UHF couplers for gas-insulated substations:a calibration technique

Methods that have been used to evaluate the performance of UHF couplers for partial discharge monitoring of gas-insulated substations are briefly reviewed, illustrating the need for a standard test procedure. A measurement scheme is proposed in which the coupler is mounted beneath an aperture in a ground plane and subjected to an incident electric field of known intensity. A TEM line is used to evaluate the technique, and a step excitation is shown to have advantages over swept frequency measurements. The frequency responses of two disc couplers and an external window coupler are measured to demonstrate the technique.