EP0774157B1 - Silicon rubber electric insulator for high-voltage applications - Google Patents

Abstract

PCT No. PCT/EP95/02699 Sec. 371 Date Jan. 29, 1997 Sec. 102(e) Date Jan. 29, 1997 PCT Filed Jul. 7, 1995 PCT Pub. No. WO96/04667 PCT Pub. Date Feb. 15, 1996An electric high-voltage insulator made from plastic comprises at least one glass fiber rod (1), at least one shield covering (2) made from silicone rubber which surrounds the glass fiber rod (1) and has concentric bulges (3) arranged along the longitudinal axis and bent in the shape of sheds in such a way that they form a convex top side and a concave or flat underside, as well as metal fittings (5) on both insulator ends. In this case, the bulges bent in the shape of sheds have at least one groove (4) on the underside preferably with a minimum depth of 1 mm.

Description

The invention relates to an electrical high-voltage insulator made of plastic comprising at least one glass fiber rod, at least one the glass fiber rod surrounding protective cover made of silicone rubber, which in the direction of the longitudinal axis of the Isolator-arranged, concentric, umbrella-shaped curvatures has a convex top and a concave or flat bottom form, as well as metal fittings on both insulator ends.

High voltage insulators for overhead lines have been out for a long time ceramic, electrically insulating materials such as porcelain or glass manufactured. In addition, isolators containing a glass fiber core and win an umbrella cover made of plastic in composite construction is becoming increasingly important, because they have a number of advantages, in addition to one lower weight also improved mechanical resistance count towards projectiles from firearms. The umbrella covers of such Composite insulators are mostly made of cycloaliphatic epoxy resins Polytetrafluoroethylene, from ethylene-propylene-diene rubbers or from Silicone rubber built.

Composite insulators with a shield cover made of silicone rubber face Composite insulators made of other shielding materials and also opposite conventional isolators have the advantage of being excellent Isolation properties when used in areas with heavily soiled Own atmosphere. That is why silicone rubber insulators are increasingly becoming one used existing overhead lines with electrical insulation problems that resulting from atmospheric contaminants, by using the conventional insulators against composite insulators with a shield cover made of silicone rubber.

• Silikongummis sind wasserabweisend. Auf Silikongummi-Oberflächen perlt das Wasser ab.
• Silikongummis senden aus ihrem Inneren niedermolekulare Siloxane an ihre Oberfläche, die ebenfalls wasserabweisend sind. Befindet sich Schmutz auf einer Silikongummi-Oberfläche, dann bewegen sich die niedermolekularen Siloxane auf die einzelnen Schmutzpartikel zu und umhüllen diese, so daß die Schmutzpartikel ebenfalls wasserabweisend werden.

The superiority of composite insulators made of silicone rubber compared to other plastic composite insulators and conventional insulators with regard to the insulation behavior in a heavily polluted atmosphere is due to two capabilities of certain silicone rubbers:

• Silicone rubbers are water-repellent. The water rolls off on silicone rubber surfaces.
• Silicone rubbers send low molecular weight siloxanes from their interior to their surface, which are also water-repellent. If there is dirt on a silicone rubber surface, the low molecular weight siloxanes move towards the individual dirt particles and envelop them, so that the dirt particles also become water-repellent.

These silicone rubber effects are described in more detail in the publication by J. Kindersberger and M. Kuhl "Effect of Hydrophobicity on Insulator Performance", published in 1989 for the 6th International Symposium on High Voltage Engineering, Paper 12.01, New Orleans 1989. For high voltage insulators for Overhead lines cause these effects that dirt on the insulators cannot be moistened and thus the electrical Surface conductivity remains low. The emergence of high-current Partial discharges are suppressed, and electrical flashovers over the entire Isolator lengths do not take place.

High voltage insulators for overhead lines in composite construction with a Umbrellas made of silicone rubber are used with umbrellas for many applications provided that are flat on their underside and can according to DE-A 27 46 870 can be manufactured by using individually prefabricated umbrellas with radial Preload on a glass fiber rod covered with silicone rubber put on and vulcanized together with it. The one for the Insulator operation can be determined by the number and the crawl Diameter of the screens can be obtained. At very strong atmospheric Contamination in the area of use of the insulators must be the creepage distance Insulators should be larger than in atmospheric areas of use Pollution. There are physical limits to the projection of the screen and screen spacing defined in IEC publication 815. To one To get a certain creepage distance per isolator length, you can use the shields not design as large in diameter and not as close together as desired Arrange. So there are natural limits for flat umbrellas.

It has therefore already been proposed to shield plastic composite insulators on the underside with grooves to extend the creepage distance equip. Such isolators are e.g. in EP-A 0 223 777 or in DE-A 11 80 017. The isolators described there have been in practice not proven. Grooves on the underside of the screen, as they do from Cap insulators made of glass or porcelain tend to deal with To fill dirt from the atmosphere. The self-cleaning properties Such isolators are bad because the grooves are not washed out by the rain can be. The result is high surface conductivities in fog so that such insulators from conventional materials to electrical Rollovers tend and those made of plastics are at risk of Creep marks or partial combustion are exposed. Therefore is used today because of the better self-cleaning ability, conventional as well as composite insulators with flat screens without grooves the bottom in areas with high atmospheric pollution. Your these isolators are provided with large creepage distances Shield diameter and a correspondingly large insulator length, however is undesirable.

GB-A-2 089 141 describes plastic composite insulators in which the individual prefabricated umbrellas were pushed onto a glass fiber rod and where the shades, which can be made of silicone rubber, are on the underside can be designed flat or according to the figures with ribs. The shield joints should be connected by metal rings or hollow cylinders be electrically bridged.

WO 92/10843 teaches cap insulators in which there is at least one porcelain portion a screen made of a polymeric material, e.g. Polydimethylsiloxane or Dimethylsiloxane / methylvinylsiloxane copolymer, is attached. The bottom of the Umbrellas can have ribs. The individual cap insulators can over metallic connecting links are coupled to isolator chains.

EP-A-0 033 848 discloses a method for producing a composite plastic insulator, in which the GRP rods by injection molding or injection molding covered with umbrellas using multi-part shapes can. Among other things, the shield cover material is Silicone rubber listed.

It was an object of the present invention to provide a high-voltage insulator which, with a greatly reduced overall length, has an approximately equal creepage distance, which at the same time fulfills the physical dimensions in accordance with publication IEC 815, which can possibly be produced at a further reduced cost, and which is excellent Has insulation properties when used in a heavily polluted atmosphere.
It is also an object to create a high-voltage insulator that has an approximately identical creepage distance with the same overall length, which at the same time fulfills the physical dimensions according to publication IEC 815, which can be produced at greatly reduced costs, and which has excellent insulation properties when used in strong polluted atmosphere.
It is also an object to provide a high-voltage insulator which, with a reduced overall length, has an equally long creepage distance, which at the same time meets the physical dimensions in accordance with publication IEC 815, which can be produced at a further reduced cost, and which has excellent insulation properties when used in a heavily polluted atmosphere having.

This object is achieved by an isolator of the type mentioned Genre solved, the distinguishing features of which can be seen in that the shield cover including the bulges made of an HTV silicone rubber consists essentially of polyvinyldimethylsiloxanes and fillers and is crosslinked with the help of peroxides or that it is made of another silicone rubber is based on polyorganodimethylsiloxanes that the Shore A hardness the shield cover including the bulges is more than 40 and that the at least one groove (4) on the underside of the curved protrusions exhibit.

Surprisingly, it was found that with silicone rubber composite insulators a groove on the bottom of the shades, contrary to the expectations of the Insulator manufacturers and users, better insulation properties result than previously known insulators made of other materials, but with similar geometric screen formation.

It is preferred according to the invention that several grooves in the area of the underside of the curvatures are arranged in an umbrella shape. The grooves should be there a minimum depth, measured as the distance from the top to the valley, from have at least 1 mm, preferably their depth should be in the range from 5 to 50 mm lie. The width of the grooves, measured as the distance between two neighboring peaks, can range from 3 to 200 mm, preferably in Range from 5 to 80 mm. It is further preferred that in the area of the grooves and their edges no sharp corners and tips occur, but these are rounded. The protruding between the grooves protruding webs can be vertically or steeply inclined. at A concentric arrangement of adjacent grooves then results in a cylindrical shape or conical bars. The grooves or webs preferably run concentrically the longitudinal axis, but they can also be guided eccentrically.

In an embodiment preferred according to the invention, the ratio of I ₄ / d to the value of 5 is to be limited in accordance with IEC publication 815: While the variable I ₄ the real creepage distance on the surface of a screen between two points, preferably in cross-section including the Longitudinal axis in the cross-sectional area, designated d stands for the shortest distance between these points by air.

Insulators according to the invention can according to that in DE-A-27 46 870 described method can be produced by the screens separately manufactured on a glass fiber rod coated with silicone rubber Radial tension pushed on and with this silicone rubber layer vulcanized together. The procedure allows extensive freedom in the choice of the length of the isolators and the choice of the desired Creepage distances taking into account the limits specified in IEC 815 for Screen projection and screen spacing.

As a material for the umbrella cover, especially for the umbrellas preferably silicone rubber, whose Shore A hardness is more than 60 is how they HTV silicone rubbers (HTV = hot-temperature crosslinking) deliver that consist of polyvinyldimethylsiloxanes and fillers and with Crosslinked with the help of peroxides. Other silicone rubbers, as far as they are Polyorganodimethylsiloxanes can also be used. Silicone rubbers, which are particularly suitable according to the invention preferably flame retardant, so that the flammability class FVO according to IEC publication 707. This can be done by incorporating the Alumina hydrate filler or use of a platinum-guanidine complex can be achieved. In addition to the improved flame retardancy also the high voltage tracking resistance HK2 and the high voltage arc resistance HL2 according to DIN VDE 0441 part 1 at least achieved. to Compliance with the high-voltage tracking resistance in HK class 2 must 5 Test specimens in a multi-stage test a voltage of 3.5 kV over 6 hours Persist. To achieve high-voltage arc resistance in HL class 2 10 test specimens must burn for more than 240 seconds Arc can be successfully exposed. The invention High-voltage insulator made of silicone rubber meets the high-voltage diffusion resistance according to class HD2 according to DIN VDE 0441 part 1.

When manufacturing the insulators according to the invention, it should also be noted that that in the shaping of the screens to be formed with grooves, the backfilling of the Form in which the umbrellas are formed, completely and if possible without Air pockets occur.

The combination of screen construction and material according to the invention offers further advantages. As is well known, silicone rubber is an expensive material because the silicon synthesis is based on pure silicon.
Flat screen constructions of silicone rubber insulators are therefore designed to minimize the use of materials, which leads to thin screens. Thin screens made of silicone rubber, in particular those of larger diameter, are therefore mechanically unstable, they tend to deform during storage and transport and can also be easily damaged mechanically. By using grooves on the underside of the umbrella, the umbrellas can be kept smaller in diameter than flat umbrellas with the same or even greater creepage distance and thereby gain a considerable degree of mechanical stability due to the stiffening effect of the grooves on the underside of the umbrella. The use of material for the grooves is low and is largely compensated for by the creepage distance obtained as a result, since the creepage distance in flat screens can only be extended by increasing the diameter, which is included in the square footage of the material calculation.

Figur 1 zeigt einen teilweisen Querschnitt des erfindungsgemäßen Isolators. Der Isolator enthält einen Glasfaserstab (1), der aus epoxidharzgetränkten Glasfasern bestehen kann, die endlos achsparallel im Stab angeordnet sind. Der Glasfaserstab (1) ist umhüllt von einer nahtlos durchgehenden Silikongummischicht (2), die an die Oberfläche des Glasfaserstabes (1) anvulkanisiert ist. Auf der Oberfläche der Silikongummischicht (2) sind Schirme (3) aus Silikongummi angeordnet, die an ihrer Unterseite mit Rillen (4) ausgestattet sind. Die Schirme (3) sind vorgefertigt, mit radialer Vorspannung auf die Silikongummischicht (2) aufgeschoben und mit dieser zusammenvulkanisiert. Am Isolatorenende befindet sich eine der beiden Metallarmaturen (5) des Isolators zur Übertragung der Zugkraft vom Glasfaserstab (1) zu der nicht dargestellten Isolatorenaufhängung. Die Metallarmatur (5) kann z.B. aus Stahl, Gußeisen oder anderen metallischen Werkstoffen bestehen und durch radiale Kompression mit dem Ende des Glasfaserstabes (1) verbunden sein. Figur 1 zeigt ein Beispiel eines erfindungsgemäßen Isolators mit alternierenden Schirmdurchmessern; es können auch Schirme gleichen Durchmessers oder Schirme mit in der Schirmabfolge anders variierenden Durchmessern verwendet werden.

Figur 2 zeigt eine schematische Darstellung von Schirmen eines Freileitungsisolators. Die wesentlichen Dimensionierungskriterien sind:

Schirmausladung   p,

Schirmabstand   s,

zugehöriger Kriechweg   I_d und

minimaler lichter Abstand zwischen 2 Schirmen   c.

The composite high-voltage insulator according to the invention will be illustrated by way of example with reference to several drawings. The drawings and examples are based on IEC publication 815, which contains rules for the construction of a high-voltage overhead line insulator, which also include the design and design of the shields:

Figure 1 shows a partial cross section of the insulator according to the invention. The insulator contains a glass fiber rod (1), which can consist of epoxy resin-impregnated glass fibers, which are arranged in the rod endlessly parallel to the axis. The glass fiber rod (1) is encased by a seamless, continuous silicone rubber layer (2) which is vulcanized onto the surface of the glass fiber rod (1). On the surface of the silicone rubber layer (2) there are screens (3) made of silicone rubber, which are provided with grooves (4) on their underside. The screens (3) are prefabricated, pushed onto the silicone rubber layer (2) with radial prestress and vulcanized together with the latter. One of the two metal fittings (5) of the insulator for transmitting the tensile force from the glass fiber rod (1) to the insulator suspension (not shown) is located at the end of the insulator. The metal armature (5) can consist, for example, of steel, cast iron or other metallic materials and be connected to the end of the glass fiber rod (1) by radial compression. Figure 1 shows an example of an insulator according to the invention with alternating shield diameters; screens of the same diameter or screens with different diameters in the screen sequence can also be used.

Figure 2 shows a schematic representation of shields of an overhead line insulator. The main dimensioning criteria are:

Projection p,

Screen spacing s,

associated creepage distance I _d and

minimum clear distance between 2 screens c.

c ≥

30 mm,

s/p ≥

0,8 für Schirme mit Rillen in der Schirmunterseite,

s/p ≥

0,65 für Schirme mit glatter Schirmunterseite,

l_d ≤

5.

The relationships between these geometric parameters are described in IEC publication 815, Appendix D and are as follows:

c ≥

30 mm,

s / p ≥

0.8 for umbrellas with grooves in the underside of the umbrella,

s / p ≥

0.65 for umbrellas with a smooth underside,

l _d ≤

5th

The creepage distance factor CF is the quotient of the total creepage distance I _t and the pitch S _t : CF = I _t / S _t ≤ 4.

The creep path I is taken into account in the profile factor PF, which can be identical to the creep path I _d , for example 2p + s I ≥ 0.7.

In Figure 3, the isolator B according to the invention is compared to the isolator represented according to the prior art VB, which is described in more detail in Example 1 become.

Figure 4 gives the result of the leakage current measurements over a test time of 1000 hours for the isolators B and VB described in Example 1 in vertical Installation position (lower polygon course) and in horizontal installation position (upper Polygons) again. The signatures identify the two-shielded isolator B and the three-shielded isolator VB.

The invention was exemplified above on a high voltage insulator for overhead lines explained in more detail. Of course it can also be used for High-voltage composite insulators with a shield cover made of silicone rubber are used, which are used as post insulators or as hollow insulators be used as a housing for transducers, bushings and the like. The invention can be advantageously used in cases where conventional insulators of specified height in atmospheric Pollution areas electrical problems with flashovers prepare. With the help of the invention, insulators can be built Creepage distance with constant overall height and atmospheric conditions can be adjusted.

Examples and comparative examples:

example 1

Two insulators were produced, as shown in FIG. 3. The isolators according to the invention were designated B1, the isolators according to the state of the art with VB1. The two types of isolators can be used as are considered electrically equivalent, because the striking distances and The creepage distances of both types are the same. All four isolators were made after method described in DE-A-27 46 870. They consisted of the same screen cover material, namely a polyvinyldimethylsiloxane Fillers that have been crosslinked using a peroxide and a Shore A hardness out of 80. The fillers consisted of pyrogenic silica and alumina hydrate. The arc resistance of this material was more than 240 s (HL 2); the high voltage tracking resistance became HK 2 classified, determined according to DIN VDE 0441, part 1. The flame resistance according to IEC publication 707 corresponded to class FVO that High voltage diffusion resistance class HD2.

In FIG. 3, (11) and (12) denote the various types of shields of the insulator B1 according to the invention, which have grooves of the type described on their underside and are shown in detail in FIG. 1. The shields (13) of the isolator VB1 are smooth on their underside. The data of the screens used are summarized in Table 1. Identification of the types of screens used screen type Creepage distance mm D1 mm D2 mm D3 mm Weight of an umbrella g 11 191 178 291 12 125 138 161 13 100 148 154

The calculation of the creepage distance of the two isolators in FIG. 3 is carried out by adding the sum of the creepage distances of the shields per isolator and also adding the insulation length L. The dimensions of the isolators and the ratios specified in IEC publication 815 are given in Table 2. Characteristics of the isolators VB1 and B1 insulator Creepage distance mm Stroke width mm L mm d mm Silicone material weight g c mm s mm p mm I _d / c s / p CF PF VB1 485 210 185 30 533 43 46 59 2.7 0.78 2.3 1.4 81 485 210 175 30 519 49 59 74 4.2 0.8 2.3 1.0

Table 2 shows that both types of isolators are those listed in IEC Publication 815 Criteria met and are largely identical electrically. The one used The amount of silicone material differs only slightly: the Insulator B1 according to the invention required 2.6% less silicone material than that Isolator VB1.

The four insulators were subjected to an electrical endurance test in one Subject to cloud chamber. The test is detailed in IEC publication 1109 described. In this test, one isolator was placed horizontally and one vertically arranged in the cloud chamber. The test voltage was 14 kV. A salt spray with a conductivity of 16 mS / cm was generated artificially. During the The leakage currents occurring at the insulators were tested continuously measured over 1000 hours. This test was done by all four isolators existed in both horizontal and vertical positions because it no arcing occurred during the test, nor did it form on the Insulators signs of creep or erosion.

Figure 4 gives a diagram with the time course of the leakage currents Isolators during the test again. The diagram shows one fundamental difference in the insulation behavior between vertical and horizontal installation position. Both isolator types showed in a vertical installation position a very similar behavior: the mean leakage currents for the Isolator B1 according to the invention 0.03 mA, for the isolator VB1 according to the prior art of technology 0.015 mA.

The situation was different with measurements on horizontally mounted isolators. Here, the isolator B1 according to the invention showed an average leakage current of 20 mA, while the isolator VB1 according to the prior art one about ten times higher leakage current of approx. 200 mA than the average. The effect of Grooves according to the invention were shown in this test at horizontal arrangement of the isolators. This test result was surprising because of insulators with grooved screens made of other materials a poorer insulation behavior than known with insulators without grooved shields is.

Example 2

The creepage distance of isolators is adapted to the later place of use. Large atmospheric contaminants require large creepage distances. For this example, isolators for a 110 kV overhead line with a creepage distance of 3350 mm were manufactured. The overall length of the insulator and thus the fixed insulation length L were specified. Table 3 lists the characteristics of the isolator VB2 according to the prior art and the isolator B2 according to the invention.

The stroke distance corresponds to the length of a stretched over the isolator Thread, with a vertically positioned insulator from the bottom edge the upper fitting outside via the screens to the upper edge of the lower Fitting is measured.

Shield type 2 was correspondingly used for the isolator B2 according to the invention Table 1 selected. The isolator VB2 was used as in Example 1 with the Umbrella type 3 equipped. Table 3 shows that both isolators are those in the IEC publication 815 criteria met. From an electrical point of view both insulators to be regarded as equivalent, since striking distance and also Total creepage distance are approximately the same size. For the isolator according to the invention B2, however, the manufacturing effort is significantly less than that of the isolator VB2 According to the state of the art. Only 19 instead of 24 umbrellas are required and the amount of silicone material for the shield cover of the invention Isolator B2 is 15.6% lower than the isolator VB2.

Example 3

If the atmosphere is particularly heavily polluted, such as those found in coastal areas with adjacent deserts, extreme creepage distances are also required. For example 3, insulators for a 110 kV line with a creepage distance of 4050 mm were produced. Isolators according to the prior art VB3 and isolators B3 according to the invention were used.

Shield type 1 was correspondingly used for the isolators B3 according to the invention Table 1 chosen. The comparative isolators VB3 were as in Examples 1 and 2 equipped with the umbrella type 3. Both isolators met those in the Criteria referred to in IEC publication 815. Based on these criteria, the Comparative isolator VB3, however, run longer than it does for 110 kV isolators is otherwise common. The isolator B3 according to the invention could, however usual length are kept. It was 17% shorter than the VB3 isolator. He required the same amount of silicone material as the comparative insulator VB3, the number of umbrellas increased from 29 to 16, i.e. by 45% be reduced. That means a clear advantage in terms of Manufacturing costs for the umbrellas.

Example 4

The advantages of the insulators according to the invention were most effective when dealing with large atmospheric contaminants and high electrical transmission voltages. Specific creepage distances of 50 mm / kV are required for conventional insulators made of porcelain and glass in heavy pollution areas near coastal desert areas. By using composite insulators with a shielding cover according to the invention made of silicone elastomers of the type described here, the specific creepage distance could be reduced to 40 mm / kV. With a transmission voltage U _max of 420 kV, an isolator creepage distance of 16800 mm was therefore necessary for composite isolators of the type described.

d =

30 mm bedeuten:

VB4

Isolator nach dem Stand der Technik mit alternierenden Schirmdurchmessern von abwechselnd 168 und 134 mm,

VB5

Isolator nach dem Stand der Technik mit einheitlichen Schirmdurchmessern von 148 mm,

B4

erfindungsgemäßer Isolator mit alternierenden Schirmdurchmessern (siehe auch Fig. 1) von 178 und 138 mm,

B5

erfindungsgemäßer Isolator mit einheitlichen Schirmdurchmessern von 178 mm,

B6

erfindungsgemäßer Isolator mit einheitlichen Schirmdurchmessern von 138 mm.

This creep path could be realized in different ways. According to the prior art, screens with a smooth underside and the same or alternating diameter can be used. Insulators with shields of the same diameter as well as with alternating shield diameters are also possible according to the invention. In this example, two types of isolators according to the prior art with alternating or uniform screen diameters were compared to three types of isolators according to the invention. With a creepage distance of 16800 mm and an insulator trunk diameter of

d =

30 mm mean:

VB4

State-of-the-art insulator with alternating screen diameters of alternating 168 and 134 mm,

VB5

State-of-the-art isolator with uniform screen diameters of 148 mm,

B4

isolator according to the invention with alternating screen diameters (see also FIG. 1) of 178 and 138 mm,

B5

isolator according to the invention with uniform screen diameters of 178 mm,

B6

Insulator according to the invention with uniform screen diameters of 138 mm.

Taking into account the rules described in IEC publication 815, there were different limit values for the dimensions for the various isolators. The dimensions of the isolators VB4, 84 and B5 were determined by the creep path factor CF, which had to be observed for these isolators with the maximum value 4, so that an isolating length L of 4200 mm resulted for these isolators. The dimensions of the isolator VB5 were predetermined by the ratio of screen spacing to screen projection (s / p). The isolator B3 was determined by I _d / c.

The dimensions resulting from these boundary conditions are shown in Table 5. In the case of alternating screen diameters, the screen overhang ratios p ₁ and p _{2 also had} to be taken into account (p ₁ - p ₂ ≥ 15 mm). The shield projection p is shown in accordance with IEC 815 in Figure 2.

Table 5 shows that isolators VB5 and B6 are longer isolators result than the others and are therefore not preferable. The The most economical solution for an isolator according to the state of the art was the Isolator VB4 with alternating screen diameters. In contrast, the Both alternatives B4 and B5 according to the invention have the advantage of one Material savings. The number of screens was the alternatives B4 and B5 significantly reduced, namely by 35% and 46%.

Insulators for this purpose had a considerable weight. The had an effect on isolators according to the prior art that When the insulators are placed horizontally on a flat surface, the shields could be permanently deformed by its own weight. This occurred especially with alternating screen diameters like the isolator VB4, where the isolator weight from the 62 large diameter screens had to be worn. The isolators B4 and B5, however, pointed mechanically stable shields, which do not deform when the insulators are transported suffered.

Claims (12)

1. An electrical high-voltage insulator of plastics comprising at least one glass fibre rod (1), at least one protective jacket (2) of silicone rubber surrounding the glass fibre rod, said jacket comprising concentric umbrella-shaped projections (3) arranged in the direction of the longitudinal axis of the insulator and curved in such a manner that they form a convex upper side and a concave or flat underside, together with metal fittings (5) on both ends of the insulator, characterised in that the protective jacket including the projections consists of an HTV silicone rubber which substantially consists of polyvinyl dimethylsiloxanes and fillers and is crosslinked with the assistance of peroxides
   or in that it consists of another silicone rubber based on polyorgano dimethylsiloxanes,
   in that the Shore A hardness of the protective jacket including the projections is more than 40 and
   in that the umbrella-shaped projections in each case comprise at least one groove (4) on the underside.
2. An electrical high-voltage insulator according to claim 1, characterised in that that two or more grooves (4) are arranged in the underside zone of the umbrella-shaped projections (3).
3. An electrical high-voltage insulator according to claim 1 or 2, characterised in that the groove(s) has/have a minimum depth, measured as the peak to valley distance, of at least 1 mm.
4. An electrical high-voltage insulator according to claim 3, characterised in that the groove(s) has/have a depth in the range from 5 to 50 mm.
5. An electrical high-voltage insulator according to any one of claims 1 to 4, characterised in that the width of the groove(s), measured as the distance between two adjacent peaks, is in the range from 3 to 200 mm.
6. An electrical high-voltage insulator according to claim 5, characterised in that the width of groove(s) is in the range from 5 to 80 mm.
7. An electrical high-voltage insulator according to any one of claims 1 to 6, characterised in that the groove(s) and the edges thereof are rounded in shape.
8. An electrical high-voltage insulator according to any one of claims 1 to 7, characterised in that the material for the protective jacket (2), in particular for the umbrella-shaped projections (3), is silicone rubber, the Shore A hardness of which is at least 60.
9. An electrical high-voltage insulator according to claim 8, characterised in that the protective jacket contains inorganic fillers, in particular pyrogenic silica.
10. An electrical high-voltage insulator according to any one of claims 1 to 9, characterised in that the protective jacket contains aluminium oxide hydrate or a platinum/guanidine complex.
11. An electrical high-voltage insulator according to any one of claims 1 to 10, characterised in that it is capable of passing a high-voltage arc resistance test over an exposure time of more than 240 s to DIN VDE 0441, part 1.
12. An electrical high-voltage insulator according to claim 11, characterised in that it is capable of passing a high-voltage leakage test with a test voltage of at least 3.5 kV over a duration of 6 hours to DIN VDE 0441, part 1.

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