Discharge Detection in Extruded Polyethylene Insulated Power Cables

An analytical study was made of the separator-filter type of discharge detector circuit when connected to long cable lengths during corona measurements of polyethylene insulated power cables. Based on this study, it is indicated how optimum detector and connecting circuit parameters can be chosen to best advantage when this type of detection equipment is used in factories where the electrical noise level is high. Under these conditions, it is indicated that a sensitivity of 4 pC (picocoulombs) is obtained on long lengths of power cables over a large range of commercial conductor sizes and voltage ratings; and that on relatively short lengths, the sensitivity is as low as 0.1 pC. It is explained that it is necessary to calibrate the particular measuring circuit with the cable load included, preferably using an exponential pulse applied to the far end of the cable, in order for the discharge measurements to have any real meaning.