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Preliminary results of interfacial space charge formed in laminated dielectrics under AC voltage application

A measurement system was developed to clarify interfacial space charge formation in the dielectric with an interface under ac voltage stress, the frequency of which could be varied from 50 to 0.00007 Hz. Measurement timing was set to eight points in each cycle of applied voltage. Such ac voltage with its peak value of 5, 10 and 15 kV was applied to a laminated dielectric consisting of low density polyethylene (LDPE) and ethylene vinyl acetate (EVA) with its total thickness of 0.5 mm to investigate phenomena of interfacial space charge formation under ac electric field. It was found that there are three frequency regions to be defined as for frequency response characteristics of the space charge formed in a dielectric by voltage application, i.e., a high frequency region, a low frequency region, and an intermediate frequency region, to which 0.00007 Hz, 50 Hz and 0.0017 Hz belong, respectively. Positive charge carriers play an important role in the formation of interfacial space charge. Characteristic features are observed on space charge distribution profiles in each frequency region.