Fronius IGTL 3.0 DC down AC issue

[sambotc]

Had to go back to a job today that wasn't fitted by my old firm, but was asked to look at. The Initial problem was easily found. Part of the remedial work involved removing the 4mm T&E that had been fitted. This was run through some mini trunking, through the outside wall, up in 25mm conduit into the loft and on to the inverter IGTL 3.0, all good. So I proceed to remove the cable as it goes out through the wall, AC isolator off, MCB off, remove from gen meter. The installer had choc blocked the earth in the trunking so removed earth. Go to push cable through wall and get a good whack off the cable. Get my meter out and I get 330 DC between earth and neutral?Left it a little while longer and double checked my meter, re-test still 330 DC?Go up to loft, isolate DC (as I should have done before I guess!) Re-test and the DC voltage is dropping off and to nothing within 10 seconds of me getting back to test.I phoned fronius tech support and they said it sounded like an issue and would get back to me, didn't hear anything. I left it all isolated once done and told the customer etcAnyway, went to another one after that, different remedial but same inverter. Out of interest I repeated the same test and got exactly the same reading?So, have I missed something here or is this very wrong? How can DC 'leak' across the TL inverter and why?

 

[SibertSolar]

Interesting.......did Fronius not offer any input/advice at all?

Andy

 

[sambotc]

Still waiting for the phone call! The first women mentioned galvanic isolation on the phone, but I think she was refering to lack of due to being a TL? Not entirely sure if i'm honest

As it was on behalf of another company, I just isolated and passed it back to said company. The odd part is that it was exactly the same on the next one?

This is the third time I have had dealings with fronius technical/service, and to be honest I haven't been bowled over by the response on any of the occasions...

If anyone has an IGTL or can get in to one easily to test, it would be interesting to hear if the same results are found.

EDIT: Just googled galvanic isolation and all makes sense, just different terminology than i am familiar with.

 

[SibertSolar]

Is the array bonded/earthed?

 

[sambotc]

Not that I could see, definitely not back to the board and no signs of anything back to local isolation AC switch at inverter. I wish I could have dug a bit deeper, but seeing as time was pushing on and I wasn't getting paid to do that I had to walk away unfortunately.

When I went to the next job, I carried out the same test and the reading were very similar (although a 3.9kw system and 3.6 IGTL) but as the inverter was throwing up a 457 fault ( grid relay failure) I couldn't try it again here either as the inverter was stuck in grid test mode for 45 mins until I left! DC was not present when the isolator was on, but as soon as I switched it off I got DC voltage.

I'm 99% sure I got the whack off the earth as I put my meter across L & N before disconnecting from gen meter, but having doubts now as to whether it was off the neutral as I was on AC when I did the test.

Really bugging me as i'd like to know whats going on! It's very likely I will be going to other properties with IGTL's in the next week or so, so if I could figure out a theory behind it, I could test and confirm.

Either this is some anomoly which is present in all IGTL's, maybe for a particular reason ( installation issue) or there could potentially be a batch of faulty inverters kicking about, not sure?

Luckily it was cloudy today, inverter was doing about 200w at the time

 

[dansk]

unless im missing something why didnt you isolate the inverter before doing any work on the line?

 

[sambotc]

Hi,

complacency I guess? I was also under the impression that the inverter will disconnect when AC power is lost or isolated to prevent shock!

I'll admit that I should have isolated DC as described in the safe shut down procedure, but this still doesn't defer from the issue of why DC voltage is present on the AC cable when AC power is lost unless i'm missing something here, I was under the impression the 2 are supposed to be entirely separated?

I'm not asking for a reason why I got a whack, just why it's there in the first place, and if this is an issue which needs flagging up.

 

[dansk]

its odd i admit, i was just curious, ive done few igtl and its got me wondering.

 

[sambotc]

Just to follow this up.

Managed to get through to that German bloke at Fronius who actually knows his stuff.

It is inherent in all TL inverters (not just fronius) apparently due to the lack of galvanic isolation. DC voltage down the earth but no current so perfectly safe.

Moral of the story, always turn the DC isolator off before working on the AC side!

 

[moggy1968]

I presume this is also connected with the problems discussed elswhere regarding the use of type A RCDs on these systems.