The 489’s protection features include:

Generator stator differential

The 489 uses high speed dual slope differential protection to detect and clear stator phase faults.

Stator phase faults. Advanced CT saturation detection algorithms provide

additional supervision through the use of directional checks that

ensures that the fault occurs inside the generator before triggering a trip,

thus maintaining immunity to saturation that may be caused by external disturbances.

100% Stator Ground

100% stator ground fault protection is provided by an overvoltage element and an

adaptive differential voltage function that responds to third harmonic imbalances at the machine

terminals and neutral.

The 489 will compare the machine neutral voltage with the grounding

current to determine if the ground fault is internal or external to the generator.

Alternate Phase Distance

Two independent phase distance elements provide time-delayed backup protection

for generator faults that are not cleared by the main system and generator protection.

This distance characteristic compensates for unit delta/shunt power transformers

located between the generator and the end of the protection zone.