Dielectric measurements for diagnosis of XPLE cable insulation

A research project was started in 1992 with the aim to develop a useful nondestructive method to determine the condition of water tree deteriorated XLPE cables in service. Since 1995 an extensive laboratory investigation has been made on cables aged in service and a large number of field measurements have been performed on cables in service. The purpose of this report is to present these results and the further development of the diagnostic procedures. This report starts with presentation of the measurement procedure. The procedure is applied both to laboratory and field measurements. In the part on laboratory investigations the ability to detect deteriorated cables is verified and measured dielectric response is related to breakdown voltages. The application of the method on cables in service is then presented. The field investigation part also includes practical considerations on the measurement procedure and on the influence of accessories and terminations.