SURGE ARRESTER WITH WINDING DESIGN AND METHOD FOR ITS MANUFACTURE

Description

[0001] The invention relates to a surge arrester with a wound design and a method for its manufacture. In particular, the invention relates to a surge arrester with an open cross-wound design made of glass fiber-reinforced plastic.

[0002] Details on surge arresters and in particular on the selection and design of their housings are known, for example, from "Metal oxide arresters in high-voltage networks", Volker Hinrichsen, 3rd edition, Publisher and Copyright © 2012: Siemens AG Energy Sector Freyeslebenstraße 1 91058 Erlangen, Germany

[0003] The state of the art is described in the documents DE68920463T2, DE68903979T2, US2005 / 207084A1, US4404614A, WO2020 / 043452A1, US2012 / 086541A1 and US6441310B1.

[0004] As explained there, in the case of surge arresters with plastic housings, in the event of a short circuit, no defined pressure builds up in the housing that could activate a pressure relief device - as is known from porcelain arresters - but the resulting arc seeks a path directly through a housing wall of the plastic housing at any location or at a location specially provided for this purpose.

[0005] In the event of such an arrester overload, it must be ensured that the plastic housing either does not break at all or that housing fragments and ejected parts fall to the ground within an area around the surge arrester, the size of which is determined depending on the surge arrester height.

[0006] Only parts weighing less than a specified weight limit, for example 60 g, may be found outside the area.

[0007] In practice, three basic types of plastic housings have become established. Firstly, those with an enclosed gas volume in the so-called tube design; secondly, those with a rod cage made of glass fiber-reinforced plastic rods that run parallel to a stack of varistors – preferably metal oxide varistors – and are attached to two end fittings or terminals – preferably made of aluminum – and are surrounded by a molded silicone housing without any gas volume (cage design); and finally, those with a winding of glass fiber threads (“winding design”), which is often applied to the varistors as a so-called prepreg. One such surge arrester with a prepreg winding is shown, for example, in US 2012 / 0086541 A1.

[0008] A problem with the known surge arresters with a winding design is that they require a certain thickness of the winding to achieve the required mechanical strength, which is problematic in the event of a short circuit, as pressure can then build up inside the winding, which can lead to fragments of the varistors being thrown further than is permissible in the event of a sudden pressure release when the housing breaks.

[0009] To counter this problem, open windings have been proposed in the past, as shown, for example, in US Pat. No. 5,043,838. In this case, the winding does not form an enclosed space; instead, a multitude of diamond-shaped, open areas without winding remain, distributed more or less regularly over the entire surface of the varistors, with only the outer silicone housing separating the varistors from the external environment. This design reliably prevents the build-up of pressure inside while still allowing good mechanical stability. If the diamond-shaped, open areas without winding are sufficiently small, it can also prevent larger fragments of the varistors from escaping to the outside.

[0010] Since surge arresters are typically in use for many years and are exposed to environmental influences such as rain, fog—even salty coastal fog—and extreme temperature fluctuations, the long-term performance of these surge arresters is particularly important. It has been shown that conventional plastic housings, preferably silicone housings, may not be sufficient to prevent water penetration, which then collects on the surface of the varistors, preferably in the open areas, and, if the winding is not well adhered to the varistors, may even creep under the winding. This causes increased power loss and leads to the failure of the surge arrester.

[0011] EP 2 748 224 B1 discloses a method for producing high-voltage insulation using appropriate UV or thermally curing plastics.

[0012] The object of the invention is therefore to provide a surge arrester of the type described which has excellent low power loss even in the long term and allows reliable and safe operation.

[0013] The object is achieved by a surge arrester according to the appended claims and by the method for its manufacture set out therein.

[0014] According to the invention, a surge arrester is provided, comprising two opposing end fittings, one or more varistors arranged between the end fittings, a winding layer provided at least on the at least one varistor, wherein the winding layer is an at least partially closed layer with a resin-impregnated glass fiber thread, and a reinforcing element extending between the end fittings, which holds the end fittings under tension, wherein the reinforcing element is an open cross-wound winding with a resin-impregnated glass fiber thread.

[0015] Preferably, in the surge arrester, a cationically crosslinking epoxy resin is used as a resin for a resin-impregnated glass fiber thread to be used for the windings, or for the glass fiber thread bundle or roving.

[0016] More preferably, the cationically crosslinking epoxy resin contains a UV initiator and / or heat initiator.

[0017] In particular, it is preferred that the cationically crosslinking epoxy resin adheres to the surface of the at least one varistor.

[0018] In a preferred embodiment, the reinforcing element is 5 to 10 times, preferably 7 times, thicker in cross section than the winding layer.

[0019] The surge arrester according to the invention preferably has a silicone outer housing.

[0020] It is also preferred that the cross-wound leaves open diamond-shaped surfaces between the resin-impregnated glass fiber threads, the angles of these diamond-shaped surfaces being between 20 and 160°.

[0021] According to the invention, a filament winding method for manufacturing the surge arrester described above is further provided, comprising the steps of: providing a stack with two opposing end fittings and at least one varistor arranged between them; winding the stack with a resin-impregnated glass fiber filament to form an at least partially closed winding layer, and partially axially winding the stack to form an open cross-wind by relative rotation of the stack with simultaneous back-and-forth movement in the longitudinal direction during the feeding of the resin-impregnated glass fiber filament.

[0022] In the following, the invention is described using a preferred embodiment with reference to the accompanying figures, in which: Fig. 1 a view of a surge arrester according to the invention, Fig. 2 the surge arrester from Figure 1without silicone casing; and Fig. 3 a detailed view of the surge arrester from Figure 2 .

[0023] How Figure 1 shows, the surge arrester according to the invention has a plastic outer housing 15, preferably a silicone outer housing, which forms a plurality of shields 17 in order to extend a creepage path for current and to avoid a continuous electrically conductive connection between the two ends of the surge arrester due to adhering water or contaminants.

[0024] The surge arrester shown has two opposing end fittings or terminals 3, which are preferably made of aluminum, and one or a plurality of varistors 5, preferably made of metal oxide, in particular zinc oxide, which are stacked between the two terminals 3.

[0025] These varistors 5 have the property that they are very good insulators below a threshold voltage, but upon reaching the threshold voltage, they change their electrical resistance non-linearly but reversibly to a small value, so that an overvoltage at one end of the surge arrester can be dissipated by a corresponding current through the surge arrester. In this way, grounded surge arresters protect other electrical components of a power grid against overvoltages.

[0026] However, as described above, if a very high current flows through the surge arrester – for example, during a lightning strike close to the arrester – it can become overloaded. In this case, an ionized gas forms within the surge arrester, which can then cause an arc. This creates high temperatures and, if appropriate countermeasures are not implemented, can also lead to high pressures, which can cause the surge arrester to burst.

[0027] The Figure 1 The surge arrester shown contains, under the plastic outer housing 15, a module 19 with the described stack of one or more varistors 5, the two end fittings 3 and a reinforcement element 13, as shown in the Figures 2 and 3 is shown in more detail.

[0028] Here, the reinforcing element 13 is designed as an open cross-wound roll 13.

[0029] To produce this cross-wound coil 13, a glass fiber thread—preferably a bundle of glass fiber threads—is passed through a resin bath and impregnated with the resin. This resin-impregnated glass fiber thread is then wound around the stack of one or more varistors 5 and the two end fittings 3. For this purpose, one end of the glass fiber thread is preferably attached to the stack, and this stack is then rotated about its longitudinal axis, while the stack is simultaneously moved along its longitudinal axis relative to a feed point of the glass fiber thread.

[0030] Insofar as reference is made in this application to a glass fiber thread, this is always to be understood as a glass fiber thread bundle or a roving.

[0031] Whenever the fiberglass thread reaches one of the ends of the stack as a result of the movement of the stack along the longitudinal axis, the direction of movement of the stack along the longitudinal axis is reversed and the fiberglass thread is guided over a shoulder of the respective end fitting while the rotation of the stack about its longitudinal axis continues.

[0032] By adjusting the speeds of these two movements, it is possible to form an open cross-wound, as in the Figures 2 and 3As shown. It is also possible to work with an offset at the end fittings. This means that when the end fitting 3 with the glass fiber thread is reached, the movement in the direction of the longitudinal axis stops, while the stack is further rotated by a predetermined angle. Subsequently, the movement in the direction of the longitudinal axis begins again, but with the opposite sign, so that the glass fiber thread is deposited on a path formed during a previous pass.

[0033] In this manufacturing process, also known as the filament winding method, the glass fiber filament runs through the resin bath and then rotates a spindle in which at least one varistor 5 and the end fittings 3 are clamped. The glass fiber filament is applied in such a way that a cross pattern is created by an additional translational movement of a laying carriage in the direction of the longitudinal axis of the stack. The precise positioning of the layers on top of one another and the angles of the winding are derived from mathematical relationships in the winding program. An open cross winding is deliberately used here, since in the event of a short circuit, gas produced in the surge arrester can escape easily and the resulting arc quickly escapes from the varistor 5 out of the housing 15.

[0034] Since the glass fiber thread forms an angle of 10 to 89°, preferably 30 to 70°, and particularly preferably 45° to the longitudinal axis of the stack, the glass fiber thread is capable of holding the two end fittings 3 and the at least one varistor 5 firmly together under tension. The open cross-wound winding can withstand both axial forces parallel to the longitudinal axis as well as bending and torsional forces, thus ensuring high mechanical strength of the stack.

[0035] In a preferred embodiment, several parallel glass fiber threads are used simultaneously as so-called roving, for example with a tex number of 2400.

[0036] In the Figures 2 and 3In the cross-wound winding 13 shown, 7 layers of such rovings are arranged one above the other, resulting in a winding cross-sectional thickness of 2 to 10 mm. The cross-sectional thickness can be adjusted depending on the desired mechanical strength. A larger cross-sectional thickness increases the mechanical strength, but this also requires more silicone to form the plastic housing 15 and more material to form the reinforcement elements, which increases the cost of the surge arrester.

[0037] According to the invention, a cationically crosslinking epoxy resin is used to impregnate the glass fiber thread. An example of such a resin is Vitralit® adhesives and casting compounds from Panacol-Elosol GmbH. These are one-component systems based on acrylate or epoxy resin that cure very quickly with UV or visible light and can be thermally post-cured as needed. With high-energy radiation, curing times of 0.5 to 60 seconds can be achieved, depending on the application. Thermal post-curing allows the adhesive to be cured even in shadowy areas after light curing.

[0038] In particular, it is preferred that the cationically crosslinking epoxy resin contains a UV initiator and / or heat initiator to effect curing either by UV irradiation or by heat.

[0039] In the preferred embodiment, as shown in Fig. 3As shown in more detail, an additional purely radial winding is provided in the area of ​​the end fittings 3 in order to enable a firm, mechanically stable connection of the open cross-wound winding 13 with the end fittings 3 and to seal it against water.

[0040] As described above, it is crucial for the practical use of the surge arrester that it retains its electrical properties even over extended periods and under changing environmental conditions. In particular, there is a risk that water will diffuse through the plastic outer housing 15 and collect in the open areas of the cross-wound winding 13 on the surface of at least one varistor 5. This increases the power loss of the surge arrester.

[0041] To counteract this problem, according to the invention, a substantially single-layer winding 9 of the resin-impregnated glass fiber thread is provided between the open cross-wound winding 13 and the at least one varistor 5, so that a closed layer is formed on the entire outer surface of the at least one varistor 5. The cationically cross-linking epoxy resin acts as an adhesive and ensures good adhesion to the surface of the at least one varistor 5.

[0042] To form this layer, which is formed as winding layer 9, the resin-impregnated glass fiber thread or roving, after being attached to the stack to be wound, is wound essentially radially around the stack, that is to say with a relative movement of the stack in the direction of the longitudinal axis that is so small in relation to the rotational speed of the stack about its longitudinal axis that only an offset of the winding is formed per revolution, which is equal to or minimally smaller than the width of the glass fiber thread or roving.

[0043] The thickness of this layer in cross section is preferably 0.1 to 0.5 mm, but is not limited thereto.

[0044] It is also possible to use a closed cross-wind instead of a substantially radial winding. This means that the winding is carried out at a higher speed in the direction of the longitudinal axis, but, as with an open cross-wind, the direction of movement is reversed upon reaching one of the end fittings 3. In this case, the rotation speed and the speed of movement in the direction of the longitudinal axis are selected so that the glass fiber threads are offset—next to one another or with slight overlap—thus forming a closed layer. However, the thickness of this layer varies more than with a substantially radial winding due to the intersecting glass fiber threads. It should be noted, however, that, on the one hand, a closed layer is created and, on the other hand, that this layer is "single-layered" in many areas.

[0045] The layer formed in the manner described above adheres well to the surface of the at least one varistor 5 due to the resin used. However, due to the low thickness and possibly the radial orientation of the glass fiber thread, this layer does not make a significant contribution to the mechanical stability.

[0046] The epoxy resin forms a layer with very high water resistance, so that water can be prevented from collecting on the surface of the at least one varistor 5. In this respect, the winding layer acts as a shielding layer against moisture.

[0047] To simultaneously provide pressure relief during a short circuit and seal the internal varistors, the thin layer 9 is wound radially or as a closed cross-wound coil beneath the open cross-wound coil 13. On the one hand, it is weak enough to open like a membrane in the event of a short circuit. On the other hand, the use of a highly water-impermeable resin provides significantly improved sealing.

[0048] Curing using UV radiation allows for complete curing directly on a winding forming machine after the windings have been applied. Module 19 can then be removed in its original shape and post-cured in an oven, allowing even areas that would otherwise remain in the shadow of UV radiation to cure.

[0049] The cationically curing epoxy resin with UV initiator and heat initiator, which is preferably used here, adheres very well to the surface of at least one varistor 5. In other words, a particular strength of the resin lies in its ability to act more as an adhesive than a resin. This prevents the accumulation of moisture on the surface of the varistor 5 and, in addition, significantly slows down the absorption of water (vapor).

[0050] The small thickness of the closed layer 9 does not represent a pressure-resistant barrier for the resulting plasma in the event of a short circuit - despite the use of the glass fiber thread - so that an internal pressure build-up is avoided.

[0051] This was confirmed in a series of tests in which surge arresters with an open cross-wound coil, surge arresters with an open cross-wound coil and an underlying closed layer, and surge arresters with a completely closed cross-wound coil were manufactured and subjected to a product-typical water immersion test (boiling test, in which the surge arrester is placed in boiling salt water for a predetermined time) and a short-circuit test. The surge arresters with an open cross-wound coil without a closed layer passed the short-circuit test, but not the water immersion test. The surge arresters with a closed cross-wound coil passed the water immersion test, but not the short-circuit test. Surge arresters with an open cross-wound coil and an underlying closed layer passed both tests.

[0052] It was shown that the surge arresters with the closed layer 9 had significantly better behavior and less impairment during the water immersion test or boiling test.

[0053] Although the invention has been described in detail above using an example, it is not limited thereto. It is preferred to have the closed layer 9 applied by the same winding device as the open cross-wound coil 13 provided thereon, simply by changing the movement speed in the direction of the longitudinal axis and / or the rotational speed and / or an offset in the end fitting 3 after the closed layer 9 has been applied. However, the two windings can also be carried out in different machines, and it is possible to cure the closed layer by UV irradiation or thermally before the open cross-wound coil 13 is applied.

[0054] Another alternative is to provide the radial winding for sealing only in the transition areas between an end terminal and the varistor 5, or between two varistors 5 of the stack. This can be achieved by guiding the glass fiber thread essentially parallel to the longitudinal axis of the stack during winding of the winding layer until it reaches a transition area, then essentially stopping the longitudinal movement and only rotating the stack once until the transition area is covered with the winding layer, and then resuming the longitudinal movement until the next transition area. Care must be taken to ensure that the adhesive effect of the resin on the surface of the varistor is sufficient to hold the already applied glass fiber thread in place when the direction of movement changes.

[0055] Although this only seals the transition areas, it also has a positive effect on the water retention test or boiling test.

Claims

1. Surge arrester with two end fittings (3) facing each other, one or more varistors (5) arranged between the end fittings, a winding layer (9) provided at least on the at least one varistor (5), wherein the winding layer (9) is an at least partially closed layer (9) with a resin-impregnated glass fiber thread; and a reinforcing element (7) extending between the end fittings (3) and holding the end fittings (3) under tension, wherein the reinforcing element (7) is an open cross-wound coil (13) with a resin-impregnated glass fiber thread.

2. The surge arrester according to claim 1, wherein the resin for the resin-impregnated glass fiber thread is a cationically crosslinking epoxy resin.

3. The surge arrester according to claim 2, wherein the cationically crosslinking epoxy resin contains a UV initiator and / or a heat initiator.

4. The surge arrester according to claim 2 or 3, wherein the cationically crosslinking epoxy resin adheres to the surface of the at least one varistor (5).

5. The surge arrester according to one of the preceding claims, wherein the reinforcement element (7) is 5 to 10 times, preferably 7 times, thicker in cross section than the winding layer (9).

6. The surge arrester according to one of the preceding claims, wherein the surge arrester comprises a silicone outer housing (15).

7. The surge arrester according to one of the preceding claims, wherein the cross-winding (13) leaves open rhomboid-shaped areas between the resin-impregnated glass fiber strands, the angles of these rhomboids being between 20 and 160°.

8. The surge arrester according to one of the preceding claims, wherein the winding layer (9) is a closed layer at least in transition areas between an end fitting (3) and a varistor (5) and in transition areas between varistors (5).

9. The surge arrester according to one of the preceding claims 1 to 7, wherein the winding layer (9) is a continuously closed layer covering an entire outer surface of the at least one varistor (5).

10. Filament winding method for manufacturing a surge arrester according to one of claims 1 to 9, comprising the steps of: providing a stack with two end fittings (3) opposite each other and at least one varistor (5) arranged between them; wrapping the stack with a resin-impregnated glass fiber thread to form an at least partially closed winding layer (9), and partially axially wrapping the stack to form an open cross-wrap (13) by relative rotation of the stack with simultaneous back-and-forth movement in the longitudinal direction during the feed of the resin-impregnated glass fiber thread.