Steady-state Simulation on Temperature and Flow Fields of ONAF Transformer

Oil-immersed transformers are widely used in all voltage levels of power networks and play a key role in the stable operation of power grid. With the rapidly increase of the electric consumption and load capacity of the transformer, high hot-spot temperature has become one of the essential issues concerned by engineering manufacturers. The driven force of oil flow is thermal buoyancy in transformer for Oil Natural /Air Forced (ONAF) cooling mode, besides, the internal oil flow paths are complex. Therefore, the heat dissipation for ONAF transformers becomes a key index determining the loading power, and it is of great theoretical and practical significance to study the oil flow distribution and temperature field. In this paper, the finite volume method is used to simulate the temperature and flow fields of a 110 kV ONAF transformer. The results show that the temperature inside transformer increases gradually with the height, and the hot-spot is found located below the low-voltage winding top. The velocity of oil in the vertical oil channels are greater than the horizontal oil channels between the coil discs. It is found that introducing washers in the transformer design can enhance the flow rate of horizontal oil channels and strengthening the heat dissipation of windings. The research results can be used to guide the evaluation of load capacity and the heat dissipation structure design of the transformer.