A new method for space charge measurements under periodic stress of arbitrary waveform by the pulsed electro-acoustic method

A new method for space charge measurement resorting to the pulsed electroacoustic (PEA) method under periodic stress of arbitrary waveform is presented. The originality of the work consists in using a long memory digital oscilloscope combined to the method used to sample one period of the HV stress into several profiles. There is no need for synchronization between pulse generation and HV stress and hence no hardware change of classic PEA system. The pulse generator provides a probing pulse of 5 ns duration, at a maximum frequency of 1 kHz. With these features, the phase of the HV stress can be resolved into 200 profiles by frequency adjustment of the pulse generator. Several periods of the HV stress are necessary for obtaining the set of profiles; however the typical measurement time is less than 20 s for f > 0.2 Hz. Preliminary results obtained on a crosslinked polyethylene film under 50 Hz ac stress are shown to demonstrate the feasibility.