JPH0552004B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF THE INVENTION This invention relates to an improvement in the structure of a power cable with a corrugated water layer, in which a corrugated water layer is provided between an insulating layer and a sheath. Description of the Prior Art FIG. 1 is a sectional view showing an example of a conventional power cable with a water layer. Here, a conductor 1, an insulating layer 2, a shielding layer 3, a percolating layer 4, and a sheath 5 are provided in this order from the center toward the outside. The shielding layer 4 is provided to prevent insulation deterioration due to water intrusion, and is usually made of a shielding tape with a laminated structure in which metal foil is sandwiched between plastic films. Served vertically or spirally wrapped. On the other hand, FIG. 2 is a sectional view showing another example of a conventional power cable with a water layer, in which the water tape constituting the water layer 4 is placed on the outer periphery of the insulating layer 2. It is provided vertically or spirally wound. By the way, in the conventional power cable with a damp water layer as shown in FIGS. 1 and 2, the metal foil material of the damp water tape constituting the damp water layer 4 is aluminum, lead, antimony, or Lead alloys each containing several percent by weight of tin have been used, but they have had the following problems. In other words, the insulation layer 2 of the power cable with a water layer
is usually made of rubber or resin material, but has a large coefficient of thermal expansion due to heat, so the outer diameter of the insulating layer 2 changes by about 1 to 3% as a result of thermal expansion and contraction due to energization. Accordingly, the shielding tape provided outside the insulating layer 2 will also be subjected to 1 to 3% strain. However, in power cables, energization and de-energization are repeated over long periods of time, so shiyamizu tape is used for long periods of time.
Subjected to 3% cyclic strain. However, while the rubber or plastic film layer that makes up Shiyazu Tape has elasticity, the metal foil made of the metal material mentioned above has extremely low elasticity.
It has the disadvantage that it becomes fatigued and cracks after being repeated several thousand times, and as a result, it loses its effectiveness as a water tape. In order to eliminate the above drawbacks, a superplastic alloy with a breaking elongation of 50% or more in the temperature range of 20 to 100°C is used as the metal foil between the insulator and the sheath. A power cable with a layered water layer has been proposed by the applicant in Japanese Patent Application Laid-Open No. 58-26412. A superplastic alloy is generally considered to be an alloy in which deformation occurs due to grain boundary sliding of fine crystal grains, and the deformation is only plastic deformation. In other words, once it is deformed, it cannot return to its original state. Therefore, thermal expansion
When subjected to repeated strain due to thermal contraction, fatigue rupture occurs due to accumulation of dislocations due to deformation. For this reason, the fatigue resistance against repeated strain has not necessarily been sufficient. OBJECT OF THE INVENTION In order to eliminate the above-mentioned drawbacks, the object of the present invention is to provide a cable insulation layer that can maintain its damping effect for a long period of time even if subjected to large repeated strains due to thermal expansion and contraction. and to provide power cables with water layer. Structure of the Invention The present invention provides a power cable with a damp water layer in which a damp water layer is provided between an insulating layer and a sheath. It consists of a metal foil made of an alloy that exhibits thermoelastic martensitic transformation, which exhibits superelastic behavior by forming sites and returning to its original crystal structure upon unloading, and a rubber or plastic film layer laminated to the metal foil. It is characterized by being composed of shiyamizu tape,
This is a power cable with a layer of water. In other words, the present invention uses a metal material exhibiting the above-mentioned superelastic behavior as the metal foil constituting the persimmon water tape, thereby forming a persimmon water layer that can withstand repeated strain over a long period of time. This provides a highly effective power cable. What is superelastic behavior (superelastic effect)? When stress is applied to a certain alloy, stress-induced martensite is generated (by causing martensitic transformation), and the alloy deforms elastically to a considerable amount of strain. When the stress is removed, the stress-induced martensite disappears and returns to the original matrix. That is, martensitic transformation is the mechanism by which the superelastic phenomenon occurs. By using a metal material that exhibits such superelastic behavior (superelastic alloy) for metal foil, even if it is subjected to repeated strain due to thermal expansion and contraction, this metal material will only deform elastically, and theoretically it will not deform. There is no accumulation of dislocations due to Therefore, compared to superplastic alloys in which dislocations accumulate due to repeated strain, superelastic alloys do not accumulate dislocations due to repeated strain and are less likely to cause fatigue fracture. The "metal foil" of this invention includes Cu-Zn-Al
Alloys exhibiting thermoelastic martensitic transformation, such as Cu-Al-Ni-based alloys, Cu-Al-Ni-based alloys, and NiTi-based alloys, can be used. However, in order to effectively utilize superelastic behavior, it is required that the reverse transformation temperature be lower than the cable operating temperature range so that the cable exhibits superelastic behavior in the cable operating temperature range. An alloy exhibiting thermoelastic martensitic transformation having the following properties is used. 3 and 4 show cross-sectional views of the power cable with a water layer of the present invention. As shown in FIG. 3, the shiyamizu tape as the shiyamizu layer 14 is
It may be provided on the inner periphery of the sheath 5, or it may be provided on the outer periphery of the insulating layer 2 as shown in FIG. Further, in each case, the persimmon water layer 4 may be bonded and integrated with the insulating layer 2 or the sheath 5, or may not be integrated. Further, the persimmon water tape constituting the persimmon water layer 14 may be provided vertically, or may be provided by spiral winding. In addition, as is clear from FIG. 5, which is a side view of the damp water tape constituting the damp water layer 14, the "rubber or plastic film layer" of the present invention is
The metal foil 14b may be laminated on both sides as shown by 14a and 14c, or only one side of the metal foil 14b may be laminated. Description of Examples Metal foils made of plastic materials shown in Table 1 were prepared and used as Invention Examples 1 to 3 and Comparative Examples 1 and 2. For both the inventive example and the comparative example, two types were prepared, one in which plastic film was laminated only on one side (2) and one in which plastic film was laminated on both sides (2). When the above-mentioned plastic tape made of metal foil and plastic film was wrapped around the inner periphery of the sheath of a rubber-plastic insulated power cable, it was possible to wrap both with good workability. For reference, a winding test was conducted using steel foil as a metal foil, and it was confirmed that the workability was somewhat inferior. However, since steel etc. are ferromagnetic materials,
Needless to say, this is inappropriate for the purpose of this invention. Next, the water permeability of the power cables prepared as described above, in which the metal foils of Examples 1 to 3 of the present invention and Comparative Examples 1 and 2 were used, and a water layer was formed with a film tape, was evaluated. When tested by weight change in an uncoated state in a steam atmosphere, no weight change was observed in any of them, confirming that they have a persimmon water effect. Furthermore, regarding the occurrence of cracks due to repeated expansion and contraction of the frost water layer, Invention Examples 1 to 3 and Comparative Example 1,
For each of 2, two types of shiyamizu tape, one-sided laminated () and double-sided laminated (), were subjected to the cyclic expansion and contraction strain expected to be received when the cable is actually used, that is, 2% cyclic strain. When the material was expanded and contracted as shown in Table 2, the results shown in Table 2 were obtained.

【table】

[Table] As is clear from the results in Table 2, Invention Example 1
It can be seen that Samples No. 3 to 3 exhibit far superior crack resistance in both the single-sided laminated type () and the double-sided laminated type (2), compared to those using conventional metal foils made of aluminum or lead. Effects of the Invention As described above, according to the present invention, the persimmon water layer generates stress-induced martensite that deforms in the temperature range in which the cable is used, and when unloaded, returns to the original crystal structure, thereby exhibiting superelastic behavior. a metal foil made of an alloy exhibiting thermoelastic martensitic transformation;
Since the shayazu tape is composed of a rubber or plastic film layer laminated to the metal foil, the metal foil of the shayamizu layer is subjected to large repeated distortions due to thermal expansion and contraction of the cable insulation layer. However, it does not break and can maintain its shiyamizu effect for a long period of time.
It is possible to reliably prevent the cable insulator from deteriorating due to water, and it is possible to realize a power cable with a water layer that can withstand use for a long period of time. Therefore, this invention is suitable for applications where the insulating layer is thick and the external diameter changes due to thermal expansion/contraction of the insulator is large, and special high voltages of 22 kV or higher, where the repetitive strain given to the water tape is large, are practical. rubber,
Suitable for plastic insulated power cables.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a conventional power cable with a water layer. FIG. 2 is a sectional view showing another example of a conventional power cable with a water layer. FIG. 3 is a sectional view showing an example of a power cable with a water layer according to the present invention. FIG. 4 is a sectional view showing another example of the power cable with a water layer according to the present invention. FIG. 5 is a side view showing an example of the structure of the aqueous layer used in the present invention. 2...Insulating layer, 5...Sheath, 14...Shrinking tape as a damp water layer, 14a, 14c...Plastic film layer, 14b...Metal foil.

Claims (1)

[Claims] 1. In a power cable with a damp water layer in which a damp water layer is provided between an insulating layer and a sheath, when the damp water layer is deformed in the temperature range in which the cable is used, stress-induced maltenescence occurs. It consists of a metal foil made of an alloy that exhibits thermoelastic martensitic transformation, which exhibits superelastic behavior by forming sites and returning to its original crystal structure upon unloading, and a rubber or plastic film layer laminated to the metal foil. A power cable with a shiyami layer, characterized in that it is composed of a shiyamizu tape. 2. The power cable with a frost water layer according to claim 1, wherein the frost water tape is provided between the insulating layer and the sheath in a longitudinally spliced or spirally wound manner. 3. The rubber or plastic film layer is
The power cable with a frosted water layer according to claim 1 or 2, wherein both sides of the metal foil are laminated. 4. The rubber or plastic film layer is
The power cable with a frosted water layer according to claim 1 or 2, which is laminated on one side of the metal foil.