[RE-wrenches] how would you measure a partial short circuit

boB Gudgel boB at midnitesolar.com
Thu Jun 30 23:30:12 PDT 2011


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-bounces at lists.re-wrenches.org
> [mailto:re-wrenches-bounces at 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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