A successful on-site PD testing experience of 11kV EPR cable insulation systems

A power generating station in the United Kingdom has reported a number of in service failures in its 11kV single core Ethylene-Propylene Rubber (EPR) insulated cables. Several industrial companies have carried out on-site condition assessment to determine whether other insulation defects were present but no conclusive results have been found due to presence of strong background electrical noise. The present authors were invited to carry out on-site testing to demonstrate the effectiveness of their denoising techniques. This paper presents the processes of the on-site cable partial discharge signal detection experience and the signal processing of the raw data. Following a brief introduction to the tests, equipments and connections, the paper analyses sources of different types of interference signals. These are found to originate mainly from UPS Inverter Supplies or 11kV Motor drive circuits. Thereafter, second generation wavelet transform (SGWT) data denoising algorithm is introduced. SGWT is proved to be an effective denoising technique for the detected data. Also presented in the paper are PD pattern identification and PD source localization methods which are used to identify the source of the PD signal. Finally the diagnosis results, with indication of potential insulation defect and cable joint problems, are provided.