EP1883934B2 - Surge arrester with a cage embodiment - Google Patents

Abstract

The invention relates to a surge arrester having at least one varistor block 1, one end fitting 3, one reinforcing element 9 which holds the varistor block 1 firmly on the end fitting 3 with a tensile load, and at least one anchoring element 27 which holds the reinforcing element 9 firmly on the end fitting 3 with a tensile load wherein the anchoring element 27 has at least one edge 29 which cuts into the reinforcing element 9. The anchoring element 27 is preferably a cutting-ring screw union.

Description

The invention relates to a surge arrester with cage design, as for example from the JP 63 312 602 is known. Surge arresters are connected in power supply systems between live lines and ground to derive in the event of an overvoltage in the line this to ground and to protect other components of the power grid. Such a surge arrester contains a stack of varistor blocks, which is held between two connection elements. This arrangement is accommodated in a housing.

To ensure that the varistor blocks contact each other well even under mechanical loads, it is necessary to hold the stack together under pressure. In such surge arresters with cage design, this is done via reinforcing elements, usually rods or ropes, preferably glass fiber reinforced plastic rods (GRP rods), which are held at the two end fittings under train.

A problem with such surge arresters is to securely fasten the reinforcing elements to the end fittings, so that the necessary strength is obtained even in the case of mechanical stresses which occur in the case of surge arresters mounted outdoors.

In the said Japanese patent application, this problem is solved in that in the end fittings grooves in the stacking direction of the varistor blocks are provided, in which the reinforcing elements are inserted, and in which the end of the reinforcing elements is provided with a thread on which a nut is screwed, which is larger in diameter than the groove in the end fitting, and so the reinforcing element - essentially by positive engagement - holds.

Although a surge arrester can be effectively formed in this way, the problem is to cut threads into the FRP rods used as reinforcing members without damaging them. This is complicated and expensive.

From the publication EP 0 646 276 Further possibilities are known, such as reinforcing elements can be anchored to the end fittings of a surge arrester. In particular, this document proposes to hold the reinforcing elements by a pin or a screw which extends perpendicular to the longitudinal direction of the reinforcing elements and is guided through a through hole by the rods. The pin or the screw are then held in a corresponding recess or a threaded hole in the end fitting.

Although it is much easier to form a hole in the direction perpendicular to the direction of expansion of the GFRP rods used as reinforcing elements than to cut a thread into them, this design involves the risk of weakening the reinforcing elements in the area of the hole in such a way that they break ,

The said European patent application also shows the possibility of setting the reinforcing elements with wedges in the end fitting. For this purpose, a tapering in the direction of the stacking means of the varistor blocks wedge between each reinforcing element and a corresponding inclined surface of the end fitting is brought and both together held together by an outer part of the end fitting under radial pressure. When tensile stress on the reinforcing elements, the wedges are dragged by friction and ensure that the reinforcing elements frictionally or frictionally held between the associated wedge and the end fitting.

In addition, the shows DE 199 40 939 the ability to hold the reinforcing elements in the end fitting in that in a conical bore of the end fitting in the direction of the stack center of the varistor blocks tapered sleeve is used with movable side walls, as a clamping sleeve, similar to the wedge of the aforementioned European patent application, the associated Reinforcing element under train holds firmly by frictional or non-positive connection.

Ultimately, in the WO 00/55869 proposed to provide the reinforcing elements at their ends with Crimphülsen and to prevent them in this way to slide through guide grooves in the end fitting.

DE 42 38 877 A1 shows a cutting ring connection for the gas-tight connection of pipes with high internal pressure. The cutting ring connection has an edge which cuts into the relatively soft material of the tube as it expands due to internal pressure.

In all of the above documents, in which the reinforcing elements frictionally or non-positively held in the end fitting, it is difficult to apply the necessary tensile strength. In particular, when bending load of the surge arrester creates a very strong tensile force on one side of the surge arrester.

With the crimping surge arresters, manufacturing is difficult because the crimping sleeve must be applied while the reinforcing element is held under tension. Also, crimping can cause uncontrolled damage to the rod.

In the surge arresters, in which the reinforcing elements are held by screws in the end fitting, this requires a considerable weakening of the reinforcing element in the region of the screw.

The object of the invention is therefore to provide a generic surge arrester with cage design that is easy to manufacture and secure anchoring of the reinforcing elements in the Ensures end fittings.

This object is achieved by a surge arrester according to claim 1 or 2. The dependent claims relate to further advantageous embodiments of the invention.

Fig. 1

eine Gesamtansicht eines gattungsgemäßen Überspannungsableiters mit teilweise weggeschnittenem Außengehäuse;

Fig. 2

den Käfig eines erfindungsgemäßen Überspannungsableiters, mit einer Endarmatur in Explosionsansicht;

Fig. 3

eine Schnittansicht entlang der Linie A-A in aus Fig. 2;

Fig. 4

das Prinzip eines Verankerungselements mit Schneidring, wie es bei dem erfindungsgemäßen Überspannungsableiter nach Fig. 2 und 3 verwendet wird;

Fig. 5

eine alternative Ausgestaltung des erfindungsgemäßen Überspannungsableiters;

Fig. 6

eine Detailansicht des Stabs mit Schneidelement nach Fig. 5.

In the following, the invention will be described in detail with reference to the accompanying drawings, in which:

Fig. 1

an overall view of a generic surge arrester with partially cutaway outer housing;

Fig. 2

the cage of a surge arrester according to the invention, with an end fitting in an exploded view;

Fig. 3

a sectional view taken along the line AA in Fig. 2 ;

Fig. 4

the principle of an anchoring element with cutting ring, as in the surge arrester according to the invention after Fig. 2 and 3 is used;

Fig. 5

an alternative embodiment of the surge arrester according to the invention;

Fig. 6

a detailed view of the rod with cutting element after Fig. 5 ,

The in Fig. 1 Cage design surge arresters shown include at least one varistor block 1. As the varistor blocks 1, known ceramic disks having a variable resistor can be used. At low voltages they work as near-perfect insulators, while at high voltages they have good conductivity. Commercially available varistor blocks are manufactured on the basis of zinc oxide (ZnO). However, the invention is not limited to such zinc oxide surge arresters, and other metal oxides as well as silicon carbide may be used for the varistor block, for example. In addition, in addition to varistor blocks 1, further blocks, such as metal blocks, or spark gap blocks may be included in the stack so as to adapt the length of the surge arrester to the requirements of the particular application.

Common varistor blocks 1 are formed as circular cylinders with a diameter of for example 5 cm and a height of about 4 cm. On both sides of the varistor blocks 1 aluminum electrodes not shown in detail are applied to ensure a better contact. It is also customary between the Varistorblöcke 1 to further improve the contact also not shown thin aluminum discs.

A stack formed by stacking such varistor blocks 1 and any metal blocks is shown in FIG Fig. 1 shown surge arrester between two end fittings 3 held. The end fittings 3 are usually formed of aluminum or stainless steel and designed so that they can be easily integrated into existing electrical installations or power grids, for example by a projecting from the surge arrester central screw 4, which makes good contact with the Varistorblöcken 1 well.

To protect against the environment, these surge arresters are surrounded by an outer housing 5, often made of silicone. The housing can be formed by spraying or pouring.

To increase the creepage path of the current 5 screens 7 are formed on the outside of the housing.

As stated, such surge arresters are subject to significant bending moments when used in the free environment. It is therefore necessary to ensure that the contacting of the varistor blocks 1 with each other and with the end fittings is maintained even with larger mechanical stresses. To achieve this glass fiber reinforced plastic rods or ropes 9 are clamped as reinforcing elements between the two end fittings 3 regularly. These hold the Varistorblöcke 1 between the two end fittings 3 together under tensile stress. Furthermore, occasionally spring elements are inserted into the stack of varistor blocks 1, so as to secure the contact even with temperature fluctuations or the like.

Hereinafter, the reinforcing elements will be referred to as rods 9, without any limitation of the invention.

Fig. 2 shows the "cage" of a surge arrester of a first embodiment of the invention. For better illustration, the varistor blocks 1 and other components of the stack have been omitted. One of the two end fittings 3 is shown exploded to illustrate the embodiment. A sectional view along the line AA is in Fig. 3 shown.

In Fig. 2 and 3 eight rods 9 are arranged at regular angular intervals along the circumference of the end fittings 3.

The end fitting 3 itself contains a first part 3A and a second part 3B. The first part 3A has eight through-holes 11 for the glass-fiber reinforced rods 9 and also eight threaded holes 13A for clamping screws 15, wherein the through holes 11 and the threaded holes 13A are alternately arranged along the circumference of the first part 3A of the end fitting. The exact number of the clamping screw connections and also the rods 9 should be selected by the person skilled in the art as required. In principle, it is possible to use only one clamping screw and / or only one (central) rod, for example when the varistor blocks 1 are designed as rings. However, arrangements are preferred in which three or more rods are distributed along the circumference of the end fitting, and in which the varistor blocks 1 are present as (circular) cylindrical disks.

The second part 3B has at the in Fig. 2 and 3 shown embodiment eight corresponding through holes 13 for the clamping screws 15 and eight only one side open recesses 17 for receiving the upper ends of the rods. 9

The first part 3A of the end fitting 3 is formed as a ring with a central passage 19. The second part 3B has in its center a guide tube 21 which can engage in the ring of the first part 3A. The guide tube 21 itself is provided on its inside with an internal thread 23 into which a further large screw 25 or a bolt can be screwed, which firmly presses the stack of Varistorblöcke 1 after assembly, wherein the rods are loaded with train.

On each rod 9, an anchoring element 27 is attached at each end. This anchoring element 27 is firmly connected to the rod 9, and ensures that under tensile load, the rod 9 remains firmly anchored in the end fitting 3.

In Fig. 3 and 4 one of these anchoring elements 27 is shown in section. In addition, it is shown how this anchoring element 27 cooperates in this preferred embodiment with the second part 3B and the first part 3A of the end fitting.

In Fig. 3 It can be seen that the through hole 13 in the first part 3A of the end fitting has a first narrow portion on the side of the varistor blocks 1 and a second further portion on the side of the second part 3B, which are interconnected via a conical portion. Even though Fig. 3 showing a conical section, this is not mandatory, a simple shoulder or step can also be used. The through hole 11 is to be formed so as to closely surround the rod 9 in its narrow portion, and to partially receive the anchoring element 27 in its wide portion. The conical section or the shoulder is designed to be complementary to the outer contour of the anchoring element 27, in order to allow a firm and secure form-fitting support of the anchoring element 27 in the end fitting 3.

The recess 17 in the second part 3B of the end fitting is also provided with a wide first portion on the open side facing the first part 3B and with a tapered portion on the closed end. The dimensions of the recess 17 and the through hole 11 are such that they can receive the anchoring element 27 in a form-fitting manner. This is below in Fig. 3 shown.

As an anchoring element 27, for example, a commercial "Ermeto screw" can be used, as it is known since the 30s of the last century Such Ermeto fittings are used in the art for connecting hydraulic pipes and are u.a. commercially available from Parker-Ermeto.

The anchoring element 27 has at least one edge 29 which rests against the rod 9 and is inclined against the direction of the tensile load.

Fig. 4 shows a detailed view of an anchoring element 27 according to the invention according to this embodiment.

The anchoring element 27 consists in the embodiment shown of three parts. A first cutting ring element 27A, a clamping sleeve 27B and a second cutting ring element 27C. The two cutting ring elements 27A and 27C are identical in construction in the embodiment shown and consist of a sleeve whose inner diameter is adapted to the outer diameter of the rod 9. On the inside of the sleeve of the cutting ring elements 27A, 27C, two cutting rings 29 or edges are formed in the embodiment shown, which cut into the surface of the rod 9 in use. The edges are preferably inclined against the direction of the intended tensile load. The material of the cutting ring elements 27A, 27C have a certain elasticity. It is possible to provide the cutting ring with a slot.

The outer contour of the cutting ring elements 27A, 27C is conical in the region of the cutting rings. wherein the diameter increases in the direction of the intended tensile load.

The bracing sleeve 27B has a tapered inner shape that is complementary to the outer contour of the cutting ring members 27A, 27C. When the grommet 27B and a cutting ring member 27A are engaged and pushed together in the axial direction of the rod 9, the cutting rings are driven to be cut into the rod 9 due to the complementary inclinations of the outer contour of the cutting ring member 27A and the inner shape of the grommet 27B. Due to the angular position of the cutting ring or so creates a positive connection between the rod 9 and the cutting ring, which continues to contract under tensile load of the rod and holds all the more. This well-known cutting ring principle, used since the thirties for connection of hydraulic pipes, ensures excellent retention of the anchoring element 27 on the rod 9 under tensile load.

In Fig. 4 As mentioned, a second cutting ring element 27C is shown. No separate clamping sleeve is provided for this cutting ring element 27C since this task is taken over by the recess 17 of the second part 3B of the end fitting.

In Fig. 4 Each cutting ring element 27A, 27C has two cutting rings 29. Designs with only one cutting ring or with three or more cutting rings are also possible.

At the end of the cutting ring elements 27A, 27C facing the intended tensile load, the cutting ring element 27A, 27C is formed smooth inside and is closed in the outer contour by a second, relatively steep cone, wherein the Diameter decreases in the direction of the intended tensile load.

This second cone is assigned a corresponding section of the bracing sleeve 27B or of the through hole 11 of the first part 3A of the end fitting 3. By axial clamping of the cutting ring element 27C and the clamping sleeve 27B and the cutting ring member 27A and the first part 3A of the end fitting 3 is formed by this shaping a deformation of the cutting ring member 27A, 27C, resulting in a frictional connection between the cutting ring member 27A, 27B and the rod. 9 leads. In the art, the pipe joint cutting ring is used for additional sealing against hydraulic fluid.

Although this non-positively contributes to the holding of the rod 9 in the anchoring element 27, this is of minor importance to the invention and can also be dispensed with altogether. For example, the second cone of the cutting ring element 27A, 27C can be dispensed with. Also, the bracing sleeve 27B and the through hole 11 may then be formed without the complementary second cone, for example with a simple shoulder or step.

With this cutting ring connection, a serious damage leading to the weakening of the rod 9 can be avoided since the cutting rings 29 do not cut very deeply into the rod 9. In addition, as it can in Fig. 4 is shown, a plurality of cutting rings 29 may be arranged one behind the other.

For mounting the surge arrester according to the invention, as in the Fig. 1 to 4 is shown, a stack of varistor blocks 1 and optionally metal blocks between the first annular parts 3A of two end fittings 3 is arranged. Subsequently, the rods 9 are guided through the provided for this purpose in the first parts 3A of the end fittings 3 through holes 11.

On one side of the stack, the rods 9 are brought to a uniform length and the anchoring elements 27 are pushed. Subsequently, the second part 3B of the end fitting is applied on this side. By means of the first clamping screws 15, which extend through the through holes 13 in the second part 3B of the end fitting and engage in the threaded holes 13A in the first part 3A of the end fitting, the first and second parts 3A, 3B of the end fitting are firmly clamped against each other. As it is in Fig. 2 is shown, the two parts of the end fitting are formed so that they receive the anchoring elements 27 completely in the corresponding recesses and enclose them.

Subsequently, the clamping screw 25 is screwed through the central opening of the end fitting, which rests against the Varistorblöcken 1 and a lying between the uppermost Varistorblock 1 and the end fitting 3 control disc made of aluminum or stainless steel.

Subsequently, the rods 5 are provided with the anchoring elements 27 on the opposite side of the Varistorstapels.

Again, the second part 3B of the end fitting 3 is applied and braced with the first clamping screws 11 against the first part 3A, as already discussed.

A second large clamping screw 25 is driven by the central thread of the end fitting 3, so that it rests against a corresponding control disk or the uppermost varistor block. With a torque wrench, the lower and upper middle large clamping screws 25 are tightened, so that the stack of varistor blocks is held together with a defined pressure.

Subsequently, the cage thus formed is provided with an outer housing. This is advantageously done by encapsulation or encapsulation of the stack of Varistorblöcken, the rods 9 and the end fittings 3. As a material for the plastic outer housing, a low-viscosity silicone has been found suitable. Such low-viscosity silicones are commercially available, and have also been used in the prior art for housing.

Simultaneously with the formation of the housing 5, the umbrellas 7 can be cast. Alternatively, it is possible to initially design the housing cylindrical and produce the screens 7 separately. The screens 7 can then be attached to the housing 5 by mechanical relaxation or by gluing. Although the separate application of the screens 7 is an additional operation, which increases the cost of the surge arrester, but in this way longitudinal seams along the surge arrester can be avoided, where can develop leakage due to contamination creepage.

Fig. 5 shows an alternative embodiment of the surge arrester according to the invention.

In contrast to the embodiment of the Fig. 2 to 4 the rods 9 are not circular in cross section. In the Fig. 5 shown rods 9 are adapted in shape to the outer contour of the stack of Varistorblöcken 1. Thus, the outer housing 5 of the surge arrester can be designed to be thinner overall, since the bars 9 have a smaller thickness with the same tensile strength. This is advantageous insofar as the low-viscosity silicone is expensive.

When using such example, circular-segment-shaped glass fiber reinforced rods 9, the principle of the cutting ring connection, however, must be modified so that instead of a continuous, the rod comprehensive, cutting ring one or more cutting blades 31, which are adapted to the rod 9 in its contour, are provided. This is on average in Fig. 5 shown.

Fig. 6 shows in greater detail the end fitting 3 and the anchoring element 27 of this embodiment.

In the embodiment of Fig. 5 and 6 is the end fitting 3 in turn formed of two parts. An inner part 3C is formed in a ring-shaped or hollow cylindrical shape, and has an internal thread 31, through which the clamping screw 25 can extend. Guide grooves are preferably formed along this inner part, which correspond in their contour to the rods 9, as shown in FIG Fig. 6 can be seen. The inner part 3C of the end fitting is surrounded by a cup-shaped outer part 3D of the end fitting, wherein the inner diameter of the cup is adapted to the outer diameter of the inner part in the region outside the grooves. The cup-shaped outer part 3D is slightly conical, in the direction of the intended tensile load, ie towards the center of the stack of Varistorblöcke 1, runs. Between the bars 9 and the outer part 3D of the end fitting wedges 33 are mounted, which also run towards the center of the stack of Varistorblöcke 1.

On the side of the wedge 33 facing the rod 9, one or more cutting blades 29 are formed transversely to the longitudinal direction of the rod 9 and are angled at an acute angle against the direction of the intended tensile load towards the center of the stack of the varistor blocks. A complementary cutting blade 29A, which is also adapted to the shape of the glass fiber reinforced rod 5, may be formed in the guide groove of the inner part 3C of the end fitting, which is not shown in the figures.

Preferably, a plurality of cutting blades 29 are formed both on the wedge 33 as well as on the inner part of the end fitting 3.

When tensile load, the rod 9 is held on the one hand non-positively between the inner part 3C and the outer part 3D of the end fitting by means of the wedge 33. On the other hand, moreover, the rod 9 is held by the cutting blades 29 between the wedge 33 and the rod 9 on the one hand and between the inner part 3 C of the end fitting and the rod 9 on the other hand positively.

The advantage of this embodiment over the embodiments of the Fig. 2 to 4 is that the assembly is simplified. By appropriate openings 37 on the bottom side of the cup-shaped outer part 3D of the end fitting, the wedges 33 can be driven after the two end fittings 3 are provided with the bars 5 and arranged around the stack of varistor blocks. After the driving of the wedges 33, the entire construction can be acted upon by the clamping screws 25 through the middle of the inner part 3 C of the end fitting with the necessary pressure.

As in the embodiment of the Fig. 2 to 4 Subsequently, the outer housing 5 is applied made of plastic.

Although in the embodiment of Fig. 5 and 6 is shown that the inner part 3C of the end fitting is formed with guide grooves 35, this is not mandatory. Instead, or in addition, the outer part 3D of the end fitting may be provided with guide grooves, or the guide grooves 35 may be completely omitted. In this case, however, a gap remains between the inner and the outer part of the end fitting, which then has to be filled with the silicone elastomer in forming the housing 5.

According to a further advantageous embodiment, it is possible to additionally apply an adhesive for further attachment of the rods 9 in the end fittings. For example, in the last-discussed embodiment, the adhesive may be introduced into the gap between the outer and inner parts of the end fitting until this gap is completely filled with adhesive.

Although the preferred embodiments of the invention have been described above, the invention is not limited to these embodiments. In particular, the number of cutting blades or cutting rings can be freely adjusted as needed. In addition, by using flexible cutting rings, the positive engagement of the cutting ring by cutting into the outer layer of the bars can be achieved by frictional engagement without damaging the surface of the bars, unless excessive tensile stress is expected. This is for example given when the surge arrester is not provided with the directly applied housing 5, but is inserted as a so-called surge arrester with tube design in a tube made of glass fiber reinforced plastic or in a ceramic housing. In this case, a substantial part of the mechanical forces is already absorbed by the pipe, and the rods serve only as an additional stabilizing element, so that is to be expected with lower tensile loads.

Although in the embodiments shown, the anchoring of the rods to the end fittings on both sides of the stack of Varistorblöcken was done in each case in the same way, this is not mandatory. For example, ropes can be used instead of glass fiber reinforced rods, which are guided in one of the end fittings for anchoring over a shoulder, and are fastened only with the opposite end fitting with anchoring elements according to the invention.

Claims (9)

1. Surge protector, comprising: at least one varistor block (1); at least one end fitting (3); at least one reinforcing element (9) which holds the varistor block (1) rigidly on the end fitting (3), said reinforcing element (9) being a glass-fibre-reinforced plastics material rod or a cable which holds the end fitting (3) and the varistor block (1) together with a tensile load; at least one anchoring element (27) which holds the reinforcing element (9) rigidly on the end fitting (3); the anchoring element (27) having at least one edge (29) which cuts into the reinforcing element (9); characterised in that the edge (29) of the anchoring element (27) is a cutting ring, which surrounds the glass-fibre-reinforced plastics material rod or the cable and cuts into the surface thereof.
2. Surge protector, comprising: at least one varistor block (1); at least one end fitting (3); at least one reinforcing element (9) which holds the varistor block (1) rigidly on the end fitting (3), said reinforcing element (9) being a glass-fibre-reinforced plastics material rod or a cable; at least one anchoring element (27) which holds the reinforcing element (9) rigidly on the end fitting (3); the anchoring element (27) having at least one edge (29) which cuts into the reinforcing element (9); characterised in that anchoring element (27) is a wedge (33) which cooperates with a corresponding inclined surface of the end fitting (3), the edge (29) being formed as a cutting blade on the side of the wedge (33) which faces the reinforcing element (9), and cutting into the reinforcing element (9) when subjected to a tensile load by the wedge (33) and the inclined surface.
3. Surge protector according to either claim 1 or claim 2, characterised in that the varistor block or varistor blocks are formed from a metal oxide, preferably ZnO.
4. Surge protector according to any one of claims 1 to 3, characterised in that the end fitting (3) or end fittings (3) are formed from a metal, preferably aluminium.
5. Surge protector according to any one of the preceding claims, characterised in that the surge protector has a housing (5) with screens (7).
6. Surge protector according to any one of the preceding claims, characterised in that a plurality of edges (29) are formed on one anchoring element (27) and cooperate with the reinforcing element (9).
7. Surge protector according to either claim 1 or claim 2, characterised in that the anchoring element (27) is connected in an interlocking manner to the reinforcing element (9) and to the end fitting (3).
8. Surge protector according to any one of the preceding claims, characterised in that the edge (29) cuts into the anchoring element (27) in the opposite direction from the tensile load.
9. Surge protector according to claim 2, characterised in that the reinforcing element is a tubular segment composed of a glass-fibre-reinforced plastics material.

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