EP1488488A1 - Method for application of wire system with mechanical support wire and current conducting wire for transmission line - Google Patents

Abstract

Method for the application of a wire system consisting of a mechanical support wire or wires and current conducting wires for power transmission lines comprising steps of attaching mechanical support wires on support structures of the transmission line directly or by means of insulators and joining separate current conducting wires to the mechanical support wires applying spacers and/or insulators. The cross-sectional area of current conducting wires is chosen to ensure that with current conducting wires loaded with their rated current and with the ambient temperature being 30 ° C, the temperature of said current conducting wires is greater than 80 ° C but does not exceed 300 ° C. According to the inventive method, the support wire is implemented as a ground wire. For reducing the tensile stress of existing phase conductor wires that according to the invention are functioning as current conducting wires, support wires are installed such that support wires and existing phase conductor wires are tensioned, taking into account the ambient temperature, to a degree that the tensile stress to which the current conducting wires are subjected is reduced by at least 20%.

Description

Method for application of wire system with mechanical support wire and current conducting wire for transmission line

The object of the present invention is a method for the application of a wire system consisting of a mechanical support wire or wires and current conducting wires for power transmission lines comprising steps of attaching mechanical support wires on support structures of the transmission line directly or by means of insulators and joining separate current conducting wires to the mechanical support wires applying spacers and/or insulators. According to the inventive method, the degree of thermal and electric insulation of mechanical and current conducting wires is determined taking into account the properties of materials used and operating conditions.

The inventive method can be applied either for modifying (upgrading) existing power lines or for constructing new ones.

Known art power transmission lines usually comprise conductors made principally of aluminium (Al, ACSR, aluminium alloys), with copper conductors applied only occasionally. The position of conductor wires is determined by insulators supported on support structures (poles), with the insulators being disposed on the poles either in a suspended or in a tensioned configuration. Wires are attached to the poles such that they are subject to a tensile stress that is established beforehand as a design parameter in such a way that safety clearances of wires to ground or to surrounding objects are . maintained under all circumstances. The greater the tensile stress of the wires, the smaller their sag becomes, which makes it possible to use smaller-size poles or increase the distance between them. Design parameters of transmission lines are usually finalised after thorough technological and cost-benefit analysis. Because mechanical properties of pure aluminium are disadvantageous for transmission line design, aluminium is usually alloyed (AASC wires) or an aluminium layer is formed around a steel core (ACSR wires). These methods have been well known for the past hundred years. High-voltage power transmission systems are implemented as meshed networks for a number of reasons, with the magnitude and direction of the power flow determined by power injected at feed points and consumed at consumption points, and also by the impedance conditions of the system. Apart from exceptional cases there are no means for directly controlling the size and direction of the power flow, so any change in power consumption or injection and impedance relations affects power flow. Such a change can be the disconnecting of a transmission line that would result in the load thereof taken over by other lines, which in unfavourable conditions may lead to overload.

Because the thermal capacity of overhead conductor wires is relatively low, in most practical cases the time constant of temperature changes is in the range of a few minutes. To prevent adverse effects caused by overloads, corrective action is needed within the time limit set by the above time constant, which means that there is practically no alternative to automatic disconnection in case of an overload. However, disconnecting an overloaded power line stops the flow of power at precisely that moment when the demand for power is greatest, so it can only be done as a last resort to prevent catastrophe, and not as a proper operation of power line control.

As we have already seen, there is usually no direct means to control power flow in a transmission system, so overload protection at least in cases of a single fault must be provided for by operational procedures and modes of operation established either in a long-term planning phase or during the operation of the power transmission system. That purports to either upgrading the affected transmission line(s) or constructing a new transmission line to take over a portion of the load.

With the constant growth of electrical loads it became necessary to increase the loadability of transmission lines as early as the first half of the last century. That could first be achieved by increasing wire diameters, and later by applying multiple wires (2...8) for each phase, positioned approximately 40-80 centimetres apart and joined together by means of spacers. This solution is known in the art as a conductor bundle. At higher voltage levels (above 300 kV) bundled conductors might be required irrespective of load to prevent radiation. According to known art solutions a conductor bundle contains wires made using the same manufacturing technology, and all wires assume the same function with respect to bearing mechanical loads and current conduction.

During the operation of the transmission line conductors are subject to Joule loss that results in the wires heating up. Because of the increase in temperature, wires extend longitudinally, increasing their sag or, in other words, reducing their electrical clearances to ground. Because conductor clearances to ground have a minimum value for safety reasons, the allowed maximum current of the transmission line must be limited. Let us call this the "geometric thermal limit."

Another limit to the maximum current of the transmission line has also be taken to account, namely the maximum allowed temperature of structural materials of the wires. For example, according to Hungarian standards the sustained operating temperature of aluminium wires of different structure and composition is, depending on their type, 70/80/80 °C, while the same wires can be operated at temperatures of 90/1 10/100 °C for one hour in special situations, with the total duration of operation at the latter temperatures not exceeding three hours per month. In case of exceptionally occurring short-time short circuits wire temperatures should not exceed 130/155/150 °C. The main reason for temperature limits is that at high temperatures structure transformation occurs in the aluminium material, which deters mechanical properties: the tensile strength and thermal resilience (capability of the material to contract to its original length) of wires gets reduced. The above standard temperature and time limits have been established to ensure that vital parameters of the wires (tensile strength and thermal resilience) do not fall down under their design values during the planned life of the wires. Let us call these limits collectively the "thermal limit of material properties."

Because of Joule loss occurring in the wires, there is a connection between the temperature of the wire and current flowing through it, so the thermal limits of geometry and of material properties indirectly constitute a limit of current load (provided that other conditions are fixed). Thus the maximum current load of wires containing aluminium is determined by conditions of geometry and also by material properties. Pushing further the limits discussed here has been the object of several development projects, which can be divided into the following categories:

• Increasing clearances of wires to ground

• Exact monitoring/control of the position of the wires

• Development of novel wire types

Increasing clearances to ground can be a solution in case the loadibility of the transmission line is principally limited by safety clearances (geometric limit), which happens quite frequently nowadays, as design principles and standards for transmission lines have changed a lot in recent decades. For instance, according to Hungarian standards the loadability of transmission lines designed before 1973 is different from that of lines applying the same conductor materials but designed after 1973. This is because before 1973 transmission line spans had to be dimensioned assuming a conductor temperature of 40 °C and safety clearances had to be established for a conductor temperature of 60 °C, whereas these temperature values have been since changed to 60 °C and 80 °C respectively. The situation is the same in certain US states. Several inventions address this problem, e.g. a solution is disclosed in US patent No. 5,777,262.

By the exact monitoring or control of the position of the wires it becomes possible to exploit the leeway or safety margin originally built into transmission line designs to compensate for changing ambient conditions such as wind speed, sunlight intensity, or air temperature. The online measurement and computer-aided evaluation of these parameters enables the dispatcher to flexibly made decisions concerning the allowable loadability of the transmission line. Disadvantages of such systems are described e.g. in US patent No. 5,235,861, which instead of measuring ambient conditions proposes the direct monitoring of wire positions, which according to the invention can be carried out more exactly and with a greater reliability. There are numerous examples of developing novel wire types. The developments usually concentrate on improving one or more of the following properties: the composition of the aluminium material can be changed by alloying, the resistivity of aluminium wires can be reduced with the application of wires with unconventional cross-sectional shape, cooling conditions are improved by applying paint on the wires, or the tensile stress to which the aluminium wire portion is subjected can be reduced by a special ACSR wire where the aluminium layer is allowed to move relative to the steel core, so essentially the aluminium portion does not take part in supporting tensile forces. The temperature rating set by the manufacturer of a particular variety of this type of wire is 250 °C, because its sag equals that of a conventional ACSR wire precisely at that temperature. A method for manufacturing such a wire is disclosed in US patent No. 5,554,826.

The common point of departure for all the above described three categories of development seems to be the fact that in case the load of the transmission line grows, so does the line loss that causes the temperature of the wires to rise, which in turn results in an increased sag threatening with the violation of safety clearances. The major differences among solutions are in the ways they propose for the prevention of sag increases and damage to wire materials. It should also be remarked that in many countries around the world the effect of sleet or ice load has to be taken into account when designing power transmission lines. For a wire made of a single material the material applied determines the modulus of elasticity (relative elongation under tensile stress) and the thermal coefficient of expansion (relative elongation caused by temperature change). For wires composed of multiple materials (e.g. ACSR) a "combined" modulus of elasticity and a "combined" thermal coefficient of expansion can be established by calculation using properties of constituent materials, or can be measured. Values fall between those characteristic of constituent materials. This means that wires made of more than one material elongate to a greater extent than wires made solely of the material with the best mechanical properties would do, which results in greater sag increase and greater reduction of safety clearance.

In the usage of the present document, "wire" refers to any construction (strand, braid, wire, tube, etc.) suitable for mechanical or current conducting purposes. "Wire system" refers to any particular combination of such wires.

A conductor suspension method comprising a separate suspension wire and one or multiple current conducting wires suspended on said suspension wire by means of spacers is disclosed in document JP 2002017013. The document also describes a method and device for stringing a new current conducting wire additionally to already-strung current conducting wires. The application of the wire assemblage consisting of a separate suspension wire and one or more current conducting wires attached thereto by means of spacers or insulators has a number of advantageous technological and economic outcomes that are not addressed in the document. These are: • Current conduction capabilities of aluminium (or another material), determined by material properties can be exploited to their full potential without adverse effects on the operation conditions or the safety of the transmission line (extension of the thermal limit of material properties)

• Electrical clearances of overhead conductors to ground can remain essentially constant (or are reduced by a relatively little amount) even when wires are heated up due to increased load (extension of the geometric thermal limit)

For utilising these potential advantages to the fullest, the wire system should be designed along the following lines:

• To extend the thermal limit of material properties, aluminium wires or wire portions should be relieved of any mechanical function.

• For the extension of the geometric thermal limit, o either a material with negligible or low thermally induced longitudinal expansion should be used for stabilising the spatial position of the wires o or the material that is used to stabilise the spatial position of the wires should be prevented from heating up.

This problem can be solved in practice by making use of the insight that mechanical requirements and requirements for current conduction can be advantageously met by wires mechanically, electrically (with regard to current conduction), and thermally separated from each other to a suitable extent. This runs counter to the conventional and widely used procedures of power transmission line design that require wires to simultaneously fulfil mechanical and current conduction criteria (which often make contradictory claims to material properties), which necessarily results in a design compromise taking into account many material properties at the same time. The wires, separated from each other to a suitable extent, can be made of conventionally used materials, or alternatively they can consist of materials that have not been used so far in the art. Individual wires may be of uniform or different materials, structure, cross-sectional size and shape, etc. Requirements for different wires with different functions can be established individually to suit needs arising from particular functions, so the appropriate materials can be selected for each function without there being a need to take into account criteria set by other functions.

The most general solution to the problems described above is a wire system that can be characterised by the following: • The wire system contains at least one wire, made of suitable material, that primarily performs a mechanical function (determining not only its own spatial position but the position of other wires by means of structures attached to it), with said wire not necessarily taking part in power transmission (referred to in the following as "mechanical wire").

• The wire system contains at least one wire, made of suitable material, that primarily performs a current conducting function, with said wire not necessarily taking part in performing mechanical functions (referred to in the following as "current conducting wire"), with the spatial position of said wire being determined by structures attached to the mechanical wire, or said wire being surrounded- by mechanical wires such that they determine the spatial position thereof.

Within the general solution there are several options of realising the invention in a number of diverse ways:

• The number, tensioning force, and cross-sectional size of the mechanical and current conducting wires should be tailored to specific needs along the whole length of and in any of the phases of the transmission line.

• In case the mechanical and current conducting wires are at the same potential and in the same phase, the wires are joined by means of spacers or insulators, with insulation voltage ratings of insulators equalling a fraction of the line voltage, with spacers or insulators installed with such a density that the mechanical load and the sag of the current conducting wire remain in the acceptable range under all operational circumstances.

• In case the mechanical wire is at ground potential, the current conducting wire is joined to the mechanical wire by means of insulators with isolation voltages equalling at least the phase voltage, with insulators being installed with such a frequency that the mechanical load and the sag of the current conducting wire remain in the acceptable range under all operational circumstances.

• In case the mechanical wire is at the phase voltage, the current conducting wire is joined to the mechanical wire by means of insulators with isolation voltages equalling at least the line voltage, with insulators being installed with such a frequency that the mechanical load and the sag of the current conducting wire remain in the acceptable range under all operational circumstances (in this case the mechanical wire partially functions as a current conducting wire of a single phase).

• The mechanical wire can directly or indirectly support the current conducting wire or wires of one or more phases with the help of suitably insulated spacers, providing at the same time for preventing conductor galloping. The mechanical wire can be made of metal (e.g. steel, zinc-coated steel, or aluminium-clad steel that has advantages of having good corrosion strength and a tensile strength surpassing that of zinc-coated steel, or, possibly, titanium alloy, etc.)

• Alternatively, the mechanical wire can be made of non-metallic material, preferably having light weight and high strength, and, in certain cases also having low thermal coefficient of expansion (e.g. Kevlar, carbon fibre plastic, Allied Signal Spectra Fiber, Thornel Carbon Fiber, Toyobo Zylon, Dyneema High Strength Polyethylene, etc.), coated if necessary to protect it against environmental hazards (e.g. UN radiation, strong electric fields).

• As far as conduction of heat and electric current are concerned, spacers can be of high or low conductivity as is required by the applied materials and specific configurations (e.g. with respect to controlling the position of maximum electric field strength or the maximum temperature of the mechanical wire).

• If necessary, spacers can be equipped with know-art damping systems.

• Electric conductivity of extension clamps of the current conducting wire can be improved by bridging (shunting) or by other means if necessary.

• In case the task is to increase electrical clearances of conductors to ground (that is, only the geometric limit is to be extended), the inventive method can be applied along the whole transmission line or only to particular sections of the line (in one or more stringing spans, or in one or more spans).

• Mechanical wires of non-metallic material may be coated with metal or with other suitable material in order to make it possible to include them in design calculations of electric fields or to protect mechanical wires from electric fields.

• Mechanical wires made of metal may or may not perform an additional current conducting function, depending on how spacers and clamps are configured.

The object of the present invention is therefore a method for the application of a wire system consisting of a mechanical support wire or wires and current conducting wires for power transmission lines, comprising steps of attaching mechanical support wires on support structures of the transmission line directly or by means of insulators and joining separate current conducting wires to the mechanical support wires applying spacers and/or insulators. The cross-sectional area of current conducting wires is chosen to ensure that with current conducting wires being loaded with their rated current and with the ambient temperature being 30 °C, the temperature of said current conducting wires is greater than 80 °C but does not exceed 300 °C.

According to a preferred way of carrying out the inventive method, the cross-sectional area of current conducting wires is chosen to ensure that with current conducting wires being loaded with their rated current and with the ambient temperature being 30 °C, the temperature of the current conducting wires is greater than 100 °C but does not exceed 250 °C.

Another object of the invention is a method for the application of a wire system consisting of a mechanical support wire or wires and current conducting wires for power transmission lines, comprising steps of attaching mechanical support wires on support structures of the transmission line directly or by means of insulators and joining separate current conducting wires to the mechanical support wires applying spacers and/or insulators. The material, dimensions, and configuration of spacers and/or insulators and the material and cross-sectional area of the support wire are chosen in such a way that the temperature of the metallic support wire remains under 120 °C while the current conducting wires are loaded with their rated current.

A further object of our invention is a method for the application of a wire system consisting of a mechanical support wire or wires and current conducting wires for power transmission lines, comprising steps of attaching mechanical support wires on support structures of the transmission line and joining a separate current conducting wire to the mechanical support wires by means of insulators. The support wire is implemented as a ground wire.

According to a preferred way of carrying out the method, at locations subject to increased wind pressure at least one current conducting wire is disposed between the support wires, or current conducting wires are disposed on both sides of at least one support wire, with said current conducting wires being shifted in a substantially horizontal direction in the proximity of the spacers and/or insulators.

According to a preferred way of carrying out the inventive method, spacers and/or insulators are disposed at unequal intervals.

According to another preferred way of carrying out the inventive method, in the middle of the stringing span spacers and/or insulators are more densely positioned.

According to yet another preferred way of carrying out the inventive method, phase conductor wires of an existing transmission line are used as current conducting wires.

A further object of the invention is a method for the application of a wire system consisting of a mechanical support wire or wires and current conducting wires for power transmission lines, comprising steps of attaching mechanical support wires on support structures of the transmission line directly or by means of insulators and joining separate current conducting wires to the mechanical support wires applying spacers and/or insulators. The method can be characterised by that support wires are installed for reducing the tensile stress of existing phase conductor wires functioning as current conducting wires, with said support wires being installed such that existing phase conductor wires and support wires are tensioned with respect to ambient temperature to an extent that the tensile stress to which the current conducting wires are subjected is reduced by at least 20%.

According to a preferred way of carrying out the inventive method, support wires are installed for reducing the tensile stress of existing corroded-core ACSR conductors, with the support wires being tensioned with regard to ambient temperature to such an extent that the tensile stress of existing corroded-core ACSR conductors is reduced by at least 20%.

According to another preferred way of carrying out the inventive method, a wire composed of non-metallic structural material is applied as support wire.

According to yet another preferred way of carrying out the inventive method, at least one support wire fabricated of metallic material is complemented by at least one current conducting wire attached thereto, producing thereby a phase conductor bundle, with said support and current conducting wires being at the same potential and in the same phase.

According to still another preferred way of carrying out the inventive method, power transmission line conductors of different material and/or cross-sectional area and/or configuration are applied as support wires and as current conducting wires.

According to a further preferred way of carrying out the inventive method, the cross-sectional area and/or material of the support wire of the transmission line varies from span to span.

The configuration, operational characteristics, and possible applications of the inventive wire system are described in more detail with reference to the following drawings:

1. View of mechanical and current conducting wires arranged in a single bundle.

2. Wires of a bundle joined by means of a spacer.

3. Schematic view of joining a mechanical and a current conducting wire using a spacer.

4. Schematic view of joining one mechanical and two current conducting wires using a spacer.

5. Schematic view of joining one mechanical and three current conducting wires using a spacer.

6. Schematic view of joining two mechanical and two current conducting wires using a spacer.

7. Schematic sectional view of joining two mechanical wires and one current conducting wire using a spacer.

8. Schematic side view of joining two mechanical wires and one current conducting wire using a spacer. 9. Schematic top plan view of joining one mechanical and one current conducting wire using a spacer.

10. Sectional view of current conducting wires suspended by means of insulators on ground wires acting as mechanical wires.

11. Side view of current conducting wires suspended by means of insulators on ground wires acting as mechanical wires.

12. Sectional view of current conducting wire suspended by means of insulators on ground wire acting as mechanical wire.

13. Side view of current conducting wire suspended by means of insulators on ground wire acting as mechanical wire.

14. Schematic view of arrangement for stringing bundled current conducting and mechanical wires, comprising wire drums, braking device for the mechanical wire, spacer installing device, and wire stringing device.

15. Sectional view of the arrangement for stringing a wire bundle using special spacers.

16. Side view showing the configuration of pulleys in the arrangement for stringing a wire bundle using special spacers.

17. Bridging an existing wire clamp for increasing current rating of wire.

18. Side view of an arrangement for transforming conventional wires into partially current conducting wires by installing a mechanical wire.

19. Sectional view of an arrangement for transforming conventional wires into partially current conducting wires by installing a mechanical wire.

20. Schematic view of a possible configuration of spacers in an arrangement for transforming conventional wires into partially current conducting wires by installing a mechanical wire (no load on mechanical wire).

21. Schematic view of a possible configuration of spacers in an arrangement for transforming conventional wires into partially current conducting wires by installing a mechanical wire (loaded mechanical wire).

Fig. 1 shows the configuration of the inventive wire system. (When in the following description of the operational characteristics of the invention references are made to numeric values, it is intended solely as indicating the order of magnitude of certain parameters depending on material characteristics, and not as a restriction of the invention to the arrangement shown in Fig. 1, or in any other ways.) The mechanical wire 1 is joined to the current conducting wire 2 by means of spacers 3. Tensile stress of the mechanical wire 1 is in the range of a few hundred N/mm², while the current conducting wire is only subject to insignificant tensile stress. The mechanical wire 1 is pulled to the tension pole 6 or suspended to the suspension pole 7 by means of an insulator 4. A jumper 5 is formed from the current conducting wire 2. During the operation of the transmission line applying the wire system shown in Fig. 1, the mechanical wire 1 either does not heat up at all or heats up to a manageable extent for the following reasons (in the following description it is implied that the mechanical wire is made of steel, and the current conducting wire is made of aluminium, not restricting the scope of the invention to wires composed of these particular materials):

• As the mechanical wire 1 is made of steel, with a resistivity almost 7 times that of aluminium, current density in the mechanical wire 1 will be around one-seventh of the current density to which the current conducting wire 2 is subject to. (Current flowing through the mechanical wire can be practically eliminated by making spacers of materials with sufficiently poor conductivity, in which case thermal loss in steel due to conducted electric current is also eliminated.)

• Because specific thermal loss on a given cross section of a conductor is determined as the product of conductivity and the square of current density, the specific thermal loss in the mechanical wire 1 will be one-seventh of the specific thermal loss of the current conducting wire 2, so the increase in the temperature of the mechanical wire 1 will also be slight relative to the current conducting wire 1.

• The cross section of the mechanical wire 1 is in practice smaller than that of the current conducting wire 2, which means better cooling conditions (the mechanical wire has relatively larger surface and therefore better heat dissipation characteristics), so the mechanical wire 1 heats up due to electric current even to a lesser amount than described above.

• The spacers 3 join the mechanical wire 1 and the current conducting wire 2 only at particular locations, so heating of the mechanical wire 1 due to heat conduction from the current conducting wire 2 remains limited. Heat transfer from the current conducting wire can be further diminished by placing the spacers 3 further apart and by improving their heat insulation characteristics.

• With a bundle distance of a few dozen centimetres heat transfer from the current conducting wire 2 to the mechanical wire 1 (either by radiation or by conduction) is kept limited, so the latter does not heat up significantly. Heat transfer can be effectively regulated by adjusting design parameters such as the relative distance and relative position of wires, and by inserting heat insulation material between them (situated preferably on the surface of one or both wires).

• According to an alternative arrangement heat transfer from the current conducting wire 2 remains insignificant even if relatively short spacers are applied, because as the temperature of the current conducting wire 2 increases, so does the sag of the wire, which results in an increased distance between the wires, thereby diminishing heat transfer.

For the above reasons, thermal separation of the mechanical wire 1 and the current conducting wire 2 results in the fact that the current load of the transmission line increases the temperature of the mechanical wire 1 to a significantly smaller extent than the current conducting wire 2 is heated. Naturally, the temperature of the mechanical wire 1 is as much affected by changes in ambient temperature as the temperature of the current conducting wire. It can be concluded that the temperature of the mechanical wire 1 is dependent upon the current load of the transmission line only to a very little extent, and thus the condition of eliminating the geometrical temperature limit is fulfilled.

Similar conditions can be achieved by making the mechanical wire 1 of a material that does not elongate (or its elongation is insignificant) as the temperature thereof is rising. An example of such a material is Kevlar, of which the thermal coefficient of expansion is a small negative value. With the application of e.g. Kevlar, or other materials with similar characteristics, as the length of the mechanical wire does not increase with increasing temperature and so the thermal sag thereof is eliminated, it becomes possible to increase the number of points of attachment between the mechanical wire 1 and the current conducting wire 2, or even to join the two directly along the whole length of the wires. It is also of advantage with this arrangement that the extra load of sleet is smaller than in the case of separate wires, and, due to the low specific weight of Kevlar, support structures of the transmission line are subjected to a relatively small extra load. Applying a suitable material the current conducting wire 2 may be fully encircled or "entwined" by the mechanical wire 1. With the mechanical wire 1 being bound around the current conducting wire 2, it can partially or entirely cover the surface thereof. Cooling conditions of the current conducting wire 2 are better in case of partial covering. It can be advantageous to place spacers 3 close to one another along the line so as to keep the relative distance of the mechanical wire 1 and the current conducting wire 2 (and therefore the combined diameter of the wire bundle, crucial for sleet formation) under a reasonably low limit. Relative position of the wires (crucial for wind pressure) can also be optimised. To arrive at a more general conclusion it can be stated that, compared to conventional conductors, the clearance of the mechanical wire 1 to ground varies during the operation of the transmission line to a lesser degree if arrangements according to the present invention are applied, either as a result of thermal insulation between the mechanical wire 1 and the current conducting wire 2, or because the elongation of the mechanical wire 1 caused by increasing temperature is kept very low (or, as in the case of Kevlar, even pressed below zero) by the proper choice of materials. Furthermore, because the current conducting wire 2 is attached by means of spacers 3 to the mechanical wire 1 several times in any given span, an increase in the current load of the transmission line does result in a reduced electrical clearance of the current conducting wire 2 to ground (disregarding for the moment the effect of ambient temperature change). This should be considered a unique and very significant achievement in power transmission technology, as known solutions having similar results involve the application of special apparatuses. Thus one of the major inventive goals, namely extending the geometric thermal limit, is now realised. The current conducting wire 2 has no mechanical function apart from carrying its own weight. Because the current conducting wire 2 is subject to little mechanical load, both the normal and emergency thermal ratings will be higher than with previous solutions as changes of mechanical properties of the aluminium conductors no longer pose a danger, so the transfer capability of the power transmission line increases. The other major goal of the invention, namely extending the thermal limit posed by material properties, is thereby settled and practically realised.

The cross-sectional area of the current conducting wire 2 is typically constant along the whole transmission line (apart from some special cases), in sharp contrast with the cross sectional area, the material composition, and tensioning force of the mechanical wire 1 that can vary along the line (depending e.g. on the length of the longest span in a given stringing span, on wind pressure, sleet or ice load, tensile stress rating, safety margin, etc.) In case the mechanical wire 1 is electrically insulated from the current conducting wire 2 (some conceivable configurations are shown in Figs. 10, 11, 12, and 13), the mechanical wire 1 is practically free from being heated up when the transmission line is loaded because there is no current flow through it and, through clearances between the wires only an insignificant amount of heat energy can reach it.

In conclusion, the following can be put forth:

• Before the present invention, the worst of the material properties had to be taken into account when establishing mechanical and electrical ratings for conductors (disregarding for the moment composite and "gap" conductors), e.g. for aluminium, the rated tensile stress (~ 80-100 N/mm ) and the temperature range of annealing (starting around 80-100 °C).

• With the present invention, it is possible to take into account the best one of the material properties when designing a transmission line (for steel, tensile strength and fatigue, for aluminium, fatigue and thermal strength), giving consideration to the mechanical safety factor in the case of steel and excess heating during short-circuit elimination. • The clearance of the wire system to ground is essentially independent of the current of the transmission line.

Based on the inventive insight, a number of advantageous ways of carrying out the invention can be conceived, some of which are presented below:

The suspension configuration of the wire bundle constituted by the mechanical wire 1 and the current conducting wire 2 joined thereto by means of spacers 3 on the support structure is, as we have already seen, shown in Fig. 1, together with the jumper 5 at the tension pole 6 and the attachment of the mechanical wire 1 employing insulators 4 to tension poles 6 and suspension poles 7.

Fig. 2 shows a schematic view of how the spacers 3 connecting the mechanical wire 1 and the current conducting wire 2 are arranged within a span.

Figs. 3, 4, 5, and 6 show schematically the arrangement of a wire system with wires of a single phase joined by spacers 3, with the system consisting of one or more mechanical wire 1 and one or more current conducting wire 2.

Figs. 7, 8, and 9 show the cross-sectional and side elevational views of mechanical wires 1 and current conducting wires 2 placed close to one another within a bundle and joined by a spacer 3. Wires are spaced closely with the intent of minimising wind pressure and sleet load on the wire system. As it is shown in Figs. 8 and 9, guard rings 8 can be mounted on the mechanical wire 1 and/or on the current conducting wire 2 with a frequency that is needed, with the purpose of preventing damage to either. According to Fig. 8, to minimise wind pressure, spacers 3 joining the wires can be distributed in such a way that wires screen one another from wind in the entire operating temperature range.

Fig. 10 is a sectional view of another arrangement of the inventive wire system, taken along a plane perpendicular to the route of the line, while Fig. 1 1 shows the side elevational view of the same arrangement. As it can be seen in the figures, the mechanical wires 1 are attached to the poles 7, with current conducting wires 2 being joined at support structures and within the span to said mechanical wires 1 by means of insulators 4. Fig. 12 and 13 show a similar arrangement. According to Figs. 10, 1 1 , 12, and 13, the mechanical wires 1 have an additional role: they protect the transmission line against lightning strokes, in other words they act as ground wires. Exploiting the principle behind arrangements shown in Figs. 10, 1 1 , 12, and 13 it becomes possible - in case support structures and ground wires are sufficiently strong -, to join the conductors of an existing transmission line to the ground wires at one place or at several places along the span by means of insulators, creating essentially the mechanical wires 1 and current conducting wires 2 belonging to the scope of the present invention (only in this case the tensioning force is reduced gradually due to annealing, with the force taken up gradually by the mechanical wire 1).

In Fig. 14 a possible procedure for installing the wire system consisting of a separate mechanical wire 1 and current conducting wire 2 is shown. The mechanical wire 1 is paid out from a mechanical wire drum 11 by a wire stringing device 15 applying a guide rope 9, with a braking device 14 for the mechanical wire retarding the motion thereof. The current conducting wire 2 is can run off from the conductor wire drum 12 substantially without being braked. Both the mechanical wire 1 and the current conducting wire 2 is passed through the spacer-installing device 13 that mounts spacers 3 on the wires with the desired frequency to join the mechanical wire and the current conducting wire 2 (instead of using a spacer-installing machine 13, spacers can also be installed manually). Wires bound together by spacers 3 pass over pulleys 10 (or over a pulley system constituted by said pulleys 10), which are suspended directly on tension pole 6, whereas on suspension pole 6 they are suspended by means of an insulator string 4.

According to another procedure, the mechanical wire 1 is strung first, with the current conducting wire (wires) 2 being strung subsequently, using sheaves. Sheaves are attached either to the mechanical wire 1 or the current conducting wire 2 in such a way that they are disposed along the route of the transmission line with a given frequency. In practice it is preferable to attach the sheaves to the mechanical wire 1, with a guide rope being strung together with the mechanical wire 1. Spacers 3 are installed after the current conducting wires 2 have been strung. In this case, the spacers 3 and the sheaves are preferably fitted into a single combined device that serves as a spacer after installation is completed and sheaves are dismounted. According to this procedure, because the "extra load" of the current conducting wire 2 is absent, a reduced-capacity wire stringing device may be used, and final tensioning of the mechanical wire can be done simply through a gear drive. In addition, it is needless to apply large tensile forces during the stringing of the current conducting wire for keeping it at a fixed distance from the ground, as the mechanical wire (already strung) helps retain the desired height.

For enabling the spacers 3 to pass over pulleys 10 a number of advantageous solutions can be conceived. In a subset of these solutions spacers 3 are specially configured to perform this task. Fig. 15 shows an example, where the spacer 3 holds the current conducting wire 2 suspended on the mechanical wire 1 in a configuration resembling the attachment method used in ski lifts. The number of pulleys 10 needed for a single suspension unit can be determined taking into account the minimum bend radius of the mechanical wire 1 and also forces and displacements arising during stringing the wires. Pulleys 10 are attached to journals 16 through bearings 17. The journals 16 are attached to a steel structure 18. If needed, the steel structure 18 can be configured such that the pulleys 10 are self-adjusting (not shown in figure). To prevent the mechanical wire 1 from jumping off the pulleys 10, the mechanical wire 1 is preferably pushed downwards by additional spring-pulleys 10 (a solution applied in certain ski lifts). Some details of the pulley system herein described are shown in Fig. 16.

Fig. 17 shows a technique for increasing the current loadability of an extension clamp 19 of an existing conductor used according to the invention as a current conducting wire 2 by adding a bridging element 20 attached to the wire by clamps 21.

According to another aspect of the invention, the mechanical wire 1 is attached to conventional transmission line conductor wires 28 by insulators disposed within the span, with the mechanical wire 1 being attached to the support structures (or supported by pulleys) along the whole stringing span, and with the conventional conductor wires 28 being mechanically attached to but electrically insulated from one another. In the configuration shown in Fig. 20 the mechanical wire 1 has no effect on the conventional conductor wires 28 (conventional conductors are in "normal" position). However, when the load of the transmission line increases, the temperature of the conventional conductor wires 28 rise as well as the elongation thereof. Consequently, the sag of the conventional conductor wires 28 would also increase were it not for the mechanical wire 1 preventing the sag from increasing. As a result of the displacement of the hinged bars and insulators, the configuration changes into what is shown in Fig. 21, as the centre of gravity of the arrangement was originally, in the "normal" position not coincident with the plane determined by the mechanical wire 1. In symmetrical cases there are no displacements. The mechanical wire 1 is preferably passed through the trunk of the suspension poles 7 and attached to the trunk of tension poles 6. In addition to what has been put forth in the drawings and the description, the invention generally provides for preventing the thermally induced increase of the sag of conductors, either separately for individual phases or for arbitrarily made up groups of conductors by suspending them using a mechanical wire 1 for each group, with suspension on the mechanical wire carried out at one or more locations in the span (e.g. at 1/3 and 2/3 of the span, or asymmetrically on hilly terrain). According to a further variety of this aspect of the invention, the conventional conductor wires 28 are elevated even in their "normal" position by the mechanical wires 1. These varieties are essentially hybrid solutions, with the mechanical load (and consequently the role) of individual wires (purely mechanical wire or combined current conducting-mechanical wire) changing according to operating conditions. The invention can be advantageously applied for upgrading existing transmission lines in the following aspects:

• Dismounting the original conductor and replacing it with new mechanical and current conducting wires (similar to constructing a new transmission line, but utilises existing support structures).

• Installing a new mechanical wire applying the existing conductors as current conducting wires (with either leaving the tensile stress thereof unchanged, reducing or eliminating the tensile stress), increasing the current loadability of extension clamp of the existing transmission line (bridging original clamps to establish alternative path for a portion of the current), taking into consideration that tensile strength is no longer required of clamps.

• The technique described above is advantageous from another point of view as well: conductors with a corroded steel core (having reduced strength) do not have to be replaced, only supplemented by one or more mechanical wires. In addition, the current loadability of conductors also increases (limits of geometry and material properties pushed further). Mechanical wires can be installed either as a new member of an existing phase bundle, or in such a way that they replace an existing conductor wire (in the latter case a new current conducting wire should also be installed in order to retain or improve loadability).

• According to a further, novel and special aspect of the inventive wire system, existing conductors are applied as current conducting wires (one or more conductors for each phase), with at least one of the conductors getting covered with a layer of high-strength material. The additional high-strength layer acts as mechanical wire, so according to this aspect of the invention there is no separate mechanical wire in the system. Instead, the mechanical wire is formed of relatively low-diameter strands wound around the existing conductor which is to act as current conducting wire. The layer of mechanical strands can be added in a factory, with the conductors removed from support structures, or, more advantageously, with the conductors remaining in place, using a preferably self-driven machine moving along the transmission line conductors and comprising a device for making the strand on-site. The strand-making device either carries material necessary for its operation or reels off strands from a transport means that is following the progress of the device on the ground.

• Dismounting existing conductors from support structures and replacing them (after the necessary modification of support structures) with mechanical wires that also assume the function of ground wires, with the existing conductors being utilised as current conducting wires and with the ground/mechanical wires being attached to the existing conductors with insulators disposed along the span. The technique can be applied equally well in cases when the tensile stress which the existing conductors are subject to remains constant, diminishes, or disappears.

• In some circumstances (e.g. when a road is constructed under an operating transmission line) it may be necessary to increase electrical clearances of existing conductors to ground. In such a case a mechanical wire according to the present invention can be installed on the transmission line to provide that the extra sag of the conductor caused by temperature increase or by sleet becomes smaller. For further increasing electrical clearances to ground, the inventive technique can be supplemented with the installation of special tension insulator strings that are capable of longitudinal displacement in the direction of the line. The special insulator strings are mounted on suspension poles.

• The present invention makes it possible to restore electrical clearances of overhead conductors to ground in such cases when due to a (contingency or planned) electrical overload of the transmission line the aluminium has lost its thermal resilience and fails to return to its normal length. The clearance can be restored by increasing the tensioning force of the steel core of the conductor. In this case, as the constituent parts of the conductor no longer work together, it can be argued that they form essentially separate mechanical and current conducting wires. Corrosion protection of the steel core should be provided for.

• The method, arrangements and techniques described referring to Figs. 20, 21, 22, and 23.

The application of the inventive wire system will now illustrated with some concrete examples.

The methods and techniques according to the present invention can be utilised in the construction of new power transmission lines as well as in the modification (upgrading) of existing lines. Voltage levels typically used are 60 kV, 110 kV, 220 kV, 300 kV, 400 kV, 500 kV, 750 kV. The invention can be applied in relation to transmission lines with any of these, or with any other voltage levels. Examples that follow here present results obtained by approximations using parameters of transmission lines with a voltage level of 400 kV, unless indicated otherwise.

Example 1

The table shows the loadability of an aluminium wire in a conventional transmission line and in a line constructed according to the present invention. (Calculations were made assuming a temperature limit of 80 and 100 °C in case of the conventional arrangement and a temperature limit of 200 and 250 °C in the case of the inventive arrangement. Ambient conditions characteristic of Hungary were used, neglecting heat transfer between wires.)

* Wire subject to insignificant tensile load only.

With transmission lines constructed according to the present invention, the tensile load of aluminium wires can be kept at a minimum if wires are joined to the supporting mechanical wires at a sufficiently great number of locations.

Example 2

The following numeric example demonstrates the magnitude of certain parameters (wire shape approximated with a parabola)

F*D = L² *W/8, where

F: tensile force (kg)

D: sag (m)

L: span (m)

W: specific mass (kg/m)

If the current conducting wire is joined every 40 metres to the mechanical wire in a span with a length of 400 m, the above equation can remain true if both the tensile force and the sag of the wire is diminished to 1/10 of their original values. (To the reduced sag value the sag of the mechanical wire has to be added to obtain the total sag of the combined wire.) As the aluminium wire is suspended at several points, its tensile load is obviously low, so it can be allowed to loose much of its tensile strength at high temperatures. If spacers are installed with a greater frequency around the point of maximum sag (20 metres, or, if necessary, 10 metres apart), the sag of the current conducting wire can be further reduced.

Example 3

In this example the material of the mechanical wire can be zinc-coated steel, used for the construction of conventional transmission lines, AluClad steel, or alternatively, ACSR with a single aluminium layer. These types of wire, together with complementary pieces of equipment, are readily available from manufacturers without need for further development, so they are ideal for the construction of new transmission lines. For instance, if the construction of a new 400 kV transmission line applying 2*500/65 ACSR wires (with a cross-sectional area of 500 mm for aluminium and 65 mm for steel per wire) is pondered, it is preferable to consider building it with 1*130 mm² steel (AluClad or ACSR) and 2*500 mm² aluminium wires. The latter combination gives a loadability increased by approx. 50%, without a significant price difference.

When modifying an existing transmission line, the type of the mechanical wire should be chosen paying attention to several conditions.

If wire bundles of 3-4 wires are used on the transmission line, it is highly probable that adding a mechanical wire (of steel, AluClad, or ACSR) will not imply a rise of wind pressure and mechanical load that could not be compensated for by reinforcing support structures in the way it is usually done when upgrading a transmission line by reconductoring it with higher diameter conventional wires.

It is also possible to replace a single wire of a phase conductor bundle with a mechanical wire, with the others left in place and subsequently used as current conducting wires.

If the task is to increase the loadability of a non-bundled phase conductor, or a phase conductor bundle consisting of fewer wires, the solution is either the complete replacing of conductors

(this virtually amounts to constructing a new transmission line designed taking into account the parameters of existing structures), or the application of a lightweight mechanical wire that has high tensile strength (Kevlar, plastics, carbon fibres, etc.)

The tensile stress of the current conducting wire need not be reduced to zero in all cases. In most instances it is sufficient to reduce the stress e.g. to half of the original value to achieve an adequate degree of mechanical safety with the increased current load, with the application of fewer (and smaller diameter) mechanical wires that, apart from being lighter, bring about a smaller wind pressure.

Spacers Known art bundled phase conductors are joined together by means of spacers, for reasons of synchronising the movement of the wires and preventing wires from lashing together under forces caused by short circuits. These spacers usually have a length of 40 cm in Hungary. In other countries transmission lines with in-bundle distances of 30-40-50-60-80-100 cm are also constructed. The distance is dependent on conditions of the specific climate (if wires are too close, icing on neighbouring wires may result in the formation of a single big ice "block," leading to mechanical overload). Wire distances of transmission lines designed according to the present invention are determined by the same conditions as are used for designing conventional transmission lines.

Always adapted to specific conditions, spacers can be of conductive, non-conductive, or even of insulating types (e.g. they can be cap and pin glass insulators, occasionally used for suspending ground wires).

According to the present invention, a number of differently configured spacers can be conceived: joining 1-2 (occasionally 3) mechanical wires and one or several (1-2-3-4-5-6, etc.) current conducting wires. (See Figs. 1, 2, 3, 4, 5, 6)

Example 4

Original wires: 2*500/65 ACSR

New wires: 1 *260 Alumoweld + 2*643 Al (the cross-sectional area of the wires has increased - if calculations were made using the original quantity of aluminium, the decrease in the sag would be even more significant)

Sags for a 400 m span (with a maximum ambient temperature of 40 °C)

Example 5

Reinforcement of a corroded 350/40 ACSR wire operating at 220 kV with Kevlar mechanical wire (tensile load of the ACSR wire = 0.)

Span 300 m.

Original wire: 350/40 ACSR

New wires: Kevlar 49 + 350/40 ACSR

After the modification not only the tensile load of the ACSR wire is reduced to zero but, as an additional effect, the loadability of the transmission line also becomes higher. Support structures, however, need to be reinforced in the usual way because of the extra weight and wind pressure.

Advantageous technological outcomes of the inventive methods

The load rating of transmission lines designed according to the present invention can be set significantly higher than the ratings of earlier lines based on compromises forced by various constraints. Future transmission lines are preferably constructed according to methods described in the present invention, because with the application of the invention the capacity of the line can be increased by more than 50% with other technological and economic parameters kept constant.

Utilising the present invention, existing transmission lines can be upgraded to a drastically higher loadability without there being a need for significant modifications to support structures and their bases.

By installing an additional mechanical wire or wires and by using existing conductors as current conducting wires the problem posed by corroded-core, reduced strength ACSR conductors can be solved, significantly increasing at the same time the transmission capacities of the line.

It is also possible according to the invention to increase electrical clearances of conductors to ground (within the spans), not excluding possibilities for the application of other methods on the poles (for example, according to another invention tension insulator strings that are allowed to move in the direction of the line are installed on suspension poles).

The inventive method can be advantageously applied for upgrading transmission lines to higher voltage ratings. The above discussed advantages, related to reduced thermal sags, can help increase voltage ratings (together with solutions of other inventions for increasing electrical clearances if necessary), which can be further improved exploiting on the one hand reduced surface electric field strengths resulting from the application of the inventive wire system, and the possibilities for using higher-diameter wires (e.g. tubular wires) without difficulty on the other. By doubling the voltage rating and increasing the maximum allowed current by 50%, power transmission capacity of a transmission line can be tripled without significant modification of support structures and their bases.

Upgrading of existing transmission lines can be completed much faster with the application of the methods according to the invention than with conventional methods, thereby reducing the time a given line is out of service and the risk of failure caused by reduced system capacity. It is also of advantage that, compared to conventional solutions, requirements of manufacturing technology, installation, and operation to be met by current conducting wires are less demanding, so wires of simpler structure, lower strength, or more advantageous construction can be used. An example of improved construction conductors can be tubular wires that can substitute for more than one conventional wire because lower electric field strengths are generated due to their higher diameter, and because of their lower combined weight compared to conventional bundled conductors, and better utilisation of material concerning skin effect. As according to the invention it is allowable without doing damage to the conductors to generate situations (even for longer periods) when wire temperatures raise above their normal value, fast removal of ice or sleet from the conductors can be carried out regularly. Because of Joule loss, sleet and ice melts and disappears from current conducting wires and icing or sleet remains present only on the surface of mechanical wires. Thus the extra mechanical load generated by sleet is reduced. Sleet removal can be performed through increasing load, by making interchanges in the network, or changing power feed. Another method for sleet removal is producing a single or multiple-phase artificial load or artificial short-circuit (preferably at one end of the transmission line) e.g. within a substation by means of a ground disconnect switch to which the short-circuit current is fed from the network through the transmission line. In some cases another artificial combination can be of advantage, where the three phases of the transmission line are set in series connection so phase impedances add up from the feed point at one end of the transmission line to the artificial load (or short-circuit) located at the other end. Disconnection or short-circuit elimination times are increased taking into account the amount of sleet on conductors and weather conditions. Due to slower disconnection or short circuit elimination a larger-than-normal increase in conductor temperatures arises, which results in sleet falling off from current conducting wires. In principle, heating up of conductors can be performed for all phases at the same time, or with one phase heated up after another. The concrete implementation of the method should be established by making calculations of systemic effects on the overall transmission grid. Generating an artificial short circuit located at one terminal point and fed from the other is advantageous for a number of reasons:

• There are circuit breakers and protections on both sides, with one acting in case of a failure as reserve equipment for the other in short-circuit elimination. (For instance, in case distance protection is used, the short circuit is located by the forward-looking stage at the short circuit location and by the backward-looking stage at the feed location, with the protection issuing disconnection orders for circuit breakers at the local and the opposite-side substation with a predetermined and programmed time delay.)

• The artificial short circuit can be realised simply and is easily controllable.

• In case the short circuit occurs at the other end of the transmission line the break switch is not excessively loaded because the short-circuit current is relatively low, especially with a single-phase short circuit.

As the invention provides for performing sleet removing operations easily and on a regular basis, it becomes possible to partially disregard the effects of extra load generated by sleet and reduce the rated mechanical load of certain elements of the transmission line. Similarly, when designing the geometry of arrangements involving wires situated above one another, cases with the upper wire being subject to sleet load while the bottom one is free from sleet can be disregarded.

According to principles of the exemplary arrangements shown in Figs. 10 and 11, compact arrangements can be designed thanks to reduced vertical distances, as galloping is virtually impossible as a result of insulators disposed along the whole length of the span, and because the tendency of conductors to undergo vertical displacement relative to each other is reduced owing to regular sleet removal and mechanical connections between the wires. Also, due to the reduced phase spacing, impedance conditions of the transmission line (together with its role in power transmission) change for the better.

If, due to regular sleet removing, the effect of sleet load can be disregarded in dimensioning the modification to an existing transmission line, the extra margin of strength becomes available for other uses, such as supporting other extra mechanical loads, caused by additional wires or by wind pressure.

It is also of advantage that conductors subjected to disparate tensile forces are less prone to galloping.

Economic and market implications of the invention

If we compare costs of constructing a new transmission line according to the invention and construction costs of conventional solutions, it is found that, although the transmission line built according to the present invention has a loadability more than 1.5 times that of the conventional one, virtually no extra costs are involved.

Similarly, costs of increasing the capacity of existing power transmission lines applying the inventive method are considerably lower than they would be with conventional solutions. Installing new mechanical wires instead of replacing corroded-core ACSR conductors is an option that has not only lower costs but solves conductor strength problems and increases power transmission capacity.

Upgrading of existing transmission lines can be completed much faster with the application of the inventive methods which reduces losses caused by the line being out of service. A very significant advantage of the invention is that the time taken up by legal and technological procedures needed to increase power transmission capacities is dramatically shortened. This is especially important nowadays, as the deregulation of power markets is proceeding fast worldwide, creating a number of uncertainties unheard of before. Addition of new generation capacities is often not coordinated with transmission system operators, and the result of ongoing competition of existing power stations could be that the load structure of the power grid may change rapidly. Also, international power trade is often hampered by bottlenecks caused by the insufficient capacity of border-crossing transmission lines. The ability to rapidly increase their transmission capacity might therefore be of tremendous benefit for power trading companies.

Construction costs of a transmission line with improved sleet removing capabilities are lower than costs of conventional transmission lines because the extra load caused by sleet can be entirely or partially disregarded in dimensioning calculations.

Advantageous environmental outcomes of the invention The inventive method has significant positive environmental effects. Because transmission lines built according to the present invention have higher capacity, fewer transmission lines may be needed, which results in a reduced need of transforming the natural environment.

Modifying the majority of existing transmission lines according to the invention might solve capacity problems for a long time.

By increasing the capacity of the transmission grid it may become possible to utilise existing generating capacities to the fullest, without transmission restrictions, which means that, as the most cost-effective generating stations are the most modern and least polluting ones, pollution caused by power generation can be reduced.

Also, by using existing conductors already operating, the environmental load related to conductor manufacturing and reconductoring, as well as to the dumping or recycling of dismounted conductors can be reduced or eliminated.

Finally, as the height of support structures can be smaller than before, compact and visually unobtrusive transmission lines can be constructed.

List of references

1 mechanical supporting wire

2 current conducting wire

3 spacer

4 insulator

5 jumper

6 tension pole

7 suspension pole

8 guard ring

9 guide rope

10 pulley

11 mechanical wire drum

12 conductor wire drum

13 spacer installing device

14 braking device for mechanical wire

15 wire stringing device

16 journal

17 bearing

18 steel structure

19 clamp

20 bridging element

21 clamp for bridging element

28 conventional conductor wire

29 ground wire

Claims

Claims

1. Method for the application of a wire system consisting of a mechanical support wire or wires and current conducting wires for power transmission lines comprising steps of attaching mechanical support wires on support structures of the transmission line directly or by means of insulators and joining separate current conducting wires to the mechanical support wires applying spacers and/or insulators, characterised by that the cross- sectional area of current conducting wires is chosen to ensure that with current conducting wires being loaded with their rated current and with the ambient temperature being 30 °C, the temperature of said current conducting wires is greater than 80 °C but does not exceed 300 °C.

2. The method according to Claim 1, characterised by that the cross-sectional area of current conducting wires is chosen to ensure that with current conducting wires being loaded with their rated current and with the ambient temperature being 30 °C, the temperature of the current conducting wires is greater than 100 °C but does not exceed 250 °C.

3. Method for the application of a wire system consisting of a mechanical support wire or wires and current conducting wires for power transmission lines comprising steps of attaching mechanical support wires on support structures of the transmission line directly or by means of insulators and joining separate current conducting wires to the mechanical support wires applying spacers and/or insulators, characterised by that the material, dimensions, and configuration of spacers and/or insulators and the material and cross- sectional area of the support wire are chosen in such a way that the temperature of the metallic support wire remains under 120 °C while the current conducting wires are loaded with their rated current.

4. Method for the application of a wire system consisting of a mechanical support wire or wires and current conducting wires for power transmission lines comprising steps of attaching mechanical support wires on support structures of the transmission line and joining a separate current conducting wire to the mechanical support wires by means of insulators, characterised by that the support wire is implemented as a ground wire.

5. The method according to any one of the preceding claims, characterised by that at locations subject to increased wind pressure at least one current conducting wire is disposed between the support wires, or current conducting wires are disposed on both sides of at least one support wire, with said current conducting wires being shifted in a substantially horizontal direction in the proximity of the spacers and/or insulators.

6. The method according to any one of the preceding claims, characterised by that spacers and or insulators are disposed at unequal intervals.

7. The method according to any of the preceding claims, characterised by that in the middle of the stringing span spacers and/or insulators are more densely positioned.

8. The method according to any of the preceding claims, characterised by that phase conductor wires of an existing transmission line are used as current conducting wires.

9. Method for the application of a wire system consisting of a mechanical support wire or wires and current conducting wires for power transmission lines comprising steps of attaching mechanical support wires on support structures of the transmission line directly or by means of insulators and joining separate current conducting wires to the mechanical support wires applying spacers and/or insulators, characterised by that support wires are installed for reducing the tensile stress of existing phase conductor wires functioning as current conducting wires, with said support wires being installed such that existing phase conductor wires and support wires are tensioned with respect to ambient temperature to an extent that the tensile stress to which the current conducting wires are subjected is reduced by at least 20%.

10. The method according to Claim 10, characterised by that support wires are installed for reducing the tensile stress of existing corroded-core ACSR conductors, with the support wires being tensioned with regard to ambient temperature to such an extent that the tensile stress of existing corroded-core ACSR conductors is reduced by at least 20%.

11. The method according to any one of Claims 1-2 or Claims 5-10, characterised by that a wire composed of non-metallic structural material is applied as support wire.

12. The method according to any one of Claims 1-2 or Claims 5-10, characterised by that at least one support wire of metallic material is complemented by at least one current conducting wire attached thereto, producing thereby a phase conductor bundle, with said support and current conducting wires being at the same potential and in the same phase.

13. The method according to Claim 12, characterised by that power transmission line conductors of different material and or cross-sectional area and/or configuration are applied as support wires and as current conducting wires.

14. The method according to any one of the preceding claims, characterised by that the cross- sectional area and/or material of the support wire of the transmission line varies from span to span.