insulator

Abstract

This reduces electric field concentration around the boundary between the first gripping fitting and the outer sheath. [Solution] The insulator 10 comprises a rod-shaped core member 20, a first gripping fitting 41 and a second gripping fitting 42 that grip both ends of the core member 20 in the axial direction, and an outer sheath 30 that covers the outer circumference of the portion of the core member 20 between the first gripping fitting 41 and the second gripping fitting 42, and has a body portion 36 and a plurality of cap portions 38, and is mainly composed of an insulating polymer material. The outer sheath 30 has a first region 31 provided at a position that includes the boundary 34a between the first gripping fitting 41 and the outer sheath 30 in the axial direction, and a second region 32 provided at a position adjacent to the first region 31 in the axial direction and closer to the second gripping fitting 42 than the first region 31. The resistivity of the first region 31 is lower than that of the second region 32.

Description

[Technical Field]

[0001] This invention relates to an insulator. [Background technology]

[0002] Conventionally, insulators are known for supporting conductors such as power transmission lines and for insulating power transmission lines from transmission towers or other equipment. For example, Patent Document 1 describes a polymer insulator comprising a core member, an outer sheath provided on the outer circumference of the core member and having a body portion and a cap (cap portion), and gripping fittings provided at both ends of the core member. When manufacturing the polymer insulator, the outer sheath is molded and provided around the core member, then the gripping fittings are set at both ends of the core member, and the gripping fittings are compressed and crimped with a die. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2001-332147 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In such insulators, electric fields sometimes concentrated around the boundary between the outer sheath and the gripping fitting on the end connected to the power transmission line, i.e., the energized gripping fitting, causing corona discharge. Therefore, it was desirable to mitigate the concentration of electric fields around the boundary between the gripping fitting and the outer sheath to suppress corona discharge.

[0005] This invention was made to solve these problems, and its main objective is to alleviate electric field concentration around the boundary between the first gripping fitting and the outer covering. [Means for solving the problem]

[0006] To achieve the main objectives described above, the present invention employs the following means.

[0007] [1] The insulator of the present invention comprises a rod-shaped core member, a first gripping fitting and a second gripping fitting that grip both axial ends of the core member, an outer covering that covers the outer circumference of a portion of the core member between the first gripping fitting and the second gripping fitting, has a body portion and a plurality of flange portions, and is mainly composed of an insulating polymer material, and is an insulator provided with the outer covering has a first region provided at a position including the boundary between the first gripping fitting and the outer covering in the axial direction, and a second region provided at a position adjacent to the first region in the axial direction and closer to the second gripping fitting than the first region, the resistivity of the first region is lower than that of the second region, and is such.

[0008] In this insulator, the outer covering has a first region and a second region. The first region is provided at a position including the boundary between the first gripping fitting and the outer covering in the axial direction of the core member. The second region is provided at a position adjacent to the first region in the axial direction and closer to the second gripping fitting than the first region. And the first region has a lower resistivity than the second region. Thereby, it is possible to relieve the electric field concentration around the boundary between the first gripping fitting and the outer covering, that is, around the boundary between the first gripping fitting and the first region.

[0009] [2] In the insulator described above (the insulator described in [1]), the plurality of flange portions have two or more types of flange portions with different diameters from each other, and the diameter of the flange portion located closest to the second region in the first region may be larger than the diameter of the flange portion located closest to the first region in the second region. By doing so, compared with the case where the diameter of the flange portion located closest to the second region in the first region is smaller than the diameter of the flange portion located closest to the first region in the second region, conversely, when the first gripping fitting is used as the charging side, it is possible to relieve the electric field concentration around the boundary between the first region and the second region. In this case, the plurality of flange portions may be alternately arranged along the axial direction with two types of large-diameter flange portions and small-diameter flange portions. In the present specification, "resistivity" means volume resistivity.

[0010] [3] In the insulator described above (the insulator described in [1] or [2]), the outer covering has a third region provided adjacent to the second region in the axial direction and closer to the second gripping fitting than the second region, and the resistivity of the third region may be higher than that of the second region. Thus, by making the resistivity of the first region, the second region, and the third region of the outer covering increase in this order, while increasing the resistivity of the third region, the difference in resistivity between the first region and the second region and the difference in resistivity between the second region and the third region can be reduced. Therefore, compared with the case where the outer covering has only the first region and the second region, it is easy to obtain both effects of reducing the resistivity of the first region to relieve the electric field concentration around the boundary between the first gripping fitting and the first region and relieving the electric field concentration around the boundary of the regions with different resistivities in the outer covering.

[0011] [4] In the insulator described above (the insulator described in any one of [1] to [3]), the insulator is used for the insulation of electrical equipment with a nominal voltage of 161 kV or less, and the resistivity R1 of the first region may be 6.0×10 12 Ω·cm or less. By doing so, when the insulator is used for the insulation of electrical equipment with such a nominal voltage, the relief of the electric field concentration around the boundary between the first gripping fitting and the first region is sufficient.

[0012] [5] In the insulator described above (the insulator described in any one of [1] to [4]), the insulator is used for the insulation of electrical equipment with a nominal voltage of 161 kV or less. Let the axial length of the first region be L1 [mm], and when the common logarithm of the ratio of the resistivity R1 [Ω·cm] of the first region to the resistivity R2 [Ω·cm] of the second region is defined as the resistance ratio Rr and e is the Napier number, the following formula (1) may be satisfied. 10 (R2 / R1) is defined as the resistance ratio Rr, and when e is the Napier number, the following formula (1) may be satisfied.

[0013] Rr≦0.00903818763e 0.00675775192L1 (1)

[0014] Here, the smaller the resistance ratio Rr between the first and second regions, the more likely it is that electric field concentration around the boundary between the first and second regions can be mitigated. Also, the longer the length L1 of the first region, the further the boundary between the first and second regions is from the first gripping fitting, and therefore the more likely it is that electric field concentration around the boundary between the first and second regions can be mitigated when the first gripping fitting is used as the energized side. Furthermore, for example, if the length L1 is sufficiently long, electric field concentration can be mitigated even if the resistance ratio Rr is large, and one value of length L1 and resistance ratio Rr influences the preferred range of the other value. The inventors have found the above equation (1) to be the preferred range for length L1 and resistance ratio Rr, taking the above influences into account. When the length L1 and resistance ratio Rr satisfy equation (1), the electric field concentration around the boundary between the first and second regions can be mitigated when the insulator is used for insulation of electrical equipment with a nominal voltage of 161kV or less, and the first gripping fitting is used on the energized side.

[0015] [6] The insulator described above (the insulator described in [5] above) may satisfy the following equation (2). By satisfying equation (2) with length L1 and resistance ratio Rr in this way, the electric field concentration around the boundary between the first region and the second region can be further reduced when the first gripping fitting is used as the energized side.

[0016] Rr≦0.0074e 0.0069L1 (2)

[0017] [7] In the above-mentioned insulator (the insulator described in any of [1] to [6] above), the insulator is used for insulating electrical equipment with a nominal voltage of 345kV or less, and the first region has a resistivity R1 of 3.0 × 10 12 It may be less than Ω·cm. This would be sufficient to mitigate the electric field concentration at the boundary between the first gripping fitting and the first region when the insulator is used to insulate this voltage.

[0018] [8] In the above-mentioned insulator (the insulator described in any of [1] to [7] above), the insulator is used for insulating electrical equipment with a nominal voltage of 345kV or less, the axial length of the first region is L1 [mm], and the logarithm of the ratio of the resistivity R1 [Ω·cm] of the first region to the resistivity R2 [Ω·cm] of the second region is log 10 When (R2 / R1) is the resistance ratio Rr and e is Napier's number, the following equation (3) may also be satisfied.

[0019] Rr≦0.0023e 0.0064L1 (3)

[0020] Similar to equation (1) described above, the inventors have found equation (3) as a preferred range for length L1 and resistance ratio Rr when the insulator is used for insulation of electrical equipment with a nominal voltage of 345kV or less. When length L1 and resistance ratio Rr satisfy equation (3), the electric field concentration around the boundary between the first and second regions can be mitigated when the insulator is used for insulation of electrical equipment with a nominal voltage of 345kV or less and the first gripping fitting is used on the energized side.

[0021] [9] The insulator described above (the insulator described in [8] above) may satisfy the following equation (4). By having the length L1 and resistance ratio Rr satisfy this equation (4), the electric field concentration around the boundary between the first region and the second region can be further mitigated when the first gripping fitting is used as the energized side.

[0022] Rr≦0.0026e 0.0061L1 (4) [Brief explanation of the drawing]

[0023] [Figure 1] Diagram illustrating the insulator device 1. [Figure 2] Diagram illustrating the modified boundary 34b. [Figure 3] An explanatory diagram of an outer covering 30 having a third region 33. [Figure 4] A graph showing the distribution of electric field strength of insulator 10 in Experimental Example 1. [Figure 5]A graph showing the distribution of electric field strength of insulator 10 in experimental example 2. [Figure 6] A graph showing the distribution of electric field strength of insulator 10 in experimental example 3. [Figure 7] A graph showing the distribution of electric field strength of insulator 10 in experimental example 4. [Figure 8] Graphs showing the relationship between resistivity R1 and length D for each of the experimental examples 5-7. [Figure 9] Graphs showing the relationship between resistivity R1 and length D for each of the experimental examples 8-10. [Figure 10] Graphs showing the relationship between the resistance ratio Rr, length L1, and evaluation results for each of the experimental examples 11-21. [Figure 11] A magnified view of a portion of Figure 10. [Figure 12] A magnified view of a portion of Figure 10. [Figure 13] A magnified view of a portion of Figure 10. [Figure 14] Graphs showing the relationship between the resistance ratio Rr, length L1, and evaluation results for each of the experimental examples 22-34. [Figure 15] A magnified view of a section of Figure 14. [Figure 16] A magnified view of a section of Figure 14. [Figure 17] A magnified view of a section of Figure 14. [Modes for carrying out the invention]

[0024] Next, embodiments of the present invention will be described with reference to the drawings. Figure 1 is an explanatory diagram of an insulator device 1 equipped with an insulator 10, which is one embodiment of the present invention. The two enlarged views in Figure 1 show the area around the boundary 34b and the area around the first gripping fitting 41 in a cross-section obtained by cutting the insulator 10 along the central axis of the core member 20.

[0025] The insulator device 1 is used to support a conductor, such as a power transmission line, and to insulate the conductor from a transmission tower or other equipment. As shown in Figure 1, the insulator device 1 comprises an insulator 10 and a connecting member 50. The insulator 10 is the main body of the insulator device 1 (insulator body) and comprises a core member 20, an outer sheath 30, and a gripping fitting 40. In this embodiment, the insulator 10 is used with its lower end in Figure 1 connected to a conductor such as a power transmission line, and its upper end connected to a transmission tower or other equipment. Therefore, the lower end of the insulator 10 in Figure 1 is also referred to as the energized side, and the upper end is also referred to as the grounded side.

[0026] The core member 20 is an insulating rod-shaped member. Examples of materials for the core member 20 include fiber-reinforced plastic (FRP). Examples of fibers in FRP include glass fibers. Examples of plastics in FRP include epoxy resin and polyester resin. In this embodiment, the core member 20 is a solid cylindrical member, but it may also be a hollow cylindrical member.

[0027] The outer sheath 30 is an insulating member provided on the outer circumference of the core member 20. In this embodiment, the outer sheath 30 is configured as an elastic insulator. The outer sheath 30 is mainly composed of an insulating polymer material, and therefore the insulator 10 is configured as a polymer insulator. Specific examples of polymer materials include silicone rubber, EPDM (ethylene-propylene-diene-monomer) rubber, and EVA (ethylene-vinyl acetate), and more specifically, silicone rubber vulcanized at high temperatures. The outer sheath 30 comprises a body portion 36 and a cap portion 38. The body portion 36 has a substantially constant diameter and is arranged to cover the outer circumferential surface of the core member 20. The cap portion 38 has a larger diameter than the body portion 36 and is formed to protrude radially outward from the outer circumferential surface of the body portion 36. Multiple cap portions 38 are arranged at intervals along the axial direction (up and down direction in Figure 1) of the core member 20. Each of the multiple caps 38 has two types of caps 38 with different diameters, specifically a large-diameter cap 38a and a small-diameter cap 38b with a smaller diameter than the large-diameter cap 38a. The large-diameter caps 38a and small-diameter caps 38b are arranged alternately, one at a time, along the axial direction. The upper surface of each of the multiple caps 38 is inclined in Figure 1. More specifically, the upper surface of each cap 38 is more inclined from the direction perpendicular to the axial direction than the lower surface. The insulator 10 is basically used in an orientation where the inclined surfaces of these multiple caps 38 face the ground. The outer cover 30 also has a first region 31 and a second region 32. Both the first region 31 and the second region 32 have multiple large-diameter caps 38a and multiple small-diameter caps 38b. Details of the first region 31 and the second region 32 will be described later.

[0028] The gripping fitting 40 is a metal member that covers and grips both axial ends of the core member 20. The gripping fitting 40 has a first gripping fitting 41 that grips one axial end (the lower end in Figure 1) of the core member 20 and a second gripping fitting 42 that grips the other end (the upper end in Figure 1). Examples of materials for the gripping fitting 40 include carbon steel and ductile cast iron. The first gripping fitting 41 and the second gripping fitting 42 are arranged symmetrically. The first gripping fitting 41 and the second gripping fitting 42 each have a main body portion 43 and a connecting portion 44.

[0029] The main body portion 43 is a cylindrical member having a bottomed insertion hole 43a formed along its central axis. The end of the core member 20 is inserted into this insertion hole 43a. A crimping portion is formed on the main body portion 43, and the gripping fitting 40 grips the core member 20 by the inner circumferential surface of the insertion hole 43a pressing against the core member 20 in the portion where this crimping portion exists. This maintains the axial tensile strength of the insulator 10 at the required value (for example, the tensile strength between the power line and the transmission tower plus a margin). Although not shown in the figure, the portion of the outer circumferential surface of the main body portion 43 where the crimping portion exists is slightly recessed compared to other portions. In other words, the portion of the main body portion 43 where the crimping portion exists has a smaller diameter (reduced diameter) compared to other portions. As shown in the enlarged view of the lower right of Figure 1, not only the lower end of the core member 20 but also the lower end of the outer sheath 30 is inserted into the insertion hole 43a of the first gripping fitting 41. Similarly, not only the upper end of the core member 20 but also the upper end of the outer covering 30 is inserted into the insertion hole 43a of the second gripping fitting 42.

[0030] The connecting portion 44 is provided on the outer side (end side) of the insulator 10 in the axial direction relative to the main body portion 43. The connecting portion 44 is a part for connecting the axial end of the insulator 10 to the connecting member 50. The connecting portion 44 is connected to the connecting member 50 using, for example, bolts and nuts (not shown).

[0031] The connecting members 50, although not shown in detail, are for connecting the insulator device 1 to other members. The insulator device 1 has two connecting members 50, one of which is provided at each of the axial ends of the insulator 10 and connected to the connecting portion 44 of the gripping fitting 40. In this embodiment, the connecting member 50 located at the upper end of Figure 1 is configured as a mounting fitting for connecting the second gripping fitting 42 of the insulator device 1 to the transmission tower, and the connecting member 50 located at the lower end of Figure 1 is configured as an overhead line fitting for connecting the first gripping fitting 41 of the insulator device 1 to the power transmission line.

[0032] The first region 31 and the second region 32 of the outer covering 30 will be described in detail. The first region 31 is located in the axial direction of the core member 20 and includes the boundary 34a between the first gripping fitting 41 and the outer covering 30. The boundary 34a is the end of the first gripping fitting 41 on the side of the second gripping fitting 42 (the upper end of the first gripping fitting 41 in Figure 1). The boundary 34a is the end of the first region 31 on the side of the first gripping fitting 41 (the lower end of the first region 31 in Figure 1), and the first region 31 is the region of the outer covering 30 from this boundary 34a upwards for a length L1 [mm] in the axial direction of the core member 20. The second region 32 is located adjacent to the first region 31 in the axial direction of the core member 20 and is closer to the second gripping fitting 42 than to the first gripping fitting 41. The first region 31 and the second region 32 are in contact vertically at the boundary 34b. Boundary 34b is the end of the first region 31 on the side of the second region 32 (the upper end of the first region 31 in Figure 1), and also the end of the second region 32 on the side of the first region 31 (the lower end of the second region 32 in Figure 1). The second region 32 is the area of ​​the outer covering 30 that extends upward from this boundary 34b to a length L2 [mm] in the axial direction of the core member 20. In this embodiment, the position of the upper end of the second region 32 in the axial direction of the core member 20 is the same as the position of the end of the second gripping fitting 42 on the side of the first gripping fitting 41 (the lower end of the second gripping fitting 42 in Figure 1). Therefore, the first region 31 and the second region 32 of the outer covering 30 completely cover the outer circumference of the portion of the core member 20 between the first gripping fitting 41 and the second gripping fitting 42. Also, the sum of lengths L1 and L2 is equal to the distance between the first gripping fitting 41 and the second gripping fitting 42.

[0033] And the resistivity of the first region 31 is lower than that of the second region 32. That is, the resistivity R1 [Ω·cm] of the first region 31 is lower than the resistivity R2 [Ω·cm] of the second region 32. Thereby, it is possible to mitigate the electric field concentration around the boundary between the first gripping fitting 41 and the outer sheath 30, that is, around the boundary 34a between the first gripping fitting 41 and the first region 31. In particular, when the first gripping fitting 41 is used as the power supply side, the electric field tends to concentrate on the boundary 34a. However, in the insulator 10 of the present embodiment, the low resistivity R1 of the first region 31 can mitigate the electric field concentration around the boundary 34a. Thereby, it is possible to suppress the corona discharge around the boundary 34a when the insulator 10 is in use.

[0034] When the insulator 10 is used for the insulation of electrical equipment with a nominal voltage of 161 kV or less (for example, the insulation between the transmission line and the iron tower described above), the resistivity R1 is 6.0×10 12 Ω·cm or less, which is preferable. By doing so, when the insulator 10 is used for the insulation of electrical equipment with such a nominal voltage, the mitigation of the electric field concentration around the boundary 34a is sufficient. The resistivity R1 may be 8.0×10 11 Ω·cm or more.

[0035] Further, when the insulator 10 is used for the insulation of electrical equipment with a nominal voltage of 161 kV or less, when the common logarithm of the ratio of the resistivity R1 of the first region 31 to the resistivity R2 of the second region 32 is defined as the resistance ratio Rr and e is the Napier's number, it is preferable that the relationship between the length L1 of the first region 31 and the resistance ratio Rr satisfies the following formula (1). Note that the resistance ratio Rr = log 10 (R2 / R1), and this formula can also be rewritten as R2 / R1 = 10 10 . Therefore, the resistance ratio Rr is the power of 10 of the ratio R2 / R1. Rr

[0036] Rr≦0.00903818763e 0.00675775192L1 (1)

[0037] Here, the smaller the resistance ratio Rr between the first region 31 and the second region 32, the more the electric field concentration around the boundary 34b between the first region 31 and the second region 32 tends to be mitigated. Also, the longer the length L1 of the first region 31, the further the boundary 34b is separated from the first gripping fitting 41, and therefore the more the electric field concentration around the boundary 34b tends to be mitigated when the first gripping fitting 41 is used as the energized side. Furthermore, for example, if the length L1 is sufficiently long, the electric field concentration at the boundary 34b can be mitigated even if the resistance ratio Rr is large, and so on. In other words, one value of length L1 and resistance ratio Rr influences the preferred range of the other value. Equation (1) represents the preferred ranges of length L1 and resistance ratio Rr, taking the above influences into account. When the length L1 and resistance ratio Rr satisfy equation (1), the electric field concentration around the boundary 34b can be mitigated when the insulator 10 is used for insulating electrical equipment with a nominal voltage of 161kV or less, and the first gripping fitting 41 is used on the energized side.

[0038] Furthermore, it is more preferable that the relationship between length L1 and resistance ratio Rr satisfies equation (2) below. By satisfying equation (2) between length L1 and resistance ratio Rr in this way, electric field concentration around boundary 34b can be further mitigated.

[0039] Rr≦0.0074e 0.0069L1 (2)

[0040] As mentioned above, the smaller the resistivity R1 of the first region 31, the more the electric field concentration around the boundary 34a between the first gripping fitting 41 and the first region 31 can be mitigated. However, since the resistance ratio Rr tends to increase as the resistivity R1 decreases, the electric field tends to concentrate around the boundary 34b between the first region 31 and the second region 32. Therefore, there is a trade-off between mitigating the electric field concentration around boundary 34a and mitigating the electric field concentration around boundary 34b. When the insulator 10 of this embodiment is used for insulating electrical equipment with a nominal voltage of 161kV or less, by reducing the resistivity R1 and satisfying equation (1), it is possible to achieve both the mitigation of the electric field concentration around boundary 34a and the mitigation of the electric field concentration around boundary 34b. Furthermore, by reducing the resistivity R1 and satisfying equation (2), it is possible to further mitigate the electric field concentration around boundary 34b while mitigating the electric field concentration around boundary 34a. As mentioned above, when the insulator 10 is used for insulation of electrical equipment with a nominal voltage of 161kV or less, the resistivity R1 is 6.0 × 10⁻⁶ 12 It is preferable that the resistivity R1 of the insulator 10 is 6.0 × 10⁻⁶. 12 It is preferable that the resistivity R1 of insulator 10 is Ω·cm or less and satisfies equation (1). 12 It is more preferable that the coefficient is less than or equal to Ω·cm and that equation (2) is satisfied.

[0041] Resistivity R1 is 6.0 × 10 12 If the value is Ω·cm or less, and / or if the above formula (1) is satisfied, then as described above, the insulator 10 can be used for insulating electrical equipment with a nominal voltage of 161kV or less. In this case, the insulator 10 is particularly suitable for insulating electrical equipment with a nominal voltage of any value between 115kV and 161kV, or for insulating electrical equipment with a nominal voltage of any value between 154kV and 161kV.

[0042] When insulator 10 is used for insulation of electrical equipment with a nominal voltage of 345kV or less, the resistivity R1 is 3.0 × 10⁻⁶ 12It is preferable that the resistivity is Ω·cm or less. This ensures sufficient mitigation of electric field concentration around boundary 34a when the insulator 10 is used for insulation of electrical equipment of such nominal voltage. The resistivity R1 is 1.0 × 10 12 It may be set to Ω·cm or greater.

[0043] Furthermore, when the insulator 10 is used for insulation of electrical equipment with a nominal voltage of 345kV or less, it is preferable that the relationship between the length L1 of the first region 31 and the resistance ratio Rr satisfies the following equation (3).

[0044] Rr≦0.0023e 0.0064L1 (3)

[0045] Even when the insulator 10 is used for insulation of electrical equipment with a nominal voltage of 345kV or less, and the first gripping fitting is used on the energized side, there are preferred ranges for the length L1 and the resistance ratio Rr, similar to equation (1) described above. Specifically, by satisfying equation (3) above, electric field concentration around the boundary 34b can be mitigated.

[0046] Furthermore, it is more preferable that the relationship between length L1 and resistance ratio Rr satisfies equation (4) below. By satisfying equation (4) between length L1 and resistance ratio Rr in this way, electric field concentration around boundary 34b can be further mitigated.

[0047] Rr≦0.0026e 0.0061L1 (4)

[0048] As mentioned above, there is a trade-off between mitigating electric field concentration around boundary 34a and mitigating electric field concentration around boundary 34b. In this embodiment, when the insulator 10 is used for insulating electrical equipment with a nominal voltage of 345kV or less, by reducing the resistivity R1 and satisfying equation (3), it is possible to achieve both mitigation of electric field concentration around boundary 34a and mitigation of electric field concentration around boundary 34b. Furthermore, by reducing the resistivity R1 and satisfying equation (4), it is possible to mitigate electric field concentration around boundary 34a while further mitigating electric field concentration around boundary 34b. As mentioned above, when the insulator 10 is used for insulating electrical equipment with a nominal voltage of 345kV or less, the resistivity R1 is 3.0 × 10 12 It is preferable that the resistivity R1 of the insulator 10 is 3.0 × 10⁻⁶. 12 It is preferable that the resistivity R1 of insulator 10 is Ω·cm or less and satisfies equation (3). 12 It is more preferable that the coefficient is less than or equal to Ω·cm and that equation (4) is satisfied.

[0049] Resistivity R1 is 3.0 × 10⁻⁶ 12 If the density is less than or equal to Ω·cm, and / or if equation (3) above is satisfied, then, as described above, the insulator 10 can be used for insulating electrical equipment with a nominal voltage of 345kV or less. In this case, the insulator 10 is particularly suitable for insulating electrical equipment with a nominal voltage of any value between 275kV and 345kV, or for insulating electrical equipment with a nominal voltage of any value between 330kV and 345kV. Of course, the insulator 10 in this case can also be used for insulating electrical equipment with a nominal voltage of 161kV or less.

[0050] Furthermore, the lower the resistivity R1, the more the electric field concentration around boundary 34a can be mitigated, and the lower the resistivity R2, the smaller the resistance ratio Rr becomes, making it easier to satisfy equations (1) to (4) and thus mitigating the electric field concentration around boundary 34b. However, the lower limits of resistivity R1 and resistivity R2 are determined to be values ​​such that the insulator 10 as a whole has the resistance value required for insulation. Also, even if resistivity R1 and R2 are low, if the lengths L1 and L2 are large, the overall resistance value of the sheath 30 will be high, so resistivity R1 and R2 are determined taking lengths L1 and L2 into consideration so that the entire sheath 30 has the resistance value required for insulation. For example, the overall resistance value of the insulator 10 (resistance value between the first gripping fitting 41 and the second gripping fitting 42) is preferably 1 MΩ or more per 1 kV of nominal voltage of the electrical equipment to be insulated.

[0051] The resistivity values ​​R1 and R2 mentioned above are those measured in accordance with JIS K 6911.

[0052] Furthermore, the portion of the outer sheath 30 below the first region 31, that is, the portion inserted into the insertion hole 43a and covered by the first gripping fitting 41, has the same material and resistivity as the first region 31 and is integrally formed with the first region 31. Similarly, the portion of the outer sheath 30 above the second region 32, that is, the portion inserted into the insertion hole 43a and covered by the second gripping fitting 42, has the same material and resistivity as the second region 32 and is integrally formed with the second region 32.

[0053] The resistivity R1 of the first region 31 of the outer sheath 30 can be adjusted by including a low-resistivity material in the first region 31, for example, in addition to the polymer material mentioned above. Examples of low-resistivity materials include at least one of carbon black, carbon nanotubes, metal powder, metal fibers, and carbon fibers. For metal powders and metal fibers, at least one of the following metals can be used: silver, copper, nickel, aluminum, zinc, etc. These metals may also be in elemental form, alloy, oxide, iodide, or halide form. Materials and methods for adjusting the resistivity of such outer sheath 30 are publicly known, for example, as described in Japanese Patent No. 3602634. If the first region 31 contains more low-resistivity material than the second region 32, the resistivity R1 can be made smaller than the resistivity R2. Therefore, the second region 32 may also contain low-resistivity material, thereby adjusting the resistivity R2 and the resistance ratio Rr. Furthermore, the resistivity ratio Rr can be adjusted by using different polymer materials as the main component in the first region 31 and the second region 32. However, in this embodiment, the second region 32 does not contain a low-resistivity material. That is, in this embodiment, both the first region 31 and the second region 32 use the same polymer material as the main component, and the resistivity R1 and resistivity ratio Rr are adjusted by adjusting the content ratio of the low-resistivity material in the first region 31. In this embodiment, the low-resistivity material is carbon black. The resistivity ratio Rr may be, for example, 4.0 or less, or 3.0 or less. The resistivity ratio Rr may be, for example, 0.5 or more, or 1.0 or more.

[0054] As shown in the figure, the uppermost of the cap portions 38 in the first region 31 is the large-diameter cap portion 38a, and the lowermost of the cap portions 38 in the second region 32 is the small-diameter cap portion 38b. Therefore, in this embodiment, the diameter of the cap portion 38 closest to the second region 32 in the first region 31, i.e., the large-diameter cap portion 38a, is larger than the diameter of the cap portion 38 closest to the first region 31 in the second region 32, i.e., the small-diameter cap portion 38b. When the diameter of the cap portion 38 closest to the second region 32 in the first region 31 is large, the electric field tends to concentrate at the tip of that cap portion 38 (the end of the part with the largest diameter). This makes it possible to mitigate electric field concentration around the boundary 34b when the first gripping fitting 41 is used as the energized side, compared to the case where, conversely, the diameter of the cap 38 located closest to the second region 32 in the first region 31 is smaller than the diameter of the cap 38 located closest to the first region 31 in the second region 32.

[0055] The length L1 may be, for example, 709 mm or more. The length L1 may be, for example, 3143 mm or less. The length L2 may be, for example, 10 mm or more. The length L2 may be, for example, 2164 mm or less. The diameter of the body 36 may be, for example, 20 mm or more. The diameter of the body 36 may be, for example, 50 mm or less, or 30 mm or less. The diameter of the cap 38 may be, for example, 100 mm or more. The diameter of the cap 38 may be, for example, 200 mm or less, or 140 mm or less. The diameter of the large-diameter cap 38a may be, for example, 130 mm or more. The diameter of the large-diameter cap 38a may be, for example, 200 mm or less, or 140 mm or less. The diameter of the small-diameter cap 38b may be, for example, 100 mm or more. The diameter of the small-diameter cap 38b may be, for example, 110 mm or less. The number of caps 38 per 1m of axial length may be, for example, 30 or more. The number of caps 38 per 1m of axial length may be, for example, 35 or less.

[0056] When the insulator 10 is used for insulating electrical equipment with a nominal voltage of 161kV or less, the length L1 may be, for example, 1193mm or less. The length L2 may be, for example, 484mm or less. When the insulator 10 is used for insulating electrical equipment with a nominal voltage of 345kV or less, the length L1 may be, for example, 979mm or more.

[0057] An example of manufacturing the insulator device 1 will be described. First, a core member 20 is formed by a well-known method. Next, an outer cover 30 is formed on the outer circumference of the core member 20, for example, using a known injection molding method. Specifically, a rubber containing the above-mentioned polymer material and low-resistance material, which will be the raw materials for the first region 31, is prepared. The region of the core member 20 that will form the first region 31 is sandwiched in a mold, and the rubber is injected from the injection port of the mold and cured to form the first region 31 of the outer cover 30 on the outer circumference of the core member 20. Similarly, a rubber that will be the raw material for the second region 32 is prepared. The region of the core member 20 that will form the second region 32 is sandwiched in a mold, and the rubber is injected from the injection port of the mold and cured to form the second region 32 on the outer circumference of the core member 20 so as to be in contact with the first region 31. Note that the formation of the first region 31 and the formation of the second region 32 may be performed in either order. Once the outer cover 30 is formed on the outer circumference of the core member 20, both ends of the core member 20 and the outer cover 30 are inserted into the insertion holes 43a of the first gripping fitting 41 and the second gripping fitting 42, respectively. The outer surfaces of the main body 43 of the first gripping fitting 41 and the main body 43 of the second gripping fitting 42 are then crimped and fixed with a die to obtain the insulator 10. After manufacturing the insulator 10 in this way, connecting members 50 are attached to both ends to obtain the insulator device 1.

[0058] As described in detail above, the insulator 10 of this embodiment has a casing 30 that comprises a first region 31 and a second region 32, and the resistivity R1 of the first region 31 is lower than the resistivity R2 of the second region 32. This makes it possible to mitigate electric field concentration around the boundary between the first gripping fitting 41 and the casing 30, that is, around the boundary 34a between the first gripping fitting 41 and the first region 31.

[0059] Furthermore, the diameter of the large-diameter cap 38a, which is located closest to the second region 32 in the first region 31, is larger than the diameter of the small-diameter cap 38b, which is located closest to the first region 31 in the second region 32. This makes it possible to mitigate electric field concentration around the boundary 34b when the first gripping fitting 41 is used as the energized side.

[0060] Furthermore, the resistivity R1 is 6.0 × 10⁻⁶ 12 The fact that the resistance is Ω·cm or less ensures sufficient mitigation of electric field concentration around boundary 34a when the insulator 10 is used for insulating electrical equipment with a nominal voltage of 161kV or less (for example, the insulation between the transmission line and the transmission tower mentioned above). Furthermore, the relationship between the length L1 of the first region 31 and the resistance ratio Rr satisfies equation (1), which mitigates electric field concentration around boundary 34b when the insulator 10 is used for insulating electrical equipment with a nominal voltage of 161kV or less. Moreover, satisfying equation (2) further mitigates electric field concentration around boundary 34b.

[0061] And the resistivity R1 is 3.0 × 10 12 The fact that the resistance is Ω·cm or less ensures sufficient mitigation of electric field concentration around boundary 34a when the insulator 10 is used for insulating electrical equipment with a nominal voltage of 345kV or less (for example, the insulation between the transmission line and the transmission tower mentioned above). Furthermore, the relationship between the length L1 of the first region 31 and the resistance ratio Rr satisfies equation (3), which mitigates electric field concentration around boundary 34b when the insulator 10 is used for insulating electrical equipment with a nominal voltage of 345kV or less. Moreover, satisfying equation (4) further mitigates electric field concentration around boundary 34b.

[0062] It goes without saying that the present invention is not limited in any way to the embodiments described above, and can be implemented in various forms as long as they fall within the technical scope of the present invention.

[0063] For example, in the embodiment described above, the boundary 34b between the first region 31 and the second region 32 was a plane perpendicular to the axial direction of the core member 20, as shown in the upper right cross-sectional view of Figure 1. However, the boundary 34b is not limited to this and may be inclined from a direction perpendicular to the axial direction of the core member 20. For example, as shown in Figure 2, the upper end of the first region 31 may be inclined so as to tuck into the interior of the second region 32. In Figure 2, the upper end surface of the first region 31 (i.e., the boundary 34b) is inclined in a cap shape, and the upper end of the first region 31 protrudes towards the second region 32 (upward) as it approaches the central axis (core member 20), tucking into the interior of the second region 32. When manufacturing an outer shell 30 of this shape, the first region 31 should be formed first, and then the second region 32 should be formed to cover the upper end of the first region 31. Conversely to Figure 2, the lower end of the second region 32 may be tucked into the interior of the first region 31.

[0064] In the embodiment described above, the boundary 34b was located on the body portion 36 of the outer cover 30, but it is not limited to this, and the boundary 34b may also be located on the cap portion 38.

[0065] In the above-described embodiment, the outer covering 30 had two regions, i.e., the first region 31 and the second region 32. However, the present invention is not limited to this, and the outer covering 30 may have three or more regions arranged along the axial direction. FIG. 3 is an explanatory diagram when the core member 20 has a third region 33. In FIG. 3, the outer covering 30 has a third region 33 provided adjacent to the second region 32 in the axial direction and closer to the second gripping fitting 42 than the second region 32. The second region 32 and the third region 33 are in contact with each other vertically at a boundary 34c. The position of the upper end of the third region 33 is the same as the position of the lower end of the second gripping fitting 42. The sum of the length L1, the length L2, and the axial length L3 [mm] of the third region 33 is equal to the distance between the first gripping fitting 41 and the second gripping fitting 42. The resistivity R3 [Ω·cm] of the third region 33 is preferably higher than the resistivity R2 [Ω·cm] of the second region 32. That is, it is preferable that R1 < R2 < R3. Thus, by making the resistivity of the first region 31, the second region 32, and the third region 33 of the outer covering 30 increase in this order, while increasing the resistivity R3 of the third region 33 to increase the resistance value of the entire insulator 10, the difference between the resistivity R1 and the resistivity R2 (for example, the resistance ratio Rr described above) can be reduced or the difference between the resistivity R2 and the resistivity R3 can be reduced. Therefore, compared with the case where the outer covering 30 has only the first region 31 and the second region 32, it is easy to obtain both effects of reducing the resistivity R1 of the first region 31 to relieve the electric field concentration around the boundary 34a and relieving the electric field concentration around the boundaries (here, the boundaries 34b and 34c) of the regions having different resistivities in the outer covering 30. When the outer covering 30 includes four or more regions, it is preferable that the resistance value of each of the four or more regions increases from the first gripping fitting 41 toward the second gripping fitting 42.

[0066] In the embodiment described above, the cap portion 38 had a large-diameter cap portion 38a and a small-diameter cap portion 38b with different diameters. However, all of the cap portions 38 may have the same diameter, or the outer cover 30 may have three or more cap portions of different diameters. In addition, in the embodiment described above, the large-diameter cap portion 38a and the small-diameter cap portion 38b were arranged alternately one at a time along the axial direction. However, other arrangement patterns may be adopted, such as arranging one large-diameter cap portion 38a and two small-diameter cap portions 38b alternately.

[0067] In the above-described embodiment, the first gripping fitting 41 may be equipped with a corona ring for suppressing corona discharge. However, in the above-described embodiment, the insulator 10 can suppress electric field concentration at the boundary 34a because the outer sheath 30 has a first region 31 and a second region 32. Therefore, compared to the case where the first region 31 and the second region 32 are not present, the corona ring can be made smaller or omitted altogether. [Examples]

[0068] The following describes specific examples of insulator 10 as implementation examples. Experimental Examples 2 to 34 correspond to embodiments of the present invention, and Experimental Example 1 corresponds to a comparative example. However, the present invention is not limited to the following embodiments.

[0069] [Experimental Examples 1-4] Experimental Examples 1 to 4 consisted of insulators 10 with various modifications to the outer sheath 30 shown in Figure 1. For each of Experimental Examples 1 to 4, the distribution of electric field strength was investigated when a voltage of 345 kV was applied between the first gripping fitting 41 and the second gripping fitting 42, with the first gripping fitting 41 being the energized side. Experimental Example 1 is an insulator 10 in which the outer sheath 30 does not have a first region 31 and a second region 32, unlike in Figure 1, i.e., the resistivity is the same throughout the entire outer sheath 30. Experimental Example 2 is an insulator 10 in which the outer sheath 30 has a first region 31 and a second region 32, similar to Figure 1. The resistivity R2 of Experimental Example 2 is the same as the resistivity of the outer sheath 30 in Experimental Example 1, and the resistivity R1 of Experimental Example 2 is set to a lower value than resistivity R2. Experimental Example 3 is an insulator 10 in which the resistivity R1 is changed to a lower value compared to Experimental Example 2. Experimental Example 4 is an insulator 10 in which the resistivity R1 and R2 are set to different values ​​than those in Experimental Examples 2 and 3, and the distance L1 is increased. Figures 4 to 7 show the distribution of electric field strength for each insulator 10 in Experimental Examples 1 to 4. In Figures 4 to 7, the horizontal axis shows the distance from the first gripping fitting 41 [mm], i.e., the axial distance from the boundary 34a, and the vertical axis shows the electric field strength [kV / mm]. In addition, the Electric Power Research Institute (EPRI) has proposed achieving the goal that "the length of the region where the electric field strength on the rubber surface continuously exceeds 0.42 kV / mm is less than 10 mm" for polymer insulators. Therefore, Figures 4 to 7 also show a straight line showing an electric field strength of 0.42 kV / mm.

[0070] As shown in Figure 4, in Experimental Example 1, which does not have the first region 31 and the second region 32, the electric field strength was high, at 3.0 kV / mm or more, around boundary 34a (the boundary between the end of the first gripping fitting 41 and the outer covering 30, i.e., the position at a distance of 0 mm from the first gripping fitting 41), confirming electric field concentration around boundary 34a. In contrast, as shown in Figures 5 to 7, in Experimental Examples 2 to 4, which have the first region 31 and the second region 32, the electric field strength around boundary 34a, i.e., the position at a distance of 0 mm from the first gripping fitting 41, was lower in all cases compared to Experimental Example 1, indicating that electric field concentration was mitigated. From this, it was confirmed that by providing the first region 31, which has a lower resistivity than the second region 32, electric field concentration around boundary 34a can be mitigated. This is thought to be because the resistivity R1 of the first region 31 in Experiments 2-4 is lower than that of the outer sheath 30 in Experiment 1, resulting in a smaller difference between the resistivity of the first gripping fitting 41 (which has a very low value because it is a conductor) and resistivity R1. In other words, in Experiments 2-4, the change in resistivity along the axial direction around the boundary 34a is smaller compared to Experiment 1.

[0071] As can be seen from comparing Figure 5 and Figure 4, in Experimental Example 2, unlike Experimental Example 1, a slight electric field concentration was observed at boundary 34b. Also, as can be seen from comparing Figure 5 and Figure 6, in Experimental Example 3, where the resistivity R1 was lower than in Experimental Example 2, the electric field concentration around boundary 34a was further reduced, and the maximum electric field strength was less than 0.42 kV / mm. On the other hand, in Experimental Example 3, the electric field was more concentrated around boundary 34b compared to Experimental Example 2. This is thought to be because the difference between resistivity R1 and resistivity R2 was larger in Experimental Example 3 because the resistivity R1 was lower than in Experimental Example 2, meaning that the change in resistivity along the axial direction around boundary 34b was larger. And, as shown in Figure 7, in Experimental Example 4, the electric field concentration at boundary 34a was reduced compared to Experimental Example 2, and the electric field concentration at boundary 34b was reduced compared to Experimental Example 3. More specifically, in Experimental Example 4, the maximum electric field strength was less than 0.42 kV / mm at both boundary 34a and boundary 34b, and there were no parts of the insulator 10 where the maximum electric field strength exceeded 0.42 kV / mm. Therefore, it was confirmed that both the electric field concentration at boundary 34a and the electric field concentration at boundary 34b could be mitigated by adjusting not only the resistivity R1 but also the resistivity R2 and the distance L. Furthermore, the same trend as in Experimental Examples 1-4 was observed when a voltage of 161 kV was applied between the first gripping fitting 41 and the second gripping fitting 42.

[0072] [Experimental Examples 5-7] Experimental Examples 5 to 7 consisted of insulators 10 that were identical except that the outer sheath 30 had a first region 31 and a second region 32, and their resistivity R1 was different from each other. Specifically, in Experimental Example 5, the resistivity R1 was 5.0 × 10⁻⁶. 12 [Ω·cm] is used, and in experimental example 6, the resistivity R1 is 6.0 × 10⁻⁶. 12 Assuming Ω·cm, in experimental example 7, the resistivity R1 is 7.0 × 10⁻⁶. 12The ratio was set to Ω·cm. For each of Experimental Examples 5 to 7, the distribution of electric field strength was investigated when a voltage of 161kV was applied between the first gripping fitting 41 and the second gripping fitting 42, with the first gripping fitting 41 being the energized side. Based on the distribution of electric field strength, the length of the region around boundary 34a where the electric field strength continuously exceeded 0.42kV / mm (axial length of core member 20) [unit: mm] was investigated for each of Experimental Examples 5 to 7. Hereafter, the "length of the region where the electric field strength continuously exceeds 0.42kV / mm" may be referred to as length D. A smaller length D means that the electric field concentration has been mitigated. Furthermore, if this length D is less than 10 mm, it means that the above-mentioned goal of the Electric Power Research Institute (EPRI) has been achieved. Figure 8 shows the relationship between the resistivity R1 and length D for each of Experimental Examples 5 to 7.

[0073] [Experimental Examples 8-10] Similar to Experimental Examples 5-7, Experimental Examples 8-10 consisted of insulators 10 with the same configuration except that the outer sheath 30 had a first region 31 and a second region 32, and the resistivity R1 was different from each other. Specifically, in Experimental Example 8, the resistivity R1 was 3.0 × 10⁻⁶. 12 Assuming Ω·cm, in experimental example 9, the resistivity R1 is 4.0 × 10⁻⁶. 12 Assuming Ω·cm, in experimental example 10, the resistivity R1 is 5.0 × 10⁻⁶. 12 The resistance was set to Ω·cm. For each of Experimental Examples 8 to 10, the distribution of the electric field strength was investigated when a voltage of 345kV was applied between the first gripping fitting 41 and the second gripping fitting 42, with the first gripping fitting 41 being the energized side. Based on the distribution of the electric field strength, the length D [mm] around the boundary 34a was investigated for each of Experimental Examples 8 to 10. Figure 9 shows the relationship between the resistivity R1 and the length D for each of Experimental Examples 8 to 10.

[0074] As can be seen from Figures 8 and 9, in both the case of applied voltages of 161kV and 345kV, it was confirmed that the lower the resistivity R1, the smaller the length D, and the more the electric field concentration around boundary 34a was reduced. Furthermore, when the applied voltage was 161kV, the resistivity R1 was 7.0 × 10⁻⁶. 12 In experimental example 7, where the resistance R1 was Ω·cm, the length D was 10 mm or more, while the resistivity R1 was 6.0 × 10⁻⁶. 12Experimental examples 5 and 6, which were less than Ω·cm, had a length D of less than 10 mm, thus achieving the above-mentioned goal. From these results, when insulator 10 is used for insulation of electrical equipment with a nominal voltage of 161 kV or less, the resistivity R1 should be 6.0 × 10⁻⁶. 12 It was confirmed that it is preferable to keep it below Ω·cm. When the applied voltage is 345kV, the resistivity R1 is 4.0 × 10⁻⁶. 12 In experimental examples 9 and 10, where the resistivity was greater than Ω·cm, the length D was 10 mm or more, whereas the resistivity R1 was 3.0 × 10⁻⁶. 12 Experimental example 8, which was less than Ω·cm, had a length D of less than 10 mm and thus achieved the above-mentioned goal. From these results, when insulator 10 is used for insulation of electrical equipment with a nominal voltage of 345kV or less, the resistivity R1 should be 3.0 × 10⁻⁶. 12 It was confirmed that it is preferable to keep it below Ω·cm. Furthermore, from a comparison of Figure 8 and Figure 9, it was confirmed that the higher the applied voltage, the lower the upper limit of the resistivity R1 required to achieve the target. This is thought to be because the electric field tends to concentrate around the boundary 34a when the applied voltage is high, and in order to mitigate the electric field concentration, it is necessary to lower the resistivity R1 further (i.e., bring the resistivity R1 closer to the resistivity of the first gripping fitting 41).

[0075] [Experimental Examples 11-21] Experimental Examples 11 to 21 consisted of insulators 10 that were identical except for various changes in length L1 and resistance ratio Rr. For each of Experimental Examples 11 to 21, the distribution of electric field strength was investigated when a voltage of 161kV was applied between the first gripping fitting 41 and the second gripping fitting 42, with the first gripping fitting 41 being the energized side. Based on the distribution of electric field strength, the length D [mm] around the boundary 34b was investigated for each of Experimental Examples 11 to 21. If the length D was less than 10mm, it was evaluated as achieving the target; if it was 10mm or more, it was evaluated as not achieving the target. Figure 10 shows a graph plotting the length L1 and resistance ratio Rr for each of Experimental Examples 11 to 21. In Figure 10, experimental examples judged to have achieved the target are shown with circles, and experimental examples judged to have not achieved the target are shown with squares.

[0076] As shown in Figure 10, when comparing experimental examples with the same resistance ratio Rr, it was confirmed that the longer the length L1, the easier it is to achieve the target (i.e., the electric field concentration at boundary 34b can be further mitigated). This is thought to be because the longer the length L1, the further away the boundary 34b between the first region 31 and the second region 32 is from the first gripping fitting 41, which is the energized side. Furthermore, when comparing experimental examples with the same or similar lengths L1, it was confirmed that the smaller the resistance ratio Rr, the easier it is to achieve the target. This is thought to be because the smaller the resistance ratio Rr, that is, the closer the resistivity R1 and resistivity R2 are, the smaller the change in resistivity along the axial direction around boundary 34b. It was also confirmed that one value of length L1 and the resistance ratio Rr influences the preferred range of the other value, such as being able to achieve the target even with a large resistance ratio Rr if the length L1 is long. In addition, a tendency was observed that the target is easier to achieve in the lower right region of Figure 10, that is, when the length L1 is long and the resistance ratio Rr is small. Based on the results in Figure 10, an approximation curve was derived that shows the boundary between experimental examples judged as not achieving the goal and experimental examples judged as achieving the goal. The dashed line in Figure 10 is the approximation curve derived from the three points of experimental examples 11, 15, and 17, which were judged as not achieving the goal, and the dashed line is the approximation curve derived from the three points of experimental examples 12, 16, and 18, which were judged as achieving the goal. The approximation curve shown by the dashed line in Figure 10 is given by equation (1A) below, and the approximation curve shown by the dashed line is given by equation (2A) below. It is considered that the goal can be achieved if the relationship between the resistance ratio Rr and length L1 in insulator 10 is located in the region to the lower right of the dashed line in Figure 10, so equation (1) above was determined based on equation (1A) below. Note that the dashed approximation curve in Figure 10, i.e., equation (1A), was set to pass through the region slightly to the lower right of experimental examples 11, 15, and 17. Therefore, the region to the lower right of equation (1A) in Figure 10, i.e., the region satisfying equation (1), does not include experimental examples 11, 15, and 17, which were determined to have failed to achieve the target. Furthermore, since it is considered that the target can be more reliably achieved if the relationship between the resistance ratio Rr and length L1 of insulator 10 is located in the region to the lower right of the dashed line in Figure 10, equation (2) above was determined based on equation (2A) below. Figures 11-13 are enlarged sections showing the positional relationship between experimental examples and the approximation curve near the approximation curve in Figure 10.

[0077] Rr=0.00903818763e 0.00675775192L1 (1A) Rr = 0.0074e 0.0069L1 (2A)

[0078] [Experimental Examples 22-34] Similar to Experimental Examples 11-21, insulators 10 were used in Experimental Examples 22-34, with the same configuration except for various changes in length L1 and resistance ratio Rr. For each of Experimental Examples 22-34, the distribution of electric field strength was investigated when a voltage of 345kV was applied between the first gripping fitting 41 and the second gripping fitting 42, with the first gripping fitting 41 being the energized side. Based on the distribution of electric field strength, the length D [mm] around the boundary 34b was investigated for each of Experimental Examples 22-34. If the length D was less than 10mm, it was evaluated as achieving the target; if it was 10mm or more, it was evaluated as not achieving the target. Figure 14 shows a graph plotting the length L1 and resistance ratio Rr for each of Experimental Examples 22-34. In Figure 14, experimental examples judged to have achieved the target are shown with circles, and experimental examples judged to have not achieved the target are shown with squares.

[0079] As shown in Figure 14, the same trend as in Figure 10 was observed when the applied voltage was 345kV. In other words, it was confirmed that the longer the length L1, the easier it is to achieve the goal (i.e., the more the electric field concentration at boundary 34b can be mitigated). When comparing experimental examples where the length L1 was the same or close to each other, it was confirmed that the smaller the resistance ratio Rr, the easier it is to achieve the goal. It was confirmed that one value of length L1 and the resistance ratio Rr influences the preferred range of the other value, for example, the goal can be achieved even with a large resistance ratio Rr if the length L1 is long. In the lower right region of Figure 14, it was confirmed that the longer the length L1 and the smaller the resistance ratio Rr, the easier it is to achieve the goal. Based on the results in Figure 14, an approximate curve was derived showing the boundary between experimental examples that were judged to have not achieved the goal and experimental examples that were judged to have achieved the goal. The dashed line in Figure 14 is the approximate curve derived based on three points in experimental examples 22, 28, and 32 which were judged to have not achieved the goal, and the dashed line is the approximate curve derived based on three points in experimental examples 23, 29, and 33 which were judged to have achieved the goal. The approximation curve shown by the dashed line in Figure 14 is given by equation (3A) below, and the approximation curve shown by the dashed line is given by equation (4A) below. Since it is considered that the target can be achieved if the relationship between the resistance ratio Rr and length L1 of insulator 10 is located in the region to the lower right of the dashed line in Figure 14, equation (3) above was determined based on equation (3A) below. Note that the dashed approximation curve in Figure 14, i.e., equation (3A), was determined to pass through a region slightly to the lower right of experimental examples 22, 28, and 32. Therefore, the region to the lower right of equation (3A) in Figure 14, i.e., the region that satisfies equation (3), does not include experimental examples 22, 28, and 32, which were determined not to have achieved the target. Furthermore, since it is considered that the target can be achieved more reliably if the relationship between the resistance ratio Rr and length L1 of insulator 10 is located in the region to the lower right of the dashed line in Figure 14, equation (4) above was determined based on equation (4A) below. Figures 15-17 are enlarged sections illustrating the positional relationship between experimental examples and the approximation curve in the vicinity of the approximation curve shown in Figure 14.

[0080] Rr=0.0023e 0.0064L1 (3A) Rr = 0.0026e 0.0061L1 (4A) [Industrial applicability]

[0081] The present invention can be used in industries such as the manufacturing of insulators for supporting conductors such as power transmission lines and insulating power transmission lines from transmission towers or other equipment, and insulator devices equipped with the same. [Explanation of Symbols]

[0082] 1 Insulator device, 10 Insulator, 20 Core member, 30 Outer cover, 31 First region, 32 Second region, 33 Third region, 34a~34c Boundary, 36 Body, 38 Cap, 38a Large diameter cap, 38b Small diameter cap, 40 Gripping fitting, 41 First gripping fitting, 42 Second gripping fitting, 43 Main body, 43a Insertion hole, 44 Connection part, 50 Connection member.

Claims

1. A rod-shaped core member, A first gripping fitting and a second gripping fitting that grip both ends of the core member in the axial direction, The outer periphery of the portion of the core member between the first gripping fitting and the second gripping fitting is covered, and the outer covering has a body portion and a plurality of cap portions, and is mainly composed of an insulating polymer material, An insulator equipped with, The outer covering has a first region provided in the axial direction at a position including the boundary between the first gripping fitting and the outer covering, and a second region provided in the axial direction adjacent to the first region and closer to the second gripping fitting than the first region. The first region has a lower resistivity than the second region. insulator.

2. An insulator according to claim 1, The aforementioned plurality of caps have two or more types of caps with different diameters. The diameter of the cap portion located closest to the second region in the first region is greater than the diameter of the cap portion located closest to the first region in the second region. insulator.

3. An insulator according to claim 1 or 2, The outer covering has a third region located adjacent to the second region in the axial direction and closer to the second gripping fitting than the second region, The third region has a higher resistivity than the second region. insulator.

4. An insulator according to claim 1, The aforementioned insulator is used for insulating electrical equipment with a nominal voltage of 161 kV or less. The first region has a resistivity R1 of 6.0 × 10 12 It is less than or equal to Ω·cm. insulator.

5. An insulator according to claim 1 or 4, The aforementioned insulator is used for insulating electrical equipment with a nominal voltage of 161 kV or less. Let L1 [mm] be the axial length of the first region, and logg be the common logarithm of the ratio of the resistivity R1 [Ω・cm] of the first region to the resistivity R2 [Ω・cm] of the second region. 10 When (R2 / R1) is the resistance ratio Rr and e is Napier's number, the following equation (1) is satisfied: Rr≦0.00903818763e 0.00675775192L1 (1) insulator.

6. An insulator according to claim 5, The following equation (2) is satisfied: Rr≦0.0074e 0.0069L1 (2) insulator.

7. An insulator according to claim 1, The aforementioned insulator is used for insulating electrical equipment with a nominal voltage of 345 kV or less. The first region has a resistivity R1 of 3.0 × 10 12 It is less than or equal to Ω·cm. insulator.

8. An insulator according to claim 1 or 7, The aforementioned insulator is used for insulating electrical equipment with a nominal voltage of 345 kV or less. Let L1 [mm] be the axial length of the first region, and logg be the common logarithm of the ratio of the resistivity R1 [Ω・cm] of the first region to the resistivity R2 [Ω・cm] of the second region. 10 When (R2 / R1) is the resistance ratio Rr and e is Napier's number, the following equation (3) is satisfied: Rr≦0.0023e 0.0064L1 (3) insulator.

9. An insulator according to claim 8, The following equation (4) is satisfied: RR2≦0.026% 0.0061L1 (4) insulator.

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