US3610856A - Molded case circuit breaker having an auxiliary contact separating spring - Google Patents

Abstract

A circuit breaker of the molded case type incorporating a spring that accelerates movement of the movable contact to the open circuit position without greatly increasing the manual effort required for closing the circuit breaker.

Description

United States Patent Inventor John De Torre Albemarle, N.C. Appl. No. 66,726 Filed Aug. 25, 1970 Patented Oct. 5, 1971 Assignee Federal Pacific Electric Company Newark, NJ.

MOLDED CASE CIRCUIT BREAKER HAVING AN AUXILIARY CONTACT SEPARATING SPRING 3 Claims, 3 Drawing Figs.

US. Cl 200/153,

Int. Cl 01h 3/00,

[50] Field of Search 200/153 G, 153 H [56] References Cited UNITED STATES PATENTS 2,803,721 8/1957 Cole 337/75 2,811,605 10/1957 Christensen et al. 337/53 Primary Examiner-J. V. Truhe Assistant ExaminerL. H. Bender Attorney- Paul S. Martin ABSTRACT: A circuit breaker of the molded case type incorporating a spring that accelerates movement of the movable contact to the open circuit position without greatly increasing the manual effort required for closing the circuit breaker MOLDED CASE CIRCUIT BREAKER HAVING AN AUXILIARY CONTACT SEPARATING SPRING This invention relates to circuit breakers and more particularly to improvements in molded case circuit breakers. In some respects this is an improvement over copending application Ser. No. 845,275 filed July 28, 1969.

As more and more electricity has been used in homes, offices and factories the capacity of the electric power distribution system serving such 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 aneconomic 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 standardized 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 capacity of molded-case circuit breakers. It is another object of the invention to improve the interrupting capacity of prior available circuit breakers with minimum external changes therein.

The invention is illustrated, in certain of its aspects, as applied to a single pole molded-case circuit breaker of wellknown construction. The invention is equally applicable to multipole molded-case circuit breakers of the type illustrated and described in detail in U.S. Pat. No. 2,923,795.

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 drawings:

FIGS. I and 2 are side views of a circuit breaker with the cover removed, shown in the contacts-open and in the contacts-closed position, respectively, illustrating the invention.

FIG. 3 is a fragmentary cross section of a portion of the mechanism in FIG. 2 viewed along the line 33 therein.

Referring to the drawings there is shown a circuit breaker of the type described in detail in U.S. Pat. Nos. 2,803,721 and 2,8l 1,605. The circuit breaker case has a first wall that cooperates with a second wall 12 to form a cavity 14. Cavity 14 contains a complete circuit breaker mechanism, including a pair of contacts, a contact-operating linkage, and an overload release means and an externally projecting operating handle 16. i

The circuit breaker shown includes a first terminal 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 arc chute 29 that includes venting passage 29b. 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 one leg of a U-shaped link made of bent wire. 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 on the ambient temperature. I

The overcurrent releasable mechanism 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 that extends integrally, through the bimetal and the pole structure, from contact arm 26.

' 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 U.S. Pat. No. 2,647,225. An electrical circuit may be traced through the circuit breaker from terminal 20 across contacts 22 and 24, into elongated contact member 26, via bimetal 38 and braid 42 to terminal 48. There is no current bypass path bridging bimetal 38 by virtue of the insulated pivot 30 which is more fully disclosed in U.S. Pat. No. 2,647,186.

Transverse coil spring 28, which serves a pivot for contact arm 26, is housed in a pair of projecting bosses 10a and 12a that extend inwardly toward one another within the cavity I4. Spring 28 biases contact arm 26 clockwise about pivot 30 when the breaker is closed and in this way 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 U.S. Pat. No. 2,681,396.

A compression spring 50 is interposed between a handle l6 and snap-lever" 54 that is carried by member 26 biasing both the contact member and the handle toward their "open" position when the circuit breaker is open. As shown in FIG. 2 this compression spring provides strong contact-opening bias when the breaker is closed. In the closed configuration of the mechanism shown in FIG. 2, actuator 32 is latched by bimetal 38 and the counterclockwise spring bias applied to contactcarrying member 26 is resisted by an overset toggle consisting of link 18 and arm 16a of handle 16. Counterclockwise motion of handle 16 is limited by the casing 10. In this configuration, spring 50 provides a limited bias for operating handle 16 in the contact-opening direction, bias that is ineffectual due to the friction forces developed at pivot 16!; when the breaker is closed and latched.

In part, the speed of opening of the contacts upon occurrence of an overload determines the interrupting capacity of the circuit 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. A novel solution is provided to the problem of increasing the opening speed of the circuit breaker by the provision of a spring 52 that operates about the boss 10a as a fulcrum. One end 52a of torsion spring 52 engages a stop 10b on the wall 10 and the other end is formed as a hook 52b extending through pivot 30 at the end of contact-carrying member 26 remote from contact 24. 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. 2. Torsion spring 52 has no effect on the elongated contact-carrying member 26 in the closed condition of the breaker, since the k spring acts only on stationary parts 100 and 10a and 10b and on the erect toggle 16a, 18. When release takes place as described below, spring 52 accelerates the movement of contact 24 to the open circuit position.

The toggle comprising arm 16a of handle 16 and link 18 lock the contacts closed, under the control of bimetal 38 that acts as a latch. Upon downward deflection of the bimetal magnetically due to current in the bimetal developing a pull of armature 380 on the bimetal toward pole 40 or by heating of current responsive bimetal 38, elongated 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 increased speed of opening of the contacts.

Spring 52 is made of relatively heavy wire. In a single-pole breaker as shown, and especially in a multipole breaker where a separate spring 52 should be used for each of the contact arms, such a spring would tend to make it hard to close the circuit breaker. This effect is largely avoided by the following particulars.

As seen in FIG. 1, which represents the breaker when open, there is a substantial space between stop b projecting inward from casing part 10 and end 52a of spring 52. Toggle 16a, 18 is in its most buckled condition at this time. As handle 16 is moved counterclockwise, toggle 16a, 18 approaches its erect state and tends to be progressively easier to operate as it approaches fully erect condition. Spring end 52a reaches stop 10b when handle 16 has moved about halfway, or a bit more, toward its "closed" position. Thus, the mechanical advantage that can be realized by the toggle approaching its erect state makes it relatively easy to close the contacts and to develop considerable stress in spring 52. When link 18 and arm 16a of the handle become aligned or erect, no manual effort at handle 16 is needed to overcome the force of spring 52 that is applied to the toggle 16a, 18. A little further motion occurs, and the toggle becomes overset, locking the breaker closed. In this overset condition of the toggle, clockwise bias on actuator 32 develops. The stress in spring 52 provides a large force that is available instantly to drive movable contact 24 open when the overcurrent latch deflects downward and releases actuator 32. This makes available a large accelerating force at the instant of contact separation. The fact that the force of breaker-52 disappears entirely when contact 24 has moved halfway toward its full open position is unimportant since by that time the contact arm is moving at high speed. The highspeed contact-opening operation attributable to the augmented bias provided by spring 52, has made possible the interruption of arcs under severe conditions, as where 10,000 amperes is available in a 240-volt circuit. Greater contactopening bias can be realized with this spring than with the auxiliary torsion spring in the above-mentioned application Ser. No. 845,285 and yet the manual effort needed for closing the circuit breaker-even multipole circuit breakers with one spring 52 per pole-remains quite reasonable.

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. I

What is claimed is:

l. A manually operable circuit breaker having an elongated movable contact member supported between its ends on a contact member pivot, said elongated movable contact member having a movable contact at one end, a companion contact engageable by and disengageable from said movable contact when the circuit breaker is closed and when it is open, respectively, said movable contact member having an actuator carried by an actuator pivot at the end of the movable contact member remote from said movable contact and bearing an overcurrent releasable latch normally restraining said actuator, a toggle including a pivoted handle and a link connected to said handle and said toggle being operable from a collapsed condition into erect condition for operating said actuator and for thereby operating said elongated movable contact member to close the contacts, spring means biasing said contact arm in the contact-opening direction, and an auxiliary spring acting on said elongated contact member in the contact opening direction wen the contacts are closed, said auxiliary spring bearing against a reaction point when the contacts are closed and when the contacts are part way open but not hearing against said reaction point when said circuit breaker is open or nearly open, whereby manual closing of the breaker is unimpeded by said auxiliary spring during the initial operation of the toggle part way toward its erect condition from its collapsed condition and the auxiliary spring is effective to accelerate the opening movement of the elongated contact member upon release of said overcurrent latch. I

2. A manually operable clrcu|t breaker in accordance with claim 1, wherein said spring has one extremity acting at said actuator pivot.

3. A manually operable circuit breaker in accordance with claim 1, further having a molded case, said molded case having an inward protrusion supporting said auxiliary spring between its extremities and an inward protrusion forming said reaction point for one of the extremities of the auxiliary spring and the opposite extremity of the auxiliary spring acting on said elongated contact arm at said actuator pivot.

Claims (3)

1. A manually operable circuit breaker having an elongated movable contact member supported between its ends on a contact member pivot, said elongated movable contact member having a movable contact at one end, a companion contact engageable by and disengageable from said movable contact when the circuit breaker is closed and when it is open, respectively, said movable contact member having an actuator carried by an actuator pivot at the end of the movable contact member remote from said movable contact and bearing an overcurrent releasable latch normally restraining said actuator, a toggle including a pivoted handle and a link connected to said handle and said toggle being operable from a collapsed condition into erect condition for operating said actuator and for thereby operating said elongated movable contact member to close the contacts, spring means biasing said contact arm in the contact-opening direction, and an auxiliary spring acting on said elongated contact member in the contact opening direction wen the contacts are closed, said auxiliary spring bearing against a reaction point when the contacts are closed and when the contacts are part way open but not bearing against said reaction point when said circuit breaker is open or nearly open, whereby manual closing of the breaker is unimpeded by said auxiliary spring during the initial operation of the toggle part way toward its erect condition from its collapsed condition and the auxiliary spring is effective to accelerate the opening movement of the elongated contact member upon release of said overcurrent latch.

2. A manually operable circuit breaker in accordance with claim 1, wherein said spring has one extremity acting at said actuator pivot.

3. A manually operable circuit breaker in accordance with claim 1, further having a molded case, said molded case having an inward protrusion supporting said auxiliary spring between its extremities and an inward protrusion forming said reaction point for one of the extremities of the auxiliary spring and the opposite extremity of the auxiliary spring acting on said elongated contact arm at said actuator pivot.

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