Generator relaying for single-axis short circuits

FOR FEAR that overcurrent relays might trip off the unit on overload when it is needed most, generators are usually not provided with relays to respond to balanced external faults. This is satisfactory practice because balanced faults on the system can be tolerated by the generator for an appreciable time. However, experience now indicates that the more closely designed modern generators should be provided with relays to detect the presence of unbalanced external faults that are not cleared in a proper time, since these may result in damage to the generator.