Motor Load Calculations

[epsngr]

Hi,

 

I need some help on this one.

 

I have been doing calculations ussing standard formulas for site load requirements for some time but I was taken off guard when my mate asked me why the absorbed power for i.e a 1.5kW rated motor is 1.7kW. I have never noticed this before now.

 

I noticed using the formulas the absorbed power is higher than the motor rated power for all motor stater types except for VSDs where the rated kW is higher than the absorbed power.

 

Is this correct? if yes, what is the explanation for this.

 

Formula - Absorbed power = shaft kW/Eff, Shaft kW = rated kW * load factor (0.9 in this case).

 

I appreciate your comments.

 

 

Regards

[Jeff Millar]

Hi,

 

I agree with your comment 100%.

 

Where did you find this formula ?

 

I never saw the formula shaft kw = rated load kw x load factor

 

What I found was continuous load = Rated LOAD / Efficiency

 

the continuous rated load can not be greater than the rated load ?

 

I am also confused like you. Seems to me continuous load should be

rated load kw x load factor.

 

I think this origionated in some software that has a glitch. How can the rated continuous load

 

used to calculate the absorbed load be greater than the rated kw load.

 

The point of a load factor is like a duty factor or diversity factor.

 

The absorbed load should be less that the rated load kw.

 

Perhaps we can share what we find, that will clarify this.

 

Jeff