US 4,503,408 AGranted

Molded case circuit breaker apparatus having trip bar with flexible armature interconnection

AssigneeWestinghouse Electric Corp.

InventorsStephen A. Mrenna, Glenn R. Thomas, Charles E. Haugh

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Abstract

A molded case circuit breaker apparatus is taught with an operating mechanism which is triggered in response to the movement of a trip bar. The trip bar in turn is responsive to current flowing in the main terminals of the circuit breaker apparatus. The trip bar is responsive to electrothermal conditions as a gradual overload increases. It is also responsive to a short circuit condition due to a magnetic reaction between an armature and an electromagnet. The armature is flexibly attached to the trip bar for flexible movement in one direction and non-flexible movement in the other direction so that a short circuit may be accommodated by a relatively small air gap by non-flexible movement of the armature and the trip bar to cause a tripping operation. On the other hand, a wide range of angular movement is available for a high degree of calibrated reaction to a wide range of overload currents because the armature member is flexibly attached to the trip bar in one direction and is held stationary against the facing magnet even after the trip bar continues movement for an otherwise non-allowable increment of electrothermal calibration.

A circuit interrupter, comprising:

(a) enclosure means;
(b) separable contact means disposed within said enclosure means for opening to protect an electrical system;
(c) operating means disposed within said enclosure means in a state of cooperation with said contact means for causing said contact means to open;
and
(d) trip means disposed within said enclosure means in a state of cooperation with said operating means for initiating said operating means to open said contact means, said trip means comprising:
(i) trip bar means capable of a predetermined amount of calibrated rotational movement in a predetermined rotational direction in reponse to thermal or magnetic stimuli for causing said initiation;
(ii) thermal means cooperative with said trip bar means for causing said predetermined amount of calibrated rotational movement in said predetermined rotational direction;
and
(iii) magnetic means attached to said trip bar means, said magnetic means comprising a magnetic armature which is attached to said trip bar means by a leaf spring, said magnetic means also comprising an electromagnet, an end portion of said trip bar being positioned between said leaf spring and said electromagnet, said electromagnet being spaced from said armature during non short-circuit electrical conditions in said system by a predetermined air gap distance, which distance encourages quick response to a short circuit electrical condition in said system by allowing said electromagnet to quickly pull said armature across said air gap in said predetermined direction and against said electromagnet thus rotating said armature correspondingly in said predetermined direction until said air gap is reduced to zero, said armature being rotationally moved less than said predetermined amount by said magnetic means, further rotation of said trip bar means in the same rotational direction by said thermal means to a place related to said predetermined amount of calibrated rotational movement being allowed within limits as said leaf spring flexes as said trip bar continues to rotate while said attached armature remains stationary against said electromagnet.

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Abstract

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