Transient recovery voltages in vacuum circuit breakers generated by the early-interruption of the inrush current of large motors

The switching of medium voltage electrical motors is typically realized by means of vacuum circuit breakers (VCBs) essentially in view of their elevated number of switching cycles. As known, switching of VCBs generates important transient recovery voltages (TRVs) that need to be properly evaluated in both VCB sizing and in the power system insulation coordination. As large medium voltage electrical motors are installed into plants typically controlled by means of Supervisory Control And Data Acquisition (SCADA) systems, maneuvers that involve the motor inrush followed by its sudden de-energization (due, in general, to the intervention of an automatic diagnostic function), resulting into important TRVs, are not unusual. The paper aims at investigating the TRVs due to this specific type of VCB switching by means of a model implemented in the EMTP-RV simulation environment. By making reference to a real plant, the validation of the implemented models is obtained by comparing the simulation results with some experimental transients provided by the plant data fault recorder. The paper finally discusses the adequacy of different countermeasures by analyzing their effectiveness for the TRVs limitation.