The Characteristic of Residual Charge for Water-tree Degraded XLPE and the Measurement Method

Abstract

Recently the measurement of residual charge has been studying as insulation deterioration diagnosis of XLPE insulated cables. Authors have studied the measurement process and the charge characteristic. The specimens are XLPE sheets of 1mm which are degraded with water-trees. There are four processes of charge removal, charge injection, ground and charge release in the measurement.
The process of charge removal was introduced to measure a little charge successfully. In the process of charge injection, it was confirmed that the relation between the applied dc voltage and the charge was examined, and the higher dc voltage was, more the charge was. In addition, it has been showed that the applied process of the dc voltage greatly influences the measured charge. In the process of ground, the grounding period is changed and the charge is measured. It has been showed that the grounding period doesn't influence the measured charge greatly. In the process of charge release, the frequency and the period of applied ac voltage were changed and the charge was measured. It has been showed that neither the frequency nor the period of ac voltage greatly influence the charge measured. In addition, the dc voltage was superimposed to ac voltage, and the charge was measured. It has been showed that the charge measured changes greatly even if the dc voltage is low. The method of the insulation deterioration measurement of cable was examined from these results, and the measurement conditions and a newer method were suggested.