MXPA97001449A - Arc resistant shield to protect a mobile contact carrier from a circu circuit breaker - Google Patents

Abstract

The present invention relates to an electrical interrupting device that includes a stationary contact carrier having a stationary contact mounted thereon, a contact carrier assembly comprising a movable contact carrier and an arc-resistant protective shield. The movable contact carrier has a movable contact mounted thereon. The movable contact carrier is movable between a closed position and an open position. The movable contact abuts the stationary contact while the movable contact carrier is in the closed position, and the movable contact is separated from the stationary contact while the movable contact carrier is in the open position. The arc-resistant protective shield is mounted on the movable contact carrier and surrounds the movable contact. The shield protects the movable contact carrier from the electric arcs generated during the circuit interruption.

Description

ARC RESISTANT SHIELD TO PROTECT A MOBILE CONTACT CARRIER OF A CIRCUIT CIRCUIT BREAKER Field of the Invention The present invention relates generally to miniature circuit breakers and, more particularly, to a lv. • arc-resistant shielding to protect a movable contact carrier from a miniature circuit breaker from the arcs generated during circuit interruption. Background of the Invention Miniature circuit breakers are used commonly to provide automatic circuit interruption upon detection of undesirable overcurrent conditions in the circuit being monitored. These overcurrent conditions include, among others, overload conditions, ground faults and short circuit conditions. 20 Miniature circuit breakers typically include an electrical contact mounted on a movable contact carrier that rotates away from a stationary contact in order to interrupt the current path. The contact carrier is pivotally mounted in a rotating blade housing 5 and a spring is used to polarize the movable contact toward the stationary contact during normal current conditions. The type of overcurrent condition dictates how quickly the contact carrier should rotate away from the stationary contact. For example, in response to overcurrent conditions at relatively low magnitudes but present for a long period of time, the circuit breakers generally employ a firing mechanism to rotate the blade housing carrying the contact carrier. As the contact carrier rotates with the blade housing, the contact on the movable contact carrier is forced away from the stationary contact. In response to overcurrent conditions at relatively high magnitudes, the circuit breakers must break (or open by blasting) the current path very quickly, reacting much more quickly than the reaction time for the trip mechanism. In this case, the contact carrier rotates to an open position before actuating the trigger mechanism. When the electrical contact in the movable contact carrier separates the stationary contact in response to an overcurrent condition, undesirable arc energy develops between the separating contacts, due to its voltage differential. This arc energy can be characterized as a discharge of electricity through a gas, where the voltage differential between the separating contacts is approximately equal to the ionization potential of the gas. The arc energy is undesirable because it has a tendency to flow back or collapse back into the free space separating the contacts, thereby exposing the movable contact carrier to the arc energy. The movable contact carrier can be eroded, melted or vaporized when exposed to arc energy without some type of protective device. If the movable contact carrier is damaged insofar as there is an excessive reduction in its cross-sectional area, the movable contact carrier may be unable to properly interrupt the circuit in response to an overcurrent condition. Accordingly, there is a need for a contact carrier assembly designed to protect the movable contact carrier from a miniature circuit breaker of an arc energy generated during a circuit interruption. SUMMARY OF THE INVENTION In an electrical interrupting device that includes a stationary contact carrier having a stationary contact mounted thereon, a contact carrier assembly comprises a movable contact carrier and an arc-resistant protective shield. The movable contact carrier has a movable contact mounted thereon. The movable contact carrier is movable between a closed position and an open position. The movable contact abuts the stationary contact while the movable contact carrier is in the closed position, and the movable contact is separated from the stationary contact while the movable contact carrier is in the open position. The arc-resistant protective shield is mounted on the movable contact carrier and surrounds the movable contact. The foregoing compendium of the present invention is not intended to represent each embodiment, or each aspect, of the present invention. This is the purpose of the figures and the detailed description that follows. BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the invention will be apparent upon reading the following detailed description and with reference to the drawings, in which: Figure 1 is an isometric view of a circuit breaker embodying the present invention; Figure 2 is a top view of the circuit breaker of Figure 1; Figure 3 is a top view of a contact carrier portion of the circuit breaker of Figure 2, showing the movable contact carrier in a closed (active) position; Figure 4 is a top view of the contact carrier portion of the circuit breaker of Figure 2, showing the movable contact carrier in an open position (inactive / triggered); Figure 5a is a top view of the movable contact carrier with a protective shield mounted thereon; Figure 5b is a top view of the movable contact carrier with a modified protective shield mounted thereon; and Figure 5c is a front view of a contact mounting section of the movable contact carrier of Figures 5a and 5b. Although the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings, and will be described in detail. However, it should be understood that it is not intended to limit the invention to the particular form described. On the contrary, the intention is to cover all the modifications, equivalents and alternatives that fall within the spirit and scope of the invention, as defined by the appended claims. Detailed Description of the Preferred Embodiment Turning now to the drawings, Figures 1 and 2 illustrate a circuit breaker 10 designed to protect its components from the arc energy generated during a circuit interruption. The circuit breaker 10 comprises a trip mechanism, a stationary contact carrier 12, a movable contact carrier 14, an exhaust vent 16, an arc runner 18, and an arc-extinguishing barrier 20. The contact carrier Stationary 12 has a stationary contact 22 mounted thereon, and the movable contact carrier 14 has a movable contact 24 mounted thereon. In response to a magnetic or thermal type overcurrent condition, the trigger mechanism causes the movable contact carrier 14 to rotate from a closed position (FIG. 3) to an open position (FIG. 4), thereby generating an electric arc. In the closed position (figure 3), the movable contact 24 abuts on the stationary contact 22 and, in the open position (figure 4) the movable contact 24 is separated from the stationary contact 22. The current path through the circuit breaker 10 extends from a line terminal formed by the stationary contact carrier 12 to a charging terminal 26. Current flows from the line terminal to the movable contact carrier 14 via stationary and movable contacts 22 and 24. From the carrier of Movable contact 14, a flexible conductor (or pigtail) 27 connects the current path to a bi-metal 28, which in turn is conductively connected to the charging terminal 26. The current flows out of the charging end of the circuit breaker via a terminal block of the loading terminal 26. As the construction and operation of the firing mechanism are quite conventional, they are not described in detail herein. Suffice it to say that the circuit breaker is of the thermal / magnetic type. In a magnetic trip, the trip mechanism operates in response to the flow of current through the circuit breaker, reaching a specified level. The high current level causes a large magnetic flux field around a yoke 30 to bring a magnetic armature 31 toward the yoke 30. The magnetically moved armature 31 rotates counterclockwise about an armature pivot 32 In response to the rotation of the armature 31 counterclockwise, a trigger lever 33 is released from its engagement within a closing window (not shown) formed by the armature 31. The release of the lever trigger 33 allows a tension spring 34 to rotate trigger lever 33 clockwise around a trigger lever post 35. One end of tension spring 34 is connected to a trigger lever hook 36, while the other end of the tension spring 34 is connected to a carrier hook 37. By turning the trigger lever 33 and its hook 36 clockwise around the post of trigger lever 35, the tension spring 34 rotates clockwise around the carrier hook 37. The rotation of the tension spring 34 beyond its position on the center causes the movable contact carrier 14 to rotate in the counter-clockwise direction. from the clock to the open position (figure 4). The position on the center of the tension spring 34 is defined by a line extending between the carrier hook 37 and a post 38 of a handle 39. When the movable contact carrier 14 is turned to the open position, the handle 39 is rotated in the clockwise direction around its post 38 to a displaced position by virtue of the engagement of the leg 40 of the contact carrier with a recess or notch 41 formed by the handle 39. In a thermal trip, the trigger mechanism operates in response to the current in the circuit breaker that reaches a predetermined percentage (eg, 135%) of the rated current for a period of time that will be determined by the unit's calibration. This high level of current causes direct heating of the bi-metal 28, which results in the bending of the bi-metal 28. The bi-metal 28 is composed of two dissimilar thermostatic materials, which are laminated or bonded together and which they expand at different rates due to increases in temperature, thereby causing the bi-metal 38 to bend. When the thermal type overcurrent condition occurs, the bi-metal 28 is heated and flexed in the opposite direction to the clock hands around its connection 42 to the loading terminal 26. As both the yoke 30 and the armature 31 are connected to the bi-metal 28, the yoke 30 and the armature 31 are carried with the bi-metal 28 which is folded . This causes the armature 31 to release its engagement from the firing lever 33. As described above with respect to the magnetic firing, the release of the firing lever 33 allows the tension spring 34 to travel beyond its position above the center, thereby to rotate the movable contact carrier 14 counterclockwise to the open position (figure 4). Figures 3 and 4 are enlarged top views of the contact carrier portion of the circuit breaker of Figures 1 and 2. Figure 3 shows the movable contact carrier 14 in its closed position, while Figure 4 sketches the carrier of movable contact 14 in its open position after a magnetic or thermal trip. The arc runner 18, the arc extinguishing barrier 20, and a protective shield 40 are constructed and arranged to protect the components of the circuit breaker from the dangerous arcs generated during circuit interruptions. The L-shaped arc runner 18 includes a pair of flattened legs 18a and 18b arranged perpendicular to each other. The leg 18a is generally parallel and adjacent to the stationary contact 22 and preferably is in contact with a stationary contact mounting surface 12a of the stationary contact carrier 12. If desired, the leg 18a can be attached to the stationary contact carrier 12. by means such as welding. The leg 18b is generally perpendicular to the stationary contact 22 and is generally parallel to a section 14a of the movable contact carrier 14. When the movable contact carrier 14 is in the closed position (figure 3), the legs 18a and 18b are generally parallel to a movable contact mounting section 14b and section 14a, respectively. With respect to the tension spring 34, the arch runner 18 is composed of a conductive material such as steel, iron, copper or conductive plastic. The thickness of the legs 18a and 18b is approximately 0.035 in. Or 0.089 cm (as seen in Figures 2-4). The transition from leg 18a to leg 18b is preferably curved. The length of leg 18b is approximately 0.30 in (0.076 cm), which is approximately twice the length of leg 18a. In response to the movable contact carrier 14 rotating to the open position (figure 4) during a circuit interruption, an electric arc is generated between the stationary and movable contacts 22 and 24. To protect the stationary and movable contact carriers 12 and 14 and the tension spring 34 of the electric arc, the arc runner 18 carries the electric arc away from the contacts stationary and movable 22 and 24 in a direction opposite to the tension spring 34. To minimize damage to the face 12a of the stationary contact carrier 12, the shorter leg 18a of the arc runner 18 carries the electric arc away from that face 12a. The arc runner 18 then directs the electric arc towards the exhaust vent 16, which is generally located in line with the initial direction of movement of the movable contact 24 when the movable contact carrier 14 starts to rotate from the closed position (FIG. 3) to the open position (figure 4). In this way, the arc runner 18 does not allow the electric arc to flow towards the tension spring 34 or other nearby components of the tripping mechanism. Moreover, the arc runner 18 serves to protect the carriers of stationary and movable contacts 12 and 14 from damages such as erosion, which can be caused by the electric arc, minimizing its exposure to the electric arc. The arc-extinguishing barrier 20 is an elongated piece of fibrous or thermoplastic material that releases gases such as the molding compound Cymel (trademark), vulcanized fiber based on cellulose, nylon 6/6, polyacetal Delrin (brand), or melamine. The molding compound Cymel is an alpha-melamine molding compound commercially available from AC Molding Compounds, of Wallingford, Connec.

United. The Delia polyacetal is commercially available from various manufacturers, including E.I. Du Pont de Nemours Co. from Wilmington, Delaware, United States. A material that releases gases is a material that releases adsorbed or occluded gases in response to its heating. The barrier 20 is preferably mounted on the base 44 of the circuit breaker 10, between the tension spring 34 and both stationary and movable contacts 22 and 24. To secure the barrier 20 within the base 44, the base 44 preferably forms a pair of generally parallel walls 44a and 44b that keep the barrier 20 loosely between them. The walls 44a and 44b prevent the barrier 20 from moving up or down, as seen in Figures 2-4. To prevent the barrier 20 from moving to the right or to the left, as seen in Figures 2-4, the barrier 20 forms a projecting portion 20a, which mates with a corresponding notch formed by the wall 44b of the base 44. The barrier 20 is generally perpendicular to the planes of the stationary and movable contacts 22 and 24, and is generally parallel to both the section 14a of the movable contact carrier 14 and the leg 18b of the arc corridor 18. shown in Figure 1, the barrier 20 is generally perpendicular to and extends over the elongated body of the movable contact carrier 14. As seen in Figures 2-4, a lower side of a central portion of the barrier 20 is located immediately adjacent to the stationary contact mounting surface 12a, while an upper side of the central portion of the barrier 20 is located in close proximity to the carrier hook 37 which supports one end of the tension spring 34. In the preferred embodiment, a right section 20b of the barrier 20 has a generally uniform thickness of approximately 0.09 in (0.23 cm). Regardless of the projecting portion 20a, a left section 20c of the barrier 20 has a thickness ranging from about 0.12 in (0.30 cm) at its extreme left edge to about 0.10 in (0.25 cm) at a location immediately above the stationary contact mounting surface 12a. Conventional techniques for extinguishing arcs in circuit breakers include the use of a slidable fiber connected to the movable contact carrier of the circuit breaker. Such a slidable fiber is disadvantageous because it is susceptible to prevent movement of the movable contact carrier with which it is connected. Moreover, the sliding fiber has a tendency to break during a resistance test.

Contrary to conventional sliding fibers, the arc-extinguishing barrier 20 is a non-moving part that is not connected to the movable contact carrier 14. In this way, the barrier 20 does not break during the resistance test. It is less susceptible to prevent movement of the movable contact carrier 14. When the movable contact carrier 14 rotates from the closed position (FIG. 3) to the open position (FIG. 4) during a circuit interruption, the extinguishing barrier of arc 20 prevents the electric arc generated between the stationary and movable contacts 22 and 24 from passing out of the arc chamber 46 and towards the portion of the base 44 containing the tension spring 34. Rather, the barrier 20 helps extinguish the arc generated during contact separation. Specifically, the arc heats the gas-evoking material of the barrier 20 to cause said gas-releasing material to release gas into the arc chamber 46. The liberated gas increases the pressure in the arc chamber 46 to cool the arc and aid the arc runner 18 to bring the arc to the exhaust vent 16. As the barrier 20 is in close proximity to the stationary and movable contacts 22 and 24, the barrier 20 provides optimum protection to the stationary and movable contact carriers 12 and 14 and their respective contacts. To improve the flow of current through the circuit breaker 10, the movable contact carrier 14 is typically composed of a highly conductive material such as copper. Although copper is preferred to increase current flow, copper is susceptible to being eroded, melted or vaporized if it is exposed to an electric arc generated during a circuit interruption. To minimize the exposure of the movable contact carrier 14 to the electric arc, a protective shield 48 is preferably mounted to the movable contact carrier 14 in the area of the contact 24. Figures 5a-b outline two types of protective shields 48 that can be used. with the movable contact carrier 14. In Figure 5a, a U-shaped protective shield 48a is physically subject to the mounting section 14b of the movable contact carrier 14 by spring action or pin connection of the shield 48a on the shield section. assembly 14b. The shield 48a is preferably comprised of a heat resistant conductive metal such as steel or iron having a melting point greater than about 2000 ° F, and the thickness of the shield 48a is selected to be in a range of about 0.025 in ( 0.064 cm) at about 0.035 in (0.089 cm). The armor 48a is manufactured using conventional stamping techniques. In Figure 5b, an L-shaped shield 48b is adhered to both the mounting section 14b and the adjacent section 14a. In one embodiment, the shield 48b is comprised of a conductive metal such as steel or iron having a melting point greater than about 2000 ° F, and the thickness of the shield 48b is selected to be in a range of about 0.025 in. (0.064 cm) to about 0.035 in (0.089 cm). In this case, the shield 48b is preferably soldered to the movable contact carrier 14. In an alternative embodiment, the shielding 48b is composed of a self-adhesive, flexible thermosetting material such as silicone, melamine, polytetrafluoroethylene (PTFE), coated glass, cloth, polyimide, or Teflon (trademark). As the conductive metal described above, the thermoformable material has a melting point greater than about 500 ° F so that the shield 48b is resistant to the high temperatures that can develop in the arc chamber 46. The thickness of the self-adhesive shield 48b (as seen in Figure 5b) is selected to be in a range of about 0.010 in (0.025 cm) to about 0.020 in (0.051 cm). In order to provide the movable contact carrier 14 with the shield 48b, the shield 48b is stamped from a uniform sheet of self-adhesive material and then adhered to the sections 14a and 14b of the movable contact carrier 14. As the shield 48b is created from the uniform sheet, one can ensure that the 48b shield has the same thickness throughout. In contrast, the prior art has provided the movable contact carrier 14 with silicone conformal coating by dipping carrier 14 into liquid silicone and allowing it to cure the silicone coating. Such a conformal coating is disadvantageous because it may not be applied uniformly to the surface of the carrier 14. Rather, the coating may be thicker in some places than in others. The protective shield 48 is manufactured to conform to the shape and geometry of the sections of the movable contact carrier 14 in which it is mounted. As best shown in Figure 5c, the shield 48 is provided with a circular opening to accommodate the movable contact 24. The shield 48 is mounted on the movable contact carrier 14 in such a manner that it adequately covers the area of the movable contact carrier. 14 which is ordinarily exposed to an electric arc during the circuit interruption, i.e. the area surrounding the movable contact 24 on the mounting section 14b. The protective shield 48 minimizes the exposure of the movable contact carrier 14 to the electric arc during circuit interruption by shielding the arc carrier 14 and re-directing the arc away from the carrier 14. The armor 48 substantially prevents the arc from coming into contact with the arc. movable contact carrier. 14, thereby preventing erosion and potential failure of carrier 14 due to excessive reduction in cross-sectional area. By preventing the erosion of the movable contact carrier 14, the protective shield 48 increases the useful life of the circuit breaker 10. Further, an important advantage of the protective shield 48 is that it provides visual confirmation to an operator that the shielding has been installed on the movable contact carrier 14 so that the carrier 14 is adequately protected from an electric arc. With respect to the prior art of forming a conformal coating on the carrier 14, such visual confirmation does not exist because the conformal coating is not easily observable by an operator. Although the present invention has been described with reference to one or more particular embodiments, those skilled in the art will recognize that many changes can be made therein without departing from the spirit and scope of the present invention. Each of these embodiments and their obvious variations are contemplated to fall within the spirit and scope of the claimed invention, which are indicated in the following claims.

Claims (21)

1. CLAIMS 1. In an electrical interrupting device that includes a stationary contact carrier having a stationary contact mounted thereon, a contact carrier assembly comprising: a movable contact carrier having a movable contact mounted thereon, said movable contact carrier being movable between a closed position and an open position, said movable contact abutting the stationary contact while said movable contact carrier is in said closed position, said movable contact being detached from the stationary contact while said movable contact carrier is in said open position; and an arc-resistant protective shield mounted on said movable contact carrier and surrounding said movable contact. The assembly of claim 1, wherein said protective shield is composed of metal and is elastically disposed on said movable contact carrier for mounting said protective shield on said movable contact carrier. The assembly of claim 1, wherein said protective shield is composed of metal and is welded to said movable contact carrier for mounting said protective shield on said movable contact carrier. 4. The assembly of claim 1, wherein said protective shield is composed of a metal selected from the group consisting of steel and iron. 5. The assembly of claim 4, wherein said protective shield has a thickness that varies from about 0. 025 in (0.064 cm) to about 0.035 in (0.089 cm). The assembly of claim 1, wherein said protective shield is composed of a self-adhesive, flexible material and is adhered to said movable contact carrier. 7. The assembly of claim 6, wherein said flexible self-adhesive material is selected from the group consisting of silicone, melamine, glass coated with polytetrafluoroethylene (PTFE), cloth, polyimide and Teflon. 8. The assembly of claim 6, wherein said protective shield has a thickness that varies from about 0. 010 in (0.025 cm) to about 0.020 in (0.051 cm). The assembly of claim 1, wherein said movable contact carrier is composed of a first material having a first melting point, and wherein said The protective shielding is composed of a second material having a second melting point greater than said first melting point. 10. The assembly of claim 9, wherein said first material includes copper. 11. The assembly of claim 9, wherein said second melting point is greater than about 500 ° F. 12. A method of manufacturing a contact carrying assembly for an electrical interrupting device, said method comprising the steps of: forming a movable contact carrier having a movable contact mounted thereon, said movable contact carrier being adapted for movement between a closed position and an open position, said movable contact abutting a stationary contact while said movable contact carrier is in said closed position, said movable contact being separated from the stationary contact while said movable contact carrier is in said open position; form an arc-resistant protective shield; and mounting said protective shield on said movable contact carrier such that said protective shield surrounds said movable contact. The assembly of claim 12, wherein said protective shield is composed of metal, and wherein said step of mounting said protective shield on said movable contact carrier includes elastically disposing said protective shield over said movable contact carrier. The assembly of claim 12, wherein said protective shield is composed of metal, and wherein said step of mounting said protective shield on said movable contact carrier includes welding said protective shield on said movable contact carrier. 15. The assembly of claim 12, wherein said protective shield is composed of metal selected from the group consisting of steel and iron. 16. The assembly of claim 15, wherein said protective shield has a thickness ranging from about 0.025 in (0.064 cm) to about 0.035 in (0.089 cm). 17. The assembly of claim 12, wherein said protective shield is composed of a self-adhesive material, I s flexible. The assembly of claim 17, wherein said step of forming said protective shield includes stamping said protective shield out of a sheet of self-adhesive, flexible material. 19. The assembly of claim 18, wherein said step of mounting said protective shield on said movable contact carrier includes adhering said protective shield to said movable contact carrier. The assembly of claim 17, wherein said flexible self-adhesive material is selected from the group consisting of silicone, melamine, glass coated with polytetrafluoroethylene (PTFE), cloth, polyimide and Teflon. 21. The assembly of claim 20, wherein said protective shield has a thickness that varies from about 25 0.010 in (0.025 cm) to about 0.020 in (0.051 cm).