HK1151384B - A method of fabricating a high-voltage insulator comprising a glass or porcelain skirt and metal parts - Google Patents

Description

Method for manufacturing a high-voltage insulator comprising a skirt of glass or porcelain, a metal part

Technical Field

The present invention relates to a method of manufacturing a high-voltage insulator comprising a skirt or "shed" of glass or porcelain, a metal cap and metal connecting feet. In this method, caps and connecting legs are sealed to the skirts of the insulator by waterproof mortar, respectively. The waterproof mortar is obtained by mixing alumina cement with sand to form a dry mixture and then mixing the resulting mixture with water.

In particular, the present invention relates to suspension and pull-stud insulators, and more particularly to "cap-pin" insulators, which comprise an insulating skirt made of dielectric material, such as tempered glass or porcelain, having a top portion fixed in a metal cap by means of an adhesive or waterproof mortar based on alumina cement, the metallic connection feet being fixed in the skirt by the same waterproof mortar.

Background

Once assembled, the suspension insulators are designed to be secured together by securing the connecting legs of one insulator to the cap of an adjacent insulator to form a string of insulators that serve as support for high and medium voltage power lines. Such insulators are able to withstand very severe weather and mechanical conditions, which require good sealing between the skirt and the connecting foot, and between the skirt and the cap.

For example, patent document FR2,031,985 discloses an electrical insulator comprising a metal cap and a metal connecting pin, together with a bell and a disc made of glass or porcelain. Firstly, the connecting feet are sealed in the bell with cement mortar and secondly the cap is fitted onto the plate. Furthermore, in order to obtain the insulator, it is necessary to bond the bell and the plate together with cement mortar.

Conventionally, sand and alumina cement are mixed to prepare a waterproof mortar. The resulting mixture is then mixed with water to obtain a waterproof mortar. Waterproof grout is deposited on either side of the skirt to seal one side of the skirt within the cap and to seal the other side of the skirt to the connecting foot.

A method for producing mortar is known in which cement, sand and silica fume are dry-mixed, and the resulting mixture is then mixed with water to which an admixture is added. For example, in patent document US 2007/0228612, a polycarboxylic acid type water reducing agent is added to water in order to reduce the water content; and in patent documents US5, 466, 289, dispersants of the ethylene copolymer type are added. Unfortunately, the resulting mortar is based on portland cement and is not of sufficient quality to seal electrical insulators.

Disclosure of Invention

It is an object of the invention to propose a method of manufacturing a high-voltage insulator as described above. In this process, a waterproof mortar having a very limited porosity, which can provide a very high mechanical strength, is used.

To achieve this object, the invention provides a method of manufacturing a high-voltage insulator comprising a glass or porcelain skirt, a metal cap and a metal connecting foot. In this method, the cap and the connecting feet are sealed to the skirt of the insulator by means of waterproof mortar, respectively. The waterproof mortar is obtained by mixing alumina cement with sand to form a dry mixture, and then mixing the resulting mixture with water. The method is characterised in that the silica fume is also dry-mixed with cement and sand and in that an aqueous solution containing a water-soluble dispersant containing a carboxyl function and a polyether segment is added to the water before the mixture is mixed with the water.

Advantageously, said silica fume makes it possible to increase the compactness of the mortar and said aqueous solution of a water-soluble dispersant comprising carboxylic functions and polyether segments, also known as "aqueous glucose solution", makes it possible to improve the wetting power of the water, so that it is possible to reduce the amount of water added to the mortar and thus to reduce the porosity of the mortar. Thus, the improved compactness of the mortar obtained by using the process of the invention, combined with a lower porosity, produces, in a complementary manner, an increase in the mechanical strength of the mortar.

Numerous tests have been carried out for preparing waterproof mortars, which have resulted in waterproof mortars having very good mechanical strength, very good compactness and very low porosity with respect to waterproof mortars of other ingredients. In particular, tests of similar composition but without silica fume or without aqueous solution have been carried out, which have not given satisfactory results.

The method of manufacturing a high-voltage insulator of the present invention may include the following features:

-the mass of aluminous cement is expressed in the range of about 50% to 80% with respect to the total mass of the mixture of sand and cement, the mass of sand is expressed in the range of about 20% to 50% with respect to the total mass of the mixture of sand and cement, the mass of silica fume is expressed in the range of about 2% to 10% with respect to the mass of the cement alone in the mortar, the mass of water is expressed in the range of about 17% to 27% with respect to the mass of the cement alone in the mortar, the mass of aqueous solution is expressed in the range of about 0.2% to 0.5% with respect to the mass of the cement alone in the mortar;

the mass of silica fume is preferably expressed as about 6%, the mass of water as about 22%, and the mass of aqueous solution as about 0.25% relative to the mass of the cement alone in the mortar;

the cement comprises alumina in an amount ranging from 30% to 75%;

the sand particle size is concentrated on a value lying in the range of about 200 to 300 micrometers (μm).

The present invention also provides a high voltage insulator comprising a glass or porcelain skirt, a metal cap and a metal connecting pin, in which the cap and the connecting pin are respectively sealed to the skirt of the insulator by means of a waterproof mortar prepared using the above method.

Drawings

Fig. 1 is a diagrammatic view of a high-voltage insulator.

Detailed Description

The invention is described in more detail below, with reference to the appended drawings, which show non-limiting examples of the invention, in which:

the only figure is a diagrammatic view of the high-voltage insulator.

The only figure shows a high-voltage insulator 1 comprising a skirt 2 made of glass or porcelain, a metal cap 4 connected to a top portion 3 of the skirt 2 by means of a mortar 5, and metal connection feet 6 connected in cavities 7 of the skirt 2 by means of the same mortar 5 as in the cap 4, the cavities 7 being inside said top portion 3 of the skirt 2.

To prepare the mortar 5 of the invention, a dry mix of alumina cement, sand and microsilica is first prepared in a standard mixer (for example, a mixer complying with standard NF EN196-1) for a duration in the range from 1 minute to 10 minutes. In this dry mix, the cement is expressed as approximately in the range of 50% to 80% of the total mass of the mixture of sand and cement, the sand is expressed as approximately in the range of 20% to 50% of the total mass of the mixture of sand and cement, and the mass of silica fume or silica fume is expressed as approximately in the range of 2% to 10% of the mass of cement alone, preferably about 6%. Preferably, the cement is selected from alumina cements, also known as "high alumina cements" or "aluminous cements", having an alumina content approximately in the range of 30% to 75%. The sand is preferably fine sand having a controlled particle size, centered on a value in the range of about 200 to 300 micrometers (μm). Since the silica fume is much smaller in size than the cement particles and the sand grains, it makes it possible to fill the voids remaining between the cement particles and the sand grains, and in a manner similar to cement, in a known manner, to fill the voids between the sand grains, thereby making it possible to increase the compactness of the mortar.

Water comprising an aqueous glucose solution is then added to the dry mix and mixing is resumed for a duration in the range of 1 minute to 15 minutes. Preferably, the aqueous glucose solution is an aqueous solution comprising a water-soluble dispersant containing carboxyl functional groups and polyether segments in an amount of about 30% of the dry extract. Such a solution is described, for example, in patent document FR2,776,285. In the process of the invention, the aqueous glucose solution acts as a plasticizer, making it possible to improve the wetting power of the water. In this way, the amount of water added to the mortar can be reduced, and thus the porosity of the mortar can also be reduced, thereby increasing its mechanical strength.

Preferably, the mass ratio of water to cement is approximately in the range of 17% to 27%, and preferably about 22%. The aqueous glucose solution is added to the water in a proportion in the range of about 0.2% to 0.5% by mass of the cement alone, and preferably about 0.25%.

At the outlet of the mixer, the moist mortar paste throttled by the outlet before being fed to the skirt 2 of the insulator 1 is obtained. It will be appreciated that the amount of mortar used is accurately outlet throttled depending on the size of the insulator.

To assemble the insulator 1 of the present invention, mortar was prepared as described above. A measured amount of mortar 5 is first fed into the cavity 7 of the top portion 3 of the skirt 2. The connecting feet 6 are then inserted into the mortar 5, while vibrations are applied to the assembly, so that the connecting feet 6 pass through the mortar until they interfere with the end walls of the cavity 7. Another measured amount of grout 5 is then deposited inside cap 4, and the top portion 3 of skirt 2 is inserted into cap 4, while vibration is also applied, in order to facilitate the positioning of skirt 2 inside cap 4. It will be appreciated that it is also possible to first place the cap 4 on the skirt 2 and then place the connecting feet 6 inside the skirt 2. The operations of fitting the metal connecting feet 6 and the metal cap 4 to the skirt 2 can also be carried out simultaneously.

Finally, the mortar is set by immersing the assembly formed by the skirt 2, the cap 4 and the connecting foot 6 in a vat of water, preferably hot water at a temperature in the range of about 50 ℃ to 70 ℃ for a duration in the range of about 60 minutes to 120 minutes. It is also possible to immerse the mortar in a vat of water at room temperature for a duration in the range from 8 hours to 24 hours. Once set in this way, the mortar is allowed to cool under ambient air at room temperature.

Example (c):

mortar based on alumina cement was subjected to mechanical strength tests and prepared using the following test protocol:

dry-mix cement and sand, if applicable, with silica for 1 minute; and is

Add mix water, if applicable, and glucose solution, then mix for 4 minutes.

The mortar was subjected to a mechanical strength test after it had been treated in water at 55 ℃ for 1 hour (hr) and 30 minutes (mins) to solidify, and then cooled in air at 20 ℃ for 1 hr. Mechanical strength was measured on specimens made on a standard NF EN196-1 impact table, the dimensions of which were 4 centimeters (cm) by 4cm by 16 cm.

Table 1 shows the results of flexural and compressive strength tests for mortars prepared using the process of the invention, conventional mortars without any admixture, and other test mortars. As can be seen from table 1, the composition of the waterproof mortar of the present invention (table 1, row 2) achieved better strength in bending and compression than the reference composition without any admixture (row 1), and the composition with silica fume only (row 3) or glucose only (row 4).

TABLE 1

Claims (7)

1. A method of manufacturing a high-voltage insulator (1) comprising a skirt (2) of glass or porcelain, a metal part cap (4) and a metal connection foot (6), in which method the cap (4) and the connection foot (6) are respectively sealed to the skirt (2) of the insulator (1) by means of a waterproof mortar obtained by mixing alumina cement with sand and silica fume to form a dry mix, and then mixing the resulting mix with water and an aqueous solution, the method being characterized in that:

adding an aqueous solution to water before mixing the mixture with the water and the aqueous solution, the aqueous solution comprising a water-soluble dispersant comprising a carboxyl functional group and a polyether segment;

wherein the mass of the aluminous cement is expressed in the range of 50% to 80% relative to the total mass of the mixture of sand and cement, the mass of the sand is expressed in the range of 20% to 50% relative to the total mass of the mixture of sand and cement, the mass of the silica fume is expressed in the range of 2% to 10% relative to the mass of the cement alone in the mortar, the mass of the water is expressed in the range of 17% to 27% relative to the mass of the cement alone in the mortar, and the mass of the aqueous solution is expressed in the range of 0.2% to 0.5% relative to the mass of the cement alone in the mortar.

2. A method of manufacturing a high voltage insulator (1) according to claim 1, wherein the silica fume is preferably present in an amount of 6% by mass, the water in an amount of 22% by mass and the aqueous solution in an amount of 0.25% by mass, relative to the mass of the cement alone in the mortar.

3. A method of manufacturing a high voltage insulator (1) according to claim 2, wherein the cement comprises aluminium oxide in an amount in the range of 30% to 75%.

4. A method of manufacturing a high-voltage insulator (1) according to claim 2, wherein the grain size of the sand is concentrated on a value in the range of 200 μ ι η to 300 μ ι η.

5. A method of manufacturing a high voltage insulator (1) according to claim 1, wherein the cement comprises aluminium oxide in an amount in the range of 30% to 75%.

6. A method of manufacturing a high-voltage insulator (1) according to claim 5, wherein the grain size of the sand is concentrated on a value in the range of 200 μm to 300 μm.

7. A method of manufacturing a high voltage insulator (1) according to claim 1 or 3, wherein the grain size of the sand is concentrated on a value in the range of 200 μ ι η to 300 μ ι η.