1. Principles & Applications
Electricity
Principles & Applications
Sixth Edition
Richard J. Fowler
Chapter 8
Alternating
Current and Voltage
© Glencoe/McGraw-Hill

2. INTRODUCTION 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. -1 -2 Ac Waveform Terminology 1st cycle 2nd cycle 3rd cycle +2 +1-1 -2
Voltage or Current
peak to
+ peak
- peak
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
peak
peak-to-peak
rms = peak
av = peak
peak = (1 / 0.707) rms = 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 =
7.07 V
8 Aav x =
12.56 Ap

6. Wave-Form Quiz The ____ dc waveform never reaches or crosses
the zero reference line.
fluctuating
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. Constant-speed Conductor
Induced Voltage in a
Constant-speed Conductor N S N S N S N S
If motion is
parallel to the
flux,
When motion
is at an angle,
When
motion is
perpendicular
to the flux,
Reversing the
direction of
motion,
no flux
is cut;
some flux is
cut;
thus
no voltage
is induced.
and some
voltage is
induced.
reverses the
polarity of
the induced
voltage.
maximum
voltage is
induced.

8. Generating a Sine Wave S N Motion is parallel to the flux.
No voltage is induced.

9. Induced voltage is 0.707 of maximum.
Generating a Sine Wave S x N
Motion is 45° to flux.
Induced voltage is of maximum.

10. Generating a Sine Wave S N Motion is perpendicular to flux.
Induced voltage is maximum.

11. Generating a Sine Wave S N Motion is 45° to flux.
Induced voltage is of maximum.

12. Generating a Sine Wave S N Motion is parallel to flux.
No voltage is induced.

13. Generating a Sine Wave S N Motion is 45° to flux.
Notice current in the conductor has reversed.
Induced voltage is of maximum.

14. Generating a Sine Wave S N Motion is perpendicular to flux.
Induced voltage is maximum.

15. Generating a Sine Wave S N Motion is 45° to flux.
Induced voltage is of maximum.

16. Generating a Sine Wave S N Motion is parallel to flux.
No voltage is induced.
Ready to produce another cycle.

17. Ac Generation Quiz Maximum voltage is produced when a perpendicular
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 Acx S
Phase 1
Phase 2
Phase 3
The
algebraic
sum of the
instantaneous
voltages of
the three
phases equals
zero.
Phase 1 is ready to go positive.
Phase 2 is going more negative.
Phase 3 is going less positive.

20. Delta Connections Delta-Connected Load Delta-Connected Source
Line 1
Phase 3
Phase 2
Phase 1
Line 2
Line 3
Delta-Connected Load
Delta-Connected Source
Each load resistor will be
connected to one of the phases.
The sum of the instantaneous
phase voltages equals zero.
For the delta-to-delta connection, Vline = Vphase = Vload.
For the delta-to-delta connection, Iline = Iphase = Iload.

21. Wye Connections Wye-Connected Source Wye-Connected Load
Line 2
Line 1
Phase 3
Phase 1
Phase 2
Line 3
Wye-Connected Source
Wye-Connected Load
For the wye-to-wye connection with a balanced load:
I line = Iphase = Iload.
Vline = Vphase = 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
are connected in series.
delta-
Phase and line currents are equal in a ____
connected system with balanced loads.
wye-
In a delta-connected system, the line current
equals ____ times the phase current.
1.732

23. REVIEW Induced Voltage Generating a Sine Wave Ac Terminology
Types of Waveforms
Induced Voltage
Generating a Sine Wave
Ac Terminology
Three-Phase Ac