Suppression of contact arcs between rail and wheel in dc electric railway systems

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The electrical contact is widely used within a wide voltage and current range. In dc electric railway systems, current density of an arc discharge between wheel and rail at a time of disconnecting large current is extremely large for a short time. Electrode (edge on rail) is strongly heated and sometimes suffers severe damage of melting and has an influence on performance. The purpose of this study is to develop a switching assist circuit for dc railway systems for suppressing contact arcs generated at times of contact opening. The circuit is composed of a voltage detection circuit, an electric power absorption circuit, and a semiconductor switch. The voltage detection circuit detects arc occurrence by voltage between electrodes and makes electrical connection to the electric power absorption circuit. By bypassing the arc current, the circuit suppresses arcs, and prevents electrode damage. The semiconductor switch was made using metal-oxide-semiconductor (MOS) field effect transistors (FET) connected in parallel and enabled a fast response time for bypassing large current. Experimental apparatus for simulating arc generation is composed of power supply (large capacitor bank), rolling contact, rails, and an inductance. Rail damages during contact arcs and its change by delay time between arc ignition and the assistant operation was examined. As the operation delay time becomes shorter, arc crater or visible change on the rail is getting small. At the operation delay time of several tens of microseconds, the rail damage is prevented.