Abstract:
The invention relates to a system and a method for assembly and maintenance of connection modules ( 3 ) in high-voltage switchgear ( 1 ). According to the invention assembly and maintenance are performed in a service bay ( 6 ) in the vicinity of the switchgear. Modules ( 3   a ) to be assembled, replaced or repaired are transported between the service bay ( 6 ) and its site ( 2   a ) in the switchgear area by a service vehicle ( 4 ). The vehicle ( 4 ), connection modules ( 3 ) and the positions for their base plates ( 2 ) are thus so adapted to each other that the service vehicle ( 4 ) can move about in the switchgear area while the switchgear is in operation. A special aspect of the invention is the custom-design of the service vehicle ( 4 ) specifically for its purpose.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in a first aspect to a system for assembly and maintenance of connection modules in high-voltage switchgear. From a second aspect the invention relates to a method for assembly and maintenance of such connection modules. From a third aspect the invention relates to a central component in such a system, namely a service vehicle. 
     2. Discussion of the Background 
     Such switchgear generally includes a large quantity of electrical apparatus, in the following termed connection modules, which are arranged in a number of lines, normally three, which lines are oriented in the same direction as the overhead power transmission lines entering and leaving the switchgear. Each connection module is normally supported individually on a stand, i.e. each breaker, each disconnector, each grounding device, each surge diverter and each current meter has its own stand. The large number of components required in an air-insulated high-voltage switchgear station, and the demand for safe electrical distance between each unit require that a conventional switchgear occupies a considerable ground area. The extension in the direction of the overhead power lines of a switchgear for a voltage level of 245-500 kV, defining the length of the switchgear station, is approximately 100-150 meter. A 420 kV switchgear station would be typically about 120 m. 
     Alternatively a plurality of electrical components may be combined in an apparatus part arranged on a common stand. Such connection modules can reduce the area occupied by the switchgear. A switchgear of such a type is described in Swedish patent application No. 96 02336-1 and various examples are described therein of how connection modules can be designed, where a common stand carries several components. The stands are placed at erection sites with base plates to anchor the stands. 
     When connection modules for a switchgear are to be assembled in a conventional manner the apparatus parts are transported to the respective erection sites, after which the parts are assembled on site by means of a mobile crane, for instance. Only when the apparatus parts are in place and have been assembled can the control cabling be installed and connected, usually directly to terminal blocks in the control devices. 
     Maintenance work such as inspection of contacts or repairs according to conventional technology is also performed on the erection site using mobile cranes or the like. Parts of the switchgear in the vicinity must be taken out of operation and rendered dead throughout the time needed for the work. Such shut-downs can entail considerable costs and it would therefore be desirable to be able to reduce or eliminate shut-downs caused by such maintenance work. 
     SUMMARY OF THE INVENTION 
     In the light of this, the object of the present invention is to provide a system for assembly and maintenance of connection modules in high-voltage switchgear in which the problems of forced shut-downs associated with conventional technology in the area are solved. 
     The system and method are thus based on all that work in connection with assembly and service being performed at a place other than within the switchgear area, and that the assembled or repaired connection module is transported out to its erection site. This means that such work is eliminated on site and no shut-down in operation need occur. 
     Transport of the connection modules could in fact be performed using a conventional fork lift truck. However, the transport places rather special demands on the transport vehicle when it is to drive a connection module out to its site, with respect to stability, anchoring of the load and accessibility in the limited space and under the special circumstances prevailing. It is therefore important that one component in the system consists of the special service vehicle defined in the claim. Such a custom-built service vehicle enables connection modules to be transported in an optimal and effective manner. 
     According to a preferred embodiment of the system according to the invention the service bay is situated indoors, which offers additional advantages since the work can then be performed protected from wind and weather as well as facilitating the installation of fixed aids such as overhead cranes and the like. 
     In another preferred embodiment the service bay is equipped with such aids and other service equipment, enabling the work to be performed effectively. The service bay according to this embodiment also includes a stock of spare parts and/or complete connection modules in reserve. When a connection module is to be repaired or serviced it can merely be transported out of the way and replaced by a similar module ready for use from stock. 
     According to a further preferred embodiment of the system, a number of grounding points are arranged within the area of the switchgear, and the service vehicle can be connected optionally to any of these grounding points. During transport of a connection module in upright position, therefore, its stand part will be grounded while its apparatus part is separated from ground by the insulators. It can therefore be transported close to live modules, and even touch these, without risk of electric flashover. 
     According to a preferred embodiment the service vehicle has a frame which is open in one direction so that it can straddle the stand of a connection module, thereby enabling fast and simple loading of the module and stable transport. 
     In a preferred variant of this embodiment the opening can be closed so that, when the stand of the module has been straddled, the vehicle has a closed frame thereby increasing its stability considerably. 
     According to another preferred embodiment the service vehicle is provided with support members, vertically movable in relation to the frame, to facilitate lifting the connection module from its base plate when it is to be transported. The support member suitably comprises a pair of beams that are raised and lowered together. 
     It is advantageous for the service vehicle to be designed with, on the one hand, a broad wheel base but, on the other hand, a narrow waist part. Stability during transport is then achieved, as well as flexibility to move between the modules in the switchgear station. To further increase its ability to turn around between the modules it is advantageous if the wheels can be steered individually. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be explained in more detail in the following description of preferred embodiments, with reference to the accompanying drawings in which 
     FIGS. 1-3 show side views of various types of switchgear where the invention is applicable, 
     FIG. 4 is a schematic illustration of the principle for the layout of a system according to the invention 
     FIG. 5 shows a side view of a service vehicle with load according to one embodiment of the invention, 
     FIG. 6 is a section along the line VI—VI in FIG. 5, 
     FIG. 7 shows a detail of the service vehicle according to FIG. 5, 
     FIG. 8 illustrates the transport of a module according to a preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates the layout of a conventional switchgear, showing how the components in a row of apparatus are arranged. In a typical switchgear of this type three identical rows of apparatus are placed parallel with each other. The overhead power transmission lines  301  are supported by three pylons  302 ,  303 ,  304 , one at each end of the row of apparatus and one in the middle. From left to right in the figure, the switchgear comprises the following units: a first group of three pillar stands  305 ,  306 ,  307 , each carrying a busbar  308 ,  309 ,  310 , which busbars are directed perpendicular to the plane of the figure, a first disconnector  311 , a first breaker  312 , a first current transformer  313 , a second disconnector  314 , a third disconnector  315 , a second breaker  316 , a second current transformer  317 , a fourth disconnector  318 , a fifth disconnector  319 , a third breaker  320 , a third current transformer  321 , a sixth disconnector  322  and a second group of three pillar stands  326 ,  327 ,  328 , each carrying a busbar  323 ,  324 ,  325 . In this conventional arrangement the row of apparatus for 420 kV is approximately 120 meter in length. 
     In FIG. 2, showing a more compact arrangement of a switchgear from the same angle as FIG. 1, the overhead power lines  101  are supported in the same way as above, by one pylon  102 ,  104  respectively, at each end of the row of apparatus and one pylon  103  in the middle. Here, too, stands  105 - 107  and  113 - 115  carrying busbars  108 - 110  and  116 - 118 , respectively are arranged outermost at each end of the row of apparatus. Between these a first stand  111 , a second stand  119  and a third stand  112  are arranged, each carrying a plurality of components including breakers and disconnectors. Such a multi-component stand is described in more detail in SE 9600123-5. Between the first multi-component stand  11  and the second multi-component stand  119  and between the second multi-component stand  119  and the third multi-component stand  112  is a space with a height of the dead zone above ground level that is higher than at the other parts of the line. 
     FIG. 3 shows yet another example of a switchgear where the invention is applicable. The row of apparatus here consists of only three units, i.e. three multi-component stands  202 ,  203 ,  204  similar to the equivalent stands in the layout according to FIG.  2 . The overhead power lines  200 ,  201  and busbars  205 - 210  are supported by a stand frame  211  located between the rows of apparatus with components. FIG. 3 illustrates only one line and one such stand frame. The switchgear comprises two such stand frames  211  with a line at the side and outside each stand frame and a line located between them. 
     To perform assembly of and service on one of the stands with its connection parts, i.e. a connection module, a system is used according to the invention as shown schematically in FIG.  4 . The connection modules are arranged within a switchgear area  1  and are arranged in the rows in X and Y direction. Each connection module is secured in the ground at a base plate  2  constituting the erection site of the module. In FIG. 4 only a few of the connection modules  3  in the switchgear are shown schematically, whereas only the erection sites  2  have been marked for the others. 
     If any of the connection modules in the switchgear needs repair or inspection, e.g. the module with base plate  2  as erection site, a service vehicle  4  is driven in to the switchgear area, up to the relevant connection module, the module then being loaded onto the service vehicle  4  in a manner to be described later. FIG. 4 shows the service vehicle  4  which is constructed as a trailer drawn by a traction vehicle  5 , on its way from the base plate  2   a  with its connection module  3   a  as load, heading for a service bay  6 . The connection module  3   a  is transported in an erect position. 
     The base plates  2  for erection of the connection modules are positioned relative to each other so that the service vehicle  4  has room to drive between them, at least along certain corridors, e.g. along the route A marked in the Figure for the service vehicle  4 . The connection module  3   a  being transported and the connection modules  3  already in place are so adjusted to each other as to allow free passage for the connection module  3   a  being transported. The service vehicle  4  is grounded and, via the trailer, also the stand of the connection module being transported. Since its apparatus part is joined to the stand via insulators, the apparatus part can, without problem, move quite close to adjacent connection modules  3  and even touching some of them can be accepted. 
     The connection module  3   a  is transported to a service bay  6  outside the area. The module can be repaired in the service bay  6  and then transported back to its place in the switchgear station. However, it is even more suitable to simply exchange the connection module  3   a  for an identical module kept in stock as a complete unit at the service bay. The connection module  3   a  to be repaired is unloaded, after which the spare connection module  3   b  is loaded onto the trailer for transport out to the erection site  2   a.    
     The service bay  6  may be situated outdoors, but it is assumed to be more advantageous for it to be situated indoors or at least under cover. A stock of complete connection modules should be kept in reserve at the service bay, at least one of each type of connection module included in the switchgear station. Alternatively, or in addition, a stock of spare parts may also be kept in the service bay. Also provided at the service bay are an overhead crane and other types of lifting gear and the tools and material necessary for repair and maintenance of the connection modules. 
     The spare connection module  3   b  is arranged in a stand-by position in the service bay  6 , erected on and anchored to a loose foot-plate  7  on the floor/ground of the service bay. It is so arranged that the service vehicle can reverse up to it and straddle the stand of the module for loading onto the trailer, as described below when describing the service vehicle. 
     Assembly of connection modules  3  can also be performed at the service bay  6  which is therefore equipped with base plate and contacts for disconnectors corresponding to those at each connection module site in the switchgear station. When the connection modules have been assembled they are adjusted to the contact units. The resistance of the current path is checked and the factory-fitted control cables connected with plug-in contacts to a testing device so that the apparatus included can be tested as to function. Most of the measures required for installing a connection module at its site  2   a  in the switchgear station can thus be performed already in the service bay, thereby reducing the work out in the switchgear station to a minimum. 
     After assembly, exchange, repair or service, the connection module is transported out to its erection site  2   a.    
     When the service vehicle  4  reaches the erection site or base plate  2  where the reserve connection module  3   b  is to be placed, it will fit without any adjustment since the base plate  2   a  and the contacts here correspond to those against which the connection module  3   b  has already been tested at the service bay  6 . The control cables from the station may already be in place and terminate in plug-in connectors so all that has to be done is plug them directly into the control cable connection of the connection module  3   b.    
     FIG. 5 illustrates the transport vehicle in the form of a trailer  4  loaded with a connection module  3   a . The connection module  3   a  is a combined module comprising disconnectors  31 ,  32 , breaker elements  33 ,  34  a central support insulator  35  and inclined operating insulators  36 ,  37  on each side of the latter, a control device  38  and a stand part  39 . Other components, not shown, are also included in such a connection module. The design of the connection module per se does not constitute any central aspect of the present invention and reference is therefore only made to said SE-9600123-5 mentioned previously, for a more detailed description of such and similar combined connection modules. The connection module being transported may naturally be of conventional type containing only one apparatus. 
     FIG. 6, showing a view along the line VI—VI in FIG. 5, illustrates a bird&#39;s-eye view of the service trailer  4 . It comprises a frame  41  provided with wheels and comprising two parallel beams  52  placed relatively close together and running in the direction of movement of the trailer. At each end of the pair of beams  52  the frame widens considerably through a construction of inclined and transverse beams  53 ,  54 ,  58 ,  59  to provide a wide base for the pairs of wheels  42 ,  43 ,  44 ,  45  at each end. The two front wheels  44 ,  45  can be steered and are operated with the aid of a link mechanism connected to the pull rod  56 . The tie bar can be angled, as shown by the position  56   a  indicated in broken lines, so that the front wheels turn. 
     The rear wheels  42 ,  43  are normally locked in a straight position by the control sticks  57 . Their two steering rods  61  can be connected together by a link  62 . When the control sticks  57  are released from their locked position the rear wheels can be steered by means of these control sticks  57 . Since all four wheels can be steered, extremely narrow turns can be performed in narrow passages. This is also facilitated by the narrow waist at the middle of the trailer. All four wheels being controllable also facilitates fine adjustment of the trailer&#39;s position when fitting it against both the support beams  47  of the apparatus stand (during loading) and against the anchoring aperture of the base plate (during unloading). 
     The front end of the frame is provided with a cross bar  54  extending across the maximum width of the whole frame, whereas its rear end consists of two short cross bars  58 ,  59 , aligned with each other and leaving an opening between them in the area between the parallel longitudinal beams  52 . This opening can be closed by a cross bar  60  which is displaceable in the direction of the cross bars  58 ,  59 . The Figure shows the cross bar  60  in closed position while its open positioned is marked with broken lines. The distance between the two longitudinal beams  52  is slightly greater than the width of the stand of a connection module. 
     A connection module is loaded onto the trailer  4  by reversing the trailer in towards the stand of the module with the cross bar  60  open and so that the two longitudinal beams  52  straddle the stand. The trailer is reversed until the stand of the connection module  3   a  is mid-way between the wheel axles of the trailer, the support beams  47  being arranged to be higher up than the support members  46 . The cross bar  60  can then be moved to its closed position so that the frame is closed and thus stable. The support member  46  is then raised to contact the support beams  47  of the stand, after which the four attachment points  46   a  are adjusted individually to the correct height level and the support beams  47  are screwed into the support member  46 . When this has been done the stand  3   a  is detached from its base plate  2   a  out in the switchgear station or from the foot-plate  7  used for assembly at the service bay  6 , after which the support member  46  is raised further to lift the entire connection module from its base plate. The connection module is thus ready for transport. 
     The support member  46  is arranged to be able to lift the connection module in a plane which is displaced vertically in a strictly horizontal position. This is important since the connection module is extremely heavy and its centre of gravity is located high up, approximately 4 m. The connection module is sufficiently firmly anchored in the support member  46  and the support member in the frame  41 , to be able to absorb the considerable bending moments in longitudinal and transverse direction which appear during transport as a result of the elevated centre of gravity of the connection module. 
     FIG. 7 illustrates how the support member  46  is raised and lowered. The support member  46  comprises two parallel mechanisms, each consisting of an upper beam  63  and a lower beam  64  parallel thereto. The upper beam  63  in each mechanism constitutes the support surface for the support beams  47  of the stand. The two beams  63 ,  64  are joined to a front hinge  65  and a rear articulation means  66 . The articulation means  65  and  66  are each articulately connected to beam  63  and beam  64  and suspended in an articulated manner in the frame of the trailer. The front articulated means  65  is connected to a hydraulic cylinder  67  by means of which it can be turned about its articulation connected to the frame. The articulation means then forces the two beams  63 ,  64  to move closer or further away from each other in a parallel movement, and the rear articulation means to follow this movement. The load-carrying surface of the support member  46  is thus lowered or raised. The two parallel mechanisms are raised and lowered synchronously. The hydraulic cylinder  67  is driven by a motor, or it may be pumped manually. Instead of the hydraulic cylinder  67  a worm gear may be used, which is operated manually or by a motor. 
     FIG. 8 illustrates schematically a connection module  3   a  during transport. The trailer  4  is connected to a grounding point  71  within the switchgear area by a flexible cable  70  that can be rolled up. The trailer and the stand part  72  of the module  3   a  are therefore grounded. The apparatus part of the module is insulated from ground by the support insulator  73  and may be brought close to surrounding live areas from adjacent modules which are in operation. The cable  70  is approximately 25 m long and when the full length of the cable has been utilized a second cable  76 , shown rolled up, can be connected to the next grounding point  75  in the direction of travel. The first cable  70  is then disconnected from the grounding point  71  and the cable  70  rolled up on the trailer. At least one grounding point must always be connected. A number of such grounding points are thus arranged within the switchgear area, the distance between them being adjusted to the length of the cables  70 ,  76  so that the cables  70 ,  76  can be connected alternately to the grounding points. 
     Although the connection modules described above are transported in upright position, which is preferable for a number of reasons, transport of the modules in lying position or oriented in some other way is also feasible and within the scope of the invention.