Abstract: Two or more rising pulse waves having different rates of voltage increase are applied to a measuring end of a cable and reflected waves from a fault point on the cable are detected to measure a turnaround propagation time between the measuring end and the fault point. Additionally, ratios of the rates of voltage increase of one pulse wave and the other pulse waves are calculated. A discharge delay time at the fault point is calculated from time differences of the measured turnaround propagation time and the ratios of the voltage increasing speeds and the discharge delay time is subtracted from the measured turnaround propagation time to calculate a real turnaround propagation time.

Abstract: In an electric cable power transmission line of the class wherein three phase metal sheath single core power cable sections are interconnected by junction boxes, two sets of ordinary junction boxes at the opposite ends of each unit line section are grounded, two sets of junction boxes are provided in each unit line section, at each set of the insulating junction boxes the sheaths of the cables of one phase on one side of the insulating junction boxes are crossconnected by cross-connecting wires to the sheaths of the cables of another phase on the other side thereby forming three loop circuits each including the grounding connections of the ordinary junction boxes, the sheaths of the cable sections and the cross-connecting wires, saturable reactors are connected in series with only one or two of the loop circuits. This arrangement reduces the number of the saturable reactors and protective devices for corrosion preventing layers as well as the inductive interference to nearby communication lines.