Optimal design of HV transformer bushing

Based on operating experience, analyses of the electric field distribution in the lower part of the bushing, and the design method used in the condenser body, it is found that for HV transformer bushings the flashover voltage in oil and the partial discharge inception voltage (PDIV) are usually lower. Two measures are suggested for improving the properties, namely, a new kind of design method and optimized shapes. The measures were shown to be successful by partial discharge (PD) measurements and flashover tests carried out on the real bushings. It is shown that the bushing´s flashover voltage in oil may be raised by modifying the shape of the lower porcelain housing, and the arrangement of electric foils in the condenser body by the new method. The experiments show that the change of lower porcelain housing shape leads to a remarkable improvement in flashover voltage in oil. The PDIV value may be raised by modifying the shape of the end shielding, which makes the maximum stress move to the bottom from the top of the end shielding, and arranging electric foils in the condenser body by the new method, which brings about an equal PD margin