JP6800437B1 - Manufacturing methods for solid cables, transmission lines, and solid cables - Google Patents

Abstract

Provide an insulating tape having excellent insulating performance. An insulating tape comprising a plastic tape containing a polyolefin resin and a paper tape bonded to at least one surface of the plastic tape, and the electric resistance of the plastic tape is 1015 Ω · cm or less at 60 ° C.

Description

The present invention relates to insulating tapes, solid cables, power transmission lines, and methods for manufacturing solid cables.

As a long-distance large-capacity DC power cable, there is a solid cable provided with an oil-impregnated insulating layer. The oil-immersed insulating layer is formed by impregnating an insulating tape wound around the outer periphery of a conductor with insulating oil. Patent Document 1 discloses that a composite tape containing kraft paper and a polyolefin-based resin film is used as the insulating tape. Kraft paper is a porous material having a large number of through holes, and a polyolefin resin film is a solid having no through holes. Therefore, the polyolefin-based resin film has a very high DC withstand voltage characteristic because it is very difficult to impregnate with insulating oil as compared with kraft paper and the insulating characteristic is hardly affected by the presence or absence of the insulating oil.

When the conductor of a solid cable is energized (when the load is on), the insulating oil of the cable expands as the conductor temperature rises. On the other hand, when the energization of the solid cable is stopped and the load is cut off (when the load is off), the insulating oil shrinks as the conductor temperature decreases. Since the temperature drop of the insulating layer is large near the conductor, the amount of shrinkage of the insulating oil is large near the conductor. Therefore, the internal pressure of the insulating oil in the region near the conductor becomes smaller than that in the region of the other portion. When the load is off, if the insulating oil does not have sufficient fluidity, the insulating oil becomes a negative pressure in the region near the conductor, further causing starvation, and voids are generated. That is, if the insulating oil does not have sufficient fluidity, it is difficult for the insulating oil to flow from the region of the other portion where the internal pressure is high to the region near the conductor where the internal pressure is low, and the internal pressure of the insulating oil decreases in the region near the conductor. This is because it cannot be compensated. When voids occur, the insulation performance of the insulating layer deteriorates. The higher the maximum temperature of the conductor when the load is on, the larger the amount of expansion of the insulating oil, and the steeper the temperature drop when the load is off, so that starvation is likely to occur and voids are more likely to occur. Therefore, the maximum temperature of the conductor when the load is turned on is limited, and the transmission capacity is limited.

Therefore, in the technique described in Patent Document 1, a medium-viscosity insulating oil is used as the insulating oil. Medium-viscosity insulating oil has higher fluidity than high-viscosity insulating oil. Due to the high fluidity of the insulating oil, voids are unlikely to occur. Therefore, in the technique of Patent Document 1, the maximum temperature of the conductor when the load is turned on can be increased, and the transmission capacity can be increased.

Japanese Unexamined Patent Publication No. 11-224546

It is desired that the operating temperature and voltage of the solid cable be further increased.
In the technique of Patent Document 1, if the voltage of the solid cable is further increased and the maximum temperature of the conductor when the load is turned on is further increased, the insulation performance of the insulating layer may be deteriorated.

Therefore, one of the objects of the present invention is to provide an insulating tape having excellent insulation performance against high temperature and high voltage. Another object of the present invention is to provide a solid cable capable of increasing the operating temperature and the voltage. Another object of the present invention is to provide a power transmission line capable of increasing the operating temperature and the voltage. Another object of the present invention is to provide a method for manufacturing a solid cable capable of increasing the operating temperature and the voltage.

The insulating tape according to the first aspect of the present invention includes a plastic tape containing a polyolefin resin and a paper tape bonded to at least one surface of the plastic tape. The electrical resistivity of the plastic tape is 10 ¹⁵ Ω · cm or less at 60 ° C.

The solid cable according to the first aspect of the present invention includes a conductor, an insulating layer provided on the outer periphery of the conductor, and insulating oil impregnated in the insulating layer. The insulating layer is formed by wrapping an insulating tape around the insulating layer. The insulating tape includes a plastic tape containing a polyolefin resin and a paper tape arranged so as to face the plastic tape. The electrical resistivity of the plastic tape is equal to or less than the electrical resistivity of the insulating oil.

The power transmission line according to the first aspect of the present invention includes a solid cable of the present invention, another cable connected in the longitudinal direction of the solid cable, and a joint provided between the solid cable and the other cable. To be equipped. The joint stops the movement of the insulating oil along the longitudinal direction of the solid cable.

The method for manufacturing a solid cable according to the first aspect of the present invention includes a step of wrapping an insulating tape around the outer periphery of a conductor to provide an insulating layer, a step of drying and degassing the insulating layer, and a step of drying and degassing. A step of impregnating the insulating layer with insulating oil and a step of providing a metal sheath on the outer periphery of the insulating layer impregnated with the insulating oil are provided. The insulating tape includes a plastic tape containing a polyolefin resin and having an electrical resistivity equal to or less than the electrical resistivity of the insulating oil, and a paper tape in contact with the plastic tape. The step of providing the metal sheath is performed at a temperature of 50% or more and 80% or less of the maximum operating temperature of the conductor.

The insulating tape has excellent insulation performance against high temperature and high voltage.
The solid cable and the power transmission line of the present invention can have a high operating temperature and a high voltage.
As the method for manufacturing the solid cable, a solid cable capable of increasing the operating temperature and the voltage can be obtained.

FIG. 1 is a cross-sectional view showing an example of a solid cable. FIG. 2 is an enlarged cross-sectional view of a part of the insulating layer in the solid cable. FIG. 3 is an explanatory diagram illustrating a DC electric field in the insulating layer and a leakage current flowing through the insulating layer during operation of the solid cable. FIG. 4A is an explanatory diagram illustrating an example of a leakage current flow in an insulating layer made of a conventional insulating tape. FIG. 4B is an explanatory diagram illustrating another example of the flow of leakage current in the insulating layer made of conventional insulating tape. FIG. 4C is an explanatory diagram illustrating still another example of the flow of leakage current in the insulating layer made of conventional insulating tape. FIG. 4D is an explanatory diagram illustrating an example of the flow of the leakage current flowing in the layer-wise direction due to the flow of the leakage current shown in FIG. 4C. FIG. 5 is a circuit diagram illustrating a leakage current flowing through each of the insulating tape and the oil gap. FIG. 6 is an explanatory diagram illustrating the flow of leakage current in the insulating layer made of the insulating tape of the embodiment. FIG. 7A is a partially enlarged cross-sectional view showing another form of the insulating layer in the solid cable of the embodiment. FIG. 7B is a partially enlarged cross-sectional view showing still another form of the insulating layer in the solid cable of the embodiment. FIG. 7C is a partially enlarged cross-sectional view showing still another form of the insulating layer in the solid cable of the embodiment. FIG. 8 is a cross-sectional view showing another example of the solid cable. FIG. 9 is a schematic configuration diagram showing a power transmission line of the embodiment.

[Explanation of Embodiments of the Present Invention]
Hereinafter, the phenomenon that may occur when the operating temperature and the voltage of the solid cable are increased in the prior art will be described first, and then the details of the embodiment of the present invention will be described.

≪Phenomenon that can occur when the voltage of a solid cable is increased in the conventional technology≫
First, an example of the solid cable 10 will be described with reference to FIGS. 1 and 2. As shown in FIG. 1, the solid cable 10 includes a conductor 11, an inner semi-conductive layer 12, an insulating layer 13, an outer semi-conductive layer 14, a metal sheath 15, and an anticorrosion layer 16 in this order from the center. In this example, the structure provided outside the anticorrosion layer 16 in the solid cable 10 will be omitted.

As shown in FIG. 2, the insulating layer 13 is configured by winding an insulating tape 20 around it. The insulating tape 20 is gap-wound so that a gap is provided between adjacent turns. The gap between adjacent turns is called the oil gap 30. The insulating tape 20 includes a plastic tape 21 and a paper tape 22. The plastic tape 21 contains a polyolefin-based resin. The insulating tape 20 shown in FIG. 2 is composed of composite tapes in which paper tapes 22 are bonded to both sides of the plastic tapes 21.

The insulating layer 13 is impregnated with insulating oil 40. Of the insulating tape 20, the paper tape 22 is porous and has a large number of through holes. The insulating oil 40 can pass through the through hole of the paper tape 22 and is impregnated in the through hole. On the other hand, of the insulating tape 20, the plastic tape 21 does not have a through hole. Therefore, the insulating oil 40 moves through the through hole in the paper tape 22 and the oil gap 30 as a flow path. An example of the flow path of the insulating oil 40 is shown by cross-hatching in FIG. In FIG. 2, for convenience of explanation, only a part of the flow path of the insulating oil 40 is shown, but originally, the insulating oil 40 flows over the entire paper tape 22 and the entire oil gap 30.

Next, with reference to FIG. 3, the DC electric field in the insulating layer 13 and the leakage current flowing through the insulating layer 13 during the operation of the solid cable 10 will be described. In FIG. 3, for convenience of explanation, only the conductor 11, the insulating layer 13, and the metal sheath 15 are shown. Further, in FIG. 3, for convenience of explanation, a part of the insulating tape 20 wound around the outer circumference of the conductor 11 is exaggerated. In FIG. 3, the direction of the DC electric field is indicated by a solid arrow, and the direction in which the leakage current flows is indicated by a dotted arrow. The flow of the DC electric field indicated by the solid arrow in FIG. 3 is correctly referred to as an electric field line, but here, it is displayed as an electric field according to the general indication that an electric field is applied.

In the solid cable 10, as shown in FIG. 3, a DC voltage is applied between the conductor 11 and the metal sheath 15, so that the diameter of the solid cable 10 is applied to the insulating layer 13 from the conductor 11 toward the metal sheath 15. A DC electric field is generated in the direction. This DC electric field is determined in proportion to the electric resistance of the insulating layer 13. Here, the electrical resistance of the substance is R, the area of the substance is S, the thickness is L, and the resistivity indicating the resistance performance of the substance is ρ. At this time, the electrical resistance R of the substance is represented by ρ × L / S. Therefore, here, the magnitude of the electric resistance R of the substance is basically indicated by the electrical resistivity ρ.

Since the DC electric field is proportional to the electrical resistivity, in the technique of Patent Document 1, a plastic tape 21 made of a polyolefin resin film having a very high DC withstand voltage characteristic is used for the insulating tape 20 constituting the insulating layer 13. ing. The plastic tape 21 made of a polyolefin resin film generally has a higher electrical resistivity than both the paper tape 22 and the insulating oil 40. Therefore, the DC electric field in the insulating layer 13 is mainly shared by the plastic tape 21 rather than the insulating oil 40 and the paper tape 22. Therefore, in the technique of Patent Document 1, it is possible to apply a DC electric field up to a high dielectric strength of the plastic tape 21, and it is expected that the voltage of the solid cable 10 can be increased.

However, in the technique of Patent Document 1, when the voltage of the solid cable 10 is increased, a phenomenon appears that the insulation performance of the insulating layer 13 is remarkably deteriorated when the load is turned off.

Direct current does not have zero potential and zero current, unlike alternating current and impulse (applied waveform with zero potential and zero current at the middle or end of the waveform). Therefore, when the load is off, a simple breaker tends to maintain and continue the discharge current as a follow-on flow by generating a discharge in the space even if the current passage is cut. This discharge and follow-on flow are more likely to occur as the DC voltage increases.

As long as a DC voltage is applied to the solid cable 10, a DC electric field is applied to the insulating layer 13 even if the energization is cut off. Therefore, under this DC electric field, a leakage current flows through the insulating layer 13 from the conductor 11 toward the metal sheath 15. On the other hand, in the insulating layer 13, as described above, the higher the maximum temperature of the conductor 11 when the load is on, the lower the temperature of the conductor 11 when the load is off, so that the area near the conductor 11 extends to the entire insulating layer 13. Shrinkage of the insulating oil 40 occurs. Therefore, in the insulating layer 13, starvation of the insulating oil 40 is likely to occur in the region near the conductor 11, and voids are likely to be generated in the oil gap 30. When a void is generated in the insulating layer 13, a current cutoff phenomenon occurs in the void, and a discharge and a follow current occur in this void. Even if voids are present in the insulating layer 13 immediately before the load is turned on due to the shrinkage of the insulating oil 40 due to the temperature drop of the conductor 11, the leakage current avoids the voids and flows in the region where the electrical resistivity is small. .. This is because the void is a space and has the highest resistance. That is, when the load is turned on, even if a void exists, the problem that discharge and follow-flow occur in the void does not occur. On the other hand, when the load is off, a void is suddenly generated in the region where the leakage current is flowing, so that the leakage current is interrupted by this void, and a problem of discharge and follow-on flow occurs in the void.

From the above, when the load is off, the leakage current flowing through the insulating layer 13 causes a discharge and a follow current in the void, and the heat generated by the discharge and the follow current burns the insulating layer 13, and the insulating performance of the insulating layer 13 is significantly deteriorated. The burnt insulating layer 13 causes carbonization with low resistance, resulting in uneven concentration of leakage current. Due to this uneven concentration of leakage current, carbonization of the insulating layer 13 continues and further expands. The voids are further increased by the discharge generated by the voids, the heat generated by the follow current, and the heat generated by carbonization. It was considered that heat generation due to discharge and follow-on flow generated in the void, heat generation due to carbonization, increase in voids, and incineration fracture of the insulating layer 13 proceeded, and finally dielectric breakdown of the insulating layer 13 was considered.

Specifically, when the electrical resistivity of the plastic tape 21 is larger than the electrical resistivity of the paper tape 22 and the electrical resistivity of the insulating oil as in the technique of Patent Document 1, the following phenomenon occurs. Conceivable. The leakage current in the insulating layer 13 flows in inverse proportion to the electrical resistivity. The following three forms can be mentioned as the flow of the leakage current.

The first form is a case where the oil gap 30 does not have a void having a high resistance and the oil gap 30 is filled with an insulating oil 40 having a resistance lower than that of the plastic tape 21. In the case of the first form, as shown in FIG. 4A, the leakage current flows through the insulating oil 40 having a relatively low resistance in the oil gap 30. The second form is the case where the insulating oil 40 is completely absent in the oil gap 30. When the insulating oil 40 does not exist in the oil gap 30, the space where the insulating oil 40 does not exist has the largest electrical resistivity. Therefore, in the case of the second form, as shown in FIG. 4B, the leakage current flows through the insulating tape 20 which constitutes most of the insulating layer 13 while avoiding the oil gap 30. In the first form and the second form described above, the leakage current does not concentrate in the local region of the insulating layer 13, and the discharge and the follow current do not occur in that region. It is unlikely that it will occur.

The third form is a case where a void is generated with the insulating oil 40 remaining in the oil gap 30. In the case of the third form, as shown in FIG. 4C, the leakage current is concentrated in a small amount of insulating oil 40 in the oil gap 30 having a small electrical resistivity while avoiding voids. In FIG. 4C, for convenience of explanation, a case where the void has a size close to the maximum is simulated. Actually, the size of the void is small at the initial stage when the void is generated in the insulating oil 40 in the oil gap 30. The void gradually increases due to the leakage current in the insulating layer 13 causing discharge and follow-on flow in the void.

When the leakage current is concentrated and flows in some insulating oil 40 in the oil gap 30, the DC electric field in the insulating layer 13 loses the uniformity in the circumferential direction of the solid cable 10 and is one in the longitudinal direction of the solid cable 10. The appearance also collapses. When a potential difference (electric field strength difference) occurs in the longitudinal direction of the solid cable 10, a large current flows through the paper tape 22 having a small electrical resistivity and the insulating oil 40 in the oil gap 30 where no voids are generated at once, as shown in FIG. 4D. Will be. That is, a non-uniform and excessive abnormal current is generated in the longitudinal direction of the solid cable 10 in the insulating layer 13. The heat generated by this abnormal current damages the insulating layer 13. In particular, due to the leakage current concentrated in the insulating oil 40 in the oil gap 30, and the increase in voids due to the discharge and the follow current generated by the voids, a large void that finally cuts off the leakage current is finally generated, and the discharge and the continuation Abnormal heat generation occurs due to the current. Due to this abnormal heat generation, carbonization occurs in which the insulating layer 13 is replaced with charcoal having a very low resistance and substantially no withstand voltage resistance to direct current, resulting in decisive insulation damage.

Here, the leakage current flowing through the insulating layer 13 and the loss that can occur in the oil gap 30 due to the leakage current are estimated.

Here, as shown in FIG. 2, the case where the insulating tape 20 is a composite tape in which paper tapes 22 are bonded to both sides of the plastic tape 21 is taken as an example. As for the insulating tape 20, the plastic tape 21 generally has a higher electrical resistivity than the paper tape 22. Therefore, in the insulating tape 20, the ratio of the voltage shared by the plastic tape 21 is very high with respect to the paper tape 22. For example, the electrical resistivity of the plastic tape 21 is 10 ¹⁹ Ω · cm at 60 ° C, the electrical resistivity of the paper tape 22 is 10 ¹⁶ Ω · cm at 60 ° C, and the thickness of each paper tape 22 is the thickness of the plastic tape 21. Consider the case where it is half of. In this case, the plastic tape 21 bears a voltage about 1000 times that of the paper tape 22. Therefore, in the following estimation, the electrical resistivity of the insulating tape 20 is the electrical resistivity of the plastic tape 21.

In the following, as the leakage current flowing through the insulating layer 13, the ratio of the leakage current flowing through the insulating tape 20 and the leakage current flowing through the insulating oil 40 in the oil gap 30 will be considered. As shown in FIG. 5, the leakage current flowing through each of the insulating tape 20 and the insulating oil 40 in the oil gap 30 is composed of a parallel circuit. In FIG. 5, V is the voltage applied to the insulating tape 20 and the oil gap 30 (insulating oil 40), R ₁ is the electrical resistance of the insulating tape 20 (plastic tape 21), R ₂ is the electrical resistance of the insulating oil 40, and i is leakage. The current, i ₁ indicates the leakage current flowing through the insulating tape 20, and i ₂ indicates the leakage current flowing through the insulating oil 40 in the oil gap 30. As described above, the electric resistance R is represented by ρ × L / S using the area S of the substance, the thickness L, and the electrical resistivity ρ of the substance. An example of each specification of the insulating tape 20 and the oil gap 30 (insulating oil 40) is as follows. The electrical resistivity ρ ₁ of the insulating tape 20 is 10 ¹⁹ Ω · cm at 60 ° C. The electrical resistivity ρ ₂ of the insulating oil 40 is 10 ¹⁵ Ω · cm at 60 ° C. The width of the insulating tape 20 is 25 mm. The thickness of the insulating tape 20 is 0.1 mm. The width of the oil gap 30 (the length of separation between adjacent turns) is 2 mm, and the thickness of the oil gap 30 is 0.1 mm. At this time, the leakage current flowing through the insulating tape 20 and the leakage current flowing through the insulating oil 40 in the oil gap 30 are obtained by V / R = V / (ρ × L / S), respectively. V is a voltage applied to the insulating tape 20 and the oil gap 30 (insulating oil 40). S is the area of the insulating tape 20 (oil gap 30), and is calculated by multiplying the length by the width. Using the above formula, the leakage current flowing through the insulating oil 40 in the oil gap 30 is about 1000 times the leakage current flowing through the plastic tape 21. According to this calculation, when the electrical resistivity of the plastic tape 21 is larger than the electrical resistivity of the insulating oil 40, it can be seen that the leakage current is concentrated in the insulating oil 40 in the oil gap 30.

Similarly, the loss in the insulating tape 20 and the loss in the insulating oil 40 in the oil gap 30 are obtained by I ² × R, respectively. I is a leakage current flowing through the insulating tape 20 (insulating oil 40). R is obtained by the above ρ × L / S. Using the above formula, the loss in the insulating oil 40 in the oil gap 30 is about 1000 times the loss in the plastic tape 21. According to this calculation, when the electrical resistivity of the plastic tape 21 is larger than the electrical resistivity of the insulating oil 40, the loss in the insulating oil 40 in the oil gap 30 is very large and cannot be ignored.

<< Details of Embodiments of the present invention >>
The present invention focuses on the leakage current flowing through the insulating oil 40 in the oil gap 30.

Using the parallel circuit shown in FIG. 5, the electrical resistivity of the plastic tape 21 is made smaller than the electrical resistivity of the insulating oil 40, and the leakage current flowing through the insulating layer 13 and the leakage current generate in the oil gap 30. Estimate the loss you will get. The specifications of the insulating tape 20 and the oil gap 30 (insulating oil 40) were the same as described above except for the electrical resistivity. The electrical resistivity ρ ₁ of the insulating tape 20 is 10 ¹⁴ Ω · cm at 60 ° C. The electrical resistivity ρ ₂ of the insulating oil 40 is 10 ¹⁵ Ω · cm at 60 ° C. In this case, the leakage current concentrated in the insulating oil 40 in the oil gap 30 is 0.01 times the leakage current flowing over the entire width of the plastic tape 21. According to this calculation, when the electrical resistivity of the plastic tape 21 is smaller than the electrical resistivity of the insulating oil 40, a leakage current flows evenly over the entire width of the plastic tape 21 and reaches the insulating oil 40 in the oil gap 30. It can be seen that the leakage current is not concentrated. Further, the loss in the insulating oil 40 in the oil gap 30 is about 0.01 times the loss in the plastic tape 21. According to this calculation, when the electrical resistivity of the plastic tape 21 is smaller than the electrical resistivity of the insulating oil 40, the loss in the insulating oil 40 in the oil gap 30 is negligibly small. When the electrical resistivity of the insulating tape 20 (plastic tape 21) and the electrical resistivity of the insulating oil 40 are the same, the leakage current concentrated in the insulating oil 40 in the oil gap 30 leaks through the plastic tape 21. It is 0.1 times the current. Even in this case, the amount of leakage current flowing through the insulating oil 40 in the oil gap 30 as compared with the case where the electrical resistivity of the insulating tape 20 (plastic tape 21) is larger than the electrical resistivity of the insulating oil 40. It turns out that is small.

The present invention is based on the above findings. First, the contents of the embodiments of the present invention will be listed and described.

(1) The insulating tape of the present invention includes a plastic tape containing a polyolefin resin and a paper tape bonded to at least one surface of the plastic tape. The electrical resistivity of the plastic tape is 10 ¹⁵ Ω · cm or less at 60 ° C.

The insulating tape of the present invention contains a polyolefin resin in a plastic tape. Therefore, the plastic tape has a high DC withstand voltage characteristic. On the other hand, the electrical resistivity of the plastic tape is 10 ¹⁵ Ω · cm or less at 60 ° C. This electrical resistivity is small compared to the electrical resistivity of conventional plastic tapes. Therefore, the plastic tape in the insulating tape of the present invention is more likely to carry an electric current than the conventional plastic tape. High voltage solid cables can have voids in the oil gap in the insulating layer, which can be a major drawback, as described above. Further, in a high voltage solid cable, leakage current tends to flow in the insulating layer. If the insulating layer is formed of the insulating tape of the present invention, the leakage current can be passed through the plastic tape. Therefore, even if a void occurs with the insulating oil remaining in the oil gap, it is possible to suppress the concentration of the leakage current in the remaining insulating oil in the oil gap, and the discharge and the follow-on flow occur in the insulating layer. Can be suppressed. Therefore, the insulating tape of the present invention has a sufficiently high DC withstand voltage characteristic by providing a plastic tape having no through hole, and can suppress the centralization of leakage current, thereby preventing heat generation of the insulating layer. , Dielectric breakdown can be suppressed. From the above, if the insulating layer is formed of the insulating tape of the present invention, the insulating performance of the insulating layer can be improved. The insulating tape of the present invention can be used as an insulating layer in a solid cable capable of increasing the voltage and transmitting a large capacity.

(2) As an example of the insulating tape of the present invention, the electrical resistivity of the paper tape is smaller than the electrical resistivity of the plastic tape.

In other words, the electrical resistivity of plastic tape is greater than the electrical resistivity of paper tape. Therefore, the sharing of the DC electric field is still performed by the plastic tape. Such insulating tapes can withstand high DC electric fields due to the plastic tapes having no through holes.

(3) As an example of the insulating tape of the present invention, the paper tape may be made of kraft paper or carbon paper.

Kraft paper and carbon paper can be well impregnated with insulating oil and can ensure good passage of insulating oil.

(4) As an example of the insulating tape of the present invention, the plastic tape and the paper tape may be configured in any of the following forms (A) to (C).
(A) The paper tape made of kraft paper or carbon paper is bonded to one surface of the plastic tape.
(B) The paper tape made of kraft paper or carbon paper is bonded to both sides of the plastic tape.
(C) The paper tape made of kraft paper is bonded to one surface of the plastic tape, and the paper tape made of carbon paper is bonded to the other surface of the plastic tape.

In each of the above-mentioned forms (A) to (C), the flow path of the insulating oil can be satisfactorily secured by laminating the insulating tape having the plastic tape and the paper tape.

(5) The solid cable of the present invention includes a conductor, an insulating layer provided on the outer periphery of the conductor, and insulating oil impregnated in the insulating layer. The insulating layer is formed by wrapping an insulating tape around the insulating layer. The insulating tape includes a plastic tape containing a polyolefin resin and a paper tape arranged so as to face the plastic tape. The electrical resistivity of the plastic tape is equal to or less than the electrical resistivity of the insulating oil.

The solid cable of the present invention includes a plastic tape having no through hole in the insulating layer. Therefore, the insulating layer has a high DC withstand voltage characteristic. On the other hand, the electrical resistivity of the plastic tape is equal to or less than the electrical resistivity of the insulating oil. In a solid cable with a high operating temperature and a high voltage, voids may occur in the oil gap in the insulating layer as described above. Further, in a high voltage solid cable, leakage current tends to flow in the insulating layer. In the solid cable of the present invention, the leakage current can be passed through an overwhelmingly wide plastic tape as compared with the oil gap. Therefore, even if a void occurs with the insulating oil remaining in the oil gap, it is possible to suppress the concentration of the leakage current in the remaining insulating oil in the oil gap, and the discharge and the follow-on flow occur in the insulating layer. Can be suppressed. Therefore, the insulating layer in the solid cable of the present invention has sufficiently high DC withstand voltage characteristics, can prevent heat generation due to leakage current, and can suppress dielectric breakdown. From the above, the solid cable of the present invention can have a high operating temperature, a high voltage, and a large capacity.

(6) As an example of the solid cable of the present invention, the electrical resistivity of the paper tape is smaller than the electrical resistivity of the plastic tape.

In other words, the electrical resistivity of plastic tape is greater than the electrical resistivity of paper tape. Therefore, the solid cable of the present invention satisfies the relationship of "electric resistivity of insulating oil ≥ electrical resistivity of plastic tape> electrical resistivity of paper tape". By satisfying this relationship, the leakage current flowing through the insulating layer can be passed through the plastic tape while sharing the DC electric field with the plastic tape. Therefore, the insulating tape can withstand a high DC electric field due to the plastic tape having no through hole, and can prevent heat generation due to leakage current and suppress dielectric breakdown.

(7) As an example of the solid cable of the present invention, it is mentioned that at least a part of the insulating layer is composed of the insulating tape of the present invention according to any one of (1) to (4) above. Be done.

The insulating tape of the present invention is a composite tape in which a plastic tape and a paper tape are bonded. Therefore, in forming the insulating layer, the insulating tape can be simply wound. Therefore, the solid cable of the present invention is excellent in productivity.

(8) As an example of the solid cable of the present invention, at least a part of the insulating layer is formed by alternately laminating the plastic tape and the paper tape.

The plastic tape and the paper tape may be configured independently of each other. Since they are configured independently of each other, there is a high degree of freedom in combining the constituent materials of the plastic tape and the paper tape. Even if they are configured independently of each other, the flow path of the insulating oil can be satisfactorily secured by alternately laminating the plastic tape and the paper tape.

(9) As an example of the solid cable of the present invention, at least a part of the insulating layer is formed by alternately laminating the plastic tape and the composite tape of any of the following (D) or (E). It can be mentioned that.
(D) A composite tape in which the paper tape made of kraft paper or carbon paper is bonded to both sides of the plastic tape.
(E) A composite tape in which the paper tape made of kraft paper is bonded to one surface of the plastic tape, and the paper tape made of carbon paper is bonded to the other surface of the plastic tape.

Since the plastic tape and the composite tape of (D) or (E) are alternately laminated, the degree of freedom of the constituent material of the tape composed of the plastic tape alone is high. On the other hand, in the composite tape of (D) or (E), the plastic tape and the paper tape are bonded to each other, and it is easier to wind the insulating tape and the insulating layer is compared with the case where all the tapes are independently configured. Easy to configure. Assuming that the plastic tape and the composite tape of (D) or (E) are alternately laminated, the plastic tape is sandwiched between the paper tapes, and the flow path of the insulating oil can be satisfactorily secured.

(10) As an example of the solid cable of the present invention, the insulating oil is a medium-viscosity insulating oil having a viscosity at 60 ° C. of 10 mm ² / s or more and less than 500 mm ² / s.

The medium-viscosity insulating oil has higher fluidity than the high-viscosity insulating oil having a viscosity of 500 mm ² / s or more at 60 ° C. Therefore, the medium-viscosity insulating oil easily flows through the flow path composed of the paper tape and the oil gap, and voids are less likely to occur in the insulating layer. If the insulating oil has a medium viscosity, migration of the insulating oil in the insulating layer in the longitudinal direction of the solid cable due to gravity is unlikely to occur. This is because the medium-viscosity insulating oil has a considerable viscosity, though not as much as the high-viscosity insulating oil. Therefore, even when the laying path of the solid cable includes a slope, migration can be effectively suppressed. In particular, since there is a slope between the bottom of the water and the land, the solid cable can be suitably used for the bottom of the water cable.

As described above, the solid cable of the present invention is mainly characterized in that "the electrical resistivity of the plastic tape is equal to or less than the electrical resistivity of the insulating oil". On the other hand, in order to share the DC electric field in the insulating layer with the plastic tape, it is desired that the electrical resistivity of the plastic tape be as high as possible. Therefore, it is desired that the electrical resistivity of the insulating oil is as high as possible. Here, as an insulating oil having a high electrical resistivity, there are mineral oil, alkylbenzene-based oil, and the like, but they have a low viscosity. High-viscosity insulating oil is often composed of mineral oil or alkylbenzene-based oil mixed with paraffin-based or wax-based oil having low electrical resistivity. Paraffinic oil and the like are mixed in order to increase the viscosity. Therefore, many high-viscosity insulating oils do not have a high electrical resistivity, such as 10 ¹³ Ω · cm at 60 ° C. On the other hand, as a medium-viscosity insulating oil, there is a polybutene-based insulating oil. The polybutene-based insulating oil does not require mixing of the above paraffin-based oils, has a certain viscosity, and can satisfy the electrical resistivity of 10 ¹⁵ to ¹⁶ Ω · cm at 60 ° C. is there.

(11) As an example of the solid cable of the present invention, a metal sheath provided on the outer periphery of the insulating layer, an anticorrosion layer provided on the outer periphery of the metal sheath, between the metal sheath and the anticorrosion layer, and the anticorrosion. It is possible to include a reinforcing layer provided on at least one of the outer periphery of the layer. The constituent material of the reinforcing layer has a higher tensile strength than the constituent material of the metal sheath.

When the load of the solid cable is turned on, the insulating oil expands as the conductor temperature rises. When the insulating oil expands, the internal pressure of the insulating oil increases, and hoop stress acts on the metal sheath. The hoop stress is a stress that tries to break the metal sheath generated inside the metal sheath. By providing a reinforcing layer with high tensile strength on the outer circumference of the metal sheath, the sharing of the hoop stress can be transferred from the metal sheath to the reinforcing layer.

(12) The power transmission line of the present invention includes the solid cable of the present invention according to any one of (5) to (11) above, another cable connected in the longitudinal direction of the solid cable, and the solid. It includes a joint provided between the cable and the other cable. The joint stops the movement of the insulating oil along the longitudinal direction of the solid cable.

When the load of the solid cable is turned on, the insulating oil expands as the conductor temperature rises. When the insulating oil expands, the internal pressure of the insulating oil increases, and the insulating oil also moves in the longitudinal direction of the solid cable. By providing a joint having an oil stop function between the solid cable and another cable, it is possible to prevent the movement of the insulating oil along the longitudinal direction of the solid cable. That is, it is possible to prevent the transfer of insulating oil from the solid cable to another cable.

(13) As an example of the power transmission line of the present invention, the internal pressure of the insulating oil at the maximum operating temperature of the conductor is 5 MPa or less.

According to the above configuration, the internal pressure of the insulating oil when the load of the solid cable is turned on can be kept below the permissible value. That is, the hoop stress acting on the metal sheath in the insulating oil can be reduced to the allowable value or less. Further, by keeping the internal pressure of the insulating oil below the permissible value, the oil stop function of the joint can be maintained. That is, it is preferable to keep the internal pressure of the insulating oil in the joint at 5 MPa or less.

In a submerged cable in which the external pressure due to seawater or the like is applied to the solid cable, the expansion pressure of the insulating oil in the solid cable is canceled by the external pressure, and the external pressure is the insulating oil when the internal pressure drops due to the shrinkage of the insulating oil when the load is off. It is expected to compensate for the decrease in internal pressure. On the other hand, when the solid cable is laid on land, the effect of the above external pressure cannot be expected. Here, if the internal pressure of the insulating oil at the maximum operating temperature of the conductor is 5 MPa or less, excessive expansion or breakage of the metal sheath can be suppressed even when the solid cable is laid on land. When the internal pressure of the insulating oil at the maximum operating temperature of the conductor satisfies a positive pressure of 5 MPa or less, the state in which the insulating oil is impregnated over the entire insulating layer can be more reliably maintained.

(14) The method for manufacturing a solid cable of the present invention includes a step of wrapping an insulating tape around the outer periphery of a conductor to provide an insulating layer, a step of drying and degassing the insulating layer, and the insulation after drying and degassing. The layer includes a step of impregnating the layer with insulating oil and a step of providing a metal sheath on the outer periphery of the insulating layer impregnated with the insulating oil. The insulating tape includes a plastic tape containing a polyolefin resin and having an electrical resistivity equal to or lower than the electrical resistivity of the insulating oil, and a paper tape in contact with the plastic tape. The step of providing the metal sheath is performed at a temperature of 50% or more and 80% or less of the maximum operating temperature of the conductor.

By wrapping an insulating tape containing a polyolefin resin and having an electrical resistivity equal to or lower than the electrical resistivity of the insulating oil and a paper tape to provide an insulating layer, there is less starvation and voids. An insulating layer having excellent insulation performance can be formed. The metal sheath can be formed at room temperature, but in that case, the maximum operating temperature of the conductor can be about 50 ° C. unless the reinforcing layer is provided. If a high-strength reinforcing layer is provided, the maximum operating temperature of the conductor can be raised to 80 ° C., and the internal pressure of the insulating oil can be maintained at 5 MPa or less. On the other hand, by forming the metal sheath at a temperature of 50% or more and 80% or less of the maximum operating temperature of the conductor, the conductor regardless of the presence or absence of the reinforcing layer as compared with the case where the metal sheath is provided at room temperature. The maximum operating temperature can be raised to 80 ° C. Further, as compared with the case where the metal sheath is provided at room temperature, the internal pressure of the insulating oil when the insulating oil expands when the load of the solid cable is turned on can be reduced. If the internal pressure of the insulating oil when the load is turned on can be reduced, the hoop stress acting on the metal sheath in the insulating oil can be reduced, the reinforcing layer can be simplified, and the reinforcing layer can be omitted. In particular, when an external pressure acts on the cable in a laying environment such as a water bottom cable, the reinforcing layer can be omitted. In addition, the movement of the solid cable in the insulating oil in the longitudinal direction can be reduced, and the oil pressure applied to the joint can be sufficiently reduced, so that the oil stop function can be simplified. Moreover, since the internal pressure of the insulating oil becomes a positive pressure when the load is turned on, the effect of infiltrating the insulating oil evenly into the insulating layer can be maintained.

In the solid cable obtained by the above manufacturing method, the internal pressure of the insulating oil when the load is off may become a negative pressure. As described above, the insulating layer in the solid cable of the present invention has sufficiently high DC withstand voltage characteristics, can prevent heat generation due to leakage current when the load is off, and can suppress dielectric breakdown. On the other hand, when the load is turned on, the insulating oil is refilled over the entire area in the insulating layer of the solid cable, so that the long-term uniformity of the dielectric strength is maintained.

(15) As an example of the method for manufacturing a solid cable of the present invention, the maximum operating temperature of the conductor is 65 ° C. or higher.

When the maximum operating temperature of the conductor is 65 ° C. or higher, a solid cable having a large transmission capacity can be obtained. When the maximum operating temperature of the conductor is high, the internal pressure of the insulating oil when expanded at that temperature increases. Even in that case, in the solid cable manufacturing method of the present invention, the internal pressure of the insulating oil when the insulating oil expands when the load is turned on can be reduced as compared with the case where the metal sheath is provided at room temperature.

[Details of Embodiments of the present invention]
Details of the embodiments of the present invention will be described below with reference to the drawings. It should be noted that the present invention is not limited to these examples, and is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

≪Solid cable≫
In the solid cable 10 of the embodiment, as described above with reference to FIG. 1, the conductor 11, the inner semi-conductive layer 12, the insulating layer 13, the outer semi-conductive layer 14, the metal sheath 15, and the anticorrosion layer 16 are arranged in this order from the center. To be equipped. When the solid cable 10 is a submerged cable, a metal tape, a protective yarn layer, an exterior wire, or the like is generally provided on the outside of the anticorrosion layer 16. In FIG. 1, a member provided outside the anticorrosion layer 16 is not shown. As shown in FIG. 2, the insulating layer 13 is formed by winding an insulating tape 20 and is impregnated with an insulating oil 40. The insulating tape 20 is gap-wound so that an oil gap 30 is provided between adjacent turns. The oil gap 30 is a part of the flow path of the insulating oil 40 (FIG. 2). The insulating tape 20 includes a plastic tape 21 and a paper tape 22. One of the features of the solid cable 10 of the embodiment is that the electrical resistivity of the plastic tape 21 is equal to or less than the electrical resistivity of the insulating oil 40. One of the features of the solid cable 10 of this example is that the electrical resistivity of the paper tape 22 is smaller than the electrical resistivity of the plastic tape 21. That is, one of the features of the solid cable 10 of this example is that it satisfies the relationship of "electrical resistivity of insulating oil 40 ≥ electrical resistivity of plastic tape 21> electrical resistivity of paper tape 22". As a configuration other than the insulating tape 20 constituting the insulating layer 13, the prior art can be appropriately used. Hereinafter, the insulating tape 20 will be mainly described in detail.

[Insulating tape]
The insulating tape 20 is configured such that the paper tape 22 is in contact with at least one surface of the plastic tape 21.

(Plastic tape)
The plastic tape 21 contains a polyolefin-based resin. Examples of the polyolefin-based resin include polypropylene, polyethylene, ethylene-propylene copolymer, and polybutene. In particular, polypropylene has excellent electrical properties and a high melting point, and can be used up to a relatively high temperature. Therefore, polypropylene can be suitably used as a constituent material of the plastic tape 21.

The plastic tape 21 has an electrical resistivity equal to or less than the electrical resistivity of the insulating oil 40. Here, the electrical resistivity of the insulating oil 40 used for the solid cable 10 is 10 ¹⁵ to ¹⁶ Ω · cm at 60 ° C. Therefore, the electrical resistivity of the plastic tape 21 is 10 ¹⁵ Ω · cm or less at 60 ° C. The electrical resistivity of the insulating oil 40 and the plastic tape 21 decreases as the temperature increases. At any temperature, the relationship of "electric resistivity of insulating oil 40 ≥ electrical resistivity of plastic tape 21> electrical resistivity of paper tape 22" is satisfied.

The plastic tape 21 bears the withstand voltage of DC in the insulating layer 13. Therefore, the electrical resistivity of the plastic tape 21 is larger than the electrical resistivity of the paper tape 22. The electrical resistivity of the plastic tape 21 is preferably 10 ¹⁴ Ω · cm or more at 60 ° C.

(Paper tape)
The paper tape 22 may be made of kraft paper or carbon paper. The paper tape 22 has a large number of through holes. The insulating oil 40 passes through the through hole of the paper tape 22 and is impregnated in the through hole. That is, the through hole of the paper tape 22 is a part of the flow path of the insulating oil 40.

The electrical resistivity of the paper tape 22 is smaller than the electrical resistivity of the plastic tape 21. In other words, the electrical resistivity of the plastic tape 21 is larger than the electrical resistivity of the paper tape 22. Therefore, the distribution of the DC electric field applied to the insulating layer 13 can be performed by the plastic tape 21 having no through hole. In order for the plastic tape 21 to share the DC electric field, the electrical resistivity of the paper tape 22 may be smaller than the electrical resistivity of the plastic tape 21, and the lower limit thereof is not limited. Therefore, when kraft paper is used, the conventional purification, that is, purification of pulp, deionization, improvement of beating degree, etc., is not performed, and the diversion of paper for ordinary paper can be mentioned. Mixing carbon particles with pulp is another way to ensure that the electrical resistivity of kraft paper is reduced. The paper tape 22, the electrical resistivity may also be mentioned diversion of carbon paper is about ¹⁰ 2 ^{~10 5 Ω} · cm.

(Arrangement form)
As the insulating tape 20, a composite tape in which paper tape 22 is bonded to at least one surface of the plastic tape 21 may be used. For example, as shown in FIG. 2, the insulating tape 20 is a composite tape in which paper tapes 22 are bonded to both sides of the plastic tape 21. Hereinafter, this composite tape will be referred to as a double-sided composite tape. The paper tape 22 in the double-sided composite tape may be a tape made of both kraft paper or a tape made of carbon paper. Alternatively, one of the paper tapes 22 may be a tape made of kraft paper, and the other may be a tape made of carbon paper. In any case, the insulating tape 20 is configured by sandwiching the plastic tape 21 with the porous paper tape 22.

As shown in FIG. 7A, the insulating tape 20 is a composite tape in which a paper tape 22 is bonded to one surface of a plastic tape 21. Hereinafter, this composite tape will be referred to as a single-sided composite tape. The paper tape 22 in the single-sided composite tape is a tape made of kraft paper or carbon paper. In this case, the other surface of the plastic tape 21 is exposed. Since the insulating tape 20 is wound to form the insulating layer 13, the paper tape 22 comes into contact with the other surface of the plastic tape 21 by winding the insulating tape 20.

As shown in FIG. 7B, the insulating tape 20 may be composed of the plastic tape 21 and the paper tape 22 independently of each other. Even if the plastic tape 21 and the paper tape 22 are configured independently of each other, the plastic tape 21 and the paper tape 22 come into contact with each other by alternately laminating and winding the plastic tape 21 and the paper tape 22. Hereinafter, a form in which plastic tapes 21 and paper tapes 22 that are independently formed of each other are alternately laminated is referred to as an independent laminated type.

As shown in FIG. 7C, the insulating tape 20 may be configured by combining the plastic tape 21 and the double-sided composite tape 20A. Even if the plastic tape 21 and the double-sided composite tape 20A are independently combined with each other, the plastic tape 21 and the paper tape 22 in the double-sided composite tape 20A are in contact with each other. Hereinafter, a form in which the plastic tapes 21 formed independently of each other and the double-sided composite tape 20A are alternately laminated is referred to as a composite laminated type.

Although not shown, the insulating tape 20 may be configured by combining the single-sided composite tape and the double-sided composite tape. Even if the single-sided composite tape and the double-sided composite tape are independently combined with each other, the plastic tape in the single-sided composite tape and the paper tape in the double-sided composite tape are in contact with each other. Hereinafter, a form in which the single-sided composite tape and the double-sided composite tape, which are configured independently of each other, are alternately laminated is referred to as a mixed lamination type.

The insulating layer 13 is formed by winding at least one of the double-sided composite tape, the single-sided composite tape, and the tape group composed of each of the laminated types. The insulating layer 13 may be composed of a double-sided composite tape, a single-sided composite tape, and a tape group composed of the above-mentioned laminated types in a mixed manner. Regardless of which insulating tape 20 is used, the plastic tape 21 and the paper tape 22 are in contact with each other in the insulating layer 13. The insulating tape 20 is gap-wound so that an oil gap 30 is provided between adjacent turns. The insulating oil 40 moves through the paper tape 22 and the oil gap 30 as a flow path. The cross-hatching in FIGS. 2, 7A, 7B, and 7C shows an example of the flow path of the insulating oil 40. In each figure, for convenience of explanation, only a part of the flow path of the insulating oil 40 is shown, but originally, the insulating oil 40 flows over the entire paper tape 22 and the entire oil gap 30.

(ratio)
The ratio of the thickness of the plastic tape 21 to the total thickness of the insulating tape 20 is preferably 40% or more and less than 90%. When the insulating tape 20 is the double-sided composite tape, the insulating tape 20 is composed of one plastic tape 21 and two paper tapes 22. In this case, the ratio of the thickness is the ratio of the thickness of one plastic tape 21 to the total thickness of one plastic tape 21 and two paper tapes 22. When the insulating tape 20 is the single-sided composite tape, the insulating tape 20 is composed of one plastic tape 21 and one paper tape 22. In this case, the ratio of the thickness is the ratio of the thickness of one plastic tape 21 to the total thickness of one plastic tape 21 and one paper tape 22.

When the insulating tape 20 is composed of a laminated tape group, the ratio of the thickness of the plastic tape 21 to the thickness of the entire tape group is preferably 40% or more and less than 90%. The tape group here refers to two tapes of the insulating tapes 20 constituting the insulating layer 13 which are laminated next to each other. When the insulating tape 20 is composed of the independent laminated tape group, the tape group is composed of one plastic tape 21 and one paper tape 22. Therefore, the ratio of the thickness is the ratio of the thickness of one plastic tape 21 to the total thickness of one plastic tape 21 and one paper tape 22. When the insulating tape 20 is composed of the composite laminated tape group, the tape group is composed of two plastic tapes 21 and two paper tapes 22. Therefore, the ratio of the thickness is the ratio of the thickness of the two plastic tapes 21 to the total thickness of the two plastic tapes 21 and the two paper tapes 22. When the insulating tape 20 is composed of the composite laminated tape group, the thickness of the tape composed of the plastic tape 21 alone is thick even if the electrical resistivity of the plastic tape 21 is slightly lowered within the range of having high dielectric strength. The dielectric strength can be maintained by increasing. Here, if the ratio of the thickness of the plastic tape 21 increases, the ratio of the thickness of the paper tape 22 that serves as the flow path of the insulating oil 40 decreases, and the movement of the insulating oil 40 may become difficult. However, by applying a medium-viscosity insulating oil that easily flows as the insulating oil 40, the movement of the insulating oil 40 can be improved.

When the thickness ratio is 40% or more, the volume of the plastic tape 21 can be increased, and the insulating layer 13 having high DC withstand voltage characteristics can be obtained. On the other hand, when the ratio of the thickness is less than 90%, the ratio of the paper tape 22 can be relatively increased, and the flow path of the insulating oil 40 can be satisfactorily secured. The thickness ratio is more preferably 60% or more and less than 80%, particularly preferably 70% or more and less than 80%.

[Action due to the relationship between the electrical resistivity of plastic tape and insulating oil]
The electrical resistivity of the plastic tape 21 is equal to or less than the electrical resistivity of the insulating oil 40. The phenomenon caused by satisfying the relationship of the electrical resistivity will be described with reference to FIG.

In the solid cable 10 having a high operating temperature and a high voltage, voids may occur in the oil gap 30 in the insulating layer 13 as described above. Further, in the high voltage solid cable 10, leakage current tends to flow in the insulating layer 13. Here, consider a case where a void is generated with the insulating oil 40 remaining in the oil gap 30. At this time, if the electrical resistivity of the plastic tape 21 is larger than the electrical resistivity of the insulating oil 40, the leakage current is concentrated on the remaining insulating oil 40 in the oil gap 30 having a small electrical resistivity while avoiding voids. (See FIG. 4C). On the other hand, in the present invention, since the electrical resistivity of the plastic tape 21 is equal to or less than the electrical resistivity of the insulating oil 40, the leakage current is a plastic having a small electrical resistivity while avoiding voids as shown in FIG. It flows on the tape 21. That is, since the leakage current flows through the plastic tape 21 that constitutes most of the insulating layer 13, the leakage current does not concentrate in the local region of the insulating layer 13. Therefore, in the present invention, even if a void is generated in the insulating layer 13, it is possible to prevent discharge and follow-flow from being generated in the void, and it is possible to prevent abnormal heat generation. Therefore, in the present invention, abnormal heat generation due to leakage current can be prevented, and dielectric breakdown can be suppressed.

≪Manufacturing method of solid cable≫
The solid cable manufacturing method includes a step of providing an insulating layer, a step of drying and degassing the insulating layer, a step of impregnating the insulating layer after drying and degassing with insulating oil, and a step of providing a metal sheath. Be prepared. Hereinafter, each step will be described. In the manufacturing process of the constituent members other than the insulating layer 13, the insulating oil 40, and the metal sheath 15 in the solid cable 10, the prior art can be appropriately used. Therefore, in the following description, the manufacturing process of the insulating layer 13, the insulating oil 40, and the metal sheath 15 will be mainly described in detail.

[Step of providing an insulating layer]
In the step of providing the insulating layer, the insulating tape 20 is wound around the outer circumference of the conductor 11 to form the insulating layer 13. The insulating tape 20 is wound with a gap so that an oil gap 30 is provided between adjacent turns.

As the insulating tape 20, the above-mentioned insulating tape 20 is used. The plastic tape 21 in the insulating table 20 has a small electrical resistivity. As a method for reducing the electrical resistivity of the plastic tape 21, for example, a paraffin-based substance or a wax-based substance, which is an oil-based chemical substance, or carbon particles may be mixed. Specifically, in the process of manufacturing the plastic tape 21, the paraffin-based substance, the wax-based substance, or carbon particles may be mixed with the pellets of the polyolefin-based resin and melt-extruded. In addition, in the process of manufacturing the plastic tape 21, when the polyolefin resin is melt-extruded, the paraffin-based substance, the wax-based substance, or the carbon particles are thrown in at the inlet of the extruder and melt-extruded together. Can be mentioned. The content of additives such as wax-based substances in the constituent materials of the plastic tape 21 can be appropriately selected so that the electrical resistivity of the plastic tape 21 is equal to or less than the electrical resistivity of the insulating oil 40.

When a stand-alone tape is used as the insulating tape 20, as shown in FIG. 7B, the tapes 21 and 22 are wound so that the plastic tape 21 and the paper tape 22 are alternately laminated. When a laminated tape is used as the insulating tape 20, as shown in FIG. 7C, the tapes 21 and 20A are wound so that the plastic tape 21 and the double-sided composite tape 20A are alternately laminated.

[Process of drying and degassing the insulating layer]
In the step of drying and degassing the insulating layer 13, air and moisture in the insulating layer 13 are removed. Specifically, the core provided with the insulating layer 13 on the outer circumference of the conductor 11 is wound around a drying tank and evacuated by heating to remove air and moisture in the insulating layer 13. Known conditions can be appropriately used for the temperature and the degree of vacuum in the drying tank in this step.

[Process of impregnating insulating oil]
In the step of impregnating the insulating oil, the insulating layer 13 after drying and deaeration is impregnated with the insulating oil 40 to form the oil-immersed insulating layer 13. After the drying and deaeration are completed, the insulating oil which has been heated and appropriately reduced in viscosity is injected into the tank, and a predetermined pressure is applied for a predetermined time to allow the insulating oil to permeate the insulating layer 13. The core is then cooled to room temperature. At the time of this cooling, a predetermined pressurization is performed and a predetermined temperature lowering rate is maintained. This is because the insulating oil 40 shrinks as the temperature drops from the maximum temperature at the time of impregnation to room temperature, and the insulating layer 13 is impregnated with the insulating oil 40 without forming voids due to the shrinkage.

The electrical resistivity of the insulating oil 40 is desired to be as high as possible. In order to improve the electrical resistivity of the insulating oil 40, as described above, it is better not to mix a thickener having a low electrical resistivity. Therefore, the insulating oil 40 is not the high-viscosity insulating oil often used for conventional solid cables, but has a viscosity at 60 ° C. of 10 mm ² / s (10 × ^10-6 m ² / s, 10 cSt) or more and 500 mm ² It is preferable to use a medium-viscosity insulating oil of less than / s (500 × ^10-6 m ² / s, 500 cSt). Since it is a medium-viscosity insulating oil, the insulating layer 13 can be easily impregnated with the insulating oil 40 even when pressed at a low temperature. In particular, even when the ratio of the thickness of the plastic tape 21 is large and the ratio of the thickness of the paper tape 22 serving as the flow path of the insulating oil 40 is small, the insulating oil 40 is easily impregnated. In addition, the medium-viscosity insulating oil facilitates circulation through the flow path composed of the paper tape 22 and the oil gap 30 during the operation of the obtained solid cable 10, and suppresses the generation of voids in the insulating layer 13. Easy to do. The insulating oil 40 may be a high-viscosity insulating oil having a viscosity at 60 ° C. of 500 mm ² / s or more. The electrical resistivity of the insulating oil 40 is 10 ¹⁵ to ¹⁶ Ω · cm at 60 ° C. Examples of such insulating oil 40 include polybutene oil (manufactured by Nippon Oil Co., Ltd., Nisseki polybutene oil HV-15, etc.). Polybutene-based insulating oil is composed of a single molecule and can stably obtain high electrical resistivity. When the plastic tape 21 made of polypropylene or the like comes into contact with the high-temperature insulating oil 40, it may swell due to the insulating oil 40 depending on the type of the insulating oil 40. In the case of a polybutene-based insulating oil, the swelling effect of the plastic tape 21 is extremely small, so that it can be suitably used as the insulating oil 40 of the present invention.

[Process of providing metal sheath]
In the step of providing the metal sheath, the metal sheath 15 is provided on the outer periphery of the insulating layer 13 impregnated with the insulating oil 40. The metal sheath 15 is made of lead or a lead alloy. The metal sheath 15 is provided by a melt extrusion coating of metal. In the prior art, the temperature at which the metal sheath 15 is provided is generally room temperature. The temperature at which the metal sheath 15 is provided here is the temperature of the cable core when the metal sheath 15 is provided. When the high-viscosity insulating oil 40 is used, the mobility of the insulating oil 40 in the insulating layer 13 is low, and starvation due to a large temperature drop when the load is off cannot be avoided. Therefore, the maximum operating temperature of the conductor 11 is about 55. Limited to ° C. Further, when the maximum operating temperature of the conductor 11 is raised to 80 to 85 ° C., the internal pressure of the insulating oil 40 becomes too large, which causes a problem that the metal sheath 15 is damaged. Therefore, when the metal sheath 15 is provided, the conventional extrusion coating at room temperature can be applied, but it may be performed at a temperature of 50% or more and 80% or less of the maximum operating temperature of the conductor 11 during operation of the solid cable 10. preferable. Hereinafter, in the temperature at which the metal sheath 15 is provided, a temperature of 50% or more and 80% or less of the maximum operating temperature of the conductor 11 during operation of the solid cable 10 is referred to as a manufacturing temperature. By providing the metal sheath 15 at the manufacturing temperature, the insulating layer 13 in the metal sheath 15 can be maintained at a positive pressure at a temperature equal to or higher than the manufacturing temperature and lower than the maximum operating temperature of the conductor 11, and the insulating oil 40 is insulated. The effect of evenly infiltrating the layer 13 can be maintained. The manufacturing temperature is, for example, 40 ° C. or higher and 75 ° C. or lower, further 50 ° C. or higher and 75 ° C. or lower, particularly 60 ° C. or higher and 70 ° C. or lower.

When the load is turned on, the insulating oil 40 expands depending on the temperature of the conductor 11. The expansion of the insulating oil 40 increases the internal pressure of the insulating oil 40. The internal pressure of the insulating oil 40 depends on the difference between the manufacturing temperature when the metal sheath 15 is provided and the maximum operating temperature of the conductor 11. When the manufacturing temperature is high, the difference from the maximum operating temperature of the conductor 11 is small, the expansion amount of the insulating oil 40 can be reduced, and the internal pressure of the insulating oil 40 can be reduced. If the internal pressure of the insulating oil 40 when the load is turned on can be reduced, the hoop stress acting on the metal sheath 15 in the insulating oil 40 can be reduced, and the movement of the solid cable 10 in the insulating oil 40 in the longitudinal direction can be reduced. That is, since the internal pressure of the insulating oil 40 when the load is turned on can be reduced, the maximum operating temperature of the conductor 11 when the load is turned on can be set high. The internal pressure of the insulating oil 40 when the load is turned on may be 5 MPa or less, further 3 MPa or less, particularly 1 MPa or less, depending on the manufacturing temperature, the presence / absence of the reinforcing layer 17, and its position.

Since the insulating layer 13 in the metal sheath 15 has a positive pressure at a temperature equal to or higher than the manufacturing temperature and lower than the maximum operating temperature of the conductor 11, the dielectric strength does not deteriorate. This is because even if the insulating layer 13 is starved and voids are generated in a temperature range lower than the manufacturing temperature, the insulating oil 40 always fills the voids when the load is turned on. In particular, in a water bottom cable in which an external pressure due to seawater or the like is applied to the solid cable 10, the solid cable 10 can be designed so that the insulating layer 13 can be prevented from becoming a negative pressure even if the temperature is lower than the manufacturing temperature.

When the solid cable 10 is in operation, if the temperature of the insulating layer 13 is lower than the manufacturing temperature and the external pressure of seawater or the like cannot be expected, the insulating layer 13 may have a negative pressure. The insulating layer 13 becomes negative pressure between normal temperature and the above-mentioned manufacturing temperature when the load is turned on, and between the temperature above the manufacturing temperature and the normal temperature when the load is turned off. In the former case, even if the oil gap 30 has voids from the initial stage of temperature rise, the leakage current avoids the voids and flows in a region where the electrical resistivity is small. Therefore, in the former case, dielectric breakdown does not occur. On the other hand, in the latter case, even if a void is generated in the oil gap 30 in the process of lowering the temperature, a large amount of leakage current is distributed to the insulating tape 20 including the plastic tape 21 having a small electrical resistivity. The insulating tape 20 constitutes most of the insulating layer 13. Therefore, in the latter case, the leakage current can be suppressed from flowing intensively to the insulating oil 40 remaining in the oil gap 30, so that dielectric breakdown does not occur.

From the above, by providing the metal sheath 15 at the manufacturing temperature, the internal pressure of the insulating oil 40 when the load is turned on can be reduced, and the maximum operating temperature of the conductor 11 when the load is turned on can be set high. The maximum operating temperature of the conductor is 65 ° C. or higher, further 70 ° C. or higher, particularly 75 ° C. or higher, 80 ° C. or higher.

≪Others≫
As shown in FIG. 8, the solid cable 10 includes a reinforcing layer 17. The reinforcing layer 17 is provided between the metal sheath 15 and the anticorrosion layer 16 and at least one of the outer circumferences of the anticorrosion layer 16. In this example, a reinforcing layer 17 is provided between the metal sheath 15 and the anticorrosion layer 16.

When the load of the solid cable 10 is turned on, the insulating oil 40 expands as the temperature of the conductor 11 rises. When the insulating oil 40 expands, the internal pressure of the insulating oil 40 increases, and hoop stress acts on the metal sheath 15. By providing the reinforcing layer 17 on the outer periphery of the metal sheath 15, most of the hoop stress can be shared. Therefore, it is preferable to provide the reinforcing layer 17 especially when the internal pressure of the insulating oil 40 when the load is turned on is as high as 5 MPa or more. The constituent material of the reinforcing layer 17 has a higher tensile strength than the constituent material of the metal sheath 15. As the constituent material of the reinforcing layer 17, for example, a metal tape such as stainless steel, an aramid fiber tape, or the like can be preferably used.

The reinforcing layer 17 can also be arranged on the outer periphery of the anticorrosion layer 16. In this case, the anticorrosion layer 16 has a cushioning effect by slightly shrinking due to the internal pressure of the insulating oil 40. Therefore, it is suitable when the internal pressure of the insulating oil 40 when the load is turned on is as low as 3 MPa and further 1 MPa or less. According to this configuration, the formation of the metal sheath 15 and the anticorrosion layer 16 by extrusion processing can be tandem processed in the same process, and the productivity can be improved. The position and strength of the reinforcing layer 17 are preferably designed appropriately according to the power transmission capacity, but the internal pressure of the insulating oil 40 when the load is turned on can also be designed according to the manufacturing temperature.

≪Power transmission line≫
When the load of the solid cable 10 is turned on, the insulating oil 40 expands as the temperature of the conductor 11 rises. When the insulating oil 40 expands, the internal pressure of the insulating oil 40 increases, and the insulating oil 40 also moves in the longitudinal direction of the solid cable 10. Therefore, as shown in FIG. 9, it is preferable that the power transmission line 100 is provided with a joint 130 having an oil stop function between the solid cable 10 and another cable connected in the longitudinal direction of the solid cable 10. The solid cable 10 of this example is a submarine cable 110, and the other cable connected in the longitudinal direction of the solid cable 10 is a land cable 120. The joint 130 stops the movement of the insulating oil 40 along the longitudinal direction of the solid cable 10. That is, the movement of the insulating oil 40 is limited to the section between the adjacent joints 130. The type of land cable 120 does not matter. The land cable 120 may be the same solid cable as the submarine cable 110, a solid cable having a different insulating layer or insulating oil constituent material, or a different type of cable such as an OF cable or a CV cable. When connecting dissimilar cables, a transition joint is used as the joint 130.

The power transmission line 100 preferably further includes a refueling tank 140 capable of replenishing the solid cable 10 with insulating oil 40. The refueling tank 140 is provided to stabilize the electrical characteristics of the joint 130. The refueling tank 140 is connected to the solid cable 10 side of the joint 130 via a refueling pipe 150. In this case, it is preferable to provide a check valve (not shown) between the joint 130 and the oil tank 140 so that the expanded insulating oil 40 in the solid cable 10 when the load is turned on does not flow back into the oil tank 140.

Further, the power transmission line 100 preferably includes a measuring unit 160 for measuring the internal pressure of the insulating oil 40 in the solid cable 10. The measuring unit 160 can measure the internal pressure of the expanded insulating oil 40 in the solid cable 10 when the load is turned on.

≪Effect≫
The insulating layer 13 in the solid cable 10 of the above-described embodiment has high DC withstand voltage characteristics, and can prevent heat generation due to leakage current starting from the negative pressure insulating oil 40 generated when the load is off, and can suppress dielectric breakdown. .. This is because the plastic tape 21 that constitutes most of the insulating layer 13 contains a polyolefin resin and has an electrical resistivity equal to or less than the electrical resistivity of the insulating oil 40. In the solid cable 10 having a high operating temperature and a high voltage, voids may occur in the oil gap 30 in the insulating layer 13. Further, in the high voltage solid cable 10, leakage current tends to flow in the insulating layer 13. In the solid cable 10 of the above-described embodiment, leakage current can be passed through the plastic tape 21. Therefore, even if a void is generated with the insulating oil 40 remaining in the oil gap 30, it is possible to suppress the concentration of the leakage current in the remaining insulating oil 40 in the oil gap 30, and the discharge continues in the insulating layer 13. It is possible to suppress the generation of current.

The DC electric field generated in the insulating layer 13 is shared by both the plastic tape 21 and the paper tape 22. At this time, since the electrical resistivity of the paper tape 22 is smaller than the electrical resistivity of the plastic tape 21, the ratio of the DC electric field shared by the paper tape 22 which is porous and inferior in DC withstand voltage characteristics can be reduced. Preferably, the proportion of the DC electric field can be reduced to a extent that is substantially negligible. In the present invention, by lowering the electrical resistivity of the plastic tape 21, the withstand voltage characteristic of the plastic tape 21 is slightly lowered. Therefore, by setting the ratio of the thickness of the plastic tape 21 to the total thickness of the insulating tape 20 to 40% or more and less than 90%, it is possible to compensate for the decrease in the withstand voltage of the plastic tape 21 due to the lowering of the electrical resistivity. Can be done. As a result, the ratio of the DC electric field shared by the plastic tape 21 can be increased, the DC electric field can be applied up to the high dielectric strength of the plastic tape 21, and the insulating layer 13 having a high withstand voltage characteristic can be easily formed. Therefore, the DC solid cable can be increased in high voltage and large capacity.

In constructing the solid cable 10 of the above-described embodiment, the insulating tape 20 having an electrical resistivity of the plastic tape 21 of 10 ¹⁵ Ω · cm or less at 60 ° C. can be preferably used.

[Additional Notes]
Further, the following additional notes will be disclosed in relation to the embodiments of the present invention described above.

[Appendix 1]
The process of wrapping an insulating tape around the outer circumference of a conductor to provide an insulating layer,
The step of drying and degassing the insulating layer and
The step of impregnating the insulating layer with insulating oil after drying and degassing, and
A step of providing a metal sheath on the outer periphery of the insulating layer impregnated with the insulating oil is provided.
The insulating tape is
Plastic tape containing polyolefin resin and
A paper tape in contact with the plastic tape is provided.
The step of providing the metal sheath is a method for manufacturing a solid cable performed at a temperature of 40 ° C. or higher and 75 ° C. or lower.

[Appendix 2]
The process of wrapping an insulating tape around the outer circumference of a conductor to provide an insulating layer,
The step of drying and degassing the insulating layer and
The step of impregnating the insulating layer with insulating oil after drying and degassing, and
A step of providing a metal sheath on the outer periphery of the insulating layer impregnated with the insulating oil is provided.
The insulating tape is
Plastic tape containing polyolefin resin and
A paper tape in contact with the plastic tape is provided.
The step of providing the metal sheath is a method for manufacturing a solid cable performed at a temperature of 50% or more and 80% or less of the maximum operating temperature of the conductor.

According to the solid cable manufacturing method described in Appendix 1 and Appendix 2, the internal pressure of the insulating oil when the insulating oil expands when the load of the solid cable is turned on is smaller than that in the case where the metal sheath is provided at room temperature. it can. In particular, according to the solid cable manufacturing method described in Appendix 1, the above effect can be obtained regardless of the maximum operating temperature of the conductor. If the internal pressure of the insulating oil when the load is turned on can be reduced, the hoop stress acting on the metal sheath in the insulating oil can be reduced. Therefore, the configuration does not use the reinforcing layer. By reducing the internal pressure of the insulating oil when the load is turned on, it is possible to reduce the movement of the solid cable in the insulating oil in the longitudinal direction. By reducing the internal pressure of the insulating oil when the load is on, the maximum operating temperature of the conductor 11 of the solid cable when the load is on can be raised from, for example, the conventional 55 ° C. to 80 to 90 ° C., and the power transmission capacity can be increased. ..

10 Solid cable 11 Conductor, 12 Internal semi-conductive layer, 13 Insulation layer, 14 External semi-conductive layer,
15 Metal sheath, 16 Anticorrosion layer, 17 Reinforcing layer 20 Insulation tape 20A Double-sided composite tape 21 Plastic tape, 22 Paper tape 30 Oil gap 40 Insulation oil 100 Transmission line 110 Submarine cable, 120 Land cable 130 Joint 140 Refueling tank, 150 Refueling pipe 160 Measuring unit

Claims (11)

With the conductor
An insulating layer provided on the outer circumference of the conductor and
A solid cable including an insulating oil impregnated in the insulating layer.
The insulating layer is formed by wrapping an insulating tape around the insulating layer.
The insulating tape is
Plastic tape containing polyolefin resin and
A paper tape arranged to face the plastic tape is provided.
A solid cable in which the electrical resistivity of the plastic tape is equal to or less than the electrical resistivity of the insulating oil. The paper electrical resistivity of the tape, solid cable according to small claim 1 than the electrical resistivity of the plastic tape. The solid cable according to claim 1 or 2 , wherein at least a part of the insulating layer is formed by winding a composite tape in which the plastic tape and the paper tape are bonded . Wherein at least a portion of the insulating layer, solid cable according to any one of claims 1 to 3, wherein the plastic tape and said paper tape is configured by alternately stacking. Any one of claims 1 to 4 , wherein at least a part of the insulating layer is formed by alternately laminating the plastic tape and the composite tape according to any one of the following (D) or (E). The solid cable described in item 1.
(D) A composite tape in which the paper tape made of kraft paper or carbon paper is bonded to both sides of the plastic tape.
(E) A composite tape in which the paper tape made of kraft paper is bonded to one surface of the plastic tape, and the paper tape made of carbon paper is bonded to the other surface of the plastic tape. The insulating oil, solid cable according to any one of claims 5 a viscosity at 60 ° C. claim 1 having a viscosity insulating oil in the less than 10 mm ² / s or more 500 mm ² / s. A metal sheath provided on the outer circumference of the insulating layer and
An anticorrosion layer provided on the outer circumference of the metal sheath and
A reinforcing layer provided between the metal sheath and the anticorrosion layer and on at least one of the outer circumferences of the anticorrosion layer is provided.
The constituent material of the reinforcing layer, solid cable according to any one of claims 1 to 6 having a higher tensile strength than the material of the metal sheath. The solid cable according to any one of claims 1 to 7 .
With other cables connected in the longitudinal direction of the solid cable,
A joint provided between the solid cable and the other cable is provided.
The joint is a power transmission line that stops the movement of the insulating oil along the longitudinal direction of the solid cable. The power transmission line according to claim 8 , wherein the internal pressure of the insulating oil at the maximum operating temperature of the conductor is 5 MPa or less. The process of wrapping an insulating tape around the outer circumference of a conductor to provide an insulating layer,
The step of drying and degassing the insulating layer and
The step of impregnating the insulating layer with insulating oil after drying and degassing, and
A step of providing a metal sheath on the outer periphery of the insulating layer impregnated with the insulating oil is provided.
The insulating tape is
A plastic tape containing a polyolefin resin and having an electrical resistivity equal to or lower than the electrical resistivity of the insulating oil.
A paper tape in contact with the plastic tape is provided.
The step of providing the metal sheath is a method for manufacturing a solid cable performed at a temperature of 50% or more and 80% or less of the maximum operating temperature of the conductor. The method for manufacturing a solid cable according to claim 10 , wherein the maximum operating temperature of the conductor is 65 ° C. or higher.

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