JPH0145684B2 - - Google Patents

Description

Claim 1: A plastic composite insulator for high-voltage overhead electric wires comprising a glass fiber reinforced plastic rod-shaped part and an attachment part at the end of the rod-shaped part, wherein a plastic shield surrounds the rod-shaped part, and a mounting part at the end of the rod-shaped part is provided. The mounting part of the plastic rod is made of metal, and the glass fibers parallel to the axis of the plastic rod are made of 55-80% by weight of SiO ₂ and 20-30% of Al ₂ O ₃ by weight.
Composite insulation as described above, characterized in that it consists of a low-boron, preferably boron-free, calcium oxide-free glass containing 5-15% by weight MgO and 0-1% by weight Na ₂ O.

2. Composite insulation according to claim 1, wherein the boron content of the glass fibers is at most 1% by weight, calculated as B ₂ O ₃ .

3. The composite insulator according to claim 2, wherein the glass fiber has a boron content of 0.01% by weight or less.

4. A composite insulator according to claim 1, in which the glass fibers are made of glass having the following composition: SiO ₂ 60-80% by weight Al ₂ O ₃ 20-30% by weight MgO 5-15% by weight Na ₂ O - % by weight .

5. Claim 1, wherein the rod-shaped part contains endless glass fibers arranged parallel to the axis with a thickness of 5 to 40 μm.
Composite insulator by term.

Description The present invention relates to a plastic composite insulator, in particular for high-voltage overhead power lines, comprising a glass fiber reinforced plastic rod, a plastic shield provided on the rod, and an attachment at the end of the rod.

For example, Federal Republic of Germany Application No. 2650363
This type of composite insulator, known from the No. The rod has electrical breakage strength, and the shield is fixed to the rod, also called the stem, in such a way that no electrical breakage occurs in the contact area, and the shield itself is electrically resistant to breakage. The shield can also be made from a material that can withstand wind, rain, UV rays, and ozone, and has extremely high leakage current resistance.

In addition to the insulation resistance, the glass fiber-reinforced plastic rod must also ensure a high degree of mechanical rigidity. Mechanical stiffness results from the material composition of fiber type and location and the combination of glass fiber and plastic.

It is known that the electrical and mechanical rigidity of glass fiber reinforced rods of composite insulation can be severely damaged by environmental influences, especially when used for long periods in overhead power lines. In order to avoid these effects, the bar is surrounded by a shield to prevent atmospheric components from entering the bar. However, so far this has not been a satisfactory success,
Insulator failure may still occur.

Other proposals (Federal Republic of Germany Application Publication No. 2650363)
The starting point is that, in particular, the ingress of water into glass fiber-reinforced plastic rods causes a weakening of their rigidity. Glass fibers are therefore used which, although consistent with the usual composition, are particularly alkali-poor. After all, glass with less alkali inherently guarantees lower water solubility,
This is because the eluted alkali can induce and promote hydrolysis of the binding resin. Additionally, the low alkali glass fibers are combined with non-saponifiable binding resins that should withstand water attack.

Despite the above-mentioned measures, especially in the case of overhead wire composite insulations, failures occurred which were initially inexplicable and even after a relatively short time of use, even under relatively low mechanical loads. Visually, the image of failure of an insulator damaged in an overhead power line is clearly different from the image of failure that occurs, for example, during continuous tests in a laboratory and during long-term stiffness tests over many years on an outdoor test stand. This is because a plastic bar reinforced parallel to the axis with endless glass fibers will break under mechanical stress as the binding resin peels off from the glass fibers and the glass fibers tear. In this case, the rod section splits in the longitudinal direction. On the other hand, most of the damage that occurs in the field is perpendicular to the longitudinal direction of the rod. The damaged surface becomes smooth.

Surprisingly, several experiments have shown that smooth fractures occurring perpendicular to the length of the rod are caused by the action of water-soluble nitric acid. It has been known for a long time that nitric acid is formed from atmospheric nitrogen when air and water meet to create an electric arc. This obviously also occurs due to the action of electrical discharges occurring on the insulating shielding membrane in the presence of dirt and moisture. In this case, the nitric acid is either scattered by the shielding membrane or penetrates further through the crack until it reaches the glass fiber reinforced plastic rod, causing smooth transverse tearing. Thus, it can be understood that rod-shaped transverse cracking has not previously occurred in laboratory experiments and has not been written about glass fiber-reinforced plastics in the literature.

It is an object of the invention to prevent transverse tears occurring in the field in composite insulations of the type mentioned at the outset.

This problem is solved in the following manner in a plastic composite insulator consisting of a plastic reinforcing bar, a plastic shield provided on the bar, and a mounting portion at the end of the bar. That is, the glass fibers in the plastic rods parallel to the axis are made of boron-poor, preferably boron-free, aluminum silicate glass. Within the framework of this invention, boron-poor glasses are glasses which have at most 1 weight percent of boron or boron compounds, calculated as B ₂ O ₃ .

Boron-free glass means boron or B ₂ O ₃
A glass containing less than 0.01 percent by weight of boron compounds, calculated as This is because lower boron contents can only be detected by trace analysis and do not affect the purpose of this invention.

Particularly advantageous are glass fibers consisting of glasses of the following composition (in weight percent): SiO ₂ 55−80 Al ₂ O ₃ 20−30 MgO 5−15 CaO − Na ₂ O 0−1 Glass fibers made of glass are preferred.

SiO ₂ 60-80 Al ₂ O ₃ 20-30 MgO 5-15 CaO - Na ₂ O - CaO-free glass fibers are particularly resistant and are therefore particularly used.

The glass fibers are preferably processed endlessly parallel to the rod axis with a thickness of 5 to 40 μm.

In combination with glass fibers processed according to the invention, it is advantageous if the alkali metal oxide content of the glass is less than 1 weight percent. If possible, the glass fiber should be alkali-free. This, as is well known, prevents water erosion and increases the electrical puncture strength.

In yet another combination according to the present invention, in order to increase the electrical puncture strength of the rod-shaped portion, a binding resin that is resistant to water erosion is used as the binding resin surrounding the glass fibers. Binding resins without hydrolyzable molecules are therefore used. Particularly suitable in this regard are glycidyl ether type epoxy resins.

In order to be able to manufacture the insulator according to the invention as economically as possible, it is advantageous to use a prefabricated insulation for the shielding membrane. Insulators of arbitrary length can be made in this way. This is because glass fiber-reinforced plastic rods can also be produced, for example, by an endless drawing process. The bar surface and the shield can be treated with an adhesive in a known manner, and
It can be joined as usual. For example, by casting, vulcanization, adhesive bonding or similar methods.

The radial connecting seams that occur between the shielding parts do not play a major role in that case. This is because glass fiber reinforced plastic rods are resistant to nitric acid and water.

Knowing the existing situation known before the present invention, it may be possible to easily come up with two solutions if necessary. One is to prevent water-soluble nitric acid from being delivered to the plastic rod. However, this method currently appears to be impracticable in practice. This is because nitric acid is diffused through the plastic, and it is not possible to guarantee over a long period of time that no cracks will occur in the shield membrane or between the shield membrane and the attachment part.

On the other hand, it is easy to see that a nitric acid-resistant material can be used for the insulating bar.

This method was also carried out within the framework of this invention. However, in an experiment in which rod-shaped materials of commercially available composite insulators were stored in nitric acid, it was found that neither the glass fibers nor the plastic of the rod-shaped materials were affected by water-soluble nitric acid, so the selection of materials did not solve the problem. I had to think that it wouldn't happen. It was therefore very surprising that the risk of transverse tearing could nevertheless be avoided by replacing the commonly used glass fiber types with boric acid-free glass fibers. It was previously unknown to conclude this phenomenon from this fact.

The attack of water-soluble nitric acid on the boron-containing glass is thought to be the cause of the horizontal cracking of the insulator. When boron-containing glass is exposed to tensile stress and nitric acid simultaneously, cracks can sprout on the surface of individual glass fibers. Those crack buds form a spiral around the glass fibers. At least in the laboratory, these crack buds are responsible for side-scattering of the rod. It is clearly not chemical attack in the sense of expansion or dissolution, but rather a type of stress cracking corrosion, which apparently does not occur in the case of boron-free glass fibers, or occurs when the elongation is large or when the acid concentration is high. arise.

It is known that low-alkali glass fibers, which are boron-free and free of boron compounds, provide sufficient resistance to mechanically stressed insulation components for high-pressure switching equipment containing sulfur hexafluoride gas. (European patent application 0028281). However, recognition of this known effect of glass fibers made of so-called R-glass cannot be immediately applied to solving the problem of the present invention. This is because the decomposition products of SF ₆ do not occur in the area where fresh air composite insulation is used, so to that extent they are not relevant.

Therefore, it has not been easy to select glass fibers containing less or no boron according to the present invention for the following reasons. That is, boron-containing glass,
Fibers of the so-called E-glass are surprisingly used for components in the electronic industry because of their very good electrical resistance, since E-glass is not attacked by water-soluble nitric acid and is therefore less susceptible to other glasses. Replacement with fibers is usually not easily considered. In order to solve the problem of the invention, this obstacle threshold must be overcome, in which case the selection according to the invention cannot easily be imagined by any proposal.

This will be explained in more detail based on the figures.

FIG. 1 is a schematic diagram of the structure used for the transverse tear strength test, FIG. 2 is a diagram of the test results, and FIG. 3 is a diagram showing an insulator according to the invention.

The test object shown in FIG. 1 is composed of a glass fiber-reinforced plastic rod-shaped part 1 and a hanging type mounting part 2. A tensile force Z can be applied to the attachment part. There is an acid tank 3 on the free length of the rod. The acid tank may be, for example, a cut-out polyethylene bottle, which slides on a rod and is sealed with an insulating strip.

FIG. 2 shows the functional relationship between the tensile force Z and the breaking time of the specimen shown in FIG. Line 4 is the tensile force of the glass fiber reinforced plastic rod/
This shows the relationship with time (here, time is the time it takes to break a single bar). This rod is not exposed to any acid action. Line 5 shows that the acid tank 3 is filled with 1N HNO ₃ (approximately 6.5% nitric acid) and the boron-containing glass fibers are contained in the glass fiber reinforced plastic rod, which causes B ₂ O ₃
The relationship between tensile force/time is shown for between 2 and 6% calculated as . Line 6 shows the fracture/time behavior of a glass fiber reinforced plastic bar whose glass fibers are boron free. The diagram of FIG. 2 thus shows a sharp time difference. The time difference is the difference between a glass fiber reinforced plastic rod of conventional composition (boron-containing glass) and that according to the invention.

The use of boron-containing glasses in electronics and also in the form of fibers in glass-fiber-reinforced plastic rods, especially in the case of composite insulators, is common (German Published Application 2746870, page 10). In electronic engineering, so-called "E-glass" is used. In this case, E stands for "electricity". Commercially available glass fibers available under the name "E-glass" all contain different amounts of boron. A certain stray zone may therefore occur at line 5 in FIG. 2. This can also be attributed to the different boron content of the E-glass. However, compared to the rod embodiment of the invention (FIG. 2, line 6), this stray zone is not significant.

FIG. 3 shows a composite insulator according to the invention. This composite insulator consists of a glass fiber reinforced plastic bar 7. This rod-shaped portion is made of glycidyl ether type epoxide resin and endless fibers arranged parallel to the axis. The fibers contain less than 0.01% boron, calculated as B ₂ O ₃ and less than 1% alkali, calculated as Na ₂ O. The insulation also consists of a shielding cover consisting of individual ready-made shields 8. These shield covers are fitted onto the rod-shaped portion and firmly connected to the rod-shaped portion mechanically and electrically. Furthermore, metal suspension attachments 9 are provided which are fixed to the ends of the composite insulator. The connection between the bar 7 and the attachment part 9 is created by known techniques such as wedging or pressing the bar.

However, depending on the type of shield cover material,
It may be advantageous to pre-manufacture the shield cover and finish it in one step. Other materials for the shielding cover may require complete recasting, overlaying, extrusion or even re-injection of the shielding cover in single-piece or multi-piece form as the most economical solution.

It is advantageous to use silicone elastomers for the shielding cover, which silicone elastomers are already well accepted as insulating materials. silicone elastomers of various consistencies with fillers, such as quartz powder or aluminum oxide hydroxides, folded according to the intended use;
Pigments and crosslinkers that correspond to the chemical structure are easy to process. Ethylene-propylene based elastomers may also be suitable as shielding materials for certain applications. Other shielding materials, such as cycloaliphatic epoxide resins or polytetrafluoroethylene, may be advantageously utilized in the case of the insulator according to the invention as well.