Partial discharge and cross interference phenomena in a three-phase construction

This paper deals with partial discharge measurement and partial discharge characteristics on a three-phase construction. A simplified model of three-phase gas insulated switchgear is used in the experiment to simulate three-phase electric field in three-phase equipment. A particle was adhered on the different positions on the conductor and on the tank to produce partial discharge. Partial discharge signals flowing on three phase conductors were measured simultaneously with three high frequency current transformers clamped on the three- phase lines through capacitive voltage divider. Partial discharge signals induced on the enclosure were measured with the current transformer and the detecting impedance. The circuit was calibrated and examined by injecting known charges from a pulse calibrator to some points in the circuit. The calibration results indicate that measuring partial discharge signals only at the enclosure or on one of the phases of three phase construction will result in the position dependent sensitivity for partial discharges. Experimental results show that partial discharge inception voltages of a particle adhered on different position differed depended on the particle position. Phase of partial discharge inception voltage also depended on the particle position. Experimental results show that partial discharge caused by a particle on one phase conductor was induced and detected on the other phase conductors. Polarity and magnitude of discharge current flowing on each phase depended on the particle position. Each particle at different position generated discharge current which flowed on each phase so that the magnitude ratios of the currents flowing on each phase were unique for each particle. These results were discussed with considering electric field characteristic in three-phase construction and coupling capacitance between three-phase conductors and between the conductors and the tank.