AC Distribution Flashcards
Split Bus System
Constant 400hz generators
Not parallel so phases do not need to match
Not designed to connect in parallel
Generator fail on split bus system
Bus bar can be supplied by one generator via busbar tie breakers
AC Distribution Parallel
Generators are on the same busbars. Full load sharing
3 phases need to be synced
Same frequency
Same voltage
Same phase
Generator Control Unit (GCU)
Fault sensed GCU opens the generator circuit breaker
Exciter control breaker tripped
Generator disconnected from it bus bar and prevented from producing electricity
Generator Control unit protection against
Ac generator over voltage
AC generator under voltage
Under frequency
Over speed
Excess current
Differential fault
Load Sharing
Control needed to ensure equal share of load
Real load + reactive load
Load Sharing Real Load is
Is the actual working load output - real power
Direct related to mechanical power supplies to alternator drive
CSDU or engine
Real Load Sharing is achieved by
Controlling the CSDU and adjusting the torque at its output shaft
Load Sharing - Reactive Load
Sum of inductive and capacitive currents and voltages expressed in kVAR
Reactive Load Sharing is achieved by
Controlling voltage output of each generator connected in parallel
Voltages identical reactive loads on each generator will be the same
Load Shedding
Reducing services when alternator failed
Split Bus system
Each generator feeds it own bus run independently
Parallel bus systems
Generators can be connected to the same bus
What happens in a split bar generator failure
Generator is cut off from it load bus
Bus tie breaker closes
Working generator able to feed to both load buses
APU can then take over
Generator failure in a parallel bus system
Generator cut off from system
Load busses will be fed from remaining generators connected to it.
Parallel Generators
Frequency/Voltage and phase sequence are the same
Not required on engine start though
Generator Control Unit
GCU automatically opens generator circuit breaker
Will trip exciter control breaker/relay
Generator disconnected from bus bar and prevented from producing electricity
GCU provides protection for
AC generator over voltage
AC generator under voltage
Under frequency
High frequency
Excess current
Differential faults
GCU connected to each generator and has direct input from fire handle
Real load sharing is achieved by
Controlling the constant speed drive unit
Reactive load sharing
Achieved by controlling the voltage output
