Christmas lights or lack of.....!

A common cause when there are a lot of over voltage failures on the same substation is a wandering neutral -  if the neutral is high resistance or disconnected at the transformer end, then the single phase loads on the 3 phases pull what should be the centre of the triangle off, in the direction of the most heavily loaded phase the less heavily loaded phases then see an unnaturally high L-N voltage - up to almost 400V if you have maximum imbalance.

A surge arrestor, while from the name you might think it would deal with that, is aimed at much larger over-voltages, but of very short duration, perhaps kV and tens of microseconds  and  is not really designed to deal with modest over-voltages for a very long time - there is no-where for the power to be dissipated.

In countries where the mains is more unreliable than the UK, it is common to have something that disconnects the load if the supply is out of limits - say above 270V or less than 170V, and that reacts within a second or two, as well as the SPD.

A suspiciously cheap example https://www.aliexpress.com/item/32977199617.html

I have not seen one on a normal installation in the UK however I have specified something rather more up-market on kit intended to go overseas and be used with "power of opportunity" supplies.

Mike.

A common cause when there are a lot of over voltage failures on the same substation is a wandering neutral -  if the neutral is high resistance or disconnected at the transformer end, then the single phase loads on the 3 phases pull what should be the centre of the triangle off, in the direction of the most heavily loaded phase the less heavily loaded phases then see an unnaturally high L-N voltage - up to almost 400V if you have maximum imbalance.

A surge arrestor, while from the name you might think it would deal with that, is aimed at much larger over-voltages, but of very short duration, perhaps kV and tens of microseconds  and  is not really designed to deal with modest over-voltages for a very long time - there is no-where for the power to be dissipated.

In countries where the mains is more unreliable than the UK, it is common to have something that disconnects the load if the supply is out of limits - say above 270V or less than 170V, and that reacts within a second or two, as well as the SPD.

A suspiciously cheap example https://www.aliexpress.com/item/32977199617.html

I have not seen one on a normal installation in the UK however I have specified something rather more up-market on kit intended to go overseas and be used with "power of opportunity" supplies.

Mike.