GB2537082A

GB2537082A - Connection mast

Info

Publication number: GB2537082A
Application number: GB1417635.8A
Authority: GB
Inventors: Ford Robert
Original assignee: ENSERVE GROUP Ltd
Current assignee: ENSERVE GROUP Ltd
Priority date: 2014-10-06
Filing date: 2014-10-06
Publication date: 2016-10-12
Anticipated expiration: 2034-10-06
Also published as: GB201417635D0; GB2537082B

Abstract

A connection system for connecting an electrical load (56, figure 5) and an electrical supply to a power grid comprising a plurality of overhead electrical transmission cables (36, 38, 40), the connection system comprising a first connection mast 10, and a plurality of conductor cables 28, 30, 32 configured to connect the first connection mast at a pre-determined connection point to the electrical transmission cables, wherein the conductor cables are configured to provide a low tension connection to the power grid. Preferably the conductor cables provide sag when the connection is made, and allows connection of renewable energy generation installations to the electrical power grid distribution network at the nearest structure 26 available. Also claimed is a method of installing the connection mast in the least time consuming process possible. Preferably the amount of sag required is calculated to ensure full range of swing of the transmission cables under an imposed load, such as ice, so that it will not cause additional load to be applied to the power grid or reduce the separation between the conductor cables below a minimum threshold.

Description

Connection Mast

FIELD OF THE INVENTION

The present invention relates to a connection mast for connecting an electrical load/supply to the power grid and to a method of connecting a connection mast to the power grid.

BACKGROUND OF THE INVENTION

The overall capacity of the UK renewable energy generation projects is continually increasing, whilst at the same time the available capacity of the existing power grid distribution network is diminishing. Due to this it is beneficial to be able to connect renewable energy generation installations to the electrical power grid distribution network at the nearest structure available.

The traditional method to connect to existing 33kV and 132kV overhead transmission line cables is to build a brand new, specific, in line terminal electrical tower which is then connected to the existing electrical power grid requiring several hundred meters of high-voltage underground or over ground cable at quite a considerable cost.

In addition to this, the process for constructing and installing a new electrical transmission tower to replace the existing tower is a very time consuming process including considerable electrical outage times while the existing tower is dismantled and the new tower is erected, which require complex electrical diversions along the network. This works are usually restricted to specific months of the year and the availability of maintaining alternative power supplies.

It is the purpose of the present invention to overcome or at least mitigate the problems associated with the prior art.

SUMMARY OF THE INVENTION

A first aspect of the invention provides a connection system for connecting an electrical load and/or an electrical supply to a power grid comprising a plurality of overhead electrical transmission cables, the connection system comprising a first connection mast, and a plurality of conductor cables configured to connect the first connection mast at a pre-determined connection point to the electrical transmission cables, wherein the conductor cables are configured to provide a low tension connection to the power grid.

Advantageously, the connection mast provides a simple method of connecting an electrical load and/or electrical supply to a power grid without the need to replace the existing electrical tower. This results in a system which enables connection to an existing overhead electrical line network with drastically reduced downtime of the power grid as the connection mast can be assembled first prior to taking the power grid circuit outage and only taking the power grid outage whilst making the connection. This removes the need for complex line diversions during connection.

In one embodiment, the plurality of conductor cables are configured to be greater in length than the separation between the connection mast and the connection point, so as to provide a sag in said cables when the connection is made.

Advantageously, the sag provided in the conductor cables is calculated so that the load applied to the power grid from any imposed load such as wind or ice is minimised. This prevents connecting the connection mast to the power grid from causing damage to the existing network. Many of the existing UK electrical towers have limited or no supporting design load information due to their age and so it is not always known how much mechanical load they can withstand.

In one embodiment, the sag is calculated to minimise a force acting on the existing electrical tower due to a short circuit load.

Short circuit load is a major issue within the power supply industry and advantageously this provides an easy method of minimising the impulse load that is applied to the power grid at the connection point.

In one embodiment, the required sag is calculated in combination with the connection mast location to ensure that swinging of the transmission cables within their full range of permitted movement under an imposed load will not cause additional load to be applied to the power grid or reduce the separation between the conductor cables below a minimum threshold.

In one embodiment, the connection mast is configured to flex under an applied load.

Advantageously, this enables the connection mast to take up the majority of the self-weight, ice and wind loads applied from/to the conductor cables.

In one embodiment, the flex at the uppermost point of the connection mast is limited to 200mm.

Advantageously, this upper limit ensures that the flexing of the tower does not take up all of the sag of the conducting cables and so ensures that the flexing of the tower does not apply any load to the power grid.

In one embodiment, the flex of the connection mast is determined by the length of the cross lead conductor cables between the connection mast and the connection point to the electrical transmission cables.

Advantageously, the length of the conductor cables affects the self-weight, ice and wind loads.

In one embodiment, the connection mast is pivotally connected to a foundation Advantageously, the enables the connection mast to be assembled at ground level and then only erected when finished, thus reducing the amount of work required to be carried out at height.

In one embodiment, a lifting apparatus is provided between the ground anchor and the connection mast to raise and lower the connection mast.

Advantageously, this provides a very easy method of raising and lowering the tower. Means that the tower can be assembled at ground level and simply raised. So less working at height. Enables a quick lowering of the tower also for emergency return to service.

In one embodiment, the connection mast comprises a plurality of tapered sections.

Advantageously, providing the connection mast in smaller sections allows for easier transport and handling of the sections.

In one embodiment, the sections are formed from folded sheet metal.

Advantageously, manufacturing out of sheet metal such as steel provides an easy method of manufacturing. The hollow shape reduces the overall weight of the tower thus reducing the need for lifting cranes and enabling easier transportation and assembly.

In one embodiment, the sections are nested end-to-end to form the connection mast.

Advantageously, this reduces the need for working at height as the tower can be assembled on the ground.

In one embodiment, the conductor cables are connected to the connection mast via a plurality of insulators secured to an outer surface of the connection mast.

Advantageously, this provides an easy method of securing the conductor cables to the connection mast.

In one embodiment, the insulators are made from a polymeric material.

Advantageously, this provides a lightweight and cheap insulator, thus further reducing the overall weight of the tower and so enabling easier handling and transport.

In one embodiment, the plurality of insulators are arranged into a plurality of columns with each column angled relative to the others.

In one embodiment, a conductor cable is connected to each column of insulators Advantageously, this ensures that the minimum phase-to-phase separation of the conductor cables attached to the connection mast is maintained.

In one embodiment, the columns of insulators can be rotated around the connection mast to provide better connection locations.

Advantageously, this enables the insulators to be positioned to enable easier connections at the ground level.

In one embodiment, the connection mast is located between 5m and 15m from the connection point.

Advantageously, this ensures that the connection mast is not too close and does not affect the existing foundations while keeping the separation short enough to minimise cable costs while ensuring that the minimum phase-to-phase separation of the conductor cables is maintained.

In one embodiment, the connection point is an electrical transmission tower.

In one embodiment, the connection of the conductor cables on the transmission tower is via a tap-in connection.

In one embodiment, the connection of the conductor cables on the transmission tower is via a loop-in/loop-out connection.

In one embodiment, the low tension connection is in the form of a compressed tee-connector.

In one embodiment, the electrical load is an electrical generator, optionally a gas turbine, and/or the electrical supply is renewable energy source, optionally a solar panel farm.

In one embodiment, the connection point is a suspension electrical tower. In one embodiment, the connection point is a tension electrical tower.

A second aspect of the invention provides a method of connecting an electrical load and/or an electrical supply to a power grid comprising a plurality of overhead transmission cables, the method comprising the steps of: selecting a desired location to connect to the power grid; selecting a first connection mast comprising a plurality of conductor cables configured to connect the connection mast to a pre-determined point on the electrical transmission cables; selecting a suitable location for the connection mast; calculating the required conductor cable length; turning the existing power grid offline; terminating each of the overhead transmission cables by inserting at least one in-line insulator; and connecting the plurality of conductor cables of the first connection mast to each of the plurality of overhead transmission cables at a first side of the in-line insulators, wherein the conductor cables are configured to provide a low tension connection to the power grid.

Advantageously, this allows any excess power from an electrical supply to be fed into the grid. Furthermore, this allows the electricity to be sent in a specific direction (i.e. depending on which side of the in-line insulator you send it to) and allows the electricity to be supplied to a specific direction/location in response to an applied electrical demand.

In one embodiment, a second connection mast comprising a plurality of conductor cables and the method comprises the step following step g) of h) connecting the plurality conductor cables of the second connection mast to each of the plurality of overhead transmission cables at a second side of the in-line insulators, wherein the conductor cables are configured to provide a low tension connection to the power grid.

In one embodiment, the connection mast comprises a plurality of tapered sections and the method further comprises the step of assembling the connection mast prior to turning the existing power grid offline.

In one embodiment, the connection mast can flex and the method further comprises a step of calculating a desired amount of connection mast flex following the step of calculating the required conductor cable length.

In one embodiment, the plurality of conductor cables are configured to be greater in length than the separation between the connection mast and the connection point to provide a sag in said cables when the connection is made.

In one embodiment, the required sag is calculated in combination with the connection mast location to ensure that swinging of the transmission cables within their full range of permitted movement under an imposed load will not cause additional load to be applied to the power grid or reduce the phase-to-phase separation below a minimum threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure IA is a schematic front view of connection mast according to an embodiment of the present invention; Figure 13 is a schematic side view of the connection mast of Figure 1A; Figure 2 is a schematic view of a connection mast connected to a suspension electrical tower according to an embodiment of the present invention; Figure 3 is a schematic view of the conductor connection of Figure 2; Figure 4 is an isometric view of a lifting apparatus secured to the connection mast of Figure IA; Figure 5 is a schematic view of a tap-in connection from a connection mast of Figure 1A to the power grid via a tension tower; Figure 6 is a schematic view of a loop-in/loop-out connection from two connection masts of Figure lA to the power grid via a tension tower; Figure 7 is a schematic view of a single loop-in/loop-out connection to the power grid via a suspension tower; Figure 8 is a schematic front view of a typical suspension clamp that is known in the art; Figure 9 is an isometric view of a connection shoe according to an embodiment of the present invention; and Figure 10 is a schematic side view of the assembly of the suspension clamp of Figure 8 and the connection shoe of Figure 9.

DETAILED DESCRIPTION OF EMBODIMENT(S)

Referring firstly to Figures l A and 1B, a simplified connection mast 10 according to an embodiment of the present invention is illustrated. The connection mast 10 is in the form of an elongate vertical pole 12 which is secured to an upper surface of a foundation indicated generally at 14. As can be seen from the figures, the connection mast 10 comprises a series of insulators 16 secured to the outer surface of the vertical pole 12.

In the present embodiment, an insulator connection mount (not shown) is first welded onto the outer surface of the vertical pole 12 and the insulator 16 is then secured to the mount, where the length of the mount can be adjusted in order to provide the correct circuit wire clearances. However, in alternative embodiments different attachment mechanisms may be used, for example the mounts may be integrally formed with the pole 12 during manufacture. The mounts are mounted to the pole 12 such that the insulators are angled upwards with respect a horizontal axis which is substantially perpendicular to the pole 12. The angle of the mount is fully adjustable to comply with the various insulator manufactures operating specifications.

The insulators 16 are arranged into three substantially vertical columns 18, 20, 22 which are arranged at 90° with respect to the other two columns. In other embodiments, the angle between each column may be higher such as 120° or lower such as 60° or anywhere therebetween. Although the location of the insulators 16 is fixed onto the surface of the pole 12, the pole itself can be rotated to adjust the location of the insulators 16 with respect to the ground in order to aid connection. Each insulator 16 within a column 18, 20, 22 has a vertical spacing of 2.5m from the insulator above and/or below in the column. However, in alternative embodiments this vertical spacing may vary as the spacing is chosen to substantially match the required separation between the three phases of the overhead electrical transmission cables (not shown). In the illustrated embodiment, the connection mast 10 is designed for connection to a 132kV overhead lines which require a 2.5m phase to phase separation between each transmission cable.

A separation of 0.5m is required for 33kV transmission cables and the insulator spacing will be selected for the type of connection required. These separation dimensions are completely variable and are designed for each electrical connection.

The three columns 18, 20, 22 of insulators 16 may be differently orientated as the insulators are able to be mounted at any points on the connection mast 10 as long as the required phase-to-phase separation is maintained. In alternative embodiments, each insulator 16 may be rotated a specific amount to the insulator directly above it resulting in a substantially helical formation around the connection mast 10. For example, in a system comprising nine insulators 16 each subsequent insulator may be rotated by 10° resulting in a 90° rotation between the top and bottom insulator.

The first column of insulators 18 comprises seven insulators 16 wherein the uppermost insulator is located proximate the top of the pole 12 and in use is designed to approximately align with the vertical height of the uppermost phase conductor of the overhead cables of the power grid (not shown). The second column of insulators 20 comprises six insulators 16 wherein the uppermost insulator substantially aligns with the second insulator of the first column 18 and in use is designed to approximately align with the vertical height of the middle phase conductor of the overhead cables of the power grid. The third column of insulators 22 comprises five insulators 16 wherein the uppermost insulator substantially aligns with the second insulator of the second column 20 and the third insulator of the first column 18 and in use is designed to approximately align with the vertical height of the lowermost phase conductor of the overhead cables of the power grid.

The pole 12 is manufactured from folded sheet metal. In this embodiment the metal is steel as it is cheap to manufacture and shape thus reducing the overall carbon footprint of the connection mast, although in alternative embodiments any suitable material may be used to construct the pole. In the illustrated embodiment, the cross section of the pole 12 is substantially square with the columns of insulators 18, 20, 22 mounted at three of the four apexes of the pole 12. In alternative embodiments, the pole may be substantially polygonal in cross section, for example hexagonal or octagonal, or the pole may be circular in cross section. Manufacturing the connection mast from folded sheet metal greatly reduces its overall weight. A 30m height connection mast for connecting to a 132kV transmission tower will weight approximately 3000kg compared to a traditional tower of approximately 12,000kg, resulting in a much cheaper point of connection structure due to the low usage of material. This large reduction in the weight of the connection system also improves the ease of transport and assembly of the connection mast with respect to a traditional lattice electrical tower comprising multiple angle and plate sections thus reducing the need for heavy lifting equipment.

Furthermore, a 30m high tower will require the base of the pole 12 to be approximately 1m in diameter which minimises the footprint and the overall visual impact of the connection mast 10.

In the illustrated embodiment, the pole 12 is formed as a unitary component where the unitary component is pivotally secured to a base section 42. In alternative embodiments, the pole 12 is formed from a plurality of sections 24 which can be nested end to end to form the complete pole 12. Providing the connection mast in sections allows for easier manufacture, transport and assembly of the connection mast. Each section 24 is tapered in shape, narrowing towards the top, and the sections are nested together top-to-bottom in order to produce a pole 12 that is the correct height for the specific connection required. In alternative embodiments the pole 12 may be provided as a unitary component.

Referring to Figure 2, the illustrated connection mast 10 is connected to an electrical transmission tower 26 in the form of a suspension tower by three conductor cables 28, 30, 32. The electrical transmission tower 26 supports three transmission cables 36, 38, 40 vertically spaced and offset from each other, which are suspended from tower insulators 34 of the tower by suspension clamps (not shown). Tower insulators 34 are provided on the electrical tower which suspend downward from the tower and are configured to pivot about the point of connection to the cross arm 27 of the transmission tower 26 under the applied load of the wind and ice. The point of connection of the conductor cables 28, 30, 32 to the transmission cables 36, 38, 40 is proximate to the suspension clamps.

The first conductor cable 28 is secured to the connection mast 10 via the first column of insulators 18 and connects the connection mast 10 to the uppermost of the three transmission cables 36. The second conductor cable 30 is secured to the connection mast 10 via the second column of insulators 20 and connects the connection mast 10 to the middle of the three transmission cables 38. The third conductor cable 32 is secured to the connection mast 10 via the third column of insulators 22 and connects the connection mast 10 to the lowermost of the three transmission cables 40. As previously described, the height of the top insulator 16 of the first 18, second 20, and third 22 columns of insulators are configured to substantially match the point of connection to the first 36, second 38, and third 40 transmission cables respectively. The position of the insulators mounted on the mast is calculated to ensure statutory phase to phase clearance is maintained under still air and swing condition for bare or ice loaded conditions at an operating temperature range from -6°C to the maximum operating temperature of the overhead line.

The conductor cables 28, 30, 32 are configured to provide a low tension connection from the connection mast 10 to the existing electrical transmission tower 26 to ensure that the minimum amount of mechanical load is applied to the existing tower 26. In many instances the condition, construction and design of the existing towers are unknown due to their age, so it is advantageous to minimise any load that is required to be applied to the towers to prevent damage.

As can be seen from the figure, the conductor cables 28, 30, 32 are designed to be longer than the horizontal separation distance S between the point of connection of the conductor cables 28, 30, 32 to the columns of insulators 18, 20, 22 and the point of connection of the conductor cables to the electrical tower 26. This excess length is configured to provide the conductor cables 28, 30, 32 with an amount of sag. This sag further reduces the amount of load that is applied to the existing tower 26 and is specifically calculated for each connection required.

The separation X between the foundation 14 of the connection mast 10 and the transmission tower 26 is typically between 5m and 15m but could be within the range of 2m to 25m. The vertical and horizontal loads produced by the wind and ice load on the conductor cables 28, 30, 32 and the wind load applied to the connection mast 10 are known as the reaction loads of the connection mast 10. These are the loads transferred down the length of the connection mast 10 and are supported by the foundation 14. Providing such a separation between the connection mast 10 and the existing tower 26 ensures that the foundations and reaction loads of the connection mast 10 do not interfere with the foundations of the existing tower 26.

Figure 2 illustrates the tower insulators 34 at their maximum 34' and minimum 34" positions with respect to the connection mast 10 under applied wind loads. The sag provided in the cables is sufficient such that even under the hill swing of the tower insulators, and as such the transmission cables 36, 38, 40, there is still an amount of sag remaining in the conductor cables to ensure that no additional load is applied to the existing tower 26. Connecting the conductor cables 28, 30, 32 to the connection mast at different heights, coupled with the amount of sag provided in said conductor cables ensures that the minimum phase to phase separation is always ensured even under full permitted movement of the transmission cables.

The pole 12 of the connection mast 10 is designed to be able to flex under an applied load. The conductor cables 28, 30, 32 will apply a load due to their weight and the pole 12 is configured to be able to flex under those loads so as to take on the majority of this load. This further ensures that the minimum amount of mechanical load, considered well within the design loads of the tower, is applied to the existing tower.

The maximum flex of the pole 12 will not exceed 200mm, and the required amount of flex of the pole 12 will be calculated for each specific connection and is dependent upon the length of the conductor cables. The amount of flex provided by the pole is determined by the thickness of the sheet metal and the diameter of the pole 12 at its top and base. The amount of flex required also incorporates the load applied onto the conductor cables 28, 30, 32 due to wind and ice build-up on the conductor cables and is calculated with an ice formation with a 10mm radial thickness forming around the conductor cables. The required flex of the tower is further calculated to withstand the applied load due to wind acting on the conductor cables 28, 30, 32. Due to this configuration the flex of the tower takes up the majority of the applied loads due to the conductor cables and as such minimises the amount of load that is applied to the existing tower 26.

The sag provided in the conductor cables 28, 30, 32 is also calculated to withstand the maximum flex of the pole 12 and is also configured to withstand any electrical short circuit load imposed onto the conductor cables 28, 30, 32. This is particularly advantageous as applied short circuit mechanical loads are a major concern within the industry and this system provides a simple and easy solution to overcoming this problem.

The approximate amount of sag required, D, is dependent upon a range of factors and this is shown schematically in Figure 3. The required sag D is calculated from the weight of the conductor cable, W, the separation between the conductor cable connection points S, and the horizontal component of the tension in the conductor cable at the trough, H, due to the self-weight of the cable and the ice load and is calculated using the following formula: WS' D gH This value is then able to be used to determine the required length of the conductor cable: L MR + S(1 D2) +24H2-) S(1 3S2 Referring to Figure 4, the base section 42 of the connection mast 10 is shown in more detail. In the illustrated embodiment the foundation 14 is in the form a concrete structure which is set into the ground. However, in areas of low soil strength piling may be used to insert poles into bores formed in the ground which concrete will be then poured into in order to form the foundation structure.

The base section 42 is permanently secured to the foundation 14 in a substantially vertical position and is hingedly connected to the lowermost section 24 of the pole 12 at two mounting points 50. The connection mast 10 is moved between a lowered position and a raised position by a lifting apparatus 44 in the form of a hydraulic cylinder which is mounted between the bottom section 24 and the foundation 14 The hydraulic cylinder 44 provides a quick and easy mechanism to raise and lower the connection mast 10 ensuring that the connection mast 10 can be brought down for repairs and raised again in a minimum amount of time, thus minimising the required amount of outages of the system. This system also ensures that in the situation of an emergency return to service, no matter what the stage of construction, the connection system can be taken down and the emergency return to service can be returned in less than 1 hour. However, in alternative embodiments the connection mast 10 may simply be secured directly to the foundations without the use of the hydraulic cylinder or a hinged connection.

Furthermore, providing the hydraulic cylinder 44 for raising and lowering the connection mast 10 enables the assembly of the connection mast 10 to take place on the ground and the assembled mast is simply connected to and raised via the cylinder 44. This is advantageous as it reduces the amount of work that has to be carried out at height and also reduces the requirement for a lifting crane during the assembly process. The foundation 14 includes a mounting surface 46 on an upper surface thereof for the hydraulic cylinder and a first end of the hydraulic cylinder 44 is releasably secured to said mount. The lowermost section 24 includes a mounting surface 48 to which the second end of the hydraulic cylinder 44 is mounted. Using these mounts 46, 48 the hydraulic cylinder 44 can be installed prior to erection of the connection mast 10 and then removed following use to minimise the possibility of damage occurring to the hydraulic cylinder while it is not in use.

The connection mast system can be erected in several days and the simplicity of the assembly of the mast means that the connection mast 10 can be assembled and erected while the existing tower circuit is still live. The actual electrical connection can be achieved in less than a day and this is the amount of power outage that this system requires for installation. This reduced outage for the system reduces the need for complex line diversions and the associated access works that are required during long power outages. As the known existing method is very time consuming and can require long periods of down time the electrical distribution, network operators limit or completely inhibit any new connections being made during the winter months when power demand is high due to the availability of alternative electrical supply routes. Furthermore, the existing method requires a six month lead time prior to any new connection in order to provide sufficient time to plan the required electrical diversions.

As this system will require only 1 day of down time it will be able to easily and repeatedly make new connections even during periods of high demand.

The base section 42 is also formed from folder sheet metal and as such defines an internal space. The base section 42 comprises a panel (not shown) to enable access to the interior space which may be used for storing equipment such as the hydraulic cylinder 44, spare parts or repair equipment.

Referring to Figure 5, a schematic view of a connection mast 10 connected to the transmission cables 36, 38, 40 of a tension tower 26 that forms part of the electrical power grid. In this embodiment, a single connection mast 10 is provided. The conductor cables 28, 30, 32 provide a low tension permanent connection to the transmission cables 36, 38, 40 in order to draw electricity from the power grid to supply said electricity to an electrical load 56.

The first conductor cable 28 is secured to the connection mast 10 via the first column of insulators 18 and connects the connection mast 10 to the uppermost of the three transmission cables 36. The second conductor cable 30 is secured to the connection mast 10 via the second column of insulators 20 and connects the connection mast 10 to the middle of the three transmission cables 38. The third conductor cable 32 is secured to the connection mast 10 via the third column of insulators 22 and connects the connection mast 10 to the lowermost of the three transmission cables 40. Each of the conductor cables 28, 30, 32 are then connected to the electrical load 56. In the illustrated embodiment, making a connection to the transmission cables 36, 38, 40 of a tension tower is done by using a standard compression or bolted tee-connector (not shown). A conductor cable 28, 30, 32 is secured to the base of the longitudinal stem of the tee-connector and the transverse section of the tee-connector comprises an elongate slit which enables the transmission cables 36, 38, 40 to be placed inside of the tee-connector which is then compressed to secure the tee-connector to the transmission cable.

Each of the transmission cables 36, 38, 40 are terminated at the tension tower 26 by two tension insulators 52 supporting the lines in either direction, with the transmission cables connected by a jumper cable 54 between the two transmission cable sections. The point of connection of the conductor cables 18, 20, 22 to the transmission cables 36, 38, 40 are proximate the tension insulators 52. In alternative embodiments, the point of connection may be made directly to the jumper cables 54.

Referring to Figure 6, a schematic view of a connection system connected to the transmission cables 36, 38, 40 of a tension tower 26 that forms part of the electrical power grid is shown. In this embodiment, a pair of connection masts 10 are provided and the conductor cables 28, 30, 32 provide a low tension connection to the transmission cables 36, 38, 40 in order to input electricity from an electrical supply (not shown) such as a renewable energy farm, for example as a wind or solar farm. The method of connection of the conductor cables to the transmission cables are substantially the same as described for Figure 5.

In alternative embodiments, if the transmission tower is a suspension electrical tower then attaching the conductor cables to the transmission cables requires terminating each of the overhead transmission cables as is illustrated in Figure 7. In this embodiment, a rigid yoke connection plate 58 is connected to the lowermost part of the suspension insulator 60. Each end of the transmission cables 36, 38, 40 is terminated with an in-line tension insulator 62 at one end of the in-line tension insulator and the opposing end of the in-line insulator is secured to the rigid connection plate 58. Connection to the transmission cables 36, 38, 40 are then made in the same way as described for Figure 6, resulting in what is known as a loop-in/loop-out connection. When a surplus of energy is generated at a renewable energy supply, the energy will be fed back into the main power grid. This configuration allows the operator to select which section of the transmission cables, and hence which direction, that the surplus energy is able to be provided to. This enables the surplus energy to be directed wherever the electricity demand is required. This configuration also allows the two connection masts to function as a jumper connection to replace the traditional jumper cable.

A suspension clamp is the equipment by which the transmission cables are connected to the insulators of the transmission towers. A suspension clamp 64 that is known in the art is illustrated in Figure 8 and comprises a mounting arrangement 66 so as to be connected to the lowermost section of the tower insulators. The suspension clamp 64 includes a substantially linear supporting section 68 that is substantially parallel to the transmission cables when in use. The supporting section 68 is substantially semicircular in cross section and is configured to receive the transmission cables. The distal ends of the supporting section 68 may be curved and angled downward to reduce the stress that is applied to the transmission cables. The suspension clamp 64 is further provided with two clamps 70, which are able to be adjusted via screws 72 to secure the transmission cables to the supporting section 68.

In an embodiment of the present invention, a connection shoe 74 is further provided that is configured to enable the suspension clamp 64 to be secured thereon. The connection shoe 74 comprises two bores 76 which are aligned along the central longitudinal axis of the connection shoe and are located proximate a bottom edge 84 of the connection shoe. In alternative embodiments the bores 76 may be positioned at a point on the connection shoe 74 that is not substantially covered by the suspension clamp 64 when assembled. In further alternative embodiments, the connection shoe 74 may include a different number of bores 76, such as 1, 3 or 4 bores. Two U-bolts 78 are provided on the connection shoe 74 which are located proximate the upper corners of said connection shoe. The length of the extension of the U-bolts 78 from the surface of the connection shoe 74 is designed to substantially match the suspension clamp 64 that is being used. The U-bolts 78 are configured to fit over the clamps 70 and are provided with an adjustment mechanism 80, in this embodiment in the form of nuts, to secure the connection shoe 74 to the suspension clamp 64 as is illustrated in Figure 9.

This suspension clamp arrangement is able to be connected to the transmission cables of the suspension tower with the cables passing through the region indicated at 82 in order to connect the transmission cables to the insulators of the transmission tower. The bottom section 84 of the connection shoe 74 extends substantially vertically downwards away from the suspension clamp 64 upon installation Upon the installation of a connection mast adjacent to the existing transmission tower, the conductor cables are then able to be clamped onto the bores 76 of the connection shoe 74. Advantageously, this provides a quick and easy method of connecting external conductor cables to the existing transmission cables of the power grid. This would remove the need to use compression tee-connectors for securement as is typically the case. Compression tee-connectors are known to apply compressive forces and hence strain to the transmission cables. This applied strain is known to be a major cause of transmission cable degradation and failure. As such, the connection shoe arrangement of Figures 9 and 10 increases the reliability of the transmission cables and thus the power grid. This arrangement would also further reduce the required connection time, and so the required power outage duration, during the connection of a connection mast to the transmission cables of the power grid.

The method of assembly of a connection mast 10 and connection to the power grid will now be described.

Prior to assembly of the connection system, a survey of the ground surrounding the existing electrical tower will first be carried out in order to determine a suitable site for the erection of the connection mast. The distance of the connection mast from the existing tower will be selected to ensure that the mast does not affect the foundations of the existing tower, typically this distance will be between 5m and 15m as has been discussed previously.

The foundation will be set into the ground proximate the existing electrical tower and may be in the form of a concrete structure set into the ground. However, in areas of low soil strength piling or screw anchors may be used to insert poles into bores formed in the ground which concrete will be then poured into in order to form the foundation structure. The base section will then be secured to the foundation The next step in the connection process will be to calculate the required length of the conductor cables in order to provide the exact amount of sag in the cables so as to ensure that minimal load is transferred to the existing tower. The amount of required flex of the connection mast tower will then need to be calculated and this in turn determines the required thickness and diameter of the connection mast tower.

The required number of sections of the connection mast tower will then be transported to the site which will then be assembled together on site. The insulator mounts can then be secured to the tower and subsequently the insulators are then mounted to the tower. This enables the conductor cables to be secured to the required insulators on the connection mast.

The assembled connection mast tower is then attached to the hydraulic cylinder which then raises the connection mast so that it is vertical. In total installation process, from surveying the local area to assembling the connection mast and then to connecting to the power grid takes around 6 weeks.

Once the connection mast has been erected a circuit of the power grid proximate the installation location will then be switched out in order to enable the connection mast to be connected to the power grid. As the tower has already been assembled, the process of making the physical connections connecting the three conductor cables to the three transmission cables of the transmission tower only requires around a day. Once the connection is made the connection mast is then able to draw out or supply energy to/from the power grid as required.

Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

Claims 1 A connection system for connecting an electrical load and/or an electrical supply to a power grid comprising a plurality of overhead electrical transmission cables, the connection system comprising a first connection mast, and a plurality of conductor cables configured to connect the first connection mast at a pre-determined connection point to the electrical transmission cables, wherein the conductor cables are configured to provide a low tension connection to the power grid.
2. The system of claim 1, wherein the plurality of conductor cables are configured to be greater in length than the separation between the connection mast and the connection point, so as to provide a sag in said cables when the connection is made.
3. The system of claim 2, wherein the sag is calculated to minimise a force acting on the existing electrical tower due to a short circuit load.
4. The system of claim 2, wherein the required sag is calculated in combination with the connection mast location to ensure that swinging of the transmission cables within their full range of permitted movement under an imposed load will not cause additional load to be applied to the power grid or reduce the separation between the conductor cables below a minimum threshold.
5. The system of any preceding claim, wherein the connection mast is configured to flex under an applied load.
6. The system according to claim 5, wherein the flex at the uppermost point of the connection mast is limited to 200mm.
7. The system according to claim 5 or claim 6, wherein the flex of the connection mast is determined by the length of the cross lead conductor cables between the connection mast and the connection point to the electrical transmission cables.
8 The system according to any preceding claim, wherein the connection mast is pivotally connected to a foundation.
9. The system according to claim 8, wherein a lifting apparatus is provided between the ground anchor and the connection mast to raise and lower the connection mast.
10. The system according to any preceding claim, wherein the connection mast comprises a plurality of tapered sections.
11. The system according to claim 10, wherein the sections are formed from folded sheet metal.
12. The system according to claim 11, wherein the sections are nested end-to-end to form the connection mast.
13. The system according to any preceding claim, wherein the conductor cables are connected to the connection mast via a plurality of insulators secured to an outer surface of the connection mast.
14. The system according to claim 13, wherein the insulators are made from a polymeric material.
15. The system according to claim 13 or 14, wherein the plurality of insulators are arranged into a plurality of columns with each column angled relative to the others.
16. The system according to claim 15, wherein a conductor cable is connected to each column of insulators.
17. The system according to any of claims 13 to 16, wherein the columns of insulators can be rotated around the connection mast to provide better connection locations.
18. The system according to any preceding claim, wherein the connection mast is located between 5m and 15m from the connection point.
19. The system according to any preceding claim, wherein the connection point is an electrical transmission tower.
20. The system according to claim 19, wherein the connection of the conductor cables on the transmission tower is via a tap-in connection.
21. The system according to claim 19, wherein the connection of the conductor cables on the transmission tower is via a loop-in/loop-out connection.
22. The system according to any preceding claim, wherein the low tension connection is in the form of a compressed tee-connector.
23. The system according to any preceding claim, wherein the electrical load is an electrical generator, optionally a gas turbine, and/or the electrical supply is renewable energy source, optionally a solar panel farm.
24. The system according to any preceding claim, wherein the connection point is a suspension electrical tower.
25. The system according to any of claims 1 to 23, wherein the connection point is a tension electrical tower.
26. A method of connecting an electrical load and/or an electrical supply to a power grid comprising a plurality of overhead transmission cables, the method comprising the steps of: a. selecting a desired location to connect to the power grid; b. selecting a first connection mast comprising a plurality of conductor cables configured to connect the connection mast to a pre-determined point on the electrical transmission cables; c. selecting a suitable location for the connection mast; d. calculating the required conductor cable length; e. turning the existing power grid offline; f terminating each of the overhead transmission cables by inserting at least one in-line insulator; and connecting the plurality of conductor cables of the first connection mast to each of the plurality of overhead transmission cables at a first side of the in-line insulators, wherein the conductor cables are configured to provide a low tension connection to the power grid.
27. A method according to claim 26, further comprising a second connection mast comprising a plurality of conductor cables and the method comprises the step following step g) of: h) connecting the plurality conductor cables of the second connection mast to each of the plurality of overhead transmission cables at a second side of the in-line insulators, wherein the conductor cables are configured to provide a low tension connection to the power grid.
28. A method according to claim 26 or 27, wherein the connection mast comprises a plurality of tapered sections and the method further comprises the step prior to step e) of i) assembling the connection mast.
29. A method according to any of claims 26 to 28, wherein the connection mast can flex and the method further comprises a step following step d) of: j) calculating a desired amount of connection mast flex.
30. The method of any of claims 26 to 29, wherein the plurality of conductor cables are configured to be greater in length than the separation between the connection mast and the connection point to provide a sag in said cables when the connection is made.
31. The method of claim 30, wherein the required sag is calculated in combination with the connection mast location to ensure that swinging of the transmission cables within their full range of permitted movement under an imposed load will not cause additional load to be applied to the power grid or reduce the phase-tophase separation below a minimum threshold.