Bushing insulator

Abstract

 A bushing insulator for external use with high-level electrical strength characteristics particularly under high environmental contamination, comprising an insulating and supporting body which internally accommodates at least one conductor, a set of sheds being provided externally to the insulating and supporting body which is made of polymeric material.

Description

[0001] The present invention relates to a bushing insulator for external use with high electrical strength characteristics; the bushing insulator according to the invention is particularly suitable for medium and high-voltage applications, i.e. for voltages greather than 1000Volt, and in conditions of high environmental contamination.

[0002] It is known that electrical equipment and devices are usually equipped with bushing insulators which are suitable to carry the voltage generated inside the device to the outside of said device by means of an insulator which connects the internal part of the device to the outside and through which an electrical conductor generally passes.

[0003] Conventional insulators are constituted by a body made of ceramic material, which is provided with sheds and is generally hollow, and inside which said electrical conductor passes, allowing to connect the inside of the device on which the insulator is fitted to the outside.

[0004] The ceramic body of the insulator has, at the end located outside the device, a metallic cap which is welded to the body of the insulator after metallizing it.

[0005] The upper cap constitutes a terminal of the insulator for connection to any external conductors. At the opposite end, i.e., at the end that enters the apparatus or device, particularly in the casing of the device, there is an additional metallic flange which is meant to permanently connect the metallized body of the insulator to the upper surface of the casing of the electrical device, in which there is a seating hole.

[0006] The weld formed between the flange and the casing of the device allows to maintain a seal with respect to the fluids, usually oil or gas, that are present in medium-voltage electrical devices.

[0007] Such devices in fact usually have oil or gas as their internal insulator and therefore the flange that connects the insulator to the casing of the device must ensure the sealing of said internal fluid in order to prevent leakages which can cause environmental problems or electrical misfunctioning.

[0008] However, the above described solution suffer some drawbacks, due mainly to the fact that the ceramic body of the insulator, made for example of porcelain, is very heavy and fragile and the hermetic seal of the welds produced in order to fix the upper cap and the lower flange is critical.

[0009] Their efficiency can in fact be evaluated only after they have been formed and the device has been filled with oil or gas, which therefore also flows in the insulator body. If the welds are not made perfectly, the sealing of the fluid is compromised and it is necessary to unweld the upper cap and the lower flange again and repeat the welding operation.

[0010] This of course entails technical and cost-related problems, since the sealing characteristics of the insulator, particularly of the lower flange and of the upper cap, are important because the fluid contained in the electrical apparatus to which the insulator is connected is usually chemically very aggressive and therefore potentially dangerous for the outside environment.

[0011] Moreover, if the insulator develops any fault and needs to be replaced, it is necessary to unweld the lower flange from the casing of the device with an awkward operation before being able to remove the insulator.

[0012] Another drawback is constituted by the fact that the welds provided in order to connect the cap to the upper end of the insulator and to connect the flange to the lower end are generally welds of the TIG (Tungsten Inert Gas) type, which are delicate.

[0013] Further drawbacks of conventional solutions reside in the fact that electrical field concentrations are produced at the seating hole of the casing of the electrical device to which the insulator is connected; moreover, the electrical cable usually accommodated in the insulator body has to be appropriately insulated.

[0014] The aim of the present invention is to provide a bushing insulator which is capable of ensuring both high electrical strength and high resistance to atmospheric pollution.

[0015] Within the scope of this aim, an object of the present invention is to provide a bushing insulator which can be easily disassembled from the apparatus to which it is connected.

[0016] Another object of the present invention is to provide a bushing insulator in which the upper cap and the lower cap are connected without requiring welds.

[0017] Another object of the present invention is to provide a bushing insulator whose body is more resistant to dynamic stresses (impacts, collisions, etcetera), i.e., less fragile and less massive than insulators made of ceramic material.

[0018] Another object of the present invention is to provide a bushing insulator, particularly for medium voltages, in which the electrical cable usually accommodated in the insulator body can also be non-insulated.

[0019] Another object of the present invention is to provide a bushing insulator which allows to avoid electrical field concentrations at the seating hole of the insulator formed in the casing of the electrical device to which the insulator is connected.

[0020] Another object of the present invention is to provide a bushing insulator which is highly reliable, relatively easy to manufacture and at competitive costs.

[0021] This aim, these objects and others which will become apparent hereinafter are achieved by a bushing insulator comprising an insulating and supporting body which internally accommodates at least one conductor, insulating sheds being provided on the external surface of said insulating and supporting body, characterized in that said insulating and supporting body is made of polymeric material.

[0022] Further characteristics and advantages of the invention will become apparent from the following detailed description of a preferred but not exclusive embodiment of the insulator according to the invention, illustrated only by way of non-limitative example in the accompanying drawings, wherein the only figure 1 is a partially sectional view of a bushing insulator executed according to the present invention.

[0023] With reference to figure 1, the bushing insulator according to the present invention, generally designated by the reference numeral 10, comprises an insulating and supporting body 2 which has a tubular shape and is made of a polymeric material, more particularly an engineering polymer. An internal conductor 1 is accommodated inside the body 2.

[0024] The body 2 is preferably made of polyphenylene sulfide or polybutylene terephthalate or a polyamide, or a syndiotactic polystyrene or for example a polyketone, reinforced with reinforcement fibers such as for example glass fiber and/or mineral filler.

[0025] The polymeric material used to provide the body of the insulator must be compatible with the insulating fluid, such as for example oil, which is raised to a high temperature when it is placed in the casing of the electrical device to which the insulator is connected. Said fluid is chemically very aggressive and therefore the chosen polymeric material must be compatible with it.

[0026] The insulating and supporting body 2 contains a conductor 1 which can be provided by an insulated cable or, thanks to the polymeric material used, by a bare cable; in this way insulation of the conductor can be prevented, as instead it occurs in conventional insulators. As an alternative, the internal conductor 1 can be formed by a bar made of conducting material which is rigidly coupled to the insulating and supporting body 2.

[0027] A shed covering 3, usually made of silicone rubber, is molded on the insulating and supporting body 2 and allows to obtain the chosen creepage distance, therefore ensuring that the insulator has high electrical strength characteristics even in highly polluted environments.

[0028] The engineering polymer used to provide the insulating and supporting body 2 has high-level electrical and mechanical performance. Owing to the particular configuration of the electrical field, which has a high gradient at the coupling of the insulator to the structure of the apparatus to which it is to be connected, the insulator has a connection to the electrical device which is illustrated hereinafter.

[0029] In particular, the electrical device or apparatus, whose casing is schematically designated by the reference numeral 15 in the figure, is provided on its upper surface with a hole meant to accommodate the lower end of the insulator 10.

[0030] The connection between the insulator 10 and the upper surface of the casing 15 is provided by means of a fixing flange 4, preferably made of metallic material or of an engineering polymer, which is connected to the lower end of the insulating and supporting body 2 of the insulator by screwing onto it.

[0031] In particular, the external surface of the lower end of the insulating and supporting body 2 is in fact provided with a thread 16 which allows engagement of the flange 4 by screwing it.

[0032] The flange 4 is shaped so as to partially enter the hole for accommodating the lower end of the bushing insulator, and is in turn threaded both internally and externally in order to allow screwing onto the lower end of the insulating body 2 of the insulator and to allow the screwing of a locking nut 14, also made of metallic material or engineering polymer, which allows to lock the insulator to the upper surface of the casing 15.

[0033] A seat 13 is provided between the flange 4 and the upper surface of the casing 15 in order to accommodate a sealing element, such as for example an O-ring gasket.

[0034] The tightening of the locking nut 14 that acts on the outer thread of the flange 4 allows to fix the bushing insulator from inside the casing of the apparatus, ensuring both mechanical strength and sealing by means of the sealing element accommodated in the seat 13.

[0035] If the flange 4 is made of conducting material, such as for example aluminum, and is shaped appropriately, as shown in the figure, it allows to act as a shield against electrical field concentrations which form at the hole for accommodating the insulator in the casing 15 of the electrical device to which the insulator 10 is meant to be connected.

[0036] The internal surface of the upper end of the insulating and supporting body 2 is threaded in order to allow the connection to an external connector 12 which is screwed on said internal surface.

[0037] Both the external connector 12 and the metallic flange 4 can also be glued to the insulating and supporting body 2 of the insulator, in addition to being screwed thereto, in order to increase the seal.

[0038] In practice it has been found that the bushing insulator according to the invention fully achieves the intended aim, since it allows to achieve a high level of mechanical and electrical strength with a reduced weight due to the use of polymeric material and with improved resistance with respect to ceramic insulators.

[0039] The problem of connecting the insulator to the casing of the electrical device is furthermore solved by avoiding welds, which are both difficult to provide and difficult to remove at a later date for maintenance or for insulator replacement.

[0040] The insulator thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept; all the details may also be replaced with other technically equivalent elements.

[0041] 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 the state of the art.

Claims

1. A bushing insulator comprising an insulating and supporting body which internally accommodates at least one conductor, insulating sheds being provided on the external surface of said insulating and supporting body, characterized in that said insulating and supporting body is made of polymeric material.

2. The bushing insulator according to claim 1, characterized in that said insulating and supporting body has a first end whose external surface is threaded for the connection of a fixing flange, said flange being suitable for connecting said insulator to the casing of an electrical device to which the bushing insulator is meant to be connected.

3. The bushing insulator according to claim 1, characterized in that said insulating and supporting body has a second end whose internal surface is threaded for the connection of an external connector.

4. The bushing insulator according to claim 1, characterized in that said insulating and supporting body is made of an engineering polymer.

5. The bushing insulator according to claim 4, characterized in that said engineering polymer is chosen among polyamide, polybutylene terephthalate, polyphenyl sulfide, syndiotactic polystyrene and polyketone, reinforced with reinforcement fibers and/or mineral filler.

6. The bushing insulator according to claim 2, characterized in that said fixing flange is threaded externally and internally for screwing to the lower end of said insulating and supporting body of the insulator and for engagement with a locking nut which is meant to allow the stable connection of said insulator to said casing of the electrical device.

7. The bushing insulator according to claim 6, characterized in that said fixing flange has, at a region where said fixing flange abuts against said casing of the electrical device, a seat for accommodating a sealing element.

8. The bushing insulator according to claim 7, characterized in that said sealing element is an O-ring gasket.

9. The bushing insulator according to one or more of claims 4 to 8, characterized in that said external connector and said fixing flange are both screwed and glued to said insulating and supporting body.

10. The bushing insulator according to one or more of the preceding claims, characterized in that said fixing flange for connecting said insulating and supporting body to said casing of the electrical device is shaped so as to partially enter a hole for accommodating said bushing insulator, which is provided on the casing of said electrical device.

11. The bushing insulator according to one or more of the preceding claims, characterized in that said at least one internal conductor is constituted by a bare electric cable.

12. The bushing insulator according to one or more of the claims fro 1 to 10, characterized in that said at least one internal conductor is constituted by a bar made of conducting material which is rigidly coupled to said insulating and supporting body and is arranged inside it.

13. The bushing insulator according to one or more of the preceding claims, characterized in that said sheds arranged outside said insulating and supporting body are made of silicone rubber.

Drawing