EP3001878A1

EP3001878A1 - Casting method for producing a protective sheath around a surge arrester and a casting mould therefor

Info

Publication number: EP3001878A1
Application number: EP14739746.7A
Authority: EP
Inventors: Bernd Kruska
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2013-07-12
Filing date: 2014-07-08
Publication date: 2016-04-06
Also published as: CN105378859A; WO2015004121A1; US20160144536A1; DE102013213688A1

Abstract

The invention relates to a casting method for producing a protective sheath (20) around a surge arrester (1), which has a cylindrical discharge element (4) arranged between two end armatures (3) and a plurality of retaining rods (5), which are clamped into the end armatures (3) and surround the discharge element (4). The casting method comprises the steps: - placing the surge arrester (1) into a first mould (10); - pouring a casting compound around the surge arrester (1) in order to mould on a supporting part (30), the inside of which nestles cylindrically around the discharge element (4) and the outside of which nestles in a fillet-shaped manner around each of the retaining rods (5); - curing the casting compound to fix the retaining rods (5) with respect to each other and with respect to the discharge element (4); - removing the surge arrester (1) with the supporting part (30) moulded thereon from the first mould (10) and placing it into a second mould; - pouring casting compound around the surge arrester (1) with the supporting part (30) moulded thereon in order to form a shield part (31), which has the external shape of the protective sheath (20); - curing the casting compound. The invention furthermore relates to a casting mould as the first mould (10) for a casting method, which has first recesses (11) for receiving the retaining rods (5) of an inserted surge arrester (1), said recesses each nestling in a fillet-shaped manner around the retaining rods (5). The advantage of the casting method and casting mould according to the invention lies in that the retaining rods and the discharge element are fixed by a supporting part moulded on during the first casting process and therefore can no longer be bent or displaced with respect to each other during the subsequent casting process.

Description

description

Casting method for producing a protective coating around a surge arrester and a casting mold therefor

The invention relates to a casting method for producing a protective coating around a surge arrester for high and medium voltage applications according to the preamble of patent claim 1, and a mold for performing the casting process.

Surge arresters, which are intended to be used outdoors, are surrounded by a protective sheath, for example of silicone. Even when used in buildings, such a protective coating, for example for

Protection against pollution, be necessary. This protective sheathing serves on the one hand to protect the surge arrester from the effects of the weather and, on the other hand, of electrical insulation. To provide a sufficient creepage path, the protective cover often has umbrellas. For the purposes of the invention, surge arresters are those which are suitable for high voltages and medium voltages.

Such protective sheaths are often applied to the surge arrester in an injection molding process. The shape of the protective casing is given by a mold, in particular an injection mold. Known casting molds have two composite semi-molds as a die, wel ^¬ che forms the negative of the outer mold. In one of the half forms of Überspannungsabieiter is inserted, thus forming a core of the mold. Then the two half-forms are put together. The die and the core together form a mold, which corresponds to the negative mold of the protective coating to be cast. When the core and composite half-molds are inserted, the mold is ejected with a casting compound such as silicone under high pressure. Depending on the viscosity of the silicone used, the pressure can range from a few megapascals (10 bar) to more than 100 megapascals (1000 bar). Through vents in the mold, the displaced by the casting compound air can escape. Alternatively, the mold may be evacuated prior to injection of the molding compound. After curing or polymerization of the casting, the half-molds are taken apart. Of the

Surge arrester is now firmly surrounded by the protective sheath and can be removed from the mold. The mold is then cleaned and is available for another casting process.

Surge arresters are often manufactured in the so-called cage design. It is one of a stack of

Varistor elements existing active part surrounded by a cage of tension elements, for example, glass fiber reinforced plastic, which are braced in end fittings and thus hold the active part together. Such a surge absorber can reach a length of several meters. Due to the high pressure of the silicone during the casting process, the active part can be bent out of its axis or the tension elements can be moved against the active part or pressed apart. This may result in the surge arrester failing the prescribed electrical and mechanical tests and being considered scrap. A Na ^¬ charity is not possible in the rule.

In the prior art, there are known ways to increase the stability of the surge arrester by adding additional components. Thus, WO 2012/062695 AI describes a stretchable sleeve, which is placed around the tension elements, and these fixed against each other.

In DE 101 04 393 C1 and EP 0 280 189 A1, support plates with recesses are described, through which the tension elements are passed and thus fixed in a plane perpendicular to the longitudinal axis of the surge arrester. In US 5,608,597 AI, the tension elements are wrapped with a bandage of glass fiber reinforced plastic and thus fixed against each other. A disadvantage of the prior art, the higher Montageauf ^¬ wall and material requirements.

The present invention has for its object to provide a casting process, the ER reliable encapsulation enables, without any active part or cage Zugele ^¬ elements deform, and at no extra

Überspannungsabieiter manages components to be mounted. Another object is to provide a mold for this purpose suits ^¬ ben.

The object of the casting method is achieved with the with ^¬ stuffs the invention according to claim. 1

For this purpose, a casting method is provided for producing a protective sheathing around an overvoltage arrester. Of the

Überspannungsabieiter has an active part with a arranged between two end fittings cylindrical discharge element. The diverter usually consists of a stack of cylindrical varistor blocks. The end fittings are located at the ends of the stack. To ensure good electrical contact between the varistor blocks, the stack must be compressed mechanically. For this purpose, a cage surrounding the discharge element of holding rods, which are clamped in the end fittings. The support rods are made of an electrically insulating and mechanically tensile material such as glass fiber reinforced plastic. The Hal ^¬ testäbe are firmly clamped with their ends in the end fittings, for example by screwing, wedging or crimping.

In the casting method according to the invention is first of

Surge arrester inserted in a first form. The first form usually consists of two half-forms, the are composable. The surge arrester is placed in one of the half molds, and the first mold is closed with the second half mold. The half molds are compressed hydraulically, pneumatically or mechanically. Seals and sealing surfaces ensure a good seal of the first shape, so that no casting compound can escape. In order to avoid air pockets in the casting compound, vents may be arranged in the first mold. Alternatively or additionally, the first mold can be evacuated. Casting compound is then poured into the first mold during a first casting process or injected under high pressure. Thereby, a support member is integrally formed with the surge arrester, the cylindrically each fillet-shaped with its inside adapts to the diverter element and, with its Au ^¬ ßenseite around each of the support rods. The casting compound is now cured, for example by heat. In the case of silicone, the chains of the casting compound crosslink and form a solid but elastic body in which the support rods are fixed. The support part thus forms an inner part of the protective cover. The support member is thus a hollow cylinder radially enclosing the discharge element with an inner diameter which corresponds to the outer diameter of the discharge element and an outer diameter which corresponds to the center distance of two opposite holding rods. After curing of Gussmas ^¬ se thus the support rods are fixed against each other and against the Ab ^¬ guide element.

The Überspannungsabieiter with integrally formed support member is now taken out of the first mold and inserted as a core in a second mold. The second form is how they will be ^¬ already used in the prior art a mold. It is a mat ^¬ rize for the outer shape of the protective coating. Of the

Überspannungsabieiter with integrally formed support member is now encapsulated in a second casting process by pouring or injecting molding compound into the second mold with casting material, where ^{¬ is formed} at a screen part having the outer shape of the protective coating. The screen part is a Hollow cylinder with outside molded shields. After the casting compound has hardened, the protective coating is finished, the surge arrester with its protective sheath can now be removed from the second mold and is ready for use. An advantage of the casting method according to the invention is that are fixed by the support member, the support rods and the discharge during the second casting operation for the shield against deformation inward towards the discharge and toward the side of the adjacent holding rod out and therefore can not be bent or moved by the casting compound , This is avoided during the first casting process for the supporting part, since the first form has a he ^¬ considerably lower volume than the second shape and therefore less room for maneuver offers.

Preferably, the casting material is not fully cured after the casting of the support ^¬ part, so that the casting compounds of the support member and screen part with ^¬ can cross-link during potting of the screen part and are so firmly connected.

The task relating to the casting mold is achieved by means of the invention according to claim 2. Accordingly has a mold as the first form of an inventive Gussverfah- ren first recesses for receiving the support rods of a defined ^¬ surge arrester, which is in each case

grooved around the support rods. The

Hollow-shaped first recesses in this case comprise the holding rods on their outer side from the longitudinal axis of the

Surge absorber seen from, preferably less than half of its circumference. The area between the support rods and the discharge element remains free. This area is filled with casting compound during the first casting process. This then encloses the support rods on their inside. After hardening of the casting compound, this nestles thereby

grooved around the inside of the support rods and fixes them for the second casting process. The area between adjacent tie rods is partially defined by the first shape. fills and stays free for the other part. In the remaining part the first part of the casting process, the support member is formed. By the fillet-shaped first recesses of the first form, the support rods are fixed during the first casting process for the support member in the first recesses and can thus also during the first casting process not ver ^¬ be inserted.

Usually the first form is composed of two half-forms. The sectional area of the two half-forms extends along the longitudinal axis. In a direction perpendicular to the cut surface, the half-molds can be assembled and taken apart. The first recesses extend in cross-section substantially in the opening direction, which facilitates the closing and opening of the first mold.

In a preferred embodiment, the first shape has second recesses for receiving the support rods, on which the support rods each rest along a surface line. While the support rods in the first recesses lie flat against a part of their lateral surface, they rest in the second recesses with only one surface line. The generatrix lies outside of the support rods viewed from the longitudinal axis. The support rods are supported from the outside. The casting compound can then almost completely surround the holding rods in the region of the second recesses during the first casting process. Only the area of the generatrix of the support rods remains free of casting compound. The support member thus almost completely encloses the support rods in the region of the second recesses. The second recesses surround the support rods egg ^¬ shaped. The depth is dimensioned such that the support rods are fully received in its diameter and the width is dimensioned such that the cured cast therein ^¬ mass virtually completely surrounds the support rods. Preferential example, the width approximately to twice diam ^¬ ser of the holding rods. The support rods are thereby fixed against bending or deformation to the outside. It is further preferred that the first mold has a plurality of lugs on ^¬ that the diverter element radially against bending different bearing ^¬ zen. The lugs extend radially to the discharge element and support it at a plurality of points distributed around the circumference of the discharge element. This prevents bending of the diverting element against the longitudinal axis during the first encapsulation.

Furthermore, an advantageous embodiment of the invention provides that the lugs are each arranged between two second recesses. The noses are thus formed by two be ^¬ adjacent legs of two adjacent U-shaped second recesses, which allows a simple design of ers ^¬ th form in the region of the second recesses.

Further, the second recesses in a longitudinal direction are arranged in the center of the first mold and both sides in the longitudinal direction connect each first off ^¬ recesses thereon is preferred. The first mold is divided into three longitudinal portions adjacent along the longitudinal axis Anei ^¬ Nander. In the middle longitudinal section, the first shape has the second recesses and the noses. In the longitudinal direction on both sides close to longitudinal sections, which have first recesses. The first shape is thus symmetrical. The support rods are in their center, ie the area that tends most to bending, almost completely enclosed by the support member and fixed so.

It is also preferable that the first mold can be composed of modules, wherein at least two modules comprise first from ^¬ recesses and at least one second module has recesses. The first form is assembled longitudinally from several ^¬ ren modules. The modules are clamped or screwed against each other. In the middle of the mold, a module with second recesses is arranged, followed on both sides by modules with second recesses. By Hinzufü ^¬ gene or removing modules with first recesses, the first mold can be extended or shortened in a simple manner and is so on different lengths of

Overvoltage arresters customizable.

In the following the invention will be explained in more detail with reference to the drawings. Showing:

Figure 1 shows a known surge arrester in a

Part sectional view, Figure 2 inserted in a first form

surge arresters,

3 shows a section through the first mold in the region of the first recesses, FIG.

FIG. 4 shows a part of the first mold with first recesses in three-dimensional representation,

5 shows a section through the first mold in the region of the second recesses,

6 shows a part of the first mold with second recesses in a three-dimensional representation, Figure 7 shows a surge arrester with molded

Support part,

8 shows a support part in a three-dimensional representation, FIG. 9 shows a section through an overvoltage arrester with a molded protective cover,

10 shows a further section through a

Surge arrester with molded protective sheath.

Corresponding parts are provided in all figures with the same reference numerals. 1, a, for example, from DE 10 2011 078 333 be known per ^¬ surge arrester 1 is shown. Of the

Surge arrester 1 has a cylindrical discharge element 4, which consists of cylindrical Varistorblöcken, which are assembled into a column. At the ends of these Säu ^¬ le are each end fittings 3, which serve the electrical connection of the surge arrester 1. Handrails 5 form a cage around the discharge element 4 and are clamped in the end fittings 3 and thus hold the discharge element 4 together. To protect against the weather is the

Surge Arrester 1 provided with a protective jacket 20. The protective sheath 20 surrounds the discharge element 4 completely. Only parts of the end fittings 3 protrude out of the protective casing 20. To the creepage between the

To extend end fittings 3, the protective sheath 20 umbrellas 21, which are distributed at equal intervals over the length of the protective sheath 20. The screens 21 have two different sizes, which are arranged alternately. The protective casing 20 has the shape of a cylindrical body which surrounds the diverting element 4 and has end regions adjoining the end side, which terminate tightly with the end fittings 3. The protective sheath 20 is often made of a polymer, such as silicone, which is applied directly to the surge arrester 1 in a casting process, often an injection molding process. One speaks then of direct encapsulation. In the previously known casting method, the protective casing 20 is completely produced in a casting process. In the inventive casting method, a support member 30 is first formed on the surge absorber 1 in a first molding process and then in egg ^¬ nem second casting process, a shielding member 31, support member 30 and screen member 31 together form the protective coating 20, which will be explained in more detail in the following figures.

FIG. 2 shows a surge arrester 1 inserted into a first mold 10. The first mold 10 extends along the longitudinal axis 17 and encloses the discharge element. ment 4. The first form 10 is together ^¬ amount is composed of two half-molds 12th The surge arrester 1 is first inserted into one of the half-molds 12. The first mold 10 is then closed with the second half mold 12. The contact surfaces of the half-molds 12 are machined so that they close tightly at entspre ^¬ chendem pressure. At the ends of the first mold 10, for example abge against the end fittings 3 abge ^¬ seals, so that no casting material can escape. The first mold 10 is composed of a plurality of modules 18, 19. A centrally arranged module 19 has not shown second recesses 15. Adjacent thereto on both sides, three modules 18 are arranged with not shown first recesses 11. The modules 18, 19 are assembled into a half-mold 12 and fixed, for example, by bracing or screwing. By inserting an additional module 18 into each half mold 12, the first mold can be extended to accommodate a longer surge absorber 1. Accordingly, by removing modules 18, the first mold 10 can be shortened.

3 shows a section through a first form 10 with inserted surge arrester 1 and already molded-on support member 30 in the region of a module 18, which Figure 4 is a Mo ^¬ dul 18 in three-dimensional representation. The first mold 10 could also be designed as a hollow circular cylinder instead of the first recesses 11 shown here. The support rods 5 would then rest against the inner wall of the hollow cylinder. Here, however, a preferred embodiment is shown in which the first mold 10 in the region of the module 18 has grooved first recesses 11. The first recesses 11 are designed as recesses which extend substantially in the opening direction 13. The first recesses 11 receive the support rods 5 and nestle against them. The support rods 5 are thus fixed with the first mold 10 closed to the outside from the longitudinal axis and also ^{seit ¬} Lich against deformation or bending supported by the first mold 10. If now casting material into the first mold 10 is ^¬ is injected, the support rods 5 are defined by the first mold 10 fixed. A bending or deformation of the support rods 5 is thereby avoided. The casting compound injected into the first mold during the first casting operation forms the support part 30 after curing. This support part 30 is a hollow-cylindrical body which fills the space between the discharge element 4 and the first mold 10. On its inside, the support member 30 nestles around the discharge element 4. On the outer ^¬ side of the support member 30, the casting material forms around the Haltestä ^¬ be holkhlförmige depressions nestling around the support rods 5. Will the first mold 10 in the opening direction

13 open, the support rods are fixed in the groove-like recesses 22 of the support member.

5 shows a section through a first form 10 with inserted surge arrester 1 and already molded-on support member 30 in the region of a module 19, Figure 6 a Mo ^¬ dul 19 in three-dimensional representation. In the region of the module 19, the first mold 10 has second recesses 15 for receiving the support rods 5. The second recesses 15 are U-shaped depressions that record in their depth the Haltestä ^¬ be 5 in its full diameter. The support rods 5 rest therein with a surface line 23 and are supported by the first mold in the region of the module 19 with the second recesses 15. The width of the second recesses 15 corresponds to about twice the diameter of a holding ^¬ rod 5. In the region of the contact surface 24 of the modules 19 adjacent second recesses 15 are joined together to form a U-shaped recess receiving two holding rods. 5 Thus, the first mold 10 can be easily opened by pulling the two half-molds in the opening direction 13. Except in the area of the contact surface 24, the legs of the U-shaped depressions of respectively adjacent second recesses 15 form lugs 16, which extend as far as the discharge element 4 and support it during the first casting operation. The diverter 4 is thereby fixed and can not be bent or deformed by injected molding compound. The poured into the second recesses 15 casting compound encloses the support rods 5 almost completely. Only in the area of the surface line 23, the holding rods 5 protrude out of the casting mass forming the support part 30.

7 shows a taken out from the first mold surge arrester 1 with a molded support member 30, the figure 8, a single support member 30. In a centrally arranged to the longitudinal ^¬ axle 17 longitudinal section 26 can be seen how the support member 30 in the area of the module 19 second recesses 15 is formed. The cured casting compound encloses the support rods 5 here almost completely. Around

Longitudinal portions 25, the support member has groove-like Ver ^¬ depressions 22 which receive the holding rods 5 and fixie ^¬ ren. For the subsequent second casting operation, the support rods 5 are fixed so that they can not be bent against each other or against the diverter 4.

For the second casting operation, the surge arrester 1 with the integrally formed support part 30 is inserted into a second shape, which is not shown here. As the second form can be used a known per se form, which has been used to produce the protective sheath 20 in a single casting process. There was so far only the

Surge arrester 1 inserted as a core. In the casting method according to the invention, the surge arrester 1 with integrally formed support part 30 serves as the core.

In Figures 9 and 10 is a section through a

Surge arrester 1 with ready-made protective casing 20 is shown. FIG. 9 shows a section in the region of the length section 26. The molded-on support part 30 can be seen around the discharge element 4, in the region radially outside of it the shield part 31 formed in the second casting process with a screen 21, in this case a screen 21 in FIG smaller of the two sizes and lying behind a screen 21 in the larger of the two sizes. FIG. 10 shows a section in one of the longitudinal sections 25. Again, the support part 30 formed in this area and the screen part 31 molded radially outwards can be seen. Here, the screen part on a screen 21 in the larger of the two sizes.

Claims

claims

1. Casting method for producing a protective coating

(20) around a surge arrester (1), the

- a between two end fittings (3) arranged Cylind ^¬ innovative diverting element (4) and

- A plurality of in the end fittings (3) clamped and the Ab ^¬ guide element (4) surrounding holding rods (5), comprising the steps:

Inserting the surge arrester (1) into a first mold (10),

Nestles casting around the surge arrester (1) with a casting ^¬ mass for conformation of a supporting part (30) which extends cylindrically with its inside to the diverter element (4) and each fillet-shaped with its outer side to each of the support rods (5), -

Hardening of the casting compound for fixing the support rods (5) against each other and against the discharge element (4),

- Remove the surge arrester (1) with

formed support member (30) from the first mold (10) and placed in a second mold,

- Overmolding the surge arrester (1) with integrally formed support part (30) with casting compound to form a

Shield portion (31), which has the outer shape of the protective sheath (20),

- Curing the casting compound.

2. First mold (10) for a casting method according to claim 1, comprising first recesses (11) for receiving the Haltestä ^¬ be (5) of an inserted surge arrester (1), each hemming groove around the support rods (5).

3. First mold (10) according to claim 2,

having second recesses (15) for receiving the holding ^¬ rods (5), against which the holding rods (5) in each case along a surface line (23).

4. First mold (10) according to any one of claims 2 or 3, characterized in that

the first mold (10) has a plurality of lugs (16) which radially support the diverting element (4) against bending.

5. First mold (10) according to claim 4

characterized in that

the lugs (16) are each arranged between two second recesses (15).

6. First mold (10) according to one of claims 3 to 5, characterized in that

the second recesses (15) are arranged in a longitudinal direction in the center of the first mold (10) and in the longitudinal direction on both sides of each first recesses (11) thereon to close ^¬.

7. First mold (10) according to one of claims 3 to 6, characterized in that

the first mold (10) of modules (18, 19) is assembled, wherein at least two modules first recesses (18) and at least one module (19), second recesses (15) has ^¬.