DNO turning off systemsDno turning off systems

[tottenham steve]

We fitted a 10kw system a few months ago, G59 approval was granted prior to installation and all was carried out correctly.
unfortunatly there is high voltage in the area so the inverters were tripping at peak generation. We have recalibrated the inverters but still have a problem.
so we have asked the DNO to look at there transformer and after investigation they have concluded that our system is causing the transformer voltage to rise above there upper tolerance and ordered the system to be shut down, leaving me £30,000 out of pocket. Has any one else had the same experience?

 

[SolarCity]

We fitted a 10kw system a few months ago, G59 approval was granted prior to installation and all was carried out correctly.
unfortunatly there is high voltage in the area so the inverters were tripping at peak generation. We have recalibrated the inverters but still have a problem.
so we have asked the DNO to look at there transformer and after investigation they have concluded that our system is causing the transformer voltage to rise above there upper tolerance and ordered the system to be shut down, leaving me £30,000 out of pocket. Has any one else had the same experience?

I'm no expert on the legal side of things but I would have thought that this is their responsibility.

Meanwhile, £30,000 for a 10kWp system? Blimey.

 

[Earthstore]

I have a friend who works for a DNO, and most of his work now is complaints about over voltage, however, it always seems to be a fault with the PV system as the DNO voltage is well within range.

What is your incoming Voltage with the PV turned off?
Then what is your voltage back at the main with the PV turned on?
The reason for asking is this is a very common installation fault where the pV supply AC cable is too small, and if the incoming voltage is on the high side, and your inverter has to up the voltage to match the mains and there are loses in your AC cable it has to go over voltage and so shuts the inverter down.

I hope this makes sense to you.

 

[Gavin A]

3 phase or single phase?

also what do you mean by "We have recalibrated the inverters"?

and which inverter have you used?

better to have the inverter cutting out due to 10 minute average over voltage at 253V occasionally, as with sunny boy inverters on G83 settings than having to remove the entire system.

I'd ask them for permission to recalibrate the inverter protection settings to prevent the overvoltage problem at the inverter.

I'm also interested in what the legal position is for situations where they've granted you permission in advance.

 

[tottenham steve]

I'm no expert on the legal side of things but I would have thought that this is their responsibility.

Meanwhile, £30,000 for a 10kWp system? Blimey.

30,000 is including V.A.T and was fitted last november, obviously prices are a lot different now.
As far as the system is concerned, incoming voltage varies but seems to peak around 251v, we have run all cableing in 10mm (we are aware of issues with companies using undersize cable). We have also changed the earthing from TT to TNCS in order to lower the impedence. If you check the small print of a uk power networks contract it says that even though they give permision to connect, they can order the system to be disconnected if they feel it causes a problem.

 

[SolarCity]

If you check the small print of a uk power networks contract it says that even though they give permision to connect, they can order the system to be disconnected if they feel it causes a problem.

I've never noticed that. Have you asked OFGEM for their advice?

 

[tottenham steve]

RE Recalibration
We have used two sunny boy 5000tl (single phase) G59 spec. we have recalibrated the upper volage limit (it will allow up to 290V)

 

[tottenham steve]

are offgem helpful

 

[Earthstore]

Well if it is making the suply run at 290V it would start popping all your appliances, that is way to high.

What are the length of your AC cable runs, from inverters to main?

Added.
Also are you the only property on this supply, or is it running a housing estate?

 

[tottenham steve]

10mtrs, and it doesnt mean the inverters run at 290v it should allow for spikes.

 

[moggy1968]

is it worth asking the DNO what work would be needed to get compliance from the network, it may be less than the 30k your at risk of losing.

 

[tottenham steve]

you may be right, Im going to try to sweet talk them tomorrow, but i was just interested to see if this a jobsworth im dealing with or whether any other members have had the same issue with a DNO

 

[Earthstore]

Sorry to ask again, but how many properties does the DNO supply from the transformer?

 

[Gavin A]

RE Recalibration
We have used two sunny boy 5000tl (single phase) G59 spec. we have recalibrated the upper volage limit (it will allow up to 290V)

do you mean you have you recalibrated the upper voltage limit to 290V? If not, what have you recalibrated it to?

You're aware that you need DNO permission to recalibrate the voltage settings, and if you've adjusted them to allow anything above 264 (IIRC) then the dno would be well within their rights to tell you to turn it off.

IMO you really need to stick to the 253V 10 minute average, and 264 volt instantaneous limits or you'll be pushing the local grid voltage outside it's legal limits.

 

[tottenham steve]

If I stick to those limits the system will disconnect, How is the system supposed to work?

 

[tottenham steve]

Having discussed the event codes with SMA, they are saying that the disconnections are caused by high grid impedence caused by an initial high grid voltage

 

[tottenham steve]

Sorry to ask again, but how many properties does the DNO supply from the transformer?

Sorry, I dont know, but its quite rural , i would guess at less than 20

 

[Earthstore]

This is my understanding here.
If all 20 houses are pulling a base load from the grid of 0.5KW, than that would use all of your 10KW produced, therefore, not pulling any from the transformer, so the voltage in the grid would stay at 251v, however, if your PV power has nowhere to go, it would then push the grid voltage up causing your problem.

My question was; what is your incoming voltage reading when your inverters say it is 290v, you need to make certain that it not an install fault, as the DNO will not get involved in that.

Do any of the other 20 houses have PV?

 

[Gavin A]

If I stick to those limits the system will disconnect, How is the system supposed to work?

I think you're in trouble then, and the DNO has obviously made a mistake in giving you permission to connect 10kW on to that line.

The problem is that if they've put their testers on the line while your system is conencted like this, it'll clearly show your system pushing the voltage up above the limits because of the changes you've made.

If the local voltage is that high, I'd think the best course of action would be to ask them to test it again for 2 weeks with your system switched off, then hope that in these 2 weeks the local grid voltage goes outside the limits anyway, then they will have to reduce the tapping on the transformer.

Explain to them that you will then reset the inverters protection settings to stay within the 253V 10 min average, and 264V instantaneous limits, and there should then be no problem.

Whatever you do, I'd try to keep the engineers on side, and defo not kick off with them as you're on very dodgy ground here, and they'd be within their rights to cut the power supply off entirely if you simply left it as is.

 

[Avontech]

We had a recent discussion with one DNO about grid voltage's as we had one system cosistently disconnecting with high grid voltages, and it seems that they've recently turned them up in rural areas !! After a very polite conversation they volunteered (without even asking) to retap the local transformer and turn the voltage down.

Speak nicely and you'll be suprised what co-operation you can get!