Regenerative braking protection for an electrically-propelled traction vehicle

A regenerative braking protective system for an electrical propulsion system on board a traction vehicle, the system comprising:

• a controllable electric power converter having a set of load terminals adapted to be connected to at least one traction motor and a pair of d-c terminals connected via a bi-directional current path to at least one current collector on the vehicle, the current collector being disposed in sliding contact with an external conductor along a right-of-way traveled by the vehicle, the conductor being energized by a wayside electric power station having at least one fundamental frequency to which it is normally connected, the wayside electric power station being the exclusive source of such fundamental frequency, the current path including a normally-closed circuit breaker that will interrupt current in this path when opened, and the converter having alternative motoring and electrical braking modes of operation;
• controllable switch means connected between the current collector and the circuit breaker in the bi-directional current path, and comprising a solid-state uncontrolled unidirectional electric valve that is poled to conduct direct current whenever the converter is operating in its motoring mode, in combination with a parallel, inversely-poled, solid-state controlled unidirectional electric valve that is able, once a suitable firing signal is applied to its control electrode, to conduct regenerative braking current while the converter is operating in its electrical braking mode, the controlled valve automatically changing from conducting to non-conducting states whenever regenerative current decreases to zero;
• bistable detecting means having a first state if the external conductor with which the current collector is in contact is energized by the fundamental frequency from the wayside electric power station and having a second state otherwise;
• and
• means effective when the converter is operating in a braking mode for applying the firing signal to the controlled valve in response to the detecting means changing from its second state to its first state.