GE 489 Instruction Manual page 62

4.6 S5 CURRENT ELEMENTS 4 SETPOINT PROGRAMMING
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:
Generator Rated MVA
Generator FLA
= --------------------------------------------------------------------------------------------------------------------- -
×
3 Rated Generator Phase-Phase Voltage
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.
NOTE
4
Figure 4–3: NEGATIVE SEQUENCE INVERSE TIME CURVES
4-24 489 Generator Management Relay GE Power Management