On 6/30/2011 10:48 PM, Marv Dargatz wrote: > > Come on, Bob. > > It’s a ground fault in the array. Just one more example why ungrounded > arrays are FAR safer. >
Could also possibly disconnect the arrays at both ends and use a voltmeter to measure resistance to ground to find it if that's what the problem is. Or use a current limited supply and measure voltage drops to zoom in on the problem. boB > See ya! > > Marv > > Director of Technology and Support, North America > > *SolarEdge Technologies, Inc.* > > Tech Support Mobile: +530.798.6770 > > Mobile: +530.392.0356 > > *From:*re-wrenches-boun...@lists.re-wrenches.org > [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *boB > Gudgel > *Sent:* Thursday, June 30, 2011 10:19 PM > *To:* RE-wrenches > *Cc:* Nick Vida > *Subject:* Re: [RE-wrenches] how would you measure a partial short circuit > > On 6/30/2011 8:35 PM, Nick Vida wrote: > > Hi wrenches. > > I had an interesting case today that I have been thinking about since > it happened. I dont have all the details because the homeownter had to > leave before I was done with the service call, but here is what I do > know. SB5000 with 2 strings of 15 modules. String one was 437 vdc, and > string 2 was 247vdc. I decided to look for a ground fault, and I > turned off the inverter. I measured for ground faults and found no > evidence of anything wrong in that regard. As the homeowner was out of > time and wanted me to go, I re-landed the wires in the dc disco, and > when I replaced the fuses, I noticed a minor arc when one of the fuses > was going it. Although I had no time to measure it, I think that there > might be a partial short circuit, possibly with one complete string > and some panels of the other string, and the remaining panels on the > second string. My mind was racing with how I could have measured for a > partial short circuit without seeing it as an arch. I can imagine such > a thing on a bigger system being a dramatic electrical event. > needless to say, I cant wait to get back there and go through the > signal path properly and find out what the electrician did. And of > course i realized that replacing the fuses in such a questionable > situation was probably not the best idea. > Do any of you have any thoughts on how one would measure for such a thing? > > nick vida > > > I'd probably use a DC clamp on ammeter. Clamp on and measure the top > and bottom current of each string... What comes in ~should~ come out. > > If it's much different on one end vs. the other end of one string, > maybe that string is conducting around the path somehow. Remember that > sometimes just turning the clamp around and measuring the opposite > polarity may measure slightly differently than the opposite polarity and > that zero calibration is usually necessary. > > boB > 鮑勃 >
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