Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02G—INSTALLATION OF ELECTRIC CABLES OR LINES, OR OF COMBINED OPTICAL AND ELECTRIC CABLES OR LINES
  • H02G7/00—Overhead installations of electric lines or cables
  • H02G7/05—Suspension arrangements or devices for electric cables or lines
  • H02G7/06—Suspensions for lines or cables along a separate supporting wire, e.g. S-hook

Definitions

• 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.
• 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.
• 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.
• 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.
• 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.
• 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.”
• 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
• 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.
• 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.
• 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)
• the wire system should be designed along the following lines:
• aluminium wires or wire portions should be relieved of any mechanical function.
• 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.
• current conducting wire a current conducting function
• 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.
• 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.
• 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.
• 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.)
• 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).
• 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).
• 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).
• 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.
• 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.
• 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.
• 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.
• spacers and/or insulators are disposed at unequal intervals.
• spacers and/or insulators are more densely positioned.
• 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%.
• 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%.
• a wire composed of non-metallic structural material is applied as support wire.
• 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.
• 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.
• the cross-sectional area and/or material of the support wire of the transmission line varies from span to span.
• Fig. 1 shows the configuration of the inventive wire system.
• 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/mm 2 , 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.
• 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):
• 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.
• 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).
• 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.
• 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.
• 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.
• a material that does not elongate (or its elongation is insignificant) as the temperature thereof is rising.
• Kevlar of which the thermal coefficient of expansion is a small negative value.
• 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.
• 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.
• 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.
• 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).
• 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.)
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• a reduced-capacity wire stringing device may be used, and final tensioning of the mechanical wire can be done simply through a gear drive.
• 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.
• 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).
• the mechanical wire 1 is preferably pushed downwards by additional spring-pulleys 10 (a solution applied in certain ski lifts).
• 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.
• 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.
• the mechanical wire 1 has no effect on the conventional conductor wires 28 (conventional conductors are in "normal" position).
• 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.
• 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.
• the mechanical wire 1 is preferably passed through the trunk of the suspension poles 7 and attached to the trunk of tension poles 6.
• 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.
• 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:
• 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.
• 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.
• 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.
• 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 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.
• 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.)
• 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.
• 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.
• 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 mm 2 steel (AluClad or ACSR) and 2*500 mm 2 aluminium wires. The latter combination gives a loadability increased by approx. 50%, without a significant price difference.
• 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.
• a mechanical wire of steel, AluClad, or ACSR
• 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.
• 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).
• 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)
• 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)
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.

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