-
The present invention relates to an electric transmission and/or distribution substation.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
A further object of the present invention is to realize an electric transmission and/or
distribution substation which allows to reduce the installation time.
-
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.
-
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.
-
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.
-
In this way, a single and compact device performs both the line interruption function and
the diverter switch maneuvers for the voltage ratio regulation.
-
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.
-
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.
-
-
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.
-
The functioning of the transformer 100 is well known in the art and therefore it will not be
further described.
-
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.
-
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.
-
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.
-
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.
-
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.
-
In another embodiment, here not shown, the selector 21 can be positioned into the casing
of the integrated switching device.
-
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.
-
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.
-
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.
-
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.
-
As an alternative, it is possible to use mechanical, or electromechanical, or pneumatic, or
hydraulic actuation means.
-
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.
-
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.
-
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.
-
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.
-
In practice, the materials employed, so long as they are compatible with the specific use, as
well as the dimensions, may be any according to the requirements and to the state of the
art.
