Patent Application
20170365937
The present invention generally relates to cable shielding. In particular, various embodiments of the invention are directed to methods and devices for electrically connecting to the metallic shield of a cable.
Power cables typically used in utility systems from 4 kV to 35 kV are comprised of several elements including a conductor that carries the electrical power, insulation around the conductor, a semiconductive layer around the insulation, a metallic shield around the semiconductive layer and finally an overall environmental jacket. Whenever such power cables are spliced or terminated, each of the cable elements must be properly reconstructed at the splice or terminating device. In particular, devices are used to reconstruct or restore the cable metallic shield. Such devices are required to ensure any steady-state and short-circuit currents can be adequately carried from one cable to the second cable, or from a cable to an earth ground connection, as required. In addition, these devices must perform adequately for the life of the cable on which they are installed, which is typically considered to be about 40 years.
Currently available devices suffer from a number of shortfalls, including:
Additionally, conventional methods of ensuring adequate contact resistance tend to deform the cable polymeric layers. Further, since cable metallic shields come in a variety of designs, including wire, tape, and longitudinally corrugated shield, as well as a variety of ampacity ratings, such as equal to the conductor, ⅓ of the conductor, 1/12 of the conductor etc., it is difficult to have a single device which is adequate for all designs.
It is therefore desirable to provide an improved device for the reconstruction or restoration of the metallic shield of a cable.
In one aspect, a device for electrically connecting a metallic shield of a cable to another electrical element includes a neutral connection portion for electrically connecting to the metallic shield of the cable and a conductor portion having a first end electrically connected to the neutral connection portion and a second end configured to connect to another electrical element. The conductor portion comprises a plurality of electrical members. The neutral connection portion comprises a flexible, electrically-conductive contact strip. The plurality of electrical members are electrically connected to the electrically-conductive contact strip. The conductor portion also includes a clamping device for biasing the electrically-conductive contact strip against the metallic shield of the cable. The electrically-conductive contact strip is configured to be wrapped around a circumference of the metallic shield of the cable. Preferably, the electrically-conductive contact strip has a length that is at least as long as the circumference of the metallic shield of the cable. In the preferred embodiment, the clamping device is a constant force spring, which can be, for example, mechanically connected to an end of the electrically-conductive contact strip. In certain embodiments, the constant force spring can be equipped with a loop (e.g., circular or U-shaped) device for easy deployment.
In certain embodiments, the plurality of electrical members extend along a top surface of the electrically-conductive contact strip, and a bottom surface of the electrically-conductive contact strip directly contacts the metallic shield of the cable. The electrical members are preferably substantially evenly spaced over at least a portion, and more preferably over substantially the entire length, of the electrically-conductive contact strip.
In some embodiments, the conductor portion further comprises a cover, with the plurality of electrical members extending from the cover. The cover is preferably configured to prevent ingress of water into the neutral connection portion.
In some embodiments, the second end of the conductor portion comprises another neutral connection portion, while in other embodiments the second end comprises a universal connection port.
In another aspect, a method for electrically connecting a metallic shield of a cable to another electrical element includes removing an environmental jacket from the electrical cable to expose the metallic shield of the electrical cable. An electrically-conductive contact strip is wrapped around at least a portion, and preferably the entirety, of the circumference of the exposed metallic shield. The electrically-conductive contact strip is electrically connected to a first end of a conductor portion. A clamping device is connected to the electrically-conductive contact strip to bias the electrically-conductive contact strip against the metallic shield. A second end of the conductor portion is electrically connected to another electrical element.
The various aspects and embodiments disclosed herein will be better understood when read in conjunction with the appended drawings, wherein like reference numerals refer to like components. For the purposes of illustrating aspects of the present application, there are shown in the drawings certain preferred embodiments. It should be understood, however, that the application is not limited to the precise arrangement, structures, features, embodiments, aspects, and devices shown, and the arrangements, structures, features, embodiments, aspects and devices shown may be used singularly or in combination with other arrangements, structures, features, embodiments, aspects and devices. The drawings are not necessarily drawn to scale and are not in any way intended to limit the scope of this invention, but are merely presented to clarify illustrated embodiments of the invention. In these drawings:
Extended connecting member 110 includes a plurality of electrically-conductive members 112 disposed within a cover 114. In some embodiments, cover 114 may be omitted. The members 112 are preferably made from electrically-conductive materials, such as copper, tin-plated copper, a copper alloy (e.g., bronze), aluminum or the like, and may be in the form of, for example, individual strands of conductive material, multi-strand wire, or flexible cable. Extended connecting member 110 preferably has a high electrical conductivity, such as 20% IACS or higher, or more low-conductivity elements 112, to allow conduction of steady state or momentary currents without exceeding 350° C. under typical current-carrying conditions. Cover 114 encloses members 112 and prevents water migration into neutral connection portion 120. Cover 114 may be made from any suitable material that can provide a moisture barrier between the electrically-conductive members 112 and external environment, such as, for example, a heat- or cold-shrinkable moisture seal or tubing, a sealing tape or a dipped coating. Members 112 extend from a first end of cover 114 to electrically connect to neutral connection portion 120 and extend from a second end of cover 114 to electrically connect to other electrical element 116.
Neutral connection portion 120 includes a flexible (e.g., malleable), electrically-conductive contact strip 122 and a clamping device 124. Clamping device 124 may be directly attached to contact strip 122, as shown in
Members 112 extending from the first end of cover 114 are physically and electrically connected to contact strip 122, preferably to the outside surface of contact strip 122. The physical connection of members 112 with contact strip 122 may be direct, as by way of weaving or threading members 112 into contact strip, by pressing members 112 into contact strip 122, or by any other suitable method, or may be indirect, such as through an intermediary, including solder, an electrically conductive (e.g., copper) mesh, or any other suitable intermediate material. Members 112 are preferably fanned out from the first end of cover 114 so that they are substantially evenly spaced over all or a portion of contact strip 122. For example, in some embodiments, the respective distances between immediately adjacent pairs of members 112 are within 25% of the occupying circumference of each other (that is, the variation in distances between adjacent members 112 may be 25% or less). Of course, other variations are possible.
Members 112 are preferably disposed over a sufficiently long portion 122a of the total length 122b of contact strip 122 such that there is no overlapping of members 112 on contact strip 122. Preferably, the portion 122a of contact strip 122 over which members 112 are disposed is sufficiently long that it can go completely around the smallest electrical cable to be serviced by device 100 without the portion 122a overlapping itself (although it may be lapped by the remaining portion(s) 122c of contact strip 122). Additionally, the total length 122b of contact strip 122 is preferably long enough to extend around the entire circumference of the largest electrical cable to be serviced by device 100. Such an arrangement of members 112 and contact strip 122 helps to ensure that the device 100 is as easy to install as possible over the desired range of electrical cables to be serviced.
As previously noted, any suitable method may be employed to physically and electrically connect members 112 to contact strip 122, such as by spot welding, soldering, pressing, etc. By way of the specific embodiment shown in
First, as shown in
Then, as shown in
As shown in
Because the electrical connection to metallic shield 3 of cable 1 is greatly enhanced by the use of contact strip 122, the design ratings of cable 1 are easier to be met including when cable 1 is operated at its designed steady-state current/temperature ratings for its full life, since the flat design of contact strip 122 prevents clamping device 124 from embedding connecting device 100 into the underlying polymeric layers of cable 1, such as semiconductive layer 4 or the underlying insulation layer.
Furthermore, flat contact strip 122 greatly reduces the assembly complexity of connector 100, as it is relatively easy to wrap around metallic shield 3 of cable 1. In addition, by having, for example, a constant force spring as clamping device 124, which is directly and firmly attached to contact strip 122, ease of application is facilitated.
The problem of inconsistent field assembly is also addressed, as integrating the design of contact strip 122 with clamping device 124 greatly improves assembly consistency.
Various embodiments of the invention also address the issues relating to inconsistent contact resistance between the cable metallic shield and the connecting device, as well as issues relating to changing contact resistance between the cable metallic shield and the connecting device as the cable heats and cools, since the flat contact strip 122 provides a constant contact resistance while providing a broad connection surface, as well as spreading the force of the clamping device 124 over a consistent area. The broad area of contact strip 122 also helps to reduce deformation of the cable polymeric layers, such as semiconductive layer 4.
A particularly advantageous aspect of certain embodiments of the invention is the use of a loop disposed through the constant force spring to assist in the deployment of the spring. Embodiments that include a constant force spring may therefore employ this aspect to facilitate the unrolling of the constant force spring around the neutral connecting portion. For example,
Use of loop 226 for deployment of constant force spring 224 is of great benefit to a worker, since high spring forces inherent in such constant force springs can otherwise make their deployment both difficult and dangerous. For example, constant force springs may be relatively difficult to get started around the target region, such as around contact strip 222, as they are quite thin. This can make deployment extremely challenging when wearing gloves. Alternatively, if a constant force spring 224 is deployed with bare hands and adequate care is not exercised for at least the first one or two wraps, the constant force spring 224 may have a tendency to try to return to its original coiled position. If this happens, the user may be injured as the spring 224 snaps off. In addition, it is potentially quite easy for the user to be cut by the relatively thin material of the spring 224, particularly if the spring 224 has a burr on an edge. Use of loop 226 can alleviate all of these issues and thus greatly simplify deployment of constant force spring 224.
When deploying connecting device 200, the user first wraps contact strip 222 around the metallic shield exposed within the splice region of the cable. Thereafter, the user grasps loop 226 to facilitate the further wrapping of constant force spring 224 around deployed contact strip 222. It will be appreciated that in embodiments in which an end 224a of constant force spring 224 is not mechanically connected to contact strip 222, the user may hold a free end of constant force spring 224 into place over and on contact strip 222 with one hand, and then use the other hand to grasp loop 226 to continue the deployment of constant force spring 224 around the splice region. It will therefore be appreciated that in certain aspects, various embodiments employ a method for deploying a constant force spring, such as constant force spring 224, around a device, such as an electrical cable, by deploying (such as by fixing, holding, etc.) an end of the constant force spring on the device (such as end 224a), engaging a loop (such as by grasping loop 226) passing through the axial opening of the constant force spring, and using the loop to pull on the constant force spring so as to wind the remainder of the constant force spring around the device. This winding process using the loop may be continued until, for example, the opposite end of the constant force spring is reached, thus finishing the deployment of the constant force spring around the device, such as around an electrical cable.
With reference to
The following discussion is in relation to first connector 300 and first cable 301. It will be appreciated that a similar set of steps are performed with respect to second connector 400 and second cable 401. With reference to
Then, as shown in
As shown in
It will be appreciated that variations to the methods and related systems discussed above are possible. For example, in one variation, the electrically-conductive members of the extended connecting member need not necessarily be initially mechanically connected to the contact strip. In such a possible variation, the contact strip, preferably with the clamping device already attached to it, such as a constant force spring, can be wound over the exposed cable metallic shield within the splice region. Then, prior to deploying the clamping device, the electrically-conductive members of the extended connecting member can be wrapped or laid over or on top of the contact strip. Thereafter, the clamping device, such as the constant force spring, can be deployed over the deployed electrically-conductive members to clamp the electrically-conductive members and the contact strip into place within the splice region over the cable metallic shield.
Or, in another variation, the cable metallic shielding within the splice region may be folded back to fully expose the underlying cable material, e.g., the semiconductive shield layer of the cable. The contact strip, preferably with the clamping device, such as a constant force spring, already attached to it, is then wound over the exposed cable material, e.g., over the cable semiconductive shield material. The cable metallic shield can then be bent back into position within the splice region, but over the now-deployed contact strip. Prior to deploying the clamping device, the electrically-conductive members of the extended connecting member can be wrapped or laid over or on top of the cable metallic shield. Then, the clamping device, such as the constant force spring, can be deployed over the electrically-conductive members to clamp the electrically-conductive members, the cable metallic shield and the contact strip into place within the splice region over the semiconductive shield layer of the cable.
Those skilled in the art will recognize that the present invention has many applications, may be implemented in various manners and, as such is not to be limited by the foregoing embodiments and examples. Any number of the features of the different embodiments described herein may be combined into a single embodiment, the locations of particular elements can be altered and alternate embodiments having fewer than or more than all of the features herein described are possible. Functionality may also be, in whole or in part, distributed among multiple components, in manners now known or to become known.
It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention. While there has been shown and described fundamental features of the invention as applied to being exemplary embodiments thereof, it will be understood that omissions and substitutions and changes in the form and details of the disclosed invention may be made by those skilled in the art without departing from the spirit of the invention. For example, it will also be appreciated that an advantage offered by specific embodiments of the present invention includes the use of a clamping device, such as a constant force spring, that is mechanically attached to the contact strip, which can greatly simplify deployment of the clamping device. However, this feature is not necessarily required of all embodiments. Moreover, the scope of the present invention covers conventionally known, future developed variations and modifications to the components described herein as would be understood by those skilled in the art.
