JPH0963379A - Suspended insulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an improved suspended porcelain insulator which can exhibit excellent dielectric breakdown strength without depending on the realization of low impedance of a glaze. SOLUTION: A suspended porcelain insulator is provided with a porcelain- made insulator 1 where a glaze is applied to a basis material surface and ceramic quality sand 4 is adhered to an inner peripheral surface and an outer peripheral surface of a head part peripheral wall 2a and a cap metal fitting 5 and a pin metal fitting 6 joined to the insulator 1 by cement 7. The relationship of (ε2-ε1<=0) is satisfied between a dielectric constant ε1 of the sand 4 and a dielectric constant ε2 of the glaze, and an electric field relieving effect of a glaze layer is exhibited, and excellent dielectric breakdown strength is realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention includes a hollow cylindrical head having a top wall and a peripheral wall, a surface of the base material is glazed, and a ceramic sand is adhered to the inner and outer peripheral surfaces of the peripheral wall. A suspension insulator comprising a porcelain insulator and a cap fitting and a pin fitting joined to the head of the insulator by cement, and particularly improved so that the dielectric breakdown strength can be greatly improved. A porcelain insulator is proposed.

[0002] The present invention comprises a hollow cylindrical head having a top wall and a peripheral wall, a surface of the base material is glazed, and a ceramic sand is adhered to the inner and outer peripheral surfaces of the peripheral wall. Regarding a suspension insulator including an insulator and a cap fitting and a pin fitting joined to the head of the insulator by cement, in particular, a porcelain insulator improved so as to significantly improve dielectric breakdown strength is proposed. To do.

[0003]

2. Description of the Related Art In order to increase the joint strength of a cap fitting and a pin fitting to an insulator in a suspended porcelain insulator, ceramic sand is adhered to the inner and outer peripheral surfaces of the insulator head to form a cap fitting and a pin fitting. A suspended porcelain insulator made by cementing the
It is widely known in the past. It is known that such a steep-wave all-penetration, which is a problem in suspended porcelain insulators, is caused by a partial breakage in the glaze between the sands adhered to the insulator head. As a means for improving the steep wave strength of a porcelain insulator and the breakdown voltage in dirty oil, lowering the impedance of the glaze applied to the surface of the base material of the insulator has been studied. The low impedance of glaze is
It is intended to reduce the voltage sharing of the glaze, paying attention to the point that the dielectric breakdown of the composite dielectric made of porcelain and glaze occurs from the surface layer.

By the way, since cement serves as an electrode between the cap fitting and the pin fitting because it is a conductor, when the ceramic sand is adhered to the inner and outer peripheral surfaces of the insulator head, the sand is generally used. However, since the shape of the electrode is indefinite, the shape of the electrode changes greatly. Since the dielectric breakdown strength is governed by such an electrode shape, the electric field relaxation effect of the glaze layer will not be sufficiently exhibited even if the impedance of the glaze is reduced.

Japanese Examined Patent Publication No. 6-53601 discloses a method for producing sand for insulators, in which a sand substrate is extruded into a noodle shape by a kneading machine, pulverized after drying, and then sized by a sizing machine to make a noodle diameter. Discloses a method of firing a granular material having substantially the same diameter as that of the present invention and having less sharp edges, and then firing. If the sand manufactured by such a method is used and the impedance of the glaze is lowered, the electric field is concentrated at the edge and acts as the starting point of penetration when the steep wave such as lightning impulse acts. As a result, it is possible to effectively eliminate the decrease in tensile strength of the insulator due to stress concentration. On the other hand, the low impedance of the glaze itself can be achieved by adding titanium or the like. Therefore,
If these measures are used together, the electric field relaxation effect of the glaze layer can be sufficiently expressed, but thermal expansion, melt flow, etc. required for porcelain and glaze materials in order to increase the tensile strength of the suspension insulator. It is generally difficult to lower the glaze impedance while simultaneously satisfying various conditions.

[0006]

Therefore, a main object of the present invention is to propose an improved suspended porcelain insulator capable of exhibiting excellent dielectric breakdown strength without depending on the low impedance of the glaze. .

[0007]

In order to solve this problem, the present invention includes a hollow cylindrical head having a top wall and a peripheral wall, the surface of which is glazed, and the inner surface of the peripheral wall. In a suspension insulator comprising a porcelain insulator having ceramic sand adhered to the peripheral surface and the outer peripheral surface, and a cap fitting and a pin fitting joined to the head of the insulator by cement, a sand insulator It is characterized by satisfying the relationship of ε2-ε1 ≤0 between the coefficient ε1 and the dielectric constant ε2 of the glaze.

For the first time, the present invention focuses on the combination of the permittivity of the sand and the glaze in the suspended porcelain insulator, and between the permittivity ε1 of the sand and the permittivity ε2 of the glaze, ε2-ε1.
It was completed based on the new finding that if the relationship of ≦ 0 is satisfied, the influence of the electrode shape is sufficiently mitigated without significantly lowering the glaze impedance, and it contributes greatly to the improvement of the dielectric breakdown strength. is there.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail with reference to the preferred embodiments shown in the accompanying drawings. The suspension insulator shown in FIG. 1 comprises an insulator 1 made of porcelain, and the surface of the base body of this insulator 1 is coated with glaze in a known manner. The insulator 1 is composed of a flange-shaped cap portion 2 extending outward in the radial direction, and a substantially cylindrical head portion 3 arranged in the center of the cap portion 2 and protruding upward. The head 3 has a cap 2 at the lower end.
And a top wall 3b continuous with the upper end of the peripheral wall 3a. Ceramic sand 4 is adhered to the inner and outer peripheral surfaces of the peripheral wall 3a. Further, with respect to the head 3, the cap metal fitting 5 is on the outer peripheral surface side, and the pin metal fitting 6 is on the inner peripheral surface side.
Are joined by. A buffer spacer 8 is inserted between the upper end surface of the pin fitting 6 and the inner surface of the top wall 3b of the head 3. The basic construction itself of such a suspension insulator is known in the prior art.

As shown in FIG. 2, the sand 4 adhered to the inner peripheral surface and the outer peripheral surface of the head peripheral wall 3a of the insulator 1 is preferably manufactured by the following method. That is, first, a sand substrate is prepared in the same manner as in the conventional case, and dehydrated by a filter press to obtain a cake containing an appropriate amount of water. This cake is put into a clay kneader and kneaded to have a pore size of 1.8 to 2.
A noodle-like molded body is obtained by extruding from a perforated plate having a large number of through holes of about 0 mm. The diameter of this molded body is
Set the same as the target maximum grain size or slightly larger. Next, this noodle-shaped molded product is dried, and is pulverized and sized by a coarse crusher and a de-sinter sizing machine into granules having substantially the same diameter as the diameter of the molded product. The de-sinter sizing machine is a device for crushing and sizing while rotating a drum provided with a large number of through holes. It is preferable that the diameter of the through holes in the drum is about 1.6 to 1.8 mm, and the rotation speed of the drum is about 200 rpm, which is much lower than in the usual case. The granules thus obtained are granules with few sharp edges, and the upper net has a size of 1.68 m.
m, the lower net is 0.84 to 1.0 mm, and the powder is screened through a sieving sieve, and then squeezed and baked. After that, the fired product is disentangled through a disintegrating sieve and finished as an insulator sand with few sharp edges. The above-mentioned crushing manufacturing method of insulator sand is described in detail in the above-mentioned Japanese Patent Publication No. 6-53601, so please also refer to the description in that publication.

In the present invention, attention is focused for the first time on the combination of the permittivity of the sand 4 and the glaze in the suspension insulator, and the permittivity ε1 of the sand and the permittivity ε2 of the glaze are equal to ε2-
It is set so that the relationship of ε1 ≤ 0 is established.
FIG. 3 is a graph showing the sharp wave breaking rate of the suspension insulator with respect to the dielectric constant difference .epsilon.2-.epsilon.1 of the glaze in the suspension insulator of FIG. 1 and the sand produced by the crushing manufacturing method. This graph is based on IEC standard No. 305 U120BS-compliant suspension insulators were used to prepare Samples 1 to 5 with different dielectric constants of sand and glaze, and IEC Technical Report 121 for these samples.
Voltage steepness of 4000 KV using the test circuit specified in 1.
/ Μs, positive wave, negative wave 10 times each, the steep wave breakdown test was performed. As is clear from the graph in Fig. 3, the permittivity ε2 of the glaze is that of the sand ε1.
If it is higher than the above, the steep wave breakdown rate is about 60% or more. On the other hand, when the permittivity ε2 of the glaze is almost equal to the permittivity ε1 of the sand, the steep wave breakdown rate is about 15%,
When the permittivity ε1 of the sand is higher than the permittivity ε2 of the glaze, the steep wave breakdown rate decreases to about 5% or less. From this experimental result, it is clear that setting the dielectric constant difference between the glaze and the sand to be ε 2 −ε 1 ≦ 0 is effective in reducing the steep wave breakdown rate in the suspension insulator.

Incidentally, in the graph of FIG. 3, the numbers in parentheses adjacent to each plot indicate the voltage steepness of 2500 Kv /
It shows the steep wave destruction rate of each sample 1 to 5 under the condition of μs. From this experimental result, it is clear that the difference in permittivity between glaze and sand is ε 2 −ε 1 ≦ 0. is there.

Next, in order to confirm the influence of the difference in dielectric constant between the glaze and the sand on the dielectric breakdown of the suspension insulator, the inventors of the present invention used the glaze and the sand based on the electric field calculation model (dimension unit: mm) shown in FIG. The maximum electric field and electric field magnitude were analyzed by changing the dielectric constant difference ε2-ε1 of. The analysis results are as shown in Table 1 below and FIGS.

[0014]

[Table 1]

As is clear from FIGS. 5 to 7, the maximum electric field is generated in the glaze portion between the sands in all the models, which is in good agreement with the results of various dielectric breakdown experiments.
Furthermore, as shown in Table 1, the maximum potential gradient in the glaze portion between the sands is the dielectric constant difference ε 2 − of the glaze and the sand.
It is relatively high in the model 1 in which ε1 is positive, and is reduced in the model 2 and the model 3 in which the dielectric constant difference ε2-ε1 is negative. That is, it is clear that when the difference in dielectric constant between the glaze and the sand is ε 2 −ε 1 ≦ 0, the voltage sharing of the glaze in the glaze portion between the sands is effectively reduced.

Since the dielectric constant is generally the sum of the dielectric constants of the crystal in the sand and the glass component, the dielectric constant of the crystal in the sand is particularly important. The dielectric constant is, for example, about 10 for alumina (corundum) crystals and about 5 to 7 for quartz crystals.
On the other hand, since it is about 5 to 7 for glass,
Inclusion of a large amount of alumina (corundum) crystals in the sand is effective as a means for increasing the dielectric constant. On the other hand, considering strength, it is disadvantageous if the sand contains a large amount of alumina (corundum) crystals, which is disadvantageous. Therefore, the content of alumina (corundum) crystals is limited by itself. It is what is done. Considering the above,
The composition of the sand used in the present invention is, for example, Al2O.
3 is 20-70wt%, SiO2 is 40-70wt%, KNaO is 2
˜6 wt%, preferably Al 2 O 3 40-60
wt% and SiO2 are in the range of 40 to 60 wt%.

Furthermore, when the relationship between the difference in the coefficient of thermal expansion between the glaze and the sand and the tensile strength of the suspension insulator is examined, as is apparent from FIG. 8, the difference in the coefficient of thermal expansion is -0.11.
If it is less than 1.0, the tensile strength is sharply reduced, while if the difference in coefficient of thermal expansion is −0.11 or more, stable tensile strength tends to be maintained. On the other hand, the difference in the coefficient of thermal expansion between the glaze and the sand and the difference in the dielectric constant between the glaze and the sand (ε
A nearly proportional relationship is recognized between 2-ε 1) and 2-ε 1). And the difference in the coefficient of thermal expansion between the glaze and the sand −
The dielectric constant difference between the two, which corresponds to 0.11, is approximately -1.4. Therefore, when the tensile strength of the suspension insulator is also taken into consideration, the dielectric constant difference between the glaze and the sand satisfies the relationship of −1.4 ≦ ε2 −ε1 ≦ 0 based on the relationships shown in FIGS. 8 and 9. Is desirable.

As is clear from the above description, according to the present invention, particular attention is paid to the combination of the permittivity of the sand and the glaze in the suspended porcelain insulator, and the permittivity ε2 between the permittivity ε1 of the sand and the permittivity ε2 of the glaze is ε2. By satisfying the relationship of −ε1 ≦ 0, it becomes possible to sufficiently alleviate the influence of the electrode shape and significantly improve the dielectric breakdown strength without particularly lowering the impedance of the glaze.

The above-described embodiment is merely an example and does not limit the present invention. Needless to say, the present invention can be implemented in various modified forms without departing from the scope thereof.

[Brief description of drawings]

FIG. 1 is a front view of a suspension insulator to which the present invention can be preferably applied, showing a half portion thereof in cross section.

FIG. 2 is a flow chart showing a manufacturing process of a sand which can be used in the suspension insulator of FIG.

FIG. 3 is a graph showing the relationship between the dielectric constant difference between the glaze and the sand and the steep wave breaking strength in the suspension insulator of FIG.

FIG. 4 is an explanatory diagram showing an electric field calculation model of a suspension insulator.

FIG. 5 is a diagram showing a calculation result of an electric field calculation model for an example of the present invention and a reference example.

FIG. 6 is a diagram showing a calculation result of an electric field calculation model for an example of the present invention and a reference example.

FIG. 7 is a diagram showing a calculation result of an electric field calculation model for an example of the present invention and a reference example.

FIG. 8 is a graph showing the relationship between the difference in thermal expansion coefficient between the glaze and the sand and the tensile strength of the suspension insulator.

FIG. 9 is a graph showing the relationship between the difference in thermal expansion coefficient between glaze and sand and the difference in dielectric constant between glaze and sand.

[Explanation of symbols]

1 insulator, 2a head peripheral wall, 4 sand, 6 cap metal fittings,
7 cement

Claims (3)

[Claims] 1. A porcelain porcelain comprising a hollow cylindrical head having a top wall and a peripheral wall, a surface of the base material being glazed, and ceramic sand being adhered to the inner and outer peripheral surfaces of the peripheral wall. An insulator and a cap fitting and a pin fitting joined to the head of the insulator by cement are provided, and the following relationship between the permittivity ε1 of the sand and the permittivity ε2 of the glaze is: ε2 −ε1 ≤0 Suspension insulator characterized by satisfying. 2. The suspension according to claim 1, wherein the following relationship is satisfied between the permittivity ε1 of the sand and the permittivity ε2 of the glaze: -1.4≤ε2 -ε1≤0. . 3. The sand is obtained by extruding a sand substrate into a noodle shape by a kneading machine, drying and pulverizing, and sizing by a sizing machine to have a diameter substantially the same as the diameter of the noodle and less sharp edges. The suspension insulator according to claim 1 or 2, wherein the suspension insulator is formed into a granular body and then fired.