Time-base alignment of PD signals measured at multiple cable ends

PD measurement is one of the proven methods to determine the insulation quality of e.g., MV power cables. Location capability gives the results much extra value. If measurements are done on long power cables (>4 km), branched cable systems or if they are performed on-line, multiple measuring setups are required to enable PD location. Recorded signals should be synchronized accurately to allow extraction of relevant location information. In this paper several methods are discussed. It is concluded that the most promising method is the injection of pulses through the cable and aligning recorded data records to these pulses. Inaccuracy introduced by time-wandering of sampling clocks can also be compensated by this technique. Measurements show the applicability of the method up to at least 8 km, producing location accuracies of approximately 0.2%.