The field failure relay MRQ1protects synchronous generators against operation outside the stable operation area due to loss of excitation. When partial or complete loss of excitation occurs on a synchronous machine, reactive power flows from the system into the machine and the apparent impedance as viewed from the machine terminals goes into the negative X region in the R-X diagram.

The field failure relay MRQ1protects synchronous generators against operation outside the stable operation area due to loss of excitation. When partial or complete loss of excitation occurs on a synchronous machine, reactive power flows from the system into the machine and the apparent impedance as viewed from the machine terminals goes into the negative X region in the R-X diagram.