sma sb1700 over voltage ac? Help pleaseeeee

[MrTrance]

Evening all, I got called out to a job the other day were the customer has 2 x SB 1700's in the loft. The complaint was that the inverters cut out every so often, he knows this because he constantly monitors his sunny beam device. The error registered as unknown and to contact the installers (not originally us, been installed 2 years +).

I spoke to sma he really couldnt help me and just tried cutting me short and to check the ac, which i did and whilst being on the job for a couple of hours I did measure a voltage on the adjacent isolators at 258v... whilst drinking tea in the loft luckily one of the inverters reset itself and I got the code disturbance ac vbr.... which I can only guess the voltage tipped 262v and the inverter cut out. Only problem I have here is that only one inverter cut out and the other didnt (connected to same radial circuit).

I since have put an optimizer in the loft, just interuppted the 4mm coming to feed both isolators.

But earlier I got the call and its still happening, I am really stuck on what to do now, both inverters fed with 220v and still happening.

Site visit booked for Monday, dredding it, don't no what i'm going to do.

Happy birthday to me lol... any help would be much appreciated.

 

[MrTrance]

To add to the post both inverters are set to g83 UK and the panel arrangements are ok with SMA's design spec

 

[jason121]

Might be worth talking to the local DNO about the incoming voltage. Are there any other PV in the same street and is the area fed via overhead cables ??

 

[Gavin A]

please take the optimiser back out, you can't back feed an optimiser like that it completely compromises the G83 protection settings as the voltage being pushed through to the house will still be over voltage beyond the optimiser, just the inverters will see 18V lower, or whatever the tapping is, and the inverters now have the resistance of the transformer to overcome - usually 2% or more losses, more at low power IIRC.

confirm the cable size is sufficient - probably 6mm2 for 3.4kW to ensure below 1% volt drop, and confirm the voltage at the incomer. If the grid voltage itself is without the inverters is over 253 then you need to get the DNO to fit voltage monitoring then drop the voltage at the tapping. If it's the inverters pushing the voltage over, then all you can do really is to reduce the volt drop on the cable as far as possible, or possibly at extra load eg immersion diversion device to pull the voltage down when output is high.

ps those inverters work on a 10 minute average protection setting of 253V to comply with the 230V + 10% requirement for maintaining the quality of the electricity supply, as well as the instantaneous 264V cut out.

 

[MrTrance]

please take the optimiser back out, you can't back feed an optimiser like that it completely compromises the G83 protection settings as the voltage being pushed through to the house will still be over voltage beyond the optimiser, just the inverters will see 18V lower, or whatever the tapping is, and the inverters now have the resistance of the transformer to overcome - usually 2% or more losses, more at low power IIRC.

confirm the cable size is sufficient - probably 6mm2 for 3.4kW to ensure below 1% volt drop, and confirm the voltage at the incomer. If the grid voltage itself is without the inverters is over 253 then you need to get the DNO to fit voltage monitoring then drop the voltage at the tapping. If it's the inverters pushing the voltage over, then all you can do really is to reduce the volt drop on the cable as far as possible, or possibly at extra load eg immersion diversion device to pull the voltage down when output is high.

ps those inverters work on a 10 minute average protection setting of 253V to comply with the 230V + 10% requirement for maintaining the quality of the electricity supply, as well as the instantaneous 264V cut out.

The DNO will just come out and measure the voltage, see its below 262 then bounce it back to me, I have had this before, the inverters are 5 metres away from the fuseboard, 4mm is very sufficient enough surely. Why are the inverters still cutting out with an optimiser in though?

 

[Gavin A]

The DNO will just come out and measure the voltage, see its below 262 then bounce it back to me, I have had this before, the inverters are 5 metres away from the fuseboard, 4mm is very sufficient enough surely. Why are the inverters still cutting out with an optimiser in though?

253V is the limit not 264, it's their statutory duty to supply electricity below 253V, it's not optional, they have to sort it if it is their problem rather than just the PV pushing it over, though sometimes you may need to be a bit insistent on this.

(2) Unless otherwise agreed in writing between the distributor, the supplier and theconsumer (and if necessary between the distributor and any other distributor likely to be
aVected) the frequency declared pursuant to paragraph (1) shall be 50 hertz and the voltage
declared in respect of a low voltage supply shall be 230 volts between the phase and neutral
conductors at the supply terminals.
(3) For the purposes of this regulation, unless otherwise agreed in writing by those persons
specified in paragraph (2), the permitted variations are—
(a) a variation not exceeding 1 per cent above or below the declared frequency;
(b) in the case of a low voltage supply, a variation not exceeding 10 per cent above or 6
per cent below the declared voltage at the declared frequency;

http://www.legislation.gov.uk/uksi/2002/2665/pdfs/uksi_20022665_en.pdf

As for why the inverters are still tripping out, not sure, is it still an overvoltage fault code? What VO unit have you installed?

 

[MrTrance]

I am not sure until site visit, but the customer was just very angry and his exact words 'its doing it again still'.

What do you mean by the inverter will see 18v lower? Getting a bit confusing, why can't the optimiser be fitted on the pv circuit, ive seen a lot of installations wired this way? Thanks

 

[Earthstore]

Optimisers are not designed to have the power flowing backwards through them.
So when generating that is what it will be trying to do.

Added... This is just a thought, but are the inverters wired in series or parallel?

 

[BruceB]

The optimiser instructions I have read specifically warn against it. What model are you using?

 

[Gavin A]

I am not sure until site visit, but the customer was just very angry and his exact words 'its doing it again still'.

What do you mean by the inverter will see 18v lower? Getting a bit confusing, why can't the optimiser be fitted on the pv circuit, ive seen a lot of installations wired this way? Thanks

VO units should never be used in this way, it's completely in breach of the G83 permissions to connect as it entirely prevents the inverter from protecting against over voltage. You haven't solved the over voltage issue, just stopped the inverters from protecting the household circuits from that over voltage.

Unless you've wired it the other way round, in which case the inverter would be seeing 18V higher than the grid voltage, or whatever the voltage difference is through the VO unit. AFAIK all VO units for domestic are fixed voltage reduction units, they reduce the voltage by either 6, 10, 12 or 18V respectively, the only exception I'm aware of being the V-Phase unit.

If you've used the V-Phase unit, then the reason it's tripping the inverter out still is that it's only rated for 8A continuous operation and you're pushing 15A through it, so it will go into bypass and there will be no benefit from it.

For reference, this is how a VO unit can be used with solar PV to reduce the voltage actually going to the house, it can't legally be used for solar to be fed through it (without a G83 / G59 relay at the mains side of it).

courtesy of the pheonix works

 

[SibertSolar]

OP - suggest you heed the repeated advice about back feeding into a VO unit but also confirm the physical wiring arrangements, especially how the inverter outputs are linked together as that would be of interest too