Multiple vehicle spark elimination system for explosive atmospheres

Claim 1

In a power system which delivers electrical power from a main source of power to at least two separately movable vehicles in an explosive atmosphere, each vehicle including a conductive frame and electrically operated equipment, the electrically operated equipment on each vehicle having at least one pair of energizing input terminals, a separate power cable for each vehicle extending between said vehicle and said main source of power, each cable having at least one pair of power conductors coupled to said energizing input terminals of the electrically operated equipment on the associated vehicle and a grounding conductor connected to the frame of the associated vehicle, the electrical field developed by the flow of current through said power conductors in each of said cables inducing an unbalanced voltage in the associated grounding conductor so there is the possibility of an induced voltage difference in the grounding conductors of a pair of said cables which can reach a given maximum value, interrupter contact means connected between said main source of power and at least one of said power cable conductors, and vehicle frame hazard protection means for operating said interrupter contact means to terminate the flow of power from said main source of power to the electrical equipment of the associated vehicle when at least one of said power conductors of each cable becomes electrically shorted to the associated grounding conductor or vehicle frame, the improvement comprising arc-preventing means for preventing the development of an arc in said explosive atmosphere when the frames of two of said vehicles come into contact with one another due to an unbalanced voltage or voltages induced in the grounding conductor of one or more of said cables, said arc-preventing means comprising saturable core reactor means in series with said grounding conductors which saturable core reactor means being unsaturated to present a high impedance to current flow under modest applied voltage conditions reaching said given magnitude and being saturated to present a negligible impedance to current flow under the voltage conditions when any of said cable power conductors becomes shorted to the associated cable grounding conductor or vehicle frame.