Page 158 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

There are several types of direct current , all of them depends up on the value of the current in value of time. A
constant DC current shows no variation in value over a period of time. Both varying and pulsating DC current
have a changing value plotted against time. The pulsating DC current variations are uniform and repeat at regular
intervals.

Generation of –AC

The shape of the voltage wave form generated by a coil rotating in a magnetic field is called a sine wave. The
generated sine wave voltage varies in both voltage value and polarity. If the coil is rotated at a constant speed
the number of magnetic lines of force cut per second varies with the position of the coil. When the coil is moving
parallel to the magnetic field it cut no lines of force therefore no voltage is generated at these instant. When
the coil is moving at right angles to the magnetic field it cuts the maximum number of lines of force . Therefore
maximum or peak voltage is generated at this instant .Between these two points the voltage varies according to
the sine of the angle at which the coil cuts the lines of force.

The coil shown in five specific position in figure .These are intermediate positions which occur during one complete
revolution of the coil position. The graph shows how the voltage increases and decreases in amount during one
rotation of the loop. Note that the direction of the voltage reverses each half cycles. This is because for each
revolution of the coil each side must first move down and then up through the field.

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CITS : Power - Electrician & Wireman - Lesson 26-29