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8/4/2019 AC Motor Ger
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AC Motor
As in the DC
motor case, a
current is passedthrough the coil,
generating atorque on the coil.
Since the current
is alternating, themotor will run
smoothly only at
the frequency of
the sine wave. Itis called a
synchronousmotor. Morecommon is the
induction motor ,
where electriccurrent is induced
in the rotating
coils rather than
supplied to themdirectly.
One of the drawbacks of this kind of AC motor is the high current which mustflow through the rotating contacts. Sparking and heating at those contacts can
waste energy and shorten the lifetime of the motor. In common AC motors themagnetic field is produced by an electromagnet powered by the same AC
voltage as the motor coil. The coils which produce the magnetic field are
sometimes referred to as the "stator", while the coils and the solid core whichrotates is called the "armature". In an AC motor the magnetic field is
sinusoidally varying, just as the current in the coil varies.
How does a motor work? AC Generator Generator and Motor DC Motor
Index
DC
Circuits
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AC Generator
The turning of a coil in a magnetic field produces motional emfs in both sides
of the coil which add. Since the component of the velocity perpendicular to the
magnetic field changes sinusoidally with the rotation, the generated voltage issinusoidal or AC. This process can be described in terms of Faraday's law
when you see that the rotation of the coil continually changes the magneticflux through the coil and therefore generates a voltage.
Voltage generation detail AC Motor Generator and Motor DC Motor
Index
DCCircuits
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Generator and Motor
A hand-cranked generator can be used to generate voltage to turn a motor. This
is an example of energy conversion from mechanical to electrical energy and
then back to mechanical energy.
As the motor is turning, it also acts as a generator and generates a "back emf ".
By Lenz's law, the emf generated by the motor coil will oppose the change thatcreated it. If the motor is not driving a load, then the generated back emf will
almost balance the input voltage and very little current will flow in the coil of the motor. But if the motor is driving a heavy load, the back emf will be less and
more current will flow in the motor coil and that electric power being used is
converted to the mechanical power to drive the load.
Demonstration AC Motor AC Generator DC Motor
Index
DCCircuits
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DC Motor Operation
This is an active graphic. Click on bold type for further illustration.
Magnetic interactions with charge
Index
Magnetic
fieldconcepts
Magneticforce
applications
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Current in DC Motor
This is an active graphic. Click on bold type for further illustration.
DC Motor Operating Principles
Index
Magnetic
fieldconcepts
Magneticforce
applications
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Magnetic Field in DC Motor
This is an active graphic. Click on bold type for further illustration.
DC Motor Operating Principles
Index
Magnetic
fieldconcepts
Magneticforce
applications
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Force in DC Motor
This is an active graphic. Click on bold type for further illustration.
DC Motor Operating Principles
Index
Magnetic
fieldconcepts
Magneticforce
applications
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Torque in DC Motor
This is an active graphic. Click on bold type for further illustration.
DC Motor Operating Principles Torque on a Coil
Variation of torque with coil angle
Index
Magnetic
fieldconcepts
Magnetic
forceapplications
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How Does an Electric Motor Work?
DC Motors AC Motors
Index
DC
Circuits
Magnetic
forceconcepts
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Induction Motor Action
Induction motors use shorted wire loops on a rotating armature and obtaintheir torque from currents induced in these loops by the changing magnetic
field produced in the stator (stationary) coils.
At the momentillustrated, the current in
the stator coil is in the
direction shown andincreasing. The induced
voltage in the coil
shown drives current
and results in aclockwise torque.
Note that this simplified
motor will turn once it isstarted in motion, but
has no starting torque.
Various techniques areused to produce some
asymmetry in the fields
to give the motor a
starting torque.Simple induction motor
Index
Magnetic
forceconcepts
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Induction in Armature Coils
Induction motor action involves induced currents in coils on the rotating
armature.
This is an active graphic. Click on the bold text for further detail.
Index
Magnetic
force
concepts
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Simple AC Induction Motor
A large percentage of small AC
motors are classed as inductionmotors. This implies that there is
no current supplied to the rotating
coils. These coils are closed loopswhich have large currents
induced in them because of their
low resistance.
An induction motor must achieve a rotating magnetic field to continue to exert
a torque on the armature coils. In this example, the rotating field is achieved
by the extra coils on the pole pieces.
More detail Induction motor principle
Index
Magnetic
force
concepts
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Simple AC Induction Motor
Induction motor principle
Index
Magnetic
force
concepts
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AC Generator
The turning of a coil in a magnetic field produces motional emfs in both sidesof the coil which add. Since the component of the velocity perpendicular to the
magnetic field changes sinusoidally with the rotation, the generated voltage issinusoidal or AC. This process can be described in terms of Faraday's law
when you see that the rotation of the coil continually changes the magnetic
flux through the coil and therefore generates a voltage.
Voltage generation detail AC Motor Generator and Motor DC Motor
Index
DCCircuits
HyperPhysics***** Electricity and Magnetism R NaveGo Back
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How Does an Electric Generator
Work?
AC Generator Generator/motor demonstration
Index
DC
Circuits
Magnetic
forceconcepts
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Generator and Motor
Identical hand-cranked generators can be used to show that a generator can
function as a motor and vice versa. If mechanical energy is put into the oneof the devices by turning the crank,
electrical energy can be produced. If
that electrical energy in the form of voltage is applied to the other, then
mechanical energy can be produced
(motor action).
In the video below, the crank of one of the devices is turned to put in
mechanical energy, resulting in electrical energy at the output. The handle
of the other device is turned because electrical input is operating it as amotor. The last segment of the film lines up the handles of the devices and
then turns the generator 1 turn. You can observe that the handle of the"motor" turns about 60% of a turn, indicating an efficiency of about 60%
for the generator/motor exchange. But that is almost twice the efficiency of
the electric generation system of the U.S., which yields electricity at about33% efficiency! The reason is that this generator/motor pair does not have
to go through the "thermal bottleneck " imposed by the second law of
thermodynamics on the common electrical generation plants which operateas heat engines.
The high efficiency of the transfer of energy from a generator to a motor finds widespread application in the operation of diesel-electric locomotives.
It is difficult to mechanically transfer energy from the powerful dieselengines to the wheels of the locomotive which have low-friction metal-to-
metal contact with the steel rails. So the power of the diesel engines is used
to run a generator, and the generated electric power is used to operate
electric traction motors to drive the wheels. The generated electric power can be very slowly and smoothly transferred to the wheels by the electric
Index
Transformer
concepts
Magneticfield
concepts
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motors which drive the axles. You don't "pop the clutch" on a big
locomotive with steel-on-steel wheels! You would just sit and spin thewheels until you melted the rails.
How does a generator work? How does a motor work?
Discussion of a generator/motor pair
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