1. Field
The disclosed concept relates generally to electrical switching apparatus and, more particularly, to electrical switching apparatus, such as circuit breakers. The disclosed concept also relates to closing assemblies and to reversal prevention mechanisms for electrical switching apparatus.
2. Background Information
Electrical switching apparatus, such as circuit breakers, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits, abnormal voltage and other fault conditions. Typically, circuit breakers include an operating mechanism, which opens electrical contact assemblies to interrupt the flow of current through the conductors of an electrical system in response to such fault conditions as detected, for example, by a trip unit. The electrical contact assemblies include stationary electrical contacts and corresponding movable electrical contacts that are typically mounted on moving (e.g., pivotable) arms.
Among other components, the operating mechanisms of some power air circuit breakers, for example, typically include a trip actuator assembly, a closing assembly and an opening assembly. The trip actuator assembly responds to the trip unit and actuates the operating mechanism. The closing assembly and the opening assembly may have some common elements, which are structured to move the movable electrical contacts between a first, open position, wherein the movable and stationary electrical contacts are separated, and a second, closed position, wherein the movable and stationary electrical contacts are electrically connected. Elements of both the closing assembly and the opening assembly move (e.g., pivot) in order to effectuate the closing and opening of the electrical contacts. A charging assembly, which includes a stored energy mechanism, is often employed to facilitate operation of the closing assembly. It can be difficult for some circuit breakers to close on a relatively high current fault, commonly referred to as a Hi-IC. In order to clear the fault, it is desirable that the electromagnetic forces caused by the Hi-IC not be permitted to blow the moving arms back, towards their opening position, once electrical current begins to flow. Such a condition is commonly referred to as, “blow back.” More specifically, at some level of fault current, the circuit breaker will not close completely (e.g., it stalls), and at even higher currents, the closing action will be reversed, blowing the arms and mechanism backwards. Separate devices exist for detecting a stalled condition, and to interact with the circuit breaker trip unit to fire the trip actuator and open the circuit breaker. The further the mechanism is from the fully closed position, the more difficult it is to trip the breaker for a given interruption current-induced electromagnetic force, because of poor mechanical advantage. Accordingly, preventing the moving arms and mechanism from blowing open facilitates the tripping process.
In stored energy circuit breakers where the stored energy mechanism (e.g., closing spring(s)) indirectly drive the mechanism through a cam shaft, a relatively complicated mechanical clutch on the cam shaft is used to prevent the mechanism from undesirably moving backwards. In other designs, such as for example where the stored energy mechanism (e.g., closing spring(s)) directly drives the mechanism, such a cam shaft clutch is ineffective.
There is, therefore, room for improvement in electrical switching apparatus, such as circuit breakers, and in closing assemblies and reversal prevention mechanisms therefor.
These needs and others are met by embodiments of the disclosed concept, which are directed to a reversal protection mechanism for a closing assembly of an electrical switching apparatus, such as a circuit breaker. Among other benefits, the reversal protection mechanism cooperates with the stored energy mechanism (e.g., without limitation, closing spring(s)) to prevent undesired blow-backs, without inhibiting recharging of the spring(s).
As one aspect of the disclosed concept, a reversal prevention mechanism is provided for a closing assembly of an electrical switching apparatus. The electrical switching apparatus includes a housing, separable contacts enclosed by the housing, and an operating mechanism for opening and closing the separable contacts. The closing assembly includes a stored energy mechanism. The reversal prevention mechanism comprises: an actuator assembly structured to be pivotably coupled to the housing; a first stop element for controlling movement of the actuator assembly; a stop assembly structured to be pivotably coupled to the housing; and a second stop element for controlling movement of the stop assembly. The stored energy mechanism is movable among a charged position, a discharged position, and a contact touch position corresponding to a point at which the separable contacts make initial electrical contact. When the stored energy mechanism is disposed in the contact touch position, the stop assembly is structured to cooperate with the actuator assembly to prevent the stored energy mechanism from moving backwards.
The actuator assembly may comprise a driver, an actuator cam, and a biasing element. The actuator cam may be pivotably coupled to the driver. The actuator assembly may be movable between an open position and a compressed position, wherein the biasing element biases the actuator assembly toward the open position. The actuator assembly may further comprise a first extension member and a second extension member, wherein the first extension member extends through the driver, and wherein the second extension member extends outwardly from the actuator cam. The biasing element may be a torsion spring, wherein the torsion spring includes a first leg, a second leg, and a number of coils disposed between the first leg and the second leg. The first leg may be biased against the first extension member, and the second leg may be biased against the second extension member.
The first stop element may be a first pin member structured to extend outwardly from the housing. The actuator cam may include a first stop edge, a second stop edge, and a cam surface. The first stop edge may cooperate with the first extension member to define the open position, the second stop edge may be structured to cooperate with the first pin member and, when the stored energy mechanism is disposed in the contact touch position, the cam surface may be structured to engage and lift the stop assembly. When the stored energy mechanism moves toward the charged position, the second stop edge may be structured to engage the first pin member and the torsion spring may be compressed, thereby moving the actuator assembly toward the compressed position to permit the stored energy mechanism to move passed the stop assembly to the charged position.
The second stop element may be a second pin member structured to extend outwardly from the housing. The stop assembly may comprise a jam stick, an actuator plate, and a spring. The actuator plate may be coupled to the jam stick, and the spring may be structured to bias the jam stick toward the second pin member. The stored energy mechanism may comprise a ram wherein, when the ram is disposed in the contact touch position, the actuator assembly is structured to pivot the stop assembly against the spring bias, thereby lifting the jam stick to engage and prevent the ram from moving backwards.
A closing assembly and an electrical switching apparatus employing the aforementioned reversal prevention mechanism, are also disclosed.
A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
Directional phrases used herein, such as, for example, left, right, upward, downward, clockwise, counterclockwise and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein.
As employed herein, the term “fastener” refers to any suitable connecting or tightening mechanism expressly including, but not limited to, screws, bolts and the combinations of bolts and nuts (e.g., without limitation, lock nuts) and bolts, washers and nuts.
As employed herein, the statement that two or more parts are “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts.
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
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Among other components, the reversal prevention mechanism 200 preferably includes an actuator assembly 202 (best shown in
The stored energy mechanism 102 is movable among a charged position (
As best shown in
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Continuing to refer to
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As previously discussed hereinabove, in operation, when the stored energy mechanism 102 (
Accordingly, it will be appreciated that the disclosed reversal prevention mechanism 200 effectively works in connection with the components (see, for example and without limitation, closing springs 104,106 and ram 108 of
While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.