On Thu, 21 Jan 2010 08:23:01 -0600, Ignoramus18274
wrote:

On 2010-01-21, wrote:
On Wed, 20 Jan 2010 16:57:41 -0600, Ignoramus29895
wrote:
Actually right now, the lathe is on a Phase-A-Matic static phase
converter. The Phase-A-Matic came with the lathe. It runs, but I am
getting only 2 HP out of 3. Maybe I should just leave it as is. I
would not be likely to use all of the HP without coolant.

I want to do the right thing, and it is not immediately obvious what
is the right thing. I know for sure that I do not need to vary input
frequency.

It seems that the phase converter route is nicest to the motor, and
lathe, but is less convenient for me.

There's now way of being sure but the odds are pretty good.

Great

VFDs increase the peak voltage stresses on the motor insulation,
Most older motors survive (all that I have used) but a few fail.
Capacitors do NOT help.

Jim, do inductors help? Those line reactors, would a line reactor help
if I installed one between the drive and the motor?

The yard stick I would use is simply based on the mechanics
of the motor installation. If it's difficult or impossible to
replace it with a modern motor then it makes sense to stick with
an RPC.

It is not very special. Here's a picture.

http://igor.chudov.com/projects/Clau...arage-0017.jpg

Looks like 184T to me, but could be an old frame size due to it having
been made in 1966.

If on the other hand it's a fairly standard motor that
could be replaced if disaster struck I would chose the VFD drive
on the basis that the increased convenience outweighs the small
increase in risk.

I also like Jim Wilkins' suggestion of trying to test insulation with a
megger. This would be my first time of using a megger. I believe I
have one from my old military surplus days.


Line reactors are useful because they slow the rise time of
the transients but, unless you've long cable runs, the effect is
not large. It's probably not worth buying a set but if you
happen to have one on hand you might as well fit them.

A megger test is certainly helpful but even that doesn't give
you full assurance. It's a very long time since I signed off
equipment but the test yardstick in those days was twice peak
working voltage plus 1000V.

Jim