Electrical Motors

<sniff, sniff>, I smell homework :)

^{"I have two different motors as follow: A. 1 phase, 110 V, 17.5 Amp. capacitor start. B. 3 phase 575 V, 2.6 Amp. Now which motor is efficient? which motor consume more power? and how? please explain in details."}

"You smell that? Do you smell that? Homework, son. Nothing else in the world smells like that. I love the smell of homework burning in the morning."

The answer to your homework question is...

It cannot be determined with the information provided. Motor efficiency is a rating assigned to a motor by the manufacturer after testing at the factory. It also has everything to do with the applied load. You have no information on either issue.

why not put a watt meter and measure?

110V single phase supply line, how do you get 575V ? where do you get 575V 3 phase? never heard the value (do not claim its non-existence, but still...)

Go through the text books and study the motor efficiency (Hint: the best will be the superconducting PM motors)

110 volts x 17.5 amps x estimated 0.85 power factor = 1636 watts = 2.193 hp. (In real life it is probably a 2 hp motor with a slightly lower power factor.)

575 volts x 2.6 amps x sqrt 3 x .85 = 2201 watts = 2.95 hp. (In real life probably a 3 hp motor.)

Thus the 575 volt motor (several countries use this voltage) is the more powerful.

But this is not the same as efficiency, which would depend on the specific characteristics of each motor. That said, higher hp motors are usually more efficient, so the 575 volt motor is probably (but not necessarily) the more efficient.

I get the same numbers as Tornado any difference in efficiency would favour the 3 ph motor. 575 is a standard canadian Motor. Conclusion is that the 110 volt motor is the least expensive to operate If that is the question. Fom nameplate data a more accurate calculation can be made. Typical manufacturers figures for efficiency could also be used to get a more accurate figure to compare .

Actually in smaller HP motors, single phase sometimes is more efficient than an equally sized (by output power) 3 phase motor. It's more accidental than anything else, a low HP 3 phase motor tends to have more mass than a 1 phase version because manufacturers don't make smaller 3 phase frames at a certain size whereas they do for single phase motors. It's not an absolute, just a pitfall to watch out for. I made that assumption for a long time before I was challenged and lost. Check out some motor mfrs data, you can find what I'm talking about.

Good point on motor efficiency. My conclusion was based on fact that the 3 ph motor would have to have an efficiency 75% or less to Match the Single Ph motor at 100% efficiency unlikel/ From a operating cost perspective the Single PH motor would likely be the least expensive to operate. Your point however is noted

575/3/60 is a Canadian voltage eh?

The question is not at what volt you are operating, there is an inherent efficiency (or lack of it) in the single phase Vs Polyphase.

So the calculation of the output KW (where the efficiency was not considered, only the pf was) is not correct.

Since this is too obviously homework, I am not going to help out, and again ask the OP , assuming he is still here, to refer the text books and look at the appropriate section.

Learn to learn. Here you may get a quick answer, a lot of members seem to be too generous, even after being pointed out that this is too obviously homework. But these are not going to help the OP in long term. Getiing an answer to one question is OK, struggling and finding the answer will help you in finding the answer for too many questions that are going to crop up in future.

The OP's question asks for the consumed (input) power, not output. Thus efficiency doesn't (yet) figure into the formula. And if I wanted to be fancy I would have said "cos(phi)" rather than "power factor."

In reply to post 7, the formula for 3-phase power is V x A x sqrt 3, not just V x A. (Also times efficiency for output power.) (Also times efficiency for output power.)

POWER = VOLTAGE X Amp

1925 = 110 X 17.5

1495 = 575 X 2.6

check out aovox motors awsume formulas there killer motors to 13 hp palm of hand