MOLDED CASE CIRCUIT BREAKER WITH AN IMPROVED ARC GAS EXTERNAL VENTING SYSTEM

Abstract: The invention relates to a molded-case circuit breaker having improved means for venting gaseous arc products. The gas venting means comprise venting slots (412) formed through a wall of the circuit breaker housing, and one-way valves (410) positioned in the slots so as to pass gaseous arc products to be vented from the housing, and to prevent the ingress of contaminants from the ambient.

Description: The present invention relates generally to molded-case circuit breakers and, more particularly, to an improved arc gas venting system therefor. Arc gases generated in molded-case circuit breakers when electrical arcs are drawn between separating contacts usually are vented through openings formed in wall portions of the insulating cases, or housings, of the circuit breakers. The rate of which venting of arc gases occurs can be critical since too little venting can result in structural damage to the case and even in explosion, while too much venting can cause external flashovers. These are problems encountered especially with physically small circuit breakers having high interrupting capacities. A further problem associated with the venting of arc gases is that foreign matter, including environmental contaminants, can enter the circuit breaker housing through the vent openings, which of course is undesirable. British patent specification 1 450 724 discloses an electrical circuit breaker having the features of the precharacterizing portion of claim 1. The elongated resilient one-way valve member to control venting gaseous arc products from the interior of the circuit breaker housing consists in that prior art device of a dustseal flap formed from a thin flat sheet of suitable resilient plastics material having one end mounted at the circuit breaker housing and its remote end resting against shoulders surrounding the vent opening of the housing. However, this prior art construction cannot solve the above-mentioned problems of proper venting control and proper prevention of contaminants entering the circuit breaker housing in a fully satisfactory manner. It is the principal object of the invention to alleviate these problems by providing an electrical circuit breaker including improved venting means, and the invention accordingly resides in an electric circuit breaker as defined in claim 1. While the presence of a pair of venting slots in a circuit breaker housing is known per se from US patent 3 707 612, the latter document does not suggest any valve means with respect to those venting openings at all. Preferred details of the circuit breaker according to the invention are defined in the subclaims. A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawing, in which: Fig. 1 is a top plan view of a molded-case circuit breaker; Fig. 2 is a side elevational view of the circuit breaker; Fig. 3 is an enlarged cross-sectional view of the circuit breaker as taken along line 3-3 of Fig. 1; Fig. 4 is an enlarged, partial, top-elevational view of an arc-gas venting system embodying the invention; Fig. 5 is an enlarged, fragmentary, side-elevational view of the system of Fig. 4; Fig. 6 is an enlarged fragmentary, cross-sectional view taken along line 6-6 of Fig. 5; and Figs. 7 and 8 are enlarged, elevational views of a valve used in the system of Figs. 4-6. The circuit breaker illustrated in Figs. 1 to 3 and generally designated with reference numeral 30 has three poles or phases. It will be understood that the invention proper, as described later herein with reference to Figs. 4 to 8, is applicable not only to this three-pole circuit breaker but also to other polyphase and to single-pole molded-case circuit breakers of both the AC and DC types. The circuit breaker 30 includes a molded, electrically insulating, top cover 32 mechanically secured to a molded, electrically insulating, bottom cover or base 34 by a plurality of fasteners 36. A plurality of first electrical terminals or line terminals 38A, 38B and 38C (Fig. 1) are provided, one for each pole or phase, as are a plurality of second electrical terminals or load terminals 40A, 40B and 40C. These terminals are used to serially electrically connect the circuit breaker 30 into a three phase electrical circuit for protecting a three phase electrical system. The circuit breaker 30 further includes an electrically insulating, rigid, manually engageable handle 42 extending through an opening 44 in the top cover 32 for setting the circuit breaker 30 to its CLOSED position (Fig. 3) or to its OPEN position. The circuit breaker 30 also may assume a BLOWN-OPEN position (Fig. 3, dotted line position) or a TRIPPED position. Subsequently to being placed in its TRIPPED position, the circuit breaker 30 may be reset for further protective operation by moving the handle 42 from its TRIPPED position past its OPEN position. The handle 42 may then be left in its OPEN position or moved to its CLOSED position (Fig. 3), in which case the circuit breaker 30 is ready for further protective operation. Preferably, an electrically insulating strip 46, movable with the handle 42, covers the bottom of the opening 44 and serves as an electrical barrier between the interior and the exterior of the circuit breaker 30. As its major internal components, the circuit breaker 30 includes a lower electrical contact 50, an upper electrical contact 52, an electrical arc chute 54, a slot motor 56, and an operating mechanism 58. Reference may be had to United States Letters Patent No. 3,815,059 for a more detailed description of the arc chute 54 and the slot motor 56. The lower electrical contact 50 (Figs. 3, 4) includes a lower, formed, stationary member 62 secured to the base 34 by a fastener 64, a lower movable contact arm 66, a pair of electrical contact compression springs 68, a lower contact biasing means or compression spring 70, a contact 72 for physically and electrically contacting the upper electrical contact 52 and an electrically insulating strip 74 to reduce the possibility of arcing between the upper electrical contact 52 and portions of the lower electrical contact 50. The line terminal 38B extending exteriorly of the base 34 comprises an integral end portion of the member 62. The member 62 includes an inclined portion 62A that serves as a lower limit or stop for the moving contact arm 66 during its blow-open operation; an aperture 62B overlying a recess 76 formed in the base 34 for seating the compression spring 70; and a lower flat section 62C through which the aperture 62B is formed. The flat section 62C may also include a threaded aperture 62D formed therethrough for receiving the fastener 64 to secure the stationary member 62 and thus the lower electrical contact 50 to the base 34. The stationary member 62 includes a pair of spaced apart, integrally formed, upstanding, generally curved or U-shaped contacting portions 62F. The contacting portions 62F each include two, spaced apart, flat, inclined surfaces 62G and 62H, inclined at an angle of approximately 45 degrees to the plane of the lower flat section 62C and extending laterally across the inner surfaces of the contacting portions 62F. A stop 62J (Fig. 3) is provided for limiting the upward movement of the contact arm 66. The contact arm 66 is fixedly secured to a rotatable pin 78 (Fig. 3) for rotation therewith within the curved contacting portions 62F about the longitudinal axis of the rotatable pin 78. Pin 78 is biased by the compression springs 68 into effective current conducting contact with the surfaces 62G and 62H of the portions 62F. In this manner, effective conductive contact and current transfer is achieved between the lower formed stationary member 62 and the lower movable contact arm 66 through the rotatable pin 78. The lower movable contact arm 66 includes an elongated rigid lever arm 66A extending between the rotatable pin 78 and the contact 72 and a downwardly protuberant portion or spring locator 66B for receipt within the upper end of the compression spring 70 for maintaining effective contact between the lower movable arm 66 and the compression spring 70. Finally, the lower movable contact arm 66 includes an integrally formed, flat surface 66C formed at its lower end for contacting the stop 62J to limit the upward movement of the lower movable contact arm 66 and the contact 72 fixedly secured thereto. The use of the compression springs 68 to provide a constant bias against the pin 78 provides an effective current path between the terminal 38B and the contact 72 while enabling the mounting of the lower electrical contact 50 in a small, compact area. The operating mechanism 58 includes an over-center toggle mechanism 80; a trip mechanism 82; an integral or one-piece molded cross bar 84; a pair of rigid, opposed or spaced apart, metal side plates 86; a rigid, pivotable, metal handle yoke 88; a rigid stop pin 90; and a pair of operating tension springs 92. The over-center toggle mechanism 80 includes a rigid, metal cradle 96 that is rotatable about the longitudinal central axis of a cradle support pin 98. The opposite longitudinal ends of the cradle support pin 98 in an assembled condition are retained in a pair of apertures formed through the side plates 86. The toggle mechanism 80 further includes a pair of upper toggle links 102, a pair of lower toggle links 104, a toggle spring pin 106 and an upper toggle link follower pin 108. The lower toggle links 104 are secured to the upper electrical contact 52 by a toggle contact pin 110. Each of the lower toggle links 104 includes a lower aperture for receipt therethrough of the toggle contact pin 110. The toggle contact pin 110 also passes through an aperture formed through the upper electrical contact 52 enabling the upper electrical contact 52 to freely rotate about the central longitudinal axis of the pin 110. The opposite longitudinal ends of the pin 110 are received and retained in the cross bar 84. Thus, movement of the upper electrical contact 52 under other than high level short circuit or fault current conditions and the corresponding movement of the cross bar 84 is effected by movement of the lower toggle links 104. The pin 106 interconnects the upper and lower toggle links 102 and 104 and allows rotational movement therebetween. The upper ends 124 of springs 92 are received within slots 126. The upper links 102 also include recesses or grooves 132 for receipt in and retention by a pair of spaced apart journals formed along the length of the pin 108. The center portion of the pin 108 is configured to be received in an aperture formed through the cradle 96 at a location spaced by a predetermined distance from the axis of rotation of the cradle 96. Spring tension from the springs 92 retains the pin 108 in engagement with the upper toggle links 102. Thus, rotational movement of the cradle 96 effects a corresponding movement or displacement of the upper portions of the links 102. The cradle 96 includes a slot having an inclined flat latch surface 142 formed therein. The surface 142 is configured to engage an inclined flat cradle latch surface 144 formed at the upper end of an elongated slot formed through a generally flat, intermediate latch plate 148. The cradle 96 also includes a generally flat handle yoke contacting surface 150 configured to contact a downwardly depending elongated surface 152 formed along one edge of the upper surface 128 of the handle yoke 88. The operating springs 92 move the handle 42 during a trip operation; and the surfaces 150 and 152 locate the handle 42 in a TRIPPED position, intermediate the CLOSED position (Fig. 3) and the OPEN position of the handle 42, to indicate that the circuit breaker 30 has tripped. The cradle 96 further includes a generally flat elongated stop surface 154 for contacting a peripherally disposed, radially outwardly protuberant portion or rigid stop 156 formed about the center of the stop pin 90. An impelling surface of a kicker 158 is also provided on the cradle 96 for engaging a radially outwardly projecting portion or contacting surface 160 formed on the pin 106 upon the release of the cradle 96 to immediately and rapidly propel the pin 106 in a counterclockwise arc from an OPEN position (Fig. 3) to a TRIPPED position, thereby rapidly raising and separating the upper electrical contact 52 from the lower electrical contact 50. During such a trip operation, an enlarged portion or projection 162 formed on the upper toggle links 102 is designed to contact the stop 156 with a considerable amount of force provided by the operating springs 92 through the rotating cradle 96, thereby accelerating the arcuate movements of the upper toggle links 102, the toggle spring pin 106 and the lower toggle links 104. The trip mechanism 82 includes the intermediate latch plate 148, a movable or pivotable handle yoke latch 166, a torsion spring spacer pin 168, a double acting torsion spring 170, a molded, integral or one-piece trip bar 172 (Fig. 13), an armature 174, an armature torsion spring 176, a magnet 178, a bimetal 180 and a conductive member or heater 182. The bimetal 180 is electrically connected to the terminal 40B through the conductive member 182. The magnet 178 physically surrounds the bimetal 180 thereby establishing a magnetic circuit to provide a response to short circuit or fault current conditions. An armature stop plate 184 has a downwardly depending edge portion 186 that engages the upper end of the armature 174 to limit its movement in the counterclockwise direction. The torsion spring 176 has one longitudinal end formed as an elongated spring arm 188 for biasing the upper portion of the armature 174 against movement in a clockwise direction. An opposite, upwardly disposed, longitudinal end 190 of the torsion spring 176 is disposed in one of a plurality of spaced apart apertures (not illustrated) formed through the upper surface of the plate 184. The bimetal 180 includes a formed lower end 192 spaced by a predetermined distance from the lower end of a downwardly depending contact leg 194 of the trip bar 172 (Fig. 3). The spacing between the end 192 and the leg 194 when the circuit breaker 30 is in a CLOSED position (Fig. 3) may be adjusted to change the response time of the circuit breaker 30 to overload conditions by appropriately turning a set screw 196, access to which may be provided by apertures 198 formed through the top cover 32. A current carrying conductive path between the lower end 192 of the bimetal 180 and the upper electrical contact 52 is achieved by a flexible copper shunt 200 connected by any suitable means, for example, by brazing, to the lower end 192 of the bimetal 180 and to the upper electrical contact 52 within the cross bar 84. In this manner, an electrical path is provided through the circuit breaker 30 between the terminals 38B and 40B via the lower electrical contact 50, the upper electrical contact 52, the flexible shunt 200, the bimetal 180 and the conductive member 182. In addition to the cradle latch surface 144 formed at the upper end of the elongated slot 146, the intermediate latch plate 148 includes a trip bar latch surface 212, an upper inclined flat portion 214 and a pair of oppositely disposed laterally extending pivot arms 216 configured to be received within inverted keystones or apertures 218 formed through the side plates 86. The torsion spring 170 includes an elongated, upwardly extending spring arm 234 for biasing the flat portion 214 of the intermediate latch plate 148 for movement in a counter-clockwise direction for resetting the intermediate latch plate 148 subsequently to a trip operation by the overcenter toggle mechanism 80 and a downwardly extending spring arm for biasing an upper portion 237 of the trip bar 172 against rotational movement in a clockwise direction (Fig. 3). The handle yoke latch 166 includes an elongated downwardly extending latch leg 240 and a bent or outwardly extending handle yoke contacting portion 242 that is physically disposed to be received in a slotted portion 244 formed in an along the length of one of a pair of downwardly depending support arms 246 of the handle yoke 88 during a reset operation. An integrally molded outwardly projecting surface 248 on the crossbar 84 is designed to engage and move the latch leg 240 of the handle yoke latch 166 out of engagement with the handle yoke 88 during the movement of the cross bar 84 from its OPEN position to its CLOSED position (Fig. 3). Preferably, the trip bar 172 includes three, enlarged armature support sections 250, one such support section 250 for each pole or phase of the circuit breaker 30. Each of the support sections 250 includes an elongated, generally rectangularly shaped pocket 252 formed therethrough for receiving a downwardly depending trip leg 254 of the armature 174. The trip bar 172 also includes a latch surface 258 (Fig. 3) for engaging and latching the trip bar latch surface 212 of the intermediate latch plate 148. The latch surface 258 is disposed between a generally horizontally disposed surface 260 and a separate, inclined surface 262 of the trip bar 172. In addition to the integral projecting surface 248, the cross bar 84 includes three enlarged sections 270. Each enlarged section 270 also includes a window 282 formed therein for receipt of one longitudinal end of the upper electrical contact 52 (Fig. 3). The opening 282 also permits the receipt and retention of a contact arm compression spring 286 and an associated, formed, spring follower 288. The compression spring 286 is retained in proper position within the enlarged section 270 by being disposed about an integrally formed, upwardly projecting boss 290. The spring follower 288 is configured to be disposed between the compression spring 286 and the base portion 284 of the upper electrical contact 52 to transfer the compressive force from the spring 286 to the base portion 284, thereby ensuring that the upper electrical contact 52 and the cross bar 84 move in unison. A first generally planar portion 296 is located at one end of the spring follower 288; and a second planar portion 298 is located at the other longitudinal end of the spring follower 288 and is spaced from the portion 296 by a generally flat inclined portion 300. During normal operating conditions, as inclined surface 302 of the base portion 284 of the upper electrical contact 52 contacts the inclined portion 300 or the junction between the portions 298 and 300 of the spring follower 288 to retain the cross bar 84 in engagement with the upper electrical contact 52. However, upon the occurrence of a high level short circuit or fault current condition, the inclined surface 302 is moved past and out of engagement with the portions 298 and 300; and a terminal portion or surface 304 of the base portion 284 engages the downwardly deflected planar portion 298 of the spring follower 288 to retain the upper electrical contact 52 in its BLOWN-OPEN position, thereby eliminating or minimizing the possibility of contact restrike. The upper electrical contact 52 also includes a contact 306 for physically and electrically contacting the contact 72 of the lower electrical contact 50 and an upper movable elongated contact arm 308 disposed between the contact 306 and the base portion 284. It is the passage of high level short circuit or fault current through the generally parallel contact arms 66 and 308 that causes very high magnetic repulsion forces between the contact arms 66 and 308, effecting the extremely rapid separation of the contacts 72 and 306. An electrically insulating strip 309 may be used to electrically insulate the upper contact arm 308 from the lower contact arm 66. In addition to the apertures 100, 218 and 226, the side plates 86 include apertures for the receipt and retention of the opposite ends of the stop pin 90. In addition, bearing surfaces 312 are formed along the upper portion of the side plates 86 for engagement with a pair of round tabs 314 formed at the lowermost extremities of the downwardly depending support arms 246 of the handle yoke 88. Each of the side plates 86 includes a pair of downwardly depending support arms 322 that terminate in elongated, downwardly projecting stakes or tabs 324 for securely retaining the side plates 86 in the circuit breaker 30. Associated with the tabs 324 are apertured metal plates 326 that are configured to be received in recesses 328. A pair of formed electrically insulating barriers 329 is used to electrically insulate conductive components and surfaces in one pole or phase of the conduit breaker 30 from conductive components or surfaces in an adjacent pole or phase of the circuit breaker 30. A preferred, embodiment of the invention will now be described with particular reference to Figs. 4 - 8 of the drawings. As seen from Fig. 4, each pole unit of the circuit breaker illustrated therein includes venting means comprising a pair of vent slots 412 in a wall portion of the housing, and a one-way valve 410 cooperating with the slots 412 in such manner as to pass gaseous arcing products to be vented from the circuit breaker housing, and to prevent ambient contaminants from entering the latter. More particularly, the two vent slots 412 extend side-by-side through an end wall of the housing cover 32, and they are separated from each other by a post 414 preferably forming an integral part of the cover 32. As seen from Figs. 16 and 18, the post 414 has a cross-sectional configuration resembling an isosceles trapezoid, the two non-parallel sides 418 of the post, together with surface portions 420 of the cover parallel thereto, forming the sidewalls of the respective vent slots 412. Thus, the vent slots 412 in each pole unit diverge with respect to each other in the direction of gas flow from the housing. Each one-way valve 410 is an elongate, resilient member comprising a single solid flexible piece or strap of sheet material, e.g. bone fiber or fishpaper (Figs. 7 and 8) which is elastically bent around the post 414 and has portions on opposite sides of the post inserted in the respective slots 412 such as to act therein as flapper-type one-way valves, as seen best from Figs. 4 - 6. As clearly apparent from Fig. 6, the vent slots 412 in the housing cover are open toward the base of the housing so that each valve 410 can be readily inserted into the associated slots 412, and also can be readily replaced with a similar valve, if desired or required, either with one having the same resilience, hence valve characteristics, or with one having a different resilience (as determined by thickness, for example) and, hence, different valve characteristics. When in use, separation of the circuit breaker contacts under load will cause electric arcs to be drawn between the separating contacts. This will result in an abrupt increase of the pressure within the circuit breaker housing which, in turn, will force the one-way valves 410 open, as indicated in phantom in Fig. 6, thereby enabling the gaseous arcing products to escape through the vent slots 412. The resultant pressure drop within the circuit breaker housing then will allow the flapper portions of the one-way valves 410 to resume their normal or valve-closed positions in which they will block any ingress of contaminants from the ambient. It will be noted that any increase in ambient pressure occurring will only tend to enhance this blocking action of the one-way valves 410.

Claims: An electrical circuit breaker comprising an insulating housing and, disposed therein, cooperating contacts and a mechanism for opening and closing the contacts, said insulating housing having pressure-responsive venting means (410) comprising an elongated resilient one-way valve member to control venting gaseous arc products from the interior of said housing and to minimize the ingress of invironmental contaminants, characterized in that said venting means comprises a pair of side-by-side vent slots (412) extending through a housing wall portion and separated from each other by a barrier (414), and that said one-way valve member (410) is a single member common to both vent slots (412) and elastically bents around said barrier (414) and having portions on opposite sides of the barrier inserted in the respective slots so as to form a one-way valve in each of said slot. An electric circuit breaker according to claim 1, characterized in that said vent slots (412) diverge with respect to one another in the gas flow direction therethrough. An electric circuit breaker according to claim 1 or 2, characterized in that said vent slots (412) are formed in a wall portion of a cover member of said housing and are open toward a base member of said housing on which said cover member is removably mounted.

Inventors: LEONE, DAVID ANTHONY
Applicants: WESTINGHOUSE ELECTRIC CORPORATION
Application year: 1985
Main classification: H01H73
IPC codes: H01H73, F16K15, H01H9