GE 489 User Manual

4-24 489 Generator Management Relay
GE Power Management
4.6 S5 CURRENT ELEMENTS 4 SETPOINT PROGRAMMING
4
The 489 has a definite time alarm and inverse time overcurrent curve trip to protect the generator rotor from overheating
due to the presence of negative sequence currents. Pickup values are negative sequence current as a percent of generator
rated full load current. The generator FLA is calculated as:
Negative sequence overcurrent maximum time defines the maximum time that any value of negative sequence current in
excess of the pickup value will be allowed to persist before a trip is issued. The reset rate provides a thermal memory of
previous unbalance conditions. It is the linear reset time from the threshold of trip.
Unusually high negative sequence current levels may be caused by incorrect phase CT wiring.
Figure 4–3: NEGATIVE SEQUENCE INVERSE TIME CURVES
Generator FLA
Generator Rated MVA
3 Rated Generator Phase-Phase Voltage×
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NOTE

GE 489 Specifications

General

Brand	GE
Model	489
Category	Relays
Language	English