GB2526580A

GB2526580A - A cable plough for encapsulating a ploughed cable during installation with a thermal medium

Info

Publication number: GB2526580A
Application number: GB1409477.5A
Authority: GB
Inventors: Nathan Flinton
Original assignee: NATHAN FLINTON POWER SOLUTIONS Ltd
Current assignee: NATHAN FLINTON POWER SOLUTIONS Ltd
Priority date: 2014-05-28
Filing date: 2014-05-28
Publication date: 2015-12-02
Anticipated expiration: 2034-05-28
Also published as: GB2526580B; GB201409477D0

Abstract

A cable plough, arranged to encapsulate a cable 110 in a primary thermal medium 190, comprises: a plough share (130, figure 3) to cut a trench, a primary thermal medium chute (140) through which the primary thermal medium passes into the trench and a cable chute 150 to guide the cable into the trench so that it is encapsulated with the primary thermal medium. Also disclosed is a method of encapsulating a cable in a primary thermal medium whilst laying the cable in a trench by; feeding the cable through a cable chute into the trench, and urging the primary thermal medium into the trench so as to embed the cable in the primary thermal medium. Preferably an auxiliary chute 160 is included which may feed out an auxiliary medium. The auxiliary medium may be loose geological matter with a particular thermal conductivity, or it may be water to moisten the primary thermal medium, or it may be a fiber optic cable. The cable plough is preferably for use with a high voltage cable and may use a pump mechanism or an Archimedes screw to urge the primary thermal medium through the chute.

Description

A Cable Plough for Encapsulating a Ploughed Cable During Installation with a Thermal Medium

Field of the Invention

This invention relates generally to the ploughing of cables and pipes in the ground.

S More specifically it relates to extra high voltage cables (typically ranging from 132kV- 520Kv) and ancillary cable pipes, pilot cables, and telecommunications cables for which poor heat dissipation to the native earth in operation can lead to lower electrical efficiency and degradation of wire and insulation leading to premature failure of the flexible cables and pipes.

Background

The thermal conductivity of soil and the ground varies with the geology and moisture content. Thus sandy ground has different thermal conductivity from clay or earthy types, and the ground after a rainstorm has a different conductivity than the same ground subject to drought. Voids or air pockets in the ground also conduct heat much more poorly than consistently packed ground.

To ensure that the cable delivers the correct rating with a high level of confidence and reliability, a known thermal medium is required immediately around the cable to effectively dissipate resistive heat to the surrounding thermal medium that is due to the ground. For lower voltage cables this can be as simple as fine particles of sand.

However, for the high voltages (llkV-66kV) and extra high voltages EHV (132kV, 275kV and 400kV) this first surrounding layer is essential to avoid the cables overheating (thus reducing their current carrying capacity). Failure to properly allow for the correct thermal medium can create hot spots that may lead to future cable failure or significant unreliability.

For electric cables that operate at low voltages and transmit low power, the varied thermal conductivity of ground surrounding the electric cable does not cause overheating. Hence low voltage cables usually only require surrounding sand for protection purposes.

Overhead cables or power lines of the same capacity dissipate their heat to the air around the conductors, removing the need for insulation. Hence despite the drawbacks of overhead lines such as view blight, safety hazards and being prone to cable breakage by high winds and snow, higher voltage lines are preferably installed as overhead lines.

PriorArt Traditionally low voltage cables are laid in a trench which is dug by a numerous excavators and earthmoving equipment or by hand with shovels. The traditional trench has earthen walls that are shored up by a casing. The casing is typically formed from concrete or wood.

In the prior art a cable is laid into either an open trench or pulled through a polymeric duct or conduit. Earth may be backfilled into the trench casing to bury the duct in the ground.

An electric cable is threaded into each duct or conduit. The duct can encase a single or bundle of cables depending on the voltage and mutual heating effects on other conduits. An electric cable is threaded into each conduit. Electric cables transmitting high voltages, such as 132kV or more, are subject to poor heat dissipation particularly in ducts and are therefore predominantly installed directly into the ground.

The heat generated is conducted away from the electrical cable by the surrounding earth.

At the lower voltages, the cables inside the ducts dissipate the heat to the air within the duct and then slowly dissipating the heat to the surrounding back fill earth. As the cables are normally not used to their full capacity this is generally sufficient for any network operator.

At the higher cable voltages, heat dissipation becomes more of a challenge due to the amount of heat generated. There is a requirement for a thermal medium that immediately encapsulates the cable to be of a certain type and density to effectively dissipate the heat away from the cable in a calculable way to maintain the current carrying capacity.

A thermal medium is made from a special mixture of materials that give the medium a known thermal conductivity and/or heat capacity and/or particle density to draw heat away from the cable. The electrical cables are prevented from overheating because the heat is effectively conducted away by the medium.

The traditional method of laying cable in the ground is expensive and slow because an open trench must first be dug. The trench is required to have shored-up walls. A protective layer or thermal medium is required to be installed. The cable is then laid and covered with the thermal medium. Finally the trench has to be backfilled with earth to bury the whole assembly. The whole process is a very environmentally invasive, time consuming and costly with wayleave swaths for installation typically 65m across.

The unit cost of overhead lines to a cable installation is ten times cheaper than laying cabling underground by the traditional method for a voltage to voltage comparison.

In order for cabling to be competitive the cable must be installed in a quick, cost efficient and environmentally sustainable manner.

There is an immediate need for a cable installation method and machine to lay buried high voltage cable in the heat dissipating thermal medium that delivers the required capacity and will not overheat in use.

Sum mary of the Invention According to one aspect of the present invention there is cable plough arranged to encapsulate a buried cable during installation in situ in a primary thermal medium which comprises: a plough share to cut a trench, a primary thermal medium chute through which primary thermal medium passes into the trench and a cable chute to guide the cable into the trench so that it is encapsulated with primary thermal medium.

The cable chute has an exit opening below ground behind the plough share and an entrance opening above ground. A cable is fed into the entrance opening and is guided by the chute to slither out of the exit opening and into the trench cut by the plough share. Laying burying cable is quick and easy with a cable plough towed behind a tractor or a tracked winch. As the tractor or tracked winch moves forward, cable is spooled off a cable drum and fed through a cable chute. Where the cable exits the cable chute a layer of primary thermal medium is urged out of the primary thermal medium chute. The cable is theleby encapsulated by the primary thermal medium as it is laid in the trench. The thermal properties of the medium, such as its conductivity, specific heat capacity and heat dissipating properties are formulated to draw heat from the encapsulated cable by conduction. The walls of the trench collapse inwards as soon as the plough share passes through the ground, thus self backfilling the trench and burying the encapsulated cable.

Preferably the cable chute has an exit opening into the primary thermal medium chute. When the cable plough is operated the cable slithers out of the cable chute exit opening and into the primary thermal medium chute. The primary thermal medium chute contains primary thermal medium and so the cable is embedded in the primary thermal medium which aids encapsulating the cable with primary thermal medium as it is laid the trench.

Preferably the cable chute has an exit opening above an exit opening for the primary thermal medium chute. When the cable plough is operated the primary thermal medium tends to form a layer in the bottom section of the primary thermal medium chute exit opening. The cable is then laid onto the primary thermal medium layer as the cable slithers out of the cable chute. The primary thermal medium layer is a protective layer that that spills into the bottom of the trench to cover sharp rocks. The electrical insulation of the cable is thereby protected by the layer of primary thermal medium from cuts by the rocks.

Preferably the primary thermal medium chute has an exit opening into the trench that is located behind the plough share. In operation, primary thermal medium spills out into the trench opened by the plough share.

Preferably the cable chute is at least partly housed inside the primary thermal medium chute so as to define a passageway for the primary thermal medium between the primary thermal medium chute and the cable chute. The narrow trench cut by the plough share is wide enough for primary thermal medium chute. The cable chute being inside the primary thermal medium chute is protected from the friction drag and sharp rocks of the trench wall by the primary thermal medium chute.

The primary thermal medium chute provides a structure to support and hold the cable chute by a cable chute support connecting the primary thermal medium chute to the cable chute.

Preferably the cable chute has an exit opening that slants upwards and forwards from its trailing edge. Preferably the primary thermal medium chute also has an opening that slants upwards and forwards from the trailing edge. Upwards means towards the ground surface in use. Forwards means towards the leading edge of the plough share. The trailing edge of the primary thermal medium chute is preferably the bottom and trailing edge of the primary thermal medium chute. The primary thermal medium chute thereby protects the cable and the cable chute from sharp objects such as rocks on the bottom of the trench.

Preferably the cable chute has a cable entrance comprising a gland that surrounds the cable where it enters the cable chute so as to restrict primary thermal medium from exiting the cable chute between the cable and the cable entrance. Optionally primary thermal medium may be pumped at high pressure into the trench through the primary thermal medium chute without backing up out of the cable entrance opening.

Preferably an auxiliary chute is connected to a peripheral part of the primary thermal medium chute. The auxiliary medium chute provides a passageway from an auxiliary medium to be urged into the trench. Depending on the position and shape of the auxiliary chute exit opening, with respect to the cable chute exit opening, the cable may be encapsulated or partially encapsulated by the auxiliary medium as the cable slithers out of the cable exit opening and is laid in the trench.

Depending on the position and shape of the auxiliary chute exit opening with respect to the primary thermal medium chute exit opening the primary thermal medium may be mixed with the auxiliary medium at the primary thermal medium chute exit opening or the auxiliary chute exit opening. Depending on the position and shape of the auxiliary chute exit opening with respect the primary thermal medium exit opening the primary thermal medium may encapsulate the auxiliary medium, the auxiliary medium may encapsulate the primary thermal medium or the primary thermal medium may be interspaced with leaves or ribs that hold the primary thermal medium and/or the cable intact and/or in position.

Preferably the auxiliary chute has an exit opening directed to mix auxiliary medium with primary thermal medium urged from an opening of the primary thermal medium chute. The primary thermal medium and auxiliary medium may thus be mixed in situ as the cable is laid in the trench. Before mixing, the primary thermal medium and auxiliary medium may be stored indefinitely. After mixing the mixture may set forming a protective layer with stable thermal properties around the cable.

Preferably the plough comprises an auxiliary medium chute arranged to guide a hollow flexible tube into the trench. Preferably the auxiliary medium chute is arranged to guide the tube into the trench where the tube is in thermal conduct with the electric cable guided into the trench through the cable chute. Heat generated by electricity in the cable conducts to the tube. This heat warms a fluid flowing through the tube. The warmed fluid is usable for warming homes, industrial facilities, and machinery. The warmed fluid also provides energy to do useful work. The warmed fluid can be routed to the surface through the pipe or through a tributary pipe where the warmed fluid can be routed through a heat exchanger, such as an air cooled radiator which cools the fluid before it is routed back underground to cool the cable.

Preferably the thermal medium chute exit is arranged to deliver the primary thermal medium so as to mutually embed the pipe and the electric cable in the thermal medium in trench. As the thermal medium is a good heat conductor with preselected thermal properties, the electric cable can be designed to carry a preselected current and be assured of operating without overheating. Before the electric cable is laid in the trench, it is possible to make a reliable calculation predicting the heat that conducted through the primary thermal medium and carried away by the fluid flowing in the pipe.

Preferably the cable plough comprises a pumping mechanism to urge the primary thermal medium through the primary thermal medium chute and/or the auxiliary medium through the auxiliary medium chute. Thereby the medium(s) may be forced into the trench under pressure. This assists with provision of a uniform flow rate and compaction of the primary thermal medium in which the cable is embedded. This assists to maintain uniform properties and prevents voids forming in the medium in which the cable is embedded. The reliability and efficiency of the cable as an electricity transmission means is thereby improved.

Preferably the pumping mechanism includes an Archimedes screw. An Archimedes screw is a simple device that capable of moving a variety of free flowing solid materials whether granulated, powdered, slurry or liquid.

Preferably the cable plough comprises a hydraulic connector to connect the pumping mechanism to a pressurized hydraulic fluid connection. Vehicles suitable for pulling a cable plough such as a tractor are typically equipped with a hydraulic pump.

The cable plough may use hydraulic fluid provided under pressure from the hydraulic pump on the vehicle through the hydraulic connector to operate the pumping mechanism.

Preferably the cable plough comprises an electrical connector to connect the pumping mechanism to an electrical current source. Vehicles suitable for pulling a cable plough such as a tractor are typically equipped with and electric generator.

The cable plough may use electricity provided by the generator on the vehicle through the electrical connector to operate the pumping mechanism.

According to a second aspect of the invention there is a method of encapsulating a cable in a primary thermal medium whilst laying the cable in a trench that includes the steps of: feeding the cable through a cable chute having an exit into the trench and urging the primary thermal medium, through a primary thermal medium chute having an exit, in the trench so as to embed the cable in the primary thermal medium in the trench.

The primary thermal medium may be a geological material or a polymeric material which is preferably specifically formulated to have thermal properties such as thermal conductivity and specific heat capacity which draw heat away from the cable by thermal conduction so as to prevent overheating of the cable in use. According to the method the cable is embedded in the cable in situ as the cable is laid in the trench. Thus the cable is protected from sharp objects in the trench as it is laid. The cable is encapsulated and laid quickly and efficiently by the simple operation of towing the cable plough with a tractor or winch.

Preferably there is a method of laying cable with a cable plough comprising the steps of using a plough share as described herein that comprises a plough share, cable chute, and primary thermal medium chute; cutting a trench with the plough share; feeding the cable through the cable chute into the trench; and urging the primary thermal medium through the primary thermal medium chute into the trench so as to embed the cable in the primary thermal medium in the trench.

The cable is thereby quickly and efficiently encapsulated in a primary thermal medium having properties specifically formulated to draw heat from the cable in operation and protect the cable in the trench.

Preferably the primary thermal medium is introduced into the trench through the primary thermal medium chute and the cable is inserted into the primary thermal medium, in the trench as the cable is fed out of the cable chute. Thus all that is required is to provide primary thermal medium and cable and a device to tow the cable plough through the ground and the cable is efficiently laid in the trench and encapsulated with the primary thermal medium.

Preferably there is a vehicle is adapted to connect to and tow the cable plough having a cable chute, primary thermal medium chute, and plough share as described herein. The vehicle has or is arranged to carry or tow a hopper to contain primary thermal medium. Preferably the hopper has a pump. Preferably the hopper is in fluid communication with the pump which is adapted to pump the primary thermal medium into a trench formed by the plough.

The success of the cable plough lies in the overall efficiency of installation in terms of speed and the significant reduction of plant and machinery on site and the associated level of manpower compared to conventional methods (Large open excavations with 6m wide haul roads) and construction swathes in excess of 65m wide.

Advantageously the cable plough lays cable quickly without the need of separately digging a trench and back filling it after the cable is laid, and the cable plough encapsulates the cable with primary thermal medium and has repeatable quality to Energy Network Association (ENA) and British Standards (BS) requirements.

The cable plough is capable of laying and burying extra high voltage (EHV) cables for reliable operation at 132kV to 520kV.

Preferably the cable plough comprises a cable drum or is arranged for use with a cable drum that is supported on tracks and is hydraulically driven from behind the cable plough or in front of the cable plough. The cable and drum are transported along with the cable plough in a one movement as a train. This train may be supported by an additional vehicle comprising a pump and a mixer to deliver a primary thermal medium and an auxiliary medium to the primary thermal medium chute and an auxiliary chute respectively.

The cable plough facilitates installation of thermally stable medium on EHV cables using the cable plough and encapsulating the thermal back fill medium around the cable as the cable is laid in trench.

Preferably the cable plough comprises a vertical hopper to contain primary thermal medium and/or an auxiliary medium to be fed into a primary thermal medium chute and/or an auxiliary chute.

Preferably the hopper is arranged on the top of the chute. Preferably the cable comprises a means to vibrate the chute(s) for gravity feed of the primary thermal medium and/or auxiliary medium through the chute(s) into the trench. Preferably hopper has a vibrating hopper base.

Preferably the cable plough comprises a tracked conveyor or is arranged for use with a tracked conveyor from an additional vehicle to feed primary thermal medium or auxiliary medium into the hopper.

Preferably the primary thermal medium chute and/or an auxiliary chute and/or a hopper comprise a pumping mechanism such as a spiral Archimedes screw arranged within a top section of the chute.

Preferably the pumping mechanism driven is so as to force primary thermal medium or auxiliary medium at a known pressure down the chute and around the cable creating.

Preferably the cable plough comprises a moisture sensor arranged to detect the moisture in the earth in the wall of the trench at the depth that the cable is laid so as to mix the primary thermal medium and auxiliary medium for the appropriate thermal properties to prevent the cable from overheating in operation.

The primary thermal medium and/or auxiliary medium around the cable enables the buried cable to dissipate the heat generated more effectively, presenting the cable plough technology as a cost effective and environmentally preferred option to bury cable as opposed to suspending cables over ground for transmission network owners.

The shape and location of the primary thermal medium chute exit opening, auxiliary medium exit opening, pressurized supply of the primary thermal medium and auxiliary medium provide for a density and compaction of the thermal medium that gives the heat dissipating qualities required by cable manufacturers and thus delivers the required cable rating.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Brief Description of the Figures

Figure 1 shows an electric cables running in conduit encapsulated in a medium

according to the prior art;

Figure 2 shows an electric cable encapsulated in a medium in a trench formed with a cable plough according to the present invention; Figure 3 shows a vehicle towing a cable plough arranged to encapsulate a cable in a medium in a furrow; Figure 4 is an isometric view of chutes arranged to encapsulate a cable in a medium in a furrow cut by a plough share; Figure 5 is a view looking straight into exit openings of the chutes; Figure 6 is top view of the chutes; Figure 7 shows a cable plough arranged to encapsulate a cable in a medium in a furrow; Figure 8 shows a cable plough with chutes that have an exit opening that slants upward and forward from its trailing edge; S Figure 9 shows a cable plough where the exit opening of the primary thermal medium chute trails the exit opening of the cable chute; Figure 10 shows an example of auxiliary chutes arranged to support the cable chute; Figure 11 shows an example of auxiliary chutes arranged to mix an auxiliary medium and a primary thermal medium; Figure 12 shows an example of an auxiliary chute forming a peripheral ring around the primary thermal medium chute; and Figure 13 shows a Venn diagram of the factors that affect buried cable overheating.

Detailed Description of the Invention

Figure 3 shows a cable plough 100 hitched to the back of a tractor 1000. The cable plough 100 comprises a plough share 130. The plough share 130 operates below the ground surface and cut a trench in the ground as the tractor 100 pulls the cable plough 100.

The cable plough 100 comprises tractor connector 300 to connect the cable plough to a vehicle or a winch cable. In operation the cable plough is either winched over the ground so as to plough the earth below and create a trench that subsequently collapses to envelope the cable. The vehicle or winch may be manually driven or self propelled. The tractor or winch may have a hydraulic drive or electric drive may be connected to devices on the cable plough such as a pumping mechanism.

The cable plough comprises a cable chute 150. The cable chute 150 has an entrance opening 152 which is above the ground surface when the plough share 130 is below the ground surface. The cable chute has an exit opening 154 which is below the ground surface when the plough share 130 is below the ground surface.

The exit opening 154 faces backwards from the plow share. In use a cable 110 is fed into the cable chute through the cable opening 152. The cable chute 150 guides the cable 110 through to the exit opening 154. In use the cable 110 slithers out the exit opening 154 and thence into the trench cut by the plough share 130.

The cable chute comprises internal rolleis and heavy walls to guide large cables associated with 132KV to 520KV through the chute.

The cable plough 100 also comprises a primary thermal medium chute 140. The primary thermal medium chute 140 has an entrance opening 142 to receive a free flowing solid substance into the primary thermal medium chute. The primary thermal medium chute 140 has an exit opening 144 which is below the ground surface when the plough share is below the ground surface.

The free flowing solid substance is a specially formulated geological material to have specified thermal conductivity. Suitable free flowing solid substances are cement bound sand, grout, or another material. Suitable free flowing solid substances are dry materials or wet materials, and slurries, and may dry to harden into a friable material. The primary thermal medium is a free flowing solid substance.

For underground cabling, the ability to deliver large current carrying capacity is based on a number of mutual relationships for dissipating the heat and the electrical influences that cables in close proximity share upon each other. A Venn diagram such as Figure 13 shows the relationship between cable spacing 410, native thermal environment 430, cable size and length 420, native thermal environment 430, volume of cement bound sand 440, sheath voltage 460 and cable rating 470.

The free flowing solid substance, such as cement bound sand, is poured or forced into the primary thermal medium chute entrance opening 142. Then the free flowing solid substance is guided by the primary thermal medium chute 140 and flows out of the exit opening 144.

The exit opening 144 of the primary thermal medium chute is arranged to direct the free flowing solid substance into the path of the cable 110.

Figure 7 shows an example of the cable chute 100 having an exit opening 254 of the cable chute 150 and an exit opening 144 of the primary thermal medium chute 140 in approximately the same plane and approximately the same distance behind the plough share 130. The free flowing solid substance flows out the primary thermal medium chute exit opening 144 where the cable 110 slithers out of the cable chute opening 154. The effect is that the cable 110 is embedded in the free flowing solid substance just as the cable 110 exits the cable chute 110 where it is laid the trench.

The trench wall then collapses around the free flowing solid substance.

Compaction of the free flowing solid substance around the cable 110 contributes to predictable and reliable thermal properties of the substance around the cable 110.

Pumping the free flowing material into the trench at a controlled flow rate or at a controlled pressure compacts a medium layer around the cable prevents unevenness in the layer around the cable 110 and thereby reduces the void content in the layer.

The layer around cable 110 contributes to reliable operation of the cable in high power and high power transmission use.

Figures 8 and 9 show examples of the cable plough where the primary thermal medium chute 140 surrounds the cable chute 150. The plough share 130 is at the front of the cable plough and the cable and primary thermal medium chute exits trail behind the plough share.

In Figure 8 the cable chute exit opening 154 and the primary thermal medium chute exit opening 144 are in the same plane. The plane is slanted so that the lower edge of the primary thermal medium chute trails behind the upper edge. The effect of this slant is for the free flowing solid medium to exit the bottom of the primary thermal medium chute 144 behind where the cable 110 exits the cable chute 154. So as the cable 110 exits the cable chute the cable is laid onto free flowing solid medium. This prevents sharp rocks which may be in the trench from touching and cutting through the cable electrical insulation, since the free flowing solid medium flows off the bottom trailing edge of the primary thermal medium chute and covers the rocks on the bottom of the trench. Then the cable is laid on top of the free flowing solid medium which is a finely granulated geological material. Another effect of the slant is for the free flowing solid medium to exit the top of the primary thermal medium chute 144 and spill onto the top of the cable 110 that has already been laid onto free flowing solid medium. So the free flowing solid medium covers the whole cable.

Thus the cable 110 is fully encapsulated by the free flowing solid medium.

Figures 8 and 9 show examples of the primary thermal medium and cable chute exit openings 144, 163, where the primary thermal medium chute 140 surrounds the S cable chute 150. The cable chute exit opening 154 is closer to the leading edge of the plough share 130 than the exit opening 144 of the primary thermal medium chute 140. The free flowing solid substance is flowing inside the primary thermal medium chute 140 where the cable 110 slithers out of the exit opening 154 of the cable chute 150. The effect is that the free flowing solid substance is compacted around the cable 110 inside the primary thermal medium chute 140. The free flowing solid substance is thereby formed around the cable 110. For free flowing solid substances that are sticky, the sheath remains intact as the cable encapsulated in the sheath exits the primary thermal medium chute 140 and is laid in the trench. A sheath of the substance with reliable and predictable thermal properties is thereby formed around the cable 110 contributing to reliable high voltage and high power operation of the electric cable.

As Figure 4 shows the primary thermal medium chute 140 is in fluid communication with a primary thermal medium hopper 180 to contain a supply of the free flowing solid medium. A pumping mechanism urges the free flowing solid medium to flow from the primary thermal medium hopper 180 and into the primary thermal medium chute 140 and thence out through the primary thermal medium chute exit opening 144. As shown in Figure 4 the primary thermal medium hopper 180 and/or the primary thermal medium chute 140 comprises an Archimedes screw 240. The Archimedes screw serves as the pumping mechanism. The pumping mechanism uses an existing hydraulic drive on the plough vehicle to power the pumps. The volumes of primary thermal medium and/or auxiliary medium may require a hopper arrangement with a conveyor belt feeding the hopper(s). The hopper may comprise an integral Archimedes screw 240 to force the primary thermal medium and/or auxiliary medium into the primary thermal medium chute 140 and auxiliary chute 160 respectively.

The auxiliary medium is a free flowing solid substance specially designed to have specified thermal conductivity and or specific heat capacity and may be cement bound sand, grout, a dry material, wet materials, or slurry, and may dry to harden into a friable material. The auxiliary medium may also be a liquid which may change the properties of the primary material when the two are mixed.

By forcing the free flowing solid medium out of the primary thermal medium chute exit opening 144 under the controlled pressure of the pumping mechanism a consistent volumetric flow rate is assured. This in turn assures that the cable 110 is embedded in a consistent thickness of the medium so that the reliability of the cable 110 is also assured. A consistent thickness of medium around the cable makes for a layer with consistent thermal properties around the cable.

The primary thermal medium is pumped and mechanically delivered to ensure a free flowing solid material is spread evenly around the cable to a minimum thickness of 75mm with repeatable quality and compaction as per the aforementioned ENA specifications. The layer of primary thermal medium 190 encapsulating the cable 110 is shown in Figure 2. Earth 194 from the collapsed walls of the trench surrounds the primary thermal medium.

As shown in Figures 4, 7, 8, 9, and 10 the cable plough 100 integrates the cable chute 150 and the primary thermal medium chute 140 together.

As shown in Figures 5, 7, 8, and 10 auxiliary chutes 160 are arranged in conjunction with the primary thermal medium chute. The auxiliary chutes have an exit opening 164 proximate to the cable chute exit opening 154 and the primary thermal medium chute exit opening 144. Thus the auxiliary chute exit opening 164 is under the ground surface in use. The auxiliary chutes also have an entrance opening 166 above ground.

The auxiliary chutes 160 are arranged to feed an auxiliary medium 250 to the region where the cable 110 is laid in the trench. The auxiliary medium can be pumped through suitable tubing from a remote pump station as required.

The auxiliary medium 250 may be a loose geological material with particular thermal properties such as thermal conductivity or specific heat capacity to enhance the thermal properties of the material in which the cable 110 is embedded. The auxiliary medium may be water to moisten the primary thermal medium so as to make it stick together and remain intact surrounding the cable before and when the trench walls collapse after the cable is laid. The auxiliary medium may be fiber optic cable paid out through the auxiliary chute 160 exit opening 164 at the same rate as an electric cable 110 is paid out through the cable chute. Thus the cable plough can simultaneously lay electric and fiber optic cable simultaneously in one trench.

The auxiliary chute entrance opening 166 may be connected to an auxiliary medium hopper that contains auxiliary loose geological material, water, or another material.

The auxiliary chute entrance opening 166 may be arranged to receive a fiber optic cable.

The primary thermal medium chute exit opening 144 is arranged to surround the cable exit opening 154 so that the primary thermal medium 190 surrounds and encapsulates the cable 110.

The auxiliary chute exit openings 164 are arranged at the periphery to the primary thermal medium chute 140. The auxiliary medium that flows out of the auxiliary chute exit openingsl64 covers the periphery of the primary thermal medium that exits the primary thermal medium chute. The effect is that the cable 110 is encapsulated by both the primary thermal medium and the auxiliary medium.

The auxiliary chute exit openings 164 may be circular or curved tube openings as shown in Figure 5 and Figure 7. The auxiliary chute exit opening 164 may have a ring cross section. This enhances the even thickness of the peripheral layer or sheath of auxiliary medium 250 around the primary thermal medium.

The auxiliary chute exit opening 164 may be located near the middle of the cross section the primary thermal medium chute opening 144, or the auxiliary chute exit opening 164 may be a plurality of auxiliary chute exit openings evenly interspersed across the primary thermal medium chute exit opening. This has the effect of mixing the primary thermal medium 190 and the auxiliary medium 250 where they exit the chutes. Where the auxiliary medium is water or another liquid that causes the primary thermal medium to stick together or set then the setting and sticking process does not start until the primary thermal medium and auxiliary material exit into the trench. The primary thermal medium and auxiliary medium are separately storable indefinitely. Primary thermal medium and auxiliary medium maybe stored in their respective hoppers.

An auxiliary pumping means may be used to urge the auxiliary medium through the auxiliary conduit 160.

Both the auxiliary medium and/or the primary thermal medium may be forced out of their chute exits at a higher pressure than the ambient air pressure at the ground surface. This may have the effect of backfilling the cable conduit 150 through the cable conduit exit opening 154. To prevent either the auxiliary medium or the primary thermal medium or both from being extruded out of the cable entrance opening 152, a gland is fixed in the cable entrance opening which forms as seal with the cable 110 and allows the cable 110 to be fed into the cable chute 150.

Both the auxiliary medium and/or the primary thermal medium can either be carried during the installation or delivered by accompanying tracked vehicles.

Figures 5, 7, 8 and 10 the show that near the primary thermal medium chute exit opening 144, the auxiliary chute 160 is housed just inside the wall of the primary thermal medium chute 140. Near the primary thermal medium chute exit opening, the auxiliary chute 160 follows the primary thermal medium chute 140. The entrance opening 162 of the auxiliary chute is adapted to receive a supply of an auxiliary medium. It may be adapted to receive the supply from a hose or a hopper that contains and provides auxiliary medium. The entrance opening of the auxiliary chute 162 is located above ground surface when the plough share 130 is located below the ground surface in use. The auxiliary chute entrance opening 162 is thereby easily connectable to a supply of auxiliary medium when the cable plough 100 is in use.

Figure 5 shows a cable chute support 156 which holds the cable chute 150 in position inside the primary thermal medium chute 140. The cable chute support 156 is connected to the primary thermal medium chute 140 and the cable chute 150. The location of the cable chute exit opening 154 with respect to the primary thermal medium chute 140 is fixed by the cable chute support 156.

Figure 5 shows the cable chute support 156 is a horizontal bar or plate located midway between the sides of the primary thermal medium chute 140 and the cable chute 150. The least dimension of the cable chute support 156, such as the thickness of the bar or plate, is arrange to be the least obstruction to free flowing solid medium passing through the primary thermal medium chute.

Figure 10 shows an arrangement of the auxiliary chute 160 that also serves as a cable chute support 156. The exit opening 162 of the auxiliary chute spans between the primary thermal medium chute 140 and the cable chute 150. This has the effect that the auxiliary medium that flows through the exit opening extends like a rib from the cable 110 and can provide structural support for both the cable and the primary thermal medium that is between the ribs.

Figure 11 shows an arrangement of the auxiliary chute 160 that also serves as a cable chute support 156. The auxiliary chute 160 has a spiral cross section in the primary thermal medium chute exit opening 144. This has the effect of enhancing mixing of primary thermal medium 190 and the auxiliary medium 250 as the primary thermal medium flows out of the primary thermal medium chute exit opening 144 and the auxiliary medium flows out of the auxiliary chute exit opening 164.

Figure 12 shows an arrangement of the auxiliary chute 160 that does not serve as a cable chute support because the auxiliary chute exit opening is formed by a peripheral rim of the auxiliary support around the primary thermal medium chute exit opening 144. The effect is that the cable 110 is encapsulated by two layers. The innermost layer is a layer of primary thermal medium 190 and the outermost layer being a layer of auxiliary medium 250. The primary thermal medium may be designed to provide a relatively soft loose granular or clay type material that provides a layer with high thermal conductivity and/or specific capacity to draw away heat from the cable 110 and prevent the cable overheating and the sheath of auxiliary medium may be a cement that hardens or a polymeric material that sets to hold the primary thermal medium as an encapsulating jacket around the cable and/or provide a physical protection layer or barrier against flooding, earth tremors, and other environmental phenomena.

In another example the relative positions of the auxiliary chute 160 and the primary thermal medium chute 140 shown in Figure 12 are reversed.

On average the EHV cables suited for delivery by this cable plough have an approximate weight of 40kg per meter and an approximate overall diameter of 175mm. The bending radius will vary. As a guide, the centre cable chute 150 needs to be 50% larger than the cable 110 including the internal friction material such as rollers or nylon slides located between the cable chute 150 and cable 110 to allow the cable 110 to slither easily through cable chute 150.

Figure 14 shows an embodiment comprising a primary thermal medium chute 140 for delivering, for example, cement bound sand delivery from a hopper 180 to the entrance opening start of the primary thermal medium chute. Hydraulically powered Archimedes screws 240 arranged twin central hopper feed tubes 170 deliver the cement bound sand to the primary thermal medium chute exit opening 144. The Archimedes screws are powered and driven at the correct speed matched to the overall speed of the cable plough train and the speed at which the cable is being installed at the correct sheath tension. The volume of cement bound sand fed from the primary thermal medium chute is thereby maintained and regulated throughout the installation of the cable to ensure the correct volume and density is achieved with repeatable quality of the primary thermal medium and the correct compaction to dissipate the heat effectively to create the SOC Isotherm evenly around the cable. A centre cable chute 150 has low profile rollers (nylon or quality grease able bearings near the top and bottom of the centre cable chute opening cross section to aid in the smooth delivery of the cable as it passes down and through the curves of the chute.

The low profile rollers also reduce friction on the cable sheath and support the cable bending radius limitations for any potential damage. The end of the primary thermal medium chute 140 nearest the primary thermal medium chute exit opening 144 is tapered with the bottom edge leading the highest edge at 45 deg. This allows the flow of cement bound sand to start into the trench prior to the cable 110 leaving the cable chute exit opening 154. This design also allows the primary thermal medium to be quality tested! assured by the cable manufacturer! cable installer before loading the primary thermal medium into the hopper or while it is the hopper, and hence before the primary thermal medium is poured into the trench.

Figure 15 shows a modified embodiment of the cable plough illustrated in Figure 14.

The Figure 15 embodiment retains the functionality of the Figure 14 embodiment including the internal rollers in the cable chute. The exit opening 144 of the primary medium chute is fluted above and below the cable chute exit opening 154. This allows a primary thermal medium to be delivered to the sides of the cable encapsulating the cable with a greater density of primary thermal medium.

Figure 16 shows another example of the cable plough chutes which design retains the functionality of the cable ploughs illustrated in Figures 14 and 15. The example shown in Figure 16 adds four auxiliary chutes 160 with exit openings 164 (ports) proximate to the cable chute exit opening 154. The auxiliary chutes are ideally situated for delivering an auxiliary medium to backfill around the cable as the cable is laid in the trench thereby improving the encapsulation of the cable and/or the thermal properties of the medium in which the cable is encapsulated. The auxiliary medium aids in the event that the primary thermal medium may not provide the correct density. The auxiliary medium aids coverage around the cable due to difficult native earth or due to a very high moisture content in the native earth. The four auxiliary chute exit openings 164 (ports) can deliver the auxiliary thermal medium as a thermal grout to fully seal and encapsulate the cable within the envelope created by the cable plough and amalgamate the primary thermal medium and auxiliary medium for a unique and innovative thermal jacket.

Figure 17 illustrates another example of the cable plough chutes which retains the prior functionality of the previous examples in Figures 14 to 16. The example in Figure 17 incorporates ducts 165 located in each corner of the primary thermal medium chute 140. Fiber optic cable with sensing equipment is delivered through the ducts 165 and through the duct exit opening 169 and thence into the trench.

Unlike subsea cable with fiber optic running within the centre of the cable, transmission asset owners require the ability to monitor the performance of the electric cable for example, cable temperature and current carrying capacity and any electrical discharge build up to relating to potential cable weaknesses and faults.

The ability to run fiber optic cable also allows the use of cable protection and tele-control equipment from substation to substation in the form of pilot cables. The location of the fiber optic delivery ducts 165 can vary depending on the requirements of the system. For example a fiber optic DTS (Distributed Temperature sensing) cable and sensors are deliverable through the fiber optic delivery duct 165. A DTS cable is thereby laid accurately and consistently alongside the total length of the electric cable delivered through the cable chute exit opening 154. Depending on sensitivity and type of the thermal sensing system, it can be laid directly on top of the cable as the cable leaves the cable chute exit opening 154.

As the cable conducts electricity the cable itself heats up, and dissipates its heat to the immediate area surrounding the cable. The hotter the cable becomes, the lower the current carrying capacity.

Present invention provides for a constant 50 deg isotherm uniformly around the cable in operation by installing a known thermal medium correctly at the correct density, and allows the constant isotherms to be predicted effectively by calculations before the cable is laid.

During peak demands of power on the network the cable manufacturers and Transmission network owners, need to accurately and dynamically understand what the characteristics of the cable area and the overall performance. The introduction of DTS and similar fiber optic systems provide this intelligence asset control.

Figure 18 shows another example of a cable plough chutes. Renewable energy plays a vital part in all businesses today. An auxiliary chute 160 located within the primary thermal medium chute 140 is arranged to deliver a hollow flexible pipe 168 through the auxiliary chute 160. As shown in Figure 18 the auxiliary chute is located in opposing corners of the primary thermal medium chute exit opening. Other locations of the auxiliary medium chute exit opening 164 that place the hollow pipe 168 proximate to the cable exit opening 154. The proximity of the hollow flexible pipe 168 to the electric cable is such that a cooling fluid flowing through the hollow pipe cools the electric cable in operation. These pipes 168 will from part of a larger heat extraction! cable cooling systems. The pipe 168 can be embedded with the cable with only earth dug from the trench surrounding them. The pipe 168 and the electric cable 110 can be mutually embedded in thermal medium delivered through the primary thermal medium chute exit opening 144 with or without and auxiliary thermal medium delivered through an auxiliary thermal medium exit opening 164.

Thus the heat generated by the electric cable can be use used to heat a fluid carried through the pipe for a useful purpose such a warming homes or industrial facilities.

The fluid carried through the pipe also serves to cool the electric cable. The pipe 168 can be installed accurately in parallel to the cable 110 in the trench while the cable is being buried. The inclusion of this cooling system will facilitate the systems on the market and enable transmission The invention has been described by way of examples only. Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the claims.

List of Integers cable plough electric cable fiber optic cable 130 plough share primary medium chute 142 primary medium chute entrance opening 144 primary medium chute exit opening cable chute 152 cable chute entrance opening 154 cable chute exit opening 156 cable chute support auxiliary chutes 162 auxiliary chute entrance opening 164 auxiliary chute exit opening fiber optic cable duct 168 hollow pipe 169 fiber optic cable duct exit opening primary medium feed tube 180 primary medium hopper primary medium 194 earth casing 220 pipe 230 conduit 240 Archimedes screw 250 auxiliary medium 300 tractor connector 410 cable spacing 420 cable size and length 430 native thermal environment 440 volume of cement bound sand 450 cement bound sand 460 sheath voltage 470 cable rating

Claims

Claims: 1. A cable plough arranged to encapsulate a buried cable during installation in situ in a primary thermal medium comprises: a plough share to cut a trench, a primary thermal medium chute arranged to channel a primary thermal medium into the trench and a cable chute arranged to guide the cable into the trench so that it is encapsulated with primary thermal medium.
2. A plough according to claim 1 wherein the cable chute has an exit opening into the primary thermal medium chute.
3. A plough according to claim 1 wherein the cable chute has an exit opening above an exit opening in the primary thermal medium chute.
4. A plough according to any preceding claim wherein the primary thermal medium chute has an exit opening into the trench that is located behind the plough share.
5. A plough according to any preceding claim wherein the cable chute is at least partly housed inside the primary thermal medium chute so as to define a passageway for the primary thermal medium between the primary thermal medium chute and the cable chute.
6. A plough according to any preceding claim wherein the cable chute has an exit that slants upwards and forwards from its trailing edge.
7. A plough according to any preceding claim wherein the cable chute has a cable entrance comprising a gland that surrounds the cable where it enters the cable chute so as to restrict primary thermal medium from exiting the cable chute between the cable and the cable entrance.
8. A plough according to any preceding claim comprising an auxiliary medium chute arranged to channel an auxiliary medium into the trench.
9. A plough according to claim 8 wherein the auxiliary medium chute is connected to a peripheral part of the primary thermal medium chute.
10. A plough according to claim 8 or 9 wherein the auxiliary chute has an exit opening directed to mix the auxiliary medium with the primary thermal medium urged from S an exit opening of the primary thermal medium chute.
11. A plough according to any preceding claim comprising a pumping mechanism to urge the primary thermal medium through the primary thermal medium chute.
12. A plough according to claim 10 wherein the pumping mechanism includes an Archimedes screw.
13. A plough according to claim 10 or 11 comprising a hydraulic connector to connect the pumping mechanism to a pressurized hydraulic fluid connection.
14. A plough according to claim 10 or 11 comprising an electrical connector to connect the pumping mechanism to an electrical current source.
15. A plough according to any preceding claim plough comprising an auxiliary medium chute arranged to guide a hollow flexible tube into the trench.
16. A plough according claim 15 wherein the auxiliary medium chute is arranged to guide the tube into the trench where the tube is in thermal conduct with the electric cable guided into the trench through the cable chute.
17. A plough according to claim 16 wherein thermal medium chute exit is arranged to deliver the primary thermal medium so as to mutually embed the pipe and the electric cable in the thermal medium in trench.
18. A method of encapsulating a cable in a primary thermal medium whilst laying the cable in a trench includes the steps of: feeding the cable through a cable chute having an exit into the trench and urging the primary thermal medium through a primary thermal medium chute having an exit in the trench so as to embed the cable in the primary thermal medium in the trench.
19. A method of laying cable with a cable plough comprising the steps of using a plough share according to any of claims ito 17; cutting a trench with the plough share; feeding the cable through the cable chute into the trench; and urging the primary thermal medium through the primary thermal medium chute into the trench so as to encapsulate the cable in the primary thermal medium in the trench.
20. A method according to claim 18 or 19 wherein primary thermal medium is introduced into the trench through the primary thermal medium chute and the cable is inserted into the primary thermal medium as the cable is fed out of the cable chute.
21. A method according to claims 17, 18, or 19 wherein the cable plough comprises an auxiliary medium chute through which an auxiliary medium is urged into the trench.
22. A method according to claim 21 whereby the primary thermal medium and cable are ere encapsulated in situ at an exit opening of the auxiliary chute within a sheath formed by the auxiliary medium.
23. A method according to claim 21 whereby the cable is encapsulated by a mixture of the primary thermal medium and the auxiliary medium that is mixed in situ at an exit opening of auxiliary chute.
24. A vehicle is adapted to receive the plough according to any of claims 1 to 14 and has a pump and a hopper to contain the primary thermal medium, wherein the hopper is in fluid communication with the primary thermal medium chute and the pump which is adapted to pump the primary thermal medium into a trench formed by the plough.
25. A vehicle according to claim 24 includes a cable drum for carrying cable.
26. A cable plough substantially as herein described with reference to the accompanying drawings.AMENDMENTS TO CLAIMS HAVE BEEN FILED AS FOLLOWSClaims: 1. An arrangement of chutes for a cable plough arranged to encapsulate a trench buried cable during installation in situ in a primary thermal medium comprising: a primary thermal medium chute arranged to channel a primary thermal medium into the trench comprising a pumping mechanism to urge the primary thermal medium through the primary thermal medium chute, and a cable chute arranged to guide the cable into a trench cut by the plough so that it is encapsulated with primary thermal medium.2. An arrangement of chutes for a plough according to claim 1 wherein the cable chute has an exit opening into the primary thermal medium chute.3. An arrangement of chutes for a plough according to claim 1 wherein the cable chute has an exit opening above an exit opening in the primary thermal medium U) chute.4. An arrangement of chutes for a plough according to any preceding claim wherein o the primary thermal medium chute has an exit opening into the trench that is located behind a plough share. r5. An arrangement of chutes for a plough according to any preceding claim wherein the cable chute is at least partly housed inside the primary thermal medium chute so as to define a passageway for the primary thermal medium between the primary thermal medium chute and the cable chute.6. An arrangement of chutes for a plough according to any preceding claim wherein the cable chute has an exit that slants upwards and forwards from its trailing edge.7. An arrangement of chutes for a plough according to any preceding claim wherein the cable chute has a cable entrance comprising a gland that surrounds the cable where it enters the cable chute so as to restrict primary thermal medium from exiting the cable chute between the cable and the cable entrance.8. An arrangement of chutes for a plough according to any preceding claim comprising an auxiliary medium chute arranged to channel an auxiliary medium into the trench.9. An arrangement of chutes for a plough according to claim 8 wherein the auxiliary medium chute is connected to a peripheral part of the primary thermal medium chute.10. An arrangement of chutes for a plough according to claim 8 or 9 wherein the auxiliary chute has an exit opening directed to mix the auxiliary medium with the primary thermal medium urged from an exit opening of the primary thermal medium chute.11. An arrangement of chutes for a plough according to any preceding claim wherein the pumping mechanism includes an Archimedes screw. IC)12. An arrangement of chutes for a plough according to any preceding claim (3 comprising a hydraulic connector to connect the pumping mechanism to a 0 20 pressurized hydraulic fluid connection.13. An arrangement of chutes for a plough according to any preceding claim comprising an electrical connector to connect the pumping mechanism to an electrical current source.14. An arrangement of chutes for a plough according to any preceding claim comprising a guide chute arranged to guide a hollow flexible tube into the trench.15. An arrangement of chutes for a plough according claim 14 wherein the guide chute is arranged to guide the tube into the trench where the tube is in thermal conduct with the electric cable guided into the trench through the cable chute.16. An arrangement of chutes according to claim 15 wherein the primary thermal medium chute exit is arranged to deliver the primary thermal medium so as to mutually embed the tube and the electric cable in the thermal medium in trench.17. A method of laying cable with a cable plough comprising an arrangement of chutes for a cable plough according to any of claims 1 to 16, comprising the steps of: using a plough share; cutting a trench with the plough share; feeding the cable through the cable chute into the trench; and urging the primary thermal medium through the primary thermal medium chute into the trench so as to encapsulate the cable in the primary thermal medium in the trench.18. A method according to claim 17 wherein primary thermal medium is introduced into the trench through the primary thermal medium chute and the cable is inserted into the primary thermal medium as the cable is fed out of the cable chute.19. A method according to claims 17 or 18 wherein the arrangement of chutes for the cable plough comprises an auxiliary medium chute through which an auxiliary medium is urged into the trench. IC)20. A method according to claim 19 whereby the primary thermal medium and cable Care encapsulated in situ at an exit opening of the auxiliary chute within a sheath O formed by the auxiliary medium.21. A method according to claim 20 whereby the cable is encapsulated by a mixture of the primary thermal medium and the auxiliary medium that is mixed in situ at an exit opening of auxiliary chute.22. A vehicle is adapted to receive a plough comprising an arrangement of chutes according to any of claims ito 16 and has a hopper to contain the primary thermal medium, wherein the hopper is in fluid communication with the primary thermal medium chute and the pump which is adapted to pump the primary thermal medium into a trench formed by the plough.23. A vehicle according to claim 22 includes a cable drum for carrying cable.24. A cable plough comprising an arrangement of chutes according to any one of claims ito 16.25. A cable plough substantially as herein described with reference to the accompanying drawings. IC)CD aD r