Chapter : 2. Magnetic Effect of Current

DC Generator

DC Generator
A DC generator stands for direct current electric generator. A DC generator produces direct current. A DC generator is also called DC dynamo. A simple DC generator is shown in figure.

Construction of a DC generator : A simple DC generator consists of a coil of insulated copper wire. The coil is placed between the two poles of a strong horseshoe magnet. In actual practice, a large number of turns of the insulated copper wire are wound on a soft iron core.
The two ends of the coil are connected to the two halves of a split ring (R1, R2 called commutator). Two carbon brushes press against the two half–rings lightly. The current is taken out through the brushes B1 and B2.
Working of a DC generator : Let the coil ABCD be initially in the horizontal position, and be rotated anticlockwise. When the coil is rotated anticlockwise, the arm AB moves downwards and the arm CD moves upwards.
The coil during this motion cuts the magnetic lines of force and an induced current is produced in the coil. According to Fleming’s right hand rule, during the downward motion of the arm AB, the induced current flows from B to A in the arm AB, and from D to C in the arm CD. The current so produced is taken out through the two half–split rings, and the carbon brushes.
After half the rotation (rotation through 180º), the arms of the coil interchanged their positions; the arm AB comes to right and the arm CD to the left. Then the arm CD starts moving downwards, and the arm AB upwards. During this half–rotation, the induced current flows from C to D in the arm CD, and from A to B in the arm AB.
The two half–split rings (R1 and R2) rotate with the coil and touch the two carbon brushed (B1,B1) one by one. As a result, each carbon brush continues to have the same polarity, (+ or –). The brush B1 always remains positive (+) terminal, and the brush B1 remains negative (–) terminal. The current so produced is called direct current (DC).
DC generator differ from an AC generator : The basic design of AC and DC generators is similar. The two generators differ only in the design of slip rings at the ends of the coil wire. An AC generator use two full rings called slip rings, one at each end of the coil wire, while an DC generator has two half–rings (called split rings) of a commutator.

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