This invention relates to an insulated electric power pole. Timber power poles are extensively used for supporting power conducting wires. Whilst timber is a popular material for use in power poles, there is increasing need for a safe and durable substitute.

Timber has in the past been in plentiful supply and being substantially non-conductive has been ideal for use in power support poles. However, with ever increasing concern about diminishing natural timber resources and the growth of electricity supply infrastructures in most major cities, it has been necessary to look at alternative materials. A popular alternative has been portland concrete (hereinafter referred to as "concrete"). Traditional concrete power poles are conductive and must be earthed if they are to be safe.

As with timber power poles, concrete power poles are normally anything from about 8 to 30 metres in height usually carrying a cross arm at or near the top to support one or more electrical conductors. The concrete power pole is insulated from the electrical conductors by porcelain insulators interposed between the cross arms and the power carrying conductors. Thus, in normal operation the concrete pole is isolated (electrically) from the electrical conductors. However, faults can and do occur from time to time which can lead to the concrete power pole becoming "live". There are several ways in which such faults may develop. For example, birds or animals may bridge across an insulator; a conductor may break free from its associated insulator and fall against the pole or onto the cross arm. The concrete pole may even be struck by lightning. In most electrical supply systems, such high current faults are automatically detected and the circuit closed down. Circuit breakers are conventionally spaced so that no matter where the fault occurs in the system the supply will be cut off in less than one second and usually

less than 0.5 seconds. Despite the rapid isolation on the occurrence of such faults the use of concrete power poles inevitably leads to an increased risk of animal or human electrocution. During the period after a fault occurs and prior to the circuit closing, the entire concrete pole becomes "live". Unless the pole to earth resistance is very low, anyone touching the pole's surface or walking nearby will almost certainly be killed. This has happened in the past on rare occasions and has resulted in human fatality and loss of animal stock whilst touching or standing close to such a pole whilst it was momently live. Due to the risks inherent in the use of concrete power support poles many governmental authorities will not use concrete poles for high voltage distribution in densely populated areas. The risk is taken in rural areas where the probability of a person being near the pole whilst it is live is considered to be very small.

A further very serious concern arising from the use of conventional concrete power poles is that the flaming carcass of a fault causing animal or bird can fall to earth and be the cause of bush fires. Intermittant arcing between a fallen conductor and a concrete power pole can also initiate bush fires.

It is thus an object of the present invention to provide a power support pole which is made with concrete, is safer than conventional concrete poles presently in use and in particular, safeguards against human fatality in the case of electrical fault.

In accordance with this present invention there is provided a pole suitable for providing a support structure for one or more conductors, the said pole comprising at least first and second elongated sections which are integrally formed and connected, wherein said first section constitutes the bottom portion of the pole and is formed from or comprises concrete and said second section is formed from a material which is substantially non-conductive.

In a first embodiment of the invention, the second section forms the upper portion of the pole. In such an

embodiment, the conductors may be carried by a cross arm affixed to the non-conductive section. Alternatively, the conductor or conductors may be held in place by a slot, groove or aperture at or near the top of the non-conductive second section. Such a pole is particularly suitable for use in single wire earth return systems as no separate insulator is required for the conductor.

In a second embodiment a third elongated section is provided to form a multi-sectioned pole. In this form of the invention, the third section forms the upper portion of the pole and the second non-conductive section is interposed between the first and third sections. Preferably, in this embodiment the third section (like the first section) is formed from or comprises concrete. The three sections of the pole are integrally formed and connected in such manner to ensure that the first and third sections of the pole are substantially electrically isolated one from the other. It will be clear from the following description that further conductive and non-conductive sections can be added to the basic structure of the aforementioned embodiments to form multi-sectioned integrally formed and connected poles if such is required in special applications.

Preferably, the first and where applicable said further conductive sections are made from steel reinforced concrete. The concrete is preferably made from a suitable aggregate and Portland cement. It may be reinforced with continuous or discontinuous reinforcement. Longitudinal strands which have been pretensioned may be used in each conductive section. Alternatively and preferably, a tubular steel reinforcing cage is used with concrete moulded through and about the cage to form the desired shape.

It is intended that the power support poles of the present invention be erected in accordance with conventional methods. The pole is usually supported by burying a significant portion of its length under the

ground. Furthermore, the pole is normally tapered being broader at the base for greater mechanical strength, although this is not necessary as poles can be made with no taper, with non-circular cross section, or with stepped cross-sections.

Each of the sections of the pole may be of varying lengths depending on the positioning of the non-conductive second section along the length of the pole and the desired length of the entire pole. Preferably, the non-conductive section or sections of the pole are positioned such that once the pole has been erected any conductive section of the pole likely to become "live" on a fault occurring will be out of normal reach for persons or animals likely to come into contact with the pole. This normally means that the top of the non-conductive second section is located between 2 to 10 metres from the ground once the pole has been inserted into and supported within the ground. The top of the second section can be located anywhere above this position dependent upon the particular application. The position of the non-conductive second section relative to the bottom of the pole will of course depend on the depth of insertion of the pole into the ground for stable and adequate support which in turn depends on the height of the pole and the load it is intended to carry.

In a standard 12.5 metre pole the insulating second section is ideally positioned approximately 5 metres from the bottom of the pole - approximately 2 metres of the bottom section being supported under the ground. It is preferred in a three sectioned pole that the bottom of the non-conductive second section be as low as possible whilst still keeping the top of the second section out of normal reach so that bridging of the non-conductive section will not readily occur. Although a rare occurrence, such bridging could, for example, occur if a dislocated conductor dropped down far enough to come into contact with the portion of the pole underneath the non-conductive section.

The non-conductive second section of the pole may be

secured to an end of the first section in any manner which is secure and able to withstand the compressive and flexural loads expected to be experienced by the pole and satisfy servicability requirements. Thus, the said non-conductive second section should be considered not only an insulating section but also a structural component of the pole capable of transferring loads from the top of the pole to the bottom. In multi-sectioned poles (i.e. three section or more) , the non-conductive second section of the pole is secured at its top end to the bottom end of the top portion of the pole. The method of securement of the second section of the pole to other sections of the pole should be such that the first section is electrically isolated from the rest of the pole. Preferably, the second section of the pole is separately moulded with protruding continuous or discontinuous reinforcing connectors which are cast into the adjacent end of the said first section of the pole. These connectors may be in the shape of strips, angles, rods or any other convenient profile. Preferably, reinforcing rods are used. Further reference in this specification is, for convenience, directed to the use of reinforcing rods. Where the second section of the pole is connected at its top end to a third conductive section, this connnection can be effected in like manner by casting reinforcing connectors into the respective adjacent ends. In such embodiment, non-conductive reinforcing rods are preferred. Alternatively, discontinuous conductive reinforcing rods may be used, provided that the rods protruding from the respective ends of the second section are electrically separated from each other within the second section. Where discontinuous conductive reinforcing rods are used in this manner, they should overlap in the vertical plane but must be separated in the horizontal plane to maintain electrical isolation between the second and first sections of the pole.

Non-conductive reinforcing rods of suitable strength can be made from thermosetting resins such as epoxy resins, polyester resins, melamine resins, phenolic resins

and the like, reinforced with any non-conductive high elastic modulus fibre such as glass, asbestos or any of the aramid fibres such as those available under the trade mark KEVLAR or hybrids of any of these materials. The actual body of the non-conductive second section may be made from any non-conductive material having sufficient strength to bear the intended load for the pole concerned, and may be annular, indented or solid in cross-section. A suitable material is a polymer concrete based on a suitable thermosetting resin. Examples of suitable resins again include epoxy resins, polyester resins, melamine resins, phenolic resins and the like. The binder in such polymer concretes is filled with electrically non-conductive filler materials such as silica sand. Binder to filler ratio can range from 5:95 to 100:0. The polymer concrete can be reinforced (apart from the reinforcing rods hereinbefore mentioned) with non-conductive short fibres or continuous fibre strands.

The non-conductive second section should be long enough to ensure that current cannot "jump" across the air gap to the first section of the pole. This length varies depending on the intended voltage to be carried by the conductors and can be calculated by methods known in the art. In a typical 66kV application, the non-conductive second section should preferably be at least 150 mm in length. Most preferably, it is at least 200 mm in length. If desired, the outer surface of the second section may be moulded to form one or more watersheds or have non-conductive sheds attached to it. Such sheds prevent a continuous water film forming across the non-conductive section during heavy rain and increase the creepage distance.

The present invention also encompasses a method for forming a pole comprising at least a first conductive section made from or comprising concrete and a substantially non-conductive second section wherein the top end of said first section is integrally connected to the bottom end of said second section, comprising: (a) casting reinforcing rods into said second section

such that they protrude from the bottom end of the said second section; and (b) integrally casting said protruding ends of the reinforcing rods into the top end of said first 5 section.

Where the pole has three sections the second section is cast with reinforcing rods protruding from either end of said second section and the reinforcing rods protruding from the top end of the non-conductive second section are

10 integrally cast into the bottom end of the third section.

The invention is more particularly described hereafter by reference to preferred embodiments wherein:-

Figure 1 is a perspective view of a three part power support pole of the present invention inserted into the 15 ground;

Figure 2 is an exploded cross-sectional view of the non-conductive second section of the pole illustrated in Figure 1 connected to first and third sections using continuous reinforcing rods; 2.0 Figure 3 is an exploded cross-sectional view of the non-conductive second section of the pole illustrated in Figure 1 connected to the first and third sections by discontinuous reinforcing rods;

Figure 4 is the section through 4-4 as shown in 25 Figure 3;

Figure 5 is a perspective view of a two part power support pole of the present invention inserted into the ground; and

Figure 6 is an exploded cross-sectional view of the 30 non-conductive second section of the pole illustrated in Figure 5 as connected to the first section.

In Figure 1 there is illustrated a power support pole generally designated 1. This pole is supported in the ground, the surface of which is indicated by a dashed 5 line. A first section 2 is separated from a third section 3 by a substantially non-conductive second section 4. The first section 2 and the third section 3 are made from steel reinforced concrete. A steel reinforcing cage extends substantially along the length of both the first

and third sections and a portland cement based concrete mixture is then moulded through and around the reinforcing cage into the desired shape. It will be seen that first section 2 and third section 3 are both slightly tapered from bottom to top. Preferably, they are hollow.

The non-conductive second section 4 interposed between the first section 2 and third section 3 is seen in greater detail in alternative embodiments shown in Figures 2 and 3. In Figure 2, there is illustrated a first embodiment. The non-conductive section 4 is formed from a styrenated unsaturated polyester resin filled with a graded silica filler. The polyester resin to filler ratio for these materials is preferably between about 5 to 20 parts resin to 95 to 80 parts filler. Most preferably, the ratio is about 14 parts resin to 86 parts filler.

The three sections of the power support pole in this embodiment are fixedly connected through the use of non-conductive reinforcing rods 5. These rods are made from a non-conductive thermosetting epoxy resin reinforced with high elastic modulus aramid fibres. Non-conductive reinforcing rods 5 extend throughout the entire length of the non-conductive section 4 and extend into the adjacent ends 6 and 7 of the first and third sections respectively. In a 8kN pole (i.e. one designed to carry a working load in the horizontal direction of 8kN) it is preferred that the reinforcing rods 5 extend at least 150 mm (and most preferably at least 300 mm) into the ends of the respective first and third sections, to secure the three sections together. The ends of reinforcing rods 5 overlap the ends of reinforcing cages 8a and 8b located respectively in the first and third sections (2 and 3). The extent of the reinforcing rod overlap with the first and third sections will of course vary depending on the load intended to be carried by the pole. The first and third sections are reinforced with both longitudinal (9) and welded circumferential (10) steel.

In Figure 3, there is illustrated an alternative embodiment connecting the non-conductive section 4 to

first section 2 and third section 3. In this embodiment, discontinuous reinforcing rods 11 and 12 extend from either end of the non-conductive section 4. The upper set of reinforcing rods 11 extend into the conductive third section of the pole 3 and terminate typically about 40 mm above the lower end of non-conductive section 4. The lower set of reinforcing rods 12 extend into the conductive first section of the pole and typically terminate about 40 mm below the upper end of the non-conductive section 4. In this embodiment, the reinforcing rods may either be made from conductive or non-conductive materials. Where the reinforcing rods are conductive, they should be spaced so that they are separated in the horizontal plane to maintain electrical isolation. This is illustrated in Figure 4. Typically, the reinforcing rods 11 and 12 are separated from each other by a distance 13 typically about 40 mm in the horizontal plane.

Figure 5 illustrates an alternative embodiment of the power support pole of this invention formed in two sections. The bottom or first section 14 is supported in the ground. Again, the surface of the ground is indicated by a dashed line. A second section 15 is secured to the first section 14 and is substantially non-conductive. A slot 16 is provided at the top of the non-conductive second section 15 suitable for supporting a conductor. The connection between the first section 14 and the second section 15 of this pole is shown in Figure 6. As can be seen in Figure 6, reinforcing rods 17 extend from the non-conductive section 15 into the conductive first section 14 to securely hold the first and second sections together. The reinforcing rods 17 overlap the reinforcing cage 18 to securely hold the two sections of the pole together. The power support pole of the present invention is preferably manufactured in accordance with the following method. First, the pre-cast second section is placed in position in a pole mould and the reinforcing cage or cages are placed in position on one or both sides of the second

section. Preferably, the steel cages and the protruding reinforcing rods overlap. Concrete is then injected into the mould to form the first and where applicable third concrete sections. In use, as can be seen from Figures 1 and 5, it is intended that the first portion (2,14) be inserted into the ground for support. Non-conductive section (4,15) is positioned so that its top is at least 3 metres from ground level. It will be apparent that if any fault occurs at or near the top of the pole when in position, the bottom or first portion (2,14) will remain electrically isolated from the fault. Besides the elimination of this conventional danger inherent in "live" concrete power poles, there is also a considerable cost saving involved in the utilization of the power support pole of the present invention, when the total cost of the pole and its accessories is compared with conventional concrete poles. The structures do not require pole earth fittings or earth rods; insulators can be shorter and cheaper and plastic covers for cross arms and pole tops are not required. In the slotted two part pole, the conductor can be seated on top of a series of poles without further costly accesories.

It is to be understood that various modifications, additions and/or alterations may be made to the configurations previously described without departing from the ambit of the invention as defined in the following claims.