ABB Relion 670 Series Applications Manual page 189

1MRK 511 407-UUS Rev. J
1. Transformer and line applications:
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2. Generator protection
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11.1.2.4 Inadvertent generator energization
When the generator is taken out of service, and stand-still, there is a risk that the generator circuit
breaker is closed by mistake.
Three-phase energizing of a generator, which is at standstill or on turning gear, causes it to
behave and accelerate similarly to an induction motor. The machine, at this point, essentially
represents the subtransient reactance to the system and it can be expected to draw from one to
four per unit current, depending on the equivalent system impedance. Machine terminal voltage
can range from 20% to 70% of rated voltage, again, depending on the system equivalent
impedance (including the block transformer). Higher quantities of machine current and voltage (3
to 4 per unit current and 50% to 70% rated voltage) can be expected if the generator is connected
to a strong system. Lower current and voltage values (1 to 2 per unit current and 20% to 40% rated
voltage) are representative of weaker systems.
Since a generator behaves similarly to an induction motor, high currents will develop in the rotor
during the period it is accelerating. Although the rotor may be thermally damaged from excessive
high currents, the time to damage will be on the order of a few seconds. Of more critical concern,
however, is the bearing, which can be damaged in a fraction of a second due to low oil pressure.
Phasor measurement unit RES670
Application manual
Underimpedance protection (circular, non-directional characteristic) (21)
Underimpedance protection (circular mho characteristic) (21)
Voltage Controlled/Restrained Overcurrent protection (51C, 51V)
Phase or Negative/Positive/Zero Sequence (Non-Directional or Directional) Overcurrent
protection (50, 51, 46, 67, 67N, 67Q)
Phase or phase-to-phase or Negative/Positive/Zero Sequence over/under voltage
protection (27, 59, 47)
Thermal overload protection (49)
Open Phase protection
Unbalance protection
80-95% Stator earth fault protection (measured or calculated 3Vo) (59GN)
Rotor earth fault protection (with external COMBIFLEX RXTTE4 injection unit) (64F)
Underimpedance protection (21)
Voltage Controlled/Restrained Overcurrent protection (51C, 51V)
Turn-to-Turn & Differential Backup protection (directional Negative Sequence.
Overcurrent protection connected to generator HV terminal CTs looking into generator)
(67Q)
Stator Overload protection (49S)
Rotor Overload protection (49R)
Loss of Excitation protection (directional positive sequence OC protection) (40)
Reverse power/Low forward power protection (directional positive sequence OC
protection, 2% sensitivity) (32)
Dead-Machine/Inadvertent-Energizing protection (51/27)
Breaker head flashover protection
Improper synchronizing detection
Sensitive negative sequence generator over current protection and alarm (46)
Phase or phase-to-phase or Negative/Positive/Zero Sequence over/under voltage
protection (27x, 59x, 47)
Generator out-of-step detection (based on directional positive sequence OC) (78)
Inadvertent generator energizing
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Section 11
Multipurpose protection
SEMOD151947-4 v2
183