PURPOSE: To conduct measurement at a place nearer to a spot of occurrence of a partial discharge in comparison with the case when the partial discharge is measured at the terminal part of a cable and to remove external noise in a partial discharge signal effectively by a gate circuit.
CONSTITUTION: A sheath circuit including an insulating spacer 12 of an insulation joint box provided in a cable line is connected with a coupling capacitor 13 and a primary winding 14 of a transformer and a partial discharge signal is taken out from a secondary winding 16 of the transformer. This signal is supplied to a gate circuit of a detecting element 20. The gate circuit is controlled to be opened and closed by a gate control signal corresponding to a signal level of a test voltage. External noise is removed from the partial discharge signal by this gate circuit.
AIHARA MITSUGI
FUJIWARA YASUTAKA
