Field of the Invention

This invention relates in general to electric power transmission line insulators. More particularly, it relates to an improved weathershed for a composite insulator.

Background of the Invention

Insulators are used to prevent the loss of electric charge or current from conductors in electric power transmission lines. A typical insulator is made from a material which has a very high resistance to electric current so that current flow through it is negligible. One type of insulator is referred to as a suspension insulator. It suspends a transmission line from an overhead support. A particular type of suspension insulator is referred to as a composite insulator.

A composite insulator may include a coated fiberglass rod surrounded by weathersheds made from a highly insulating material (see, for example, Kuhl U.S. Patent No. 4,217,466, or, Bauer U.S. Patent No. 4,246,696) . A common approach has been to cover the fiberglass rod with an insulating coating. The weathersheds are molded from rubber or other polymeric material and then bonded to the coated rod using a polymer based adhesive. Metal fittings are provided at

each end of the rod for connecting one end to a support pylon and the other end to a power line.

The weathersheds and the fiberglass rod are made from different material in order to enhance the performance of the two components in their distinct functions. In general, the rod takes the mechanical stress and contributes to the insulation function, while the weathersheds provide the majority of the insulation. The weathersheds also increase the distance which leakage currents must travel from one metal fitting to the other. The weathersheds must be fitted in such a way that no electric conduction can occur through the seam between a weathershed and the coated rod. Each weathershed must have good stability in all weather conditions. Furthermore, it must be of sufficient thickness to prevent its electrical resistance from being overcome. Additional information regarding the operation and construction of composite insulators may be found in U.S. Patent Nos. 3,898,372; 4,267,403; 4,331,833; and 4,355,200.

Summary of the Invention

A primary object of the present invention is to provide an improved weathershed for composite insulators.

It is another object to provide a weathershed which is lightweight and easy to manufacture.

It is a further object to provide a weathershed having a reduced electric field gradient.

It is still another object to provide a weathershed having a reduced tendency to trap contaminants such as dust, water and air pollutants.

It is yet another object to provide a weathershed which creates a maximum leakage current distance.

The foregoing and other objects are realized in accord with the present invention by providing a

weathershed having a molded body with a hub and a skirt. The thickness of the skirt is substantially uniform from the hub to its annular outer edge. This maximizes leakage current distance while, at the same time, minimizing material usage. The annular outer edge is radially curved between upper and lower faces of the skirt to reduce the value of the electric field gradient. Other edges or external corners on the body are also curved.

Brief Description of the Drawings

The invention, including its construction and method of operation, together with additional objects and advantages thereof, is illustrated in the following drawings, in which:

Figure 1 illustrates a composite insulator embodying features of the present invention;

Figure 2 is a vertical sectional view taken through a portion of the insulator shown in Figure 1; and

Figure 3 is an enlarged sectional view taken along line 3-3 of Figure 1.

Description of the Preferred Embodiment

Figure 1 illustrates a composite insulator 10 embodying the present invention. The insulator 10 may be used to insulate any of a variety of electric power transmission lines (not shown) , including high tension lines (typically 100-400 KV) or distribution lines (typically 15-35 KV) . A transmission line normally includes a set of conductors, usually bare, which are supported by a series of supporting structures such as wooden H-frames or steel towers, for example. With a distribution line, the supporting structures may be conventional wood poles.

The insulator 10 may be connected to the power line in variety of connection configurations, including

"suspension," "deadend" and "post" connections. The general structure of the insulator 10 is essentially the same, regardless of the manner in which it is connected to the power line or the support.

As shown in Figure 1, the composite insulator 10 comprises a rod 20, a shield layer 30 and a plurality of weathersheds 40 fastened to the shielded rod. Metal fittings 22 are attached to each end of the rod 20 for connecting one end of the rod to a support pylon (not shown) and the other end to a power line (also not shown) .

Suitable materials and methods of construction for the rod 20 and the shield layer 30 are described in U.S. Patent No. 4,217,466 to Kuhl, and U.S. Patent No. 4,246,696 to Bauer et al. Suitable materials for the weathersheds 40, along with adhesives and methods for attaching the weathersheds 40 to the shield layer 30, are also disclosed in Kuhl and Bauer et al. The entire disclosures of both of these patents are incorporated herein by reference.

The rod 20 is generally elongated and may be made as a composite structure from glass fibers and a resin produced by pultrusion. Since the rod 20 must support the entire tension load to which the insulator 10 is subjected, it is important that the rod be of high mechanical strength as well as high dielectric strength. The glass fibers are ^' resin bonded into an elongated, cylindrical rod 20 having a smooth exterior surface of substantially uniform diameter. The bonding resin must provide a good mechanical bond and have high dielectric strength to ensure that the completed rod will have the desired insulation capability. However, the tensile strength of the rod is imparted, in large measure, by the fibers. Accordingly, it is desirable that the fibers constitute a large part of the cross section of the rod.

The rod 20 h s an extrusion applied shield layer 30 which consist, of an envelope of silicone or other elastomer that is current peak-proof and weather resistant. The shield 30 provides an intermediate layer of material between the rod 20 and the weathersheds 40. The shield 30 protects the rod 20 from deleterious material and may be made from a mono-functional or poly- functional polymer. Each weathershed 40 is mounted on the rod 20 by inserting the rod through an aperture 43 (see Figure 3) in the weathershed 40. The weathersheds 40 may be secured to the shield layer 30 with an adhesive. Alternatively, the weathersheds 40 and the shield layer 30 may be cross-linked together.

Turning now to Figures 2 and 3, the construction of a weathershed 40 is illustrated in greater detail. The weathershed 40 is preferably molded from a flexible, yet sturdy, synthetic material. Molding is accomplished by conventional injection and/or compression molding techniques. Suitable synthetic materials include EPDM rubber, silicone rubber, and other materials having similar properties. In the preferred embodiment shown, silicone rubber is employed.

The weathershed 40 has a disc-like body 42 with a slight bell shape. The body 42 includes a central hub 44 through which the aperture 43 extends, and an outwardly extending skirt 41. An adhesive primer is applied to the internal face of the aperture 43 to bond the weathershed 40 to the shield layer 30 on the rod 20.

The annular outer edge 48 of the skirt 41 is radially curved between the upper face 49 and lower face 50 of the skirt 41. This continuously rounded edge 48 configuration reduces the value of the electric field gradient across the weathershed 40. This edge 48 configuration also reduces the tendency to trap contaminants such as dust or water, for example, on the upper face 49 of the skirt 41. Two other external edges

or corners 51 and 52 on the hub 44 are also continuously curved for the same purpose.

The skirt 41 of the weathershed 40 has a substantially uniform thickness. To accomplish this the lower face 50 extends substantially parallel to the upper face 49 from the outer edge 48 of the skirt 41 to the hub 44 of the weathershed 40. As a result, an annular depression 53 is formed around the hub 44 in the lower face 50. Uniform thickness is maintained throughout the skirt 41 of the weathershed 40 without compromising the vertical height of the hub 44. Consequently, the surface area of the internal aperture 43 face is also maximized, resulting in an increased bonding surface for attaching the weathershed 40 to the shield layer 30 on the rod 20. The distance from the hub 44 to the outer edge 48 of the skirt 41 is also maximized, thus maximizing the travel distance for leakage current.

The weathershed 40 configuration which has been described minimizes the material needed to manufacture the weathershed. Thus, the weight of the weathershed 40 is minimized. The use of a reduced amount of material allows a faster process cycle to be utilized when curing the weathershed 40 during manufacture. In particular, the depression 53 allows better and faster penetration of curing heat into the body 42 of the weathershed 40. Overall production quality is improved while providing a less expensive product.

While a preferred embodiment of the invention has been described, it should be understood that the invention is not limited to it. Modifications may be made without departing from the invention. The scope of the invention is defined by the appended claims, and all devices that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.