ATTACHMENT OF INSULATORS TO OVERHEAD POWER LINE POLES

Abstract: A device for the connection of an insulator (4) to the top of an overhead power line pole (1) comprises a pair of supports (8) fitted to opposite sides of the top of the pole (1), and a top plate assembly (9, 10). The top plate assembly (9, 10) is pivotally connected to the top of one of the supports (8) and secured to the top of the other. The top plate assembly (9, 10) supports the insulator (4) in a position substantially co-axial with the pole (1).

Description: Title - Attachment of Insulators to Overhead Power Line Poles This invention relates to the field of power transmission, and in particular to the attachment of insulators to overhead power line poles. Electricity is supplied to consumers by the generating companies predominantly through a national network of overhead transmission and distribution lines. The overhead line, or conductor as it is referred to, is held aloft either on steel towers or wooden or steel poles. The towers carry higher voltage conductors, and the poles carry conductors in the range 1 lkV to 132kV. Irrespective of whether the conductor is carried on a tower or a pole it is separated from the structure and other conductors by an insulator, essentially to stop a short circuit. Insulators loosely resemble a series of elliptical electrically insulated discs joined together in a column, and are made either of a ceramic or polymeric material. Various fittings (known as "gains") are available to connect insulators to the carrying structures. Known forms of gain suffer from a number of disadvantages. They may, for example, need to be fitted to the pole in such a way that they give rise to non-axial forces. This can give rise to damage to the pole. The manner of fitting may also leave the top of the pole exposed, thereby increasing the risk of water damage. In addition, the gain may be difficult to fit to poles which vary in size, as in practice is generally the case. The gain may also not permit ready inspection of the condition of the top of the pole, and may also be difficult to access for maintenance work. There has now been devised an improved form of gain which overcomes or substantially mitigates the above mentioned disadvantages. According to the invention there is provided a device for the connection of an insulator to the top of an overhead power line pole, said device comprising a pair of supports adapted to be fitted to opposite sides of the top of the pole, and a top plate assembly pivotally connected to the top of one of said pair of supports and adapted to be secured to the top of the other of said pair of supports, the top plate assembly further being adapted to support the insulator in a position substantially co-axial with the pole when the top plate assembly is so secured to the other of said pair of supports. The device according to the invention is advantageous primarily in that it enables the insulator to be mounted substantially axially on the pole. This minimises non-axial forces on the pole and reduces the concomitant risk of damage to the pole. The pivotal connection of the top plate assembly to one of the supports also facilitates access to the insulator and conductor for maintenance work and the like. In preferred embodiments, the device also facilitates inspection of the top of the pole and is adjustable, enabling it to be fitted to poles of somewhat differing dimensions. According to another aspect of the invention, there is provided an overhead power line pole having fitted to the top thereof a device comprising a pair of supports fitted to opposite sides of the top of the pole, and a top plate assembly pivotally connected to the top of one of said pair of supports and secured to the top of the other of said pair of supports, the top plate assembly supporting an insulator in a position substantially co-axial with the pole. The pivotal movement of the top plate assembly is preferably limited. For example, suitable formations may be provided on the supports to restrict the range of movement of the top plate assembly. The arrangement of the top plate assembly is preferably such that the top plate assembly covers the top of the pole and thereby protects the top of the pole from weather damage. However, it is also preferred that the top plate assembly is spaced from the top of the pole so that the condition of the top of the pole may be readily inspected. The top plate assembly is most preferably secured to the other of the pair of supports by means of bolts. Most preferably, such bolts pass through openings which are elongated. This enables the top plate assembly to be secured to the support whenever the separation of the supports falls within a range of distances, ie to accommodate a range of pole sizes. The insulator may be of generally conventional form, most typically being of ceramic or polymeric material. The device according to the invention may be fitted to poles of any material, most commonly the pole being wooden, or of steel or concrete. The device may be used to support insulators for conductors of any voltage, most commonly 66kV and 132kV conductors. A currently preferred embodiment of the invention will now be described in greater detail, by way of example only, with reference to the accompanying drawings, in which Figure 1 is a perspective view of the top portion of an overhead power transmission line pole fitted with a top gain in accordance with the invention; Figure 2 is a more detailed perspective view of the top gain shown in Figure 1 ; Figure 3 shows perspective views of three major components which make up the top gain, viz (a) a main support channel, (b) an angle bracket and (c) a top plate; and Figure 4 is a side view in section of part of the pole of Figure 1, showing the manner in which side insulators are fixed to the pole. Referring first to Figure 1, an overhead transmission line pole 1 is fitted with three insulators 2,3,4 arranged in a conventional configuration. The two side insulators 2,3 are fixed to the pole 1 by means of brackets 5,6 a short distance below the top of the pole 1 and project outwardly at a slight angle to the horizontal. The top insulator 4 is mounted on a top gain 7 in accordance with the invention. The gain 7 is shown on a larger scale in Figure 2 and comprises a pair of support channels 8 (shown in more detail in Figure 3a), a pair of angle brackets 9 (see Figure 3b) and a top plate 10 (Figure 3c). The support channels 8 are fixed at opposite sides of the top of the pole 1, the sides of the pole 1 being cut away to provide a pair of diametrically opposed flats for secure mounting of the channels 8. The channels 8 are fixed in place by a pair of bolts 11 which pass through preformed openings in the channels 8 and the pole 1. The top gain 7 is completed by a top plate assembly comprising the angle brackets 9 and the top plate 10. The support channels 8, angle brackets 9 and top plate 10 are made of coated mild steel (though any other appropriate material, capable of withstanding the ambient conditions and loads, may alternatively be used). The angle brackets 9 have near one end thereof a cylindrical pin 12 which locates in a corresponding hole in the side face of one of the support channels 8. At the other end of the angle bracket 9 there is provided a slot 13 through which a bolt can be passed to engage a nut and secure the angle bracket 9 to the other one of the support channels 8. The top plate assembly is completed by the top plate 10 itself, which is bolted to the two angle brackets 9 by means of four bolts 16 which pass through pre- formed openings 17 close to the four corners of the top plate 10. The top insulator 4 is mounted on the top plate 10 (by means of bolts, which are not visible in the drawings, passing through four fixing holes 19 near the centre of the top plate 10) such that it stands substantially co-axial with the pole 1. This prevents eccentricity brought about by vertical loading and minimises side loads. The top plate 10 protects the top of the pole 1 from weather damage, yet the space between the top plate 10 and the top of the pole 1 allows the condition of the top of the pole to be checked readily. The provision of the slots 13, rather than simple round openings, to receive the bolts which secure the top plate assembly to the support channels 8 means that the top gain 7 can be fitted to poles 1 having a range of sizes. Thus, variation in the size of the pole 1 can be accommodated, the top insulator 4 being substantially co-axial with the pole 1 in all cases. In the assembled top gain 7, when the bolts which secure the top plate assembly to the support channels 8 are removed the top plate assembly can be pivoted about the pins 12. Pivoting movement of the top plate assembly is restricted by limiting lugs 18 provided on the support channels 8. The lugs 18 serve to limit pivotal rotation of the top plate assembly to an angle of approximately 105 ° . Thus, by removing the bolts 14 the top plate assembly can be rotated into a position in which it is much easier to fit the top insulator 4 to the top plate 10. The fact that the range of rotation is restricted prevents accidental contact of the top insulator 4 with the side insulators 2,3. The rotational action also facilitates maintenance and repair work, in that the top insulator 4 can be swung down to a more suitable working height for ease of access. Finally, Figure 4 shows the manner in which the side insulators 3,4 are fixed to the pole 1. A pair of bores 21 ,22 pass diametrically through the pole 1 and are parallel to each other. Threaded headless bolts 23 ,24 are inserted into each of the bores 21 ,22 such that the ends of the bolts 23 ,24 project from both ends of the bores 21,22. Nuts 25 are then engaged with each end of each bolt 23,24 and tightened so that the bolts 23,24 are captivated on the pole 1 with an approximately equal length of bolt 23,24 projecting at each side. The brackets 5,6, to which the insulators 2,3 are fixed, are then mounted in turn on the bolts 23,24, the brackets 5,6 being provided with openings through which the ends of the bolts 23,24 pass. Finally, nuts 26 are engaged with the bolts 23,24 to captivate the brackets 5,6 between the nuts 26 and the pole 1. This method of fixing the side insulators 2,3 has the advantage that, although mounted on common bolts 23,24, the two side insulators 2,3 may be fitted and removed independently.

Claims: Claims 1. A device for the connection of an insulator to the top of an overhead power line pole, said device comprising a pair of supports adapted to be fitted to opposite sides of the top of the pole, and a top plate assembly pivotally connected to the top of one of said pair of supports and adapted to be secured to the top of the other of said pair of supports, the top plate assembly further being adapted to support the insulator in a position substantially co-axial with the pole when the top plate assembly is so secured to the other of said pair of supports. 2. A device as claimed in Claim 1 , wherein pivotal movement of the top plate assembly is limited. 3. A device as claimed in Claim 2, wherein formations are provided on the supports to restrict the range of movement of the top plate assembly. 4. A device as claimed in any preceding claim, wherein the top plate assembly covers the top of the pole and thereby protects the top of the pole from weather damage. 5. A device as claimed in any preceding claim, wherein the top plate assembly is spaced from the top of the pole so that the condition of the top of the pole may be readily inspected. 6. A device as claimed in any preceding claim, wherein the top plate assembly is secured to the other of the pair of supports by means of bolts. 7. A device as claimed in Claim 6, wherein such bolts pass through openings which are elongated so that the top plate assembly can be secured to the support whenever the separation of the supports falls within a range of distances. 8. An overhead power line pole having fitted to the top thereof a device comprising a pair of supports fitted to opposite sides of the top of the pole, and a top plate assembly pivotally connected to the top of one of said pair of supports and secured to the top of the other of said pair of supports, the top plate assembly supporting an insulator in a position substantially co-axial with the pole.

Inventors: FORD ROBERT, FORD, ROBERT
Applicants: AMEC POWER LIMITED, FORD ROBERT, FORD, ROBERT
Application year: 1999
Main classification: H01B17
IPC codes: H01B17