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Title:
A METHOD FOR MOUNTING SWITCHGEAR UNITS ON A LATTICE TOWER FOR HIGH-VOLTAGE OVERHEAD POWER LINES
Document Type and Number:
WIPO Patent Application WO/2021/074815
Kind Code:
A1
Abstract:
A method for mounting switchgear units (9) on a lattice tower (12) for high-voltage overhead electric transmission lines comprises the actions of preparing at least one pole (10) of the switchgear unit (9), capable of modifying the configuration of the electrical grid; placing said pole in proximity to a lattice tower (12) of the overhead electric transmission line; providing a first and a second primary coupling element (14, 16), able to support the weight of the pole (10) of the switchgear unit (9); connecting one end of each of these first and second primary coupling elements (14, 16) to the pole (10) of the switchgear unit (9); vertically raising the pole (10) of the switchgear unit (9), up to a height equal to or greater than a height (L); connecting the free end of the second primary coupling element (16) to the structure of the lattice tower (12) at a first anchorage point (P1); and loading the pole (10) of the switchgear unit (9) on the second primary coupling element (16), gradually loosening the first primary coupling element (14).

Inventors:
DI BARTOLOMEO EVARISTO (IT)
POLINELLI DARIO (IT)
SPEZIE ROBERTO (IT)
Application Number:
PCT/IB2020/059651
Publication Date:
April 22, 2021
Filing Date:
October 14, 2020
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
TERNA S P A (IT)
International Classes:
H02B5/02; E04H12/24; H02B3/00; H02B5/06; H02G1/00
Domestic Patent References:
WO2001050487A12001-07-12
Foreign References:
US20080061632A12008-03-13
DE29622637U11997-03-13
JP5822220B12015-11-24
Attorney, Agent or Firm:
SAVOCA, Agatino et al. (IT)
Download PDF:
Claims:
CLAIMS

1. Method for mounting switchgear units (9) on a lattice tower (12) for high-voltage overhead electric transmission lines, comprising the actions of: a) providing at least one pole (10) of the switchgear unit (9), comprising a line circuit breaker (lib) and/or line disconnectors (11a), adapted to modify the configuration of the power grid; b) placing said pole (10) of the switchgear unit (9) in proximity of a lattice tower (12) of the overhead electric transmission line; c) providing a first and a second primary coupling element (14, 16), adapted to support the weight of the pole (10) of the switchgear unit (9); d) connecting one end of each of said first and second primary coupling elements (14, 16) to the pole (10) of the switchgear unit (9); e) connecting the free end of the first primary coupling element (14) to a lifting apparatus (20), adapted to lift the pole (10) to a height equal to or higher than a height (L) at which said pole (10) is to be permanently positioned on the lattice tower (12); f) lifting the pole (10) of the switchgear unit (9) vertically to a height equal to or greater than said height (L), and approaching said pole (10) to the body of the lattice tower (12); g) connecting the free end of the second primary coupling element (16) to the structure of the lattice tower (12) at a first anchorage point (PI), at a height greater than the height (L) at which said pole (10) of the switchgear unit (9) is to be permanently positioned on the lattice tower (12), by means of a traction element (22), configured so as to tension and/or release the primary coupling elements (14, 16) towards the corresponding anchorage point; and h) loading the pole (10) of the switchgear unit (9) on the second primary coupling element (16) and, at the same time, gradually loosening the first primary coupling element (14), until the second primary coupling element (16) is perpendicular to the ground, following the total loading of the pole (10) of the switchgear unit (9).

2. Method according to claim 1, further comprising the operations of: i) disengaging the end of the first primary coupling element (14) from the hook of the lifting apparatus (20), and connecting said end of the first primary coupling element (14) to the structure of the lattice tower (12) at a second anchorage point (P2), at a height above the height (L) at which said pole (10) of the switchgear unit (9) is to be permanently positioned on the lattice tower (12); and j) translating the pole of the switchgear unit (10) from the first anchorage point (PI) to the second anchorage point (P2) until the first primary coupling element (14) is perpendicular to the ground.

3. Method according to any one of the preceding claims, wherein steps (h)-(j) are repeated by disengaging from the respective anchorage point (PI, P2) the end of the second to last primary coupling element (16, 14) to have been connected to the lattice tower (12), and attaching said end of the primary coupling element (16, 14) to an additional anchorage point (P3), until the pole (10) of the switchgear unit (9) is translated along the longitudinal axis y to the desired position.

4. Method according to any one of the preceding claims, further comprising the action of lowering the pole (10) of the switchgear unit (9) by means of said first and second primary coupling elements (14, 16) down to the height (L) at which said pole (10) of the switchgear unit (9) is to be permanently positioned on the lattice tower (12).

5. Method according to any one of the preceding claims, wherein the actions of roto- translating the pole (10) of the switchgear unit (9) among the anchorage points (PI, P2, P3) along a longitudinal axis (y) and/or of lowering the aforesaid pole by means of said first and second primary coupling elements (16, 14) down to the final positioning height (L) on the lattice tower (12) are carried out by pulling or releasing said first and second primary coupling elements (14, 16) by means of traction elements (22) to which said primary coupling elements (14, 16) are connected at said anchorage points (PI, P2, P3).

6. Method according to any one of the preceding claims, wherein step (d) is carried out by securing the ends of each of said first and second primary coupling elements (14, 16) to a lifting jig (18), which in turn is secured to the pole (10) of the switchgear unit (9), said lifting jig (18) being adapted to allow the coupling and lifting of the pole (10) of the switchgear unit (9). 7. Method according to claim 6, wherein step (d) is carried out by securing the ends of said first and second primary coupling elements (14, 16) to a point on the lifting jig (18) not belonging to the transverse centerline M of the pole of the switchgear unit (10), in case the distribution of the weights of the pole (10) of the switchgear unit (9) is not symmetrical with respect to said transverse centerline M, in such a way as to keep said pole (10) in a horizontal position during handling.

8. Method according to any one of the preceding claims, wherein the anchorage points (PI, P2, P3) are placed in spatial succession along the longitudinal axis (y).

9. Method according to any one of the preceding claims, comprising the action of controlling the oscillation of the pole (10) of the switchgear unit (9) by tightening or releasing guide elements (24) connected to said pole (10), in such a way as to avoid undesirable movements during the lifting, translation and lowering actions.

10. Method according to any one of the preceding claims, comprising the action of juxtaposing a plurality of poles (10) of the switchgear unit (9) on the lattice tower (12), each pole (10) of the switchgear unit (9) being adapted to be connected to one of the phases of the overhead electric transmission line.

11. Method according to any one of the preceding claims, wherein the anchorage points (PI, P2, P3) are defined at the mechanical joints to which several rods of the lattice grid forming the lower surface of the beam of the lattice tower (12) are joined.

12. Method according to any one of the preceding claims, wherein step (e) is carried out by connecting the first primary coupling element (14) to the lifting apparatus (20) by means of a secondary coupling element (20').

13. Method according to any one of the preceding claims, comprising the operation, when the anchorage points (PI, P2, P3) on the structure of the lattice tower (12) are placed on a vertical plane offset from the vertical positioning plane of the pole (10) of the switchgear unit (9), of transversally centering the pole (10) of the switchgear unit (9) along a transverse direction (z), perpendicular to the longitudinal axis (y), by means of a translation along said transverse direction (z).

14. Method according to any one of the preceding claims, comprising the operation of rotating the lateral poles (10) of the switchgear unit (9) about the longitudinal axis (y), by tensioning and releasing a traction element (22), attached at one end to the pole (10) of the switchgear unit (9), and at the other end to a further anchorage point (P), located on the lattice tower at the mechanical joints at which a plurality of members of the latticework are joined.

15. Method according to any one of the preceding claims, wherein, repeating the actions described in reverse sequence, it is possible to remove one pole (10) of the switchgear unit

(9).

Description:
A method for mounting switchgear units on a lattice tower for high-voltage overhead power lines

Technical field

This invention relates, in general, to the sector of infrastructures for the transport of electricity; more specifically, the invention relates to a method for mounting switchgear units on a lattice tower for high-voltage overhead electric transmission lines.

Prior art

High-voltage electrical switchgear devices are known for the operation of sections of an overhead electric transmission line, for example, the switchgear unit (for disconnection only) illustrated in patent document WO 01/50487.

Switchgear units are generally installed in power stations and substations to offer all or part of the functions typically found in an electrical substation. Typically, such equipment is placed on the ground and mounted on metal racks, in order to ensure, by means of the elevation from the ground, the electrical safety clearances of the live parts from the personnel and from the related transport vehicles and equipment.

The traditional installation in a power station involves transporting the metal rack and the high-voltage apparatus, forming the switchgear unit, to the installation site, moving the rack by means of an external lifting apparatus (typically a crane or a truck with crane), positioning it on a prearranged reinforced concrete foundation and fixing it thereto. Subsequently, the switchgear unit is moved by means of an external lifting device (typically a crane or a truck with crane), positioned on the rack, aligned and fixed thereto. This is followed by the activities of aligning the electrical phases to the normal operating position, wiring and testing.

In the case of installations of switchgear units on power line supports, such as, for example, the known disconnecting devices, traditionally, said switchgear units are mounted on elevated platforms, crossarms or cantilevered reticulated beams, specially constructed on said supports and accessible from above. In these cases, the installation consists of transportation to the work site, lifting by means of an external apparatus (crane, crane truck, truck with crane or helicopter) and positioning in the fixing position by means of the same lifting apparatus. This is followed by the actions of fixing, aligning the electrical phases to the normal operating position, wiring and testing.

In order to allow the movement of the aforesaid equipment, the final placement of said equipment is usually made accessible from above, without hindrance. In particularly complex cases, it is necessary to interrupt the raising of the lattice tower, used to accommodate the disconnecting device, during its construction, or to remove parts thereof to allow the placement of the switchgear apparatus, with the consequent prolongation of the mounting times and the related unavailability of the power line of which the lattice tower is a part.

Summary of invention

An object of this invention is to overcome the aforementioned problems.

To achieve this result, a method for moving and mounting electrical switchgear apparatuses (hereinafter referred to as “switchgear unit”) on lattice towers of the transmission grid is proposed. The method according to the invention allows the installation of these devices on towers that are already fully constructed, without having to interrupt the mounting of said towers and without the need to remove structural parts.

The procedure here proposed allows to reduce the downtime of the line to which the tower involved in the installation belongs. The procedure makes it possible to free the installation of the switchgear apparatuses from the activity of raising the lattice tower, and therefore simplifies the management of the operational stages of the construction site. The procedure allows the installation of the switchgear units on transmission line towers which are not accessible by crane trucks or bulky lifting equipment and without the use of helicopter installations. The method further allows the installation of the switchgear units inside the profile of the tower, without needing to install crossarms or cantilever beams, ensuring less visual interaction, since the apparatus is covered by the lattice of the tower, as well as a placement in a more barycentric position to minimize the structural requirements of the tower.

A method according to this invention comprises specific operating sequences aimed at hoisting a pole of the switchgear unit to a height equal to or greater than that in which this unit will be fixed to the tower, hooking a traction element, such as a chain hoist, to a specific point on the tower structure, gradually loading the aforesaid pole using said traction element and allowing its release from the first external lifting means. The process may be expediently repeated more than once, due to the use of several traction elements, coupled on special fittings to the beam of the "Delta" type tower used, until reaching, in subsequent steps, a specific alignment point relative to the vertical axis of the tower, suitable for placing the switchgear unit in the final mounting position provided on the tower.

A method according to this invention further comprises specific operating sequences for rotating the lateral poles of the switchgear unit. These operations make it possible to give the poles the required inclination in the operating configuration, as well as to bring them back to a vertical position, in order to facilitate their removal (reducing the working time for removing the poles of the switchgear unit) if replacement or maintenance in the factory is required. In the event of the switchgear unit out of service, these operations also allow the lateral poles of said unit to be rotated towards the central pole, reducing the overall dimensions and freeing up space on the tower for the installation of equipment for the electrical bypass of the switchgear unit. It is thus possible to re-establish, in a short time, the electrical operability of the line on which the switchgear unit is installed in case of unavailability of said switchgear unit or parts thereof. The proposed procedure has been designed to be applicable also in reverse, in order to remove the switchgear apparatus from the tower, without having to remove structural parts thereof.

The procedure allows to reduce the downtime of the power line to which the tower belongs, even in the case of removal of the apparatus for decommissioning or removal of said equipment or parts thereof for maintenance and testing in the factory.

The aforesaid and other objects and advantages are achieved, according to an aspect of the invention, by a method for mounting a pole of the switchgear unit on a lattice tower for high-voltage overhead electric transmission lines having the features defined in claim 1. Preferred embodiments of the invention are defined in the dependent claims.

Brief description of the drawings

The features of some preferred embodiments of a method according to the invention will now be described. Reference is made to the accompanying drawings, wherein:

- Fig. 1A and IB are respectively a schematic front and side view of a lattice tower, being part of a grid infrastructure intended to transport electricity in an overhead electric transmission line, and arranged for the installation of a switchgear unit, according to an embodiment of the invention;

- Fig. 2 A and 2B are respectively a schematic front and top view of the tower on which a switchgear unit is mounted, wherein a plurality of anchorage points on the tower is visible, according to an embodiment of the invention;

- Fig. 3A and 3B are schematic lateral views, respectively, of a lattice tower and of a pole of a switchgear unit arranged to be mounted on such a lattice tower, according to an embodiment of the invention;

- Fig. 4A and 4B are schematic views illustrating two steps of the mounting method wherein, respectively, the pole of the switchgear unit is first raised and then brought closer to the lattice tower, according to an embodiment of the invention; - Fig. 5A to 5C are schematic views illustrating a sequence of steps of the mounting method, wherein a pole of the switchgear unit is hooked to and loaded on a first anchorage point on the lattice tower structure (Fig. 5A) by means of a first traction element (in the example illustrated, a chain hoist). This loading involves the gradual unloading from an external crane used for the initial lifting (Fig. 5B), until it is possible to proceed with the removal of the hook of the external crane (Fig. 5C), according to an embodiment of the invention;

- Fig. 6A and 6B are schematic views illustrating two steps of the mounting method, wherein, respectively, a pole of the switchgear unit is translated by the action of a second chain hoist, connected to a second anchorage point on the lattice tower structure, while the first chain hoist is removed, according to an embodiment of the invention;

- Fig. 7A and 7B are schematic views illustrating two steps of the mounting method, respectively wherein a pole of the switchgear unit is further translated by a third traction element (in the illustrated example, a chain hoist), connected to a third anchorage point on the lattice tower structure, until a specific alignment point is reached on the vertical of the fixing position on the tower, from where it is then gradually lowered towards the final fixing position, according to an embodiment of the invention;

- Fig. 8A and 8B are schematic views illustrating the final steps of the mounting method wherein the three poles of the switchgear unit are rotated into the final operating position; and

- Fig. 9A and 9B are schematic views illustrating the operation for closing the poles of the switchgear unit (preliminary to the disassembly phase), which is carried out by acting on chain hoists connected to specific anchorage points arranged on the structure of the lattice tower.

Detailed description

Before describing in detail a plurality of embodiments of the invention, it should be clarified that the invention is not limited in its application to the construction details and configuration of the components presented in the following description or illustrated in the drawings. The invention is capable of assuming other embodiments and of being implemented or constructed in practice in different ways. It should also be understood that the phraseology and terminology have a descriptive purpose and should not be construed as limiting.

Furthermore, throughout this description and in the claims, with regard to the expressions indicating positions and orientations, the “vertical,” “longitudinal” and “transverse” directions are identified respectively by the “x,” “y” and “z” axes.

Referring by way of example to Fig. 1, a method for mounting a switchgear unit 9 on a support or lattice tower 12 for high-voltage overhead electric transmission lines comprises the action of providing at least one switchgear unit 9 adapted to carry out the operation of the sections a, b of the overhead power transmission line, on which this switchgear unit 9 is to be installed.

The switchgear unit 9 is adapted to modify the configuration of the electrical grid, interrupting and re-establishing its continuity at predetermined points, eliminating any electrical faults, and carrying out the safety operation by disconnecting and grounding parts of the system.

As illustrated by way of example in Fig. 1A and IB, the switchgear unit 9 comprises a plurality of poles 10, each in turn comprising a circuit breaker lib and line disconnectors 11a. These elements of said poles 10 of the switchgear unit 9 are housed inside a casing containing an insulating fluid and are connected to the conductors of the overhead electric transmission line.

It is understood that the method according to the invention also applies to similar or equivalent apparatuses, which incorporate for example one or more devices and additional functions with respect to simple disconnection, such as interruption of nominal and fault currents, as well as grounding sections of the transmission line. Furthermore, where the weights allow it, the method according to the invention may be applied directly to a three- phase switchgear unit complete with all three of its poles 10 (so that it may be installed on the lattice tower with a single lifting and mounting operation), as well as, in succession, to the three poles 10 forming a three-phase switchgear unit (which may therefore be hoisted and placed on the lattice tower 12 separately). Furthermore, in this description, the expression “lattice tower” means a traditional vertical support for the conductors of an overhead transmission line, the lattice tower of which is formed by a reticular structure that delimits an internal volume adapted to accommodate, at least in part, the profile of the switchgear unit 9.

The method further comprises the operations of placing the pole 10 of the switchgear unit 9 in proximity to a lattice tower 12 of the overhead electric transmission line; providing first and second primary coupling elements 14, 16 (in the form, for example, of ropes, cables, chains, belts, etc.), adapted to support the weight of the pole 10; connecting one end of each of said first and second primary coupling elements 14, 16 to said pole 10; connecting the free end of the first primary coupling element 14 (expediently, by means of a special secondary coupling element 20’, such as a rope, belt, etc.) to the hook of a lifting apparatus 20 (for example, a crane or a jib), adapted to lift the pole 10 to a height equal to or greater than a height L at which said pole must be firmly positioned on the lattice tower 12; vertically raising the pole 10 of the switchgear unit 9 up to a height equal to or greater than said height L (Fig. 4A); bringing everything closer to the lattice tower body (Fig. 4B); connecting the free end of the second primary coupling element 16 to the structure of the lattice tower 12 at a first anchorage point PI (located at a height greater than the height L) by means of a traction element 22 (for example a chain hoist, or other equipment or operating machine configured in such a way as to tighten and/or release the primary coupling elements 14, 16 in the direction of the corresponding anchorage points), as schematically shown in Fig. 5A; loading the pole 10 on the primary coupling element 16 and, at the same time, gradually loosening the primary coupling element 14 (Fig. 5B) until the second primary coupling element 16 is perpendicular to the ground, following the total loading of the pole 10 of the switchgear unit 9; unhooking and removing the lifting equipment 20 (Fig. 5C), together with the secondary coupling element 20’, if any.

If a further translation is required to bring the pole 10 of the switchgear unit 9 to the desired position, it is possible to proceed with the connection of the first primary coupling element 14 to the structure of the lattice tower 12, at a second anchorage point P2 (Fig. 6A), by means of a traction element 22 (for example a chain hoist). By means of a rototranslational action, obtained by acting in combination on the two traction elements 22, it is possible to move the pole 10 until the element 14 is perpendicular to the ground (Fig. 6B).

The method may be repeated several times, disengaging the second to last primary coupling element to have been connected to the lattice tower 12, and the respective traction element 22, and connecting them at a further anchoring point, until the pole 10 of the switchgear unit 9 is translated along the longitudinal axis y, to the desired position. The longitudinal axis y is positively oriented in the direction of approach of the pole 10 of the switchgear unit 9 to the vertical axis x of the lattice tower 12 (as schematically shown also in Fig. 4 A and 4B).

For example, if, following the first two translations along the longitudinal axis y, a third one is required, according to the method described above, to bring the pole 10 of the switchgear unit 9 to the final position, it will be possible, starting from the position of verticality of the primary coupling element 14 connected to the second anchorage point P2 (Fig. 6B), to connect the end of the second primary coupling element 16 to the structure of the lattice tower 12 at a third anchorage point P3 (Fig. 7A), and to translate the pole 10 of the switchgear unit 9 until it reaches the desired position along the longitudinal axis y (Fig. 7B).

Expediently, once the pole 10 of the switchgear unit 9 has been brought into the position corresponding to that in which it is to be fixed to the lattice tower 12, this pole 10 may be lowered by means of the traction elements 22, connected to the primary coupling elements 14, 16, to the height L wherein said pole 10 of the switchgear unit 9 is firmly positioned on the lattice tower 12 (Fig. 7B).

Preferably, the action of connecting one end of each of said first and second primary coupling elements 14, 16 to the pole 10 of the switchgear unit 9 is performed by securing these ends to a lifting jig 18 (Fig. 3B), which may be a rigid bar or a flexible element such as a rope, a cable, a belt, etc., adapted to allow the anchoring and lifting of the switchgear unit 10.

According to an embodiment, this action of connecting the primary coupling elements 14, 16 to the lifting jig 18, is performed by securing the ends of said first and second primary coupling elements 14, 16 to a point on the lifting jig 18 not belonging to the transversal center line M of the pole 10 of the switchgear unit 9 (Fig. 3B). This is particularly advantageous when the weight distribution of the pole is not symmetrical relative to this transverse center plane M, so that, in order to keep said pole 10 in a horizontal position during lifting, it is necessary to attach the primary coupling elements 14, 16 to the lifting jig 18 eccentrically with respect to the plane M.

Expediently, in relation to each pole 10 of the switchgear unit, the anchorage points PI, P2, P3 are aligned and lie on the same plane yz, perpendicular to the vertical axis x of the lattice tower 12.

The anchorage points PI, P2, P3 are suitably placed at the mechanical joints formed by the convergence of several rods of the lattice grid that make up the lower surface of the tower beam, that is the structural part of the tower 12 with a parallelepiped shape, arranged horizontally, with the major extension in the direction of the transverse axis z of the tower; this structure has the function of closing, from the perspective of static mechanics, the top part of the tower 12, by binding at their top the two structural branches that extend from the tower body and open transversely, progressively to the top, to create in the interior of the tower the space necessary for the final placement of the switchgear unit 9; the central conductor is also tensioned on this beam, and the peaks used to anchor the ground wires as well as the cantilevered crossarms for the attachment of the lateral conductors may be connected thereto.

The aforesaid anchorage points PI, P2, P3, engaged in successive moments, are placed in spatial succession on the structure of the lattice tower 12 along the longitudinal axis y (illustrated schematically in Fig. 2B and 3A). According to an embodiment, the anchorage points PI and P3, around which the first and last rototranslational moving of the pole 10 of the switchgear unit 9 occur respectively, are located on the outer perimeter sides of the structure of the lattice tower 12, while the intermediate anchorage points P2 are interposed between these terminal anchorage points PI, P3 along the axis y.

According to an embodiment, the method further comprises the action of controlling the oscillation of the pole 10 of the switchgear unit 9, by tightening or releasing guide elements 24 (Fig. 3B), connected to the same pole 10, so as to avoid unwanted movements of the pole during the actions of lifting, translation and lowering.

According to a further embodiment, the method further comprises the action of juxtaposing a plurality of poles 10 of the switchgear unit 9 at the same height L of the lattice tower 12 (Fig. 8A and 8B), each pole 10 of the switchgear unit 9 being adapted to be connected to one of the phases of the overhead electric transmission line.

According to an embodiment, a further transverse centering action is provided for the pole 10 of the switchgear unit 9 along a direction z perpendicular to the longitudinal axis y (visible for example in Fig. 2B, 8A and 8B). It is in fact possible that the anchorage points PI, P2, P3 on the beam of the lattice tower 12 are placed on a vertical plane that does not coincide with the vertical positioning plane of the pole of the switchgear unit (as shown by way of example in Fig. 8A, wherein a distance d between the two vertical planes is visible). This may be due to the fact that the anchorage points are preferably located at the structural joints of the lower face of the lattice tower beam, which are not always placed on the vertical of the final support point of the unit 10. In this case, once the pole 10 of the switchgear unit 9 has been aligned in the desired position on the plane xy, it may be centered in the final position with a further movement along the axis z, for example, by means of a translation conducted by the guide elements 24.

According to an embodiment, the method further comprises the action of rotating the lateral poles 10 of the switchgear unit 9 about the longitudinal axis y to give them the inclination required by the operating configuration (Fig. 8B), or an inclination towards the central pole, aimed at minimizing the dimensions of the switchgear unit (Fig. 9B) in exceptional conditions (service outage due to a fault), as a preliminary activity for disassembly and removal of the lateral poles 10 of the switchgear unit 9. In this case, the rotation of the lateral pole 10 of the switchgear unit 9 is carried out by releasing or pulling a traction element 22, attached at one end to the pole 10 of the switchgear unit 9, by means of suitable belts 26, if necessary, and, at the other end to a further anchorage point P, defined on the lattice tower at the mechanical joints at which several rods of the lattice are joined and, preferably, coinciding with one of the anchorage points PI, P2, P3 intended for handling the other poles 10 (Fig. 9A).

According to an embodiment, the method may be applied by repeating the actions described in reverse order, to remove a pole 10 of the switchgear unit 9, for example, if it is necessary to replace it or to carry out maintenance or overhaul in the factory.

Various aspects and embodiments of a method for mounting switchgear units on a lattice tower for high-voltage overhead electric transmission lines according to the invention have been described. It is understood that each embodiment may be combined with any other embodiment. Furthermore, the invention is not limited to the described embodiments, but may be varied within the scope defined by the appended claims.