Electrical switching apparatus, and conductor assembly and shunt assembly therefor

A shunt assembly is provided for an electrical switching apparatus including a conductor assembly having a load conductor and a movable contact assembly with a number of movable contact arms. The movable contact assembly is movable in response to a fault current. The shunt assembly includes a number of flexible conductive elements each having a first end electrically connected to the load conductor, a second end electrically connected to a corresponding one of the movable contact arms, and a number of bends disposed between the first and second ends. At least one constraint element is disposed proximate a corresponding one of the bends and constrains movement of the flexible conductive element in response to the fault current, thereby translating the magnetic repulsion force associated with the fault current into a corresponding torque of the movable contact arms of the movable contact assembly.

CROSS REFERENCE TO RELATED APPLICATION

This Application is related to commonly assigned, copending application Ser. No. 11/549,277, filed Oct. 13, 2006, entitled “Electrical Switching Apparatus, and Conductor Assembly and Independent Flexible Conductive Elements Therefor,” which is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to electrical switching apparatus and, more particularly, to conductor assemblies for electrical switching apparatus, such as circuit breakers. The invention also relates to shunt assemblies for circuit breaker conductor assemblies.

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.

The electrical contact assemblies of low-voltage circuit breakers, for example, generally comprise a conductor assembly including a movable contact assembly having a plurality of movable contacts, and a stationary contact assembly having a plurality of corresponding stationary contacts. The movable contact assembly includes a plurality of movable contact arms or fingers, each carrying one of the movable contacts and being pivotably coupled to a contact arm carrier. The contact arm carrier is itself pivotable about a number of pivot pins, pivoted by a protrusion or arm on the pole shaft of the circuit breaker operating mechanism to move the movable contacts into and out of electrical contact with the corresponding stationary contacts of the stationary contact assembly. The contact arm carrier includes a contact spring assembly structured to bias the fingers of the movable contact assembly against the stationary contacts of the stationary contact assembly in order to provide and maintain contact pressure when the circuit breaker is closed, and to accommodate wear.

“Blow-on” schemes are commonly employed by low-voltage circuit breakers and are discussed, for example, in U.S. Pat. No. 6,005,206, which is hereby incorporated herein by reference.

The movable contact assembly is electrically connected to a generally rigid conductor of the conductor assembly by flexible conductors, commonly referred to as shunts. More specifically, each shunt is coupled at one end to the generally rigid conductor, and at the other end to a corresponding one of the fingers of the movable contact assembly. The shunts include a number of bends to accommodate the motion of the contact arm carrier and fingers with respect to the generally rigid conductor during a trip condition. Specifically, under over-current or fault conditions, energy flowing through the shunts results in a magnetic repulsion force which tends to straighten the bends of the shunts. However, the magnetic repulsion force is, in general, not translated into torque of the fingers of the movable contact assembly as efficiently and effectively as possible, resulting in blow-on performance of the circuit breaker that is less than desired. In other words, it is desirable to transfer the magnetic repulsion force associated with the shunts into positive torque (e.g., rotation) of the fingers in order to load the electrical contacts and thereby withstand relatively high fault currents.

There is, therefore, room for improvement in shunt assemblies for low-voltage circuit breaker conductor assemblies.

SUMMARY OF THE INVENTION

These needs and others are met by embodiments of the invention, which are directed to a conductor assembly for an electrical switching apparatus such as, for example, a low-voltage circuit breaker, and a shunt assembly therefor, which optimizes the forces on the movable arms of the conductor assembly and thereby improves the withstand performance of the circuit breaker.

As one aspect of the invention, a shunt assembly is provided for an electrical switching apparatus. The electrical switching apparatus includes a conductor assembly having a load conductor and a movable contact assembly with a number of movable contact arms. The movable contact assembly is movable in response to a fault current. The shunt assembly comprises: at least one flexible conductive element including a first end structured to be electrically connected to the load conductor, a second end disposed distal from the first end and being structured to be electrically connected to a corresponding one of the movable contact arms, and a number of bends being disposed between the first end and the second end; and at least one constraint element structured to be disposed proximate a corresponding one of the bends. In response to the fault current, the at least one flexible conductive element is subject to a magnetic repulsion force having a tendency to straighten the number of bends of such flexible conductive element. The at least one constraint element is structured to constrain movement of such flexible conductive element, in order to translate the magnetic repulsion force into a corresponding torque of the movable contact arms of the movable contact assembly.

The at least one constraint element may comprise a restraint member, wherein the restraint member is structured to be coupled to a portion of the movable contact assembly in order that the restraint member does not move independently with respect to the movable contact assembly. When the at least one flexible conductive element is subject to the magnetic repulsion force, the restraint member may abut such flexible conductive element at or about the corresponding one of the bends. The restraint member may include a first side and a second side, wherein the second side of the restraint member includes a curved surface corresponding to a portion of the corresponding one of the bends.

The at least one flexible conductive element may be structured to move among a first position and a second position corresponding to the electrical switching apparatus being subject to the fault current. The number of bends may be a first bend and a second bend. The restraint member may be a first restraint member disposed at or about the first bend, wherein the at least one constraint element further comprises a second restraint member, and wherein, when the at least one flexible conductive element is disposed in the first position, the second restraint member is disposed at or about the second bend in order to constrain movement of the second bend. The at least one flexible conductive element may be a plurality of shunts and, when the shunts are subject to the magnetic repulsion force, the first restraint member may be structured to impose a first restraining force on each of the shunts normal to the first bend thereof, and the second restraint member may be structured to impose a second restraining force on the shunts normal to the second bend thereof.

As another aspect of the invention, a conductor assembly for an electrical switching apparatus comprises: a load conductor; a movable contact assembly comprising a number of movable contact arms, the movable contact assembly being structured to move in response to a fault current of the electrical switching apparatus; and a shunt assembly comprising: at least one flexible conductive element including a first end electrically connected to the load conductor, a second end disposed distal from the first end and being electrically connected to a corresponding one of the movable contact arms, and a number of bends being disposed between the first end and the second end, and at least one constraint element disposed proximate a corresponding one of the bends. In response to the fault current, the at least one flexible conductive element is subject to a magnetic repulsion force having a tendency to straighten the number of bends of such flexible conductive element. The at least one constraint element constrains movement of such flexible conductive element, in order to translate the magnetic repulsion force into a corresponding torque of the movable contact arms of the movable contact assembly.

As another aspect of the invention, an electrical switching apparatus comprises: an enclosure; a stationary contact assembly housed by the enclosure and including a number of stationary electrical contacts; and a conductor assembly housed by the housing, the conductor assembly comprising: a load conductor, a movable contact assembly comprising a number of movable contact arms each having a movable contact, the movable contact being movable into and out of electrical contact with a corresponding one of the stationary electrical contacts of the stationary contact assembly in response to a fault current of the electrical switching apparatus, and a shunt assembly comprising: at least one flexible conductive element including a first end electrically connected to the load conductor, a second end disposed distal from the first end and being electrically connected to a corresponding one of the movable contact arms, and a number of bends being disposed between the first end and the second end, and at least one constraint element disposed proximate a corresponding one of the bends. In response to the fault current, the at least one flexible conductive element is subject to a magnetic repulsion force having a tendency to straighten the number of bends of such flexible conductive element. The at least one constraint element constrains movement of such flexible conductive element, in order to translate the magnetic repulsion force into a corresponding torque of the movable contact arms of the movable contact assembly.

The movable contact assembly may further comprise a first side plate, a second side plate, and at least one pivot member extending between the first side plate and the second side plate. The restraint member may include a first side, a second side, a first end of the restraint member, and a second end of the restraint member disposed opposite and distal from the first end of the restraint member. The movable contact assembly may further comprise a contact spring assembly disposed between the first side plate and the second side plate, and the contact spring assembly may comprise a housing and plurality of biasing elements housed by the housing. The first side of the restraint member may be disposed adjacent the housing of the contact spring assembly, and may include a protrusion which engages the housing of the contact spring assembly in order to maintain the position of the restraint member with respect to the contact spring assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For purposes of illustration, embodiments of the invention will be described as applied to a device for efficiently translating the magnetic repulsion force in generally S-shaped shunts for low-voltage circuit breaker conductor assemblies into torque of the movable contact arms of the movable contact assembly of the breaker, although it will become apparent that they could also be applied to translate such force in flexible conductive elements which are arranged in any suitable number and/or configuration for use in a wide variety of electrical switching apparatus (e.g., without limitation, circuit switching devices and other circuit interrupters, such as contactors, motor starters, motor controllers and other load controllers) other than low-voltage circuit breakers.

Directional phrases used herein, such as, for example, left, right, top, bottom, upper, lower, front, back, 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.

FIG. 1shows an electrical switching apparatus, such as a low-voltage circuit breaker2, including a conductor assembly50and shunt assembly100therefor, in accordance with embodiments of the invention. The low-voltage circuit breaker2includes an enclosure4(shown in simplified form in phantom line drawing inFIG. 1), a stationary contact assembly10(partially shown inFIGS. 4A and 4B) including a number of stationary electrical contacts12(one stationary electrical contact12is shown inFIGS. 4A and 4B), and the conductor assembly50, which is housed by the enclosure4. Although one conductor assembly50is shown inFIG. 1, it will be appreciated that the circuit breaker2may have any suitable number of poles (circuit breaker2ofFIG. 1has three poles) and corresponding conductor assemblies50therefor.

As shown inFIGS. 1,2,4A and4B, the conductor assembly50includes a load conductor52, a movable contact assembly54, and the aforementioned shunt assembly100. More specifically, the movable contact assembly54includes a number of movable contact arms56(see, for example, the six movable contact arms56of the example movable contact assembly54shown inFIG. 1; see also the five movable contact arms56shown inFIG. 2) each having a movable contact58structured to be movable into (FIG. 4A) and out of (FIG. 4B) electrical contact with a corresponding one of the stationary electrical contacts12(FIGS. 4A and 4B) of the stationary contact assembly10(FIGS. 4A and 4B) in response to a fault current (e.g., without limitation, an over current condition; and overload condition; an under voltage condition; a relatively high level short circuit or fault condition; a ground fault condition; an arc fault condition) of the circuit breaker2.

The shunt assembly100includes at least one flexible conductive element102having a first end104and a second end106disposed distal from the first end104. The first end104is structured to be electrically connected to the load conductor52, and the second end106is structured to be electrically connected to a corresponding one of the movable contact arms56of the movable contact assembly54. The example shunt assembly100includes five (FIG. 2) or six (FIG. 1) flexible conductive elements102(one shunt102is shown in hidden line drawing inFIG. 1; two shunts102are visible in the isometric view ofFIG. 2; and one shunt102is shown in section inFIGS. 4A and 4B), one for each movable contact arm56of the movable contact assembly54. The example flexible conductive elements102are shunts comprised of layered conductive ribbon (un-numbered but partially shown in exaggerated form inFIG. 2), and include first and second bends108,110disposed between the first and second ends104,106, as shown. Such shunts102are described in greater detail, for example, in U.S. patent application Ser. No. 11/549,277, which has been incorporated herein. The manner in which the first and second ends104,106of the shunts102are electrically connected and mechanically coupled to the load conductor52and corresponding movable contact arm56, respectively, and the general operation of the conductor assembly50, for example, in response to the fault current, is also discussed, for example, in U.S. patent application Ser. No. 11/549,277.

It will be appreciated that the conductor assembly50could contain any suitable alternative number and configuration of shunts102other than those shown and described herein, without departing from the scope of the invention. It will also be appreciated that, although the example shunts102include two bends108,110, resulting in a shunt102which is generally S-shaped (best shown inFIGS. 4A and 4B), each shunt102could alternatively have any suitable number of bends (e.g., without limitation, one bend; more than two bends) and corresponding configuration (not shown).

In response to the fault current, the shunts102are subject to a magnetic repulsion force having a tendency to straighten the bends108,110thereof. This tendency to straighten has caused known shunt designs to be relatively in-effective in transmitting motion of the shunts102into the desired corresponding blow-on torque of the movable contact arms56of the movable contact assembly54. This inhibits the circuit breaker2(FIG. 1) withstand. Specifically, blow-on performance and associated withstand, is lower than desired. The blow-on and withstand performance of the circuit breaker (FIG. 1) relates to the ability of the movable contact assembly54to move (e.g., apply torque to) the movable contact arm56and associated movable electrical contact58in a manner which maintains electrical contact between the movable electrical contact58and the corresponding stationary electrical contact12, as shown inFIG. 4A, in order to withstand a pre-determined fault current (e.g., without limitation, current rating), without opening the separable contacts12,58, as shown inFIG. 4B.

The disclosed conductor assembly50and shunt assembly100therefor, address and overcome the aforementioned disadvantage by providing at least one constraint element120structured to constrain movement of the shunts102, and thereby effectively translate the magnetic repulsion force into a corresponding torque of the movable contact arms56of the movable contact assembly54. In other words, the constraint element120functions somewhat like a fulcrum for the shunts102to resist in-efficient movement (e.g., straightening of the bends108,110) thereof, and instead directly transmit the energy associated with the magnetic repulsion force into effective electrical contact force to improve withstand performance. In particular, the magnetic repulsion force is translated into torque of the movable contact arms56and movable electrical contacts58thereof. As will be discussed herein, to accomplish this objective, the example shunt assembly100includes two constraint elements, a first restraint member120and a second restraint member130. The first restraint member120is coupled to a portion of the movable contact assembly54in order that it does not move independently with respect thereto. The first restraint member120is disposed at or about the first bend108of each shunt102and, when the shunt102is disposed in the un-actuated position ofFIG. 4A, the second restraint member, which in the example shown and described herein is a shunt block130disposed proximate the load conductor52, is disposed at or about the second bend110, in order to constrain movement of the second bend110of the shunt102.

Operation of the shunt assembly100will now be described with reference toFIGS. 4A and 4B. For economy of disclosure, only one shunt102of the shunt assembly100will be described with respect to the restraint members120,130. It will, however, be appreciated that the other shunts102are also controlled (e.g., without limitation, directed; constrained) by the first and second restraint members120,130in substantially the same manner. Specifically, the shunts102are movable among a first (e.g., closed) position (FIG. 4A) and a second (e.g., open) position (FIG. 4B) corresponding to the circuit breaker operating mechanism (not shown) having tripped open the separable contacts12,58open in response to a trip condition. Specifically, when the shunt102is disposed in the first position ofFIG. 4A, the first bend108of the shunt102is constrained by the first restraint member120, and the second bend110of each shunt102constrained by the second constraint member130. When the shunt102is subject to the magnetic repulsion force in response to a fault current, the first and second bends108,110of the shunt102have a tendency to straighten. At this point, the first restraint member120abuts the shunt102at or about the first bend108and resists the first bend108from straightening, and the second restraint member130resists the second bend110from straightening. The difference in position between this blow-on condition and the closed position ofFIG. 4Ais relatively insignificant and, therefore, for economy of disclosure, has not been expressly shown. In this manner, the magnetic repulsion force is transferred directly to the second end106of the shunt102, in order to provide torque of the corresponding one of the movable contact arms56of the movable contact assembly54(clockwise about pin member64in the direction indicated by arrow66ofFIG. 4A) until the circuit breaker operating mechanism (not shown) opens the separable contacts12,58(FIG. 4B). More specifically, when the shunt102is subject to the magnetic repulsion force, the first restraint member120imposes a first restraining force132on the shunt102normal to the first bend108thereof, and the second restraint member130imposes a second restraining force134on the shunt102normal to the second bend110thereof, as indicated generally by arrows132and134ofFIG. 4A. In this manner, energy of the magnetic repulsion force is effectively and efficiently directed down the shunt102to the second end106thereof and into torque of the movable contact arms56of the movable contact assembly54.

As shown inFIGS. 2,3A,3B,3C,4A and4B, the example first restraint120includes a first side122and a second side124. The second side124has a curved surface126corresponding to a portion of the first bend108of the shunt102(FIGS. 2,4A and4B).

As shown inFIGS. 1,2,4A and4B, the example movable contact assembly54includes a first side plate60, a second side plate62, and at least one pivot member64extending therebetween. The first restraint member120, in addition to the aforementioned first and second sides122,124, also includes a first end136and a second end138disposed opposite and distal from the first end136(best shown inFIGS. 2,3A,3B and3C). The example first restrain member120includes an elongated aperture140which extends between the first and second ends136,138of the restraint member120and receives a fastener (e.g., pin member) of the movable contact assembly54(FIGS. 2,4A and4B). The example first restraint member120is a single-piece member extending between the first and second side plates60,62of the movable contact assembly54, although it will be appreciated that any suitable alternative number and configuration of constraint elements (e.g., without limitation, a cylindrical dowel (not shown)) could be employed without departing from the scope of the invention.

The example movable contact assembly54further includes a contact spring assembly70, which is also disposed between the first and second side plates60,62. More specifically, the contact spring assembly70includes a housing72and a plurality of biasing elements74(one biasing element74is shown in the exploded view ofFIG. 2) housed by the housing72. Each of the biasing elements74is structured to bias a corresponding one of the movable contact arms56and the movable contact58coupled thereto, toward electrical connection with a corresponding one of the stationary electrical contacts12(one stationary electrical contact is shown inFIGS. 4A and 4B). Specifically, the movable contact arms56are biased clockwise about pivot member64in the direction indicated by arrow66inFIG. 4A. Contact spring assemblies aredescribed, for example, in U.S. patent application Ser. No. 11/549,277, w hich has been incorporated herein. As best shown inFIGS. 3A-3C, the first side122of the example single-piece first restraint member120includes a generally planar portion142and a protrusion144extending outwardly from the planar portion142. The first side122of the example first restraint member120is disposed adjacent the housing72of the contact spring assembly70, and the protrusion144engages a portion of the housing72, as shown inFIGS. 4A and 4B, in order to maintain the position of the first restraint member120with respect thereto. In this manner, the first restraint member120pivots with the contact spring assembly70, but not independently with respect thereto, as previously discussed.

Accordingly, the disclosed low-voltage circuit breaker2(FIG. 1), and conductor assembly50(FIGS. 1,2,4A and4B) and shunt assembly100(FIGS. 1,2,4A and4B) therefor, provide a mechanism (e.g., without limitation, at least one constraint element120,130) for effectively and efficiently transmitting motion of the flexible conductive members (e.g., shunts102) of the conductor assembly50into torque of the movable contact arms56of the movable contact assembly54, to improve the withstand of the circuit breaker2(FIG. 1).