The influence of mass moisture invading on electrical features for oil-impregnated paper bushing

Oil-impregnated paper bushing (OIP) is one of the key devices for power transformers. Recently, some explosion accidents were initiated by bushing invaded by mass moisture, which could destroy the power transformer. In order to study the influence of mass moisture on the characteristics of dielectric loss (tanδ), capacitance and partial discharge (PD) of OIP, a 25kV transparent glass-bushing model was designed and ultrasonic humidifier conducted moisture invading. After moisture invading one-hour and stewing 12 hours, the online measurements of tanδ, capacitance and PD were used for OIP model under applied AC voltage of 10kV, 15kV, 20kV, 25kV and 30kV separately. The results show that tanδ increased from 0.62% to 0.72% under the AC voltage of 10kV and the increase of its magnitude under the voltage from 10kV to 30kV was 33.88%. The capacitance increased from 102.6pF to 103.8pF under the AC voltage of 10kV and the increase of its magnitude under the voltage from 10kV to 30kV was about 0.28%. The PD character was almost unchanged under the voltage from 10kV to 30kV. It is indicated that the change of dielectric loss tanδ is much higher than the PD character for OIP under mass moisture invading. Therefore, the online monitoring of dielectric loss tanδ should be reconsidered and expended to detect the serious moisture defect of OIP. It is applicable to the condition monitoring of moisture of bushings. It may provide reference for the condition monitoring and maintenance of OIP for the operation of the power system.