Re: [RE-wrenches] Unisolar Intermittent Ground Fault
Hi Robert, Get a mega Ohm meter, isolate the home runs and perform a test. You should get 550 MOhms. If not, there's something likely wrong with that string that's causing the intermittent ground fault. Or, have someone stand on the ground with a hose pointing it at the roof and try to find it using the voltage method you've been doing. Date: Mon, 26 Nov 2012 16:55:16 -0800 From: Robert Nuese robertnu...@sonic.net To: re-wrenches@lists.re-wrenches.org Subject: [RE-wrenches] Unisolar Intermittent Ground Fault Message-ID: 9c067b77-378b-40ed-ab44-ff966dc20...@sonic.net Content-Type: text/plain; charset=us-ascii 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. nt. Any recommendations? Probably needs to be someone within 100 miles of Sebastopol CA. Thanks, Robert Nuese ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Unisolar Intermittent Ground Fault
Robert, Having installed hundreds of Uni-Solar modules, the only failure I every experienced was a framed US64 that had the PV negative short to frame. Flexing the module would create intermittent failure. You have PV laminates so your ground fault may be to the metal roof. I might be stating the obvious but here's my list of tests: I would disconnect and hi-pot test each laminate (ref. sec. 4.6, pg 48, Installation Guide, AA4-3670-05, 10/05). If that does not produce results, apply pressure with a heavy roller up and down the edges where the diodes and cell interconnect traces are while testing. Check all wire penetrations into the channel. Make sure all wire expansion rules were followed, look for stressed wire. Check for any screws installed in other than the two approved areas. There are two versions of laminates. One has a VERY narrow area. 0.65 by 2.75, for screw penetration (ref. sec. 3, pg 17, Installation Guide, AA4-3670-05, 10/05). A misplaced screw may have allowed water to migrate to the trace areas and be providing a path through the screw. RIP Stan and Uni-Solar, A brilliant mind and the best performing PV's ever. Larry Crutcher Starlight Solar Power Systems On Nov 26, 2012, at 5:55 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
Re: [RE-wrenches] Unisolar Intermittent Ground Fault
Let us know what the megohmmeter says. FWIW: There is some precedent for premature product failure in a roof-integrated product manufactured by Energy Conversion Devices (Uni-Solar): http://www.utsandiego.com/news/2012/sep/14/tp-flawed-solar-panels-removed-at-schools/?printpage=all On Nov 27, 2012, at 10:12 AM, Larry Crutcher, Starlight Solar Power Systems wrote: Robert, Having installed hundreds of Uni-Solar modules, the only failure I every experienced was a framed US64 that had the PV negative short to frame. Flexing the module would create intermittent failure. You have PV laminates so your ground fault may be to the metal roof. I might be stating the obvious but here's my list of tests: I would disconnect and hi-pot test each laminate (ref. sec. 4.6, pg 48, Installation Guide, AA4-3670-05, 10/05). If that does not produce results, apply pressure with a heavy roller up and down the edges where the diodes and cell interconnect traces are while testing. Check all wire penetrations into the channel. Make sure all wire expansion rules were followed, look for stressed wire. Check for any screws installed in other than the two approved areas. There are two versions of laminates. One has a VERY narrow area. 0.65 by 2.75, for screw penetration (ref. sec. 3, pg 17, Installation Guide, AA4-3670-05, 10/05). A misplaced screw may have allowed water to migrate to the trace areas and be providing a path through the screw. RIP Stan and Uni-Solar, A brilliant mind and the best performing PV's ever. Larry Crutcher Starlight Solar Power Systems On Nov 26, 2012, at 5:55 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
[RE-wrenches] Unisolar Intermittent Ground Fault
Thanks to the Wrenches who have offered good advice. In answer to several of you who suggested megger testing, No, I'm afraid I don't own a megger. It had become clear to me that this might well be a useful tool in my case, but the things are expensive. I've managed to install pv systems for 10 years without one, so I can't justify buying one just for this one issue. I also had the impression that megger testing may be a bit hard to interpret, and perhaps incon- clusive, especially for someone with no previous experience. Now Larry Crutcher has drawn my attention to a Unisolar installation guide (newer than versions I've got) that gives instructions on how to use the megger to test a Unisolar installation. This is just what I need. I'm a bit surprised that the Unisolar techs I'd spoken to on several occasions about my problems had never talked about megger testing, or these instructions. So, I need a megger, at least temporarily. The Unisolar instructions call for the use of the BM21 or other quality megger. The BM21 is no longer in production. There are a confusing array of different models available. Can anyone offer suggestions about other models that would or would not be suitable for my use? According to the Megger co. website the new model that replaces the BM21 is the MIT525, which I can buy online for $3,576. Whew! On the other hand, I gather I can buy a Fluke 1507 insulation tester for $500. Would that be adequate? Anyway, even at that much cheaper, for solving one problem in 10 years, it would make more sense to rent… I called a few of the equipment rental agencies in my neighborhood, but none had ever heard of a megger. Does anyone have any idea where I could rent one - or is there a wrench in my neck of the woods (70 miles north of San Francisco) who would like to rent me theirs? Or does anybody have a suggestion about a particularly good deal on buying one? Or maybe there is a nearby wrench who I could hire to help, someone with a megger, who already knows how to use it.? Here is a big question. I had assumed that such testing would have to be done on de-energized circuits, which for the solar panel part would mean at night. The Unisolar instructions don't mention this. They say to disconnect each string and then short each out before the test, using a jumper. This strikes me as odd, and a bit scary. Would it not be better to do this on a de-energized circuit at night? Thanks very much for any further information, Robert Robert, Having installed hundreds of Uni-Solar modules, the only failure I every experienced was a framed US64 that had the PV negative short to frame. Flexing the module would create intermittent failure. You have PV laminates so your ground fault may be to the metal roof. I might be stating the obvious but here's my list of tests: I would disconnect and hi-pot test each laminate (ref. sec. 4.6, pg 48, Installation Guide, AA4-3670-05, 10/05). If that does not produce results, apply pressure with a heavy roller up and down the edges where the diodes and cell interconnect traces are while testing. Check all wire penetrations into the channel. Make sure all wire expansion rules were followed, look for stressed wire. Check for any screws installed in other than the two approved areas. There are two versions of laminates. One has a VERY narrow area. 0.65 by 2.75, for screw penetration (ref. sec. 3, pg 17, Installation Guide, AA4-3670-05, 10/05). A misplaced screw may have allowed water to migrate to the trace areas and be providing a path through the screw. RIP Stan and Uni-Solar, A brilliant mind and the best performing PV's ever. Larry Crutcher Starlight Solar Power Systems ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Unisolar Intermittent Ground Fault
Someone earlier suggested contacting Solmetric in Sebastapol: http://www.solmetric.com/contact-us.html Their PVA I-V curve tracer is a great troubleshooting tool, and they also carry a Megger MIT 430 insulation tester: http://www.solmetric.com/megger-mit430.html Maybe they have a kit (PVA + Megger) that they use in-house that you could rent you for a day? It's worth asking, especially since you are in the neighborhood. On Nov 27, 2012, at 5:32 PM, Robert Nuese wrote: Thanks to the Wrenches who have offered good advice. In answer to several of you who suggested megger testing, No, I'm afraid I don't own a megger. It had become clear to me that this might well be a useful tool in my case, but the things are expensive. I've managed to install pv systems for 10 years without one, so I can't justify buying one just for this one issue. I also had the impression that megger testing may be a bit hard to interpret, and perhaps incon- clusive, especially for someone with no previous experience. Now Larry Crutcher has drawn my attention to a Unisolar installation guide (newer than versions I've got) that gives instructions on how to use the megger to test a Unisolar installation. This is just what I need. I'm a bit surprised that the Unisolar techs I'd spoken to on several occasions about my problems had never talked about megger testing, or these instructions. So, I need a megger, at least temporarily. The Unisolar instructions call for the use of the BM21 or other quality megger. The BM21 is no longer in production. There are a confusing array of different models available. Can anyone offer suggestions about other models that would or would not be suitable for my use? According to the Megger co. website the new model that replaces the BM21 is the MIT525, which I can buy online for $3,576. Whew! On the other hand, I gather I can buy a Fluke 1507 insulation tester for $500. Would that be adequate? Anyway, even at that much cheaper, for solving one problem in 10 years, it would make more sense to rent… I called a few of the equipment rental agencies in my neighborhood, but none had ever heard of a megger. Does anyone have any idea where I could rent one - or is there a wrench in my neck of the woods (70 miles north of San Francisco) who would like to rent me theirs? Or does anybody have a suggestion about a particularly good deal on buying one? Or maybe there is a nearby wrench who I could hire to help, someone with a megger, who already knows how to use it.? Here is a big question. I had assumed that such testing would have to be done on de-energized circuits, which for the solar panel part would mean at night. The Unisolar instructions don't mention this. They say to disconnect each string and then short each out before the test, using a jumper. This strikes me as odd, and a bit scary. Would it not be better to do this on a de-energized circuit at night? Thanks very much for any further information, Robert Robert, Having installed hundreds of Uni-Solar modules, the only failure I every experienced was a framed US64 that had the PV negative short to frame. Flexing the module would create intermittent failure. You have PV laminates so your ground fault may be to the metal roof. I might be stating the obvious but here's my list of tests: I would disconnect and hi-pot test each laminate (ref. sec. 4.6, pg 48, Installation Guide, AA4-3670-05, 10/05). If that does not produce results, apply pressure with a heavy roller up and down the edges where the diodes and cell interconnect traces are while testing. Check all wire penetrations into the channel. Make sure all wire expansion rules were followed, look for stressed wire. Check for any screws installed in other than the two approved areas. There are two versions of laminates. One has a VERY narrow area. 0.65 by 2.75, for screw penetration (ref. sec. 3, pg 17, Installation Guide, AA4-3670-05, 10/05). A misplaced screw may have allowed water to migrate to the trace areas and be providing a path through the screw. RIP Stan and Uni-Solar, A brilliant mind and the best performing PV's ever. Larry Crutcher Starlight Solar Power Systems ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive:
Re: [RE-wrenches] Unisolar Intermittent Ground Fault
http://www.amazon.com/Extech-380260-Autoranging-Digital-Insulation/dp/B000EWW2UA/ref=sr_1_1?ie=UTF8qid=1354065758sr=8-1keywords=extech+insulation $239 On Tue, Nov 27, 2012 at 7:32 PM, Robert Nuese robertnu...@sonic.net wrote: Thanks to the Wrenches who have offered good advice. In answer to several of you who suggested megger testing, No, I'm afraid I don't own a megger. It had become clear to me that this might well be a useful tool in my case, but the things are expensive. I've managed to install pv systems for 10 years without one, so I can't justify buying one just for this one issue. I also had the impression that megger testing may be a bit hard to interpret, and perhaps incon- clusive, especially for someone with no previous experience. Now Larry Crutcher has drawn my attention to a Unisolar installation guide (newer than versions I've got) that gives instructions on how to use the megger to test a Unisolar installation. This is just what I need. I'm a bit surprised that the Unisolar techs I'd spoken to on several occasions about my problems had never talked about megger testing, or these instructions. So, I need a megger, at least temporarily. The Unisolar instructions call for the use of the BM21 or other quality megger. The BM21 is no longer in production. There are a confusing array of different models available. Can anyone offer suggestions about other models that would or would not be suitable for my use? According to the Megger co. website the new model that replaces the BM21 is the MIT525, which I can buy online for $3,576. Whew! On the other hand, I gather I can buy a Fluke 1507 insulation tester for $500. Would that be adequate? Anyway, even at that much cheaper, for solving one problem in 10 years, it would make more sense to rent… I called a few of the equipment rental agencies in my neighborhood, but none had ever heard of a megger. Does anyone have any idea where I could rent one - or is there a wrench in my neck of the woods (70 miles north of San Francisco) who would like to rent me theirs? Or does anybody have a suggestion about a particularly good deal on buying one? Or maybe there is a nearby wrench who I could hire to help, someone with a megger, who already knows how to use it.? Here is a big question. I had assumed that such testing would have to be done on de-energized circuits, which for the solar panel part would mean at night. The Unisolar instructions don't mention this. They say to disconnect each string and then short each out before the test, using a jumper. This strikes me as odd, and a bit scary. Would it not be better to do this on a de-energized circuit at night? Thanks very much for any further information, Robert Robert, Having installed hundreds of Uni-Solar modules, the only failure I every experienced was a framed US64 that had the PV negative short to frame. Flexing the module would create intermittent failure. You have PV laminates so your ground fault may be to the metal roof. I might be stating the obvious but here's my list of tests: - I would disconnect and hi-pot test each laminate (ref. sec. 4.6, pg 48, Installation Guide, AA4-3670-05, 10/05). - If that does not produce results, apply pressure with a heavy roller up and down the edges where the diodes and cell interconnect traces are while testing. - Check all wire penetrations into the channel. - Make sure all wire expansion rules were followed, look for stressed wire. - Check for any screws installed in other than the two approved areas. There are two versions of laminates. One has a VERY narrow area. 0.65 by 2.75, for screw penetration (ref. sec. 3, pg 17, Installation Guide, AA4-3670-05, 10/05). A misplaced screw may have allowed water to migrate to the trace areas and be providing a path through the screw. RIP Stan and Uni-Solar, A brilliant mind and the best performing PV's ever. Larry Crutcher Starlight Solar Power Systems ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org -- Chris Mason President, Comet Systems Ltd www.cometenergysystems.com Cell: 264.235.5670 Skype: netconcepts ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios:
[RE-wrenches] Unisolar Intermittent Ground Fault
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 ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Unisolar Intermittent Ground Fault
Have you tried a megger? The 1,000v setting should display any breakdown areas. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Unisolar Intermittent Ground Fault
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 ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
