JP3429234B2 - DC transmission line - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a submarine power transmission line using a power cable most suitable for long-distance and large-capacity transmission.

[0002]

2. Description of the Related Art Conventionally, for long-distance, large-capacity DC cables, kraft paper is used as an insulating tape material, and high-viscosity insulating oil (for example, 25 to 100 cst at 120 ° C., 500 at the maximum cable temperature (50 to 60 ° C.)). A solid cable (Mass-Impregnated Cable: Non-Draining Cable: Non-Draining Cable) impregnated with ~ 2000 cst) has been used.

To increase the capacity of a solid cable,
It suffices to realize high voltage and large current. Among them, in order to increase the current, it is only necessary to use a conductor having a cross-sectional area as large as possible or to raise the maximum operating temperature of the conductor as much as possible. On the other hand, higher voltage and higher temperature are related to the performance of the insulator.
It is impossible without the development of new technology.

In recent years, solid cables using a polyolefin resin film as an insulating material have been proposed in order to transmit a large capacity, which has been difficult or impossible to achieve with conventional kraft paper insulated solid cables. It's coming. For example, a cable that can be used at a high voltage of direct current (DC) of 500 kV or more or at a conductor maximum temperature of 60 ° C. or more (for example, about 80 ° C.) is being studied.

However, even in this case, the insulating oil used is the high-viscosity insulating oil used in the conventional solid cable. This means that in order to prevent the electrical characteristics from deteriorating under any conditions, the insulating oil of the cable impregnated at the factory should not be unevenly distributed or depleted (Starvation) due to the flow phenomenon (migration). Because it must be. That is, especially in the case of long-distance submarine solid cables, since the cable line is too long to supply or absorb insulating oil at both ends, the flow phenomenon does not occur even at the maximum operating temperature of the cable (usually 55 ° C or less). This is because it has been said that only the high viscosity oil of

[0006]

However, in the conventional solid cable, the following problems have become serious obstacles in order to increase the capacity by increasing the voltage and operating at high temperature.

When the load is turned off (OFF) after the conductor reaches the maximum temperature when the load is turned on (ON), the temperature of the vicinity of the conductor is rapidly lowered, and the insulating oil contracts. High-viscosity oil cannot move rapidly from the outer side to the inner side of the insulating layer, so that starvation of the insulating oil occurs in the vicinity of the conductor, and voids are generated, which may significantly reduce electrical performance.

That is, as the maximum temperature of the conductor used increases, the amount of insulating oil that expands increases, making it difficult to treat the insulating oil and reducing the viscosity of the insulating oil and making it easier to migrate. Also the load
There is a problem that high electrical stress cannot be easily applied to the cable insulator because the temperature drop at the time of OFF becomes steeper and severe starvation easily occurs and large voids are easily generated.

Further, attempts have been made to apply a polyolefin resin film or a composite insulating tape of the polyolefin resin film and kraft paper. However, compared to kraft paper made of porous natural wood pulp fiber, the polyolefin resin film is more liquid. Since there is no hole through which the oil can flow, high-viscosity insulating oil cannot pass through. Therefore, when the cable core is impregnated with the insulating oil in the factory, the thicker the insulating layer, the more difficult or impossible the impregnation becomes. As a result, it has been almost difficult to increase the ratio of the polyolefin resin film in order to improve the industrial productivity or achieve the intended purpose.

Therefore, a main object of the present invention is to provide a power transmission line using a submarine solid cable capable of high voltage transmission and high temperature use for large capacity transmission.

[0011]

DISCLOSURE OF THE INVENTION The present invention solves the above problems, and is characterized in that a power transmission line is constituted by a cable using insulating oil of medium viscosity as insulating oil of a solid cable.

Here, the medium viscosity insulating oil refers to an insulating oil having a viscosity at 60 ° C. of not less than 10 centistokes (cst) and less than 500 centistokes (cst). In particular, the SP value (Solubility parameter: solubility index) of the insulating oil is preferably within a range of ± 1.5 from the SP value of the polyolefin resin film used for the insulating layer. Specific examples of the medium-viscosity insulating oil include polystyrene-based insulating oil, polybutene, mineral oil, synthetic oil mainly containing alkylbenzene, heavy alkylate, or a mixture containing at least one of these. When using these mixed insulating oils,
In particular, dodecylbenzene (DDB) with the optimum SP value should be included.
And are preferred.

It is desirable to use a tape containing a polyolefin resin film for at least a part of the cable insulating layer used in the line of the present invention. The tape containing the polyolefin-based resin film includes an insulating tape of the polyolefin-based resin film alone, and a composite tape obtained by laminating kraft paper on one side or both sides of the polyolefin-based resin film. In particular, it is preferable that the composite tape in which the kraft paper is laminated on both sides of the polyolefin resin film and the insulating tape of the polyolefin resin film alone are alternately wound and applied to the insulating layer.

It is also preferable to form at least one of ρ (resistivity) -grading and ε (dielectric constant) -grading in the insulating layer. For example, a composite tape in which kraft paper is laminated on both sides of a polyolefin resin film is used as the insulating tape, and the grading is configured by changing the thickness ratio of the polyolefin resin film to the total thickness of the insulating tape. Of course, the insulating tape used may include a kraft paper having a thickness of 0, that is, a polyolefin resin film alone.

Furthermore, when a composite tape in which kraft paper is laminated on both sides of a polypropylene film is used as an insulating layer, the ratio of the thickness of the polypropylene film to the total thickness of the composite tape is 40% or more and less than 90%. Is appropriate. In particular, it is even more preferable to set this ratio to more than 60%.

Usually, a solid cable is provided with a metal sheath (usually covered with lead) on the outer periphery of the insulating layer, but it is also preferable to form a reinforcing layer on the outer periphery of this metal sheath. The reinforcing layer plays a role of sharing and reinforcing the hoop stress applied to the metal sheath (stress that tends to break the metal sheath inside the metal sheath caused by hydraulic pressure). Therefore, it is desirable that the material of the reinforcing layer has a high tensile strength, and examples thereof include metal tapes such as stainless steel, polyamide, imide resin tape (trade name: Kevlar), and the like.

The solid cable has the medium viscosity insulation.
It can be obtained by impregnating the oil as it is with the conventional method.
It

Further, the power transmission line of the present invention comprises an undersea solid cable made of the above-mentioned solid cable laid on the undersea, and a land cable connected to both terminals of this undersea solid cable through oil-stop connection boxes. With
This oil stop connection box is arranged at the beach, and the land cable is connected to an oil tank for supplying insulating oil having a viscosity of medium or less to the land cable.

Even if the land cable is a solid cable, the OF cable (Self-Contained Oil-Fill) is used.
ed Cable). If the land cable is a solid cable, insulating oil having a medium viscosity or less is supplied from the oil supply layer, and if it is an OF cable, insulating oil having a low viscosity is supplied from the oil supply layer. In addition, in the above-mentioned line, connect an oil supply pipe to the sea bottom solid cable side of the oil stop connection box, connect this oil supply pipe to the oil supply tank, and supply medium viscosity insulating oil from the oil supply tank to the sea bottom solid cable. It is preferable to configure. further,
It is more preferable to provide a check valve on this oil supply pipe so that the medium viscosity insulating oil can flow only to the oil stop connection side.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below, including the background to the present invention. After being installed, the submarine cable receives seawater pressure proportional to its depth from the outside toward the inside. Generally, a pressure multiplied by a rate of 1 kg / cm ² is applied from the outside of the cable to the inside of the cable every 10 m. For example, OF in the metal sheath of a submarine cable.
When the low-viscosity insulating oil used for the cable is filled, the insulating oil has sufficient fluidity. That is, the oil pressure can propagate to all oils in a sufficiently short time. Therefore, the cable is subjected to pressure from outside to inside, which is obtained by multiplying the difference in specific gravity between seawater and this low-viscosity insulating oil by "a rate of 1 kg / cm ² every 10 m".

Regarding the oil pressure inside the insulator, which regulates the electrical performance of the insulator, the pressure obtained by multiplying the specific gravity of the oil by "a rate of 1 kg / cm ² per 10 m" is uniformly applied as the internal oil pressure. . Therefore, with the OF cable, high hydraulic pressure can be easily obtained, and stable electric performance can be easily ensured.

However, in a solid cable filled with insulating oil having an extremely high viscosity, the insulating oil does not guarantee the above-mentioned fluidity and exhibits discontinuity. That is, even if the pressure of a part of the oil fluctuates, the pressure fluctuation hardly propagates to the oil of another part or does not propagate at all in a sufficiently short time. Alternatively, even if some oil flows, other parts do not follow the flow within a sufficiently short time or do not follow at all. Therefore, it was presumed that the cable receives the water pressure proportional to the depth of the seawater from the outside to the inside, just as the solid rod receives the outside water pressure of the seawater 100%.

Further, because of the discontinuity of the insulating oil described above,
The oil pressure itself inside the insulator cannot be increased in proportion to the water depth, so the insulator should be sufficiently impregnated with insulating oil at each part of the cable, and the cable should be used only within the range of operating conditions where the electrical performance of each part can be maintained. I've been thought not to go. Therefore, the operating temperature is limited to about 55 ° C or less, and the operating voltage is also limited to about 450 kV or less.
(Cable Dependent Voltage Control) had to be adopted. When the load is cut off (reduced), the CDVC takes a sufficient time to reduce the operating voltage before starting the operation, and alleviates the electrical stress applied to the void that may occur in the insulating layer near the conductor when the load is cut off. This is a special operation system that cuts off (reduces) the load. However, it is a major obstacle in terms of free operation.

On the other hand, what is most problematic is the oil starvation in the insulating layer in the vicinity of the conductor due to the rapid temperature drop when the load is turned off after full load and the resulting oil contraction. To compensate for the decrease in hydraulic pressure in the vicinity of the conductor that occurs when the load is turned off, first increase the internal hydraulic pressure in that part, and then reduce the volume decrease due to the oil temperature decrease by expanding the volume by compensating for the hydraulic pressure in that part. It is preferable to keep. Next, if the insulating oil quickly moves from the outside of the insulating layer having high hydraulic pressure to the inside to compensate for the decrease in the internal hydraulic pressure, starvation does not occur. For that purpose, it is preferable that the insulating oil to be applied has such a low viscosity that the continuity of oil flow can be maintained, or even the solid cable insulating oil has the lowest possible viscosity.

The continuity of these oil flows and the ease of oil migration from the outside to the inside are also related to the magnitude of the fluid resistance (oil flow resistance) of the insulator to the oil. In an insulating layer that partially contains a resin film that does not permeate insulating oil, insulating oil flows only around the resin film tape,
Inevitably the oil flow resistance is higher than that of the craft insulation layer. Therefore, in a solid cable containing such a resin film in the insulator, use insulating oil with the lowest possible viscosity to allow the penetration of insulating oil and to compensate for the hydraulic pressure drop near the conductor when the load is off. It is preferable.

From the above basic consideration, the present inventors have examined the development of a solid cable using insulating oil that satisfies the following items. <Indicator for low viscosity of insulating oil> Even when an insulating layer including a composite tape of a polyolefin resin film and kraft paper or a polyolefin resin film tape embossed on the surface (see Japanese Patent Publication No. 61-26168) is used, Viscosity is low enough to allow easy impregnation. Particularly in the case of a composite tape, the impregnation of insulating oil can be sufficiently facilitated even when the thickness ratio of the polyolefin resin film is about 80%.

At a depth of sea water of about 100 m or more, the viscosity should be low enough not to generate a negative pressure when the load is cut off.

In particular, even a solid cable of kraft paper insulation or a solid cable made of an insulator containing a polyolefin resin film should have a low viscosity to the extent possible to avoid using the CDVC system.

Even if a negative pressure is generated in the insulating layer due to the magnitude of the load and the way of blocking, the viscosity is low enough to be confined to the local portion directly above the conductor.

<Indicator for high viscosity of insulating oil> Solid during cable handling (manufacturing, laying, connecting cables at the site, removing, and when the metal coating of the cable is damaged due to some accident) Viscosity is high enough so that insulating oil does not easily leak from the cable ends and damaged parts.

The high-hydraulic insulating oil whose viscosity has decreased at high temperature under full load exerts the influence of its expansion in the longitudinal direction of the cable, and is low enough that a large amount of oil moves to both ends of the cable line. Not be viscosity. However, if this effect cannot be ignored, consider taking other measures.

[0032] When the stripped metal sheath of the cable with the joint work of the cable, endlessly flows without it cables inside the insulating oil is pushed up by the insulating oil of the differential pressure of the outer water pressure and the cable based on the water depth, construction joints The viscosity is not so low that it cannot be processed. As a type of joint, a local joint (site joint: Site-Joint) that is applied when a solid cable laid on the seabed is jointed on the sea and finished in a series of lengths,
Repair joints (Repair-Joint (RJ)) applied when repairing accident points of cables under almost the same working conditions, stop joints (SJ) or transitions applied at beaches. Examples include joints (TJ).

Under the above conditions, the viscosity is high enough to prevent oil dripping and leakage of insulating oil from the damaged portion even at the maximum operating temperature.

(Test Example) In order to find insulating oil under the above conditions, the following tests were conducted. <Relationship between migration of insulating oil and seawater depth (seawater pressure)> 400 to 500 with an insulator thickness of 20 to 25 mm in a container
A kV class kraft paper insulated solid cable was placed and immersed in water, and the water pressure was changed to simulate the depth of seawater. The seawater pressure is expressed as “water depth (m) / 10 (kg / cm ² )”.

The structure of the cable used is shown in FIG. Figure 1
1 is a cross-sectional view showing the structure of an example of a DC submarine solid cable. In order from the center, conductor 1, inner semiconductive layer 2, oil-impregnated insulating layer 3, outer semiconductive layer 4, metal sheath 5, anticorrosion layer 6,
It comprises a metal tape 7, a protective yarn layer 8 and a sheathing wire 9.

The oil-immersed insulating layer 3 is formed by impregnating wound kraft paper tape with insulating oil. Here, high-viscosity oil was used as the insulating oil. As the insulating tape, a composite tape obtained by laminating kraft paper on one side or both sides of a polyolefin resin film or an insulating tape made of a polyolefin resin film alone may be used.

In some cases, the outer semiconductive layer 4 may include a metal tape or a metallized paper obtained by laminating kraft paper with a metal tape inside. In the case of a submarine cable, a lead sheath is usually used as the metal sheath 5. Polyethylene (PE) is mainly used for the anticorrosion layer 6 in a submarine cable. As for the metal tape 7, usually about two metal tapes are wound together with the cloth tape. Since this metal tape comes into contact with seawater, a zinc-coated steel tape, bronze (bronze), brass or the like is often used from the viewpoint of corrosion protection.

The protective yarn layer 8 is a bedding (seat floor).
It consists of jute 81 or serving jute 82. In recent years, artificial fibers such as polypropylene yarn are often used instead of natural jute. The exterior wire 9 is formed by winding an iron wire, a zinc-coated iron wire, or the like in a single or double winding. Sometimes artificial armor wires such as aramid fibers are also used.

The above solid cable is energized so that the conductor can be heated to a predetermined temperature, and a heat cycle test is performed by turning on and off the energization while changing the water pressure, and the pressure applied to the end of the cable. It was made possible to read the change of the internal pressure of the cable (especially the pressure of the conductor part) with a meter.

As a result of this test, the water pressure was 7 to 10 kg / cm ^2.
(If the unit is almost the same even if it is replaced by atmospheric pressure) If kept above, heat cycle of 1-3 cycles (from room temperature to 50-
After 60 ° C., it was found that, in the kraft paper insulating layer having holes, even if the conventional high viscosity oil was used, a negative pressure could be maintained in the vicinity of the conductor without load and a positive pressure could be maintained. It is considered that this is because water pressure causes external pressure to be transmitted to the insulating oil in the insulating layer through the lead cover.

In order to evaluate the above experimental results of the kraft paper-insulated solid cable, a computer was used to conduct a conductor loss due to the current flowing through the conductor when the cable was turned on and off, the heat flow was diffused, and the temperature of the cable insulator was increased. And the resulting changes in the excessive oil pressure of the insulating oil were calculated sequentially. An example of the result is shown in FIG.

When the load is turned on, the hydraulic pressure on the conductor side suddenly rises, the hydraulic pressure on the metal sheath side follows with the change in time, and when the temperature inside the cable insulator disappears and a steady state is reached, the pressure of the insulating oil inside the cable The movement due to the difference disappears and the pressure becomes almost constant. On the other hand, when the load is cut off, the hydraulic pressure drops sharply due to the steep temperature drop directly above the conductor, and the insulating layer immediately above the conductor becomes slightly negative pressure, but over time, the hydraulic pressure immediately below the metal sheath also changes. Finally, it can be seen that the movement of the oil disappears and the pressure of the entire cable becomes a little positive.

This calculation result very well simulates the experimental result, and it is possible to evaluate the effect when various conditions are changed by using this computer simulation. A solid cable of 400-500 kV class with a conventional structure that uses a combination of kraft paper insulating tape and high-viscosity insulating oil, with a maximum conductor operating temperature of 50-60
It was also found that the maximum hydraulic pressure is approximately 10 kg / cm ² inside / outside at ℃.

Next, using the same high-viscosity oil, a hydraulic pressure change was similarly tested as a composite tape (PPLP) having an insulating layer laminated with kraft paper on both sides of a polypropylene (PP) film. Here, the PP thickness ratio k “(PP film thickness) / (total thickness of PPLP)” in PPLP is 10, 40, 60,
The test was conducted by changing it to 80%. Furthermore, the temperature of the heat cycle was changed from room temperature to 50 to 60 ° C and 80 to 90 ° C.

When the high temperature part of the heat cycle is 50 to 60 ° C., as expected, PPLP causes a slower pressure return when the load is cut off than the kraft paper cable. The larger the ratio k is, the slower the pressure returns. Therefore, it was found that negative pressure is likely to be generated in the vicinity of the conductor depending on the size of the load and the breaking condition. However, it was found that when the high temperature part of the heat cycle is 80 to 90 ° C., negative pressure is unlikely to occur.

Furthermore, the viscosity at 60 ° C. is drastically 40.
A similar experiment was conducted with a PPLP insulated solid cable impregnated with 0-500 cst medium viscosity oil. As a result, 50-60
It was found that the negative pressure characteristics (easiness of generation of negative pressure and the range of negative pressure) in the vicinity of the conductor at the time of load shedding were significantly improved at both C and 80 to 90 ° C.

This is because the oil flow resistance is proportional to the viscosity of the oil, and the lower the viscosity of the insulating oil, the easier the movement of the oil. In other words, when the oil expands and contracts due to the temperature difference and the volume (amount) per unit volume changes and the oil moves, the product of the oil flow and the oil flow resistance in the path of the part where the oil flow occurs is the hydraulic pressure difference. Therefore, if the viscosity is lowered, a difference in hydraulic pressure is likely to occur.

Next, when a similar hydraulic pressure change test was conducted on a solid cable impregnated with 10 cst of medium viscosity insulating oil at 60 ° C., almost no negative pressure was generated.

These results suggest the following. Even with a solid cable impregnated with high-viscosity solid insulating oil, some depth of water (for example, 70-100m)
If the cable is laid to the above depth, the internal pressure of the oil in the cable is pushed by the external pressure and becomes positive even when there is no load. At both ends of the submarine cable, that is, at shallower seas, a negative pressure may occur at no load unless insulating oil having a somewhat low viscosity is used or new measures are taken.

Below a certain viscosity (eg 4 at 60 ° C.)
Solid cable impregnated with solid insulating oil (0 to 500 cst or less) does not generate negative pressure when the load is cut off, or even if it is very limited, for example, when it is laid in the sea shallower than 100 m and full load Conductor current density 1.5A
This occurs only when a large current of / mm ² or more is applied and the load is suddenly cut off. Therefore, it is possible to avoid the generation of negative pressure by modifying the structure of the solid cable. Moreover, even if the actual operating conditions are limited and the measures are taken, it is considered that there is almost no harm.

When the load is suddenly cut off at full load,
In order to prevent a negative pressure from being generated in the vicinity of the conductor, it is preferable to make the hydraulic pressure uniform in the cable as high as possible when the load is full.

The state of the item is also preferable when the applied voltage is increased to increase the transmission capacity of the cable.

In the case of realizing a new cable in which the maximum operating temperature of the solid cable is raised from about 50 to 55 ° C to 80 ° C, the viscosity of the insulating oil decreases logarithmically as the temperature rises. Lowers the oil flow resistance,
Negative pressure is less likely to occur when the full load is cut off.

When realizing a new cable in which the maximum operating temperature of the solid cable is raised from about 50 to 55 ° C to 80 ° C, the temperature change from normal temperature with no load to the maximum temperature of about 80 ° C becomes larger than the conventional temperature. . Therefore, the increase in the hydraulic pressure in the cable at the maximum load becomes large, and a countermeasure against this is necessary. This is important even when the above items are taken into consideration.

<Insulating Oil Impregnation Process and Insulating Oil Viscosity>
Based on the above studies, we examined the impregnation process of insulating oil and the viscosity of insulating oil, which are the most central and difficult to control for the production of solid cables. First, the outline of the insulating oil impregnation process will be described.

In the conventional solid cable, the cable core is wound around a drying tank and heated and evacuated to remove air and moisture in the insulator. When the cable core is completely dried, high viscosity solid insulating oil, which has been heated to a temperature of a few hundreds of degrees Celsius and whose viscosity has been lowered, is poured into the tank, and a predetermined pressure is applied for a predetermined time to fill the insulation with oil. Infiltrate. After that, the cable core is cooled to room temperature, but since the insulating oil shrinks due to the temperature drop from the maximum impregnation temperature to room temperature, the above-mentioned predetermined pressurization is performed and cooling is performed while maintaining a predetermined temperature drop rate.

Here, the heating temperature of the insulating oil is selected within a range in which the performance of the insulating layer does not deteriorate. When the insulating layer is kraft paper only, a temperature in the range of 110 to 140 ° C. is usually selected. In addition, when the insulating layer includes a polyolefin resin film, the maximum allowable temperature is determined in consideration of their melting points in oil. The melting point in oil is 110 ° C for polyethylene.
Inside and outside, the temperature of polypropylene is about 130 to 140 ° C.

The pressure applied during impregnation with insulating oil is a gauge pressure (atmospheric pressure expressed as 0 kg / cm ² ) of 1 to 3 kg / cm ^2.
The degree is selected. Further, the period required for cooling is approximately 1 to 3 months from the maximum impregnation temperature to room temperature, depending on the amount of the cable core to be dried.

If the temperature of the injected insulating oil is increased within a range satisfying the above conditions, the higher the temperature is, the lower the viscosity becomes, and the impregnation itself becomes easier. However, it takes an enormous amount of time to cool the enormous amount of cable cores to the room temperature only by the cooling means from the outside of the tank, which impairs the industrial productivity. Therefore, it is highly preferable to apply the temperature as low as possible under the condition that sufficient impregnation is performed.

(Impregnation of Kraft Paper Insulating Layer) FIG. 3 shows the relationship between typical insulating oil and typical temperature and viscosity of the medium viscosity solid insulating oil used in the present invention. In the case of a conventional solid cable consisting of an insulator made only of kraft insulating paper tape, if high-viscosity oil is injected at a maximum temperature of 110 to 120 ° C, it can be sufficiently impregnated irrespective of the insulation thickness. For example, it has been confirmed that even an insulating single layer having a thickness of 20 to 25 mm, which is considered to be necessary for a 500 kV class solid cable by design, can be sufficiently impregnated. However, the pressure cooling requires a very long time, for example, 1 to 3 months, and its improvement has always been a big problem.

The low-viscosity insulating oil in FIG. 3 is for an OF cable, and can be impregnated at room temperature because it is a liquid having sufficient fluidity at room temperature, and can be impregnated in a very short time of, for example, 1 to 3 days. However, it is a dry liquid at room temperature, does not satisfy the above-mentioned <index regarding the viscosity of insulating oil>, and cannot be used as a solid insulating oil.

On the other hand, when the same cable was impregnated with the medium-viscosity insulating oil of FIG. 3, that is, 10 to 500 cst oil at 60 ° C. by the same impregnation process as described above, all were within a short period of one month. It was found that it can be impregnated with, and is very preferable from the viewpoint of productivity.

(Impregnation of PPLP Insulating Layer) Next, a solid cable using PPLP based on PP as a representative of a polyolefin resin as an insulating layer was prototyped and the impregnation characteristics were investigated. At this time, a PP ratio k of 40% or more and less than 90% was selected. First, the reason for selecting the PP ratio k will be described.

FIG. 4 shows the structure of PPLP in which kraft paper is laminated on both sides of PP film, the resistivity ρ (Ωcm) of the insulating material surrounding PPLP, and the direct current (DC) stress distribution proportional thereto. In the first place, the dense PP film is
Although it has overwhelmingly high DC withstand voltage characteristics compared to porous kraft paper, it was discovered during the development of alternating current (AC) insulation tape that it was brittle when the electric streamer directly hits the surface. In order to improve this and to secure an oil passage, PPLP with kraft paper laminated on both sides of PP film was developed.

Initially, the PPLP developed for AC cables was
Kraft paper with a relatively low airtightness (for example, about 1500 Gurley seconds) to achieve low loss {low dielectric constant (ε), low loss angle (tanδ)} and high impulse (Imp.) Withstand voltage. Was being laminated. Also, the Institute of Electrical Engineers of Japan [A52-A53 (1972, Vol. 97, No. 8)] 40
As shown in Figs. 4 and 5 of "Study on polypropylene laminated paper for ultra-high voltage and ultra-high voltage power cables" on pages 3 to 410, when the PP and B ratios are 40 to 50%, both AC and Imp. It had been. Therefore, it is very difficult and expensive to increase the PP ratio k. Therefore, the PP ratio of 40 to 60 is required for the conventional AC (DC) OF cable.
% PPLP has been used.

The present inventors have found that the DC solid cable is
As a result of conducting research with the belief that there should be a PPLP suitable for it, the following was found. Due to the difference in ρ between kraft paper and PP film, DC stress concentrates on PP film with excellent DC withstand voltage.
The DC withstand voltage should increase in proportion to the ratio k. The fragility of the PP film surface is the boundary area of the PP film surface where the fibers of the PP kraft paper are entangled in the case of PPLP made by extruding molten PP between two pieces of kraft paper (poundary zone: shaded area in Fig. 4). ) Can overcome. In the case of DC cables, there is no dielectric loss caused by alternating current, so there is no limitation on the kraft paper to be laminated. Therefore, using a kraft paper with a slightly higher airtightness, such as 3000 Gurley seconds or more, the PP ratio is 40 to 50.
When it exceeds%, the weak point that Imp. Withstand voltage starts to decrease can be overcome.

From this point of view, the PPLP having a high PP ratio, which is not necessary in the past and was difficult to be industrially produced in the past, has the same overall thickness as the conventional one (100 〜150μm) Developed. A detailed example of the manufacturing method is shown in Japanese Patent Application No. 8-321192, for example, when the PP ratio exceeds 80%.
You can get PPLP.

FIG. 5 shows an example of electrical performance measured using these materials. As expected, along with the improvement of the PP ratio, the DC breakdown stress has dramatically improved linearly. Immediately beyond the conventional peak, Im
It can be seen that the withstand voltage is improved even at p.

Further, FIG. 6 shows the comparison of the DC withstand voltage value with the high airtightness kraft paper for DC which has been used for the conventional solid cable by the ratio. Originally, in order to use an expensive insulating tape with a high-level and complicated structure such as PPLP, it is necessary to expect such an improvement effect. From Figure 6, PP ratio is 4
If it is less than 0%, the effect of improving the DC withstand voltage value is small, so
It was judged that 40% or more is preferable. On the other hand, PP with high PP ratio
It is also the core of this patent about how LP is suitable for solid cables other than DC withstand voltage, and how advantageous it is to have various types of PPLP with different PP ratios, so I will explain later. I will add it.

First, the PP ratio k = 40% and the insulation thickness is 15 m.
A m-sized cable (prototype example 1) was prepared and impregnated with a conventional high-viscosity insulating oil in the same manner as the impregnation process described above. As a result, the impregnation time was considerably longer than that of the kraft paper cable, but sufficient impregnation was possible.

Next, a cable having an insulation thickness of 23 mm (Prototype Example 2) was made using the same PPLP as that of Prototype Example 1 and impregnated with high viscosity insulating oil by the same method as the impregnation process described above. It was found that a very high pressure and a long time are required to impregnate the innermost layer of, and it was found that a great improvement is required in industrial production.

Using the same cable as the prototype example 2, FIG.
When impregnated with about 500 cst of insulating oil at 60 ° C. among the medium viscosity insulating oil (Prototype Example 3), it was easier to impregnate than the conventional kraft paper impregnation conditions.

Next, using PPLP having a PP ratio of more than 80%, 5
A cable having an insulation thickness of 20 mm, which is estimated to be the insulation thickness of a cable equivalent to 00 to 700 kV, was made and impregnated with the medium viscosity insulating oil used in Prototype Example 3 by the same method as the impregnation process described above (Prototype Example 4 ), It was possible to barely impregnate the innermost layer. However, it is very difficult in industrial production, and it has been found that use of insulating oil having a viscosity higher than this is not preferable.

Furthermore, the cable having the same structure as the prototype 4 has 6
When impregnated with a medium viscosity insulating oil of 30 to 400 cst at 0 ° C. (Prototype Example 5), the ease of impregnation was remarkably improved as the viscosity decreased. From this, 500 when using PPLP
It has been found that insulating oils with viscosities below cst are preferred.
In the case of the kraft paper cable as well, as described above, it was found that the impregnation is significantly facilitated, the maximum impregnation temperature can be lowered, and the impregnation time can be shortened, which is very preferable for industrial production.

Under the above consideration, the viscosity of the oil satisfying the above-mentioned <Indicator regarding the viscosity of insulating oil> was investigated. The survey status and results are also explained.

Assuming that the temperature was below 40 ° C. assuming that the room temperature was south of Japan, the dripping condition of the insulating oil impregnated in the cable from the cable cross section was observed. In the case of a conventional solid cable with kraft paper alone insulation, if it is 50 cst or more at 40 ° C., it will not be continuously blown out, but it will be bleeding out and can be sufficiently sealed with a vinyl tape or the like. 15 more
Even if it was lowered to about cst, it was possible to seal somehow,
Its handling has become quite difficult. However, when the ambient temperature was set to 5 to 20 ° C. assuming north of Japan, even with the same insulating oil, the bleeding was remarkably reduced in proportion to the increase in viscosity.

If this becomes an insulating tape containing a polyolefin resin film layer (eg PPLP), it will be 15cs at 40 ° C.
Even at t, the amount of oil in the insulating layer decreases and PP with no holes
Since the film layer exhibits a very large oil flow resistance, the degree of oil bleeding was extremely small as compared with the case of using kraft paper alone.

This will be described with reference to FIG. Figure 7
In the portion of the kraft paper 10, 30 to 50% are holes, and the insulating oil is contained therein, and the insulating oil is allowed to pass through. On the other hand, the PP film layer 11 may absorb the insulating oil but does not cause it to flow out of the film, and does not allow the insulating oil to pass through. The insulating oil moves through the holes in the kraft paper fibers and the butt gap (oil gap) of the tape as the oil passage 12, so that the bleeding amount is about half or less at a PP ratio of 40%. The bleeding amount was 10% or less at a ratio of 80%. Therefore,
Even at 15 cst at 40 ° C, if the PP ratio is 40% or more, it is extremely convenient as a solid cable.

From the above, the insulating oil is 15 at 40 ° C.
It has been found that viscosities above cst, ie above about 10 cst at 60 ° C. are preferred (see FIG. 3).

Summarizing these results, it is preferable that the solid insulating oil has a viscosity of 10 to 500 cst when it is unified and viewed at 60 ° C. (a temperature with allowance for the maximum conductor temperature of the craft solid cable). Insulating oil with the optimum viscosity is selected by selecting the materials that make up the insulating layer, PP ratio k, PP and kraft paper composition ratio of the entire insulating layer, solid cable transmission capacity, transmission design conditions including load cutoff method, and solid cable. It may be done in consideration of the environment used.

<Increasing Internal Hydraulic Pressure by Reinforcing Layer> Next,
A means for preventing negative pressure in the vicinity of the conductor at the time of load shedding, which is the most key of the solid cable, will be described. From the above-mentioned examination, even in the case of the conventional kraft paper-insulated solid cable, when medium viscosity insulating oil is used, a negative pressure is generated when the load is cut off in almost any case when the internal pressure changes in FIG. I knew I wouldn't let it.

The insulating layer containing the polyolefin resin film was examined using the above PPLP. In this case, due to the high electrical insulator proof strength of PPLP, the maximum operating temperature should be kept within 50 ° C, which is the same level as the conventional kraft paper solid cable, and the operating voltage should be from 500kV to 450kV.
There are an attempt to increase the capacity by increasing it to 600 kV or 700 kV class and an attempt to increase the maximum operating temperature to within about 80 ° C. to increase the capacity. Alternatively, there is an attempt to combine both of them to further increase the performance and capacity. In any case, in order to improve the performance, it is necessary to increase the ratio of the polyolefin resin film, but if this is done, the oil flow resistance explained in FIG. It is preferable to take measures.

Therefore, here, the prevention of negative pressure by increasing the hydraulic pressure inside the solid cable will be examined. As can be seen in Fig. 2, after a certain time has passed since the load current was passed, the temperature gradient in the cable saturates and becomes constant, and the expansion of the insulating oil ends accordingly, and the differential pressure generated at that time It has already been explained that the oil causes negative pressure unless it moves radially from the outside to the inside. The ease of oil movement at this time is inversely proportional to the magnitude of the oil flow resistance of the insulating layer, and is proportional to the hydraulic pressure difference applied from the outside to the inside.

When the oil passage is limited to the kraft paper and is reduced as in PPLP, the oil flow resistance increases, but if medium viscosity insulating oil is used, the oil flow resistance decreases according to the viscosity ratio. Are in a mutually offsetting relationship. Moreover, the higher the full load temperature, the lower the viscosity, which is preferable. To increase the difference in oil pressure, the oil pressure that becomes constant at full load,
That is, the hydraulic pressure just before the load is cut off in FIG. 2 should be increased.

By the way, when the cable is used at a high temperature, the oil expands in proportion to the temperature difference between the normal temperature and the high temperature. Therefore, if the volume of the insulating layer does not increase to absorb the difference, the hydraulic pressure rises significantly. Will be shown. This is preferable for increasing the hydraulic pressure immediately before the load is cut off, and should be actively used. However, the high hydraulic pressure must be able to withstand the metal sheath of the cable (usually a lead sheath). If unbearable, the metal sheath may expand and not allow the pressure to rise, or if it becomes worse, the metal sheath may rupture or may suffer metal fatigue due to repeated load cycles. This was another reason for limiting the maximum operating temperature ever.

On the other hand, in the structure of the conventional solid cable shown in FIG. 1, the highly elastic polyethylene (PE) anticorrosion layer 6 was present immediately above the metal sheath 5 (lead coating). This was to combine the lead extruder and PE extruder in tandem to make production easier and cheaper. Further, from the viewpoint of negative pressure, the conventional solid cable has limited the operating temperature to a low level, so that the hydraulic pressure does not rise and it is not a particular problem.

Further, a metal tape 7 for protecting the internal pressure is applied to the outside of the anticorrosion layer 6, but since seawater reaches that portion, the material of the metal tape 7 is limited to zinc coated steel, bronze or brass. It was None of these tapes have high tensile strength. Moreover, the effect of corrosion protection is unavoidable, and in this respect too, high internal pressure protection cannot be expected.

Therefore, the present inventors have found that a reinforcing layer (not shown) for protecting the internal pressure of the metal sheath 5 is provided inside the anticorrosion layer 6 having a high elastic modulus, that is, immediately above the metal sheath 5. As the material of the reinforcing layer, stainless steel (SUS), aramid fiber, etc., which can easily obtain high tensile strength and are easily industrially available, can be used. Above all, SUS304, which is advantageous in terms of price, is preferable. The reinforcing layer may be formed by winding a cloth tape together with the SUS tape, if necessary.

SUS304 is liable to cause corrosion when it comes into contact with seawater, and aramid fibers or the like may be deteriorated by seawater. However, since the reinforcing layer is housed inside the anticorrosion layer, it is convenient because it is protected from seawater. The tensile strength of SUS can easily be about 40 kg / mm ² (kilogram / square centimeter) or high tension SUS of 100 kg / mm ² (kilogram / square centimeter) or more. A high internal pressure resistant cable can be easily realized by forming a tape having a required thickness and winding the required number of sheets.

The maximum measured hydraulic pressure and the computer-calculated hydraulic pressure in the solid kraft paper cable of FIG. 1 are transiently 10 kg / cm ^{2 or more} directly above the conductor, but the constant hydraulic pressure after stabilization is at most 2-4 kg / cm. It was about ² .

On the other hand, by providing the reinforcing layer directly above the metal sheath, a constant hydraulic pressure after stabilization can be easily maintained.
It was possible to achieve kg / cm ² or higher. In addition, if a cushion layer such as a cloth tape is appropriately provided under the SUS tape, that is, between the lead sheath and the SUS tape, it is convenient that this constant constant pressure can be easily controlled. The constant pressure that is reached depends on the degree of impregnation of the insulating oil in the factory, the distance between the cable core and the metal sheath in the metal sheath extrusion process, the degree of deformation of the metal sheath, and the insulation oil warmed in the metal sheath extrusion process. It changes intricately depending on the temperature and the ambient temperature of the cable installation point or the depth of seabed installation.

It was found that, in the case of the kraft paper solid cable in which a saturated constant pressure of about 10 kg / cm ² or more was obtained, almost no cable produced a negative pressure after the load was cut off.

Next, a new solid cable using a PPLP tape capable of raising the maximum operating temperature to within 80 ° C. was examined. In this case, the temperature difference between the ambient temperature (no-load temperature) and the maximum conductor temperature becomes large, so the hydraulic pressure is 100 kg / cm ² unless the expansion / contraction of the lead cover is counted in the calculation.
The above pressure is obtained. Even in this case, tensile strength 100kg / mm ²
It can be reinforced by using (kilogram / square centimeter) SUS and winding it with a safety factor of 2 so that the total of multiple tapes is about 1 mm.

However, in practice, various uncertain conditions that influence the constant pressure to be reached and insulating oil are added to the completed solid cable.
It is difficult to impregnate it with 100%, and due to the presence of expansion and contraction of the reinforcing layer and the metal sheath,
It is rare for the pressure to rise to this level.

Further, in the case of PPLP, the volume of insulating oil that expands is much smaller than that of kraft paper in the first place, and PPLP contracts due to pressure to absorb the increase in oil pressure, which also reduces the increase in internal hydraulic pressure. It turned out to work. In order to expect more of this effect, it is preferable to increase the PP ratio of PPLP, and PP with k = 80% or more is suitable for high temperature use solid cables.

In order to enhance the effect of this PPLP, it is sufficient to increase the ratio of the resin film layer to the entire insulating layer while maintaining that the kraft paper layer as the oil passage alternates with the resin film layer.

FIG. 8A shows PP film 21 and kraft paper 22.
An insulating layer using only the composite tape 20 in which the layers are laminated. In this case, the resin film ratio k of the composite tape 22 is 40%.
If so, the whole insulating layer is 40%.

However, as shown in FIG. 8B, if the composite tape 20 and the tape 30 of the resin film alone are alternately laminated, 22 layers of kraft paper are surely formed on both sides from the viewpoint of each resin film layer. Means that the oil passage and the cushion layer are secured. For example, if the tape thickness is the same and the resin film ratio k of the composite tape 20 is 40%,
By this alternate winding, the resin film ratio of the entire insulating layer is 7
It can be increased to 0%. As a result, the amount of insulating oil per unit volume can be reduced, the amount of shrinkage of the film due to internal pressure can be increased, and the oil flow resistance of insulating oil can be reduced, which is extremely preferable for medium viscosity insulating oil solid cables.

Further, the ratio of the kraft paper layer which originally has a low resistivity and is considered to hardly share the DC stress decreases, and the ratio of the resin film layer resistant to the DC stress increases, which is also preferable in terms of electric performance.

<Structure of Transmission Line> This increase in internal pressure due to temperature difference and expansion of insulating oil is a phenomenon that occurs over the entire length of the cable, and naturally occurs near the end of the cable. Therefore, when the medium viscosity insulating oil is heated to a high temperature to reduce the viscosity, the expanded oil may damage the terminal. Therefore, as shown in FIG. 9, an oil stop connection box 41 (stop joint: Stop-Joint) is provided in the vicinity of both ends of the seabed solid cable 40, preferably on the beach where the seabed is separated from the land where the ambient temperature is different.
Is preferably provided to connect the land portion cable 42 to prevent the hot insulating oil from moving due to expansion. The type of the land cable 42 does not matter. If the type of land cable 42 is different from the seabed solid cable, a deformed joint or a transition joint (Transiti
on Joint (TJ)) is used.

By the way, as described above, about 70 to 10
A solid submarine cable having a depth of 0 m or less, that is, a cable near the beach, may have a negative pressure when there is no load because the external water pressure is insufficient. In particular, when the cable is laid by lacking the insulating oil in the cable metal sheath, this tendency becomes remarkable, which is not preferable in terms of electric performance when a load is applied.

Therefore, the oil supply tanks 43 are provided at both terminals in order to maintain the insulating oil inside both terminals of the transmission line and replenish these insufficient oils, thereby slightly pressurizing the insulating oil having a viscosity of medium viscosity or less. It is preferable that the insulating oil can be supplied.

When the submarine solid cable 40 is a conventional kraft paper cable and is directly drawn into both terminals (not shown) without going through the oil stop connection box, an oil tank is provided at both terminals. Supply insulating oil with medium viscosity or less.

When the submarine solid cable 40 is a solid cable having an insulating layer containing polyolefin resin and is used at high temperature, as shown in FIG. 9, the oil supply pipe 44 is connected to the submarine cable side of the oil stop connection portion 41. It connects with the oil supply layer 43 and supplies oil. Of course, the on-ground cable 42 also has an oil tank 43
And the insulating oil is also supplied to the land cable 42.
In this case, it is preferable to install a check valve between the oil stop connection box 41 and the oil supply tank 43 so that the oil does not flow back from the seabed solid cable 40 to the oil supply tank 43 due to the high temperature and high oil pressure when loaded.

The land cable 42 on the land side of the oil stop connection portion 42 may be an OF cable or a solid cable.
The insulating oil in the oil tank may be appropriately changed according to the type of cable. That is, for the OF cable, low-viscosity insulating oil may be used, and for the solid cable, oil of medium viscosity or less may be used.

<Relationship between SP Value of Insulating Oil and SP Value of Polyolefin Resin Film> Here, an insulating tape using a polyolefin resin film as at least a part is used for a solid cable, and its electric performance is exhibited without any limitation. In order to achieve this, it is important to select the combination of the SP value (solubility index) of the film and insulating oil.

FIG. 10 shows the SP values of the resin polymer and oil in comparison. Further, FIG. 11 shows the relationship between the absorption amount of the mineral oil type insulating oil (SP value is less than 8) and the Imp. Fracture strength in each resin film, and FIG. 12 is the impregnated with the mineral oil type insulating oil having the SP value of less than 8. Imp. Breaking strength of resin film SP of resin film
Shown in relation to the value.

From these figures, it is understood that the closer the SP value of the resin film is to the SP value of the insulating oil, the more the resin film absorbs the insulating oil and improves the electric performance. Improvements in electrical performance are observed over AC, impulse, and DC. Especially in the case of polyolefin resin film, S
It was found that when a synthetic oil having a P value of 8, that is, an alkylbenzene-based insulating oil (for example, dodecylbenzene-based insulating oil: DDB) is used, this effect is remarkable, and both DC and impulse fracture strength can be improved by 10%.

As the medium viscosity insulating oil that brings out such effects, polyester type insulating oil, polybutene type insulating oil,
It is preferable that the viscosity is adjusted by using one or more kinds of mixed insulating oils such as mineral oil type insulating oil, alkylbenzene type insulating oil or heavy alkylate which is one of them.

Further, in order to make this effect remarkable, it is preferable to secure a sufficient oil absorption amount of the resin film in advance. For that purpose, it is effective to use a low viscosity oil having an SP value close to the film layer to sufficiently absorb the oil and then impregnate the solid cable with the optimum medium viscosity insulating oil.

Low viscosity insulating oil for OF cable is 10 at room temperature.
Insulating oil with a viscosity of cst or less and very easy to impregnate. Among them, the alkylbenzene type insulating oil DDB has an SP value of 8 and is extremely well absorbed by the polyolefin type resin film. Therefore, after the cable core is dried, it is impregnated with DDB in advance and then kept at 80 ° C. or higher for 24 hours or longer so that the film absorbs oil. Then, if DDB is deoiled and the medium viscosity insulating oil is impregnated, the above-mentioned effects can be stably obtained with almost no decrease in productivity.

<Grading of Insulating Layer> Further, since the present inventors have obtained an insulating tape having a different composite ratio of kraft paper and polyolefin resin film,
By skillfully combining these, the stress sharing of the solid DC cable was optimized and the performance of the cable was improved.
The insulating tape here includes a tape made only of kraft paper, a composite tape made of kraft paper and a polyolefin resin film, and a tape made only of a polyolefin resin film.

For example, kraft paper (dielectric constant ε = 3.4,
Resistivity ρ = 10 ¹⁴ -10 ¹⁸ Ω · cm), PPLP (k = 40%)
(Equivalent, ε = 2.8, ρ = 10 ¹⁶ to 10 ¹⁸ Ω · cm), as shown in FIG. 13, a kraft paper tape layer is placed in the A zone on the conductor and the C zone directly below the metal sheath in the center. Place PPLP in zone B, which will be the main insulating layer. As a result, the distribution of design stress in the A and C zones can be reduced by ε-grading for impulse, and ρ-for DC.
Grading can also reduce the design stress distribution in the A and C zones. Usually, a place where the insulating layer contacts the conductor and the metal sheath can be a big weak point, so that it is extremely preferable to reduce the stress distribution in this portion as shown in FIG.

Further, as described above, it is possible to prevent the negative pressure by covering the area directly above the conductor, which may have a negative pressure when the load is cut off, with an insulating layer having a resistivity lower than that of the main insulating layer. This is even more preferable for solid cables, since it will not share stress in certain weak areas.

Further, for example, in the insulating layer region close to the conductor, PP
If a PPLP with a ratio of k = 80%, a PPLP with a ratio of k = 60%, and a PPLP with a ratio of k = 40% are placed outside the PPLP, the higher the K, the higher the resistivity ρ. Ρ-grading in the direction of relieving the DC stress in the insulating layer at the time is possible. In this configuration, even if it is a medium viscosity insulating oil, if you want to use an insulating oil with a viscosity as high as possible under various design conditions, the ratio of kraft paper is higher toward the outside of the cable and the oil flow resistance is smaller, so impregnation is relatively It is easy and preferable.

Although the case where two or three kinds of insulating tapes are used has been described above, a more rational insulation design can be achieved by performing grading using more kinds of insulating tapes, and one kind of insulating tape can be used. This is an epoch-making progress from the viewpoint of the conventional cable that can only use materials.

[0117]

As described above, according to the power transmission line of the present invention, the following effects can be obtained. It is possible to use a solid cable at high temperature and increase its capacity. Negative pressure is not generated in the insulating layer near the conductor when the load is cut off, and the occurrence of voids is suppressed to prevent deterioration of electrical performance. Insulating oil does not easily leak from the cable end when handling the cable. By providing the reinforcing layer, the hydraulic pressure inside the cable can be increased and the metal sheath is not damaged.

In the cable used in the line of the present invention, the insulating layer is securely impregnated with the medium-viscosity insulating oil without impregnating the low-viscosity insulating oil, so that the insulating layer can be reliably insulated. Can be impregnated.

Further, the transmission line of the present invention can prevent the cable end portion from being damaged by the expansion of the insulating oil at the time of full load by the oil stop connection box, and by providing the oil supply tank, it can be connected from the beach to the land. Insulation oil can be supplied to the cable to suppress starvation.

In particular, by connecting the sea bottom solid cable side of the oil stop connection box and the oil supply tank with an oil supply pipe, and providing a check valve on this oil supply pipe, the sea bottom solid cable is filled with medium-viscosity insulating oil. It is possible to supply the gas and suppress backflow to the oil tank.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a submarine solid cable.

FIG. 2 is a graph showing changes in hydraulic pressure in a solid cable due to ON / OFF of a load for different positions of an insulating layer.

FIG. 3 is a graph showing a relationship between a representative insulating oil and a representative temperature-viscosity of a medium viscosity solid insulating oil used in the present invention.

[Fig. 4] Structure of PPLP laminated with kraft paper on both sides of PP film and resistivity ρ of insulating material surrounding PPLP
It is explanatory drawing which shows the direct-current (DC) stress distribution proportional to ((ohm) cm).

FIG. 5 is a graph showing the relationship between PP ratio k and breaking stress.

FIG. 6 is a graph showing the ratio of DC withstand voltage values of PPLP and high airtight kraft paper for DC in relation to PP ratio k.

FIG. 7 is an enlarged sectional view of an insulating layer made of PPLP.

FIG. 8A is a partial sectional view of an insulating layer in which PPLP is laminated, and FIG. 8B is a partial sectional view of an insulating layer in which PPLP and a polypropylene film are alternately laminated.

FIG. 9 is a schematic configuration diagram of a power transmission line of the present invention.

FIG. 10 is an explanatory diagram comparing SP values of resin polymer and oil.

FIG. 11: Mineral oil-based insulating oil (SP) in each resin film
It is a graph which shows the relationship between the amount of absorption and the Imp.

FIG. 12 is a graph showing the Imp. Fracture strength of a resin film impregnated with a mineral oil-based insulating oil having an SP value of a little less than 8 in relation to the SP value of the resin film.

FIG. 13 is an explanatory cross-sectional view of a cable having an insulating layer that is graded.

FIG. 14 is an explanatory diagram showing a stress distribution of an insulating layer between a conductor and a metal sheath.

[Explanation of symbols]

1 conductor 2 inner semiconductive layer 3 oil-impregnated insulating layer 4 outer semiconductive layer 5 metal sheath 6 anticorrosion tank 7 metal tape 8 protective yarn 9 exterior wire 10 polypropylene layer 11 craft paper layer
12 Oil passage 20 Composite tape 21 Polypropylene layer 22 Kraft paper 30 PP single tape 40 Subsea solid cable 41
Oil stop connection box 42 Land cable 43 Oil supply layer 44 Oil supply pipe

Front page continued (72) Inventor Jun Yoda 1-3-3 Shimaya, Konohana-ku, Osaka City Sumitomo Electric Industries, Ltd. (72) Inventor Takahiro Horikawa 1-3-3 Shimaya, Konohana-ku, Osaka Sumitomo Electric Industrial Co., Ltd. Osaka Works (72) Inventor Yuichi Ashibe 1-3-3 Shimaya, Konohana-ku, Osaka Sumitomo Electric Industries Co., Ltd. Osaka Factory (72) Inventor Morihiro Seki 1-3-3 Shimaya, Konohana-ku, Osaka Sumitomo Electric Industries, Ltd. Osaka Works (56) Reference JP 10-283852 (JP, A) JP 62-44904 (JP, A) JP 59-198823 (JP, A) JP 56 −53522 (JP, A) Yukio Saito, Yuichiro Take, Electrical insulating paper, Nihon, Corona Publishing, December 20, 1969, first edition, P308-324 (58) Fields investigated (Int.Cl. ⁷ , DB name) ) H01B 7/14 H01B 9/06 H01B 13/00

Claims (6)

(57) [Claims] 1. A seabed solid cave laid on the seabed.
And both ends of this submarine solid cable with oil stoppers.
DC with land-based cables connected via connecting boxes
A transmission line, The submarine solid cable has insulating oil around the conductor.
This is a DC solid cable with an impregnated insulation layer
At least part of the insulating layer of the polyolefin resin
Using insulating tape containing rum,This insulation tape is made of polypropylene film and craft
Paper composite tape, for the total thickness of this composite tape
Polypropylene film thickness ratio k is over 60% 90
% (Excluding the range of 70% or less), The insulating oil has a viscosity at 60 ° C of 10 cst or more and 500 cst or less.
Fully filled with medium viscosity insulating oil and pre-insulated with low viscosity insulating oil
Impregnated into the insulating layer without impregnating the layer, The oil stop connection box is located at the beach, Insulating oil of medium viscosity or less is used for the land cable.
The tank to supply oil to the onshore cable must be connected.
Characterized byDirect currentPower transmission line. Wherein the ratio k is DC transmission line of claim 1, wherein less than 80% or more 90%. 3. A DC transmission line of claim 1, wherein the vapor density of the kraft paper in submarine-portion solid cable, characterized in that at least 3,000 Gurley seconds. 4. A SP value of insulating oil, DC transmission line according to any one of claims 1 to 3, characterized in that in the range of ± 1.5 of the SP value of polyolefin resin film
Road . 5. A method according to claim 1-4, characterized in that land portion cable is <br/> solid cable using a medium-viscosity insulating oil
The DC transmission line described in any one of 1. 6. An oil supply pipe is connected to the sea bottom solid cable side of the oil stop connection box, and the oil supply pipe is connected to an oil supply tank,
The DC power transmission line according to any one of claims 1 to 5, wherein the DC oil transmission tank is configured to supply the medium-viscosity insulating oil to the undersea solid cable.