Abstract: The power supply installation for a direct current railroad comprises two diode bridge-connected circuits, only two thyristor breakers each connected in parallel to each of the two diode bridge-connected circuits, four dc disconnecting switches each connected between a diode bridge-connected circuit and one of four electric car power supply lines constituting a double track, separately. Further, the two diode bridge-connected circuits are connected by a dc disconnecting switch closed only in case of an accident. In case a ground fault occurs at a power supply line, a powering current to the defective line is interrupted by one of the breakers, together with an extension power supply current supplied from an adjacent substation, without exerting an influence of accident upon the other power supply lines. Further, even if one of the breakers is broken, powering currents are kept supplied to all the power supply lines through a mutual spare bus bar.