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Old December 28th 07, 07:20 AM posted to rec.crafts.metalworking
[email protected] pentagrid@yahoo.com is offline
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First recorded activity by DIYBanter: Sep 2007
Posts: 116
Default 3 phase 200V, on (nominal 240) rotary phase converter

On Fri, 28 Dec 2007 13:27:12 -0800 (PST), willray
wrote:


Greetings -

Looking for some advice on running a piece of equipment with a 3-phase
motor. It's tagged at 200V, with a nameplate that says "rerated to
above
specifications by G.E."

The tool is headed for a new shop that I'm building (of very old
equipment),
so I don't have a dedicated 3-phase solution for the shop yet.

I run a small rotary converter in my current shop, and it does well
enough for my lathe, shaper, and mill. I was gearing up to put a much
larger
rotary in the new shop (have a really nice 15HP idler, and other bits
set
aside), but now I'm wondering if I should really run this one off of a
VFD, since I can theoretically limit maximum voltage on one of those.

Relatively naive physics suggests that up to some reasonable level.
over-voltage really shouldn't be a problem for an induction motor -
short of
stall conditions, it ought to draw less current, and probably run
cooler.

Of course, my naive physics has been known to get me in trouble a time
or two, as well.

Any suggestions, most greatly appreciated - this particular machine is
a fairly sacreligious query here, as it's a 1900's-vintage J. A. Fay
and Egan
woodworking Jointer, but in my defense, there's a Rivett 1030F that'll
be going online right across the aisle, just as soon as I work out
440V 3ph.

Will Ray

P.S. Any suggestions on "soft starting" a 15HP idler, such that I
could
realistically spin it up on my new shop's 200A feed (and preferably on
a
100A branch circuit), would also be delightful.



Reasonable overvoltage is no problem. The no load
losses will increase but it will draw slightly less full load
current and run cooler.

The problem is that, taken too far, the iron losses will
increase as it approaches saturation. Pretty well any motor is OK
at +10% on nominal. Most will tolerate +20% unless you are using
it at continuouse full load at maximum rated ambient temperature.

A useful insurance is to check that the measured full load
line currents are not significantly higher than the rated full
load current.

A sure fire idler soft start system is to use a small pony
motor to prerun it up to half speed.

Jim