motor speed/power
motor speed/power
(OP)
We have a 200kW 315L motor 6 pole 974 rpm not driven from an inverter. If we were to use an inverter to lower the speed to 780rpm how would we calculate the new power roughly before a test was performed?
Thanks
Thanks





RE: motor speed/power
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: motor speed/power
Thanks
RE: motor speed/power
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: motor speed/power
"Will work for (the memory of) salami"
RE: motor speed/power
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: motor speed/power
Thanks
RE: motor speed/power
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: motor speed/power
Thanks
RE: motor speed/power
The actual power (the power consumed by the fan at 80% of rated speed) is a lot less. The affinity laws are used to calculate actual consumed power and that results in Reduced Speed Power = Original Power *(Speed Ratio)3 so that P80=P100*0.83=200*0.51=103 kW
Have a look at http://www.engineeringtoolbox.com/affinity-laws-d_...
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: motor speed/power
"The 160kW is the possible MECHANICAL power of the motor."
Now see why we use still use Horsepower? For us, I would say that the possible mechanical power of the motor at that speed would be 214HP, but the kW that is consumed by the motor to move the air at 80% speed will be a factor of the affinity law, based on the actual kW consumed at full speed.
So aside from my half joking reference to units of measurement, you cannot really calculate the consumed kW based on speed and motor rated kW alone, because you don't know what the motor power consumption really was even at full speed. The only vald formula is Pfs (Power at full speed) x .512 (the cube of 80%). If you have not measured the actual kW at full speed, you can only guess. An educated guess that will result in a "no worse than..." answer, but still a guess.
"Will work for (the memory of) salami"
RE: motor speed/power
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: motor speed/power
"Will work for (the memory of) salami"
RE: motor speed/power
BTW, there is a slight difference in the definition of the US and European HP.
US: 550 foot-lbf/second = 550*0.3048*0.45359 Nm/s = 760.39827600 = 760 W
Europe: 75 newton-meters/second = 75*9.80665 = 735.49875 = 736 W
Now, for some reason, that isn't entirely correct since all seem to agree that 1 US HP equals 745.7 W.
Lost in translation? Or lost due to friction in the NBS/NIST? Or doesn't the (Swedish) definition of an inch (25.4 mm) apply? With one inch = 25.4, one foot sould correspond to 12*25.4 mm = 0.3048 m.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.