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.
Sensitive Directional Power
The 489 provides low forward and reverse power elements to prevent generator
movement from damaging the prime mover.
Each element has separate power pickup level and operating delay settings for alarms and trips.
Circuit Breaker Faults
The embedded circuit breaker fault feature in the 489 improves system reliability
without the additional cost of providing a separate circuit breaker fault relay.
When a circuit breaker fault is detected, the 489 can be configured to operate
one of its four available digital outputs to signal upstream equipment to quickly isolate the fault.
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