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(11) | EP 1 113 548 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Electric substation |
(57) An electric transmission and/or distribution substation connected to a multi-phase
power line, comprising:
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[0002] In particular, the substation according to the invention, thanks to the structure of some of its components, allows reducing the number of components and the maintenance needs. Moreover, land occupation and visual impact can be reduced with respect to conventional substations, by applying a solution which is unique in its simplicity and effectiveness both from the point of view of production costs and of practical applications.
[0003] It is known that conventional substations use one or more power and/or distribution transformers, which are electrically connected, on one side, to the phases of a high-voltage power line, and on the other side, to a plurality of medium- and low voltage equipment.
[0004] In particular, each transformer comprises a tank which contains a magnetic core, electric windings, and an insulating fluid; further, each transformer is equipped with a plurality of bushings which allow electrical connections with the phase conductors and with the medium-and low voltage equipment.
[0005] An on-load tap changer, which comprises a selector and a diverter switch, is operatively connected to the transformer; the on-load tap changer, which can be positioned inside or outside the tank, is suitable to vary the transformation ratio of the transformer so that the voltage supplied to the medium-and low voltage equipment can be appropriately regulated. In particular: the selector of the on-load tap changer has the task to change without load the position of the voltage regulation from one tap of the winding to the following one; the diverter switch, which acts on load after the selector positioning, has the task to switch the current from one pointer of the selector to another one through auxiliary contacts and limiting resistances connected in parallel to each pointer.
[0006] The electrical connection between transformers and phase conductors is realized by the interposition of a plurality of switchgear elements, such as circuit breakers and disconnectors, which allow the realization of different electrical schemes according to the applications, and ensure the correct functioning of the substation.
[0007] At the present state of the art, the connections between transformers and switchgear elements are realized according to two main configurations, which have some drawbacks and disadvantages.
[0008] In particular, according to a first solution, the switchgear elements are disposed on the substation yard and are connected to the bushings of the transformer by means of conductor systems, such as busbars. In this case, the presence of conductors, which are positioned in air, causes a significant increase of the overall dimension of the substation, thus negatively increasing the land occupation and the visual impact; furthermore, the presence of busbars in air makes it necessary the use of busbars protections, for example against lightnings, and frequent maintenance interventions.
[0009] In a second solution, known in the art as "GIS" ("Gas Insulated Substation"), the switchgear elements are positioned inside a metal-clad casing which is filled with a pressurized dielectric gas, generally sulphur exafluoride (SF6); further, also the conductors which connect the switchgear elements and the bushings of the transformer are housed, at least partially, in gas insulated ducts.
[0010] Although this solution is constructively compact and functionally effective, it needs a significant amount of SF6, in order to provide the required insulation; this kind of gases, besides requiring a particular structure, which is extremely expensive and therefore effects the costs of the substation, have a negative environmental impact. As a matter of fact, it is necessary to adopt particular safety systems in order to avoid and/or indicate any losses and leaks of the gas; in this cases, losses and consequent leaks of the gas might in fact cause malfunctions of the substation and environmental contamination problems; moreover, frequent maintenance interventions are also required.
[0011] This obviously has a negative impact on the constructive complexity of the substation and on its overall reliability; furthermore, with this solution the substation has a structure which is not easily transportable and requires significant installation time, which can not be prefabricated and, once installed, can not be relocated.
[0012] Independently of their layout, electric substations require frequent maintenance because of on-load tape changer operations in mineral oil, which is the most widely used insulating medium for power transformer. As it is known from the state of the art, the diverter switch has the task to break small currents very often during even a single day, thus enhancing degradation of both insulating oil and its own contact. Moreover the diverter switch usually has a complex mechanism and need proper actuation means.
[0013] In order to reduce maintenance requirements of on-load tape changers, vacuum diverter switches have been developed, but this solution is neither technically simple nor economically convenient in many cases.
[0014] The aim of the present invention is to realize an electric transmission and/or distribution substation which allows to reduce its maintenance needs and number of components by using an integrated switching device able to perform both the function of line breaking and diverting switch. Moreover, the overall dimension of the substation can be reduced by applying a compact layout, thus allowing to reduce the land occupation and the visual impact when compared to conventional substations.
[0015] Within the scope of this aim, an object of the present invention is to realize an electric transmission and/or distribution substation whose structure, at least partially, can be easily transported on the installation site, and, once installed, can be easily relocated.
[0016] A further object of the present invention is to realize an electric transmission and/or distribution substation which allows to reduce the installation time.
[0017] A further object of the present invention is to realize an electric transmission and/or distribution substation which allows reducing maintenance interventions and use of protection systems.
[0018] A further object of the present invention is to realize an electric transmission and/or distribution substation which is highly reliable, relatively easy to manufacture and at low costs.
[0019] This aim, these objects and others which will become apparent hereinafter are achieved by an electric transmission and/or distribution substation connected to a multi-phase power line, which comprises:
- a transformer having a tank which contains a magnetic core, electric windings and a first dielectric fluid;
- a selector for regulating the voltage ratio of the transformer;
- an integrated switching device comprising a casing which contains a moving element comprising at least a first moving contact and a second moving contact, a first fixed contact which can couple/uncouple to said first moving contact, and a plurality of second fixed contacts that can couple/uncouple to said second moving contact, being said first fixed contact electrically connected to the power line, and said moving element and related first contact and second contact connected to the transformer windings through the selector; and first actuation means which are operatively connected to said first moving element and related first contact and second contact.
[0020] In this way, a single and compact device performs both the line interruption function and the diverter switch maneuvers for the voltage ratio regulation.
[0021] In addition, adopting a compact layout for the transformer bay, as directly connecting the integrated switching device to the transformer tank, or positioning the switching device inside the tank, a unique substation module can be formed. The substation module can be easily prefabricated, transported and, if necessary, relocated from one site to another one.
[0022] Further characteristics and advantages of the invention will become apparent from the description of preferred embodiments of the electric substation according to the invention, illustrated only by way of non-limitative example in the accompanying drawings, wherein:
Figure 1 is an electrical scheme illustrating the transformer bay of the electric transmission and/or distribution substation, according to the invention;
Figure 2 is a schematic view of an integrated switching device which task is to perform both the function of high voltage circuit breaker and diverter switch to be used in the electric substation according to the invention.
[0023] With reference to figure 1, the electric substation according to the invention comprises a power and/or distribution transformer, designated by the reference numeral 100. The transformer 100 has a tank 101 which contains a first dielectric fluid having mainly an insulation function, a magnetic core, which is not shown in the figure, and electric windings 102. The selector 21 is positioned on the line side of the high voltage winding. An integrated switching device 22, suitable for performing both the function of line breaking and diverting switch, is operatively connected to the windings 102 through the selector 21; the integrated switching device can vary the transformation ratio, so that the voltage supplied by the transformer can be adjusted according to the requirements of the service, and can interrupt the line in case of short circuit or any other operation need. The interruptive function can be performed in concomitance with any voltage regulation operation.
[0024] The functioning of the transformer 100 is well known in the art and therefore it will not be further described.
[0025] The integrated switching device can be positioned inside the transformer tank. In the preferred but not exclusive embodiment shown in figure 1, the integrated switching device 22 is positioned outside the tank 101; it is connected to and mechanically supported by said tank and it can be electrically connected to the selector 21 by means of a suitably shaped kinematic chain and high voltage bushings or proper separation systems. Moreover, in another embodiment, not shown, the integrated switching device can be enclosed in a vessel, being said vessel directly connected to and mechanically supported by the transformer tank. Applying this layout, the overall dimensions of the transformer bay in particular, and of the substation in general, are drastically reduced, with a very simple and effective solution. In fact, the bushings of the transformer 100, along the power line side, and the busbars which connect electrically the transformer itself and the interruption elements, are completely eliminated, thus reducing the number of components in air, the maintenance interventions required, and consequently increasing the overall reliability of the substation. Further, the transformer 100 and the integrated switching device 22, possibly enclosed into the same vessel, form a module which can be easily transported and relocated.
[0026] According to a preferred embodiment, shown in figure 2, the integrated switching device 22 comprises a casing 1, which is hermetically sealed, and contain a moving element 6 comprising contacts 2 and 3, driven by the moving element 6. The contact 3 can couple/uncouple to fixed contact 4, positioned inside the casing 1, for example by a linear movement of element 6, thus closing or interrupting the line current. A plurality of fixed contact 5 can be positioned on the internal surface of the casing 1, which can be coupled/uncoupled to moving contact 2, for example by rotating element 6, thus performing the load current switching from one tap of the high voltage winding to another one. The moving element 6 is connected to first actuation means, here not shown, that are arranged so as to determine a coupled movement of the moving element 6, i.e. a translation for coupling/uncoupling the contacts 3 and 4, and a rotation for coupling/uncoupling the contacts 2 and 5.
[0027] Alternatively, proper actuation means, operatively connected to the casing of the integrated switching device, can be provided in order to perform the coupling/uncoupling of contacts 2 and 5 by rotating the casing itself. Other layout can be conceived, which do not change the basic concept of the integrated switching device hereabove exposed.
[0028] For the sake of simplicity, in the description particular reference is made to a single phase of the power line 23; clearly, for each phase of the line 23, an integrated switching device 22 can be used.
[0029] The electric substation according to the invention can comprise at least one disconnector, which is electrically interposed between the integrated switching device and the power line. The disconnector has a fixed contact and a corresponding moving contact, according to solution well known in the art; second actuation means are operatively connected to the moving contact of the disconnector in order to provide its coupling/uncoupling with the corresponding fixed contact. In particular, the disconnector can be positioned outside or inside the casing of the integrated switching device, according to the applications and/or to specific needs. When the integrated switching device is enclosed in a vessel, also the disconnector can be positioned inside said vessel.
[0030] In another embodiment, here not shown, the selector 21 can be positioned into the casing of the integrated switching device.
[0031] The integrated switching device 22 can be insulated in vacuum, or in a preferred embodiment, a second dielectric fluid can be provided inside the casing 1.
[0032] Said first dielectric fluid and/or said second dielectric fluid can be constituted by non-flammable fluids, in particular by a dielectric fluorinated fluid, such as sulphur hexafluoride (SF6). Alternatively, the dielectric fluorinated fluid can be chosen among the group constituted by perfluorocarbons, or fluorocarbons or perfluoropolyethers; in particular, the use of perfluoropolyethers allows to increase safety and non-flammability of the transformer bay, and to reduce the environmental impact.
[0033] The first and second dielectric fluids can be the same or different form each other. In case of different fluids, the first dielectric fluid can comprise a mineral oil, or a vegetal oil, or a perfluoropolyether, and the second dielectric fluid can comprise a mixture of sulphur hexafluoride and nitrogen, or pure nitrogen gas; clearly, other combinations can be adopted.
[0034] Further, the first actuation means and/or the second actuation means can comprise a motor with position control; in particular, the use of a servomotor entails considerable advantages in terms of precision and speed of execution of the operations.
[0035] As an alternative, it is possible to use mechanical, or electromechanical, or pneumatic, or hydraulic actuation means.
[0036] Considering the various phases of the power line 23, the first actuation means can comprise a single motor with position control, operatively connected to the moving element 6 of each integrated switching device 22, according to a solution which is cheap and effective at the same time. Alternatively, the first actuation means can comprise, for each phase, a motor with position control, operatively connected to the moving element 6 of the corresponding integrated switching device 22.
[0037] In an equivalent manner, also the second actuation means can comprise a unique motor with position control, operatively connected to the moving contact of each disconnector, or, for each phase, a motor with position control, operatively connected to the moving contact of the corresponding disconnector.
[0038] In practice it has been found that the electric substation according to the invention allows to achieve the intended aim and objects, since it is composed by a reduced number of components and the switching of load current from one tap to another is performed in a most reliable way, thus reducing maintenance needs. Moreover the electric substation can be realized according to a very compact layout which allows reducing the land occupation and the visual impact, that can be prefabricated, easily transported and even relocated.
[0039] The electric substation thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept; for example, other components, such as measuring transformers and/or various kind of protections, can be positioned inside the casing 1. All the details may also be replaced with other technically equivalent elements.
1. An electric transmission and/or distribution substation connected to a multi-phase
power line, characterized in that it comprises:
- a transformer having a tank which contains a magnetic core, electric windings and a first dielectric fluid;
- a selector for regulating the voltage ratio of the transformer;
- an integrated switching device comprising a casing which contains a moving element comprising at least a first moving contact and a second moving contact, a first fixed contact which can couple/uncouple to said first moving contact, and a plurality of second fixed contacts that can couple/uncouple to said second moving contact, being said first fixed contact electrically connected to the power line, and said moving element and related first moving contact and second moving contact connected to the transformer windings through the selector; and
- first actuation means which are operatively connected to said first moving element and related first moving contact and second moving contact.
2. An electric substation according to claim 1 characterized in that said casing is directly
connected to and mechanically supported by said tank.
3. An electric substation according to claim 2 characterized in that the electric connection
between the integrated switching device and the selector is realised through at least
a high voltage bushing.
4. An electric substation according to claim 1 characterized in that said casing is positioned
inside the transformer tank.
5. An electric transmission and/or distribution substation according to one or more of
the preceding claims characterized in that it comprises at least one disconnector
interposed between the integrated switching device and the power line, said disconnector
having at least a third fixed contact and a third moving contact which can couple/uncouple
to each other, and second actuation means which are operatively connected to said
third moving contact.
6. An electric substation according to one or more of the preceding claims characterized
in that the integrated switching device is enclosed in a vessel.
7. An electric substation according to claim 6, characterized in that said selector is
positioned inside said vessel.
8. An electric substation according to one or more of the preceding claims, characterized
in that said first actuation means comprise, for each phase, a motor with position
control.
9. An electric substation according to one or more of the preceding claims characterized
in that said first actuation means comprise a single motor with position control,
operatively connected to the moving contacts of each integrated switching device.