Correct Answer - Option 2 : the EMF method
Concept:
Normally for voltage regulation calculation, we use the following methods.
1. Synchronous impedance or emf method
2. Armature turn or mmf method
3. Zero PF or Potier method
Synchronous impedance method (EMF Method):
- The synchronous impedance method of calculating voltage regulation of an alternator is otherwise called the EMF method.
- The synchronous impedance method or the EMF method is based on the concept of replacing the effect of armature reaction with an imaginary reactance.
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This method is not accurate as it gives a result that is higher than the original value. That's why it is called the pessimistic method.
- For calculating the regulation, the synchronous method requires the armature resistance per phase, the open-circuit characteristic, and the short circuit characteristic.
Armature turn method:
It is also known as the MMF method. It gives a value which is lower than the original value. That's why it is called an optimistic method.
To calculate the voltage regulation by MMF Method, the following information is required. They are as follows:
- The resistance of the stator winding per phase
- Open circuit characteristics at synchronous speed
- Field current at rated short circuit current
Potier triangle method:
- This method depends on the separation of the leakage reactance of armature and its effects.
- It is used to obtain the leakage reactance and field current equivalent of armature reaction.
- It is the most accurate method of voltage regulation.
- For calculating the regulation, it requires open circuit characteristics and zero power factor characteristics.