Pulsed Electro-acoustic (PEA) technique has been extensively used to resolve space charge distribution in dielectrics subjected to high dc electric fields. However, the amount of space charge which accumulates in an insulation subjected to an ac electric field is significantly smaller than under dc field. Also, the ac field gives rise to a capacitive charge component and this makes it more difficult to measure the actual space charge accumulation in insulation subjected to ac voltage. A modified PEA method was used to study space charge evolution at various phase angles of the ac voltage. It is shown that charge injection from the electrode into the insulation usually initiates at the electric field value at which the peak of the PEA profile at the electrodes reverses polarity.
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