I figured you'd have something to say bout this. And if you didn't chime in, I would have called your attention. Thanks for replying.As long as the insulation can handle it then yes they would run just fine and work like one bigger higher voltage motor.
I can see a problem with varying load of each and, the difference in slip frequency is going to unbalance things.
Not something I would tend to do!
Particularly in a VFD application.
Max.
Or are you thinking about VFD spikes? (I didn't say it, but yes, this is/would be a VFD application).
Consider the voltage differential between the live line and the earth grounded stator cores.
In the Us most 480 VAC three phase systems are 277/480 Wye connected so that no line insulation is seeing more than 277 VAC between it and ground.
Although There are applications where corner grounded 480 VAC is used as well so I personally I don't see it as being much of a concern really given a properly built motor should be built to withstand at least several KV of voltage potential between the windings and frame without breakdown issues.
Mechanically coupled I take to be mechanically locked shaft to shaft so there is no variances in slip ratios just the same as when two motors are wired parallel and sharing a common load with their shafts locked together.
Series or parallel operation the electrons making the magnetic fields could care less.
Where was VFD operation mentioned?
I once had to consider running 2 identical motors, identical loads in parallel off of a VFD, I contacted WEG who supplied the VFD and they confirmed that as long as the load was identical, it should be OK.
Is this a sensorless vector or the more simple variable frequency VFD?
Can you guarantee the identical load for each?
Max.
It seems to me that it would be a lot simpler to run the motors in parallel, with no need for a transformer.I didn't consider that because this would be powered by an isolated step up transformer after the VFD
here's the thing: I need 60kW worth of motor at the end of a 200m cable. I need to seriously cut back on the amps or else voltage drop will quickly consume all of applied voltage and the we end up with tens of kW dissipated in the cable and a stalled burning motor.It seems to me that it would be a lot simpler to run the motors in parallel, with no need for a transformer.
Before I saw that you were thinking of using a transformer, I thought that you would be better to step the voltage down with a transformer and run the motors in parallel.
I think that if you ran two motors in series, and one got loaded more, it could not take much more current, so the voltage on the loaded one would reduce, resulting in too much voltage on the other one, possibly saturating it. I would try parallel first, especially if it meant not needing a transformer.
The wire is rated 4.5kV. It's a subsea power umbilical. The application is a subsea saw tool. Pretty much exactly like the bandsaw analogy but with a few twists.It looks good to me, and if the motors have been meggered, I wouldn't worry about the applied voltage, except you may want to check the wire you're using for it's voltage rating. I see the advatage of this being smaller wire due to lower current, and disadvantage of needing wire with a higher voltage rating.
Jeff
Sounds reasonable to me but then I am one of the few who doesn't mind practicing the 'experiment until it fails' method of learning either.
[...]
Personally I won't guarantee your motors wired in series running a higher than stock voltage will work but everything I know about transformers and motors and the added benefits of running them submerged in oil would have me trying a test run that way.
To be honest I would be half tempted to try running all four in series as well with the pressurized oil containment system in place. Especially so if they were VFD rated motors that have the higher than standard winding insulation built in.
That's my thoughts.
OK I posted, 5sec later I get a "there have been new replies " message, I refresh, I see my post twice. I only clicked once.wtf why this doublepost thing again?
Sounds like we have similar thoughts on test methods and it sounds like we're on the same page; the page I was on when I decided to post this. Thanks for humoring me.
I just wanted to see if I could get at least one person (one person who knows what they're talking about) to not call me crazy before I open my mouth about it in the real world.
I got that, I got your "blessing" - or at least your withholding of condemnation, so that's good enough for me. If it fails miserably I'll tell everybody it was all your idea.
I am going to ask for money to test this wacky idea (w/ fractional hp motors first) and if I get the green light I'll keep you in the loop.
Again sorry for disclosing everything in baby steps; I know that must have been annoying. I think we can agree that this is way way "outside the box" and when you compile all the ways in which it flies in the face of typical, it probably sounds preposterous. But examining each aspect alone, they all seem to have their own merit.
Thank you for your time and experience.
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