Draw and explain working of universal motor. Give two applications of universal motor.
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Working of Universal Motor:

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A universal motor works on either DC or single phase AC supply. When the universal motor is fed with a DC supply, it works as a DC series motor. When current flows in the field winding, it produces an electromagnetic field. The same current also flows through the armature conductors. According to basic motor principle, when a current carrying conductor is placed in the magnetic field, it experiences a mechanical force. Thus mechanical force is exerted on the current carrying armature conductors and torque is produced on rotor. Therefore the rotor starts to rotate. 

When fed with AC supply, it still produces unidirectional torque. Because armature winding and field winding are connected in series, they carry same current. Hence, as polarity of AC voltage changes and current reverses its direction, the direction of current in armature conductors and magnetic field in the air-gap reverses at the same time. The direction of magnetic field and the direction of armature current reverse in such a way that the direction of force experienced by armature conductors remains same. Thus unidirectional torque is produced and motor continues to run in the same direction. Thus, regardless of AC or DC supply, universal motor works on the same principle as that of DC series motor. Since motor works on both the type of supply: AC or DC, it is referred as Universal motor.


Applications of Universal Motor: 1) Mixer and Food processor 2) Heavy duty machine tools 3) Grinder 4) Vacuum cleaners 5) Drills 6) Sewing machines 7) Electric Shavers 8) Hair dryers 9) Cloth washing machine

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Working of universal motor:

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i) Working of universal motor with DC supply:

 * When the universal motor is fed with a DC supply, then current flows in the field winding, it produces an electromagnetic field. The same current also flows through the armature conductors.

 * According to basic motor principle, when a current carrying conductor is placed in the magnetic field, it experiences a mechanical force and torque exerted on the current carrying armature conductors, therefore the rotor starts to rotate.

ii) Working of universal motor with AC supply:

 * When fed with AC supply, current flows through armature and field winding. So current carrying armature conductors are in magnetic field experiences mechanical force and ultimately produces unidirectional torque, because armature winding and field winding are connected in series, they carry same current.

 * Hence, as polarity of AC voltage changes and current reverses its direction, the direction of current in armature conductors and magnetic field in the air-gap reverses at the same time.

 * The direction of magnetic field and the direction of armature current reverses in such a way that the direction of force experienced by armature conductors remains same.

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Application of Universal Motor :

1) Mixer

2) Food processor

3) Heavy duty machine tools

4) Grinder

5) Vacuum cleaners

6) Refrigerators

7) Driving sewing machines

8) Electric Shavers

9) Hair dryers

10) Small Fans

11) Cloth washing machine

12) portable tools like blowers, drilling machine, polishers etc 


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Figure of Universal motor:

image 


Operation of universal motor on A.C. and D.C. supply:  

*A universal motor works on either DC or single phase AC supply. When the universal motor is fed with a DC supply, it works as a DC series motor. When current flows in the field winding, it produces an electromagnetic field. The same current also flows from the armature conductors. When a current carrying conductor is placed in an electromagnetic field, it experiences a mechanical force. 

*Due to this mechanical force, or torque, the rotor starts to rotate. The direction of this force is given by Fleming's left hand rule. 

*When fed with AC supply, it still produces unidirectional torque. Because, armature winding and field winding are connected in series, they are in same phase. Hence, as polarity of AC changes periodically, the direction of current in armature and field winding reverses at the same time. Thus, direction of magnetic field and the direction of armature current reverses in such a way that the direction of force experienced by armature conductors remains same. 

*Thus, regardless of AC or DC supply, universal motor works on the same principle that DC series motor works.  

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