This application is a 35 U.S.C. § 371 national stage application of PCT International Application No. PCT/EP2020/077676 filed on Oct. 2, 2020, which in turn claims foreign priority to European Patent Application No. 19204259.6, filed on Oct. 21, 2019, the disclosures and content of which are incorporated by reference herein in their entirety.
The present disclosure relates to a shed for an insulator of an electrical conductor.
The outermost structure of a range of power products, e.g. bushings, instrument transformers, cable terminations, breakers, surge arrestors and other insulators, is often made up of sheds. The sheds serves several purposes. They increase the creep path from voltage to ground, increasing the flashover voltage. They also act as weather protection in the case of outdoor equipment. The tips of the sheds are however rather narrow which leads to significant electric field increase in the vicinity of the tips, especially for sheds where the electrical conductor passes longitudinally through the roll of the insulator, generating radial electrical fields.
A high radial electric field outside the shed tips can lead to a corona discharge which degrades the material and leads to losses. There is also a limit on discharges during product testing. Increasing the shed thickness is possible to a degree but adds significant material cost.
It is an objective of the present disclosure to provide a shed having a reduced electrical field at the shed tip, without compromising other desired properties, such as creep distance, and without additional material cost.
According to an aspect of the present disclosure, there is provided an insulator for electrically insulating an electrical conductor. The insulator comprises a roll defining a central longitudinal through hole along a longitudinal axis of the insulator. The through hole is arranged for allowing an electrical conductor to pass there through. The insulator also comprises at least one shed arranged on an outer surface of the roll. The shed comprises a shed tip having an outer non-flat curvature defined by a plurality of different radii of curvature and comprising a most distal point of the shed. An end radius of curvature at the most distal point of the curvature is larger than a first radius of curvature at one side of the most distal point and a second radius of curvature at the other side of the most distal point.
According to another aspect of the present disclosure, there is provided a method of producing an insulator. The method comprises extruding at least one shed onto an outer surface of a roll defining a central longitudinal through hole along a longitudinal axis of the insulator. The shed comprises a shed tip having an outer non-flat curvature defined by a plurality of different radii of curvature and comprising a most distal point of the shed. An end radius of curvature at the most distal point of the curvature is larger than a first radius of curvature at one side of the most distal point and a second radius of curvature at the other side of the most distal point.
In an insulator where the electrical conductor passes through a central longitudinal through hole of the roll of the insulator, the electrical field formed will be substantially radial, implying that an electrical field will be formed outside the radially most distant, herein also called distal, parts of the shed, i.e. at the shed tips. By means of a relatively large radius of curvature at the most distal point of the shed, the electrical field at said point may be reduced. On the other hand, it is not desired with a flat surface (the radius of curvature nearing infinity) at the most distal point, i.e. a surface parallel with the longitudinal axis of the insulator, since this would instead concentrate the electrical field to either side of said flat surface.
To achieve the desired curvature in accordance with the disclosure, it may not be possible to use traditional materials, such as porcelain, or production methods, such as casting, for producing the insulator. Instead, the sheds may be formed by extrusion onto the roll of the insulator.
It is to be noted that any feature of any of the aspects may be applied to any other aspect, wherever appropriate. Likewise, any advantage of any of the aspects may apply to any of the other aspects. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.
Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the element, apparatus, component, means, step, etc.” are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. The use of “first”, “second” etc. for different features/components of the present disclosure are only intended to distinguish the features/components from other similar features/components and not to impart any order or hierarchy to the features/components.
Embodiments will be described, by way of example, with reference to the accompanying drawings, in which:
Embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments are shown. However, other embodiments in many different forms are possible within the scope of the present disclosure. Rather, the following embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like numbers refer to like elements throughout the description.
In an alternative embodiment, the sheds 2 may be formed from a continuous or discontinuous spiral around the roll 5 and along the longitudinal axis 3.
The roll 5 defines the central longitudinal through hole of the insulator 1, through which hole the electrical conductor 4 may pass. However, also other components may be arranged within the roll 5, e.g. a condenser core arranged between the roll 5 and the conductor 4. The roll 5 may be of any rigid electrically insulating material, e.g. comprising a thermosetting or curable resin, such as epoxy. The roll may be reinforced, e.g. by glass fibres. One material for forming the roll 5 is glass fibre reinforced epoxy, for example.
The roll 5 may be cylindrical, as in
The conductor 4 may e.g. be a hollow tube of an electrically conducting material, such as copper and/or aluminium.
The sheds 2 may be extruded onto the roll 2, and the sheds may be made from an electrically insulating extrudable material, e.g. comprising an elastomer such as a silicone rubber.
Embodiments of the insulator 1 may be used in e.g. electrical bushings, instrument transformers, cable terminations, breakers, surge arrestors etc., especially where a radial electrical field is formed. It is envisioned that the insulator may be especially useful in high-voltage (HV) bushings, e.g. transformer bushings.
Connecting the upper and lower surfaces 14 and 15 to each other, there is a convex curved, e.g. ellipsoid, end surface which is in the sectional
In accordance with the present disclosure, the curvature 11 is defined by a plurality of different radii of curvature R, r1 and r2 (i.e. the curvature is not circular). The radius of curvature at the most distal point (in relation to the longitudinal axis 3) of the curvature is herein called the end radius of curvature R. In addition to the end radius of curvature R, the curvature 11 has a first radius of curvature r1, which may be called an upper radius of curvature, which is a radius of curvature of a portion of the curvature 11 between the most distal point and the first point 12, and a second radius of curvature r2, which may be called a lower radius of curvature, which is a radius of curvature of a portion of the curvature 11 between the most distal point and the second point 13.
In accordance with the present disclosure, the end radius of curvature R is larger than both the first radius of curvature r1 and the second radius of curvature r2, i.e. R>r1 and R>r2. The first and second radii of curvature r1 and r2 may be the same or different, but both are smaller than the end radius of curvature R. The curvature 11 is thus flattened, but not flat, at its most distal point, e.g. being elliptical in shape. In some embodiments, the end radius of curvature R is at least twice as large as the first radius of curvature r1 and/or at least twice as large as the second radius of curvature r2, i.e. R>2r1 and/or R>2r2.
A tip thickness T may be defined as a largest thickness of the shed tip 10 of the shed 2 in the section of
In the embodiment of
In some embodiments of the present disclosure, the end radius of curvature R is larger than half of the tip thickness T, i.e. R>T/2, e.g. equal to or larger than the tip thickness T, i.e. R≥T. In some embodiments, the end radius of curvature R is within the range of 0.6T to 10T, e.g. within the range of 0.7T to 3T.
In some embodiments of the present disclosure, the first radius of curvature r1 and/or the second radius of curvature r2 is smaller than half the tip thickness T, i.e. r1,r2<0.5T, e.g. equal to or smaller than a quarter of the tip thickness, i.e. r1,r2≤0.25T.
In some embodiments of the present disclosure, the first radius of curvature (r1) and/or the second radius of curvature (r2) is within the range of 0.05T to 0.45T, e.g. within the range of 0.1T to 0.4T.
When the relation b/a is 1, the cross section of the shed tip is circular, i.e. perfectly rounded. As b/a is reduced the field is also reduced, but attains a maximum when b/a is approximately 0.5. This is because the first radius of curvature r1 and the second radius of curvature r2 have not been considered, which yields abrupt transitions between the flat upper and lower outer surfaces of the shed tip and the curvature of the end of the shed tip. When the first radius of curvature r1 and the second radius of curvature r2 are included in the simulation, the left part of the curve shown in
The present disclosure has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the present disclosure, as defined by the appended claims.
Number | Date | Country | Kind |
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19204259 | Oct 2019 | EP | regional |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2020/077676 | 10/2/2020 | WO |
Publishing Document | Publishing Date | Country | Kind |
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WO2021/078495 | 4/29/2021 | WO | A |
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20220328215 A1 | Oct 2022 | US |