JP5323452B2 - Rubber / plastic insulated lead sheath cable - Google Patents

Description

  The present invention relates to a rubber / plastic insulated lead sheath cable for electric power.

  The OF cable based on the lead sheath employs a structure in which a metal tape (stainless steel tape or galvanized steel strip) is wound around the lead sheath to reinforce the oil pressure inside the lead sheath. In the case of an OF cable, a hydraulic oil compensation device is installed to keep the hydraulic pressure inside the lead sheath constant, so the lead sheath can be used even if the cable core undergoes thermal expansion / contraction due to power load fluctuations. The oil pressure on the inside of the lead sheath hardly changes, and the repeated distortion deterioration of the lead sheath due to the fluctuation of the oil pressure hardly occurs.

  On the other hand, in the case of a rubber / plastic insulated lead sheath cable, generally, an inner semiconductive layer, a rubber / plastic insulating layer, an outer semiconductive layer, and a lead sheath are sequentially provided outside the central conductor. If the cable core is defined from the central conductor to the outer semiconductive layer, the pressure (internal pressure) inside the lead sheath fluctuates due to thermal expansion / contraction of the cable core due to fluctuations in the transmission load. There is a problem that the lead sheath is repeatedly strained due to thermal expansion / contraction of the core. In particular, in the case of submarine cables or submarine cables, water pressure is applied to the outside of the lead sheath, so the lead sheath expands and contracts following the thermal expansion and contraction of the cable core. Deterioration becomes significant.

  Conventionally, the cable core has been provided by providing a cushion layer between the outer semiconductive layer and the lead sheath, or by providing a cushion layer and a reinforcing layer for the lead sheath fatigue problem of rubber / plastic insulated lead sheath cables. A method of reducing the amount of expansion force transmitted to the lead sheath, a method of suppressing the expansion of the lead sheath by providing a reinforcing layer by winding a metal tape on the outside of the lead sheath, or a combination of these methods A method for reducing fatigue due to expansion / contraction of the material is known (for example, see Patent Documents 1 and 2).

  It is thought that the cyclic strain deterioration of the lead sheath is determined by the accumulation of the cyclic strain change width of the lead sheath that is received during the use of the cable. It is necessary to make sure that the accumulated amount does not exceed the allowable amount. Although it depends on the material of the lead sheath, it is generally assumed that it will undergo thermal expansion / contraction once a day for 30 years (approximately 10,000 repeated strains), and the allowable strain change width of the lead sheath at that time Is about 0.15%. Therefore, it is necessary to take measures to reduce the lead sheath fatigue of the rubber / plastic insulated lead sheath cable so as not to exceed the allowable strain change width of the lead sheath.

Japanese Utility Model Publication No. 5-79814 JP-A-8-249939

  In rubber / plastic insulated lead sheath cables, the thermal expansion / contraction of the cable core inside the lead sheath is large due to temperature changes due to load fluctuations in power transmission, etc., and a cushion between the conventionally proposed cable core and lead sheath is used. In the method of providing the layer, the repeated strain that the lead sheath is subjected to may not be sufficiently reduced. In particular, in a submarine / underwater cable in which water pressure is applied to the outside, the lead sheath tends to shrink following the contraction of the cable core, and the lead sheath is likely to be repeatedly fatigued, as compared to the land cable. In addition, since the lead sheath is always subjected to external water pressure, the cushion layer is always subjected to a compressive force, and the cushion effect cannot be obtained as expected. Furthermore, depending on the design of the cushion layer, the thermal expansion / contraction of the cushion layer itself may cause an adverse effect of promoting the expansion / contraction of the lead sheath. As described above, it is considered that merely providing a cushion layer between the cable core and the lead sheath has a small effect of reducing the repeated strain received by the lead sheath.

  Next, regarding the method of reducing the distortion of the lead sheath by providing a cushion layer and a reinforcement layer by winding a metal tape between the cable core and the lead sheath, although there is an effect of providing the reinforcement layer, In the structure in which the lead sheath is directly provided on the cable, there are problems in manufacturing the cable and design problems with respect to the mechanical behavior of the cable. Therefore, in reality, a semiconductive presser tape winding layer is provided on the metal tape winding reinforcing layer, and a lead sheath is provided thereon. Since the shrinkage is directly transmitted to the lead sheath, the effect of reducing the repeated strain of the lead sheath cannot be obtained as expected. Moreover, taking a complicated structure in which a metal tape-wrapped reinforcing layer is provided inside the lead sheath deteriorates cable manufacturability and leads to an increase in cost. Absent.

  The most realistic and effective method that has been considered in the past is that a cushion layer is provided between the cable core and the lead sheath, and a reinforcement layer formed by winding metal tape or the like on the outside of the lead sheath. It is a method of providing. This method can be expected to reduce the amount of thermal expansion force of the cable core transmitted to the lead sheath by the cushion layer and at the same time suppress the amount of expansion of the lead sheath by the reinforcing layer. However, this method has a high risk of damage to the lead sheath due to the edge of the metal tape of the reinforcing layer biting into the lead sheath because the lead sheath expands outwardly due to the expansion force of the cable core. . In order to avoid this, it is conceivable to take a structure in which a flooring tape such as a nonwoven fabric is wrapped around a lead sheath like a OF cable to form a cushion layer, and a reinforcing layer by winding a metal tape is provided thereon. Compared to the internal pressure inside the lead sheath of an OF cable, the internal pressure due to the thermal expansion of the cable core inside the lead sheath is higher in the rubber / plastic insulated lead sheath cable. There is a risk that the lead sheath will be deformed and local mechanical fatigue of the lead sheath will occur.

  In view of the above problems, an object of the present invention is to provide a rubber / plastic insulated lead sheath cable with reduced fatigue deterioration of the lead sheath.

  The rubber / plastic insulated lead sheath cable according to the present invention is a rubber / plastic insulation in which a first cushion layer is provided between a cable core and a lead sheath, and a second cushion layer and a reinforcing layer are sequentially provided outside the lead sheath. A lead sheath cable, characterized in that the product of the linear thermal expansion coefficient and the Young's modulus of the second cushion layer is greater than the product of the linear thermal expansion coefficient and the Young's modulus of the first cushion layer. is there.

  In the rubber / plastic insulated lead sheath cable according to the present invention, the second cushion layer is preferably formed by extrusion molding of a resin.

  In the rubber / plastic insulated lead sheath cable according to the present invention, the reinforcing layer is preferably formed by winding a metal tape.

  In the rubber / plastic insulated lead sheath cable according to the present invention, the reinforcing layer may be formed by tape winding with a high strength fiber tape or a high strength fiber-resin composite tape.

  In the rubber / plastic insulated lead sheath cable according to the present invention, the product of the linear thermal expansion coefficient and the Young's modulus of the second cushion layer is the product of the linear thermal expansion coefficient and the Young's modulus of the first cushion layer. It is preferably 20 times or more.

The inner radius of the first cushion layer is r ₁ , the outer radius is R ₁ , the thickness is d ₁ (= R ₁ −r ₁ ), the linear thermal expansion coefficient of the material is β ₁ , and the Young's modulus is E ₁ . . Similarly, the inner radius of the second cushion layer is r ₂ , the outer radius is R ₂ , the thickness is d ₂ (= R ₂ −r ₂ ), the linear thermal expansion coefficient of the material is β ₂ , and the Young's modulus is E. ₂ . The amounts of change in thickness in the radial direction when the first cushion layer and the second cushion layer undergo free thermal expansion with respect to the temperature rise ΔT are denoted by Δd ₁ and Δd ₂ , respectively. Here, for the sake of simplicity, consider the case where the first cushion layer thermally expands only to the outside (not thermally expands to the inner cable core side), and the second cushion layer thermally expands only to the inside (outside Consider the case where there is no thermal expansion on the reinforcing layer side. Then, the change amount Δd ₁ of the thickness of the first cushion layer and the change amount Δd ₂ of the thickness of the second cushion layer are approximately described by the following [Equation 1] and [Equation 2], respectively. The However, (gamma) is a constant depending on the direction of thermal expansion.

Here, if the force necessary to suppress the thermal expansion of the first cushion layer and the second cushion layer with respect to the temperature increase ΔT is defined as a thermal expansion force F ₁ and a thermal expansion force F ₂ , Approximately described by the following proportional relationship of [Equation 3] and [Equation 4].

Formula 3, from [Equation 4], as an index representing the thermal expansion force of the first cushioning layer and a second cushion layer, respectively considering the thermal expansion force index alpha ₁ and the thermal expansion force index alpha _2, the following It is defined by [Equation 5] and [Equation 6].

  It shows that thermal expansion force is so large that said thermal expansion power index | exponent is large. Therefore, as an index representing the difference in thermal expansion force between the first cushion layer and the second cushion layer, the thermal expansion force index ratio K is defined by the following [Equation 7].

Here, the term (1 + r ₁ / R ₁ ) and the term (1 + R ₂ / r ₂ ) are parts determined by the structure of the first cushion layer and the second cushion layer (ratio of inner radius to outer radius). However, the values of the two are usually considered to be largely unchanged, so for the sake of simplicity, the influence of these terms can be ignored, and the simple thermal expansion index of the first and second cushion layers Α ₁ ′ and α ₂ ′ are defined by the following [Equation 8] and [Equation 9], respectively, and the simplified thermal expansion force index ratio K ′ is defined by the following [Equation 10].

  The larger the above-mentioned thermal expansion force index ratio K and simple thermal expansion force index ratio K ′, the greater the action of pressing the lead sheath inward by the thermal expansion of the second cushion layer, and the greater the effect of suppressing the expansion of the lead sheath. .

In the present invention, the expansion of the second cushion layer provided outside the lead sheath is suppressed more than the thermal expansion force of the first cushion layer provided inside the lead sheath after suppressing the expansion in the radial direction by the reinforcing layer. The thermal expansion force is increased. That is, the thermal expansion force index α ₂ and the simple thermal expansion force index α ₂ ′ of the second cushion layer are made larger than the thermal expansion force index α ₁ and the simple thermal expansion force index α ₁ ′ of the first cushion layer. It is a thing. By adopting this structure, when the cable core is thermally expanded due to temperature rise, the action of pressing the lead sheath inward using the thermal expansion force of the second cushion layer is generated, and the lead sheath is expanded. It can be effectively suppressed. Therefore, the amount of expansion and contraction of the lead sheath is reduced, and fatigue deterioration can be reduced.

  In the present invention, when the second cushion layer is formed by extrusion molding of the resin, the inner surface of the second cushion layer becomes smooth, so even if the second cushion layer is strongly pressed against the lead sheath by its thermal expansion force It is possible to prevent the lead sheath from being deformed or damaged without biting into the lead sheath. It is also easy to ensure the thickness of the second cushion layer necessary for suppressing the expansion of the lead sheath.

In the present invention, the thermal expansion force index α ₂ (or simple thermal expansion index α ₂ ′) of the second cushion layer is set to be the thermal expansion index α ₁ (or simple thermal expansion index α of the first cushion layer). By setting it to 20 times or more of ₁ ′), the action of pressing the lead sheath inward using the thermal expansion force of the second cushion layer can be more reliably generated. This is equivalent to setting the thermal expansion force index ratio K (= α ₂ / α ₁ ) or the simplified thermal expansion force index ratio K ′ (= α ₂ ′ / α ₁ ′) to 20 or more, and the simplified thermal expansion force. Considering the index ratio K ′, the product of the linear thermal expansion coefficient β ₂ and the Young's modulus E ₂ of the _second cushion layer is the product of the linear thermal expansion coefficient β ₁ and the Young's modulus E _{1 of} the first cushion layer. By making it 20 times or more, the action of pressing the lead sheath inward using the thermal expansion force of the second cushion layer can be generated more reliably.

  FIG. 1 shows an embodiment of the present invention. This rubber / plastic insulated lead sheath cable has a first cushion layer 4, a lead sheath 5, a second cushion layer 6 on the outside of a cable core 3 comprising a central conductor 1 and a rubber / plastic insulation layer 2 on the outer side thereof. The reinforcement layer 7 for suppressing expansion is sequentially provided. The central conductor 1 is generally composed of a copper stranded wire, and the rubber / plastic insulating layer 2 is composed of an internal semiconductive layer 2a, a rubber / plastic insulating layer body 2b, and an external semiconductive layer 2c. Usually, the inner semiconductive layer 2a, the rubber / plastic insulating insulating body 2b, and the outer semiconductive layer 2c are formed by a coextrusion method, and these three layers are integrated.

  The first cushion layer 4 is formed by tape winding with a semiconductive cushion tape. The second cushion layer 6 is formed by resin extrusion or cushion tape winding, but is preferably formed by resin extrusion. Further, the second cushion layer 6 may be configured by providing a floor tape winding layer on the outside of the extruded layer of resin. The reinforcing layer 7 suppresses the second cushion layer 6 from expanding outward, and can be formed by winding a metal tape such as a stainless steel tape or a galvanized steel strip. The reinforcing layer 7 can also be formed by tape winding with a high strength fiber tape or a high strength fiber-resin composite tape.

In this rubber / plastic insulated lead sheath cable, the product of the linear thermal expansion coefficient and the Young's modulus of the second cushion layer 6 (simple thermal expansion force index α ₂ ′) is the linear thermal expansion coefficient of the first cushion layer 4. And the Young's modulus (simple thermal expansion force index α ₁ ′). Thereby, the thermal expansion force of the second cushion layer is made higher than the thermal expansion force of the first cushion layer, the expansion and contraction of the lead sheath 5 are suppressed, and the fatigue deterioration is reduced. This principle is as follows.

  As the temperature of the cable core 3 rises, the temperature of the first cushion layer 4 and the second cushion layer 6 also rises, so that the first cushion layer 4 and the second cushion layer 6 both thermally expand. At this time, since the first cushion layer 4 has the cable core 3 on the inner side, the first cushion layer 4 is not easily displaced toward the inner surface side and is easily displaced toward the outer surface side, whereas the second cushion layer 6 is provided with a reinforcing layer on the outer surface side. Since there is 7, it is difficult to displace to the outer surface side, and it is easy to displace to the inner surface side. For this reason, the second cushion layer 6 functions to suppress the expansion of the lead sheath 5 when the temperature rises. And the effect which suppresses expansion | swelling of the lead sheath 5 becomes large, so that the thermal expansion force of the 2nd cushion layer 6 is large with respect to the 1st cushion layer 4. FIG. The thermal expansion force depends on the temperature and the temperature increase range (see Equations 3 and 4), and increases as the temperature increase range increases. Also, the linear thermal expansion coefficient tends to increase as the temperature increases. The thermal expansion amount of the cable core 3 also increases as the temperature increase range increases. However, the present invention is a mechanism that suppresses the expansion of the lead sheath 5 using the thermal expansion force of the second cushion layer 6, so the temperature increase range is The larger the is, the greater the thermal expansion force of the second cushion layer 6 and the stronger the action of pressing the lead sheath 5 inward. Therefore, the expansion of the lead sheath 5 can be effectively suppressed following the temperature change. This also applies to the case where the temperature decreases. When the temperature decreases and the thermal expansion amount of the cable core 3 decreases, the thermal expansion amount of the second cushion layer 6 also decreases. Therefore, pressing the lead sheath 5 inward more than necessary does not occur.

  In order to effectively generate the thermal expansion force of the second cushion layer 6, the restraining force of the reinforcing layer 7 with respect to the second cushion layer 6 is important, and the lead sheath 5, the second cushion layer 6. It is preferable that the magnitude relationship of the Young's modulus of the reinforcing layer 7 increases in the order of the second cushion layer 6, the lead sheath 5, and the reinforcing layer 7. With respect to the first cushion layer 4, it is important to provide sufficient cushioning properties against the thermal expansion of the cable core 3, and the rubber / plastic insulation layer 2, the first cushion layer 4, and the lead sheath 5 are made of Young. It is preferable that the magnitude of the rate increases in the order of the first cushion layer 4, the rubber / plastic insulating layer 2, and the lead sheath 5.

  In the rubber / plastic insulated lead sheath cable according to the present invention, the second cushion layer 6 is preferably formed by extrusion molding of resin. When the second cushion layer 6 is formed by extrusion molding of resin, the inner surface of the second cushion layer 6 can be made smoother than when it is formed by tape winding. Even if it is strongly pressed against the lead sheath 5, the lead sheath 5 is not digged in, and damage to the lead sheath 5 can be prevented. Further, in order to increase the thermal expansion force of the second cushion layer 6, the thickness of the second cushion layer 6 is also an important factor (see Equations 6 and 7). In order to secure the thickness of the second cushion layer effective to suppress the expansion of the lead sheath by tape winding, it is necessary to increase the number of tape winding layers, which is not a good solution in terms of cable manufacturing. If the second cushion layer is formed by resin extrusion, the second cushion layer can be easily formed in one step, and the second cushion layer is effective in suppressing the expansion of the lead sheath. It is easy to ensure the thickness. Further, even when the reinforcing layer 7 is formed by winding with a metal tape, it is possible to prevent the edge portion of the metal tape from damaging the lead sheath 5. In some cases, the second cushion layer 6 can be used as a cable anticorrosion layer.

  In addition, it is thought that the thermal expansion force increases as the thickness of the second cushion layer increases (see Equation 6), and the effect of suppressing the expansion of the lead sheath increases. However, the thickness of the second cushion layer increases. The higher the temperature rise due to heat generated in the cable center conductor during power transmission, the more disadvantageous the cable thermal design, and the higher the cable manufacturing cost, the second cushion. The thickness of the layer is preferably selected appropriately in consideration of these problems. From the above, it is preferable to select a material having a low thermal resistance as the material for the first cushion layer and the second cushion layer.

  In the rubber / plastic insulated lead sheath cable according to the present invention, the reinforcing layer 7 is preferably formed by winding a metal tape. As the metal tape, a stainless steel tape or a galvanized steel strip can be used. As the thickness of the metal tape winding layer, it is preferable to select a thickness at which the action of pressing the lead sheath inward by the thermal expansion force of the second cushion layer effectively works when the temperature rises.

  In the rubber / plastic insulated lead sheath cable according to the present invention, the reinforcing layer 7 may be formed by winding a reinforcing tape with a high-strength fiber tape or a high-strength fiber-resin composite tape. That is, as a tape material used for forming the reinforcing layer 7, instead of a metal tape, a tape formed of high-strength fibers having high Young's modulus and low elongation (aramid fiber, glass fiber, carbon fiber, etc.), and these A high-strength fiber-resin composite tape in which an epoxy resin or the like is impregnated and cured can be used. The thickness of the tape winding layer made of high-strength fiber tape or high-strength fiber-resin composite tape is selected so that when the temperature rises, the action of pressing the lead sheath inward with the thermal expansion force of the second cushion layer works effectively It is preferable to do.

Next, calculation results for confirming the effect of the present invention will be described. Central conductor 1 of the test cable is a copper twisted wire cross-sectional area 500 mm ^2, the rubber-plastic insulating layer body 2b are cross-linked polyethylene having a thickness of 13 mm.

The first cushion layer 4 is formed by winding a semiconductive cushion tape, and has a thickness of 1.1 mm, an inner diameter of 60.3 mm, and an outer diameter of 62.5 mm. The semiconductive cushion tape has a linear thermal expansion coefficient β ₁ of 1.0 × 10 ⁻⁴ [1 / ° C.] and a Young's modulus E ₁ of 4.41 × 10 ⁷ [Pa]. Therefore, the thermal expansion of the first cushion layer defined by [Equation 5] with the linear thermal expansion coefficient β ₁ , Young's modulus E ₁ , inner diameter (inner radius) and outer diameter (outer radius) of the first cushion layer 4. The force index α ₁ is 8.66 × 10 ³ [Pa / ° C.] and the simple thermal expansion force index of the first cushion layer defined by the product of the linear thermal expansion coefficient β ₁ and Young's modulus E _{1 of} [Equation 8] α ₁ ′ is 4.41 × 10 ³ [Pa / ° C.]. The thickness of the lead sheath 5 is 3.3 mm.

The second cushion layer 6 is formed by extrusion molding of polyethylene, and has a thickness of 4.5 mm, an inner diameter of 69.1 mm, and an outer diameter of 78.1 mm. Regarding the linear thermal expansion coefficient β ₂ of the second cushion layer 6, the linear thermal expansion coefficient of plastic generally tends to increase as the temperature increases. In the case of polyethylene, 2.0 × 10 ⁻⁴ [1 / ° C. at 20 ° C. ], 7.0 × 10 ⁻⁴ [1 / ° C.] at 60 ° C., and 1.0 × 10 ⁻³ [1 / ° C.] at 90 ° C. The Young's modulus E ₂ of the second cushion layer 6 is 1.47 × 10 ⁸ [Pa] in the case of polyethylene, and therefore the thermal expansion force index α ₂ of the second cushion layer 6 defined by [Equation 6] is It is 6.27 × 10 ⁴ [Pa / ° C.] at 20 ° C., 2.19 × 10 ⁵ [Pa / ° C.] at 60 ° C., and 3.13 × 10 ⁵ [Pa / ° C.] at 90 ° C. The simple thermal expansion force index α ₂ ′ of the second cushion layer defined by [Equation 9] is 2.94 × 10 ⁴ [Pa / ° C.] at 20 ° C. and 1.03 × 10 ⁵ at 60 ° C. [Pa / ° C.] and 1.47 × 10 ⁵ [Pa / ° C.] in the case of 90 ° C. In both cases, the thermal expansion power index α ₂ and the simple thermal expansion power index α ₂ ′ of the second cushion layer 6 are larger than the thermal expansion power index α ₁ and the simple thermal expansion power index α ₁ ′ of the first cushion layer 4. The thermal expansion force index ratio K defined by [Equation 7] is 7.2 at 20 ° C, 25.3 at 60 ° C, and 36.2 at 90 ° C, and the simplified heat defined by [Equation 10]. The expansion index ratio K ′ is 6.7 at 20 ° C., 23.3 at 60 ° C., and 33.4 at 90 ° C. The reinforcing layer 7 is formed by winding two galvanized steel strips having a thickness of 0.5 mm, and the thickness thereof is 1 mm.

FIG. 2 shows that in the above rubber / plastic insulated lead sheath cable, in order to confirm the effect of the second cushion layer 6, the linear thermal expansion coefficient of the second cushion layer 6 is set to 2.0 × 10 ⁻⁴ [1 / ° C. ] To 1.0 × 10 ⁻³ [1 / ° C.] in the range of 1.0 × 10 ⁻⁴ [1 / ° C.] and the thickness of the second cushion layer 6 is changed. 3 is a result of calculating the circumferential strain of the lead sheath 5 due to thermal expansion in a steady state when 1200 A is energized. The calculation is based on the assumption that the base temperature around the cable is 20 ° C in the atmosphere.

From the result of FIG. 2, the region where the linear thermal expansion coefficient of the second cushion layer is small (in the case of 2.0 × 10 ⁻⁴ to 5.0 × 10 ⁻⁴ [1 / ° C.]), or the simple thermal expansion index ratio K ′ is In the small region (6.7 to 16.7), the lead sheath strain tends to increase with increasing thickness of the second cushion layer, and lead increases as the linear thermal expansion coefficient and the simplified thermal expansion index ratio K ′ increase. Although the increase in sheath strain tends to decrease, it can be seen that the second cushion layer is ineffective in reducing lead sheath strain. On the other hand, when the linear thermal expansion coefficient of the second cushion layer is about 6.0 × 10 ⁻⁴ [1 / ° C.] and the simple thermal expansion index ratio K ′ is increased to about 20, the thickness of the second cushion layer Even if increases, the strain of the lead sheath hardly changes (similar to the strain of the lead sheath without the second cushion layer). When the linear thermal expansion coefficient and the simple thermal expansion force index ratio K ′ are further increased, the lead sheath distortion is monotonously reduced with respect to the increase in the thickness of the second cushion layer, and the lead sheath distortion is reduced. It can be seen that it appears prominently. From this, it can be seen that the greater the thermal expansion force of the second cushion layer, the greater the effect of reducing the distortion of the lead sheath.

FIG. 3 shows the relationship between the thermal expansion force index ratio K and the lead sheath distortion when the thickness of the second cushion layer is changed in the range of 0.5 mm to 8 mm with respect to the calculation result of FIG. Similarly, FIG. 4 shows the relationship between the simple thermal expansion force index ratio K ′ and the lead sheath distortion. From the results of FIGS. 3 and 4, when both the thermal expansion force index ratio K and the simple thermal expansion force index ratio K ′ are 20 or more, the effect of reducing distortion of the lead sheath by inserting the second cushion layer Can be seen. Further, from the results of FIG. 3, in the region where the thermal expansion index ratio K is 20 or more, the lead sheath distortion is reduced as the thickness of the second cushion layer is increased with respect to the thermal expansion index ratio K. Although the effect increases, the effect tends to be saturated, and it can be seen that when the thickness of the second cushion layer is in the range of 4 mm to 8 mm, the curves are almost the same. From this, if the thermal expansion index ratio K is determined, it is not a good idea to increase the thickness of the second cushion layer more than necessary, and the thickness of the second cushion layer in this embodiment is appropriate to be 4.5 mm. It can be said that it is thick. Also, from the results of FIGS. 3 and 4, when considering the thickness of the second cushion layer in the range of 3 mm to 8 mm, the thermal expansion force index ratio K and the simple thermal expansion that are effective in reducing the distortion of the lead sheath The setting range of the value of the force index ratio K ′ is in the range of 20 to 40, and setting the thermal expansion force index ratio K and the simple thermal expansion force index ratio K ′ to 40 or more is an overdesign, and 40 or more It turns out that there is no need to In order to suppress the lead sheath strain to 0.15% or less, which is the allowable strain change width of the lead sheath with respect to about 10,000 repetitive strains, the thermal expansion force index ratio K and the simple thermal expansion force index ratio K ′ are 25 or more. It turns out that it should just set to. In the case of the second cushion layer having a thickness of 4.5 mm in this example, the temperature of the second cushion layer is about 50 ° C., and the linear thermal expansion coefficient at that time is 6.0 × 10 ⁻⁴ [1 / ° C. Therefore, the thermal expansion force index ratio K and the simple thermal expansion force index ratio K ′ are both about 20, corresponding to the case where the effect of reducing the distortion of the lead sheath begins to be obtained. This calculation example is for a cable up to the reinforcing layer of the galvanized steel strip winding. However, in the actual cable, an anticorrosion layer or an iron wire armor is provided outside the reinforcing layer of the galvanized steel strip winding. Therefore, the temperature of the second cushion layer is about 60 ° C., and the coefficient of linear thermal expansion at that time is about 8 × 10 ⁻⁴ [1 / ° C.]. Both ratios K ′ are 25 or more, and the strain of the lead sheath can be reduced to 0.15% or less which is the allowable strain change width of the lead sheath. From the comparison of the results of FIG. 3 and FIG. 4, lead can be derived from the simple expansion force index ratio K ′ defined only by the product of the linear thermal expansion coefficient and the Young's modulus of the material instead of the thermal expansion index ratio K. This is sufficient for grasping the tendency of the effect of reducing the strain of the sheath, and is an important index for selecting the material of the second cushion layer.

FIG. 5 shows the calculation result of the relationship between the current flowing through the center conductor 1 and the distortion of the lead sheath when the thickness of the second cushion layer 6 is 4.5 mm in the above rubber / plastic insulated lead sheath cable. is there. The linear thermal expansion coefficient of the second cushion layer is 1.0 × 10 ^{− in} the range from 2.0 × 10 ⁻⁴ [1 / ° C.] to 1.0 × 10 ⁻³ [1 / ° C.] similarly to the calculation result of FIG. ⁴ is a result of calculating the circumferential strain of the lead sheath 5 due to thermal expansion in a steady state when the central conductor is energized, set in increments of ⁴ [1 / ° C.]. The calculation is based on the assumption that the base temperature around the cable is 20 ° C in the atmosphere.

As the energization current of the center conductor increases, the strain of the lead sheath increases. However, as the linear thermal expansion coefficient β ₂ of the second cushion layer increases, the degree of increase in the strain of the lead sheath decreases. It can be seen that the thermal expansion force of the cushion layer effectively acts to reduce the distortion of the lead sheath. Here, the linear thermal expansion coefficient of the second cushion layer is temperature-dependent, and when the energization amount of the central conductor is small and the temperature is low, the linear thermal expansion coefficient is small (for example, 2.0 × 10 ⁻⁴ [20 ° C. 1 / ° C]), the effect of reducing the distortion of the lead sheath due to the thermal expansion force of the second cushion layer can hardly be expected, or conversely it works to promote thermal expansion, but the energization is small and the temperature is low In the region, since the amount of expansion of the cable core is also small, the lead sheath does not swell until it significantly affects the fatigue of the lead sheath, which is not a problem. What is important is when the energization amount is large and the temperature is high, and the expansion amount of the cable core is large. In this case, the linear thermal expansion coefficient of the second cushion layer is also increased due to the temperature rise. The thermal expansion force of the cushion layer effectively reduces the strain of the lead sheath.

  In this calculation example, the cable up to the reinforcing layer of the galvanized steel strip winding was examined, but the second case is also applied to the cable in which the anticorrosion layer or the iron wire armoring is provided outside the reinforcing layer of the galvanized steel strip winding. Needless to say, the thermal expansion force of the cushion layer effectively acts on the reduction of the distortion of the lead sheath. The second cushion layer can also serve as an anticorrosion layer by using polyvinyl chloride in addition to polyethylene.

  In the above embodiment, a single-core AC or DC rubber / plastic insulated lead sheath cable has been described. However, even if a three-core rubber / plastic insulated lead sheath cable is used, three cable cores are used. In contrast, the first cushion layer, the lead sheath, the second cushion layer, and the reinforcement layer are sequentially provided on the outside of each, thereby reducing the distortion of the lead sheath using the thermal expansion force of the second cushion layer. Can be obtained.

Sectional drawing which shows one Embodiment of the rubber-plastic insulation lead sheath cable which concerns on this invention. In order to confirm the effect that the second cushion layer and the thickness reduce the circumferential distortion of the lead sheath, the linear thermal expansion coefficient β (or simple thermal expansion force index ratio K ′) of the second cushion layer is changed. The graph which shows the result of having calculated the relationship between the thickness of a 2nd cushion layer, and the magnitude | size of distortion of a lead sheath. The graph which shows the result of having summarized the relationship between the thermal expansion force index ratio K with respect to the thickness of a 2nd cushion layer, and the distortion | strain of a lead sheath with respect to the calculation result of FIG. The graph which shows the result of having summarized the relationship between the simple thermal expansion force index ratio K ′ with respect to the thickness of the second cushion layer and the strain of the lead sheath with respect to the calculation result of FIG. 2. In order to confirm the effect that the linear thermal expansion coefficient β (or simple thermal expansion force index ratio K ′) of the second cushion layer reduces the distortion in the circumferential direction of the lead sheath, the thickness of the second cushion layer is constant. And the graph which shows the result of having calculated the relationship between the magnitude | size of the energization current of a center conductor, and the magnitude | size of distortion of a lead sheath, changing the linear thermal expansion coefficient of a 2nd cushion layer.

Explanation of symbols

1: Central conductor 2: Rubber / plastic insulating layer 2a: Internal semiconductive layer 2b: Rubber / plastic insulating layer body 2c: External semiconductive layer 3: Cable core 4: First cushion layer 5: Lead sheath 6: Second Cushion layer 7: reinforcement layer

Claims (5)

  A rubber / plastic insulated lead sheath cable in which a first cushion layer is provided between a cable core and a lead sheath, and a second cushion layer and a reinforcing layer are sequentially provided outside the lead sheath. A rubber / plastic insulated lead sheath cable characterized in that the product of linear thermal expansion coefficient and Young's modulus is greater than the product of linear thermal expansion coefficient and Young's modulus of the first cushion layer.   2. The rubber / plastic insulated lead sheath cable according to claim 1, wherein the second cushion layer is formed by resin extrusion.   3. The rubber / plastic insulated lead sheath cable according to claim 1, wherein the reinforcing layer is formed by winding a metal tape.   The rubber / plastic insulated lead sheath cable according to claim 1 or 2, wherein the reinforcing layer is formed by tape winding with a high strength fiber tape or a high strength fiber-resin composite tape.   The rubber according to claim 1, wherein the product of the linear thermal expansion coefficient and the Young's modulus of the second cushion layer is 20 times or more and 40 times or less of the product of the linear thermal expansion coefficient and the Young's modulus of the first cushion layer.・ Plastic insulated lead sheath cable.

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