DC GENERATOR PRINCIPLE AND WHY ARE USED COMMUTATOR IN DC GENERATOR ??
21 hours ago VIRENDRA CHAUHAN
dc-generator-principle-used-commutator-dc-generator
DC GENERATOR AND COMMUTATOR
The initial stage of electricity was of the d. c. form. D. C. generators were developed after obtaining the electricity from the chemical effect so there was much importance of d. c. generators.
At present, generation, transmission, distribution and applications are in the a. c. form so the importance of d. c. generator has reduced.
It finds application in d. c. arc welding etc.
In this chapter, we shall study the principle of operation, construction, types, characteristic, armature reaction etc. of d. c. generator.
PRINCIPLE OF D.C. GENERATOR
D.C. GENERATOR CONVERTS MECHANICAL ENERGY IN TO ELECTRICAL ENERGY.
Let us first understand this.
Field winding produces magnetic field in d. c. generator. Armature is coupled to the prime mover.
Prime mover produces torque so the armature rotates.
The armature cuts the magnetic field so the emf is induced in the armature.
When load is connected to the armature, electric current flows from the armature conductors, through load and back to the armature conductors.
Now, as current flows through the armature and it is in the magnetic field, torque is produced due to it.
This torque is called the back torque because the direction of this torque is opposite to the torque of the prime mover.
If the load on the generator is increased, the back torque increases so the torque of the prime mover also increases and the input power to the prime mover increases.
In this way, the generator converts mechanical energy in to electrical energy.
Let us now understand how d. c. generator produces emf.
A coil abcd is kept in the magnetic field and it is rotated in the clockwise direction.
Conductors a b and c d cut the magnetic field and as a result, the emf is induced in them.
This emf is,
e = B l v volt
Where, B = magnetic flux density in tesla
l = length of conductor in meters
v = Velocity pf conductor in m/Sec.
Direction of the induced emf can be found from Fleming’s right hand rule.
Stretch the fore finger, middle finger and the thumb of your right hand mutually perpendicular to one another.
Keep the fore finger in the direction of the magnetic field and thumb in the direction of motion of the conductor, then the middle finger shows the direction of emf induced in the conductor.
The figure shown, the coil rotates in the clockwise direction so conductor a b goes in the upward direction.
So the direction of emf induced in it is from a to b. Conductor c d goes in the downward direction so the direction of emf induced is from c to d Conductor b c travels in the direction parallel to the field so no flux is cut by it and no emf is induced in it.
DC GENERATOR COMMUTATOR
NEED FOR DC GENERATOR COMMUTATOR
EMF INDUCED IN THE CONDUCTOR
First, we shall see that the emf induced in d. c. generator is a. c.
Then we shall study that how it is converted in to d. c. with the help of commutator.
Rings and brushes are used to take the emf outside.
As shown in figure. lead ‘a’ of the armature coil be connected to the ring P. and lead ‘b’ be connected to ring Q.
Brush R is kept on ring P and brush S is kept on ring Q.
Load RL is joined across brushes R and S. Electric current flows in the direction a b c d Q S Y X R P a. Current through the load RL flows in the direction from Y to X.
EMF INDUCED AFTER 180° ROTATIONS OF COIL
After rotation of 180° positions of conductors a b and c d are inter changed.
So the direction of emf induced in them reverses. Electric current flows in the direction d c b a P R X Y S Q d.
Now the current through the load flows in the direction from X to Y.
Thus, the direction of current reverses art every half rotation.
Hence, the emf induced in the armature
is alternating in nature.
USE OF SPLIT RING
Now Instead of taking two separate ring, and split it in to ” let us take a single ring. and split it in halves and separate them by providing insulate between them.
Join leads a and b to the halves as shown in figure.
In this condition the current flows in the direction a b c d Q ‘Y X R P a that means the current through to load flows from Y to X.
USE OF SPLIT RING
After the rotation of 180° the positions of the conductors will be interchanged at the same time, positions of the halves of the rings will also be Interchanged.
But, lead a will remain connected to P and b will remain connected to Q. Now part of the Angle P will face brush S and Q will face the brush R.
Direction of emf reverses in conductors a b and c d but if we observe carefully, it will be found that the direction of current through the load remains the same i.e., from Y to X.
If we now take two coils, we have to make four parts of the ring and if we take 8 coils.
we have to divide the ring in to 16 parts.
So we have to divide the ring in to parts double the number of Ring with such more numbers of parts is called commutator.
This commutator is made of stripe of copper with mica insulation between the adjacent strip one end the lead of armature coil is connected.
Brushes made of carbon are placed on the commutator.
If we now take two coils, we have to make four parts of the ring and if we take 8 coils.
we have to divide the ring in to 16 parts.
So we have to divide the ring in to parts double the number of Ring with such more numbers of parts is called commutator.
This commutator is made of stripe of copper with mica insulation between the adjacent strip one end the lead of armature coil is connected.
Thus, the emf induced in the armature is A.C. but it is converted in to D.C. using the commutator.
NOW WE HAVE MORE LEARN ABOUT MACHINE DC GENERATOR COMMUTATOR, DC GENERATOR PRINCIPLE AND MORE ABOVE KNOWLEDGE.
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