US 3345485 A
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Description (OCR text may contain errors)
INVENTOR ATTORNEY Oct. 3, 967 E. l. ENGEL.
CIRCUIT BREA KER HAVING IMPROVED ARCING CONTACT STRUCTURE Filed Dec. 50, 1964 2 Sheets-Sheet l EDWARD I. ENGEL Filed Dec. 50, 1964 E. l. ENGEL CIRCUIT BREAKER HAVING IMPROVED ARCING CONTACT STRUCTURE 2 Sheets-Sheet 2 u uuv INVENTOR EDWARD I. ENGEL 'BY/M )M. 78m
ATTORNEY United States Patent() CIRCUIT BREAKER HAVING IMPROVED ARCING CONTACT STRUCTURE Edward I. Engel, Matawan, NJ., assignor to Federal Pacic Electric Company, a corporation of Delaware Filed Dec. 30, 1964, Ser. No. 422,240 7 Claims. (Cl. 200-146) ABSTRACT orV THE DrscLosURE A circular breaker of the type having face-to-face main contacts and laterally engaging arcing contacts. The arc- 'ing contacts momentarily by-pass the main contacts immediately after the main contacts move open for avoiding arcs at the main contacts. The arcing contacts include a pair of physically parallel elongated conductors pivoted to the moving main contact and biased together electrodynamically by the current iiowing therein when the main contacts move open and a companion contact in lateral face engagement with both said conductors and disposed between them to be gripped forcibly during moments when high currents flow in the' elongated c011- ductors.
This invention relates generally to power circuit breakers and more particularly to the moving arcing contact assembly for such apparatus,
Each pole of an illustrative circuit breaker that is described in detail below includes a moving contact arm that carries main and arcing contacts into and out of contact engagement with companion stationary contacts. The main contacts are in substantially normal contact engagement with companion stationary contact and the arcing contacts are in substantially lateral face engagement with 'their companion contact. The arcing contacts are designed to part from companion stationary arcing contact only after the main moving contact arm has separated from its companion contact. Similarly, the arcing contacts engage their companion contact before the main contacts touch each other during the closing operation. The arcing con- 'tact assembly herein described may advantageously be employed together with a moving main contact assembly =such as that shown and described in U.S. Patent No. 3,158,720 whichis assigned to the assignee of the present invention.
Ari object of the present invention resides in the pro- Vision of an improved arrangement of the arcing contact assembly wherein retransfer of@ current from' the arcing contact assembly to the main contact assembly isavoided Aduringthe breaker opening operation. i
Yet another object of this invention is a provision of an arcing contact assembly wherein the blow-off effects due to the electrodynamic forces is minimized and the contact pressure between'the moving arcing contacts and j the stationary arcing Contact is enhanced without 'additional' structure or mechanism.
A further object of this invention relates to improvements in arcing contact assemblies wherein increased resistance to blow-oli effects are achieved without developing excessive contact pressure such as would impose an excessive mechanical load on the contact-closing mechanism.
The illustrative embodiment of the invention which has been'generally referred to above as incorporating the various novel features of the invention, is more fully described in the remainder of this specification, from which further novel features, objects and advantages will become apparentln the following description reference is made to the accompanying drawingsvforming part of v this disclosure.
In the drawings:
FIG. 1 is a side elevation of an illustrative circuit breaker embodying features of the invention;
FIG. 2 is a front elevation of the apparatus in FIG. l viewed from the left thereof, showing one pole with portions omitted and other portions broken away, this structure being similar to that shown and described in U.S. Patent No. 3,158,720 cited above;
FIG. 3 is a view similar to FIG. 1, of the moving contact assembly of a single pole, including main and arcing contact arms, the parts being shown with the arcing contacts in lateral face engagement with the stationary arcing contact and the main contacts parted; and
FIG. 4 is a plan view of a portion of the apparatus of FIG. 1 showing the moving arcing contacts in lateral face engagement of the stationary arcing contact.
It should be understood that although only one pole is illustrated in the drawings, the invention is particularly applicable to multi-pole circuit breakers of the type shown and described in U.S. Patent No. 3,097,275 which is assigned to the same assignee as the present invention. It is also contemplated that the operating mechanism of that patent will be employed in operating the contact structure herein described.
Referring now to the drawings, the illustrative pole comprises a block of insulation 10 which is carried by the frame 12. Each block 10 supports the stationary and movable contacts in the pole. Each pole has a pair of rearwardly projecting terminals 14 and 16. Terminal 14 extends through the block of insulating to the front thereof where it bears the stationary arcing contact 18. A number of side-by-side main contact members 20 have hinge ends 22 that are biased by springs 24 into a groove 26 in terminal 14. Contact segments 28 are brazed to the exposed faces of members 20.
When the circuit breaker is closed as illustrated in FIG. 1, main contact members 20 are forcibly displaced to the right against their compression springs 24 by the cooperating movable main contact arm 30 which has contact segment 32 secured thereto. The contacts 28, 32 are in face or butt engagement. When contact arm 30 is operated to the left (as described in further detail below) so as to open the circuit breaker, compression springs 24 drive main coutactmembers 20 clockwise about their hinge ends 22. Ears 34 of contact members 20 limit their counterclockwise movement by engagement with stationary pin 36 (FIG. 3) supported between portions of the main contact assembly. In this way the main contacts 28, 32 are 'under substantial spring bias from the instant -of .engagement of contact arm 30 with the contact members 20.
Terminal member 16 provide a conductive path through block 10 and through a two-turn over-current coil 38, forward through a lhinge block 40 to movable contact -arm 30. Cooperating with the over-current coil 38 is movable armature 42 and associated structure whose de- -tails are unnecessary to an understanding of the present invention.
As described in the aforementioned Patent 3,158,720 movable contact arm 30 is formed of a pair of vertical bars 30a brazed to and thus united by horizontal part 30b. Contact arm 30 has a pair of laterally spaced hooks 44 (see also FIG. 3) that are received in slots 46 formed in block 40, one for each hook 44. A shaft 48 is united to block 40 and extends across the slots 46 in which hooks 44 are received. Members 30, 40 and 48 are of copper advantageously silver-plated, and form a hinge connection with extremely low resistance and high current capacity. Contact pressure is maintained between moving contact arm 30 and shaft 48 by a pressure roll 50 and a spring bias means to be described.
The conductivity of the hinge joint is excellent during normal conditions when currents of the order of 800 or 1,000 amperes may be carried. However, when shortcircuit current of the order of 50,000 amperes are to be carried, the pressure between moving Contact arm 30 and the hinge shaft 48 is greatly increased by virtue of the geometry of the conductors providing the main current path through the circuit breaker. There is a broad current loop extending horizontally through terminal 14 downward through the main contacts 20 and contact arm 30, and horizontally through terminal 16. This loop provides electrodynamic force tending to shift movingcontact arm 30 to the left. Contact arm 30 thus tends to pivot clockwise about a mechanical operating pivot 49 (described below) building up the contact pressure of moving contact arm 30 against shaft 48. This tendency of member 30 to move to the left in FIG. l is resisted -by the hooks 44 extending about shafts 48. Consequently, it is safe for notches defined by hooks 44 and the opposite portion 52 of arm 30 to open outwardly of the current loop through parts 14, 20 and 16.
The movable contact arm 30 bears a pair of laterally separated movable arcing contact arms 54 having contact portions 56y which cooperate with the stationary arcing contact 18. The movable arcing contact arms 54 are pivoted on the main `contact arm 30 on a conductive bushing 58y (FIG. 3) at the mechanical operating pivot 49. The lateral separation between the arcing contact arms 54 is determined by a pair of opposed spacers 60 (FIG. 2) which are positioned therebetween about a bolt 62. The spacers and the moving contacts 54 are tightly clamped together by a nut 64 on the bolt. A connecting block 66 is interposed-between the moving contact arm 30 and arcing contact arms 54 and is adapted to pivot on the spacers 60. Rocker member or lever 68 is carried on a pivot pin 70 which passes through moving contact varm 30. In the closed condition of the circuit breaker, as illustrated in FIG. 1, and even when main contacts 28 and 32 are parted (FIG. 3) the arcing contact arms 54 are biased toward the stationary arcing contact 18 by compression spring 72 which acts against the block 66. The coil spring is guided on rod 74 which is secured at one end to the block 66. An insulated bushing 76 is interposed between the spring 72 and the block 66 to inhibit f the flow of current through the spring. Rod 74 works slidably in a suitable bore in a shaft 78 that is rotatably mounted in rockermember 68. The arcing contact arms '54 are biased clockwise, as a unit, by the spring 72 and pivot about the bushing 58 through which pin 49 is received in the moving contact arm 30. Arcing contacts 18 and 54 engage at a point spaced vertically about the main contacts 28 and 32,` the arcing contact arms extending well up into an arc chute 73, only part of which is shown by phantorned lines in FIG. 1. Paired movable arcing contacts and arc chutes of the type contemplated for use herein are shown and described` in U.S. Patent No. 2,429,846.
Referring to FIG. 4 the stationary arcing contact 18 includes a substantially U-shaped member 80 which is secured to the terminal member 14. The stationary arcing contact 18 has an arcing tip portion 84 which comprises a block 86 having arcing contact material applied to the end 84a and lateral faces 84h thereof. Block 86 is received between the legs of the U-shaped member 80. Insulator members 90 are positioned on the lateral faces 8412. The block 86 and the insulators 90 are secured to the U-shaped member by a bolt and nut which provide ajoint of good electrical conductivity and high mechanical strength. The leading edge of the arcing contact material is chamfered at 84C to cooperate with the beveled portions 56a of the arcing contact arms during the con- .tact closing operation.
In a typical circuit lbreaker fabricated according to the teachings of the present invention, the spacers 60 between the arcing contact arms 54 provide a separation of threeeighths of an inch at that point. The contact arms are substantially parallel and measure four inches in length from the block 66 to the portions 56 which engage the stationary arcing contact 18. The width of the tip 84 of the stationary arcing contact 18 is one-half inch where it is in lateral face engagement with the arcing contact 56. The arms 54 a-re fabricated from a high-strength modified copper alloy such as Olin No. 605 and therefore although they have a typical cross section of one-quarter inch by seven-eighths of an inch and have been work hardened, they are still sufficiently resilient to be deflected so as to accommodate the interposition of the stationary contact 18 therebetween. Measurements have shown that a force of lforty pounds must be applied to the arcing contact arms 54 laterally of the engaged face 84b of the arcing contact 18 in order to cause it to separate therefrom.
The reaction of the upward 4pressure by spring 72 against the arcing contact arms S4 is applied to rocker member 68 in a manner that also develops heavy bias of roller 50 against shaft 48. The short lever arm between roller 50 and pivot pin 70 provides mechanical advantage that magnities the force applied to shaft 48 by the spring 72 which acts on the longer lever arm between the axis of shaft 74 and pivot pin 70. The bias on roller 50 provides normal operating contact pressure at the main hinge contact 44, 48 of the movable contact arm 30, this pressure being at its maximum in the contact closed or on position.
Compression springs 92 act between portions of members 30 and 68 well above the pivot'pin 70 to augment the pressure developed by spring 72 between elements 44 and 48 when the circuit breaker is closed, and to provide hinge contact pressure when the circuit breaker is open and spring 72 no longer applies bias to rocker 68. The pressure of springs 92 assures proper mechanical pivoting operation of the contact arm in times when the arcing contacts 54, `18 are disengaged and it also provides good electrical contact at hinge 44, 48 when the contacts are being opened. This is an important concern in the event that the circuit breaker is tripped open to interrupt the currents of short-circuit magnitude, 50,000 amperes for example. This augmented hinge-contact pressure is produced without correspondingly increasing the clockwise bias acting on the arcing contacts 54. Any excessive in-y crease in the arcing-contact bias beyond the value needed for establishing normal operating contact pressure would unnecessarily increase the force required to close the circuit breaker.
Shaft 49 extends laterally beyond both side faces of moving contactarm 30 and into the U-shaped member 94 carried by the common bar 96 which operates `all the main contact arms and the arcing contacts of all the poles of the circuit breaker. The bar 96 and U-shaped member 94 form a driving link for moving the contact arms 30 between the open andr closed position thereof. A pair of oppositely disposed holes 98 are provided in each of the U-shapedv members 94 to provide access to the nut and bolt 62, 64 which secure the arcing contact arms 54 together. Upon removal of pivot pin 49 and this nut and bolt, the arcing contact arms may be replaced.
When the circuit breaker is open, the movable arcing contacts 54 are spaced well away from the stationary arcing contact 18. At this time, clockwise displacement of the arcing contacts 54 relative to the contact arm 30 due to the clockwise bias of spring 72 is adjustably limited by nut 100. When the circuit breaker is in its closed configuration as illustrated in FIG. 1, nut or stop 100 has a small but definite separation from shaft 78. This spacing is made large enough to insure counterclockwise travel of moving contact arm 30 to a sufiicient angle in an opening stroke to allow ear 34 of the main contact members 20 to be arrested by pin 36 and for a definite separation to be developed between the main contacts represented 'by members 20 and contact arm 30. When the main contacts 20, 30 separate, the current flowing there.
through is transferred to the arcing contacts 54 and 18. The arcing contact armk 54, main contact larm 30 and the terminals 14 and 16 also form a broad current loop which tends to expand and which could result in blowing-off the arcing contact arms 54 from the stationary arcing contact 18. However, the arcing contact arms 54 are in lateral face engagement with the arcing contact 18 and the current flowing through the arms 54 is owing in the same direction as indicated by the arrows in FIG. 2 resulting in a mutual attraction between the arms. This mutual attraction enhances the contact pressure between the arms and the stationary contact at a time when maximum current s liowing therethrough. Any tendency of the contacts 56 to lift from the faces 84h of stationary arcing contact 18 is resisted by the already stressed arms 54 in a direction transverse to their normal pivotal path. The pinch effect aforedescribed prevents restrike of the arc between the main contacts 28, 32 due to blowing oi of the arcing contact arms 54 from the companion contact 18 but does prevent opening of the breaker.
During continued contact-opening travel of moving contact arm 30, shaft '78 comes into engagement with stop 100, as'shown in FIG. 3. From this point on, operation of tie bar 96 in the opening direction provides positive drive to separate the arcing contacts 56 from the stationary arcing contact 18.
It may now be considered that the circuit breaker is open or in an intermediate position with the main and arcing contacts parted rather than in the closed position shown. In the parted-contact condition springs 72 and 92 bias rocker member 68 counterclockwise about pivot 70 and thereby develop relatively heavy pressure of roller 50 against shaft 48. The reaction force resulting at shaft 70 and contact arm 30 acts to force hooks 44 of the moving contact arm 30 against the face of shaft 4S opposite roller 50.
When the circuit breaker is open and is to be closed, tie bar 96 is shifted to the right and the pivots 49 of the several poles are swung clockwise in unison about the common axis of the respective shafts 48. Moving arcing contact arms in each pole Wipe across and engage the companion contacts 18 as the complementary carnming surfaces 56a, 84o formed thereon cooperate to deflect the moving arms 54 to each side of the stationary contact. The continued movement of the arcing contact arms 54 is arrested by the engagement of the ends of the arms and the insulators 90 (FIG. 3). During the inward movement the moving arcing contacts 56 in each pole engage the companion contacts and nuts 100l lift from shaft 78 as pivot shafts 49 continue their travel to the right. Thereafter, the moving cont-act arm 30 engages its companion contact members 20 in each of the poles of the breaker. Drive or tie bar 96 continues for a short distance after initial engagement of the main contacts 28 and 32, building the contact pressure up by shifting the main contact 28 to the right, and increasing the compression that is maintained initially in springs 24 by ears 34 and pin 36.
The aforedescribed construction of the moving contact and stationary arcing contact results in the elimination of the problems attributable to blow-off of the arcing contacts at the time that the short-circuit current is transferred from the main contacts to the arcing contacts without a substantial increase in the normal operating force required to close the circuit breaker. The pinch-eifect enhances the contact pressure between the moving arcing contacts and stationary arcing contact at a critical time during the opening of the breaker without requiring the addition of complex structures to the moving or stationary assemblies,
The term circuit breaker as used in this application applies to apparatus intended to carry high currents and to interrupt currents of short-circuit magnitude; and accordingly the term circuit breaker is used in a generic sense, to apply also to switches having similar duty requirements.
The foregoing represents the presently preferred form in which the various aspects of the invention may be applied. However, various modications will readily occur to those skilled in the art and, therefore, the invention should be broadly construed in accordance with its full spirit and scope.
What I claim is:
1. A circuit breaker including first and second terminal members, a movable main contact arm, a pair of relatively elongated slender resilient arcing contact arms pivotally mounted on said main contact arm, companion main contacts and a companion arcing contact electrically connected to said first terminal member, means pivotally mounting said main contact arm for movement from a closed position wherein said main contact arm abuts said companion main contacts and said arcing contact arms straddle said stationary arcing contact and are in lateral face engagement therewith to an open position, a driving link connected to said main contact arm for moving said -main Contact arm and said arcing contact arms between said open position and said closed position, means electrically connecting said main Contact arm to said second terminal member, said resilient arcing contact arms being urged toward one another against the lateral faces of said companion arcing contact to enhance the contact pressure therebetween by electrodynamic forces due to high currents flowing through said arcing contact arms when said main contacts part.
2. A circuit breaker according to claim 1 wherein the portions of said arcing contact arms that engage the stationary -arcing contact are spaced apart a given distance in the open position and are biased further apart by the interposition of said stationary arcing contact therebetween to thereby build contact pressure between the arcing contact arms and said stationary arcing contact.
3. A circuit breaker according to claim 2 wherein said portions of said arcing contact arms that engage said stationary arcing contact and the leading edge of said stationary arcing :contact are provided with complementary camming surfaces for inteiposing said stationary arcing conta-ct between said pair of arcing contact arms.
4. A circuit breaker according to claim 1 wherein means are provided adjacent the lateral surfaces of said stationary arcing contact for limiting the extent of engagement between said arcing contact arms and said stationary contact.
5. A circuit breaker according to claim 4 wherein said contact engagement limiting means are formed of insulation.
6. A circuit breaker including first and second terminal members, a movable main contact arm, a pair of relatively long slender resilient arcing contact arms pivotally mounted at one end of said main contact arm, spacer means cooperating with said arcing 4contact arms adjacent said main contact arm, said spacer means constraining the arcing contact arms to a given separation, companion main contacts and a companion stationary arcing contact electrically connected to said lirst terminal member, means pivotally mounting said main Contact arm for movement from a closed position wherein said main contact arm abuts said companion main contacts and said arcing contact arms straddle said stationary arcing contact and are in lateral face engagement therewith to an open position, a driving link connected to said main contact arm for Imoving said main Contact arm and said arcing contact arms between said opened position and said closed position, the portion of said stationary arcing contact received in lateral face engagement between said arcing contact arms being of a width greater than the separation between said arcing contact arms whereby contact pressure is built up between said arcing contact arms and said stationary contact, means electrically connecting said main contact arm to said `second terminal member, said arcing contact arms being driven toward one an-other against the lateral faces of said stationary arcing contact by electrodynamic forces due to high currents flowing through said arcing contact arms when said main contacts part.
7. A circuit breaker including rst and second terminal members, a movable main contact arm having a movable main contact, a pair of elongated resilient substantially `parallel arcing contact arms pivotally mounted 0n said main contact arm and carrying respective movable arcing contacts, companion main and arcing'contacts electrically connected to said first terminal member, said arcing contact arms and said main contact arm being electrically connected to said second terminal, means pivotally mounting said Imain -contact arm and said arcing contact arms thereon for movement between an open position and a closed position wherein said m-ain contacts are in engagement and wherein said arcing contacts are in engagement, said arcing contact arms being arranged to effect closing Vof the arcing contacts slightly in advance of closing of the main contacts and opening ofthe arcing contacts `slightly later than opening of the main contacts,
and said arcing contact arms being arranged to dispose and bias said arcin-g contacts in the closed position thereof in lateral face engagement with said companion arcing contact at opposite sides thereof, the contact pressure of said arcing contact arms against the lateral faces of said companion arcing contact being enhanced upon parting of said main contacts and transfer of high -currents to said arcing contact arms, the enhanced contact pressure being due to electrodynamic reaction between said elongated arcing contact arms.
References Cited UNITED STATES PATENTS 1,206,296 5/1912 Badeau 200-146 2,227,507 1/1941 MacNeil 20G-146 2,632,829 3/1953 Hobbs et al. 200-162 3,158,720 11/1964 vWiktor 200--146 ROBERT S. MACON, Primary Examiner.