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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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    Well, the voltage rise on the consumer side of the meter is not the DNOs problem,  and presumably the inverters trip limit of 264V was designed to allow for some of that. (inverters sold in places like South America, where the wiring is thinner and the regulation more erratic are programmed with wider default limits)

    There is a general problem that all the transmission and distribution in the UK is designed assuming the voltage slope is downhill from the power station as the source to the consumer as the load. Obviously reversing roles and that direction of slope has some serious implications, and there will be cases, designed for nearly 250V at the transformer and 20V or drop to the consumer, where reversing that slope takes things out of spec. Ideally the DNO would move a transformer tap, but that may not be so easy for them to do if then the folk at the other end of town drop out of permitted tolerance in the other direction.

    One solution might  be a local voltage reducer  in the building ( a low voltage high current winding to oppose, or buck, the incoming supply, auto-transformer style)  so the 250V DNO side is then transformed down to more like 230-235 V in the building, better for the inverters, and better for things like the life of  light fittings too.



    how big is the supply, and how much PV power are we talking?

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  • 0
    Well, the voltage rise on the consumer side of the meter is not the DNOs problem,  and presumably the inverters trip limit of 264V was designed to allow for some of that. (inverters sold in places like South America, where the wiring is thinner and the regulation more erratic are programmed with wider default limits)

    There is a general problem that all the transmission and distribution in the UK is designed assuming the voltage slope is downhill from the power station as the source to the consumer as the load. Obviously reversing roles and that direction of slope has some serious implications, and there will be cases, designed for nearly 250V at the transformer and 20V or drop to the consumer, where reversing that slope takes things out of spec. Ideally the DNO would move a transformer tap, but that may not be so easy for them to do if then the folk at the other end of town drop out of permitted tolerance in the other direction.

    One solution might  be a local voltage reducer  in the building ( a low voltage high current winding to oppose, or buck, the incoming supply, auto-transformer style)  so the 250V DNO side is then transformed down to more like 230-235 V in the building, better for the inverters, and better for things like the life of  light fittings too.



    how big is the supply, and how much PV power are we talking?

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