If the voltage stages are unstable (ie: power stays on, but the particular voltage level differs lots within the 220V common), then I think that's the sort of scenario wherever an AVR is useful. For those who have a sizable Place of work with many units, then the Eaton Eaton https://marcoxaazz.glifeblog.com/32785178/the-definitive-guide-to-uninterruptible-power-supply-calculator