UK mains voltage to change?
Before the 1990s, the UK mains voltage supply was a nominal 240V +/-6%, which allowed it to ‘legally’ vary between 226V and 254V. Then as part of European harmonisation the UK adopted a nominal of 230V and the tolerance bands were set to +10% / -6%, thus allowing the delivered voltage to be between 216V to 253V. This was somewhat of a bureaucratic exercise, with very little changing to the delivered voltage in many cases. It should be noted that some countries in Europe had been at a nominal of 220V and they then moved to a 230V nominal.
The relevant authorities in the UK are now considering a full implementation of the 230 +/-10% tolerance, as opposed to the +10 / -6%, this will allow delivered voltage to be between 207V and 253V.
Before embedded local generation, Solar PV and Wind, the DNOs typically ran the network voltage towards the higher tolerances, but still conform (not too high) in the summer with lighter loading, then in the winter the loading could pull the voltages down and still be conformant (not too low), basically building in headroom to allow for greater volts drop. A voltage sweet spot if you like. With the roll out of particularly solar PV generation, voltage dropping is less of an issue and the prevalent problem is now voltage rise, due to distributed generation.
To explain. The DNOs have set their voltage set high to allow for voltage drop due to loading, so some high voltage is baked-in. This works well in the winter, the headroom stops the volts falling below the 216V, however, in the summer this higher voltage setting comes back to bite, distributed solar generation has the double effect of firstly servicing the loads in that particular property, reducing the grid loading and then if it exports, taking some of the neighbouring properties’ loads off as well. The net effect is to push the voltage even higher, this can cause sensitive equipment such as solar/wind inverters, battery inverters and EV chargers to trip.
We need a lower sweet spot, but if we simply lower the voltage, there is a distinct possibility that it will on occasion breach the 216V,… we need a lower limit, 207V, the nominal voltage can then be set lower and allow for a greater variance on +/- volts. The change is still at the proposal stage and if it goes ahead most customers won’t see much of a change. It should reduce the instances of inverter and charger trips due to high grid voltage. You may want to set the lower voltage limits on equipment down from 216 to 207, this should reduce any resets at lower voltages.
Over the years, we have seen a shift from voltage complaints being frequently about low delivered voltage, recently we have noticed that many complaints are for high delivered voltage. Some analysists believe the voltage swings away from the nominal are only going to get worse, as we generate during the day and charge cars and home batteries in the evenings. eFIXX have a good article on this:-
https://www.efixx.co.uk/Articles/Proposed-Changes-to-UK-Mains-Voltage-Limits-Explained