Thank you:
To all Wrenches who responded to the question about Megger testing.
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.
To briefly sum up the information, as I understand it:
* Solar arrays can and should be high pot tested
* Check with module manufacturer before
proceeding, as warranty issues are possible
* The UL method of testing requires the
terminals, of an unilluminated string or array, to be spliced together.
* High voltage testing is done between the spliced leads and ground
* This will:
* totally protect the internal components of the modules
* give the most uniform results
* An easy and safe way to test for potential
ground faults during routine installation is to:
* Remove the fuses or positive connection to the inverter
* Remove surge arrestors
* Connect the Megger negative to ground
* connect the Megger positive to the negative PV wire
* Test at either 500 or 1000 V to 100 kOhms
Best regards,
Drake
Drake Chamberlin
Athens Electric
OH License 44810
CO license 3773
NABCEP Certified PV
At 09:11 PM 11/17/2010, you wrote:
Content-Type: multipart/alternative;
boundary="----=_NextPart_000_0062_01CB8682.CEC07160"
Content-Language: en-us
Meggerers,
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.
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):
1. Open all fuse holders and make sure no
fuses are mounted in the holders.
2. Remove any connected surge arrestors
from the circuits as these will conduct during the test and may fail.
3. Remove the grounded feeder conductor so
there is no connection to the inverter.
4. Connect the negative of the Insulation
Tester to the grounding connection in the combiner box.
5. Connect the positive of the Insulation
Tester to the negative connection in the combiner box.
6. Apply either 500V or 1000V to the
negative connection and wait for the insulation
resistance to achieve at least 100kOhms.
Insulation resistance will vary based upon
module construction, moisture on the modules
and conduit systems, and cycle of the moon (oh
wait, thats 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.
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.
Happy testing and dont forget to use your gloves.
Bill.
From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Bill Hoffer
Sent: Wednesday, November 17, 2010 4:36 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Megger for array testing
Joel
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.
UL1703 Section 21 Leakage Current Test specifies
shorted module output circuits System Voltage is the test level required
21.5 All accessible parts and surfaces are to be
tested for leakage current. The positive and negative
terminals of an unilluminated module are to be
connected together and to one terminal of a dc power
supply. Both polarities of the source connection
are to be used, unless it can be shown that one polarity
will represent both. Leakage currents are to be
measured between the part or surface and the other
terminal of the power supply. System Voltage is the test level required and
UL1703 Section 26 Dielectric Voltage-Withstand
Test does not specify shorted module outputs,
but does specify 2 x system voltage plus 1000V
UL1703 27 Wet Insulation Test does specify
Shorted output terminals of the module (and only 500vdc)
27.3 After two min of immersion in the solution,
the insulation resistance between the shorted output
terminals of the module or panel and the
solution is to be measured, in both polarities, with an instrument
having a voltage of 500 Vdc.
43 Factory Dielectric Voltage-Withstand
Test Also doe snot specify shorted out puts
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!
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.
Bill
Bill Hoffer PE
Sunergy Engineering Services PLLC
2504 Columbia Ave NW
East Wenatchee WA 98802-3941
<mailto:suneng...@gmail.com>suneng...@gmail.com (509)470-7762
Cell(509)679-6165
On Wed, Nov 17, 2010 at 9:05 AM, Joel Davidson
<<mailto:joel.david...@sbcglobal.net>joel.david...@sbcglobal.net> wrote:
Hello Drake,
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.
Joel Davidson
----- Original Message -----
From: <mailto:drake.chamber...@redwoodalliance.org>Drake
To: <mailto:re-wrenches@lists.re-wrenches.org>RE-wrenches
Sent: Wednesday, November 17, 2010 7:36 AM
Subject: [RE-wrenches] Megger for array testing
Hello Wrenches,
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.
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.
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:
Clamp the Fluke 1587 negative to the enclosuer ground.
Put the positive test lead to the negative conductor from the array and test
Put the positive test lead to the positive conductor from the array and test
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.
The conductors would be removed from their
terminals at the inverter and be in free air.
The conductors would be continuous through the
string of 10 Sanyo 210 modules.
My questions are:
Does anyone see a problem in this approach?
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?
Is there any danger to diodes or other PV components?
Thanks in advance.
Drake
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