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DNO voltage limits and solar PV generation

Harry Macdonald
A local bowls club has installed solar PV which is working very nicely - most of the time.

However on a really good day up to 8 of the 53 panels trip out reporting overvoltage. The trip is set to 264V (240V + 10%).

The meter is in a small house at the edge of the property, about 50m from the main switchboard, connected by a fairly substantial cable, (at least 2 sizes bigger than the DNOs incoming cable). We have called the DNO who have been and measured the incoming voltage as 252V, so just below the limit of 253V (at the time of their visit).

Exactly how the voltage rise is distributed between the incoming cable and the cable from the MCB board to the roof isn't clear but the voltage at the MCB board is regularly above 253V and so is the voltage on any appliance connected to a lightly loaded circuit.

The DNO say they can monitor the voltage but unless it goes above 253V they will not reduce the voltage as it is within limits.

How can the club ensure that their equipment is not subject to over voltage?

Do the DNOs limits need to be reviewed now that electricity flow to a premises is not always in the same direction?
  • 0
    I'm with Mapj on this one, a simple buck transformer dropping maybe 15-20 volts would fix all the issues, to my mind?
  • 0
    What is the size of the array in kW?


    Regards,


    Alan.
  • 0
    It appears that this P.V. system is surplus to requirements, offers nothing useful and is the cause of trouble.


    Z.
  • 0

    Zoomup:

    It appears that this P.V. system is surplus to requirements, offers nothing useful and is the cause of trouble.


    Z.




     

    I would hope it's offering free electricity.  And tax-free income if it qualifies for feed-in-tariffs.  If it's an older system, the FIT payments could be a few thousand pounds per year.
  • 0

    I'm with Mapj on this one, a simple buck transformer dropping maybe 15-20 volts would fix all the issues, to my mind?



    It might 'avoid' overvoltage problems on the consumer side of the buck transformer, but the DNO side would still have to be pushed above statutory limits (253V) to export full power - (possibly pushing the HV network above its limits too locally?)  which I expect the DNO would take a very dim view of.


       - Andy.
  • 0

    The maximum and minimum Voltage levels must be set and controlled, so reset them. That is what I meant.



    I'm guessing Z means pick more conventional (lower) limits (e.g. max 253V rather than 264V) - that way other equipment connected to the same remote DB as the PV inverter(s) won't be subject to overvoltage. The downside is of course that the inverter(s) will be shut down much more often and so production will be lost. Perhaps another approach would be to have other equipment and the PV inverter(s) on separate submains back to the origin - so the PV inverter could keep it's higher setting (presumably to account for v.d. within the installation) without cooking other appliances.

         - Andy.
  • 0
    The voltage in G.83 connected devices is deliberately set high, so that you don’t get unexpected load cutting in and out and causing instability in the public electricity system. There are two alternatives really.


    You could change the parameters, which would invalidate the standard G.83 approval for the inverter. You would then need to approach the DNO for a G.59 (or the newer G.99) connection. The new settings would need to be modelled and approved by the DNO, as well as them having to undertake a full set of commissioning tests on the inverter to prove all the parameters. Depending on the system size and the local DNO network, there could be some contribution required from the customer for network reinforcement. 


    The other method is to do a proper system design for the PV connection, which is likely to show that it needs to be connected at the meter position, and not the “customer end” of the sub main. 


    The G.83 (and replacement G.98) settings do save the customer a fair amount of time and money over a bespoke solution such as G.59 / G.99. 



    Regards,


    Alan.
  • 0
    I am guessing that the actual consumption of electricity at the bowls club is intermittent and generally low, so there aren’t any loads in the club house to lower the voltage.


    Perhaps an immersion to heat hot water in a large well insulated storage cylinder would help.


    Andy B.
  • 0
    Thanks all.


    New cable would be 50m underground which doesn't come cheap nor does a buck transforrmer, I'd guess.


    System is 15kW nominal so I'd expect over 10kW (40A) on a good day.


    Latest news is that the DNO is going to record the voltage at the cut out for 2 weeks. If it rises above 253 we can probably expect them to reduce the voltage 2 1/2% which will solve the problem.


    The bigger issue is do we need to revise the various G standards to allow for the possibility of small premises having significant generation and, if so, who does it?
  • 0
    And if there’s more producers than consumers on the local network will that create an island of higher voltage?


    Andy B

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