Influence Of Moisture For Insulation Of Bushing And Its Mechanism

Moisture may affect the electrical and dielectric properties of Oil Impregnated Paper bushing(OIP).The deterioration of electrical performance on insulation due to moisture,which might diffuse into the insulation under certain circumstances and in most cases,they are the origin causes of bushing failures and breakdown in power system in general.There are different sources of stress that might be result in degradation of insulation of bushing.Partial discharges(PD)are ones of the main sources of electrical insulation degradation.This project was mainly concentrated on the influence of moisture to the PD behavior of oil impregnated bushing.The characteristics of PD activities due to moisture and its influence on the insulation properties of OIP bushing was studied.The measurements always give global results about the bushing characteristics change and they do not include the influence of moisture on bushing.In order to handle this problem,different moistening methods OIP bushing such as moisture ingress,injection of moisture of oil impregnated bushing was focused on.Partial discharge behavior using the different moisture injection method such as the use of injecting water directly in dried paper,injecting water in an impregnated model,paper wrapped with water and impregnated and poor dry models were used.Capacitance(C),Dissipation Factor(DF),PD,moisture in paper recorded and analyzed.The results showed that the moisture had an effect on both on capacitance,dissipation factor and might lead to PD.Discharge phase of moisture impregnated model concentrated and strongly developed in range of 0°?90°,180°?270°,and 330°?360° with shape characteristic looks like mountain can be sign of PD due to the moisture.It was found that the main sources of partial discharge due to the moisture was foil edge.Moisture effect was more distinguishable axially than radially.Number and maximum magnitude of PDs increased with time until reaching a peak value.Finally,both parameters decrease with time and puncture breakdown occurs in the sample.It might be provided valuable reference for the condition monitoring and maintenance of OIP for the operation of the power system.