Evaluating the calibration of UHF couplers for partial discharge detection

The validity of a recently proposed calibration scheme for the UHF couplers that are used to detect partial discharge in gas insulated substations is investigated. The measured UHF pulse power from a coupler is compared with the predicted output power calculated using its calibrated sensitivity. The theoretical basis for the comparison is presented and demonstrated. In an experiment using an external window coupler, the difference between the two values was only 0.3dB. The results endorse the test procedure and standard conditions adopted for coupler calibration. The use of coupler calibration results to determine the required amplitude of pulses for pulse injection testing of UHP monitoring systems is discussed.