Grid over voltage shutting down my PV array

[Jomarkh]

Monitor now fitted, the National Grid chap reckons they'll need to tap the transformer in the local substation. He checked during install and mains volts was 251/252V

Definitely on the high side

 

[Everest]

Monitor now fitted, the National Grid chap reckons they'll need to tap the transformer in the local substation. He checked during install and mains volts was 251/252V

that's good. I'd agree with that as 252v is only 1v below statutory maximum. Hence it will definitely be more than 253V when you are exporting or when grid voltage is generally higher ( = weekend, early afternoons when sunny). Should be straightforward for them to do that, though will likely take a month or two for the DNO to send out planned maintenance disconnection information to others on your circuit. If the LV transformer is very old and contains PCBs they will likely replace it, rather than change the tap.