The present invention relates to a kind of large or medium capacity automatic ac voltage regulator which is used for stablizing the low voltage (220V-380V) ac power supply. It is composed of a multiple brush contact type voltage regulator with divided sector output, a secondary winding directly wound on the voltage regulator and a reversible driving system for controlling and protecting the circuit source, a closed loop voltage regulating circuit, an inverse time-lag electronic protection circuit for runaway voltage and overload current, a fuse, brush carrier limit switch and ac contactor. Its advantages are: high accuracy of voltage regulation, fast in reponse, good in dynamic stablity, very well in protection function, high overall reliability, small size, large capacity, simple construction, low cost and convenient for observation, operation and maintenance. |