EP1865517A2

EP1865517A2 - Feedthrough insulator for electrical transformers

Info

Publication number: EP1865517A2
Application number: EP07109028A
Authority: EP
Inventors: Silvio Dal Lago
Original assignee: Comem SpA
Current assignee: ABB Schweiz AG
Priority date: 2006-06-05
Filing date: 2007-05-28
Publication date: 2007-12-12
Also published as: EP1865517A3; UA91525C2; RU2007120613A; BRPI0701670A; RU2455717C2; ITVI20060166A1

Abstract

A feedthrough insulator (10) for electrical transformers, comprising an insulating body (18), which includes an outer portion (14), to be arranged in air, coupled with an inner portion (15) in the electrical transformer tank, in which the outer and inner insulating portions (14, 15) are crossed axially by a metallic tie rod (11), which acts as an electrical conductor. In particular, the outer insulating portion (14) has a series of fins (17), positioned close together and suitably sized, in order to obtain high dielectric characteristics; moreover, at least one part of the entire insulating body (18) has a combined insulating coating, formed from the coupling of a layer of silicon, covering the underlying epoxy resin, which, in turn, surrounds the electrical conductor (11). Inside the epoxy resin a metallic screen (19) is also embedded, provided with arms (20), which has the dual purpose of screening the metallic attachment components and the support base (21), for example on the tank of the transformer, and of being used as condenser for the capacitive intakes, consisting of the aforementioned arms (20).

Description

The present invention refers, in general, to a feedthrough insulator for electrical transformers and to improvements to such an insulator, compared to conventional insulators made according to the prior art. The adopted technical solution lends itself particularly to use in medium-high voltage feedthrough insulators, however it can irrespectively be used in all types of feedthrough insulators to be applied between an electrical conductor and a transformer tank.
It is known that feedthrough insulators allow the passage of an electrical conductor under voltage through an obstacle, consisting for example of a transformer tank, ensuring a seal, in terms of electrical voltage, between the free end of the conductor and the point of attachment onto the insulator tank, with sufficiently high values with respect to the operating values.
Conventional feedthrough insulators comprise a tie rod, which acts as an electrical conductor and that axially crosses a first portion of an insulating body, arranged in air and placed outside of the tank, and a second portion of the insulating body placed inside of the tank, advantageously coupled with the outer portion.
Moreover, the insulating parts of the insulator, both outer and inner, are made from epoxy resin and/or ceramic materials, such as porcelain, for the intrinsic characteristics of such materials of high rigidity, good mechanical strength and good resistance to temperature variations.
It is also known to use the ceramic material according to a mixture that has been suitably studied, from the point of view of the composition and heat treatment, so as to improve the rigidity values of the material.
The finished product is also conventionally covered by a layer of material suitable for making an extremely smooth outer surface, in order to ease the self-washing of the insulator when it rains.
Moreover, it is necessary for the surface layer of the insulator to have the same dilation coefficient as the porcelain or the resin, of which the insulating body consists, to avoid the formation of surface cracks and fissures, which can, over time, lead to the insulator breaking.
Overall, the fragility of the insulating parts made from ceramic material is also worth noting; indeed, these insulating parts require that the user take special care every time they have to be handled.
Moreover, with insulators made from ceramic material the complete filling of the transformer requires an air vent on the top part of the insulator itself.
Finally, in medium-high voltage insulators made from ceramic material a metallic coating is made on the bottom part of the insulator (portion indicated with X in the attached figure 1, which illustrates a conventional medium-high voltage ceramic insulator), in order to screen the metallic attachment areas, excluding the support plane, for example of the transformer.
The purpose of the present invention is, therefore, to avoid the quoted drawbacks and, in particular, to make a feedthrough insulator for electrical transformers, which ensures better insulating characteristics compared to those of conventional insulators, above all in critical environmental conditions and in contaminated areas in general, and that has, at the same time, a rigid and robust structure, such as to be handled without requiring any special care and to resist perfectly to atmospheric agents of whatever type.
Another purpose of the present invention is to make a feedthrough insulator for electrical transformers, which allows better characteristics of functionality and reliability to be obtained, compared to conventional insulators.
A further purpose of the present invention is to make a feedthrough insulator for electrical transformers, which allows the production and design costs of the insulator to be reduced, compared to the prior art, and that allows all of the assembly operations of the structure to be substantially simplified.
A further purpose of the invention is to make a feedthrough insulator for electrical transformers, which ensures greater resistance to knocks, compared to known types of insulators.
Another purpose of the invention is to make a feedthrough insulator for electrical transformers that does not need the air venting operation at the moment of filling the transformer with oil.
The last but not least purpose of the invention is to make a feedthrough insulator for electrical transformers, which has a metallic screen embedded in the resin, provided with small arms, which has the dual purpose of screening the metallic attachment parts, including the support base, for example, of the transformer, and of acting as a condenser for the capacitive intakes.
These and other purposes are accomplished by a feedthrough insulator for electrical transformers, according to the attached claim 1.
The other dependent claims contain detailed characteristics of the invention.
Further purposes and advantages of the present invention shall become clearer from the following description, relative to a preferred but not limiting example embodiment of the feedthrough insulator for electrical transformers, which is the object of the present invention, and from the attached drawings, in which:

figure 1 is a partial longitudinal view partially in section of a conventional ceramic feedthrough insulator for electrical transformers, where an area, indicated with X, which has a metallic surface treatment for screening is highlighted;
figure 2 is an overall perspective view of a feedthrough insulator for electrical transformers, according to the present invention;
figure 3 is a longitudinal section view of the feedthrough insulator for electrical transformers of figure 2, according to the invention;
figure 4 is an enlarged view of a detail of the feedthrough insulator for electrical transformers, according to figure 3, according to the present invention.

At this point it should be pointed out that the technical solution according to the invention lends itself particularly well to being adopted in medium-high voltage feedthrough insulators for electrical transformers, however it can be used analogously, without any problems, for all types of feedthrough insulators.
With reference to the aforementioned figures, a feedthrough insulator for electrical transformers, made according to the present invention, is generically indicated with 10.
The insulator 10 is suitable for being fixed to the top part of the electrical transformer tank (not illustrated in the figures), at a respective opening, defined on it. As suitably highlighted in the attached figures, the feedthrough insulator 10 has a mainly longitudinal extension and is crossed axially by a metallic tie rod 11, which acts as an electrical conductor.
The tie rod 11 has a top end 12 that, in operative condition, remains outside of the tank, and a bottom end 13, intended to remain inside the tank of the transformer, after having crossed its quoted opening.
The insulator comprises an insulating body, wholly indicated with 18, of which a first portion, generically indicated with 14, is arranged in air and is crossed axially by the tie rod 11, whereas a second portion, indicated with 15, to be arranged inside the tank, essentially consists of an inner insulating body 16, also crossed axially by the metallic tie rod 11.
In particular, according to the invention, the outer insulating body 14 has a series of fins 17, made in a large number and close together, as well as suitably sized, in order to increase the length of the escape line, compared to conventional insulators and, therefore, optimise the dielectric characteristics of the insulator.
Moreover, the portion of insulator in air 14 is formed from an insulating coating made from silicon, equipped with fins 17, which cover a more inner layer made from epoxy resin, which, in turn, surrounds the metallic conductor 11.
This type of combined insulation, at the same time, allows excellent electrical insulation characteristics and adequate outer protection of the insulator, the structure of which is extremely robust and does not need special care during transportation and/or installation.
Such a type of coating, in practice, allows the use of the insulator in any critical environmental conditions and, in particular, in contaminated areas, since it has excellent electrical characteristics and resists well to knocks, as well as to the direct action of atmospheric agents.
In operative position, the insulating body 16 is placed inside the electrical transformer tank and surrounds the bottom end 13 of the metallic tie rod 11.
In example embodiments, the attachment of the body 16 to the tie rod 11 can be carried out through a threading in the bottom end of the tie rod 11, or else by means of a suitable punching on the tie rod 11 itself; alternatively, the inner insulating body 16 can be obtained individually by moulding or else by overmoulding on the tie rod 11, so as to constitute, in practice, a single piece.
A further advantageous characteristic of the invention is represented by the fact that inside the layer of epoxy resin of the insulating body 18 a metallic screen 19 is embedded, equipped with respective arms 20, which has the purpose of screening the metallic attachment components and the support base, for example, of the transformer, indicated with 21 in the attached figures.
Such a construction, as well as ensuring an adequate distribution of the electrical field, determines the further possibility of having, integrated in the structure, a capacitive intake.
It has been said how the special combined insulation and the special arrangement of the electrical screen 19 ensure excellent dielectric characteristics, rigidity and mechanical resistance to knocks.
Moreover, such a structural coating ensures an excellent resistance to thermal variations and to the fluids present inside the transformers.
Yet another important advantage is obtained considering that the feedthrough insulator according to the invention is obtained by the assembly of a reduced number of components, compared to the known types of insulators, and it does not require any particular maintenance, thanks to the surface coating, which, in practice, shields it from the direct action of atmospheric agents.
From the description that has been made, the characteristics of the feedthrough insulator for electrical transformers, object of the present invention, are clear, just as its advantages are also clear.
Finally, it is clear that the feedthrough insulator in question can undergo numerous modifications and variations, without for this reason departing from the novelty principles inherent to the inventive idea, just as it is clear that, in the practical embodiment of the invention, the materials, the shapes and the sizes of the illustrated details can be whatever according to the requirements and they can be replaced with other technically equivalent elements.

Claims

Feedthrough insulator (10) for electrical transformers, of the type with longitudinal extension and comprising an insulating body (18), which includes an outer portion (14), to be arranged in air, coupled with an inner portion (15) in an electrical transformer tank, in which the outer and inner insulating portions (14, 15) are crossed axially by a metallic tie rod (11), which acts as an electrical conductor, characterised in that at least said outer portion (14) of the insulating body (18) has a series of fins (17), positioned close together and suitably sized, in order to obtain high dielectric characteristics.
Feedthrough insulator (10) according to claim 1, characterised in that at least one portion of said insulating body (18) has a combined insulating coating, formed from the coupling of at least one layer of silicon, covering an underlying epoxy resin structure, which, in turn, surrounds said metallic tie rod (11).
Feedthrough insulator (10) according to claim 2, characterised in that inside said epoxy resin structure at least one metallic screen (19) is embedded, provided with arms (20), which has the purpose of screening the metallic attachment parts and the support base (21) of the insulator, for example on the tank of the transformer.
Feedthrough insulator (10) according to claim 1, characterised in that said metallic tie rod (11) has a top end (12) that, in operative state, remains outside of the tank of the transformer, and a bottom end (13), intended to remain inside the tank.
Feedthrough insulator (10) according to claim 1, characterised in that said portion (15) inside the tank includes at least one inner insulating body (16), with shaped structure, crossed axially by said metallic tie rod (11).
Feedthrough insulator (10) according to claim 5, characterised in that said inner insulating body (16) is attached to said metallic tie rod (11) through a threading or else by means of a punching.
Feedthrough insulator (10) according to claim 5, characterised in that said inner insulating body (16) can be obtained individually by moulding or by overmoulding on said tie rod (11).
Feedthrough insulator (10) according to claim 1, characterised in that it can be used in critical environmental conditions and, in particular, in contaminated environments.
Feedthrough insulator (10) according to claim 1, characterised in that it has at least one capacitive intake.
Feedthrough insulator (10) according to claim 1,
characterised in that the venting of air is not foreseen at the moment when the transformer is filled with oil.