Novel inductive sensor solutions for on-line partial discharge and power quality monitoring

Networks of medium voltage have spread over a long distance through underground cables. The aim to prolong the life span of existing network assets increases the need for condition monitoring to prevent unplanned and long lasting interruptions. Continuous on-line partial discharge (PD) measurement is an excellent way to determine the overall health of the medium voltage (MV) components and to detect developing faults in underground cables. A sensor is an essential part of the PD monitoring system which measures the high frequency PD signals. PD sensors can be used to measure power frequency current and harmonic currents on the MV side to estimate the thermal loading of transformer or incoming cable provided that the sensors have a suitable frequency response for measuring low frequency signals as well. A novel inductive sensor is described in this paper which allows both PD measurements as well as power quality (PQ) measurements at frequency range below 2.5 kHz. Authors did experiments on different ferrite cores in order to design the best possible sensor which can be used for both PD and PQ measurement. Characteristics of the sensors, including sensitivity, saturation current, and frequency bandwidth, as well as relative errors are provided and analyzed under laboratory conditions. At the end, developed sensors are compared with a commercial HFCT sensor, the Rogowski coil and power quality current sensors to show the capability of the sensors to be used for PD and PQ measurements.