Fault on SMA Inverter? or outside influence

[Eco Chap]

Hi all. Im after some input from other pv installers (or anyone in the know) about an installation we installed a few months back.

In short its a <4KW installation with a SMA TL inverter on a TT arrangement. A few weeks after installation I got a message saying the RCD had tripped, not a problem I thought as Id temporarily fitted a 30mA RCD whilst I was waiting on delivery of a 100mA RCD from the supplier (Hager). Went back changed RCD and checked the whole system, tested out fine as expected so off I went on my mary way. Phone call a week later saying RCD had tripped a couple of times. Arranged another visit thinking right likely to be faulty RCD (strange as Ive never had an issue with the Hager products). Trip times tested fine and ramp tested within limits but changed the RCD again anyway. Phone call last week, RCD tripped again except it occurred when the client was in, he said it tripped the RCD on our PV board when they had a power cut (work being done on their street). So he try'd to imitate a power cut by turning the isolator off before the board yet nothing happened to the RCD. The same occurred a couple of days later, powercut - RCD tripped. Now this could all be a coincidence (Inverter may well have tripped before powercut) but my question would be is it at all possible for the installation to be tripped from outside the property? Baring in mind the rest of the installation is RCD protected at 30mA yet they arent effected. My other thought is that the Inverter itself may well be faulty but I have no means or knowledge on identifying a fault on an SMA inverter (Fronius seem to have their logging system down to a tee). My next move is to replace the inverter with one we have on the shelf and to send the current one of for a lengthy reply from SMA.

Thanks in advance, Joe.

 

[Gavin A]

does the solar side actually require an RCD for any 17th edition reasons?

if not, then the solution would seem fairly simple - dual pole MCB (we've got some from ebay from caravan places that seem fine at 16 amp dual pole), and no RCD.

 

[pvman]

Hager RCDs often trip when PV is on the same board. Hager are aware of this and if you speak to their technical department they should be able to help.

Putting the PV on a separate small consumer unit is probably the easiest solution.

Tom

 

[Worcester]

There are ways to do a TT install of a PV system so that it doesn't need to be RCD protected, - you've got to design it very carefully, and make sure you have low Zs permanently and reliably assured.

Whatever you do don't just swap it for one that doesn't trip - some don't trip because they are flooded with DC and hence will never trip, so therefore the protection isn't being applied.

 

[jason121]

Didn't he say TT system

 

[Eco Chap]

Yep on a TT system. Thanks for the reply guys. Im going to change the TL inverter for the time being (as a quick solution). If that fails the old one will go back in and I will begin the attempt as Worcester says to acquire a stable earth. His property is in a built up area so there may well be an opportunity to bring the DNO's earth in too.

 

[Worcester]

If it's a built up area, they (the DNO) may well switch it to TN-C-S (PME) for you for nought, - what are the neighbours on?

 

[Eco Chap]

Mythed now guys. Switched inverter but still trips the rcd. Will convince the client to switch to a pme supply but I'm still left stumbling over why any of the other rcd's in the property aren't effected.

 

[Earthstore]

Is it on a dedicated RCD or a shared one?

 

[Eco Chap]

Dedicated

 

[Eco Deal]

Just do the wiring in contaiment and forget the RCD??? easy...

 

[Gavin A]

can I just check - is this only happening when there's a powercut?

 

[Gavin A]

I think if that's the case, that it's likely that the inbalance is on the DNO side of things, eg the trip at the transformer is deliberately or accidentally sending part or all of the generation current from the PV system to earth instead of returning it via the neutral.

Given that these transformers weren't designed to take current flowing in that direction, there's no particular reason why they'd have been designed to elliminate such effects.

 

[Eco Chap]

Quick update. Western Power fitting PME system next Monday, not raised any problems with their existing installation so fingers crossed this will solve the issue and I cant spend a little less time with the client

Thanks for all the input guys.