JPH09298828A - Power cable line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrict the occurrence of water in an insulator over a long period of time by forming a lean oxygen atmosphere around an insulator where cross - linking polyolefine is used. SOLUTION: An inert gas such as nitrogen gas is pressured by pump 34a to one inert gas storage tank 32a, a gas regulating valve 31a is opened and the inert gas is introduced to a gap 6a of an airtight casing 5, at the same time, a gas pressure regulating valve 31b is opened and air is discharged. By doing this, the air in a lean oxygen space 10 is pushed out by the inert gas and discharged from a gas stop casing 7 to a gap 8a through the gas pressure regulating valve 31b, and the inside of the lean oxygen space 10 is replaced by the inert gas. In this way, if the whole of the current system of the line is kept by the lean oxygen atmosphere lower than 10 capacity % of oxygen concentration, then the oxygen partial pressure in the cross - linking polyethylene insulator contained in the line is always kept low and, as a result, no water is produced even though heat is generated due to power applying heat cycle or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line of a crosslinked polyolefin insulated power cable, in which generation of water in the crosslinked polyolefin insulator due to heat generation during energization is suppressed, and electrical characteristics are kept good for a long period of time. Regarding the electric power cable line.

[0002]

2. Description of the Related Art Recently, a power cable using cross-linked polyethylene as an insulator is often called a cross-linked polyethylene insulated power cable or CV cable.
However, this cross-linked polyethylene insulated power cable (hereinafter simply referred to as “cable”) is heated inside the cross-linked polyethylene insulation (hereinafter simply referred to as “insulator”) when it is heated during manufacturing, laying, or actual use. It has been a problem that the electrical characteristics of the cable are impaired, such as the generation of water and the formation of voids.

Therefore, the cause of this water generation was searched.
Generally, dicumyl peroxide (hereinafter referred to as DCP) is used as a cross-linking agent for cross-linking the insulator.
It is known that the water generated in the crosslinked polyethylene is generated by the decomposition of DCP. That is, upon cross-linking, DCP decomposes to give acetophenone,
It produces methane, cumyl alcohol, etc. The cumyl alcohol produced here undergoes a secondary decomposition reaction when heated, producing water together with α-methylstyrene.

[0004]

As a method for preventing the generation of water in the insulator, for example, Japanese Patent Laid-Open No. 4-342731.
The gazette proposes a method of heating to a temperature of 75 ° C. or lower at which the secondary decomposition reaction of cumyl alcohol is suppressed to reduce the water content in the insulator in advance, and then reheating to 85 to 95 ° C. ing. Further, JP-A-4-355013 proposes a method of volatilizing and removing a decomposition residue of DCP, which is a causative substance of water generation, by heating and drying a crosslinked insulator. However, these methods are not practical because heating and drying take an extremely long time, and it is impossible to prevent generation of water due to heating during installation of a power cable or heat cycle after installation.

As a method other than heating and drying, for example, a method has been proposed in which an aliphatic amine or an isocyanic acid ester is added to an insulator as an antiaging agent to suppress the secondary decomposition reaction (respectively, Kaihei 1-24330
6 and JP-A-63-289715). However, these anti-aging agents may expire relatively quickly due to blooming or the like, and it is not preferable to use a large amount of these anti-aging agents as they also affect the insulation performance.

As a result of research on the above problems, the present inventors have previously found that the oxygen concentration in the insulator is involved in the thermal decomposition of cumyl alcohol, and the oxygen concentration in the insulator is controlled to be 0. We proposed a cross-linked polyethylene insulation cable with 5% by volume or less (Japanese Patent Application No. 5-291048).
Although this cable can well suppress the generation of water due to heating, it is practically difficult to keep the oxygen concentration in the insulator at 0.5% by volume or less for a long period after the cable is laid. It was

[0007]

Therefore, the inventors of the present invention have provided a cable in Japanese Patent Application No. 7-82223 in which the oxygen concentration around the crosslinked polyethylene insulator is 10% by volume or less. Specifically, this cable can be obtained, for example, by providing a void inside the metal sheath of the cable and replacing the air in the void with an inert gas such as nitrogen gas. However, an actual power cable line (hereinafter simply referred to as “line”) is configured to include, for example, a terminal connection part and an intermediate connection part in addition to the power cable, and a cross-linked polyethylene insulator is also used for these connection parts. Therefore, even in these parts, there is a possibility that the characteristics may deteriorate due to a heat cycle during energization. The present invention has been made to solve the above problems, and an object thereof is to provide a line in which generation of water in an insulator is suppressed for a long period of time.

[0008]

[Problems to be Solved by the Invention] The above-mentioned problem is to provide a power cable line comprising a power cable using cross-linked polyolefin as an insulator and a connecting portion, and a dilute oxygen atmosphere being formed around these insulators. It can be solved by doing. This dilute oxygen atmosphere is preferably formed by an inert gas. In addition, in the line, an inert gas storage tank for supplying an inert gas to the diluted oxygen atmosphere, a gas pressure adjusting means for adjusting the gas pressure of the diluted oxygen atmosphere, a pressure sensor for detecting the gas pressure of the diluted oxygen atmosphere, and a diluted gas It is preferable that any one or more of the oxygen sensors that detect the oxygen concentration of the oxygen atmosphere be provided.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an embodiment of the line of the present invention. In FIG. 1, the energizing system of this line is roughly composed of a terminal connecting portion 1, a cable 2, an intermediate connecting portion 3, and a gas stop connecting portion 4.
The terminal connection part 1 is made of a member that electrically connects the power supply side or power reception side (neither is shown) equipment and the cable 2, and the intermediate connection part 3 and the gas stop connection part 4 connect the cables to each other. It consists of members. These connections are
In both cases, crosslinked polyethylene is used as an insulator.

The terminal connection portion 1 and the intermediate connection portion 3 are housed in airtight casings 5a and 5b, respectively, and gaps 6a and 6b are provided between the airtight casings 5a and 5b and the respective connection portion bodies 1 and 3. Has been formed. Further, the gas stop connection portion 4 is housed in a gas stop casing 7, and a gap 8 is provided between the gas stop casing 7 and the body 4 of the gas stop connection portion, which is partitioned for each terminal of the connection portion.
a and 8b are formed.

The cable 2 is a single-core type cable in this embodiment, and the conductor 21, the inner semiconductive layer 22, and the crosslinked low-density polyethylene insulation are sequentially provided from the center as shown in FIG. A cable unit 25 including a body 23, an outer semiconductive layer 24, and the like, an aluminum airtight sheath 27, and a polyvinyl chloride anticorrosion layer 28. Between the cable unit 25 and the airtight sheath 27,
A gap 26 is formed.

In the line of FIG. 1, the airtight casings 5a, 5b, 7 at the respective connecting portions are connected to the airtight sheath 27 of the cable, and the gaps 6a, 6b, 8a in these airtight casings and the cable The gap 26 in the airtight sheath 27 forms an integrally continuous dilute oxygen space 10.

In the gas-tight casing 5a of the terminal connection part 1 and the gas-stop casing 7 of the gas stop connection part 4, inert gas storage tanks 32a and 32b are provided by gas pipes 33 via gas pressure adjusting valves 31a and 31b, respectively. It is connected.

At an appropriate position in the dilute oxygen space 10 of the line,
A gas pressure sensor 41 is provided, and this gas pressure sensor 41 is electrically connected to a gas pressure monitor 42. Separately from this, at an appropriate position in the dilute oxygen space 10 of the line,
An oxygen sensor 51 is provided, and the oxygen sensor 51 is electrically connected to the oxygen monitor 52.

In this line, a dilute oxygen atmosphere can be formed around the insulator over the entire power supply system. That is, for example, one inert gas storage tank 32a
Then, an inert gas pressurized by using the pump 34a, for example, nitrogen gas is filled, the gas pressure adjusting valve 31a is opened, and the inert gas is introduced into the gap 6a of the airtight casing 5a. At the same time, the gas pressure adjusting valve 31b is opened to bring it into an exhaust state.

As a result, the air in the lean oxygen space 10 is pushed out by the inert gas and discharged from the gap 8a of the gas stop casing 7 via the gas pressure adjusting valve 31b,
The inside of the diluted oxygen space 10 is replaced with an inert gas.
The oxygen sensor 51 and the oxygen monitor 52 are operated to monitor the oxygen concentration in the dilute oxygen space 10, and the oxygen concentration is a specified value,
For example, when it becomes 10% by volume or less, the gas pressure adjusting valve 31
Close b. The inert gas is continuously supplied from the inert gas storage tank 32a, and the gas pressure in the lean oxygen space 10 is measured by the gas pressure sensor 41 and the gas pressure monitor 42 within a specified range of atmospheric pressure or higher, for example, 0 kgG / cm ² to. 1 kg
When the pressure becomes within the range of G / cm ² , the gas pressure adjusting valve 31a is adjusted so that the gas pressure in the dilute oxygen space 10 is always kept within the specified range.

The information output from the gas pressure sensor 41 and the oxygen sensor 51 is input to the computer 60, and the computer 60 keeps the gas pressure and the oxygen concentration in the dilute oxygen space 10 within the specified range. The control information is output to the pressure adjusting valves 31a and 31b, the pumps 34a and 34b, the gas pressure monitor 42, the oxygen monitor 52, and the like.
Further, when the gas pressure in the lean oxygen space 10 decreases and / or the oxygen concentration rises due to damage to the line, the gas pressure monitor 42 and / or the oxygen monitor 52 instructs to give an alarm. As a result, this line is always maintained in a state in which a dilute oxygen atmosphere is formed, and when an abnormality occurs in the dilute oxygen space 10, the line is immediately notified.

If the entire power supply system of the line is always brought to a dilute oxygen atmosphere having an oxygen concentration of 10% by volume or less, the partial pressure of oxygen in the crosslinked polyethylene insulator contained in the line is always sufficient. The temperature is kept low, and as a result, water is not generated in the insulator even if heat is generated by an electric heat cycle or the like.

In the line of the above embodiment, the gas stop connecting portion 4 has a gap between the main body and the gas stop casing 7,
The gaps 8a, 8 are separated by each terminal of the connecting portion.
It is formed so as to be b. This facilitates maintenance management by dividing the length of the dilute oxygen space 10 into a certain section in a long-distance line, makes it easy to find and repair the abnormal portion when an abnormality occurs, and .. has the effect of reducing the volume of the active gas storage tanks 32a.

In the line shown in FIG. 1, inert gas storage tanks 32a and 32b are provided at both ends of the section, respectively. This is for supplying the inert gas from the one inert gas storage tank 32a and collecting the waste inert gas containing air in the other inert gas storage tank 32b, and the inert gas used is nitrogen. One of the inert gas storage tanks 3 can be used if it can be released into the atmosphere, such as gas.
2b can be omitted.

When the lines are actually laid, for example, in the case of three-phase alternating current using the single-core cable shown in FIG. 2, the lines of the above-mentioned embodiment are laid in parallel in three lines. At this time, the inert gas storage tanks 32a and 32b for each section
Can be shared for three lines. The present invention can also be applied to a three-core collective sheath type cable and a triplex type (single-core three-core twisted type) cable. When a triplex type cable is used, an airtight sheath can be provided in each of the single-core units, but an airtight sheath may be provided on the outer periphery where the three cores are twisted together. When connecting these cables, each connection part may be branched as needed.

The dilute oxygen atmosphere has an oxygen concentration of 10% by volume.
The following is preferable. If it exceeds 10% by volume, the oxygen partial pressure in the insulator becomes high and water is easily generated by heating. To keep the oxygen concentration below 10% by volume,
For example, the diluted oxygen space 10 may be decompressed by a vacuum pump or the like. However, in order to realize a stable dilute oxygen atmosphere for a long term, it is preferable to replace the air in the space with an inert gas and keep the internal pressure higher than atmospheric pressure.

Examples of the inert gas used include nitrogen gas, neon gas, argon gas and SF ₆ gas. Nitrogen gas is preferable from the economical point of view, and SF ₆ gas is preferable when improvement in insulation performance is required. The gas pressure is 0 kgG / cm ^{2 to 1} kg.
It is preferably within the range of G / cm ² . Gas pressure is 0
If it is lower than kgG / cm ² , outside air (oxygen) may enter when there is a pinhole in the track, and 1kg.
If it exceeds G / cm ² , special pressure resistance is required for the casing of the connecting portion and the like, which increases costs.

[0024]

Since the electric power cable line of the present invention has a dilute oxygen atmosphere formed around the cross-linked polyolefin insulation, generation of water in the insulation due to heat generation by electric current is suppressed, and electrical characteristics are improved. Is well maintained over the long term. If the dilute oxygen atmosphere is formed by the inert gas, stable electric characteristics can be maintained in the power cable line for a long period of time. The power cable line has an inert gas storage tank, gas pressure regulator, pressure sensor,
If at least one of the oxygen sensors is provided, the oxygen concentration in the dilute oxygen atmosphere is maintained at a sufficiently low level for a long period of time, and / or the oxygen concentration is monitored to immediately detect an abnormality. be able to.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a power cable line of the present invention.

FIG. 2 is a cross-sectional view showing an example of a cross-linked polyethylene insulated power cable.

[Explanation of symbols]

1 ... Termination connection part, 2 ... Power cable, 3 ... Intermediate connection part,
4 ... Gas stop connection, 10 ... Dilute oxygen atmosphere

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kouri Utsunomiya 1-5-1 Kiba, Koto-ku, Tokyo Inside Fujikura Stock Company

Claims (3)

[Claims] 1. A power cable line comprising a power cable using cross-linked polyolefin as an insulator and a connecting portion, and a dilute oxygen atmosphere being formed around these insulators. 2. The power cable line according to claim 1, wherein the dilute oxygen atmosphere is formed by an inert gas. 3. An inert gas storage tank for supplying an inert gas to the diluted oxygen atmosphere, a gas pressure adjusting means for adjusting the gas pressure of the diluted oxygen atmosphere, a pressure sensor for detecting the gas pressure of the diluted oxygen atmosphere, and a diluted oxygen atmosphere. The power cable line according to claim 1, wherein any one or more of oxygen sensors for detecting oxygen concentration are provided.