The disclosed concept relates to electrical switching apparatus, such as, for example, circuit breakers and, more particularly, to circuit breakers employing a slot motor. The disclosed concept further relates to slot motors.
Electrical switching apparatus, such as circuit breakers, are employed in diverse capacities in power distribution systems. A circuit breaker may include, for example, a line conductor, a load conductor, a fixed contact and a movable contact, with the movable contact being movable into and out of electrically conductive engagement with the fixed contact. This switches the circuit breaker between an ON or closed position and an OFF or open position, or between the ON or closed position and a tripped or tripped OFF position. The fixed contact is electrically conductively engaged with one of the line and load conductors, and the movable contact is electrically conductively engaged with the other of the line and load conductors. The circuit breaker may also include an operating mechanism having a movable contact arm upon which the movable contact is disposed.
Upon initial separation of the movable contact away from the stationary contact, an electrical arc is formed in the space between the contacts. The arc provides a means for smoothly transitioning from a closed circuit to an open circuit, but produces a number of challenges to the circuit breaker designer. Among them is the fact that the arc results in the undesirable flow of electrical current through the circuit breaker to the load. Additionally, the arc, which extends between the contacts, often results in vaporization or sublimation of the contact material itself. Therefore, it is desirable to extinguish any such arcs as soon as possible upon their propagation.
To facilitate this process, circuit breakers typically include arc chutes which are structured to attract and break-up the arcs. Specifically, each arc chute includes a plurality of spaced apart arc plates. As the movable contact is moved away from the stationary contact, the movable contact moves past the ends of the arc plates, with the arc being drawn toward and between the arc plates. The arc plates are electrically insulated from one another such that the arc is broken-up and extinguished by the arc plates.
In order to successfully interrupt a DC circuit, the circuit breaker needs to generate an arc voltage higher than the system voltage to stop the current flow. A challenge with interruption is that there is often not enough current-induced magnetic force and gas dynamics to force the arc into the arc chute. One known approach to address this issue involves the placing of large permanent magnets in the arc chute to drive the arc into the arc chute. However, among other disadvantages, large permanent magnets are costly and significantly increase the size of the arc chute.
There is thus room for improvement in electrical switching apparatus and in slot motors therefor.
These needs and others are met by embodiments of the disclosed concept, which are directed to an electrical switching apparatus and slot motor therefor, in which a plurality of permanent magnets are located on a support element of the slot motor.
As one aspect of the disclosed concept, a slot motor for an electrical switching apparatus is provided. The slot motor comprises: a support apparatus including a support element having a first leg and a second leg located opposite the first leg, the first leg having a first inner surface, the second leg having a second inner surface facing the first inner surface; a plurality of permanent magnets including a first permanent magnet and a second permanent magnet, the first permanent magnet being located on the first leg, the second permanent magnet being located on the second leg; and a number of U-shaped plates coupled to the support element. The first inner surface and the second inner surface are located between the first permanent magnet and the second permanent magnet.
As another aspect of the disclosed concept, an electrical switching apparatus comprises: at least one pair of separable contacts structured to move into and out of engagement with each other in order to connect and disconnect power, respectively; at least one arc chute located at or about the pair of separable contacts in order to attract and dissipate an arc and ionized gases which are generated by the pair of separable contacts moving out of engagement with each other; and at least one slot motor comprising: a support apparatus comprising a support element having a first leg and a second leg located opposite the first leg, the first leg having a first inner surface, the second leg having a second inner surface facing the first inner surface, a plurality of permanent magnets comprising a first permanent magnet and a second permanent magnet, the first permanent magnet being located on the first leg, the second permanent magnet being located on the second leg, and a number of U-shaped plates coupled to the support element. The pair of separable contacts are located between the first permanent magnet and the second permanent magnet. The first inner surface and the second inner surface are located between the first permanent magnet and the second permanent magnet.
A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
As employed herein, the statement that two or more parts are “connected” or “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts.
As employed herein, the statement that two or more parts or components “engage” one another shall mean that the parts exert a force against one another either directly or through one or more intermediate parts or components.
As employed herein, the terms “generally U-shaped” or “generally U-shape” or “general U-shape” shall mean that the shape of a corresponding structure has the general shape of the letter “U” in which the bottom of such letter or structure is rounded, generally round, square, generally square, or partially round and partially square, or has the general shape of a base member with two leg (or arm) members extending normal or generally normal from the ends of the base member.
The first and second permanent magnets 180,182 are high-energy permanent magnets (e.g., without limitation, a Samarium Cobalt (Sintered) S2869 material, or a Neodymium Iron Boron (Sintered) N2880 material). The material of the permanent magnets 180,182 advantageously generates a relatively high magnetic field, thereby allowing the permanent magnets 180,182 to be relatively small. However, it is within the scope of the disclosed concept for similar suitable alternative, yet larger, permanent magnets (not shown) to be employed, which produce a comparable magnetic field, but are made of different materials. Additionally, the material of the permanent magnets 180,182 also provides the permanent magnets 180,182 with a relatively high curie point, thereby allowing the permanent magnets 180,182 to withstand relatively high temperatures (i.e., due to heat exposure from the arc) and not lose their magnetic properties.
Non-limiting examples of the insulation material of the support element 102 are a suitable glass fiber-filled polyamide 66 and a suitable glass fiber-filled polyester. One example is Rosite®3550D, which is marketed by Industrial Dielectrics, Inc. of Noblesville, Ind. Another example is Zytel® PLS90G30DR BK099, which is marketed by E. I. du Pont de Nemours and Company of Wilmington, Del. This material advantageously assists in outgassing, responsive to an arcing event, as will be described below.
The support element 102 includes a first leg 104, a second leg 106, and a middle portion 108 extending between the first leg 104 and the second leg 106. The first leg 104 has a first inner surface 110, and the second leg 106 has a second inner surface 112, which faces the first inner surface 110. The first and second inner surfaces 110,112 are preferably planar and parallel to one another. As shown, the first inner surface 110 and the second inner surface 112 are located between the first permanent magnet 180 and the second permanent magnet 182, a configuration that advantageously allows the support element 102 to assist with outgassing, as will be discussed below.
Continuing to refer to
The disclosed concept will be further appreciated with reference to the following Examples. It will be appreciated that the Examples provided herein are for purposes of illustration only and are not intended to limit the scope of the disclosed concept.
Each of the permanent magnets 180,182 may extend from proximate the middle portion 108 to proximate a respective distal end portion 114,116 of a respective one of the legs 104,106. Additionally, the permanent magnets 180,182 may have the same magnetic orientation, for example, with a south pole located proximate the lamination 140 and a north pole located opposite the south pole (i.e., between the south pole and the arc chute 10).
A computer generated illustration of the magnetic flux field generated by the slot motor 100 for a given direction of current interruption is shown in
As stated above, the material of the support element 102 advantageously assists in outgassing, responsive to an arcing event. That is, when the arc is driven sideways (i.e., from the separable contacts 6,8 directly toward one of the first and second inner surfaces 110,112), the respective first or second inner surface 110,112 is partially vaporized, advantageously causing the arc to be driven into the arc chute 10. Stated differently, when the arc hits the first inner surface 110 or the second inner surface 112, the releasing of gases pushes the arc into the arc chute 10.
As a result of including the permanent magnets 180,182, the slot motor 100 is advantageously able to interrupt the circuit at relatively high current levels in addition to low current levels. More specifically, the permanent magnets 180,182 impart a novel magnetic force on the electrical arc to drive the arc sideways, and the support element 102, by way of outgassing, is advantageously able to drive the arc into the arc chute 10. This novel mechanism is superior to the mechanisms of prior art slot motors (not shown), which rely entirely on the magnetic field generated by the laminations, a mechanism that is often insufficient to drive the arc into the arc chute at low current levels. More precisely, prior art slot motors generate a magnetic field that is proportional to the current. As a result, at low current levels there is a low magnetic field which has little or no effect in moving the arc into the arc chutes. By contrast, the instant slot motor 100, by including the permanent magnets 180,182, generates a relatively high magnetic field that is independent of the current. Thus, at low current levels there is sufficient magnetic field to move the arc toward the respective permanent magnets 180,182 to generate gassing at the respective inner surfaces 110,112. Furthermore, by locating the permanent magnets in the slot motor 100 (e.g., and not the arc chute 10 as is the case with prior art circuit breakers), the permanent magnets 180,182 are able to be relatively small to drive the arc against the respective inner surfaces 110,112, in order that the arc can be driven into the arc chute 10 with a combined magnetic and fluid-dynamic force, thereby saving space in the arc chute 10 and reducing overall cost.
Additionally, referring again to
The arc plates 12,14,16 also each have an edge portion 13,15,17 extending from proximate the first leg 104 to proximate the second leg 106. This is distinct from prior art arc chutes (not shown) in which the arc plates extend from proximate a slot motor away from the slot motor. It will be appreciated that the disclosed novel geometry of the arc plates 12,14,16 advantageously allows for more space and volume to receive the high current arc.
The example of
Continuing to refer to
By employing the relatively small permanent magnets 280,282,284,286, costs to manufacture the slot motor 200 can be reduced. It will also be appreciated that by employing the third and fourth permanent magnets 284,286, the polarity of the magnetic field can be non-uniform, as well as be uniform. More specifically, the magnetic field is uniform when the polarity of the third and fourth permanent magnets 284,286 corresponds to (i.e., is oriented the same as) the polarity of the first and second permanent magnets 280,282. However, the magnetic field is non-uniform when the polarity of the third and fourth permanent magnets 284,286 is reversed (i.e., is opposite) with respect to the polarity of the first and second permanent magnets 280,282. In a reversed configuration, the resulting magnetic field would be reversed toward a top of the slot motor 200, and thus cause the arc to bend in a serpentine path, which can improve interruption. The serpentine path stretches the arc so that the arc has more engagement with the arc plates 12,14,16, thus resulting in better cooling of the arc. As a result, a higher arc voltage is generated, which corresponds to an improved interruption for the circuit breaker 2.
The example of
It will also be appreciated that in this example there is a reversed magnetic field. More specifically, the permanent magnets 380,382 impart a magnetic force on the electrical arc toward a respective inner surface of the support element at the bottom of the support element, and the magnetic field is reversed at the top of the support element such that at the top of the support element, the electrical arc will be driven toward the opposing inner surface.
Although the examples disclosed herein have been described in association with the permanent magnets 180,182,280,282,284,286,380,382, it will be appreciated that a suitable alternative slot motor (not shown) may have an alternative number, shape, and/or configuration of permanent magnets in order to perform the desired function of driving the electrical arc into a support element.
Accordingly, it will be appreciated that the disclosed concept provides for an improved electrical switching apparatus 2 and slot motor 100,200,300 therefor, in which a plurality of permanent magnets 180,182,280,282,284,286,380,382 combined with outgassing allows the electrical switching apparatus 2 to not only be able to interrupt low current levels, but also be able to interrupt relatively high current levels.
While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.