Study of Thermal Field Distribution under Internal Crack Defects in the Valve-side Bushing of the Converter Transformer

The valve side bushing of converter transformer is the core component of converter transformer. The change of internal temperature field is very important to the safe operation of converter transformer and power grid. Due to production irregularities and aging factors, various structural defects are prone to appear inside the bushing. Among them, crack defects will increase the electromagnetic loss in the casing and change its temperature field distribution, which may also cause excessive local temperature of the casing with the accumulation of operating time, thus causing safety accidents. In order to better represent the tube under different defects, this paper proposes a crack equivalent model analysis method and develops an example of electro-thermal hybrid defects based on the Phoenix energy scheme. First, the internal crack fault characteristics are analyzed, the crack defect location is determined according to the fault location of the bushing during actual operation, and the heat loss calculation method of the bushing under the defect is proposed. Then, the electro-thermal coupling model of the valve-side sleeves of the commutator transformer is established by combining with the heat transfer mode, physical properties, boundary conditions and defect states of the sleeves. Finally, a curve fitting process using the mean of the data is proposed to compare the simulation results with the actual measurement results, and the galvanic thermal counseling inaccuracy of the model is within 3% of the calculation. According to this model, the structure of the defective bushing can be obtained in various operating environments, which is of great importance for the condition assessment and online monitoring of the valve-side sleeve.