Apparatus and method utilizing nonconductive tube means containing an ionized gas for corona testing of insulated electrical cables

Claim 1

THE METHOD OF LOCATING A DEFECT IN THE INSULATION OF AN INSULATED ELECTRIC CABLE THAT COMPRISES: ADVANCING A CABLE, THE CONDUCTOR OF WHICH IS AT A REFERENCE POTENTIAL, THROUGH A VOLUME OF AN IONIZED GAS THAT IS CONTAINED WITHIN THE BORE OF AN ELECTRICALLY NON-CONDUCTIVE TUBE THAT HAS A CABLE ENTERING END AND A CABLE EXITING END; MAINTAINING WITHIN THE TUBE AN ALTERNATING CURRENT VOLTAGE THAT HAS A MAXIMUM VOLTAGE DIFFERENTIAL AT A ZONE WITHIN THE TUBE AND A VOLTAGE PROGRESSIVELY DECREASING TO SAID REFERENCE POTENTIAL IN BOTH DIRECTIONS FROM THE HIGH VOLTAGE ZONE TOWARD THE ENDS OF THE TUBE, WHEREBY A DEFECT IN THE INSULATION CAN RESULT IN CORONA; DETECTING ELECTRIC CORONA IMPULSES EXTERIOR OF THE TUBE AT A POINT ALONG ITS LENGTH INTERMEDIATE THE HIGH VOLTAGE ZONE AND THE CABLE EXITING END OF THE TUBE, AND UTILIZING THE DETECTED IMPULSES TO LOCATE THE DEFECT.