The machine which converts mechanical energy into A.C. electrical energy, is known as alternator.
An alternator works on the principle of Faradays Law’s of electromagnetic induction. The Working principle can be stated as, “Whenever a conductor cuts the lines of force, an e.m.f. is induced in that conductor”. This induced e.m.f. is directly proportional to the rate of change of flux and the number Of conductors.
Let there are two magnetic poles ‘N’ and ‘S’ as shown in Fig. 17.1 and a loop of conductor ABCD is placed in between the magnetic poles North and South. Let the loop ends are connected to two sliprings. Now whenever the conductor loop is rotated, it experiences the magnetic flux of different nature i.e. North and South. Let the direction of rotation be clockwise, the conductor be at position number l, where the direction of motion and direction of the flux are parallel so there will not be any linkage between the magnetic field and the conductor, resulting no e.m.f. When the conductor moves to position number 2, it experiences some linkage and producing the e.m.f. as shown according to the Fleming’s right hand rule the direction Can be found as outwards. At position number 3, the conductor has maximum linkage and resulting the production of e.m.f. maximum in outward direction. Thus there will be some e.m.f. induced in 4th position, and in fifth position, the motion of conductor and flux are parallel so no e.m.f. will be produced as shown in Fig. 17.1.
In the sixth position, the direction Of motion is reversed or say changed, the e.m.f. ‘induced will be inward as shown. At position seventh the maximum cutting angle will cause maximum production of e.m.f. as shown, at position 8th the e.m.f. will be comparatively less and at position number 1 same cycle will again start. 1
Fig. 17.1 Production of e.m.f.
Now as both conductor are connected to slip rings and if we plot a graph for the values of e.m.f. thus obtained a curve will be obtained generally known as sine wave. So the e.m.f. thus obtained will have the magnitude periodically changing after a fixed interval of time, such e.m.f. is known as A.C. and the machine producing A.C. is called alternator. In alternator we are having more number of conductors, which are systematically placed over the armature to obtain a smooth curve.