Phase Characteristics of Space Charge Signal under AC Non-uniform Electric Field in PEA Method

The treeing phenomena are well known as an initiation process of electrical breakdown in the electric power cables. It is discussed that the charge injection from electrode is related to the growth of the tree. The space charge measurement technique by the pulsed electro-acoustic ( PEA) method is widely used. However, the measurement technique in the non-uniform electric field has not been realized in PEA method. The space charge distribution signal ( PEA signal) in a line-plate electrode system in an epoxy resin specimen has been measured. The observed results show that the PEA signals in the epoxy resin in line-plate electrode system has information of the space charge distribution in non-uniform electric field. This technique could contribute the investigation of electrical breakdown phenomena due to electrical treeing. In this report, the PEA signals have been measured under various frequency AC fields in range of DC to 60Hz at 20kV/mm. The obtained results show the injected charges from the line electrode were accumulated near the plate electrode charge in the low frequency AC fields.