JPH02129816A - Resin molded branch bushing - Google Patents

Abstract

PURPOSE:To improve adhesion to cast resin and eliminate cracks caused by the thermal shock and enable excellent corona resistance and air tightness by providing the formation film made of Na2Co3/Na2CrO4.4H2O on the surface of an embedded conductor made of aluminum. CONSTITUTION:After an aluminum embedded conductor 2 of a T type branch bushing is cleaned, it is dipped in a solution prepared by mixing 2 solution, where 15g/l of Na2CrO4.4H2O is prepared, with a solution, where 45g/l of Na2CO3 is prepared, at the rate of 3/1 with respect to Na2CO3/NaCrO4 4H2O. At this stage, the temperature of the treated solution is maintained at 90-95 deg.C, and the dip time is 10-15 minutes. After the etching film 3 is performed on the embedded conductor 2 and the conductor is sufficiently washed by the water, it is dried to eliminate the moisture. The conductor 2 having the film 3 mainly composed of the aluminium oxide is embedded in the mold, and the cast resin 1 mainly composed of the epoxy resin is embedded in the mold under the vacuum condition. The T-type branch bushing formed with an insulating layer made of the resin 1 is thus obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a cast bushing using an aluminum member as a center conductor, and particularly relates to a pretreatment method for the member.

(Prior Art) Cast insulation has both electrical insulation function and structural function, and is widely used in the field of solid insulation for high-voltage equipment because it allows products with complex shapes to be obtained without voids. Also, recent electrical equipment.

It is desired to reduce the total cost and reduce the installation space by increasing the capacity and making the device more compact, and the various parts used are also required to have high added value.

For this reason, in various electrical equipment, combinations of silicone oil, fluorocarbon liquid, petroleum-based insulating oil, and solid insulation,
Alternatively, it is common to use a combination of sulfur hexafluoride (hereinafter referred to as SF6), fluorocarbon gas, and solid insulation.

Therefore, the various insulating parts used are required to have not only mechanical properties but also high-level electrical insulation properties and airtightness against insulating oil and gas.

For example, SF, gas insulated type closed switchboard (hereinafter C-
(referred to as GIS) is a C-
A T-shaped branch bushing is used to connect the inside of the GIS and the external power source and load side.

The T-shaped branch bushing is manufactured by a casting method using a casting material whose main component is epoxy resin.

In addition, the embedded conductor of the T-shaped branch bushing is made of copper at the negative part, and it is lightweight, easy to process, has a cost, and has a coefficient of thermal expansion close to that of cast material, and is less prone to cracking. Aluminum conductors are widely used.

The embedded conductor 2 of the T-type branch bushing is the T-shaped branch bushing shown in FIG.
As can be seen from the cross-sectional view of the type branch bushing, it consists of approximately 105 members with different outer diameters and a φ22 member.

The embedded conductor 2 is manufactured by processing each member into a predetermined shape in advance and integrating them by welding, or by molding both parts at once by forging. Therefore, as a matter of course, a rounded portion A is formed at the base of the embedded conductor 2. In the case of cast insulation, the processed part A of this R is the most important part, and is the part where stress concentration is forced.

The epoxy resin, which is the main component of the casting material 1, always undergoes volumetric contraction during curing, and remains in the casting resin 1 as residual stress.

Furthermore, due to changes in ambient temperature, the embedded sensing element 2 and the casting resin 1
Thermal stress due to the difference in thermal expansion coefficient is taken into account. Therefore, in the processed part A of R, compared to the smooth part of the embedded conductor 2,
Fairly high levels of stress occur. If this stress is greater than the adhesive strength between the casting material 1 and the embedded conductor 2, peeling will occur, causing leakage of SF and gas, generation of corona harmful to electrical insulation, and cracking of the casting material 1. do. Gas leaks, coronas, and cracks eventually cause short circuits in equipment, leading to serious accidents.

For this reason, conventionally, the surface of the embedded sensitive body 2 is coated with sandblasting or a resin coating (hereinafter referred to as primer) made of epoxy resin, phenol resin, cyanoacrylate, etc.
is formed to improve the adhesive strength between the casting resin 1 and the embedded conductor 2.

However, in modifying the adhesive strength by sandblasting, particles of a predetermined size are sprayed to make the surface rough, and the adhesive strength is improved by what is generally called an anchoring effect. However, the surface roughness due to sandblasting is usually 45 to 130p.
If a large amount of rough and deep parts remain, as shown in Figure 2, it will be difficult to completely fill the recesses on the surface of the embedded conductor 2, which has a particularly rough surface, with the casting resin 1. Thereafter, microvoids 4 are present on the surface of the buried conductor 2. The existence of this microvoid 4 is harmful to the corona,
In particular, the presence of microvoids 4 in devices used at high voltages, such as T-type branch bushings, has a significant impact on electrical insulation properties.

In addition, in the case of surface treatment with a primer, the primer is widely used because it is interposed as a thin film between the casting resin 1 and the embedded sensitive body 2 and contributes to improving the adhesive strength of both.

However, compared to sandblasting, which mechanically improves adhesive strength, primer treatment uses chemical adhesion and is considerably inferior in adhesive strength.

Further, the primer is an organic substance and does not contain an inorganic fabric material. For this reason, the primer has a large coefficient of thermal expansion, and due to the difference in coefficient of thermal expansion with the embedded conductor 2, cracks are likely to occur in the thin film of the primer when subjected to rapid heating and cooling.

The occurrence of cracks in the primer not only deteriorates the corona properties but also induces cracks in the casting material 1, and has a serious effect on gas leakage.

(Problem to be solved by the invention) The present invention has been made in view of the above-mentioned problems.
By modifying the surface of the aluminum embedded sensing element 2 and greatly improving its adhesion with the casting resin 1, it is possible to obtain a T-shaped branch bushing for C-GIS with excellent corona resistance and airtightness. This is the purpose.

[Structure of the invention]

(Means and Effects for Solving the Problems) The present invention provides a coating with a thickness of 0.1 to 0.3 a on the surface of the aluminum embedded conductor 2 using sodium chromate (Na2Cr04.4 H2O) and anhydrous soda carbonate (Nat C03).
It is characterized in that a chemical conversion film 3 of m is formed and the surrounding area is cast with a pattern resin 1 whose main component is epoxy resin.

(Example) Examples will be described below. There are various methods for surface treatment of aluminum, and various treatment chemicals are used. For this reason,
4 types of treatment liquids, such as Nippon Barker's Bonderite #
713 and Alpond CRN, Chemibonder 334 from Japan CB Chemical Co., Ltd. and Na2CO3/Na2 according to the present invention.
The tensile shear adhesive strength was compared using an aluminum plate treated with a CrO4.4H2O treatment solution.

The test was conducted using an aluminum plate 5 with a thickness of 1.6 mm.
Test pieces were prepared according to IS K 6850 and their properties were investigated.

The adhesive contains 60% inorganic filler mainly composed of silica powder.
% or more of casting resin 1 was used and cured for a specified time. For comparison, conventional sandblasting and primer treatment products were also investigated. Table 1 shows the tensile shear adhesive strength of each.

Table 1 As shown in Table 1, the product treated according to the present invention shows the highest value. This is thought to be because the chemical conversion film 3 has extremely fine independent protrusions, and the casting resin 1 penetrates into these parts, mechanically improving the adhesive strength.

As described above, since the adhesive force is high, and the film itself is uniform with an average thickness of 0.1 to 0.3 μs and is very thin, microvoids 4 harmful to electrical insulation are less likely to remain compared to sandblasting.

Next, a specific example of the T sub-branch bushing according to the present invention will be described.

FIG. 1 shows a sectional view of a T sub-branch bushing according to the present invention. After degreasing the aluminum embedded conductor 2,
An aqueous solution of Na2CrO4.4■,0 adjusted to 15##t and Na2Co3 of 459. The aqueous solution adjusted to IQ was
a2CO3/NaCr0. ” It is immersed in a solution adjusted at a ratio of 4H2O=3/1. At this time, the temperature of the treatment liquid is maintained at 90 to 95°C, and the immersion time is preferably 10 to 15 minutes.

After the buried conductor 2 coated with the chemical conversion film 3 is thoroughly washed with water, the moisture is removed by drying.

The embedded conductor 2 having the chemical conversion film 3 mainly composed of aluminum oxide thus obtained is assembled into a mold (not shown), and a casting resin 1 mainly composed of epoxy resin is placed in the mold under vacuum. By pouring and heating and curing, a T sub-branch bushing in which an insulating layer of casting resin 1 is formed around the embedded conductor 2 is obtained.

Test results using the T sub-branch bushing obtained in this way will be explained. For comparison, the pretreatment of the embedded hot body 2 of the T sub-branch bushing by the conventional method was as follows: As mentioned above, in the case of sandblasting, it is expected that there will be problems with the corona characteristics, so primer treatment was performed. The embedded conductor 2 was used.

The primer is an epoxy resin primer (product name;
AZ15/l (Z15, manufactured by Ciba Geigy) was used.

Table 2 shows the corona characteristics of each T sub-branch bushing and the results of a 160 KV/1 minute withstand voltage test.

The thermal test in the table is conducted as one of the reliability tests for resin molded parts, and the thermal shock is applied repeatedly to the resin molded parts, resulting in the difference in thermal expansion coefficient between casting resin 1 and embedded conductor 2. The purpose is to investigate the presence or absence of cracks in the casting resin 1 and peeling between the casting resin 1 and the embedded conductor 2 due to thermal stress.

The conditions of the thermal test used in the present invention were 98 to 100'
One cycle is 1 hour of immersion in warm water of C, and after taking it out from the hot water, 1 hour of immersion in cold water of 0 to 2 °C.
Do it until the cycle.

Table 2 vi: Corona starting voltage ve: Corona extinction voltage Since the T sub-branch bushing is required to have airtightness, an airtightness test using a helium detector was conducted after the thermal test. As a result, a T-shaped branch bushing using a conventional primer-treated embedded core has a 5Xl0-5t
orr.

It shows very small QCs characteristics.

As is clear from the above results, the T-shaped branch bushing of the present invention has excellent airtightness and does not crack even when subjected to repeated thermal shocks, and can significantly improve corona characteristics.

〔Effect of the invention〕

As mentioned above, Na is applied to the surface of the aluminum embedded conductor.
By providing a chemical conversion coating with 2GO3/Na2CrO4.4H2O, the adhesive strength with the casting resin is improved,
It has excellent airtightness, does not crack even under severe thermal shock, and can maintain excellent corona resistance.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part of a T-shaped branch bushing showing an embodiment of the present invention, and FIG. 2 is a sectional view showing the state of adhesion between the sandblasted surface and the casting resin. 1...Casting resin 3...Etching film A...R processing part

Claims (1)

[Claims] Na_2CrO_4・4H_ on the surface of the aluminum conductor
A resin characterized in that a chemical conversion film with a thickness of about 0.5 μm or less is formed using a mixed solution of a 2O solution and a Na_2CO_2 solution, and an insulating layer is provided on the film using a casting material whose main component is an epoxy resin. Molded branch bushing.