Reducing Arc-Flash Hazards: Installing MV-Controllable Fuses on the Secondary Side of the Transformer in a Pumped Storage Plant

The 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 switching device that will respond to the protective relaying fast enough to mitigate the incident energy. In many existing installations, medium-voltage (MV) controllable fuses are already installed to provide transformer protection. Before the development of an MV-controllable fuse, the MV fuse would have to be replaced with an MV circuit breaker or circuit switcher to have relay control of the MV protective device. This replacement would have significant equipment and construction costs and require extensive equipment outage time. The MV-controllable-fuse method uses the existing fusegear protecting the primary side of the transformer. The protective relay senses the arc fault and signals the controllable fuse to change to a fasteracting time-current response. The incident energies can be reduced from 200 cal/cm² to lower than 8 cal/cm² on the secondary side of the transformer. This article reviews an installation using an MV-controllable fuse to mitigate the incident energy on the equipment connected to the secondary side of the transformer.