Trouble with a 3 phase motor

[nicky123]

Here is mty problem:

3-Phase motor for air extraction


Motor 1:
220/440 Y V
HP:5
I: 15.8/7.9 amp
RPM: 1740
FP:0.78
n:79.4%
Tn/To: 20.4/47nm
FS 1.5


Motor 2:
220/440 Y V
HP:7.5
I: 21.8/10.9 amp
RPM: 3480
FP:0.87
n:77.4%
Tn/To: 20.4/47nm
FS 1.5


Problems:
1. The motor 1 was burned out after one month running because electricity failure ( the motor was single phasing; problem with the electricity supplier )
2. The motor 1 was not extracting enough air.
Solution:
1. The electricity problem was fixed by installing some component to avoid working with 1 phase.
2. Motor 2 was installed.
3. The motor 2 now is extracting enough air.


Poblems:
1. After one day running, the motor 2 burned out.
Solution:
1. Motor 2 was rewound with the same characteristics of motor 1. The motor is now running without problem since 2 month ago.


Problems:
1. Is not extracting enough air.


Overall, is seems like the extractor is working ok with motor 1 but is not extracting enough air, but with a motor 2 is extracting enough air but burned out after one day running.


Aditional data:
1. The motor is fed by a transformer of 30kva, this transformer also fed an air conditioner of 60.000 BTU/h and others minor electrical appliance.
2. The extractor was installed to extract air using 15m of duct.
3. I have no data about cfm or pressure required.
4. The extractor is 30'' size.


Questions:
1. Possibles causes why motor 2 burned out.
2. How can i know which motor fix ?
3.Possibles solution to make the extractor to extract enough air.

 

[Darkwood]

You haven't given us your location and 3ph voltage in your area?
You haven't told us how you motor is connected (star or delta)?
You haven't told us how your starting your motor?
Why are your motors burning out, where's your overload protection and what is it set at if you have?
Have you measured the current on each phase when the motor is running

Just a few questions to start the ball rolling, motors burn out for numerous reasons so asking that question and just showing us plate details wont give us any clues, is the impellor running free and clear of ducting (not catching and jamming)... the voltage needs to be checked when air con is on and loaded up also current demand on transformer.

And lastly what is your background so we can adapt our answers and questions to your level of knowledge.

 

[Darkwood]

P.s. Welcome to the forum.

 

[Knobhead]

The answer is in your question. Look at the motor RPM.

 

[johnboy6083]

0.86 poles at 50Hz so in other words this motor if its a 4 pole motor will need to run at 232 hz?

 

[Bobster]

Are these direct drive or attached to a gearbox?

 

[UNG]

No mention whether the other loads are three phase but I would think that the air con is three phase at 17.6Kw

Could be one or more problems here but again there is a lack of info or pics

 

[Marvo]

A make and model number for the fan would be helpful.

Why would the fan have a second motor that's completely different to the first one?

If any motor burns out due to mechanical overload or phase failure then the protection is incorrectly designed.

 

[Darkwood]

The answer is in your question. Look at the motor RPM.

yep you get me tony, 11hr shift and missing the obvious :drunk:

 

[nicky123]

You haven't given us your location and 3ph voltage in your area?
You haven't told us how you motor is connected (star or delta)?
You haven't told us how your starting your motor?
Why are your motors burning out, where's your overload protection and what is it set at if you have?
Have you measured the current on each phase when the motor is running

Just a few questions to start the ball rolling, motors burn out for numerous reasons so asking that question and just showing us plate details wont give us any clues, is the impellor running free and clear of ducting (not catching and jamming)... the voltage needs to be checked when air con is on and loaded up also current demand on transformer.

And lastly what is your background so we can adapt our answers and questions to your level of knowledge.

I only have basic knowledge about motor, nothing deep. Im trying to figure out what was the problem and how can i fix it, because i asked many people who work with extractor-motor, and no one have any certain idea or solution. Im not in my country (venezuela) right now, and the people who I left running the place, i dont want them to purchased another motor and burn it again, because motor is expensive, and is illogical to play burning motor until find the right one.

The major problem was because the people who installed the system was totally irresponsible and then they dissapear. I have no idea about the extractor requirement, and no information at all in the extractor, i only have the info of the motor that was installed.

About your questions:
1.You haven't told us how you motor is connected (star or delta)?
Star
2.You haven't told us how your starting your motor?
The motor is connect directly, using pulley and strap. ( thats what you mean?)
3. Why are your motors burning out, where's your overload protection and what is it set at if you have?
No protection when the first motor burned out, thats why the motor was running with one phase and burned out when the electricity failure happen in the city. And then they installed a protection before installing the second motor, but still burned out.
4.Have you measured the current on each phase when the motor is running?
Im not sure, i wasnt there in that time, and the person who i left running the place have no idea or dont remember.

I know that theres lack of a lot of information, im just trying to have an idea or possible solutions, or figure out if there is any kind of solution, or if the problem is because of the electricity or because motor load or something else.

It seems like the 5hp motor with 1740 rpm is running without problem, but is not extracting air ( BIG ISSUE) but with a motor of 7.5hp and 3480 rpm burned out.
I cant neither install a to high hp motor, because of my 30kva restriction.

The thing is, what can i do to make the system extract more air without burning the motor.

Thanks a lot!

 

[nicky123]

A make and model number for the fan would be helpful.

Why would the fan have a second motor that's completely different to the first one?

If any motor burns out due to mechanical overload or phase failure then the protection is incorrectly designed.

Why would the fan have a second motor that's completely different to the first one?
Because when i purchased the second one, wasnt available any motor with the same characteristic of the first one, and i need a motor urgently in that moment and i thought that with a higher speed motor it will extract more air and solve the problem.

 

[nicky123]

The air conditioner is 3 phase and the other appliance like computer, refrigirator, tv, router,lamps,etc are 1 phase. Im going to try to get some pics.
Thanks

 

[nicky123]

Are these direct drive or attached to a gearbox?

Pulley and stramp, im not sure what is a gearbox.
Thanks

 

[poppypiesdad]

Pictures would be good , have had a situation when one motor was exacting and the other motor inputting in the same unit meaning that both motors were working against each other and kept tripping . This was a scratching head for a bit until the apprentice commented that they weren't wired the same way. Bit embarrassed that i didn't see it , but easy fix , dont think its helping that the motors are too different sizes,
There isnt anything jammed in the blades is there?

Jamie

 

[Knobhead]

I give up

View attachment 10587

 

[nicky123]

Pictures would be good , have had a situation when one motor was exacting and the other motor inputting in the same unit meaning that both motors were working against each other and kept tripping . This was a scratching head for a bit until the apprentice commented that they weren't wired the same way. Bit embarrassed that i didn't see it , but easy fix , dont think its helping that the motors are too different sizes,
There isnt anything jammed in the blades is there?

Jamie

No, no, no, no. The extractor ONLY WORK WITH ONE MOTOR. I replace the motor 1 for motor 2, because motor1 was burned out for been one phasing ( supplier problem). When I replace motor 1 for motor 2, motor 2 burned out too and I dont know why. I rewound motor 2 to the same characteristics of motor 1. So, now the extractor is working ok with 1740 rpm and 5HP, but is not extracting enough air, so I still have a problem to fix, i want to make the extractor to extract more air but without burning out the motor.

 

[Darkwood]

regarding your replies to my previous post No 10# i can access you've replaced motor A for a larger motor i.e. 5 to 7.5... i believe these will be the same frame mount/shaft center heights so shouldn't be a issue there... the big question here is 'where is your overload protection' ??? If your control circuit was adequate your motors shouldn't burn out...
I suspect a supply issue but motor A could have burnt out for many reasons-
We haven't got anywhere near enough info' which you've said you are not in a position to supply, and i wouldnt think fitting a 7.5 motor as been a issue but i assume its either been connected wrong or got supply issues (voltage, phase down etc) and the lack of control circuit with an overload protection or incorrect setting of overload means the motors will fail again and again.
Contact a local company who do motors let them do a proffesional view on this on site and have them fit the appropriate protection for motor.... you wont get any better answers on here as we have all come to a dead end with lack of info-- be nice to let us know if you get it sorted and the reasons for the problems thanks.

 

[nicky123]

regarding your replies to my previous post No 10# i can access you've replaced motor A for a larger motor i.e. 5 to 7.5... i believe these will be the same frame mount/shaft center heights so shouldn't be a issue there... the big question here is 'where is your overload protection' ??? If your control circuit was adequate your motors shouldn't burn out...
I suspect a supply issue but motor A could have burnt out for many reasons-
We haven't got anywhere near enough info' which you've said you are not in a position to supply, and i wouldnt think fitting a 7.5 motor as been a issue but i assume its either been connected wrong or got supply issues (voltage, phase down etc) and the lack of control circuit with an overload protection or incorrect setting of overload means the motors will fail again and again.
Contact a local company who do motors let them do a proffesional view on this on site and have them fit the appropriate protection for motor.... you wont get any better answers on here as we have all come to a dead end with lack of info-- be nice to let us know if you get it sorted and the reasons for the problems thanks.

I'll already contact a proffesional to view the site, the one who replace the motor, he said that it is because ''maybe'' the rpm of the second motor is to high, and thats why he rewound the second motor to the same characteristis of the first one, but still havent fix the problem which is that the extractor is not extracting enough air. I call him again and no reply.
I call a second professional, and he said to solve the extracting issue by installing another motor with 7.5hp with 3480 rpm, he said that shoulnt be a problem. If it is not a problem, why is burned out the second motor when it was installed.
But, neither the first professional or the second one has gave me any enough suitable answer ( both have differents points of view and nothing concret) , and before trying to buy another motor and playing to burn it, i want to have more information about how all this motor things works, to be more careful before making any decission.
To clarify my doubts, what is exactly the ''overload protection''? To try to take a picture of it.
Another question, it is possible that the second motor was burned out because is not powerfull enough to do the same work but with 3480rpm?
Thanks for your comments.

 

[Darkwood]

your first supposedly professional obviously dosn't have a clue what he's doing, first of all when a motor burns out you need to find the cause before you replace, occasionally this may not be clear so when checking and running new motor you would do all the tests necessary to confirm that supply, control and running of motor is sound.
It seems that the first proffesional hasn't done this an although i dont know the contractual rules in your country he should be liable for the replacement if the fault can be sourced to something he should have checked.

An overload is a device that monitors the amount of current been drawn by each phase into the motor, and if it is set up correctly ie - to the rating of the motor, then it will (if there is a overcurent to the motor) trip. This will usually break the control circuit and drop out a contactor maybe - so shutting power off to motor. Any electrician going to view this issue 'if competent' should have checked all this out, from the comments and actions of both your electricians .. it sounds like neither knows what they are doing.
I wouldn't connect a motor up if its control system wasn't giving adequate protection, the rpm shouldn't be an issue but as mentioned before too little info to give you any verdict..... motors and controls is a complex subject for someone who dosn't have basic knowledge of it so im not going down the road of explaining how they work and are controlled especially when we dont have info of control system.

 

[Knobhead]

Motor speed is a major issue with fans. Centrifugal forces can destroy a fan. Seeing a fan launched out of the top of a building isn’t something I want so see again.

 

[Darkwood]

Motor speed is a major issue with fans. Centrifugal forces can destroy a fan. Seeing a fan launched out of the top of a building isn’t something I want so see again.

He said that the second one burnt out in a day but see your point the C - forces could have destroyed bearings etc jamming motor and burning it out, the thought hadn't crossed my mind but think ive been spending too long on closed loop inverter controlled systems - got my blinkers on i think, but either way OP is lacking info and the guys he's had out to fix the motor dont seem to know what they are doing so a dead end for helping him.

 

[Marvo]

This thread is beginning to worry me. There's some things that make no sense to me whatsoever. For example how do you rewind a 4-pole motor and make it into a 2-pole motor or vice versa? I didn't know this was even possible.

There's a balancing act you've got to play assuming this is an axial fan. On one side of the equation you have the motor shaft power, on the other side you have the speed of rotation and the blade angle. Where the right balance lies depends on many things such as the power characteristics of the blade set and the static pressure of the system and so on.

Without many accurate details there's no way we can assist you any further.

 

[Engineer54]

Quite agree Marvo, there's a lot more to specifying a motor, than is at first apparant. It takes a lot of experience and know how, and very little from what you can gain out of books.

 

[Knobhead]

I’ve said my piece, now I’m washing my hands of it.