144 Electrical Power Systems Technology
they rotate. No current is induced into the conductors at position A, and
the resulting current flow through the load will be zero. If the conductors
are rotated 90° in a clockwise direction to position B (Figure 6-3B), they
will pass from the minimum lines of force to the most concentrated area of
the magnetic field. At position B, the induced current will be maximum,
as shown by the waveform diagram of Figure 6-3F. Note that the induced
current rises gradually from the zero reference line to a maximum value at
position B. As the conductors are rotated another 90° to position C (Figure
6-3C), the induced current becomes zero again. No current flows through
the load at this position. Note, in the diagram in Figure 6-3F, how the in-
duced current drops gradually from maximum to zero. This part of the
induced AC (from 0° to 180°) is called the positive alternation. Each value
of the induced current, as the conductors rotate from the 00 position to the
1800 position, is in a positive direction. This action could be observed vi-
sually if a meter were connected in place of the load.
When the conductors are rotated another 90° to position D (Figure
6-30), they once again pass through the most concentrated portion of the
magnetic field. Maximum current is induced into the conductors at this
position. However, the direction of the induced current is in the opposite
direction from that of position B. At the 270 position, the induced current
is maximum in a negative direction. As the conductors are rotated to posi-
tion E (same as at position A), the induced current is minimum once again.
Note, in the diagram of Figure 6-3E, how the induced current decreases
from its maximum negative value back to zero again (at the 360° position).
The part of the induced current from 180° to 360° is called the negative al-
ternation. The complete output, which shows the induced current through
the load, is called an AC waveform. As the conductors continue to rotate
through the magnetic field, the cycle is repeated.
AC Sine Wave
The induced current produced by the method discussed above is in
the form of a sinusoidal waveform or sine wave. This waveform is referred
to as a sine wave because of its mathematical origin, based on the trigono-
metric sine function. The current induced into the conductors, shown in
Figure 6-3, varies as the sine of the angle of rotation between the conductors
and the magnetic field. This induced current produces a voltage. The in-
stantaneous voltage induced into a single conductor can be expressed as:
Vi = Vmax × sin θ