating in the low voltage tank wall of a power transformer, which is near to the low voltage bushings. The power transformer considered in this paper is rated as 44/58/73 MVA, 230/34.5 kV, ONAN/ONAF/ONAF. Hot spots in the tank were discovered by thermography during a laboratory temperature rise test under overload condition (82 MVA). Gases were also detected in the transformer oil during this test. The hot spots problem was solved using aluminum electromagnetic shields in the tank wall. Temperatures were measured before and after installing the aluminum shields in the tank wall of the power transformer. It was found that aluminum shields considerably reduce stray losses and overheating in the tank wall. As a result, the proposed solution in this paper, which has been validated by measurements, significantly reduces the risk of potential failures of power transformers during service.