JP2000221232A - Water tree testing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reproduce such a large water tree that occurs in an actual power cable insulated with a crosslinked polyolefin-based electrical insulating composition without using any actual power cable, by using a sheet composed of the electrical insulating composition mixed with water tree accelerating deteriorating foreign matters. SOLUTION: In a water tree testing method, an integral sheet-like sample prepared by sticking a sheet composed of a crosslinked polyolefin-based electrical insulating composition mixed with water tree deteriorating foreign matters to both surface of a semiconductor element is used. One or two or more kinds of matters selected from among metal power, electrolytic materials, and aggregated compounding agent are used as the foreign matter. The metal powder includes copper powder, iron powder, aluminum powder, etc., and the electrolytic materials include sodium chloride, potassium chloride, lithium chloride, barium chloride, sodium nitrate, potassium nitrate, etc. The aggregated compounding agent include crosslinking agents, crosslinking assistants, aging preventing agents, lubricants, fillers, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water tree test method. More specifically, the present invention relates to a crosslinked polyolefin-based electrical insulating composition, which can quickly and accurately achieve water tree resistance of a crosslinked polyolefin-based electrical insulating composition used as an insulator of an insulated power cable. The present invention relates to a water tree test method that can be evaluated using a sheet-like sample without using an insulated power cable.

[0002]

2. Description of the Related Art Polyolefin resins, such as polyethylene, ethylene copolymers and polypropylene, are typical hydrocarbon-based synthetic resins and therefore have excellent electrical properties and are widely used as electric insulating materials for electric wires and cables. Practical.

[0003] In particular, a crosslinked polyethylene electric insulating composition formed by cross-linking polyethylene, an ethylene copolymer or the like has higher heat resistance than an uncrosslinked polyethylene electric insulating composition. It is prized as an electrical insulating material for accessories.

However, a crosslinked polyethylene insulated power cable obtained by insulatively coating the crosslinked polyethylene-based electrical insulating composition on a conductor directly or via another insulating layer has a problem in that moisture,
When several factors such as minute foreign matter and local high electric field overlap,
It is known that tree-like electrical defects, so-called water trees, occur in crosslinked polyethylene. It is also known that such water trees, when extended, cause electrical breakdown of the crosslinked polyethylene insulated power cable.

[0005] For this reason, the cross-linked polyethylene-based electrical insulation composition used as an insulator of the cross-linked polyethylene insulated power cable is in a stage prior to application to the cross-linked polyethylene insulated power cable, ie, directly on the conductor or another insulating layer. It is important that the cross-linked polyethylene-based electrical insulating composition is preliminarily selected by a water-resistant tree test before the insulating coating is performed via the resin.

In the conventional water tree test method, the following crosslinked polyethylene-based electrically insulating composition sheet samples with electrodes were used.

A. Preparation of uncrosslinked polyethylene-based electrical insulating composition First, an uncrosslinked polyethylene-based electrical insulating composition is prepared by blending a crosslinking agent, water tree deterrent, and other necessary special compounding agents with polyethylene as the base resin. I do.

A non-crosslinked polyethylene electrical insulation set for comparison is also prepared in which one kind of foreign matter is mixed to simulate a local high electric field portion.

B. Preparation of Uncrosslinked Polyethylene Sheet Next, the uncrosslinked polyethylene electrical insulating composition compound is prepared by kneading the uncrosslinked polyethylene electrical insulating composition obtained above with a kneading roll.

Next, the obtained uncrosslinked polyethylene-based electrical insulating composition compound is placed in a mold of a press machine, and then pressed at a temperature of 120 ° C. to produce two polyethylene sheets having a thickness of 2 mm.

C. Preparation of Crosslinked Polyethylene Sheet Sample with Electrode Next, a semiconductive electrode was sandwiched between the two polyethylene sheets obtained above, and then pressed by a press crosslinking apparatus.
By press-crosslinking at a temperature of 0 ° C. for a predetermined time, a crosslinked polyethylene sheet sample with electrodes formed by integrating them is prepared.

D. Water Treeing Test Next, the crosslinked polyethylene sheet sample with an electrode obtained above is set in a water tree test device, and a water tree accelerated deterioration test is performed under a predetermined voltage and moisture.

FIG. 1 is an explanatory sectional view showing a water tree test apparatus.

In FIG. 1, 1 is a copper test container of a test water tank, 2 is ground, 3 is water, 4 is a crosslinked polyethylene sheet sample with electrodes, 41 is a crosslinked polyethylene sheet, 42 is a semiconductive electrode, and 5 is a high voltage application. It is a lead wire needle.

The water temperature is periodically changed from room temperature to 90 ° C.
6 hours → 90 ° C., 8 hours repetition). As the power application condition, an AC voltage having a frequency of 1000 Hz and a voltage of 3 kV AC is applied for 300 hours.

After the test, the crosslinked polyethylene sheet 41 is thinly sliced from the crosslinked polyethylene sheet sample 4 with electrodes, and a crosslinked polyethylene slice sheet having an extremely thin thickness is collected. Then, the crosslinked polyethylene slice sheet is subjected to boiling dyeing with a methylene blue aqueous solution for a predetermined time, and the maximum length of the bow title tree is examined by microscopic observation.

This conventional water tree test method using a crosslinked polyethylene sheet sample with electrodes is effective for a screening test for determining the quality of many crosslinked polyethylene electrical insulating compositions. Further, the conventional water tree test method using a crosslinked polyethylene sheet sample with electrodes can also evaluate extremely small foreign substances present in a crosslinked polyethylene insulator of a crosslinked polyethylene insulated power cable.

[0018]

By the way, when a large number of water trees generated in the insulated power cable of the crosslinked polyolefin-based electric insulating composition actually laid and operated are examined in detail, the generated water trees are as follows. They vary from small to unusually large.

Of these various water trees, the unusually large water trees did not occur in the conventional water tree test using a crosslinked polyethylene sheet sample with electrodes. If a strict tree test method that can reproduce such an abnormally large water tree is found, the strict tree test method is most suitable for a water tree resistance evaluation test of a crosslinked polyolefin-based electric insulating composition.

The present invention has been made in view of such a point, and an object of the present invention is to solve the above-mentioned disadvantages of the prior art and to provide an actual insulated power cable of a crosslinked polyolefin-based electric insulating composition. Rather than simply testing using a cross-linked polyolefin-based electrical insulating composition sheet-like sample, it can also reproduce a large water tree that would be generated by an actually installed and operated cross-linked polyolefin-based electrical insulating composition-insulated power cable. It is another object of the present invention to provide a water tree test method capable of quickly and accurately evaluating the water tree resistance.

[0021]

The gist of the present invention lies in the following three points.

(1) A water tree test method characterized by using a crosslinked polyolefin-based electrically insulating composition sheet obtained by adding and blending water tree accelerated and deteriorated foreign matter.

(2) A sheet-like sample obtained by laminating and integrating a crosslinked polyolefin-based electric insulating composition sheet in which water tree-promoting degraded foreign matter is additionally added to both surfaces of a semiconductive electrode. Tree test method.

(3) A sheet-like sample obtained by laminating and integrating a crosslinked polyolefin-based electric insulating composition sheet on both surfaces of a semiconductive electrode via a dispersion layer of water tree-promoted degraded foreign matter, and using water. Tree test method.

In the present invention, the water tree-promoted deteriorating foreign matter is preferably one or more selected from metal powders, electrolyte substances, and compounding agent aggregates.

In the present invention, the water tree-promoted foreign matter is preferably a combination of a metal powder and an electrolyte substance.

In the present invention, it is more preferable that the metal powder is copper powder and the electrolyte substance is sodium chloride as the water tree-promoted foreign matter.

In the present invention, the metal powder includes copper powder (particle diameter = about φ2 μm), iron powder (particle diameter = about φ2 μm), aluminum powder (particle diameter = about φ2 μm), and the like.

In the present invention, the electrolyte substance includes salts,
For example, sodium chloride, potassium chloride, lithium chloride,
There are barium chloride, sodium nitrate and potassium nitrate.

In the present invention, the compounding agent aggregates include aggregates such as a crosslinking agent, a crosslinking assistant, an antioxidant, a lubricant, and a filler.

[0031]

Next, examples of the water tree test method of the present invention will be described together with a conventional comparative example.

(Materials and Contaminants Used in Making Uncrosslinked Polyethylene Electrical Insulating Composition) First, the uncrosslinked polyethylene electrical insulating composition used in the examples of the water tree test method of the present invention and the conventional comparative examples was prepared. The material and water tree accelerated and deteriorated foreign matter will be described.

A) Base polymer: low density polyethylene (density = 0.920, MI = 1 g / 10 min) b) Crosslinking agent: dicumyl peroxide c) Antioxidant: 4,4-thiobis (3-methyl-6)・ T ・ butylphenol) d) Foreign matter a. Copper powder (particle size = about φ2 μm) b. Iron powder (particle size = about φ2 μm) c. Aluminum powder (particle size = about φ2 μm) d. Sodium chloride e. The material of the uncrosslinked polyethylene-based electrical insulating composition used in the examples of the water tree test method of the present invention and the conventional comparative example is a low-density polyethylene as a base polymer, and dicumyl peroxide as a crosslinking agent. And antioxidants such as 4,4-thiobis (3-methyl-6.t.butylphenol).

The amounts of these components are 2.5 parts by weight of dicumyl peroxide and 4,4-thiobis (3-methyl-6.t.butylphenol) based on 100 parts by weight of the low-density polyethylene as the base polymer. 0.25 parts by weight was blended.

Further, these include copper powder, iron powder,
Aluminum powder, sodium chloride, and a compounding agent aggregate were blended.

The amount of these foreign substances is 0.1 part by weight based on 100 parts by weight of the low-density polyethylene as the base polymer. Even when two or more kinds of foreign substances are blended, the total amount of the foreign substances is as low as that of the low-density polyethylene 10 as the base polymer.
0.1 parts by weight with respect to 0 parts by weight.

(Preparation Method of Crosslinked Polyethylene Sheet Sample with Electrode in Water Tree Test) The test sample was almost the same as the crosslinked polyethylene sheet sample with electrode used in the conventional water tree test method, and was prepared as follows. .

A. Preparation of Uncrosslinked Polyethylene Electrical Insulating Composition First, dicumyl peroxide as a crosslinking agent and 4,4-thiobis (3-methyl-6.t) as an antioxidant were added to 100 parts by weight of low-density polyethylene as a base polymer. (Non-crosslinked polyethylene-based electricity) of a specific weight part and one containing no foreign substances shown in (a) to (e) above, or one or two or more of them. An insulating composition was prepared.

B. Preparation of Uncrosslinked Polyethylene Sheet Next, the uncrosslinked polyethylene-based electrical insulating composition was kneaded with a kneading roll to prepare an uncrosslinked polyethylene-based electrical insulating composition compound.

Next, the obtained uncrosslinked polyethylene-based electrical insulating composition compound was placed in a mold of a press machine, and then press-crosslinked at a temperature of 120 ° C. to obtain a thickness of 2%.
Two mm polyethylene sheets were prepared.

C. Preparation of Crosslinked Polyethylene Sheet Sample with Electrode Next, a semiconductive electrode was sandwiched between the two polyethylene sheets obtained above, and then pressed by a press crosslinking apparatus.
By press-crosslinking at a temperature of 0 ° C. for a predetermined time, a crosslinked polyethylene sheet sample with an electrode was prepared by integrating them by pressing.

(Water Tree Test Method) First, the crosslinked polyethylene sheet sample with electrodes obtained above was set in the water tree test apparatus shown in FIG.

Next, the water temperature of the water tree tester is changed periodically from room temperature to 90 ° C. (repeating the room temperature from 16 hours to 90 ° C. for 8 hours).
z, an AC voltage of 3 kV AC was applied for 300 hours.

After completion of the test, the crosslinked polyethylene sheet 41 of the crosslinked polyethylene sheet with electrode sample 4 was thinly sliced to obtain an extremely thin crosslinked polyethylene slice sheet.

Then, the crosslinked polyethylene slice sheet was subjected to boiling dyeing with an aqueous methylene blue solution, and the maximum length of the bow title tree was examined by microscopic observation.

(Test Results) Table 1 shows the results of the water tree test in the case of the example of the present invention and the conventional comparative example.

[0047]

[Table 1]

As can be seen from Table 1, the maximum length of the bow title of the crosslinked polyethylene sheet samples of Comparative Examples 1 to 6 containing only one kind of foreign matter is as small as 110 to 470 μm.

On the other hand, the maximum length of the bow title of the crosslinked polyethylene sheet samples of Examples 1 to 11 containing at least two kinds of foreign substances was 580 to 41370 μm.
And big.

That is, when it is desired to evaluate the water resistance of the crosslinked polyethylene-based insulating composition, Examples 1 to 3 of the present invention are used.
As shown in 11, the crosslinked polyethylene insulating composition to be evaluated is additionally blended with at least two or more foreign substances, and then the crosslinked polyethylene insulating composition further blended with at least two or more foreign substances has a water tree resistance. By performing the evaluation test, the most severe evaluation of water tree resistance becomes possible.

In the examples of the water tree test method of the present invention, the following three points of the present invention are exemplified for (2), but similar results can be obtained for (1) and (3). Needless to say.

(1) A water tree test method characterized by using a crosslinked polyolefin-based electrically insulating composition sheet obtained by adding and blending water tree-promoted degraded foreign matter.

(2) Water characterized by using a sheet-like sample obtained by laminating and bonding a crosslinked polyolefin-based electric insulating composition sheet in which water tree-promoting degraded foreign matter is additionally added to both surfaces of a semiconductive electrode. Tree test method.

(3) A sheet-like sample obtained by bonding and integrating a crosslinked polyolefin-based electrically insulating composition sheet on both surfaces of a semiconductive electrode via a dispersion layer of water tree-promoted deteriorating contaminants. Tree test method.

[0055]

According to the water tree test method of the present invention, the test is carried out simply by using a cross-linked polyolefin-based electric insulating composition sheet-shaped sample without using an actual crosslinked polyolefin-based electric insulating composition insulated power cable. It is capable of reproducing a large water tree such as that generated in an insulated power cable with a cross-linked polyolefin-based electric insulating composition installed and operated, and capable of quickly and accurately evaluating the quality of the water tree resistance. Which is industrially useful.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view showing a water tree test device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Copper test container 2 Earth 3 Water 4 Crosslinked polyethylene sheet sample with electrode 41 Crosslinked polyethylene sheet 42 Semiconductive electrode 5 High voltage application lead wire needle

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akishi Katagai 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Prefecture Power Systems Research Laboratory, Hitachi Cable, Ltd. (72) Inventor Yoshinao Murata 5 Hidaka-cho, Hitachi City, Ibaraki Prefecture No. 1-1, Hitachi Cable Co., Ltd. Power System Laboratory F-term (reference) 2G015 AA27 CA20 DA01 2G050 AA02 AA07 BA03 BA10 BA20 CA04 CA10 DA03 EA01 EA10 EB07 EC06

Claims (7)

[Claims] 1. A water tree test method comprising using a crosslinked polyolefin-based electric insulating composition sheet obtained by adding and blending water tree-promoting degraded foreign matter. 2. The water tree test method according to claim 1, wherein the added amount of the degraded foreign matter accelerated by water tree is 0.1 part by weight based on 100 parts by weight of the polyolefin polymer. 3. The water tree test method according to claim 1, wherein the water tree accelerated and deteriorated foreign matter is at least one selected from metal powders, electrolyte substances, and compounding agent aggregates. . 4. The water tree test method according to claim 1, wherein the water tree accelerated and deteriorated foreign matter is a combination of two kinds of a metal powder and an electrolyte substance. 5. The method according to claim 4, wherein the metal powder is copper powder and the electrolyte substance is sodium chloride. 6. A sheet-like sample obtained by laminating a cross-linked polyolefin-based electric insulating composition sheet on both surfaces of a semiconductive electrode and setting the same in a water tank of a water-resistant tree test apparatus,
Next, an AC voltage is applied between the water in the water tank and the semiconductive electrode, and then a water tree is used to evaluate water tree resistance from bow titles generated in the crosslinked polyolefin-based electrically insulating composition sheet. In the test method, the crosslinked polyolefin-based electric insulating composition sheet is obtained by additionally mixing water tree-promoting degraded foreign matter. 7. A sheet-like sample formed by laminating a cross-linked polyolefin-based electric insulating composition sheet on both sides of a semiconductive electrode and setting the same in a water tank of a water-resistant tree tester,
Next, an AC voltage is applied between the water in the water tank and the semiconductive electrode, and then a water tree is used to evaluate water tree resistance from bow titles generated in the crosslinked polyolefin-based electrically insulating composition sheet. In the test method, a water tree test method is characterized in that the sheet-shaped sample is one in which water tree-promoting deteriorating foreign matter is dispersed at an interface between the semiconductive electrode and the crosslinked polyolefin-based electric insulating composition sheet.