Overvoltages in secondary circuits of medium-voltage switchgear generated by multiple reignitions of circuit breakers

During switching operations in the high-voltage system, transient voltages and currents occur that can generate overvoltages in the secondary circuits of switchgear. The investigations reported in this article are focused on medium-voltage air-insulated switchgear. The introduced model is able to identify the coupling mechanisms. The coupling via the instrument transformers and the secondary wiring to the electronic equipment is described. At first, the frequency-dependent coupling is explained for each secondary component. These are instrument transformers, the secondary wiring, and the electronic equipment. Then it is shown how to combine these components in order to get a complete description of the interfering mechanisms.