A discussion of degraded voltage relaying for nuclear generating stations

Nuclear generating stations utilize degraded voltage relaying schemes to protect electrical equipment against sustained low voltage conditions. Typical design involves the use of degraded voltage relays (DVRs) which, when actuated, automatically disconnect the safety buses from the degraded offsite power source and initiate reconnection to an alternate source such as the diesel generator. Although the industry recognizes the importance of ensuring that adequate voltage is supplied to critical plant equipment, the method of achieving this goal is a matter of ongoing discussion. Arguments are presented for and against automatic disconnection of the power source when a degraded voltage condition is sensed by the DVRs.