Any existing source for 3-phase motor to run in either CW or CCW? 5

[MotoGP]

Seasons' Greetings to all Electrical Gurus:

I am presently employed by a mining company that owns one specialized piece of equipment known as an "agglomerator" which, in appearance, appears to be two large diameter cylinders that rotate about their respective axis in opposite directions.

The cylinders' opposing direction of rotation is a design requirement.

The two (2) drivers are both 3-phase, 4160 V, 500 h.p., 1800 r.p.m. motors; one is configured to turn CW and the other CCW.

During some asinine installation "misadventures", where in the past CW-rotating motors have been installed in the required CCW-rotating position, I have been informed that the panic move was to send the motor(s) to one of the plant shops, where the stator was somehow configured to influence the "transformation" between CW and CCW rotation such that it was later installed with the desired result...sort of.

(1) Perhaps it is only some "tribal knowledge" that I picked up somewhere, nonetheless I thought that to perform this sort of hijinx results in, among other problems, an unwanted appearance of destructive eddy currents. Please let me know if this notion is correct, and, if so, what this should mean to me from a technical standpoint.

(2) Would any electric motors exist, with the parameters that I have described above, such that there is a "safe-and-correct" (and relatively simple way) to influence the 3-phase motor to turn in either of the CW or CCW directions while maintaining an absence of unwanted eddy currents?

Very simple questions for the likes of those reading this enquiry, I'm sure. Puzzles the heck out of me though!

Thanks for your time and consideration...Happy Holidays!

 

[dpc]

AFAIK, the basic motor itself (stator/rotor) could care less which direction it is turning (three-phase induction motor).

The magnetic circuit, including eddy currents doesn't care much either, I wouldn't think.

The problems come with the cooling fans, anti-reverse ratchets, bearing slingers, etc. that do expect a certain direction of rotation.

It's very easy to change the rotation of a three-phase motor - just swap any two leads.

A motor will generally have a direction of rotation indicated by the manufacturer. Ignore that at your peril.

 

[jraef]

A motor will generally have a direction of rotation indicated by the manufacturer. Ignore that at your peril.

An AC motor dpc? I have yet to see one that does! Rotation is relative to the applied power. Maybe you meant that MACHINES often indicate a required rotation direction, but not the motor itself. AFAIK, AC motors are designed to rotate in either direction.

...the panic move was to send the motor(s) to one of the plant shops, where the stator was somehow configured to influence the "transformation" between CW and CCW rotation such that it was later installed with the desired result.

MotoGP, you were had! The only possibility is that the motors were custom designed and had directional cooling fans, but that is extremely rare. Agglomerators typically use standard off-the-shelf AC motors, nothing that special about them. What they probably did (once they stopped laughing) was to label the motor leads so that the installing electrician would connect them properly! Did they come back later to tell you that you needed a right-handed crescent wrench to put the connection box cover back on?

By the way, you need to send that electrician back to school if he didn't know that!

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[dpc]

jraef,

You're probably right. I was thinking of hollow-shaft vertical motors with anti-reverse ratchets, but that's really an add-on to the motor, I suppose.

 

[jraef]

I knew you knew. I was just being persnikety I guess.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[aolalde]

It depends on the motor size. Certainly small and medium size motors are bi-directional. Lots of Large Motors are manufactured for a specific rotation ( an arrow plate is attached to the frame) and as stated by DPC normally the main problem is proper cooling. Direction of Rotation does not have any influence on Eddy Currents.

 

[stardelta]

Lets not forget the specialy designed motors used for fan and close-coupled pump applications that have a threaded shaft, the fitment may come loose due to inertia if it spins in the wrong direction. I am sure the all the other repair guys have seen plenty of seized up pumps with an impeller thats spun off and jammed in the volute that come in with the comment "we just fitted it, turned it on and its taking out the overloads!"

 

[jraef]

Huh. I must be lucky I guess.
In the hundreds of MV motors I have worked with, I have never seen an arrow on the motor, unless it was applied AFTER it was biult on to the machine, and by machine, I include pumps, fans etc. The one I had with a nameplate indicating it had a directional cooling fan came with simple instructions as to flipping the fan over, and even then only because it was a close coupled motor where the air flow would have been partially blocked by the machine if it went the other way. Most big motors have a ducted cover that will either push or pull air across the frame. Rotation direction is irrelevent.

The point I was making however was that the motor itself could care less as far as the windings go. Rotation direction has more to do with the machine it is used on, be it a pump, fan or anything else. The machine he was working on should not have had any backspin ratchets etc. Someone telling him they reconfigured anything to "transform" it from CW to CCW was probably pulling his leg.

Eng-Tips: Help for your job, not for your homework Read faq731-376