Motor Principle
- An Electric motor is a machine which converts electric energy into mechanical energy. Its action
is based on the principle that when a current-carrying conductor is placed in a magnetic field, it
experiences a mechanical force whose direction is given by Fleming’s Left-hand Rule and whose
magnitude is given by F = BIl Newton.
- Constructionally, there is no basic difference between a d.c. generator and a
d.c. motor. In fact, the same d.c. machine can be used interchangeably as a
generator or as a motor. D.C. motors
are also like generators, shunt-wound or
series-wound or compound-wound.
- In Figure a part of multipolar d.c.
motor is shown. When its field magnets
are excited and its armature conductors are supplied with current from the supply mains, they experience
a force tending to rotate the armature. Armature conductors
under N-pole are assumed to carry current downwards (crosses)
and those under S-poles, to carry current upwards (dots). - By
applying Fleming’s Left-hand Rule, the direction of the force on
each conductor can be found. It is shown by small arrows placed above each conductor. - It will be
seen that each conductor can be found. It will be seen that each conductor experiences a force F
which tends to rotate the armature in anticlockwise direction. - These forces collectively produce a
driving torque which sets the armature rotating. - It should be noted that the function of a commutator in the motor is the same as in a generator.
- By
reversing current in each conductor as it passes from one pole to another, it helps to develop a continuous
and unidirectional torque.
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