• 80-95% Stator earth fault protection (measured or calculated 3Vo) (59GN)• Rotor earth fault protection (with external COMBIFLEX RXTTE4 injectionunit) (64F)• Underimpedance protection (21)• Voltage Controlled/Restrained Overcurrent protection (51C, 51V)• Turn-to-Turn & Differential Backup protection (directional NegativeSequence. Overcurrent protection connected to generator HV terminal CTslooking into generator) (67Q)• Stator Overload protection (49S)• Rotor Overload protection (49R)• Loss of Excitation protection (directional pos. seq. OC protection) (40)• Reverse power/Low forward power protection (directional pos. seq. OCprotection, 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/undervoltage protection (27x, 59x, 47)• Generator out-of-step detection (based on directional pos. seq. OC) (78)• Inadvertent generator energizing10.1.2.4 Inadvertent generator energization SEMOD151947-4 v2When the generator is taken out of service, and stand-still, there is a risk that thegenerator circuit breaker is closed by mistake.Three-phase energizing of a generator, which is at standstill or on turning gear, causesit 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 todraw 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% to70% 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% ratedvoltage) are representative of weaker systems.Since a generator behaves similarly to an induction motor, high currents will developin the rotor during the period it is accelerating. Although the rotor may be thermallydamaged from excessive high currents, the time to damage will be on the order of afew seconds. Of more critical concern, however, is the bearing, which can be damagedin a fraction of a second due to low oil pressure. Therefore, it is essential that highspeed tripping is provided. This tripping should be almost instantaneous (< 100 ms).Section 10 1MRK 505 370-UUS AMultipurpose protection272 Busbar protection REB670 2.2 ANSIApplication manual
