In order to investigate the rationality of determining insulation margin of oil-immersed power transformers with standard lightning impulse and the effectiveness of utilizing double-exponential non-standard lightning impulse in insulation tests

we studied the effects of double-exponential impulse waveforms on the discharge characteristics of oil gap and oil-impregnated pressboard. The results show that the breakdown voltage of oil gap and oil-impregnated pressboard increases as the wavefront becomes longer or the wavetail gets shorter. The wavefront has greater influences on the breakdown characteristics of oil-impregnated pressboard

while the wavetail affects oil gap much more remarkably. Based on the experimental data

the corresponding empirical formula is summarized

and the electrical equivalence between the breakdown voltage of oil-paper insulation under non-standard lightning impulse and standard lightning impulse is established with the front time and tail time as the time parameter. The results of this study can provide an important support for the insulation design and test of oil-immersed power transformers.