One of the relay-controlled autotransformer AC stabilized power supply circuits

When the input AC voltage changes in the range of 170-260V, its output AC voltage
  changes in the range of 187-231V. The transformer ratio is k=24/220=0.11.
    When the input voltage is lower than 170V, relay KAI is closed (set by adjusting potentiometer RPi), and the output voltage is
  170×(l+k)-170×(1+0. 11) =187 (V); when the input voltage is When the voltage is higher than 260V, KA2 pulls in (adjust
RP2 setting), and the output voltage is 260×(lk)-260×(1-0. 11)-231(V); when the input voltage is between 170~
260V When , both KAi and KA2 are released, and the output voltage is equal to the input voltage.