with thyristor-based SVCs. However, the TCR draws a nonsinusoidal current, and in single-phase systems, these have a high level of third harmonic (up to 34% of the fundamental). As a result, this topology requires a bulky LC shunt filter tuned to the third harmonic. To avoid this drawback, a new structure, based on CCIs was proposed. The case study is a 60-MVA substation close to Paris. The substation is phase-tophase connected to a 225-kV three-phase transmission line. The initial circuit, presented in Figure 4, includes two fixed compensation banks with antiharmonic inductors (L 1 and L 2) . Overhead Line L1 L2 c2 c1 60-MVA Fixed Substation 225-kV Transformer Compensation Transmission Line iLoad (Trains) Vline Rails Figure 4. A 25-kV, 50-Hz ac railway line power supply. Overhead Line L1 C1 LF1 iin1 C2 LF2 iout1.1 ac Vin1.1 L3 L2 Already-Existing Compensation Banks Vout1.1 iin2 Co1 iout2.1 ac Vin2.1 ac α C3 V1 ac α iout1.2 ac Vin1.2 Vout1.2 V2 N1 ac Vout1.N1 Vout2.2 α N2 iout1.N2 ac Co1 Co2 ac Vin2.N2 Vout2.N2 Co2 ac α New Compensation Bank iout2.2 Vin2.2 iout1.N1 ac Vin1.N1 Vline ac Co1 ac α Co2 Vout2.1 α N1 Step-Up ac Choppers Rails N2 Step-Up ac Choppers Figure 5. A new topology of a reactive power compensator. 18 1 16 0.8 Reactive Power (Mvar) ac Chopper Duty Cycle α 0.9 0.7 0.6 0.5 0.4 0.3 0.2 12 ∆Q = 3 Mvar 10 Initial Circuit With ac Chopper 8 0.1 0 19 14 20 21 22 23 24 25 26 Vline (kV) 27 28 29 6 19 (a) 20 21 22 23 24 Vline (kV) 25 26 27 (b) Figure 6. The (a) duty cycle and (b) reactive power are plotted versus the line voltage. IEEE Elec trific ation Magazine / s ep t em be r 2 0 1 4 9