CA2707975A1 - Duct system for accommodating power cables - Google Patents

Abstract

The invention relates to a duct system for accommodating power cables, having the following features or elements:
having a trench which is provided in the earth; having an accessible duct which is cast or prefabricated in the trench and comprises a material based on concrete; the material of the duct has a thermal conductivity which is at least 3.0 W/(m- k); bodies for accom-modating and/or dissipating thermal energy are arranged outside the duct.

Description

Duct system for accommodating power cables The invention relates to a duct system for accommodating and guiding power cables, in particular high-voltage cables.
Such duct systems are described, for example, in WO 2006/012855 Al, designated therein as an infrastructure duct. Furthermore, DE 201 13 897 U1 describes a duct which is assembled from individual finished segments. DE 44 24 051 Al describes a duct system for accommodating power cables, having a traversable duct, through whose wall a fluid can be conducted for better heat dissipation. Using graphite-containing backfill material for better heat dissipation from power lines laid in the ground is known from DE 199 64 341 B4.

High-voltage systems for transmitting electrical power have been implemented up to this point in the great majority using overhead lines. This is a result in particular of the low investment costs and the mature technology.

The disadvantages of the overhead line are in particular the relatively high power losses, the level of the electromagnetic field even at large distances, and the high running maintenance outlay. The high susceptibility to extraordinary weather influences in particular is disadvantageous for the supply reliability.
Furthermore, the high level of land use is disadvantageous. The consequences resulting therefrom have been assigned up to this point to the so-called external costs in particular, through which ecological effects may be included in particular, such as the agricultural and ecological interference and partition function in biotopes and also the hazard potential for birds.

A further disadvantage is the predefined regulation behavior, an automatic disconnection of the line from the network occurring in the event of a defined load of the line, in particular the overhead line. This shutdown can result in extensive power outages in the extreme case.

2 All of the listed points also have direct economic consequences, because more and more frequently usage fees must be paid for the right-of-way and/or ecological compensation payments are also required. A further burdensome state of affairs, which has not been included up to this point in the comparative calculations, is the planning permission of such line right-of-ways, which has become more and more difficult and cumbersome due to the disappearing acceptance. These are not only the damages from the time delay, which are reflected in particular in the absence of supply possibilities for alternative forms of energy such as wind energy and/or missed chances for power sales, but rather also cause significant costs of legal proceedings, up to the point of corresponding areas becoming unsuitable.

Buried high-voltage cables come into consideration as a frequently discussed alternative. The main disadvantages of buried cables are the higher investment costs, the complex engagements in the ground, and the longer repair time in case of faults.
In the event of overloads of the cable, drying out of the bedding materials is a hazard, which results in poorer heat dissipation in future. This results in an increase of the power losses and more rapid aging and other hazards to the cable insulation up to thermal destruction. Buried cables are also subject to the danger of being cut through during excavation work, for example, by a digger shovel. High-voltage cables are therefore only ascribed half of the life expectancy of an overhead line in the majority of the literature.

All advantages of high-voltage cables, in particular the low power losses, without the above-mentioned disadvantages may be used in the case of laying of the cable in a duct system. The laying of cables in tunnel-shaped infrastructure ducts (ISD) is known; however, because the constructions of the ISD up to this point have been very costly, it was exclusively used in those cases in which other laying possibilities were precluded.

3 A very substantial problem of buried high-voltage cables is the described strong heat development having the disadvantages resulting therefrom.

The invention is based on the object of providing a duct system for accommodating and guiding power cables and reducing or remedying the problems connected with the occurrence of heat.

This object is achieved by the features of Claim 1.

Accordingly, the ISD for accommodating the power cables is produced from a material based on concrete, and this material is selected or equipped in such a manner that it has a thermal conductivity which is significantly greater than the thermal conductivity of typical construction concrete. The thermal conductivity is to be at least 3.0 W/(K*m). Furthermore, bodies for absorbing and/or dissipating thermal energy are situated outside the ISD.

Such an underground ISD fundamentally offers, in addition to the good heat dissipation of the duct to the surrounding earth, the possibility of additional cooling of the high-voltage cables guided therein, i.e., the dissipation of their heat losses with the aid of a flowing medium such as flowing era. This can be implemented, on the one hand, in that vertical air intakes and air outlets to the surroundings are provided at specific intervals: in this case, the opposing air columns in two air outlets will ensure that because of the temperature-dependent density difference of the air, the entire air column in the duct is set into movement, so that natural convection occurs.
The air outlets are higher than the air intakes, so that the natural convection is amplified.

The air cooling in the channel may be intensified with the aid of forced circulation of the air, in that, for example, fans in the air intakes and outlets ensure intensive circulation of the air in the ISD. Such forced circulation is particularly advantageously

4 performed at times in which power for the operation of the fans is available cost-effectively, for example, at night.

The cooling effect may be increased by suctioning or carrying along water through the air, so that the arising vaporization energy withdraws heat from the environment.
The effectiveness of the described types of air cooling is a function, however, of the temperature of the outside air supplied to the duct. It is thus much less in summer - or even has a negative effect at higher temperatures - than in winter.
If one wishes to become independent from these seasonal variations, refrigerators may be used for air precooling in the area of the air intake. Such refrigerators have high investment costs, however, and cause additional losses and loss costs during operation.
An open trench is to be provided during the production of the ISD according to the invention. Its clearance is significantly wider than the external diameter of the ISD, because workspaces are required on both sides of the ISD. These may be used, before backfilling of the trench, for the purpose of housing pipes therein, preferably made of concrete, plastic, copper, or steel and/or stainless steel. These pipes are to be used as earth-air heat exchangers (EAHE) and therefore must have a cross-section sufficient for the desired air circulation. Transverse connections between these pipes and ISD, on the one hand, and between these pipes and the earth surface, on the other hand, are to be produced at appropriate intervals with the aid of pipe pieces, so that an air exchange can be performed at these points between these pipes and the ISO and/or between these pipes and the environment. These pipes are laid at the greatest possible interval from one another and from the ISD, i.e., as much as possible in the area of the embankment, and/or insulated to the ISD.

The pipes may either be laid a) directly in the backfilled soil or b) within liquefied soil used for trench backfilling according to Figure 1, or c) within concrete walls.

5 Instead of the pipes, any other cavities in the concrete walls also come into consideration.

To improve the thermal conductivity of the material of the ISD, additives having higher thermal conductivity may be added to the material, for example, graphite (natural or expanded), carbon nanotubes, phase-changing materials, or anthracite. The additives are not only to be used for better heat dissipation of the ISD into the surrounding earth, but rather also for the purpose of more rapidly activating the phase-changing materials, which are additionally proposed as an additive, and which are capable of storing large quantities of heat.
The workspace surrounding the ISD can be filled with temporarily liquefied soil (TLS), which is produced, by adding lime, cement, water, and plasticizer, from the occurring excavation masses and is additionally enriched, for example, using graphite, carbon nanotubes, phase-changing materials, or anthracite, in order to accelerate the heat evacuation into the surrounding earth of the ISD still further. Any additive having higher thermal conductivity comes into consideration.

In addition, the homogeneous trench backfilling has the result that the ISD
and earth-air heat exchangers are optimally enclosed. In addition, critical intermediate construction states may thus be avoided, and more rapid construction progress and additional stabilization of the static system are achieved.

Multiple earth-air heat exchangers may be installed in the workspace. These earth-air heat exchangers are used, on the one hand, for pre-cooling the outside air which is sucked by convection or mechanically into the ISD and also, in the event of

6 correspondingly lower outside temperatures, for the thermal activation of the surrounding soil as an additional cooling reserve for corresponding load states.

It can be decided on a case-by-case basis here whether cold outside air at less than +5 is to be injected directly into the ISO in the event of mechanical ventilation in winter and the EAHE is also exclusively used for mechanically cooling the soil or, in the case of convective ventilation, the charging of the duct cooling air by a few degrees in connection with the cooling of the surrounding earth is to be accepted. In summer, air can first be injected into the EAHE and then into the ISO to encourage convection. Under extreme conditions, i.e., at higher temperatures, the sucked-in outside air is first guided through the pipelines of the EAHE and thus pre-cooled and only subsequently supplied to the ISD. Of course, it is also conceivable to use the ISD itself as the EAHE, in that corresponding fans are provided in the inner chamber of the ISD, for example.
The EAHE may be implemented, for example, by laying individual sections of cement/concrete pipes and fitting them to one another. According to the proposal, these pipes may also be saved in that mandrels or hollow cylinders, which have a partition layer, such as a foil, on their surface, are introduced into the trench area to be filled with liquefied soil or lean concrete by a casing before the filling, so that they may be withdrawn after the solidification of the material enough that they may be provided with a partition layer again and the next trench section can be filled. An inflatable casing could also be considered.

If the work space backfill is water-impermeable, a drainage nonwoven material is situated over the work space backfill and also on the trench wall of the work space before the backfilling. In order that the introduced surface water can collect, a gravel bed is situated in the lower groin of the workspace.

The preparation of the building site is performed by typical soil stabilization using a lime-cement mixture, to which graphite (natural or expanded), anthracite, carbon

7 nanotubes, or phase-changing material may also be added, however, in order to improve the thermal transmission conductivity here.

In order to improve the sliding of the structure on the foundation, which is important in concrete technology, the prepared and flat-graded building site is covered with an aluminum foil. Graphite powder or another lubricant is scattered thereon and a further aluminum foil is laid over it, on which concrete work is then performed.

In addition to the EAHE in the longitudinal direction, a semicircular curved earth-air heat exchanger is connected to the duct, above the highest cable and below the lowest cable. Before the reentry into the ISD at the bottom, the possibility is provided by a constriction of the fiber cement pipe via the so-called Venturi effect of sucking in water, which additionally results in vaporization cooling and simultaneously strengthens the buoyancy forces in the chimney.
The air introduced by the earth-air heat exchanger in the longitudinal direction into the ISO is removed again via a chimney which is as tall as possible. At the base of the chimney, the possibility exists of situating an updraft turbine, using whose energy an output turbine for blowing air into the ground heat exchanger is mechanically or electrically operated, in order to reinforce the cooling effect of the ventilation system.
In addition, the effect of natural convection results in the ISD through the chimney, in which a heated air column stands, which becomes more intensive with increasing chimney height. Improved cable cooling also already results in the ISO through the convection even without forced ventilation.

In normal operation, but in particular in the event of ultrahigh load or overload of the cable facility and at times of lower power prices, forced ventilation can be operated using an induction conductor system, which is guided parallel to the high-voltage cables in the ISO and withdraws electrical power from the high-voltage cable system.
The cooling system thus becomes independent of an external power supply of the

8 ISD. For example, the entire duct system can be thermally activated at night, when the ambient temperature and in particular the air temperature fall, in that cold air is supplied to the pipelines, the ISD, and/or the remaining EAHE via forced circulators, which are operated using less expensive nighttime current.
If phase-changing material is used, it is also thermally activated in that the phase-changing material dissipates the thermal energy stored therein to the environment and simultaneously changes its phase, in that it solidifies, for example.
During the day and at relatively high ambient or air temperatures, forced circulation may be dispensed with, because sufficient "cold" is present in the duct system to compensate for the elevated temperatures - also as a result of the power losses in the power cables - so that the natural convection can ensure sufficient cooling. The phase-changing material absorbs a part of the heat at elevated temperatures, in that it again changes its phase and becomes liquid, for example.
For the case of a particularly high load of the ISD, in particular by the masses of the earth lying above it, fibers of materials having increased strength, such as steel fibers, may be added to the material of the ISD. Alternatively thereto, a conventional reinforcement of the ISD can be provided, the reinforcement preferably being produced in one layer and being able to be bent appropriately according to the load curves so that it lies once on the inside and once on the outside. Such a single-layer reinforcement can also be used for the purpose of fixing cooling pipes if additional component activation by coolant water is provided. Such an additional pipe system suggests itself either for further cooling and performance increase of the system or also for obtaining additional heat using heat pumps, if corresponding heat consumers are located close to the ISD.

Such cooling pipes, made of concrete, plastic, copper, or stainless steel, for example, may also be laid in the thermally activated workspace, of course. If additional cooling is required, typical geothermal probes may be used outside the workspace.

9 The earth-air heat exchangers of approximately 60 cm internal diameter, which are laid on the bottom in and/or partially below the workspace, can be embedded with the TLS in such a manner that an interval of 20 cm to the ISO is kept open with the aid of a temporary casing, for example, which is provided with thermal insulation made of crushed glass after hardening and withdrawal of the casing, for example.

Thermal insulation can also be performed above this earth-air heat exchanger, which could also comprise crushed glass. In addition, it is to be covered according to the invention using geotextile before the further workspace backfilling is performed using the temporarily liquefied soil material.

A thermal insulation is optionally also applied over the two EAHE of approximately 40 cm diameter housed in the further course of the workspace.

In warm countries, thermal insulation can additionally also be attached above the ISD.

A reinforcement in the form of fibers, in particular metal or plastic fibers, can be admixed with the fill soil, so that a special resilience of the fill soil can be ensured.
Brackets made of concrete and/or polymer concrete, for example, may be provided in the interior of the ISD for guiding the power lines, in which the power lines are guided and held down, so that tearing of the cables out of the brackets is prevented in the event of a short-circuit. A reinforcement can also be admixed with the brackets in such a manner that additional plastic or metal fibers ensure increased strength.
The following advantages result from the following invention:

1. Simple laying without problems.
2. Ideal mechanical protection of the cables, thus greater availability.
3. Retrofitting capability - for example, later laying or replacement (retrofitting) of cable systems;
- for example, upgrading of cables by retrofitting with ventilation or cooling systems and/or also later reinforcement of these systems.
4. Multiple usage by various systems (all media of supply and removal).
5 5. Rapid fault finding and repair of the cables, thus greater availability.
6. Simple and rapid repair/maintenance without excavation, floor damage, etc.
7. Auxiliary conductors, for example, for magnetic field compensation, are easy to guide along.
8. Temperature monitoring which is simple to implement (system for overload

10 alert and for carrying capacity prognosis).
9. Higher power reserves/overload capability.
10. Reduced transmission losses in relation to burying because of the lower cable temperatures in the ISD.

11. Increase of the conduction capacity and/or reduction of the power losses at strong load times by thermal pre-activation of the system.

12. No substantial thermal ground load - no drying of the ground, i.e., saving of thermal stabilization of the cable trench.

13. Full usability of the right-of-way above the ISD.

14. Magnetic shielding easy to implement, also sectionally.

15. Use of slim cables having minimized outlay, because: the cables are protected, well accessible, and little strained.

16. Simple cross bonding (or one-sided shield grounding), also in the case of four-core systems (three-phase current systems having core redundancy) and in the case of bipolar systems.

17. Favorable configurations for bipolar cable systems.

18. No disturbance by trench opening in the road or sidewalk area.

19. Minimization of the right-of-way length.

20. Cable occupancy independent of the building project.

21. Easy and rapid repair and optionally also replacement of the cables.

22. Only slight thermal or electromagnetic influence of human beings.

23. High redundancy even in the case of occupancy with only one line strand (because the cable can be overloaded due to the thermal reserves in ISD
system). The rapid repair capability was already noted.

24. The use of cables having aluminum conductors, as a function of the further raw material price development, is more possible than in the case of burying, for example.

25. Significantly reduced right-of-way width in relation to ground burying.

The invention is explained in greater detail on the basis of the drawing. In the figures:
Figure 1 a shows a duct system having an ISD in a vertical section, pipelines being situated in a body.

Figure lb shows a duct system as in Figure 1a, but having an additional ISD, which is used as the EAHE.

Figure 2 shows a detail from a duct system, again in a vertical section, having an ISD (partially cutaway) and the environment located adjacent to the ISD.
Figure 3 shows a perspective view of brackets for the ISD.

Figure 4 shows a sectional view of the subject matter of Figure 3 along arrows A-A.
A duct system having an underground traversable ISD 3 is shown in Figure 1, the ISD
3 being formed by an ISD wall 4 which is essentially rectangular in cross-section. The ISD 3 is sunk entirely into the earth below an earth surface 9. The ISD wall 4 is implemented as curved in the upper area of the ISD 3, in order to ensure better pressure distribution of the weight forces acting on the ISD 3. In order to improve the thermal conductivity of the ISD 3, additives, such as graphite (natural or expanded), carbon nanotubes, phase-changing material, other compacted carbon or anthracite, and metal chips may be added to the material - concrete in the present case -so that the thermal conductivity is significantly greater than that of typical construction concrete.
The ISO wall 4 envelops an inner chamber 7 of the ISD 3, in which power cables are guided. The power cables 1, which run essentially parallel to the longitudinal axis of the ISO 3, are situated on the vertical sides of the ISD wall 4 in the inner chamber 7. The power cables 1 may be guided along the ISD 3 with the aid of retainers 8, for example, in the form of a cantilever shelf or in the form of a hook, which are attached to the inner walls of the ISD wall 4. Furthermore, it is also conceivable to implement such retainers 8 for guiding power cables 1 on the ceiling and/or on the floor of the ISD 3. A further embodiment of such retainers is shown in Figures 3 and 4.

Bodies 5 for absorbing and dissipating thermal energy are situated laterally outside the ISD wall 4. The bodies 5 have pipelines 6 in their interior. The pipelines 6 may comprise concrete, plastic, steel, stainless steel, or another material, for example.
They are used in the present case as earth-air heat exchangers, so that the air flowing through them can absorb or discharge heat from the earth. It would also be conceivable, of course, to fill the interior of the pipelines 6 with a medium, such as water, so that in the event of damage of the pipelines 6, for example, during excavation work, environmentally hazardous substances cannot escape into the earth. The body 5 has a rectangular shape viewed in cross-section in the present case, the pipelines 6 being situated in parallel one above another. It is conceivable to situate the body 5 in another cross-sectional shape, for example, or even to situate the pipelines 6 directly in the earth, free of a body 5.

Such a configuration is shown in Figure 2. As is obvious, a total of three pipelines 6 are situated in a trench 10 below the earth surface. In the present case, the two upper pipelines 6.1 and 6.2 situated in the workspace have the same diameter. The pipeline 6.3 situated below the pipelines 6.2 has a larger diameter. All pipelines may be situated as desired in the workspace according to the space required.

The pipelines 6 may be backfilled in the trench 10 via temporarily liquefied soil (TLS), which is produced from the excavated masses by adding lime, cement, water, and plasticizer, for example. However, it can additionally be enriched with graphite (natural or expanded), anthracite, steel chips, phase-changing material, carbon nanotubes, or other compacted carbons, in order to accelerate the heat dissipation into the surrounding earth of the ISO 3 still further. The pipeline 6.3 and also the remaining pipelines 6 may also be produced by casting the TLS. For this purpose, a mandrel having the diameter of the pipeline 6.3 is laid in the trench 10 and backfilled using the temporarily liquefied soil. After hardening of the concrete, the mandrel is removed and a hollow pipe body 11 results. Of course, it is also conceivable to produce the pipelines through an inflatable casing, for example, a hose fillable using air or water, instead of the mandrel. An intermediate space 12 can be provided between the front side of the pipe body 11 assigned to the ISO wall 4, which is provided with thermal insulation made of crushed glass, for example. In the present case, an additional pipeline 6.4 which is semicircular in cross-section is situated directly on the outer ISO wall 4 of the ISO 3 in the depth between the pipelines 6.1 and 6.3. It is also used as the heat exchanger.

The pipeline 6.4 can be hollow inside, or can have or implement one or more lines for transporting of medium such as gas - for example, air - or a liquid such as water. The pipeline 6.4 can be connected to conduct medium to the other pipelines 6 and/or additional ISD 3. The pipeline 6.4 is preferably connected to the ISD wall 4 so that a passage of the medium guided in the pipeline 6.4 through the ISD wall 4 or through the ISD 3 itself is possible. An upper curve end 6.4.1 of the pipeline 6.4 is advantageously situated above the highest power cable 1 and a lower curve end 6.4.2 is situated below the lowest power cable 1 on the ISD 3. For example, the ISO
wall 4 facing toward the pipeline 6.4 can have recesses into which the two curve ends 6.4.1, 6.4.2 of the pipeline 6.4 protrude. To seal the passage, any sealant which appears suitable to one skilled in the art may be used. In addition, a passage hole may be provided in the ISD wall 4, which corresponds to the internal diameter of the pipeline 6.4, for example, so that medium can be guided out of the pipeline 6.4 into the inner chamber 7 of the ISD 3 or past it back out of the ISD 3.
Recesses are also provided in the ISD wall 4 in the inner chamber 7 of the ISD
3 at the height of the passage, an upper pipe socket 6.4.3 and a lower pipe socket 6.4.4 engaging in the corresponding recess in each case. The pipe sockets 6.4.3, 6.4.4 are also sealed in relation to the passage as described above. The two pipe sockets 6.4.3, 6.4.4 have an enlarged opening diameter, in the present case in the form of a notch which is not perpendicular to the longitudinal axis of the pipe sockets 6.4.3, 6.4.4. Of course, all possible opening shapes of the pipe sockets 6.4.3, 6.4.4 which enlarge the opening cross-section are conceivable.

The pipe sockets 6.4.3, 6.4.4 are advantageously situated so that the opening of the upper pipe socket 6.4.3 enlarged by the notch points essentially downward toward the power cable 1 and the opening of the lower pipe socket 6.4.4 essentially points upward toward the power cable 1. Another configuration of the openings of the pipe sockets 6.4.3, 6.4.4 would also be possible.
The pipe sockets 6.4.3, 6.4.4 accommodate the rising medium volume stream, i.e., the air which is heated and rises upward because of the power losses of the power cable 1 here, and guides it into the pipeline 6.4. Because the pipeline 6.4 functions as an EAHE, the heated air is preferably cooled, the heat being dissipated to the surrounding earth (TLS), the pipelines 6, or a further EAHE surrounding the pipeline 6.4. The colder medium - the colder air - in the pipeline 6.4 sinks downward and is supplied back to the inner chamber 7 of the ISD 3 at the lower pipe socket 6.4.4.

The pipeline 6.4 can be selected in all conceivable shapes and various cross-sections and cross-sectional shapes corresponding to the required cooling power. The cross-section can also change at least continuously along the longitudinal extension of a pipeline 6.4. The pipelines 6.4 and the associated passages and/or the pipe sockets 6.4.3, 6.4.4 may be attached to the entire ISD wall 4. The pipeline 6.4 may have a shape deviating from the curve and may also have multiple pipe sockets 6.4.3, 6.4.4 per pipeline 6.4. A plurality of pipelines 6.4 and pipe sockets 6.4.3, 6.4.4 can be 5 provided, which are situated at intervals to one another - for example, every 50 cm -in the longitudinal direction of the ISD 3. Forced circulators such as fans, which may be situated in the pipeline 6.4 or in the immediate environment thereof, are also conceivable.

10 All of the above-mentioned materials, such as stainless steel, and material additives, such as carbon nanotubes, are conceivable for the pipeline 6.4 and for the pipe sockets 6.4.3, 6.4.4.

A second ISD 3 is additionally situated spaced apart from an existing ISD 3 in Figure 15 1 b. The additional ISD 3 can be free of power cables or retainers for this purpose and can be used as an additional pipeline and/or as an additional EAHE. For this purpose, the additional ISD 3 can have a medium-conducting connection to the existing and/or the pipeline 6. A plurality of additional ISD 3 can also be situated adjacent to one another or one above another in the trench 10. An additional ISD 3 used as an EAHE can also be used as part of an underground transport system (CargoCap) or fulfill additional other tasks.

A hole can additionally be provided in the pipelines, which can be implemented in the form of a Venturi nozzle (not shown). This hole is preferably implemented as a passage hole through the pipeline. The hole can extend further into the workspace of the trench 10 and can be connected to a water-guiding line, for example. A
partial vacuum is generated in the hole by the air flowing past the hole, which sucks water into the interior of the pipeline. This water preferably vaporizes, so that it absorbs energy and additionally amplifies the cooling effect.

If a material which is water-impermeable is used for backfilling the trench 10, the inner side of the trench 10, i.e., the side facing toward the ISD 3, must be lined using a drainage nonwoven material 13. Such a drainage nonwoven material 13 is also situated on the earth surface 9 and/or below the earth surface 9. For better removal of the collecting water, a gravel bed 14 is provided in the lower groin of the trench 10, so that water collects in the gravel 14 and can drain away there.

Of course, it is also conceivable that the pipeline 6 and in particular the ISD 3 are not cast directly in the trench 10, but rather are introduced as finished elements into the trench 10.

Two brackets 15, 16 are shown in Figure 3, which enclose a power cable 1. The brackets 15, 16 assume the function of the retainers 8 from Figure 1. The lower bracket 16 is preferably implemented as L-shaped in cross-section, while the upper bracket 15 has a Z-shaped cross-section. A cable guide 17 is located in the cavity 18 enclosed by the two brackets 15, 16.

The cable guide 17 is shown in detail in Figure 4. In its interior, it comprises a curved opening, preferably of circular cross-section, so that the cable is guided in a comparatively large radius (shown exaggerated here) by the brackets 15, 16.
This saddle-like support of the power cable 1 allows a continuous retainer, for example, in the form of a cantilever shelf, to be dispensed with, so that the power cable 1 is only supported by the brackets 15, 16 at specific intervals. For this purpose, a plurality of brackets 15, 16 is situated along the ISD 3. The spacing of the brackets 15, 16 to one another is varied depending on the cross-sectional diameter and number of the power cables 1 per bracket 15, 16. In addition, multiple brackets 15, 16 may be situated one above another, so that multiple lines, in particular power cables 1, may be guided in parallel and one above another along the ISD 3. By tensioning the brackets 15, against one another, the power cable 1 is prevented from tearing out of the brackets 15, 16, as occurs in the event of a short-circuit, for example, so that the power cable 1 is not damaged in this case. The brackets 15, 16 may also comprise a material based on concrete and may also be enriched using the above-mentioned additives having increased thermal conductivity. Fiber cement or a construction made of steel or other suitable materials is also conceivable as the material for the brackets 15, 16.
The brackets 15, 16 may also be implemented deviating from the L or Z cross-sectional shape. In this case, they must have a retaining force so that they may reliably guide and hold down the cables running therein.

The cable guide 17 comprises four parts 17.1, 17.2, 17.3, 17.4 in the present case.
The surfaces of the parts 17.1, 17.2, 17.3, 17.4 facing toward the power cable 1 have concave indentations, so that the power cable 1 can rest flush therein. The sides of the parts 17.1 through 17.4 opposite to the power cable 1 each have a bevel.
The brackets 15, 16 also have a corresponding counter contour - in the present case, the brackets 15, 16 are implemented in the form of a truncated pyramid in their cross-section - so that the bevels can be clamped with one another non-positively and/or positively in the longitudinal direction of the power cable 1.

During the installation of the brackets 15, 16, the power cable 1 is introduced into the cavity 18 and/or the bracket 15 is installed on the bracket 16. The two lower parts 17.3, 17.4 of the cable guide 17 are subsequently each inserted from the corresponding side between power cable 1 and bracket 16. Subsequently, the two remaining parts 17.1, 17.2 are also inserted from both sides into the cavity 18. In order to achieve a flush rest of the cable in the parts, the parts are driven into the interior of the bracket with application of force. The surfaces of the parts facing toward the cable are preferably to rest without play on the surface of the power cable 1, so that movements of the cable - for example, as a result of thermal expansion -and thus the rubbing of the installation of the power cable 1 in the cable guide 17, are prevented. Through the additional tensioning of the two brackets 15, 16 against one another, the parts are pressed against one another, so that the power cable 1 is additionally secured against slipping in the cable guide 17.

The embodiment according to the invention simultaneously represents a type of tension relief for power cables 1. The contours of the brackets 15, 16 and the cable guide 17 are dimensioned so that a longitudinal expansion of the power cable 1 is made possible to a certain extent by displacement of the cable guide 17 in the brackets 15, 16 through the bevels, simultaneously, the power cable 1 is prevented from slipping through the cable guide 17 in that in the event of increased tensile stress of the power cable 1, the parts are moved in the traction direction along the bevels, the parts moving toward one another and strengthening the clamping effect.
Because of the wedges of the parts placed against one another, the tensile stress of the power cable 1 is independent of the direction of the traction. The power cable 1 is also prevented from breaking or tearing out of the brackets 15, 16 as a result of a short-circuit, in the case of which powerful forces could be released.

It is conceivable to provide multiple passages in the cable guide 17, so that a plurality of cables, for example, also data cables or cooling lines for power cables 1, are guided in parallel in only one cable guide. Correspondingly, the openings of the cable guide 17 may also be different. All suitable materials, in particular low-flammability and heat-conducting plastics, however, come into consideration as the material for the cable guide 17.

List of reference numerals 1 power cable 3 infrastructure duct (ISD) 4 ISD wall 5 body 6,6.1,6.2 6.3, 6.4 pipeline 6.4.1 upper curve end 6.4.2 lower curve end 6.4.3 upper pipe socket 6.4.4 lower pipe socket 7 inner chamber 8 retainer 9 earth surface 10 trench 11 pipe body 12 intermediate space 13 drainage nonwoven 14 gravel bed 15, 16 bracket 17 cable guide 17.1, 17.2 17.3, 17.4 part 18 cavity

Claims (5)

1. A duct system having the following features and/or elements:
1.1 having a trench (2) provided in the earth;
1.2 having a traversable duct (3) for accommodating power cables (1) and infrastructure lines in its interior, which is cast in the trench (2) or prefinished, its wall (4) containing a material based on concrete;
1.3 the material of the duct (3) having a thermal conductivity which is at least 3.0 W/(m*K);
1.4 bodies (5) for absorbing and/or dissipating thermal energy being situated outside the duct (3).

2. The duct system according to Claim 1, characterized in that the material of the duct wall (4) contains the following additives, either individually or in combination:
- steel chips;
- natural or expanded graphite;
- anthracite;
- phase-changing material;
- carbon nanotubes;
- other compacted carbons.

3. The duct system according to Claim 2, characterized in that the material enclosing the duct wall (4) also contains the listed additives individually or in combination.

4. The duct system according to Claims 1 through 3, characterized in that the space enclosing the duct (3) contains pipelines (6).

5. The duct system according to Claim 4, characterized in that the pipelines (6) are used for guiding gas, in particular air, or liquids, in particular water.