1. What is the other name for distribution factor ?
Ans: Breath factor
2. What is the value of distribution factor for a uniformly distributed 3 phase winding.
Ans: Distribution factor for a uniformly distributed 3 phase winding with 60 phase spread is 0.955.
3. What is mean by " armature reaction " of a synchronous machine ?
Ans: The effect of armature flux on the main field flux is known as armature reaction. armature reaction has Shape changing effect on unity pf. fully demagnetizing at zero pf lagging condition and fully magnetizing at zero pf leading.
4. What is the effect of armature reaction for an alternator for zero power factor lagging ?
Ans: Wholly demagnetizing
5. Which parameter of load effect the armature reaction of an alternator ?
Ans: power factor of load
6. Does the armature mmf of an alternator delivering a capacitive load magnetize or demagnetize the main field ?
Ans: Magnetizes
7. When the load on alternator is varied, its terminal voltage also found to vary why ?
Ans: With the variation in the load on an alternator, voltage drop due to 1. Armature resistance 2. armature leakage reactance 3. on account of armature reaction vary , so its terminal voltage varies.
8. By which tests synchronous reactance of synchronous machine is determined ?
Ans: By open circuit and short circuit test synchronous reactance of synchronous machine is determined.
10. Why is the short circuit characteristics of an alternator is linear ?
Ans: The short circuit characteristic is normally straight line through the origin because the net excitation is so small that there is no saturation in the magnetic circuit.
11. What do you mean by the short circuit characteristic of an alternator ?
Ans: The short circuit characteristic of an alternator is a curve (usually straight line passing through the origin) plotted between short circuit current and field current while the alternator being driven at its rated speed.
12. What are the effect on voltage regulation of an alternator of power factor 1. at lagging power factor and 2. at leading power factor
Ans: The regulation of an alternator is positive and increase with decrease with lagging power factor. The regulation of an alternator improves first with decrease in leading power factor become unity and further decrease in leading power factor makes the regulation negative and increasing.
13. Why voltage regulation of alternator is negative for leading power factor ?
Ans: When the power factor is leading, the effect of armature flux is to assist the main flux , hence to generate more emf and so to increase the terminal voltage when the alternator is loaded. Thus the terminal voltage of an alternator decrease when the load of leading power factor (capacitive load) is thrown off and voltage regulation is negative.
14. What are the different method of finding out the voltage regulations in alternators ?
Ans : 1. Synchronous impedance method 2. ampere turn method 3. potier for zero power factor method
15. Name the method giving the pessimistic value of the regulation of an alternator.
Ans: Synchronous impedance or emf method
16. Why does synchronous impedance method give a poorer voltage regulation ?
Ans: In synchronous impedance method of determination of voltage regulation synchronous reactance is assumed to be constant while actually it varies with saturation (at low saturation its value is higher because the effect of armature reaction is larger than that at high saturation ).
17. Which method of regulation is called pessimistic and why ?
Ans: Synchronous impedance or emf method of determination of voltage regulation of an alternator is pessimistic method.
18. What are the use of potier tringle ?
Ans: Potier triangle is used in determination of voltage regulations of an alternator.
19. Which quantity is used to determined using the zero power factor characteristic of a synchronous machine ?
Ans : Leakage reactance drop , voltage drop due to armature reaction and armature reaction ampere turns.
20. What are the characteristics required for potier method of computing voltage regulation ?
Ans: OCC, SCC and zero power factor full load voltage characteristic