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Discuss Over Voltage Problem in the Solar PV Forum | Solar Panels Forum area at ElectriciansForums.net

B

besafe

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We recently installed a 10kW system on a rural farm building.
The pre-existing incoming voltage was 257V ..... a single phase supply fed from a dedicated pole mounted transformer next to the building.
Being subject to G59 regs, the overvoltage cut-out has to be set at 253V.
I spoke to the DNO (YEDL) to address the pre-existing high voltage ..... it was like pushing water uphill.
Eventually (and I mean several weeks later) they replaced the transformer and agreed to put it on the lowest tap setting.
The problem:
They have put it on the lowest tap setting = 249V off-load (during the day) .... what's happening with the european norm of 230V
Once the sun kicks in, the G59 Inverters (2x4kW SMA) take in turns to cut-out due to over voltage.
The DNO just quotes, it's within 230 +10% and -6%
This must be a national problem. Certainly in the rural areas.
Has anyone else had this problem.
I know I could send in a request to DNO seeking permission to raise the over voltage level ... but that's not acceptable IMO.
Any feedback would be appreciated, before I start pushing that water back uphill.
 

jason121

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Arms
Re set inverters to 264v -10% 0f 240v, but ask permission from DNO, they should allow this, i have done this several times on installs.
 
E

Earthstore

  • Thread Starter Thread Starter
  • #3
What size are your AC cables to the inverters?
And how long is the AC cable run?
 
B

besafe

  • Thread Starter Thread Starter
  • #4
Hi
They are 10mm over approx 70M
I also think the old pole transformer was buffering the exported voltage, as the rise in voltage (although too much) is not as significant.
Thanks
 
B

besafe

  • Thread Starter Thread Starter
  • #6
I had thought that myself .... but not convinced. I decided to wait until the incoming supply was addressed.
Thanks for your feedback
 

SolarCity

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Arms
I'd have said cable too small also. At the very least, the 10mm cable is exacerbating the problem. It may not solve the problem, but it will definitely help.

If you're down to 249v at supply then you'll want to make sure that your volt drop is as low as you can possibly get it.
 

Gavin A

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Arms
I'm very surprised you got permission from YEDL to connect that system in that situation.

We had a similar situation where the 10kW requested got knocked back, and we had to install a 3.68kW (AC) system.

You're also looking at a 3.3% volt drop along a 10mm2 cable of that length, and with 8kW being squeezed down it it really isn't any surprise at all that you're having major problems.
 
E

Earthstore

  • Thread Starter Thread Starter
  • #9
So with your loss on the 10mm AC cable from your inverters they will have to output around 257V to match the grid,
Me thinks you will have to upgrade your 10mm cable, the DNO are within tolerance, although high, it is still within tolerance.
 
B

besafe

  • Thread Starter Thread Starter
  • #10
Many thanks ..... a lesson learnt.
 
B

besafe

  • Thread Starter Thread Starter
  • #11
Thanks for your response ... it does look like the cable size isn't helping.
With regards the DNO, permission was granted under the SSEG Guidance Note 2 Relaxation which ran for a year and expired in March 2012.
Although it has expired, it may be possible to quote it and still get permission. To be honest, I had to send the doc to them because they were totally unaware of it.
So thanks again, another lesson learnt.
 

Gavin A

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Arms
if you got permission under G83 stage 2, did that permission specify G59 settings? We had permission for a 50kW system under that which still specified G83 (from YEDL), so worth double checking the original permissions.

Alternatively, I believe it's acceptable to fit a G59 relay at the actual grid connection point, which supplies the G59 protection, then you can set the inverter to a higher voltage to allow for the losses in the cables.
 

SolarCity

-
Arms
Alternatively, I believe it's acceptable to fit a G59 relay at the actual grid connection point, which supplies the G59 protection, then you can set the inverter to a higher voltage to allow for the losses in the cables.
Brilliant idea. This may be a better option than changing the cable.
 

Worcester

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Mentor
Arms
Alternatively, I believe it's acceptable to fit a G59 relay at the actual grid connection point, which supplies the G59 protection, then you can set the inverter to a higher voltage to allow for the losses in the cables.
It's more than acceptable, in fact in some circumstances it's the only way to connect - we have some installations were they are fed by a massive Voltage Optimiser - all the power to the site goes through it, the PV connections for various practical reasons had to be connected downstream of the VO (the'se aren't your couple of hundred quid domestic jobbies ...) so even though the inverter is G59 certified it's irrelveant, because the connections is managed by an 'upstream' G59 relay.

Also works with really long cable runs, so long as nothing else is attached, and you don't mind the losses :) Use a G59 relay at the Grid connection point and a remote relay ( can be up to 250m away - it's only a signalling link) to cut the grid from the inverters.

You can then effectively disiable the grid monitoring on the inverters as the remote G59 sensors are manging the grid conenction parameters.

Just make sure no other electrical equipment is attached on the same circuit else the higher volatges may then damage those items..
 

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