Effect of high voltage transients on surface discharge characteristics of oil-paper insulation

Condition assessment of power components such as power transformers and their bushings depends on the interpretation of data obtained from the monitoring systems. Various defects in their insulation would behave differently under electrical stresses. Surface discharge on the oil-paper interface is one of the defects which can be responsible for the failure of those components. Power system transients can impose stresses on the insulation of the power transformers and their bushings. This study investigates the effect of transients such as lightning impulses on the surface discharge characteristics of oil-impregnated paper. Two configurations, needle and rod (IEC-b), are used here. Two distinctive situations occur on paper due to these different configurations. The corresponding effect is shown in the form of variation in the partial discharge numbers and phase-resolved patterns. In the needle electrode configuration, the paper remains un-aged and the applied impulses cause a prompt change in the total number of discharges which decays fast. However, with the rod electrode, the paper gets carbonized and the applied impulses cause a decrease in the total number of discharges. The influence of moisture content in oil-impregnated paper was also studied. For this case, the total number of discharges considerably increase after applying impulse.