10/03/2020

Alternator Interview Question Answer - 3

What is direction of the alternator voltage and bus bar (a) Fully darkness and (b) Fully brightness period of lamp during synchronizing of alternators?

During synchronizing of two alternators

Fully darkness

• The alternator voltage is direct phase opposition to the bus bar voltage.

Fully brightness

• The alternator voltage is in phase with bus bar voltage.

How many phase should be synchronize in order to synchronize three phase alternators?

• Only one phase

What is resultant emf if the two alternators are in exact synchronism?

• Zero

Which alternator works as (a) Motor (b) Generator due to any uncertainty of synchronized two alternators?

• Due to any uncertainty of the synchronized conditions of the alternator, synchronizing current flows in the local circuit.
• When the synchronizing current flows is in the same direction as that of emf that machine acts as a generator.
• Similarly, when the synchronizing current flows in the opposite direction of the emf that machine acts as a motor.

What is happened when two alternators having slightly different voltages under synchronized condition?

Synchronizing of alternators – Slight different voltage

• Under synchronized condition if the voltage of alternator A is increased that of alternator B, the resultant voltage is in phase with voltage A which sets up synchronizing current.
• This synchronizing current is 900 lagging behind of resultant voltage. This lagging current produces demagnetizing effect on the alternator A therefore its voltage is reduced.
• The alternator B runs as a synchronous motor, taking current of 900 leading therefore its field is strengthen thus its voltage is increased. These two voltages act together resulting stable condition established.

When two alternators are properly synchronized, distribution of load on each alternator depends upon which parameters?

• When two alternators are properly synchronized, distribution of the load on each alternator depends upon power input to its prime – mover.

Describe the effect of excitation on the two synchronized alternator.

Effect of steam supply on synchronized alternator

• Let us consider that two alternator A and B are synchronized.
• The excitation of the both alternators is same.
• If the steam supplies of the alternator A increases, its active power increases. Similarly the active power output of the alternator B decreases.
• However there is no effect on the sharing of the reactive power between two alternators.

Describe the condition for maximum power output in the alternator.

• Load angle or torque angle is equal to 900

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