The present invention relates to composite insulators and more particularly, relates to composite insulators suitable for high-tension, open-air use.

Many different types of electrical insulators suitable for high-tension open-air use are known in the art. Generally, they fall into two different classes - a first being one in which the insulators are generally of a relatively homogeneous material and the second being one wherein two or more materials are used for different functions. These latter are generally called composite insulators.

Insulators of a single material were widely used by electrical utilities for a number of years. Generally they are of a ceramic or porcelain material. While porcelain is a very suitable material due to its resistance to damage by electrical discharges, weathering and chemicals, it is relatively heavy and can shatter on impact. Thus, there have been cases of severe injury resulting from the shattering of porcelain insulators. In some places, they are damaged due to people deliberately throwing objects at the insulators or even shooting at them.

The deficiencies of the porcelain insulators has led to the development of composite insulators which generally comprise a central core covered by an outer insulating coating. The central core is provided to perform the mechanical function of the insulator while the protective

coating is provided to protect the central core from external agents and to prevent electrical discharge.

Composite insulators for high-tension use must conform to specific electrical requirements. Thus, the carrier rod must be electrically insulating in its axial direction and the insulating layer must be secured thereto in a manner that no electrical conduction can occur at the seam between the insulating cover and the interior carrier rod. The insulating cover performs several functions including providing resistance to weathering, UV, ozone, etcetera. The cover should also have good mechanical resistance to cold and good electrical tracking resistance. Desirably the insulating cover should be flexible, halogen- free and flame retardant.

While many composite insulations have been proposed in the art, they have generally not received wide acceptance because they have not shown that they retain the required properties over an extended period of time i.e. they have tended to degrade. It is believed that at least a portion of the problems relates to the sealing between the internal rod and the external insulating cover. The weakness has been found to be the point at which the end fittings are attached to the insulator.

It is accordingly an object of the present invention to provide the composite insulator which is both light weight and can meet the electrical and mechanical requirements of electrical utilities for insulators.

It is a further object of the present invention to provide a composite insulator wherein a thermoplastic material is used as an outer covering.

It is a further object of the present invention to provide a composite insulator wherein end pieces are securely fitted to the insulator to overcome problems of moisture infiltration.

According to one aspect of the present invention there is provided a composite insulator for use with an end fitting the insulator comprising an interior elongated structural rod of an electrically insulating material, the rod having a pair of opposed ends, and an outer coating about the structural rod, the coating terminating adjacent each of the opposed ends to thereby provide an uncoated rod end portion on which the end fitting is adapted to be mounted and also provide a generally radially extending abutting surface, the outer coating having a plurality of radially extending sheds integrally formed therewith, the coating having at least a first annular step formed adjacent said uncoated rod end portion so as to thereby provide a second generally radially extending abutting surface, both the abutting surfaces being designed to abut mating surfaces on the end connector, the coating being formed of a thermoplastic elastomer comprising a blend of a polyolefin resin with an olefin copolymer rubber wherein the rubber is in the form of small particles of cured rubber in the resin matrix.

In a further aspect of the invention, there is provided a composite insulator for high voltage electrical installations, the insulator comprising an interior elongated structural rod of an electrically insulating material, the rod having a pair of opposed ends, an outer coating about the structural rod, the coating terminating adjacent each of the opposed ends to thereby provide an uncoated end portion and also provide a first generally radially extending abutting surface, an end fitting having a recess formed therein, the end fitting being mounted on one end of the structural rod such that the uncoated rod end portion fits within the recess, the outer coating having a plurality of radially extending sheds integrally formed therewith, the coating having at least one annular step formed adjacent the uncoated rod end portion to thereby provide a second generally radially extending abutting surfaces, the end fitting also having a pair of generally radially extending abutting surfaces adapted to mate with the abutting surfaces of the coating, the coating being formed of a thermoplastic elastomer.

In greater detail, the internal rod or core of the composite insulator of the present invention may be formed of any number of suitable materials having the desired insulating and mechanical properties required. Typically, it would include a central core of fibers such as resin coated fibers. It is conventional that the interior rod or core be of a cylindrical configuration.

The outer coating is preferably molded onto the interior core and is of a thermoplastic material. Conventionally, thermoplastic materials have not been utilized as they have a relatively low melting point. However, the design of the insulator of the present invention permits the use of a thermopastic material which provides numerous advantages such as ease of handling and the capability of recycling.

In the preferred embodiment of the invention, there outer insulating cover is formed of a thermoplastic material. Conventionally, such thermoplastic materials have not been employed as they have a relatively low melting point. However, with the present invention, it has been found that a thermoplastic material may be utilized.

The preferred type of thermoplastic elastomer would comprise a blend of a polyolefin resin, an olefin copolymer rubber, in which the rubber is in the form of small particles of cured rubber in the resin matrix. As will be understood by those knowledgeable in the art, one could include conventional additives such as flame retardant compounds.

The outer coating is molded to preferably have a plurality of spaced apart sheds formed thereon as is known in the art. In a preferred embodiment, the sheds are formed as annular rings having a substantially uniform thickness. In conventional insulators, the sheds usually have a frustoconical configuration whereas in the practise of the

present invention, the sheds may be formed to be relatively thin in the form of an annular ring having a substantially uniform thickness. The thickness of the rings may vary; a preferred thickness is between 1.0 mm and 20 mm and even more preferred, is a thickness of between 1.25 and 10 mm.

As is conventional, the composite insulator is adapted to receive an end fitting at one or both ends thereof. The type of end fitting may vary depending upon the particular use.

According to the practice of the present invention, and in the preferred embodiment thereof, the insulator has its outer coating terminating at a point short of an end of the interior elongated structural rod. It is on this uncoated rod portion that the end fitting is placed. Conveniently, the end fitting may have an annular recess adapted to receive the central core or structural rod component of the composite insulator.

In a preferred embodiment, there end fitting has, on the inner surface of the annular recess, a plurality of annular grooves such that when the end fitting is attached by a crimping operation, the interface between the surface having the annular grooves and the structural rod will be enhanced.

According to the present invention, there are provided a plurality of radially extending mating abutting surfaces between the outer coating and the end fitting, with respect to the outer coating, one such radially

extending abutting surface is formed at the point of termination of the coating with respect to the interior elongated structural rod. In order to provide at least one further radially extending abutting surface, at least one annular step is formed in the outer coating adjacent its point of termination on the structural rod.

A particularly preferred embodiment of the invention utilizes an adhesive between the core and the outer coating; the adhesive/sealant is preferably an amino saline monomer in a solvent of butyl isobutyl ketone.

At the point where the outer thermoplastic coating and the end fitting abut, one may use a silicon coating on the adjacent surfaces to assist in the sealing of the thermoplastic material with the metallic material of the end fitting.

Having thus generally described the invention, reference will be made to the accompanying drawings illustrating an embodiment thereof, in which:

Figure 1 is a perspective view of a composite insulator and associated end fittings according to the present invention;

Figure 2 is a side elevational view, partially in section, of the composite insulator of Figure 1; and

Figure 3 is a detailed view of the interconnection between the end connector and insulator as shown in Figure 2.

Referring to the drawings in greater detail, and by reference characters thereto, there is illustrated a composite insulator which is generally designated by reference numeral 10. Composite insulator has a first end fitting 12 at one end thereof and a second end fitting 14 at an opposed end.

Composite insulator 10 includes a central core 16 which is an elongated structural rod of an electrically insulating material. About central core 16 is an outer coating 18 of a thermoplastic material.

Formed integrally with outer coating 18 are a plurality of radially extending sheds 20. For molding purposes, there is provided a radius between the coating surrounding the central core 16 and sheds 20, the radius being generally designated by reference numeral 22 and which radius should normally be between approximately 2 mm and 6 1/2 mm in order to avoid contraction problems.

As may be best seen in Figure 3, outer coating 18 has a slightly bulging side wall section 26 adjacent one end thereof for reasons discussed hereinbelow. This bulging provides an annular step 28 which is formed in coating 18 to thereby provide a first generally radially extending abutting surface 30. Outer coating 18, in the illustrated embodiment, is provided with a second annular step 32 to thereby provide a second radially extending abutting surface 34. A third radially extending abutting surface 36 is formed at the point of termination of coating 18 with

respect to central core 16.

End fitting 12 has an annular recess generally designated by reference numeral 38. As is known in the art, a slightly enlarged section forming a sacrificial anode 42 may be provided. As may be seen in Figure 3, the interior wall of end fitting 12 has annular steps therein to form three radially extending abutting surfaces which are adapted to abut surfaces 30, 34 and 36 of outer coating 18. This triple sealing is further enhanced by the application of an adhesive as previously described to the annular steps and abutting surfaces.

To enhance the retention (tensile strength) of the composite insulator, end fitting 12 may have a plurality of annular rings 41 formed on the interior wall about recess 38 such that during the crimping operation, the deformation of center core 16 will permit a tighter gripping.

The insulator is sized such that when end fitting 12 is placed in position, a slight deformation of outer coating 18 occurs to thereby provide bulging portion 26. As outer coating 18 is a thermoplastic material, an enhanced sealing effect is achieved.