Patent Description:
Overhead high voltage power transmission or distribution systems typically have a plurality of electrically conductive cables. Spacer clamp arms are used to reduce the possibility of the conductive cables contacting one another, the generation of corona discharge, and the creation of electrical stress and interference. The spacer clamp arm has an elongated arm portion and a cable keeper end portion at one end of the arm. A spacer clamp arm grips a respective conductive cable at the keeper end portion. The other end of the spacer clamp arm is attached to a frame which may have one or more additional spacer clamp arms attached. The spacer clamp arms permit a limited amount of movement of the spacer clamp arms with respect to the frame, and also provide a controlled electrically semi-conductive path between the spacer clamp and the frame, both of which are usually made of metal.

The keeper end portion defines an opening through which a conductive cable passes. The keeper end portion has a hinge structure that can pivot between an open and closed position. In the open position, the keeper end portion of the spacer clamp arm receives the conductive cable. The spacer clamp arm is then clamped shut. A molded rubber clamp liner is placed between the conductive cable and the keeper end portion of the spacer clamp arm.

The known clamp liner is typically rated for use up to <NUM> degrees centigrade of continuous conductive cable temperature. With the advent of composite core conductors and increased demand for electrical power, conductive cable temperatures often exceed the limit of the known clamp liner. Silicone rubbers can withstand the relatively high surface temperatures but have poor electrical semi-conductive properties. Thus, a need exists for an improved clamp liner capable of withstanding relatively higher conductor temperatures with good electrical semi-conductive properties at a reasonable cost.

This summary is provided to introduce concepts in a simplified form that are further described below in the detailed description.

According to the invention, an improved liner for use with a cable spacer clamp arm is provided. The liner includes a first portion formed in a generally arcuate configuration and made from a first elastomeric material. A second portion is formed in a generally arcuate configuration and is receivable within the first portion. The second portion is made from a second elastomeric material different from the first material. The first portion attaches to the second portion.

According to to the invention, a liner for use with a cable spacer clamp arm is provided. The liner includes a pair of liner halves. Each liner half has a first portion formed in a generally arcuate configuration and made from a first semi-conductive elastomeric material. A second portion of each liner half is formed in a generally arcuate configuration and is receivable within the first portion. The second portion is made from a second semi-conductive elastomeric material different from first semi-conductive elastomeric material. The first portion attaches to the second portion. An inner concave surface is on each first portion. An outer convex surface is on each second portion and is sized and shaped to be received in intimate contact with the inner concave surface of a respective first portion.

According to the invention, an apparatus includes a conductive cable. A spacer clamp arm receives the conductive cable. A liner is receivable in the spacer clamp arm and receives the conductive cable. The liner includes a first portion formed in a generally arcuate configuration and made from a first elastomeric material. A second portion of each liner half is formed in a generally arcuate configuration and is receivable within the first portion. The second portion is made from a second elastomeric material different from the first elastomeric material. The first portion attaches to the second portion. An inner concave surface is on the first portion. An outer convex surface is formed on the second portion and is sized and shaped to be received in intimate contact with the inner concave surface of the first portion.

The following description and drawings set forth certain illustrative embodiments, aspects and implementations. These are indicative of but a few of the various ways in which one or more aspects may be employed. Other aspects, advantages, and novel features will become apparent from the following detailed description when considered in conjunction with the accompanying drawings.

The claimed subject matter is described with reference to the drawings, in which like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide an understanding of the claimed subject matter. It will be apparent, however, that the claimed subject matter can be practiced without these specific details.

This disclosure relates to spacer dampers of the type typically used for spacing bundled electrical conductors suspended from transmission pylons, towers or poles. In particular, this disclosure relates to a clamp arm liner or bushing for use in cable spacer clamp arms of such spacer dampers or other cable securing and support mechanisms.

Overhead transmission lines typically operate at voltages in the range of 275kV to 400kV, and may operate at up to 600kV. At these voltages, it is important that spacer dampers and other spacers that incorporate spacer clamp arms and related components are designed to achieve the required minimum corona discharge performance, in order to avoid the generation of visible corona during operation. Visible corona may be generated particularly in areas where electrical stress is concentrated. Thus, the spacer clamp arms are generally designed to avoid sharp edges and protrusions.

In order to operate effectively on transmission lines at 400kV and above, overhead line components such as spacer dampers must be capable, in practice, of achieving corona free performance at voltages above 340kV phase to ground. Typically, on twin conductor bundles, such performance has only been achieved using metallic clamps which directly grip relatively hard aluminum alloy conductors. Although adequate performance is easier to achieve when using triple, quad or hex bundles, there is a growing trend for existing twin bundle conductors to be replaced with new high current composite core conductors in the same twin bundle configuration, rather than increasing the number of conductors, where it is desired to transmit increased electrical power. This is because increasing the number of conductors will require a costly upgrade in infrastructure. Upgrading the conductors economically allows existing infrastructure configurations to be used, despite the increased cost of the conductors themselves.

However, the new generation of conductors is being introduced, which places new demands on the clamps used to secure them. These conductors are composite core conductors made of mixed metals, or metal and synthetic materials in combination. The composite core conductors typically use a high tensile composite core (e.g., comprising steel, carbon fibre, etc.) with an outer layer (e.g., comprising pure aluminum) and/or an air cooled construction (e.g., GTZASCR).

The new composite core conductors can be used at high temperatures, typically above <NUM>, and are, therefore, able to transmit increased power. Previously, in order to increase power transmission in an electrically conductive cable or transmission line, it was usual to increase the number of conductors in the bundle from two to three or four, typically using an All Aluminum Alloy Conductor (AAAC). With the increased power carrying capacity of the new generation of composite core conductors, there is likely to be a tendency to use just two conductors ('twin-bundled conductors'), but at increased power. The economic benefits of this include a reduction in the need to strengthen pylon, tower or pole metal work when increasing the number of conductors, by utilizing twin conductors at increased power.

Composite core conductors of the type described above are entering service around the world in increasing numbers. Compared with the conventional aluminum alloy conductors, or conductors having at least a hard aluminum alloy outer layer, the pure aluminum outer surface of these composite core conductors is much softer, and more prone to damage. In particular, the composite core conductors are typically intended for use at very high tensions in service, and at temperatures, for example above <NUM>, at which pure aluminum starts to "creep". This combination of high tension and high temperature leaves the conductor particularly prone to being damaged or abraded by metal clamps, especially when vibration is present in the conductor span. In this connection, it should be noted that operating conductors at increased tensions increases the stress in the conductor. This increase in tension and stress leads to a reduction in the self-damping of the conductor and an increase in vibration amplitude, especially at high frequencies, which in turn increases vibration. This lowers the number of cycles that can be absorbed over the life of the conductor without failure, and makes it more important to effectively clamp the conductor at the clamp arm and damp the conductor.

In addition, due to the increased power loads typically carried by these new composite core conductors, the failure or breakage of a conductor strand is much more serious than on conventional conductors, since there is little or no extra power carrying capacity in failure mode. There is, therefore, a need for spacer dampers and clamping components suitable for gripping these new composite core conductors at the relatively high temperatures without damaging, by vibration, the soft aluminum outer surface of the conductor, while still providing the required slip resistance at high tensions. Furthermore, these components also need to be capable of providing corona free performance at about 340kV phase to ground.

The cable spacer dampers include a spacer clamp arm. The spacer clamp arm is provided with a clamp liner or bushing which surrounds the conductor within the clamp arm. The clamp liner is used to enable the spacer clamp arm to grip soft aluminum conductor material, even at relatively high temperatures, while maintaining a target slip resistance and electrical resistance between about <NUM>-<NUM> MΩ, without causing damage to the conductor. Preferably, the geometry of the clamp arm and clamp liner relative to the conductor is arranged to provide in the region of <NUM>%-<NUM>% compression in the clamp liner when the clamp arm is secured to the conductor, and preferably around <NUM>%, which has been found to provide the required slip resistance at temperatures of above <NUM>.

The known clamp liner is typically rated for use up to <NUM> of continuous conductor temperature. With the advent of the new composite core conductors and increased demand for electrical power, conductor temperatures often exceed the limit of the known clamp liner. Thus, a need exists for an improved clamp liner.

One or more aspects of an improved clamp liner <NUM> for a cable spacer system <NUM> (e.g., <FIG>) will now be described, by way of example, with reference to the accompanying drawings. The clamp liner <NUM> protects a conductive cable <NUM> received therein by reducing bending strain on the cable <NUM> at a point where the cable <NUM> enters the spacer system <NUM>. Given that the clamp liner <NUM> may be compressed to some degree, the clamp liner <NUM> also provides a degree of dampening with regard to vibrations along or within the cable.

The improved cable spacer system <NUM> includes at least one electrically conductive cable <NUM> and at least one cable spacer clamp arm <NUM>. The cable spacer clamp arm <NUM> is illustrated in <FIG> in a closed or clamped position securing the conductive cable <NUM> along the axis A of the conductive cable. In <FIG>, the spacer clamp arm <NUM> is illustrated in an open exploded position or condition illustrating the location and configuration of an improved clamp liner <NUM>, constructed according to the one aspect, along the axis A of the conductive cable.

Overhead high voltage power transmission or distribution systems typically have a plurality of electrically conductive cables, such as the conductive cable <NUM>. Spacer dampers (not shown) with spacer clamp arms <NUM> (<FIG> and <FIG>) are used to minimize the possibility of the electrically conductive cables <NUM> contacting one another, minimize the generation of corona discharge and minimize stress and electrical interference between or among conductive cables.

The exemplary spacer clamp arm <NUM> is for use in spacer dampers for the separation of multiple transmission conductive cables, such as the conductive cable <NUM>. The spacer clamp arm <NUM> includes a central arm portion <NUM>, a first or attachment end portion <NUM>, and an opposite second or keeper end portion <NUM>. The keeper end portion <NUM> includes a hinge structure and is located at an end distal from the spacer damper frame. In use, that the spacer clamp arm <NUM> can be hinged between open and closed positions, and clamped around the conductive cable <NUM>. At least the distal end of the keeper end portion <NUM> of the spacer clamp arm <NUM> is preferably formed in the general shape of a sphere which is truncated in a direction along the axis A. This shape has been found to provide improved corona performance, particularly at high transmission voltages.

In order to further improve the corona performance of the spacer clamp arm <NUM>, a hinge arrangement is preferably formed using a hidden hinge pin (not shown), which is located within blind bores or slots in the spacer clamp arm or keeper members. The hidden hinge pin does not extend beyond the outside surface of the distal end of the spacer clamp arm <NUM>, thereby allowing the exterior surface to include a reduced number of discontinuities and provide a smoother exterior contour. In other words, the exterior surface of the distal end of the spacer clamp arm <NUM> forms a continuous surface over the ends of the hinge pin. With this arrangement, it has been found possible to achieve corona free performance at about 340kV phase to ground, on a twin bundle conductor.

The keeper end portion <NUM> has a hinge structure that enables pivot between a closed position or condition, as illustrated in <FIG>, and an open position or condition, as illustrated in <FIG>. In the open position, the keeper end portion <NUM> of the spacer clamp arm <NUM> receives the conductive cable <NUM>. The spacer clamp arm <NUM> is then moved to the closed or clamped position to secure the conductive cable <NUM>. The spacer clamp arm <NUM> permits a limited amount of movement of the spacer clamp arm and conductive cable <NUM> with respect to the frame. The spacer clamp arm <NUM> also provides a controlled electrically semi-conductive path between the spacer clamp arm and the frame, both of which are usually made of metal.

The keeper end portion <NUM> has an upper portion <NUM> that is relatively pivotal relative to lower portion <NUM>. The lower portion <NUM> is integrally formed into the central arm portion <NUM> of the spacer clamp arm <NUM>. The upper portion <NUM> is movable to the closed position, illustrated in <FIG>, to clamp and retain the conductive cable <NUM> within the spacer clamp arm <NUM>.

The aspect of spacer clamp arm <NUM> shown in <FIG> and <FIG> has been designed to achieve the required radio interference voltage (RIV) and corona performance on twin bundled conductors at voltages above 340kV phase to ground. This is achieved through the unique geometry of the spacer clamp arm <NUM> described above.

The first or attachment end portion <NUM> of the spacer clamp arm <NUM> connects to a spacer damper frame (not shown), which may have one or more additional spacer clamp arms attached, for relative pivotal movement. The keeper end portion <NUM> defines an opening <NUM> through which the conductive cable <NUM> is receivable.

A suitable fastener, such as a bolt or pin (not shown) is used to secure the upper portion <NUM> of the keeper end portion <NUM> to the lower portion <NUM> of the keeper end portion when the spacer clamp arm <NUM> is in the closed position. The clamp liner <NUM> is compressed by about <NUM>% of its volume when the spacer clamp arm <NUM> is secured about the conductive cable <NUM> and the upper portion <NUM> is sufficiently fixed to the lower portion <NUM>.

In use, the conductive cable <NUM> is secured within the keeper end portion <NUM> of the spacer clamp arm <NUM>. A clamp liner <NUM> is located in the opening <NUM> between the conductive cable <NUM> and the keeper end portion <NUM>. The clamp liner <NUM> (<FIG>) has a pair of substantially identical liner halves <NUM>.

A molded rubber clamp liner <NUM>, according to one aspect, is placed between the conductive cable <NUM> and the keeper end portion <NUM> of the spacer clamp arm <NUM>. The clamp liner <NUM> protects the conductive cable <NUM> and also provides a degree of damping.

Each of the liner halves <NUM> is formed into an approximately semi-circular cross-section configuration. Each of the liner halves <NUM> is placed in respective semi-circular recesses of the keeper end portion <NUM> which define the opening <NUM>.

The clamp liner <NUM> (<FIG>) includes two substantially identical liner halves <NUM>. Each of the liner halves <NUM> includes an outer portion <NUM> and an inner portion <NUM>. A half <NUM> of the clamp liner <NUM> can be molded or extruded as separate parts of their respective different material.

Each outer portion <NUM> of the liner halves <NUM> includes an opening <NUM> located approximately centrally, but each outer portion could be located anywhere along the arcuate length of the outer portion. Each of the inner portions <NUM> includes a projection <NUM> that is receivable in the opening <NUM> in the outer portion <NUM>. This connects the outer and inner portions <NUM>, <NUM> together and prevents relative axial and rotational movement between the outer and inner portions. The outer portion <NUM> and inner portion <NUM> of the liner half <NUM> can also be affixed by mechanical or other suitable means such as a lateral extruded profile, or by use of a plastic or metal rivet, self-tapping screw or other suitable means.

The outer portion <NUM> and inner portion <NUM> may be attached together or formed in a variety of ways. In the example illustrated in <FIG> and <FIG>, a mechanical connection is shown. It will be apparent that any type of mechanical fastening arrangement may be used, such as interlocking grooves, mechanical fasteners or adhesive bonding. It is also contemplated that the outer and inner portions <NUM>, <NUM> can be formed separately and then molded together under heat and pressure in order to bond the outer and inner portions together. It is also contemplated that the outer and inner portions <NUM>, <NUM> be co-extruded and integrally formed as one piece with two different materials.

The outer portion <NUM> of each liner half <NUM> includes an outer concave annular surface <NUM> (<FIG> and <FIG>) that is receivable about a convex inner surface <NUM> (<FIG>) of the keeper end portion <NUM> of the spacer clamp arm <NUM>. This interaction minimizes or prevents relative axial movement between the clamp liner <NUM>, conductive cable <NUM> and the spacer clamp arm <NUM>.

Each of the outer portions <NUM> also includes an annular inner concave surface <NUM> that extends completely around the outer periphery of the clamp liner <NUM>. This annular inner concave surface <NUM> of the outer portion <NUM> receives an outer annular convex surface <NUM> of the inner portion <NUM> extending around the outer periphery of the inner portion <NUM>. This interaction prevents relative movement in a direction along the axis A between the inner and outer portions <NUM>, <NUM>.

The profile of the interfacing surfaces <NUM>, <NUM> has been designed as such to provide a lateral interference fit so that slip loads for the conductive cable <NUM> in the direction of the axis A (e.g., typically in excess of <NUM>-<NUM> kN) do not cause the inner portion <NUM> to separate from the outer portion <NUM>. The attachment, fixing or bonding is only used as a method to keep the inner and outer portions <NUM>, <NUM> together during manufacture, transit, application and installation.

According to one aspect, the clamp liner <NUM> is made of a high temperature resistant and semi-conductive elastomer capable of providing a secure grip without damage to the conductive cable <NUM> at temperatures above <NUM>. In particular, the clamp liner <NUM> enables the spacer clamp arm <NUM> to grip the conductive cable <NUM> while maintaining a relative slip resistance of <NUM> kN for one minute. Preferably, this performance is achieved at temperatures above <NUM> on round or trapezoidal conductors. More preferably, the material that the clamp liner <NUM> is made from is also capable of resisting atmospheric ozone for a period of at least <NUM> years, and preferably <NUM> years, while continuing to meet the specified temperature, slip resistance, semi-conductive and electrical resistance requirements.

The outer surface of each clamp liner <NUM> is shaped to correspond to the inner surface of the keeper end portion <NUM>. An inner surface <NUM> of each clamp liner <NUM> is shaped to correspond to the size and/or shape of the conductive cable <NUM> to which the spacer clamp arm <NUM> is intended to be clamped. In this way, when the clamp liners <NUM> are positioned in the opening <NUM>, and the spacer clamp arm <NUM> is in the closed position, the clamp liner <NUM> fills the opening <NUM> and defines the inner surface <NUM> through which the conductive cable <NUM> can pass. The clamp liner <NUM> is made from an elastomeric material which provides a degree of resilience for damping, such that a controlled gripping pressure can be applied to the conductive cable <NUM>. The clamp liner <NUM> also has a controlled size of the inner surface <NUM> relative to the diameter of the conductive cable <NUM>, thereby reducing the strain at the interface between the conductive cable and the clamp liner.

Each liner half <NUM> of the clamp liner <NUM>, according to one aspect, has the outer portion <NUM> and the inner portion <NUM> made from different semi-conductive elastomeric materials. The outer portion <NUM> is made from a semi-conductive fluoroelastomer compound, such as ethylene propylene diene monomer (EPDM). The inner portion <NUM> is made from a different semi-conductive fluoroelastomer compound, such as vinylidene fluoride hexafluoropropylene (FKM). The outer portion <NUM> occupies more than <NUM>% of the volume in each liner half <NUM> of the clamp liner <NUM>, and preferably about <NUM>%. The inner portion <NUM> occupies less than <NUM>% of the volume in each liner half <NUM> of the clamp liner <NUM>, and preferably about <NUM>%. This configuration provides excellent performance at a reasonable cost by using a minimal amount of the relatively costly FKM.

When using these elastomeric material compounds, it has been found that the required slip resistance can be achieved at temperatures up to about <NUM> when the geometry of the spacer clamp arm <NUM> and clamp liner <NUM> relative to the conductive cable <NUM> is arranged to provide in the region of <NUM>% compression of volume in the clamp liner when the spacer clamp arm is secured to the conductive cable. This performance has been achieved on both round and trapezoidal conductors.

According to another aspect intended for even higher temperature service, for example up to about <NUM> or even about <NUM>, the outer portion <NUM> is made from a semi-conductive fluoroelastomer compound, such as vinylidene fluoride hexafluoropropylene (FKM). The inner portion <NUM> is made from a different semi-conductive fluoroelastomer compound containing an even higher amount of fluoride than FKM, such as perfluoroelastomer (FFKM). The outer portion <NUM> occupies more than <NUM>% of the volume in each liner half <NUM> of the clamp liner <NUM>, and preferably about <NUM>%. The inner portion <NUM> occupies less than <NUM>% of the volume in each liner half <NUM> of the clamp liner <NUM>, and preferably about <NUM>%.

When using these compounds, it has been found that the required slip resistance can be achieved at temperatures up to about <NUM> when the geometry of the spacer clamp arm <NUM> and clamp liner <NUM> relative to the conductive cable <NUM> is arranged to provide in the region of <NUM>% compression of volume in the clamp liner when the spacer clamp arm is secured to the conductive cable. This performance has been achieved on both round and trapezoidal conductors.

The material selection for the clamp liner <NUM> is not limited to EPDM, FKM and FFKM. The material selection for the clamp liner <NUM> could from a broad range of elastomers where different temperature, gripping or electrically semi-conductive, resistance and capacitive properties are required. The material selection for the clamp liner <NUM> may depend on a limiting factor such as cost or the electrical, chemical or mechanical property in contact with the conductive cable <NUM> or spacer clamp arm <NUM>.

According to yet another aspect, liner halves <NUM> of a clamp liner <NUM> are provided as a single piece unit. At least one of the liner halves <NUM> of the clamp liner <NUM> is integrally formed as a single piece unit. A liner half <NUM> of the clamp liner <NUM> can be molded or extruded as separate parts of their respective different material. An outer portion <NUM> and an inner portion <NUM> of the liner half <NUM> can be co-extruded to provide the single piece half. Alternatively the outer portion <NUM> and inner portion <NUM> of the liner half <NUM> can be co-molded by use of compatible curing agents in the constituent elastomers that enable a mechanical cross linking between the outer portion <NUM> and the inner portion <NUM> extruded to provide the single piece half. The outer portion <NUM> and inner portion <NUM> of the liner half <NUM> can even be molded or extruded separately and bonded through use of a post mold vulcanization process (hot or cold) or adhesive bonding to provide the single piece half.

Thus, improved clamp liners <NUM>, <NUM> are provided according to any aspect or combination of aspects. It will be appreciated that application of the clamp liners is not limited to spacer dampers but that one or more of the clamp liners provided herein may be used in other interphase spacers (e.g., such as those not having dampening mechanisms). One or more of the clamp liners provided herein may, for example, be used on clamping attachments for transmission line accessories attached to high temperature conductors such as but not limited to Stockbridge TypeVibration Dampers, Brettele Dampers, Festoon Dampers, Conductor clamps etc..

Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as "upper", "lower", "above", and "below" refer to directions in the drawings to which reference is made. Terms such as "left", "right", "front", "back", "rear", "bottom" and "side", describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms "first", "second" and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context.

When introducing elements or features of the present disclosure and the exemplary aspects, the articles "a", "an" and "the" are intended to mean that there are one or more of such elements or features. The terms "comprising", "including" and "having" are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance.

Claim 1:
A liner (<NUM>) for use with a cable spacer clamp arm (<NUM>), with a keeper end portion having a general sphere shape, the liner comprising a pair of liner halves, each liner halves having:
a first portion (<NUM>) formed in an arcuate configuration and made from a first high temperature resistant and semi-conductive elastomeric material receivable in the keeper end portion of the spacer clamp arm; and
a second portion (<NUM>) formed in the arcuate configuration and made from a second first high temperature resistant and semi-conductive elastomeric material and adapted to receive a portion of a cable (<NUM>),
wherein the first portion attaches to the second portion, and:
the first portion includes an inner concave surface (<NUM>) that extends around an inner periphery of the first portion (<NUM>) is; and
the second portion includes an outer convex surface (<NUM>) that extends around an outer periphery of the second portion (<NUM>),
wherein the inner concave surface of the first portion receives the outer convex surface of the second portion, to provide an interfacing surface interaction between the first portion and the second portion with a profile of the interfacing surfaces to prevent relative movement between the first portion and the second portion in an axial direction along the cable.