AC induction motor (1 Viewer)

[allstarr69]

do we really need to know this? the closest thing i can find on it in the syllibus is:


"compare the structure and function of a generator to an electric motor"

 

[Jezzabelle]

9.3.5

1)describe the main features
of an AC electric motor

a) perform an investigation to
demonstrate the principle of an AC
induction motor

yes you need to know it yes its in the syllabus

1) AC electric motors(converts electrical to mechanical energy) have two essential features, a rotor (the moving part ..duh) and the stator (the stationary part)... note; some also have slip rings to bring electricity to and from the motor. THEY DO NOT REQUIRE A COMMUTATOR beause AC automatically reverses 50 times per second. this gives them an advantage over DC ,motors as commutators have associated problems of sparking (contributes to ozone), loss energy in brushes, wearing of the brushes.
The induction motor is the most common type of AC motor, it works on the principle that a rotating magnetic field will exert a torque on a stationary coil. The stator sets up a changing magnetic field(which is relatively easily produced by AC) and this induces an electric current in the rotor by the process of induction. this current inturn produces an opposing magnetic field (lenz's law) and these fields interact with the rotating field and drag the rotor around. (eg. power drill)

 

[allstarr69]

ahh i see... didnt see it on 9.1- 9.3 and assumed it wasnt there lol.
Thanks for the info

 

[tennille]

What did you do for the first hand investigation, because we never did it?

 

[BillyMak]

Got a needle, so it was stuck up in the air, put an aluminium disc on top, so it was horizontal and balancing. Then got a piece of string and tied a magnet to it, and wound the string up, then let the magnet spin above the disc.

 

[jumb]

Got a needle, so it was stuck up in the air, put an aluminium disc on top, so it was horizontal and balancing. Then got a piece of string and tied a magnet to it, and wound the string up, then let the magnet spin above the disc.

Then what happened?

 

[BillyMak]

The disc spun the same direction as the magnet.

 

[tennille]

Thanks....

 

[Jezzabelle]

The disc spun the same direction as the magnet.

but wouldnt the eddy currants produce a magnet field that oppposes the original field... making it turn opp direction?

 

[tempco]

Looking at the aluminium disc from above, the magnetic field from the magnet would be into the page. So the conventional current in the disc moves in an anti-clockwise direction. That's as far as I can go...

How does the rotation of the magnet change the magnetic flux threading the aluminium disc?

 

[Atotoi]

Hehe not just a pretty face jezzabelle ...

Eddy currents (through electromagnets) are used predominantly to stop Rollercoasters and Trains arent they?
as They dont cause as much friction as regular braking systems.. anymore i should know concerning eddy currents?

 

[tempco]

Induction heating and induction breaking are the importance ones... also, induction breaking is a lot smoother, and there isnt much wear when compared to regular breaking systems.

 

[Jezzabelle]

Induction heating and induction breaking are the importance ones... also, induction breaking is a lot smoother, and there isnt much wear when compared to regular breaking systems.

and induction cook tops for the grannies in the retirement homes

 

[Tommy_Lamp]

The eddy currents induced try and oppose the direction of the magent, so they get pulled along with it.

 

[boz]

our prac was spinning a bar magnet ( stuck to a drill) below a suspended aluminium disc. Eddy currents where produced in the disc setting up a magnetinc feild to appose the motion of the spinning magnet, this magnetic field in turn (excuse the pun) follows the external magnetic field, spinning.