AC 3 phase electric motor 4

[atvhead]

Hello all, I am new here and this is my first post. I did search through the postings as best I could to find an answer to my question, but no luck. My question is: in a constant speed AC 3 phase, is the voltage & motor RPM proportional? For example: if I have a 460v motor operating at 1750RPM if the voltage is increased to 575v, will the motor speed now be 2188RPM? Thanks everyone.

confused Mech. Eng
Bob

 

[LionelHutz]

I've seen no evidence that any motor manufacturer is using different insulation in their 575V motors compared to their 460V motors. There may be one out there but it would not be typical of everyone else.

I also know one manufacturer that just rivets their VFD rated tag to a standard motor and charges more for it. If you have one of their standard motors and point fingers at them for failing on a VFD they will even come back and tell you it's the same motor as a VFD rated one and therefore the motor construction can't be the problem.

So, I would expect the 460V motor to be as likely to survive on a 600V VFD as a 575V motor will.

But, I think poorly wound 575V motors failing when controlled by VFD's will help keep some motor shops in business (in 600VAC use areas). I know of many cases where it was cheaper in the long run to just pay for a good rewind vs getting another free replacement from the manufacturer.

 

[atvhead]

i want to thank everyone for the input. this has been a tremendous help. i do know that this motor does not have a VFD, it is simply 575volt to a constant speed 460volt motor. since in fact this motor (to my knowledge) has not failed or even kicked out a fail safe, then it just isnt drawing a high amp to do real damage to itself, plus the fact it has been running like this for 6 years. i have informed the customer that this is not the correct motor and my recommendation is to replace it with the correct 575volt. the customer has his own electrical engineers and you would think someone would have questioned this during installation! but anyway, thanks everyone!

Bob
_innov8_

 

[jraef]

Huh, now that I re-read your original post I see that you never said it was controlled by a VFD. How did we get there then? Sometimes this group wanders off on tangents a bit I fear ;-)

(that last part was meant as a gross understatement joke)

I also know one manufacturer that just rivets their VFD rated tag to a standard motor and charges more for it.

I think I know of whom you speak, but if I'm not mistaken, their claim is that they have a unique winding method that increases the Corona Inception Voltage capabilities of their standard design motors. I read their paper, it failed to convince me.

 

[waross]

Hi jraef;
it was more of a suggestion than a direct statement:

yes, the motor is not operating "properly". Obviously, many other factors change with the operation of 575volts in the 460volt motor. If it is a VFD, which i believe it is, would it be possible at all to run 575volt in the 460volt motor and expect a motor base speed increase? thanks for the quick response!

respectfully

 

[atvhead]

Sorry, my fault for leading everyone to a VFD.

There is no VFD present on this motor.

Bob
_innov8_

 

[LionelHutz]

if I'm not mistaken, their claim is that they have a unique winding method that increases the Corona Inception Voltage capabilities of their standard design motors

No, they just claim to use special wire which apparently also means they can just mush wind the coils and also not worry about using any extra coil-coil or slot insulation. Oh well, they're not the only manufacturer doing a really poor job of winding motors.

 

[HCBFlash]

Don't blame yourself ATV, this happens sometimes. Perhaps a new thread will get started.

As you can see, VFDs are the present black hole in the industrial AC motor field. If you keep your distance you won't get sucked in. (Oh boy, I feel another thread comin' on!)

As far as my own previous post goes, nothing against Kieth's website, but it's marke's website, LMPhotonics.com that's more educational as far as motors go.


flash



Me wrong? I'm just fine-tuning my sarcasm!

 

[itsmoked]

I would certainly agree with that! Mark designs VFDs I just use them once in a while.

HCBFlash; That's just my tag line so people can contact me if they desire. That way they can send me poison snakes in boxes, etc.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com