cost of running motor

[bobwh]

anyone can calculate the cost of running a 3 phase 250 kw motor for 10 hours at 0.32p per kwh

 

[electricpete]

Assume the motor is full load and 250kw represents the output power.

You need to assume an efficiency to convert to input power. Let's say approx 90%.

That gives input power ~ 1.1x250kw.
kwxhrs = 1.1x250kwx10hr
cost = 1.1x250kwx10hr x 0.32p/(kw hr) = 1.1x250x10x.32 "p"

 

[electricpete]

Although the motor load establishes the power, not the motor. Just because nameplate says 250kw doesn't mean it's pulling 250kw.

 

[Farkel]

Not so quick fellows; what about power factor penalty charges
plus demand charges if they apply. Also there may be a duty cycle involved with different loads at different times. What parameters are available to answer these questions?

 

[electricpete]

Farkel - agreed. Depends on rate structure.


I think one other factor to consider is where did the 250kw come from? If it is motor nameplate, it may not represent actual loading in-service.

 

[Marke]

Jbartos
I have seen this comment about IEC motor rated in input power before, but all the IEC motors that I have used are rated in shaft power. Any examples??

Best regards,


Mark Empson

http://www.lmphotonics.com

 

[UKpete]

No examples, but domestic appliances such as food mixers and vacuum cleaners in the UK are rated on their input power, at least they were in the past. (This meant that designers were under no pressure to improve motor efficiency as the input power was the selling point). It only applied to fractional horsepower, I have never seen it applied to anything larger.

I can't quote the relevant standards as I sit here though.

 

[Marke]

Hello UKpete
Yes, that certainly makes sense, they are appliances rated with power input as opposed to motors on their own.
Best regards,

Mark Empson

http://www.lmphotonics.com