Improvement and application of dynamic thermal circuit model for oil-immersed power transformer

The feasibility of increasing operating capacity of existing power transformers is studied based on a novel dynamic thermal circuit model in this paper. Hot-spot temperature of a transformer is the most important parameter to determine the operation capacity. However, only top-oil temperature is monitored and hot spots usually appear at windings. In this paper, a dynamic thermal circuit model considering environment factors and operation conditions is established. To implement and verify the dynamic thermal circuit, the real-time loss and cooling thermal resistance of the transformer is calculated firstly. And then hot-spot temperature based on the average oil temperature is calculated for a period of 24 hours. The calculated result is compared with the measured temperature data under the same conditions. The comparison shows that the accuracy of the proposed model is satisfactory. The proposed model is then used to evaluate the feasibility of increasing operating capacity. The evaluation indicates that the continuous operating capacity can be increased. After capacity increased, the transmission energy can increase remarkably, while the service life is reduced lightly.