Abstract: A dc power supply circuit connects a plurality of dc circuit breakers to a semi-conductor converter, returning again to the semi-conductor converter through a dc driving part such as an electric railcar connected to each dc circuit breaker. A second dc circuit breaker of larger capacity than the above-mentioned dc circuit breakers is provided in a return circuit and opened when a short circuit current is detected. A current decreasing means opens the second dc circuit breaker to decrease the short circuit current and includes, for example, a series-circuit of a resistor R and a reactor L. The dc power supply circuit has a large interruption capacity with low resistance loss.

Abstract: A commutation type DC breaker having a commutation circuit electrically connected in parallel to a main contact. The main contact is connected between a DC power supply and a load. The commutation circuit is a series circuit of a commutation capacitor, a reactor and a commutation switch, with an energy absorption device electrically connected in parallel to the main contact. A switch or a breaker for preventing the flow of commutation current from the commutation circuit to the load in a non-load opening mode is connected between an electrical connection point (P), of the main contact and the commutation circuit, and the load and is opened substantially simultaneously with the opening of the main contact, or before the closure of the commutation switch. In this manner, the safety on the load in the non-load opening mode is enhanced.

Abstract: A commutating type DC circuit breaker arrangement comprising: a vacuum circuit breaker having a movable electrode and stationary electrode; a series circuit of a capacitor, a saturation reactor and a commutating switch which is connected in parallel with the vacuum circuit breaker; and an electrical relay for detecting a predetermined electrode open position at which a sufficient insulating distance between the movable electrode and the stationary electrode is maintained via movement of a predetermined position on an actuating rod for the movable electrode and for closing the commutating switch in response to the detection of the predetermined electrode open position.

Abstract: A DC power supply circuit arrangement for supplying DC power from a power source through a common conductor to a load, comprises a plurality of switches connected between the power source and the common conductor and/or between the common conductor and the load, each of the switches having one terminal connected to the power or the load and the other terminal connected to the common conductor, an energy absorber having two terminals, a first diode connected between the one terminal of each of the plurality of switches and one of the two terminals of the energy absorber in a polarity so as to allow a current to flow from the one terminal of the switch to the one terminal of the energy absorber, a second diode connected between the one terminal of each of the plurality of switches and the other terminal of the energy absorber in a polarity so as to allow a current to flow from the other terminal of the energy absorber to the one terminal of the switch, and a circuit connecting the other terminal of the energy a