The present invention refers to a system for regulating a load voltage (C) in power distribution circuits comprising at least: a regulation transformer (2) operatively arranged in series between a power source (F) and the load (C), the power source (F) being capable of providing a supply voltage (VAL) to the load (C); a measuring device (5) operatively associated to the load (C), the measuring device (5) being capable of measuring at least one value of an electric signal of the load (SCA); a control device (4) operatively associated to the measuring device (5), the control device (4) being capable of comparing the value of the electric signal of the load (SCA) with a pre-established reference value and providing a correcting electric signal (SCO); and an actuation device (3) operatively associated to the control device (4), wherein the actuation device (3) is capable of providing an adjustment voltage (VAJ) proportional to the correcting electric signal (SCO), the adjustment voltage (VAJ) being applicable to fixed electric taps of the primary winding of the regulation transformer (2), the fixed electric taps being configured to remain immovable when there is a variation of the adjustment voltage (VAJ), the regulation transformer (2) being capable of transforming the adjustment voltage (VAJ) into a regulation voltage (VRE), the regulation voltage (VRE) being added in module and phase to the supply voltage (VAL). The present invention also refers to a method executed by the above-mentioned system.