US3743981A

US3743981A - Circuit breaker

Info

Publication number: US3743981A
Application number: US00288876A
Authority: US
Inventors: R Geleziunas
Original assignee: CEB Ltd
Current assignee: Commander Electrical Equipment Inc; CHALLENGER CARIBBEAN CORP; CEB Ltd
Priority date: 1972-09-13
Filing date: 1972-09-13
Publication date: 1973-07-03
Anticipated expiration: 1990-07-03

Abstract

A circuit breaker having a trip arm which extends through a slot in a magnet and rests directly on the end of a pivoted bimetal strip. The magnet has a curved end resting loosely in a curved slot in the plastic housing of the breaker, a straight portion overlying the end of the bimetal strip, and an end section spaced away from the bimetal strip. During a short circuit the magnet, since it is free floating in the housing, is free to accelerate rapidly and slam against the bimetal strip, tripping the breaker rapidly.

Description

United States Patent [1 1 Geleziunas July 3, 1973 [54] CIRCUIT BREAKER 2,902,550 9/1959 Stanback et al. 335/35 [75] Inventor: Rimas J. Geleziunas, Don Mills,

Ontario, Canada Primary Exammer-Harold Broome a Attorney-Theodore C. Jay, Robert T. Orner et a]. [73] Assignee: CEB Limited, New York, NY.

[22] Filed: Sept. 13, 1972 57 ABSTRACT PP N04 288,876 A circuit breaker having a trip arm which extends through a slot in a magnet and rests directly on the end 52 US. Cl 335/23, 335/37, 335/43 of e pivoted bimetal n The magnet has a curved end 51] Int. Cl. Hlh 73/48 resting loosely in e eurved in the Pleelie housing of 58 Field of Search 335/23, 18, 19, 20, the breaker, a Straight Perrion overlying the end of 335/21, 22 24, 36, 37 38 39, 4O, 41 42 bimetal strip, and an end section spaced away from the 43 44 45 4 172 173 174 175 17 bimetal Strip. During a short circuit the magnet, since it is free floating in the housing, is free to accelerate [56] References Cited rapidly and slam against the bimetal strip, tripping the UNITED STATES PATENTS breaker I 2,904,655 9/1959 Gelzheisek et a1 335/45 5 Claims, 10 Drawing Figures 3 Sheets-Sheet 1 & ww/

Patented July 3, 1973 3,743,981

3 Sheets-Shut 2 EEK &\\i

Patented July 3, 1973 3,743,981

3 Sheets-Shoot 3 FIG. .9

CIRCUIT BREAKER BACKGROUND OF THE INVENTION This invention relates to a circuit breaker, and more particularly, it relates to a circuit breaker having a floating magnet for faster opening.

Circuit breakers are required to open very rapidly upon occurrence of a short circuit. Normally the opening should occur within about one-half cycle or less of the line current, to avoid or minimize damage to equipment and wiring.

Conventional circuit breakers employ a bimetal strip through which the current to be interrupted is passed. The bimetal strip is linked to a trip arm so that when the bimetal strip is moved in a given direction, the trip arm is released, allowing a spring to open the circuit breaker. Conventional circuit breakers also usually employ a so called magnet, which normally is a strip of ordinary unmagnetized steel. When a short circuit occurs, the resultant high current through the bimetal strip heats it, tending to curl it in a direction so as to release the trip arm, and in addition the magnetic field generated by the current attracts the magnet, which is pulled toward the bimetal strip to assist in opening the circuit breaker. Usually the magnet is tightly pivoted and its impact against the bimetal strip is limited.

SUMMARY OF THE INVENTION In a circuit breaker, according to the invention, comprises a housing, a fixed contact, a movable contact movable between a closed position in which it contacts said fixed contact and an open position in which it is disconnected from said fixed contact, thus to open and close said circuit breaker, a bimetal strip through which an electrical current to be interrupted may flow, a trip arm, connection and bias means mechanically connecting said trip arm and said bimetal strip for movement of said bimetal strip in a predetermined direction to cause movement of said trip arm to a predetermined position, and said connection and bias means further including means mechanically connecting said trip arm and said movable contact for movement of said trip arm to said predetermined position to cause said movable contact to move from its closed to its open position to interrupt said electrical current, the improvement comprising:

a. an elongated magnet strip having a body portion and an end portion, said end portion being curved to form a pivot;

b. means in said housing defining a curved slot for loosely retaining said end portion of said magnet strip, to allow pivoting of said body portion of said magnet strip about said end portion;

c. and means loosely supporting said body portion of said magnet strip in a position beside said bimetal strip to allow movement of said body portion in said predetermined direction towards said bimetal strip;

so that a predetermined current flow in said bimetal strip creates a force attracting said body portion of said magnet strip to said bimetal strip, said body portion being operative to rotate about said end portion and to push said bimetal strip in said predetermined direction to open said circuit breaker.

According to the invention, the circuit breaker magnet is free floating, rather than being pivoted, and is provided with a curved end to guide it during its movement. Because of the free floating action of the magnet, critical tolerances for the magnet are reduced, and in addition the restraints on rapid acceleration of the magnet are minimized, so that during a short circuit, the magnet can move very rapidly and with considerable impact against the bimetal strip, thus opening the circuit breaker extremely rapidly.

In a preferred embodiment of the invention, the trip arm extends through a slot in the magnet and rests directly on one end of the bimetal strip. This simple latching action permits very compact construction of the circuit breaker, and it is found that a circuit breaker, according to the invention, contained in a three-quarter inch wide case, can interrupt currents of up to 10,000 amperes.

DESCRIPTION OF THE DRAWINGS Further objects and advantages of the invention will appear from the following description, taken together with the accompanying drawings, in which:

FIG. 1 is a plan view, partly in section, of a circuit breaker according to the invention;

FIG. 2 is a section along lines 2-2 of FIG. 1;

FIG. 3 is a perspective view of the trip arm of the FIG. 1 circuit breaker;

FIG. 4 is a perspective view of the bimetal strip of the FIG. 1 circuit breaker;

FIG. 5 is a sectional view showing the magnet of the FIG. 1 circuit breaker and part of the casing of the circuit breaker;

FIG. 6 is a view of a portion of the circuit breaker of FIG. 1 but showing the contacts in tripped position;

FIG. 7 is a view similar to FIG. 6 but showing the contacts reset and open;

FIG. 8 is a perspective view of a magnet booster of the FIG. 1 circuit breaker;

FIG. 9 is a plan view ofa split pin of the FIG. 1 circuit breaker; and

FIG. 10 is a perspective view of a portion of an arc chute of the FIG. 1 circuit breaker.

DETAILED DESCRIPTION OF THE INVENTION Reference is first made to FIG. 1, which shows a typical circuit breaker 10 according to the invention. (The circuit breaker 10 is a single pole breaker; a multiple pole breaker will be referred to presently.) The circuit breaker 10 includes a plastic housing 11 having a metal contact 12 projecting from one end thereof and adapted to be secured to a bus bar, to energize the circuit breaker. The metal contact 12 includes a contact button 14 which engages a corresponding contact button 16 of a movable metal contact 18.

The movable contact 18 is normally moved by a molded plastic actuator or handle 20, which is used when it is desired to open or close the circuit breaker.

manually. The actuator 20 includes a rounded upper surface 22 which rides in a rounded opening 24 in the housing 11, and further includes a rounded guide shoulder 25 riding in a curved track 26 in the housing. Shoulders 27, 28 on the actuator form stops which limit forward and rearward movement of the actuator, and stub shafts 29 on the actuator are setin wells 29a in the housing, to limit movement of the actuator (see also FIG. 2).

As view from the side (FIG. 2), the actuator 20 is of forked configuration, having a pair of spaced parallel side plates 30 which define between them an enlarged opening 32. Near the bottom of the side plates 30 and on the inner surfaces thereof, there is provided a pair of opposed V-shaped cam surfaces 34 which receive and guide one end of the movable contact 18.

The movable contact 18 is shaped (FIG. 2) generally in the form of a tuning fork, having a pair of forked rounded ends 36 which are received within the V of the cam surfaces 34. The ends 36 of the movable contact 18 are biased into the V of the cam surfaces 34 by a relatively strong spring 38, one end of which is hooked into an aperture 40 in the movable contact 18 and the other end of which is hooked into an aperture 42 in a trip arm 44.

The trip arm 44, shown in perspective in FIG. 3, is generally L-shaped and is pivoted at one end 46 on a plastic pin 47 molded integrally with the housing ill. The trip arm 44 extends upwardly from the plastic pin 47, to a shoulder 48 which contains an aperture 49 carrying a metal reset pin 50 movable with the trip arm. From the shoulder 48 the trip arm 44 extends to the right as drawn and through the opening 32 between the two side plates 30 of the actuator 20. From the actuator the trip arm 44 extends onwardly through a slot 51 in a magnet 52 (to be described) and terminates in a tip 54 which rests on one end 56 of a bimetal strip 58.

The bimetal strip 58, shown alone in FIG. 4, is of standard rectangular construction except that a short pin 60 is welded thereto and projects from each side thereof. The pin 60 is received in a socket 62 formed in the plastic housing, so that the bimetal strip 58 rotates about thepin 60. A reset spring 64 received in another socket 66 in the plastic housing forces the lower end 68 of the bimetal strip 58 to the right as drawn, while an adjusting screw 70 which extends through a nylon nut 72 mounted in a slot 74 in the housing adjusts the initial position of the bimetal strip. The pin 60 is located closer to the lower end 68 of the bimetal strip than to the upper end 56, so that small adjustments of the adjusting screw 70 will have an appreciable effect on the position of the end 56 of the bimetal strip, and to allow easy movement of the end 56 of the bimetal strip.

The magnet 52, also shown in FIG. 5, is a strip of mild steel, rectangular as viewed from the front or rear, and having a curved end 76 and a main body 78. The main body 78 is divided into a first portion 80 which lies against the end 56 of the bimetal strip 56 and which contains the slot 50, a second portion 82 which slopes from the end of the first portion 86 away from the bimetal strip, and a third straight elongated portion 84 which extends from the end of the second portion generally parallel to the bimetal strip. The curved end 76 is loosely received in a curved slot 86 in the plastic housing ll, so that the main body of the magnet is free to pivot about the curved end '76 and also to move bodily to a limited extent towards the bimetal strip 58. The corners 87 of the slot are rounded to reduce interference with movement of the magnet. The main body 78 of the magnet rides loosely on small raised beads 83 (FIGS. 1, 5) one on each side of the housing, with sufficient clearance between the magnet, the housing, and the trip arm so that the magnet encounters a minimum of friction during its movement toward the bimetal strip. Movement of the magnet away from the bimetal strip is limited by a wall 89 formed as part of the plastic housing 11.

A copper conductor 90 is secured to the movable contact 18 and extends and is secured to the bottom end 68 of the bimetal strip 58. From the upper end 56 of the bimetal strip, another copper conductor 92 extends to a contact 94 to complete the circuit through the circuit breaker.

The operation of the circuit breaker is as follows. When a short circuit occurs, a very large current is passed through the bimetal strip 58. A small current bypasses the bimetal strip, being passed through the spring 38 and trip arm 44,. but the effect of this is slight and can be eliminated by insulating the tip 54 of the trip arm 44.

The large current through the bimetal strip 58 tends to curl the tip of the bimetal strip to the right as drawn, in the direction of arrow A, and in addition the very large magnetic field created by the current draws the magnet 52 towards the bimetal strip. The first portion of the magnet, being in direct contact with the tip 56 of the bimetal strip, pushes the tip 56 of the bimetal strip strongly in the direction of arrow A, moving the bimetal strip 58 out from under the tip 54 of the trip arm.

With the tip 54 of the trip arm 44 unsupported, the spring 38 draws the trip arm downwardly in the direction of arrow B. The trip arm 44 pivots about pin 47, carrying the aperture 42 in the trip arm (and with it, the upper end of the spring 38) in the direction of arrow B. As soon as the axis of the spring 38 moves past the longitudinal centre line 96 of the movable contact 18, the force of the spring 38 snaps the movable contact 18 in the direction of arrow C, opening the circuit breaker. Movement of contact 18 is limited by stop 98, which forms part of the plastic housing 11. At the same time, the reaction at the ends 36 of movable contact 18 against the cam surfaces 34 of the actuator 20 moves the actuator in the direction of arrow D, returning the actuator to its off position. This situation, in which the circuit breaker is open, is diagrammatically illustrated in FIG. 6.

To reset the circuit breaker, the user first pushes the actuator 26 in the direction of arrow E (FIG. 6). This pushes the bottoms of the actuator side plates 30 against the reset pin 50, pivoting the trip arm 44 in the direction of arrow F (FIG. 6). This lifts the tip 54 of the trip arm 44 clear of the bimetal strip 58. As soon as the tip 54 of the trip arm 44 clears the end 56 of the bimetal strip, the reset spring 64 forces the end 56 of the bimetal strip in the direction of arrow G (FIG. 6), moving the end 56 of the bimetal strip into position beneath the tip 54 of the trip arm as shown in FIG. 7. The circuit breaker is now ready to be reset by moving the actuator 20 in the direction of arrow H.

As the actuator 26 is moved in the direction of arrow H, the movable contact 18 is forced downwardly, but the extent of its downward movement is limited by the spring 36. In addition the contact 18 cannot move further to the right because of the stop 98 formed in the plastic casing. As the actuator 20 continues to move, the upper ends 36 of the contact 18 are carried in the direction of arrow I (FIG. 7), and as they are carried past the axis of spring 38, the force of the spring snaps the bottom end of the movable contact 18 in the direction of arrow J, closing the circuit breaker.

In some cases a magnet booster may be added. The

booster, shown at 162 in FIGS. 1 and 8, is simply a mass of iron which increases the attractive force on the magnet during a short circuit. The booster 102 is located in depressions 104 formed in each side of the housing 11 and is backed by a divider wall 106 of the housing (wall 106 also forms a support for contact 94).

The configuration shown for the magnet 52 is highly advantageous. The curved end 76 of the magnet 52 allows easy pivoting of the magnet in the curved slot 86, and because of the generous tolerances between the magnet and the housing, resistance to movement of the magnet is minimized. Therefore, when a short circuit occurs, the magnet is free to move extremely rapidly and to slam against the bimetal strip, to unlatch the trip arm 44.

The circuit breaker will also trip if an overload current occurs, i.e. if any current occurs of magnitude greater than that for which the breaker is rated. Normally the circuit breaker 10 will remain closed for a preset period of time during occurrence of small overloads, to prevent nuisance tripping. (For example the circuit breaker if rated at amperes will pass a current of e.g. amperes for a period of about 20 seconds before tripping.)

The arrangement shown facilitates linking of two or three of the single units described to form a multiple pole circuit breaker in which tripping of one unit or pole will trip the others. Specifically, it will be seen that the central portion 110 of the bimetal strip 58, located between the end 56 of the bimetal strip and the pivot pin 60, is spaced from the magnet 50 and from the wall 106 of the housing 11. In this area one or both sides of the housing plastic casing 11 may be cut away as indicated in dotted lines at 112, and one end of a split pin 114 (also shown in FIG. 9) may be inserted over the bimetal strip 58 and over the corresponding bimetal strip of an adjacent circuit breaker unit or pole secured sideby-side with the circuit breaker unit or pole 10. In this manner, movement of the bimetal strip of one circuit breaker pole will, via the pin 114, also move the bimetal strip of the other circuit breaker pole, so that both will open at the same time if a short circuit or overload current occurs in either. Thus, a multi-pole common trip circuit breaker can conveniently be formed, by connecting together the bimetal strips of circuit breaker poles secured side-by-side.

When the circuit breaker 10 opens due to a short circuit, an arc usually occurs at contact buttons 14, 16. This are is permitted to exit via an arc chute 118 formed in part by stop 98 and wall 120 in the plastic housing, and in part by a metal member 122 (FIG. 10) which helps to contain the arc and protect the plastic of the housing.

What has been shown and described herein is an improved circuit breaker.

I claim:

1. ln a circuit breaker of the kind comprising a housing, a fixed contact, a movable contact movable between a closed position in which it contacts said fixed contact and an open position in which'it is disconnected from said fixed contact, thus to open and close said circuit breaker, a bimetal strip through which an electrical current to be interrupted may flow, a trip arm, connection and bias means mechanically connecting said trip arm and said bimetal strip for movement of said bimetal strip in a predetermined direction to cause movement of said trip arm to a predetermined position, and said connection and bias means further including means mechanically connecting said trip arm and said movable contact for movement of said trip arm to said predetermined position to cause said movable contact to move from its closed to its open position to interrupt said electrical current, the improvement comprising:

so that a predetermined current flow in said bimetal strip creates a force attracting said body portion of said magnet strip to said bimetal strips said body portion being operative to rotate about said end portion and to push said bimetal strip in said predetermined direction to open said circuit breaker.

2. A circuit breaker according to claim 1 wherein said body portion of said magnet strip includes a first short portion normally lying in close proximity to and parallel to said bimetal strip, a second portion at the end of said first portion and directed away from said bimetal strip, and an elongated third portion at the end of said second portion and oriented generally parallel to said bimetal strip, said third portion being spaced from said bimetal strip, so that when said third portion begins to move towards said bimetal strip, said first short portion presses against said bimetal strip to move the latter in said predetermined direction.

3. A circuit breaker according to claim 2 wherein said first portion includes a slot therein, said trip arm extending through said slot and having a tip which rests directly on one end of said bimetal strip, said tip constituting a portion of said connection and bias means, said bimetal strip being mounted for movement of said end thereof out from under said tip during occurrence of a short circuit or overload current, said connection and bias means including means biasing said tip of said trip arm against said bimetal strip, so that when said bimetal strip is moved out from under said tip, said trip arm moves to said predetermined position to open said circuit breaker.

4. Apparatus according to claim 3 including a pivot pin secured to said bimetal strip at a position intermediate the ends of said bimetal strip; said housing including socket means for accommodating the ends of said pin to allow pivoting of said bimetal strip about said pin.

5. Apparatus according to claim 4 wherein said bimetal strip includesa central portion located between said one end of said bimetal strip and said pivot pin, said central portion of said bimetal strip being spaced from said magnet and from said housing to allow the split end of a pin to be inserted thereover, whereby said circuit breaker may form one pole of a multi-pole circuit breaker and said bimetal strip of such circuit breaker pole may be linked to the bimetal strip of another circuit breaker pole by such pin, to form at least a two pole common trip circuit breaker.

' l II

Claims

1. In a circuit breaker of the kind comprising a housing, a fixed contact, a movable contact movable between a closed position in which it contacts said fixed contact and an open position in which it is disconnected from said fixed contact, thus to open and close said circuit breaker, a bimetal strip through which an electrical current to be interrupted may flow, a trip arm, connection and bias means mechanically connecting said trip arm and said bimetal strip for movement of said bimetal strip in a predetermined direction to cause movement of said trip arm to a predetermined position, and said connection and bias means further including means mechanically connecting said trip arm and said movable contact for movement of said trip arm to said predetermined position to cause said movable contact to move from its closed to its open position to interrupt said electrical current, the improvement comprising: a. an elongated magnet strip having a body portion and an end portion, said end portion being curved to form a pivot; b. means in said housing defining a curved slot for loosely retaining said end portion of said magnet strip, to allow pivoting of said body portion of said magnet strip about said end portion; c. and means loosely supporting said body portion of said magnet strip in a position beside said bimetal strip to allow movement of said body portion in said predetermined direction towards said bimetal strip; so that a predetermined current flow in said bimetal strip creates a force attracting said body portion of said magnet strip to said bimetal strip, said body portion being operative to rotate about said end portion and to push said bimetal strip in said predetermined direction to open said circuit breaker.

5. Apparatus according to claim 4 wherein said bimetal strip includes a central portion located between said one end of said bimetal strip and said pivot pin, said central portion of said bimetal strip being spaced from said magnet and from said housing to allow the split end of a pin to be inserted thereover, whereby said circuit breaker may form one pole of a multi-pole circuit breaker and said bimetal strip of such circuit breaker pole may be linked to the bimetal strip of another circuit breaker pole by such pin, to form at least a two pole common trip circuit breaker.