If the voltage ranges are unstable (ie: power stays on, but the particular voltage amount varies a lot from your 220V typical), then I feel that's the kind of state of affairs where an AVR is useful. Although I wouldn't stress too much about what poor power quality would do https://sergioyzfml.thekatyblog.com/32551427/5-simple-statements-about-uninterruptible-power-supply-calculator-explained