Trouble with a 3 phase motor

[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.