The Influence of Ambient Temperature on Physical Field in Oil-immersed Transformer

In order to study the influence of cold start temperature on the operating characteristics of oil-immersed transformers in arctic regions, this paper establishes a 50MVA/110kV oil-immersed transformer simulation model by finite element software. The internal distribution characteristics of temperature, oil flow and electric field of the oil-immersed transformer during cold start process are studied in different ambient temperature. The research results show that the hot-spot temperature increases rapidly within 10 hours. The rising rate of the hot-spot temperature reduces after 10 hours until the thermal balance is reached after 30 hours approximately. The temperature rises of hot-spot are $77^{\circ}\mathrm{C}$ and $72.8^{\circ}\mathrm{C}$ at $- 40^{\circ}\mathrm{C}$ and $20^{\circ}\mathrm{C}$ ambient temperature respectively. The lower cold start temperature, the higher temperature rise of the hot-spot. But because the ambient temperature is too low, the absolute temperature of the hot-spot inside oil-immersed transformer during cold start is not high. The temperature change results in a slight distortion of electric field near the windings, which may bring discharges with an existing defect.