Voltage stability with mechanically switched capacitors using Vacuum Circuit Breakers in the High-Voltage Grid

This Paper shows one of the possibilities, where Vacuum Circuit Breakers (VCBs) can be utilized in flexible AC transmission systems in the High-Voltage Grid. Although VCB can only switch at a low repetition rate in comparison to electronic switching devices, it is justifiable to use them, if the main focus is lying on a cost-effective device with a selected working operational range. VCBs are used in this case as switching elements as they can be switched more often without maintenance compared to other circuit breakers. In this paper mechanically switched capacitors, which are connected to a node in the h.v. system in order to enhance the voltage quality at this node and to avoid a voltage collapse are investigated. As VCBs are mainly available in the medium voltage range a transformer will be used to connect the mechanically switched capacitors to the h.v. system. Based on a simulation it could be shown, that the mechanically switched capacitors using VCBs can stabilize the voltage of the node in case of disturbances in the power system like faults. The electrical stress on the VCBs and on the capacitors for different simulation cases is assessed. The simulation is performed with PSCAD.