MV controllable fuses installed to reduce ARC flash on transformer secondary

Mitigation of arc flash incident energy is important to increase safety. One method is to reduce the duration of the arc flash by using protective relays to sense an arc flash fault. This method requires a supply-side overcurrent protective device that will respond to the protective relaying fast enough to mitigate the incident energy. In many existing installations, MV transformer primary fuses are already installed to provide transformer protection. Before the development of a MV controllable fuse, the MV fuse would have to be replaced with a MV circuit breaker or circuit switcher to have relay control of the MV protective device. This replacement would have significant equipment/construction costs and would require extensive equipment outage time. The MV controllable fuse method uses the existing fusegear protecting the primary side of the transformer. The protective relaying senses the arc fault and signals the controllable fuse to change to a faster acting time-current response. Incident energies can be reduced from 200 Cal/cm² to below 8 Cal/cm² on the transformer secondary. This paper reviews an installation using a MV controllable fuse to mitigate the incident energy on the equipment connected to the transformer secondary.