Unit 16
Alternating Current
Unit 16 Alternating Current
Objectives:
• Discuss differences between direct and
alternating current.
• Be able to compute instantaneous values
of voltage and current for a sine wave.
• Be able to compute peak, RMS, and
average values of voltage and current.
• Discuss the phase relationship or voltage
and current in a pure resistive circuit.
Unit 16 Alternating Current
• The single greatest advantage of
alternating current is that AC current can
be transformed and DC current cannot be
transformed.
• This allows high-voltage electrical power
to be distributed with smaller wires and
lower amperage.
• The electrical power is then transformed to
a lower voltage where it is needed.
Unit 16 Alternating Current
Alternating current flows first in one direction
and then in the other direction.
Unit 16 Alternating Current
A graph view of a square wave.
Unit 16 Alternating Current
A square wave alternating current produced by a
switch and two batteries.
Unit 16 Alternating Current
The sine wave is the most common of all the AC
wave forms.
Unit 16 Alternating Current
The sine wave is produced by rotating machines.
Unit 16 Alternating Current
One sine wave is 360 electrical degrees.
Unit 16 Alternating Current
The voltage at any point along the sine wave is
equal to the maximum, or peak, value times the
sine of the angle of rotation.
Unit 16 Alternating Current
As the loop approaches 90° of rotation, the flux
lines are cut at a faster rate.
Unit 16 Alternating Current
E(INST) = E(MAX) x SINE θ
E(INST) = the voltage at any point on the
wave form
E(MAX) = the maximum, or peak, voltage
SINE θ = the sine of angle theta, the angle
of rotation
Unit 16 Alternating Current
Instantaneous values of voltage along a sine wave.
Unit 16 Alternating Current
Peak, Peak-to-Peak, and RMS values along a sine
wave.
Unit 16 Alternating Current
RMS = Peak x 0.707
Peak = RMS x 1.414
Unit 16 Alternating Current
In a pure resistive circuit, the voltage and current
are in phase.
Unit 16 Alternating Current
Skin Effect – In an AC circuit, the electrons
are forced to the outside of the conductor.
Unit 16 Alternating Current
Review:
1. Most of the electrical power generated in
the world is alternating current.
2. Alternating current can be transformed
and direct current cannot.
3. Alternating current reverses its direction
of flow at periodic intervals.
Unit 16 Alternating Current
Review:
4. The most common AC wave form is the
sine wave.
5. There are 360 degrees in one complete
sine wave.
6. Sine waves are produced by rotating
machines.
Unit 16 Alternating Current
Review:
7. The instantaneous voltage at any point on
a sine wave is equal to the peak, or
maximum, voltage times the sine of the
angle of rotation.
8. The peak-to-peak voltage is the amount of
voltage attained by the wave form.
9. The peak value is the maximum amount of
voltage attained by the wave form.
Unit 16 Alternating Current
Review:
10. The current and voltage in a pure resistive
circuit are in phase with each other.