US3599136A - Molded-case circuit breaker having improved overcurrent releasable latch - Google Patents

Abstract

A circuit breaker of the molded case type incorporating an overcurrent releasable latch including a low-profile armature return spring which is better able to withstand hot arc-generated gasses without damage.

Description

United States Patent John DeTorre;

Henry S. Wingard, both 01 Albemarle, N.C. 845,274

July 28, 1969 Aug. 10, 1971 Federal Pacific Electric Company Inventors Appl. No. Filed Patented Assignee MOLDED-CASE CIRCUIT BREAKER HAVlNG IMPROVED OVERCURRENT RELEASABLE LATCH 4 Claims, 3 Drawing Figs.

Int. Cl ..H01h71/16, H0111 71/64, H01b75/12 Field olSearch 335/37, 43;

[56] References Cited UNITED STATES PATENTS 3,317,867 5/1967 Powell 337/70 X 3,240,902 3/1966 Gelzheiserw. 337/71 X 3,134,871 5/1964 Norden .1 335/37 Primary Examiner- Bernard A. Gilheany Assistant Examiner- Dewitt M. Morgan Altorneys Paul S. Martin and Richard M. Rabkin ABSTRACT: A circuit breaker of the molded case type incorporating an overcurrent releasable latch including a lowprofile armature return spring which is better able to withstand hot arc-generated gasses without damage.

PATENTEDMIGIOBH 3,599,136

INVENTORS 40 .1 JOHN DETORRE F|G 3 BY HENRY swmsmo EL d M 2W MOLDED-CASE CIRCUIT BREAKER HAVING IMPROVED OVERCURRENT RELEASABLE LATCH This invention relates to circuit breakers and more particularly to improvements in molded case circuit breakers.

As more and more electricity has been used in homes, offices and factories the capacity of the electric power distribu tion system serving these places has been increased to keep up with the increased demand. The increase in capacity has been accomplished by installation of additional and larger transformers and conductors. With the increased capacity has come an increase in the available short-circuit current.

Molded case circuit breakers have been widely employed in the distribution and control of electricity and their popularity continues to increase. In the past the standard circuit breakers which had a short-circuit current-interrupting capacity of 5,000 amperes have been satisfactory. However, in view of the increased short-circuit currents available now, and the even greater currents which, it is expected, will be available in the future, it is important that the interrupting capacity of the circuit breakers be increased. Additionally, from an economic viewpoint the improved circuit breakers must be interchangeable with, and if possible externally identical to, the prior units so as to allow continued use of the unchanged panelboards, accessories and the like and to permit improvement or upgrading of existing installations.

Therefore, it is an object of this invention to improve the short-circuit current interruption rating of molded case circuit breakers. It is another object of the invention to improve the interrupting rating of prior available circuit breakers with minimum exterior changes therein.

The invention is illustrated, in certain of its aspects, as ap plied to a multipole molded case circuit breaker. Such a circuit breaker is illustrated and described in detail in U.S. Pat. No. 2,923,795 and that description is incorporated herein by reference.

The nature of the invention and its further objects and features of novelty will be better appreciated from the following detailed description of the illustrative embodiment which is shown in the accompanying drawing forming part of this disclosure. In the drawings:

FIG. 1 is a side view of an end pole of a three-pole circuit breaker embodying certain aspects of the novel overcurrent releasable latch with the cover removed and certain parts being shown in fragmentary section. The mechanism is shown in the contacts-closed (closed-circuit) position;

FIG. 2 is a side view of the overcurrent releasable latch of FIG. I on a greatly enlarged scale; and

FIG. 3 is a plan view of the overcurrent releasable latch as viewed along the line 3-3 therein.

Referring to the drawings there is shown one end pole of a three-pole circuit breaker of the type described in detail in U.S. Pat. no. 2,923,795. The circuit breaker case has an inner wall that cooperates with an outer wall not shown to form an internal cavity. This cavity and the other like cavities (not shown), contain a complete circuit breaker mechanism, ineluding a pair of contacts, a contact-operating linkage, an overload release means; and a common release means which forms a part of each pole of the three-pole circuit breaker. Common operating means, including externally projecting handle 16, is provided for simultaneous operation of all of the poles. A common trip-bar mechanism 18 is operatively connected to all of the poles.

The mechanism of each pole is the same as the mechanism for each of the other poles and only one is shown in detail. Each pole includes a first terminal 20 rigidly carrying a stationary contact 22. Movable companion contact 24 engages contact 22 when the circuit breaker is closed, movable contact 24 being supported on elongated contact-carrying member 26. Contact-carrying member 26 is pivoted near its center on a transverse coil spring 28. The contacts engage and disengage within a well-known type of are chute 29 that includes metallic arc-splitter plates 29a, venting passage 29b and metallic vent screen 290. Carried on pivot 30 in an insulating bearing (not shown) at the end of contact member 26 remote from contact 24, is an actuator 32 having a bearing 34 which receives a portion of the trip-bar mechanism 18. An ambient temperature compensating bimetal 32a has its upper end curved about bearing 34 and its lower end, which constitutes its latched end, is slidably guided by a formed portion of actuator 32 so that the lower tip of bimetal 32a is projected to a variable extent in dependence of the ambient temperature.

The overcurrent releasable latch 37 includes a currentresponsive bimetal 38 that is united at one end to the contact arm 26, providing electrical connection and a rigid mechanical connection at this point. The elongated contact member 26 constitutes a conductive support that carries and-unites bimetal 38 and the magnetic pole structure 40 of a tripping electromagnet. The pole structure 40 is also united to'bimetal 36 and to contact arm 26 by a rivet 261) that extends integrally through the bimetal and the pole structure from contact arm 26. Pole structure 40 is wider than the bimetal 38 and extends all the way across the bimetal except for a cutout portion to accommodate a conductor 42 of flexible conductive braid that is united to the bimetal adjacent its right-hand end as viewed in the drawings. A magnetic armature 44 is positioned on the side of bimetal 38 opposite from pole structure 40 and has lateral pivots 44a retained in notches in the pole structure as shown. Armature 44 is wider than bimetal 38 at the right of pivot 44a and extends into latching engagement with actuator 32. Armature 44 terminates to the left of the pivots 44a. A low-profile spring 46 biases the armature counterclockwise about pivots 4411.

Referring to FIGS. 2 and 3 the illustrated embodiment of the novel overcurrent releasable latch will now be described in greater detail. The pole structure 40 includes a pair olspacedparallel poles 40a that extend beneath the armature 44 and provide access between them for the braid 42. A pair of arms 40b, 40c cooperate with the armature 44 and its pivots 44a to retain and guide the armature. Each of the arms 40b is bent over slightly toward its companion arm 400 to trap the armature pivots 44a therebetween. Armature 44 has one end 44b in line with its pivots 44a. its other end 44: cooperates with the actuator tip 32a as will be described. A loop 44d formed from the body of the armature for cooperation with bimetal 38, as will be explained below, is provided adjacent the terminal end 44c(FlG.. 2).

One end of a low-profile spring 46 is anchored vertically by the junction of the elongated moving contact member 26 and bimetal 38 which meet at an acute angle. Horizontal anchoring is provided by a pair of upturned spring ears 46b that engage opposite faces of the member 26 to provide lateral stability for the spring 46. Spring 46 has a reversely bent portion 46c which passes through a slot 448 intermediate the bends. Spring end 46d bears against the underside of the armature 44. The portion of spring 46 above the armature is substantially flat providing a low profile. Spring 46 is relatively stiff but is resiliently bowed between its ends with the result that end 44: of the armature is urged away from the pole structure 40 in a counterclockwise direction as the armature moves about its pivots 44a. Spring 46 may advantageously be made from phosphor bronze strip material by well-known fabrication techniques.

As noted above bimetal 38 is secured to the contact-carrying member 26, between the member 26 and pole piece 40, by means of the rivet 26b. The free end 38b of the bimetal passes through the armature loop 44d. A layer of insulation 38c, interposed between the bimetal and the armature, prevents the current flowing through the braid 42 from bypassing the bimetal 38. Bimetal 38 deflects on sustained overloads causing armature end 44d to release actuator end 3211.

In the event of a severe short circuit the current passing through the bimetal causes the armature 44 to be attracted toward the pole pieces 40a. In moving toward the pole pieces the armature overcomes spring 46 and the end of the armature 44c releases the actuator tip 32a initiating the opening of the circuit breaker. When the contacts part under such circumstances a large amount of hot gasses are generated by the are between the contacts and the hot gasses expand within the casing. Ideally such gasses should pass through the arc chute 29 to the exterior of the casing. However, it has been found that a certain amount of the hot gasses blow back toward the overcurrent releasable latch 37. The gasses are hot enough for a long enough period of time that damage to the armature spring 46 could result but for the novel construction described. Loss of restorative force due to loss of temper of the spring stock could result in the armature not returning to the actuator-engaging position and the consequent inability of the circuit breaker to be closed. The low profile of spring 46 in the direction of movement of hot arc-generated gasses reduces the exposure of the spring to said gasses and increases the reliability of the circuit breaker.

Flexible braid 42 has one end connected to bimetal 38 and its opposite end is joined to terminal 48, of a form suitable for panelboard plug-in installation as disclosed in US Pat. No. 2,647,225. An electrical circuit may be traced through the circuit breaker from terminal across contacts 22 and 24, into elongated contact member 26, via bimetal 38 and braid 42 to terminal 38. There is no current bypass path bridging bimetal 38 by virtue of the insulated pivot which is more fully disclosed in US Pat. No. 2,647,186.

Transverse coil spring 28, which serves a pivot for contact arm 26, is housed in a pair of cylindrical bosses 10a and 120 that extend inwardly toward one another within the cavity 14. Spring 28 provides contact pressure between the contacts 22 and 24 and permits overtravel of the contact-carrying member 26 as more fully explained in US Pat. No. 2,681,396.

A compression spring 50 is interposed between respective projections on contact-carrying member 26 and handle 16 biasing both the contact member and the handle to their open position when the circuit breaker is open. As shown in FIG. 1 this compression spring provides strong contact-opening bias when the breaker is closed. In the closed configuration of the mechanism shown in FIG. 1, actuator 32 is latched by armature 44 and the counterclockwise spring bias applied to contact-carrying member 26 is resisted by an overset toggle consisting of trip bar 18 and pivoted handle 16. Counterclockwise motion of handle 16 is limited by the casing l0. In this configuration, spring 50 provides a limited bias for operating handle 16 in the contact-opening direction.

In part, the speed of opening of the contacts upon occurrence of an overload determines the interrupting rating of the circuitry breaker. The speed of opening is largely dependent upon the force of compression spring 50. An increase in force of spring 50 could produce faster opening. However, spring 50 and pivot spring 28 are in opposition and therefore an increase in force of spring 50 will result in a reduction in contact pressure. An increase of force in spring 50 is therefore not suitable as a way of increasing the speed of opening. In order to increase the opening speed of the circuit breaker a torsion spring 52 is positioned about the boss 10a. One end 52 engages a stop on the wall 10 (shown in dotted lines, FIG. 1) and the other end of the spring 52 is formed as a hook 52b for engagement with the contact-carrying member 26. Spring 52 is positioned so that it reacts between the casing wall 10 and the contact arm to pivot the contact arm 26 counterclockwise about spring 28 as viewed in FIG. 1. Torsion spring 52 acts on the elongated contact-carrying member 26 in the same direction as pivot spring 28 when the contacts are closed and, therefore, spring 52 actually increases the contact pressure.

Upon release of the contact-carrying member, spring 52 accelerates the movement of contact 24 to the open-circuit position.

The toggle comprising handle 16 and trip bar 18 lock the contacts closed, under the control of armature 44 of the overcurrent releasable latch 37. Upon downward deflection of the armature magneticall or by pressure from current-responsive bimetal 38, elongate contact-carrying member 26 IS driven counterclockwise by spring 50 and by spring 52, as actuator 32 swings clockwise about its pivot 30. Springs 50 and 52 are now free to accelerate the separation of the contacts 22, 24. The addition of spring 52 contributes to increased contact pressure and increased speed of opening of the contacts with only a small, barely noticeable to the operator of handle 16, increase in the force required to close the circuit breaker.

The molded case circuit breaker illustrated and described above is a three-pole, 70a., 240v. unit and is fully compatible with presently installed panelboards. Although shown and described as a three-pole breaker it will be readily apparent to those skilled in the art that certain aspects of the invention are equally applicable to circuit breakers having one, two or more poles. Molded case circuit breakers, fabricated according to the teachings of this invention, have been successfully tested at 10,000 a. interrupting capacity.

The resetting and reclosing of the aforedescribed circuit breaker is shown and described in detail in US Pat. No. 2,923,795 and is incorporated herein by reference.

While only one embodiment of the invention has been shown and described in detail it will be readily apparent to those skilled in the art that various changes and modifications may be made herein without departing from the spirit and scope of the invention.

What we claim is:

l. A molded case circuit breaker having a stationary contact, an elongated movable contact member supported on a pivot between its ends, said elongated movable contact member having a contact at one end engageable with and disengageable from said stationary contact, and having an actuator pivoted at its opposite end and having an overcurrent releasable latch normally restraining said actuator, and a pivoted handle and a link connected to said handle forming a toggle for operating said actuator and for thereby operating said elongated movable contact member to close the contacts, said overcurrent releasable latch being carried by and movable with said elongated movable contact member, said overcurrent releasable latch including a current-responsive bimetal, a magnetic pole structure adjacent said bimetal, an armature pivoted at one end on said pole structure and engaging said actuator at the other to thereby latch said actuator, and resilient means reacting between said contact member and said armature for biasing said armature into an actuatorlatching position, said resilient means having a low profile in the direction of movement of hot arc-generated gasses when said circuit breaker opens whereby the exposure of said resilient means to said gasses is minimized.

2. A circuit breaker according to claim 1 wherein said resilient means is a substantially flat spring member.

3. A circuit breaker according to claim 2 wherein said overcurrent releasable latch is joined to said elongated movable contact member at an acute angle, said flat spring member having one end thereof engaged with said joint whereby said flat spring member is provided with a reaction point.

4. A circuit breaker according to claim 3 wherein said flat spring member has a pair of formed portions in engagement with said elongated movable contact portion to provide lateral stability for said flat spring member.

Claims (4)

1. A molded case circuit breaker having a stationary contact, an elongated movable contact member supported on a pivot between its ends, said elongated movable contact member having a contact at one end engageable with and disengageable from said stationary contact, and having an actuator pivoted at its opposite end and having an overcurrent releasable latch normally restraining said actuator, and a pivoted handle and a link connected to said handle forming a toggle for operating said actuator and for thereby operating said elongated movable contact member to close the contacts, said overcurrent releasable latch being carried by and movable with said elongated movable contact member, said overcurrent releasable latch including a current-responsive bimetal, a magnetic pole structure adjaCent said bimetal, an armature pivoted at one end on said pole structure and engaging said actuator at the other to thereby latch said actuator, and resilient means reacting between said contact member and said armature for biasing said armature into an actuator-latching position, said resilient means having a low profile in the direction of movement of hot arc-generated gasses when said circuit breaker opens whereby the exposure of said resilient means to said gasses is minimized.

2. A circuit breaker according to claim 1 wherein said resilient means is a substantially flat spring member.

3. A circuit breaker according to claim 2 wherein said overcurrent releasable latch is joined to said elongated movable contact member at an acute angle, said flat spring member having one end thereof engaged with said joint whereby said flat spring member is provided with a reaction point.

4. A circuit breaker according to claim 3 wherein said flat spring member has a pair of formed portions in engagement with said elongated movable contact portion to provide lateral stability for said flat spring member.

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