Solar inverter SUN2000-5KTL-L1 intermittent shutdown

Hi All,

My solar inverter keeps shutting down due to grid overvoltage alarm. I have read up forums and online articles and understand why this is occuring but I still have some doubts. Appreciate the experts here to share your opinion.

1. Lodged a complaint to installer. Installer keeps blaming grid overvoltage from energy distributor. No voltage rise calculation or troubleshooting done by installer so far. Installer increased sustain voltage threshold 10mins average from 255v to 258v within allowable limit and this reduces the shutdown occurrence but problem still occuring.

2. Lodged a complaint with energy distributor. Case under investigation. No ETA.

3. Inverter settings – 253v recovery start, 258v sustain voltage shutdown.

When inverter is shutdown after grid overvoltage (>258v) I quickly did a measurement on voltage at my house power socket using smart meter, it says 248v. This should be grid voltage as the inverter is already shut and keep looking for 253v and below to resume operations. After some time inverter came back online and could see Solar inverter FusionSolar app reporting 257v, and my home smart meter measurement around 256v. What I dont understand is why there is a difference on voltage captured by my smart meter 248v vs Inverter FusionSolar app 254v when Inverter is shutdown and waiting for grid connection. Sound like the inverter is seeing 6 to 8v higher than what is supplied by grid. I would assume if I am getting 248v at home socket then inverter should resume operation since threshold for recovery is 253v but it keeps waiting looking for grid connection, and FusionSolar App shows around 254v inverter output. 

What could be the problem here? 1) inverter, 2) installation and 3) grid?

Thanks