Field of the invention

The present invention relates to a method for installing high voltage conductors through a landscape, and is especi¬ ally related to the areas which can be utilized for private houses and industry, or to areas in which the high voltage masts inhibit the expansion of further residential and industrial areas.

Discussion of prior art

In connection with the installation of high voltage conduc¬ tors in the form of overhead transmission lines between large high voltage masts, it has often been raised objec¬ tions against not only the space required by such high vol¬ tage masts and high voltage overhead lines, and also against the dominating position reflected by such an installation in a ^' landscape, but also against the dangers being related to high voltage overhead transmission lines, especially in the higher voltage ranges, for example 400 kV.

in residential areas in which the overhead transmission lines are supplied to the individual residential blocks or private houses, the voltage will as a rule be lower after having been transformed to a lower value in an appropriate transformer station, and in order to avoid disfiguring high voltage masts the current will often be supplied by means of cables which have been buried in the ground. Such a bury in the ground requires the digging of trenches, which can be both time consuming and expensive, the cable path usually taking an undulating course depending on the ground which - the trench is to follow. Further, the digging of such a trench will also include the blasting away of rocky con¬ tours, which can involve difficult working operations and disfiguring wounds in the landscape.

Short description of the invention

An object of the present invention is to give instructions for a method for installing high voltage conductors through a landscape, wherein the above discussed disadvantages are eliminated.

In accordance with the invention it is suggested that the installation of high voltage conductors through a landscape is taking place in one or more drilling holes which have been drilled through the landscape.

In the invividual drilling holes the high voltage conductor can then take the form of an insulated conductor, for exam- pie a high voltage oil cable.

Since the high voltage conductors are laid in drilling holes underneath the ground, the conductor path can find its way following a stright as possible line, which involves simple pulling of the conductors, as well as minimum drilling lengths and minimum length of the conductor or cable, hich in turn reduces the material expenses and reduces the trans¬ mission losses.

Above the ground the landscape can then be untouched, and consequently be utilized for example for residential objec¬ tives, as parks, for industrial purposes or for any other purposes, whilst avoiding disfiguring high voltage masts and possibly perilous side ^" effects from the high voltage conductors.

In dependence of the available drilling technique and the landscape in question, the drilling can be carried out in various different manners.

For example there may be drilled a plurality of lesser sub¬ stantially parallel holes corresponding to the number of user phases, there being additionally possibly drilled a further parallel hole for a spare conductor.

A second alternative is to the fact that a common larger hole is drilled for all of the conductor phases.

In order to protect the invividual phase conductors , especi- ally in those cases wherein is drilled a lesser drilling hole for each phase, there may in each drilling hole be pro¬ vided a fluid tight pipe, for example a fully welded PVC- pipe. This pipe can apart from serving as a protection of the individual phases also serve as a longitudinal container for cooling fluid, and in this connection it might be appro¬ priate that in the pipe there is also provided a fluid pipe for the filling and recirculation of fluid in the pipe en¬ closing the phase conductor.

Possibly, in the case of a common drilling hole, each phase conductor may be enclosed by a pipe which not only serves for protecting the individual cable against for example fal¬ ling rock or accession of water, but which also serves for *y the supply and circulation of a co'oling fluid, possibly in . combination with fluid pipe and fluid pump.

If, due to drilling technological and landscape prevailing reasons, there is used only one drilling hole, each of the phase conductors may be arranged in its own rack, there being in the common drilling hole possibly arranged a fan and a cooling aggregate for cooling during the operation of the conductors.

In order to avoid unfavourable accumulation in the drilling holes, for example acccession of water or other liquid, the drilling holes should preferably have an appropriate slant¬ ing, which can also be utilized in connection with the cir¬ culation of fluid in the protecting pipe. Possibly, the fluid pipe can at its one end be connected to a pump for the filling and/or circulation of fluid in the pipe enclosing the phase conductor.

Brief discussion of the drawings

In the following the invention will be further described, reference being had to the drawings illustrating various embodiments of the invention.

Figure 1 is a diagrammatical view illustrating the prin¬ ciple of the present method for installing high voltage conductors.

Figure 2 illustrates diagrammatically a first alternative for the implementation of a method according to the inven¬ tion.

Figure 3 illustrates diagrammatically a second and a third alternative for implementing the method according to the invention.

Description of embodiments

In Figure 1 it is diagrammatically illustrated how the pre¬ sent invention can be realized. To the left of the Figure it is illustrated how the high voltage conductors 1 in the form of overhead transmission lines on high voltage masts 2 are conducted above a soil ground 3 to an area of rock ground 4, at which point the overhead transmission lines 1 have been brought to the ground level and have been past through the rock ground 4 through pre-drilled drilling holes 5 extending from a left enterance zone 6 to a right exit zone 7.

It is to be understood that the overhead transmission lines 1 at the entrance zone 6 merge into conductors la having appropriate insulation for the introduction into the dril¬ ling holes 5, and such conductors may suitably be for exam¬ ple oil cables .

At the exit zone 7 the cables la in the drilling hole 5 may merge into corresponding cables lb which have been laid in trenches 8 following the surface of the associated building area, possibly after the voltage has been transformed down to an appropriate voltage level.

Since the high voltage contuctors la have been laid in dril¬ ling holes 5, the landscape above the rock ground 4 can be utilized for building objectives, whether this relates to - residential houses or plant buildings or a mixture thereof, without leaving unnecessary space for high voltage masts and overhead transmission lines.

Since the conductors ^" or cables la have been installed in drilling holes 5 which preferably extend along a straight line, the installation itself through the drilling hole 5 will have a minimum extention, a fact which involves that minimum conductor length is required for the transmission.

It is to be understood that the above discussed method for the installation of high voltage conductors can be carried out not only in connection with novel high voltage path, but also in connection with existing overhead transmission lines, especially such which are ready for restoration, sub- stantial maintenance or expansion. If drilling hole path of the above illustrated type are implemented, it is possible that the buildings along the existing high voltage overhead path can be utilized for residential buildings, which is especially the case in connection with heavely populated places where the value of the site is very high.

Further, it is to be understood that inspection and mainten¬ ance of high voltage conductors which have been installed in a drilling hole path, would be substantially simpler than of overhead transmission lines which especially during winter are subjected to winter storms including snow and ice loads which can subject the high voltage material to heavy damages and subsequent risk for current supply disruption.

In Figure 2 there is illustrated a first embodiment of the method according to the present invention. Here, there are drilled four lesser substantial parallel drilling holes, 5a, 5b, 5c and 5d, respectively, in a rock ground 4, there being contemplated a separate drilling hole for each conductor phase, an oil cable lr. Is, It, respectively, in three of the drilling holes, whereas the forth drilling hole 5d may serve as a spare with or without cable.

In each drilling hole 5a-5c there is provided a fully elded PVC-pipe _r 10a, 10b and 10c, respectively, serving for the protection of the respective cable, it being understood that the pipes lOa-lOc being inserted into the respective dril¬ lings 5a-5c before the individual cable is pulled through the associated pipe.

In order to avoid that the individual cables during opera¬ tion, i.e.-vnder tension and conducting current, should be overheated, said pipes lOa-lOc may be used for the filling and recirculation of cooling medium, for example a cooling fluid wich can be supplied or circulated by means of a fluid pipe, 11a, lib and lie, respectively, which at the one end may be connected to a pump in order to exercise the neces¬ sary circulation or filling up of cooling liquid.

It is to be understood that if the drilling holes 5a-5d are provided with an appropriate slanting from the entrance zone 6 to the exit zone 7 (see Fig. 1) then a natural movement of the cooling fluid may be brought forth by means of this slanting.

Possibly, there may to the fluid pipe be connected pumps at both ends for the circulation of cooling fluid 12, such that in this case it can be talked about a closed circulation system.

By the alternative illustrated in Figure 2, one will as a

starting point drill four longitudinally extending holes having a diameter of approximately 30 cm through the rock ground 4. Each hole is thereafter provided with its own fully welded PVC-pipe lOa-lOc, whereafter the individual cables lr, Is, It are pulled through its respective pipe together with a fluid pipe, 11a, lib and lie, respectively. Cooling liquid, for example water, will during operation be pumped to the highest point of the drilling holes, where¬ after the water can flow towards the lowest point in the drilling holes, for thereby achieving a cooling of the cables due to recirculation of the cooling liquid. The water level in the PVC-pipes should always be so high that the upper part of the cable is covered. •

Possibly, the heat from the cooling water may be used to keep the enterence zone and the exit zone of the drilling hole path free from snow and ice during winter.

In Figure 3 there are illustrated a second and a third em- bodiment of how the method according to the invention can be implemented. Jnsted of three or four relatively lesser moun¬ tain holes of diameter approximately 30 cm, there is here drilled a common larger hole 105 , and in this hole there are suspended three pipes, 110a, 110b and llO.c, respectively, in which are treaded individual cables, lOlr, 101s and lOlt, respectively.

As appearing from Figure 3, each phase conductor is arranged separated by means of a devider means, here illustrated by dashed lines and being given the designation 112, said sup¬ porting or devider means 11-2 being arranged at equal spac- ings along the extention of the drilling holes 105.

In order to achieve an appropriate cooling of the cables during operational conditions a first solution may include the arrangement of water in the individual protecting pipes HOa-llOc, substantially in the same manner as discussed in connection with the embodiment according to Figure 2.

As an alternative there may also be used cooling air, it then not necessarily being required to use said protecting pipes, but by means of appropriate fans and cooling aggre¬ gates there may be achieved sufficient circulation of the air for this to give sufficient removal of exess heat from the cables during operation.

By using said installation of cable through drilled holes the value of the sites located below, over and close to the conductor path may be increased. The conditions relating to the preservation of natural recourses can be coped with by such installation through national parks. The overhead transmission lines will disappear from the forest, especial¬ ly at the ridges where they are very prominent.

It is to be understood that various forms for cooling medium may be used. In those cases where it is contemplated to use pipes around the individual conductors , the pipes may serve as longitudinally extending containers for co _. oling fluid. Examples of such fluids can be water to which are added appropriate materials for improving the cooling effect, and for improving the insulating properties of the conductors against the environments. Also other media can be used, for example in connection with super conductors, which then ren- ders a combined cooling and reduced electric resistance in the conductors.