section 2
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Section 2. AC Circuits. Chapter 12. Alternating Current. Objectives After completing this chapter, the student should be able to: Describe how an AC voltage is produced with an AC generator. Define alternation, cycle, hertz, sine wave, period, and frequency. - PowerPoint PPT PresentationTRANSCRIPT
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Section 2
AC Circuits
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Chapter 12
Alternating Current
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• Objectives– After completing this chapter, the student
should be able to:• Describe how an AC voltage is produced with an
AC generator.
• Define alternation, cycle, hertz, sine wave, period, and frequency.
• Identify the parts of an AC generator.
• Define peak, peak-to-peak, effective, and rms.
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• Explain the relationship between time and frequency.
• Identify and describe three basic nonsinusoidal waveforms.
• Describe how nonsinusoidal waveforms consist of the fundamental frequency and harmonics.
• Understand why AC is used in today’s society.
• Describe how an AC distribution system works.
• Identify and use the math associated with AC.
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• Nikola Tesla– The father of Alternating Current (AC).
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• AC generator produces an alternating voltage using the principles of electromagnetic induction.
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( B ) No voltage is induced when the conductor is moved parallel to the lines of force.
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( C ) As the loop is rotated, it passes through more lines of force, and the maximum voltage is induced when the loop is at right angles to the lines of force.
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( D ) As the loop continues to rotate, fewer lines of force are cut and the induced voltage decreases.
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( E ) Again, the maximum voltage is induced when the loop is at right angles to the lines of force.
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( F ) As the loop returns to its original position, the induced voltage returns to zero.
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• Cycle– Each time the AC generator completes one
revolution.– Its output voltage is referred to as one cycle of
output voltage.– It produces one cycle of output current in a
complete circuit.
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– The two halves of a cycle are called alternations.
– Two complete alternations make up a cycle.– One cycle per second is called a hertz (Hz).
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• Armature– The rotating loop of wire.
• Sinusoidal waveform– Also called a sine wave.– The waveform produced by an AC generator.– Can be produced by mechanical and electronic
methods.– Identical to the trigonometric sine function.
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• AC values– Each point on a sine wave has two numbers
associated with it.• The degree of rotation.
– The angle to which the armature has turned.
• The amplitude.– The maximum departure of the value of an alternating
current or wave from the average value.
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• Peak value– The absolute value of the point on the
waveform with the greatest amplitude.
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• Peak-to-peak value– The vertical distance between two peaks.
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• Effective value– The amount that produces the same degree of
heat in a given resistance as an equal amount of direct current.
– Can be determined by the root-mean-square (rms) process.
– Also called the rms value.
– Erms = 0.707Ep.
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• Period– The time required to complete one cycle of a
sine wave.– Measured in seconds.– The letter t is used to represent period.
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• Frequency– The number of cycles that occur in a specific
period of time.– Expressed in terms of cycles per second.– Unit of frequency is called a hertz.– One hertz equals one cycle per second.
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• Nonsinusoidal waveforms– Generated by specifically designed electronic
circuits.– Represent either current or voltage.
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• Square waveform
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• Triangular waveform
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• Sawtooth waveform
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• Square waveform– Useful as an electronic signal because its
characteristics are easily changed.
• Triangular Waveform– Used primarily as electronic signals.
• Sawtooth Waveform– Used to sweep the electron beam across the
screen, creating an image, as in television sets.
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• Fundamental frequency– Represents the repetition rate of the waveform.
• Harmonics– Higher frequency sine waves that are exact
multiples of the fundamental frequency.• Odd harmonics are odd multiples of the
fundamental frequency.• Even harmonics are even multiples of the
fundamental frequency.
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• Square waveforms– The fundamental frequency and all odd
harmonics.
• Triangular waveforms– The fundamental frequency and all odd
harmonics, 180 degrees out of phase.
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• Sawtooth waveforms– Composed of odd and even harmonics, with the
even harmonics 180 degrees out of phase with the odd harmonics.
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• In Summary– AC is the most commonly used type of
electricity.– Cycle– Alternations– Hertz– Sinusoidal waveform or sine wave– Peak value of a sine wave
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– Effective value of AC– Determine effective value by rms process.– The rms value of a sine wave– Period (t)– Frequency (f)– The relationship between frequency and period
is: f = 1/t
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– Nonsinusoidal Waveforms• Square waves
• Triangular waveforms
• Sawtooth waveforms