说明：  The under frequency relay is a solid state device that functions to protect the load in the event generator frequency decreases below preset limits. It actuates when the frequency decreases to 55 hertz for 60-hertz operation and 46 hertz for 50-hertz operation. Upon actuation, contacts within the relay close to signal the annunicator and open to de-energize the generator breaker (contactor), resulting in a display of the fault condition and removal of the load the generator.