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--></style></head><body lang="EN-US" link="blue" vlink="purple"><div class="WordSection1"><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546a">Hi Corey,</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546a"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546a">I’ve done a lot of ground fault troubleshooting over the years with isolated and non-isolated inverters and I have often seen the type of bleedoff that you describe below for the ungrounded conductors. But, it really should start zeroing out to under five volts within about 10 seconds. I’m not being terribly accurate with my numbers here – it seems to vary for each project. If it hangs at 50 V for a while you might indeed have a “leakage” issue such as moisture conducting through an abraded conductor or splice. That’s where the insulation tester comes in handy. </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546a"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546a">I have a Fluke 1503 insulation tester which has worked fine for my purposes. </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546a"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546a">Chris Mason’s post about the low impedance meter is interesting. I have a few meters including a Fluke 116 which apparently has a low impedance (loZ) setting. If you have a meter with a low impedance setting maybe you could try that? </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546a"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546a">Best,</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546a"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546a">August</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546a"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546a">Luminalt</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546a"> </span></p><div style="border:none;border-top:solid #b5c4df 1.0pt;padding:3.0pt 0in 0in 0in"><p class="MsoNormal">
<b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> <a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a> [mailto:<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a>] <b>On Behalf Of </b>Chris Mason<br>
<b>Sent:</b> Friday, March 28, 2014 1:30 PM<br><b>To:</b> RE-wrenches<br><b>Subject:</b> Re: [RE-wrenches] Capacitive Discharge Test Results</span></p></div><p class="MsoNormal"> </p><div><p class="MsoNormal">If you are using a high resistance meter, you may be experiencing phantom voltages. Here's a Fluke paper on it.</p>
<div><p class="MsoNormal"><a href="http://support.fluke.com/find-sales/Download/Asset/2105317_A_w.pdf">http://support.fluke.com/find-sales/Download/Asset/2105317_A_w.pdf</a></p></div><div><p class="MsoNormal"> </p></div><div>
<p class="MsoNormal">You might also discuss with the manufacturer putting a 1M ohm resistor from the center of the strings to the grounded roof to bleed off any stray voltage. It would only bleed 1mA at 1000V so it would not affect performance. Usually this voltage is apparent when the strings have not connected to the load.</p>
</div></div><div><p class="MsoNormal" style="margin-bottom:12.0pt"> </p><div><p class="MsoNormal">On Fri, Mar 28, 2014 at 3:41 PM, Corey Shalanski <<a href="mailto:cshalanski@joule-energy.com" target="_blank">cshalanski@joule-energy.com</a>> wrote:</p>
<div><p class="MsoNormal">Fellow Wrenches,</p><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal">We recently commissioned a 220kW rooftop PV system and are having some inverter malfunction issues. The system details are as follows:</p>
</div><div><p class="MsoNormal">- Inverters: Power One Aurora Trio-27.6 (x7)</p></div><div><p class="MsoNormal">- Modules: Stion STN-130 (x1690)</p></div><div><p class="MsoNormal">- Array: Strings of 14-16 modules each, 8 strings per combiner, 1 combiner per MPPT input</p>
</div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal">It has been less than two months since we commissioned the system, and we have already seen five of the inverters malfunction. While troubleshooting these issues the inverter manufacturer had me measure positive-to-ground and negative-to-ground voltage readings. At the inverter level I measured instantaneous voltages of 100-200V before seeing a bleedoff; at the string level the voltages were 10-20V before bleedoff.</p>
</div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal">The inverter manufacturer is concerned with the magnitude (~200V) of this instantaneous voltage and also the delay in bleeding off to zero - after about five seconds the voltage level was still approximately 50V (but still dropping). The manufacturer is claiming that this residual voltage should drop to zero much more rapidly AND the presence of such a delayed bleedoff indicates significant "leakage" coming from the array.They are further claiming that this leakage is responsible for the damage to the inverters. They suggested using a megger to test insulation resistance throughout the installation.</p>
</div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal">My questions to the group:</p></div><div><p class="MsoNormal">- Is there any truth in the inverter manufacturer's claims?</p></div><div><p class="MsoNormal">
- Do my field measurements seem out of range from what others are seeing with ungrounded arrays?</p></div><div><p class="MsoNormal"> </p></div><div><p class="MsoNormal">Thanks for any information you can provide.</p></div>
<div><p class="MsoNormal">--</p></div><div><p class="MsoNormal">Corey Shalanski</p></div><div><p class="MsoNormal">Joule Energy</p></div><div><p class="MsoNormal">New Orleans, LA</p></div><div><p class="MsoNormal"><img border="0" id="_x0000_i1025" src="https://mailfoogae.appspot.com/t?sender=aY3NoYWxhbnNraUBqb3VsZS1lbmVyZ3kuY29t&type=zerocontent&guid=d6f2eb5c-dd4d-40e9-8599-8f2a37cd7dcf"><span style="font-size:7.5pt;font-family:"Euphemia","sans-serif";color:white">ᐧ</span></p>
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<br></p></div><p class="MsoNormal"><br><br clear="all"></p><div><p class="MsoNormal"> </p></div><p class="MsoNormal">-- <br>Chris Mason</p><div><p class="MsoNormal">President, Comet Systems Ltd</p></div><div><p class="MsoNormal">
<a href="http://www.cometenergysystems.com" target="_blank">www.cometenergysystems.com</a></p></div><div><p class="MsoNormal">Cell: 264.235.5670</p></div><div><p class="MsoNormal">Skype: netconcepts</p></div></div></div></body></html>