1. Field of the Invention
The present invention relates generally to latches and more specifically to a blow-open current limiting circuit breaker having an improved anti-rebound latch.
2. Description of the Prior Art
Current limiting breakers of the type described in U.S. Pat. No. 4,178,618 to Khalid include a blow-open design which facilitates opening of the contacts during the first milliseconds of an extreme overcurrent condition. The blade is accelerated to a high velocity by the increasing fault current and tends to rebound from its open position faster than the tripping response time of the circuit breaker mechanism. Accordingly, means must be provided to delay or hold the blade in the open position until the mechanism trips and supports the blades in the open position. If the blade is not held in the open position, the rebounding blade may reclose under a fault condition in which the excessive current can cause the contacts to weld together. It is also desirable to prevent restriking of arcs between the contacts to stop the current as soon as possible at maximum current level. Blow-open forces will cause current limiting within approximately 0.6 milliseconds; however, the blade, if not restrained in an open position, will immediately rebound and move toward a contact closed position far sooner than the 6 milliseconds it may take for the mechanism to open the circuit.
An electromagnetically actuated anti-rebound latch is described in U.S. Pat. No. 4,409,573 to DiMarco et al which also desribes some of the typical prior art latching mechanisms that utilize springs to bias a latch toward a contact arm to move the latch into a notch in the contact arm when the contact arm of the circuit breaker is blown open by electrodynamic forces to thereby retain the contact arm in an open position.