For several years, monitoring of MV power cables with a two-sensor based, partial discharge monitoring system (2BPM) has been proven to be an effective instrument for diagnosing MV underground power cables. Partial discharges (PD’s) from weak spots can be detected and located, both continuously and on-line. Based on the same technology, the DNO’s Alliander and Enexis, together with DNV and Locamation improved the system such that it can now also detect and locate faults (breakdowns) in MV cables typically locating these to within 1 % of the cable length. This is a unique new possibility to guard MV cables. Moreover, these results are obtained regardless of the circuit’s grounding philosophy (impedance earthed, isolated neutral, etc.) or short circuit current. In this paper a short introduction will be given on the functionally of the 2BPM system. Different from traditional monitoring equipment for MV cables, it works with two sensors placed at both cable ends. Both sensors measure the arrival time of the travelling waves associated with PD’s or faults. For the required time synchronization between sensors, it uses own injected pulses. Knowing the difference in arrival time, any PD activity or fault can be pinpointed within 1 % of the cable length between the two sensors. The maximum distance between two sensors is 4 to 12 km (depending on the cable type and the wish to measure PD or faults or both). It is even allowed to have substations along the cable circuit being monitored, since travelling waves from PD pulses and faults easily pass such substations.
Learning from online monitoring of MV-cables with PD and fault location
In this paper a short introduction will be given on the functionally of the 2BPM system.