Overcurrent-tripping device for circuit breaker

A circuit breaker comprising:

• a case,
• a pair of fixed contact shoes situated in the case,
• a movable contact shoe movably situated in the case, said movable contact shoe forming a conduction path together with the fixed contact shoes,
• a contact spring attached to the movable contact shoe to urge the movable contact shoe to the fixed contact shoes,
• an opening-and-closing mechanism attached to the movable contact shoe for opening and closing the movable contact shoe to control the circuit breaker,
• an overcurrent-tripping device for detecting an overcurrent flowing through the conduction path so that the opening-and-closing mechanism performs a tripping operation for opening the movable contact shoe, said overcurrent-tripping device having a yoke disposed above the movable contact shoe and having a hole therein, an electromagnet disposed on the yoke above the movable contact shoe to surround the hole and operated when a short-circuit current flows through the conduction path, a movable iron core situated in the electromagnet and located above the movable contact shoe, said movable iron core being attracted by the electromagnet when the short-circuit current flows through the conduction path and moved linearly toward the movable contact shoe, and a spring situated inside the electromagnet to urge the movable iron core located in the electromagnet in a direction away from the movable contact shoe, and
• a push rod situated between the movable iron core and the movable contact shoe and arranged linearly with respect to the movable iron core, said push rod passing through the hole and slidably disposed in the electromagnet so that when the short-circuit current flows through the conduction path, the movable iron core is attracted by the electromagnet linearly downwardly along a moving direction of the push rod by overcoming an elastic force of the spring and pushes the push rod to separate the movable contact shoe from the fixed contact shoe, to thereby immediately and directly drive the movable contact shoe in an opening direction.