Download Unit 15 Alternating Currents

Unit 15 Alternating Current
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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 15 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 15 Alternating Current
Alternating current flows first in one
direction and then in the other
direction.
Unit 15 Alternating Current
A graph view of a square wave.
Unit 15 Alternating Current
A square wave alternating current
produced by a switch and two batteries.
Unit 15 Alternating Current
The sine wave is the most common
of all the AC wave forms.
Unit 15 Alternating Current
The sine wave is produced by rotating machines.
Unit 15 Alternating Current
One sine wave is 360 electrical degrees.
Unit 15 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 15 Alternating Current
As the loop approaches 90° of rotation, the flux
lines are cut at a faster rate.
Unit 15 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 15 Alternating Current
Instantaneous values of voltage along a sine wave.
Unit 15 Alternating Current
Peak, Peak-to-Peak, and RMS
values along a sine wave.
Unit 15 Alternating Current
RMS = Peak x 0.707
Peak = RMS x 1.414
Unit 15 Alternating Current
In a pure resistive circuit, the
voltage and current are in phase.
Unit 15 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 15 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 15 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 15 Alternating Current
Review:
10. The current and voltage in a pure resistive
circuit are in phase with each other.