2) Explain, using diagrams, armature reaction in a dc motor, the effects it has on the motor and methods to reduce it.
Explanation:
DC motor: A DC motor is any class of electrical machines that converts direct current electrical power into mechanical power. The most common types rely on magnetic fields.
Armature: The part of an electrical motor or generator that produces an electric current when it turns in a magnetic field.
Magnetic flux: Magnetic flux is the number of magnetic field lines (also called as magnetic flux density) passing through A closed surface such as conducting coil. The SI unit of magnetic flux is the weber(Wb).
So in this case, a DC motor, two sorts of magnetic(attractive) fluxes are available, ‘armature flux’ and ‘primary
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The armature flux superimposes with the primary or main field flux and, henceforth, aggravates the fundamental field flux (as appeared in third figure of above picture). This impact is called as armature reaction in DC motors.
The adverse effects of Armature Reaction
The effect of armature reaction is well illustrated in the figure below
1) Armature response debilitates the principle flux. If there should arise an occurrence of a DC generator, weakening of the fundamental flux lessens the produced voltage.
2) Armature response mutilates the fundamental flux, subsequently the position of M.N.A. gets moved (M.N.A. is opposite to the flux lines of fundamental flux). Brushes ought to be set on M.N.A., else, it will prompt starting at the surface of brushes. Thus, because of armature response, it is difficult to decide the precise position of M.N.A.
3) For a loaded DC generator, MNA will be moved toward the pivot (direction of rotation). Then again, for loaded DC motor, MNA will be moved in the course inverse to that of the rotation.
Methods to reduce
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