Richard L Ratico wrote:
Interesting question, Mick. It may depend on the point in the cycle when the
transformer lost power and the duration of the blip.
Dick Ratico
--- You wrote:
Before I present a suggestion, here's a question:
If by chance William is able to energize the transformer without tripping
the breakers, what if there is a brief break in the power...such as a
half-second?
I don't suppose there's capacitance here...more like magnetic flux...but
would there be a brief window before the transformer bleeds down and
requires another equally strong inrush current?
One thing that can (and does) happen is that, depending on where in the
AC cycle the AC source
went away, it can leave the transformer magnetized in one polarity or
another. Then, when
the AC source comes back on, it ~may~ return in a polarity to further
magnetize the transformer
core in the SAME direction it was magnetized in, and that can saturate
the transformer core
giving you basically, a short across the AC source. That's where the
majority of unknown and
intermittent surges come from IMHO and experience. If the
transformer is way bigger than it
needs to be for a particular application, or if the wire it is wound
with is small enough and has high
enough resistance, then the current is more limited.
This can also be a problem just turning an inverter off and back on
again. Capacitors charging up
is also a reason for surging of course.
2.5 cents
boB
Or...would a tiny blip in the input power result in another big surge
requirement?
Mick Abraham, Proprietor
www.abrahamsolar.com
Voice: 970-731-4675
2010/5/13 Richard L Ratico <richard.l.rat...@valley.net>
Sorry for the additional post here, but it includes a typo correction:
Bill,
Not a lot of personal experience with this issue. The one time I had to
deal
with it, we were able to leave the circuit on, once we got it energized.
As you know, the crux of the problem is the nature of the voltage relative
to
it's cycle when connection is attempted.
An internet search resulted in this explanation that was very helpful. See:
http://www.opamp-electronics.com/tutorials/inrush_current_2_09_12.htm
As I understand it now, counterintuitively, you don't want to switch at the
zero
crossing. SS relays aren't my strong suit either, but if they connect at
that
moment.......
Is your step up transformer actually designed by the manufacturer to be a
step
up unit, or are you using a step down unit in reverse?
Again, according to information found in my search, not personal
experience, the
latter can contribute to higher than expected inrush.
Dick Ratico
--- You wrote:
Thanks for the reply. To clarify, we have tried his with one transformer
and with two transformers. Our success rate is lower powering one
transformer. My hunch is that the capacitance of the feeder is
buffering...
I wonder if I use a large solid state relay with zero crossing switching I
might have better luck.
William Miller
At 06:23 PM 5/12/2010, Richard L Ratico wrote:
Bill,
Your branch circuit breaker is pretty small.
Are you energizing both transformers simultaneously? If so, it might help
to
energize them individually.
The branch breaker can be up to 250% of the step up transformer's primary
rating. 10kVA/240V=41A.
41A x 2.5=100A. (round numbers). To do this you would also need
overcurrent
protection on the transformer secondary.
Of course, you've already got the 100A main tripping. That's why I asked
if
you're
energizing them simultaneously.
Transformer inrush can be a real problem.
Hope this helps.
Dick Ratico
Solarwind Electric
--- You wrote:
Friends:
I have on off-grid client that is trying to eliminate winter generator run
time. He has a rental on another corner of the property that has grid
power. When it was installed, he put in an extra meter, hoping to use it
to run a utility back up feeder to charge batteries.
We are now installing this feeder. We purchased two 10KVA 240/600 volt
transformers to bump the voltage to 600 and then back down to 120/240.
Here's the problem: when we energize the circuit breaker that feeds the
transformer, the circuit breaker AND the main breaker trip. The
transformer is 10KVA, the main is 100 amps and the branch breaker is
60A. The breakers hold sometimes but trip other times. This is obviously
an inrush problem. How do I correct this problem?
Thanks in advance,
--- end of quote ---
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