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Which condition is not necessary for parallel working of an alternator ?
Same frequency
Same phase sequence
Same terminal voltage
Same KVA rating
Same KVA rating
Parallel working of alternators, also known as synchronizing, requires the incoming machine to match the busbar conditions exactly. While frequency, phase sequence, and terminal voltage must be identical to avoid circulating currents and synchronization surges, the KVA rating is not a condition for synchronization and can be different.
Parallel working of alternators, also known as synchronizing, requires the incoming machine to match the busbar conditions exactly. While frequency, phase sequence, and terminal voltage must be identical to avoid circulating currents and synchronization surges, the KVA rating is not a condition for synchronization and can be different.
E=2тАЛ╧АfN╧ХKwтАЛ тАФ EMF equation of an alternator
P=XsтАЛEVтАЛsin╬┤ тАФ Power transfer equation during parallel operation
When alternators are connected in parallel, they form a common busbar. Any mismatch in voltage magnitude results in reactive circulating currents, while a mismatch in phase angle or frequency causes real power circulating currents. The KVA rating is purely a measure of the machine's capacity; different-sized machines can share a load proportionally based on their individual capacities and governor characteristics.
Synchronizing must be done when the phase difference is zero.
A phase sequence mismatch would cause massive short-circuit currents.
Terminal voltage must be equal to avoid reactive power circulation between machines.
Alternators of different KVA ratings can operate together if their per-unit impedances are compatible.
Increased reliability of supply
Higher efficiency at partial loads
Complex synchronization circuitry required
Potential for large circulating currents if conditions are not met
Grid-connected power plants
Industrial captive power systems
Synchronizing is typically performed using synchroscopes or the three-lamp method.
Option D is the correct answer because KVA rating determines the load-sharing capability, not the synchronizing condition.
D is correct тАФ The KVA rating of alternators does not affect the synchronization condition; they can be connected in parallel regardless of their individual ratings.
Remember the mnemonic 'V-F-P-S': Voltage, Frequency, Phase sequence, and Synchronous phase are mandatory for parallel connection.