UHF COUPLERS FOR GAS-INSULATED SUBSTATIONS - A CALIBRATION TECHNIQUE

Methods that have been used to evaluate the performance of UHF coupler s for partial discharge monitoring of gas-insulated substations are br iefly reviewed, illustrating the need for a standard test procedure. A measurement scheme is proposed in which the coupler is mounted beneat h 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 frequen cy measurements. The frequency responses of two disc couplers and an e xternal window coupler are measured to demonstrate the technique.