抄録
Detection signals obtained under the application of commercial AC voltage can be explained by two kinds of current mode, namely generation mode which is correspond to void discharge and transmission mode which is composed of conductive path and signal source contained in the line voltage of the operating cables. By the circuit restrictions of cable shielding layer capacitor earthing and also to avoid the effect of DC stray current, detection frequency for in-service measurement needed to select lower than AC frequency and also higher than DC.
At the water tree deteriorated cable specimen, 1Hz (lower than commercial AC voltage) signal was obtained by transmission mode under the operating voltage stress. Furthermore, existence of the generation mode was suggested by the dried water tree deteriorated cables, because the micro discharge seemed to be existed in the non-conductive dried micro void of deteriorated cables.
