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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<br>
<br>
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<br>
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.<br>
<br>
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<br>
sometimes just turning the clamp around and measuring the opposite
polarity may measure slightly differently than the opposite polarity
and<br>
that zero calibration is usually necessary.<br>
<br>
boB<br>
鮑勃
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