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Nowadays, in several European Railway networks, the old DC supply systems are severely limited by line‐voltage drops. In some sectors, it is not possible to increase traffic or to operate locomotives at their nominal ratings. To increase the capacity of a DC supply system, without additional substations, the authors propose a new three‐wire supply system which restores the overhead line voltage with multilevel DC choppers operating as voltage boosters. Circuits using a third wire with a negative or a positive polarity are considered and compared. Case studies are presented for the French and Italian rail networks. Finally, experimental results performed on a test platform of the French railways, are presented in the case of a double 1.5 kV supply system. [ABSTRACT FROM AUTHOR]