EP1846932A1

EP1846932A1 - Method for coating a varistor block with an electrically insulating coating, and varistor block for a surge arrester

Info

Publication number: EP1846932A1
Application number: EP06708002A
Authority: EP
Inventors: Bernd Kruska; Rolf-günter RAUTMANN
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2005-02-11
Filing date: 2006-02-03
Publication date: 2007-10-24
Also published as: RU2007133804A; US20080136578A1; KR20070108236A; RU2382428C2; BRPI0608280A2; CN101116153A; CN101116153B; DE102005007146A1; WO2006084822A1

Abstract

Disclosed are a method for coating a varistor block with an electrically insulating coating as well as a varistor block for a surge arrester. A varistor block (1) is formed from several varistor elements (2a, 2b, 2c, 2d) while an electrically insulating coating (5, 5a, 5b) is disposed around the varistor elements (2a, 2b, 2c, 2d). The electrically insulating coating (5, 5a, 5b) rests directly on a surface of the varistor block (1). Unwanted gas molecules are removed from the joining area between a surface of the varistor block (1) and the coating (5, 5a, 5b) before or while the electrically insulating coating (5, 5a, 5b) is applied to the varistor block (1)

Description

2005 P 02497 DE

description

Method for sheathing a varistor block with an electrically insulating sheath and varistor block for a surge arrester

The invention relates to a method for sheathing a varistor block for a surge arrester having an electrically insulating sheath as well as to a varistor block which can be produced according to this method.

It is known to use overvoltage arresters in electric power transmission networks. Surges occur, for example, by lightning strikes in overhead lines. The overvoltage arresters serve to cause their breakdown in the event of overvoltages. For this purpose, the surge arresters are equipped with varistor blocks. These varistor blocks have a very high or a very low impedance as a function of an applied voltage. By a corresponding dimensioning resp. Selection of the varistor block can thus be controlled depending on the voltage level of the electric power transmission network Ableitstrompfad. By means of the current flowing through the Ab ^¬ leitstrompfad leakage current, the overvoltage is reduced. After reaching an uncritical voltage level, the varistor block again assumes a very high impedance, so that the leakage current path is almost completely interrupted.

To form a varistor for surge ^¬ abieiter metal oxide is used. The metal oxide is brought into a block form, for example, by sintering or pressing. Due to the process, the surface of the varistor block has a certain roughness. To reduce the roughness and the surface with a certain mechanical 2005 P 02497 DE

To provide strength, it is known to wrap the varistor blocks tightly, for example with plastic tapes, so that the complete varistor block is enveloped and only the electrical contacting points necessary for interconnecting the block in a leakage current path remain free.

This wrapping must be done with a very high-quality plastic, as the varistor blocks are used in the medium, high and highest voltage ranges. There occur high electric-see fields that load electrical insulation ^¬ strong. The electrically insulating sheath must be wrapped very carefully in order to allow no free spaces on the Va ^¬ ristorblock. Due to the high quality and costly insulating material, the amount of insulating material should be kept as low as possible.

The application of the electrically insulating sheath is comparatively complicated and, despite the most careful application of the sheath, the quality of the sheath varies.

The invention is therefore based on the object of specifying a method which allows a rapid sheathing of a varistor block with an electrically insulating sheath and thereby allows a high quality of the transition from the varistor block to the electrically insulating sheath.

This is according to the invention in a method of the initially named kind ge ^¬ solved by the s are removed before and / or during application of the wrapper to the varistor between the casing and a surface of the varistor block gas molecules located. 2005 P 02497 DE

By the removal of gas molecules which are between the electrically insulating sheath and a surface of the varistor block, a comparatively rapid Aufle ^¬ gen is of the electrically insulating sheath enables directly to the surface of the varistor block. By Entfer ^¬ tion of the gas molecules unwanted entrapment of gases between the varistor block and the electrically insulating sheath is largely prevented. Since during the on ^¬ the envelope brin supply now is no longer paying attention to gas inclusions, faster application of the insulating sheath can be done in the varistor. This provides faster completion of the varistor blocks. For example, it can be provided that a negative pressure is generated between the envelope and the surface of the varistor block. Due to the pressure prevailing in the border area a pressure I can now, for example, solierband easily wound around the varistor The pressure prevailing outside the joint overpressure presses the tape to the Va ^¬ on ristorblock. Another effective manufacturing method may provide that the electrically insulating sheath is arranged around the varistor block like a tube. With such an arrangement, removal of the gas molecules in the contact area can take place even before the actual application of the envelope to the varistor block. In addition to the removal of gas molecules, it is of course also possible to remove any foreign bodies such as dusts from the joint area. Electrically insulating sheaths are advantageously formed from cured or at least partially cured plastics.

A particularly advantageous embodiment may provide that the application of the envelope takes place in an evacuated room. 2005 P 02497 DE

A particularly effective removal of gas molecules from the region of the support of the electrically insulating sheath on the varistor block can be achieved by evacuation of a complete room. In this case, for example, within ^¬ within a pressure-resistant boiler, a strong negative pressure, also referred to as vacuum generated. This ensures that both gas arranged in the joining region and gas around the entire assembly is removed. As a result, subsequent flow of undesired gas molecules into the support region of the electrically insulating sheath is hardly possible anymore.

A further advantageous embodiment can provide that the envelope is deformed under the action of thermal energy.

In particular, when using an evacuated space, it is advantageous to deform the envelope under the action of heat and to use the resulting change in shape to form a force- ^fit connection between the varistor block and the electrically insulating sheath. This has the advantage that additional adhesion promoters can no longer be introduced into the joint area, since due to the change in shape there is a sufficient angle-rigid connection between the insulating enclosure and the varistor block. It may also be provided to additionally introduce into the joint an adhesion promoter such as hot melt adhesive, fats or the like.

Advantageously, it can furthermore be provided that the s as

Enclosure at least partially a shrink tube is used. 2005 P 02497 DE

Shrink sleeves are available inexpensively in a variety of sizes as yard goods cost. Since the varistor block is to be completely surrounded by the electrically insulating covering, except for its electrical contacting points, heat-shrinkable tubes are particularly suitable for achieving a gap-free

Form surface on the varistor block. Furthermore, shrink tubes are easily deformed by the action of thermal energy. They develop a comparatively high moment of force. As a result, the varistor block is supported in its mechanical stability. Furthermore, the outgoing of the shrink tube force can be used to wei ^¬ tere elements, such as fitting body to attach the connection points on the varistor block to fix and position. When choosing a suitable shrink tube, the wall thickness can be chosen such that the shrink tube itself is a kind of cushion layer around the varistor block. This makes it possible for the metal used to form a varistor, wel ^¬ ches is relatively brittle, to protect against mechanical damage. This results in further advantages with regard to a simplified transport of varistor blocks.

A further object of the invention is to specify a varistor block that can be used for a surge arrester, wherein the surge arrester has an enclosure made of an electrically insulating material. The varistor block should have a high mechanical stability and be well protected against external mechanical forces.

According to the invention this is achieved with a varistor of the type starting vorste ^¬ above in that the envelope UNMIT ^¬ telbar rests on a surface of the varistor block and during and / or prior to application of the enclosure on 2005 P 02497 DE

Varistor block between the varistor block and envelope gas molecules are removed.

The direct support of the electrically insulative covering on a surface of varistor protects these ical before me ^¬ load. Occurring forces are attenuated by the envelope or. distributed over a larger surface area. Cavities are avoided by the gas molecules removed from the contact area between the electrically insulating enclosure and the varistor block. In addition to the mechanical stabilization of the varistor block, a dielectrically stable connection is created between the varistor block and the electrically insulating sheath. By an almost inclusion-free fitting of the electrically insulative covering on the outer surface of the varistor block the formation is suppressed by part ^¬ discharges. Such partial discharges can lead to long-term use of the Varistorblockes that its electrical properties are negatively beeinfluß st and, where appropriate, a breakdown of the electrically insulating sheathing. Such breakdowns would constitute a ground fault in an electric energy transmission network which is intolerable.

A further advantageous embodiment may provide that the varistor block having a plurality of varistor elements joined together, the joining points are at least partially covered by the Umhül ^¬ lung.

A varistor block may, for example, be composed of several varistor elements. These sub-blocks at ^¬ all game, of the same metal are made or assembled from various metal oxides to ER by a certain resistance behavior of the varistor 2005 P 02497 DE

aim . In addition, it can be provided that metal blocks or other electrically conductive elements are inserted into the varistor block assembled from a plurality of varistor elements. In order to produce the lowest possible contact resistance between the individual elements, they must be pressed together with a high force. The strain of the varistor elements can advantageously be applied from the elekt ^¬ driven insulating sheath. By covering the joints with the electrically insulating sheath a lateral displacement of the individual varistor elements is prevented against each other, so that after application of the envelope is a compact, consisting of many elements and the I solierumhüllung existing arrangement. Furthermore, the overlaps of the joints often cover the gaps and projections which are often present there, and produce an outer, smooth surface. In particular, racks of the feet ^¬ between the individual varistor elements, it is important NEN the undesirable gas molecules in time for entfer ^¬ so that the I solierumhüllung intimately abuts on the surface of the varistor block.

In order to achieve a high mechanical strength of the varistor ^block , it can furthermore be provided that end pieces are arranged at mutually remote ends of the varistor block, which have shoulders which are covered by the covering.

Ends arranged at opposite ends are advantageously provided with shoulders, which are also covered by the electrically insulating sheath. This is advantageous in particular when using a shrink tubing since a shrink tubing can also have a shrinkage effect in several dimensions. For one thing 2005 P 02497 DE

a snug fit of the shrink tube to the surface of the varistor block, on the other hand, the shrinkage effect for clamping a varistor block, which is assembled from different Va ^¬ ristorelementen used. End pieces of the varistor block, for example, end fittings can be used, the nen ^¬ the formation of a contact point for the integration of the varistor block in a Ableitstrompfad. By overlapping the shoulder, an all-round covering of the varistor block is furthermore ensured, so that the penetration of foreign bodies or moisture is prevented.

Advantageously, it can be provided, which is the s Umhül ^¬ lung at least partially from a heat-shrinkable tube is formed.

The at least partial use of shrink tubing, in particular a complete shrinkage of the varistor block with a shrink tube, allows a rapid application of the electrically insulating sheath.

Embodiments of the invention are shown schematically in the drawings below and described in more detail below ben ^¬ .

It shows the

1 shows a section through a varistor block with an applied directly on its surface e- lektrisch insulating enclosure, the 2005 P 02497 DE

FIG. 2 shows a varistor block during the application of an electrically insulating sheath according to a first method, and

3 shows a varistor block when applying an electrically insulating sheath according to a second method.

1 shows a section through a varistor block 1. The varistor block 1 has a plurality of varistor elements 2a, 2b, 2c, 2d. The varistor 2a, 2b, 2c, 2d are se beispielswei ^¬ cylindrical shape and disposed with their cylinder axes coaxial with a Varistorblockhauptachse. 3 The end faces of the varistor elements 2a, 2b, 2c, 2d are each arranged lying against each other. As a varistor 2a, 2b, 2c, 2d sintered Metalloxidblöcke ver ^¬ example, are reversible. Moreover, between the varistor elements 2a, 2b, 2c, 2d and metallic blocks or metallic Gehäu ^¬ se can be used. Depending on the available metal oxides, these can have different dimensions. Means of the metallic blocks, which are inserted into the varistor block 1, then a length compensation of the entire varistor block 1 can be achieved. In addition, a Metalli ^¬ shear block can serve as a thermal sink. Furthermore, see between the varistor elements 2 a, 2 b, 2 c, 2 d housing assemblies are used, in the example, monitoring ^{¬ facilities} for the temperature of the varistor block 1 are introduced ^{¬ introduced} . At the opposite ends of the varistor block 1 each end pieces 4a, 4b are arranged. The end pieces 4a, 4b are designed as connection fittings, that is, they are designed as electrically conductive body having connection points, by means of which the varistor ^¬ ristorblock 1 can be introduced into a Ableitstrompfad. Of the 2005 P 02497 DE

entire varistor block 1 is surrounded by an electrically insulating sheath 5. The electrically insulating sheath 5 is formed for example from a wrapping of a plurality of ribbons or also, as in the present example of Figure 1, formed from a shrink tube. The electrically insulating sheath 5 is located directly on the lateral surface of the varistor block 1, that is, between the joining region of the varistor block 1 and the electrically insulating Umhül ^¬ ment 5 are no gas inclusions or other body arranged net. In order to impart a high adhesion of the electrically insulating sheath 5 on the varistor block 1, however, an adhesion promoter, such as, for example, a sufier free melt adhesive or the like, may additionally be arranged there.

The end pieces 4a, 4b have in the axial direction of the Varistorblockhauptachse 3 away from each other shoulders. These shoulders are formed by tapering the circumference of the end pieces 4a, 4b with respect to the varistor block main axis 3. The electrically insulating sheath engages around the shoulders of the end pieces 4a, 4b, so that the end pieces 4a, 4b and the varistor elements 2a, 2b, 2c, 2d are pressed against one another by the electrically insulating sheath 5.

By the electrically insulating sheath 5 of the varistor block 1 is protected against mechanical influences from the outside. Furthermore, the surface of the varistor block 1 is smoothed outwardly by the electrically insulating sheath 5 and the joints of the varistor elements 2 a, 2 b, 2 c, 2 d are covered by the electrically insulating sheath 5. 2005 P 02497 DE

In FIGS. 2 and 3, two methods are presented which serve to apply an electrically insulating sheath to a varistor block 1. Equivalent components are provided in the figures with the same reference numerals as in the figure 1.

In the figure 2, the varistor block 1 is provided with an electrically insulating sheath 5a. The electrically insulating sheath 5a is formed of a plurality of turns wound on the varistor block 1. Insulating tapes 6 are firmly wound onto the varistor block 1 for this purpose. In this variant too, the bands 6 surround the shoulders of the end pieces 4a, 4b and thus form an intimate connection between the end pieces 4a, 4b and varistor elements 2a, 2b, 2c, 2d. In order to ensure the closest possible concern of the insulating tapes on the surface of the varistor block 1, a strong negative pressure is generated in the immediate area of the winding zone of the insulating tapes 6. By a clever arrangement of a plurality of bands 6 and a corresponding action technique, a removal of unwanted gas molecules can be effected in the immediate area of the winding zone. As a result, a negative pressure is generated there relative to the surroundings, whereby the insulating tapes 6 are pressed tightly onto the upper surface of the varistor block 1.

In addition to the forfeiture of individual insulating tapes 6 around the varistor block 1, however, this method can also find application in the use of a shrink tubing. There, a corresponding negative pressure is then generated in the interior of the shrink tubing and the tube shrunk onto the varistor block 1. Even with such an embodiment, the individual joints between the varistor elements 2a, 2005 P 02497 DE

2b, 2c, 2d and the end pieces 4a, 4b completely surrounded by the electrically insulating sheath 5a.

To a falling apart of the adjacent Varistorele- elements 2a, 2b, 2c, 2d or. Also, to prevent the end pieces 4a, 4b during the application of the sheath, these can be glued together or held in a corresponding jig. It can be provided that the clamping device is removed after complete encasing with the electrically insulating sheath 5a and the clamping forces are completely applied by the electrically insulating sheath 5a.

FIG. 3 shows a further possibility of applying an electrically insulating sheath 5b. In the present case, a varistor block 1 is arranged inside a space evacuated by gas molecules 8. By means of a vacuum pump 9 unwanted gas molecules from the space 8 are removable. It can be provided that the evacuation is carried out during the application of the envelope to the varistor element 1 and / or that an evacuation also takes place before the beginning of the application of the insulating covering. In the interior of the evacuated space 8, a varistor block 1 is arranged in a known training. The varistor block 1 is surrounded by a shrink tube 5b, which represents an electrically insulating sheath. Due to the evacuation of the evacuated space 8 only a negligible number of gas molecules is present in this room. In a heat supply via a heater 10 is a AufSchrumpfung the shrink tube 5b. The shrink tube 5b can thereby unmit ^¬ immediacy cling to the surface of the varistor block 1. Due to the prevailing vacuum in the evacuated space 8, the inclusion of voids between the 2005 P 02497 DE

Shrink tube 5b almost impossible. The length of the shrink tubing 5b is dimensioned such that it lays over the shoulders of the end pieces 4a, 4b and the end pieces 4a, 4b with the interposition of the varistor elements 2a, 2b, 2c, 2d against each other pres st. This creates a mechanically stable block that has a smooth outer surface. To keep the end ^¬ pieces 4a, 4b as well as the varistor elements 2a, 2b, 2c, 2d of the varistor block 1 before the shrink-with the shrink tube 5b in position corresponding to-additional retaining devices may be provided, or it may be a bonding of the individual varistor elements 2a, 2b, 2c, 2d and the end pieces 4a, 4b are made for assembly.

In addition to the use of a shrink tubing, further production methods for applying an electrically insulating covering 5 can also be used in the evacuated space 8. Thus, in the evacuated space 8, a winding device can be arranged, which forfeits insulating tapes around the varistor block 1, thus producing an electrically insulating sheathing.

Claims

2005 P 02497 DEPatentansprüche

1. A method for sheathing a varistor block (1) for a Überspannungsabieiter with an electrically insulating sheath (5, 5a, 5b), characterized in that before and / or during application of the sheath (5, 5a, 5b) on the varistor block (1 ) between the sheath (5, 5a, 5b) and a surface of the varistor block (1) located gas molecules are removed.

2. The method according to claim 1, characterized in that the application of the envelope (5, 5a, 5b) takes place in an evacuated space (8).

3. The method according to claim 1 or 2, characterized in that the envelope (5, 5a, 5b) is deformed under the action of thermal energy.

4. Method according to one of claims 1 to 3, characterized in that at least partially a heat-shrinkable tube is used as the sheathing (5, 5a, 5b).

5.Varistorblock (1) for a surge arrester, comprising a sheath (5, 5a, 5b) made of an electrically insulating material, characterized in that the sheath (5, 5a, 5b) directly on a surface of the varistor block (1) rests and during and / or prior to application of the sheath (5, 5a, 5b) to the varistor block 2005 P 02497 DE

(1) gas molecules located between the varistor block and the cladding are removed.

6. Varistor block according to claim 7, characterized in that the varistor block (1) has a plurality of varistor elements (2a, 2b, 2c, 2d) joined to one another, the joints of which are at least partially covered by the sheath (5, 5a, 5b).

7. varistor block according to claim 5 or 6, characterized in that at opposite ends of the varistor block (1) end pieces (4a, 4b) are arranged, the shoulders, wel ^¬ che of the sheath (5, 5a, 5b) are covered.

8. varistor block according to one of claims 5 to 7, d a d u r c h e c e n e c e in that the sheath (5, 5 a, 5 b) is at least partially formed from a shrink tube.