High-voltage high-frequency transformers are usually operated for a long time at a non-sinusoidal voltage with a frequency of 1～20 kHz. To study the withstand voltage capability of windings and inter-turn insulation

we experimentally investigated the high-frequency insulation characteristics of Nomex paper

modified DMD composite paper

PET film and PI film under 1～20 kHz

0～20 kV of high-frequency excitation voltage. The two-parameter Weibull statistic method was used to calculate the insulation failure efficiency of insulation materials

and the relationship between breakdown voltage and frequency was analyzed. The U-t characteristic curves and characteristic formulae of the insulation material were calculated based on the power function model

and the variation of U-t characteristics with frequency under high frequency square wave voltage was analyzed. Finally

we studied the effects of insulation thickness on the breakdown voltage at different frequencies. The experimental results show that the characteristic breakdown voltage based on the Weibull distribution decreases with the increase of the frequency

and the drop rate reaches the maximum at 1～5 kHz. The U-t characteristic curve shifts with the increase of frequency

and the high-frequency thermal effect is the main cause of breakdown voltage drop and shortened insulation life in long-term operation. The non-uniformity of the electric field and the increase of heat can cause the breakdown voltage to change non-linearly with the thickness. The increase of the frequency expands the trend of non-linear change.