Electrical Bushing Pdf

Electrical bushing - ABB Research Ltd. FIELD OF THE INVENTIONThe present invention relates to the field of high voltage technology, and in particular to high voltage bushings for providing electrical insulation of a conductor. BACKGROUND OF THE INVENTIONHigh voltage bushings are used for carrying current at high potential through a plane, often referred to as a grounded plane, where the plane is at a different potential than the current path.

High voltage bushings are designed to electrically insulate a high voltage conductor, located inside the bushing, from the grounded plane. The grounded plane can for example be a transformer tank or a wall. In order to obtain a smoothening of the electrical potential distribution between the conductor and the grounded plane, a bushing often comprises a number of floating, coaxial foils made of a conducting material and coaxially surrounding the high voltage conductor, the coaxial foils forming a so called condenser core. The foils could for example be made of aluminium, and are typically separated by a dielectric insulating material, such as for example oil impregnated or resin impregnated paper.

Transformer Bushing Pdf Thu. ABB offers a broad range of products and services to the original equipment manufacturers and users of electrical apparatus, including power and distribution transformers.

The coaxial foils serve to smoothen the electric field distribution between the outside of the bushing and the inner high voltage conductor, thus reducing the local field enhancement. The coaxial foils help to form a more homogeneous electric field, and thereby reduce the risk for electric breakdown and subsequent thermal damage. Such coaxial foils typically provide efficient capacitive grading of the electric field within the bushing. However, a local field enhancement in the vicinity of the foil edges typically remains. The enhanced field at the foil edges limits the operational voltage that can be applied between the high voltage conductor and the grounded plane. Efforts to grade the electric field at the foil edges of a bushing condenser core are disclosed in U. S. Here, double layer foils containing an electrically conducting layer and an insulating layer are coaxially arranged around a high voltage conductor, where the insulating layer has a high dielectric constant.

At the foil edges, the double layer foils are folded so that the insulating layer encloses the electrically conducting layer in order to improve the ability of the bushing to withstand partial corona discharges and surge voltages. The techniques for reducing the field stress at the foil edges discussed in U.

S. 4,3. 70,5. 14 increase the radius of the condenser core, and therefore the radius of the bushing. As the electric power technology advances, higher voltages can be employed in various applications and bushings which may withstand higher potentials are therefore required. At the same time, the physical space available to a bushing is typically limited. Therefore, it is desired to find bushings that have an improved relationship between voltage- withstanding properties and bushing diameter. SUMMARY OF THE INVENTIONAn object of the present invention is to provide a bushing having an improved relationship between voltage- withstanding properties and bushing diameter.

An electrical bushing is an insulated device that allows the safe passage of electrical energy through an earth field. Download as PDF, TXT or read online from Scribd. Flag for inappropriate content. More information Show. CONDENSER BUSHINGS TYPES S1 AND OS1-----exceed 400 amperes, the condenser is wound on a copper tube and the lead is fished through from the winding to the terminal cap of the bushing. Practical Guide To Electrical Grounding Practical Guide To Electrical Grounding An Publication W. Keith Switzer $28.95 U.S. First Printing, First Edition, August 1999 G157LT99 Grounding Book COVER 9/10/1999 2:40 PM Page 1.

3 RIP – active part The main insulation of the bushing is a dry, solid, Resin Impregnated Paper – RIP insulation, with aluminium foils inserted. In order to optimise the electrical field in axial and radial direction, the.

This object is achieved by an electrical bushing for providing electrical insulation of a conductor extending through the bushing. The bushing comprises at least one conductive foil concentrically arranged around the conductor location, and at least one field grading material (FGM) part, comprising (and typically made from) a field grading material and at least partly arranged in the extension of at least part of a foil edge of a conductive foil. The FGM part and the conductive foil, in the extension of which the FGM part is arranged, are in electrical contact. The electrical field at the foil edge will thus be graded by the FGM part at local electric field strengths above the electric field threshold of the field grading material. Since an enhanced electric field strength at the foil edges is often limiting when attempting to decrease the dimensions of a bushing designed for a particular voltage, or when attempting to increase the nominal voltage for a particular bushing dimensioning, the field grading achieved by the FGM part at the foil edge allows for an improved relationship between voltage- withstanding properties and bushing diameter.

The field grading material can advantageously be a non- linear field grading material. When a non- linear field grading material is used, an FGM part will typically provide efficient field grading over a larger range of voltages. The field grading material could for example be chosen such that an electrical field threshold of the field grading material, above which the field grading capability of the field grading material increases non- linearly with increasing electric field strength, lies above the local electric field strength expected at the foil edge at the nominal voltage of the bushing.

Oftentimes, the field grading material will be chosen such that the electrical field threshold of the field grading material lies above the local electric field strength expected at the foil edge at twice the nominal voltage of the bushing. In some embodiments, a field grading material will be used that has an electric field threshold which lies below the local electric field strength expected at the foil edge at the nominal voltage of the bushing. By using an FGM part that provides field grading also at nominal voltage, aging effects around the foil edges may be mitigated. In one embodiment, an extension distance over which an FGM part extends beyond at least part of the conductive foil edge substantially corresponds to the interfoil separation distance. Hereby can be achieved that the originally enhanced electric field strength at the foil edge can be reduced to a similar level to that found in the bulk of the condenser core. The extension distance could for example be selected such that the electric field strength at the edge of the FGM part will be below the partial discharge inception threshold of the dielectric insulating material even for voltages above twice the nominal voltage of the bushing.

The bushing may comprise a plurality of concentrically arranged conductive foils, each conductive foil having two outer foil edges. In one embodiment, an FGM part is arranged in the extension of substantially every outer foil edge, for example in the extension of every outer foil edge at which the local field would otherwise be considerably enhanced. In some geometries, the local field enhancement at some foil edges, for example the edges of the innermost foil, may not experience as strong local field enhancement as the majority of the conductive foils.

By equipping substantially every outer foil edge of the bushing with an FGM part, the risk of bushing failure due to a local enhancement of the electrical field at outer foil edges can be minimized for situations when the stress is evenly distributed among the foil edges, such as for example at nominal voltage or withstand voltage. A conductive foil of an electric bushing may have inner edges, such as for example edges of an opening in the conductive foil through which conductive leads can be arranged, or edges between by two cylindrical and axially displaced conductive foil parts forming the conductive foil. In one embodiment, an FGM part is at least partly arranged in the extension of at least part of an inner foil edge. Efficient field grading can thus be achieved also around such inner foil edges. In order to further improve the field grading properties of the FGM part, the outer edge of the FGM part can be of a field grading geometrical shape.

The FGM part could for example be made from a tape of field grading material having non- linear electric properties. Alternatively, the FGM part could for example be formed by field grading material that has been applied to at least part of a dielectric insulator arranged to provide insulation between adjacent conductive foils. Further aspects of the invention are set out in the following detailed description and in the accompanying claims. BRIEF DESCRIPTION OF THE DRAWINGSFIG.

FIG. 2 illustrates results from simulations of the electric field in the vicinity of conductive foil edges with and without an FGM part. FIG. 3a- c shows different examples of how an FGM part can be arranged at an outer foils edge of a cylindrical conductive foil. FIG. 4 shows an example of an FGM part arranged at an inner edge of a conductive foil. FIG. 5a shows results of simulations of the electric field strength in the axial direction of a bushing in the vicinity of a conductive foil edge for a number of different values of the extension distance. FIG. 5b shows results of simulations of the electric field strength in the axial direction of a bushing in the vicinity of a conductive foil edge for a number of different values of the extension distance, for a different FGM material than in FIG.

FGM part having an edge which is geometrically arranged to further provide geometrical field grading. FIG. 7 is a graph showing simulation results of the electric field strength in the vicinity of a conductive foil edge with (continuous line) and without (broken line) an FGM part. DETAILED DESCRIPTION OF THE INVENTIONFIG. At each end of the conductor 1. However, some bushings 1. The condenser core 1. FIG. 1 comprises a number of foils 1.

The dielectric insulator 1. The foils 1. 20 are typically coaxially arranged, and could for example be made of aluminium or other conducting material. The foils 1. 20 could be integrated with the dielectric material, or separate from the dielectric material.

Integration of the foil with the dielectric material could for example be achieved by means of a vacuum metallisation process, or by applying conductive ink to the dielectric material. A condenser core 1. FIG. The foils are often of cylindrical shape. Oftentimes, the axial length of an outer foil 1. The bushing of FIG. The flange 1. 25 can be used for connecting the bushing 1.