# Help: 3 Phase Induction Motor Problem

Discussion in 'Homework Help' started by ParagM, Nov 6, 2014.

1. ### ParagM Thread Starter New Member

Nov 6, 2014
2
1
I will be helpful if someone solve this problem,
A 4 pole, 1440 rpm, 3 phase induction motor is operated from a per phase voltage of 240 V, 50 Hz and driving a constant toque load. Calculate the following at f=25 Hz, airgap flux = constant = 4.8.
i. Supply voltage per phase
ii. Slip
iii. Slip frequency
iv. Percentage rotor loss

I have calculated synchronous speed Ns=120f1/p =1500
slip s = Ns-N / Ns = 0.04 & slip freq fr = s f1 = 2

segecious likes this.
2. ### WBahn Moderator

Mar 31, 2012
20,225
5,749
I'm just guessing here, but I suspect your instructor believes it would be helpful if YOU at least attempted to solve YOUR homework.

Sep 20, 2014
52
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Bahn if you don't want to help him then why are you trolling his topic? He has obviously attempted the problem.

Apr 5, 2008
17,121
3,001
Hello,

When he made an attemp, he should show it here.
That way we can see where he needs assistance.

Bertus

Sep 20, 2014
52
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Bertus, did you read this? I know you are smarter than me.

I have calculated synchronous speed Ns=120f1/p =1500
slip s = Ns-N / Ns = 0.04 & slip freq fr = s f1 = 2

Sounds a lot like an attempt.

Sep 20, 2014
52
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Paragm how did you get Synchronous speed?

7. ### WBahn Moderator

Mar 31, 2012
20,225
5,749
It's an attempt at half of the problem. For the other half, he explicitly asked to be given the answer without any further effort.

Sep 20, 2014
52
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Bahn you are a smart man and I'm sure a great person, but I think you are a little too quick to judge people. You do not know how long Parag spent trying to figure out what to do next for this 3 phase power problem. When I was in engineering school, it would sometimes take me hours upon hours to solve problems and I'd still get the wrong answer. When I read your posts here, I interpret them as judgmental, almost as if you are trying to scare people away from engineering because they aren't trying hard enough. Sometimes people get stuck and they need help even if its just a small inch to set them in the right direction....Also I noticed you joined in 2012, when I was in college and asked questions on this board in 2008 I never ran into a person like you.

9. ### WBahn Moderator

Mar 31, 2012
20,225
5,749
You're right, I have no idea how long Parag spent trying to work the other half because he has given no indication or evidence of trying at all. If he has spent hours trying, then it shouldn't be hard to post SOMETHING to show for it instead of just asking for someone to supply the answer to him. If you've read very much of my stuff on these boards at all, then you will have seen numerous examples of when I have been more than willing to work with someone for page after page after page to walk them through their struggles, going as far back to first principles as necessary. But I do ask that the person make (and show) their efforts to work their own problems so that we can guide them in their struggles based upon what they are doing right and what they are doing wrong.

As for you never running into a person like me in 2008.... so? What's your point?

Sep 20, 2014
52
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When I was here in 2008 nobody would throw things back in my face like i see you doing with this guy, and other guys here like in the laplace topic. I see you coming down on people hard for deriving extremely complex equations, not everyone is a genius like you are.

11. ### panic mode Senior Member

Oct 10, 2011
1,420
347
WBahn is doing the best thing any student in trouble could hope for, you just don't see it...

12. ### WBahn Moderator

Mar 31, 2012
20,225
5,749
I'm not going to come down hard on someone for deriving an extremely complex equation -- you need to review that thread if you think that is what is happening. I will come down on someone for refusing, after several attempts, to start asking if their results make any sense compared to easily seen limiting cases. I will also come down on people for failing to use units, particularly when not doing so has already resulted in them either making a mistake or failing to catch a mistake that tracking units would have caught. I just guess that's baggage that comes from seeing someone die because they couldn't be bothered to track their units (and having come within about three feet of being that person instead).

Sep 20, 2014
52
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I apologize Bahn.

14. ### ParagM Thread Starter New Member

Nov 6, 2014
2
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Thanks vu2nan & others for devoting your valuable time!
This question is from university paper & I have given problem statement as it is.
I think, the question is incomplete.
Still, any kind of help will be appreciated.