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3 phase motor (Read 10469 times)
supra59
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3 phase motor
Jul 25th, 2011, 6:20pm
 
Hi guys got a problem with a 3 phase machine and im baffled, this machine is for cutting marble it as 4x 3 phase motors just wired it up to the main  and one of the motors goes the wrong way so i thought simple swap the phase at the motor, and all should be well, but it made no difference still goes the wrong way no mattter what phases i use, checked the phase rotation with my meter and the machine is correct and incoming phases are correct, if anyone can shine some light on this would be a great help.

thanks Paul
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« Last Edit: Jul 25th, 2011, 6:21pm by supra59 »  
 
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Lectrician
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Re: 3 phase motor
Reply #1 - Jul 26th, 2011, 7:30am
 
Although supply in TP, are you sure this one motor is also TP? Perhaps stating the obvious!
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Re: 3 phase motor
Reply #2 - Jul 26th, 2011, 10:53am
 
Was it really going the wrong way or did it just look like it due to the strobe effect of the lighting?
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Re: 3 phase motor
Reply #3 - Jul 26th, 2011, 11:09am
 
It will if the Phases are crossed CW and or not wired up right.
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Re: 3 phase motor
Reply #4 - Jul 26th, 2011, 4:21pm
 
I know that. What I meant was it's easy to fool yourself into thinking a motor is spinning the wrong way then swap the phases and low and behold it's still spinning the wrong way (because it was spinning the right way to start with). Don't ask how I know  Embarrassed but fortunately the motor didn't have a propeller attached.



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« Last Edit: Jul 26th, 2011, 4:22pm by CWatters »  
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Re: 3 phase motor
Reply #5 - Jul 26th, 2011, 11:10pm
 
I know nothing about 3 phase, but Stoday was on about star and delta a couple of days ago.
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supra59
Re: 3 phase motor
Reply #6 - Jul 26th, 2011, 11:59pm
 
Hi guys thanks for the quick replies i'm hundred percent this motor is 3 phase and its defo going the wrong way watched the fan when turned off, its a real strange one just cant think of any way to correct it other than swapping the phases which i did, further more there's no neutral to the machine so i'm sure all the motors are 3 phase my only thoughts could it be the control gear that controls the motor? still don't understand even if it was
so if any other ideas would be welcomed
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Re: 3 phase motor
Reply #7 - Jul 27th, 2011, 6:11am
 
Why not post a pic showing the data plate.
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Re: 3 phase motor
Reply #8 - Jul 27th, 2011, 6:45am
 
If it is a standard three phase motor, swapping any two phases (only) will swap the direction of rotation.  Difficult to help further Undecided

Is it a direct on line motor (controlled directly by a single contactor/overload)?  Not inverter driven for speed control or anything?

You actually swapped the two phases in the motor terminal housing?  Not in the control panel or anything?

Definitely swapped two phases, and not confused any possible thermal cutout terminals?

Star/Delta would have 6 terminals and 6 cables for the motor (the ends of all 3 windings), this allows you to connect the motor in star of delta config, designed for use with a timed star/delta starter unit (starts at low speed, high torque, and then switches to high speed, low torque).
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Re: 3 phase motor
Reply #9 - Jul 27th, 2011, 11:14am
 
I'm on shakey ground here but... what happens if you have a missing phase in the motor? I half remember that a three phase motor might still run but in a random direction?
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Re: 3 phase motor
Reply #10 - Jul 27th, 2011, 11:51am
 
It would just hum, draw a hug current on the two connected phases, and hopefully operate the overload before the windings burnt out!

I believe, although never tried, that if you spin the rotor of a motor with only two phases connected that it may spin judderally (if thats a word!) and then stop.

We do quite alot of work with supplies for refrigerated vehicles - the TPN 32amp plugs/couplers often do not get pushed fully onto the socket/inlet, and arc and burn the brass pins shorter and shorter until one phase drops, often burning a motor out.
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Re: 3 phase motor
Reply #11 - Jul 28th, 2011, 2:59pm
 
Lectrician wrote on Jul 27th, 2011, 11:51am:
I believe, although never tried, that if you spin the rotor of a motor with only two phases connected that it may spin judderally (if thats a word!) and then stop.


It will spin as normal and if on low load it will run forever, on full load  the windings will burn out. I'm pretty certain that it will spin in either direction.
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Re: 3 phase motor
Reply #12 - Jul 28th, 2011, 10:00pm
 
hi again thanks to all the peeps who as replied and tryed to sort this problem out with me, it is a star delta motor 6 terminals, three terminals at the top and three at the bottom, the bottom three is where the three phases connect to the motor, the top three terminals are linked together which im pretty sure is wired as star, i think this motor is going to have to run the wrong way as im out of ideas as for correcting this problem, as lectrician said swapping any of the two phases should have corrected this but its not weird !! on the note of a phase going down the motor goes much slower and hums or lets say when i have had this in the past it did lol, and as for where i changed the connections it was at the motor not at the control board maybe its something in the control panal thats causing the problem ? but if it is im not going to get involved with that  ,the thing is when i do swap the phases, it shows up on my meter its wrong at the motor when i do a phase rotation test, the only bonus is the pump still seems to work ok but it just bothered me as to why this was happening, i hate leaving something when i know its not right if theres anymore info i could give you guys just ask, anyway once again thankyou for all your help with this matter  
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« Last Edit: Jul 28th, 2011, 10:17pm by supra59 »  
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