Surge arrester having a winding structure and method for manufacturing the same

Abstract

To provide a surge arrester with low power loss, enabling reliable and safe operation, and a manufacturing method for the same.SOLUTION: The surge arrester includes two opposing end portion fixtures 3, one or more varistors 5, disposed between the end portion fixtures 3, a closed winding layer 9, provided on the varistors 5, and a reinforcing element 7, which is an open cross winding 13 and extends between the end portion fixtures 3 and keeps the end portion fixtures 3 under tension.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a surge arrester having a winding structure and a method for manufacturing the same. In particular, the present invention relates to a surge arrester provided with an open cross winding formed from a glass fiber reinforced plastic.

Background Art

[0002] Details regarding surge arresters, particularly regarding the selection and design of their housings, are known, for example, from "Metalloxid-Ableiter in Hochspannungsnetzen", Volker Hinrichsen, 3rd edition, publisher and copyright (c) 2012: Siemens AG Energy Sector Freyeslebenstrase 1 91058 Erlangen, Germany (https: / / cache.industry.siemens.com / dl / files / 132 / 109747132 / att_918329 / v1 / Metalloxid-Ableiter_in_Hochspannungsnetzen_-_Grundlagen.pdf).

[0003] As explained therein, when a surge arrester having a plastic housing short-circuits, generally, there is no increase in the clear pressure within the housing (the pressure can operate a pressure relief device, as known from ceramic arresters), and instead the arc generated instead directly reaches any point or a point specially designed for this purpose through the housing wall of the plastic housing.

[0004] In the case of an overload of such an arrester, it is necessary to ensure either that the plastic housing does not break, or that the housing fragments and released parts fall to the ground within the area around the surge arrester, and the size of the area is defined based on the height of the surge arrester.

[0005] Only parts that fall below each predetermined weight limit, for example, parts weighing less than 60g, may be found outside the area.

[0006] In practice, three basic types of plastic housings have been established. These plastic housings include, firstly, a sealed gas-volume plastic housing in the form of a so-called tube; secondly, a plastic housing with a bar cage formed from glass fiber-reinforced plastic bars that extends parallel to a laminate of varistors (preferably metal oxide varistors) and is fixed to two end fittings or terminals (preferably formed from aluminum), and surrounds a molded silicone housing (cage shape) without a gas volume; and thirdly, a plastic housing with a winding ("winding structure") formed from glass fiber yarn, which is often applied to varistors as a so-called prepreg.

[0007] A known problem with surge arresters with a wound structure is that a certain thickness of winding is required to obtain the necessary mechanical strength, but this thickness becomes a hindrance in the event of a short circuit. This is because, in this case, the pressure rises inside the winding, and fragments of the varistor may fly out beyond acceptable limits, more so than in the case of a sudden pressure release when the housing breaks.

[0008] To address this problem, open windings have been proposed in the past, for example, as shown in U.S. Patent No. 5042838. In this case, the winding does not form a closed space, leaving numerous rhomboid open regions without windings. These open regions are distributed almost regularly across the entire surface of the varistor, and only the outer silicon housing isolates the varistor from the external environment within these regions. This structure reliably prevents pressure buildup inside while still achieving excellent mechanical strength. If the rhomboid open regions are sufficiently small, it can also prevent relatively large fragments of the varistor from reaching the outside.

[0009] Surge arresters typically operate for many years and are exposed to environmental influences such as rain, fog (including salt-laden coastal fog), and extreme temperature changes during this time; therefore, the long-term behavior of these surge arresters is particularly important. In this process, it has been found that conventional plastic housings, preferably silicone housings, are insufficient to prevent water ingress under certain conditions. In this case, water accumulates on the surface of the varistor, preferentially in open areas, and even gradually penetrates beneath the windings if the adhesion of the windings to the varistor is insufficient. This increases power loss and can lead to surge arrester failure. [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] Therefore, the object of the present invention is to provide the aforementioned type of surge arrester that has low power loss even over long periods of time and can operate reliably and safely. [Means for solving the problem]

[0011] This objective is achieved by the surge arrester as described in the attached claims and by the method for manufacturing the surge arrester as described in the attached claims.

[0012] The present invention provides a surge arrester comprising two opposing end fittings, a varistor disposed between these end fittings, a winding layer provided on the varistor and being at least partially closed, and a reinforcing element extending between the two end fittings and maintaining these end fittings under tension, and being an open cross winding.

[0013] Preferably, in the surge arrester, a cationic crosslinked epoxy resin is used as the resin for the resin-impregnated glass fiber yarn to be used for winding, or for the glass fiber yarn bundle or roving.

[0014] More preferably, the cationic crosslinked epoxy resin contains a UV initiator and / or a thermal initiator.

[0015] In particular, it is preferable that a cationic crosslinked epoxy resin adheres to the surface of at least one varistor.

[0016] In a preferred embodiment, the reinforcing element has a cross-section that is 5 to 10 times, preferably 7 times, thicker than the winding layer.

[0017] The surge arrester according to the present invention preferably has a silicon outer housing.

[0018] Furthermore, in cross-winding, it is preferable that the open rhombic region remains between the resin-impregnated glass fiber threads, and that the angle of this rhombic region is 20 to 160°.

[0019] Furthermore, the present invention provides a method for manufacturing the aforementioned surge arrester, comprising the steps of: preparing a laminate having two opposing end fittings and a varistor positioned between them; winding the laminate with resin-impregnated glass fiber yarn to form at least a partially closed winding layer; and partially winding the resin-impregnated glass fiber yarn around the laminate in the axial direction to form an open cross winding by rotating the laminate relative to the laminate and moving it back and forth in the longitudinal direction while supplying the resin-impregnated glass fiber yarn. [Brief explanation of the drawing]

[0020] [Figure 1] This is a diagram showing the surge arrester according to the present invention. [Figure 2] Figure 1 shows a surge arrester with the silicon housing removed. [Figure 3] Figure 2 is a detailed view of the surge arrester. [Modes for carrying out the invention]

[0021] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, the surge arrester according to the present invention has a plastic outer housing 15 (preferably, a silicon outer housing). This housing has a plurality of shields 17 for lengthening the surface path for current and for avoiding a continuous conductive connection between the two ends of the surge arrester via adhering water or contaminants.

[0022] The illustrated surge arrester has two end fittings 3 (terminals) facing each other, preferably made of aluminum, and one or more varistors 5, preferably made of metal oxide (especially zinc oxide). The varistors 5 are laminated between these two terminals 3. This varistor 5 has the property of being a very good insulator when the voltage is below the threshold voltage, but when the threshold voltage is reached, its electrical resistance changes non-linearly and reversibly to a small value so that the surge at one end of the surge arrester is reduced by an appropriate current flowing through the surge arrester. In this way, the grounded surge arrester protects other electrical components of the power grid from surges.

[0023] However, as described initially, when a very high current flows through the surge arrester, for example, when a lightning strike occurs near the arrester, the surge arrester may be overloaded. In this case, ionized gas may occur in the surge arrester, and then an arc may be formed. In the process, high temperature is generated, and high voltage may also be generated if appropriate measures are not taken, which may lead to the rupture of the surge arrester.

[0024] The surge arrester shown in FIG. 1 includes a module 19 under the plastic housing 15, and the module has a laminate of varistors 5, two end fittings 3, and a reinforcing element 9, as shown in more detail in FIGS. 2 and 3.

[0025] Here, the reinforcing element 9 is formed as an open crossover winding 13.

[0026] To manufacture this cross winding 13, glass fiber yarn (preferably a bundle of glass fiber yarn) is guided through a resin bath to impregnate the glass fiber yarn with resin. The resin-impregnated glass fiber yarn is then wound around the laminate of the varistor 5 and the two end fittings 3. For this reason, preferably one end of the glass fiber yarn is fixed to the laminate, which is then rotated around its longitudinal axis, while at the same time the laminate is moved along its longitudinal axis relative to the supply point of the glass fiber yarn.

[0027] In this application, when the term "glass fiber yarn" is used, it means a bundle of glass fiber yarn or roving.

[0028] Whenever the glass fiber thread reaches one end of the laminate as a result of movement along the longitudinal axis of the laminate, the direction of movement along the longitudinal axis of the laminate is reversed, and the glass fiber thread is guided across the shoulders of each end fitting while the rotation of the laminate about its longitudinal axis continues.

[0029] Because the speeds of these two movements are equal, an open cross winding can be formed as shown in Figures 2 and 3. An offset at the end fitting is utilized in this process. That is, when the glass fiber yarn reaches the end fitting 3, movement in the longitudinal axis direction stops, but the laminate is rotated by a predetermined angle. Then, movement in the longitudinal axis direction resumes, but with the opposite sign so that the glass fiber yarn is positioned on the track formed during the previous iteration.

[0030] In this manufacturing process, also known as the filament winding method, glass fiber threads are extended through a resin bath, and then at least one varistor 5 and end fittings 3 are clamped by the rotation of a spindle. During this process, the glass fiber threads are applied such that a cross pattern is created by further translational movement of the installation carriage in the direction of the longitudinal axis of the laminate. The precise vertical positioning of the layers and the winding angles are determined by the mathematical relationships of the winding program. The reason for using open cross windings is that in the event of a short circuit, the gas generated in the surge arrester can escape easily, and the generated arc can rapidly travel from the varistor 5 to the outside of the housing 15.

[0031] Since the glass fiber threads include angles of 10 to 89°, preferably 30 to 70°, and particularly preferably 45° with respect to the longitudinal axis of the laminate, the glass fiber threads can firmly hold the two end armatures 3 and varistors 5 using tension. In other words, such open cross windings can withstand axial forces, bending forces, and torsional forces parallel to the longitudinal axis, thereby ensuring high mechanical strength of the laminate.

[0032] In a preferred embodiment, multiple parallel glass fiber threads, for example 2400 tex, are used simultaneously as so-called roving.

[0033] In the cross-winding 13 shown in Figures 2 and 3, seven layers of such rovings are arranged to overlap each other in each case, such that the cross-sectional thickness of the winding is 2 to 10 mm. The cross-sectional thickness can be set according to the desired mechanical strength. A larger cross-sectional thickness increases the mechanical strength, but requires more silicon to form the plastic housing 15, as well as more material to form the reinforcing elements, which makes the surge arrester more expensive.

[0034] According to the present invention, a cationic crosslinked epoxy resin is used to impregnate glass fiber yarn. Examples of such resins include Vitralit® adhesives and potting compounds provided by Panacol-Elosol GmbH. These are single-component systems based on acrylate or epoxy resins that cure very quickly under UV or visible light and can be post-cured thermally as required. Depending on the application, curing times of 0.5 to 60 seconds can be achieved by high-energy irradiation. As a result of thermal post-curing, the adhesive can also be cured in a shaded area following light curing.

[0035] In particular, the cationic crosslinked epoxy resin preferably contains a UV initiator and / or a thermal initiator to induce curing by either UV irradiation or heat.

[0036] In a preferred embodiment, as shown in detail in Figure 3, radial windings are additionally provided in the area of ​​the end fitting 3 to facilitate a mechanically stable fixed connection between the open cross winding 13 and the end fitting 3 and to provide a water seal.

[0037] As mentioned at the beginning, regarding the actual use of surge arresters, it is important that they maintain their electrical properties over relatively long periods and under changing environmental conditions. In this regard, there is a particular risk that water will diffuse through the plastic housing 15 and collect at the open areas of the crossed windings 13 on the surface of the varistor 5. This increases the power loss of the surge arrester.

[0038] To address this problem, according to the present invention, a substantially single layer winding 9, which is a resin-impregnated glass fiber yarn, is provided between the open cross winding 13 and the varistor 5, thereby creating a closed layer across the entire outer surface of the varistor 5. A cationic crosslinked epoxy resin acts as an adhesive, providing good adhesion to the surface of the varistor 5.

[0039] To form this layer, which will be formed as the winding layer 9, the resin-impregnated glass fiber yarn or roving is fixed to the laminate to be wound around, and then wound substantially radially around the laminate, i.e., with low relative movement in the direction of the longitudinal axis of the laminate with respect to the rotational speed of the laminate around its longitudinal axis, such that only a winding offset equal to or less than the width of the glass fiber yarn or roving is formed with each rotation.

[0040] The thickness of this layer in cross-section is preferably 0.1 to 0.5 mm, but is not limited to this.

[0041] Instead of a nearly radial winding, a closed cross winding can also be used. That is, in the case of an open cross winding, the winding is performed with a greater speed of movement in the longitudinal axis direction, and when it reaches one of the end fittings 3, the direction of movement is reversed. Now, the rotational speed and the speed of movement in the longitudinal axis direction are selected so that the glass fiber threads are laid with an offset (adjacent to each other or with a slight overlap) to form a closed layer. However, due to such glass fiber threads, the thickness of this layer changes more significantly than in the nearly radial winding case described above. However, it should be noted that in this case, a closed layer is formed first, and that this layer is "single layer" to a considerable extent.

[0042] Due to the resin used, the layer formed by the aforementioned method adheres well to the surface of the varistor 5. However, due to the small thickness of the glass fiber threads and their arbitrary radial arrangement, this layer does not make a significant contribution to mechanical stability.

[0043] The epoxy resin forms a highly watertight layer, preventing water from accumulating on the surface of the varistor 5. In this respect, the winding layer acts as a shielding layer against moisture.

[0044] Therefore, in order to simultaneously obtain pressure release in the event of a short circuit and when sealing the internal varistor, the thin layer 9 beneath the open cross winding 7 is wound "radially" or as a "closed cross winding". Firstly, the thin layer is weak enough to open like a film in the event of a short circuit. Secondly, if a highly waterproof resin is used, a significantly improved tightness is obtained.

[0045] Curing by UV irradiation promotes complete curing directly by the machine used to form the winding after the winding has been applied. Subsequently, module 19 can be removed in a dimensionally stable manner, and module 19 can be post-cured in an oven so that even areas remaining in the UV irradiation shadows are cured.

[0046] Cationic crosslinked epoxy resins, preferably with UV and thermal initiators, adhere very well to the surface of varistor 5. In other words, the specific strength of the resin is greater when acting as an adhesive than as a resin. This prevents moisture from accumulating on the surface of varistor 5 and further significantly slows down water (vapor) uptake.

[0047] In the event of a short circuit, the thin, closed layer 9, despite the use of glass fiber threads, does not act as a pressure barrier against the generated plasma, thus preventing an increase in internal pressure.

[0048] This was confirmed in a series of tests. In this series of tests, surge arresters with open cross windings, surge arresters with open cross windings and a closed layer below them, and surge arresters with fully closed cross windings were manufactured and subjected to typical product water immersion tests (boiling tests in which the surge arrester is placed in boiling salt water for a predetermined period of time) and short-circuit tests. Surge arresters with open cross windings but no closed layer passed the short-circuit test but failed the water immersion test. Surge arresters with closed cross windings passed the water immersion test but failed the short-circuit test. Surge arresters with open cross windings and a closed layer below them passed both tests.

[0049] The surge arrester with the closed layer 9 showed remarkably good results in the water storage test or boiling test, and was found to have virtually no problems.

[0050] Although the present invention has been described in detail above based on an example, the present invention is not limited thereto. Preferably, the formation of the closed layer 9 and the formation of the open cross winding 7 are carried out by the same winding device, in which case only the travel speed in the longitudinal axis direction and / or rotation speed and / or offset at the end fitting 3 after the application of the closed layer 9 need to be changed. However, the two windings can also be carried out by different machines, and the closed layer can be cured by UV radiation or thermally before the application of the open cross winding 13.

[0051] A further alternative involves providing radial windings solely for sealing purposes in the transition region between the end terminals and the varistor 5, or in the transition region between two varistors 5 in the laminate. This can be achieved by guiding the glass fiber threads substantially parallel to the longitudinal axis of the laminate until they reach the transition region as the winding layer is wound, after which longitudinal movement is substantially stopped and only rotation of the laminate occurs until the transition region is covered by the winding layer, after which longitudinal movement resumes to the next transition region. In this case, it should be noted that the adhesive effect of the resin on the surface of the varistor is sufficient to hold the already applied glass fiber threads when the direction of movement is changed.

[0052] This only achieves a seal in the transition region, but it also has a positive effect on water storage tests or boiling tests.

Claims

1. Two opposing end fittings (3), A laminate consisting of varistors (5) arranged between these end fittings, A layer provided on this varistor (5) and at least partially closed, comprising a winding layer (9) formed by winding resin-impregnated glass fiber yarn around the laminate, Extending between the two end fittings (3) and maintaining these end fittings (3) under tension, and with respect to the reinforcing element (7) which is an open cross winding (13), A surge arrester equipped with this feature.

2. The surge arrester according to claim 1, wherein the resin used in the resin-impregnated glass fiber yarn is a cationic crosslinked epoxy resin.

3. The surge arrester according to claim 2, wherein the cationic crosslinked epoxy resin comprises a UV initiator and / or a thermal initiator.

4. The surge arrester according to claim 2 or 3, wherein the cationic crosslinked epoxy resin adheres to the surface of the varistor (5).

5. The surge arrester according to any one of claims 1 to 4, wherein the reinforcing element (7) has a cross-section that is 5 to 10 times, preferably 7 times, thicker than the winding layer (9).

6. A surge arrester according to any one of claims 1 to 5, further comprising a silicon outer housing (15).

7. A surge arrester according to any one of claims 1 to 6, wherein an open rhombic region is formed between the resin-impregnated glass fiber threads in the open cross winding, and the angle of this rhombic region is 20 to 160°.

8. The aforementioned baristas are provided in multiple locations. The surge arrester according to any one of claims 1 to 7, wherein the winding layer is a closed layer in at least the transition region between the end fitting (3) and the varistor (5), and the transition regions between the plurality of varistors (5).

9. The surge arrester according to any one of claims 1 to 7, wherein the winding layer is a continuously closed layer that covers the entire outer surface of the varistor (5).

10. The steps include preparing a laminate having two opposing end fittings and a varistor positioned between them, The steps include winding the laminate with resin-impregnated glass fiber yarn to form a winding layer that is at least partially closed, The steps include: supplying the resin-impregnated glass fiber yarn while rotating the laminate relative to it and moving it back and forth in the longitudinal direction, thereby partially winding the resin-impregnated glass fiber yarn axially around the laminate and the partially closed winding layer to form an open cross winding; A method for manufacturing a surge arrester, comprising the characteristics of a surge arrester.

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