Thinking more about the Megger test of an array, is seems impossible,
despite that fact I've been told it could be done. If I put the
tester positive to the 500 V DC negative, that would put two 500 V
sources in series for 1000 VDC. If I put the positive to positive,
the resulting voltage to ground would be zero. What is the trick?
At 10:36 AM 11/17/2010, you wrote:
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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