Repetition Rate of Partial Discharges in Low Voltage Cables
Diagnostic testing of low voltage cables by partial discharge measurement has several difficulties. One of them is that the cables are not designed to be partial discharge free at their test voltage. As partial discharge impulses may originate from numerous spots even in new cables, it is expected that impulses reach the termination with high repetition rate. The propagation of impulses in low voltage cables differs from the medium and high voltage cables; there is no lossy semiconducting layer or layers, but the cross section of the conductors are lower. The measurement method of partial discharges has to be adjusted to the discharge type and the propagation path as these determine the frequency content of the individual impulses, and the time resolution of the system has to be appropriate for the expected repetition rate. Measurements have been performed on various types of cables by different methods. Based on the results suggestions are given on the suitable measurement methods.