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

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