Motor
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A motor is a mechanism by which electrical energy is converted into mechanical energy both in principle and design a D.C. motor is the reverse of a D.C. generator.
Working Principal:
When a conductor carrying current is placed in a magnetic field, tends to move at right angle to the field.
In fig a two pole motor is shown under north and south poles. The current in coil under North Pole is inward while in coil under South pole it is outward as shown in fig. A. Force will act on both side of the coil which will tend to rotate the coil in the anticlock wise direction as given by the Fleming’s left hand rule as shown in fig. B. This force will act till the conductor are in the magnetic field. The motion however, is not smooth and to make the motor run smoothly. The single coil is replaced by several coils set at equal inclination to each other.
When a coil starts rotating , after a very short time the side of the coil B will come under the North pole and side A under the South pole .In this way the current in coil side B is inward while the coil side A it is outward, it is automatically changed with the help of the commutator . At this way again an anticlock wise known force known as Magnetic drag will act on the coil then the coil will rotate continuously in a definite direction.
D.C. motors can be classified into different types.There are three main types of D.C. motors.
- Series Wound Motor
- Shunt Wound motor
- Compound motor
Series Wound Motor:
In this motor the field winding is connected in series with the armature and carries the full armature current. The field winding has only a few turns of thick wire to keep the resistance low and hence to reduce the losses as shown in fig.. When the load on the motor is light only a small current is needed to produce the required torque therefore at light loads. The flux is weak and the sped is high. But on heavy load the current is large and consequently the flux is strong and the speed is low therefore the current of the motor depends upon the load
Usage:
The series motor is best suitable for tradition work because of its high starting torque. It is also used extensively for cranes fans and hoists.
Shunt Motor:
The motor in which the field winding is connected across that is in parallel with the armature terminals is called a shunt motor. It has a very large resistance to keep the losses low. By being wound with thin wire of a large number of turns A shown in fig
Usage:
shunt motor is generally used in blowers. Lathes and driving the shafts etc. Where constant speed is required although the load caries widely.
Compound Wound Motor:
This consists of two field coils, one containing large number of turns and is in parallel with armature and the other, containing only a few turns and is in series with the armature is called compound motor. This thus possesses the advantages of both the series and shunt wound motors.
Usage:
These motors are used where the load varies suddenly form. No load to full load as in punch presses rolling mills, printing press, flours mills etc.
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