CN113412522A

CN113412522A - Elastic tubular high voltage insulator

Info

Publication number: CN113412522A
Application number: CN202080013613.2A
Authority: CN
Inventors: B·莫里兹
Original assignee: Hertzmann Power Co
Current assignee: Hertzmann Power Co; HM Power AB
Priority date: 2019-02-11
Filing date: 2020-02-10
Publication date: 2021-09-17
Also published as: EP3924984A4; SE543113C2; WO2020167218A1; SE1930052A1; EP3924984A1

Abstract

A tubular insulator (1) for a high voltage element (8), the insulator comprising an insulating structure, wherein an inner surface of the insulator is in electrical contact with the high voltage element (8) and an outer surface of the insulator is connected to ground potential, and wherein a plurality of conductive layers (4) are arranged between the outer and inner surfaces. Substantially, the entire insulator has elastic or stretchable characteristics so that the insulator can be deformed or bendable into a predetermined shape different from the shape in a state where no external force is applied to the insulator.

Description

Elastic tubular high voltage insulator

Technical Field

The present invention relates to high voltage insulation. More precisely, the invention relates to a tubular body providing insulation between an inner surface and an outer surface having different electrical potentials. More particularly, the present invention relates to tubular insulators having multiple conductive layers to control the electric field distribution. In particular, the present invention relates to insulators having tapered ends.

Background

Insulators comprising a plurality of conductive layers forming a capacitor element are most commonly found in electrical bushings. Such bushings are devices that transmit current at high potential through a grounded barrier, such as a transformer tank. To reduce and control the electric field, capacitor bushings have been developed. The capacitor bushing facilitates electrical stress control by inserting a floating equalizer plate integrated into the core of the bushing. The condenser core reduces the electric field gradient and distributes the electric field along the length of the insulator. Thus avoiding electric field concentration and thus avoiding partial discharge and flashover.

In general, the known basic principle is to make a cylindrical insulation structure for high-voltage components, wherein one inner surface of the insulation structure is in electrical contact with the high-voltage component, the outer surface of the insulator is connected to ground potential, and there are several conducting layers between said outer and inner surfaces, between the innermost and outermost conducting layers the conducting layers have different lengths in the axial direction, the distance in the axial direction being several times longer than the distance in the radial direction. The aim is to reduce the electric field at the interface of the insulation with the ambient air. The reason is that the specific electrical resistance of air is much lower than that of solid insulating material.

The condenser core of the bushing is usually wound from paper or crepe paper as a spacer. The equalizing plate is composed of a metal layer. The metal layer is typically made of aluminum. These cylindrical plates are positioned coaxially to achieve an optimal balance between external flashover and internal puncture strength. The paper spacer ensures a defined position of the electrode plates and provides mechanical stability.

The condenser core is impregnated with oil (OIP, oil impregnated paper) or resin (RIP, resin impregnated paper). The advantage of RIP bushings is that they are dry (oil-free) bushings. The core of an RIP bushing is wound from paper, wherein an aluminium plate is inserted in place between adjacent paper windings. The resin is then introduced during the heating and vacuum process of the core.

Bushings are used to insulate the conductors carrying high voltage currents through the grounded enclosure. It is a challenge to safely accomplish this task without flashover because the size of the cannula is very small compared to the size of the device to which it is connected. The bushing needs to handle not only electrical and thermal stresses, but also mechanical stresses. Thus, the sleeve is made of a rigid material to support the conductor inside. The rigid casing of the bushing comprises most commonly a porcelain or fiberglass tube. Most commonly, the conductive layer is made of aluminum foil.

From US 5227584, a barrier for a field control type capacitor in a transformer bushing terminal is previously known. The purpose of the barrier is to overcome flashovers between the transformer and the conductor of the transformer. This is achieved by the geometry of the barrier.

From US 7742676, a method for producing a high voltage bushing is previously known. The object of the method is to provide a more time-saving production of the casing. This is achieved by using an electrical layer with openings, thus providing the base material to be pierced.

Disclosure of Invention

The main object of the present invention is to find a way to provide a bendable and very flexible tubular body for insulating high voltage elements/conductors from ground potential.

According to the invention, this object is achieved by a tubular insulator as defined by the features in the independent claim 1.

Briefly, a tubular insulator for a high voltage element comprises an insulating structure, wherein an inner surface of the insulator/structure is in electrical contact with the high voltage element and an outer surface of the insulator/structure is connected to ground potential. A plurality of electrically conductive layers are disposed between the outer and inner surfaces and separated by a layer of electrically insulating material. The conductive particles or the powder material are embedded in the matrix material at a molecular level, the matrix material being substantially the same molecules as the insulating material, so that the insulator has elastic characteristics such that the insulator can be deformed into a predetermined shape different from a shape in a state where no external force is applied to the insulator/structure.

Preferred embodiments are described in the dependent claims.

According to the invention, the tubular insulator is made of an elastic and stretchable insulating material comprising a conductive layer containing carbon powder or other conductive powder or particles. In an embodiment, the conductive layer is formed in a stretchable insulating material. The stretchable insulating material may comprise an elastomeric compound as well as a plastic compound. In an embodiment, the insulating material comprises an elastomer, silicone rubber, or EPDM rubber. The expression "elastic" is best understood to mean a rubber material. In an embodiment of the invention, the flexible tubular body has a first tapered end and a second tapered end. The taper may be different depending on whether the conductor terminates in the atmosphere or in the fluid. By the tapered end, the electric field gradient can be smoothly distributed. It is possible to avoid electric field concentration that might otherwise lead to partial discharges.

The field stress at the ends of the conductive layer is high. The objective is to reduce the electric field level below the flashover tolerance in air at the insulation boundary.

Another object is to reduce the number of conductive layers to a minimum for cost and manufacturing reasons.

One common method of achieving electrical stress control of high voltage cable terminations is the so-called stress cone. Basically, the insulation thickness increases at high stress areas, allowing the electric field to become low when reaching the boundary between the insulation and the air.

The present invention addresses the need to achieve all of the goals by combining stress control using very little conductive layers with increased thickness portions of the insulating material outside the ends of the conductive layers. The invention also solves the problem of adapting the shape to another shape without destroying the insulating properties. The reason for changing the shape by applying an external force is to make one or both of manufacturing and assembling easier.

In an embodiment of the invention, the bendable tubular body is made as a straight body and then shaped to fit the bent conductor. In the case of a bendable conductor, an insulator is threaded onto the conductor, and then the conductor and insulator are bent together. In the case of a curved solid electrode, a stretchable insulator is threaded onto the curved structure.

In an embodiment, the layers are inverted, meaning that the shortest layer in the axial direction is located at the inner diameter of the insulator and the longest layer is located at the outer diameter of the insulator. This design is suitable for use in cable terminations and cable joints.

In another embodiment of the invention, the outer insulation comprises a flange to increase the creepage distance. The flange is located just outside the end of the conductive layer to allow for a reduction in the electric field level at the insulation/air boundary.

In a further development of the invention, the bendable insulation forms part of a current transformer for high-voltage use. The current transformer includes a bendable core formed into a ring with openings to clamp around the high voltage conductor. It is noted that the openable ring comprises only one opening and no joint. A flexible insulator surrounds a portion of the core and carries the secondary winding. Thus, the secondary winding receives ground potential and can read current at ground level.

In one aspect of the invention, the object is achieved by a tubular insulator for a high voltage element, the insulator comprising an insulating structure, wherein an inner surface of the insulating structure is in electrical contact with the high voltage element and an outer surface of the insulating structure is connected to ground potential, and a number of conductive layers are provided between said outer and inner surfaces, wherein substantially the entire insulating structure material is preferably homogeneous and has elastic or stretchable properties such that the insulating structure is deformable or bendable into a predetermined shape different from the shape in a state in which no external force is applied to the insulating structure.

Preferred embodiments and features of the invention are set forth below.

-the insulator/structure comprises an elastic material having rubber properties,

the conductive layer comprises carbon particles or powder or other conductive material dispersed in an elastomeric material,

the conductive layer has substantially the same elastic properties as the material of the non-conductive material (i.e. the insulating structure),

-the conductive layers have different lengths in the axial direction between the innermost conductive layer and the outermost conductive layer, the distance in the axial direction being longer than the distance in the radial direction, preferably the distance in the axial direction being several times longer than the distance in the radial direction,

-the length in the axial direction of the innermost conductive layer is longer than the length of the outermost conductive layer, and vice versa,

-the length of the electrically conductive layer in the axial direction increases continuously or stepwise from the inner surface to the outer surface and vice versa,

the lengths of the electrically conductive layers in the axial direction are substantially equal and the electrically conductive layers are axially displaced relative to each other from the inner surface to the outer surface and vice versa.

The thickness of the insulating material portions or intermediate insulating portions between the conductive layers differs between each conductive layer,

providing the same or substantially the same molecular and polymer matrix in both the insulating layer and the electrically conductive layer, the insulator or structure being deformable in any direction, preferably by more than about 10% elongation, without any separation and/or voids being created within or between the layers, the insulating layer and the electrically conductive layer.

The insulating structure or insulator has a tapered shape at least one end, preferably at both ends,

the insulating structure or insulator further comprises an additional insulating material, such as a radially extending flange or disc located axially at or near an end region of the conductive layer,

-the insulating structure is similarly tapered at both ends to reduce the electric field at the surfaces of the insulating structure having a different potential than the inner conductive element on both sides of the middle portion,

the insulating structure is tapered at one end (where the conductive layer has a continuously longer extension near the inner high voltage element) and conversely at the opposite end.

In another aspect of the invention, a tubular insulator for insulating a high voltage conductor from ground potential may be provided, the tubular insulator comprising an insulating structure comprising a plurality of coaxially oriented conductive layers to control the electric field distribution, wherein the insulating structure has elastic or stretchable properties such that the insulator is deformable or bendable to assume a predetermined shaped structure, such as a predetermined bent structure.

In another aspect of the present invention, there may be provided a current transformer for a high voltage electrical power line, the current transformer comprising an electrical power line enclosure core, a tubular insulator and a secondary winding carried by the insulator, the tubular insulator comprising an insulating structure comprising a plurality of coaxially oriented conductive layers to control the electric field distribution, wherein the insulating structure has elastic or stretchable properties such that the insulator is deformable or bendable to assume a predetermined shaped configuration.

In another aspect of the invention, a cable termination or cable joint for a high voltage cable may be provided, the cable termination or cable joint comprising a tubular insulator comprising an insulating structure comprising a plurality of coaxially oriented conductive layers to control the electric field distribution, wherein the insulating structure has elastic or stretchable properties such that the insulator is deformable or bendable to assume a predetermined shaped configuration.

Another important aspect is the capacitive distribution of the voltage of each conductive layer. The voltage between each layer is proportional to the capacitance. The voltage distribution between all layers may be equal if the thickness of the insulation between the conductive layers varies inversely with the length of the layers. The invention makes it possible to optimize both the axial length and the thickness to achieve the best possible use of the insulating material.

Finally, the aim is to maintain the electrical resistance even when the entire insulation is deformed, i.e. for example bent, stretched and/or pressed. The present invention satisfies this objective by using the same or substantially the same molecules throughout the insulator. Carbon powder or other conductive material is integrated in the matrix of this molecule, and both the insulating material between the conductive layers and the outer insulation have the same or substantially the same molecule. When final curing is performed, the cross-linking between all interfaces produces a single macromolecule. Any mechanical stress applied during the forming/deformation process does not result in internal separation or formation of voids or gaps. The insulating properties are also maintained after shaping or deformation.

Drawings

Other features and advantages of the present invention will become more readily apparent to those of ordinary skill in the art from the following detailed description taken in conjunction with the accompanying drawings in which:

figure 1 is a cross-section of an insulator according to the invention,

fig. 2 is a cross-section of a current transformer comprising an insulator according to the invention, wherein the insulator has a rectilinear shape before being bent into a full circle,

FIG. 3 is a perspective view of a current transformer according to the present invention, and

fig. 4 is a cross-section of a cable terminal according to the invention mounted on a cable.

Detailed Description

Fig. 1 shows an insulator 1 according to an embodiment of the invention. The insulator 1 is made of an elastic material and comprises an insulating structure comprising an intermediate insulating portion 2 and a conductive layer 4. A hollow channel for accommodating a conductor of a high voltage system is arranged in the center of the insulator. Any type of conductor, such as a transformer bushing, that passes through a hole having a different voltage than the conductor may be suitable for use with the present invention.

The insulator 1 comprises a first conductive layer forming a channel. This layer will be in contact with the conductor to be received in the hollow channel. The insulator further includes a second conductive layer defining an outer surface of the insulator. In the embodiment shown, the insulator comprises several intermediate conductive layers 4, cylindrically or coaxially oriented in the insulator between the first conductive layer and the second conductive layer. The outermost conductive layer is shorter than the innermost conductive layer. The insulator is made of an elastic material and has a stretchable characteristic. Elastic materials are to be understood as materials having a significant ability to elongate and/or compress, such as rubber-like materials or rubber-based materials. The stretchable capability allows the insulator to bend to assume a curved configuration. Thus, the conductive layer should also be stretchable and therefore not solid. Although shown in solid lines in the drawings, the conductive layer 4 contains carbon or other conductive powder or particles. In an embodiment, the conductive material is introduced into a polymer material similar to the insulating material. In an embodiment, the polymeric material comprises silicone rubber.

The conductive material (e.g. carbon powder) is embedded at the molecular level in a matrix material which is the same or substantially the same molecules as the insulating material 2 between the conductive layers 4. As used herein, "intercalated" refers to the immovable immobilization of carbon particles between molecules in the matrix of the elastomeric compound. When fully cured, the cross-linking between the conductive layer and the insulating layer forms a single elastic molecule that can be shaped or deformed without creating any voids or gaps between the conductive layer and the insulating layer.

The conductive layer may be much thinner than the insulating layer. For example, the thickness of the conductive layer may range from about 0.2mm to about 0.02mm, while the thickness of the insulating layer may be on the order of a few mm, such as from about 0.5mm to about 5mm, e.g., in embodiments, the thickness of the conductive layer is between 0.05mm and 0.02 mm.

The additional insulating material 6 fills the shape of the thicker insulating portion having ends close to the conductive layer. In an embodiment, this additional insulating material may be in the form of a radially extending flange or disc 7 located axially at or near an end region of the conductive layer. This arrangement extends the creepage distance along the interface of the insulation with the air. The electric field strength in air will also be substantially reduced in this way, since the highest electric field can be reduced into air at the conductive end portions.

Fig. 2 shows an embodiment in which the insulator 1 is moulded as a complete insulating structure to accommodate the magnetic core 8 and the secondary winding 10. The outer contour is formed by the insulation 6 and the flange 7. The secondary winding wire is led out from the cylinder 9. The insulating material layer and the conductive material layer are cross-linked after curing to form the insulator 1. In this connection, it may be noted that curing (a process well known in the polymerization field) generally involves heating in the presence or absence of a catalyst.

In particular, the entire insulator may be bent to assume a predetermined shaped configuration. This shape may have any design, but is most conveniently a bend or curve. The insulator may also stretch or expand in the radial direction. The bending capability may have the ability to form an angle between a first corner leg (angular leg) and a second corner leg. The first corner leg has a line from one end point to a midpoint of the insulator. The second corner leg has a line from the other end point to the midpoint of the insulator. This intermediate angle may be of the order of at least 45 degrees.

In a development of the invention, the insulator is used as part of a current transformer. Fig. 3 shows a current transformer installed on a high voltage line 5. For example, the magnetic core 8, which may be realized in the form of a wire or a strip, assumes the same potential as the high voltage line and the secondary winding assumes ground potential. The insulator is molded into an original straight shape. The advantage of molding the insulator into a straight shape is that it is easier to insert the straight wire core. In addition, the secondary winding is more easily wound on a straight cylindrical surface. The entire current transformer can then be bent in any way, eventually making the ends magnetically connected.

In use, the current transformer is hung from a high voltage conductor. So that the core also receives a high voltage potential. In order to insulate the secondary winding, the core is covered with an insulator according to the invention. The insulator follows the curved shape (curve) of the core.

Fig. 4 shows an embodiment of the invention for a cable termination. The insulator 11 differs from the insulator 1 only in shape. The steps of the layers are reversed in inner diameter. The left and right sides of the insulator are mirror images. This may be a basic shape that may be applied to a cable termination. The electric field grading is similar. However, this embodiment may have almost the same axial length on each layer, resulting in a uniform voltage distribution if each layer has the same thickness.

The conductive layer 12 of the high voltage cable is stripped. The conductor 14 and the cable insulation 15 extend beyond the cable conductive layer 12. The

integral insulators

11 and 6 have a smaller inner diameter than the cable insulation 15 in a relaxed state. The result is that the

insulators

11 and 6 can squeeze the cable sufficiently to expel any air and exclude any voids from being formed between the two. The conductor 13 is connected between the conducting layer 12 of the cable and the outer conducting layer of the insulator 11. In a similar manner, conductor 13 connects conductor 14 with the innermost conductive layer of insulator 11.

Therefore, for the insulators 1 and 11, a material having rubber or synthetic rubber properties is preferable in both the conductive layer and the electrically insulating layer. Among the synthetic rubbers, silicone rubbers (based on crosslinked polysiloxanes or polydimethylsiloxanes) and EPDM rubbers (ethylene-propylene-diene rubbers) are considered as preferred compounds on account of their mechanical properties (usually tensile strength), temperature resistance and weather resistance, and of course also their insulating ability and elastic properties. However, other synthetic rubbers may also be considered as alternatives, such as, for example, butadiene rubber, chloroprene rubber or chloroprene rubber, or nitrile rubber, and other rubbers not mentioned.

It is further preferred that the conductive layer and the insulating layer are the same or substantially the same molecular and polymer matrix. That is, slight differences in composition may be acceptable as long as the compounds are compatible upon curing to form crosslinks between layers without departing from the scope and spirit of the invention. As a non-limiting illustration of the expression "identical or substantially identical" molecules and polymer matrices, reference may be made to the inclusion of butadiene CH₂＝CH-CH＝CH₂Isoprene or methylbutadiene CH₂＝C(CH₃)-CH＝CH₂And dimethylbutadiene CH₂＝C(CH₃)-C(CH₃)＝CH₂The elastomeric compound and the synthetic rubber of the polymer of (a) will be considered to be the same or substantially the same molecular and polymer matrix, for example, for the purpose of forming an insulator, if appropriate.

Conductive polymers are commercially available and typically are doped with carbon (C) to the extent that contact is made between the carbon particles. Techniques for dispersing carbon particles in polymeric materials have been developed and perfected by industry companies. However, other conductive elements than carbon, such as copper or aluminum, may be used in the present invention if appropriate. Although advantageous, the scope of the invention is not limited to the embodiments presented, but also covers other embodiments which may become natural to a person skilled in the art after reading the present disclosure.

Claims

1. A tubular insulator (1, 11) for a high voltage element (8, 14), the insulator comprising an insulating structure, wherein an inner surface of the insulator is in electrical contact with the high voltage element (8, 14) and an outer surface of the insulator is connected to ground potential, and wherein a plurality of electrically conductive layers (4) are arranged between the outer and inner surfaces and separated by a layer (2) of electrically insulating material, characterized in that electrically conductive particles or powder material are embedded at the molecular level in a matrix material, which is substantially the same molecule as the insulating material, whereby the insulator (1, 11) has elastic properties such that it is deformable to a predetermined shape different from the shape in a state in which no external force is applied to the insulator.

2. Tubular insulator according to claim 1, wherein the insulator (1, 11) comprises an elastic material having rubber properties.

3. Tubular insulator according to claim 1 or 2, wherein the conductive layer (4) comprises carbon powder dispersed in an elastic material.

4. Tubular insulator according to any one of claims 1-3, wherein the conductive layers have different lengths in the axial direction between the innermost and the outermost conductive layers, the distance in the axial direction being longer than the distance in the radial direction, preferably the distance in the axial direction being several times longer than the distance in the radial direction.

5. The tubular insulator according to claim 4, wherein the length in axial direction of the innermost conductive layer is longer than the length of the outermost conductive layer, or vice versa.

6. Tubular insulator according to claim 4, wherein the length of the electrically conductive layer (4) in the axial direction increases continuously or stepwise from the inner surface to the outer surface and vice versa.

7. Tubular insulator according to any one of claims 1-3, wherein the lengths of the electrically conductive layers (4) in the axial direction are substantially equal and the electrically conductive layers (4) are axially displaced relative to each other from the inner surface to the outer surface and vice versa.

8. Tubular insulator according to one of the preceding claims, in which the insulating-material layer (2) between the conductive layers (4) differs in thickness between each layer.

9. Tubular insulator according to any one of the preceding claims, wherein the provision of the same or substantially the same molecular and polymer matrix in both the insulating layer (2) and the conductive layer (4) enables the insulator (1, 11) to be deformed in any direction with an elongation of more than about 10% without any separation and/or voids being created between the insulating layer and the conductive layer.

10. The tubular insulator according to any one of the preceding claims, wherein the insulator has a tapered shape at both ends (3).

11. The tubular insulator according to any one of the preceding claims, wherein the insulator further comprises an additional insulating material, such as a radially extending flange or disc (7) located axially at or near an end region of the conductive layer (4).