The power capacitor will age continuously with time in its long operation cycle of several decades

mainly caused by operating overvoltage. Internal insulation of capacitor — the oil-film dielectric will suffer from the decline of insulation state and even the early failure of insulation after it has been subjected to multiple impulse voltages. In order to have a preliminary judgment of oil-film dielectric with different aging degree

an oil-film dielectric aging and testing platform is established to apply multiple impulse voltage

and the partial discharge( PD) under AC and polarization and depolarization current( PDC)method are used respectively. The results show that the initial discharge voltage of PD decreases with the aging degree of oil film dielectric

and the maximum depolarization current of PDC curve increases. Finally

the above changes are explained by the changes of the internal molecular structure of oil-film dielectric under the impulse voltage.