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A three - phase alternator is wound with a 60 degree phase spread armature winding and develops 300 kVA. If the armature is reconnected utilizing all the coils for single-phase operation with a phase spread of 180 degree, the new rating of the machine will be
- a)300 kVA
- b)200 kVA
- c)100 kVA
- d)250 kVA
Correct answer is option 'B'. Can you explain this answer?
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A three - phase alternator is wound with a 60 degree phase spread arma...
kVA rating, αEf ∝ kd
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A three - phase alternator is wound with a 60 degree phase spread arma...
The given question is related to the rating of a three-phase alternator when the armature winding configuration is changed. Let's analyze the question step by step to understand the solution.
1. Initial Configuration:
- The alternator is wound with a 60-degree phase spread armature winding.
- The alternator develops a power of 300 kVA.
2. Armature Reconnection:
- The armature is reconnected to utilize all the coils for single-phase operation.
- The new configuration has a phase spread of 180 degrees.
3. Determining the New Rating:
- To find the new rating of the machine, we need to consider the power developed by each phase in the new configuration.
- In a three-phase system, the total power is divided equally among the three phases.
- In the initial configuration, the power developed by each phase is 300 kVA / 3 = 100 kVA.
4. Power Distribution in Single-Phase Operation:
- In the new configuration, the power developed by each phase will be different.
- Since the armature winding has a phase spread of 180 degrees, only two phases will be active at a time.
- Let's consider two cases to determine the power developed by each phase:
a) Case 1: Phase A and Phase B are active:
- In this case, the power developed by each phase is 100 kVA.
b) Case 2: Phase B and Phase C are active:
- In this case, the power developed by each phase is also 100 kVA.
- As we can see, in both cases, the power developed by each phase remains the same, which is 100 kVA.
5. New Rating of the Machine:
- Since the power developed by each phase remains the same in single-phase operation, the new rating of the machine will be the same as the initial rating.
- Therefore, the new rating of the machine will be 200 kVA (100 kVA per phase x 2 phases).
In conclusion, when the armature winding configuration of a three-phase alternator with a 60-degree phase spread is changed to a single-phase operation with a 180-degree phase spread, the new rating of the machine will be 200 kVA.
1. Initial Configuration:
- The alternator is wound with a 60-degree phase spread armature winding.
- The alternator develops a power of 300 kVA.
2. Armature Reconnection:
- The armature is reconnected to utilize all the coils for single-phase operation.
- The new configuration has a phase spread of 180 degrees.
3. Determining the New Rating:
- To find the new rating of the machine, we need to consider the power developed by each phase in the new configuration.
- In a three-phase system, the total power is divided equally among the three phases.
- In the initial configuration, the power developed by each phase is 300 kVA / 3 = 100 kVA.
4. Power Distribution in Single-Phase Operation:
- In the new configuration, the power developed by each phase will be different.
- Since the armature winding has a phase spread of 180 degrees, only two phases will be active at a time.
- Let's consider two cases to determine the power developed by each phase:
a) Case 1: Phase A and Phase B are active:
- In this case, the power developed by each phase is 100 kVA.
b) Case 2: Phase B and Phase C are active:
- In this case, the power developed by each phase is also 100 kVA.
- As we can see, in both cases, the power developed by each phase remains the same, which is 100 kVA.
5. New Rating of the Machine:
- Since the power developed by each phase remains the same in single-phase operation, the new rating of the machine will be the same as the initial rating.
- Therefore, the new rating of the machine will be 200 kVA (100 kVA per phase x 2 phases).
In conclusion, when the armature winding configuration of a three-phase alternator with a 60-degree phase spread is changed to a single-phase operation with a 180-degree phase spread, the new rating of the machine will be 200 kVA.
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