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3 phase Induction motor standard sizes

3 phase Induction motor standard sizes

3 phase Induction motor standard sizes

(OP)
I was of the understanding that 3 phase induction motors came in standard sizes,

2.2kw,4kw,5.5kw,7.5kw,11kw,15kw etc

However we have been offered a motor that is rated 6.3kW and the manufacturer stated that its basically a 5.5kw motor ran 20% faster because its on a 60Hz supply.

Has anyone seen this before?

RE: 3 phase Induction motor standard sizes

The manufacturer; That would be sales, not tech support, right?
In the NEMA world that would probably be 1.15% service factor.
If a 50 Hz motor is run on 60 Hz
And if the V/Hz ratio is maintained (20% increase in voltage) the rating will be 5.5 kW x 60 Hz/ 50 Hz or 6.6 kW.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 3 phase Induction motor standard sizes


If we have a core of motor 5.5 kW, 50 Hz and we want to make the winding for 60 Hz, we will get approximately 15% more power ( not 20 %) ie 6,325 kW, because the maximum allowed flux densities in air gap, back iron and teeth are not the same for 50 and 60 Hz.

RE: 3 phase Induction motor standard sizes

Hi zlatkodo,

Out of curiosity, what do you consider the maximum allowed flux densities in air gap, back iron and teeth for 50 and 60 Hz?
ponder

RE: 3 phase Induction motor standard sizes

Since rpm=60*f/p [f=frequency[50 or 60 Hz] ;p=no.of pole pairs.] at 60 Hz rpm will be 20% more [as manufacturer stated].
As P=k*Tq*rpm [Tq=load=motor torque. P=required power] then
if Tq=constant P60Hz=1.2*P50Hz. 5.5 kw motor will draw 6.6 kw and will be hot. If Prated=6.3 kw the required power 6.6 kw will be only 5% more then rated [I think it may work].However, if the supplied voltage will be 20% more at 60 Hz [let's say 480 V at 60 Hz instead 400 V at 50 Hz], then 5.5 kw will be suitable as waross said.
By the way, if E~k*f*B*S and if E~V=constant and f raise then B decrease-no problem of saturation, I think.

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