3 phase Induction motor standard sizes

[Lc85]

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?

 

[waross]

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

 

[zlatkodo]

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.

 

[Clyde38]

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?

 

[7anoter4]

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.