Wang, P, Lewin, P L and Sutton, S J,
Calibration of Capacitive Couplers for Online PD Detection in HV Cables
IEEE Electrical Insulation Magazine, 21, (3), .
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On-line partial discharge (PD) detection for high voltage cable systems is important as it ensures that possible faults can be detected and remedied before catastrophic failure occurs. Of growing interest is the use of non-conventional field coupling techniques to detect PD signals and the VHF capacitive coupler sensor is finding increasing application in PD detection systems due to its low cost, reliability and applicability to online detection. However, it has a major disadvantage as it is very difficult to quantify the sensor output voltage in terms of the conventional PD quantity, apparent charge. Proposed methods rely on pulse injection either at the cable termination or via another coupler in order to obtain a calibration ratio, these approaches have been assessed experimentally. In addition, frequency response (FR) measurements have been taken and used to generate a transfer function relating the coupler output to signals present on the cable core conductor. The transfer function has been used as the central component of a simulation model that estimates the calibration ratio. Good agreement has been achieved between the simulation model output and experimental results. PD tests have also been undertaken on a section of 66kV HV cable, containing an earthed needle within the cable dielectric. Obtained results have been compared with measurements using the conventional electrical detection method. Results indicate that a better estimation of reduced charge is possible using a frequency response measurement to provide coefficients for a simulation model than existing pulse injection calibration methods.
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