Device to limit Transient Recovery Voltage

This paper summarizes the main results about design and evaluation of a device to reduce Transient Recovery Voltage (TRV) magnitude in medium voltage switching equipments. Zinc Oxide (ZnO) devices are modeled in an Electromagnetic Transients Program (EMTP), being applied as an alternative to limit TRV peaks in circuit breakers and reclosers of 15 kV and 72.5 kV voltage class. The assessment of device effectiveness in elimination of three-phase ungrounded and kilometric faults is performed with the purpose of providing information for testing and future deployment. Laboratory conditions are reproduced digitally describing the absorved energy by the device as a function of fault current and TRV frequency. The most severe cases allow the use of ZnO varistors commercially available, giving feasibility to achieve limiter devices. Results obtained in studies presented good agreement, showing that operations preliminarily qualified as unsafe can become permissive. Financial support usually used to replace equipment by another with higher voltage class can be reduced.