Centrifugal fan motor having same KW at 50 and 60 Hz 3

[edison123]

Don't the fan affinity laws for centrifugal fans say that power is proportional to cube of the speed?

Muthu

http://www.edison.co.in

 

[edison123]

Little - If V/Hz is maintained, the motor power does go up. Simple math.

Muthu

http://www.edison.co.in

 

[stevenal]

What happens to losses when the voltage, frequency, and mechanical load all increase? Perhaps the manufacturer doesn't consider the motor cooling to be sufficient to handle higher losses at 1755RPM.

 

[iop95]

V/Hz it's not maintained.
Frequency ratio: 60/50 = 1.2
Voltage ratio: 460/400 = 1.15... so at 60Hz flux is lower with 4.3%, that mean about 8.9% lower torque than at 50Hz.
Even rated speed ratio is about 1.22 that don't mean 1.22x more power at 60Hz because torque at 60Hz is lower.
One standard motor power value is 2.2kW and even that motor from design calculation and in real tests has maybe 2.4-2.5kW it was rated at 2.2kW.

 

[jraef]

Muthu,
I think that is not a centrifugal fan, it is axial, so the affinity laws for centrifugal loads don’t apply. They likely know that at 120% speed on 60Hz, that fan doesn’t move any more air.

But to your point on what the motor nameplate says, I agree, but there is a slight catch here. The 2.2kW is a MECHANICAL output rating, meaning a specific amount of torque at a specific speed. If the torque stays the same and the speed increases by 20%, the kW increases by 20%. The only way the kW rating could stay the same is if the torque DECREASES when the speed increases. That would happen if you gave it 400V at 60Hz, but by giving it 460V, the V/Hz ratio is almost the same as it is at 400/50.

And that “almost” might be the issue here. By rating it at 460V, not 480V, the calculated kW at the higher speed but slightly reduced torque comes out to only 2.3kW, which is within 5% of the 50Hz rating, but not a standard rating, so maybe they just called it close enough.

That’s kind of not like Siemens though to be honest…


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[electricpete]

Little - If V/Hz is maintained, the motor power does go up. Simple math.
A 50 Hz to 60 Hz operation automatically upgrades the motor capacity by 20%.

I agree with you on that point at least to a good approximation (and setting aside that the v/hz is not quite maintained as iop95 mentioned). Itsmoked gave us a FAQ on the subject faq237-1224

The two nameplate ratings are based on two different standards (IEC and NEMA). The NEMA rating has a lower current, so I'd say you clearly have more thermal margin built into the NEMA 2.2 kw 460v/60hz rating than in the IEC 2.2 kw 400v/50hz rating. If you're so inclined you could ignore the NEMA standard rating and look instead at the NEMA SF rating 1.15 and I'll be it ends up with ballpark similar thermal margin as the IEC rating in this particular case.

I don't know the details of how those two standards (NEMA vs IEC) compare on thermal margin in general.


=====================================
(2B)+(2B)' ?

 

[edison123]

OEM's use one single frame for 2,4,6 poles to get decreasing outputs. The rating definitely is proportional to speed. That's why americans went for 60 Hz, more bang for the buck. Also, higher the speed, better is the efficiency.

Jeff, it's a centrifugal fan - axial suction and radial delivery.

It's a misleading bad nameplate, german oem or not.

Muthu

http://www.edison.co.in

 

[LionelHutz]

I'd say it's the service factor making the difference. A 1.0 service factor would mean the 60Hz rating is 2.5kW, about what would be expected compared to the 50Hz rating.

 

[zlatkodo]

A tricky nameplate.
It is not a general purpose motor but a special one for particular applications (part of bigger machine). Thus, you cannot completely rely on the data from the nameplate.
You can design a motor eg. for 3 kW; 460 V; 60 Hz and mark it on the nameplate as 2.2 kW .
Such a motor will be capable of delivering 2.2kW at 400V, 50Hz for sure.