Lessons In Electric Circuits Volume II AC Chapter 1
... be produced across the wire coils as that shaft is rotated, in accordance with Faraday's Law of electromagnetic induction.
This is the basic operating principle of an AC generator, also known as an ALTERNATOR
: Figure below ALTERNATOR
operation Notice how the polarity of the voltage across the wire coils reverses as the opposite poles of the rotating magnet pass by.
... ire coils reverses as the opposite poles of the rotating magnet pass by.
Connected to a load, this reversing voltage polarity will create a reversing current direction in the circuit.
The faster the ALTERNATOR
's shaft is turned, the faster the magnet will spin, resulting in an alternating voltage and current that switches directions more often in a given amount of time.
While DC gene ...
... neral principle of electromagnetic induction, their construction is not as simple as their AC counterparts.
With a DC generator, the coil of wire is mounted in the shaft where the magnet is on the AC ALTERNATOR
, and electrical connections are made to this spinning coil via stationary carbon ldquo;brushes rdquo; contacting copper strips on the rotating shaft.
All this is necessary to switch the c ...
... revolving at high speed.
If the atmosphere surrounding the machine contains flammable or explosive vapors, the practical problems of spark producing brush contacts are even greater.
An AC generator ALTERNATOR
does not require brushes and commutators to work, and so is immune to these problems experienced by DC generators.
The benefits of AC over DC with regard to generator design is also ...
... vely, over time.
AC stands for ldquo;Alternating Current, rdquo; meaning voltage or current that changes polarity or direction, respectively, over time.
AC electromechanical generators, known as ALTERNATOR
s , are of simpler construction than DC electromechanical generators.
AC and DC motor design follows respective generator design principles very closely.
A transformer is a pair of mut ...
Secondary voltage = Primary voltage secondary turns / primary turns Secondary current = Primary current primary turns / secondary turns AC waveforms When an ALTERNATOR
produces AC voltage, the voltage switches polarity over time, but does so in a very particular manner.
When graphed over time, the ldquo;wave rdquo; traced by this voltage of alternating ...
... ces AC voltage, the voltage switches polarity over time, but does so in a very particular manner.
When graphed over time, the ldquo;wave rdquo; traced by this voltage of alternating polarity from an ALTERNATOR
takes on a distinct shape, known as a sine wave : Figure below Graph of AC voltage over time the sine wave In the voltage plot from an electromecha ...
... nator takes on a distinct shape, known as a sine wave : Figure below Graph of AC voltage over time the sine wave In the voltage plot from an electromechanical ALTERNATOR
, the change from one polarity to the other is a smooth one, the voltage level changing most rapidly at the zero ldquo;crossover rdquo; point and most slowly at its peak.
If we were to g ...
7071 315 0.
7071 150 0.
5000 330 0.
5000 165 0.
2588 345 0.
2588 180 0.
0000 zero 360 0.
0000 zero The reason why an electromechanical ALTERNATOR
outputs sine wave AC is due to the physics of its operation.
The voltage produced by the stationary coils by the motion of the rotating magnet is proportional to the rate at which the magn ...
... due to a rotating magnet follows that of a sine function, so the voltage produced by the coils follows that same function.
If we were to follow the changing voltage produced by a coil in an ALTERNATOR
from any point on the sine wave graph to that point when the wave shape begins to repeat itself, we would have marked exactly one cycle of that wave.
This is most easily shown by spannin ...
... y corresponding points on the graph.
The degree marks on the horizontal axis of the graph represent the domain of the trigonometric sine function, and also the angular position of our simple two pole ALTERNATOR
shaft as it rotates: Figure below ALTERNATOR
voltage as function of shaft position time Since the horizontal axis of this graph can mark the passage ...
... ay mee fah so lah tee yes, the same pattern immortalized in the whimsical Rodgers and Hammerstein song sung in The Sound of Music covers one octave from C to C.
While electromechanical ALTERNATOR
s and many other physical phenomena naturally produce sine waves, this is not the only kind of alternating wave in existence.
Other ldquo;waveforms rdquo; of AC are commonly produced withi ...
... rm of an AC voltage or current is crucial to its impact in a circuit, we need to be aware of the fact that AC waves come in a variety of shapes.
REVIEW: AC produced by an electromechanical ALTERNATOR
follows the graphical shape of a sine wave.
One cycle of a wave is one complete evolution of its shape until the point that it is ready to repeat itself.
The period of a wave is the ...