The generator used to convert mechanical energy into electrical energy. According to the output power, the generator classified into two types;
- AC Generator
- DC Generator
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An AC generator produces an alternating power and DC generator produces a direct power. Both generators work based on the principle of Faraday’s law of electromagnetic induction.
According to the faraday’s law, when a conductor moves in a magnetic field and cuts the flux, it induces an electromotive force (EMF) in a conductor. And the magnitude of this flux depends on the rate of change of flux. The current will pass through the conductor due to the EMF.
Now, let’s understand the working principle of the DC generator.
Working Principle of DC Generator by Single loop Generator
To understand the working of DC generator, take a single loop generator. The figure of this generator is as shown in the below figure.
A loop made from two conductors. Conductor-1 is AB and conductor-2 is CD. A single loop ABCD made from these conductors.
As shown in the above figure, a rectangular loop of a conductor (ABCD) rotates between two magnets. The magnets can be a permanent magnet or electromagnet. It is used to create a magnetic field. The direction of the magnetic field is always from N-pole to S-pole.
When the loop rotates, it cuts the magnetic flux lines. And it induces EMF in a loop. This loop is a closed path. So, the current will flow through the loop. The direction of current determined by the Fleming’s Right-Hand Rule.
In Fleming’s Right-hand Rule, thumb, index finger and middle finger of right-hand makes perpendicular to each other. Then thumb indicates the direction of rotation of loop, index finger indicates the direction of the magnetic field, and the middle finger indicates the direction of the flow of current through the loop.
Now for the above arrangement, if we find the direction of the current, it will be from A to B in conductor-1 and C to D in conductor-2.
Now, the loop rotates inside the magnetic field and it comes vertical position. Conductor CD is on top and AB is the opposite side of CD. This arrangement is as shown in the below figure.
Here in this condition, there is no chance to cut flux lines because the loop is perpendicular to the flux lines. Therefore, EMF is not induced in this condition.
Now, the loop further rotates and again comes in a horizontal position. The left conductor is AB and the right conductor is CD. This arrangement is as shown in the below figure.
This condition is opposite to the first condition. Here, the loop is parallel to the flux lines. And so, the flux cutting is maximum. So maximum EMF will produce in this condition.
If you apply Fleming’s Right-Hand Rule and find the direction of the current, it will be from B to A in conductor-1 and D to C in conductor-2. This direction of current in the opposite direction than the direction of current in the first case.
The loop completes half rotation and the current complete half cycle. So, we can conclude that, when the loop is parallel with the magnetic flux line, the current is zero and when the loop is perpendicular to the magnetic flux line, the current is maximum.
The generator is also working on this principle. But here we have seen that the current changes its direction. This must not happen in the case of DC.
So, the commutator is used to avoid the reversal of current and it produces DC current.
Working Principle of Generator with Commutator and Brush
The end terminals of the loop are connected with commutators (p and q). The commutators are connected with brushes and load as shown in the below figure.
Now in the first case, the direction of current is by showing the arrowhead. The current will flow ABXYCD. In this condition, brush-1 is connected with commutator p and brush-2 is connected with commutator q. Brush-1 is positive and brush-2 is negative.
So, the direction of current through the load is X to Y.
In the second case, the current will flow DCXYBA. In this condition, brush-1 is connected with commutator q and brush-2 is connected with commutator p. The polarity of brushes remains as it is.
Hence, the direction of current from the load is X to Y which is similar to the previous case. Now if you make the current waveform, it is not pure DC. It will be pulsating DC as shown in the below figure. One complete rotation of the loop generates one cycle of current.
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