Design optimization of multicoil traction transformers to limit psophometric currents

In railway traction applications the modulation of electrical traction drives in the range of radio frequencies produces currents harmonics. To ensure correct operation modes of the signaling circuits, the levels of interference magnitudes have to be reduced. Psophometric current (P.C.) gives an indication of the interference level produced by traction equipment: it takes into account the harmonic content of the waveform of primary current of the multibody traction transformer. To limit the P.C. a properly sized additional winding on the multicoil transformer used to supply the traction equipment is considered. In the paper the system is analyzed by means of the mathematical model and some design guidelines are proposed.