The automatic voltage regulators provide voltage stabilisation from instable networks single phase (STM) or three phase (STT) even with important phases voltages assymetry and/or important unbalanced load (STY). The STY, STT, STM series voltage regulators are equipped with an electronic sensing circuit which controls a motor driven variable autotransformer. This one feeds a buck-boost transformer connected in series between the supply and the load in order to regulate the voltage. STT and STY series are available for three phase network. STT serie : - Regulation on the average of the 3 phase. - Withstand an unbalanced load of 50 % STY serie : - Independant regulation on each phase - Withstands a total unbalanced load (100 %) - Adjust the voltage assymetries betwwen phases.