Study on insulation characteristics of oil-impregnated paper bushing under the combined effect of electrical-thermal

In order to investigate the insulation characteristics of AC oil-impregnated paper bushing during its operation, the electrical-thermal combined test platform was established to carry out the insulation characteristics tests under different oil temperature condition and different load condition. The change law of dielectric loss factor, capacitance, insulation resistance and frequency domain dielectric spectrum for AC oil-impregnated paper bushing under different oil temperature and different load conditions were mastered and the mechanism of the change law for these parameters were analyzed systematically based on the dielectric polarization theory as well. The results showed that the change of transformer oil temperature will lead to the regular change of insulation performance parameters of AC oil-impregnated paper bushing. The influence of different loads on the insulation performance of the bushing was mainly concentrated on the thermal effect, and the change of load would be finally reflected by the change of the internal temperature of the bushing. With the same oil temperature, when the bushing, which was applied with voltage and current simultaneously, was under the different load condition, it had worse insulation performance than the one with single assessment factor. Therefore, it can be more accurate to grasp the insulation characteristics of the bushing when insulation characteristics tests with electrical-thermal combined effect were taken, and will provide a strong support for the evaluation and diagnosis of bushing as well.