Molded Case Circuit Breaker

Abstract

A molded case circuit breaker comprising a contact arm movable between circuit closed and open positions, a collapsible mechanism including a releasable member having one end normally engaged with a latch member of an automatic trip unit, a pair of toggle links provided between the movable contact arm and the releasable member, and a tension spring stretched between a manually operable handle and a toggle knee of the toggle links, the other end of the releasable member having a wedge member swingably mounted thereto. When an automatic trip occurs, the wedge member slidably enters between one of the toggle links and a stationary pin secured to the molded case to prevent the contact arm from rebounding toward its circuit closed position.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to molded case circuit breakers of the type including a spring-biased releasable member releasably held by an automatic trip unit in a position to maintain a movable contact in its closed position. More particularly, the invention relates to such circuit breakers as characterized herein including means for preventing rebound of the movable contact member toward its closed position following release of the releasable member.

2. Description of the Prior Art

An example of a molded case circuit breaker of the character described herein is disclosed in U.S. Pat. No. 3,134,879 of George E. Gauthier et al., assigned to General Electric Company.

The prevention of rebound of the movable contact arm toward the circuit closed position upon the occurence of automatic release due to an overloaded condition is required in order to sufficiently maintain the power interruption performance of the molded case circuit breaker without increasing the size thereof.

According to the teaching of the U.S. Pat. No. 3,134,879, a hook-like extension is provided on a releasable member to engage with a movable contact arm upon the occurence of an automatic tripping operation and thereby prevent rebound of the movable contact arm back toward the circuit closed position. In addition, a spring-biased swingable member is pivotally supported in the molded case of insulating material, one end of which is urged against one of a pair of toggle links of a collapsible mechanism to keep the collapsible mechanism in a position so as to maintain the largest interruption distance of the movable contact arm from its circuit closed position.

Although molded case circuit breakers as heretofore known have been successfully used, some problems remain which prevent them from being entirely satisfactory. In accordance with the circuit breaker disclosed in U.S. Pat. No. 3,134,879, for example, two components, namely the hook-like extension of the releasable member for engaging a slot in the movable contact arm and the swingable member supported in the molded casing so that its front edge engages one of a pair of toggle links, were required. As a result, the circuit breaker is expensive to manufacture and it also is complicated to assemble.

In addition, in electric circuit breakers of substantial capacity, such as 2000 amperes, relatively heavy parts and heavy operating springs are required to maintain the necessary contact pressure. Accordingly, a substantially large shock is repeatedly imposed on the toggle link by the thin front edge of the swingable member every time that automatic release occurs. As a result, mechanical fatigue of the toggle linkage, the toggle knee and the pins for pivotally supporting the link ends frequently occurs so that the circuit breaker cannot achieve the performance initially intended.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a new, improved and unique open and closing mechanism for use in a molded case circuit breaker having minimum parts for preventing a movable contact arm from rebounding toward its initial closed position upon being operatively moved to its open circuit position.

Another object of the present invention is to provide a new, improved and unique molded case circuit breaker of the character described having improved resistance to mechanical fatigue of the collapsible mechanism thereof, including the toggle linkage and the pivotally supporting pins thereof.

In accordance with one aspect of the invention, the foregoing objects and others are attained through the provision of a molded case circuit breaker which comprises a molded case formed of a suitable insulating material, at least one movable arm mounted in the molded case so as to be capable of movement between closed and open circuit positions, an automatic trip unit having a latch member capable of movement to a releasable position in response to an overloaded circuit condition, a releasable member pivotally supported in the molded case and having one end thereof normally engaged by the latch member, a pair of toggle links pivotally engaged with each other at their one ends, with the other ends of the toggle links being pivotally engaged, respectively, to the releasable member and the movable contact arm, a manually operable handle pivotally supported in the molded case and movable between the circuit closed and open positions, a tension spring stretched between the manually operable handle and the interconnecting knee point of the toggle links, a stationary guide member mounted in the molded case, and a wedge member swingably mounted on the releasable member, the wedge member being capable of sliding between one of the toggle links and the stationary guide member when the releasable member is automatically tripped by the latch member while the manually operable handle is positioned in the circuit closed position.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description when considered in connection with the accompanying drawings, wherein like reference numerals designate like or corresponding parts throughout the several views, and in which:

FIG. 1 is an elevational view, in section, of one embodiment of a molded case circuit breaker constructed in accordance with the present invention;

FIG. 2 is a partial view of FIG. 1 showing the manually operable handle in its open position; and

FIG. 3 is a partial view of a molded case circuit breaker with the handle shown in a circuit open position having resulted from an operation of the automatic trip unit.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to the drawings, and more particularly to FIG. 1 thereof, a molded case circuit breaker is shown having an insulating casing 10 of an electrically insulating material, such as, for example, phenol resin, a line terminal conductor 11 mounted on a base 17 of the casing and a load terminal conductor 12 mounted on the same. The line terminal conductor 11 has a stationary main contact 13 at one end thereof and an auxiliary stationary arcing contact 14 at an intermediate portion thereof in its lengthwise direction.

A trip unit 15 having a latch member 16 which includes a conventional thermally actuated trip unit and an electromagnetic operated trip mechanism, is mounted in the casing 10 at a leftward portion thereof, as seen in the Figure, and the line terminal conductor 12 is introduced into the trip unit 15 for exciting a magnetic pole unit of the electromagnetic trip mechanism and for heating a bi-metallic unit of the thermally actuated trip unit, as is well known. The line conductor 12 is finally connected to a conductor 18 also mounted on the base 17.

A movable contact arm 19 is pivotally mounted in the casing 10 for supporting a movable main contact 20 for engaging with and separating from the main stationary contact 13 to carry out the making and breaking operations of an electric circuit and a movable arcing contact 21 for engaging with and separating from the auxiliary stationary contact 14.

For convenience of illustration, only one movable contact arm 19 and its associated parts and a single arrangement of stationary contacts 13 and 14 supported on the load terminal conductor 11 have been shown but it is to be understood that generally there are other movable contact arms and load terminal conductors arranged perpendicularly to the surface of illustration in parallel fashion to thereby provide a poliphase or multi-pole type circuit breaker. In order to simultaneously carry out "make and break" movement of the aforementioned movable contact arms 19, an operating rod 210 is provided at one end thereof extending over the parallel movable contact arms 19.

A manually operable handle 22 is provided, having an upper end thereof extending through a slidable top cover 220 arc-tightly sealing the casing 10 and a lower end pivotally mounted on a pin 23 secured in the casing 10. A releasable member 24 having one end normally engageable with the latch member 16 of the trip unit 15 is also provided. A pair of toggle links 25 and 26 are rotatably pivoted to each other at respective ends thereof by a pin 27 which acts as a toggle knee. The toggle link 25 has its other end rotatably pivoted to the releasable member 24, and the toggle line 26 has its other end rotatably pivoted to the movable contact arm 19.

A tension type spring 28 is stretched between the handle 22 and the toggle knee 27, and thus when the spring 28 is positioned as shown by the manual operation of the handle 22, the toggle links 25 and 26 are straightened so as to engage the contact 20 of the movable contact arm 19 with the stationary contact 13 of the load terminal conductor 11 because of the engagement of the releasable member 24 with latch member 16 of the trip unit 15.

If it is required to manually open the circuit, the handle 22 is shifted to the left from the position shown in FIG. 1. In this way, when the axis of tension spring 28 passes across the center line of the straightened toggles 25 and 26, the collapsible linkage including toggle links 25 and 26 and releasable member 24, is collapsed, as shown in FIG. 2, to cause the movable contact arm 19 to rotate counterclockwise to thereby respectively separate the movable contacts 20 and 21 from the stationary contacts 13 and 14. It is noted, however, when this occurs, that the one end of the releasable member 24 remains engaged with the latch member 16 of trip unit 15.

The releasable member 24 carries on its rightwardly disposed side, as viewed in FIG. 1, a swingable wedge member 29 being pivoted thereon by a pin member 30. A cooperating stationary pin member 31 is supported on an upstanding leg member 32 which is mounted in the casing 10.

As is well known, an arc chute generally indicated by the reference numeral 33 is mounted in the casing 10 so as to surround the arcing contacts 14 and 21. The chute includes a pair of side walls 34, only one being shown, made of an insulating material, and a plurality of stacked arc-extinguishing metal plates 35, each having a V-shaped slot 36 for elongation of the electric arc to be initiated between the separated arcing contacts 14 and 21.

When the manually operable handle 32 is positioned in the "ON" position to engage the movable contact 20 of movable contact arm 19 with the stationary contact 13 of load terminal conductor 11, the electric circuit made may be traced from line terminal conductor 12 through conductor 18, movable contact arm 19, movable contact 20 and stationary contact 13 to load terminal conductor 11.

For convenience of illustration, the molded case circuit breaker of FIG. 1 has been shown as having only one trip unit 15. Actually, a trip unit 15 is, however, provided for each pole or phase of the poli-phase circuit breaker, and the thermally actuated and electromagnetically operated trip mechanism mounted in each trip unit are responsive to an excessive current condition existing in each pole or phase to cause the common latch member 16 to release the hook extension of releasable member 24 through a rotatable trip bar, not shown, extending through the respective trip units 15 when an excessive current condition occurs in at least one of the poles or phase conductors of the circuit breaker.

When the extension portion of releasable member 24 becomes free from the latch member 16, the tension spring 28 will lift the toggle knee 27 of toggle links 25 and 26 rapidly upward, being accompanied by the pivotal movement of the movable contact arm 19 as well as the releasable member 24. Thus, the movable main contact 20 can be separated in a no-arc state from the stationary main contact 13 because the separation of the movable arcing contact 21 from the stationary arcing contact 14 is behind the main contact separation. The electric arc initiated between the separated arcing contacts 14 and 21 is elongated in the slots 36 of the stacked metal plates 35 to be divided into a plurality of shortened arcs by the stacked metal plates, and then is extinguished.

During the separation movement of the movable contact arm 19, the swingable wedge member 29 will be lifted up through the releasable member 24 by the spring 28. In this way, the swingable wedge member 29 will slide in between one side of the toggle link 25 and the stationary pin 31. The final stage of this movement is shown in FIG. 3, where the toggle link 25 is shown being supported by the stationary pin 31 through the wedge member 29 in a fixed position which in turn maintains the movable contact arm 19 at its highest level, or at its most separated position above the stationary contacts 13 and 14.

From the above, in accordance with the present invention, it can be understood that the largest open-pole distance between the stationary and movable contacts when an automatic trip occurs can be assured by only one part, that is, the swingable wedge member 29 which slides in between the toggle link 25 and the stationary pin 31 to prevent rebound of the movable contact arm 19 toward its initial circuit closed position. The molded case circuit breaker having a large interruption capacity can be thus manufactured inexpensively by using less components than those of the prior art, and accordingly it becomes easier to assemble and manufacture the breaker. Furthermore, since the wedge member 29 has a side which can slide smoothly along the side of toggle link 25, the same can smoothly slide in between the toggle link 25 and the stationary pin 31 without any shock when an automatic trip occurs, and accordingly there will be no mechanical fatigue of the toggle linkage or the collapsible mechanism after repeated automatic trips.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

What is claimed as new and desired to be secured by Letters Patent of the

1. A molded case circuit breaker comprising:

a molded case made of an insulating material;

at least one stationary contact mounted in said molded case;

at least one movable arm having a movable contact mounted thereon to be engageable with said stationary contact, said movable arm being capable of movement between circuit closed and open positions;

an automatic trip unit having a latch member capable of movement to a releasable position in response to a predetermined overload condition of said circuit;

a releasable member pivotally supported in said molded case and having one end normally engageable with said latch member to maintain said movable contact arm in said circuit closed position;

a pair of toggle links having substantially rectilinear side surfaces and pivotally engaged with each other at respective ends thereof, said toggle links having their other ends respectively pivoted to said releasable member and said movable contact arm;

a manually operable handle pivotally supported in said molded case and movable between circuit closing and opening positions;

a tension spring stretched between said manually operable handle and the interconnecting point of the ends of said toggle links;

a stationary pin mounted in said molded case; and a wedge member swingably mounted on said releasable member, said wedge member having a pair of substantially rectilinear cam surfaces, the first of which linearly slides along a facing rectilinear said surface of one of said toggle links and the second of which linearly slides along said stationary pin when an automatic trip of said releasable member is caused by said latch member being moved to said releasable position while said manually operable

2. The molded case circuit breaker according to claim 1, further comprising a vertical support member rigidly mounted on said molded case, said stationary pin being affixed to said vertical support member substantially

3. The molded case circuit breaker according to claim 1, wherein the pivot point of said wedge member on said releasable member is separate and distinct from said pivot point of said toggle link on said releasable member.