US3023288A - Circuit breaker bimetal heater - Google Patents

Description

Feb. 27, 1962 A. BODENSCHATZ E TAL CIRCUIT BREAKER BIMETAL HEATER Filed Aug. 25, 1959 M5 4 r'ra A/EYS VIA United States Patent Ofiice 3,023,288 Patented Feb. 27, 1962 3,023,288 CIRCUIT BREAKER BIMETAL HEATER August Bodenschatz. Philadelphia, Pa., and Carl E- Gryctko, Haddon Heights, NJ., assignors to l-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Aug. 25, 1959, Ser. No. 835,882 6 Claims. (Cl. 200-116) Our invention relates to a bimetal heater having a U-shape bend wherein the bent section is provided with a heat sink and is more specifically directed to a circuit breaker bimetal heater which has a high heat conductivity material connected at the base of the U formed by the heater.

Heaters for bimetals of the type used to operate a trip latch in a circuit breaker are generally formed of a U-shaped conductive member having one leg of the U adjacent the bimetal. The bent portion of the U is normally the weakest part of the heater because the metal normally has a reduced cross-section at the point. Furthermore, under light overload, current density at the inner surface of the U is great enough to cause fusing, while under heavy overload the current will become concentrated on the periphery by the magnetic force to produce substantial blow-off forces which will tend to rup ture the weakest portion of the heater.

The essence of the present invention is to provide a heat sink at the bent portion of the bimetal heater which will thermally strengthen the heater at this critical area by permitting rapid heat absorption to decrease the rate of increase in temperature.

Accordingly, a primary object of our invention is to provide a novel bimetal heater.

Another object of our invention is to provide a novel means for increasing the thermal capacity of a bent conductor.

A further object of our invention is to increase the thermal capacity of a current conductor having a bend therein by providing a heat sink at the bend.

A still further object of our invention is to provide a heat sink at the bend of a U-shaped bimetal heater.

These and other objects of our invention will become apparent from the following description when taken in connection with the drawings, in which:

FIGURE 1 shows the manner in which an indirectly heated bimetal unit operates as a trip unit for a circuit breaker wherein the bimetal heater is modified in accordance with the present invention.

FIGURE 2 illustrates the bimetal and bimetal heater of FIGURE 1.

FIGURE 3 illustrates a second embodiment of our novel invention.

FIGURE 4 is a partial cross-sectional view of FIGURE 3 when taken across the lines 33.

Referring now to FIGURE 1, we have generally illustrated one type of circuit interrupter that can be equipped with an indirectly heated bimetal for automatically operating the circuit breaker. The circuit breaker construction shown in FIGURE 1 is fully disclosed in copending application Serial No. 622,042, filed November l4, 1956, entitled End Mounting of a Current Limiting Device Associated With a Circuit Breaker, in the name of William Harold Edmunds and assigned to the assignee of the present invention, now issued as U.S. Patent Number 2,924,688 on February 9, 1960.

More specifically, FIGURE 1 shows a circuit interrupter comprised of a circuit breaker portion and a current limiting portion 11 which is mechanically and electrically associated with the circuit breaker portion 10. It is to be noted that FIGURE 1 illustrates a side cross-sectional view of only one phase of an interrupting unit which could be a multiphase unit. The circuit breaker portion 10 is comprised of a molded housing 12 which has a stationary contact 13 connected to a disconnect terminal 14 which is adapted to plug into a cooperating disconnect of a panel board (not shown). A movable contact 15 is movable into and out of engagement with respect to stationary contact 13 under the influence of an operating mechanism generally shown as operating mechanism 16. The operating mechanism 16 may be operated either automatically in a manner to be described hereinafter or manually under the influence of a manually operating handle 17 which protrudes through an opening in the cover of molded case housing 12. For details of operation of this mechanism, refer-.

ence is made, for example, to U.S. Patent No. 2,574,093, issued November 6, 1951, entitled Adjustable Trip," in the name of William Harold Edmunds and assigned to the assignee of the present invention.

The circuit breaker operating mechanism 16 is normally spring biased to an open position and is held engaged through a latch means (not shown) including trip link 18 which is normally latched by latch member 19 carried in trip unit housing 20. Latch member 19 is carried on a tripper bar 21 which is pivotally mounted at pivot 22. To operate the circuit breaker to a disengaged position, it will be apparent that a counter-clockwise rotation of tripper bar 21 will release trip link 18 to permit automatic circuit breaker operation.

Tripper bar 21 is operable by any one of several automatic trip means. The first of these is a magnetic trip means which includes pivotally mounted armature 23 which cooperates with a solenoid formed by winding 24 which is in series with the circuit breaker current path and a magnetic core 25. Upon the occurrence of a fault above some predetermined magnitude, winding 24 will magnetize core 25 to such an extent that armature 23 will be attracted thereto and thus engage plunger 26 which extends through core 25. Plunger 26 is terminated by an extending member 27 which is preferably of nonmagnetic material. Member 27 is movable into engagement with extension 28 which is connected to tripper bar 21 in any desired manner whereby operation of armature 23 and plunger 26 will cause a rotation of extension 28 and thus drive the tripper bar 21 in a counter-clockwise rotation to trip the circuit breaker.

A further manner in which the circuit breaker may be tripped is through a current limiting fuse system which includes current limiting fuse 2911 which is connected in series with circuit breaker contacts. Since this operation is fully described in the above noted copending application Serial No. 622,042, it will not be more fully described hereinafter, it being sulficient to understand that the operation current limiting fuse 29a will permit a striker pin 30 to be ejected therefrom and into engagement with the upper portion of auxiliary tripper bar 31 which is pivotally mounted at pivot 32. This' will cause a rotation of auxiliary tripper bar 31 in a clockwise direction whereby rod 33 is permitted to move to the left under the influence of its biasing spring 34. An upper extension 29 is connected to tripper bar 21 and this upper extension is carried within a slot 35 of rod 33. Therefore, upon operation of fuse 29a, tripper bar 31 will be rotated counter-clockwise to again cause tripping of the circuit breaker.

The third automatic trip unit for the system and the trip unit to which the invention is directed is the overload trip which includes indirectly heated bimetal 36 mounted with respect to its U-shaped heater 37. Heater 37 is electrically connected in series with the circuit breaker contacts 13 and 15 and the electrical circuit through the combination circuit interrupter. More specifically, the complete circuit extends from disconnect contact 14, stationary contact 13 and movable contact 15 heretofore described. The movable contact 15 is electrically connected to conductor 38 over the pigtail 39. The opposite end of conductor 38 is then electrically connected to heater 37 and the opposite end of heater 37 is connected to one end of winding 24 through conductor 40. The opposite end of winding 24 is connected to disconnect terminal 41 over conductor 42 and disconnect terminal 42a of fuse 29a. The other plug-in terminal 43 of fuse 29a is then connected to disconnect 44 which, in turn, is electrically connected to the main circuit interrupter disconnect 45 which is connectible to the other terminal of the circuit breaker panel-board previously mentioned in connection with terminal 14. For further details of this construction, reference is again made to copending application Serial No. 622,042.

Under overload conditions, the heater 37 will heat sufficiently to cause bimetal 36 to deflect to the left until it engages adjustable screw 46 whereby continued motion of bimetal 36 will cause extension 29 which carries screw 46 to be moved to the left and thus rotate tripper bar 21 in the trip direction.

In accordance with the present invention, a heat sink 47 is connected to the bend in U-shaped heater 37 whereby the thermal strength of the heater is increased at this critical area.

This construction is best seen in FIGURE 2 wherein the U-shaped bend 48 of heater 37 is more clearly shown. The bimetal heater 37 is generally designed to provide a maximum of heat transfer to the bimetal 36. The bimetal 36 is, therefore, supported directly at the foot of heater 37 along the surface 49 as by spot-welding so that the heat of the heater will enter the bimetal at this portion by conduction. Radiant heat is also added to the bimetal by providing a very small space 50 between the freely movable portion 36 and on the heater legs.

As will be apparent from the circuit breaker construction of FIGURE 1, in order to conserve trip unit space, the heater must return on itself and in so doing makes a sharp bend 48. This bend 48 of the heater is normally the weakest part of the heater for several reasons. First, the metal will often have a reduced cross-section at the bend to permit the bend to be made more easily. Next, under comparatively light overload current conditions, the current will tend to have a greater current density toward the interior of the bend so that fusing begins at this portion and moves progressively outward. Finally, for comparatively high overloads or short circuits, there will be substantial magnetic blow-off forces exerted on the bend because the two conductor portions forming the legs of the U carry currents in opposite directions. Thus, as the heater weakens with increased temperatures, the magnetic forces may become strong enough to rupture the heater at the U-shaped bend.

In order to prevent the substantial increase in temperature at the U-shape bend, we provide a heat sink 47 at the bend which will operate to rapidly absorb heat under any of the above noted overload conditions. Member 47 is a material which could be copper and is characterized in having a relatively high heat conductivity and may be brazed or silver soldered to U-shape bend 48.

Clearly, the heat sink 47 may take many various forms. One such form is illustrated in FIGURES 3 and 4 which is identical to FIGURE 2 with the exception of the heat sink construction. In FIGURES 3 and 4, however, the heat sink is formed of a conductive pin 51 which is supported or cradled in the U-shaped bend by bending it for slightly more than 180.

As best seen in FIGURE 4, endwise dislodging of pin 51 may be achieved by staking the heater material of heater 37 at staked portions 52 and 53. The pin 51 can additionally be silver soldered and brazed in place to give a maximum of heat conduction in the critical area while the heater wrap of greater than and staked portions 52 and 53 will confine the pin while the soldering is in a molten stage.

While FIGURE 4 shows that pin 51 may be axially retained by stake portions 52 and 53, it will be clear to those skilled in the art that pin 51 may be staked in any desired manner. For example, the staking may comprise of the peening over of a portion of the material of pin 51 with respect to heater 37.

In the foregoing, we have described our invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of our invention within the scope of the description herein are obvious. Accordingly, we prefer to be bound not by the specific disclosure herein but only by the appending claims.

We claim:

1. A heater for an indirectly heated bimetal; said heater being formed of a substantially U-shaped member having elongated legs joined at a bent portion; said legs having confronting surfaces whose widths are materially greater than the thicknesses of said legs; one of said legs having said bimetal directly connected thereto; said bimetal being an elongated member extending substantially parallel to said leg having said bimetal connected thereto; said bimetal being deflected away from said last mentioned leg at least partially due to heat caused by the flow of electrical current through said substantially U-shaped heater; a heat conductive member; said heat conductive member being connected to said bent portion of said heater and serving as a heat sink for said heater.

2. A heater for an indirectly heated bimetal; said heater being formed of a substantially U-shaped member having elongated legs joined at a bent portion; said legs having confronting surfaces whose widths are materially greater than the thicknesses of said legs; one of said legs having said bimetal directly connected thereto; said bimetal being an elongated member extending substantially parallel to said leg having said bimetal connected thereto; said bimetal being deflected away from said last mentioned leg at least partially due to heat caused by the flow of electrical current through said substantially U-shaped heater; a heat conductive member; said heat conductive member being connected to said bent portion of said heater and sewing as a heat sink for said heater; said conductive member being comprised of a pin; said pin being directly connected to said heater at the interior of said bent portion.

3. A heater for an indirectly heated bimetal; said heater being formed of a substantially U-shaped member having elongated legs joined at a bent portion; said legs having confronting surfaces whose widths are materially greater than the thicknesses of said legs; one of said legs having said bimetal directly connected thereto; said bimetal being an elongated member extending substantially parallel to said leg having said bimetal connected thereto; said bimetal being deflected away from said last mentioned leg at least partially due to heat caused by the flow of electrical current through said substantially U-shaped heater; a heat conductive member; said heat conductive member being connected to said bent portion of said heater and serving as a heat sink for said heater; said conductive member being comprised of a pin; said pin being directly connected to said heater at the interior of said bent portion; said bent portion bending for greater than 180 to substantially retain said pin; and stake means for retaining said pin within said bent portion in an axial direction of said pin.

4. In a .circuit breaker; said circuit breaker including a pair of cooperable contacts movable into and out of engagement with respect to one another and an operating mechanism for controlling said movement of said contacts; an automatic trip means operatively connected to said operating mechanism for automatically operating said contacts from said engaged position to said disengaged position; said trip mechanism including an indirectly heated bimetal and a heater associated therewith; said heater being comprised of elongated U-shape member electrically connected in series with said cooperable contacts; said bimetal being directly connected to one leg of said U-shaped heater and extending substantially parallel with said last mentioned leg of said heater; said U-shaped heater having another leg; said legs having confronting surfaces whose widths are materially greater than the thicknesses of said legs; said U-shape of said heater being defined by a bent portion; a heat conduction member; said heat conduction member being directly connected to said bent portion and defining a heat sink for said bent portion.

5. In a circuit breaker; said circuit breaker including a pair of cooperable contacts movable into and out of engagement with respect to one another and an operating mechanism for controlling said movement of said contacts; an automatic trip means operatively connected to said operating mechanism for automatically operating said contacts from said engaged position to said disengaged position; said trip mechanism including an indirectly heated bimetal and a heater associated therewith; said heater being comprised of elongated U-shape member electrically connected in series with said cooperable contacts; said bimetal being directly connected to one leg of said Ushaped heater and extending substantially parallel with said last mentioned leg of said heater; said U-shaped heater having another leg; said legs having confronting surfaces whose widths are materially greater than the thicknesses of said legs; said U-shape of said heater being defined by a bent portion; a heat conduction member; said heat conduction member being directly connected to said bent portion and defining a heat sink for said bent portion; said conductive member being comprised of a pin carried within said bent portion.

6. In a circuit breaker; said circuit breaker including a pair of cooperable contacts movable into and out of engagement with respect to one another and an operating mechanism for controlling said movement of said contacts; an automatic trip means operatively connected to said operating mechanism for automatically operating said contacts from said engaged position to said disengaged position; said trip mechanism including an indirectly heated bimetal and a heater associated therewith; said heater being comprised of elongated U-shape member electrically connected in series with said cooperable contacts; said bimetal being directly connected to one leg of said U-shaped heater and extending substantially parallel with said last mentioned leg of said heater; said U-shaped heater having another leg; said legs having con fronting surfaces whose widths are materially greater than the thicknesses of said legs; said U-shape of said heater being defined by a bent portion; a heat conduction member; said heat conduction member being directly connected to said bent portion and defining a heat sink for said bent portion; said conductive member being comprised of a pin carried within said bent portion; said bent portion being bent for greater than said pin being retained within said bent portion by virtue of said greater than 180 bend; said bent portion further including a stake means for retaining said pin in an axial direction.

References Cited in the file of this patent UNITED STATES PATENTS 448,879 Dewey Mar. 24, 1891 1,976,781 Graves Oct. 16, 1934 2,088,420 Koch July 27, 1937 2,697,148 Slebodnik Dec. 14, 1954 2,796,507 Young June 18, 1957 2,866,039 Epstein Dec. 23, 1958

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