GE Multilin 489 Instruction Manual page 194

5–84
Courtesy of NationalSwitchgear.com
GE Multilin
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FIGURE 5–22: Voltage Dependent Overload Protection at 100% Voltage
Unbalance Bias
Unbalanced phase currents will cause additional rotor heating that will not be accounted
for by electromechanical relays and may not be accounted for in some electronic
protective relays. When the generator is running, the rotor will rotate in the direction of the
positive sequence current at near synchronous speed. Negative sequence current, which
has a phase rotation that is opposite to the positive sequence current, and hence, opposite
to the rotor rotation, will generate a rotor voltage that will produce a substantial rotor
current. This induced current will have a frequency that is approximately twice the line
frequency, 100 Hz for a 50 Hz system or 120 Hz for a 60 Hz system. Skin effect in the rotor
bars at this frequency will cause a significant increase in rotor resistance and therefore, a
489
VOLTAGE DEPENDENT
OVERLOAD PROTECTION at 100% V
3 4 5 6
MULTIPLES OF FULL LOAD AMPS
489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 5: SETPOINTS
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808829A3.CDR