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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?
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  • 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.
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  • 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.
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