Design and performance of a ZnO device to reduce transient Recovery Voltage peaks

With the continued growth of power systems, it is possible that Transient Recovery Voltage (TRV) requirements lead circuit breakers to failure. In the medium voltage networks, studies have been made to evaluate the design and performance of a device which can reduce TRV peaks. The basic cell and its structure are presented and modeled in an Electromagnetic Transients Program (EMTP). The device is composed by Zinc Oxide (ZnO) varistors and its non linear characteristic allows reducing TRV magnitude when used across the breakers during interruption of three-phase ungrounded and kilometric faults. Data from the Northeast Brazilian Power System Grid of ENERGISA are used in the case studies. Simulations are carried out with ATP (Alternative Transients Program). Important aspects of planning are addressed to ensure a correct TRV diagnosis, which may come up with saving investments that would be used to replace circuit breakers or reclosers by others equipments with higher voltage class.