[EMAIL PROTECTED] wrote:
I don't have a lot of experience with power systems either (though a couple
of recent projects have been quite an education by fire), but I'm thinking that
given the numbers, it's possible there's some mechanical problem. If the big
motor starts up under an abnormally heavy load it may require a surge
capability up to many times its rated continuous load. Any chance there could be
something mechanically binding, such that it comes up stalled? You may need to look
at both motor and generator for not only their continuous ratings, but also
compare the motor's startup current with the generator's surge rating. I'd tend
to want a surge rating on the generator with a generous margin, because the
mfrs tend to be a bit "optimistic" in such ratings. If the load has a large
inertia, the generator is going to need a correspondingly large inertia
(flywheel). A bigger generator may indeed be the answer - not for the continuous rating
but for the startup surge. But first I'd check to be sure there isn't
something mechanically wrong with the load, or maybe even electrically wrong with the
controller.
More like a wiring error IMHO, I have had a similar problem in Au where
an electrician did not realise what 208V equipment was :( Drew a hell of
a lot of current for a few reasons ;)
As to the voltage conversion, be careful how you're measuring things. I may
have this backwards, but I believe 208V normally refers to a delta connection,
whereas 240V refers to a wye connection. Picture the voltages of each phase as
an equilateral triangle centered at and spinning about the origin. The sides
of the triangle are 208V long, and each of the corners is 120V from the
origin, which represents the neutral. Thus if you measure one phase of a delta
connection (where you're measuring between two of the phase wires) you see 208V,
vs. measuring from a phase to the neutral where you see 120V. I lost a factor of
two somewhere in the visualization, but the basic concept is correct. Is it
possible that you've somehow crossed up the motor connections such that it's
expecting a delta connection but you've supplied a wye connection? That too
would account for a very heavy current.
There is a mathematical formula for this, but stuffed if I can remember
this (besides it is 0815 on a Sundry morning and I have not had the
wakeup levels of caffeine or nicotine yet)
You might want to try one posting over at the regular PEDA forum, asking for
replies to come over here. I thought I was signed up here but never got any
posts till I recently resubscribed; there may be others in the same boat.
Steve Hendrix
Regards,
Kat.
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