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Thank you:<br><br>
To all Wrenches who responded to the question about Megger
testing.<br><br>
The information discussed here is of major importance to photovoltaic
installers, and clearly has been understood different ways. The
List is a great resource which helps increase the quality and reliability
of solar electric installations. <br><br>
To briefly sum up the information, as I understand it:
<ul>
<li>Solar arrays can and should be high pot tested
<ul>
<li>Check with module manufacturer before proceeding, as warranty issues
are possible
</ul>
<li>The UL method of testing requires the terminals, of an unilluminated
string or array, to be spliced together.
<ul>
<li>High voltage testing is done between the spliced leads and ground
<li>This will:
<ul>
<li>totally protect the internal components of the modules
<li>give the most uniform results
</ul>
</ul>
<li>An easy and safe way to test for potential ground faults during
routine installation is to:
<ul>
<li>Remove the fuses or positive connection to the inverter
<li>Remove surge arrestors
<li>Connect the Megger negative to ground
<li>connect the Megger positive to the negative PV wire
<li>Test at either 500 or 1000 V to 100 kOhms
</ul>
</ul>Best regards,<br><br>
Drake <br><br>
<font color="#000080">Drake
Chamberlin<x-tab> </x-tab>
<br>
Athens Electric<br>
OH License
44810<x-tab> </x-tab><br>
CO license 3773<br>
NABCEP Certified PV<br><br>
</font>At 09:11 PM 11/17/2010, you wrote:<br>
<blockquote type=cite class=cite cite="">Content-Type:
multipart/alternative;<br>
<x-tab> </x-tab>
boundary="----=_NextPart_000_0062_01CB8682.CEC07160"<br>
Content-Language: en-us<br><br>
Meggerers,<br>
<br>
Although shorting the terminals to perform the megger tests may provide
the most uniform voltage profile, it is difficult to perform on many
arrays and adds unnecessary complexity to a test that needs to become
routine for all PV installations.<br>
<br>
The appropriate way to perform the test at the combiner box level for
negatively grounded systems is as follows (voltage would be applied
backwards for a positively grounded array):<br>
<br>
1. Open all fuse holders and make sure no
fuses are mounted in the holders.<br>
2. Remove any connected surge arrestors
from the circuits as these will conduct during the test and may
fail.<br>
3. Remove the grounded feeder conductor so
there is no connection to the inverter.<br>
4. Connect the negative of the Insulation
Tester to the grounding connection in the combiner box. <br>
5. Connect the positive of the Insulation
Tester to the negative connection in the combiner box.<br>
6. Apply either 500V or 1000V to the
negative connection and wait for the insulation resistance to achieve at
least 100kOhms.<br>
<br>
Insulation resistance will vary based upon module construction, moisture
on the modules and conduit systems, and cycle of the moon (oh wait,
that’s the PMS proceduresorry)actually irradiance and temperature can
make a difference. By adding 500V or 1000V to the negative side of the
strings, the positive side is going to go to 1000V or 1500V. This does
not violate the listing of the product as this is a temporary test. These
types of tests are customary for 600Vac wiring systems and they should be
mandatory in PV systems of any size operating above 100V. If the module
is damaged by this test, it was a faulty module since all module internal
wiring is required to withstand 2200V to ground throughout the
unitdiodes and all. By testing in the normal voltage bias that the
product sees during operation, it will more thoroughly stress the higher
voltage parts of the array which are more critical for the long-term
reliability of the PV system.<br>
<br>
If a resistance of 100kOhms cannot be achieved, take all the
grounded-side string conductors loose from the combiner block and test
each one individually to see if there are variations in resistance. If no
variations exist, the modules might be a more leaky variety and a new,
lower threshold would need to be established with the help of the module
manufacturer.<br>
<br>
Happy testing and don’t forget to use your gloves.<br>
<br>
Bill.<br>
<br>
<b>From:</b> re-wrenches-bounces@lists.re-wrenches.org
[<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org" eudora="autourl">
mailto:re-wrenches-bounces@lists.re-wrenches.org</a>] <b>On Behalf Of
</b>Bill Hoffer<br>
<b>Sent:</b> Wednesday, November 17, 2010 4:36 PM<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> Re: [RE-wrenches] Megger for array testing<br>
<br>
Joel <br><br>
You are correct about the UL testing requiring 2 x system voltage plus
1000 volts. The UL requirement is also to ramp up to the full voltage in
5 sec and held for 1 min, which I believe most meggers are capable
of. The test is considered a failure if greater than 50 uA current
is measured. The difference is that the connection is between the
shorted outputs of the module and the ground. In the case of the
required factory tests one end of the high pot testing device is
connected to the frame (ground) and one point is connected to both the
negative and positive module terminals shorted together. In
the UL test it is done with the module submerged one terminal of the high
pot tester is connnected to a ground plane in the water and the other
terminal is connected to the negative and positive terminals shorted
together. In both cases the voltage potential across the module
terminals (through the module) is 0, but between the terminals and
ground is the 2 x system voltage plus 1000. The module never sees
2200 volts potential across the cells and diodes. The test is
normally run again reversing the polarity, but the terminals still are
shorted together. I have performed this test in the factory and
observed it being done this way during UL testing. <br>
<b><br>
UL1703 Section 21 Leakage Current Test </b>specifies shorted module
output circuits System Voltage is the test level required<br><br>
21.5 All accessible parts and surfaces are to be tested for leakage
current. <b>The positive and negative<br>
terminals of an unilluminated module are to be connected together and to
one terminal of a dc power<br>
supply.</b> Both polarities of the source connection are to be used,
unless it can be shown that one polarity<br>
will represent both. Leakage currents are to be measured between the part
or surface and the other<br>
terminal of the power supply. System Voltage is the test level
required and <br><br>
<b>UL1703 Section 26 Dielectric Voltage-Withstand Test </b>does not
specify shorted module outputs, but does specify 2 x system voltage plus
1000V<br><br>
<b>UL1703 27 Wet Insulation Test</b> does specify Shorted output
terminals of the module (and only 500vdc)<br>
27.3 After two min of immersion in the solution, the <b>insulation
resistance between the shorted output<br>
terminals of the module or panel and the solution is to be measured, in
both polarities</b>, with an instrument<br>
having a voltage of 500 Vdc.<br><br>
<b>43 Factory Dielectric Voltage-Withstand Test</b> Also doe snot
specify shorted out puts<br><br>
The IEC 61215 is more explicit in all test cases it specifies using the
shorted output terminals for all these tests. IMHO the IEC is the
better document to follow (which is what the listing agencies all do when
things are not defined well in UL1703). The industry will be much
better off once we standardize with the IEC!<br><br>
In my experience all three tests for UL listing are performed in the same
way on shorted output terminals. I would recommend that the megger
test be performed in the same way especially for field confirmation
procedures for commissioning a system. This will still give you the
intended results (identifying a potential short to ground) without the
risk of applying unnecessary voltage across the module cells or
diodes. I do not want to be explaining a failed module to the
manufacturer or customer after subjecting it to 2200 + volts across the
cells or diodes! You would never meg across an inverter input
either, even though they are also high pot tested for listing. Of
course standard procedures for megging wire runs without the inverter or
modules in the circuit can be done at those higher levels without a
problem.<br><br>
Bill<br><br>
Bill Hoffer PE<br>
Sunergy Engineering Services PLLC<br>
2504 Columbia Ave NW<br>
East Wenatchee WA 98802-3941<br>
<a href="mailto:SunEngSer@gmail.com">SunEngSer@gmail.com</a>
(509)470-7762<br>
Cell(509)679-6165<br><br>
<br>
On Wed, Nov 17, 2010 at 9:05 AM, Joel Davidson
<<a href="mailto:joel.davidson@sbcglobal.net">
joel.davidson@sbcglobal.net</a>> wrote:<br>
Hello Drake,<br>
<br>
I think you should talk to a Sanyo Solar engineer to get accurate
information. Every Sanyo and other brand UL listed modules must be
dielectric voltage-withstand factory tested to 2 times system voltage
plus 1,000 volts. I hi-pot test modules in the factory at 3,000 volts so
they will meet UL and also IEC standards. I megger field test arrays at
1,000 volts to find module, connector, and wiring problems. Megging at
500 volts is ok, but it may not reveal wire insulation problems.<br>
<br>
Joel Davidson<br>
<br>
<dl>
<dd>----- Original Message ----- <br>
<dd>From:</b>
<a href="mailto:drake.chamberlin@redwoodalliance.org">Drake</a> <br>
<dd>To:</b>
<a href="mailto:re-wrenches@lists.re-wrenches.org">RE-wrenches</a> <br>
<dd>Sent:</b> Wednesday, November 17, 2010 7:36 AM<br>
<dd>Subject:</b> [RE-wrenches] Megger for array testing<br>
<dd> <br>
<dd>Hello Wrenches,<br>
<br>
<dd>Looking through the archives on using a Megger for testing
modules, it appears that it is best to keep voltages to 500VDC. I
read all that I could find. <br><br>
<dd>Talking to a Sanyo representative, I was told that keeping test
voltage under 600 would not void the warranty or be an issue with
UL. He said they have tested Sanyo modules up to 1000 VDC with no
problems.<br><br>
<dd>As a final test on a system, I want to Megger test the array from the
terminations at the inverter. The approach I'd plan to use is:
<dd>Clamp the Fluke 1587 negative to the enclosuer ground.
<dd>Put the positive test lead to the negative conductor from the array
and test
<dd>Put the positive test lead to the positive conductor from the array
and test
<dd>All tests would be done at 500 V. The modules are illuminated,
but there is no significant reading from either positive or negative
terminal to ground.
<dd>The conductors would be removed from their terminals at the inverter
and be in free air.
<dd>The conductors would be continuous through the string of 10 Sanyo 210
modules.
<dd>My questions are:
<dd>Does anyone see a problem in this approach?
<dd>Since the array often has 500 VDC open circuit readings and shows no
indication of a fault whatever, would this test accomplish anything more
than the standard voltage to ground tests I've already done?
<dd>Is there any danger to diodes or other PV components?
<dd>Thanks in advance.<br><br>
<dd>Drake <br><br>
</dl> <br>
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