In order to study the accumulative effect of the lightning impulse voltage wave actually invading the power transformer and the standard lightning impulse voltage wave（SLIW） defined by the IEC on oil-paper insulation

based on the actual recorded invading lightning impulses in a substation

a damped alternating oscillation voltage was applied to the turn-to-turn insulation model which simulates the actual situation of insulation system in transformers. The U-N characteristics under impulse voltages were determined

and the electric parameters

such as relative dielectric constant

were measured before/after the accumulative tests. The experimental results showed an evident accumulative effect of the oil-paper insulation under multiple damped alternating oscillation impulse voltages. And the U-N characteristic curves of oil-paper insulating showed exponential variation under the impulse voltage of different waveform parameters. Meanwhile

the cumulative resistance of oil-paper insulation to damped alternating oscillation impulse voltage wave was superior to that of standard lightning impulse voltage wave under the same voltage amplitude

which indicated that the standard lightning impulse voltage wave had strict insulation requirements under the same voltage amplitude. Furthermore

both the relative dielectric constant and the dielectric loss factor of oil-paper insulation obviously increased with the increase of the accumulation times

which also showed that the effect of multiple impulse voltage on oil-paper insulation performance was obvious.