U-shaped cradle for circuit breaker

Nov. 3, 1964

Filed May 9, 1961

E. R. WORTMANN 3,155,802

U-SHAPED CRADLE FOR CIRCUIT BREAKER 6 Sheets-Sheet 1

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Nov. 3, 1964

E. R. WORTMANN 3,155,802

U-SHAPED CRADLE FOR CIRCUIT BREAKER

Filed May 9, 1961

Sheets-Sheet 2

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Nov. 3, 1964

E. R. WORTMANN

3,155,802

U-SHAPED CRADLE FOR CIRCUIT BREAKER

Filed May 9, 1961

Sheets-Sheet 3

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Nov. 3, 1964

E. R. WORTMANN

3,155,802

U-SHAPED CRADLE FOR CIRCUIT BREAKER

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Nov. 3, 1964

E. R. WORTMAN N

U-SHAPED CRADLE FOR CIRCUIT BREAKER

3,155,802

Filed May 9, 1961

Sheets-Sheet 5

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Nov. 3, 1964

E. R. WORTMAN N 3,155,802

U-SHAPED CRADLE FOR CIRCUIT BREAKER

Filed May 9, 1961

Sheets-Sheet 6

<img file="US3155802A_D0006.tif" />

3455,802

Patented Nov. 3, 1964

United States Patent Office _m|......-- _|||||M ........ || contact travel of prior art devices. In prior art devices, during the tripping operation the movable contact arm moved ’very hitle during the initial large movement of the cradle until such time as the knee of the toggle was moved 5 over center. By this time the operating springs had expended most of their energy, so that movement of the contact arm thereafter for most of its travel was at a relatively slow speed.

In the device to be hereinafter described, the knee of 10 ihe toggle rests against the cradle when the circuit breaker is closed. Upon automatic tripping the cradle and toggle move as a unit for a very short distance. Thereafter, a stationary surface is engaged by a rounded surface of one of the toggle links, driving the knee of the toggle over 15 center very soon after movement of the cradle is initiated and while the operating springs are still heavily loaded. Thus, from this point on, movement of the contact arm is very rapid, resulting in improved interruption.

lhe construction to be hereinafter described is such 20 tnas. witn the contacts fully separated after an automatic tripping operation, the rounded surface of the toggle, previously mentioned, is positioned extremely close to a stationary surface. If the movable contact tends to rebound, the rounded surface reengages the stationary surface, thereby limiting the rebound of the contact arm to a very short travel. Additional travel is strongly resisted by the operating spring. In addition, oscillations are very slight since the operating spring is very lightly loaded until the surfaces engage on rebound.

in prior art circuit breakers, as the contacts are brought into engagement the toggle linkage, as it is brought over center, has the movement thereof abruptly arrested by engagement with a surface positioned normal to its direction or toggle travel. This places a great strain on the 35 connecting pins of the toggle and cradle. In the device of this invention, upon circuit breaker closing, the knee of the toggle engages a surface of the cradle positioned at an incline with respect to the knee direction of travel. The sloping surface permits overtravel with the contact ⁴⁰ pressure spring absorbing excess energy.

Accordingly, a primary object of this invention is to provide a novel contact operating mechanism for a circuit breaker.

_ Another object is to provide a contact operating mechanism in which the cradle is a U-shaped member with the toggle linkage and operating springs placed between the arms of the U.

Still another object is to provide a novel circuit breaker mechanism for obtaining a large contact motion together with a high closing force.

A still further object of this invention is to provide a contact operating mechanism with novel means for reducing wear of the cradle and toggle linkage pins.

_c Another object is to provide an operating mechanism for a multi-phase circuit breaker which requires only a single operating spring.

These as well as other objects of this invention shall become· readily apparent after reading the following description of the accompanying drawings in which:

FIGURE 1 is a perspective of a circuit breaker constructed in accordance with the teachings of the instant invention. The cover of the circuit breaker is removed to reveal the internal mechanism thereof.

FIGURE 2 is a plan view of the circuit breaker in ⁶⁰ FIGURE 1 with the cover removed.

FIGURE 3 is a cross-section taken through the center phase of the circuit breaker through line 3—3 of FIGURE 2 looking in the direction of arrows 3—3.

FIGURES 4-7 are side elevations of the contact ⁷⁰ operating mechanism with certain elements partially cut away. In FIGURE 4 the circuit breaker is in the closed position. In FIGURE 5 the circuit breaker, after having

155 8G2

U-SHAPED CRADLE FOR CIRCUIT BREAKER Ernest R. Wortniann, Drexel HH1, Pa., assignor to I-T-E

Circnii Breaker Company, Philadelphia, Pa., a corpo· ration of Pennsylvania

Fifed May 9, 1961, Ser. No. 188,812 11 Claims. (CL 200—153)

This invention relates to multi-phase molded case circuit breakers in general and more particularly to a novel construction for the contact operating mechanism thereof, including a U-shaped cradle the utilization of which achieves faster contact speed and enables greater contact separation for a given overall case size.

In multi-phase molded case circuit breakers it is customary to utilize a single contact operating mechanism for all phases, typically, a circuit breaker of this type is a three-phase unit in which the current carrying paths through the phases are identical and parallel to each other with the single operating mechanism positioned in the center phase.

The contact operating mechanism usually comprises a latchable cradle mechanism for supporting a toggle linkage operatively connected to move the movable contacts into and out of engagement with the stationary contacts under the influence of the mam operating springs. With the cradle unlatched the mechanisms cannot operate the toggle linkage so as to bring the contacts into engagement.

In previous designs the cradle was placed in the center plane of the mechanism between the toggle linkages and go the operating springs. As larger contact travel was required in order to obtain greater contact separation, it became necessary to move the cradle pivot away from the area of contact motion or else shape the movable contact arm in such a manner as to clear the cradle bushing when the contacts were disengaged. Either prior art arrangement required increased overall mechanism height which is usually not available. It was thought that moving the cradle bushing would solve the problem. However, it was found that additional clearance for the operating springs was required when the cradle bushing was moved.

As a means of saving material and space circuit breaker designers have for years been striving to achieve more compact constructions. For the reasons outlined above, a limiting factor appeared to be the cradle bushing.

The instant invention overcomes the difficulty of the prior art by providing a latchable cradle constructed as a U-shaped member with the bushings therefor extending outwardly from the arms of the U. The toggle linkage 50 and operating springs are placed between the arms of the U. Since the cradle bushing does not span the toggle linkage and spring area, the cradle bushing does not interfere with movement of the spring or contact linkage, so that greater contact travel and increased operating forces are possible within smaller space limits than was possible with prior art constructions.

Prior art constructions, in order to preserve symmetry, required that an equal number of springs be positioned on each side of the cradle. Thus, at least two springs were required. With the utilization of a U-shaped cradle, a single operating spring may be utilized, thereby reducing the number of parts and the number of handling operations required during assembly. Even when two springs are utilized they may be placed side by side in the center plane of the mechanism so that overall width may be maintained at a minimum. In prior art constructions the springs were on opposite sides of the center plane.

The circuit breaker construction to be hereinafter described includes means whereby contact travel is more rapid during an automatic tripping operation than in

3,155,802

Ο been in a closed position, is tripped and the upper toggle linkage has just engaged a stationary surface of the frame, which will rapidly force the knee of the toggle over center. In FIGURE 6 the mechanism is in the tripped open position. In FIGURE 7 the mechanism is in the manual open position.

FIGURE 8 is an exploded view of the contact operating mechanism.

Now referring to the figures; circuit breaker 10 is provided with a molded insulating housing comprising base 11 and removable cover 12 joined along line 13. Circuit breaker 10 is a three-phase unit, so that base 11 is divided into three parallel compartments by partitions 14, 15. Each of the parallel compartments houses the current carrying members for the respective phases.

Since each phase is comprised of identical current carrying members, only the current carrying parts of the center phase will be described. These current carrying parts comprise load terminal connecter 16, load terminal 17, the looped extension 18 thereof extending through instantaneous trip magnet 19, through a portion 20 of terminal 17 having a reduced cross-section so as to serve as an indirect heater for bimetal time delay tripping element 21. The current path continues through conductor 22, flexible braid 23, movable contact arm 24, and movable contact 25 to stationary contact 26, which is mounted upon line terminal strap 27, having tulip line terminal connecter 28 mounted thereto· by screw means 29.

The movable contacts 25 of all three phases are operated simultaneously into and out of engagement with their respective stationary contacts 26 by means of a. single operating mechanism 3® which is positioned in the center compartment. Each of the movable contact arms 24 is pivotally mounted at 31 to its individual U-shaped holder 32 between the arms thereof. Each holder 32 is provided with a portion 33 which defines a rectangular opening having insulating tie rod 34 disposed therein. Tie rod 34 extends througn all thiee housing compartments so that the contact arm holders 32 of all three phases are mounted thereto·. The outer phases are each provided with angle brackets· 35 which provide support for bearing pins 36 to which holders 32 are pivotally mounted. It is clearly seen that movement of tie rod 34 brings about the simultaneous movement of all three contact arms 24.

Leaf spring 37, fixedly mounted to holder 32 by rivet 38, acts upon adjusting screw 39 to urge contact arm 24 in a counterclockwise direction with respect to FIGURE 3 toward engagement with holder surface 4®.^ As clearly shown in FIGURE 3, when contacts 25, 2b are in engagement, contact arm 24 is spaced from holder surface 4®. In the outer two phases, screw means 41 secures load terminal member 17, conductor 2-2 and bracket 35 to base 11, while in the center phase screw means 41 secures load terminal strap 17, conductor 22 and mechanism frame 42 to base 11.

Frame 42 is a somewhat U-shaped member having pins 44 extending outwardly from the arms thereof. Operating member 45 straddles frame 42 with pins 44 being disposed within the open ended slots 43 at the lower end (with respect to FIGURE 1) or operating member 45. Manual operating Handle 49 is mounted at the upper end or member 45 and includes a portion extending externally of housing 11,. 12 through aperture 50 in cover 12. Spring 51, interposed between member 45 and handle 49 biases a portion of handle 49 against the inner surface of cover 12.

Intermediate latch member 46 is pivotally mounted on shaft 47 whose ends are guided by elongated slots 48 in the load end of frame 42. Spring 52, interposed between frame 42 and latch member 46, biases latch member 46 counterclockwise about pivot 47 toward latching position. Latch extension 53 of member ¢6 extends toward the breaker load end and is engageabls with latch plate 54 carried by common tripper bar 55,

Bar 55 is an insulating member extending across all three base compartments being pivotally mounted at the ends thereof to uprights 56. Tension spring 57 biases bar 55 counterclockwise to latching position, which is established through its engagement with adjusting screw 58 threadably mounted to one of the uprights 56.

Operating mechanism 3® also· includes cradle 60, a toggle linkage comprising links 62, 63, and operating spring means 64, 65. As best seen in FIGURE 2, cradle 6¾ is a generally U-shaped member whose web 61 faces the load end of circuit breaker 1® when cradle 60 is in latched position as in FIGURES 4 and 7. Cradle 68 is maintained in this position through the engagement of latch plate ©6, mounted to web 61, with the web 67 of intermediate latch member 46, whose extension 53 is in engagement with latch plate 54, carried by tripper bar 55. Cradle 6Θ is biased to its tripped position of FIGURE 6 by spring means 64, 65, as will become evident as this description proceeds.

Common tripper bar 55 is rotatable in a clockwise direction upon the occurrence of predetermined circuit conditions to release the cooperative engagement of members 53, 54 and 66, 67. That is, upon the occurrence of a persisting fault the free end of bimetal 21 deflects to the right with adjusting screw 68 engaging tripper bar extension 69. Upon the occurrence of a severe overload, armature 7® will be attracted by magnet 19 with adjusting screw 71 moving to the left to engage tripper bar extension 72.

Pins 77 extending outwardly from the arms of cradle 60 pivotally mount cradle 60 to frame 42. Toggle linkage 62, 63 as well as spring means 64, 65 are mounted between the arms of cradle 60. It is to be noted that each of the toggle links 62, 63 are split members.

Lower toggle link 63 is connected at one end to movable contact arm 24 at pin 31 while the other end is connected to pin 73 which forms the knee of toggle linkage 62, 63. Upper toggle link 62 is connected at one end to pin 73 and at the other end is pivotally connected at 74 to cradle 60. The upper ends of springs 64, 65 are secured to operating member 45 while the lower ends of springs 64, 65 are secured to plate 75 which is pivotally mounted to pin 73. Collars 76 position links 62, 63 axially on pin 73.

Springs 64, 65 are tension members so it is readily seen that they bias cradle 60 counterclockwise about pins 77, bias operating member 45 against pins 43, and bias contacts 25, 26 both into and out of engagement depending upon the position of toggle knee 73.

Circuit breaker 10 is operated manually between the On (FIGURE 4) and Off (FIGURE 7) positions by means of handle 49. With circuit breaker 1® closed movement of handle 49 to the right with respect to FIGURE 4 moves the upper end of springs 64, 65 to the right. . At such time as the force of springs 64, 65 acts along the line positioned to the right of the line joining knee 73 and pivot 74, knee 73 will be drawn over center to the right and contacts 25, 26 will be operated to the disengaged position of FIGURE 7. It is to be noted that contact arm 24 has passed through a line extending between the cradle bushings formed by spaced pins 77 so that a large contact separation is obtained. The open position of contact arm 24 is established by the engagement of holder projections 78 with cradle 60 near its pivot 77.

In operating contacts 25, 26 into engagement toggle knee 73 moves rapidly to the left with respect to FIGURE 7. Its movement must be arrested in a very short time interval. This is accomplished by having the ends of knee pin 73 engage cradle surface 85. It is to be noted that surface 85 is positioned at a substantial incline, approximately 45°, with respect to the direction of travel of pin 73 just prior to its stoppage. . Inclined surface 85 causes a downward component of force to be exerted on contact arm holder 32 with this component of force being absorbed by contact arm biasing spring 37.

3,155,802

As circuit breaker 10 operates from the On position of FIGURE 4 to the tripped position of FIGURE 6, cradle 60 and toggle links 62, 63 move substantially as a unit clockwise about bushing 77 for a short distance during which the contacts remain engaged. Thereafter, as seen in FIGURE 5, the rounded cam surface 80 engages the frame inward extension 81.

Cradle 60 continues counterclockwise carrying the pivot 74 for toggle link 62 to the left forcing toggle knee 73 rapidly to the right. Thus, for a relatively short cradle movement toggle knee 73 moves over center and an almost fully loaded spring means 64, 65 is then free to bring about rapid contact separation.

Not only does the engagement of surfaces 80, 81 serve to kick toggle knee 73 over center but it also serves as an anti-rebound means. That is, when circuit breaker 10 trips open, contact arm 24 tends to rebound closed from the tripped position of FIGURE 6. In doing so toggle 62, 63 must be extended soon bringing cam surface 80 into engagement with frame 42 at 81. Continued movement of contact arm 24 toward closed position is strongly resisted by springs 64. 65 which in this position require strong forces for loading thereof.

Cradle 60 is returned to latched position through the engagement of operating member projection 83 which engages cradle 60 at 84.

Although there has been described preferred embodiments of this invention, many variations and modifications will now be evident to those skilled in the art and, therefore, the scope of this invention is to be limited not by the specific disclosure herein detailed, but only by the appended claims.