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On 7/1/2011 12:07 AM, boB Gudgel wrote:
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On 6/30/2011 11:35 PM, boB Gudgel wrote:
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On 6/30/2011 8:35 PM, Nick Vida wrote:
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<div>Hi wrenches.<br>
<br>
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. <br>
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.<br>
Do any of you have any thoughts on how one would measure
for such a thing?<br>
<br>
nick vida</div>
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<br>
<br>
"<span style="font-family: "Courier New";"> I noticed
a minor arc when one of the fuses was going it."<br>
<br>
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<br>
I see what you were saying. When the fuse was going "IN" ...
Into the fuse holder.<br>
<br>
Could it be that the inverter was connected (but turned off
otherwise) and it arced as the inverter input capacitors were
charging up ?<br>
<br>
If so, then the current would die to nothing soon after the fuse
was in place. A clamp meter would show<br>
that too.<br>
<br>
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<br>
<br>
ONE more thing on this... Because the strings were at slightly
different VOC's, it's possible that the<br>
higher Voc string will back feed the lower voltage string and you
may very well see a small arc if the fuse<br>
is connecting the two strings together. No ground fault needed for
that to happen.<br>
<br>
boB<br>
<br>
<br>
<br>
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