US3161747A

US3161747A - Automatic circuit breaker having a combined latch and contact unit pivoted to a contact carrier

Info

Publication number: US3161747A
Application number: US122822A
Authority: US
Inventors: Thomas M Cole
Original assignee: Federal Pacific Electric Co
Current assignee: Federal Pacific Electric Co
Priority date: 1961-07-10
Filing date: 1961-07-10
Publication date: 1964-12-15
Anticipated expiration: 1981-12-15
Also published as: GB949283A

Description

Dec. 15, 1964 T. M. COLE 3,161,747

AUTOMATIC CIRCUIT BREAKER HAVING A COMBINED LATCH AND CONTACT UNIT PIVOTED TO A CONTACT CARRIER Filed July 10, 1961 FIG.3

INVENTQR. THOMAS M. COLE ATTORNEY United States Patent 3,161,747 AUTOMATIC CIRCUIT BREAKER HAVING A. CQM- BINED LATCH AND CONTACT UNIT PIVOTED TO A CONTACT CARRIER Thomas M. Cole, Harrison, N.Y., assignor to Federal Pacific Electric Company, a corporation of Delaware Filed July 10, 1%1, Ser. No. 122,822 11 Claims. (Cl. '200--116) The present invention relates to circuit breakers having self-contained overload-release means.

An object of this invention resides in providing improvements in a well-known type of circuit breaker mechanism having a pivoted cont-act arm on a fixed pivot, an overload-release latch carried by the contact arm and a normally latched pivoted actuator, with a view to increased sensitivity, improved thermal and magnetic tripping, and reduction in cost. Certain features of the invention will be recognized as having broader application but, because the invention has particular merit in relation to this type of circuit breaker, it is disclosed in that connection.

As will be seen from the detailed description below, the illustrative embodiment of the invention is of the type having an enclosing case of molded insulation containing a pivoted contact arm, an actuator pivoted to one end of the arm and a contact-and-latch unit pivoted to the opposite end. The pivoted unit has a movable contact that cooperates with a companion contact when the circuit breaker is closed. The pivoted contact-and-latch unit and the arm or carrier have a relationship between them, established by contacting parts of each, that locates the latch for engagement by the actuator. In the embodiment shown, the latch is a current-carrying bimetal, and the thermal calibration is established by adjusting the configuration of the carrier, the bimetal latch and the latched actuator. This relationship almost entirely controls the overload time-delay tripping level. With this arrangement the carrier which is a relatively large part can be of inexpensive sheet metal, rather than of copper or copper alloy used in corresponding prior-ant circuit breakers. This sub-assembly is calibrated by a bending operation before it is assembled to the remainder of the circuit breaker parts and completed in its molded casing.

The contact-and-bimetal-latch unit is pivoted into its calibrated attitude in relation to the actuator during opening operation of the moving contact by the opening spring. It is this spring which also biases the handle toward its open position.

The two illustrative embodiments described below also include a short-circuit magnetic tripping mechanism that cooperates with the pivoted latch-and-contact unit. Because the pivoted latch incorporates the bimetal, the tripping electromagnet is only required to overcome latch friction for releasing the breaker. This means that there is no need for the electromagnet to bend the overcurrent bimetal, in effecting magnetic tripping. For low-rated circuit-breakers this may be important. Only a small coil will effect almost instant tripping magnetically at relatively modest short-circuit current. Magnetic tripping in such breakers usually is desired at ten times the thermal or delay tripping level. It becomes important, in breakers calibrated (for example) for ampere thermal tripping, to effect magnetic tripping at only 150 amperes using an internal tripping coil of minimum size and minimum series impedance in the protected circuit. This performance is achieved due to the pivoted bimetaland-contact construction in the disclosed embodiments without resort to additional separate complicating auxiliary latch arrangements. A further feature, in this connection, is the pre-calibration of the magnetic tripping sensitivity of each circuit breaker using a bending ICC operation and without, therefore, necessitating adjustment screws and the like. Notably, both magnetic and thermal calibration may be effected without the second adjustment upsetting the first.

The nature of the invention, and its various advantages, objects and features will be more fully appreciated from consideration of the two illustrative embodiments shown in the accompanying drawings and described in detail below. In the drawings:

FIG. 1 is a side elevation of an illustrative embodiment of the invention, with one side wall of the casing removed to reveal the internal mechanism;

FIG. 2 is an enlarged view of a portion of the circuit breaker in FIG. 1, partly in cross-section, with the contacts closed;

FIG. 3 is a fragmentary cross-section of the mechanism in FIG. 2, further enlarged, as viewed from the plane 33 of FIG. 2;

FIG. 4- is an enlarged cross-section of a portion of the circuit breaker in FIG. 1 as viewed from the line 4-4; and

FIG. 5 is another embodiment of the invention viewed as in FIG. 1.

Referring now to the embodiment in FIGS. 1 to 4, a circuit breaker is shown having a rear casing wall 10, a front casing wall 12 (FIG. 4) and a pair of terminals 14 and 16. A moving contact arm or carrier 18 is supported between its ends on a pivot spring 20. An operating handle 22 having a pivot 22a has bearings (not shown) in the opposite casing walls. Handle 22 is connected by a rigid U-shaped wire link 24 to a so-called bell-crank or pivoted actuator 26 that has an insulated bearing (not shown) at the right-hand end of contact arm 18. A contact-opening spring 28 acts downward against a portion of contact arm 18 to the lefit of pivot 20 as seen in FIG. 1, thereby applying counterclockwise bias to the contact arm 18. Spring 23 also applies clockwise bias to handle 22, both in the open position illustrated and in its closed position at the left-hand extreme position allowed by the casing. Spring 28 thus applies sustained bias to handle 22 and contact arm 18 urging them in their respective oil or open positions. A depending portion 18a of the contact arm has an integral extrusion or pivot 1812 that supports contact element 36 of copper having a contact portion 30a of sintered silver-tungsten. Contact portion 30a cooperates with a corresponding sintered silver-tungsten contact 14a carried by the wireconnecting terminal 14. Contact

portions

14a and 30a cooperate in a region of the casing which forms an arc chamber and has a vent 32 to the exterior.

A current-responsive bimetal 34 is joined by a rivet 3612 (which extends integrally from element 30) so that bimetal 34 and contact element 3% form a unit that is pivotally supported by contact arm IS. A stop Illa projects from the rear casing wall so as to underlie bimetal 34.

Another depending portion of the contact arm carries a coil 36 of flexible copper braid joined to bimetal 3 5 near the right hand extremity of the bimetal, the braid having an extension 38 that is united to plug-in terminal 16 of the circuit breaker. Coil 36 is formed about a coil form 4d of insulation, and the successive turns of the braid are separated from each other by insulation on the braid itself or as ribs (not shown) on coil form 40. The coil form fits tightly on core 42 of magnetic material riveted to contact-arm portion 180. The axial length of core 42 is sli htly less than that of the coil form 4-0, so that there is no danger of electrical contact being made between bimetal 34 and core 42. Contact arm 18 is formed of magnetic material such as sheet iron, and has an car 18:! extending perpendicular to the plane of the drawing (FIGS. 1 and 2), so that a magnetic circuit is formed including core 42, and

contactarm portions

18c and 18d that is closely coupled to bimetal 34. The bimetal is of magnetic material, and acts as an armature attracted toward coil 36 when the latter is energized; and a supplemental magnetic part may be added to bimetal 34- if desired.

In the open condition of the circuit breaker, the parts appear as illustrated in FIG. 1. Contact arm 18 is biased counterclockwise by spring 23. An integral car He of the contact arm presses downward against contact element 3d, with the result that spring 2% drives contact arm 18 and contact element 30 as a unit until bimetal 34 strikes casing projection or stop 10a. This stop limits counterclockwise movement of contact arm 18, and it also provides counterclockwise bias for unit 30-34 about pivot 18b. This insures engagement of the

pivoted unit

30, 34 with portion 18c of the carrier 18, and locates the right-hand end of the bimetal 34 for latching engagement with the lower end of actuator 26.

In order to close the circuit breaker, operating handle 22 is moved counterclockwise about its pivot to apply thrust to link 24 and in that way to bias actuator 26 clockwise, into latched engagement with bimetal 34. Further operating effort applied to the handle drives contact arm 13, actuator 25, bimetal 34, and contact element St) clockwise as a unit about pivot 20. Handle 22 and link 24 constitute two links of an operating toggle. When this toggle approaches its fully extended condition, contact

portions

30a and 14a engage. Further effort applied to the handle 22 builds up contact pressure, forcing pivot spring 20 to flex downward (FIG. 4) and thus building up contact pressure. The operating toggle moves somewhat overcenter and locks the circuit breaker mechanism with the contacts closed when the projecting portion 221) of the handle reaches the left-hand or closed extremity of its stroke permitted by the casing. During the contact-closing operation of the mechanism, bimetal 34 lifts away from casing projection 10a; but bimetal 34 is arrested by latch friction so as to remain in the triangular configuration 18-2644 shown in FIG. 2.

Theparts in the configuration represented in FIG. 2 involve a strong upward pressure of contact portion 39a against contact portion 14a, developed by spring 20 as previously described. The contact face of contact 14a is flat, as shown, and the upper surface of contact portion 30a is upwardly convex. The plane that is tangent to the point of engagement between

contact portions

14a and 30a coincides with the face of contact 14a in the construction shown. This plane is perpendicular to the plane that contains both the axis of pivot 18b and the point of contact engagement. Because of the rightangled relationship between these planes, the pressure at the contacts develops neither clockwise nor counterclockwise torque of contact element 39 about pivot 18b. By like token, endwise pressure of actuator 26 against bimetal 34 is arranged to provide direct thrust along the length of the bimetal through the axis of pivot 18b. Because of this arrangement, thrust along bimetal 34 does not produce any torque that biases bimetal 34 counterclockwise (which would tend to hold it in the latched configuration shown) nor does actuator 26 produce any clockwise torque that might tend to deflect bimetal 34 in the releasing direction. The mechanism in its closed condition as illustrated in FIG. 2 is thus entirely stable mechanically. The only significant force acting on the

unit

30, 34 tending to hold it latched against clockwise movement about pivot 18b in response to a magnetic deflecting force is the latch friction at the latched end of the bimetal.

Current through the circuit breaker flows from terminal 14 through contact portions 14a and 3tla, through contact element 30 and bimetal 34, through coil 36 and flexible lead 38 to terminal 16. In the event of a moderate current excess, bimetal 34 heats gradually. The left-hand end of bimetal 34 is fixed in position by pivot 18b and stop 1842. Heating of the bimetal causes it to deflect downward until it is clear of actuator 26. When this occurs, springs 20 and 28 are free to restore the parts to the configuration in FIGS. 1 and 4.

The bimetal effects thermal release of the circuit breaker, responding to persistent but moderate overload currents. Moderate overload currents of short duration such as are caused during the starting of a motor or during the in-rush current of an incandescent lamp do not effect thermal release of the circuit breaker. However, in the event of a severe, sudden overload current (even if only of short duration) release is effected by electromagnetic means including coil 36, core 42, and contact-

arm portions

18c and 18d which attract the bimetal downward. The avoidance of any net mechanical torque acting on bimetal-and-

contact unit

30, 34 minimizes the tripping torque required of the electromagnet. Reset of

unit

36, 34 by stop a rather than by a spring contributes to this result. For this reason, the electromagnet which attracts bimetal 34 need be of relatively modest strength.

It acts on a long lever arm close to the latching point and effects release merely by overcoming the latch friction between actuator 26 and bimetal 34.

It has been found that the mechanism shown provides a high order of magnetic tripping sensitivity. A practical embodiment of the circuit breaker illustrated has tripped magnetically in response to an instantaneous current of 150 amperes, using a coil of only three turns on a relatively small core of ordinary sofit iron. The mechanism in FIG. 1 is thus an eminently successful circuit breaker that may be adjusted to provide a nominal IS-amperc rating determined by thermal-release adjustment, and with a ISO-ampere magnetic tripping adjustment. Where bimetals of higher ratings are used it is apparent that the coil may be made smaller and omitted entirely, the bimetal itself then acting as a flux source to cooperate with the magnetic structure below bimetal 34 and thus effect magnetic tripping without dependence upon a coil as such.

Contact arm 18 includes a pair of slots 18 and 18g. When the circuit breaker is closed as in FIG. 2, a taper pin may be driven progressively into slot 18], gradually reducing the gap between bimetal 34 and the magnetic circuit 4218c18d. Momentary bursts of current of -magnetic-tripping level can be passed through the coil at intervals, while maintaining normal latch pressure. When the gap is reduced to the proper size by this adjustment, the latch will trip. Subsequently, the latch is engaged again and current of the proper thermal calibration level is passed through it for the required time interval. A taper pin is driven into slot 18g to spread the edges of that slot and thereby decrease the amount of overlap of actuator 26 across the end of bimetal 34 until release occurs.

Slots 187 and 18g thus provide independent magnetic and thermal overload-release adjustments without resort to complicating adjustment-screw mechanisms. As a matter of practice, these adjustments are effected at a time prior to the assembly of the parts of FIG. 2 in an insulating housing, using appropriate fixtures for this purpose. Thereafter, when the circuit breaker is assembled into its housing, no further calibrating operations are needed.

A modification is shown in FIG. 5. A modified electromagnet is shown mounted in the bottom of the case 10; Electromagnet 36 is spaced far from bimetal 34' when the circuit breaker is open as shown in FIG. 5; but when the circuit breaker is closed, bimetal 34 moves within a short-gap distance from the electromagnet 36. Casing portion 10a forms a stop that engages bimetal 34 and biases [the bimetal against stop portion 18c prior to contact-closing operation of the mechanism. The

embodiment of FIG. 5 has the advantage of reduced mass of parts which must move to break the circuit in response to an overload current, thereby effecting some 1 what faster contact-opening operation than the embodiment of FIG. 1. This advantage becomes particularly significant where circuit breakers of very high magnetic sensitivity are needed, that is, where magnetic response to low values of current may be desired. Larger coils may be mounted as in FIG. 5 without concern over the mass and inertia effects involved. It will be appreciated that the core in electromagnet 36 may be U-shaped in the embodiment of FIG. 5 if still higher magnetic sensitivity is needed or desired.

In both of the embodiments in FIGS. 1 and 5, spring 20 which is stressed in the closed condition of the circuit breaker exerts counterclockwise bias on carrier 18 about the pivot of actuator 26, this being in mechanically arrested position when the circuit breaker is latched closed by the toggle actuator 22, 24. The counterclockwise bias of spring 20 develops contact pressure, this bias being considerably greater than the relatively softer elfort of spring 28. The latter spring is a push-off spring which biases carrier 18 and the movable contact 30 counterclockwise and effects contact-opening when actuator 26 is released.

Comparable springs are found in circuit breakers of the general form illustrated in which a bimetal and a pivoted actuator latched by the bimetal are carried on a pivotaliy supported contact carrier. In these circuit breakers, an operating toggle drives the actuator against the birnetal and then drives the three elements as a unit (including the bimetal, the pivoted contact arm and the actuator) for driving the movable contact against a companion contact. In the present instance, however, contact-

andlaitch unit

30, 34 is pivoted to the carrier. Notably, there is no torque from such springs that acts between carrier 18 and

unit

30, 34.

- In the closed condition of the circuit breaker illustrated inFIGS. l and 5 (as well as in similar prior art circuit breakers wherein the moving contact is fixed to the pivoted contact carrier) link 24 applies thrust to actuator 26 in the closed condition of the breaker. This thrust has a clockwise component biasing the lower end of the actuator against the active end of bimetal latch 34. This biasing component is derived largely from spring 20. The tripping force at the latch end of bimetal 34 required to overcome the latch friction and the friction at

contacts

14a, 30a may amount to little more than an ounce in a practical device. The contact pressure derived from the same spring 20 in that practical device is approximately 20 times as great. It should be understood however that various other spring arrangements for developing contact pressure and latch engagement are known in circuit breakers of the type illustrated which may be utilized in place of the particular spring complement shown.

To minimize friction at the contacts as a factor in determination of the magnetic tripping sensitivity, the radius from the contact point of elements 14a, 39a to the axis of pivot 18b should be minimized. The bimetal latch 34 in the form illustrated is about five times as long as the radius of the contacts.

The foregoing specific embodiments of the invention in its various aspects are presently preferred, but it will be apparent that the features of the invention may be utilized in different applications and in modified forms. Therefore, it is appropriate that the invention should be broadly construed in accordance with its full spirit and scope.

What I claim is:

l. A circuit breaker including a movable contact and a companion contact, a contact carrier movable between open and closed positions, an actuator pivoted to said contact carrier, an overcurrent latch for said actuator pivoted to said contact carrier, operating means for said actuator, said carrier, said latch, and said movable contact, and resilient means for providing contact pressure, said movable contact being fixed to said latch, and the pressure of said companion contact against said movable contact being directed along a line extending substantially from the pivotal axis of said latch.

2. A circuit breaker including a pivoted contact carrier, an actuator pivoted to the carrier, 2. combined contact-and-latch unit pivoted to said carrier and including a movable contact and further including an overcurrent latch co-operable with said actuator, a companion contact engageable by said movable contact, an opening spring acting on said carrier for driving the carrier and the movable contact therewith in the contact-opening direction, a stop for said combined unit interposed in the opening path thereof and arranged to drive said unit pivotally against a portion of said carrier, thereby to establish a reset relationship between said latch and said pivoted actuator, a pivoted handle and a drive connection from said handle to said actuator for driving the actuator into engagement with said latch in said reset relationship and thereafter for driving the actuator, the carrier, and the contact-and-latch unit in the contact closing direction, said handle and said connection constituting a toggle that is erect when the contacts are closed.

3. A circuit breaker including an enclosing casing of insulation, a movable contact and a companion contact, an elongated carrier for said movable contact, a pivot in the casing supporting said contact-carrier between the ends thereof, an actuator pivoted to one end of the contactcarrier, overload release means including a latch normally latching said actuator when the circuit breaker is closed, a driving toggle articulated to said actuator and including an operating handle for driving and locking the contactcarrier closed, and an opening spring biasing said contact-carrier open, said movable contact and said latch being united and being pivoted as a unit to said carrier, and said calrier and said unit having co-operating stop portions for arresting said latch in a reset position in the path of said actuator, and means biasing said stop portions into cooperation at least when said circuit breaker is lopen 4. A circuit breaker including a movable contact and a companion contact, a contact carrier movable between open and closed positions, an actuator pivoted to said contact carrier, an overcurrent latch for said actuator pivoted to said contact carrier, operating means for said actuator, said carrier, said latch, and said movable contact, and resilient means for providing contact pressure, said movable contact being fixed to said latch, and the pressure of said companion contact against said movable contact being directed along a line extending substantially from the pivotal axis of said latch, and electromagnetic means co-operating with said latch for effecting releasing deflection thereof.

5. A circuit breaker including a movable contact and a companion contact, a contact carrier movable between open and closed positions, an actuator pivoted to said contact carrier, an overcurrent latch for said actuator pivoted to said contact carrier, operating means for said actuator, said carrier, said latch, and said movable contact, and resilient means for providing contact pressure, said movable contact being fixed to said latch and con stituting a combined latch-and-contact unit, means biasing the combined unit in its resetting direction only While the contacts are apart, and magnetic means energized by current through the circuit breaker and co-operating with said combined unit in effecting tripping deflection of the latch.

6. A circuit breaker including a contact carrier, a contact-and-latch unit pivoted to said carrier and including a movable contact and further including an overcurrent latch, an actuator co-operable with said latch and with said carrier, actuating means for driving said actuator for closing operation of said carrier subject to the control of said latch, a companion contact engageable by said movable contact, an opening spring acting on said carrier for driving the carrier and the movable contact therewith in the contact-opening direction, a stop for said combined unit interposed in the opening path thereof and arranged to drive a portion of said unit against a portion of said carrier, thereby to establish a reset relationship between said latch and said actuator, and electromagnetic means arranged to effect mutual separating movement of said portions and thereby to effect tripping deflection of said latch'free of restraint by latch-restoring spring bias.

7. A circuit breaker including a movable contact and a companion contact, a contact carrier having a supporting pivot between its ends, an actuator pivoted to one end of the contact carrier, overload release means including a current-responsive bimetal latch normally latching said actuator when the circuit breaker is closed, a driving toggle articulated to said actuator and including an operating handle for driving and locking the contact-carrying arm closed, and an opening spring biasing said contact-carrying arrn open, said movable contact and said bimetal latch being united and being pivoted as a unit to said carrier, and said carrier and said unit having co-operating stop portions for arresting said unit with said latch in the path of said actuator, and means biasing said unit in the direction to effect mutual cooperation of said stop portions at least when the circuit breaker is open.

8. A circuit breaker including a movable contac and a companion contact, a contact carrier movable between open and closed positions, a releasable member pivoted to said contact carrier, a bimetal latch for said releasable member pivoted to said contact carrier, operating means for said carrier and said movable contact to close the contacts, said movable contact being fixed to said bimetal latch as a unitary pivoted element, and cooperating stops on said carrier and said unitary pivoted element, said stops forming a reaction point that acts with the pivot of the pivoted element to fix one end of the bimetal latch in position to eifect deflection of the latch end of the bimetal latch when heating occurs.

9. A circuit breaker including apivoted contact carrier, a releasable element pivoted to the carrier, a contact-andlatch unit pivoted to said carrier and including a movable contact and an overcurrent latch co-operable with said releasable element, a companion contact engageable by said movable contact, and an opening spring acting on said carrier and reacting at a point remote from said overcurrent latch for driving the carrier and the movable contact therewith in the contact-opening direction.

10. A circuit breaker including an enclosing casing of insulation, a movable contact and a companion contact, an elongated carrier for said movable contact, a pivot in the casing supporting said contact-carrier between the 50 2,887,548

ends thereof, a releasable member pivoted to one end of the contactcarrier, overload release means including a bimetallic latch normally latching said releasable member when the circuit breaker is closed, said movable contact and said latch being united and being pivoted as a unit to said carrier, said carrier and said unit having cooperating stop portions coacting with the pivot of the pivoted unit to restrain one end of the pivoted unit in one direction, to provide for latch releasing deflection of the other end of the bimetallic latch when heated, and electromagnetic release means acting on said contact-- and-latch unit about the pivot thereof, said stop means including a bendable adjusting constriction to calibrate the magnetic tripping sensitivity and said contact carrierincluding a bendable adjusting constriction for adjusting the extent of latch engagement of said releasable member with respect to said bimetallic latch and thereby to calibrate the thermal tripping sensitivity.

11. A circuit breaker including a movable contact and a companion contact, a contact carrier movable between open and closed positions, an actuator ivotedto said contact carrier, an overcurrent latch for said actuator pivoted to said contact carrier, operating means for said actuator, said carrier, said latch and said movable contact for driving said contact carrier into its closed position, saidmovable contact and said latch being fixed to each other so as to constitute a combined unit, the pressure of said companion contact against said movable contact being directed along a line substantially through the pivotal axis of said latch, said-combined unit and said contact carrier having mutually cooperating stops in the reset condition of the circuit breaker, means biasing said unit in the direction to effect cooperation of said stops with each other at least in the open condition of the circuit breaker so that said latch may be arrested in an initial reset relationship with said actuator, and electromagnetic means cooperating with said latch and energized by current through'the circuit breaker for effecting pivotal movement of said combined unit in the direction to effect release movement of said latch out'of engagement with said actuator.

References Cited in the file of this patent UNITED STATES PATENTS 2,696,540 Christensen Dec. 7, 1954 2,806,103 Gelzheiser Sept. 10, 1957 2,842,635 Cole July 8, 1958 2,876,308 Christensen Mar. 3, 1959 Middendorf May 19, 1959

Claims

9. A CIRCUIT BREAKER INCLUDING A PIVOTED CONTACT CARRIER, A RELEASABLE ELEMENT PIVOTED TO THE CARRIER, A CONTACT-ANDLATCH UNIT PIVOTED TO SAID CARRIER AND INCLUDING A MOVABLE CONTACT AND AN OVERCURRENT LATCH CO-OPERABLE WITH SAID RELEASABLE ELEMENT, A COMPANION CONTACT ENGAGEABLE BY SAID MOVABLE CONTACT, AND AN OPENING SPRING ACTING ON SAID CARRIER AND REACTING AT A POINT REMOTE FROM SAID OVERCURRENT LATCH FOR DRIVING THE CARRIER AND THE MOVABLE CONTACT THEREWITH IN THE CONTACT-OPENING DIRECTION.