An Improved Thermal-electric Analogy Model for Evaluating Loading Capability of Oil-immersed Transformers

The load capacity of oil-immersed transformers affects the safety of power system operation. In order to fully exploit and utilize the load capacity of transformer, a novel improved model is proposed based on the principle of thermal- electric analogy. Firstly, solar radiation is introduced as a new heat source, and the thermal conductance is modified by considering the effect of temperature on oil viscosity. Then, a transformer load capacity evaluation model based on the thermal-electric analogy principle is proposed under the constraint conditions of top-oil temperature, hot-spot temperature, relative life loss, and auxiliary equipment capacity level. Finally, a 50 MVA transformer is carried out for oil temperature and load capacity. The results demonstrate that compared with Tang-model and the transformer guidelines, the error of the top-oil temperature and the hot-spot temperature of the new model is smaller. In addition, for periodic loads, transformer load capacity also represents different characteristics, which provides a guide for exploiting the load potential of power transformers.