Supply system intended for forming an electric circuit for powering a tractive unit, railway facility and unit including such a supply system

The system has a mains power supply including a negative power supply line (42) having an electrical potential in phase opposition to an electric potential of a contact wire (34). A positive power supply line (44) includes an electric potential identical to that of the contact wire and a carrying cable (36), where a position of the negative supply line is located between a position of the positive supply line and a position of a geometrical center (48) between the carrying cable and the contact wire to reduce the impedance of an electrical supply circuit. Independent claims are also included for the following: (1) a railway installation (2) a railway assembly.