Capacitor energising transient limiter for mitigating capacitor switch-on transients

Capacitors are prone to two major types of energising transient phenomenon: transient overvoltage and inrush current (charging current). Energising transients will shorten the lifetime of the capacitor, and furthermore they will damage the contacts of the switching device. This study proposes a rectifier type capacitor energising transient limiter (CETL) for mitigating the isolated capacitor and back-to-back capacitor switch-on transients. The operating condition of the proposed circuit can be divided into two states: the charging suppressive mode and the steady state with its initial transient. During the charging suppressive mode, a pair of diode strings conducts automatically and then the DC reactor provides high impedance at the instant of switching on in order to suppress the capacitor energising transients. During the steady state with its initial transient, all diodes of the bridge rectifier conduct simultaneously and the limiter freewheels; therefore the limiter acts as a short circuit and has no effect. Thus, it is not necessary to increase the capacitor-rated voltage when the CETL is used. In this study, experiments and simulations are carried out to demonstrate the feasibility of the proposed limiter circuit.