Features of controlled switching under normal and emergency operating conditions in medium voltage networks

Abstract

The change of operating conditions by circuit breaker switchings or initiation of emergency conditions (short circuits) is accompanied with transient processes. The physical nature of a transient process is redistribution of the stored energy between inductive and capacitive network elements. In some cases, circuit breaker opening may induce high-frequency overvoltages, while circuit breaker closing may cause high inrush currents, and emergency conditions may initiate overcurrents. These have a negative influence on electrical parameters of the network and cause the accelerated equipment deterioration. Controlled switching involves serial switching of each phase according to the given algorithm at the instant of current or voltage zero crossing. Such switching allows eliminating dangerous inrush currents and overvoltages and increasing the switching life of the equipment. Controlled switching is efficient under normal operating conditions both at circuit breaker closing, and at circuit breaker opening. Controlled closing of a reactive load by a circuit breaker allows minimizing inrush currents, while controlled opening reduces the probability for restrikes and overvoltage generation. Controlled opening of short circuit currents gives a possibility to reduce time of arcing to minimal values, which provides decreasing the electrical erosion of an arc-extinguishing device and increasing the circuit breaker life time. As a result, it improves power quality parameters, increases the life time of the power equipment and enhances switching capabilities of a circuit breaker.