[RE-wrenches] Unisolar Intermittent Ground Fault

[Kelly Larson]

If you're in Sebastopol you could ask Paul Hernday at Solmetric if the PVA would help.

Blessings,
Kelly


On Nov 26, 2012, at 4:55 PM, Robert Nuese wrote:

> Dear Wrenches
> 
> I've been experiencing a troubleshooting problem that you may be able to
> help me with.  Or, can anyone refer me to someone, maybe an electrical
> engineer?, who I could hire to help.
> 
> About 7 years ago I installed Unisolar modules on all the roofs of a complex
> of 12 mixed use buildings and one commercial building. These fed the
> grid through a variety of Fronius IG and SMA SunnyBoy inverters.
> 
> Ever since, we have had occasional intermittent ground faults on a few of
> the roofs, and more frequent ones on one roof. At least some of these I
> suspect were caused by the roofer. Standard procedure on the Unisolar
> modules is to put two screws through them that hold on the roof ridge
> z-strip metal closure piece. These also keep the modules from sliding off
> the roof in extreme hot weather. I found a number of screws placed
> slightly outside the allowed screw zone. After I'd moved the screws
> (and removed the raised metal edges the screws had made in the roof,
> and put insulation between roof and module in those locations), this has
> seemed to fix some problems. Similarly, putting tefzel patches, per Uni-
> solar instructions, on some big dings and scratches may have fixed some
> others.
> 
> However, I still occasionally, rather rarely, get ground fault indications
> on some inverters, and rather regularly get them on one specific IG 3000.
> Some times the indication is just in the software, and the problem disappears
> through resetting by disconnecting the inverter and reconnecting to reset the
> software. However, on that worst Fronius, it has usually blown the 1 amp
> ground fault fuse, indicating that there very likely has been a ground fault.
> 
> I suspect that these ground faults are brought on by thermal expansion and
> contraction, that may only occasionally, and briefly, bring hot and ground
> elements of the system into close enough proximity. Dampness seems to
> play a part, the ground faults almost always occur during the rainy season,
> and usually during a rainy period.
> 
> But whenever I get out to the site to test the system, the ground fault is
> always gone. I test by disconnecting both wires of each string, measuring
> the total voltage across, and then the voltage from each to ground. If there
> is a clear voltage to ground, then there is a ground fault, and its location in
> the string can be easily determined. If the voltage steadily goes toward
> zero, then a ground fault is not clearly present, and the location of where
> one had been is totally obscure.
> 
> I've done very thorough visual inspection of the roofs, and also of the
> disconnects, junction boxes, and gutters that the wires pass through.
> As mentioned, the modules have had some problems, and I've fixed them
> all, as well as can be done. The wires all seem fine. Well connected, neat,
> not close to raw metal edges, insulation ok, etc.
> 
> I've asked Unisolar (before they went bankrupt, now they don't answer the
> phones), and they've just recommended the testing I've done, and not had
> any other ideas. Same with Fronius - they think it's outside of the inverter,
> and the blown fuses support that position.
> 
> I could go on with more details about what I've done and thought about,
> for instance, is the Fronius too sensitive? But I'll catch my breath and see
> if anyone else has some input before I go into more detail.
> 
> SO what am I missing? What test should I do? How can I fix this problem?
> 
> OR does anyone know of somebody with more expertise who I could hire
> to help? I'm a fairly experienced solar installer, but I think this might be
> something that requires an electrical (or electronic?) engineer with a deep
> understanding of electrical theory, and with some advanced test equipment.
> Any recommendations? Probably needs to be someone within 100 miles of
> Sebastopol CA.
> 
> Thanks,
> Robert Nuese
> 
> 
> 
> 
> 
> 
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