AboutWill Expertise Three phase electic motors, controls and related problems or failures, three phase motor installation issues, performance issues, connections, data and duty cycle information. All other electic motors. Specialty motors, repair concerns, performance concerns, obsolete motors and solutions. Other specialty equipment issues. Lost nameplate data and identification, lost connection data.
Also DC motors of all types.
See my profile under Home/electrical at this site
Experience 30 plus years in the electrical motor and apparatus repair industry. VP level management of repair facilities, current owner of my own specialty repair and consulting firm.
Organizations EASA, IBEW [retired], other specialty organizatons, Lubrication, Vibration EDI, Triboelectric Councils
Publications Currently fielding concerns at this site under "Home Electrical"
Education/Credentials 4 year technical, College level specific courses, EASA repair courses, vibration analysis electronic and electrical trade school.
Expert: Will Date: 5/23/2008 Subject: KWH savings of a 3ph motor vs. 1ph motor
Question Given that 3-phase motors are more energy efficient than single-phase motors. Is there a way to compute the KWH savings of a 3-phase motor vs. a single-phase motor? Motors are rated at 220VAC, 60 Hz, 3HP.
Answer Yes, but all things must be equal, voltage applied to single or three must be exactly name plate, load must be exact on both motors, duty cycle, code letter, design letter, so on.
In general for single phase take 746 x HP divided by volts x amps x power factor
Three phase 746 x HP divided by 1.732 x volts x amps x power factor.
That will give you efficiency, and you can go from there, remember we can only talk in general terms, because even an energy saving motor is required to have every parameter just as written, and any deviation blows the savings.
Think about it, there are 1 HP motors, 2 HP motors 3 HP motors, so on
But do you ever see a 3.78 HP motor or a 4.10 HP motor
Do you suppose manufacturers' of all the different widgets in the world make them to an exact HP?
Many motors are say 75 HP when a 65 or 68 HP motor would work fine, but the next smallest size is 60HP.
Then there is the question of is it better to slightly overload a motor or slightly over size it, and that all depends on the steel used for laminations, the copper alloy used for the rotor bars and end rings, the quality of the bearings, and many more parameters.
So your question is a good one, by formula you can come up with an answer, but in the real world there are a ton of factors that determine energy use.
Most do not understand that even the voltage in your home is not standard, they have a range to meet, some homes are running 242 volts and blowing out light bulbs, where others could be running 199 and running higher currents do to low voltage. Motors are your big energy hogs, and good you are looking into it, but there is more than just a simple formula to deal with.
SOME MOTORS ACTUALLY RUN MORE EFFICIENT, COOLER, AND SO ON, WHEN THE VOLTAGE IS LOWER THAN RATED WHILE OTHERS ARE BETTER OFF WHEN THE VOLTAGE IS A BIT HIGHER THAN RATED.
Very complex subject, you do know that the waste in energy of a motor is every volt that is used to overcome friction [bearings] windage [fans or other protrusions that stir air] circulating current loss in the iron stack, and the overall quality built into the motor.
Hope that helps, there are times that single phase will be a better choice and times when three phase will be a better choice, but the selection process involves more than phase, it is all mentioned above.
