Polymer bushing

Abstract

To provide a polymer bushing which has an electric field relaxation layer composed of zinc oxide, and has stable electric field relaxation performance for a long period.SOLUTION: A polymer bushing comprises: an internal conductor; an insulation cylinder arranged on the outer periphery of the internal conductor; a shielding metal fitting which is embedded in the insulation cylinder concentrically with the internal conductor; a body portion coating the outer periphery of the insulation cylinder; and a plurality of umbrella-shaped pleat formed on the outer periphery of the body portion in such a way as to be separated in a longitudinal direction; and an electric field relaxation layer which is arranged along the interface between the insulation cylinder and the polymer coating body, whose rear end is connected to the shielding metal fitting. The electric field relaxation layer is composed of a zinc oxide layer obtained by mixing a resin material and zinc oxide powder, and an electric field relaxation performance value after 30 years predicted on the basis of a deterioration index acquired in a period shorter than 30 years is 65% or more of a design value of an electric field relaxation performance value.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a polymeric cannula. [Background technology]

[0002] In recent years, from the viewpoint of reducing the weight, slimming, and size of sleeves, standardizing sleeve types, and simplifying the manufacturing process, polymer sleeves with a solid insulation structure (completely dry type) have been put to practical use, in which a polymer coating made of silicone rubber or the like is directly molded onto the outer surface of an insulating tube made of epoxy resin or the like. Such polymer sleeves are called direct molded types.

[0003] In direct-molded polymer sleeves, the polymer covering typically has a body that covers the outer periphery of the insulating tube and umbrella-shaped pleats formed at intervals in the longitudinal direction on the outer periphery of the body. To improve corona resistance, an electric field relaxation layer is disposed at the interface between the insulating tube and the polymer covering. For example, Patent Documents 1 and 2 disclose the formation of an electric field relaxation layer using zinc oxide (ZnO), which has varistor properties. Varistor properties are nonlinear current-voltage characteristics (IV characteristics) in which the resistance value drops sharply and current begins to flow when a voltage above a certain level is applied. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2004-522259 [Patent Document 2] Special Publication No. 2000-503454 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, it is expected that the electric field relaxation effect of the above-mentioned zinc oxide layer will decrease to some extent over the long term. Specifically, the decrease in the electric field relaxation effect means a decrease in the varistor voltage. However, in the early stages of manufacture, it has not been established what characteristics the electric field relaxation layer must have in order to have a stable electric field relaxation effect over the long term.

[0006] An object of the present invention is to provide a polymer sleeve having an electric field relaxation layer made of zinc oxide and having stable electric field relaxation performance over a long period of time. [Means for solving the problem]

[0007] The polymer sleeve according to the present invention comprises: an inner conductor; an insulating tube disposed around the outer periphery of the inner conductor; a shielding metal fitting embedded in the insulating tube concentrically with the inner conductor; a polymer covering having a body portion covering the outer periphery of the insulating tube and a plurality of umbrella-shaped pleats formed at intervals in the longitudinal direction on the outer periphery of the body portion; an electric field relaxation layer disposed along the interface between the insulating tube and the polymer covering, the rear end of which is connected to the shielding metal fitting; The electric field relaxation layer is composed of a zinc oxide layer made by mixing a resin material and zinc oxide powder, and the electric field relaxation performance value after 30 years, predicted based on a deterioration index obtained in a period shorter than 30 years, is 65% or more of the design value of the electric field relaxation performance value. [Effects of the Invention]

[0008] According to the polymer sleeve of the present invention, the electric field relaxation layer made of zinc oxide has stable electric field relaxation performance for a long period of time, so that the reliability of the polymer sleeve can be significantly improved. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a partial cross-sectional view showing the overall structure of a polymer sleeve according to an embodiment. [Figure 2]FIG. 2 is a diagram showing the influence of temperature and voltage degradation on the electric field relaxation performance. [Figure 3] FIG. 3 is a diagram showing the effect of repeated surge degradation on the electric field relaxation performance. [Figure 4] FIG. 4 is a diagram showing the influence of moisture absorption deterioration on the electric field relaxation performance. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0011] Fig. 1 is a partial cross-sectional view showing the overall configuration of a polymer sleeve 1 according to an embodiment of the present invention. In the following, the upper side in the drawing will be referred to as the "front side S1" and the lower side as the "rear side S2." The polymer sleeve 1 shown in Fig. 1 is an equipment bushing having a head portion H on the rear side S2 to be placed in electric power equipment such as a transformer.

[0012] As shown in Figure 1, the polymer sleeve 1 includes a rod-shaped inner conductor 10 located in the center, an insulating tube 20 provided on the outer periphery of the inner conductor 10, a shielding metal fitting 30 formed integrally with the insulating tube 20, a polymer coating 40 provided on the outer periphery of the insulating tube 20, and an electric field relaxation layer 50 located at the interface between the insulating tube 20 and the polymer coating 40.

[0013] The inner conductor 10, insulating tube 20, shielding metal fittings 30, polymer coating 40, and electric field relaxation layer 50 are integrally formed by molding. Specifically, the insulating tube 20 is molded with the inner conductor 10 and shielding metal fittings 30 set in a mold. The molded insulating tube 20 is then set in a mold for molding the electric field relaxation layer, and the electric field relaxation layer 50 is molded on the outer surface of the insulating tube 20 (in this embodiment, the outer surface of the large-diameter portion 23 of the insulating tube 20, which will be described later). Furthermore, the molded electric field relaxation layer 50 is set in a mold for molding the polymer coating, and the polymer coating 40 is molded on the outer surfaces of the insulating tube 20 and the electric field relaxation layer 50. In the polymer sleeve 1, when a voltage is applied, the inner conductor 10 is at a high potential, and the shielding metal fittings 30 are at a ground potential.

[0014] The inner conductor 10 is made of a conductive material suitable for conducting electricity, such as copper, aluminum, a copper alloy, or an aluminum alloy. In the polymer sleeve 1, both ends (a leading end 11 and a trailing end 12) of the inner conductor 10 are exposed from the insulating tube 20. The leading end 11 of the inner conductor 10 is connected to an overhead line or a drop line (not shown), and the trailing end 12 of the inner conductor 10 is connected to a high-voltage conductor in an electric power device.

[0015] The insulating tube 20 is made of a hard plastic resin material with high mechanical strength, such as epoxy resin or FRP (Fiber Reinforced Plastics). In this embodiment, the insulating tube 20 has a small-diameter section 21 formed in a straight cylindrical shape at the front end side S1, a tapered section 22 that gradually increases in diameter from the small-diameter section 21 toward the rear end side S2, and a large-diameter section 23 formed in a straight cylindrical shape at the rear end side S2 of the tapered section 22. The rear end of the insulating tube 20 forms a head section H that is placed inside the electric power equipment. Here, the rear end of the insulating tube 20 refers to the rear end side S2 of the large-diameter section 23, i.e., the portion connected to the large-diameter section 23 on the rear end side S2 from the flange section 32 of the shielding metal fitting 30.

[0016] If the diameter of the insulating tube 20 is increased overall, the surface potential of the polymer sleeve 1 can be easily reduced, but this reduces the earthquake resistance and bending load resistance required of the polymer sleeve 1. By making the insulating tube 20 have a structure consisting of a small diameter section 21, a tapered section 22, and a large diameter section 23, it is possible to achieve both electrical performance and earthquake resistance and bending load resistance.

[0017] The shielding metal fitting 30 has a cylindrical portion 31 embedded concentrically with the inner conductor 10 in the insulating tube 20, and a flange portion 32 extending radially outward from the rear end of the cylindrical portion 31. The cylindrical portion 31 has electric field relaxation properties and relaxes the electric field of the polymer sleeve 1. The polymer sleeve 1 is fixed to the electric equipment in an airtight and watertight manner by connecting the flange portion 32 with a connecting member (not shown) such as a bolt while it is placed on the case C of the electric power equipment via a sealing member (not shown) such as an O-ring.

[0018] The polymer coating 40 is made of a material with excellent electrical insulation properties (for example, a polymeric material such as silicone polymer). The polymer coating 40 is formed so as to cover the outer periphery of the insulating tube 20 excluding the head portion H. In other words, the polymer coating 40 is formed so as to cover the outer periphery of the insulating tube 20 on the tip side S1 of the flange portion 32 of the shielding metal fitting 30. The polymer coating 40 has a body portion 41 that covers the outer periphery of the insulating tube 20, and a plurality of umbrella-shaped folds 42 formed on the outer periphery of the body portion 41 at intervals in the longitudinal direction.

[0019] The electric field buffer layer 50 is formed of a zinc oxide layer obtained by mixing a resin material (for example, an epoxy resin in the embodiment) with zinc oxide (ZnO) powder. In the embodiment, the electric field buffer layer 50 is formed by mixing 80% by mass or more and 95% by mass or less of zinc oxide (ZnO) powder with epoxy resin. If the amount of zinc oxide (ZnO) powder in the electric field buffer layer 50 is less than 80% by mass, the initial value of the switching point changes and the electric field buffering performance becomes insufficient. Therefore, it is preferable that the amount of zinc oxide (ZnO) powder mixed with the epoxy resin be 80% by mass or more. Furthermore, if the amount of zinc oxide (ZnO) powder in the electric field buffer layer 50 exceeds 95% by mass, it may be impossible to form a zinc oxide layer using the epoxy resin as a binder. Therefore, it is preferable that the amount of zinc oxide (ZnO) powder mixed with the epoxy resin be 95% by mass or less.

[0020] The electric field relaxation layer 50 is formed integrally with the insulating tube 20 by molding on the outer circumferential surface of the insulating tube 20. That is, the electric field relaxation layer 50 is provided along the interface between the insulating tube 20 and the polymer coating 40 in the polymer sleeve 1. The rear end of the electric field relaxation layer 50 is electrically connected to the shielding metal fitting 30.

[0021] By forming the electric field relaxation layer 50 from zinc oxide (ZnO), a nonlinear material, the increase in current density changes suddenly when the electric field of the epoxy resin layer (i.e., the electric field relaxation layer 50) in which zinc oxide (ZnO) powder is dispersed exceeds a threshold value. The electric field (V / mm) at this changing threshold value is called the switching point (SP). When a voltage is applied to the internal conductor 10 and the electric field exceeds the threshold value, the electric field relaxation layer 50 relaxes the electric field applied to the polymer sleeve 1. By forming the electric field relaxation layer 50, the electric field distribution is optimized, thereby improving the electrical performance of the polymer sleeve 1.

[0022] The electric field relaxation layer 50 is designed to satisfy a predetermined electric field relaxation performance value. The electric field relaxation performance value is a numerical representation of the electric field relaxation performance of the electric field relaxation layer 50, and is, for example, the switching point (SP). The electric field relaxation performance value may be the electric field at the switching point (SP), or may be a value obtained by converting the varistor voltage into an electric field.

[0023] The electric field relaxation performance value of the electric field relaxation layer 50 satisfies the design value at the initial stage of manufacture. However, the electric field relaxation performance value of the electric field relaxation layer 50 decreases with long-term use. In this embodiment, in order to ensure stable electric field relaxation performance after 30 years, the electric field relaxation performance value SP(30) after 30 years is predicted based on the degradation index K obtained in a period shorter than 30 years, and the electric field relaxation layer 50 is formed so that the predicted electric field relaxation performance value SP(30) is greater than the allowable limit value SP(L). The allowable limit value SP(L) is set to, for example, 65% or more of the design value SP(i). Furthermore, a period shorter than 30 years may be a few hours after manufacture or a few years (e.g., 3-4 years).

[0024] When an electric field relaxation layer 50 having a small electric field relaxation performance value, specifically a switching point (SP) lower than the allowable limit value SP(L) (for example, less than 65% of the design value SP(i)), is used, the electric field relaxation layer 50, which is a zinc oxide layer, generates heat when the polymer sleeve 1 is used normally, and if the heat generated exceeds the glass transition temperature (Tg) of the epoxy resin, this may affect the insulating performance of the polymer sleeve 1 and ultimately lead to insulation breakdown of the polymer sleeve 1.

[0025] The degradation index K is an index that is a factor in the long-term performance degradation of the electric field relaxation layer 50, and includes, for example, at least one of the temperature-voltage degradation index KT, the repeated surge degradation index Ki, and the moisture absorption degradation index Kw. The temperature-voltage degradation index KT is the degradation rate of the electric field relaxation performance value after 30 years, calculated by linear extrapolation based on measurement data when a voltage is applied under specified conditions (temperature, voltage, and time). The repeated surge degradation index Ki is the degradation rate of the electric field relaxation performance value when a surge voltage is applied equal to the number of switching surges (e.g., 2,000 times) expected to be received over 30 years. The moisture absorption degradation index Kw is the degradation rate of the electric field relaxation performance value when the moisture inside the electric field relaxation layer 50 is saturated (water absorption and dissipation are in equilibrium).

[0026] When one of the temperature-voltage degradation index KT, repeated surge degradation index Ki, and moisture absorption degradation index Kw is used alone as the degradation index, the electric field relaxation performance value SP(30) after 30 years is calculated by multiplying the design value SP(i) of the electric field relaxation performance value by the selected degradation index. When a composite degradation index that combines the temperature-voltage degradation index KT, repeated surge degradation index Ki, and moisture absorption degradation index Kw is used as the degradation index, the electric field relaxation performance value SP(30) after 30 years is calculated by multiplying the design value SP(i) of the electric field relaxation performance value by each of the selected multiple degradation indexes.

[0027] The temperature-voltage degradation index KT, the repeated surge degradation index Ki, and the moisture absorption degradation index Kw are each preferably 0.9 or greater. When one of these indices is used alone, the allowable limit value SP(L) is 65% of the design value SP(i). Therefore, the electric field relaxation performance value SP(30) after 30 years is greater than the allowable limit value SP(L) because the design value SP(i) is multiplied by 0.9 or more. When the combined degradation index is used, the electric field relaxation performance value SP(30) after 30 years is obtained by multiplying the design value SP(i) by the temperature-voltage degradation index KT, the repeated surge degradation index Ki, and the moisture absorption degradation index Kw and by 0.9 or more three times. Therefore, the electric field relaxation performance value SP(30) after 30 years is greater than the allowable limit value SP(L) (65% of the design value SP(i)).

[0028] Fig. 2 is a diagram showing the influence of temperature and voltage application degradation on the electric field relaxation performance. Fig. 2 shows the rate of deterioration of the electric field relaxation performance value with respect to the voltage application time when a voltage application test was conducted using a test piece under test conditions (for example, a test temperature of 70°C and an electric field strength equivalent to an operating voltage of 97 kV) set based on the conditions during actual operation of a 154 kV polymer sleeve 1.

[0029] The test piece was a 50 mm x 50 mm x 4 mm thick sheet formed using the same method as the electric field relaxation layer 50 of the polymer sleeve 1, and was made of a zinc oxide layer made by mixing epoxy resin and zinc oxide powder. Circular electrodes were formed by applying conductive paint to both sides of the sheet, and a voltage was applied to one circular electrode as the high-voltage side and the other circular electrode as the low-voltage side.

[0030] The degradation rate of the electric field relaxation performance value is based on the design value (100%) of the electric field relaxation performance value. Note that a voltage application test can be performed under conditions more severe than those during actual operation, and the degradation rate can be calculated by converting it to the conditions during actual operation using Arrhenius' law (10°C x 2 law).

[0031] The degradation rate of the electric field relaxation performance value shown in FIG. 2 is nothing other than the temperature-voltage degradation index KT. As shown in FIG. 2, the temperature-voltage degradation index KT decreases linearly with the voltage application time. Therefore, the temperature-voltage degradation index KT after 30 years can be calculated by linear extrapolation based on the measurement data. In the example shown in FIG. 2, the temperature-voltage degradation index after 30 years (262,800 hours) can be predicted to be 0.9 or higher. In other words, by designing the electric field relaxation layer 50 to have the characteristics shown in FIG. 2, the polymer sleeve 1 can maintain stable electric field relaxation performance even after 30 years.

[0032] FIG. 3 is a diagram showing the effect of repeated surge degradation on the electric field relaxation performance. FIG. 3 shows the degradation rate of the electric field relaxation performance value for each longitudinal position of the electric field relaxation layer 50 when an actual device is operated under conditions equivalent to those during actual operation of a 154 kV polymer sleeve 1 and 2,000 lightning impulse voltages (e.g., 750 kV, two conditions: positive and negative) equivalent to the switching surges experienced over 30 years are applied. The degradation rate of the electric field relaxation performance value is based on the design value (100%) of the electric field relaxation performance value. The longitudinal position is based on the end of the rear end side S2 of the electric field relaxation layer 50 (0 mm).

[0033] The degradation rate of the electric field relaxation performance value shown in Fig. 3 is nothing but the predicted repetitive surge degradation index Ki after 30 years. As shown in Fig. 3, the repetitive surge degradation index Ki after 30 years is predicted to tend to vary depending on the longitudinal position of the electric field relaxation layer 50, but even at the point with the greatest degradation, the repetitive surge degradation index is 0.9 or more. In other words, by designing the electric field relaxation layer 50 to have the characteristics shown in Fig. 3, the polymer sleeve 1 can maintain stable electric field relaxation performance even after 30 years.

[0034] Fig. 4 is a diagram showing the effect of moisture absorption degradation on electric field relaxation performance. Fig. 4 shows the water absorption rate and the degradation rate of electric field relaxation performance value versus exposure time (data obtained every 7 days) when a test piece (test piece) of a 154 kV polymer sleeve 1 is exposed to a predetermined temperature and humidity environment (for example, 70°C x 90% RH).

[0035] The test specimen was a 50 mm x 50 mm x 4 mm thick sheet, similar to the one described above with reference to Figure 2, and was formed from a zinc oxide layer made from a mixture of epoxy resin and zinc oxide powder. Circular electrodes were formed by applying conductive paint to both sides of the sheet, with one circular electrode acting as the high-voltage side and the other as the low-voltage side, and a voltage was applied to the sheet in this state.

[0036] The degradation rate of the electric field relaxation performance value is based on the design value of the electric field relaxation performance value (100%). The water absorption rate is calculated from the change in the mass of the sheet, with the initial moisture content as the reference (0%).

[0037] As shown in FIG. 4, the moisture content inside the electric field relaxation layer 50 increases with exposure time, eventually saturating as the absorption and dissipation balance. In the example shown in FIG. 4, it reaches saturation after approximately 700 hours. Meanwhile, the electric field relaxation performance value decreases as the water absorption rate increases and becomes constant when the moisture inside the electric field relaxation layer 50 is saturated. Therefore, in FIG. 4, the degradation rate of the electric field relaxation performance value when the moisture inside the electric field relaxation layer 50 is saturated can be regarded as the moisture absorption degradation index after 30 years. In other words, by designing the electric field relaxation layer 50 to have the characteristics shown in FIG. 4, the polymer sleeve 1 can maintain stable electric field relaxation performance even after 30 years.

[0038] As described above, the polymer sleeve 1 according to the embodiment has the following characteristics either alone or in appropriate combination.

[0039] That is, the polymer sleeve 1 includes an inner conductor 10, an insulating tube 20 arranged on the outer periphery of the inner conductor 10, and an electric field relaxation layer 50 that is embedded in the insulating tube 20 and relaxes the electric field when a voltage is applied to the inner conductor 10. The electric field relaxation layer 50 is made of a zinc oxide layer made by mixing a resin material with zinc oxide powder, and the electric field relaxation performance value SP(30) after 30 years predicted based on a deterioration index K obtained in a period shorter than 30 years is 65% or more of the design value SP(i) of the electric field relaxation performance value.

[0040] Specifically, the degradation index K includes at least one of a temperature-voltage degradation index KT, which indicates the degradation rate of the electric field relaxation performance value after 30 years, calculated by linear extrapolation based on measurement data when voltage is applied under specified conditions; a repeated surge degradation index Ki, which indicates the degradation rate of the electric field relaxation performance value when a surge voltage is applied the number of times expected to be received in 30 years; and a moisture absorption degradation index Kw, which indicates the degradation rate of the electric field relaxation performance value when moisture inside the electric field relaxation layer 50 is saturated.

[0041] According to the polymer sleeve 1, the electric field relaxation layer 50 made of zinc oxide has a stable electric field relaxation function for a long period of time, so that the reliability of the polymer sleeve can be significantly improved.

[0042] The invention made by the inventor has been specifically described above based on an embodiment, but the present invention is not limited to the above embodiment and can be modified within the scope of the gist thereof.

[0043] For example, in the embodiment, the polymer sleeve of the present invention is described as being applied to a bushing for equipment, but the polymer sleeve of the present invention can also be applied to a through-wall bushing or a cable termination in which a cable terminal is attached to the rear end side S2 of the insulating tube 20 instead of the head portion H. In this case, the cable termination may be an inner cone type in which a stress cone is pressed into the housing portion of the insulating tube 20 by a compression device, or an outer cone type in which a rubber block insulator is attached across the outer periphery of the rear end side of the insulating tube 20 and the cable insulator.

[0044] For example, in the embodiment, the electric field relaxation layer 50 is described as being provided only on the outer periphery of the large diameter portion 23, but the length of the electric field relaxation layer 50 is not limited as long as it is provided at the interface between the insulating tube 20 and the polymer coating 40 and the rear end is electrically connected to the shielding metal fitting 30.

[0045] For example, in Figure 1 of the embodiment, the umbrella-shaped pleats 42 of the polymer covering 40 are illustrated as having three sizes (radial lengths), namely, small, large, and extra-large. However, as long as the polymer sleeve 1 has predetermined performance, the shape of the pleats 42 is not particularly limited, and they may have two sizes, namely, small and large.

[0046] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0047] 1 Polymer sleeve 10 Inner conductor 20 Insulating tube 30 Shielding bracket 40 Polymer coating 50 Electric field relaxation layer

Claims

1. an inner conductor; an insulating tube disposed around the outer periphery of the inner conductor; a shielding metal fitting embedded in the insulating tube concentrically with the inner conductor; a polymer covering having a body portion covering the outer periphery of the insulating tube and a plurality of umbrella-shaped pleats formed at intervals in the longitudinal direction on the outer periphery of the body portion; an electric field relaxation layer disposed along the interface between the insulating tube and the polymer covering, the rear end of which is connected to the shielding metal fitting; the electric field relaxation layer is composed of a zinc oxide layer obtained by mixing a resin material and zinc oxide powder, and the electric field relaxation performance value after 30 years predicted based on a deterioration index obtained in a period shorter than 30 years is 65% or more of the design value of the electric field relaxation performance value; Polymer sleeve.

2. The deterioration index is a temperature / voltage application degradation index that indicates the rate of degradation of the electric field relaxation performance value after 30 years, calculated by linear extrapolation based on measurement data when voltage is applied under specified conditions; A repeated surge deterioration index indicating the deterioration rate of the electric field relaxation performance value when a surge voltage is applied the number of times that it is expected to be received in 30 years, and a moisture absorption deterioration index indicating a deterioration rate of the electric field relaxation performance value when the moisture inside the electric field relaxation layer is saturated; at least one of: The polymeric sleeve of claim 1.

3. the temperature / voltage application deterioration index, the repeated surge deterioration index, and the moisture absorption deterioration index are each 0.9 or more; The polymeric sleeve of claim 2.

4. The electric field relaxation layer is composed of the zinc oxide layer containing the zinc oxide powder in an amount of 80% by mass or more and 95% by mass or less. The polymer sleeve according to any one of claims 1 to 3.

Images