# Unit 15 Alternating Current - PowerPoint PPT Presentation

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Unit 15 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.

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Unit 15 Alternating Current

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### Unit 15 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 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 fluxlines 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 valuesalong 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:

• 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.

### Unit 15 Alternating Current

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.

### Unit 15 Alternating Current

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.

### Unit 15 Alternating Current

Review:

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