In order to study the aging characteristics of oil-paper insulation

we prepared oil-paper samples at different aging time and studied the time-domain spectroscopy of samples by the polarization/depolarization current method.Moreover

we proposed an algorithm for improving time-domain spectroscopy based on wavelet transform theory.Then

the aging characteristic parameters of oil-paper insulation were extracted from the improved time-domain spectroscopy.Results show that time-domain spectroscopy can reflect the overall polarization of oil-paper insulation

and the spectrum peak will appear when measurement time exceeds 1 000 s.Then

after wavelet algorithm processing

the time domain dielectric spectrum can reflect three main polarization processes of oil-paper insulation（oil

paper and interface of oil-paper）.Peaks’ values and times of improved time-domain spectroscopy correspond to the intensity and responding speed of different polarization processes

respectively.Finally

the values of spectrum peaks have a good exponential relationship with aging times of oil-paper insulation which can be used as an aging characteristic parameters of different parts of oil-paper insulation.