Thermofluidic investigations of oil natural transformer: Closed‐loop modelling and experimental validation

Abstract

Excessively high temperatures inside a power transformer can accelerate the ageing rate and even cause unplanned outages. Accurately estimating the hot‐spot temperature (HST) of a power transformer is important for regulating the load and ensuring long‐term operation. In this study, a closed‐loop model of a 110‐kV product transformer with an oil natural/air forced (ONAF) cooling mode is built to predict HST, in which the compression ratio of windings, equivalent heat source and radiator geometry are considered. According to the flow field of the winding, the ‘dead oil zone’ and reverse oil flow are observed in the horizontal oil channels. The accuracy of the proposed model is experimentally validated by temperature‐rise tests. The results show that the absolute errors between the measured results and simulation are below 5°C, and the average error is ∼2°C. Furthermore, the arrangements of windings and radiators are studied to enhance the oil circulation. By adding 5 washers to the high‐voltage winding, the average temperature can be decreased by 6°C compared with the case without a washer. Elevating the radiator can also mitigate the characteristic temperatures, and the optimal height difference between the radiator and winding centre is suggested to be 0.66 m.