WO2011026519A1

WO2011026519A1 - Hollow electric insulator and manufacturing thereof

Info

Publication number: WO2011026519A1
Application number: PCT/EP2009/061397
Authority: WO
Inventors: Jakub Korbel; Leopold Ritzer; Patrick Meier; Reto Weder; Martin Lakner
Original assignee: ABB Research Ltd Switzerland
Current assignee: ABB Research Ltd Switzerland
Priority date: 2009-09-03
Filing date: 2009-09-03
Publication date: 2011-03-10
Anticipated expiration: 2012-03-03

Abstract

A hollow medium voltage or high voltage (composite insulator body comprising a plurality of layer portions of a first winding member wound in helical convolutions in a direction of a longitudinal axis defined by the insulator body, wherein a winding direction of the helical convolutions is tangentially with respect to the longitudinal axis and extends between a first end portion and a second end portion of the insulator body, wherein said winding direction is inclined to the longitudinal axis such that the longitudinal axis and said winding direction enclose a winding angle; the first winding member having a tensile strength in the winding direction which exceeds a tensile strength of the winding member transversely to the winding direction; the plurality of layer portions comprising a first layer portion being wound with a first winding angle and a second layer portion being wound with a second winding angle wherein an absolute value of the second winding angle differs from an absolute value of the first winding angle; and wherein the first winding member is fixed with a compound.

Description

DESCRIPTION

Hollow electric insulator and manufacturing thereof

TECHNICAL FIELD

The present invention refers to a hollow electrical insula- tion system based on composite composition. The electrical insulator tubular being in particular a high-voltage and/or medium voltage insulator body.

BACKGROUND OF THE INVENTION

Today, the use of fiber reinforced polymer compositions, hereinafter referred to as FRP's, as a suitable material for building electrical insulators for high and medium voltage applications is known. Commonly, these insulators are manufactured by winding strands of fibers through a polymer resin such as epoxy on a mandrel. The strands are wound on the mandrel by applying a predefined feed motion of the polymer strands back and fro along the mandrel in a longitudinal defined by the mandrel. This results in an in^¬ sulating body comprising several layers of strands that are aligned in a positive winding angle during a forward motion and in a negative winding angle during a backward motion caused by an escapement. For manufacturing reasons the di^¬ rection of the feed motion is changed in two opposed end sections of the future insulating body. After completing a curing process these end sections are cut off. Then, the cut section is finished such that the remaining intermedi^¬ ate portion becomes the desired insulating body.

The US-A-4, 495, 381 discloses an electrical insulator of such a type comprising an insulating section that is made of several layers of fiber band that is drawn through a liquid resin bath onto a rotating mandrel. Figure 6 and the correspondent description attend to the manufacturing process of the insulator. Winding the two successive lay^¬ ers of fiber bands are wound on a mandrel by the positive and negative winding angle in opposing convolutions re^¬ sults in a regular winding pattern.

Further, tubular electrical insulators are known in the art that are produced by winding a fiber glass filament on a cylindrical mandrel in a helical manner with respect to a longitudinal axis, i.e. the rotating axis of the man^¬ drel, from a first end portion of the mandrel to the oppo- site second end portion thereof. Eventually, the plurality of helical convolutions of the fiber that are wound on the mandrel form a first layer. Once the second end portion is reached the pitch direction of the winding guide of the fiber supply is reversed and a second layer is wound on top of the first layer with a winding angle that is di^¬ recting in the opposite direction towards the first end section. Once the first end section is reached the second layer is completed and a new, i.e. a third layer is wound in the same manner as the first layer until the desired wall thickness is achieved. After termination of a curing process the hollow FRP insulator is stripped off the man^¬ drel .

Both prior art techniques have in common that they are suitable mainly for electrical insulators that are subject to static loads. An electrical insulator delimits a gas chamber, typically a pressurized gas comprising SF6. An electrical insulator must not only be able to delimit the insulating gas in its interior at an about constant pres^¬ sure but also at dynamic load conditions that attack its interior wall surfaces extending in the longitudinal di^¬ rection. If the electrical insulator is integrated in a high current device, e.g. a generator circuit breaker, it must be able to endure two main situations. The first situation is known as short line fault (SLF) and the sec- ond situation is known as terminal fault (TlOOa) . Especially in the TlOOa case, a high gas pressure is gen^¬ erated within a comparatively short period of time. This results in a shock wave which has to be born by the struc^¬ ture of the insulator. When seen in the context of the present invention, said shock wave applies a dynamic load onto the insulator. Typically, the maximum pressure value of the shock wave, i.e. the burst pressure, exceeds the static load by far. The burst pressure may be in a range of about 60 bars or more.

Unfortunately known electrical insulators cannot be used for high end applications such as isolators of circuit breaker chambers of high or medium voltage applications, for example, since they have a comparatively poor sustain- ability if dynamic loads are applied. This is because such known insulators are usually made of epoxy resin, which is known to be a rather brittle material rather than having good mechanical stress values. Attempts to manufacture a reliable insulator being made of epoxy resin based FRP structures led to comparatively thick walled insulators. Such thick walled insulators are often that heavy such that can not be handled easily, e.g. lifted by one person only during the manufacturing process or during mainte^¬ nance or repair.

BRIEF SUMMARY OF THE INVENTION A first object of the present invention relates to a manu^¬ facturing method for creating hollow FRP insulators, in particular high voltage and medium voltage insulators, that are suitable for housing gas insulated electrical equipment in their interior in case that the insulation gas is under high pressure. A second object of the present invention relates to such electrical insulators.

These objects are solved by the subject-matter as set forth in the independent claims whereas particular embodi^¬ ments are claimed by the dependent claims. In a first aspect, a method for manufacturing a tubular high-voltage and/or medium voltage insulator body is dis^¬ closed. Said method comprises the following activities:

• Providing a winding device comprising a rotatable winding mandrel and winding guide for guiding an elongated winding member from a winding supply de^¬ vice to the winding guide in a winding direction tan- gentially towards the winding mandrel, wherein the winding mandrel defines a longitudinal axis and ex^¬ tends longitudinally between a first end portion and a second end portion, wherein said winding direction is inclined to the longitudinal axis such that the longitudinal axis and said winding direction enclose a winding angle;

• Forming a first layer portion of the insulator body by winding a first winding member in a coiled manner with respect to the longitudinal axis with a first winding angle, wherein the first winding member has a tensile strength in the winding direction which ex^¬ ceeds a tensile strength of the winding member trans^¬ versely to the winding direction;

• Forming a second layer portion of the insulator body by winding the first winding member in a coiled man^¬ ner with respect to the longitudinal axis with a sec^¬ ond winding angle, wherein an absolute value of the second winding angle differs from an absolute value of the first winding angle;

• Fixing the first winding member with a compound in a curing process.

The winding angle is the key factor for mechanical per^¬ formance of the insulator in terms of sustainability to stress. Commonly the strength of the FRP is approximately 20 times higher in direction of the fibers than in paral^¬ lel direction. Thus, the first winding member has to be oriented to carry the mechanical stresses arising of the internal pressure, bending as well as torsion in the most effective way. An optimized winding angle of the FRP for carrying the stresses while loaded by internal pressure leads to a fully tailored electrical insulator.

The full extent of the present inventions becomes clear when focusing on the actual load/stress types and con^¬ straints that are present at the different longitudinal portions of the insulator body. When investigating the me^¬ chanical load distribution within the shell wall of the tubular, hollow electrical insulator one has to consider the boundary conditions. Commonly, the opposite end por^¬ tions of the insulator having a cross-section of a circu^¬ lar ring are hold in place in a gas-tight manner by metal^¬ lic ring-shaped clamps that are fixed to an adjacent metal housing such that the insulator shell acts as an insulat- ing membrane. When focusing closer on the stress in the shell wall of the insulator in case of a high pressure ap^¬ plied by a shock wave, e.g. during the application of a burst pressure in the interior of the insulator, the mem^¬ brane-like shell wall bulges convexly between the two end portions, such that the largest inner diameter of the in^¬ sulator measured perpendicularly to the longitudinal axis is located somewhere in between the end portions in the direction of the longitudinal axis, presumed that the wall thickness is evenly distributed along the entire length of the insulator. At an insulator geometry of an even diame^¬ ter and an even shell wall thickness, the following stresses are to be assessed. Proximate to the compara^¬ tively rigid, i.e. stiff clamps, the finite insulator wall elements are subject to internal pressure as well as to tensile stress acting in the direction of the longitudinal axis of the insulator tube. When considering also the thickness of the insulator wall, the finite insulator wall elements are also subject to bending relative to the lon^¬ gitudinal axis. In addition thereto are those finite insu- lator wall elements that are located in between the two end portions with respect to the longitudinal axis also subject to hoop stress running in a circumferential, i.e. tangential direction with respect to the longitudinal axis whereas the hoop stress values exceed the tensile stress values by far.

The inventive concept addresses to these different re- quirements in stress handling of the winding member at the different locations along the longitudinal axis in the shell wall, hereinafter referred to simply as wall for en^¬ hanced readability, in that a more radial flexibility is conferred to the insulator by varying at least one of the first and second winding angle between the first and the second end portion when seen in the direction along the longitudinal axis at the time of forming one layer.

If the first as well as the second winding angle are changed monotonously for the successive layers, e.g. in that the winding angle is chosen to be small at the inner^¬ most layer and chosen to be large at the outermost, i.e. last layer, these different demands in regard of the stress to be born by the finite insulator wall elements that are located in between the two end portions in the direction of the longitudinal axis are satisfiable with a lower total number of winding layers than the total number of winding layers of a traditional insulator being wound by appliance of just one constant winding angle.

The somewhat contravening demands of a good axial tensile strength proximate to the end portions and a good hood strength longitudinally in between said end portions is achievable according to the present invention in a very effective manner without excessive undue compromises.

Although the main load is formed by the internal pressure in the above-mentioned description, additional loads originating from the clamps may cause additional tension stresses and/or bending moments in the radially inner lay^¬ ers or plies. However, good mechanical results are achiev^¬ able if the first layer is wound with a minimal first winding angle. If the electrical insulator is subject to additional loads such as axial pressure or tension, torsion and/or bending moments, the comparatively weak end portions of the insu^¬ lator body may require a different handling and/or other measures to deal with.

Now let us return to the main load case originating of the internal pressure. In a basic embodiment, the first and second layers are tubular layers, in particular tubular layers having a cylindrical, ring shaped cross section. Although the manufacturing process is demanding, the ad^¬ vantages conferred to an electrical insulator are mani^¬ fold.

In a first embodiment, the increased mechanical perform^¬ ance of the inventive electrical insulator allows to re- duce the overall mass of the electrical insulator by about 30% in an operating state of the electrical insulator, presumed that the mechanical load remains unchanged and presumed that its longitudinal end portions are fixed ap^¬ propriately. As a result, such an insulator may be lifted and handled by one person only instead of two persons. In other words, the inventive insulator body contributes es^¬ sentially to a more compact overall dimension of a medium voltage or high voltage installation since the insulator allows smaller insulation distances compared to a metallic housing.

In a second embodiment, the mass of the electrical insula^¬ tor is comparable to the mass of a conventional one. How^¬ ever, the comparatively superior mechanical performance allows an increase of the sustainable inner gas pressure of about 30% in an operating state of the electrical insu^¬ lator presumed that its longitudinal end portions are fixed appropriately.

Moreover, the variation in the winding angle allows manu^¬ facturing fully customized electrical insulators depending on the applicable demands. As an example, both the winding of insulators having a constant wall thickness and vari- able wall thickness along their length is feasible. The purpose of variable thickness of the tube is the clamping or optimal mechanical stress distribution. Thus, this also contributes to the freedom in design of the electrical in- sulator.

Moreover, the safety of the medium voltage or high voltage installation is improved in case of excessive pressure causing the housing to burst. In contrast to a metallic housing that has a latent danger of forming shrapnel-like metal projectiles when bursting does the FRP polymer insu^¬ lator body according to the present invention burst softer in that the fibers maintain the insulator particles to^¬ gether even in a burst case. If it comes to the worst there are merely polymeric parts of the insulator body that are broken of the burst section. Thus the invention contributes at least to a reduced environmental damage in case of a burst due to internal pressure overload compared to known metallic installations.

In a further embodiment even winding with a varied winding angle in the same layer becomes possible leading to fur^¬ ther applications that have not been possible before.

If the winding process produces irregularities in thick^¬ ness it is possible to compensate them during the subse^¬ quent winding in that multiple transverse windings of the first winding member are used to create a locally thicker layer .

In addition or as an alternative to tailoring a bending stiffness versus a normal stiffness in different direc^¬ tions (Χ,Υ,Ζ) by thickness variations during the winding process, the mechanical performance is customizable by winding the first (interior) layer or ply with a winding angle that is as small as possible as it is subject to ax^¬ ial stresses and winding a radially outer, in particular the outermost, layer or ply with a maximal winding angle. The technical effect is a reduced axial stress in the in- terior layer as well as a reduced hoop or membrane stress in the area between the end portions of the insulator.

The term medium voltage is understood hereinafter as a voltage being in a range between about 1 to about 72 kV whereas voltages higher than 72 kV are referred to as high voltage .

Electrical insulators manufactured according to the inven^¬ tive method are particularly useful for housing high cur^¬ rent equipment. The term high current is understood in this context as a current being more than 15 kA, in par^¬ ticular a current of about 30 kA or above.

For the following description, the term high pressure is to be understood as an internal gas pressure in the area of more than 20 bars up to 60 bars or more.

In the context of the present disclosure, the term winding member is to be understood in a broad sense not being lim^¬ ited to one single winding member such as a single fiber, but also enclosing several strands of fibers as well as fiber bundles or rovings . Furthermore it shall encompass also any kind of suitable fabrics having a predefined main orientation allocated to bear a maximum stress load.

The definition compound shall be understood broadly as a pourable, preferably liquid mixture of a dielectric mate^¬ rial. As an example, a polymer compound of a polymeric resin, e.g. epoxy resin, plus additives, where necessary in an unsolidified state of the polymer compound. Said polymer compound is used and understood hereinafter to be the material resulting in a duroplastic material, also known as thermosetting plastic or thermosetting polymer. The polymer compound comprises a thermosetting compound typically comprising epoxy resin or acrylate resin or un^¬ saturated polyester or other resins used for electrical insulations or a combination thereof.

Depending on the requirements and the feasibility during the manufacturing process, the operation of connecting the winding members of the different layers and convolutions with a compound, for example a polymer, is conducted prior to the step of forming the first and second layers. De^¬ pending on its purpose, the compound may be resinous, syn- thetic or polymeric. As an example, the wetting process may be performed by drawing the further winding member through a liquid polymeric bath prior to the step of form^¬ ing the first and second layers, for example.

All thermosetting plastics, also referred to as thermo- sets, are polymer materials that irreversibly cure form. The step of curing is achieved through heat, e.g. at a temperature above 100 degrees centigrade, through a chemi^¬ cal reaction, i.e. a two-part epoxy, for example, or irra^¬ diation such as electron beam processing. Depending on their chemical compositions, acrylates and epoxies can also cure at room temperature, for example.

The curing process transforms, also referred to as fixing step, forms the resin into a plastic or rubber by a cross- linking process. Where applicable, energy and/or catalysts are added that cause the molecular chains to react at chemically active sites (unsaturated or epoxy sites, for example) , linking into a rigid, three dimensional struc^¬ ture. The thermosetting epoxide polymer cures (polymerizes and crosslinks) typically when mixed with a catalyzing agent or hardener.

The present manufacturing method is not limited to the creation of tubular insulator bodies but shall also encom^¬ pass cone-shaped, convex, concave longitudinal shapes, where necessary even with different wall thicknesses along the longitudinal axis, but also to non-circular cross- section shapes such as polygonal or rectangular cross- sections, where required.

Depending on the required mechanical properties of the in^¬ sulator body to be produced, the at least one of the abso- lute value of the first winding angle and the absolute value of the second winding angle is varied during the winding process from a radially inner layer to a radially outer layer of the insulator body. The variation may be realized at least partially by a gradual increase of the first and/or second winding angle. In example of the in- ventive insulator body, a radially inner first layer may feature a small winding angle and is thus well suited for carrying tensile stress in the direction of the longitudi^¬ nal direction (Z) while a radially outer layer has a large winding angle such that is suited optimally for bearing hoop stress.

The selection of at least one of the first and the second winding angle depends on the diameter and/or the length in the direction of the longitudinal axis of the insulator body to be wound.

In an embodiment of the method, at least one of the abso^¬ lute value of the first winding angle and the absolute value of the second winding angle is varied between the first end portion and the second end portion in the direc^¬ tion of the longitudinal axis during the winding process of the first layer portion and the second layer portion, respectively. In other words, the winding angle is varied during the winding process of winding the very same layer portion. Such a winding angle variation can be performed by a controlled, preferably stepless escapement device or mechanism running essentially along the longitudinal axis. Such a manufacturing method leads to an insulator body whose pitch distance of two neighboring convolutions of at least one layer in the direction of the longitudinal axis is different.

Good mechanical values of an insulator body are achievable if at least one of the absolute value of the first winding angle and the absolute value of the second winding angle is varied monotonously increasingly or monotonously de- creasingly, in particular in a step-wise or continuous fashion, during the winding process from a radially inner layer to a radially outer layer and/or within one layer of the insulator body. The term monotone variation of winding angle between odd and even layer number, in particular the term monotone itself is to be understood in a mathematical sense/term in that several subsequent layers may have the same winding angle before the latter is in^¬ creased/decreased again.

If the loads demand it, an inverse situation is also con^¬ ceivable where the at least one of the first and the sec^¬ ond winding angle of the inner layer is larger than the at least one of the first and the second winding angle of the outer layer.

Embodiments of the method comprise at least one of the ab^¬ solute value of the first winding angle and the absolute value of the second winding angle that is varied monoto- nously increasingly or monotonously decreasingly, in par^¬ ticular in a step-wise or continuous fashion, during the winding process from a radially inner layer to a radially outer layer and/or within one layer of the insulator body at every layer having an odd layer number. By winding so, a gradual variation of winding angle between every odd layer can be realized, for example.

Where applicable, the method is characterized in that at least one of the absolute value of the first winding angle and the absolute value of the second winding angle is var- ied monotonously increasingly or monotonously decreas^¬ ingly, in particular in a step-wise or continuous fashion, during the winding process from a radially inner layer to a radially outer layer and/or within one layer of the in^¬ sulator body at every layer having an even layer number. An insulator wound that way features a gradual variation of winding angle between every even layer, for example.

Good mechanical values of an insulator body are achievable in terms of wall thickness and weight if the at least one of the absolute value of the first winding angle and the absolute value of the second winding angle of a radially inner layer of the insulator body is smaller than the ab- solute value of the first winding angle and the absolute value of the second winding angle of a radially outer layer of the insulator body.

Embodiments of winding angles for the method are set for the at least one of the first and second winding angle to be in a range of about 2 degrees to about 90 degrees, in particular in a range of about 5 to about 70 degrees, more particular in a range of about 9 degrees to about 50 de^¬ grees. With such an insulator good mechanical load sus- tainability is achievable.

Depending on the manufacturing process and the demands on the insulator, the first winding member is a band or rov^¬ ing of plural strands of fibers, preferably continuous strands of fibers. At least one layer is wound such that two consecutive convolutions of the band are arranged at least partially in an overlapping manner with respect to the longitudinal axis.

In a basic embodiment, one of the first winding angle and the second winding angle is a positive winding angle and one of the second winding angle and the first winding an^¬ gle is a negative winding angle with respect to the longi^¬ tudinal axis .

In case of fiber reinforced insulators having winding mem^¬ bers comprising epoxy soaked glass fibers, chemically ag- gressive gas particles such as acidic oxides, e.g. SiC>2, have a corrosive effect on the insulator body. For such or similar cases the corrosion sensitive first and second layers are protectable by a corrosion resistant protective layer. A convenient and economic method for producing such insulators is achieved if prior to the step of forming the first layer portion at least one base layer portion of the insulator body is formed by winding a second winding mem^¬ ber in a coiled manner with respect to the longitudinal axis with a third winding angle on the mandrel. Where re- quired the corrosion resistant radially innermost portion of the insulator tube comprises several layers or layer portions of the second winding member, e.g. if a certain minimal thickness of the protective base layer is re^¬ quired .

The third winding angle is selected to be positive or negative with respect to the longitudinal axis. Further he may be selected to be small, medium or large depending on the technical demands on the base layer as well as on sub^¬ sequent first and/or second layer portions.

In an embodiment, the second winding member is a strip- shaped tissue, in particular a tissue comprising at least one of a fabric or a fleece. Good results are achievable with a polyester fabric or a polyester fleece.

In a basic embodiment of the method, a convolution of the second winding member is wound such that it contacts a neighboring convolution of the second winding member of the same layer in an overlapping manner.

Depending on the compound and its processability, the method employs a step of wetting at least one of the first winding member and the second winding member with a com- pound prior to the step of forming the first layer, the second layer and the base layer, respectively, in particu^¬ lar by drawing the first winding member through a liquid polymeric bath.

If the end portions of the insulator are still considered as too weak to sustain the mechanical stresses, these weak portions can be locally improved. In this case, the method comprises an additional step of embedding at least one lo^¬ cal enforcement element between the layers, particularly in between the at least one of the first end portion and the second end portion of the insulator body. The local enforcement element can be a fabric, in particular a fab^¬ ric having a predefined mechanical tensional strength in at least direction for structurally conferring or improv^¬ ing at least one stress withstand capability to/of the in- sulator body. One embodiment of such a local enforcement element comprises at least one pre-preg. In a particularly advantageous manufacturing method, sev^¬ eral electrical insulators are wound on the mandrel at the same time as one single tubular insulator body. Thereaf^¬ ter, the hollow tube in cut in longitudinal ring-like por- tions and their end surfaces machined and/or finished, if required. By doing so the inventive method contributes to an economical production of insulator bodies that may have different mechanical performance abilities depending on the location of the place with a local winding angle ori- entation where the cut is performed. In an embodiment where one common insulator body has been wound with vary^¬ ing winding angles of at least the first or second winding angle at least twice, two mechanical identical insulator bodies may be derived if the cut is placed in about the mid-length, provided the angle variation is equal in both longitudinal tube portions.

Moreover, the cutting allows an economic manufacturing of electric insulators having different wall thicknesses with respect to their longitudinal axis.

In a second aspect, a hollow high-voltage and/or medium voltage insulator body is disclosed that comprises a plu^¬ rality of layer portions of a first winding member wound in helical convolutions in a direction of a longitudinal axis defined by the insulator body. A winding direction of the helical convolutions is tangentially with respect to the longitudinal axis and extends between a first end por^¬ tion and a second end portion of the insulator body. Said winding direction is inclined to the longitudinal axis such that the longitudinal axis and said winding direction enclose a winding angle. The first winding member has a tensile strength in the winding direction which exceeds a tensile strength of the winding member transversely to the winding direction. The plurality of layer portions com^¬ prising a first layer portion is wound with a first wind- ing angle and a second layer portion being wound with a second winding angle wherein an absolute value of the sec^¬ ond winding angle differs from an absolute value of the first winding angle. Eventually, the first winding member is fixed with a compound, e.g. in a curing process.

Appointing different winding angles to certain fibers con^¬ tributes essentially to an optimized exploitation of the stress bearing abilities of the fibers resulting in an in^¬ sulator body that is able to withstand both a static load as well as a dynamic pressure shock wave originating from a pressurized medium present in the interior of the insu^¬ lator body.

For further advantages and the technical effects of such an insulator body please see the description relating to the manufacturing method which applies likewise to the in^¬ ventive insulator body.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the invention and many of the advantages thereof will be readily obtained as the same becomes better understood by reference to the follow^¬ ing detailed description when considered in connection with the annexed schematic drawings, wherein:

Figure 1 shows a three dimensional view of first embodi- ment of a tubular electric insulator body hav^¬ ing a ring-like cross section in its longitudi^¬ nal direction;

Figure 2 shows a longitudinal section of the first em^¬ bodiment as shown in figure 1, where the insu^¬ lator body is clamped at its end portions and where no internal gas pressure is applied;

Figure 3 shows the longitudinal section as shown in fig^¬ ure 2 but where an internal gas pressure is ap^¬ plied;

Figure 4 shows a partial sectional view of the section

IV in figure 3;

Figure 5 shows a simplified winding scheme using a mini^¬ mal winding angle; Figure 6 shows a simplified winding scheme using a lar^¬ ger winding angle than that shown in figure 5;

Figure 7 shows a simplified winding scheme using a maxi^¬ mal winding angle; and

Figure 8 shows a simplified winding scheme where differ^¬ ent winding angles are applied at different longitudinal portions of the insulator body.

In the drawings identical and/or functionally identical elements parts and designated by identical reference nu^¬ merals, unless indicated otherwise.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of the inventive winding process of a tubular medium voltage or high voltage composite insulator body la is represented by figure 1. Figure 1 shows par^¬ tially six convolution portions of the first winding mem^¬ ber 2 which wound at six different winding angles CCl to Cc6 respectively of increasing absolute winding angle values but with the same positive first winding angle a . For easing the understanding, the six winding members are displayed in the very same tangential winding point 4 of an essentially cylindrical mandrel (not shown) in a place where a shell line 6 runs essentially parallel with a lon^¬ gitudinal axis 7 defined by the rotatable mandrel. The longitudinal axis 7 is at the same time the rotating axis of the mandrel 5 running in the direction X. Transversely thereto, a full circumferential, tangential line 8 runs about the longitudinal axis 7 on a shell surface of the mandrel. The ring-like cross section of the insulator body extends in a plane Y-Z that is extending perpendicularly to the direction X.

The strength of the composite insulator is approximately twenty times higher in the direction in which the first winding members runs than in a direction running trans- versely thereto. The first winding member is a fiber, in particular a glass fiber, but other fibers, such as carbon (graphite) , polymer (aramid) or combination fibers, may be used with or without their occurrence in rovings, bundles and the like. Although a variety of glass fibers would be suitable, the preferred fiber is "E-glass". "E-glass" is an inexpensive, electrical grade fiber having high me^¬ chanical strength. According to the invention, the con^¬ tinuous strand of fibers forming the first winding member 2 is "wetted" in a controlled manner in a liquid resin bath (not shown) . For example, the fibers are coated with a polyester, vinyl ester, epoxy, phenolic, thermoplastic polymer or other material having similar properties. The resin must provide a good mechanical bond and preferably be suitable for high temperature molding.

Then, the first winding member is repetitively wound from one end portion 13to the other end portion 14 by forming multiple loops or helix-like convolutions in case of the circle-cylindric cross section of the insulator body 1.

The maximum stress allowed by the first winding member 2 wound along the maximal angle

(the closest to 90 DEG of the full tangential line 8) is significantly larger than that of the first winding member wound under the angle

and much greater than that of the fibers wound along the angle and so on. See also figures 5 to 7 for refer-

ence .

The mandrel 5 and the shell surface 9 of the mandrel are not shown in figure 1 but in figure 5 where they are indi^¬ cated by a dash double-dotted line in. The dominant hoop stress direction 10 is indicated by the arrows running in the circumferential direction.

Prior to winding a first layer with the first winding mem^¬ ber, a cylindrical base layer (not shown) is formed by em^¬ ploying a second winding element 3 to a third layer 3 formed by a strip-like protective polyester fleece for the purpose of providing a corrosion resistant base layer (shown partially in the lower part of figure 2 as an op- tion leading to an insulator body lc) . The wall structure of the insulator body lc resulting of such a manufacturing method leads to a set-up as shown at the broken insulator wall 17b at the second end portion 14 of the insulator body lc. The polyester fleece is applied on the mandrel in a helical manner by applying a maximized third winding an^¬ gle and by winding a consecutive convolution of the sec^¬ ond, strip-shaped winding member in a partially overlap^¬ ping manner on the preceding convolution of the same base layer. The fleece is impregnated with the compound, e.g. an epoxy resin composition and afterwards wound around the rotating mandrel up to a predefined layer thickness. Imme^¬ diately afterwards, a radially outer layer set comprising at least one of the first and second layer is formed by winding the first winding member around said base layer. Then, the winding is continued until a desired thickness and orientation of winding members is reached. The first winding member is impregnated with the same compound as the second winding member prior to the winding process. The polyester fleece is applied on the mandrel in a heli^¬ cal manner by applying a maximized third winding angle and by winding a consecutive convolution of the second, strip- shaped winding member in a partially overlapping manner on the preceding convolution of the same base layer.

This angle is the key factor for mechanical performance of the insulator. Commonly the strength of the FRP is ap^¬ proximately 20 times higher in direction of the fibers than in parallel direction. Therefore, the first winding member 2, e.g. the fibers have to be oriented to carry the stresses in the most effective way. Since the radially in^¬ nermost first layer portion 11 is exposed to axial stresses, the first winding angle of said layer is se^¬ lected to be as small as possible (such as indicated by figure 5), the e.g. radially outermost second layer por- tion 12 has to carry the hoop stress and therefore the second winding angle is as high as possible, i.e. maximal (values are nearly 90° as shown in figure 7. Winding an- gles of the layer located radially in between the inner^¬ most first layer and the radially outermost second layer have values between the initial first winding angle and the last second winding angle (see figure 6 for refer- ence) . The plurality of layers of the first winding ele^¬ ment 2 leads to an insulator wall 17a such as indicated in figure 3 and the upper half of figure 2.

Together with figure 5 and figure 6 it becomes clear that after at least two helical wound tubular layer portions, e.g. a first layer portion 11 and a second layer portion 12 are developed with the first winding member 2, the winding pattern is changed to an almost circumferen^¬ tial/tangential winding with a large winding angle such as shown in figure 7. The first winding angles shown in fig- ures 5 to 7 have the same orientation, i.e. are all posi^¬ tive angles for the purpose of easy understanding. In this embodiment, the first winding member has been brought back from the second end portion 14 to the first end portion 13 by winding a further first/second layer with the first/second winding angle remaining unchanged with re^¬ spect to its absolute value but with a negative winding angle with respect to the longitudinal axis. With other words, these layers exist but have not been shown for clarity reasons.

Varying the winding angles during the winding process ad^¬ dresses specifically to the different mechanical stresses that are to be found in the shell wall elements of the in^¬ sulating body along in the direction of the longitudinal axis 7. This is explained best in a most basic embodiment of the inventive insulator body of tubular shape with an even wall thickness, whereas the profile of the tube is symmetrical in respect to the longitudinal axis defined by the insulator such as shown in figure 2. For the sake of improved clarity, the insulator wall 17 is not displayed as a cross-hatched area in the sectional views of figures 2 and 3. The first layer and the second layer have not been displayed separately in the set of figures as it would be detrimental to the understandability . Said insu^¬ lator body 1 is clamped in gas tight manner at each of its end portions, i.e. at its first end portion 13 and its second end portion 14 in particular by metallic clamps 15 having a much higher stiffness than the composite insula^¬ tor body 1. Upon exposure of the insulator body 1 by an internal pressure caused by an insulating medium, in par^¬ ticular insulating gas such as SF6, for example, the insu^¬ lator shell wall 17 deforms in between the first end por- tion 13 and the second end portion 14 sooner than at the clamps 15a, 15b, causing the insulator to deflect and/or deform to a barrel-shape. The internal pressure pi causes the main load for the following explanation. Figure 3 shows the longitudinal section as shown in figure 2 but where an internal gas pressure pi is applied. The stress situation in an area IV at the clamp 15a is shown and ex^¬ plained with reference to figure 4. In this condition, the first winding member 2 of the first layer portion 11 is bent around an edge line of the circumferenting clamp 15 shown in an edge point 16 in figure 4 such that the shell wall 17 is deflected off the longitudinal axis 7 the more it is distanced from the clamp 15a in the longitudinal di^¬ rection Z. The force applied perpendicularly to the ra^¬ dially inner surface of the insulator wall 17 is indicated as force Fi. Hence, the tensile stress value in a finite wall element proximate to the clamps, i.e. at an end por^¬ tion of the insulator body (indicated by double-headed ar^¬ row 18), exceeds the value of the hoop stress 10 running in a circumferential direction with respect to the longi- tudinal axis. Entirely different thereto is the stress situation in a finite wall element located at about equi^¬ distance between the first and the second end portions 13, 14 of the insulator body since there it is the hoop stress value that exceeds the tensile stress value by far. The hoop stress results mainly of the main load, i.e. the in^¬ ternal pressure in the hollow/cavity of the tubular insu^¬ lator body 1. Thus the inventive concept resides in orienting as many fibers as possible such that all or at least most mechani^¬ cal stresses are carried in the most effective way. This is achieved by allocating fibers having a first winding angle to carry mainly the tensile stress and to allocate fibers being wound at a second, different winding angle to carry mainly the hoop stress leading to an insulator body that features an optimized stress distribution selected for each specific layer or portion thereof. As a result, the burden of stress in the fibers can be kept at a mini^¬ mum which is positive in terms of an enhanced overall de^¬ vice security both during regular use as well as in case of a failure.

In addition, this gives the opportunity to find the opti- mal thickness for specific internal pressure loading.

An inventive variation of that inventive concept is shown in figure 8 that discloses an insulator lb where an abso^¬ lute value of the first winding angle

and an absolute value of the second winding angle

are varied between the first end portion 13 and the second end portion 14 in the direction of the longitudinal axis dur^¬ ing the winding process of the first layer portion Hand the second layer portion 12, respectively. In figure 8 only a selected number of first winding elements 2 are displayed for showing the winding angle variation sche^¬ matically only. Thus the lines representing the first winding member that is pulled in the winding direction with a certain winding angle are not shown in a detailed side view where the first winding member 2 would be visi- ble as a curve rather than the schematic straight section shown in any of figures 5 to 8.

In addition, figure 8 shows that cutting a first longitu^¬ dinal section 19 at the first cutting lines 20 leads to a first tubular electrical insulator in the second longitu- dinal section 21 whose mechanical performance is different to a second tubular electrical insulator in the second longitudinal section 21 that was derived by cutting the insulator body lb along the second cutting lines 22 owing to the different orientation of the first winding angle convolutions with respect to the longitudinal axis 7 at both lateral ends of the respective longitudinal sections. The first and second cutting lines 20, 22 are displayed by a dash-double-dotted and a dotted line, respectively.

List of Reference Characters

1 tubular electrical insulator body

2 first winding member

3 second winding member

4 tangential winding point

5 mandrel

6 shell line

7 longitudinal axis

8 full tangential line

9 shell surface of mandrel

10 hoop stress direction

11 first layer portion

12 second layer portion

13 first end portion

14 second end portion

15 c1amps

16 edge point / edge line

17 shell wall

18 tensile stress direction

19 first longitudinal section

20 first cutting line

21 second longitudinal section

22 second cutting line

Claims

A method for manufacturing a tubular high-voltage and/or medium voltage insulator body (la, lb), com^¬ prising the following steps:

a) Providing a winding device comprising a rotatable winding mandrel (5) and winding guide for guiding an elongated winding member from a winding supply device to the winding guide in a winding direction tangentially towards the winding mandrel, wherein the winding mandrel defines a longitudinal axis (7) and extends longitudinally between a first end por^¬ tion (13) and a second end portion (14), wherein said winding direction is inclined to the longitu^¬ dinal axis such that the longitudinal axis and said winding direction enclose a winding angle;

b) Forming a first layer portion (11) of the insulator body by winding a first winding member (2) in a coiled manner with respect to the longitudinal axis (7) with a first winding angle, wherein the first winding member (2) has a tensile strength in the winding direction which exceeds a tensile strength of the first winding member transversely to the winding direction;

c) Forming a second layer portion (12) of the insula^¬ tor body by winding the first winding member (2) in a coiled manner with respect to the longitudinal axis with a second winding angle, wherein an abso^¬ lute value of the second winding angle differs from an absolute value of the first winding angle;

d) Fixing the first winding member (2) with a compound in a curing process.

The method according to claim 1, wherein at least one of the absolute value of the first winding angle and the absolute value of the second winding angle is var^¬ ied during the winding process from a radially inner layer to a radially outer layer of the insulator body.

3. The method according to claim 1 or 2, wherein at least one of the absolute value of the first winding angle and the absolute value of the second winding angle is varied between the first end portion and the second end portion in the direction of the longitudinal axis during the winding process of the first layer portion and the second layer portion, respectively.

4. The method according to any one of claims 1 to 3, wherein at least one of the absolute value of the first winding angle and the absolute value of the sec^¬ ond winding angle is varied monotonously increasingly or monotonously decreasingly, in particular in a step^¬ wise or continuous fashion, during the winding process from a radially inner layer to a radially outer layer and/or within one layer of the insulator body.

5. The method according to any one of claims 1 to 3, wherein at least one of the absolute value of the first winding angle and the absolute value of the sec^¬ ond winding angle is varied monotonously increasingly or monotonously decreasingly, in particular in a step^¬ wise or continuous fashion, during the winding process from a radially inner layer to a radially outer layer and/or within one layer of the insulator body at every layer having an odd layer number.

6. The method according to any one of claims 1 to 3, wherein at least one of the absolute value of the first winding angle and the absolute value of the sec^¬ ond winding angle is varied monotonously increasingly or monotonously decreasingly, in particular in a step^¬ wise or continuous fashion, during the winding process from a radially inner layer to a radially outer layer and/or within one layer of the insulator body at every layer having an even layer number.

7. The method according to any one of claims 4 to 6, wherein the at least one of the absolute value of the first winding angle and the absolute value of the sec^¬ ond winding angle of a radially inner layer of the in^¬ sulator body is smaller than the absolute value of the first winding angle and the absolute value of the sec^¬ ond winding angle of a radially outer layer of the in^¬ sulator body.

8. The method according to any one of claims 1 to 7, characterized setting the at least one of the first and second winding angle to be in a range of about 2 degrees to about 90 degrees, in particular in a range of about 5 to about 70 degrees, more particular in a range of about 9 degrees to about 50 degrees.

9. The method according to any one of claims 1 to 8, characterized in that the first winding member is a band or roving of plural strands of fibers, preferably continuous strands of fibers, and wherein at least one layer is wound such that two consecutive convolutions of the band are arranged at least partially in an overlapping manner with respect to the longitudinal axis .

10. The method according to any one of claims 1 to 9, wherein one of the first winding angle and the second winding angle is a positive winding angle and wherein one of the second winding angle and the first winding angle is a negative winding angle with respect to the longitudinal axis.

11. The method according to any one of claims 1 to 10, wherein prior to the step of forming the first layer portion at least one base layer portion of the insula^¬ tor body is formed by winding a second winding member in a coiled manner with respect to the longitudinal axis with a third winding angle on the mandrel.

12. The method according to claim 11, wherein the second winding member is a strip-shaped tissue, in particular a tissue comprising at least one of a fabric or a fleece, in particular a polyester fabric or fleece.

13. The method according to claim 11 or 12, wherein a con^¬ volution of the second winding member is wound such that it contacts a neighboring convolution of the sec^¬ ond winding member of the same layer in an overlapping manner .

14. The method according to any one of claims 11 to 13, wherein the third winding angle is a positive winding angle with respect to the longitudinal axis.

15. The method according to any one of claims 1 to 14, characterized by wetting at least one of the first winding member and the second winding member with a compound prior to the step of forming the first layer, the second layer and the base layer, respectively, in particular by drawing the first winding member through a liquid polymeric bath.

16. The method according to any one of claims 1 to 15, wherein at least one local enforcement element is em- bedded between the layers, particularly in at least one of the first end portion and the second end por^¬ tion of the insulator body, the local enforcement ele^¬ ment being in particular a fabric, in particular a fabric having a predefined mechanical tensional strength in at least direction for structurally con^¬ ferring or improving at least one stress withstand ca^¬ pability to/of the insulator body, more particularly the local enforcement element comprising at least one pre-preg .

17. The method according to any one of claims 1 to 16, wherein at least one tailored insulator section is de^¬ rived by cutting a longitudinal section (19, 21) out of the cured insulator body along a cutting line (20, 22) .

18. A hollow medium voltage or high voltage (fiber rein^¬ forced polymer) composite insulator body (la, lb) com^¬ prising a plurality of layer portions of a first wind^¬ ing member (2) wound in helical convolutions in a di^¬ rection of a longitudinal axis (7) defined by the in^¬ sulator body, wherein a convoluting direction of the helical convolutions is tangentially with respect to the longitudinal axis and extends between a first end portion and a second end portion of the insulator body, wherein said convoluting direction is inclined to the longitudinal axis such that the longitudinal axis and said convoluting direction enclose a winding angle;

the first winding member having a tensile strength in the winding direction which exceeds a tensile strength of the winding member transversely to the winding di^¬ rection;

the plurality of layer portions comprising a first layer portion being wound with a first winding angle and a second layer portion being wound with a second winding angle wherein an absolute value of the second winding angle differs from an absolute value of the first winding angle;

and wherein the first winding member is fixed with a compound .

19. The insulator body according to claim 18, wherein at least one of the absolute value of the first winding angle and the absolute value of the second winding an^¬ gle of a radially inner layer is different from at least one of the absolute value of the first winding angle of a radially outer layer of the insulator body.

20. The insulator body according to claim 18 or 19, wherein the first layer portion and the second layer portion belongs to the same layer such that a pitch distance of two neighboring convolutions of the same layer is different.

21. The insulator body according to claim 20, wherein the first layer portion is located at the first end por^¬ tion and the second end portion of the insulator body and wherein the second layer portion is located in be^¬ tween the first end portion and the second end portion of the insulator body.

22. The insulator body according to claim 20 or 21, wherein the winding angle varies, in particular varies steadily, in between the first layer portion and the second layer portion.

23. The insulator body according to any one of claims 18 to 22, wherein at least one of the absolute value of the first winding angle and the absolute value of the second winding angle varies monotonously increasingly or monotonously decreasingly, in particular in a step^¬ wise or continuous fashion, in between a radially in^¬ ner layer to a radially outer layer and/or within one layer of the insulator body.

24. The insulator body according to any one of claims 18 to 22, wherein at least one of the absolute value of the first winding angle and the absolute value of the second winding angle varies monotonously increasingly or monotonously decreasingly, in particular in a step^¬ wise or continuous fashion, in between a radially in^¬ ner layer to a radially outer layer and/or within one layer of the insulator body at every layer having an odd layer number.

25. The insulator body according to any one of claims 18 to 22, wherein at least one of the absolute value of the first winding angle and the absolute value of the second winding angle varies monotonously increasingly or monotonously decreasingly, in particular in a step^¬ wise or continuous fashion, from a radially inner layer to a radially outer layer and/or within one layer of the insulator body at every layer having an even layer number.

26. The insulator body according to any one of claims 23 to 25, wherein the at least one of the absolute value of the first winding angle and the absolute value of the second winding angle of a radially inner layer of the insulator body is smaller than the absolute value of the first winding angle and the absolute value of the second winding angle of a radially outer layer of the insulator body.

27. The insulator body according to any one of claims 18 to 26, wherein the at least one of the first and sec^¬ ond winding angle is in a range of about 2 degrees to about 90 degrees, in particular in a range of about 5 to about 70 degrees, more particular in a range of about 9 degrees to about 50 degrees.

28. The insulator body according to any one of claims 18 to 27, characterized in that the first winding member is a band or roving of plural strands of fibers, pref^¬ erably continuous strands of fibers, and wherein at least one layer is wound such that two consecutive convolutions of the band are arranged at least par^¬ tially in an overlapping manner with respect to the longitudinal axis.

29. The insulator body according to any one of claims 18 to 28, wherein one of the first winding angle and the second winding angle is a positive winding angle and wherein one of the second winding angle and the first winding angle is a negative winding angle with respect to the longitudinal axis.

30. The insulator body according to any one of claims 18 to 29, wherein at least one base layer portion of the insulator body is arranged under the first layer por^¬ tion, and wherein said at least one base layer portion comprises a second winding member being wound in a coiled manner with respect to the longitudinal axis with a third winding angle.

31. The insulator body according to claim 30, wherein the second winding member is a strip-shaped tissue, in particular a tissue comprising at least one of a fab^¬ ric or a fleece, in particular a polyester fabric or fleece .

32. The insulator body according to claim 30 or 31, wherein two neighboring convolutions of the second winding member of the same layer contact one another in an overlapping manner.

33. The insulator body according to any one of claims 30 to 32, wherein the third winding angle is a positive winding angle with respect to the longitudinal axis.