Effect of repeated impulses on OIP

Oil impregnated cellulose paper (OIP) constitute major insulation of transformer windings. The cellulose insulation determines the lifespan of a transformer. Many of the transformer failures are mainly due to frequent application of over-voltages. It is necessary to analyze the degradation of OIP with respect to time interval between the impulse overvoltages. Cellulose degradation is usually characterized in terms of scission fraction which is given by degree of polymerization (DP). In this paper, an attempt has been made to analyze the degradation of OIP for different impulse voltages and time interval between the successive impulse voltages. Detailed experimental analyses are carried out for impulse overvoltages of 1.2/50μs, 0.4/50μs and 0.064/50μs by maintaining the time interval of 1 second, 3 seconds and 5 seconds between the successive impulses.