Abstract: A polyphase static reactive compensator comprising a main saturated reactor (SR1) connected in series with a number of smaller saturated reactors (SR2-4) of graded voltage rating. The smaller reactors are shunted by respective thyristor switches (TV2-TV4) so that selected combinations of reactors can be obtained to provide control of the overall operating voltage. The slope of the overall characteristic can be controlled by switching through successive reactor combinations. Further refinement of the overall characteristic can be obtained by phase control of the smallest reactor (SR4) thyristor switches (TV3) or, in an alternative form of the invention, by the use of a single reactor (SR1) having a primary winding, a closed mesh secondary winding (19) and a phase-controlled auxiliary reactor (AR, ACR) constituting a load on the closed mesh winding. The two forms of the invention may be combined in one equipment.