SM Field Overcurrent/ Undercurrent

The 869 relay provides monitoring of overcurrent and loss of DC field

excitation input to the rotor of a synchronous motor. These elements

respond to DC current input from the direct current transducer.

SM Field Overtemperature

The 869 relay provides protection of the rotor winding against overheating

by exploiting the direct proportionality between temperature and

resistance. This elements responds to rotor resistance to detect rotor

temperature. When magnitude of the field resistance or temperature

exceeds the Pickup level for the time specified by the Pickup Delay setting.

SM Field Overvoltage/ Undervoltage

Excitation system output voltage to the rotor is monitored using these

elements, corresponding to DC Field voltage measured across the field

winding or exciter terminals. DC voltage is brought to the relay terminals

through the voltage divider network, provided with the relay.