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I could see how they might get confused between hi-pot
something-or-other and capacitance.<br>
But for hi-pot arc-over, you don't really have to have much
capacitance. Just one spot with<br>
too little spacing for it to arc across is enough to fail. i.e.
Hi pot problems unfortunately don't<br>
creep up usually, they just happen when you pretty much least
expect it.<br>
<br>
oOOOPS. Forgot... In addition, if you somehow do try to measure
the capacitance of the array,<br>
there will probably want to be at least some PV current flowing
from plus to minus when they<br>
are shorted so early morning or evening would work as well as full
short circuit current during<br>
the day I would think.<br>
<br>
Some current because the measurement might not get the full array
of capacitance to ground<br>
if all those PV diodes aren't at least forward biased which would
happen when light out.<br>
Don't want any current through the capacitance meter itself of
course.<br>
<br>
boB<br>
<br>
<br>
<br>
On 3/13/2014 11:29 PM, Jerry Shafer wrote:<br>
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cite="mid:CAMUFgmXFAMbusizYvBhC7S_ZZ4SC4xEZj-V6EHrojS7bqRt+uA@mail.gmail.com"
type="cite">
<p dir="ltr">I had this issue way back with pvl's unisolar and it
was always written off as hi pot leakage in the conductors and
its good to see that it was put to paper </p>
<div class="gmail_quote">On Mar 13, 2014 11:20 PM, "<a
moz-do-not-send="true" href="mailto:boB@midnitesolar.com">boB@midnitesolar.com</a>"
<<a moz-do-not-send="true" href="mailto:boB@midnitesolar.com">boB@midnitesolar.com</a>>
wrote:<br type="attribution">
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Interesting app note. Interesting problem. <br>
<br>
How far from this metal roof (grounded I presume) is the
bottom of the modules ?<br>
<br>
This app note is mainly talking about the area of the
module from the mounting bracket which should<br>
be quite a bit less than the modules area from a distance
above a grounded metal plate like this roof.<br>
<br>
How far above the metal roof are the modules ? If they
are real close, raising them slightly might<br>
be enough to lower that capacitance enough to stop the TL
from tripping.<br>
<br>
Another thing you could do, but would of course cost money
would be to split the array up for<br>
more inverters.<br>
<br>
This app says that 1400 nano-Farads is an approximate
point for problems. That's for 50 Hz.<br>
It will be around 6/5 worse at 60 Hz.<br>
<br>
If you have a capacitance meter (impedance bridge or
meter), you could measure the capacitance<br>
of the array. Disconnect the + and - from the inverter
first of course. Then, tie the plus and<br>
minus of the combined array together and connect that to
one terminal of the capacitance meter.<br>
Connect the other lead of the capacitance meter to the
roof and/or ground and it ~should~ show<br>
the capacitance you are interested in.<br>
<br>
This is one of those newer compromises associated with the
higher efficiency TL inverters (anybody's,<br>
not just SMA's of course), and also the newer code
requiring TL (non-isolated) inverters above 300 volts<br>
and everything else new we have to all learn about. <br>
<br>
<br>
Welcome to the future ! ( from Firesign Theater's
"I think we're all [solar] bozos on this bus" )<br>
<br>
<br>
boB<br>
<br>
<br>
<br>
On 3/13/2014 7:31 PM, Marco Mangelsdorf wrote:<br>
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<p class="MsoNormal">Friends,</p>
<p class="MsoNormal">We have run across an odd technical
problem at our commercial install at a laundromat on
our island. Attached is the description of the issue
from SMA. We don’t know much except that we are
switch out the TL inverters to the old style US
inverters because SMA has no fix for the phantom
ground tripping. The issue is beyond our feeble
understanding. <br>
</p>
<p class="MsoNormal">Any observations to share?</p>
<p class="MsoNormal">Thanks,</p>
<p class="MsoNormal">marco</p>
<br>
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