50hz 230v 12000 rpm motor....how?

[bhm1712]

as in the title, a motor with these specs...how is it possible???

if we take into account RPM = 120 f / number of poles

that would mean that the number of poles would be 0.5.....not possible.

this is in relation to a wound rotor ac motor. this is the only thing i cannot understand in relation to electric motors and nobody at my works can explain either.

if there is no frequency controller, and the supply is 50hz , how can this speed be achieved?

 

[holmslaw]

..

 

[ban-all-sheds]

http://en.wikipedia.org/wiki/Electric_motor#Universal_motors

 

[flameport]

If the motor really is 12000 rpm, the frequency isn't 50Hz, more likely to be 400.

 

[big-all]

you shure its not geared !!!

 

[ban-all-sheds]

A series-wound motor is referred to as a universal motor when it has been designed to operate on either AC or DC power. The ability to operate on AC is because the current in both the field and the armature (and hence the resultant magnetic fields) will alternate (reverse polarity) in synchronism, and hence the resulting mechanical force will occur in a constant direction.
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Universal motors generally run at high speeds, making them useful for appliances such as blenders, vacuum cleaners, and hair dryers where high RPM operation is desirable. They are also commonly used in portable power tools, such as drills, circular and jig saws, where the motor's characteristics work well. Many vacuum cleaner and weed trimmer motors exceed 10,000 RPM, while Dremel and other similar miniature grinders will often exceed 30,000 RPM.

 

[ericmark]

The number of poles may control speeds of squirrel cage motor but there are many more types of motor and many as just as happy with AC or DC and frequency of course has no effect on the speed of a motor designed to work on AC/DC.

 

[bhm1712]

thats what i thought....

however you are incorrect about the 230 volt wound rotor motor. There is such a thing...we have many at work for transpec conveyors where variable speed is required ( not all have been changed to VFD's yet)

This is why certain AC motors have brushes, to allow for applying resistance into the rotor circuit to reduce rotor speed, and also on larger motors to help reduce starting current and increase torque.

I have just rechecked the motor in question. It is a C.E SET

the data plate says 230 volts 50hz 12000 rpm. It is from a washing machine.

 

[bhm1712]

i think B.A.S has answered my query

It must be a series wound motor but i have been mistaken when looking at the rotor and slip rings to assume its a wound rotor ac

 

[holmslaw]

..

 

[bhm1712]

there is such a thing as an AC wound rotor induction motor....this is different to a universal or series wound motor. Like a standard ac motor the max speed is dictated by the number of poles and frequency of supply. However, the slip rings allow constant unswitched connection to the rotor windings which enable different impedances to be applied, thus varying the speed

an example would be an car alternator but used as a motor....

 

[holmslaw]

..

 

[bhm1712]

why have i turned the thread into gibberish?

i have stated facts....

i was mistaken by thinking the motor was a wound rotor induction motor, and couldnt understand how it could achieve such a high rpm. I have now, through the help of people on here worked out that its a series wound universal motor.

i then simply stated that there certainly is such a thing as a wound rotor AC induction motor.

something that you dont know does not mean it is gibberish!

do a bit of research and find out about wound rotor induction motors.....they exist!

 

[ban-all-sheds]

bhm - you should be aware that holmslaw doesn't do being wrong, or admitting mistakes...