Brief explanation of Armature Reaction in Telugu by #groot tom

Armature reaction is the effect on the main field flux of that flux set up by the currents in the armature winding. The effect is the same for both lap- and wave-wound machines. Armature reaction in d.c. generators Armature reaction is the effect on the main field flux of that flux set up by the currents in the armature winding. The effect is the same for both lap- and wave-wound machines. In a machine called the amplidyne, the armature reaction is utilised but in the d.c. generator (and the d.c. motor), armature reaction produces effects which are undesirable. For simplicity, a two-pole machine will be considered but the effects described are repeated for each pair of poles. Armature reaction effects are the same for all modes of operation of d.c. motors and generators. Fig. 3.7 shows the two main poles of a d.c. generator and the distribution of the magnetic flux which crosses the airgap and enters the armature. This is the flux distribution existing when the generator is on no load and it is seen to be symmetrically distributed with respect to the poles. The poles carry concentrated coils and the rectangular m.m.f. distribution set up when these coils carry current produce a rectangular flux distribution because the m.m.f. is acting on a uniform airgap and so the flux is proportional to the m.m.f. at any point.  Sign in to download full-size image FIG. 3.7. No-load flux distribution in a d.c. machine. The convention that has been used when drawing the diagram is that when the direction of the flux from the poles is downward, the waveform is drawn below the reference OX and when the flux is in an upwards direction, the waveform of flux distribution is drawn above this line. The vertical chain line drawn between the poles represents the geometrical neutral plane (G.N.P.) and under no load conditions, the magnetic neutral plane (M.N.P.) coincides with the G.N.P. This flux distribution can be shown on an oscilloscope if a search coil connected to a C.R.O. is made to rotate in the magnetic field. So far, the flux distribution due to the main poles only has been considered. The flux distribution that would exist if only the armature windings carried current will now be discussed. It is assumed in the diagram, Fig. 3.8, that the conductors are moving from right to left and hence by Fleming's right-hand rule, the direction of the e.m.f. induced in the conductors is as shown. If it is also assumed that the brushes are so placed on the commutator that they are always connected to coils lying in the middle of the interpolar gap, that is, to coils lying in the G.N.P., the ⊕ and ⊙ also represent the direction of the current in the armature conductors. Note that all the conductors lying between adjacent G.N.P.s carry current in the same direction.  Sign in to download full-size image FIG. 3.8. Flux produced by armature current in a d.c. machine. The effective m.m.f. of any winding is the resultant of the m.m.f. set up by each coil carrying a current. A single armature coil may be represented as shown in Fig. 3.9(a), the coil sides being numbered in this case by 1, 1′. Progressing round the armature from coil side 1, we come to coil side 1′ and then back to coil side 1 again. This coil is represented in a different way in Fig. 3.9(b). From 1 to 1′ below the coil, Fig. 3.9(a), the flux enters the rotor from the stator and from 1′ to 1 above the coil, the flux leaves the rotor and enters the stator.