MXPA99007621A - Reverse deflection prevention arrangement for a bimetal in a circuit breaker - Google Patents

Abstract

A reverse deflection prevention arrangement is provided for use in a circuit breaker for preventing a bimetal from bending in a direction opposite its normal thermal deflection. The reverse deflection prevention arrangement includes a tab portion extending from a yoke and a corresponding block member disposed on the inside surface of a circuit breaker cover. The tab portion engages the block member when the bimetal is forced to deflect in the direction opposite its normal deflection. An alternate embodiment of the reverse deflection prevention arrangement includes a reinforcement member secured to one end of the bimetal. The reinforcement member strengthens and supports the bimetal so that it is prevented from bending in the direction opposite its normal thermal deflection.

Description

ARRANGEMENT FOR PREVENTION OF REVERSAL DEFLEXION FOR A BIMETAL IN A CIRCUIT CIRCUIT BREAKER Field of the Invention The present invention relates generally to circuit breakers and, more particularly, relates to an arrangement that prevents reverse deflection for a bimetal at a circuit breaker. # Background of the Invention The use of circuit breakers is widespread in current residential, commercial and industrial electrical systems, and constitutes an indispensable component of such systems to provide protection against overcurrent conditions. Various circuit breaker mechanisms have been developed Circuit breaker, and have been refined over time based on factors specific to the application such as current capacity, response time, and the desired type of reset function (manual or remote) of the circuit breaker. . One type of circuit breaker mechanism employs a thermo-magnetic trip device to "trip" a latch in response to a specific range of overcurrent conditions. The trigger action is caused by a deflection Significant in a bimetal element that responds to changes in temperature due to resistance heating caused by the flow of electrical current through the bimetal. The bimetal element is typically in the form of a blade and operates in conjunction with a bolt, so that the blade deflection releases the bolt after a time delay corresponding to a predetermined overcurrent threshold in order to "break" "the current circuit associated with it. Additionally, circuit breaker mechanisms of this type often include an electromagnetic array that includes a yoke and armature that are attracted to each other to release the bolt in the presence of an extremely high current or short circuit condition. Occasionally, the bimetals used in this type of circuit breaker would be overheated and would deviate in the direction of their normal thermal deflection to a position where they become permanently deformed and do not undergo deflection back to their original shape. To overcome this problem, a stop member was placed at the base of the circuit breaker to prevent the bimetals from deflecting in the direction of their normal thermal deflection to a position beyond the point where they deform permanently. However, there is a problem in some circuit breakers during extremely high current short circuit tests. During these tests, the high magnetic forces of repulsion cause the bimetal to be repelled away from a current carrying terminal and biased in a direction opposite its normal thermal deflection, or inverse deflection. This inverse deflection causes the bimetal to be permanently deformed, which renders the circuit breaker inoperative because the bimetal can no longer deviate the distance required to release the bolt. There is an additional problem in circuit breakers that operate at ambient temperatures below room temperature, or 24 ° C. When the room temperature ^^ falls below 24 ° C, the bimetal deviates in the direction? opposite to its normal thermal deflection. If the ambient temperature falls sufficiently below 24 ° C, the bolt may not be released in the presence of a short circuit condition. Consequently, there is a well-defined need for an improved circuit breaker that avoids the aforementioned limitations. In accordance with the present invention, a novel reverse deflection prevention arrangement is provided to prevent the bimetal from deviating in the opposite direction to its normal thermal deflection. 0 Compendium of the Invention One objective of the present invention is to provide an arrangement for a Circuit breaker that minimizes the magnitude of the reverse deflection that forces the bimetal to suffer during interruption tests of high short circuit current. The above objective is achieved by providing a single reverse deflection prevention arrangement for use in a circuit breaker to prevent a bimetal from bending in the opposite direction to its normal thermal deflection. The reverse deflection prevention arrangement includes a tongue portion extending from a yoke and a corresponding block member disposed on the inner surface of a circuit breaker cover. The tab portion links the block member when the bimetal is forced to deflect in a direction opposite its normal deflection. According to another embodiment of the present invention, the reverse deflection prevention arrangement includes a reinforcing member secured to one end of the bimetal. The reinforcing member strengthens and holds the bimetal so that it is prevented from bending in the opposite direction to its normal thermal deflection. BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the present invention will become apparent upon reading the following detailed description and with reference to the drawings, in which: Figure 1 is a perspective view of a circuit breaker including an arrangement of Yoke cap embodying the present invention; Figure 2 is a side view of the circuit breaker shown in Figure 1; Figure 3 is a perspective view of a cover embodying the present invention and that may be used in the circuit breaker of Figure 1; Figure 4 is a perspective view of a bimetal terminal assembly embodying the present invention and that can be used in the circuit breaker of Figure 1; Figure 5 is a side view of the bimetal terminal assembly shown in Figure 4; Fig. 6 is a perspective view of a bimetal terminal set f incorporating another embodiment of the present invention and which can be used in the circuit breaker of Fig. 1; and Figure 7 is a side view of the bimetal terminal assembly shown in Figure 6. Although the invention is susceptible to various modifications and alternative forms, a specific embodiment thereof has been shown as an example in the drawings. drawings and will be described in detail. However, it will be understood that it is not intended to limit the invention to the particular form described. On the contrary, the intention is to cover or all the modifications, equivalents and alternatives that fall within the spirit and scope of the invention, as defined by the appended claims. Description of Preferred Embodiment Forms Turning now to the drawings, Figures 1 and 3 illustrate a circuit breaker having a novel reverse deflection prevention arrangement embodying the principles of the present invention to prevent a bimetal from bending over. the direction opposite to its normal thermal deflection. The reverse deflection prevention arrangement will be described in more detail below by following a brief description of the overall operation of the exemplary circuit breaker. As shown in Figures 1 and 2, the circuit breaker includes a base 12 and a corresponding cover 14.

^^ Base 12 carries all the internal components of the circuit breaker LU circuit. The current path through the circuit breaker starts at a line terminal 16, and from the line terminal 16 the current path passes through a flexible pig tail 18. The flexible pig tail 18 is attached to a secondary blade 20 having a movable contact 22 (shown in Figure 2), which couples with a stationary contact 24. The current flows through the movable and stationary contacts 22, 24 to a middle terminal 26, which is configured in an S-shape. The other side of the middle terminal 26 includes another stationary contact 28 connected to the same. Opposite to the stationary contact 28 is an even moveable contact 30 (shown in Figure 2) attached to a primary blade 32. Current flows through the stationary and movable contacts 28, 30, through the first blade 32, and towards one end of a primary flexible connector 5 or pigtail 34 (shown in Figure 2). The other end of the flexible primary connector 34 is attached to a bimetal 36, which provides the thermal trip characteristics for the circuit breaker. Finally, the current flows from the bimetal 36 through a load terminal 38 and out of the load end of the circuit breaker. The circuit breaker also includes a trigger lever 42, a handle 44, a magnetic armature 46 (shown in Figure 2), a primary arc stack 48 and a yoke 50.

^^ These components are used to implement the manual operation IU on / off, thermal trip separation and electromagnetic trip separation of the primary contacts 28 and 30. For additional information regarding the overall construction and operation of the circuit breaker shown in Figure 1, reference may be made to circuit breakers having similar construction, which are disclosed in U.S. Patent Nos. 5,680,081; 5,430,419; 5,498,847; and 5,428,328, assigned to the assignee hereof and incorporated herein by reference. 0 The normal operation of turning on and off the primary blade 32 occurs in response to the rotation of the handle 44 in a clockwise or counterclockwise movement. In response to the rotation of the handle 44 in either direction, the first blade 32 and 5 is to open or close the circuit via the movable primary contact 30 and the stationary primary contact 28. The illustrated circuit breaker utilizes magnetic firing protection characteristics and conventional thermal to interrupt overload and short-circuit current conditions. The circuit breaker is ready to be triggered when the trigger lever 42 is linked or closed in an opening (not shown) in the armature 46. In response to a predetermined short circuit current flowing through the bimetal 36, the armature The magnet 46 is brought to a predetermined distance to the yoke 50. This allows the trigger lever 42 to disengage from the magnetic armature 46 and rotate clockwise, which in turn allows the primary blade 32 to rotate. counterclockwise to the triggered position. This results in the primary blade contact 30 separating from the stationary contact 28 and interrupting the flow of current, the bimetal member 36 being heated and biased in the counterclockwise direction to allow the trigger lever 42 dissociates from the magnetic armature 46, followed by the same sequence of events discussed above, resulting in the primary blade contact 30 separating from the stationary contact 28. Related trigger arrangements are shown in US Pat. Nos. 2,902,560; 3,098,136; 4,616,199; 4,616,200; and 5,245,302, each of which was assigned to the assignee of the present and is incorporated herein by reference. Figures 4 and 5 illustrate a more detailed view of a bimetal terminal assembly that includes the yoke 50, the bimetal 36 and the loading terminal 38. The bimetal 36 is welded to the line terminal and the yoke 50 is welded to the bimetal 36. To be certified by Under riters Laboratories Inc., circuit breakers must undergo and pass several tests. One of these tests requires the circuit breaker to interrupt a very high short circuit current condition and then be able to operate normally by interrupting the normal overload current conditions later. As illustrated in Figures 5 and 7, the current flows through the bimetal 36 and the charging terminal 38 in the direction of the arrows I. The current flows through the bimetal 36 and the charging terminal 38 in opposite directions, thereby forming a magnetic repulsion force Fm between the bimetal and the charging terminal due to electromagnetic forces oppositely disposed therein. Under normal operating conditions, the magnetic repulsion force Fm does not cause a problem. However, when the current in the current path approaches the levels existing during extremely high short-circuit current tests, the magnetic repulsion force Fm causes the bimetal to bend in the clockwise direction, the opposite direction of its normal thermal deflection, or inverse deflection. Bimetals are designed so that they undergo deflection in a normal direction of thermal deflection in response to the heat generated by the current flowing through them and return to their original form once the heat dissipates. The bimetals can bend, a short distance, in the opposite direction to their normal thermal deflection without being damaged; however, if they are bent beyond a predetermined deformation point, they will not return to their original shape. Due to the aforementioned extremely high short circuit current tests, the magnetic repulsion force Fm causes the bimetal to bend beyond its deformation point, thus permanently deforming the bimetal and rendering the circuit breaker inoperative. . This problem is solved by means of the novel reverse deflection prevention arrangement, by which the bimetal is prevented from bending beyond its point of deformation. Figures 3, 4 and 5 show a preferred embodiment of the reverse deflection prevention arrangement. As shown, the reverse deflection prevention arrangement is provided including a block member 52 (FIG. 3) molded into the interior of the cover 14 and a tongue portion 54 (Figures 4 and 5) extending from the yoke 50. The block member 52 and the tongue portion 54 are correspondingly positioned so that the tongue portion cooperatively engages the block member when the magnetic force of repulsion Fm attempts to bend bimetal 36 in the opposite direction to its direction of normal thermal deflection. In this way, the bimetal is prevented from deforming permanently during extremely high short circuit current conditions. This novel reverse deflection prevention arrangement also provides the advantage of allowing the circuit breaker to ^^ circuit operates more efficiently when the temperatures of circuit breaker operation are below ambient temperature, or 24 ° C. In a traditional circuit breaker, when the operating temperature falls below 24 ° C, the bimetal undergoes deflection in the opposite direction to its normal thermal deflection. As the operating temperature is further reduces below 24 ° C, the bimetal can m possibly deflect to a position that causes the trigger lever to be positioned too far towards the armature. In this position, it is difficult for the firing lever to disengage from the armor during short-circuit conditions. As stated before, the reverse deflection prevention arrangement of the present invention prevents the bimetal from bending in the opposite direction to its normal thermal deflection. For example, when the operating temperature falls below 24 ° C and the bimetal 36 tries to undergo deflection in the direction As opposed to its normal thermal deflection, the tongue portion 54 links the block member 52 to prevent further reverse bending. In this way, keeping the firing lever 42 in the correct position of engagement with the magnetic armature 46, thereby allowing the firing lever to disengage from the magnetic armature during a short circuit condition. Figures 6 and 7 show a bimetal terminal assembly incorporating an alternate solution to prevent the bimetal from bending in the opposite direction to its normal thermal deflection. This alternate embodiment of the reverse deflection prevention arrangement of the present invention prevents the bimetal from deflecting in the opposite direction to its normal thermal deflection; however, it is not as effective as the preferred embodiment previously described. The reverse deflection prevention arrangement of the alternate embodiment of the present invention is shown having a reinforcing member or plate 56 welded to the bimetal 36. The plate 54 is located at the end of the bimetal 56 where it is bent in response to the magnetic force of repulsion Fm. In this place, the plate 56 reinforces and supports the bimetal, thereby preventing it from bending in the opposite direction to its normal thermal deflection so that it can withstand the magnetic force of repulsion Fm without becoming permanently deformed. Additionally, plate 56 holds the bimetal to prevent it from bending in the opposite direction to its normal thermal deflection when the operating temperature falls below 24 ° C.

Those skilled in the art will readily recognize that various changes and modifications may be made to the present invention, without departing from the true spirit and scope thereof, which are set forth in the following claims. For example, the tab portion may be disposed over the bimetal instead of the yoke and the block member may be located on the base instead of the cover.

Claims (9)

1. CLAIMS 1. A circuit breaker that has a bimetal to initiate the interruption of a current path, where certain electromagnetic forces can cause the bimetal to suffer deflection in a direction opposite to its normal thermal deflection, the circuit breaker comprising: a base; a cover arranged on the base; a yoke arranged on the bimetal; and reverse deflection preventing means for preventing the bimetal from deflecting in the opposite direction to its normal thermal deflection when the electromagnetic forces force the bimetal to undergo deflection in the opposite direction to its normal thermal deflection. The circuit breaker according to claim 1, wherein the reverse deflection preventing means includes: a stop member formed on the cover; and a tongue member extending from the yoke, cooperatively corresponding to the stop member, the tongue member engageable with the stop member to prevent the bimetal from deflecting in the opposite direction to its normal thermal deflection. The circuit breaker according to claim 1, wherein the reverse deflection preventing means includes a reinforcing member secured to the bimetal. 4. An inverse deflection prevention arrangement for preventing a bimetal from bending in a direction opposite its normal thermal deflection in a circuit breaker having a cover disposed in a base and a yoke secured to the bimetal, the prevention arrangement of reverse deflection comprising: a stop member formed in the cover; and ^^ a tongue member extending from the yoke, Corresponding cooperatively to the stop member, the tongue member engageable with the stop member when the magnetic forces of repulsion force the bimetal to undergo deflection in the opposite direction to its normal thermal deflection direction to prevent the bimetal from deflecting in the address 15 opposite its normal deflection direction. ^ A 5. A circuit breaker, comprising: a base and a cover; a stationary contact disposed in the base; a blade disposed at the base; 20 a movable contact disposed in the blade and movable and in and out of engagement with the stationary contact; a release lever capable of releasably closing, mounted on the base and releasable from a closed position for movement to a fired position to effect the separation of the stationary and movable contacts; a bimetal disposed in the base to cause release of the firing lever from the closed position, the bimetal having a normal direction of thermal deflection and an opposite direction of thermal deflection; a yoke secured to the bimetal; and reverse deflection preventing means for preventing the bimetal from bending in a direction opposite to its normal thermal deflection. The circuit breaker according to claim 5, wherein the reverse deflection prevention means includes: a stop member formed in the cover; and a tongue member extending from the yoke, cooperatively corresponding to the stop member, the tongue member engageable with the stop member to prevent the bimetal from deflecting in the opposite direction to its normal thermal deflection. The circuit breaker according to claim 5, wherein the reverse deflection preventing means includes a reinforcing member secured to the bimetal to reinforce the bimetal, thereby preventing the bimetal from being biased in a direction opposite to its bimetal direction. Normal thermal deflection in response to a repulsive force generated between the load terminal and the bimetal. 8. A circuit breaker having a base and a cover, the base carrying a line terminal and a load terminal that are electrically connected through an electrical circuit extending between them, the circuit breaker comprising: a first Contact; a second contact; a blade that carries the second contact and movable between (i) a first position where the second contact is linked to the first contact and corresponding to a closed electrical circuit condition between the line terminal and the load terminal and (ii) a second position where the second contact is remote from the first contact and corresponding to an open electrical circuit condition where said electrical circuit is not completed between the line terminal and the charging terminal; means responsive to the current, including an armature and a bimetal and yoke assembly for detecting a predetermined over-current or short-circuit condition in the electrical circuit and for moving the armature a predetermined distance in response thereto; trigger means associated with the means responsive to the current to move the contact carrier from the first to the second position in response to movement of the armature a predetermined distance; and an inverse deflection prevention arrangement for requesting that the bimetal suffer deflection in a direction opposite to its normal thermal deflection in response to a magnetic repulsion force generated between the load terminal and the bimetal, the inverse deflection prevention arrangement including: a stop member formed in the cover; and a tongue member extending from the yoke, cooperatively corresponding to the stop member, the tongue member engageable with the stop member for ^^ prevent the bimetal from suffering deflection in the opposite direction to 10 its normal deflection direction. 9. A circuit breaker that has a base and a cover, the base carrying a line terminal and a load terminal that are electrically connected through an electrical circuit that extends between them, the circuit breaker 15 circuit comprising: B a first contact; a second contact - a blade that carries the second contact and movable between (i) a first position where the second contact is linked to the first contact and corresponding to a closed electrical circuit condition between the line terminal and the charging terminal and (ii) a second position where the second contact is remote from the first contact and corresponding to an open electrical circuit condition where said electrical circuit is not completed between the line terminal and the load terminal; current-responsive means including an armature and a bimetal and yoke assembly for detecting a predetermined over-current or short-circuit condition in the electrical circuit and for moving the armature a predetermined distance in response to it; trigger means associated with the means responsive to the current to move the contact carrier from the first to the second position in response to the movement of the armature the predetermined distance; and a reinforcing member secured to the bimetal to prevent the bimetal from deflecting in a direction opposite to its normal thermal deflection in response to a magnetic repulsion force generated between the load terminal and the bimetal.