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Small grid-tie inverters? - Page 15

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Posted by Vaughn Simon on June 25, 2008, 8:55 pm

    I was talking more about the general principle, but you are more precisely
correct, the AC side was a synchronous motor.  In fact, back then I had no idea
that an induction motor could serve as an AC generator.

   Most folks automatically figure that the motor would have to reverse
direction to switch the direction of power flow, but that is not the case.   In
fact, they would happily go instantaneously from float to supplying full power
to the power buss with barely a grunt.  They were the perfect UPS (for the
technology of the times).

   We also used another bit of old technology that you can still find in UPSs,
the resonant (Sola) transformer.  We used a SOLA transformer (with it associated
capacitor) to store just enough energy to carry us for a Hz or two while a
mechanical relay switched power busses.


Posted by daestrom on June 25, 2008, 10:48 pm
Vaughn Simon wrote:

Yep.  Also regulated the output to NI's and PPI's despite voltage dips on
the vital bus.  Mag-amps hated voltage variations.

(remember, "When taking reactor protection from 'coincident' to 'single'
protection, *always* go through 'starboard test', *never* through 'port
test'."  If you know what that means, you *are* an old salty dog submariner

Posted by daestrom on June 25, 2008, 10:56 pm
 daestrom wrote:

Or was it always go through 'port test'??  Now I can't remember.

Posted by Cydrome Leader on June 30, 2008, 2:57 pm


They still make flywheel UPSes. The market for these seems to be factories
or places with lighting that cannot restart instantly after power loss.
The flywheel spins for X seconds or whatever it takes to switch to your
generator. High speed transfer switches for switching between different
utility feeds seems to be a big deal for the same reason.


I've not seen any modern ferroresonant UPSes, probably because of their
efficiency, but for plain and good quality power conditioning,
ferroresonant transformers cannot be beat. No solid state power converter
comes with 20 or 25 year warranties.

Posted by Vaughn Simon on June 30, 2008, 7:10 pm

   They still make them, but you are buying ancient technology.   Against my
better judgment, I replaced one with a brand new unit just last week.  Best
Power is now Powerware.  Ferroresonant transformers seem to have very high core
losses.  I have a Sola regulator here in my study that would make a good foot
warmer.  Judging from the temperature rise, it must vampire 20 or 30 watts 24/7.
Fortunately, I stopped using it years ago, and now I wonder why I didn't throw
it out years ago.


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