Semiconducting layer as an attractive PD detection sensor of XLPE cables

Online monitoring of high voltage (HV) cross linked polyethylene (XLPE) cables is a major requirement and interest of utilities for reliable operation of underground cables. Although XLPE cables have a relatively reliable insulation system, however since its insulating material is less resistant to partial discharges (PD), the failure risk increases significantly after occurrence of any partial discharge. Therefore sensitive sensors and a reliable detection system are required for an effective cable life management. Due to attenuation effects of semiconducting layers of XLPE cables on high frequency components of partial discharge signal, the detection process is easily distorted with application of conventional sensors such as high frequency current transformers (CTs). In this paper a new sensitive internal sensor of partial discharge signal, the semiconducting layer, is introduced which is available normally in the H.V. XLPE cables and access can be easily provided at the terminals and also at some specific distances from the terminals, i.e. every one hundred meters, if the manufacturer was asked for. Two 11 kV, XLPE cable setups are employed for study of high frequency signals and partial discharge signals propagation in the XLPE cable and its semiconducting layers. The J Marti´s frequency dependent cable model is employed for simulation of partial discharge signal propagation in the core conductor and semiconducting layers of single phase XLPE cables