WO2009049377A1

WO2009049377A1 - Cross arm

Info

Publication number: WO2009049377A1
Application number: PCT/AU2008/001545
Authority: WO
Inventors: Gregory James Nunn
Original assignee: Farallon Capital Pty Ltd
Priority date: 2007-10-19
Filing date: 2008-10-17
Publication date: 2009-04-23

Abstract

A cross-arm for supporting electric cables from a utility pole comprising an elongate core surrounded by at least one fibre reinforced resin layer, wherein the elongate core comprises wood.

Description

CROSS ARM

Background of the Invention

The present invention relates to a cross arm for power poles and in particular to a cross arm for supporting power lines above ground utilising power poles.

Description of the Prior Art

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Above ground power lines are usually carried on spaced apart poles having one or more horizontal cross arms. The cross arms are traditionally made of old growth hardwood as this has good strength and electrical properties. However, the availability of such old growth hardwood timbers is decreasing due to the over-exploitation of forests. Furthermore, softwood or plantation timbers are generally considered unsuitable being are more prone to damage by pests, as well as degradation arising from absorption of water and the effects of airborne pollutants. Steel has been used but is generally considered to be an undesirable alternative due to its conductive nature.

It has been proposed to use insulating material for cross arms and these generally involve the use of some form of fibre reinforced material employed to form the cross arm with a wide variation in designs from quite simple arrangements to arrangements which are quite complex and expensive.

US Patent No 4,682,747 to King et al describes a cross arm for supporting electric utility wires where the cross arm is made from insulating material, having an inner structure formed of alternate layers of polyester resins and synthetic fabric. The cross arm utilises an inner core composed of polyester resins and particulate matter, or polyurethane foam with a central metal reinforcing bar. The cross arm is modular in nature, and supporting members are integral with the unit facilitating installation.

While this arrangement serves to provide a cross arm structure that eliminates the problem of a conductive cross arm, due to the requirement for the specialised construction of the outer shell and the materials utilised in the inner core this solution represents a very expensive alternative to the timber or metal cross arms.

Another problem associated with this type of cross arm is the possible development of electrical tracking on the surface of the cross arm which results from erosion of the cross-arm uppermost surface when exposed to an environment of ultraviolet radiation and or heavy pollution. This issue is particularly problematic when cross arms are installed on distribution voltage classes greater than 11,000V.

In particular, this allows the surface of the cross arm to become hydrophilic or "wet" during a rain event, allowing electric conductive layers to develop and leakage current to flow. These leakage currents can dry the wet layers and form small electrical arcs, which attack/damage and erode the external surface of the cross arm. The resulting erosion penetrates the reinforcing fibres closer to the surface and electrical tracking develops causing power outages and risks personal linesman safety. This problem is exacerbated by the cross arm design which allows for a build up of contaminants in the corners of the central triangular portion.

US Patent No 5,605,017 to Fingerson et al discloses a hollow horizontal beam for use as a cross arm. This may be used as tangent cross arm or a dead-end and includes a hollow fibre reinforced beam with a bushing inserted into a transverse hole in the beam. The hollow beam is pultruded and includes end caps to seal the beam. In order to secure insulators or other functional components holes are placed in the beam. A bushing assembly is used to support axial loads applied to the beam when through bolting. The focus of the invention in this case is on the construction of the bushing assembly and the interplay between the bushing assembly and the holes which are predrilled into the pultruded member. The bushing assembly has washers operative to provide a seal against the beam surface which is aided by pressure applied to the bushing assembly via the bolts. This arrangement has a number of problems that arise due to the environmental affect of thermal expansion and contraction and natural weathering, which can allow moisture to enter the internal cavity via a failure of the mechanical seal at the bushing assembly and/or end cap. The resulting internal moisture build up can result in electrically conductive layers to form allowing leakage currents to flow, which can in turn damage and erode the internal surface of the cross arm allowing tracking to occur. The resulting erosion penetrates the reinforcing fibres closer to the internal surface with electrical tracking developing causing power outages and risks to the personal safety of linesmen.

A further problem arises due to the use of the relatively large holes required for the anti-crush bushings assemblies. Relatively large holes can weaken the cross arm when exposed to bending forces over time. This in conjunction with the above referenced problems arising from moisture and pollution further exacerbate damage to the cross arm.

Also exacerbating these problems is the structure of the beam arising from a pultrusion process which lays the reinforcing fibres in a non-optimal configuration.

US Patent No 6,834,469 to Fingerson et al, discloses a pultruded beam with a reinforcing member located within the interior of the beam. The reinforcing member is positioned to absorb any compressive forces resulting from either mounting of the beam to a utility pole or mounting other elements to the beam. Fingerson et al recognises the problem of moisture ingress into the interior of a fibre reinforced beam of this kind regardless of the precautions taken to seal the openings.

The beam possesses the same problems arising from the pultrusion process and the other problems associated with the beam of Fingerson et al's earlier patent.

US Patent No 6,347,488 to Koye describes a cross arm for a utility pole where the cross arm includes an elongated, hollow bar member moulded from synthetic material such as a sheet moulding compound of polyester glass reinforced plastic. The bar member has a first end, a second end opposite the first end, a plurality of through holes for mounting the cross arm to utility poles with fasteners and for mounting electrical line support insulators. The disclosed cross arm remains hollow and provide no core crush resistance as proposed by Fingerson et al nor is there any effort made to prevent ingress of moisture into the interior of the cross arm. Consequently over time, moisture can enter and accumulate in the interior of the cross arm via the through holes and or ends of the cross arm giving rise to the arcing and tracking problems referred to above as well as the possibility of surface build up of contaminants leading to arcing and again the same degradation to the cross arm.

International Application No WO2007/070966 to Preformed Line Products (Australia) Pty Ltd recognises at page 2 lines 10 to 14 the problems associated with pultruded hollow sections leading to a difficulty in mounting components as well as risking ingress of water over time. These problems have also been referred to above. The solution in this patent specification is to provide a solid cross arm rather than one that is hollow with some form of internal reinforcing structure. The focus of this patent specification is in terms of a fixed length integrated cross arm where the cross arm design has a complex shape including sheds, mounting brackets and other features all moulded into one fixed length integrated cross arm.

The resulting cross arm is complicated to manufacture in commercial quantities and expensive to produce. In addition it is expensive to transport as the associated cross arm is of complex profile which results in the inefficient use of packaging. As the design incorporates fixed insulators at nominal spacing's, integrated mounting hardware, etc; there is no ability for the utility to vary conductor spacing, insulation levels or increase creepage distance to match specific pollution environments. Furthermore the integrated cross arm does not offer the utility the ability to mount other standard electrical apparatus to the cross arm e.g. cut out fuses, LV fuse brackets, etc, or the ability to be a direct replacement for existing cross arm installations without resulting in expensive conductor re-tensioning and clearance adjustments. Maintenance and servicing of this type of cross arm is also expensive as failure results in the entire integrated cross arm needing replacement. This reasoning also applies to the same applicant in relation to its International Application No WO 01/23691 as well as the above referenced US Patent No. 4,682,747.

Other arrangements employing beams with cores include US Patent No. 4,262,047 and French Patent No. 1445447. US Patent No. 4,262,047 describes a generally horizontal log of fibre glass honeycomb material defining side by side upstanding adjacent cells substantially throughout the log. The log includes a hard outer covering enclosing the log on all sides. The covers is bonded to the opposing side surface of the log and the opposite sides of the log include vertical bores there through having thrust sleeves of substantially the same length tightly received in and extending through the vertical bores.

However, the honeycomb structure does not provide crush resistance, with this function being performed by the sleeves. Furthermore, the honeycomb structure includes hollow cells allowing entry of moisture into any one or more of the cells leading to arcing and tracking into the interior of the cross arm as well as the possibility of surface build up of contaminants leading to arcing and again the same degradation to the cross arm.

US Patent No. 3,013,584 to Reed et al. describes a proposal to utilise glass fibre reinforced plastics in other parts of utility pole lines apart from the cross arm where a hollow pole structure has an inner and outer ring joined by radially extending connectors. In addition, the inner tube may be filed with plastic foam. This is said to improve the rigidity in the flexural strength by the provision of a liner comprising a tubular sleeve made up of a plurality radially disposed circumferentially spaced apart strip of cellulosic fibres impregnated with a thermosetting resin.

As noted in similar arrangements, since the cross arm has hollow cells, the cross arm suffers from the same problems arising through the possible entry of moisture into any one or more of the cells leading to arcing and tracking into the interior of the cross arm as well as the possibility of surface build up of contaminants leading to arcing and again the same degradation to the cross arm.

US Patent No. 6,609,345 to Schauf et al. describes a structural member and method of manufacturing same with these structural members primarily for use in power poles. They may be used as part of the poles or as the cross arm. This patent describes an extruded cross arm cut from an extruded hollow body which may be filled with foam. The extrusion is made by utilising chopped glass rovings and forcing the plastic and rovings material through an extruder. At the same time as the extrusion is taking place, plastic parts and an additional foaming agent is introduced into the extruder so that the resulting material has spaces or voids as a result of the foaming action during the extrusion process. The extruded member may be made solid with the said voids or may be made in hollow embodiments that are later foam filled. Another example of the application of a foam filled fibre reinforced resin cross arms is disclosed in French Patent-No. 1445447.

The beam possesses the same problems arising from the pultrusion process and the other problems associated with the beam of Fingerson et al's earlier patent. That is the surface of the cross-arm degraded with ultraviolet light and pollution build-up, which allows leakage currents to flow leading to surface erosion and tracking in the fibre reinforcing layer of the cross arm.

Thus, the cross arms described above do not provide the simplicity and versatility of a traditional hardwood cross arm. Even though they have the benefit of using predominantly insulating material they are not as good as the hardwood cross arm both in terms of cost and flexibility particularly in relation to be able to fix anywhere to the cross arm.

Summary of the Present Invention The present invention seeks to substantially overcome, or at least ameliorate, one or more disadvantages of existing arrangements.

In a first broad form the present invention seeks to provide a cross-arm for supporting electric cables from a utility pole comprising an elongate core surrounded by at least one fibre reinforced resin layer, wherein the elongate core comprises wood.

Typically the at least one fibre reinforced resin layer is bonded to the core.

Typically the core provides support to the fibre reinforcement layer.

Typically the core provides crushing resistance to the cross-arm, thereby allowing through bolting of the cross-arm to allow fitment of the cross-arm to a utility pole or fitment of accessories to the cross-arm.

Typically the core provides crushing resistance to the cross-arm, thereby preventing buckling of the at least one fibre reinforced resin layer. Typically the core prevents accumulation of foreign matter inside the cross-arm.

Typically the or each fibre reinforced resin layer provides stiffness to the cross-arm.

Typically the or each fibre reinforced resin layer provides an outer insulating layer.

Typically the or each fibre reinforced resin layer comprises a fibre reinforcement layer impregnated with resin.

Typically the or each fibre reinforced resin layer comprises alternating layers of resin and fibre reinforced resin.

Typically the elongate core comprises a low density wood.

Typically the wood is selected from the group comprising pine, spruce and balsa wood.

Typically the wood is treated with Copper Chromium Arsenate.

Typically the core has sufficient strength to engage and retain a treaded fastener.

Typically the cross-arm further comprises an outer insulating layer surrounding the cross- arm.

Typically the outer insulating layer comprises a further resin layer.

Typically the elongate core is of substantially constant cross section.

Typically the cross-section of the elongate core is quadrilateral.

Typically at least one longitudinal surface of the cross-arm is convex.

Typically the cross-arm is of a hexagonal cross-sectional shape.

Typically the elongate core comprises at least one groove formed therein to provide an interlocking element between the core and the surrounding layers.

Typically the grooves are formed along substantially all of the length of the core. Typically at least one fibre reinforced resin layer comprises fibres orientated substantially aligned with a central longitudinal axis of the cross-arm.

Typically at least one fibre reinforced resin layer comprises bi-directional fibres orientated at a first angle from a central longitudinal axis of the cross-arm.

Typically at least one fibre reinforced resin layer comprises tri-directional fibres, wherein a first layer is orientated an angle substantially aligned with a central longitudinal axis of the cross-arm, and second and third layers are orientated at a second angle from a central longitudinal axis of the cross-arm.

Typically the resin comprises at least one of : a) cycloaliphatic epoxy (CEP) resin; b) hydrophobic cycloaliphatic epoxy (HCEP) resin; and c) Huntsman hydrophobic cycloaliphatic epoxy Araldite CY5622.

Typically the fibre reinforced resin layer is between 1 mm and 8 mm thick.

Typically the fibre reinforced resin layer is between 1.5 mm and 5 mm thick.

In a second broad form the present invention seeks to provide a cross-arm for supporting electric cables from a utility pole comprising an elongate core surrounded by at least one fibre reinforced resin layer, wherein the elongate core comprises foam material.

Typically the at least one fibre reinforced resin layer is bonded to the core.

Typically the core provides support to the fibre reinforcement layer.

Typically the core prevents accumulation of foreign matter inside the cross-arm.

Typically the or each fibre reinforced resin layer provides stiffness to the cross-arm. Typically the or each fibre reinforced resin layer provides an outer insulating layer.

Typically the outer insulating layer comprises a further resin layer.

Typically the elongate core is of substantially constant cross section.

Typically the cross-section of the elongate core is quadrilateral.

Typically at least one longitudinal surface of the cross-arm is convex.

Typically the cross-arm is of a hexagonal cross-sectional shape.

Typically the grooves are formed along substantially all of the length of the core.

Typically at least one fibre reinforced resin layer comprises fibres orientated substantially aligned with a central longitudinal axis of the cross-arm.

Typically the fibre reinforced resin layer is between 1 mm and 8 mm thick.

Typically the fibre reinforced resin layer is between 1.5 mm and 5 mm thick.

Typically the elongate core comprises a plastic foam.

In a third broad form the present invention seeks to provide a method of manufacturing a cross-arm for supporting electric cables from a utility pole comprising the steps of providing a core and applying at least one fibre reinforced resin layer to the core.

Typically the step of applying at least one fibre reinforced resin layer comprises wrapping the core in a fibre reinforcement material and applying resin.

Typically the resin is applied using a vacuum assisted injection moulding process.

Typically the method further includes the step of forming holes in the cross-arm for mounting the cross-arm to a utility pole.

Typically the step of providing the core includes forming grooves in the core.

Typically the core comprises a low density wood.

Typically the core comprises foam.

Typically the core comprises a plastic foam.

In a fourth broad form the present invention seeks to provide a method of installing accessories to a cross-arm for use with a utility pole, comprising the steps of forming a hole in the cross-arm and inserting a threaded fastener directly into the core so that the threads engage the core material thereby retaining the fastener in position.

Typically the fastener is a coach bolt.

Typically the utility pole supports electric cables transmitting electricity of up to 80,000 Volts.

Typically the cross-arm is tilted such that an upper surface is not perpendicular to the utility pole.

Typically the cross-arm is tilted about the longitudinal axis such that an upper surface is not perpendicular to the utility pole.

Brief Description of the Drawings

An example of the present invention will now be described with reference to the accompanying drawings, in which: -

Figure 1 is an end view of an example of a traditional cross-arm;

Figure 2 is an end view of an example of a cross-arm for supporting power lines; Figure 3 is a sectioned view of the cross arm of Figure 2 mounted to a pole;

Figure 4A is a side view of the cross-arm shown of Figure 2;

Figure 4B is a schematic side view of a cross-arm showing loads applied to the cross-arm;

Figure 5 is a sectioned view of a cross-arm according to another example;

Figure 6 is a sectioned view of a cross-arm according to another example; Figure 7 is a sectioned view of a cross-arm according to another example;

Figure 8 is a sectioned view of a cross-arm according to another example;

Figure 9 is a sectioned view of a cross-arm according to another example;

Figure 10 is a sectioned view of a core including a grooved surface;

Figure 11 is a sectioned view of a cross-arm including the grooved core of Figure 10; Figure 12 is a sectioned view of a core including a channelled surface;

Figure 13 is a sectioned view of an example of the attachment of an accessory to a cross arm;

Figure 14 is a sectioned view of an example of a cross-arm including a sleeve for mounting accessories; Figure 15 is a sectioned view of a second example of a cross-arm including a sleeve for mounting accessories;

Figure 16 is an end view of an example of a cross arm having an end cap; Figure 17 is a side view showing a partial section of the cross-arm of Figure 16; Figure 18 is a sectioned view of the end cap;

Figure 19 is an end view of an example of a cross arm having a moulded end; Figure 20 is a sectioned view of the cross arm of Figure 20;

Figure 21 is a process flow chart showing a method of manufacturing a cross-arm according to one example; Figure 22 is a process flow chart showing a method of manufacturing a cross-arm according to another example; and

Figure 23 is a schematic diagram showing a method of manufacturing a cross-arm according to another example.

Detailed Description of the Preferred Embodiments Figure 1 shows an example of a typical cross-arm arrangement. Electric cable 10 is connected to cross arm 12 by an insulator 11. A threaded fastener is inserted through cross- arm 12 and retained using nut 13. Typically, such arrangements use a high density hard wood such as Ironbark Eucalypt, or the like, for cross-arm 12. Such wood typically comes from old-growth forests that may be greater than 150 years old. Global stocks in such wood are diminishing and due to the age of the trees, it is not easily replenished.

An example of a cross-arm for supporting electric cables 10 from a utility pole 19 will now be described in more detail with respect to Figures 2 to 20.

In the example of Figures 2 and 3, the cross-arm 14 comprises an elongate core 15 surrounded by at least one fibre reinforced resin layer 16, wherein the elongate core 15 comprises wood. In use, insulators 11 may be retained in place by a threaded fastener 20 extending through the cross-arm and attached with a nut 13. The cross arm may then be attached to a utility pole, using a bolt 25, held in place by a nut 26. In particular, the cross-arm 14 includes a core 15 of low density wood, comprising for example balsa wood or pine. Preferably the core is made from seasoned radiate pine, strength group SD6, in accordance with Australian Standards AS 1720.1, Table 2.2. However other low density woods may also be used for the core material.

Advantageously, low density woods are commonly available, and therefore can be procured at a low cost. Low density woods such as pine are farmed on a sustainable basis to yield millable trees at about 25 to 30 years of age, and can therefore be replenished much easier. Low density woods can also be easily machined into a desired shape, thereby reducing machining costs. A further advantage is that low density woods are also light in weight. Therefore a cross-arm of this form is of a low overall weight and is therefore easier to handle to install, with less risk of personal injury to linesman.

The wooden core may also be treated with commonly available wood treatment such as Copper Chromium Arsenate (CCA) for example. CCA treatment of the wooden core is used to protect the timber from insect attack and fungal decay. By providing additional resistance to these elements, the probable life of a core treated in this way is prolonged.

A fibre reinforced resin layer 16 is applied to core 15 to completely surround core 15. Fibre reinforced resin layer 16 is a resin impregnated reinforcement layer generally formed by impregnating a layer of fibre reinforcement material with resin.

It is generally desirable for the fibre reinforcement material to be completely covered by the resin, thus protecting the fibre reinforcing material from external elements and preventing any damage. The fibre reinforcement layer may be applied directly to the core 15 before the application of the resin, which then impregnates the fibre material. Alternatively, resin may be applied to the core 15 before the fibre reinforcement material, in which case it may be necessary to apply a further coat of resin over the fibre reinforcement material to ensure the fibre reinforcement is completely covered and therefore protected.

Fibre reinforced resin layer 16 may comprise multiple layers of resin and fibre reinforcement material. Fibre reinforced resin layer 16 may also comprise layers of resin without any fibre reinforcement material. Fibre reinforced resin layer 16 is generally between 1 mm and 8 mm thick, and preferably between 1.5 mm and 5 mm thick. A dimensional tolerance of +/- 2.5 mm may be applied to the external form.

Advantageously, core 15 supports the fibre reinforced resin layer 16, thereby resulting in a much stronger cross-arm. Core 15 also provides crushing resistance in the event of through bolting, as shown in Figure 3, whereas a hollow or foam core cross-arm would provide less crush resistance. Cross-arm 14 will generally have a minimum crush resistance from the tightening of a M24 through bolts with washers of 150Nm or 259kg axial clamping force.

Alternatively, rather than pass through the cross arm, accessories can be bolted directly to the core, by having a threaded fastener, such as a coach-bolt 40, that screws directly into the core 15, as shown in Figure 13, and as will be described in more detail below.

Thus, the wooden core 15 provides a medium into which a bolt 40 can be screwed, thereby allowing accessories to be easily fitted in the field. In contrast, prior art arrangements typically use hollow cross-arms with a small wall thickness that does not provide enough material for a threaded fastener to engage the wall. Also, cross-arms with a core that is very soft cannot accept threaded fasteners directly because the core is too soft to retain a thread. To overcome this, prior art arrangements often require custom mountings for accessories, which are fitted during manufacture, thereby limiting the position in which accessories can be mounted to the cross arm. In contrast, the wooden core allows accessories to be attached by bolting into the cross arm 14 at any location, as would have been achieved with typical hardwood configurations.

Core 15 also prevents ingress and therefore accumulation of moisture, contaminants and vermin. Build up of such foreign matter is undesirable because it results in degradation of the cross-arm, thereby reducing the probable lifespan of cross-arm 14.

Core 15 also provides crush resistance to cross-arm 14, thus preventing fibre reinforced resin layer 16 from buckling under loading.

Fibre reinforced resin layer 16 provides stiffness and also superior strength. Fibre reinforced resin layer 16 also provides an outer insulating layer to protect cross-arm 14 from external elements. Dependent on the application, cross-arms are required to withstand different voltage levels. Advantageously, by altering the thickness of an outermost layer 30, the insulation properties of the cross arm may be tailored to suit a specific application. Therefore a cross-arm for a low voltage application does not comprise unnecessary layers and can therefore be manufactured at a lower cost.

Cross-arm 14 provides a balance between core material and the outer layer, so that the two are complimentary in alleviating problems associated with existing cross arms of the fibre reinforced resin type.

The fibre reinforcement material is preferably orientated such that the fibres lie substantially collinear with the longitudinal axis of cross-arm 14. Referring to Figure 4A and 4B, cross- arm 14 is generally, but not exclusively, subject to bending stress due to loads applied at the end of cross-arm 14. These loads can be applied through insulators 11, which support electric cables 10. The load is transferred to the centre of cross-arm 14 where it is connected to utility pole 19, via a bolt 25, or a bracket 24. Cross-arm 14 may also be mounted to utility pole 19 using alternative arrangements. Fibre reinforcement material is strongest is a direction parallel to the fibres, and when orientated such that the fibres lie substantially collinear with the longitudinal axis of cross-arm 14 the bending stress is appropriately carried. Referring to Figure 4B, a side view of a loaded cross-arm 14 can be seen in a deformed state. As indicated by the arrows, an upper surface of cross-arm 14 is in tension, whilst a lower surface is in compression. Typically, a cross-arm shall have a maximum deflection of 12% when loaded to its minimum failing load. Cross-arm 14 may be braced, generally with a single or double brace, to support both cantilever and tensile loadings.

It is also possible to have alternating layers of fibre reinforcement material arranged in either a bi-directional or tri-directional arrangements. A bi-directional arrangement involves pairs of layers which are orientated so that the fibres are arranged at positive and negative values of a first angle. A tri-directional arrangement includes a bi-directional arrangement as previously described, however a number of layers are orientated such that the fibres lie substantially collinear with the longitudinal axis of cross-arm 14. Commonly available fibre weaves have fibres generally orientated at 0 degrees, +/-45 degrees and 90 degrees to a longitudinal axis of the material. The fibre reinforcement material may comprise for example glass fibres, however other suitable reinforcement materials may be used. "E" type glass fibres or an equivalent are particularly suitable. Alternatively, Kevlar may also be used, as may natural fibres, such as hemp, or the like. It is preferable that the fibre reinforcement material comprises multiple layers of a typical heavy weight tri-directional cloth which, when combined with resin has a modulus of elasticity of at least 20,000MPA and an ultimate tensile strength of at least 400Mpa.

Cross-arm 14 may also comprise an outer insulation layer 30, as can be seen in Figures 5 to 8, to provide additional protection from the weather, external elements, or to provide additional electrical properties in higher voltage applications. This layer may comprise resin or another fibre reinforced resin layer. The outer insulation layer may also comprise another coating, for example a silicone coating. An example of such a coating is SYLGARD HVIC+ available from Dow Corning. Such a coating enhances the hydrophobic properties of the cross-arm 14 and assists in preventing moisture entering the cross-arm 14 or the accumulation of dust or other contaminants on cross-arm 14.

The resin layer preferably comprises a thermosetting epoxy resin, preferably a liquid hot cure, hydrophobic cycloaliphatic epoxy (HCEP) resin suitable for outdoor application in severe environmental environments. It is preferable if the resin exhibits hydrophobic properties. A particular example of such a resin is Huntsman hydrophobic cycloaliphatic epoxy Araldite CY5622, however other commercially available resins may be suitable. The purpose of resin in composite structures is known. In this arrangement, the resin not only supports the fibre reinforcement material, but bonds with the wooded core.

It is preferable to use a hydrophobic resin which provides superior hydrophobicity, and reduces "wetting" of the surface of the cross-arm. Reduced wetting of the surface of the cross-arm results in lower leakage currents and discharge activities which in turn reduce probability of fiashover and possibility of surface erosion which improves service life. It is also possible to use vinyl ester or another equivalent resin to impregnate the glass fibre, and use another resin for an external covering layer. The impregnation resin may contain additives that act as a flame retardant, low shrinkage agent or pigment. In one example, the resin is introduced by a vacuum assisted injection moulding process or a vacuum assisted resin transfer moulding process. Advantageously, by using such a moulding process the external shape of the cross arm can be more accurately controlled compared with a pultrusion process. As can be seen in Figures 6 to 9, cross-arm 14 can be moulded into any desirable shape, particularly one that does not allow water to sit on a surface uppermost in use. In comparison, a "square profile" pultrusion process often results in beams having concave surfaces along the longitudinal sides, caused by resin shrinkage. This allows water to pool on a top surface, therefore leading to arcing and tracking. Pollutants can also build on top of cross-arms, leading to further degradation of the cross-arm. Such problems may be overcome by using a vacuum assisted injection moulding process.

Alternatively, cross-arm 14 may be manufactured without the use of a mould by wrapping a core 15 in a fibre reinforcement material and brushing or spraying resin over the fibre reinforcement.

Core 15 is shaped to a desired shape prior to fibre reinforced resin layer 16 being applied. Core 15 is of a generally constant cross sectional shape, and prepared using commonly available wood working techniques. Referring to Figures 6 to 9, a number of alternative shapes are possible including generally circular, triangular, square, an irregular four sided quadrilateral shape, a five sided shape or a hexagonal shape. If it preferable to have the surfaces uppermost in use arranged to be tilted relative to the utility pole to allow water to run off. Such an arrangement can be seen in Figure 2 where a ridge is formed of sloping sides 17 and 18. Alternatively, a surface uppermost in use may be convex to allow water and/or pollutants to run off.

Core 15, and subsequently cross-arm 14 may also be of a generally square cross section, but installed, or arranged to be installed, such that an upper surface is tilted relative to the utility pole such that it is not perpendicular. Advantageously, such an arrangement does not allow water and/or pollutants to sit on top of the cross-arm 14.

Referring to Figure 10, according to one example core 15 may be provided with grooves 33, separated by ridges 34. Grooves 33 are generally formed along the length of core 15 and assist in resin flow, thereby ensuring that the fibre reinforcement material is fully "wet" during moulding. Corners 35, 36, 37 and 38 are bevelled or radiused along the full length of the core to aid wrapping prior to moulding.

Grooves 33 increase the amount of contact area between the core and the fibre reinforced resin layer, thereby advantageously increasing the strength of the bond between the fibre reinforced resin layer and the core, resulting in a stronger cross-arm. Such grooves 33 may also reduce buckling in a compression loading mode and reduce wall slip of the core relative to the fibre reinforced resin layer.

Additional resin may be applied over the grooves so that a smooth outer surface can be achieved, as can be seen in Figure 11 , or alternatively the outer surface may be grooved.

In may be desirable to provide a stronger cross-arm 14, therefore grooves 33 may be channels 49, as particularly shown in Figure 12. Channels 49 formed in core 15 provide a mechanical interlock between the core and the fibre reinforced resin layers. Channels 49 are shown as having a square cross-section however other shapes especially those providing an undercut, for example a dove tail, may also be used. Channels 49 provide a more positive interlock between the core and the fibre reinforced resin layer, thereby further increasing the strength of the cross-arm.

The addition of grooves 33 and channels 49 to the core provides additional strength to cross arm 14 because typical resin shrinks when curing, thereby further grasping the core 15 and interlocking with the grooves or channels.

Referring to Figure 13, it can be seen that in one example cross-arm 14 can receive a screw 40 directly inserted into the cross-arm 14. Advantageously, core 15 comprises a wood which is strong enough to allow a screw thread to be formed in core 15. By directly engaging a screw thread, core 15 does not require any additional parts to connect accessories to cross- arm 14. Any accessories, such as fuses or links, brackets, etc can be quickly and easily fitted to cross-arm 14, thereby increasing the ease of installing the cross-arm. As can be seen in Figure 13, connecting an accessory to cross-arm 14 can be achieved using a threaded fastener that screws directly into the core. Alternatively, this may be achieved by having a threaded fastener that passes through the entire cross arm, in a manner similar to the attachment of the insulator 11 in Figures 2 and 3.

Core 15 also provides cross-arm 14 with a moisture barrier to prevent accumulation of foreign matter inside cross-arm 14.

Referring to Figures 14 and 15, though holes may be provided by introducing a sleeve 54 into cross-arm 14. Sleeve 54 may be introduced by drilling a hole in cross-arm 14 and gluing it in place, as can be seen in Figure 14, or more typically, sleeve 54 may be moulded into cross- arm 14 when fibre reinforced resin layer 16 or 30 is applied as seen in Figure 15. However, when a wooden core 15 is used, such a sleeve may not be required.

Figures 16-18 illustrate an example of an end cap 56 that may be used to seal ends of the cross arm. In this example, the end cap 56 includes spigots 57 which enable it to be aligned in predrilled holes 58 and glued in position a shown. More typically, Figures 19 and 20 show where ends 59 are moulded in situ and are contiguous with the side walls.

Referring to Figures 21 and 22, a flow chart outlines the manufacturing process of a cross- arm according to some examples. Referring firstly to Figure 21, the process starts with steps 210, preparing the resin. This involves mixing resin, accelerator, hardener, filler and silanes together in a primary mixer using a de-gas mixing process. This mixture is then fed into a delivery injection system, step 212, where it is pressurised in preparation for moulding. In step 214, the core is prepared by machining it to the desired shape. Step 216 comprises the wrapping of the core with fibre reinforcing material. Step 216 may include wrapping the core in multiple layers. In step 218, the wrapped core is preheated, prior to moulding of the resin (step 220). The moulding process 220 may be completed using an injection moulding machine. In particular, an injection moulding machine utilising a vacuum assist method may be used. Alternative gelation moulding processes may be used. After moulding (step 220), the cross-arm undergoes a post curing process (step 222). Steps 220 and 222 may both require the addition of heat to the cross-arm. After step 222, the cross-arm may undergo finishing process 224. Finishing process 224 may include cleaning and/or polishing of the cross-arm, installing any accessories required and packing. Referring to Figure 22, a flow chart illustrates an alternative cross-arm manufacturing process. The process starts with step 310, preparing the resin. In this alternative process, step 310 includes mixing resin, catalyst and filler together using an appropriate mixing process. This resin mixture is then fed into a delivery injection system, step 312, in preparation for moulding. In step 314, the core is prepared by machining it to the desired shape. Step 316 comprises the wrapping of the core with fibre reinforcing material. Next, moulding process 318 may be completed using an injection moulding machine. In particular, an injection moulding machine utilising a vacuum assist method may be used. Step 316 may include wrapping the core in multiple layers. After moulding (step 318), the cross-arm undergoes the step of applying a hydrophobic coating 320. After step 320, the cross-arm may undergo finishing process 322. Finishing process 322 may include cleaning and/or polishing of the cross-arm, installing any accessories required and packing.

Referring to Figure 23, it can be seen that fibre reinforcement is wrapped directly around core 15, as per steps 216 and 316. The wrapped core 15 is inserted into a tool cavity and clamped shut as part of the moulding process 220, 318.

The above described examples have focussed on the use of a core formed from a wooden material, such as pine. However, alternative materials can be used depending on the preferred implementation.

In one example, the wooden core is replaced by plastic foam or other similar material. In this example, the cross arm is manufactured using the above described technique core is still used to support the fibre during a wrapping process. Thus, the core acts in exactly the same way as the wooden core, allowing fibre to be wrapped around the core and then impregnated with resin.

Previously, arrangements that have used foam have achieved this by forming an outer shell of resin material, often manufactured using a pultrusion process, and injected the foam material into the outer shell. Advantageously, by wrapping a core in fibre reinforcement prior to moulding, a better bond between the fibre reinforced resin layer and the core is obtained, resulting in a stronger cross-arm. Additionally, using a structural foam core to which the fibre impregnated resin is subsequently applied, allows the foam to have desired structural properties, and in particular, a hardness and resilience, that cannot be achieved when foam is injected into an existing cavity, as in the prior art. Also, the chances of internal defects are reduced because a core can be checked prior to it being wrapped in a reinforcement material. Also, other previously discussed drawbacks with pultrusion processes are prevented.

It will be appreciated that the features described above with respect to the wooden core, such as the use of a grooved or channelled core surface can also be implemented using this technique, thereby typically enhancing the strength of the resulting cross arm, which is not achievable using the prior art techniques.

Use of foam is not generally as desirable as using the wood for a number of reasons. For example, the wood can be grown naturally, thereby reducing the manufacturing requirements. Secondly, the wood inherently provides adequate support for receiving bolts or other fixing means, which is not necessarily the case with all foams. Furthermore, the wood provides inherent crush resistance, thereby avoiding the need for supporting sleeves (although as described above with respect to Figures 14 and 15 these can be utilised), which again cannot be achieved using all foams.

A further benefit of growing trees to supply the core material, is that the wooded areas act as carbon dioxide sinks. As the resulting wood is used substantially in it's natural form, the cross arm using a wooden core acts to remove carbon dioxide from circulation that would not otherwise be removed if other core materials were selected.

Accordingly, whilst a foam or other core material, which is capable of supporting a fibre wrapping process, may be used, the core material is preferably formed from replenishable wood, such as fast growing pine, spruce, balsa or the like.

The embodiments have been described by way of example only and modifications are possible within the scope of the invention disclosed.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims

1. A cross-arm for supporting electric cables from a utility pole comprising an elongate core surrounded by at least one fibre reinforced resin layer, wherein the elongate core comprises wood.

2. The cross-arm as claimed in claim 1, wherein the at least one fibre reinforced resin layer is bonded to the core.

3. The cross-arm as claimed in either claim 1 or claim 2, wherein the core provides support to the fibre reinforcement layer.

4. The cross-arm as claimed in any one of the preceding claims, wherein the core provides crushing resistance to the cross-arm, thereby allowing through bolting of the cross-arm to allow fitment of the cross-arm to a utility pole or fitment of accessories to the cross-arm.

5. The cross-arm as claimed in any one of the preceding claims, wherein the core provides crushing resistance to the cross-arm, thereby preventing buckling of the at least one fibre reinforced resin layer.

6. The cross-arm as claimed in any one of the preceding claims, wherein the core prevents accumulation of foreign matter inside the cross-arm.

7. The cross-arm as claimed in any one of the preceding claims, wherein the or each fibre reinforced resin layer provides stiffness to the cross-arm.

8. The cross-arm as claimed in any one of the preceding claims, wherein the or each fibre reinforced resin layer provides an outer insulating layer.

9. The cross-arm as claimed in any one of the preceding claims, wherein the or each fibre reinforced resin layer comprises a fibre reinforcement layer impregnated with resin.

10. The cross-arm as claimed in any one of the preceding claims wherein the or each fibre reinforced resin layer comprises alternating layers of resin and fibre reinforced resin.

11. The cross-arm as claimed in any one of the preceding claims, wherein the elongate core comprises a low density wood.

12. The cross-arm as claimed in any one of the preceding claims, wherein the wood is selected from the group comprising pine and balsa wood.

13. The cross-arm as claimed in any one of the preceding claims, wherein the wood is treated with Copper Chromium Arsenate.

14. The cross-arm as claimed in any one of the preceding claims, wherein the core has sufficient strength to engage and retain a treaded fastener.

15. The cross-arm as claimed in any one of the preceding claims, wherein the cross-arm further comprises an outer insulating layer surrounding the cross-arm.

16. The cross-arm as claimed in claim 15, wherein the outer insulating layer comprises a further resin layer.

17. The cross-arm as claimed in any one of the preceding claims, wherein the elongate core is of substantially constant cross section.

18. The cross-arm as claimed in any one of the preceding claims, wherein the cross- section of the elongate core is quadrilateral.

19. The cross-arm as claimed in any one of claims 1 to 17, wherein at least one longitudinal surface of the cross-arm is convex.

20. The cross-arm as claimed in any one of claims 1 to 17, wherein the cross-arm is of a hexagonal cross-sectional shape.

21. The cross-arm as claimed in any one of the preceding claims, wherein the elongate core comprises at least one groove formed therein to provide an interlocking element between the core and the surrounding layers.

22. The cross-arm as claimed in any one of the preceding claims, wherein the grooves are formed along substantially all of the length of the core.

23. The cross-arm as claimed in any one of the preceding claims, wherein at least one fibre reinforced resin layer comprises fibres orientated substantially aligned with a central longitudinal axis of the cross-arm.

24. The cross-arm as claimed in any one of the preceding claims, wherein at least one fibre reinforced resin layer comprises bi-directional fibres orientated at a first angle from a central longitudinal axis of the cross-arm.

25. The cross-arm as claimed in any one of the preceding claims, wherein at least one fibre reinforced resin layer comprises tri-directional fibres, wherein a first layer is orientated an angle substantially aligned with a central longitudinal axis of the cross- arm, and second and third layers are orientated at a second angle from a central longitudinal axis of the cross-arm.

26. The cross-arm as claimed in any one of the preceding claims, wherein the resin comprises at least one of : a. cycloaliphatic epoxy (CEP) resin; b. hydrophobic cycloaliphatic epoxy (HCEP) resin; and c. Huntsman hydrophobic cycloaliphatic epoxy Araldite CY5622.

27. The cross-arm as claimed in any one of the preceding claims, wherein the fibre reinforced resin layer is between 1 mm and 8 mm thick.

28. The cross-arm as claimed in any one of the preceding claims, wherein the fibre reinforced resin layer is between 1.5 mm and 5 mm thick.

29. A cross-arm for supporting electric cables from a utility pole comprising an elongate core surrounded by at least one fibre reinforced resin layer, wherein the elongate core comprises foam material.

30. The cross-arm as claimed in claim 29, wherein the at least one fibre reinforced resin layer is bonded to the core.

31. The cross-arm as claimed in either claim 29 or claim 30, wherein the core provides support to the fibre reinforcement layer.

32. The cross-arm as claimed in any one of claims 29 to 31, wherein the core provides crushing resistance to the cross-arm, thereby allowing through bolting of the cross- arm to allow fitment of the cross-arm to a utility pole or fitment of accessories to the cross-arm.

33. The cross-arm as claimed in any one of claims 29 to 32, wherein the core prevents accumulation of foreign matter inside the cross-arm.

34. The cross-arm as claimed in any one of claims 29 to 33, wherein the or each fibre reinforced resin layer provides stiffness to the cross-arm.

35. The cross-arm as claimed in any one of claims 29 to 34, wherein the or each fibre reinforced resin layer provides an outer insulating layer.

36. The cross-arm as claimed in any one of claims 29 to 35, wherein the or each fibre reinforced resin layer comprises a fibre reinforcement layer impregnated with resin.

37. The cross-arm as claimed in any one of claims 29 to 36, wherein the or each fibre reinforced resin layer comprises alternating layers of resin and fibre reinforced resin.

38. The cross-arm as claimed in any one of claims 29 to 37, wherein the core has sufficient strength to engage and retain a threaded fastener.

39. The cross-arm as claimed in any one of claims 29 to 38, wherein the cross-arm further comprises an outer insulating layer surrounding the cross-arm.

40. The cross-arm as claimed in claim 39, wherein the outer insulating layer comprises a further resin layer.

41. The cross-arm as claimed in any one of claims 29 to 40, wherein the elongate core is of substantially constant cross section.

42. The cross-arm as claimed in any one of claims 29 to 41, wherein the cross-section of the elongate core is quadrilateral.

43. The cross-arm as claimed in any one of claims 29 to 42, wherein at least one longitudinal surface of the cross-arm is convex.

44. The cross-arm as claimed in any one of claims 29 to 43, wherein the cross-arm is of a hexagonal cross-sectional shape.

45. The cross-arm as claimed in any one of claims 29 to 44, wherein the elongate core comprises at least one groove formed therein to provide an interlocking element between the core and the surrounding layers.

46. The cross-arm as claimed in any one of claims 29 to 45, wherein the grooves are formed along substantially all of the length of the core.

47. The cross-arm as claimed in any one of claims 29 to 46, wherein at least one fibre reinforced resin layer comprises fibres orientated substantially aligned with a central longitudinal axis of the cross-arm.

48. The cross-arm as claimed in any one of claims 29 to 47, wherein at least one fibre reinforced resin layer comprises bi-directional fibres orientated at a first angle from a central longitudinal axis of the cross-arm.

49. The cross-arm as claimed in any one of claims 29 to 48, wherein at least one fibre reinforced resin layer comprises tri-directional fibres, wherein a first layer is orientated an angle substantially aligned with a central longitudinal axis of the cross- arm, and second and third layers are orientated at a second angle from a central longitudinal axis of the cross-arm.

50. The cross-arm as claimed in any one of claims 29 to 49, wherein the resin comprises at least one of : a. cycloaliphatic epoxy (CEP) resin; b. hydrophobic cycloaliphatic epoxy (HCEP) resin; and c. Huntsman hydrophobic cycloaliphatic epoxy Araldite CY5622.

51. The cross-arm as claimed in any one of claims 29 to 50, wherein the fibre reinforced resin layer is between 1 mm and 8 mm thick.

52. The cross-arm as claimed in any one of claims 29 to 51, wherein the fibre reinforced resin layer is between 1.5 mm and 5 mm thick.

53. The cross-arm as claimed in any one of claims 29 to 52, wherein the elongate core comprises a plastic foam.

54. A method of manufacturing a cross-arm for supporting electric cables from a utility pole comprising the steps of providing a core and applying at least one fibre reinforced resin layer to the core.

55. The method of manufacturing a cross-arm as claimed in claim 54, wherein the step of applying at least one fibre reinforced resin layer comprises wrapping the core in a fibre reinforcement material and applying resin.

56. The method of manufacturing a cross-arm as claimed in claim 55, wherein the resin is applied using a vacuum assisted injection moulding process.

57. The method of manufacturing a cross-arm as claimed in any one of claims 54 to 56, further including the step of forming holes in the cross-arm for mounting the cross- arm to a utility pole.

58. The method of manufacturing a cross-arm as claimed in any one of claims 54 to 57, wherein the step of providing the core includes forming grooves in the core.

59. The method of manufacturing a cross-arm as claimed in any one of claims 54 to 58, wherein the core comprises a low density wood.

60. The method of manufacturing a cross-arm as claimed in any one of claims 54 to 59, wherein the core comprises foam.

61. The method of manufacturing a cross-arm as claimed in claim 60, wherein the core comprises a plastic foam.

62. A method of installing accessories to a cross-arm for use with a utility pole, comprising the steps of forming a hole in the cross-arm and inserting a threaded fastener directly into the core so that the threads engage the core material thereby retaining the fastener in position.

63. The method of installing a cross-arm to a utility pole as claimed in claim 62, wherein the fastener is a coach bolt.

64. The method of installing a cross-arm to a utility pole as claimed in any one of claims 62 to 63, wherein the utility pole supports electric cables transmitting electricity of up to 80,000 Volts.

65. The method of installing a cross-arm to a utility pole as claimed in any one of claims 62 to 64, wherein the cross-arm is tilted such that an upper surface is not perpendicular to the utility pole.

66. The method of installing a cross-arm to a utility pole as claimed in claim 65, wherein the cross-arm is tilted about the longitudinal axis such that an upper surface is not perpendicular to the utility pole.

67. A cross-arm for supporting electric cables from a utility pole substantially as hereinbefore described with reference to the drawings and/or examples.

68. A method of manufacturing a cross-arm for supporting electric cables from a utility pole substantially as hereinbefore described with reference to the drawings and/or examples.

69. The method of installing a cross-arm to a utility pole substantially as hereinbefore described with reference to the drawings and/or examples.