Abstract: An improved reactive power compensator for a transmission line is effective to correct voltage transients and overloads of diverse kinds. The reactive power developed by a conventional main reactive element such as a DC-bias controlled choke in the compensator is varied in accordance with an error signal representative of the difference between the instantaneous voltage across a particular junction of the line and a reference value. Excitation for the main element is supplied by a variable shunt reactance which exhibits a no-load inductive power loss that is large compared to the magnetization power loss of a conventional distribution transformer. The shunt reactance has an exciting winding coupled across the line at the junction and a power winding inductively coupled to the exciting winding for feeding the main reactive element.