Study on the Electromagnetic Thermal Coupling Analysis Method for Valve Side Bushing of Converter Transformer Under Multi-frequency Harmonic Current

The valve side bushing of UHV converter transformer works in the environment with high temperature and strong AC / DC electromagnetic stress, which leads to the degradation or decomposition of insulation materials, and even appears insulation defects. Therefore, it is very important to master its temperature distribution or running status of the bushing. In order to analyze the temperature distribution of the bushing, this paper proposed an electrical-thermal calculation method and builds an electrical-thermal coupling model based the finite element method. Firstly, according to current waveform of the bushing during the actual running, the harmonic characteristics of the current can be determined and the heat loss calculation method for the bushing under multifrequency harmonic current is proposed. Then, the Calculation method of temperature field distribution is proposed by combining the heat transfer mode, the material characteristics and defect states for the bushing. Finally, an electrical-thermal coupling model for the valve side bushing of UHV converter transformer can be built. Compared between the simulation and actual measurement date, the result show that the calculation error of the electrical-thermal coupling model is within 2%. Based on the model, the temperature distribution of the bushing under different operation conditions can be obtained, which can provide an analysis method for the states evaluation and structural design of the bushing.