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? 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 --- > --- end of quote --- > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > >
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