Abstract:
A by-pass system for overhead power lines may include: a housing; a bearing frame in the housing; an outdoor termination linked to the bearing frame; and/or an electrical cable electrically connected to the outdoor termination. The bearing frame may be configured to move between a stand-by position of the outdoor termination and an operating position of the outdoor termination. A by-pass system for overhead power lines may include: a housing; a bearing frame connected to the housing; an outdoor termination connected to the bearing frame; and/or an electrical cable electrically connected to the outdoor termination. The bearing frame may be configured to move between a stand-by position of the outdoor termination and an operating position of the outdoor termination.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a by-pass system for overhead power lines. 
       BACKGROUND OF THE INVENTION 
       [0002]    An overhead power line is an aerial electric power transmission line, comprising one or more bare electric conductors suspended by towers or pylons. Since most of the insulation is provided by air, overhead power lines are generally a convenient method of transmission for large quantities of electric energy and are therefore mainly used for carrying high voltage (HV) current (typically higher than 30-35 kV). The overhead power lines need towers for being supported and insulators for insulating the structure of the towers (typically lattice type steel towers) from each conductor of the overhead electric energy transmission line; the ends of the insulated cable are connected to the overhead power lines at the relevant terminal stations or substations by means of components, called terminations, suitable to provide the required transition from the bare conductor of the aerial line, insulated by air, to a cable, having a conductor covered by an insulation layer and an earthed electric screening. 
         [0003]    Overhead power lines typically comprise substations as part of electrical generation, transmission, and distribution system. For example, substations transform voltage from high to low, or the reverse, connect the overhead power lines to cabled lines, or perform any of several other functions of the electric network. 
         [0004]    Ordinary and extraordinary maintenance need to be performed on overhead power lines, especially in the substations, for example when refurbishment and reconstruction of tower and overhead power lines occurs; when restoration or expansion in substations is required; when power transformers, circuit breakers, switchgears, shunts, or other components of a substation are to be replaced. 
         [0005]    Such operations are performed by disconnecting all the components involved in the maintenance activity from the electric transmission line. Temporary by-pass systems which connect input and output points within the substations are used in order to guarantee the continuity of electric power supply to the users during the maintenance period. Typically, at least one of the ends of the by-pass system, or both of them, is connected to the overhead power line. 
         [0006]    An example of by-pass system for overhead power lines is described in HVSBL January 2006 by Silec Cable (www.sileccable.com/Portals/france/pdf/en/2151_HVSBL.pdf). 
         [0007]    According to this publication, a three phase High Voltage Stand-By Link (HVSBL) system is composed of three lengths of cable equipped with two synthetic terminations pre-mounted in factory; three dedicated drums allowing storage, transportation and unwinding and rewinding of the lengths equipped with their terminations; six metallic structures for supporting the terminations during use (optional). 
         [0008]    The illustrated link systems are conditioned on dedicated metallic drums fitted out to contain and protect the cable equipped with its two terminations. A three phase link system may comprise one single drum of 2.6 m in diameter equipped with three compartments allowing to install on the same drum the three phases of a 90 kV HVSBL of 20 m, to three specific drums of 4.7 m each one containing one phase of a 225 kV HVSBL of 350 m. Generally, the terminations are installed in protections (tube or under-frame) positioned and fastened on the inner side of the drum (for transportation). Termination length increases with voltage and can be comprised between 1.8 m for 90 kV and 2.8 m for 225 kV. Drums delivered, laying equipment and routine tools are transported by truck from a storage yard to the installation site. A metallic structure supporting the terminations during operation can be a metallic structure allowing the mechanical support of a termination; each termination is lifted by a crane for being positioned on the top of a respective metallic structure and mechanically coupled thereto. 
         [0009]    Typically, the installation procedure of temporary by-pass links for a three-phase power line comprises the following steps:
       unloading three link-bearing drums from a truck, by means of a crane;   unwinding a cable length of each link from each drum and lay it down to the site of connection of the outdoor termination thereof;   providing the site of connection with a supporting structure for each outdoor termination of each link;   connecting each outdoor termination to the overhead power line and the other cable end to another power line.       
 
         [0014]    Such a procedure takes a substantial amount of time (e.g. many work weeks, especially in case of termination for voltage higher than 200 kV), and this is a critical, especially in case of a line failure to be restored. 
         [0015]    Due to the necessity of maintaining or repairing overhead power lines, by-passing certain positions or points of an electric energy transmission line is usually a mandatory operation to guarantee safe condition and to guarantee the electric power supply to the users. 
         [0016]    The Applicant has observed that it would be advantageous to have short operating time for providing by-pass on electric energy transmission lines. 
         [0017]    In particular, the Applicant has tackled the problem of providing a by-pass system for overhead power lines which requires shorter time and few staff for being installed in the field, compared with conventional ones. 
       SUMMARY OF THE INVENTION 
       [0018]    The Applicant found that the above mentioned problems can be solved by a by-pass link system for AC high voltage electric lines comprising, for each phase, an outdoor termination, a cable length and a cable joint, pre-assembled and transportable to the site of connection with the overhead power line. 
         [0019]    In particular, the Applicant has found that quick installation of a by-pass link system can be obtained by arranging an outdoor termination, a cable length and a cable joint on a supporting apparatus, movable from an idle position to an operating position and further acting as a bearing structure for supporting the outdoor termination in operation mode for the time during which the by-pass link is operated. 
         [0020]    In one aspect, the present invention relates to a by-pass system for overhead power lines comprising
       a housing;   a bearing frame in said housing,   an outdoor termination linked to the bearing frame,
 
wherein said bearing frame is movable between a stand-by position and an operating position of the outdoor termination;
   an electrical cable electrically connected to outdoor termination.       
 
         [0025]    In a preferred embodiment the housing of the present by-pass is transportable. In particular, a transportable housing can be arranged on a vehicle or can be part of a vehicle. 
         [0026]    In the stand-by position the outdoor termination is inside said housing, so that transportation can be enabled with reduced bulk, and extends at least partially outside said housing in operating position of the outdoor termination. 
         [0027]    Preferably, said electrical cable is attached to the bearing frame for being moved integrally with said outdoor termination between the stand-by position and the operating position of the outdoor termination. 
         [0028]    Preferably, said bearing frame is rotatable within the housing about an axis of rotation for moving from the stand-by position to the operating position. 
         [0029]    Conveniently, typically for use for a three phase electrical line, three bearing frames are housed within the housing. 
         [0030]    Preferably, at least two bearing frames are spaced lengthwise within the housing. 
         [0031]    Preferably, three bearing frames are housed within the housing, and the relevant axes of rotation are at angle with each other in the vertical plane. 
         [0032]    In a preferred embodiment, the bearing frame comprises a beam having a substantially curved shape, said outdoor termination is mechanically secured to a first end of said beam and said electrical cable is attached to said beam. Preferably, said bearing frame comprises a plurality of struts having first ends attached to said beam and second ends converging towards a hinge forming the axis of rotation of the bearing frame. 
         [0033]    Preferably the by-pass system comprises a central bearing frame and two side bearing frames holding relevant outdoor terminations, arranged on opposite sides relative to the central bearing frame, in which the axis of rotation of the central bearing frame has a substantially horizontal lay and the axes of rotation of the side bearing frames are inclined relative to the axis of rotation of the central bearing frame, whereby the central bearing frame is rotatable in a first substantially vertical plane and the side bearing frames are rotatable in respective second and third planes, diverging upwise. 
         [0034]    Preferably, a prefabricated cable joint is connected to the end of the electrical cable opposite to the end connected to the outdoor termination. 
         [0035]    Advantageously, the cable joint provided at the second end of the electrical cable is of the type enabling quick connection to the electric network (plug-in connection). 
         [0036]    Preferably, the housing holds an actuator operably connected with the bearing frame for causing the movement thereof between said stand-by position and said operating position of the outdoor termination. 
         [0037]    More preferably, said actuator is a linear actuator, operating on an axis not intersecting the axis of rotation of the bearing frame. 
         [0038]    In a second aspect the present invention relates to a method for operating a by-pass of a section of an electric line having an overhead end, which comprises:
       providing a by-pass system including a bearing frame contained in a housing, with an outdoor termination linked to the bearing frame and an electrical cable electrically connected to said outdoor termination at an end thereof;   disposing said by-pass system in the proximity of said section of an electric line, while bearing frame is in a stand-by position;   moving said bearing frame in an operating position of the outdoor termination;   electrically connecting said outdoor termination to said overhead end of the electric line section.       
 
         [0043]    Preferably, the method further comprises providing a prefabricated cable joint attached to an end of said electrical cable opposite to the end electrically connected to said outdoor termination and electrically connecting said prefabricated joint to an end of said section of an electric line opposite to said overhead end. 
         [0044]    Within the present description, the term “transportable” means designed for being transferred from a place, for example a remote storage, to the place of operation. 
         [0045]    The term “outdoor termination” as used herein refers to a component in which an end of an insulated electric cable is accommodated, having a connector for connection with an aerial electric line, connected with the cable conductor, and a insulation and screening structure suitable for providing insulation between the connector and the earth. 
         [0046]    Within the present description, with “active position” or “operating position” it is meant a position in which the outdoor termination can be electrically connected to an overhead power line. In this position the termination is arranged for operating in the line, both from a mechanical and the electrical point of view . 
         [0047]    Within the present description, with “stand-by position” it is meant a position in which the outdoor termination is housed and enveloped inside the housing for protection, storage and transportation. 
         [0048]    Within the present description, as “electrical cable” is intended an insulated electrical cable, unless otherwise specified. 
         [0049]    The bearing frames allow the electrical connection lines of the by-pass system as a whole, and the outdoor terminations in particular, to be easily and quickly placed in a condition ready for operation. This allows avoiding the need to perform a direct management of the outdoor terminations which require hauling and supporting means for being moved and transported as independent parts of a by-pass link. 
         [0050]    The bearing frame allows the outdoor termination to be held in position for the electric connection without the need of mounting additional props or the like, as required by the known by-pass systems. 
         [0051]    Preferably, the housing is associated with a plurality of wheels for road transportation. 
         [0052]    More preferably, the housing is supported on a truck trailer. 
         [0053]    Preferably, the housing comprises side walls, a top wall and a base wall, said walls forming a container enclosing the bearing frame and the electrical connection line when the bearing frame is in stand-by position. 
         [0054]    Preferably, at least said top wall is at least partly removable to provide a top opening in the container. 
         [0055]    Within the present description the term “horizontal” denotes a spatial orientation substantially parallel to the ground. 
         [0056]    Preferably, the central bearing frame and the respective outdoor termination lie in a substantially vertical plane, the axis of rotation of the bearing frame being perpendicular to such vertical plane. 
         [0057]    Within the present description the term “vertical” denotes a spatial orientation substantially perpendicular to the ground. 
         [0058]    In the preferred embodiment of the invention the side bearing frames and the respective outdoor terminations lie in planes skewed relative to the vertical plane, the axes of rotation of the side bearing frames being perpendicular to the respective skewed plane. 
         [0059]    For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term “about”. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0060]    The present invention will be now described more fully hereinafter with reference to the accompanying drawings. 
           [0061]      FIG. 1  is a schematic side view of a by-pass system for overhead power lines, according to an embodiment of the present invention, in a stand by position. 
           [0062]      FIG. 2  is a schematic lateral view of the by-pass system for overhead power lines of  FIG. 1  in an operating position. 
           [0063]      FIG. 3  is a top view of the by-pass system for overhead power lines of  FIG. 2 . 
           [0064]      FIG. 4  is a rear view of the by-pass system for overhead power lines of  FIG. 2 . 
           [0065]      FIG. 5  is a detail of the bearing frame and of the termination and cable attached thereto. 
           [0066]      FIG. 6  is a detail of a phase of the movement to locate the termination and bearing frame in operating position. 
           [0067]      FIG. 7  is a detail showing the termination and bearing frame secured in the operating position. 
       
    
    
     DETAILED DESCRIPTION 
       [0068]    With reference to the annexed figures, reference numeral  1  globally denotes a by-pass system for overhead power lines. 
         [0069]    The by-pass system of the invention is adapted to be used for by-passing a section of an electrical line wherein at least one by-pass point is overhead. The by-pass system of the invention is preferably used on high and very high voltage electrical lines, wherein by high voltage it is meant a voltage in the range between 30 kV and 150 kV and by very high voltage it is meant a voltage higher than 150 kV. 
         [0070]    The by-pass system  1  shown in the figures is an example for use on 220 kV voltage lines and the relevant substations. 
         [0071]    The by-pass system comprises three bearing frames  2 , arranged within a housing H, which are movable between a stand-by position (shown in  FIG. 1 ) and an active or operating position (shown in  FIG. 2 ). 
         [0072]    An electrical connection line  9 , comprising an electrical cable  4  and an outdoor termination  3  is supported by each bearing frame  2 . 
         [0073]    As shown in  FIG. 2 , the outdoor termination  3  is secured, at its bottom end  3   b,  to a baseplate  15  of the relevant bearing frame  2  and has its upper end  3   a  ready for being electrically connected to the overhead power line via an aerial conductor  3   c  when the by-pass system is in operating position. 
         [0074]    The electrical cable  4  has its first end  4   a  electrically and mechanically connected to the outdoor termination  3 . The second end  4   b  of the electrical cable  4  is ready for being connected to a cable  100  ( FIGS. 2 and 3 ), for example an electrical cable intended to be electrically connected to the second by-pass point (as shall be better explained hereinafter). 
         [0075]    The electrical cable  4  is attached to the relevant bearing frame  2  for being moved integrally with the outdoor termination  3  between the stand-by position and the operation position of the by-pass system  1 . 
         [0076]    The by-pass system  1  further comprises actuators  5  active on the relevant bearing frames  2  for moving the same between the stand-by position and the active position. 
         [0077]    The actuators  5  are preferably linear actuators, such as hydraulic jacks, screw jacks or the like. Alternatively, other actuators can be used, such as gear type actuators or the like. 
         [0078]    In a further alternative, the actuators can be missing and, in such case, the bearing frames  2  are moved in operating position by means of an external apparatus, such as a crane or the like. 
         [0079]    The bearing frames  2  comprise a beam  6  having a substantially curved shape. In particular, the beam  6  has two substantially rectilinear end portions  6   a,    6   b,  upper and lower respectively, joined to each other by a curved portion  6   c.  As from  FIG. 2 , the two rectilinear portions  6   a,    6   b  have axes a1 and a2 which are at an angle α to each other. The angle α ranges between 15° and 80°, preferably between 30° and 60°, even more preferably is of about 45°, depending on the overall size of the housing, in order to have the bearing frame  2  and the outdoor termination  3  fully enclosed within the housing H and to have the outdoor termination  3  and the second cable end  4   b  in a position ready for operation when the bearing frame  2  is raised. 
         [0080]    In a preferred embodiment of the invention, the beam  6  is made of steel and has a cross-section designed to maximise the ratio between bending and twisting strength and weight. For example, the beam  6  can be a square tube, or can have T or U shaped cross-section. 
         [0081]    The outdoor termination  3  is steadily secured to the upper end portion  6   a  of the beam  6  and the second end  4   b  of the electrical cable  4  is mechanically supported to the lower end portion  6   b  of the beam  6 . 
         [0082]    Preferably, the electrical cable  4  is secured to the beam  6  in a few points along the beam, in addition to the upper and lower end portions  6   a,    6   b  of the beam  6 , by collars  6   d  or the like. 
         [0083]    The bearing frames  2  comprise a hinge  7  rotatable about an axis of rotation X1. 
         [0084]    In the present description and in the following claims, by “hinge” it is meant any structural element that forms a constraint which allows the bearing frames  2  to rotate about an axis of rotation. 
         [0085]    In the embodiment shown in the annexed figures, hinge  7  is an assembly including a sleeve  7   a  rotating about a pin  7   b  supported by the crossbeam  18  of the housing H. The hinge  7  is arranged spaced apart from the beam  6  by the side of the beam concavity. 
         [0086]    The hinge  7  is connected to the beam  6  by means of a plurality of struts  8  having first ends  8   a  connected to the beam  6  and second ends  8   b  converging towards the axis of rotation X1 and connected to the sleeve  7   a  of hinge  7 . 
         [0087]    The bearing frames  2  are rotatable about the axes of rotation X1, X2, X3, respectively. The passage of the bearing frames  2  from the stand-by position to the active position takes place through the rotation of the same about said axes of rotation X1, X2, X3. 
         [0088]    In order to carry out the movement of the bearing frames  2 , the actuator  5  is active on the bearing frames  2 . 
         [0089]    The actuator  5  is set up for exerting a direct force along a substantially rectilinear direction that does not intersect the axis of rotation X1, X2, X3 (as the case may be) of the bearing frames  2 . In particular, actuator  5  comprises two ends  5   a,    5   b,  respectively hinged to the bearing frame  2  and to a platform  10  of the housing H. In particular, end  5   a  of the actuator  5 , hinged to the bearing frame  2 , is arranged near the upper end portion  6   a  of the beam  6  of the bearing frame  2 , close to the outdoor termination  3 . 
         [0090]    In this way, the force exerted by the actuator  5  causes the rotation of the bearing frame  2  around the hinge  7 . 
         [0091]    The housing H of the by-pass system  1  further comprises supporting elements  11 ,  12  on which the bearing frames  2  rest when in the stand-by position. The supporting elements  11 ,  12  are preferably in the form of bracings or struts, solid with the platform  10  of the housing H, so as to hold and lock firmly the bearing frames  2  and the outdoor termination  3  relative to platform  10  during transportation. 
         [0092]    The supporting elements  11  preferably act on the upper end portion  6   a  of the beam  6  of the bearing frame  2 . 
         [0093]    Preferably, the supporting elements  12  act on the outdoor termination  3  at the upper end  3   a  of the same ( FIG. 1 ). 
         [0094]    As from  FIG. 2 , the bearing frames  2  are detached from the supporting elements  11 ,  12  when the actuators  5  are operated to raise the bearing frames in the operating position. 
         [0095]    If convenient, the supporting elements  11 ,  12  can be removed during the by-pass system operation (and placed again in position for transportation). 
         [0096]    When a bearing frame  2  is raised in the operating position, as shown in  FIGS. 6 and 7 , crosspieces  13  are located on the housing H (for example manually) and attached thereto by screws, fasteners or the like. 
         [0097]    Conveniently, as shown in  FIG. 6 , the bearing frame  2  is raised higher than the final operating position, allowing room to insert and secure the crosspieces  13 , and thereafter lowered ( FIG. 7 ) to locate the bearings  13   a,  attached to the baseplate  15 , over the crosspieces  13 . 
         [0098]    When the bearing frame  2  is in its final operating position the bearings  13   a  can be firmly secured to the crosspieces  13 , enabling the actuator  5  to be relieved from the load. 
         [0099]    The housing H is conveniently made in the form of a rigid frame extending over the platform  10 . Conveniently the housing H has the size of a freight container, so that it can be carried by a truck trailer, or, alternatively, as shown in  FIGS. 1-4 , it can itself be equipped with a plurality of wheels  14  so as to form a trailer or semitrailer. 
         [0100]    The housing H conveniently comprises a platform  10 , side walls  16 , and a top wall  17 . Such walls form a containment case enclosing the bearing frames  2  and the outdoor terminations  3  when the bearing frames  2  are in stand-by position. 
         [0101]    The top wall  17  is at least partly movable for forming a top opening, so that the outdoor terminations  3  can protrude out of the housing H when the bearing frames  2  are in the active position, as shown in  FIGS. 2 and 4 . 
         [0102]    Preferably, the side walls  16  are movable too, for allowing easier access to the inside of the apparatus. 
         [0103]    In a preferred embodiment of the invention, a by-pass system  1  comprises three outdoor terminations  3  (one for each of the three phases of an overhead power line) to each one of which respective bearing frames  2  are associated. The bearing frames  2  and the other elements of the by-pass system  1  described above and associated to each outdoor termination  3  are substantially identical to each other with the exception of the following. 
         [0104]    The bearing frames  2  of each outdoor termination  3  are supported on a crossbeam  18  of the housing H and are rotatable about respective axes of rotation X1, X2, X3 ( FIG. 4 ). Such axes of rotation X1, X2, X3 are not parallel to each other. 
         [0105]    In particular, the central bearing frame  2 C is supported with rotation axis X1 with substantially horizontal lay, while the left and right bearing frames  2 L and  2 R, arranged on opposite sides relative to the central one, have axes of rotation X2, X3 inclined in opposite directions. Preferably, the axes of rotation X2, X3 of the left and right bearing frames  2 L and  2 R are inclined mirror-wise relative to the vertical plane P1 of the central bearing frame  2 C. 
         [0106]    The inclination of the axes of rotation X2, X3 of the left and right bearing frames  2 L and  2 R is such that the corresponding planes P2, P3 ( FIGS. 3 and 4 ) perpendicular thereto are diverging upwise, preferably by an angle β with respect to the vertical plane P1 preferably in the range between 2° and 45°, more preferably in the range between 5° and 20°, even more preferably of about 10° (actual value of angle β depending on the size of the outdoor termination  3  and of the housing H). 
         [0107]    The central bearing frame  2 C and the respective outdoor termination  3  lie in a first substantially vertical plane P1 ( FIGS. 3 and 4 ) and the axis of rotation X1 of the respective bearing frame  2  is perpendicular to the first plane P1. 
         [0108]    The left and right bearing frames  2 L and  2 R and the respective outdoor terminations  3  lie in respective second and third planes P2, P3 ( FIGS. 3 and 4 ) perpendicular to the axes of rotation X2, X3 of the bearing frames  2  and, accordingly, skewed relative to the first plane P1, by the angle β. 
         [0109]    In this way, the rotation of the bearing frames  2  of the left and right bearing frames  2 L and  2 R causes, in addition to the raising of the same, a progressive reciprocal separation between the relevant left and right outdoor terminations and between such terminations and the central termination, allowing the terminations  3  to be kept in close position, so as to have a size suitable for road transportation and to be separated when in operation by an amount sufficient to avoid discharges while connected to the overhead electric network. 
         [0110]    The second end  4   b  of the electrical cable  4  is set up for being electrically and mechanically connected to an extension electrical cable  100  (as shown in  FIGS. 2 and 3 ). 
         [0111]    Such electrical cable  100  has the function of linking the by-pass system  1 , connected to the overhead electric line by one end of the section to be bypassed, to the second end of the section to be bypassed. 
         [0112]    In case the second end of the section to be bypassed is an overhead point, the extension cable  100  shall provide the connection from a first by-pass system  1  and a second, similar by-pass system  1  connected to such overhead point. 
         [0113]    In case the second end of the section to be bypassed is a point on the ground (or underground), the extension cable  100  shall provide the connection to such point on the ground with a relevant joint. 
         [0114]    In order to allow an easy and correct connection of the electrical cable  4  to the extension cable  100 , the by-pass system comprises a cable joint  19  for each electrical cable  4  (that is, for each of the three electrical cables  4 ). 
         [0115]    An example of cable joint that may be used is described in document U.S. Pat. No. 5,316,492; cable joints of this type are commercially available, under the trademark CLICK FIT® (for example the model CFJ-CFJX) sold by the Applicant. 
         [0116]    The cable joints  19  are conveniently connected to the relevant bearing frames  2  by means of latches  4   d  or the like ( FIG. 5 ). 
         [0117]    The platform  10  comprises one or more holding elements  10   a  for each extension cable  100 , to which the extension cable  100  are secured in operation ( FIG. 2 ). 
         [0118]    The extension cable  100  can be conveniently transported in the operation place wound on a drum, wherefrom it is unwound during the laying operations of the by-pass system, so as to provide a sufficiently long connection, for example 50 metres, in a limited space (that determined by the drum). 
         [0119]    Preferably, a corresponding extension cable  100 , wound on a relevant a drum is provided for each outdoor termination  3 . 
         [0120]    In operation, the three extension cables  100  are preferably laid close each other and latched together in a trefoil arrangement, so as to form a single cord. 
         [0121]    Preferably, one end of each extension cables  100  is provided with a connecting connector mating with a respective cable joint  19 , and readily insertable thereinto, so as to provide a quick installation. 
         [0122]    More preferably, both ends of the extension cables  100  are provided with connecting connectors mating with joints of the same type of the joint  19 , in order to speed up the connection phase by both opposite sides of the extension cables  100 . 
         [0123]    In operation, the by-pass system  1  is transported by a truck trailer or the like in the proximity of the overhead power line where the bypass is to be made. 
         [0124]    The housing H is then secured in place with suitable stands  20  or the like and the bearing frames  2  are unlatched from the supporting elements  11 ,  12  for allowing the bearing frames  2  to be moved. 
         [0125]    During these operations, the side and top walls  16 ,  17  of the housing H are opened, to provide easy access. 
         [0126]    The actuators  5  are then operated, so as to rotate the bearing frames  2 , preferably one at a time. 
         [0127]    The outdoor terminations  3  then emerge from the top opening of the housing H, reaching the condition suitable for the operation. 
         [0128]    At that stage, the crosspieces  13  are placed in the relevant positions so as to hold the bearing frames  2  and the outdoor terminations  3  in the reached position. 
         [0129]    Subsequent to the rotation of the bearing frames  2 , the second end  4   b  of the cable  4  and the joint  19  attached thereto reach a position suitable for being electrically connected to the extension cable  100 . The electrical cables  4  and the extension cables  100  are then mechanically and electrically joined and steadily constrained to platform  10 . 
         [0130]    Once these operations have ended, the by-pass system is ready to be electrically connected to the electrical line to be by-passed.