In case your voltage degrees are unstable (ie: power stays on, but the actual voltage level may differ a good deal from the 220V normal), then I think that's the sort of scenario in which an AVR is helpful. For giant power units, dynamic uninterruptible power supplies (DUPS) are sometimes https://claytonknnkj.fitnell.com/74580226/the-greatest-guide-to-uninterruptible-power-supply-cyberpower