"DoN. Nichols" writes:


Yes. If you turn out to need a little more capability to start
the saw, hang another three phase motor on the RPC, start it after the
RPC is started, and it will help to start the saw.

I'm debating in my head if adding a flywheel to a RPC will improve its
ability to start big motors. I can generate arguments both way in my
head, but Machines 450 was 20+ years ago, and while I loved the class,
they say the mind is the first thing to go...



In one manner of thinking a VFD is just a special UPS. Years ago, I
worked at a company that made big 3 phase UPS's, as from the 10KW to 10MW
size.

These were ferroresonant UPS's. In mechanical terms, a FR system is a
transmission with a slip clutch and a big flywheel. You can lock the
output shaft, run it all day and nothing gets bothered. [You may know the
brand "Sola transformer"...]

In EE terms, they are short-circuit proof, and the FR 'tank' stablizes
the output across several cycles of line glitches.

A standard lab test for new designs involved a large 3 phase motor.
I recall it was ~4 ft diameter and 6+ long. No doubt it was surplus
from the steel mill.

You started the inverter module [Bigger units were usually collections
of 10KW modules...] up, and closed the breaker to the motor. Not much
happened; the humming got louder but that was it. If you looked at the
metering, you'd see the module was at 100% output power but so what, the
motor was still stopped.

Then, if you looked oh so closely, you could see it twitch and s l o w l y
turn a little and then more and ever so slowly it could be seen to be gaining speed....

Over 10-30 minutes, the motor would evenually come up to ~850 RPM, and the
current would drop to something normal. The module had passed..
--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433