Patent Application
20140002215
The present invention relates generally to electrical contact assemblies, and more particularly to electrical contact apparatus within electrical contact assemblies.
Mechanical devices for electrical switching may need to survive a fault or short-circuit condition, in which the electrical current through the electrical device may be many times larger than the device's continuous current rating (the so-called rated current). If such a fault current lasts even a few seconds, the conductive parts of the electrical device may be degraded or even melt, and the electrical device may be destroyed, or otherwise may not continue to function as intended. This may also possibly damage other components connected to the electrical device. One remedy is to design the electrical device to detect the fault current and to interrupt it, as for example in a circuit breaker. However, the ability to interrupt large fault currents comes at a substantial cost, and may dictate the use of refractory metals, arc-splitters, and magnetic arc deflection.
If a second electrical device is protected by a first device, which will interrupt the current (e.g., a fuse or a circuit breaker), then there may be no need to add the cost of interrupting capability to the second device. However, while the fault current is flowing, a repulsive force proportional to the square of the current will act to separate the electrical contacts of the second device. This repulsive or “blow-apart” force has been dealt with in prior electrical devices by providing a spring bias to the movable contacts thereby providing an opposing force of sufficient magnitude to hold the contacts in a closed condition, i.e., to prevent the electrical contact from blowing apart. If the contacts blow apart, even though only slightly, they may arc or weld, and the second device may be destroyed or compromised. Such electrical devices may have quite heavy contact biasing springs.
Thus, it should be recognized that during a short-circuit condition, due to very high electrical fault currents flowing axially through the electrical contacts (e.g., contact buttons) of the contactor apparatus, the blow-apart force is developed in the contact region that acts to separate the electrical contacts. As a result, the contact pressure normally produced by the biasing spring(s) and/or actuator of the contactor is decreased. The net result is increased power loss in the electrical contact region, which may lead to contact welding or to other undesirable effects.
Thus, electrical contact apparatus adapted to offset the aforementioned lowered contact force are desired.
In a first embodiment, an electrical contact apparatus is provided. The electrical contact apparatus includes a first contact member having a first end and a second end, and a first contact at the second end, a second contact member having a first end and a second end, and having a second contact at the second end, a movable contact member received adjacent to the second ends of the first contact member and the second contact member, the movable contact member having third contact positioned adjacent the first contact, and fourth contact positioned adjacent the second contact, the third and fourth contacts of the movable conductor member being configured and adapted to be moved into and out of engaging contact with the first contact and the second contact; and a first armature positioned adjacent to at least the first contact and third contact and operable to produce a force to cause the movable contact member to remain closed upon application of current through the first contact member, movable contact member, and second contact member.
In yet another aspect, a contact assembly is provided. The contact assembly includes a contact apparatus having a first contact member having a first end and a second end, and a first contact at the second end, a second contact member having a first end and a second end, and having a second contact at the second end, a movable contact member received adjacent to the second ends of the first contact member and the second contact member, the movable contact member having third contact positioned adjacent the first contact, and fourth contact positioned adjacent the second contact, the third and fourth contacts of the movable conductor member being configured and adapted to be moved into and out of engaging contact with the first contact and the second contact, and a first armature positioned adjacent to at least the first contact and third contact and operable to produce a force to cause the movable contact member to remain closed upon application of current through the first contact member, movable contact member, and second contact member; and an actuator mechanism coupled to the movable contact member and adapted to open and close the contact apparatus.
In a method embodiment, a method of operating a contact apparatus is provided. The method includes providing a contact apparatus having a first contact member having a first contact, a second contact member having a second contact, a movable contact member received adjacent to the first contact member and the second contact member, the movable contact member having third contact positioned adjacent the first contact, and fourth contact positioned adjacent the second contact, and a first armature positioned adjacent to at least the first contact and third contact, and producing a closing force to cause the movable contact member to remain closed, the closing force produced upon application of current through the first contact member, movable contact member, and second contact member.
In yet another aspect, an electrical contact apparatus is provided. The electrical contact apparatus, comprising a first contact member having a first contact, a movable contact member having an opposing contact positioned adjacent to the first contact, the first contact and opposing contact being configured and operable to be moved into and out of engaging contact, and an armature positioned adjacent to the first contact and opposing contact and operable to produce an electromagnetic force opposed to a blow-apart force produced when a fault current is passed through the first contact member and movable contact member.
In another method embodiment, a method of operating a contact apparatus is provided. The method includes providing a contact apparatus having a first contact member with a first contact, a movable contact member with an opposing contact, the first contact and opposing contact being configured to be moved into and out of engaging contact, and an armature positioned adjacent to the first contact and opposing contact, and producing an electromagnetic force opposed to a blow-apart force produced when a fault current is passed through the first contact member and movable contact member.
Still other aspects, features, and advantages of the present invention may be readily apparent from the following detailed description by illustrating a number of example embodiments and implementations, including the best mode contemplated for carrying out the present invention. The present invention may also be capable of other and different embodiments, and its several details may be modified in various respects, all without departing from the scope of the present invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. The invention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention.
In view of the foregoing difficulties, improved electrical contact apparatus and assemblies are provided. Embodiments of the invention provide improved contact structure that are configured and adapted to allow “shaping” of the distribution of a magnetic field in the region of the movable contact member (sometimes referred to as a contact bridge) by a suitable placement of one, and preferably two, magnetically-permeable armatures. The high-permeability armatures can be either solid, powdered metal, or packaged together as a stack of laminations. The high-permeability armatures may be steel or iron, for example. Other suitable high permeability materials may be used.
Embodiments of the electrical contact apparatus and assembly have been described herein are useful in contactor apparatus, electrical contact devices where it is important to keep electrical contacts closed during fault or otherwise high current conditions, motor starters, disconnect switches, and the like.
As will become apparent, the electrical contact apparatus may advantageously allow the engaging electrical contact or contacts of the movable contact member to be urged more forcefully into contact with the electrical contact or contacts of the stationary contact member (e.g., contact pads). Accordingly, instances of contact separation causing contact welding and/or degradation may be minimized or avoided.
These and other embodiments of the electrical contact apparatus, contact assemblies, and methods of operating the contact assemblies and apparatus are described below with reference to
Referring now in specific detail to
The electrical contact apparatus 100 may include a first contact member 102 having a first end 104 and a second end 106 opposed from the first end 104. The first contact member 102 may include a first contact 108, such as a conventional contact button, located and secured at the second end 106. First contact 108 may be a contact made of a silver-coated copper or silver-coated, copper-alloy material, for example. Other suitable contact materials may be used. First contact member 102 may include one or more features 110 (
Electrical contact apparatus 100 may include a second contact member 114, also having a first end 116 and a second end 118, and which may have a third contact 120 secured at the second end 118. The second contact member 114 and third contact 120 may be identical to the first contact member 102 and first contact 108. The second contact member 114 may include one or more features 115 (
Electrical contact apparatus 100 includes, as shown in
A first armature 128 is positioned adjacent to at least the first contact 108 and third contact 124 and is operable to assist in producing an electromagnetic force to cause the movable contact member 122 to remain closed upon application of current through the first contact member 102, movable contact member 122, and second contact member 114. The force causes the first contact 108 and third contact 124 to be urged into engaged contact more forcefully.
A second armature 129 may be provided and may operate to urge the second contact 120 and fourth contact 126 into engaged contact more forcefully upon application of an electrical current through the first contact member 102, movable contact member 122, and second contact member 114.
First and second armatures 128, 129 may comprise a magnetically-permeable material, such as SAE 1008 or SAE 1010 steel. Other magnetically-permeable materials may be used. Optionally, the first and second armatures 128, 129 may comprise a powdered metal material. The powdered metal material may be a powdered iron, such as F-0000-10, -15, or -20 powdered iron per MPIF Standard 35. The density of the powdered metal material may be between about 6.0 g/cm3 and about 7.5 g/cm3, for example. Other densities and types of powdered metal materials including powdered metal alloys may be used. In other embodiments, the first and second armatures 128, 129 may be formed from a solid formed channel of magnetically-permeable material, and may be have rounded corners. The first and/or second armatures 128, 129 may be laminated steel in some embodiments.
First armature 128 may comprise a transverse portion 128T and two side portions 128S1, 128S2 extending from ends of the transverse portion 128T, thus forming a U-shaped armature. The side portions 128S1 and 128S2 may extend substantially perpendicularly from the transverse portion 128T, in some embodiments wherein the two side portions 128S1, 128S2 extend alongside of lateral sides of the first contact member 102 and second contact member 114. The transverse portion 128T extends along the underside of the first contact member 102, as shown. Second armature 129 may be substantially identical to first armature 128. The first and second armatures 128, 129 may be securely fastened to the undersides of the first contact member 102 and the second contact member 114, such as by suitable fasteners (e.g., screws) or the like. Any suitable fastening means may be used.
In operation, the current flowing through the first contact member 102, movable contact member 122, and second contact member 114 functions to induce and create a significant magnetic field that produces a significant electromagnetic force acting to urge the contacts 124, 126 of the movable contact member 122 into more intimate contact with the contacts 108, 120 of the first and second contact members 102, 114. This electromagnetic force tends to keep the contacts closed, and, thus, assists any force that may be provided by contact springs (not shown). Thus during short circuit or fault conditions, the contact pairs 108, 124, and 120, 126 have a reduced tendency to separate and the contact force may be maintained at an appropriate level. This created electromagnetic force offsets the blow-apart force produced tending to open the contact pairs 108, 124 and 120, 126 due to current flow axially through the first and third contacts 108, 124 and the second and fourth contacts 120, 126.
In the depicted embodiment, the first and second armatures 128, 129 may have, as shown in
In the depicted embodiment, the first and second armatures 228, 229 are configured as described for the single contact embodiment. In particular, the two side portions 228S1 and 228S2 extend alongside of lateral sides of the first contact member 202 as shown in
The supplemental armatures 640A, 640B, 642A, 642B may be made of a magnetically-permeable metal, such as steel as described herein. The supplemental armatures 640A, 640B, 642A, 642B may have a flat bar shape, and may be coupled to the surface of the conductive portions 622A, 622B opposite the contacts, as shown. Furthermore, the supplemental armatures 640A, 640B, 642A, 642B may be aligned with and preferably overlay the respective sides of the armatures 628, 629. The supplemental armatures 640A, 640B and 642A, 642B may extend alongside of the lateral sides of the conductive portions 622A, 622B in some embodiments. An air gap between the ends of the armatures 628, 629 and the respective ends of the supplemental armatures 640A, 640B, 642A, 642B may be greater than about 1 mm and less than about 10 mm. Other gaps may be used. The center gaps between the respective ends of the supplemental armatures 640A, 640B and between the ends of supplemental armatures 642A, 642B allow for limited independent motion of the conductive portions 622A, 622B. The center air gaps respective ends of the supplemental armatures 640A, 640B, 642A, 642B may be greater than about 0 mm and less than about 10 mm. Other center air gaps may be provided
The side air gap between the ends of the respective sides of the respective U-shaped first armature 728 and the L-shaped first supplemental armature 740A (and between the U-shaped first armature 728 and the L-shaped second supplemental armature 740B) should be less than about 10 mm, for example. The side air gap may be greater than 1 mm in some embodiments. Other side air gaps dimensions may be used. Likewise, the air gap between the ends of the sides of the respective U-shaped second armature 729 and the L-shaped first supplemental armature 742A and between the U-shaped second armature 729 and the L-shaped second supplemental armature 742B may be greater than 1 mm and may be less than about 10 mm, for example. Other gap dimensions may be used. In some embodiments, the thickness of the transverse portion of the L-shaped armatures 740A, 740B, 742A, 742B may be thicker than the side portions to enlarge the center air gap area in order to minimize loss in field strength through the center air gap. The center air gap between the center ends of the L-shaped armatures 740A, 740B and 742A, 742B may be between about 0 mm and 10 mm, for example.
A side air gap between the ends of the sides of the respective first armature 828 and the first supplemental armature 840A (and between the first armature 828 and the second supplemental armature 840B) may be greater than about 1 mm and less than about 10 mm, for example. Other side air gap dimensions may be used. The same air gaps may be provided between the ends of the sides of the respective second armature 729 and the first supplemental armature 842A and the second supplemental armature 842B. Other gap dimensions may be used. The center air gap measured in the transverse direction between the ends of the first and second supplemental armatures 840A, 840B at the center should be as small as possible without mechanical interference, and may be between about 0 mm and 10 mm in some embodiments. Conductive members 822A, 822B containing contacts may be actuated by a spring-loaded actuator mechanism 850 (shown as a dotted line).
Each of the above-described embodiments has the same purpose of supplementing the available contact force during a short circuit or fault condition. Thus, these additional armatures providing a spatial distribution of magnetically-permeable steel in the region of the moving contacts provide additional contact force assisting the force already provided by contact springs (not shown).
In one or more embodiments, such as those shown in
In addition, the movable contact member 922 may include supplemental armatures 940 and 942 that may be solidly coupled and attached at the longitudinal ends of the movable conductive member 922C adjacent to the armatures 928, 929, as shown. The supplemental armatures 940, 942 may have any of the shapes described herein and are adapted to move with the conductive portions 922C.
The actuator mechanism 955 may be any suitable mechanism configured and operational to move the movable contact member 922 between an open (contact disengaged) and closed (contacts engaged) condition. In the depicted embodiment, the actuator mechanism 955 comprises an actuator 958 coupled to a frame member 960. Frame member 960 may be coupled to the actuator 958 and also to an insulating support 962 for supporting the stationary first and second contact members 902, 914. Frame member may be made of an insulating plastic material, such as a fiber-reinforced plastic, for example. Other suitable insulating materials may be used. Actuator 958 may include coils 964A, 964B, a central pole 965, and a surrounding magnet 968, such as a NyFeB magnet having a ring or other suitable shape. Other suitable magnets may be used. The actuator mechanism 955 may include a shaft 967 coupled to a central shaft 970 of the actuator 958. Shaft 967 may include an insulating portion 969 and a spring support 962. Spring support 962 includes one or more springs allowing the movable contact member 922 to be urged into contact with the contacts of the first and second contact members 902, 914 with a suitable biasing spring force. The actuator mechanism 955 is coupled to the movable contact member 922 and is adapted to open and close the contact apparatus 901.
The method 1000 includes, in 1004, providing producing a closing force, which may be an electromagnetic force, to cause the movable contact member to remain closed, the closing force being produced upon application of an electrical current through the first contact member, movable contact member, and second contact member. A second armature may be provided to balance the closing forces on the first and second contacts. The closing forces may be further augmented by adding supplemental armatures that move as part of the movable contact member wherein magnetic fields produced in the armatures attract the supplemental armatures.
In addition, the contact apparatus 1100 may include bar-shaped supplemental armature 1140 that may be solidly coupled and attached as part of the movable contact member 1122, as shown. The supplemental armature 1140 may be attached to the surface such as by suitable fasteners (e.g., screws or the like). Supplemental armature 1140 and armature 1128 may be made of, for example, a magnetically-permeable steel, such as SAE 1008 or SAE 1010 steel or other suitable magnetically-permeable material. Magnetic attraction forces may be produced between the armature 1128 and supplemental armature 1140 to supplement the contact closing forces present due to spring bias and/or actuator forces.
The method 1200 includes, in 1204, producing an electromagnetic force opposed to a blow-apart force produced when an electrical fault current is passed through the first contact member 1102 and movable contact member 1122. The blow-apart force is produced, in particular, when the current passes axially through the first contact 1108 and opposing contact 1124. Electromagnetic force produced in opposition of the blow-apart force may be a Lorenz force when no supplementary armature is provided. Electromagnetic force produced in opposition of the blow-apart force may be a magnetic attraction force acting on the supplementary armature when a supplementary armature (e.g., 330, 440, 540, 640A, 640B, 740A, 740B, 840A, 840B, 940, 1140) is provided on the movable contact member (e.g., 122, 222, 322, 422, 522, 622, 722, 822, 922, and 1122). In any event, the electromagnetic force is opposed to a blow-apart force and operates to reduce or eliminate the propensity of the electrical contacts to separate.
While the invention is susceptible to various modifications and alternative forms, specific embodiments and methods thereof have been shown by way of example in the drawings and are described in detail herein. It should be understood, however, that it is not intended to limit the invention to the particular apparatus, assemblies, or methods disclosed, but, to the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the scope of the invention.
This application claims priority from U.S. Provisional Patent Application Ser. No. 61/665,988 filed on Jun. 29, 2012, entitled “SOLUTION FOR ENHANCEMENT OF CONTACT FORCE DURING FAULT CURRENT IN CONTACTOR DEVICE,” the disclosure of which is hereby incorporated by reference in its entirety herein.
| Number | Date | Country | |
|---|---|---|---|
| 61665988 | Jun 2012 | US |
