Star-Delta wirings polarity

[LearningTechMan]

Someone have an idea of the impact of having one of the 3 motor windings reversed (exemple: if wires U1-U2 and V1-V2 are connect normaly but W1-W2 are swapped.

Will it start, and if yes, what will append to the phases currents of the motor ? Two coils will be opposed to the reversed one? Will it result in unbalanced currents?

Thanks

 

[dArsonval]

Hook all your "stuff" [up] as posted... put some power to it... and give us your Report.

Thanks.

 

[ozsalty]

It will "hum" it head off...been there done that..

 

[squeeky]

May turn. Won't get up to speed. No torque and it will get hot. Been there, done that.

 

[Skogsgurra]

If no load on shaft, it will probably run and hum.
If some load connected, you can't tell about running, but it will hum.
If respectable load connected, it will not run, but it will hum.
In all cases it will get hotter than normal and hopefully trip the protection before it burns.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[squeeky]

Did the test today. Didn't have time to check currents or look at phase distortion. It was done at the MCA builder so I could not push the issue. Motor ran the right direction. Sounded like it had a bearing problem. It was at absolute no load bare shaft. Putting a plank on the shaft to try add load kicked the motor away. 5.5kW 4 pole.

 

[LearningTechMan]

OK , there is the exact situation:
On a compressor we have a 150 HP rebuilt motor, 575V , 6 wires (3 windings) , control by a set of 3 (new)contactors for proper star-delta running.
Windings are equals in resistance ( 0,0310 0,0312 0,0309 ohm) Voltages delta is acceptable (577 581 587)
Lines currents With Load are(142 152 165)and phases currents are (102 70 93)
Lines currents Without Load ( 62 55 74)and phases currents are ( 50 18 44)...!

The compressor run well! motor don't overheat ...but overloads tripped 5 or 6 times and also, a 225A fuse blow once on phase 1 and an other day on phase 2 ) ...all that in approx. 20 days and usualy at start.

I would like to find an answer to those unbalanced Phases currents , i know voltage do affect it in part (arround 4 percents)...but not enougth to explain a currents variation like 50 18 44 !
Unfortunately this compressor can not be stop to long, and doing tests like reversing a winding on a 150 Hp is a high risk, that's the reason why i joinned your intelligent work forum...theory before practice.

(Thank you for the first answers and specialy squeeky for the test!)

I stay tune...

 

[zlatkodo]

doing tests like reversing a winding on a 150 Hp

Do not do that.

For these voltages the voltage unbalance is below the 1% and it can not be the reason for the enormous difference in the currents.

- First, you need to measure the currents for two different phase-arrangements (L1, L2, L3 and L2, L3, L1) in order to determine whether the reason for the unbalance is in the motor or supply.
- The reason for the fuse blow may be a well known issue with star-delta starter in a short period of (no-voltage) time between the "start" (star) and "run" (delta) position.
[URL unfurl="true"]http://winding.wix.com/design[/url]

 

[squeeky]

I have a thought. I am traveling and am working off the tablet. I know from experience that when you do the power wiring, Red in Star must go to Blue in delta. What if there was a power wiring problem and there was the phase reversal in the control cubicle? Also what would happen if you were running two phases with one phase going yellow to yellow while the other two phases are Red to Blue and the other Blue to Red?

I would check all the power wiring and cables. Is there a field isolator? If so, it will be a six pole unit. Any problem there?

What was done to the compressor motor prior to the problem starting? Was this from new? When you trip the overload is it at the transition from star to delta or on start up. Same question for the fuses.

 

[waross]

Red to Blue and Blue to Red? The motor will work fine but the rotation will be reversed.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[squeeky]

Hi Waross, trying to figure out if it is single phasing because of a power wire error rather than an error with terminals reversed in the motor winding side. I'm giving the benefit of the doubt to the manufacturer or rewinder. This is why I asked is it a new challenge on an existing installation and if so, what has changed. Does it run in star and then trip in delta or at the delta transition.

 

[electricpete]

There has been described on the forum a check you can do for wiring polarity of the motor (with motor offline)

thread237-270521

Hook up an oscope with 3+ channels to all three phases, observing marked lead polarity. Manually rotate the motor and you should see a small induced voltage. If hooked properly, you can see the normal pattern of three phases all approx 120 degrees apart. If hooked improperly, one phase is flipped 180, so phase relationship changes dramatically to be something like 3 positive peaks 60 degrees apart followed by 3 negative peaks 60 degrees apart.


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(2B)+(2B)' ?

 

[rhatcher]

I am guessing that your 'line' current readings are taken from the three line leads going to the running delta connection and that your 'phase' current readings are taken from one of the phase leads at each delta connection point. Specifically, the phase readings would be taken from lead T1 at the T1-T6 connection, T2 at the T2-T4 connection, and T3 at the T3-T5 connection.

If so, my guess is that the T2-T5 phase is reversed.