Power One 3.6 OUTD Inverter will not start in the morning - Riso fault

[rgf1]

My installation has 2 strings. Sometimes the Riso test fails on one string - showing a Riso of less than 1 Mohm. Therefore it fails the start sequence. I have had the supplier inspect this after a failure and he has diligently checked for water leaks, fretted insulation etc. and he has remade the isolator connections etc. - just to dot the I's etc. He found no fault. The Inverter started immediately after this - reading 20 Mohms on each string when one is isolated.

It does seem to be something to do which rainy conditions and I am very near the sea which would perhaps give salt in the air.

I have developed a work round, which is to switch off string 1 - (which seems to be the fault string) let the inverter start and then turn String 1 back on. The Riso is then at 20 Mohms. The other weird thing is that once the inverter has started then both strings immediately read 20 Mohms. Even when one string is switched off to test the fault.

Both strings are putting out virtually identical power and there is no evidence that the output is affected at all.

Could this be an Inverter fault? As the Riso reading seems to be back up at 20 Mohms immediately.

Is there some form of test for this. I am not an electrical engineering expert, but I guess that if a megger was used, this would fry the panels etc.

I have also noticed that running on one string there seems to be a Temperature display - called Boost - what is this.

Any diagnostic help would be much appreciated.

 

[Noshocks]

I was on a training course with Power one last week, one string reads 20mohms when channel is switched off because its open circuit so I would expect that, I would suspect the connections before the inverter, has string Mohms been tested in rainy weather. Swap the strings and if the same channel drops out you'll know the cause.

 

[jason121]

Ring power-one technical and has the array been earthed

 

[rgf1]

Thanks so far for the help. I do not quite understand Jason's comment.. Jason, do you mean has the negative side of both strings been earthed to the inverter earth. OR do you mean has the positive side been inadvertently earthed so that it has blown some component in the inverter?

It started yesterday OK and also today - so it is all intermittent.

I am just about to phone Power One, but all help from the forum gurus is really appreciated. I just wondered whether anyone else has had this trouble and solved it.

Thanks

rgf1

 

[SolarCity]

First thing to do would be to test between earth and both positive and negative of each string. There is no issue with using a 'Megger' on a PV circuit as the panels are rated at 1000v anyway.

My guess is that there is a fault between your array and the bonded mounting kit - possibly a pinched cable somewhere which is why it it intermittent and worse in wet conditions.

 

[jason121]

Thanks so far for the help. I do not quite understand Jason's comment.. Jason, do you mean has the negative side of both strings been earthed to the inverter earth. OR do you mean has the positive side been inadvertently earthed so that it has blown some component in the inverter?

It started yesterday OK and also today - so it is all intermittent.

I am just about to phone Power One, but all help from the forum gurus is really appreciated. I just wondered whether anyone else has had this trouble and solved it.

Thanks

rgf1

That will be the responce from power-one because TL inverter. any way thats what they said to me.
Mine kept tripping RCD, Did a ramp test on RCD and was tripping at 19ms very sensitive

 

[SolarCity]

Why did you put it on an RCD? It's best to avoid if you can - 100mA if you can get away with it.

 

[jason121]

Install on shed from domestic supply small holding. Fuse board in shed already wired thru RCD, not any more.

 

[Gavin A]

it's possibly a capacitance issue - google capacitance and solar PV panels, as my brain hurts trying to explain it, but it happens mostly in damp dewy conditions at the start and end of the day.