Introduction

Introduction

In the last chapter we have seen how an e.m.f. gets induced in an alternator. As long as the alternator terminals are open i.e. no load is connected to an alternator, the induced e.m.f. is same as the voltage available at the terminals. Thus terminal voltage per phase V_ph and induced e.m.f. per phase E_ph are same as long as alternator is on no load.

But when the alternator is loaded, the armature of an alternator carries current. We know that, any current carrying conductor produces its own flux. Hence on load, armature of an alternator produces its own flux called armature flux. This flux has significant effect on the performance of an alternator on load. The terminal voltage V_ph no longer remains same as induced e.m.f. E_ph on load conditions. The performance of an alternator on load is mathematically expressed by a parameter called voltage regulation.

This chapter explains the effect of the armature flux on the performance of an alternator and various analytical and graphical methods of finding the voltage regulation of an alternator.

Parameters of Armature Winding

There are three important parameters of an armature winding of an alternator. These are,

1. Armature resistance R_a

2. Armature leakage reactance X_L

3. Reactance corresponding to armature reaction

Let us discuss these three parameters in detail which will help us to draw an equivalent circuit of an alternator. The equivalent circuit and the concept of synchronous impedance plays an important role in determining the regulation of an alternator.