On 6/30/2011 11:35 PM, boB Gudgel wrote:
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
What does this part of your question mean ??
"I noticed a minor arc when one of the fuses was going it."
I see what you were saying. When the fuse was going "IN" ... Into the
fuse holder.
Could it be that the inverter was connected (but turned off otherwise)
and it arced as the inverter input capacitors were charging up ?
If so, then the current would die to nothing soon after the fuse was in
place. A clamp meter would show
that too.
boB
boB
boB
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