Roupen

That would depend on the specifics of the failure, the shaft power that is intended to be drawn from it, and the abilities of the <...we...>, making the question impossible to answer from this distance.

You have a damaged motor. I would first find out why and how the motor was damaged, burnt out can mean so many different things. This information should dictate your course of action.

If this is a new motor then you may have found a hidden fabrication flaw, contact the manufacturer and have them honor their warranty. If this motor has served a long life then buy a replacement motor. If this motor ran longer than the warranty but for less time than anyone expected then see what caused the failure. An overvoltage spike or abrupt change in the mechanical load can be tricky to mitigate. Debris damaging windings begs the question of how the debris got there. A wire break from vibration fatigue or a loose connection might be fortuitously repaired by a clever technician.

If you have to get the pump running before the overfilled reservoir dam fails then what are you doing asking silly questions on the internet. Try anything that might work to move that water, even as many garden hose siphons as you can find!

No, that would not be good practice....

If one of the windings is burned out you need to have the motor rewound or replaced. I assume you have 6-coils that can be wired for high/low voltage operation: If one leg or one winding has opened it wouldn't be advisable to operate the motor, even if you could get the motor rotating it wouldn't develop rated horsepower and you risk further damage to the motor. Depending on size you will spend less rewinding rather than replacing.

Thank you for your positive contribution.

To give further details of the situation: a star-delta wind motor (2.2kw, 3-phase, 50hz) of a centrifugal fan is burnt. The fan and motor are brand new. Contractor has done some wrong connection. We notice that the connection was not properly done. We take it to the rewind process who wind it only on delta (unfortunately we did not consult the factory about type of motor). We cannot order the motor because of late delivery. After installation of the motor the current drawn is above the rated current (9A instead of 6.2A). We consult the factory. The manufacturer informs that the motor should be run on star. Now the question: between delta and star, and the actual status, can we run the motor that was supposed to be winded on star and is wrongly winded on delta by installing an auto transformer 3phase 380V to 220V 3phse?

<...To give further details...>

It is quicker to give as much information as possible in the original posting.

It comes as no surprise to see figures around 6A on start and 9A on delta. However, if the rated current is 6.2A then the motor is awfully close to its top operating limit, which is why the motor manufacturer has recommended a star connection: to protect the motor against damage.

That the motor got burnt indicates either all is not well with the motor overload protection device, or all is not well with the motor's thermal protection device, or perhaps both.

Fundamentally, the motor is undersized for the mechanical load being presented to it, and someone has twiddled with it to make it go regardless of the undersizing. That's why it got burnt.

If in doubt, consult a qualified local Electrical Engineer to review the installation and make recommendations for improvements. Any increase to the size of the motor needs to take place with full sight of the protection arrangements and the method and size of the cable installation, which is the purpose of the review.

Yes you can do this, make sure the current rating of the boost or buck windings is equal to or greater than your motor current.

You can also do this with two single phase transformers connected in open delta. The secondary winding is rated for the voltage you want to buck, the primary voltage for your supply voltage.

<...can do this...>

It all depends upon whether the original poster wants to burn the motor out for a second time, really.

"If you always do what you've always done, you will always get what you've always had." _{- Anon}

The motor was rewound to the wrong voltage, that was the original perhaps poorly described question. The OP just wants to know if he can run it through an auto transformer, and yes, it certainly can.

It would be interesting to learn whether the motor survives the experience, being fundamentally undersized for the mechanical load as indicated by its burning out in the first place. Perhaps the Original Poster will advise the outcome of this experience. Presumably a carbon dioxide fire extinguisher will be nearby, one wonders?

Thank you for all contributors. I will let you know about the outcome

I would be nervous using an auto transformer in a delta power line to star load configuration. My concern is if the the star junction of this motor wants a fourth lead, a neutral. If that internal node is connected to the chassis but no bonding to ground occurs a future hazard may happen if the three currents are not well balanced.

The motor connection is only 3 wires, always a balanced load. A given 3 phase induction motor could be connected star or delta internally, you still just hook 3 wires to it.

Ask the "rewind process" what voltage the motor is wound for. If it is wound for 220 volts per phase (as it would receive in 380 volt star) then supplying 220 volts to delta should be Okay. You seem to indicate failure occurred because of contractor's error (not an overload).

It seems strange for the rewind shop to do what you've described. Normally they would rewind it in the same configuration as they received it. It is possible that when they connected the wires they did it for the star low voltage configuration, if this is the case you can rewire it for the higher voltage following the star wiring diagram I included previously. If they connected it for low voltage operation the motor would draw more current at the same load than it did with the high voltage configuration. Have you checked the terminal box in the motor to see how the connections have been made?

I also understand from this "electric motor 3phase 380/3/50 is burnt out can we operate the motor" that he is trying to run a burned out motor. The only way to get this job done is a new motor or rewind. He can can get it done right this time by giving all the info for rewinding. The only other concern is that this motor is to small for the job it is used for. To advice on that the group need more information and he should get professional advice from a supplier and a guarantee on what they suggest.

I agree, that was my initial statement in my first post. An open winding, even one of six, would need to be replaced. Roupen responded to me saying they had rewound the motor, but it appeared to have been incorrectly wound in a delta configuration instead of the star. I suggested he check the way the terminals were connected in the rewound motor because the company rewinding the motor may have connected the six windings for 190V operation instead of the 380V they were using. He thought the motor had been rewound as a delta; I said it was unlikely, as those rewinding the motor would have looked at the nameplate which shows the motor configuration. This information should provide the rewinder with all he needs to repair the motor. Whether the motor is undersized is a separate issue which I haven't addressed because there is not enough information for me to make a judgement; besides, I'm the electrical type. I let the mechanical type tell me how much horsepower they need.

The star windings and the delta windings are one and the same coils, so no, you have no good windings in the motor to make it turn.

Roupen, a electric motor have only windings to make up the coils that will electro magnetically drive or Rotate the output shaft. Star and Delta is the way one would connect it to the electricity source. You need a 3 phase power source to run a 3 phase winded motor. Star connection is Low voltage over the coils and Delta connection is full supply over the coils.

The mechanical load of a fan is roughly proportional to the cube of the tip speed. To "get away with it" in the short term, one might be able to reduce the rotational speed of the fan by (6A/9A)^¹/₃, or to around 87% of that presently, provided suitable pulleys or gearing intervene between the two, and suitable alterations can be made to reduce the speed using it.

That is not a substitute for a review of the process engineering aspects of the fan and the effects of its delivering a lower flowrate!

Neither is it a substitute for a full review of the suitability of the motor sizing, circuit cabling and motor protection arrangements!

If it's burnt out, what gives you the impression that it can be operated in any way at all?

Read the thread...

The motor is f****d. Why would adding something else into the circuit unf*** it?

Again, read the thread.

Repetition is unnecessary.