Support for supporting overhead electrical cables

Abstract

 The support comprises a body (1, 2, 3) of electrically insulating material, such as polymeric material, providing a plurality of flanges (10) arranged in spaced parallel planes, and a plurality of individual insulating members (20) of, for example, silicone rubber, each mounted about the periphery of a respective one of the flanges (10) and being sized to increase the radius of curvature of the periphery of the flange (10). The insulating members (20) serve to descrease the local stresses in the electric field that normally occur at the peripheries of the flanges (10) particularly under damp weather conditions, thereby preventing flash-over.

Description

[0001] This invention relates to a support for supporting overhead electrical cables.

[0002] High voltage, for example 132kV, overhead electrical cables are often supported by supports mounted on cross-arms carried by a tower or wooden pole, each support comprising a body of electrically insulating material providing a plurality of flanges arranged in spaced parallel planes.

[0003] Supports of such a shape are used since they provide a long creepage path over their surface between their ends thus providing good protection against flash-over between a supported cable and the supporting tower during adverse atmospheric conditions.

[0004] Such supports have been made of porcelain material, but recently they have been made of polymeric material since the greater strength of such material enables the flanges, known as sheds, to be made thinner, thus enabling a greater number of flanges to be provided in a support of a given length. Further, under normal dry or rainy atmospheric conditions the modification to the electric field surrounding a support in use, caused by the flanges, is much smaller for supports made of polymeric material than for supports made of porcelain material.

[0005] However, it has been discovered that under certain atmospheric conditions, for example low temperature, low wind speed, heavy mist, and an upward air flow around a support, the whole surface of the support, and not just the upwardly facing surfaces thereof as is normal, becomes sufficiently wetted to be significantly electrically conductive.

[0006] This is particularly so if the surface of the support has a coating of an ionisable material, such as salt from the atmosphere, thereon.

[0007] When a support is so wetted and thus electrically conductive, the surrounding electric field can be modified to such an extent that local high stresses arise at the peripheries of the flanges, these giving rise to the ejection of charged water particles from the peripheries. If the surrounding atmosphere is sufficiently damp and the wind speed sufficiently low the supports can become enveloped in a charged atmosphere which can result in flash-over occurring.

[0008] According to this invention there is provided a support for supporting overhead electrical cables, comprising a body of electrically insulating material providing a plurality of flanges arranged in spaced parallel planes, characterised by a plurality of individual insulating members each mounted about the periphery of a respective one of said flanges and being sized to increase the radius of curvature of the periphery of said one flange.

[0009] With a support according to this invention the insulating members, which can be in the form of silicone rubber rings, serve to increase the local radius of curvature at the peripheries of the flanges, and thus serve, in use, to decrease the local stresses that occur at these positions, whereby the conditions leading to the production of an enveloping charged atmosphere about the support are avoided.

[0010] The radius of curvature provided by the insulating members is determined by the need to increase the radius of curvature of the flanges sufficiently to avoid local high stresses, while ensuring that sufficient spacing is maintained between adjacent insulating members to prevent flash-over occuring under rainy atmospheric conditions.

[0011] This invention will now be described by way of example with reference to the drawing, in which:-

Figure 1 shows three known forms of support to which the invention can be applied:

Figure 2 is a side view, partly in section, of part of a support according to the invention; and

Figure 3 shows a detail of the support of Figure 2.

[0012] Figure 1 shows three supports each comprising a body 1, 2 or 3 of electrically insulating material, such as polymeric material, providing a plurality of circular flanges 10 arranged in spaced parallel planes, and having at one end 4 a fitting for connection to a cross-arm carried by a tower or wooden pole and at the other end 5 a fitting for connection to a cable to be supported. The body 1 provides flanges 10 all of the same diameter and lying in planes inclined to the longitudinal axis of the support; the body 2 provides flanges 10 of alternating relatively large and relatively small diameter lying in planes perpendicular to the londitudinal axis of the support; the body 3 provides flanges 10 of alternating relatively large and relatively small diameter lying in planes inclined to the longitudinal axis of the support.

[0013] Figures 2 and 3 show a support with a body 1 as shown in Figure 1, with which a plurality of individual insulating members 20 in the form of circular cross-section silicone rubber rings, are mounted about the peripheries of respective ones of the flanges 10, the members 20 being sized to increase the radius of curvature of the peripheries of the flanges 10. As shown in Figure 3, each member 20 is formed with an inwardly open groove 21 which receives a peripheral edge portion of the associated flange 10 whereby the member 20 is retained on the flange 10. The depth of the groove 21 is the maximum possible compatible with retaining sufficient strength for the member 20. A self-vulcanising material is provided in the groove 21 in order to fill any indentations in the surface of the flange 10 caused, for example, by weathering and/or discharge activity.

Claims

1. A support for supporting overhead electrical cables, comprising a body (1) of electrically insulating material providing a plurality of flanges (10) arranged in spaced parallel planes, characterised by a plurality of individual insulating members (20) each mounted about the periphery of a respective one of said flanges (10) and being sized to increase the radius of curvature of the perhiphery of said one flange (10).

2. A support as claimed in Claim 1, characterised in that the body (1) is of polymeric material.

3. A support as claimed in Claim 1 or Claim 2, characterised in that the insulating members (20) are rubber rings.

4. A support as claimed in Claim 3, characterised in that each rubber ring (20) is formed with a groove (21) to receive a peripheral edge portion of the associated flange (10).

5. A support as claimed in Claim 4, characterised in that the groove (21) contains a self-vulcanising material.

Drawing