1. Field of the Invention
The invention relates generally to switchgear devices and, more particularly, to maintenance-free electrical bus assemblies. The invention further relates to electrical enclosures having a maintenance-free electrical bus assembly.
2. Background Information
Electrical bus assemblies for switchgear devices (e.g., without limitation, electrical switching apparatus, such as circuit switching devices and circuit interrupters such as circuit breakers, contactors, motor starters, motor controllers and other load controllers), which are mounted in an electrical enclosure, must be routinely inspected.
Specifically, preventative maintenance (PM) inspections are required to ensure that fastener assemblies which electrically couple the various bus joints of the electrical bus assembly together, have not loosened over time. A loose electrical bus assembly could result in substantial damage to electrical equipment, electrical system failure, and perhaps even human injury. Accordingly, industry standards and regulations require that PM inspections of electrical bus assemblies be performed as often as every six months, and in some instances, even more frequently.
In a switchgear cabinet, for example, the electrical bus assembly for the switchgear devices housed within the cabinet is generally disposed toward the back of the cabinet. Thus, in order to perform the aforementioned PM inspections of the electrical bus assembly, access to the back of the cabinet is required. However, in certain applications access to the back of the cabinet is limited or altogether unavailable, such as, for example, where the cabinet is disposed with the back of the cabinet adjacent a wall. Under such circumstances access to the electrical bus assembly is limited to that which is available through the front of the cabinet, if any. Some of the bus joints of the bus assembly are not accessible for the PM inspections.
By way of example,
Fastener locking mechanisms (e.g., without limitation, prevailing torque-type nuts) and fastener securing techniques, such as, for example, the use of chemical additives such as LOCTITE®, which are commonly employed to secure various non-electrical fastener assemblies, are generally not acceptable in electrical applications. Specifically, some prevailing torque-type nuts include an insert made of a material, such as, for example, nylon, which becomes soft when heated, and defeats the prevailing torque function and plastically deforms such that the desired preload of the components being fastened cannot be maintained. Other prevailing torque-type nuts rely upon a relatively small mechanical deformation (e.g., dent) to generate a restraining torque to prevent turning. Such known prevailing torque-type nuts exhibit an unpredictable amount of torque to be overcome when installing the nut, which in turn can create a joint that may not be sufficiently tight for optimum electrical conductivity without “over-tightening” the fastening system. Likewise, chemical additives for securing fastener assemblies often break down when exposed to elevated temperatures, and lose their locking effect, for example, becoming loose due to vibration. They can also disrupt electrical conductivity.
In view of the foregoing, one prior proposal has been to weld the bus joints of the electrical bus assembly which cannot be accessed for routine inspection, as opposed to using mechanical fasteners (e.g., bolts; nuts; a combination of bolts, washers, and nuts). However, welding undesirably increases the manufacturing costs and complexity of the electrical bus assembly. It also renders the bus assembly incapable of being readily modified in the future.
There is a need, therefore, for an electrical bus assembly which is substantially maintenance-free (i.e., it does not require periodic inspection and/or maintenance), without requiring welding of the electrical bus members comprising the bus assembly.
There is, therefore, room for improvement in electrical bus assemblies, and in electrical enclosures having electrical bus assemblies.
These needs and others are met by embodiments of the invention, which are directed to a maintenance-free electrical bus assembly, and to an electrical enclosure for housing switchgear devices which employ a maintenance-free electrical bus assembly.
As one aspect of the invention, a maintenance-free electrical bus assembly is provided which comprises: a plurality of electrical bus members; at least one bus joint, each of the at least one bus joint comprising an electrical connection of two or more of the electrical bus members; and a fastener assembly fastening the at least one bus joint and maintaining the electrical connection between the electrical bus members of the at least one bus joint, the fastener assembly comprising: at least one first fastening element including a plurality of first threads, and at least one second fastening element including a plurality of second threads, the second threads of the at least one second fastening element being structured to threadably engage the first threads of a corresponding one of the at least one first fastening element, wherein the second threads of the at least one second fastening element are further structured to perpetually secure the first threads and the corresponding one of the at least one first fastening element, in order to resist undesirable loosening of the at least one bus joint once the fastener assembly has been fastened.
The first fastening element of the fastener assembly may comprise a number of bolts and the second fastening element of the fastener assembly may comprise a number of nuts, wherein the electrical bus members are perpetually secured in electrical communication between the bolts and the nuts of the fastener assembly when the bolts and the nuts are tightened. The fastener assembly may further comprise at least one third fastening element, such as a washer, wherein at least one washer is disposed between at least one of the bolts and one of the electrical bus members, and the nuts and one of the electrical bus members.
The electrical bus members may comprise a plurality of power bus bars electrically connected together between a number of bolts and nuts, or the electrical bus members may comprise at least one first electrical bus member and at least one second electrical bus member, wherein the first fastening element of the fastener assembly comprises at least one threaded fastener having a plurality of first threads, and the second fastening element of the fastener assembly comprises at least one threaded portion of the first electrical bus member, wherein the at least one threaded portion includes a plurality of second threads which engage the first threads of a corresponding threaded fastener, and wherein the first electrical bus member is perpetually electrically connected to the second electrical bus member when the corresponding threaded fastener is tightened. The threaded fastener may comprise a bolt and the second electrical bus member may include an aperture, wherein the bolt is inserted through the aperture of the second electrical bus member.
The second electrical bus member may comprise a single power bus bar, and the first electrical bus member may comprise a current transformer bushing having an end, wherein the at least one threaded portion comprises a threaded bore in the end of the current transformer bushing, and the at least one aperture comprises a single aperture of the single power bus bar. A single bolt may be inserted through the single aperture of the single power bus bar and perpetually secured within the threaded bore of the current transformer bushing when the single bolt is tightened, thereby resisting the current transformer bushing from loosening with respect to the single power bus bar. The first electrical bus member may alternatively comprise a rigid, solid conductor having an end, the at least one threaded portion may comprise a plurality of threaded bores in the end of the rigid, solid conductor, the at least one second electrical bus member may comprise at least one power bus bar and the at least one aperture may comprise a plurality of apertures in the power bus bar. One of a plurality of bolts may be inserted through each of the apertures of the power bus bar and be perpetually secured within a corresponding one of the threaded bores of the rigid, solid conductor when the bolt is tightened, thereby resisting the rigid, solid conductor from loosening with respect to the at least one power bus bar. The at least one bus joint may comprise a spout joint, wherein the rigid, solid conductor comprises a spout conductor. Alternatively, a plurality of power bus bars may be connected to the current transformer bushing, the rigid, solid conductor, the spout conductor, or any other suitable electrical bus member, as defined herein.
The second threads of the at least one second fastening element may comprise a SPIRALOCK® thread form.
As another aspect of the invention, an electrical enclosure comprises: a plurality of sides; at least one switchgear device disposed on or between the sides; and a maintenance-free electrical bus assembly coupled to the at least one switchgear device, the maintenance-free electrical bus assembly comprising: a plurality of electrical bus members, each of the electrical bus members being in electrical communication with at least one of the at least one switchgear device, at least one bus joint, each of the at least one bus joint comprising an electrical connection of two or more of the electrical bus members, and a fastener assembly fastening the at least one bus joint and maintaining the electrical connection between the electrical bus members of the at least one bus joint, the fastener assembly comprising: at least one first fastening element including a plurality of first threads, and at least one second fastening element including a plurality of second threads, the second threads of the at least one second fastening element being structured to threadably engage the first threads of a corresponding one of the at least one first fastening element, in order to perpetually secure the first threads and the corresponding one of the at least one first fastening element, and to resist undesirable loosening of the at least one bus joint once the fastener assembly has been fastened.
The electrical enclosure may be a switchgear cabinet, wherein the plurality of sides of the switchgear cabinet comprises a top, a bottom, and first and second sidewalls, and wherein the at least one switchgear device is coupled to at least one of the top, the bottom, and the first and second sidewalls of the switchgear cabinet. The at least one bus joint of the maintenance-free electrical bus assembly may comprise a plurality of bus joints, wherein at least one of the bus joints is substantially inaccessible and wherein, when the fastener assembly is fastened, the fastener assembly secures the at least one of the bus joints, perpetually. The switchgear device may have a predetermined operating life expectancy, wherein the fastener assembly of the maintenance-free electrical bus assembly is structured to secure the bus joint of the maintenance-free electrical bus assembly for at least as long as the predetermined operating life expectancy of the switchgear device.
A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
Directional phrases used herein, such as, for example, front, back, top, bottom, and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein.
As employed herein, the term “switchgear device” means a circuit interrupter, such as a circuit breaker (e.g., without limitation, low-voltage or medium-voltage or high-voltage); a motor controller/starter; a contactor; and/or any suitable device which selectively switches voltage, current or power.
As employed herein, the term “electrical bus” or “electrical bus member” means a rigid, solid conductor which carries or transfers voltage, current or power; a power bus bar; a power bus bar connection point; a finger cluster; a power bus bar connection point inside an electrical enclosure (e.g., without limitation, a switchgear cabinet); and/or a power bus structure for a switchgear device, but expressly excluding any grounded conductor (e.g., as used in a frame, enclosure or housing for a number of electrical devices).
As employed herein, the phrase “fastener” and “fastening element” refers to any suitable connecting or tightening mechanism expressly including, but not limited to, screws, bolts and the combinations of bolts and nuts (e.g., without limitation, lock nuts) and bolts, washers and nuts, and further includes any known or suitable component having a plurality of threads (e.g., without limitation, a threaded bore or aperture) structured to threadably engage the threads of another fastening element.
As employed herein, the phrase “thread form” refers to the particular shape, orientation and/or configuration of the plurality of threads of a particular fastening element.
As employed herein, the statement that two or more parts are “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts.
As employed herein, the term “perpetually” refers to the substantially permanent or everlasting duration of the connection which is provided by a fastener assembly in accordance with embodiments of the invention. Specifically, the fastener assembly, once fastened, will never unintentionally come loose. In other words, the fastener assembly and the bus joint which it secures does not have to be inspected (i.e., it is maintenance-free) because it will remain secure for at least as long as the predetermined life expectancy (e.g., without limitation, about 15 years to about 50 years or more) of the switchgear device with which it is employed.
As employed herein, the term “number” shall mean one or an integer more than one (i.e., a plurality).
In
As shown in
Each fastener assembly 108,208,308 includes at least one first fastening element 110,210,310 having a plurality of first threads 112,212,312, and at least one second fastening element 114,214,314 including a plurality of second threads 116,216,316. The second threads 116,216,316 of each second fastening element 114,214,314 are structured to threadably engage the first threads 112,212,312 of a corresponding first fastening element 110,210,310, in order to perpetually secure the first threads 112,212,312 and the associated corresponding first fastening element 110,210,310, and thereby resist undesirable loosening of the bus joint 106,206,306 once the fastener assembly 108,208,308 has been fastened (see, for example, fastened fastener assembly 208 of
The maintenance-free electrical bus assembly 100,200,300 will be further understood and appreciated with reference to the following EXAMPLES, which will now be discussed individually with reference to
In
Each bolt 110 in
Accordingly, it will be appreciated that the maintenance-free electrical bus assembly 100 provides for a bus joint (e.g., corner bus joint 106) which does not need to be periodically inspected. More specifically, in an application such as EXAMPLE 1, shown in
It will be appreciated, as will now be discussed, that the electrical bus members could comprise any known or suitable electrical bus members, as defined herein, other than the power bus bars 102,104 shown in
More specifically,
EXAMPLE 3, shown in
Accordingly, embodiments of the invention provide a maintenance-free electrical bus assembly wherein the fastener assemblies of one or more bus joints perpetually secure any known or suitable combination of electrical bus members in the desired configuration, thereby substantially eliminating the need to perform periodic preventive maintenance (PM) inspections of the bus joints.
While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the at 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 invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.
Number | Name | Date | Kind |
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4361724 | Olashaw | Nov 1982 | A |
4886468 | Harton et al. | Dec 1989 | A |
5244423 | Erickson et al. | Sep 1993 | A |
5282707 | Palm | Feb 1994 | A |
6141206 | Bruner et al. | Oct 2000 | A |
6619161 | Blair | Sep 2003 | B1 |
Number | Date | Country | |
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20080038949 A1 | Feb 2008 | US |