EP1355327A2 - Surge voltage arrester and method to produce such a surge voltage arrester - Google Patents

Abstract

The device has two fixed mounted current connections (2,3), a non-linear electrical resistance, two electrodes (6,8) at a distance apart along one axis and a resistance body (7) consisting of a matrix with an embedded powder filler with varistor properties. The resistance body is made of a compound material that can be cold shaped and is compressed to form the non-linear electrical, resistance between the electrodes. AN Independent claim is also included for the following: (a) a method of manufacturing an inventive surge voltage arrester.

Description

TECHNICAL AREA

The invention is based on a surge arrester according to the Preamble of claim 1. The invention also relates to a method for Manufacture of such a surge arrester. The surge arrester contains two fixed power connections and one non-linear electrical resistance, containing two in the direction of an axis from each other spaced electrodes and a resistance body from one Polymer composite with a polymeric matrix and one in the matrix embedded, powdery filler with varistor behavior. The filler contains generally a sintered varistor granulate with predominantly spherical Doped metal oxide particles. The particles are crystalline, through Grain boundaries separate grains. Over there comparable surge arresters with non-linear resistors Additional processes based on a sintered ceramic can be omitted Surge arrester relatively simple and in a wide variety of shapes getting produced.

STATE OF THE ART

A surge arrester of the aforementioned type can be used, for example, in DE 198 24 104 A1 or R.Strümpler, P.Kluge-Weiss and F.Greuter "Smart Varistor Composites ", Proceedings of the 8th CIMTECH-World Ceramic Congress and Forum on New Materials, Symposium VI (Florence, June 29 - July 4, 1994) be removed. This surge arrester contains a non-linear one electrical resistance with a resistance body from a one Polymer matrix and a composite material contained therein powder.

The powder used is a granulate which was produced by sintering a spray-dried varistor powder on the basis of a zinc oxide doped with oxides of Bi, Sb, Mn, Co, Al and / or other metals. These granules have spherical particles shaped like a soccer ball with varistor behavior, which are made up of crystalline grains separated by grain boundaries. The diameter of these particles is up to 300 µm. By changing the dopants and the sintering conditions, the electrical properties of the sintered granulate, such as the non-linearity coefficient α _B or the breakdown field strength U _B [V / mm], can be set over a wide range. For power applications in a surge arrester, two electrodes are cast into the polymer composite during the manufacture of the resistance body or, after the resistance body has been manufactured, applied in the form of a metal layer to its surface.

EP 0 875 087 B1 describes a composite material based on a polymeric in particular elastomeric, matrix and a powder embedded in this matrix described. A granulate is used as powder, which also by Sintering a spray-dried varistor powder based on one with oxides produced from Bi, Sb, Mn, Co, Al and / or other metals doped zinc oxide has been. These granules have a spherical shape shaped like a football Particles with varistor behavior, which consist of crystalline, through grain boundaries separate grains are constructed. The particles have diameters up to a maximum of 125 µm and have a size distribution, which one Gaussian distribution follows. This material is used in cable connections and Cable terminations used and forms voltage-controlling layers there.

A surge arrester with a varistor based on microspheres doped zinc oxide, which is first sintered and then pressed or only pressed and then sintered is known from US 5,231,370 A. Since the microspheres as The initial product for the varistor is initially in the form of a gel Production of the surge arrester is relatively complex. Besides, it is not exclude that when sintering between the individual microspheres Air gaps remain, which are the dielectric strength of the varistor and thus also reduce the surge arrester. In the above Document also mentions that sintered microspheres are not only considered Varistors, but also used as a filler for electrical rubber goods can be.

No. 5,955,936 A describes a PTC resistor made of a polymer composite, containing a polymer matrix and an electrically conductive embedded therein Filler. To contact this resistor, two electrodes are made a metal foam, which is used directly or via conductive layers are electrically conductively connected to the composite.

PRESENTATION OF THE INVENTION

The object of the invention is as set out in the claims based on specifying a surge arrester of the type mentioned in the introduction, which is easy to manufacture despite good protection characteristics, and at the same time to create a process with which to solve a very economical variety of surge arresters required for various protection tasks can be manufactured.

In the surge arrester according to the invention, the resistance body of formed a cold formable polymer composite and to form a non-linear electrical resistance pressed between two electrodes. Because of the cold deformability, the resistance body is more constant Surface pressure on the electrodes, so that inhomogeneities on the Interface between the resistance body and electrodes avoided and a low contact resistance is achieved. During operation of the surge arrester Current surges occurring as a result of switching operations or lightning strikes with high Current amplitudes can be due to the homogeneous and low-impedance Contact resistance between the electrodes and the resistance body be safely led in resistance without one leading to premature Failure of the surge arrester leading to local overheating non-linear resistance is to be feared.

A particularly uniform surface pressure is achieved if the matrix of a polymer based on a liquid, a gel or an elastomer is formed and preferably contains a silicone or a mixture of silicones. Other suitable polymers are flexible polyurethanes, epoxies, fats or oils.

Other wide-meshed polymers and fine-pored polymers are also suitable Foams. By filling a liquid polymer, such as a silicone oil, or of a weakly cross-linked polymeric gel with the filler becomes a paste executed composite reached.

In general, the filler-containing surfaces of the resistance body lie to the electrodes. Due to the direct contact of the varistor property having filler particles with the electrodes Contact resistance and thus the ohmic resistance of the non-linear Resistance when discharging an overvoltage is kept low.

The surge arrester preferably has a resistance body housing. The nonlinear resistance is not just that protected housed, but it is also the housing Surface pressure necessary force absorbed. This force can be particularly effectively by a preloaded spring or by pressing one precursor element of the cold-formable polymer composite Resistor body are generated between the electrodes. Because here the Resistance body because of the cold deformability of the polymer composite in generally with a lateral surface arranged between the two electrodes is supported on the housing, the dimensions of the precursor element still quite significantly from the definitive dimensions of the resistance body differ. Such a surge arrester according to the invention can be manufactured extremely inexpensively.

For many applications it is sufficient if the housing is elastic is deformable or shrinkable. The for pressing the Resistance body necessary force can be by tensioning or by Shrinkage of the housing are generated.

In order to compensate for changes in volume of the resistance which occur when the Surge arresters caused by heating, it recommends itself, the housing is stiffened in the direction of the axis and in the circumferential direction train elastically deformable. The longitudinal stiffening can, for example, by a predominantly axially directed, steep cross wrap can be achieved. Through the Longitudinal stiffeners are the dimensions of the resistance body in axial Direction kept constant. Those caused by warming Volume changes of the resistance body then act because of this Cold formability in changes in its radial dimensions. This Changes are made from the elastically deformable in the circumferential direction Housing added. The surge arrester developed in this way can adapt to the prevailing operating conditions through "breathing".

It is advisable to re-use the composite in one - for example using sealing rings part of the housing sealed on the outside. Is the composite executed as a paste and then it has a polymer with a relatively low Viscosity, such as oil in particular, the polymer also reaches a Volume change of the resistance body or the polymer composite is not outward.

The volume change of the resistance body can also be done electrically conductive, cold-formable and reversibly compressible intermediate layer be compensated for between the composite and one of the two Electrodes is arranged. This layer can also be used for the electrical Contact between the resistance body and the electrode can be improved.

It is especially for low and medium voltage applications Manufacturing technology advantageous if the housing is made of several parts, and when the force necessary to press the resistance body through Bracing two relatively movable parts of the housing generated becomes.

It has a particularly low contact resistance Surge arrester from at least one of the two electrodes is porous. The material of the resistance body then hugs when pressing particularly close to the porous and therefore rough surface of the Resistance body and then penetrates into the pores at the same time. To a Passing through the material of the resistance body, especially when used a liquid matrix, to prevent and to form a uniform To ensure resistance bodies with a homogeneous current flow however the size of the pores at least in one direction to the axis, for example perpendicular or parallel to it, not be significantly larger than that average size of the filler particles.

Suitable materials for a porous electrode are metal nonwovens, especially those based on stainless steel, copper or bronze, metal foams, advantageously those based on nickel or aluminum, or sintered bodies, preferably based on bronze, brass, copper, silver or nickel. These materials not only have good electrical properties, but can also be firmly integrated into the resistance body to form a low contact resistance. Boundary layer problems leading to the failure of the surge arrester are largely avoided in this way. The boundary layer between the electrode and the resistor does not become a power-limiting factor even with high current loads, so that power consumption of up to 200J / cm ^{2 is} possible. If the porous electrode is designed as a metal fleece or as a metal foam, it can easily be deformed by pressing. The desired pore size can thus be generated in a particularly simple manner. By punching, embossing, grinding or other similar mechanical processing methods, the porous electrode can be given a predetermined desired geometric shape.

Are metal fleece, metal foam or sintered body on a power connection or another current-conducting part of the surge arrester applied, so the porous electrode made of such a material can optionally have a very small layer thickness, for example 0.1 mm. The Despite its small thickness, the electrode has a supporting body that holds it high mechanical strength. Typical layer thicknesses move between 0.1 and 10 mm. The connection between porous electrode and current-carrying body is advantageously by soldering, gluing with conductive Gluing, sintering (sintered electrodes) or ultrasonic welding.

The surge arrester according to the invention can be particularly advantageous manufacture if from a starting body formed by the polymer composite a cold deformable precursor element is separated, and if that Precursor element with the formation of contact surfaces between two electrodes arranged and forming the nonlinear electrical resistance is pressed. In general, but especially in High voltage applications, the precursor element is in the form of a disc or have plate. The starting body is then expedient after Kind of a sausage or a band. Then he can go through Extrusion can be produced continuously and the precursor element can be Separation of the pane or plate can be achieved very easily. The Surge arresters can not only be manufactured extremely cost-effectively, A control of the weight of the precursor elements can also be used constant quality of the surge arrester within a narrow Tolerance range can be reached. Due to the possibility of producing the Surge arrester the resistance body when pressing the Giving precursor elements different shapes can be done in very simple Instruct the electrical properties of the surge arrester different protection requirements can be adjusted.

If the polymer composite is in the form of a gel or paste, one can advantageous development of the inventive method Precursor element in one closable and two fixed Housing containing electrodes pressed and the housing after reaching a predetermined pressure value are closed. Through this Process steps are carried out with particularly simple means and without additional Machining a precisely adapted to practically any housing geometry Resistance body reached.

When the polymer composite is formed as an elastomer, this can Precursor element in a not necessarily closable Housing can be used, then the precursor element with two Electrodes contacted and then by moving one of the two Electrodes are pressed up to a predetermined pressure value. hereby can be a good enough for many applications in a particularly simple manner Surge arresters are manufactured.

DESCRIPTION OF THE DRAWINGS

Fig.1

eine Aufsicht auf einen Schnitt durch eine erste Ausführungsform eines Überspannungsableiters nach der Erfindung,

Fig.2

eine Aufsicht auf einen Schnitt durch ein Gehäuse einer zweiten Ausführungsform des Überspannungsableiters nach der Erfindung während des Füllens mit einem als Gel ausgeführten Polymerverbundstoff.

These and other advantages of the invention are explained in more detail below with reference to drawings. Here shows:

Fig.1

2 shows a plan view of a section through a first embodiment of a surge arrester according to the invention,

Fig.2

a plan view of a section through a housing of a second embodiment of the surge arrester according to the invention during filling with a polymer composite designed as a gel.

WAY OF CARRYING OUT THE INVENTION

The surge arrester shown in Figure 1 has a hollow cylinder executed housing 1, in each of which at the upper and lower ends designated internal thread is embedded. The one at the top Internal thread works together with the external thread as a screw executed power connector 2, while the one provided at the lower end Internal thread also interacts with the external thread as Screw made power connector 3. Between the two Power connections 2 and 3 arranged along the cylinder axis, not designated are a compression spring 4 as well as in each case from top to bottom Circular disk executed a pressure body 5, an electrode 6 Resistor body 7 and an electrode 8.

The housing 1 is made of a mechanically and electrically high-quality insulating material educated. A suitable insulating material is, for example, a ceramic, such as Porcelain, or a plastic based on a polymer, such as one preferably fiber-reinforced thermoset, in particular an epoxy, or one Thermoplastic, such as an acrylate, such as PMMA. For outdoor use can provide the housing with ribs or shields that extend the creepage distance be made of a material suitable for outdoor use. The housing takes over especially support and support functions.

The power connections 2 and 3, the pressure plate 5 and the electrodes 6 and 8 are each formed by an electrically highly conductive metal. Such metals are typically copper, nickel, aluminum, stainless steel and alloys on the Base copper, such as bronze or brass, and / or aluminum.

Sintered bodies, primarily made of bronze, brass, copper, nickel, are used as electrodes or silver, metal foam, such as fine-pored nickel foam or coarse-pored, uniaxially compressed aluminum foam, metal fleece or mesh, compressible graphite in layer or foil form, on solid bases sintered porous metal layers, such as bronze, or sandblasted Metal body, such as aluminum or copper, is used. The porous Metal layers can be sintered in one or more layers and thicker about 0.1 mm and up to a few centimeters. By mechanical Editing, such as punching, embossing, grinding and / or turning, can do that Electrodes 6, 8 are given a well-defined shape, with the Shaping especially make sure that the electrodes on their Have contact surface on the resistance body 7 rounded edges.

The compression spring can be made of a highly conductive metal alloy, such as on the Base made of steel or bronze, but can also be made from a moderate or non-conductive material, such as plastic. In general it is Compression spring over several current conductor elements acting as a contact band bridged. These elements not shown in Fig.1 connect the Power connection 2 and the pressure plate 5 with each other in an electrically conductive manner.

The resistance body is made from a cold-formable polymer composite a polymeric matrix and a powdery one embedded in the matrix Filler formed with varistor behavior. The polymer forming the matrix is in the generally a gel or an elastomer, preferably each based on Silicone, but can also be a liquid, such as preferably an oil, for example the base mineral or silicone oil. The filler contains varistor particles doped metal oxide with a predominantly spherical structure, the particles composed of crystalline grains separated by grain boundaries are. Production and properties of the filler are in the stated state of the Technology described. To improve the electrical contact between the individual varistor particles and thus the energy consumption of the Surge arrester, the filler can contain a few percent by weight of metal powder contain.

To improve the contact between the polymer composite existing resistance body 7 and the electrodes 6, 8 can - as in Fig.1 is shown - in addition two electrically conductive, cold-formable and elastic reversibly compressible intermediate layers 12, 13 may be provided. This Intermediate layers generally consist of an electrically highly conductive, compressible polymer composite, preferably one with conductive powder, such as nickel or titanium diboride, and especially polymeric hollow microspheres (such as those sold under the trade name Expancel) filled polymeric gel, but can also be used as an electrically conductive foam or as another electrically conductive, compressible body with spring action (fleece, Tissue). The intermediate layers 12, 13 not only improve that electrical contact, but can also change the volume of the Compensate resistance body 7. In this way you prevent extremely effectively Overstretch a rigid housing.

A resistor body typical of the surge arrester according to the invention had the following formulation in parts by weight (GT): SYLGARD 527 A 100 GT SYLGARD 527 B 100 GT filler 1000 GT

SYLGARD is one of Dow Corning under this trade name distributed silicone resin. The filler corresponded to that in the prior art Filler described in DE 198 24 104 A1.

The polymer composite was made by mixing the above Output components manufactured. Here, the components were Mixed room temperature and then at a negative pressure of typically 50 vented up to 100 mbar. Alternatively, in another manufacturing process the filler is pre-evacuated at a pressure of approx. 1 mbar and then at a Pressure of approx. 100 mbar with that by mixing the two aforementioned Resin components formed silicone infiltrates. To achieve a high Filling levels, the infiltrated samples were spun in a centrifuge. Alternatively, a high degree of filling can be achieved by squeezing out excess Silicone resin can be achieved. After a curing time of approx. 24 hours at A cold-formable, rubber-like polymer material became room temperature educated.

In the embodiment according to FIG. 1, the polymer composite was in shape of a sausage-shaped body and was made from it as Precursor element for the resistance body 7 a substantially circular trained material disc separated. This precursor element was in the already housing 1 containing the power connection 3 and the electrode 8 brought. Thereafter, the electrode 6, the pressure body 5 and brought the compression spring 4 into the housing 1 and then the one thus formed The stack is screwed using the power connector 2. By screwing of the two power connections 2 and 3 relative to one another is the compression spring 4 compressed. The pressure plate 5 loaded with compression force now presses the Electrodes 6 and 8 from above and from below against the precursor element. Because of its good cold formability, this element is used in one relatively low pressure of a few, for example 1 to 2, bar to Resistor body 7 pressed. This resistance body 7 has two Gaps without a gap on the electrodes 6 and 8 and one without gaps on the inner surface of the casing. By pressing becomes a nonlinear electrical inserted into the housing without a gap Resistance formed. The pressure is also a sufficiently high one and evenly distributed contact pressure between the Filler particles and the electrodes reached. A metallization of the face of the resistance body 7 can therefore be omitted.

The breakthrough field strength U _B [V / mm], the nonlinearity coefficient α _B and the. Were produced on two embodiments 1 and 2 of the surge arrester according to the invention with a cylindrical resistance body 7 of approx. 40 mm diameter and a height of approx maximum power P [J / cm ³ ] determined. The values determined are entered in the table below. In embodiment 1, electrodes made of sintered bronze 7 and in embodiment 2 electrodes made of sandblasted aluminum were used. In Comparative Example 3, the electrodes were poured into the polymer composite.

Example 4 relates to an embodiment of the invention Surge arrester, in which the polymer composite as a paste with approx. 85 Parts by volume of filler and approx. 15 parts by volume of silicone oil. The Electrodes were made of sintered bronze.

As shown in FIG. 1, other electrodes can alternatively be used become. For example, as shown, the electrode 6 made of nickel foam and the Electrode 8 consist of a sintered bronze and can also be shown as both electrodes 6 and 8 by gluing, soldering, sintering or welding the pressure plate 5 or the power connection 3. Alternatively, you can both electrodes are made of the same material, such as sintered bronze, and can only one or neither of the two electrodes with the associated electrical conductive support body.

To determine U _B and α, the DC current-voltage characteristic curves of the three samples were determined and from this the breakdown field strength U _{B of} the associated resistance was determined at a current density of 1x10 ^-4 [A / cm ² ]. For each of the three surge arresters, α _B was taken from the slope of the tangent to the assigned, logarithmic, assigned current-voltage characteristic curve at the point determined by the breakdown field strength U _B.

P was determined from current pulse experiments in which the resistors in a test device were exposed to several 8/20 µs current pulses with current density amplitudes up to 1 [kA / cm ² ] at electrical field strengths up to 800 [V / mm]. sample U _B [V / mm] α _B P [J / cm ³ ] 1 229 41 62 2 233 44 80 3 220 30 77 4 159 55 201

From this it can be seen that surge arresters according to the invention, though they were made much easier and cheaper, electrical Have properties that match the corresponding properties of a the surge arrester largely manufactured to match. The surge arrester designed according to sample 4 with a pasty polymer composite can perform particularly well take up. This surge arrester can be used anywhere where the surge arrester requires a high level of energy absorption.

As can be seen from Fig. 2, when using a paste designed Polymer composite (liquid polymer that is highly filled with filler) or a weakly cross-linked, filled gel, the one marked with arrows Precursor element through an opening 9 in a closable Housing 10 are pressed. The two electrodes 6 and 8 are fixed in the Housing arranged. Since they are guided through the housing wall, they can can also be used as a power connection. The pressing force in Housing interior of the resistance body formed, which to the gapless Inside of the housing, in particular the two electrodes 6 and 8, is pressed. By closing the opening 9, for example squeezing one Housing approach 11, the surge arrester can be completed.

LIST OF REFERENCE NUMBERS

1

casing

2, 3

power connectors

4

compression spring

5

pressure vessels

6, 8

electrodes

7

resistance body

9

opening

10

casing

11

housing extension

12, 13

interlayers

Claims (20)

Surge arrester with two fixed current connections (2, 3) and with a non-linear electrical resistance, comprising two electrodes (6, 8) spaced apart in the direction of an axis and a resistance body (7) made of a matrix and a powdery filler embedded in the matrix with varistor behavior, characterized in that the resistance body (7) is formed from a cold-deformable composite and is pressed to form the nonlinear electrical resistance between the two electrodes (6, 8). Surge arrester according to claim 1, characterized in that the matrix is formed by a polymer based on a liquid, a gel or an elastomer, preferably based on silicone. Surge arrester according to one of claims 1 or 2, characterized in that filler-containing surfaces of the resistance body (7) bear against the electrodes (6, 8). Surge arrester according to one of Claims 1 to 3, characterized in that the resistance body (7) is arranged in a housing (1, 10) which receives the force required for pressing the resistance body (7). Surge arrester according to Claim 4, characterized in that the resistance body (7) is supported on the housing (1, 10) with a lateral surface arranged between the two electrodes (6, 8). Surge arrester according to one of claims 4 or 5, characterized in that the force is generated by a spring (4). Surge arrester according to one of claims 4 or 5, characterized in that the electrodes are held stationary in the housing, and that the force is generated between the electrodes when a precursor element of the resistance body formed from the cold-deformable composite is pressed in. Surge arrester according to one of claims 4 or 5, characterized in that the housing (1, 10) is designed to be elastically deformable or shrinkable, and in that the force is generated by relaxing the prestressed housing or by shrinking the housing. Surge arrester according to claim 8, characterized in that the housing (1, 10) is longitudinally stiffened in the direction of the axis and is elastically deformable in the circumferential direction. Surge arrester according to one of claims 4 or 5, characterized in that the housing is constructed in several parts, and that the force is generated by bracing two parts of the housing which are movable relative to one another. Surge arrester according to one of claims 1 to 10, characterized in that at least one of the two electrodes (6, 8) is porous. Surge arrester according to claim 11, characterized in that the size of the pores in a given direction to the axis is not larger than the average size of the filler particles. Surge arrester according to one of claims 11 or 12, characterized in that the at least one electrode (6, 8) is designed as a metal fleece, metal foam or sintered body. Surge arrester according to Claim 13, characterized in that metal fleece, metal foam or sintered body are applied to a support body of the surge arrester designed as a power connection (3) or pressure plate (5). Surge arrester according to one of Claims 1 to 14, characterized in that an electrically conductive, cold-deformable and reversibly compressible intermediate layer (12, 13) is arranged between the composite and one of the two electrodes (6, 8). Surge arrester according to one of Claims 4 to 15, characterized in that the composite material is provided in a part of the housing (1) which is sealed off from the outside. A method for producing a surge arrester according to claim 1, characterized in that a cold-deformable precursor element is separated from a starting body formed by the polymer composite, and that the precursor element is arranged with the formation of contact surfaces between two electrodes (6, 8) and pressed to form the nonlinear electrical resistance becomes. Method according to claim 17, characterized in that when the polymer composite is formed as a gel or paste, the precursor element is pressed into a closable housing (10) containing two fixed electrodes (6, 8), and that after reaching a predetermined pressure value, the housing ( 10) is closed. A method according to claim 17, characterized in that when the polymer composite is formed as an elastomer, the precursor element is inserted into a housing (1), contacted with two electrodes (6, 8) and subsequently by shifting one (6) of the two electrodes (6, 8) is pressed up to a predetermined pressure value. Method according to one of claims 17 to 19, characterized in that the precursor element in the form of a disc or plate is separated from a sausage or band-shaped starting body.

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