Current limiting device for overcurrent protection

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William F. Weldon
Herbert H. Woodson

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United States Patent and Trademark Office


A current limiting device for use with a circuit breaker in an electric power system utilizes mutual inductance variation between movable windings to limit current to safe levels. In the device, first and second coil windings are electrically connected for current flow therethrough and magnetically linked for mutual inductive coupling. The effective inductance of the connected coil windings is functionally related to the relative physical positioning of the coil windings. The coil windings are movable relative to one another, so as to provide for variation in the effective inductance of the two coils. Structure is provided for disposing the coils in an initial relative positioning, the structure being yieldable to a force produced between the coils due to a predetermined magnitude of current flow through the coils. The force produced between the coils acts to change the relative positioning of the coils, increasing the effective inductance, and thereby limiting the current therethrough. In an alternative arrangement, movement of the coils to designated positions of relative placement due to a predetermined magnitude of current flow therethrough may be utilized to open a set of electrical contacts or to trigger a conventional circuit breaker interrupting the circuit.



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