3-D thermal analysis for the valve-side bushings of HVDC converter transformer and application in the evaluation of current-carrying connections defects

To analyze the overheating problem of the valve-side bushings of high voltage direct current (HVDC) converter transformer, which is mainly caused by current-carrying connections defects at copper-aluminium transition region in the bushing, this paper set up a 3-D electromagnetic-thermal analysis model for the valve-side bushings, and a method was proposed to calculate the thermal distribution of the valve-side bushings under the influence of current-carrying connections defects. Based on this model, the details of an example were shown in this paper, and the numerical results agreed with the measured results within 1%. Then, the temperature field distribution characteristics of valve-side bushing under different working current I, defect degree k, and ambient temperature T-amb were determined. According to the characteristics, the temperature difference Delta T and working current I of the bushing were applied to evaluate contact resistance at the copper-aluminium transition region of the bushing, which can be provided by a novel method to evaluate for current-carrying connections defects in the valve-side bushings.