Contributed by:
Types of Waveforms,
Induced Voltage,
Generating a Sine Wave,
Ac Terminology,
Three-Phase Ac
1.
Electricity
Principles & Applications
Sixth Edition
Richard J. Fowler
Chapter 8
Alternating
Current and Voltage
©2003 Glencoe/McGraw-Hill
2.
• Types of Waveforms
• Induced Voltage
• Generating a Sine Wave
• Ac Terminology
• Three-Phase Ac
3.
Electrical Waveforms
Alternating current or voltage
Pulsating direct current or voltage
Fluctuating direct current or voltage
4.
Ac Waveform Terminology
Voltage or Current 1st cycle 2nd cycle 3rd cycle
+2
+1 + peak
peak
0 to
peak
- 1 - peak
-2 0 0.2 s 0.4 s 0.6 s
Time
T = period = time to complete 1 cycle = 0.2 s
f = frequency = 1 / T = 1 / 0.2 s = 5 Hz
Peak amplitude can be either negative or positive.
Peak-to-peak amplitude includes both the - and + peaks.
5.
Specifying Sine-Wave Amplitude
rms = 0.707 peak
av = 0.637 peak
peak peak-to-peak
peak = (1 / 0.707) rms = 1.414 rms
peak = (1 / 0.637) av = 1.57 av
peak = peak-to-peak / 2
Examples:
20 Vp-p / 2 = 10 Vp and 10 Vp x 0.707 = 7.07 V
8 Aav x 1.57 = 12.56 Ap
6.
Wave-Form Quiz
The ____ dc waveform never reaches or crosses fluctuating
the zero reference line.
The part of the waveform that includes its complete
negative and positive excursions is called a ____. cycle
The ____ is the time required to complete one cycle. period
The base unit of frequency is the ____. hertz
For a sine wave, 30 VP = ____ V. 21.21
For a sine wave, 10 AP-P = ____ A. 3.535
For a sine wave, 25 V = ____ VP. 35.35
7.
Induced Voltage in a
Constant-speed Conductor
N N N N
S S S S
If motion is When motion When Reversing the
parallel to the is at an angle, motion is direction of
flux, no flux some flux is perpendicular motion,
is cut; thus cut; and some to the flux, reverses the
no voltage voltage is maximum polarity of
is induced. induced. voltage is the induced
induced. voltage.
8.
Generating a Sine Wave
Motion is parallel to the flux.
No voltage is induced.
9.
Generating a Sine Wave
S
N
Motion is 45 to flux.
Induced voltage is 0.707 of maximum.
10.
Generating a Sine Wave
Motion is perpendicular to flux.
Induced voltage is maximum.
11.
Generating a Sine Wave
x
Motion is 45 to flux.
Induced voltage is 0.707 of maximum.
12.
Generating a Sine Wave
Motion is parallel to flux.
No voltage is induced.
13.
Generating a Sine Wave
S
x
N Motion is 45 to flux.
Notice current in the Induced voltage is
conductor has reversed. 0.707 of maximum.
14.
Generating a Sine Wave
Motion is perpendicular to flux.
Induced voltage is maximum.
15.
Generating a Sine Wave
x
Motion is 45 to flux.
Induced voltage is 0.707 of maximum.
16.
Generating a Sine Wave
Motion is parallel to flux.
No voltage is induced.
Ready to produce another cycle.
17.
Ac Generation Quiz
Maximum voltage is produced when a
conductor is moving ____ to the flux. perpendicular
No voltage is produced when a conductor
is moving ____ to the flux. parallel
When a conductor is moving at 45° to the
flux, the voltage is ____ of maximum value. 0.707
For a two-pole generator, one cycle of ac is
produced during ____ revolution(s). one
To produce a sine wave the flux field
must be ____. uniform
18.
Three-Phase Waveform
Phase 1 Phase 2 Phase 3
120 120 120
240 Phase 2 lags phase 1 by 120
Phase 3 lags phase 1 by 240
Phase 2 leads phase 3 by 120
Phase 1 lags phase 3 by 120
19.
Generation of Three-Phase Ac
Phase 1 Phase 2 Phase 3
The
S
algebraic
sum of the x x
instantaneous
voltages of
the three
phases equals
zero.
Phase 1 is ready to go positive.
Phase 2 is going more negative. N
Phase 3 is going less positive.
20.
Delta Connections
Line 1
e1
Ph
as
as
Ph
e2
Line 2
Phase 3
Line 3
Delta-Connected Source Delta-Connected Load
The sum of the instantaneous Each load resistor will be
phase voltages equals zero. connected to one of the phases.
For the delta-to-delta connection, Vline = Vphase = Vload.
For the delta-to-delta connection, Iline = 1.732 Iphase = 1.732 Iload.
21.
Wye Connections
Line 1
Line 2
Ph
2
se
as
a
e1
Ph
Phase 3
Line 3
Wye-Connected Source Wye-Connected Load
For the wye-to-wye connection with a balanced load:
I line = Iphase = Iload.
Vline = 1.732 Vphase = 1.732 Vload.
There is no voltage between the source and load star points.
22.
Three-Phase Ac Quiz
In a three-phase system, the phases are separated
by ____ electrical degrees. 120
In a three-phase system, the phase coils are
separated by ____ mechanical degrees. 120
The algebraic sum of the instantaneous phase
voltages equals ____. zero
The phase coils in a ____ connected source delta-
are connected in series.
Phase and line currents are equal in a ____ wye-
connected system with balanced loads.
In a delta-connected system, the line current
equals ____ times the phase current. 1.732
23.
REVIEW
• Types of Waveforms
• Induced Voltage
• Generating a Sine Wave
• Ac Terminology
• Three-Phase Ac
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