Commutator !!
Seriously misunderstood component of the motor, and the part that is the prime reason why DC motor is able to function, the commutator is the object of the day.
But first things first. Lets have a background check on DC motor.
A DC motor consists of 4 major parts.
Stator
Rotor
Commutator
Brush Contact
Image Credits: http://www.evworks.com.au
Stator: It's job is simple and important. Create the magnetic field powerful enough to drive the rotor. It can be either permanent magnet or contain field windings.
Rotor: It links with the stator field and develops a torque to rotate. It contains rotor coils connected to the ccommutator.
Now comes the hero of the day.
Commutator:
a. It aids the rotor in maintaining a constant N-S pole with respect to the stator field.
b. It helps rotor generate the required torque.
So how does it actually help the rotor ?
Simple laws of electromagnetism !!!
Consider this simplified front view of a DC motor.
Stator: Red
Rotor: Yellow
Brushes: Blue
Commutator: Black
If DC is applied to the stator winding, a field is generated. Consider the north and south pole created across the stator as shown in the figure.
The brushes are connected to the commutator. The armature winding originates from the commutator and passes through the slots in the rotor. For eg., armature winding would commence from commutator 'a', pass through rotor slot 'A', pass through rotor slot 'C' and finally terminate at commutator 'c'. So in this case current flows from commutator 'a', to rotor coil 'A', to rotor coil 'C' and returns to the source via 'c'.
Application of right hand thumb rule would give the rotor magnetic field, with the N-S poles as shown. These are just the basics of Electromagnetism. Now comes the real role of commutator.
Look into the diagram carefully.
The north pole of rotor and that of stator would repel each other. Stator cannot move, and hence all the force would be exercised on the rotor. This force would create a torque, subsequently resulting in anticlockwise rotational motion. Thus the rotor would come to a new position now.
Now looking at the diagram we can see the commutator 'a' which was initially connected to the positive terminal through brush, is now connected to the negative terminal. But a noteworthy point is that, the rotor magnetic field is still at the same position with respect to stator field (or might shift slightly). This is an important observation. Why on earth is it important ?????? Let's see...
Consider a DC motor without commutator. The rotor winding would be connected to the source by slip rings , as in a 3 phase slip ring induction motor.
Referring to the diagram above, the DC motor is similar to the previous one; only difference being the absence of commutator and brush. Initially the rotor would experience an anticlockwise torque. It would rotate until the N-pole of the rotor reaches the S-pole of the stator.
What after that ???
Nothing at all. It wont move an inch. It would get locked.
Then how does having commutator help ???
As I said earlier, even though the rotor or the commutator rotates, the resultant field of the rotor is steady or constant with respect to the stator. This is the job of the commutator; to maintain a constant rotor field with respect to the stator. Hence the rotor would constantly experience a torque due to the interaction between stator and rotor field.
Thus as stated earlier, the DC motor is able to operate because of the commutator. It is one of the most important part of DC motor.
See it's that simple !!!
Would catch up with some interesting facts and explanation. Till then Adios !!
But first things first. Lets have a background check on DC motor.
A DC motor consists of 4 major parts.
Stator
Rotor
Commutator
Brush Contact
Image Credits: http://www.evworks.com.au
Stator: It's job is simple and important. Create the magnetic field powerful enough to drive the rotor. It can be either permanent magnet or contain field windings.
Rotor: It links with the stator field and develops a torque to rotate. It contains rotor coils connected to the ccommutator.
Now comes the hero of the day.
Commutator:
a. It aids the rotor in maintaining a constant N-S pole with respect to the stator field.
b. It helps rotor generate the required torque.
So how does it actually help the rotor ?
Simple laws of electromagnetism !!!
Consider this simplified front view of a DC motor.
Stator: Red
Rotor: Yellow
Brushes: Blue
Commutator: Black
If DC is applied to the stator winding, a field is generated. Consider the north and south pole created across the stator as shown in the figure.
The brushes are connected to the commutator. The armature winding originates from the commutator and passes through the slots in the rotor. For eg., armature winding would commence from commutator 'a', pass through rotor slot 'A', pass through rotor slot 'C' and finally terminate at commutator 'c'. So in this case current flows from commutator 'a', to rotor coil 'A', to rotor coil 'C' and returns to the source via 'c'.
Application of right hand thumb rule would give the rotor magnetic field, with the N-S poles as shown. These are just the basics of Electromagnetism. Now comes the real role of commutator.
Look into the diagram carefully.
The north pole of rotor and that of stator would repel each other. Stator cannot move, and hence all the force would be exercised on the rotor. This force would create a torque, subsequently resulting in anticlockwise rotational motion. Thus the rotor would come to a new position now.
Consider a DC motor without commutator. The rotor winding would be connected to the source by slip rings , as in a 3 phase slip ring induction motor.
Referring to the diagram above, the DC motor is similar to the previous one; only difference being the absence of commutator and brush. Initially the rotor would experience an anticlockwise torque. It would rotate until the N-pole of the rotor reaches the S-pole of the stator.
What after that ???
Nothing at all. It wont move an inch. It would get locked.
Then how does having commutator help ???
As I said earlier, even though the rotor or the commutator rotates, the resultant field of the rotor is steady or constant with respect to the stator. This is the job of the commutator; to maintain a constant rotor field with respect to the stator. Hence the rotor would constantly experience a torque due to the interaction between stator and rotor field.
Thus as stated earlier, the DC motor is able to operate because of the commutator. It is one of the most important part of DC motor.
See it's that simple !!!
Would catch up with some interesting facts and explanation. Till then Adios !!
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