US3697915A

US3697915A - Circuit breaker having means for increasing current carrying capacity

Info

Publication number: US3697915A
Application number: US83913A
Authority: US
Inventors: Theodore Brassard
Original assignee: Texas Instruments Inc
Current assignee: Texas Instruments Inc
Priority date: 1970-10-26
Filing date: 1970-10-26
Publication date: 1972-10-10
Anticipated expiration: 1989-10-10

Abstract

A miniature, trip-free, ambient compensated circuit breaker has improved calibration means and is particularly adapted for high current ratings. A bell crank latch, rotatably carried by manual actuating means, is normally engaged with an ambient-compensated catch for holding stationary and movable contacts in engagement to close a circuit. Current-responsive means is adapted to release the latch from the catch to open the circuit in response to an overload in the circuit. The movable contacts are mounted on a bridge member which in turn is attached to one leg of a Ushaped spring element with the other leg securely attached to the bell crank. In one embodiment, the current responsive means is calibrated by dual adjusting screws and in a second embodiment by a single adjusting screw.

Description

United States Patent Brassard 1 Oct. 10,1972

[54] CIRCUIT BREAKER HAVING MEANS 21 Appl. No.: 83,913

[52] US. Cl. ..337/74, 337/84, 337/101, 337/111 [51] Int. Cl. ..H0lh 71/16, HOlh 73/30 [58] Field of Search... ..337/70, 71, 72, 73, 74, 75, 337/76, 77, 78, 79, 80, 81, 82, 83, 84, 104, 111, 373, 375, 99, 101, 63, 57, 347, 360,

2,418,537 4/1947 Wood ..337/84 Primary Examiner-Bernard A. Gilheany Assistant ExaminerDewitt M. Morgan Attorney-Harold Levine, Edward J. Connors, Jr., John A. Haug, James P. McAndrews and Gerald B. Epstein l 57] ABSTRACT A miniature, trip-free, ambient compensated circuit breaker has improved calibration means and is particularly adapted for high current ratings. A bell crank latch, rotatably carried by manual actuating means, is normally engaged with an ambient-compensated catch for holding stationary and movable contacts in engagement to close a circuit. Current-responsive means is adapted to release the latch from the catch to open the circuit in response to an overload in the circuit.

4 37 379 The movable contacts are mounted on a bridge member which in turn is attached to one leg of a U- [56] References Cited shaped spring element with the other leg securely at- UNITED STATES PATENTS tached to the bell crank. ln one embodiment, the current responsive means is calibrated by dual adjusting 3,361,882 H1968 Clarke Screws and i a Second embodiment y a Single j 2,122,693 7/1938 Maseng ..337/70 mg Screw 3,265,835 8/1966 Wood ..337/63 1,966,444 7/1934 Guett ..337/71 X 12 Claims, 5 Drawing Figures 96 74 FT 102 I6 90 68 a4 18 I .92\ I04 22 miminummmz I 3.697.915

' sum 1 UP 2 In ven tor, Theodore Brassard,

Att y.

PATENTEDBBT 10 m2 3.697.91 5 SHEET 2 0F 2 In van tar,

Thcodore Brassard,

CIRCUIT BREAKER HAVING MEANS FOR INCREASING CURRENT CARRYING CAPACITY This invention relates to circuit breakers, and more particularly, to a new and improved circuit breaker of the thermostatic type for applications in which it is desired to interrupt an electrical circuit under predetermined conditions. Circuit breakers of the type described in U.S. Pat. No. 3,361,882 have found wide acceptance in the market place and are very effective for many applications, however, their usefulness is limited to relatively low current ratings, e.g., 20 amperes or below. I

It is an object of this invention to provide a new and improved circuit breaker particularly suitable for relatively high current ratings, e.g., up to 35 amperes and higher, for protection of electrical circuit components against excessive transients, sustained overloads, and short circuits; to provide a circuit breaker of the class described which is fully trip-free; to provide such a circuit breaker which is snap acting; to provide such a circuit breaker which is easily calibrated and adjusted for automatic operation; to provide such a circuit breaker which indicates when it is in the tripped condition; to provide such a circuit breaker which can be used as a manually operated switch without deleterious effects on its function of responding properly to overload currents; to provide such a circuit breaker for relatively high current ratings having increased contact forces; to provide such a circuit breaker which is economical to manufacture and is readily adapted to mass production; and especially to provide such a circuit breaker which is of small size, light weight, and exceedingly compact construction.

Other objects and advantages of the novel and improved circuit breaker of this invention appear in the following detailed description of two preferred embodiments of the invention.

The invention accordingly comprises the elements and combinations of elements, features of construction and arrangements of parts which will be exemplified in the structures hereinafter described and the scope of the application of which will be indicated in the appended claims.

In the accompanying drawings in which several of the various possible embodiments of the invention are illustrated:

FIG. 1 is a partial elevation of a circuit breaker made in accordance with the invention with the front half of the casing removed and with the contacts in the disengaged or open circuit position;

FIG. 2 is a partial elevation of a circuit breaker similar to FIG. 1, but with the contacts in the engaged or closed circuit position;

FIG. 3 is a perspective view of the current responsive means and dual calibrating screws depicted in FIGS. 1 and 2;

FIG. 4 is a perspective view of the movable contact assembly used in the circuit breaker; and

FIG. 5 is a partial elevation of a second embodiment of a circuit breaker with the front half casing removed, and the embodiment employing an alternate calibration means.

The dimensions of certain of the parts as shown in the drawings may have been modified or exaggerated for the purpose of clarity of illustration.

Referring now to the drawings, and more particularly to FIGS. 1 to 4, one embodiment of this invention takes the form of a thermostatic single phase circuit breaker (although equally applicable to multiphase circuit breakers) generally indicated by reference numeral 10 and includes a housing which may be formed of two shells or halves to facilitate assembly thereof. A back casing half 12 cooperates with a similar front casing half which has been removed for the purpose of illustration, and may be made of any suitably strong, insulating and arc-resistant material or the like. A compartment 14 is defined in the casing and receives therein ambient compensation assembly 16 which includes an elongated catch member 18 attached at its lower end to a compensating bimetallic member 20 and a catch return spring 22. A motion transfer plate 24 is slidably mounted in the casing and is adapted to transfer motion from a current responsive bimetallic trip arm 26 to the ambient compensation assembly 16.

As best seen in FIG. 3, trip arm 26 is generally U- shaped having distal leg portions which arebrazed to tab

portions

28 and 30 of terminal 32 and stationary contact arm 40 respectively. Terminal 32 also is provided with platform 34 and slot 36 which cooperate with the casing for firmly locking the terminal in its intended location. A notch is provided in terminal 32 just below tab portion 28 to facilitate calibration in a manner to be explained below. Stationary contact arm 40, opposite tab portion 30, is provided with another upstanding portion 42 on its distal end which mounts stationary contact 44. Another stationary contact 46 is mounted on portion 48 of terminal 50.

Calibration screws

52,54 are inserted in apertures provided in the side wall of the casing and are threaded in

plates

56, 58 respectively.

Plates

56, 58 are slidably inserted between

bosses

60 and 62 formed in the cas- Latch plunger is one part of the manual actuating means and is movable between a first open .circuit switch position and a second closed circuit position as indicated in FIGS. 1 and 2 respectively. Since any suitable manual actuating means can be employed with the instant invention and since it does not relate to the invention per se, details of the manual actuating means have not been shown, but reference may be had to U.S. Pat. No. 3,361,882 referred to supra, for a complete description of one such suitable actuating means. Latch plunger 70 mounts pin 72 which in turn pivotally mounts movable contact assembly 74, the main elements of which comprise bell crank latch 76, movable contact spring 78 and contact bar 80. Bell crank latch 76 is provided with bore 82 which receives pin 72 in plunger 70 and is movable therewith. Another bore 84 is provided in bell crank latch 76 to permit attachment of one end 86 of spring 88, The other end 90 of spring 88 is attached to pin 92 mounted in the wall of casing 12. It will be noted that spring 88 places a clockwise torque on bell crank 76 as viewed in FIGS. 1 and 2 tending to rotate bell crank 76 about pin 72. Bell crank 76 is also provided with tongue or latch 94 which contacts catch 18 in such a way that further clockwise rotation of bell crank 76 is precluded as long as the catch 18 remains in the position shown. Contact spring 78 is secured to bell crank 76 by means of angle brackets 96 on opposite faces of the bell crank. As seen in FIG. 4,

cutout portion 98 is provided in contact spring 78 to permit insertion of bell crank 76. Contact spring 78 is bent back on itself in a U-shaped configuration and is retained by lip 100 on bell crank 76. Thus, as plunger 70 is forced downwardly when latch 94 contacts catch 18, a counterclockwise torque is placed on the contact assembly 74. In the FIG. 2 contacts closed position, lip 100 separates from the contact spring 78 so that spring 78 will provide an effective contact force. In order to stiffen contact spring 78,

ribs

102, 104 are located on the leg portions. Use of brackets 96 and

ribs

102, 104 provide increased contact force which is required due to the increased instantaneous let-through currents to which the circuit breaker is subjected under short circuit fault condition compared to prior art breakers referenced above. That is, the electrodynamic repulsion forces at the contact faces increase in a higher current rating device due to the higher let-through currents. Insulating mat 106 is mounted on that portion of contact spring 78 which is contiguous to the contact area to preclude damage to the spring in the event of arcing. A mechanical connection is effected between contact spring 78 and contact bar 80 as by upsetting several projections from the contact bar which are received in mating apertures in the spring plate and headed over.

Contacts

114, 116 are brazed to tab portions 110, 108 respectively of contact bar 80. Stop wall 118 is provided in casing 12 to limit the motion of contact bar 80 in the open contacts direction.

Electrical current passes through the circuit breaker from terminal 32 through trip arm 26, stationary contact arm 40, contact 44, movable contact 114, contact bar 80, movable contact 116, contact 46 to terminal 50. As mentioned above, trip arm 26 is composed of bimetal and functions as a current sensitive element since the electrical current passing therethrough will cause it to heat up with the bight portion deflecting to the right as viewed in FIGS. 1 and 2 upon increasing temperature. It will be seen that as the bight portion of arm 26 deflects a predetermined distance it will contact motion transfer plate 24 and continued deflection will be transferred through plate 24 to displace ambient compensation assembly 16 until latch 94 of bell crank 76 is no longer held by catch 18. When latch 94 clears catch 18, bell crank 76 is pivoted clockwise about pin 72 under the action of spring 88 thereby disengaging the contacts and opening the electrical circuit.

The circuit breaker is calibrated by biasing

tabs

28 and 30 via calibrating

screws

52, 54 respectively. As

tabs

28 and 30 are bent, the distance between the bight portion of trip arm 26 and transfer plate 24 is diminished thereby decreasing the distance trip arm 26 has to travel before the circuit breaker is tripped to open the circuit. Two calibrating screws are employed since terminal 32 is relatively massive to attain the low conductivity required for the designed high ampere ratings. Therefore, the circuit breaker is designed so that neither excessive force nor relatively complicated configuration will be required which would result if a single calibrating member were employed. Notch 38 is provided below tab 28 to facilitate this operation. The dual calibration screws also permit maintaining the alignment of trip arm 26 in its calibrated position, that is it affords the ability to more easily prevent the trip arm 26 from going askew and possibly binding against the casing side walls.

As mentioned above, the circuit breaker is designed for especially high current levels through the use of several design features. The terminals, stationary contact arm and movable contact bar are all made of relatively thick, massive, low-conductivity materials, trip arm 26 is joined to

tabs

28, 30 by brazing as are all of the contacts to their supporting structure so that no high resistance spots will occur in the current path. Further, contact force has been increased without diminishing operating forces.

As seen in FIG. 4, contact spring 78 is securely attached to bell crank 76 by right angle members 96 on both sides of the bell crank on the leg of the U-shaped spring member 78 removed from the contact bar 80. This attachment may be effected by welding since spring 78 does not form a part of the current path. When the contacts are in the engaged, circuits closed position, a force is applied through member 70, as indicated by the arrow in FIG. 2, downwardly on bell crank 76 through bracket 96 to contact spring 78 to apply a high force on the contacts through contact bar 80. In this position, lip 100 of bell crank 76 separates slightly from the contact bar and that portion of spring 78 contiguous thereto. As soon as latch 94 separates from catch 18 and bell crank 76 pivots clockwise tongue 100 applies a direct force against the contact bar to cause the contacts to separate and assists opening should a contact weld occur.

Ribs

102, 104 are provided in the contact spring, in addition to brackets 96, to prevent buckling thereof with concomitant loss of spring force. Securing contact spring 78 to the bell crank 76 by brackets 96 intermediate the bight portion and the end of one of the legs results in a high contact force when the contacts are in the closed circuit position as well as providing in cooperation with lip 100 a stiff member to facilitate opening of the contacts, particularly if a contact weld should occur.

As described in U.S. Pat. No. 3,361,882 referenced above, ambient compensation is provided by assembly 16. Upon heating due to the changes in ambient temperature, the end of bimetal compensating member 20 will move to the right approximately the same distance that the bight portion of trip arm 26 moves to the right under the influence of the same ambient temperature and thus the relative spacing between these two respective ends will remain constant. This means that in order to trip at a given electric current level, the bight portion of arm 26 must always deflect the same distance in order to move the bimetal compensating member 20 a sufficient distance to trip latch 94 from catch 18. The end of compensating member 20 can move under influence of ambient temperature without substantially affecting the position of catch 18'.

The device is so-called trip-free since if plunger 70 is held inwardly of the casing by externally applied force, and the trip arm 26 moves to the right (as seen in FIGS. 1 and 2) to move the ambient compensation member 20 to the right and thus free latch 94 from catch 18, then, even though pin 72 is held stationary, the tension spring 88 will act on the bell crank to pivot it clockwise to pull

movable contacts

114, 116 from

stationary contacts

44, 46.

FIG. 5 depicts a second embodiment of this invention in which the circuit breaker is calibrated by a single calibration screw mounted centrally on the bight portion of U-shaped trip arm 26. A nut may conveniently be attached to trip arm 26 to provide screw threads for adjustably mounting screw 132. A plate 124 is mounted on plate 24 in a receiving aperture 126 and presents a downwardly extending tab 128 aligned with screw 132. Aperture 122 is provided in casing 12 to permit access to screw 132. Once the device is calibrated, sealing compound 134 may be placed about the head of screw 132 to lock it in position. Alternatively, rather than employing plate 124, a radially extending flange may be provided in the end of screw 132 which will cooperate with motion transfer plate 24. This embodiment is well suited for particularly high current rating devices in which the trip arm, designed for high current levels, is sufficiently massive and stiff that contacting screw 132 with a tool and turning it will not cause any deflection of the trip arm itself upsetting the calibration thereof.

It will be appreciated that the single calibration means could be provided equally well on the opposite side of plate 24 to cooperate with compensating bimetallic member or on member 20 itself.

It will be seen that by means of this invention, a circuit breaker is provided which is compact, reliable, easily calibrated and particularly suited for relatively high current ratings.

It should be understood that although particular embodiments of the circuit breaker have been described by way of illustration, this invention includes all modifications and equivalents thereof falling within the scope of the appended claims.

lclaim:

1. A circuit breaker comprising:

a casing;

stationary contact means mounted in the casing;

movable contact means movably mounted in the casing and movable into and out of engagement with the stationary contact means;

overcurrent means mounted in the casing including a catch movable from a latch retaining position to a latch releasing position upon occurrence of overcurrent conditions;

the movable contact means including a latch engageable with the catch; manual actuating means operatively connected to the movable contact means to move the movable contact means into engagement with the stationary contact means upon actuation of the actuating means when the latch engages with the catch;

ambient compensation means mounted in the casing offsetting movement in the overcurrent means due to changes in ambient temperature;

the overcurrent means including a substantially U- shaped thermostatic member having two distal leg portions connected by a bight portion, the bight portion operatively connected to the catch, the bight portion movable to cause movement of the catch, terminal means including two upstanding mounting tabs separately supported in the casing, each tab having first and second surfaces on opposite sides thereof, the two distal leg portions attached to respective tab portions on said first surfaces and camming means mounted in the casing to cam the said second surfaces to adjust the effective position of the bight portion of the thermostatic member to thereby calibrate the circuit breaker.

2. A circuit breaker according to claim 1 in which the camming means to adjust the effective position of the bight portion of the thermostatic member include separate threaded members mounted in the casing aligned with the two upstanding mounting tabs.

3. A claim according to claim 2 in which the thermostatic member is brazed to the tab portions.

4. Overcurrent means according to claim 1 in which one mounting tab is formed from a main terminal and the other mounting tab has a leg extending therefrom, the leg having a distal end for mounting thereon a stationary contact.

5. A claim according to claim 1 in which the operative connection between the bight portion of the thermostatic member and the catch includes a motion transfer plate slidably mounted in the circuit breaker to transfer motion from the thermostatic member to the catch.

6. A circuit breaker according to claim 1 in which the movable contact means includes a spring plate bent back upon itself in a generally U-shaped configuration having a bight portion joining two legs, at least one movable contact supported on an end of one of the legs; and a cutout section formed in the bight portion, the latch made in the form of a bell crank and located partially within the cutout section, and means fixedly attaching the bell crank to the other leg of the spring plate. 7. A circuit breaker according to claim 6 in which the bell crank is attached to the other leg of the spring plate intermediate the end of the leg and the bight portion.

8. A circuit breaker according to claim 6 in which the means fixedly attaching the bell crank to the other leg of the spring plate comprise two L-shaped brackets located on opposite sides of the bell crank.

9. A circuit breaker according to claim 6 in which the movable contact means further includes an elongated contact bar having two ends, contact seats extending from each end, a contact mounted on each contact seat, the bell crank formed with a lip portion, the spring plate biasing the contact plate toward the lip applying a force to the lip when the contacts are out of engagement and applying a force to the contacts when the contacts are in engagement.

10. A claim according to claim 9 in which means are provided to stiffen both legs of the spring plate.

11. A circuit breaker comprising: a casing; stationary contact means mounted in the casing; movable contact means movable into and out of engagement with the stationary contact means;

overcurrent means mounted in the casing including an overcurrent sensor movable upon occurrence of overload conditions, a catch, and a motion transfer member mounted between the sensor and the catch, the motion transfer member transferring motion from the sensor to the catch;

the movable contact means including a bell crank having a latch engageable with the catch;

manual actuating means operatively connected to the movable contact means to move the movable contact means into engagement with the stationary contact means upon actuation of the actuating means when the latch engages with the catch;

the overcurrent sensor including a substantially U- shaped thermostatic member having two distal leg portions connected by a bight portion, the bight portion movable to cause movement of the catch through the motion transfer member, terminal means including two upstanding mounting tabs separately supported in the casing, each tab having first and second surfaces on opposite sides thereof, the two distal leg portions attached to respective tab portions on said first surfaces;

camming means mounted in the casing to cam the said second surfaces to adjust the effective spacing between two members of the overcurrent means to calibrate the circuit breaker;

the movable contact means further including a spring plate bent back upon itself in a generally U-shaped configuration having a bight portion joining two legs, at least one contact supported on an end of one of the legs; and

a cutout section formed in the bight portion of the spring plate receiving the bell crank, the bell crank fixedly attached to the other leg of the spring plate, the bell crank formed with a lip portion limiting movement of the spring plate maintaining the spring under stress.

12. A circuit breaker comprising:

a casing;

stationary contact means including at least one stationary contact mounted in the casing;

movable contact means including at least one movable contact movably mounted in the casing and movable into and out of engagement with'the stationary contact;

actuating means mounted in the casing and including a manually movable member and a bell crank connected to the manually movable member, the bell crank operatively connected to the movable contact means so that actuation of the actuating means will cause movement of the bell crank and at least a portion of the movable contact means;

return spring means attached to the movable contact means to move the movable contact out of engagement with the stationary contact;

the movable contact means including a spring plate bent back upon itself in a generally U-shaped configuration having a bight portion joining two legs, a contact bar mounting the movable contact supported on an end of one of the legs; and

the bight portion of the spring plate formed with a cutout section which receives the bell crank, the bell crank attached to the other leg of the spring plate, the bell crank formed with a lip portion extending over a portion of the contact bar to limit the movement of the spring plate thereby maintaining the spring plate under stress whereby when the contacts are in engagement the contact pressure is increased by the bias applied by the spring plate and upon disengagement of the contacts contact welds will tend to be broken by the transfer of force from the return spring through the lip to the contact bar effectively bypassing the spring plate, and means to prevent loss of contact pressure due to buckling of the spring plate, said means including stiffening means and a permanent connection between the bell crank and the other leg.

Claims

1. A circuit breaker comprising: a casing; stationary contact means mounted in the casing; movable contact means movably mounted in the casing and movable into and out of engagement with the stationary contact means; overcurrent means mounted in the casing including a catch movable from a latch retaining position to a latch releasing position upon occurrence of overcurrent conditions; the movable contact means including a latch engageable with the catch; manual actuating means operatively connected to the movable contact means to move the movable contact means into engagement with the stationary contact means upon actuation of the actuating means when the latch engages with the catch; ambient compensation means mounted in the casing offsetting movement in the overcurrent means due to changes in ambient temperature; the overcurrent means including a substantially U-shaped thermostatic member having two distal leg portions connected by a bight portion, the bight portion operatively connected to the catch, the bight portion movable to cause movement of the catch, terminal means including two upstanding mounting tabs separately supported in the casing, each tab having first and second surfaces on opposite sides thereof, the two distal leg portions attached to respective tab portions on said first surfaces and camming means mounted in the casing to cam the said second surfaces to adjust the effective position of the bight portion of the thermostatic member to thereby calibrate the circuit breaker.

6. A circuit breaker according to claim 1 in which the movable contact means includes a spring plate bent back upon itself in a generally U-shaped configuration having a bight portion joining two legs, at least one movable contact supported on an end of one of the legs; and a cutout section formed in the bight portion, the latch made in the form of a bell crank and located partially within the cutout section, and means fixedly attaching the bell crank to the other leg of the spring plate.

7. A circuit breaker according to claim 6 in which the bell crank is attached to the other leg of the spring plate intermediate the end of the leg and the bight portion.

11. A circuit breaker comprising: a casing; stationary contact means mounted in the casing; movable contact means movable into and out of engagement with the stationary contact means; overcurrent means mounted in the casing including an overcurrent sensor movable upon occurrence of overload conditions, a catch, and a motion transfer member mounted between the sensor and the catch, the motion transfer member transferring motion from the sensor to the catch; the movable contact means including a bell crank having a latch engageable with the catch; manual actuating means operatively connected to the movable contact means to move the movable contact means into engagement with the stationary contact means upon actuation of the actuating means when the latch engages with the catch; the overcurrent sensor including a substantially U-shaped thermostatic member having two distal leg portions connected by a bight portion, the bight portion movable to cause movement of the catch through the motion transfer member, terminal means including two upstanding mounting tabs separately supported in the casing, each tab having first and second surfaces on opposite sides thereof, the two distal leg portions attached to respective tab portions on said first surfaces; camming means mounted in the casing to cam the said second surfaces to adjust the effective spacing between two members of the overcurrent means to calibrate the circuit breaker; the movable contact means further including a spring plate bent back upon itself in a generally U-shaped configuration having a bight portion joining two legs, at least one contact supported on an end of one of the legs; and a cutout section formed in the bight portion of the spring plate receiving the bell crank, the bell crank fixedly attached to the other leg of the spring plate, the bell crank formed with a lip portion limiting movement of the spring plate maintaining the spring under stress.

12. A circuit breaker comprising: a casing; stationary contact means including at least one stationary contact mounted in the casing; movable contact means including at least one movable contact movably mounted in the casing and movable into and out of engagement with the stationary contact; actuating means mounted in the casing and including a manually movable member and a bell crank connected to the manually movable member, the bell crank operatively connected to the movable contact means so that actuation of the actuating means will cause movement of the bell crank and at least a portion of the movable contact means; return spring means attached to the movable contact means to move the movable contact out of engagement with the stationary contact; the movable contact means including a spring plate bent back upon itself in a generally U-shaped configuration having a bight portion joining two legs, a contact bar mounting the movable contact supported on an end of one of the legs; and the bight portion of the spring plate formed with a cutout section which receives the bell crank, the bell crank attached to the other leg of the spring plate, the bell crank formed with a lip portion extending over a portion of the contact bar to limit the movement of the spring plate thereby maintaining the spring plate under stress whereby when the contacts are in engagement the contact pressure is increased by the bias applied by the spring plate and upon disengagement of the contacts contact welds will tend to be broken by the transfer of force from the return spring through the lip to the contact bar effectively bypassing the spring plate, and means to prevent loss of contact pressure due to buckling of the spring plate, said means including stiffening means and a permanent connection between the bell crank and the other leg.