HIGH CURRENT DOUBLE-BREAK ELECTRICAL CONTACTOR

Abstract: Stationary contact, terminal and arc-runner structure for a high-current double-break electrical contactor that affords longer contact life. Each sta­ tionary contact (66,80) and turn-back arc-runner (68,82) is connected to the associated terminal (52,72). Each arc-runner (68,82) is V-shaped and has a slot (68e,82e) at its turn-back or bight portion (68b,82b) through which the associated stationary contact (66,80) extends so that its contact tip (66b,80b) is thereabove for engagement by the bridging contact (36). The stationary contacts (66,80) allow substantially straight-through current flow, no turn-back current loop, when the contacts (66,36,80) are closed under normal current conditions to retain maximum contact pressure. But at the moment of the contact opening under high overload current conditions, the arcs migrate toward the sides between the arc-runners (68c,82c) and the outer ends of the bridging contact (36) so that a turn-back condition occurs in the current flow path in­ ducing heavy magnetic blowout forces on the respective arcs outwardly and upwardly toward the splitter plates (88,90) to efficiently extinguish the arcs.

Description: This invention relates to a high-current double-break contactor having an insulating housing, a movable bridging contact, a pair of stationary contacts mounted in the housing, and means for moving the movable contact into and out of engagement with the pair of stationary contacts, wherein each of the stationary contacts have a turn-back configuration whereby current flow therethrough will induce a laterally outwardly directed magnetic blowout force. Contact structures of this type cause the current arcs established upon contact opening to provide magnetic fields in directions to force such arcs outwardly, thereby to extinguish the arc by known principles. While such contact structures are desirable for high current interruption when the contacts open, they are undesirable during high inrush currents when the contacts close because they tend to force the contacts open which in turn produces secondary arcs that abrade the contact material resulting in increased contact wear and a tendency for the contacts to weld closed. Stationary contacts such as shown in published European Patent application EP-A-0 140 173 (Siemens) overcome the above problem by providing a separate arc runner having a turn-back configuration adjacent the stationary contact. The contacts have a straight through current path when closed that provides no magnetic forces tending to open the contacts. On opening of the contacts, an arc drawn between the stationary and movable contacts is transferred to the arc runner whereupon the turn-back configuration of the arc runner provides the desired magnetic forces to blow the arc outwardly for extinguishing by known principles. Since magnetic fields are significant factors in blowing the arc outward, it is important that the elements of the stationary contact structure be conducive to producing strong magnetic fields. To this end, when the arc runner is a separate member from the stationary contact, the arc runner is customarily made of steel because of its magnetic advantages and because it resists erosion from the affects of the arc better than non-ferrous materials. However, one of the known principles of arc extinguishing employed in such contact structures is temperature reduction of the arc, and the heat absorbing qualities of steel are significantly low compared to other materials, such as copper. In particular, heat quickly penetrates the surface of copper, and where significant mass is provided by using heavy gauge copper, such heat spreads within the mass of material at a much faster rate than in steel or brass wherein it remains at the surface because of the short time period of the arc. This invention provides a high-current double-break contactor having an insulating housing, a movable bridging contact, a pair of stationary contacts mounted in said housing, and means for moving said movable contact into and out of engagement with said pair of stationary contacts, said stationary contact comprising a connector terminal; and a U-shaped arc runner conductor having a slot at its closed end, one leg of said arc runner supported along said connector terminal; characterized by a contact support on said connector terminal including; a contact tip on said contact support, said connector terminal, contact support and contact tip providing a straight-through current path to said movable contact when said movable contact is in engagement with said stationary contact tip; and opposite sides of said slot of said arc runner disposed adjacent respective opposite sides of said contact support, the other leg of said arc runner extending along said contact tip and directed away from said contact tip and said movable contact for providing a turn-back current loop when said movable and stationary contacts are separated under high current conditions affording maximum arc blowout force for rapidly separating said contacts and moving said arc along said arc runner other leg away from said movable contact and said contact tip, wherein said arc runner conductor is formed of heavy gauge copper. This invention further provides a high-current double-break contactor of the above described type wherein said contact support comprises a solid block of electrically conductive material affixed to said connector terminal and disposed in said arc runner slot, said contact tip being affixed on a surface of said block proximate said other leg of said arc runner. A solid block of electrically conductive material affords several advantages over structures wherein a contact tip is mounted on the end of a cantilevered strip. The solid block approach provides a better thermal dissipation path, permits better brazing of the contact tip thereto which consequently improves both performance and manufacturing process, better absorbs mechanical impact of the movable contact upon contact closure, thereby imparting less contact bounce, and is positionally more stable because it experiences less distortion due to heat recycling operation. An embodiment of this invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a vertical cross sectional view of a high current double-break electrical contactor embodying the invention taken substantially along line 1-1 of Fig. 2 to show the stationary and movable contacts, terminals, arc runners, the arc splitter structure and electromagnet. Fig. 2 is a top view of the contactor of Fig. 1 with one-half of the cover broken away at substantially line 2-2 of Fig. 1 to show a top view of the movable and stationary contacts, terminals, arc runners, the contact carrier and the terminal lugs. Fig. 3 is a fragmentary horizontal cross sectional view taken substantially along line 3-3 of Fig. 1 to show a top view of the terminals, the stationary contacts and their associated arc runners. Fig. 4 is an isometric view of one of the stationary contacts and associated arc runner. Description of the Preferred Embodiment Referring to Fig. 1, there is shown a high current double-break electrical contactor constructed in accordance with the invention. As shown therein, the contactor is provided with an insulating housing including a base 2 and a cover 4 connected to one another by any suitable means such as clamps 5, or the like shown in Fig. 2. While a contactor of this type may have a variable number of poles, a three-pole contactor has been illustrated for exemplary purposes as shown in Fig. 2. Base 2 is provided with a horizontal contact-supporting part 6 at its upper portion and has a compartment 8 therebelow for housing an electromagnet 10 comprising a magnet frame 12, an operating coil 14 and an armature 16. A pair of terminals 18 extend from coil 14 toward the left for connection to an electrical circuit. Base 2 is supported on a mounting plate 20 having the usual holes or the like for mounting the contactor on a mounting panel and a leaf spring 22 is positioned between mounting plate 20 and magnet frame 12 for allowing limited movement of the magnet frame with respect to armature 16. When coil 14 is energized, armature 16 is magnetically drawn to the poles of magnet frame 12 against the bias of a helical return spring 24 positioned between coil 14 and armature 16 as shown in Fig. 1. Consequently when coil 14 is deenergized, return spring 24 will lift armature 16 to its open position shown in Fig. 1. An insulating contact carrier 26 is secured to armature 16 by conventional means such as, for example, a leaf spring 28 extending at its midportion through a hole in the armature and secured at its opposite ends into slots in contact carrier 26. Contact carrier 26 is molded of plastic material or the like and has a central upstanding movable contact carrier portion 30 that extends upwardly through a hole 32 in top portion 6 of the base and also through a hole 34 in cover 4. Hole 32 closely fits around contact carrier portion 30 to guide the latter in its reciprocal vertical movement when the electromagnet is energized and deenergized. A normally open movable bridging contact 36 is mounted on contact carrier 30 in a conventional manner. For this purpose, contact carrier 30 is provided with a lateral hole 38 therethrough having a bump 40 at its upper portion for retaining the upper end of a helical compression spring 42 the lower end of which surrounds a bump 44 on the central upper surface of movable bridging contact 36 to retain the movable bridging contact on the contact carrier and also to bias it downwardly against the lower surface 46 of hole 38, thus to provide the necessary contact pressure when the contacts close. As shown in Fig. 1, the contactor is provided with a pair of stationary contact-terminal and arc runner assemblies 48 and 50 as shown in Figs. 1 and 3. Left-hand terminal assembly 48 shown in Fig. 1 comprises an elongated terminal member 52 seated in a lateral groove 4 in upper member 6 of the base and having a box lug 56 secured to its outer end. Box lug 56 is of conventional rectangular form having a lateral hole therethrough and a tapped hole extending down from its top into which a set screw 58 is threaded for clamping the stripped end of an electrical wire that has been inserted in the hole therebelow. Terminal 52 is provided with means for rigidly securing the same onto upper portion 6 of the base 2. For this purpose, a screw 60 may be inserted up through a hole 62 in upper portion 6 of the base and a nut 64 is threaded on the upper end of this screw to clamp terminal 52 into its channel 54 in upper portion 6 of the base. Terminal 52 is made of electrically conductive metal such as copper. Contact-terminal and arc runner assembly 48 also comprises a contact 66 of extruded copper or the like and an arc runner 68 of heavy gauge copper or the like as shown in Figs. 1 and 4. Arc runner 68 is provided with an inwardly extending horizontal portion 68a and a re-entrant or turn-back portion 68b extending outwardly and upwardly to provide an arc runner portion 68c as shown in Fig. 1. The bight portion 68b of the horizontal and re-entrant portions 68a and 68b is provided with a slot 68e as shown in Fig. 2 through which stationary contact 66 extends and extending into a clearance slot 68f for access to screw 70. The contactor is also provided with means for securing stationary contact 66 and arc runner 68 to top portion 6 of the base. For this purpose, the left-hand portion 66a of contact 66 and the horizontal portion 68a of arc runner 68 are provided with holes through which a screw 70 extends into threaded engagement in a tapped hole 52a in terminal 52. As will be seen in Fig. 1, contact tip 66b of stationary contact 66 which may be silver cadmium oxide or the like extends up through slot 68e slightly above turn-back portion 68b of the arc runner for engagement by contact tip 36a of movable contact 36. Contact-terminal and arc runner assembly 50 is similar to contact-terminal and arc runner assembly 48 just described except that it is on the right-hand side of the contactor and therefore in reversed relationship. Contact-terminal and arc runner assembly 50 similarly includes an elongaged terminal member 72 secured to upper portion 6 of the base by a screw 74, in this case screw 74 being threaded into a tapped hole in terminal 72 rather than being secured by a nut 64 as in the case of contact-terminal and arc runner assembly 48 hereinbefore described to show these alternative methods of securing the terminal onto the base. A similar box lug 76 is secured to the outer end of terminal 72, this box lug having a set screw 78 for clamping the stripped end of an insulated electrical wire therein. Contact-terminal and arc runner assembly 50 further includes a similar stationary contact 80 extending up through a slot in the bight portion of an arc runner 82 and both stationary contact 80 and arc runner 82 being secured by a screw 84 to terminal 72. As a result, contact tip 80a extends slightly above the bight portion of arc runner 82 for engagement by contact tip 36b of movable bridging contact 36 when the electromagnet is energized. As shown at the left-hand portion of Fig. 1, a screw terminal 86 may additionally or alternatively be connected to elongated terminal 52 by having a perforated end portion thereof clamped under the head of screw 60. It will be apparent from Fig. 2 that in a three-pole contactor such as the one therein illustrated, only the center pole contact carrier 30 extends up through a hole 34 in the cover for coupling to external apparatus such as, for example, an auxiliary contact set mounted thereon and that contact carriers 30' of the two poles on either side of the center pole need not extend through the cover. As shown in Fig. 1, two sets of arc splitter plates 88 and 90 are mounted within cover 4 directly above the respective arc runners 68c and 82c to receive the arcs that are blown outwardly therealong to be broken up and extinguished. An important aspect of the invention is to provide stationary contacts 66 and 80 that extend through the slotted bight portions 68d and 88d of the arc runners in order to allow straight-through current flow on low current operation to retain maximum contact pressure but to provide turn-back current conduction loops on high current operation to afford maximum arc blowout force when the contacts are opened under high current overload conditions thereby to quickly remove the electric arcs and their associated heat from the contact tips and to move the arcs outwardly along the arc runners and into the splitter plates to rupture and efficiently extinguish the same. For this purpose, the current will flow toward the right through terminal 52 and then upwardly through stationary contact 66 and its contact tip 66b and then through contact tip 36a and movable contact 36, contact tips 36b and 80b, stationary contact 80 and terminal 72. It will be apparent that this current flow was straight through the left stationary contact and then through the movable bridging contact and the right stationary contact. However, under overload conditions, the movable bridging contact 36 will be tripped open causing arcs to form between the stationary and movable contact tips which will be moved out onto the left and right arc runners 68c and 82c. It will be apparent that this will provide turn-back current conduction loops. For this purpose, current will flow through terminal 52 to the right and then upwardly through stationary contact 66 and the bight portion 68d of arc runner 68 and then toward the left and upwardly along arc runner 68c and then across the open contact gap to the left end of movable bridging contact 36 and through this movable bridging contact to the right end thereof and then through the air gap to arc runner 82c, to the left and downwardly along arc runner 82c and through stationary contact 80 and the bight portion 88d of the arc runner and then to the right through terminal 72. These turn-back current conduction loops will afford maximum arc blowout forces to the left and right respectively under high current conditions to quickly remove the electric arcs and their associated heat from the contacts into the arc splitter plates to rupture and efficiently extinguish the same. The size of the turn-back current conduction loops will, of course, be dependent upon the relative size of the stationary contacts with respect to the bight portions of the arc runners. But the important thing is that the turn-back current conduction loops are produced only under high overload current trip conditions to get the maximum arc blowout force whereas under normal operating current conditions the current will flow straight through the contacts to maintain maximum contact pressure when it is needed.

Claims: A high-current double-break contactor having an insulating housing (2,4), a movable bridging contact (36), a pair of stationary contacts (48,50) mounted in said housing (2,4), and means (10,30) for moving said movable contact (36) into and out of engagement with said pair of stationary contacts (48,50), said stationary contact (48,50) comprising: a connector terminal (52,72); and a U-shaped arc runner conductor (68,82) having a slot (68e,82e) at its closed end, one leg (68a,82a) of said arc runner supported along said connector terminal; characterized by a contact support (66,80) on said connector terminal (52,72) including; a contact tip (66b,80b) on said contact support (66,80), said connector terminal (52,72), contact support and contact tip providing a straight-through current path to said movable contact (36) when said movable contact is in engagement with said stationary contact tip; and opposite sides of said slot of said arc runner disposed adjacent respective opposite sides of said contact support, the other leg (68b,82b) of said arc runner extending along said contact tip and directed away from said contact tip and said movable contact for providing a turn-back current loop when said movable and stationary contacts are separated under high current conditions affording maximum arc blowout force for rapidly separating said contacts and moving said arc along said arc runner other leg away from said movable contact and said contact tip, wherein said arc runner conductor is formed of heavy gauge copper. The high-current double-break contactor as claimed in claim 1 wherein: said contact support (66,80) comprises a solid block of electrically conductive material affixed to said connector terminal (52,72) and disposed in said arc runner slot (68e,82e), said contact tip (66b,80b) being affixed on a surface of said block proximate said other leg (68b,82b) of said arc runner.

Inventors: BUTTERWORTH, EDMUND MORTON
Applicants: EATON CORPORATION
Application year: 1986
Main classification: H01H9
IPC codes: H01H9