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Unit 15 Alternating CurrentPowerPoint Presentation

Unit 15 Alternating Current

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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.

- 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.

Alternating current flows first in one direction and then in the other direction.

A graph view of a square wave.

A square wave alternating current produced by a switch and two batteries.

The sine wave is the most common of all the AC wave forms.

The sine wave is produced by rotating machines.

One sine wave is 360 electrical degrees.

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.

As the loop approaches 90° of rotation, the fluxlines are cut at a faster rate.

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

Instantaneous values of voltage along a sine wave.

Peak, Peak-to-Peak,and RMS valuesalong a sine wave.

RMS = Peak x 0.707

Peak = RMS x 1.414

In a pure resistive circuit, the voltage and current are in phase.

Review:

- Most of the electrical power generated in the world is alternating current.
- Alternating current can be transformed and direct current cannot.
- Alternating current reverses its direction of flow at periodic intervals.

Review:

- The most common AC wave form is the sine wave.
- There are 360 degrees in one complete sine wave.
- Sine waves are produced by rotating machines.

Review:

- 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.
- The peak-to-peak voltage is the amount of voltage attained by the wave form.
- The peak value is the maximum amount of voltage attained by the wave form.

Review:

- The current and voltage in a pure resistive circuit are in phase with each other.