US 3631369 A
Description (OCR text may contain errors)
United States Patent Inventor Appl. No.
Filed Patented Assignee BLOWOF'F MEANS FOR CIRCUIT BREAKER  References Cited UNITED STATES PATENTS 2,719,203 9/1955 Gelzheiser et al. 337/110 X Primary Examiner-Bernard A. Gilheany Assistant ExaminerDewitt M. Morgan Attorney-Ostrolenk, Faber, Gerb & Soffen ABSTRACT: A circuit breaker having automatic fault respon- L CH sive trip means for releasing a latch to permit the operating 5Chlms,4D -1wlng Fi mechanism to open the contacts is provided with a bafi'le which extends into the arcing gas venting passage. The baifle U.S.Cl 337/110, is connected 0 the latch and is positioned transverse to the 200/144 R flow of arcing gases through the venting passage, so that upon Int. Cl I-I0lh 9/30, the occurrence of Severe overload conditions, rapid gas pres Holh 33/02H0lh7l/o0 sure buildup in the passage will act to move the bafile and Field of Search 337/110, thereby physically moving he latch toward tripping position 335/201 200/144 prior to movement of the latch by the fault current responsive means. i
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JA 7 l x k 6 3/ i l I I J6 35 2% i l Q 95 :L 1 l BLOWOFF MEANS FOR CIRCUIT BREAKER LATCH This invention relates to circuit interrupters in general, and more particularly relates to means for utilizing gas pressure buildup during current interruption for physically rapidly moving the operating mechanism trip-free latch to trip position on the occurrence of severe overload conditions.
Circuit breakers of the type illustrated in U.S. Pat. No. 2,996,589 issued Aug. 15, 1961 to F. E. Myers for a Pivoted Biinetal are of relatively compact construction and are generally intended to operate in circuits having continuous currents in the range of from -100 amperes. This type of circuit breaker includes a thermal overload means for automatic tripping under sustained light overloads, and is also provided with a magnetic trip means that operates rapidly upon the occurrence of more severe overloads. However, when such circuit breakers are installed in circuits capable of delivering very high currents, such circuit breakers have been damaged when called upon to interrupt extremely severe short circuits. Difficulties encountered in this area have been due primarily to the fact that the magnetic trip means does not respond fast enough, and as a result the contacts restrike after initial separation caused by magnetic blowoff forces.
The instant invention overcomes this difficulty by utilizing pressure buildup derived from gases generated during initial contact separation to physically move the latch toward its tripping position. Under conditions of severe overload, it has been found that with the instant invention gas pressure buildup is so rapid that forces generated thereby cause movement of the latch toward tripping position prior to movement thereof caused by the current responsive automatic tripping means.
Accordingly, a primary object of the instant invention is to provide means for more rapid tripping of a circuit breaker under severe overload conditions.
Another object of this invention is to utilize pressure built up by gases generated during the striking of an are between separating contacts to physically move a mechanism holding latch toward its tripped position in advance of movement thereof by current responsive trip means.
These objects as well as other objects of this invention will become readily apparent after reading the following description of the accompanying drawings in which:
FIG. 1 is a side elevation of a circuit breaker constructed in accordance with teachings of the instant invention, with the housing cover part removed to reveal the operating elements.
FIG. 2 is an end view looking in the direction of arrows 2-2 of FIG. 1.
FIG. 3 is a fragmentary cross section taken through line 3 3 of F 1G. 1, looking in the direction of arrows 3-3.
FIG. 4 is an exploded perspective of the operating mechanism latch and selected elements mounted in the vicinity thereof.
Now referring to the Figures, circuit breaker 11 includes base 18 of molded insulating material having an open side capped by removable molded insulating cover 20, mating along line 19 and secured by rivets 21. Stationary contact 22 is mounted to extension 23 of female stab-type line terminal 24 disposed in a suitably shaped recess located at one end of base 18. Lower end 25 of line terminal 24 is accessible through a slot formed through the cooperation of base 18 and cover 20, for engagement by a male line terminal blade stab of a panelboard. Cooperating with stationary contact 22 is movable contact 26 mounted to the lower end of movable contact arm 27 having its upper end abutting a pivot forming formation of manual operating member 28. Upper end 14 of member 28 extends through an opening in the top of base 18 for manual operation of circuit breaker 11. Manual operating member 28 pivots about outboard protrusions 29 thereof, which are entered into suitable recesses (not shown) on base 18 and cover 20.
Parallel plate slotted arc extinguishing means, located in arc chute 99, is operatively positioned to receive and extinguish electric current arcs drawn between contacts 22, 26 upon separation thereof. Elongated venting passage 90 in base 18 extends from are chute 99 to exhaust opening 91, located in the right wall of housing 18, 20 at a point below load terminal 56. Passage is adapted to guide arcing gases from are chute 99 to a location remote from the bussing (not shown) to which line terminal 24 is connected.
Operating mechanism 30, for moving cooperating contacts 22, 26 into and out of engagement, includes latchable cradle 31 pivoted at one end thereof on base protrusion 32. Pin 70 extends laterally from cradle 31 for engagement by lower extension 13 of operating member 28 to operate cradle 31 in a counterclockwise direction to the reset or latched position of FIG. 1. One end of main operating spring 33 is tied to cradle 31 at a point intermediate the ends thereof and the other end of spring 33 is tied to contact arm 27. Spring 33 is always tensioned, thereby urging contact am 27 upward to seat with its pivot formation (not shown) on manual operating member 28. The other end of cradle 31 comprises latch tip 34 engageable by latch 35 secured to control member 36 by rivet 12.
Control member 36 is an elongated bimetallic element, secured near the upper end thereof, pin 37 having its ends disposed in bearing recesses of base 18 and cover 20. Magnet 38 is secured to control member 36 near the lower end thereof by rivet 12. Bifurcated member 39, soldered to control member 36 below magnet 38, is provided with legs 41a, 41b to which the respective flexible conductive braids 40a, 40b are secured. Braids 40a, 40b are also secured to opposite sides of contact arm 27 to provide dual electrical paths between arm 27 and bimetallic element 36.
Control member 36 is biased in a clockwise direction with respect to FIG. 1 by coiled compression spring 40 disposed in recess 40' of base 18, with one end of spring 40 abutting the left wall 42 of recess 40 and the other end of spring 40 abutting the portion of control member 36 positioned above pivot 37. The normal position of control member 36 is set by adjusting screw 43, which extends through an opening in base 18, and is received by nut 44 disposed in a suitable recess in base 18. The end of screw 43 opposite head 45 thereof abuts one leg of tensioning member 46, thereby forcing tensioning member 46 against control member 36 to bodily move control member 36 counterclockwise about pivot 37 as a center.
When magnet 38 is energized sufficiently by high overload current flowing through control member 36, magnet 38 is attracted to relatively stationary armature 47, whose legs 48, 49 are disposed in oversized recesses (not shown) in base 18, and whose other legs 52, 53 are disposed in similar oversized recesses (not shown) in cover 20. Leaf spring 54, disposed within a recess of base 18 with the offset lower end of spring 54 abutting armature 47, urges armature 47 against the leftmost walls of the aforesaid oversized recess. Insulating sheet 55 is interposed between spring 54 and conducting braid 57 which electrically connects load terminal member 56 to control member 36, with sheet member 55 protecting braid 57 from damage which would result if braid 57 were to rub against the sharp edge of spring 54. Terminal member 56 is entered into wire grip 58, disposed at the end of base 18 remote from cooperating contacts 22, 26.
Thus, the current carrying path through circuit breaker 11, beginning at the load side thereof, consists of terminal 56, braid 57 to the upper end of bimetallic control member 36, through control member 36 and bifurcated member 39, through the parallel paths formed by braids 40a, 40b to contact arm 27, and through contact arm 27 and engaged cooperating contacts 26, 22 to line terminal 24.
1n a manner well known to the art, when cradle 31 moves from its latched or reset position of FIG. 1 in a clockwise direction to a TRIPPED position, end 65 of kicker 66 pivoted at 67 to cradle 31, engages contact arm 27 with a hammerlike blow, thereby ensuring separation of contacts 22, 26 even though there is a tendency for these contacts to weld. The path of kicker tip 65 is dictated by the movement of pivot point 67 and the fact that the other end 68 of kicker 66 is disposed within base recess 69.
The portion of circuit interrupter described up to this point is representative of prior art structures. insulating baffle 95, extending downwardly beyond the lower end of control member 36, is secured thereto by rivet l2. Baffle 95 is constructed of a thin sheet of melamine glass or other suitable stiff, yet flexible, insulating sheet material. The lower end of baffle 95 extends through gap 97 in formation 98, of base 18, constituting the upper wall of passage 90. Baffle 95 is positioned transverse to the longitudinal axis of passage 90 to substantially block passage 90. However, as seen clearly in FIG. 3, the bottom and both side edges of baffle 95 are spaced from the wall defining passage 90 and the lower edge of baffle 95 is notched at 96 to provide additional clearance, thereby preventing excessive buildup of gas pressure. The flexible nature and mounting of baffle 95 permits limited flexing thereof to prevent buildup of excessive pressure in passage 90.
Upon the occurrence of light overloads over an extended period of time, bimetal control member 36 heats sufficiently so that deflections of the lower end thereof to the right with respect to FIG. 1 moves latch 35 to the right to a position clear of latch tip 34 to unlatch cradle 31. Upon the occurrence of more severe overload conditions, latch 35 is tripped through the attraction of magnet 38 to armature 47. Upon the occurrence of extremely severe overload conditions, even before magnet 38, 47 and/or bimetal 36 have had an opportunity to move latch 35 to release cradle 31, magnetic blowoff forces generated by these high currents will cause a slight separation of contacts 22, 26 drawing a high current arc therebetween. However, if latch 35 is not tripped, the contacts will restrike as current zero approaches, and at a later point in the cycle the contacts will separate and another are will form. In the absence of baffle 95, this harmful contact restrike will occur.
A very severe overload current are will generate arcing gases that will, in short order, build up high pressure that seeks to escape through passage 90. However, in so doing, such pressure subjects baffle 95 to a force directed from left to right with respect to FIG. 1, with this force being of sufficient magnitude to pivot control members 36 in a counterclockwise direction toward tripping of latch 35. The buildup of gas pressure is so rapid that initial movement of latch 35 is the result of force generated by the arcing gases. This movement occurs even before the effects of the current responsive automatic tripping means (bimetal 36 and/or magnet 38, 47) is effective to move latch 35 to a tripping position. Thus, under severe overload conditions, the presence of baffle 95 in venting passage 90 causes a more rapid tripping of latch 35 to release cradle 31 and operate mechanism 30 before contacts 22, 26 are able to restrike.
Although there have been described preferred embodiments of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited not by the specific disclosure herein but only by the appending claims.
The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:
1. A circuit interrupter including cooperating contact means; an operating mechanism connected to said contact means for opening and closing the latter; said operating mechanism including a releasable member; latch means for maintaining said member in an operating position wherein said operating mechanism is selectively operable to open and close said contact means; first means responsive to overload currents in said interrupter for automatically tripping said latch means under predetermined overload conditions to release said member, thereby causing said operating mechanism to open said contact means; an arc chute to receive electric current arcs drawn between said contact means upon opening thereof during current interruption, and assist in extinguishing said arcs; guide means for directing gas pressure, derived from arcing gases formed in said are chute, against second means connected to said latch means to physically move said latch means toward its tripped position during very severe overload conditions in advance of latch tripping by said first means. I
2. A circuit interrupter as set forth in claim I, m which the guide means includes an elongated passage; said second means including a baffle disposed in said passage and mounted for limited movement lengthwise of said passage; said baffle connected to said latch means and forming a barrier extending across a substantial portion of the transverse cross-sectional area of said passage to intercept and be moved by arcing gases flowing from said are chute through said passage.
3. A circuit interrupter as set forth in claim 2, in which there is a housing wherein the previously recited elements and disposed; a first and a second terminal means at respective first and second ends of said housing; said are chute positioned in the vicinity of said first end; said passage extending to an exit opening in said housing located at said second end.
4. A circuit interrupter as set forth in claim 2, in which said first means includes a movable control member to which said latch means and said baffle are mounted.
5. A circuit interrupter as set forth in claim 4, in which said control member includes a current-carrying elongated bimetal element; a pivotal mounting for said element at one end thereof; said baffle secured to said element and extending beyond the other end thereof; said latch means secured to said element intermediate the ends thereof.