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For parallel operation alternator must have same
Excitation
KVA
Speed
Voltage
Voltage
For successful parallel operation of alternators, the terminal voltage of the incoming alternator must be exactly equal to the existing busbar voltage. Mismatch in terminal voltages leads to the flow of circulating reactive currents, which can damage the alternator windings or cause protection systems to trip.
For successful parallel operation of alternators, the terminal voltage of the incoming alternator must be exactly equal to the existing busbar voltage. Mismatch in terminal voltages leads to the flow of circulating reactive currents, which can damage the alternator windings or cause protection systems to trip.
EpтАЛ=4.44fN╬жKwтАЛ тАФ Induced EMF equation for alternator
IcircтАЛ=Z1тАЛ+Z2тАЛE1тАЛтИТE2тАЛтАЛ тАФ Circulating current due to voltage difference
Before connecting an alternator to an infinite bus, the 'synchronization' conditions must be met: equal frequency, equal phase sequence, equal phase angle, and equal terminal voltage. If the terminal voltages differ, the reactive power exchange occurs via the circulating current flowing through the low-impedance stator windings. If frequencies are mismatched, the machine will suffer from synchronizing power surges causing mechanical stress.
Terminal voltage matching is essential to prevent reactive current circulation.
Frequency must be identical to avoid power oscillations.
Phase sequence must be the same to prevent short-circuiting phases during closure.
Phase angle (or phase position) must be identical at the instant of switching.
Increases reliability of the power system.
Allows efficient loading by adding/removing units based on demand.
Requires complex synchronization equipment.
Synchronization errors can cause severe mechanical damage.
Power generating stations
Microgrids and industrial captive power plants
Excitation (Option A) is adjusted to control terminal voltage and reactive power, but it is not a requirement to have identical excitation settings on both machines.
KVA (Option B) refers to the rating; machines of different ratings can operate in parallel.
Speed (Option C) determines frequency (f=120PNтАЛ), so speed must be identical for machines with the same number of poles.
D is correct тАФ The terminal voltages of the incoming alternator and the busbar must be exactly equal to prevent uncontrolled circulating reactive currents.
Remember the mnemonic 'V-F-P-P': Voltage, Frequency, Phase Sequence, and Phase angle must be matched for successful synchronization.