Characterization of oip under repeated impulses

Power transformer insulation is subjected to repeated impulses during lightning strokes, auto-reclosure of circuit breakers and HVDC converter operation. Oil Impregnated Paper (OIP) is the major winding insulation of power transformer. In this work, the effect of repeated impulses on OIP has been studied using Voltage-Number (V-N) characteristics. An attempt has been made to characterize the effect of repeated impulses on OIP using various electrical parameters like AC breakdown strength, DC breakdown strength, Impulse voltage-time (v-t) characteristics, Capacitance and Dissipation factor of OIP. Moreover, the effect of voltage magnitude and number of impulses on the severity of degradation of OIP has been analyzed at the design voltage level and at a voltage higher than the design voltage level.