Riso Low

[karagoncoloz]

Dear friends,
i have searched "riso low" in forum but it returned nothing.
I guess it is impossible not to talk about "riso low" issue at this forum but i have to open a new therad anyway.
The situation is , one of my inverter's (transformerless) DC input channel IGBTs are burned. I look at the plant's messages and i see this invertor has "riso low" messages.

The question is how can i handle "riso low" issue? what is the inspection steps for insulation, which meters should i use?
thanks!

[Mike90250]

bummer. The transformer - less inverters are pretty new, it should be covered by warranty I hope.

[PNjunction]

A Fluke 1587 insulation meter might help pin point the problem on the system. The most obvious stuff to me would be to inspect the array for "frog-hairs", or other hurried construction techniques.

I have never worked with one, so I can't really comment on it.

[inetdog]

Just a guess that "riso low" is referring to a low isolation resistance, probably on the DC input side somewhere. That could be a ground in what should be an ungrounded panel array, or it could be the result of an internal failure in the inverter.
Can you at least tell us whether this is a GTI, and give us manufacturer and model?

[karagoncoloz]

Seems to be Solved

Dear friends,
I did a lot of inspections, measurements of Voltage and current etc...
I observed some big mistakes and solved them. But it still gives the same error less occasion.
Then i find out that some underground DC cables are remains wet always.
After some magic trick made on strings, all DC cables are rescued from underground.
Now Inverter seems just fine...

thank you!

[bcroe]

Dear friends,
I did a lot of inspections, measurements of Voltage and current etc...
I observed some big mistakes and solved them. But it still gives the same error less occasion.
Then i find out that some underground DC cables are remains wet always.
After some magic trick made on strings, all DC cables are rescued from underground.
Now Inverter seems just fine... thank you!

Glad you found the ground leakage. Here is how I test that. With some decent sun, the
array is completely disconnected from the inverter. My 2 pole DC disconnect switch does
that. This tester has enough bulbs in series, to about match the open circuit voltage of
my array, some 450 volts. Connecting it to the 2 array wires, it should light drawing a
fraction of an amp. Then connect it between a good ground (the inverter ground) and
one array terminal; it should be completely dark. Then connect it between ground and
the other array terminal, same thing. If there is any sign of power through the bulbs,
you have a low resistance to ground somewhere. A DVDM can't do this alone, because
it will read static charges. An analog meter could be used for very high resistance
faults. Bruce Roe

[karagoncoloz]

Glad you found the ground leakage. Here is how I test that. With some decent sun, the
array is completely disconnected from the inverter. My 2 pole DC disconnect switch does
that. This tester has enough bulbs in series, to about match the open circuit voltage of
my array, some 450 volts. Connecting it to the 2 array wires, it should light drawing a
fraction of an amp. Then connect it between a good ground (the inverter ground) and
one array terminal; it should be completely dark. Then connect it between ground and
the other array terminal, same thing. If there is any sign of power through the bulbs,
you have a low resistance to ground somewhere. A DVDM can't do this alone, because
it will read static charges. An analog meter could be used for very high resistance
faults. Bruce Roe

Man, you rock!
I read about this shape of measurement in an article or some panel producer application manual, but i did not understand what it says. now i got it.
what a fool i am ))
thank you!