Working Principle of DC Generator by Single loop Gen.

To understand the working of the 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 is 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 permanent magnets or electromagnets and 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. Fleming’s Right-Hand Rule determines the direction of the current.

In Fleming’s Right-hand Rule, the thumb, index finger and middle finger of the right hand make perpendicular to each other. Then thumb indicates the direction of rotation of the loop, the 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 current direction, 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 comes vertical position. Conductor CD is on top, and AB is on 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 suitable 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 current direction, it will be from B to A in conductor-1 and D to C in conductor-2. This current direction is in the opposite direction than the current direction 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 current reversal, producing 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 associated with brushes and load, as shown below.

Now in the first case, the current direction 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 current direction from the load is X to Y, which is similar to the previous case. If you make the current waveform, it is not pure DC. Instead, it will be pulsating DC, as shown in the below figure. Finally, one complete rotation of the loop generates one cycle of current.