Unit 15 Alternating CurrentObjectives:

• 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, voltageSINE 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 CurrentReview:

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.