Under the reactive power Absolute measurement mode

the dynamic reactive compensator should be adopted in single-track electrification railway which has small freight volume and small number of trains.The calculation of the maximum reactive power compensation capacity and optimum design of FC filter circuit are key-points of scheme design.Traction supply designer should calculate three type of traction substation′s feeder current.As the short-time maximum current can incarnate the change of train running status

even the number of the trains

it should be adopted to calculate the maximum reactive power compensation capacity.The design principle of FC filter circuit optimum design in traction substation is concluded

and the best disposition algorithm of filter circuit facility capacity is given in this paper.The successful application has demonstrated that the algorithm can minimized the total compensation capacity and satisfy certain technology index requirements of filtering rate without changing the total reactive power compensation capacity.