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We've been having an issue for a while with DC Isolation faults. It happens mostly when it rains and won't clear up until it's had a few good dry days. But also some mornings (maybe because of dew?) we'll get DC Isolation faults. We've tried everything to isolation where the problem is and have replaced both inverters already but the system still persists. One thing I noticed is that when the system was reinstalled, many of the Unirac Grounding Clips were missing. I know these are important, but could they be the cause of these DC Isolation faults?
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I very much doubt the grounding clips have anything to do with ground
current leakage. Check out the integrity of the wiring. Do you know how
much leakage current flows? How is your array configured?
In my string inverter cas,e I would unplug BOTH leads of a string and see
if the leakage goes away. To test a disconnected string, under sun see if
any power can be drawn from either end to ground (which must flow thru
a ground fault. I use this test setup to detect current of a fraction of an amp,
4 bulbs in series handle my 400VDC system. If the current is much less,
use a plain old voltmeter. BUT a very high impedance meter, esp a digital
type, will be too sensitive to static charges. SO put a resistor to draw maybe
0.1A, IN PARALLEL with the volt meter leads to drain off static and show
real flow. good luck, Bruce Roe
PVtestLt.JPG
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Bruce. I really like your tester but you might have to provide a circuit diagram to those people that want to build one but don't really know how.Comment
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The wiring has been replaced and we're still having the issue. Weird thing is that it's not all the time. Is that normal? When it's dry, it works perfectly fine. But if we have a bad storm or there's a lot of moisture, then we get the faults.
I have 2 inverters, each one hooked up to 20 panels with optimizers at each panel. At first I had each 20 panel set on 1 string but then we broke it out to 2 strings thinking that might have been the issue. But we're still getting these faults even with 2 strings and new wires. Trying to figure out the best way to isolate the problem but it's complicated because on days that are great to work on it, I don't get any faults. Any thoughts on how water would affect the current leakage?Comment
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Water will affect current leakage. You could have one bad panel. I don't know if you have a combiner box you can use to disconnect array sections.
BE VERY careful if there is light. PV panels in a string can generate 100's of volts and quickly ruin a MC4 connector if it's connected/disconnected live. And that high
voltage can also make you un-alive quicklyPowerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-ListerComment
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Enough light bulbs wired in series to withstand the array voltage is not much.
I FORGOT TO SAY, I only connect/disconnect panel wiring in the dark, under
a work light. Plug the MC4s with dummys (latches ground off), then connect
a meter under the sun. Even those bulbs draw a nice arc. Bruce RoeComment
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You mentioned optimizers I'm guessing Solar Edge? They use the brand Multi Contact for their connectors that is now owned by Staubli . What brand are the connectors from the modules? Solar Edge has posted on their tech pages that "compatible" connectors can cause ground fault problems. They recommend all connectors be of the same manufacturer or have been tested and certified by a 3rd party to be compatibleLast edited by Mike 134; 04-14-2022, 07:15 AM.Comment
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Oh man, we've replaced a bunch of the connectors as well. This problem is so crazy because I've been told it could be literally any part of the system. One tech told me it was the inverters. So we replaced both inverters and that wasn't it. Then it was the wires, we ran new wiring and split the strings. That wasn't it. We replaced a bunch of the connectors, still not it. They suggested it could be bad optimizers (no idea which ones) or bad modules. That's pretty much every aspect of the system.Comment
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I'll need to check, that was another installer that gave up on this job. I'm thinking I will try with the process of elimination now and see if I can narrow down where the problem is. Try just 1 string of 10, then add another string of 10, etc until I start seeing some faults again. Hopefully this will help me at least narrow down the problem to a single string of 10 and then I can work from there.Comment
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Oliver84 , it was implied that you have a Solar Edge system. Solar Edge has an app note for isolation fault detection. Whether or not the procedure works, I have no idea.Comment
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Thank you, the setApp doesn't work with my inverters even though they're solarEdge but I have done the same thing on the inverter itself. You can go into the maintenance menu and look at the DC Isolation Diagnostics menu and it'll help you locate the string. However, we've never been able to find this to be accurate. We've had probably 5 or 6 other technicians out here trying to find this "leak" and nobody's been able to find it yet. I'm in South Florida and apparently there aren't any recommended SolarEdge contractors out here to help.
I believe we may have isolated the problem within 8 panels. I have 32 that seem to be working but we would need a good rain storm to be sure. I'll post an update after we get some rain and see if the faults come back.Comment
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