Terminal connection part for power cable

Abstract

This terminal connection part for a power cable comprises: a stress cone that has an insulating part and a semiconductive part which are integrally molded such that the insulating part covers a portion of the semiconductive part, the insulating part being disposed in a manner covering the outer circumference of a cable insulator of the power cable, the semiconductive part being disposed in a manner covering the outer circumference of an external semiconductive layer of the power cable; a cylindrical insulating bushing that has ribs on the outer circumferential surface, that covers, from the outer side, a terminal part of the power cable including at least a portion where the stress cone is attached, and that is filled internally with insulating oil; an upper fitting that closes the upper-side opening of the insulating bushing; a lower fitting that closes the lower-side opening of the insulating bushing; an upper electrode part that is provided on the upper side of the insulating bushing; and a lower electrode part that is provided on the lower side of the insulating bushing. The vertical distance (L3) between the lower end of the upper electrode part and the upper end of the lower electrode part per voltage of the nominal voltage in an AC system and / or the operating voltage in a DC system is 6-20 mm / kV. The leading end position of the semiconductive part in the stress cone is located, within 20-40% with respect to the distance (L3), at a position above the upper end of the lower electrode part. The ratio (L2 / L1)×100 is 10-20% and said ratio is defined by: the interface distance (L1) in the vertical direction between the outer circumferential surface of the cable insulator and the insulating oil; and the total interface distance (L2), in the interface between the insulating part of the stress cone and the insulating oil, of an the interface distance (L21) in the radial direction from a triple junction portion where the outer circumference of the cable insulator, the upper surface of the insulating part of the stress cone, and the insulating oil join to the outer circumference of the upper surface of the insulating part, and of an interface distance (L22) in the vertical direction from the upper end of the insulating part to the height of the leading end position of the semiconductive part in the stress cone on the outer circumferential surface of the insulating part.

Description

Power cable terminations

[0001] The present disclosure relates to a termination for a power cable.

[0002] The power cable termination includes a stress cone made of a synthetic elastomer and attached to the power cable, and a cylindrical insulating porcelain tube that covers the power cable from the outside, with an insulating medium injected into the insulating porcelain tube.

[0003] For example, Patent Document 1 describes a power cable termination structure that includes a power cable, a porcelain tube, a conductor fixing portion that fixes the conductor of the power cable to one end of the porcelain tube, a base portion to which the other end of the porcelain tube is fixed, a tubular electric field relief member that is disposed at an end of the outer semiconductive layer of the power cable, and an insulating fluid sealed within the porcelain tube, with the aim of suppressing the application of large stress to the electric field relief member due to expansion and contraction of the power cable. The power cable termination structure of Patent Document 1 includes a tubular cover member that is provided at a position corresponding to the through hole in the base portion on the outer surface of the power cable, a sealing member that seals between the outer surface of the cover member and the inner surface of the through hole, and a protruding member that protrudes radially outward from the cover member from a portion of the outer surface of the cover member that is disposed within the porcelain tube.

[0004] However, in conventional power cable terminations such as those described in Patent Document 1, the triple junction where the cable insulation of the power cable, the insulation of the stress cone, and the insulating oil intersect is prone to electric field concentration, making it a likely starting point for breakdown of the insulation of the stress cone, and breakdown of the insulation of the stress cone can occur from the triple junction. In particular, the higher the voltage class, the stronger the overall electric field within the termination, increasing the risk of stress cone breakdown. Furthermore, the increased weight of the stress cone and the increased friction at the interface between the stress cone and the power cable can make it difficult to insert the stress cone into the power cable.

[0005] Japanese Patent Application Laid-Open No. 2020-182270

[0006] The object of the present disclosure is to provide a termination connection part for a power cable that can suppress electric field concentration at the triple junction part while maintaining the insertability of the stress cone into the power cable and increase the dielectric breakdown resistance of the insulator part of the stress cone.

[0007] [1] A power cable comprising: a stress cone having an insulator portion and a semi-conductor portion, the insulator portion being integrally molded so as to cover a part of the semi-conductor portion, the insulator portion being arranged so as to cover the outer periphery of the cable insulation of the power cable, and the semi-conductor portion being arranged so as to cover the outer periphery of the outer semi-conductive layer of the power cable; a cylindrical insulating tube having pleats on its outer periphery surface, covering from the outside an end portion of the power cable including at least a portion where the stress cone is attached, and the inside of which is filled with insulating oil; an upper metal fitting that closes an upper opening of the insulating tube; a lower metal fitting that closes a lower opening of the insulating tube; an upper electrode portion provided on the upper side of the insulating tube; and a lower electrode portion provided on the lower side of the insulating tube, wherein the vertical distance (L3) between the lower end of the upper electrode portion and the upper end of the lower electrode portion per at least one of the nominal voltage in an AC system and the operating voltage in a DC system is 6 m or less. a ratio (L2 / L1) x 100 defined by the sum of the interfacial distances (L2) of the vertical interfacial distance (L1) between the outer surface of the cable insulator and the insulating oil, and the radial interfacial distance (L21) from a triple junction where the outer periphery of the cable insulator, the upper surface of the insulator of the stress cone, and the insulating oil intersect to the outer periphery of the upper surface of the insulator, and the vertical interfacial distance (L22) from the upper end of the insulator on the outer surface of the insulator to the height of the tip position of the semi-conductor portion of the stress cone, is 10% or more and 20% or less. [2] The electrical termination for a power cable according to the above [1], wherein the area of ​​the upper surface of the insulator portion of the stress cone is 1 to 25 times the cross-sectional area of ​​the cable insulator of the power cable. [3] The electrical termination for a power cable according to the above [1] or [2], wherein the insulator portion of the stress cone is formed from a synthetic elastomer.

[0008] According to the present disclosure, it is possible to provide a termination connection part for a power cable that can suppress electric field concentration at the triple junction part while maintaining the insertability of the stress cone into the power cable and increase the dielectric breakdown resistance of the insulator part of the stress cone.

[0009] Fig. 1 is a longitudinal cross-sectional view showing an example of a power cable termination according to an embodiment. Fig. 2 shows test results showing the relationship between the vertical position between the lower end of the upper electrode and the upper end of the lower electrode and the surface electric field of the insulated porcelain tube when the vertical distance (L3) between the lower end of the upper electrode and the upper end of the lower electrode is changed for at least one of the nominal voltage when the power cable termination is an AC system and the operating voltage when the power cable termination is a DC system. Fig. 3 shows test results created based on the measurement results of Fig. 2 showing the relationship between the vertical distance (L3) between the lower end of the upper electrode and the upper end of the lower electrode and the maximum surface electric field of the insulated porcelain tube for at least one of the nominal voltage when the power cable termination is an AC system and the operating voltage when the power cable termination is a DC system. Figure 4 shows test results showing the relationship between the ratio γ of the tip of the semi-conductor portion located above the upper end of the lower electrode portion relative to the distance (L3) and the maximum surface electric field of the insulating tube and the maximum surface electric field of the stress cone. Figure 5 shows test results showing the relationship between the ratio γ of the tip of the semi-conductor portion located above the upper end of the lower electrode portion relative to the distance (L3) and the Impulse flashover voltage. Figure 6 shows test results showing the relationship between the ratio (L2 / L1) x 100 and the electric field of the triple junction portion.

[0010] Hereinafter, a detailed description will be given based on an embodiment.

[0011] As a result of extensive research, the inventors focused on the surface resistance ratio at the interface between the insulating oil and the stress cone and cable insulator, and discovered that by newly designing the internal structure of a termination connection part for a power cable including a stress cone, and lowering the electric field at the triple junction part to alleviate electric field concentration, it is possible to suppress electric field concentration at the triple junction part, improve the dielectric breakdown resistance of the insulator part of the stress cone while maintaining the insertability of the stress cone into the power cable, and have completed the present disclosure based on this finding.

[0012] The power cable termination includes an insulator portion and a semiconductive portion, the insulator portion being integrally molded to cover a portion of the semiconductive portion, the insulator portion being arranged to cover the outer periphery of the cable insulation of the power cable, and the semiconductive portion being arranged to cover the outer periphery of the outer semiconductive layer of the power cable. The power cable termination includes a stress cone, a cylindrical insulating tube having pleats on its outer periphery and covering the terminal portion of the power cable, including at least the portion where the stress cone is attached, and the interior of the insulating tube is filled with insulating oil, an upper fitting closing an upper opening of the insulating tube, a lower fitting closing a lower opening of the insulating tube, an upper electrode portion provided above the insulating tube, and a lower electrode portion provided below the insulating tube. The power cable termination has a vertical distance (L3) between the lower end of the upper electrode portion and the upper end of the lower electrode portion per at least one of the nominal voltage in an AC system and the operating voltage in a DC system of 6 mm / kV to 20 mm / kV. In the power cable termination, the tip position of the semiconductive portion of the stress cone is located 20% to 40% above the upper end of the lower electrode portion relative to the distance (L3). In the power cable termination, the ratio (L2 / L1) x 100, defined as the sum of the interfacial distances (L2) between the outer peripheral surface of the cable insulator and the insulating oil, the radial interfacial distance (L21) between the triple junction where the outer periphery of the cable insulator, the upper surface of the insulator of the stress cone, and the insulating oil intersect to the outer periphery of the upper surface of the insulator, and the interfacial distance (L22) between the upper end of the insulator on the outer peripheral surface of the insulator and the height of the tip position of the semiconductive portion of the stress cone, is 10% to 20%.

[0013] 1 is a longitudinal cross-sectional view showing an example of a power cable connection terminal 1 (hereinafter simply referred to as the connection terminal) of the embodiment. As shown in Fig. 1, the power cable connection terminal 1 of the embodiment includes a stress cone 3, an insulating porcelain tube 4, an upper fitting 5a, a lower fitting 5b, an upper electrode 6a, and a lower electrode 6b.

[0014] The stress cone 3 constituting the termination connection part 1 has an insulator part 31 and a semi-conductor part 32, and is attached to the power cable 2. The stress cone 3 is integrally molded so that the insulator part 31 covers part of the semi-conductor part 32. The semi-conductor part 32 is provided on the low-voltage side below the stress cone 3. No electric field relaxation layer to relieve electric field concentration is provided around the outer periphery of the stress cone 3.

[0015] The insulating portion 31 of the stress cone 3 is made of a synthetic elastomer such as ethylene propylene diene rubber or silicone rubber, and the semi-conductive portion 32 is made of semi-conductive rubber.

[0016] The power cable 2 fitted with the stress cone 3 has, from the inside out, a cable conductor 21, a cable insulator 22, an outer semiconductive layer 23, a shielding layer (not shown), and a cable sheath (not shown). At the terminal portion 2a of the power cable 2, a step stripping process is performed so that the cable conductor 21 is exposed from the cable insulator 22, the cable insulator 22 is exposed from the outer semiconductive layer 23, the outer semiconductive layer 23 is exposed from the shielding layer (not shown), and the shielding layer is exposed from the cable sheath (not shown). The cable insulator 22 is made of a plastic such as cross-linked polyethylene. The power cable 2 may be a power cable for AC transmission or a power cable for DC transmission.

[0017] Regarding the stress cone 3 attached to the terminal portion 2a of the power cable 2, the insulator portion 31 is arranged to cover the outer periphery of the cable insulator 22 of the power cable 2 that has been step-stripped, and the semi-conductive portion 32 is arranged to cover the outer periphery of the outer semi-conductive layer 23 of the power cable 2.

[0018] The insulator portion 31 of the stress cone 3 is cylindrical. The upper end of the insulator portion 31 on the high-voltage side does not have a so-called tapered portion where the outer dimensions of the insulator portion 31 (the thickness of the insulator portion 31) gradually decrease, and the thickness of the insulator portion 31 is uniform or approximately uniform along the longitudinal direction of the power cable 2. The upper surface of the insulator portion 31 is perpendicular or approximately perpendicular to the longitudinal direction of the power cable 2.

[0019] By not having the tapered portion, the stress cone 3 can avoid a decrease in ease of insertion into the power cable 2 and suppress a decrease in surface pressure. In particular, from the viewpoint of further improving these effects, it is preferable that the area of ​​the upper surface of the insulator portion 31 of the stress cone 3 is 1 to 25 times the cross-sectional area of ​​the cable insulator 22 of the power cable 2.

[0020] The insulating porcelain tube 4 is cylindrical and has a plurality of pleats on its outer surface provided at regular intervals along the longitudinal direction of the insulating porcelain tube 4. The insulating porcelain tube 4 is not particularly limited as long as it is made of a material having insulating properties, and may be made of, for example, ceramic, rubber, or plastic such as fiber-reinforced plastic.

[0021] An upper fitting 5a that closes the upper opening of the insulating porcelain tube 4 is provided on the upper, high-voltage side of the insulating porcelain tube 4. The upper fitting 5a seals the upper opening of the insulating porcelain tube 4. A cable conductor 21 of the power cable 2 is inserted into a through-hole (not shown) provided in the upper fitting 5a. Furthermore, as shown in Fig. 1, the termination part 1 may include a shield ring 51 that covers the upper fitting 5a from above.

[0022] A lower fitting 5b that closes the lower opening of the insulating porcelain tube 4 is provided on the lower side, which is the low-voltage side, of the insulating porcelain tube 4. The lower fitting 5b seals the lower opening of the insulating porcelain tube 4. The outer semiconductive layer 23 of the power cable 2 is inserted into a through hole (not shown) provided in the lower fitting 5b. A sealing fitting (not shown) that secures the power cable 2 may be inserted from outside the outer semiconductive layer 23 into the through hole (not shown) of the lower fitting 5b.

[0023] The insulating porcelain pipe 4 covers the terminal portion 2a of the power cable 2 from the outside, including at least the portion where the stress cone 3 is attached, and the inside of the insulating porcelain pipe 4 is filled with insulating oil i.

[0024] An upper electrode portion 6a, which is a high-voltage electrode portion, is provided on the upper side of the insulating porcelain tube 4. The upper electrode portion 6a has the same potential as the cable conductor 21 of the power cable 2. A lower electrode portion 6b, which is a ground electrode, is provided on the lower side of the insulating porcelain tube 4. The lower electrode portion 6b has the same potential as the ground.

[0025] In order to reduce the risk of discharge along the surface of the insulating porcelain tube 4 during high-voltage power transmission with a transmission voltage of 500 kV or more, it is preferable that the length of the insulating porcelain tube 4 along the longitudinal direction of the power cable 2 be longer than conventional, for example, 7.0 m or more.

[0026] As a result of the insulating porcelain tube 4 being longer than conventional, the interface distance (L1) increases compared to conventional termination connections, the ratio (L2 / L1) changes, and the respective resistance contributions of the interface distance (L1) and the interface distance (L2) change.

[0027] Here, the interfacial distance (L1) is the distance (L1) of the interface in the vertical direction between the outer peripheral surface of the cable insulator 22 and the insulating oil i, i.e., the vertical length of contact between the outer peripheral surface of the cable insulator 22 and the insulating oil i. The interfacial distance (L1) corresponds to the vertical length of the exposed portion of the stripped cable conductor 21 inside the insulating porcelain tube 4.

[0028] In addition, the interface distance (L2) is the total interface distance (L2 = L21 + L22) of the radial interface distance (L21) from the triple junction portion 7 to the outer periphery of the upper surface of the insulator portion 31 at the interface between the insulator portion 31 of the stress cone 3 and the insulating oil i, and the vertical interface distance (L22) from the upper end of the insulator portion 31 on the outer periphery of the insulator portion 31 to the height of the tip position of the semi-conductor portion 32 in the stress cone 3.

[0029] Considering each component, including the resistance (R1) at the interface distance (L1) and the resistance (R2) at the interface distance (L2), as a resistance circuit, in order to lower the electric field at the triple junction 7, which is the part where the outer periphery of the cable insulator 22, the top surface of the insulator portion 31, and the insulating oil i intersect, it is better for the ratio of R1 to R2 to be close to 1:1. In conventional termination connections, the ratio of R1:R2 is about 50:1.

[0030] Considering this situation, it is effective to shorten L1 and lengthen L2 (especially L22) compared to conventional terminations in order to reduce the difference between R1 and R2. In other words, the length of the insulator portion 31 of the stress cone 3 along the longitudinal direction of the power cable 2 is longer than conventional. In the termination 1 of the embodiment, for example, R1:R2 = approximately 20:1.

[0031] Figure 2 shows test results showing the relationship between the vertical position between the lower end of the upper electrode portion 6a and the upper end of the lower electrode portion 6b and the surface electric field of the insulating porcelain tube 4 when the vertical distance (L3) between the lower end of the upper electrode portion 6a and the upper end of the lower electrode portion 6b is changed per at least one of the nominal voltage when the termination connection portion 1 is an AC system and the operating voltage when the termination connection portion 1 is a DC system.

[0032] 2, when the distance (L3) per voltage is short, the surface electric field on the lower electrode portion 6b side of the insulating porcelain tube 4 becomes high, and the overall surface electric field of the insulating porcelain tube 4 becomes high. On the other hand, when the distance (L3) per voltage is long, the overall surface electric field of the insulating porcelain tube 4 becomes low, but the peak of the surface electric field in the part of the insulating porcelain tube 4 surrounding the stress cone 3 (approximately 70 to 80% position) becomes sharp and high.

[0033] Figure 3 shows test results, created based on the measurement results of Figure 2, that show the relationship between the vertical distance (L3) between the lower end of the upper electrode portion 6a and the upper end of the lower electrode portion 6b and the maximum value of the surface electric field of the insulating porcelain tube 4, per at least one of the nominal voltage when the termination connection portion 1 is an AC system and the operating voltage when the termination connection portion 1 is a DC system.

[0034] Test results to date have shown that discharges occur when the maximum value of the surface electric field of the insulating porcelain tube 4 is 0.1105 (% / mm) or more. Based on this technical knowledge and examination based on Figures 2 and 3, the vertical distance (L3) between the bottom end of the upper electrode portion 6a and the top end of the lower electrode portion 6b per voltage, either the nominal voltage when the termination connection portion 1 is an AC system or the operating voltage when the termination connection portion 1 is a DC system, is set to be between 6 mm / kV and 20 mm / kV.

[0035] Figure 4 shows test results showing the relationship between the ratio γ of the tip position of the semi-conductor portion 32 located above the upper end of the lower electrode portion 6b relative to the distance (L3), and the maximum value of the surface electric field of the insulating porcelain tube 4 and the maximum value of the surface electric field of the stress cone 3. Figure 5 also shows test results showing the relationship between γ and the Impulse flashover voltage. As shown in Figure 1, the semi-conductor portion 32 extends upward from the lower end of the stress cone 3, and the tip position of the semi-conductor portion 32 is the position of the upper end of the semi-conductor portion 32 on the stress cone 3. These test results were obtained using a 154 kV-class power cable 2.

[0036] As shown in Figure 4, when γ is small, the surface electric field of the insulating porcelain tube 4 becomes high, increasing the risk of discharge on the surface of the insulating porcelain tube 4, while when γ is large, the surface electric field of the stress cone 3 becomes high, increasing the risk of discharge on the surface of the stress cone 3. In addition, the standard (JEC-3408, Institute of Electrical Engineers of Japan, Electrotechnical Standards Committee Standard) stipulates that the stress cone will not be destroyed even if the impulse flashover voltage is 1035 kV or higher. In Figure 5, conditions under which neither breakdown of the stress cone 3 nor flashover on the surface of the insulating porcelain tube 4 occurred even when the impulse flashover voltage was 1035 kV or higher are indicated by a circle, and conditions under which at least one of breakdown of the stress cone 3 and flashover on the surface of the insulating porcelain tube 4 occurred when the impulse flashover voltage was less than 1035 kV, i.e., conditions under which the standard was not met, are indicated by an x.

[0037] Based on this technical knowledge, and considering Figures 4 and 5, it was decided that the tip position of the semi-conductor portion 32 in the stress cone 3 relative to the above distance (L3) should be positioned 20% to 40% above the upper end of the lower electrode portion 6b.

[0038] Figure 6 shows test results showing the relationship between the ratio (L2 / L1) x 100 and the electric field at the triple junction 7. As shown in Figure 6, when the ratio (L2 / L1) was less than 10%, the stress cone 3 was destroyed. Furthermore, when the ratio (L2 / L1) was greater than 20%, the stress cone 3 was too long, making it impossible to insert the stress cone 3 into the power cable 2, or making it difficult to insert the stress cone 3 into the power cable 2.

[0039] Based on this technical knowledge and consideration based on FIG. 6, the ratio (L2 / L1)×100 defined by the interface distance (L1) and the interface distance (L2) is set to 10% or more and 20% or less.

[0040] As described above, when the distance (L3) per voltage for at least one of the nominal voltage and the operating voltage is within the above range, the tip position of the semiconductive portion 32 relative to the distance (L3) is within the above range, and the ratio (L2 / L1) x 100 is within the above range, the electric field concentration at the triple junction portion 7 can be suppressed while maintaining the insertability of the stress cone 3 into the power cable 2, and the dielectric breakdown resistance of the insulator portion 31 of the stress cone 3 can be improved. In particular, even in high-voltage transmission with a transmission voltage of 500 kV or more, the effect of suppressing the electric field concentration at the triple junction portion 7 and improving the dielectric breakdown resistance of the insulator portion 31 can be maintained. Furthermore, when the distance (L3) per voltage for both the nominal voltage in an AC system and the operating voltage in a DC system is within the above range, the termination connection portion 1 can be used in both AC and DC systems, improving design efficiency and enabling a more streamlined product lineup.

[0041] According to the embodiment described above, by focusing on the surface resistance ratio of the interface between the insulating oil and the stress cone and the cable insulator, the internal structure of the power cable termination including the stress cone is newly designed, and by lowering the electric field at the triple junction and mitigating electric field concentration, it is possible to suppress electric field concentration at the triple junction in the termination and improve the dielectric breakdown resistance of the insulator part of the stress cone.Furthermore, it is possible to maintain the insertability of the stress cone into the power cable.

[0042] Although the embodiments have been described above, the present invention is not limited to the above embodiments, but includes all aspects encompassed by the concept and scope of the claims of the present disclosure, and can be modified in various ways within the scope of the present disclosure.

[0043] Next, examples and comparative examples will be described, but the present disclosure is not limited to these examples.

[0044] (Examples 1-4, 8-14 and Comparative Examples 1-2, 5-9) Using a DC system termination connection having the configuration shown in Figure 1, the vertical distance (L3) between the lower end of the upper electrode portion and the upper end of the lower electrode portion, γ, and the ratio (L2 / L1) x 100 per operating voltage of the DC system were set to the values ​​shown in Table 1. Tests were conducted under conditions based on the IEC standard at an operating voltage of 525 kV for Examples 1-4, 8-12, and 14 and Comparative Examples 1-2, 5-6, and 8-9, an operating voltage of 170 kV for Example 13, and an operating voltage of 320 kV for Comparative Example 7. The stress cone insulators were then visually inspected for damage starting from the triple junction. The results are shown in Table 1. In Table 1, ○ indicates that the stress cone insulator was not damaged, and × indicates that the stress cone insulator was damaged. Furthermore, the insertability of the stress cone into the power cable was evaluated for Examples 1 to 4, 8 to 14 and Comparative Examples 1, 5, and 9. As a result, the stress cone could be easily inserted into the power cable in the above Examples, but the stress cone could not be easily inserted into the power cable in the above Comparative Examples.

[0045] (Examples 5 to 7 and Comparative Examples 3 and 4) Using the termination connection part of an AC system having the configuration shown in Figure 1, tests were conducted under conditions based on the JEC standard at a nominal voltage of 154 kV, with the vertical distance (L3) between the lower end of the upper electrode part and the upper end of the lower electrode part, γ, and the ratio (L2 / L1) x 100 set to the values ​​shown in Table 1 per nominal voltage of the AC system. The stress cone's insulator was then visually inspected for damage starting from the triple junction. The results are shown in Table 1. Furthermore, the insertability of the stress cone was evaluated for Examples 5 to 7, and the stress cone was easily inserted into the power cable.

[0046]

[0047] As shown in Table 1, in Examples 1 to 14, the distance (L3) per at least one of the nominal voltage and the operating voltage, the ratio γ of the tip position of the semi-conductor portion located above the upper end of the lower electrode portion relative to the distance (L3), and the ratio (L2 / L1) x 100 were all within the specified ranges, so that the stress cone's insertability into the power cable was maintained while preventing breakdown of the insulator portion of the stress cone starting from the triple junction. On the other hand, in Comparative Examples 1 to 9, at least one of the distance (L3) per at least one of the nominal voltage and the operating voltage, the ratio γ of the tip position of the semi-conductor portion located above the upper end of the lower electrode portion relative to the distance (L3), and the ratio (L2 / L1) x 100 were outside the specified ranges, so that the stress cone's insertability into the power cable and / or the prevention of breakdown of the insulator portion of the stress cone starting from the triple junction could not be maintained.

[0048] Next, the insertability of the stress cone into the power cable was evaluated in detail for Examples 1 to 7 and Comparative Examples 1 and 2. Specifically, the insertability of the stress cone was evaluated when the area of ​​the upper surface of the insulator part of the stress cone relative to the cross-sectional area of ​​the cable insulator of the power cable was the value shown in Table 2. The results are shown in Table 2.

[0049]

[0050] As shown in Table 2, in Examples 2 to 6 and Comparative Example 2, the area of ​​the upper surface of the insulator portion relative to the cross-sectional area of ​​the cable insulator was within a specified range, thereby improving the ease of inserting the stress cone 3 into the power cable 2.

[0051] REFERENCE SIGNS LIST 1 Power cable terminal connection part (terminal connection part) 2 Power cable 2a Power cable terminal part 21 Cable conductor 22 Cable insulator 23 Outer semiconductive layer 3 Stress cone 31 Insulator part 32 Semiconductive part 32a Tip of semiconductive part 4 Insulating porcelain tube 41 Fold 5a Upper metal fitting 5b Lower metal fitting 51 Shield ring 6a Upper electrode part 6b Lower electrode part 7 Triple junction part i Insulating oil

Claims

1. A stress cone having an insulator portion and a semi-conductor portion, the insulator portion being integrally molded so as to cover a portion of the semi-conductor portion, the insulator portion being arranged to cover the outer periphery of the cable insulation of a power cable, and the semi-conductor portion being arranged to cover the outer periphery of the outer semi-conductive layer of the power cable; a cylindrical insulating tube having pleats on its outer periphery surface, covering from the outside the terminal portion of the power cable including at least the portion where the stress cone is attached, and the inside of which is filled with insulating oil; an upper metal fitting that closes the upper opening of the insulating tube; a lower metal fitting that closes the lower opening of the insulating tube; an upper electrode portion provided on the upper side of the insulating tube; and a lower electrode portion provided on the lower side of the insulating tube, wherein the vertical distance (L3) between the lower end of the upper electrode portion and the upper end of the lower electrode portion per at least one of the nominal voltage in an AC system and the operating voltage in a DC system is between 6 mm / kV and 20 mm / kV; a ratio (L2 / L1) x 100 defined by the sum of the interfacial distances (L2) of the vertical interfacial distance (L1) between the outer surface of the cable insulator and the insulating oil, and the radial interfacial distance (L21) between the triple junction at the interface between the outer periphery of the cable insulator, the upper surface of the insulator of the stress cone, and the insulating oil, where the radial interfacial distance (L21) is from the triple junction at which the outer periphery of the cable insulator, the upper surface of the insulator of the stress cone, and the insulating oil intersect, to the outer periphery of the upper surface of the insulator, and the vertical interfacial distance (L22) from the upper end of the insulator on the outer periphery of the insulator to the height of the tip position of the semi-conductor portion on the stress cone, is 10% or more and 20% or less.

2. A termination connection part for a power cable as described in claim 1, wherein the area of ​​the upper surface of the insulator part of the stress cone is between 1 and 25 times the cross-sectional area of ​​the cable insulator of the power cable.

3. A termination for a power cable according to claim 1 or 2, wherein the insulator portion of the stress cone is formed from a synthetic elastomer.

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