Can anyone tell me a good way of determining power savings in 3 phase motors by using high voltage instead of low voltage? Assuming full load on motors.

 

The difference between 230/460 volt motors of the same horsepower and, for example 4160 volt motors, the high voltage motor is larger, weighs about twice as much, costs about five times as much, takes twice as long to rewind, costs over twice as much to repair and uses the same amount of kilowatts of power. I'm not sure that was what you were looking for or not but this info and alot more can be found at: http://www.marathonelectric.com

 

Responding to W. Hinton's Thu, Jan 2, 5:34pm reply:

Your generalization is greatly exaggerated! I don't think Todd asked for a low-voltage, LV, to medium-voltage, MV, conversion, but from 208 to say 230 or 460 Volts.

My response to Todd's query is, "ask motor manufacturers for their efficiency tables!"

The LV - MV selection is much more involved. This undertaking, called a voltage break-point study, is a normal engineering requirement on jobs of significant magnitude.

Regards,
Phil Corso, PE
(Boca Raton, FL)
[[email protected]]

 

Focus on the reason that the higher voltage motor is more efficient: less current which = less copper heating losses.
Copper heating power losses are related to the square of the current ( Ploss = I^2 * Rcopper). If you increase the voltage, for the same power output, the current should decrease which should decrease your copper losses, all other things being the same.

Of course, you could simply just assume that your load is the same now as it was before, and multiply voltage and current together and compare. Vnew * Inew = Pnew versus Vold * Iold = Pold. This would show how much power you are saving with the new motor.

 

Running a 208 volt motor at 230 or 240 would increase the core losses, probably more than the decrease in copper losses.

 

Todd,

I think that you must clarify for us whether you are asking about 230 vs 460V, or Low Voltage vs Medium Voltage, or applying 500V to a motor rated for 460V operation. Your question leaves too many other issues open to interpretation (or misinterpretation actually).

 

You're correct Phil, The generalization was not accurate. The cost between 240/480 volt motor is not about 5 times the cost it actually is about 5.3928571 times as much to go to a 4160 volt motor of 100 hp of the same rpm: see enclosed quote.
--------------------------------------------------
Bill

This information came out of the Marathon catalog because they actually
publish all that you asked for, amps, wt, ect.

100HP 1800RPM 230/460Volts 228/114Amps 405T Frame 1277Lbs. Cost $2800
Repair/Rewind $1399 3days

200HP 1800RPM 460Volts 225Amps 445T Frame 2280Lbs. Cost $5,300 Repair/Rewind
$2149 4days

100HP 1800RPM 2300/4160Volts 30/17Amps 447/9T Frame 2800Lbs. Cost $15,100
Rewind $7550 7days

200HP 1800RPM 2300/4160Volts 47/27Amps 447/9T Frame 2875Lbs. Cost $16,800
Rewind $8400 7days

Please let me know if you need anymore info.

Best Regards
Jeff York
Account Manager
York Electric Motors, Inc.
--------------------------------------------------
As for what cost savings can be had, you must weigh the equipment costs, the labor and costs for all interfacing materials and rigging time and materials to convert and schedule equipment downtime to make the conversion, the cost of high voltage/medium voltage sqitchgear and starters, relaying, startup and calculating payback and locating funding for the project. I believe this to be costly and time comsuming.

If the question was to run a 208 volt motor on 230 volts then it will work just fine. The slip will be lower, the effeciency will be higher, the torque will be higher, the current will be lower and the motor will run cooler. Running this motor connected for the high voltage connection would be similar to running on 240 when connected for low voltage connection but the current would be half as much. Still the information you are looking for is at http://www.marathonelectric.com

 

Bill,

I didn't question your veracity regarding LV to MV comparisons. I questioned your interpretation of Todd's query, which I interpreted as lower LV to higher LV.

I apologize for making you angry!

Regards,
Phil Corso, PE
(Boca Raton, FL)
[[email protected]]