EP0968554A1

EP0968554A1 - A high-voltage switchgear station

Info

Publication number: EP0968554A1
Application number: EP98907310A
Authority: EP
Inventors: Kjell Johansson; Jan Karlsson; Mats Leijon; Leif Sköld; Lars Walfridsson; Dan Windmar
Original assignee: ABB AB
Current assignee: ABB AB
Priority date: 1997-02-24
Filing date: 1998-02-23
Publication date: 2000-01-05
Also published as: ZA981493B; WO1998037606A1; AU6315198A; CN1252179A; SE9700640L; SE9700640D0; JP2001512657A

Abstract

The present invention relates to a high-voltage switchgear station comprising a plurality of electric apparatus. According to the invention, the electric apparatus are arranged in an air-insulated, earthed metal enclosure (1). The invention also relates to a switchgear module for use in such a switchgear station. The module according to the invention comprises a metal enclosure (1) with air-insulated electric apparatus enclosed therein. The invention also relates to a method of constructing a high-voltage switchgear station. According to the method, the switchgear station is built out of modules according to the invention, the apparatus therein being connected together, and the metal enclosures being earthed.

Description

A HIGH-VOLTAGE SWITCHGEAR STATION

The present invention relates to an electric switchgear station of ^"the type defined in the preamble to claim 1, to a switchgear module for use in such a switchgear station and to a method of building such a switchgear station.

Conventional switchgear stations for high voltage are generally placed outdoors and take a considerable a- mount of space. The switchgear station is assembled on site and the apparatus connected together. In view of its size and, in the eyes of many people, its unsightly appearance, switchgear stations have generally had to be located far from residential districts and other areas frequented by people. They are therefore often located far from built-up areas. In many cases this results in undesired restriction of their localisation. Besides which, the construction of a switchgear station on site is relatively costly.

In the present patent application the concept of high voltage relates to a voltage level of 72.5 kV and upwards, preferably 145 - 420 kV.

In an attempt to achieve more compact switchgear stations, it is already known to enclose the switchgear apparatus in hermetically sealed gas containers, with the apparatus surrounded by SFζ-gas. The gas causes increased resistance to flashover, thus enabling the requirements for a safe distance between apparatus at different voltage levels to be reduced so that a more compact manner of construction is possible. However, enclosing the apparatus in such gas containers is ex- tremely expensive. The enclosed gas must also be monitored for leakage risks. This further increases oper- ating costs and does not entirely eliminate the threat to the environment constituted by a gas container.

Gas-insula-ted switchgear stations of this type are therefore complicated, take a long time to repair after a fault, and complicate any extension with additional compartments, particularly after a long time when it may be difficult to obtain spare parts. The service life of switchgear stations is approximately 30 years.

In order to attain a switchgear station avoiding the drawbacks related to the air-insulated outdoor or sealed gas-insulated kind, it is known to enclose the switchgear station in a air-insulated building.

Thus, DE-A-41 39 177 discloses such a switchgear station having an outer building in which the electric apparatus are housed. The apparatus are arranged in chassis allowing to be mounted to each other within the building.

Furthermore, FR-A-2 566 199 discloses a unit for a switchgear having an outer shell around the apparatus, which is air-insulated. The unit has partitions divid- ing it into a large number of compartments in rows in two directions, having electric apparatus provided in the compartments. A similar switchgear station is disclosed in FR-A-2 530 881.

The switchgear station known through these disclosures overcome to some extent the drawbacks entailing the conventional switchgear stations initially discussed.

Regarding the possibility to attain a switchgear sta- tion that is compact, flexible and reliable in this manner, however, some shortcomings remain. In the light of this, the object of the present invention is to provide an enclosed, air-insulated switchgear station that is compact, flexible and reliable, and in addition allows rational erection and mainte- nance, and providing a higher safety level to service personnel .

According to a first aspect of the invention, these objects are achieved by a high-voltage switchgear station of the type described in the preamble to claim 1 having the special features defined in the characterizing part of this claim, according to a second aspect by a switchgear module of the type described in the preamble to claim 15 having the special features defined in the characterizing part of this claim, and according to a third aspect by a method as described in the preamble to claim 37 having the special features defined in the characterizing part of this claim.

Thanks to building the switchgear station by metal enclosed unit, each unit being a separate construction module, a very high degree of flexibility is attained in that each unit as such constitutes a protecting shell. Thereby, the need for a surrounding building is eliminated as well. The unit can be connected and built up into a switchgear station designed to respond to various requirements. The limitation of having to stick to a certain layout as a consequence of all apparatus being arranged in one single enclosure with partition walls is avoided.

According to a preferred embodiment, the compartments formed by the metal enclosures have direct access from the interior of the station. Thereby, maintenance and repais are facilitated. The need for special service paths within the station itself is eliminated, which makes a more compact layout possible. Thanks to the switchgear apparatus being to a greater or lesser extent located in metal enclosures, the safety distance normally required between apparatus with different potentials can be greatly reduced. In switchgear context, the safety distance means the minimum distance in the air required between high voltage and the part in a plant on which service or repair work is to be performed. This distance comprises a distance determined by the voltage the equipment must be able to withstand without flashover, termed the least free air distance, and also a distance necessary to obtain a safety factor for maintenance and repairs. The first- mentioned distance may be reduced when apparatus are placed in earthed enclosures with controlled environment. The second distance can be disregarded if an earthed metal wall (enclosure) exists between high- voltage and the apparatus which is to undergo maintenance or repair. The environment inside the enclosure is per se air, as in the case of apparatus in conventional switchgear stations in the open air, but the environment can be controlled in a completely different way inside such an enclosure in comparison with outdoors, and rain is of no consequence. The pressure, temperature, content of particles, moisture and fluctuating movement of the air, as well as the nature of the electrode surfaces, all affect how great the resistance to flashover will be for the air in an electrode gap with relatively homogenous field. It is primarily the increased feasibility of controlling these parameters when the air is enclosed that allow shorter free air distances to be accepted so that the construction becomes more compact. The porcelain can also be dimensioned with shorter leakage paths. This facilitates the location of high-voltage switchgear stations in built-up areas, both from the financial and the environmental aspect. The switchgear station is suitably designed so that each individual metal enclosure contains electric apparatus related to one and the same phase.

An electric flashover in air leads to ionisation of air molecules. If high-voltage electric conductors are placed very close together, e.g. in order to obtain a compact structure, the ionised air from the primary flashover will contribute to secondary flashovers involving other conductors than that/those involved in the primary flashover. For three-phase systems, it is well known that electric flashovers to earth in one phase have less after-effects for three-phase networks than a flashover between more phases. When the phases and the apparatus are separated in individual enclosures, therefore, multi-phase faults caused by ionised air can be eliminated in the switchgear station. Separation thus increases the possibility of reducing the free air distance.

An individual metal enclosure preferably encloses a plurality of high-voltage electric apparatus. This enables reduction of the dimensions of the switchgear station, and the advantages of module a switchgear station can be exploited, as well as reducing the manufacturing and operating costs.

In practice, however, it is impossible to house all high-voltage apparatus for a phase inside the same enclosure since some apparatus must be isolated from others and must be taken out for maintenance and service while other apparatus are still in operation. When switchgear apparatus must undergo such maintenance, servicing may constitute a dangerous work operation. The small dimensions complicate accessibility. A safety measure for satisfactory operation and personal safety is to divide the high-voltage switchgear station into enclosures for each current-path out of the enclosure to a place other than the switchgear station mentioned hexe, and individual enclosures for apparatus that section the current-path which connects the enclosures .

In another preferred embodiment of the invention, the metal enclosures are in the form of rectangular boxes stacked on top of and beside each other. This permits rational combination of the switchgear station, facilitates transport of the units and also facilitates manufacture of the enclosures and the apparatus enclosed therein.

In this embodiment, three boxes are preferably stacked one on top of the other, each box containing electric apparatus related to one of the three phases, thereby achieving an expedient and easily surveyed structure of the switchgear station. This embodiment is particularly suitable when the alternative of internal busbars described below is used.

In alternative preferred embodiments, the busbars per- taining to the switchgear station are located either outside or inside the metal enclosures. The former case offers great flexibility- in exchanging individual metal enclosures in the switchgear station, but on the other hand the reduction in space in comparison with a conventional switchgear station is not fully exploited.

The latter case, i.e. with internal busbars, does not offer the same degree of flexibility, but the size of the switchgear station can be reduced more than when external busbars are used. Normally, therefore, the local external conditions and priorities will determine which of the aspects mentioned above is most important and consequently which alternative should be chosen. In a preferred embodiment the switchgear station is so designed that a positive pressure of filtered air prevails inside the enclosures. This positive pressure is relatively weak but has the effect of preventing particles from penetrating in and causing serious disturbance of the electric fields. This increases the feasibility of having short free air distances.

One advantage of the switchgear station according to the invention is that each module can be provided with monitoring equipment that senses the state and the course of events inside the modules. The sensed values can be transmitted to a control unit that need not be located immediately beside the rest of the switchgear station. In a preferred embodiment, the switchgear station is designed in this way. The signals are transmitted to the control centre via optocable and are processed in microprocessors. The increased opportu- nity to keep a careful watch on the switchgear station enables maintenance according to fixed schedules to be reduced and to a great extent replaced by maintenance when the control signals indicate that such is necessary.

The above and other advantageous embodiments of the switchgear station according to the invention are defined in the claims dependent on claim 1.

In a switchgear station according to the invention, it is advantageous to use modules of the type defined in claim 15.

Depending on the nature and location of the region around the switchgear station, the modules are provided with means for connection to either overhead lines or cables. The first alternative may be advantageous in outer parts of a community where overhead lines can be drawn without much problem and where the more expensive laying of^" ground cables can be avoided, but in urban areas ground cables may be necessary and the modules should therefore be adapted therefor.

When the switchgear station is designed with external busbars, the modules according to a preferred embodi- ment are provided with means for connection thereto, suitably in the form of pantograph disconnectors. Functional and safe connection of the modules is thus obtained to the external busbars and the modules can easily be moved or replaced.

When the switchgear station is designed with internal busbars, the individual modules suitably contain sections thereof. This entails an additional step in the module concept and the advantages it offers. In a pre- ferred embodiment of this alternative, a dielectric screen is arranged at the passage of the busbar through the enclosure so that, should an electric arc occur inside an enclosure, it is prevented from passing from the flashover point to adjacent enclosures, and the damage is thus limited. To further reduce this risk, according to a preferred modification of this embodiment the busbar is provided with a surrounding insulating layer close to the dielectric screen.

A considerable advantage of basing the construction of the switchgear station on modules of this type is that they can be supplied as prefabricated units. That the modules are prefabricated thus constitutes an important preferred embodiment . They can thus be manufactured at the factory, enabling rational and cost-efficient production of the modules, regardless of local conditions where the switchgear station is to be erected. The apparatus in the modules and the module connections can also be tested at the factory and the switchgear station can thus essentially be put together using plug-in units.

According to a preferred embodiment, the section of a busbar situated in a module consists of cable terminations. Damage caused by an electric arc is thus re- stricted to the module where the arc arose. The modules can also easily be separated if the cable is to be extended.

In another preferred embodiment, the module includes a truck breaker. This enables several disconnection points to be operated in a single movement, which also contributes to reduced module size. A truck breaker can also easily be taken out of the module for maintenance .

In yet another preferred embodiment, the module is provided with a screen member that can be manoeuvred to assume a position in which a part of the interior of the module is screened from the remaining part This means, for example, that the section of the busbar located in the module can be screened off from the apparatus in the module. With the screen lowered, service can be performed on the apparatus even if the busbar is current-carrying.

The above and other advantageous embodiments of the switchgear module according to the invention are defined in the claims dependent on claim 15.

In a third aspect, finally, the invention relates to a method of constructing a high-voltage switchgear station as defined in claim 37, where the opportunities for exploiting the rationalisation advantages offered by the switchgear module according to the invention are made use of.

The invention is more fully explained in the following more detailed description of preferred embodiments thereof, with reference to the accompanying schematic drawings, in which

Figures 1-3 show schematic views in perspective of alternative embodiments of the switchgear station according to the invention, Figures 4-6 show schematic views from above of additional embodiments of the switchgear station according to the invention,

Figure 7 is a horizontal section through a switchgear station according to one embodiment of the invention, Figure 8 is an enlarged part section of the switchgear station shown in Figure 7 with the apparatus in a first position, Figure 9 is a section as in Figure 8 but with the apparatus in a different position, Figure 10 is a view in perspective of a module accord- ing to the invention, with one side wall of the enclosure removed, Figure 11 is a vertical section through a module according to an alternative embodiment of the invention, Figures 12-16 show different details of the apparatus in a module according to the invention, Figure 17 is a vertical section through a module according to yet another alternative embodiment of the invention, Figure 18 shows a section through a detail according to Figure 17. Figure 1 shows in perspective how a switchgear station according to the invention might look. The switchgear station is dimensioned for nine three-phase current lines and -comprises 27 switchgear modules in the form of rectangular containers or boxes 1 with uniform dimensions, where each box may have a width of 2 m, a length of 4.5 m and a height of 3 m. The boxes are stacked in threes, one on top of the other, with one box for each phase in a line, and the stacks are placed close together. The switchgear station shown thus has a length of 18 m, a width of 4.5 m and a height of 9 m. All the boxes have metal walls and are earthed. Each module is provided with doors 2, drawn in on only one of the boxes in the Figure, through which service per- sonnel can gain access to the interior of the module but only under certain conditions and restrictions which will become apparent further on in the description. The interior of the lowermost modules can be accessed directly from ground level whereas stairs and walkways are arranged to enable access to the two upper rows of modules. The switchgear station shown is much smaller than a conventional switchgear station of equivalent type and requires as little as about 1/4 the area. The embodiment shown in Figure 1 is of the in- ternal busbar type, these running inside the modules in the longitudinal direction of the switchgear station and passing between the walls to adjacent modules. This type offers the most compact design. Since the switchgear station is based on the use of identical boxes, a discrete and uniform exterior can be obtained that will easily fit in with the surroundings in an acceptable manner even in urban areas.

A switchgear station of this type may be arranged to be connected to earth cables as shown in Figure 2 in a six-compartment embodiment, or to overhead lines as shown in an embodiment with four compartments in Figure 3. Figures 2 and 3 also illustrate how each of the modules is provided with a cable connection 3 or overhead line connection 4, respectively.

Both the cable embodiment in Figure 2 and the overhead line embodiment in Figure 3 may in either of the alternatives have external busbars and/or internal busbars.

In the overhead lines embodiment, it may be advanta- geous to arrange the adjacent stacks of modules a certain distance apart in order to create a greater distance between the phases. In this case docking modules may be placed between the equipment modules.

Figure 2 also shows symbolically how the switchgear station may be provided with a unit comprising a fan 90 and air filter 92 connected to the switchgear station by means of an air duct 91, thereby placing the switchgear enclosures under a slight positive pressure with filtered air.

The switchgear station may also be provided with a control unit 93 which, via a signal lead 94 such as an op- tocable, controls and monitors the switchgear station.

Figures 4-9 illustrate schematically a bird's-eye view of a number of other examples of switchgear stations according to the invention.

Figure 4 illustrates an embodiment with overhead lines 5 in three lines with busbars 6, 7, 8 arranged outside the switchgear modules. The switchgear station is of the single busbar type. The switchgear station transformers are designated 9. Each switchgear module 1 is connected to its own busbar by means of a disconnector 10, suitably of pantograph type, arranged on the upper side of the module. Figure 5 also illustrates an exam- pie with overhead lines 5 and external busbars 6, 7, 8, 6X 1 ' , 8', but is of the double busbar type. As is clear from the two Figures, each phase 5a, 5b, 5c in a line is connected to its own module. Relatively great flexibility as to the layout of the switchgear station is obtained with embodiments of the type shown in Figures 4 and 5 and individual modules can easily be exchanged for maintenance and service, for instance.

In a corresponding view, Figure 6 shows an example of a switchgear station with internal busbars. The flexibility is less here than in the embodiments shown in Figures 4-5, but less space is required for this switchgear station. In this example the modules for the three phases are placed one on top of the other in a stack 11, and each phase 5a, 5b, 5c in each line 5 is connected to one of the three modules in the stack 11. The illustrated layout can be used for various types of arrangements of busbars such as single busbars, single busbars in an H-connection, and busbars connected in a ring.

All the examples shown in Figures 4-6 are of course also applicable for ground cable connections.

Figure 7 shows a schematic horizontal section through a switchgear station according to the invention with internal busbars, comprising nine modules of which six are breaker modules la, lb, Id, If, lh, li and the re- maining three lc, le, lg are sectioning modules by which the busbar is divided into four sections 12a-12d. The purpose of dividing, the busbar into sections is that if a fault occurs in one of the breaker modules la, the defect module can be isolated and the intact part of the switchgear station can be supplied from one of the connections at either end of the switchgear station. The defect module can then be repaired while ad- jacent modules are in operation. The disconnectors and breakers in the modules can be pulled back from the connections with the busbar 12.

This is illustrated further in Figures 8 and 9 which show the modules lc-e in Figure 7 on a larger scale. Figure 8 shows the arrangement in connected position and Figure 9 in disconnected position. In the position shown in Figure 8 the busbar is closed since its sec- tions 12a, 12b and 12c are connected with each other through the disconnectors 13c and 13d of the sections lc and le, while the truck breaker 14d is in switched- on position.

If repair work is to be performed on the busbar section 12b or equipment connected to this, it is separated by the disconnectors 13c and 13e being pulled back to the position shown in Figure 9. At the same time the truck breaker 14d in module Id is pulled back, after which busbar 12b is connected to earth potential via earthing means. This position is illustrated in Figure 9. Maintenance and repairs can now be performed on the busbar section 12b since it is disconnected and earthed. This is best done via module Id. The advan- tage of not having to use modules lc and le for this is that the adjacent sections 12a and 12c of the busbar need not be disconnected. Movable curtains 15c, 15e are arranged in modules lc and le, that can be pulled out from their retracted position to the screening po- sition shown in Figure 9 where the equipment in each module is screened from the busbar 12. When the curtains are pulled out as shown in Figure 9, service and maintenance work can be performed on the equipment without the busbar having to be made currentless.

Figure 10 illustrates schematically and in perspective the interior of a module with a truck breaker 14. The module might be module Id, for instance, in Figure 8. The module 1 comprises an earthed metal enclosure with ceiling 16, floor 17, front end wall 18, rear end wall 19 and two^" side walls, of which only one, 20, is visi- ble in the Figure. The metal enclosure forms a paral- lel-epipedic box having a length 4.5 m, width 2 m and height 3 m, and the walls may consist of 2 mm corrugated steel sheet. The rear end wall comprises two doors 21. The metal enclosure is provided with a cable connector 3 and cable termination 22. The busbar 12 consists of an aluminium pipe with a diameter of approximately 200-250 mm that conducts the current to/from equipment in adjacent enclosures, a tight dielectric barrier 49 being arranged at its exit through the side wall 20. Electric arcs are thus prevented from moving through the switchgear station. The busbar 12 is provided with an insulating layer 55 from the dielectric screen 49 and a short distance along the busbar. A material other than aluminium may naturally be used for the busbar.

The large diameter of the aluminium pipe results in the field strength at its surface being less and the field in the air is thus more homogenous.

A truck runs on a pair of iron rails 23 on the floor 17 of the enclosure, the truck carrying the equipment of the truck breaker 14 arranged to be displaceable from a connected position to a disconnected position when the truck breaker is pulled back towards the rear end wall 21. The frame of the truck is of aluminium or painted steel. In the Figure, the truck breaker is shown in a position immediately prior to connection. The rails 23 consist of angle sections oriented with one corner up- wards and the truck wheels 24 correspond thereto. The travelling movement of the truck breaker is achieved by a control device 25 on the truck, provided with a stop 27 fixed in the floor 17 of the enclosure.

A single-pole circuit breaker 28 is fitted horizontally on the truck and provided at its end with a contact 31 with a counter-contact 32 on the busbar. Around the contact 31 the breaker is provided with a screen 29 in order to achieve a desired electric field distribution in the relatively short air gap between the current path and the enclosure 15. The breaker 28 is supported by a pin insulator 33 resting on the bottom plate 34 of the truck. A metal screening body 30 is arranged where the breaker 28 rests on the pin insulator 33 and has the same function as the screen 29. An upwardly di- rected conductor 35 leads via a screen body 36 at its upper end, and a horizontal conductor 37, is electrically connected to an upper contact 38. The conductors 35 and 37 consist of aluminium pipes. The upper screen body 36 is supported by a horizontal pin insulator 39 fitted to a back plate 40 of the truck. The porcelain of the breaker 28 is shorter than normal in order to reduce the length of the truck and thus the length of the module. The shorter length is possible thanks to the screen bodies mentioned and since the leakage paths can be made shorter as no consideration need be given to rain.

The upper contact 38 is arranged for connection to a counter-contact (not shown) on the cable termination 22, which counter-contact is surrounded by a screening body 39. A downwardly directed pin insulator 40 supports the counter-contact of the cable termination 22. A surge arrester 41 is also provided between the screening body 39 and the front wall 18 of the enclo- sure 15 in order to take care of dangerous over- voltages . By means of a control device 42, an earthing device 43 can be connected via its contact 44 to the current path entering via the cable 3 so that this is connected to earth potential.

The front wall 18 of the enclosure is provided with a relief hatch 45 through which over-pressure arising at a flashover inside the enclosure can be conducted away.

A metal screen 46, preferably of the roller blind type, shown in rolled-up position here, is arranged on the inside of the front wall. The screen 46, connected to earth, is operated by a control device 47 and can be rolled out along a guide rail 48 arranged on the inside of both side walls 20. When extended, the screen 46 screens off the area around the busbar from the rest of the interior of the enclosure. The screen 46 can of course be arranged in some other manner than illustrated, e.g. in the ceiling 16 of the module or running vertically from the furthest side wall 20 to the nearest. The screen may also be in the form of a folding door instead of a roller blind.

Manipulating the truck to move backwards disconnects the current-path between the counter-contact 32 of the busbar 12 and the counter-contact of the cable termination 22. Only then, i.e. when the current is disconnected and the truck is moved to a position where it is disconnected from other equipment in the module, can the earthing device 43 be operated so that its contact 44 is connected to the counter-contact of the cable termination 22, thereby connecting the current path in in-coming cable 3 with earth potential. In this position, with the truck pulled towards the rear wall 19, the metal screen 46 can be pulled out to screen the busbar 12. The screen cannot be rolled out unless the cable termination 22 is earthed and the truck pulled back.

The doors -21 can only be opened when the screen 46 is in this extended position, whereupon maintenance personnel can gain access to the space inside the enclosure, but not to the screened-off area. The truck can now be rolled out of the enclosure if so required.

Figure 11 shows schematically a module similar to that in Figure 10, but having an external busbar. Here too the module is connected to an earth cable and provided with a cable termination 22b. As described above, the truck breaker 14' can travel in the module and is pro- vided with a lower contact 62 for connection to the cable termination 22b. Its upper contact 63 is connected to a lead-through 50 from a pantograph disconnector 10 for connection to or disconnection from an external busbar (not shown) above the pantograph disconnector, as shown in Figures 4 and 5. The disconnector 10 is operated by a separate, rotatable insulator 60 beside the lead-through. In this case a lead-through 50 of standard type can be used. The rotary movement of the insulator 60 is controlled by a control device 64 and the movement is transmitted to the gear housing 65 of the pantograph disconnector. An earthing device 66 operated by a control device 67 can connect the cable termination 22b with earth when the current-path is open so that the in-coming cable is connected to earth potential. When the current-path is open, this earth device 68 moves the device 69 down to contact with the counter-contact 70 of the lead-through thereby connecting the latter to earth potential. In this embodiment also a surge arrester (not shown) is arranged to take care of dangerous over-voltages. Figure 12 shows an alternative embodiment for manipulation of the pantograph disconnector 10. The disconnector 10 is connected to or disconnected from the busbar 6 by a rotating control rod placed centrally in the lead-through and extending through the ceiling 16 of the enclosure.

Figure 17 shows an embodiment of a module with an external busbar (not shown) , which, as in Figure 11, is connected via a pantograph disconnector 10 with lead- through 50 which is operated in the same manner by a rotating insulator 60. In the embodiment in Figure 13, the enclosure is connected to an overhead line 79 instead of to a ground cable as in Figure 11.

The disconnector is connected to the high-voltage terminal 76 from the overhead lines by a circuit breaker 71 with screened terminals 74 and 75. The high-voltage terminal 76 is arranged on a combined lead- through/disconnector/earthing device (LDE) 78. Earthing is achieved via the rod 87 in a manner described in more detail below in connection with Figure 18. The pantograph disconnector 10 and LDE can be operated only when the breaker 71 is in its off position. The breaker's terminal 74 is connected to earth potential by means of the earthing device 72, operated by the device 73 , which can only be done when the LDE high- voltage terminal is earthed. Access to the module is permitted only when both terminals are connected to earth.

Figure 18 illustrates the function of the combined lead-through/disconnector/earthing device 78 in Figure 17.

The LDE unit 78 comprises an insulating casing 81 for passage through the ceiling 16 of the enclosure. In- side this, an extension 86 of the high-voltage terminal 80 extends downwardly, terminating in a contact 82. A movable contact 83 is arranged on a rotatable screw rod 87 extending upwardly into the insulated casing 81, said contact 83 communicating with the high-voltage terminal 76. The screw 87 can be turned by means of a control device 84 so that it is displaced upwards or downwards. The screw 87 is shown in its uppermost position, in which the contacts 82 and 83 are connected so that the current is carried from the overhead lines 79 to the high-voltage terminal 76. At the lower end of the screw is an earth terminal 85 which, in the case shown, is not in contact with the screw 87.

The screw 87 can be moved downwards from the position shown by turning the screw 87, so that the contact 83 is separated from the contact 82 and the overhead lines are thus disconnected from the high-voltage terminal 76. In this lower position, the lower end of the screw 87 is moved down into contact with the earthed terminal 85 so that the high-voltage terminal 76 is earthed.

The equipment in the sectioning modules shown in Figures 8 and 9 is also preferably supported on a travel- ling truck. Such a truck sectioner 13 is constructed in accordance with the same principles as the truck breaker described in connection with Figure 10, and reference is therefore made to this.

The contacts on the truck sectioner and truck breaker for connection to the internal busbars, as well as the equivalent contacts on the busbar, should be maintenance-free, i.e. without movable parts. Figure 13 shows an example of how the contact and counter-contact for. a truck breaker may be designed. The contact 31' - on the breaker 28' is of female type whereas the - counter-contact 32' on the busbar 12 is of male type. The jaw of the contact 31' is provided with contact means 51 that spring out of the way when the counter- contact 32' is inserted.

Figure 14 shows an alternative embodiment of maintenance-free contact and counter-contact. In this embodiment measures have also been taken that facilitate keeping the dimensions of the module as small as possible in order to achieve a compact switching station. The compactness results in a high and relatively uniform field strength over air distances from high voltage to earth. The counter-contact 32" of the busbar 12 has therefore been provided in this embodiment with a surrounding dielectric barrier 52.

When the contact 31" of the breaker 28" is moved to connection with the counter-contact 32" of the busbar 12, the barrier 52 will surround these and prevent sparks from the contacts from triggering flashovers be- tween contact and earth. The dielectric barrier 52 may also be designed to assist in guiding the contacts into the correct position in a connecting operation.

Another device that facilitates keeping the dimensions of the modules as small as possible is illustrated in Figure 15. In the Figure the in-coming cable 3 is passed through the wall 18 of the metal enclosure to a cable termination 22". A metal ring is arranged around the cable at the inner end of the cable termination and electrically connected thereto so that the ring 56 acquires high-voltage potential. Between this and the enclosure wall 18 are more such rings 57, 58, attached to the insulating surface 59 of the cable termination 22". These latter rings will thus be on a floating po- tential. The field distribution is controlled ca- pacitively between high-voltage and earth through these rings 56, 57, 58. The stress is therefore reduced at the most vulnerable points around the stress cone 61 of the cable termination 22". This embodiment of the cable termination, together with the controlled climate inside the module, enables it to be made shorter than normal.

As described above, when the variant with an internal busbar is used, this is made of an aluminium pipe. In an alternative embodiment, shown in Figure 16, the bus- bar 12' is instead composed of cable terminations 53a-f. When the cable terminations meet in pairs, they are braced by a support insulator 54 mounted on the front wall of the enclosure.

A special contact-free capacitive voltmeter with screening is used to measure the voltage, this having the advantage of being considerably smaller than conventional voltmeters, and of thus being suitable for use in a module according to the invention without no- ticeably increasing its size. It is also capable of measuring rapid transients. Such a voltmeter is described in Swedish patent application 9602785-9.

To eliminate temperature and condensation problems that may arise in certain outdoor applications, the modules may be provided with double walls with insulation between them.

Claims

C L A I M S

1. A high-voltage switchgear station comprising a plurality "of electric apparatus, characterized in that the station is built of connectable units, at least two of which include each an earthed metal enclosure (1) in which at least one electric apparatus is enclosed.

2. A high-voltage switchgear station as claimed in claim 1, wherein the interior of the units have direct access from the exterior of the station.

3. A high-voltage switchgear station as claimed in claim 1 or claim 2, wherein at least some of the metal enclosures (1) encloses one single electric apparatus each.

4. A high-voltage switchgear station as claimed in any of claims 1-3, wherein each metal enclosure (1) en- closes electric apparatus related to one phase only.

5. A high-voltage switchgear station as claimed in any of claims 1-4, wherein each metal enclosure (1) is shaped substantially as a parallel-epipedic box.

6. A high-voltage switchgear station as claimed in claim 5, wherein said boxes are arranged close together and stacked on top of each other to a height of three boxes, and wherein each of three boxes stacked one on top of the other contains electric apparatus related to a different phase in a line.

7. A high-voltage switchgear station as claimed in any of claims 1-5, provided with busbars (6, 7, 8) lo- cated outside the metal enclosures.

8. A high-voltage switchgear station as claimed in any of claims 1-6, provided with busbars (12) that pass through the metal enclosures.

9. A high-voltage switchgear station as claimed in any of claims 1-8, provided with means (4) for connection to overhead lines.

10. A high-voltage switchgear station as claimed in any of claims 1-8, provided with means (22) for connection to ground cables (3) .

11. A high-voltage switchgear station as claimed in any of claims 1-10, wherein at least one of said metal enclosures (1) , together with the electric apparatus enclosed therein, comprises a substantially prefabricated module.

12. A high-voltage switchgear station as claimed in any of claims 1-11, provided with members (90) to maintain over-pressure in the enclosures (1), and with filter means (92) to filter the air supplied to the enclosures .

13. A high-voltage switchgear station as claimed in any of claims 1-12, wherein each enclosure (1), together with the apparatus enclosed there, constitutes a switchgear module and that the switchgear station consists of at least two different types of modules (lc, Id, le) and at least two modules of at least one of the types .

14. A high-voltage switchgear station as claimed in any of claims 1-13, comprising a control unit (93) situated apart from the metal enclosures, sensors arranged in the metal enclosures, and signal transmitters (94) between the sensors and the control unit.

15. A switchgear module for use in a switchgear station as claimed in any of claims 1-14, characterized in that the module comprises a metal enclosure (1) with one single compartment and encloses air-insulated electric apparatus therein.

16. A switchgear module as claimed in claim 15, provided with means (4, 78) for connection to overhead lines (5) .

17. A switchgear module as claimed in claim 15, provided with means (22) for connection to ground cables (3) .

18. A switchgear module as claimed in any of claims 15-17, wherein said apparatus are related to one of the phases in a three-phase line.

19. A switchgear module as claimed in any of claims 15-18, provided with means (10) for connection to external busbars (6, 7, 8).

20. A switchgear module as claimed in claim 18, wherein said means include at least one pantograph disconnector ( 10) .

21. A switchgear module as claimed in any of claims 15-20, comprising at least one section (12) of a busbar enclosed in the enclosure.

22. A switchgear module as claimed in claim 21, wherein said section (12) terminates at a passage through one of the walls of the enclosure, a dielectric screen (49) being arranged at the passage.

23. A switchgear module as claimed in claim 22, wherein an insulating layer (55) is arranged around part of the busbar, said layer extending a short distance from said screen.

24. A switchgear module as claimed in claim 21, wherein said section consists of at least one cable termination (53a).

25. A switchgear module as claimed in any of claims 15-24, including a truck (14).

26. A switchgear module as claimed in any of claims 15-25, including manoeuvrable screen members (15; 46) arranged to be manoeuvred to an open or closed position, in which closed position a part of the interior of the module is screened from the remaining part.

27. A switchgear module as claimed in claim 26, wherein said screened-off part houses said section of the busbar (12) .

28. A switchgear module as claimed in any of claims 15-26, provided with doors (2; 21) allowing one person access to the interior of the module.

29. A switchgear module as claimed in claim 28 when dependent on claim 27, wherein the door (2; 21) can only be opened when the screen member (15; 46) is in closed position, and that access is only possible to said remaining part of the interior of the module.

30. A switchgear module as claimed in any of claims 26-29, wherein the screen member (15; 46) is only able to assume closed position if the current is disconnected and the truck has been manoeuvred to such a po- sition that the busbar (12) is isolated from the other apparatus in the module.

31. A switchgear module as claimed in any of claims 15-30, wherein the metal enclosure (1) is substantially in the form of a parallel-epipedic box.

32. A switchgear module as claimed in any of claims 15-31, wherein at least one of the contacts (31') and counter-contacts (32' ) pertaining to the apparatus is without movable parts.

33. A switchgear module as claimed in any of claims 15-32, wherein at least one of the contacts (31") and counter-contacts (32") pertaining to the apparatus is provided with a dielectric shield (52) surrounding the contact member.

34. A switchgear module as claimed in any of claims 15-33, comprising a cable termination (22") situated inside the module and consisting of an insulating material (59) extending from one wall (18) of the enclosure, a first metal element (56) electrically connected to the cable (3) at the end of the insulating material facing away from the wall (18), and at least one additional metal element (57, 58) arranged between the wall (18) and said first metal element (56), said additional metal element (57, 58) being electrically isolated from both said first metal element (56) and the wall (18).

35. A switchgear module as claimed in any of claims 15-34, wherein a voltmeter is arranged inside the module, said voltmeter being capacitive and without contact .

36. A switchgear module as claimed in any of claims 15-35, constructed as a prefabricated unit.

37. A switchgear module as claimed in claim 16, wherein said means comprises a combined unit (78) for lead-through, isolation and earthing.

38. A switchgear module as claimed in claim 37, wherein said combined unit comprises an insulating body

(81) extending through a wall part (16) in the module, a fixed contact in the body (81) connected to a high- voltage terminal (80) connected to the overhead line (71) , and a contact (83) movable in the body and connected to a high-voltage terminal (76) inside the module, which movable contact (83) is arranged to be displaced by means of an axially movable, conducting rod (87) extending in the body (81), said rod being arranged to be isolated from earth when the contacts (82, 83) are in contact and connected to earth when the contacts (82, 83) are not in contact.

39. A method of constructing a high-voltage switchgear station, characterized in that the switchgear station is at least partially built of modules of the type defined in any of claims 15-38, the apparatus in the modules being connected together and the metal enclo- sures being earthed.

40. A method as claimed in claim 39, wherein at least some of the modules are delivered to the site of the switchgear station already prefabricated and tested.