Correct Answer - Option 3 : Zero power factor method
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:
- The synchronous impedance method of calculating voltage regulation of an alternator is otherwise called as the EMF method.
- The synchronous impedance method or the EMF method is based on the concept of replacing the effect of armature reaction by an imaginary reactance.
- This method gives result which 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 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 also called a general method of voltage regulation.
- It is the most accurate method of voltage regulation.
- For calculating the regulation, it requires open circuit characteristics and zero power factor characteristics.
The following assumptions are made in this method.
- The armature resistance is neglected.
- The O.C.C taken on no-load accurately represents the relation between MMF and voltage on load.
- The leakage reactance voltage is independent of excitation.
- The armature reaction MMF is constant.
