PPT: Single-Phase AC Circuits | Basic Electrical Technology - Electrical Engineering (EE) PDF Download

 Page 1


Electrical Circuits Electrical Circuits
Page 2


Electrical Circuits Electrical Circuits
2
AC Fundamentals
Ø Previously you learned that DC sources have ?xed polarities and constant
magnitudes and thus produce currents with constant value and unchanging
direction
Ø In contrast, the voltages of ac sources alternate in polarity and vary in
magnitude and thus produce currents that vary in magnitude and alternate in
direction.
Page 3


Electrical Circuits Electrical Circuits
2
AC Fundamentals
Ø Previously you learned that DC sources have ?xed polarities and constant
magnitudes and thus produce currents with constant value and unchanging
direction
Ø In contrast, the voltages of ac sources alternate in polarity and vary in
magnitude and thus produce currents that vary in magnitude and alternate in
direction.
3
AC Fundamentals
Ø Sinusoidal ac Voltage
One complete variation is referred to as a cycle.
Starting  at  zero,
the  voltage increases  to  a  positive  peak  amplitude,
decreases  to  zero,
changes  polarity,
increases to a negative peak amplitude,
then returns again to zero.
Ø Since the waveform repeats itself at regular intervals, it is called a periodic signal.
Ø Symbol for an ac Voltage Source
Lowercase letter e is used
to indicate that the voltage varies with time.
Page 4


Electrical Circuits Electrical Circuits
2
AC Fundamentals
Ø Previously you learned that DC sources have ?xed polarities and constant
magnitudes and thus produce currents with constant value and unchanging
direction
Ø In contrast, the voltages of ac sources alternate in polarity and vary in
magnitude and thus produce currents that vary in magnitude and alternate in
direction.
3
AC Fundamentals
Ø Sinusoidal ac Voltage
One complete variation is referred to as a cycle.
Starting  at  zero,
the  voltage increases  to  a  positive  peak  amplitude,
decreases  to  zero,
changes  polarity,
increases to a negative peak amplitude,
then returns again to zero.
Ø Since the waveform repeats itself at regular intervals, it is called a periodic signal.
Ø Symbol for an ac Voltage Source
Lowercase letter e is used
to indicate that the voltage varies with time.
4
Sinusoidal ac Current
Ø During the ?rst half-cycle, the
source voltage is positive
Ø Therefore, the current is in the
clockwise direction.
Ø During the second half-cycle, the
voltage polarity reverses
Ø Therefore, the current is in the
counterclockwise direction.
Ø Since current is proportional to voltage, its
shape is also sinusoidal
Page 5


Electrical Circuits Electrical Circuits
2
AC Fundamentals
Ø Previously you learned that DC sources have ?xed polarities and constant
magnitudes and thus produce currents with constant value and unchanging
direction
Ø In contrast, the voltages of ac sources alternate in polarity and vary in
magnitude and thus produce currents that vary in magnitude and alternate in
direction.
3
AC Fundamentals
Ø Sinusoidal ac Voltage
One complete variation is referred to as a cycle.
Starting  at  zero,
the  voltage increases  to  a  positive  peak  amplitude,
decreases  to  zero,
changes  polarity,
increases to a negative peak amplitude,
then returns again to zero.
Ø Since the waveform repeats itself at regular intervals, it is called a periodic signal.
Ø Symbol for an ac Voltage Source
Lowercase letter e is used
to indicate that the voltage varies with time.
4
Sinusoidal ac Current
Ø During the ?rst half-cycle, the
source voltage is positive
Ø Therefore, the current is in the
clockwise direction.
Ø During the second half-cycle, the
voltage polarity reverses
Ø Therefore, the current is in the
counterclockwise direction.
Ø Since current is proportional to voltage, its
shape is also sinusoidal
5
Generating ac Voltages (Method A)
Ø One  way  to  generate  an  ac  voltage  is  to  rotate  a  coil  of  wire  at  constant
angular velocity in a ?xed magnetic ?eld
Ø The magnitude of the resulting voltage is proportional to the rate at which ?ux
lines are cut
Ø its polarity is dependent on the direction the coil sides move through the ?eld.