Reduction of capacitor aging by the use of transient-free diode-based synchronous switch

This paper discusses an application of hybrid diode based switches, investigating its positive impact on the life of the capacitors. Switching of shunt capacitors in distribution systems can give rise to current and voltage transients. The major factors influencing the life of the components are the inrush current and the overvoltages occurring during the energizing transient, as well as the probability of prestrike and restrike. Switching overvoltages can trigger partial discharges in the capacitor insulation system, thus leading to a progressive degradation, until complete breakdown occurs. We apply a probabilistic life model, originally developed for cables subject to transients, to obtain numerical estimates for capacitors. Results show a decrease of the capacitor reliability at the design lifetime, caused by the transients, when traditional switching devices are used. In applications where capacitors are switched more frequently, a more severe decrease of reliability can occur. On the other hand, the use of a synchronized switch provides several advantages, namely: substantial reduction of inrush current and switching overvoltages compared to other switching technologies; and reduction of probability to have restrikes or prestrikes. These in turn increases the useful life of the capacitors.