41
|
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.
|
42
|
How many phase should be synchronize in order to synchronize three phase
alternators?
|
|
Only one phase
|
43
|
What is resultant emf if the two alternators are in exact synchronism?
|
|
Zero
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44
|
Which alternator works as a ( a ) Motor ( b ) Generator due to any
uncertainty of synchronized two alternator?
|
|
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.
- When the
synchronizing current flows in the opposite direction of the emf that machine
acts as a motor.
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45
|
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.
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46
|
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.
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47
|
Describe the effect of excitation on the two synchronized alternator.
|
|
Effect
of excitation on synchronized alternator
- Let us consider that two alternator A and B are synchronized.
- Each alternator supplies one half of the active load and one half of
the reactive load.
- If the excitation of alternator A increases, its power factor reduces
but the reactive power supplied by its increases.
- Similarly the power factor of alternator B increases but reactive power
supplied by its decreases.
- However the effect of kW shares by the two alternators is negligible.
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48
|
Describe the effect of steam supply 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.
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49
|
Describe the condition for maximum power output in the alternator.
|
|
Load angle or torque angle is equal to 900
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