EP1749335B1 - Surge arrester - Google Patents

Description

The invention relates to a surge arrester having a short circuit mechanism between a center electrode and an outer electrode.

Surge arresters of the type mentioned are usually used to protect telecommunications equipment against transient overvoltages, such as those resulting from lightning strikes. In this case, by igniting the surge arrester, the outer electrode is short-circuited by means of an arc with the center electrode. As soon as the overvoltage occurs, the arc extinguishes and the switching path between the middle and outer electrodes is again insulating.

In order to maintain the protective function just described even if a surge arrester fails, arresters can be equipped with additional functions. In this context, mechanisms for securing the arrester in a thermal overloading are known (English: Fail safe), in which between a spring clip and the outer electrode, a fuse made of solder material or an insulating film is arranged, the movement of the spring clip at too high a temperature releases, then bridges the switching path of the arrester between the center electrode and the outer electrode and thus short-circuited.

Such a surge arrester is z. B. from the document DE 101 34 752 known. The short-circuit mechanism is triggered by heat in the event of a fault.

From the publication US 5,282,109 A a surge arrester according to the preamble of claim 1 is known, which has both a fail-safe mechanism, which is formed by a fusible material between the gas cartridge and the end contacts, as well as a vent-safe mechanism. This provides in case of failure of the device, such as ventilation of the gas cartridge, an alternative discharge path over a spark gap between a spring clip, a contact element and the center electrode available.

Object of this invention is to provide a surge arrester, which is characterized in case of failure by a secure contact between the short-circuited electrodes.

This object is achieved by claim 1. Further embodiments will become apparent from the other claims.

According to at least one embodiment of the invention, a surge arrester is provided with a ceramic body, at least one outer electrode and at least one further electrode, in which an electrically conductive, spaced from the outer electrode by an air gap contact element is provided, which is normally biased by a spring mechanism. The spring mechanism exerts on the contact element a spring force in the direction of the outer electrode. Between the further electrode and the contact element an electrically conductive connection is provided. The air gap between the outer electrode and the contact element is arranged in a preferably hermetically sealed cavity. The contact element biasing spring mechanism is z. B. triggered by heat, wherein the contact element is released, is pressed by the spring force on the outer electrode, thus generating a short circuit between the outer electrode and the further electrode.

The further electrode is preferably a center electrode which is arranged between two outer electrodes.

The fact that the cavity is completed, it is protected when embedding the arrester in a silicone gel against the gel. The gel is used, for example, as moisture protection of the arrester.

The contact element is preferably arranged completely in the sealed cavity. The cavity may be identical to the air gap.

The electrically conductive connection between the center electrode and the contact element is preferably designed in the form of a spring clip attached to the center electrode. The spring clip exerts a spring force on an electrically conductive, spaced from the outer electrode contact element.

The contact element may, for. B. be fixed by means of a meltable mass in an opening of a metal plate, which is at least partially positively embedded in an insulating holder which is disposed between the metal plate and the outer electrode.

In a particularly preferred embodiment, when the mass is not molten, the contact element is spaced from the outer electrode. In a molten mass, the contact element is pressed by the spring clip against the outer electrode.

In a variant of the invention, the contact element protrudes into an opening of the metal plate and is fixed by means of a fusible mass in this metal plate. The contact element is preferably formed as a metal bolt.

The meltable mass (for example solder, preferably soft solder) ensures a sealed closure of the closed cavity. The fusible mass is required to fix the contact element in the metal plate and therefore may be provided in a small amount which must ensure that the contact element is retained in the metal plate. The attachment of the contact element in the metal plate can be made with appropriate dimensioning of the bolt or the hole with a very small amount of meltable mass, resulting in the advantage of a quick release mechanism.

The metal plate with the preferably positively inserted metal bolt, which is preferably soft soldered into the opening of the metal plate is in a remote area of an insulating holder, the z. B. is formed as an insulating, preferably arranged positively.

On the outwardly facing end face of the metal bolt in the direction of the outer electrode, a spring force is exerted to generate a bias of a fixed to the central electrode electrically conductive spring clip. The spring clip also serves as the electrical connection between the center electrode and the metal stud. The spring clip is preferably made of a spring material, for. B. made of spring steel.

The spring clip forms the spring mechanism. The spring clip, the metal plate and the contact element together form a short-circuit mechanism.

In the event of a fault, an inadmissibly high heating is generated in the arrester, with the meltable mass melting, which is why the contact element is pressed against the outer electrode by the spring clip, a short circuit being generated between the center and outer electrodes.

In a further variant of the invention, the short-circuit mechanism comprises a metal plate electrically connected to the center electrode and a resilient contact element having a spring preferably formed as a leaf spring, the fixed end of which is preferably fixed to the metal plate and the free end of the unmeltable meltable mass is preferably held in the prestressed state at a distance from the outer electrode. The spring mechanism is formed in this case by the resilient contact element itself.

The spring is preferably as a folded leaf spring, d. H. formed in a meandering cross-section with a plurality of meander sections, wherein the opposite sides of the respective meander section are resiliently compressed by a meltable mass or soldered together soft under bias. The leaf spring is normally held by the meltable mass in a prestressed state at a distance from the outer electrode.

As the meltable mass melts and loses its strength, the collapsed leaf spring unfolds and creates a short circuit between the metal plate and the outer electrode.

This variant of the invention has the advantage, especially when using a viscous gel in the vicinity of the arrester, since the spring mechanism is arranged completely in the closed cavity and therefore isolated from the environment. By the complete separation from the environment, the movement of the released spring element can no longer be prevented by the gel.

The middle and outer electrodes are preferably made of copper. The coefficient of thermal expansion of the copper differs greatly from that of the ceramic, which can affect the tightness of the interface between the ceramic body and the outer electrode under temperature load. To compensate for the difference in the coefficients of thermal expansion between the ceramic body and the Cu electrode, a ring or frame is used, which is fastened on the outer electrode (preferably hard soldered). As a material of the ring, a material with a thermal expansion coefficient is preferably used, which is approximately equal to the expansion coefficient of the ceramic body, such as. FeNi.

In a preferred variant, the insulating holder is preferably inserted into the ring (eg FeNi ring) or frame in a form-fitting manner. In this case, between the outer electrode, the insulating holder and the metal disc, a tightly closed cavity, in which the air gap between the outer electrode and the contact element is arranged. The insulating holder can, for. Example, be used in a remote area of the outer electrode made of FeNi or a similar material with respect to thermal expansion outer electrode. In the latter case can be dispensed with the ring or frame.

In a preferred variant, the metal plate is pressed into the insulating holder and the insulating holder in the ring. This prevents the penetration of the gel into the closed cavity or into the air gap.

The metal plate is preferably made of brass or another suitable metal or metal alloy.

The insulating holder is preferably made of a temperature-resistant plastic whose melting temperature is above the melting temperature of the meltable mass, which is typically about 220 ° C. The plastic is preferably characterized by a good spring action, which ensures a good interference fit between the insulating holder and the metal disc.

In the event of a fault, ie when a certain limit voltage U _max is exceeded, a sparkover occurs between the middle and outer electrodes, whereby the electrodes heat up.

The heat generated at the outer electrode is transmitted to the contact element and the metal disc by the heat radiation of the outer electrode in the direction of the closed cavity. The heat generated at the center electrode is transmitted to the contactor or metal disc through the spring clip.

Figur 1A

ausschnittsweise einen Federmechanismus eines in Figur 2 gezeigten Ableiters

Figur 1B

ausschnittsweise einen Federmechanismus mit einem verjüngten Kontaktelement

Figur 2

einen Ableiter im Normalzustand

Figur 3

den Ableiter gemäß Figur 2 beim Ansprechen des Fe- dermechanismus im Fehlerfall

Figur 4A

ausschnittsweise einen Federmechanismus eines in Figur 5 gezeigten Ableiters im vorgespannten Zu- stand

Figur 4B

den Federmechanismus gemäß Figur 4A beim Ansprechen des Federmechanismus im Fehlerfall

Figur 4C

den in eine Halterung eingesetzten Federmechanismus gemäß Figur 4A

Figur 5

einen weiteren Ableiter im Normalzustand

Figur 6

den Ableiter gemäß Figur 5 beim Ansprechen des Fe- dermechanismus im Fehlerfall

In the following, the arrester is explained in greater detail on the basis of exemplary embodiments and the associated figures: The figures show diagrammatic and not true-to-scale representations of various embodiments. Identical or equivalent parts are designated by the same reference numerals. It show schematically

Figure 1A

a detail of a spring mechanism of a FIG. 2 shown arrester

FIG. 1B

partially a spring mechanism with a tapered contact element

FIG. 2

an arrester in normal condition

FIG. 3

the arrester according to FIG. 2 when the spring mechanism responds in the event of a fault

FIG. 4A

a detail of a spring mechanism of a FIG. 5 shown arrester in the prestressed state

FIG. 4B

the spring mechanism according to FIG. 4A when responding to the spring mechanism in case of failure

FIG. 4C

the spring mechanism inserted into a holder according to FIG. 4A

FIG. 5

another arrester in the normal state

FIG. 6

the arrester according to FIG. 5 when the spring mechanism responds in the event of a fault

An exemplary surge arrester before and after the response of the spring mechanism is in Figures 2 or 3 shown.

Figure 1A shows a fragmentary schematic cross-section of a spring mechanism of a in FIG. 2 shown surge arrester.

The contact element 7 has the shape of a round bolt, which projects through a round hole in a metal plate 5 a. The mechanical connection between the contact element 7 and the metal plate 5a is made by a fusible mass 6 along the hole edge of the metal plate 5a. The metal bolt is soldered so soft in a metal plate 5a.

The fusible mass may be formed in an advantageous embodiment of the invention as a solder. In conjunction with solderable materials for the contact element and the spacer element so a very simple connection between the contact element and spacer element is possible. In addition, the tin alloys used for solder ensure that the connection between the contact element and the spacer element is quickly released with sufficient heat.

The metal plate 5a has a preferably centrally disposed opening for receiving the contact element 7. The metal plate 5a is preferably in the form of a disk inserted in an insulating holder 5b. The insulating holder 5b has a stepped portion for receiving the Metal plate 5a on.

The contact element 7 can, as in FIG. 1B indicated, at a lying between the outer electrode 2 and the metal plate 5a section 11 have a taper 12.

The spring mechanism further comprises an electrically conductive spring clip 3, which is attached to the center electrode 1 of the arrester, see Figures 2 and 3 , The spring clip 3 engages on the end face of the outer electrode 2 and holds the contact element 7 in a prestressed state by exerting on the outer end face of the contact element 7 a spring force F in the direction of the outer electrode 2.

The spring clip 3, the metal plate 5a and the contact element 7 are designed such that, when the meltable mass 6 becomes liquid, the spring clip 3 and the contact element 7 can slide along the opening of the metal plate 5a.

The contact element may in a variant of the invention mechanically fixedly connected to the spring clip 3 or be part of the spring clip 3.

Between the contact element 7, the metal plate 5a, the insulating holder 5b and the outer electrode 2, a cavity 22 is formed. The cavity 22 is sealed by the meltable mass 6. The metal plate 5a is against the ring 16 and the insulating holder 5b each z. B. sealed by interference fit. The ring 16 is soldered or welded on the outer electrode 2. Thus, a tight closure of the cavity against a gel and possibly moisture is achieved.

Between the center electrode 1 and the outer electrode 2, a gas-filled ceramic body 19 is arranged. The ceramic body is preferably filled with a noble gas. The arrester is preferably formed symmetrically with two outer electrodes and optionally with respect to the center electrode. The center electrode 1 is preferably arranged between two ceramic bodies. The middle and outer electrodes 1, 2 are each connected by soldering with the ceramic bodies 19.

The middle and outer electrodes 1 and 2 are preferably made of Cu. However, it is possible in another variant that the middle and / or outer electrode consists of FeNi.

On the outer electrode 2 at the edge of a ring 16 is arranged, which preferably consists of an iron-nickel alloy. In the ring 16, the insulating holder 5b is inserted. The outer electrode 2 has, in the region facing the contact element 7, a recess for forming an air gap 20. The air gap 20 is arranged in the tightly closed cavity 22.

The FIG. 2 corresponds to the normal state of the surge arrester, ie the state before the response of the spring mechanism. By appropriate design of the dimensions of the elements involved in the protection mechanism, it can be achieved that the spring clip 3 displaces the contact element 7 so far in the direction of the outer electrode 2 that the contact element 7 is under the application of a contact pressure, which in turn arises from the spring clip 3 (residual spring force). presses on the outer electrode 2, whereby the electrical contacting of the outer electrode 2 is achieved with the spring clip 3 and thus with the center electrode 1 when triggering the short-circuiting mechanism.

In the event of a fault, the fusible mass 6 melts due to the heat generated in the surroundings of the arrester. In this case, the contact element 7 is released and pressed by the spring force F of the spring clip 3 on the outer electrode 2, see FIG. 3 , In this case, the center electrode 1 and the outer electrode 2 are short-circuited via the spring clip and the contact element 7.

In FIGS. 4A to 6 a further embodiment is shown, in which the contact element 7 is biased by an elastic deformation.

The contact element 7 has a leaf spring 21 with a fixed end 21a and a free end 21b. The fixed end 21a of the leaf spring is fixed to the metal plate 5c, e.g. B. brazed. The free end 21b of the leaf spring is z. B. biased by soldering to the metal plate 5c or another portion (eg., Fixed end) of the leaf spring.

It is advantageous if the leaf spring 21, as in FIG. 4A shown schematically, in the form of a "concertina" is formed, the folded portions are held together in the normal state by soldering and thus biased.

The leaf spring 21 and the spring clip 3 can, for. B. be made of CuBe.

In the event of a fault, the meltable mass melts, releasing the leaf spring which is preloaded by folding. The folded leaf spring jumps apart. In FIG. 4B is shown after the response of the spring mechanism unfolded leaf spring.

In FIG. 4C is the spring mechanism inserted into the insulating holder 5b according to FIG FIG. 4A shown.

In FIGS. 5 and 6 is the in FIGS. 4A and 4B schematically shown spring mechanism shown before or after the response.

This in FIG. 4C shown structure is, as in FIG. 5 indicated, preferably inserted by interference fit in the ring 16 or in a remote area of the outer electrode 2. Here, the metal plate 5c is pressed by the spring force of the spring clip 3 against the insulating holder. The metal plate 5c has no openings.

In this variant of the invention, the closed cavity 22 is formed between the outer electrode 2, the insulating holder 5b and the metal plate 5c. Movable parts of the spring mechanism (i.e., the contact element formed as a leaf spring) are here completely arranged in the closed cavity 22.

In FIG. 5 It can be seen that the free end of the leaf spring 21 is held at a distance from the outer electrode 2, wherein an air gap 20 to be bridged in the event of a fault is formed therebetween.

In FIG. 6 is the surge arrester according to FIG. 5 shown after the response of the spring mechanism. The meltable mass 6 was softened by the heat of the flashover. The free end of the leaf spring is pressed by the spring force against the outer electrode 2 and so over the metal disc and the spring clip secure contact between the outer and center electrode ago.

Although only a limited number of possible developments of the invention could be described in the embodiments, the invention is not limited to these. It is possible in principle, the interference fit of the parts used by another type of embedding, z. Pouring, to replace. The invention is not limited to the number of schematically illustrated elements. The safety mechanism described is of course not limited to the protection of only one switching path between the center electrode 1 and the outer electrode 2. By symmetrical completion and the second switching path between the center electrode 1 and the other outer electrode can be secured in a corresponding manner.

LIST OF REFERENCE NUMBERS

1

center electrode

2

outer electrode

3

spring clip

5a

metal plate

5b

insulating bracket

5c

metal plate

6

meltable mass

7

contact element

11

Section of the contact element 7

12

Rejuvenation of the contact element 7

16

Ring made of an iron-nickel alloy

19

ceramic body

20

Air gap between the contact element 7 and the outer electrode. 2

22

cavity

21

leaf spring

21a

fixed end of the leaf spring 21st

21b

free end of the leaf spring 21st

F

spring force

Claims (24)

1. Surge arrester having at least one outer electrode (2) and at least one further electrode (1),

   - in which an electrically conductive contact element (7) which is separated from the outer electrode (2) by an air gap (20) is prestressed by a spring mechanism, the spring mechanism exerting a spring force (F) on the contact element (7) in the direction of the outer electrode (2),

   - in which an electrically conductive connection is provided between the further electrode (1) and the contact element (7),

   - the air gap (20) between the outer electrode (2) and the contact element (7) being arranged in a tightly sealed cavity (22),

   characterized in that an electrically conductive contact is formed directly between the outer electrode (2) and the contact element (7) when thermal overloading occurs.
2. Surge arrester according to Claim 1,
   in which the electrically conductive connection between the further electrode (1) and the contact element (7) takes the form of a spring clip (3) attached to the further electrode (1).
3. Surge arrester according to Claim 1,
   in which the spring clip (3) exerts a spring force (F) on an electrically conductive contact element (7) separated from the outer electrode (2).
4. Surge arrester according to one of Claims 1 to 3,
   in which the contact element (7) is attached by means of a fusible mass (6) in an opening in a metal plate (5a), the metal plate (5a) being embedded at least partially with a form fit in an insulating holder (5b) which is arranged between the metal plate (5a) and the outer electrode (2).
5. Surge arrester according to one of Claims 1 to 4, in which the contact element (7) is separated from the outer electrode (2) when the mass (6) is not molten.
6. Surge arrester according to one of Claims 2 to 5, in which the contact element (7) is pressed against the outer electrode (2) by the spring clip (3) when the mass (6) is molten.
7. Surge arrester according to one of Claims 4 to 6, in which the cavity (22) is delimited by the contact element (7), the metal plate (5a), the insulating holder (5b) and the outer electrode (2).
8. Surge arrester according to one of Claims 1 to 7, in which the cavity (22) is sealed by the mass (6).
9. Surge arrester according to one of Claims 2 to 8, in which the contact element (7) is connected to the spring clip (3) in a mechanically fixed manner or is a component part of the spring clip (3).
10. Surge arrester according to one of Claims 2 to 9, in which the contact element (7) has the form of a bolt.
11. Surge arrester according to one of Claims 2 to 10, in which the metal plate (5a) is a disc.
12. Surge arrester according to Claim 10 or 11,
    in which the contact element (7) has a constriction (12) on a section (11) which is located between the outer electrode (2) and the metal plate (5a).
13. Surge arrester according to one of Claims 2 to 12, in which the fusible mass (6) is solder.
14. Surge arrester according to one of Claims 2 to 13, in which the outer electrode (2) has at the edge a ring (16), which is composed of an iron-nickel alloy.
15. Surge arrester according to one of Claims 2 to 14, in which the spring clip (3) is produced from a spring steel.
16. Surge arrester according to Claim 1,

    - in which the contact element (7) is arranged in the tightly sealed cavity (22).
17. Surge arrester according to Claim 16,

    - in which an electrically conductive metal plate (5c) is provided, at least partially embedded in an insulating holder (5b), and

    - in which the contact element (7) has a spring, the fixed end of which is connected to the metal plate (5c) in a fixed manner.
18. Surge arrester according to Claim 17,
    in which the free end of the spring is kept at a distance from the outer electrode (2) by means of a fusible mass (6).
19. Surge arrester according to Claim 17 or 18,
    in which the free end of the spring is pressed against the outer electrode (2) when the mass (6) is molten.
20. Surge arrester according to one of Claims 17 to 19, in which the spring is formed as a leaf spring (21).
21. Surge arrester according to one of Claims 17 to 20, in which the electrically conductive connection between the further electrode (1) and the contact element (7) takes the form of a spring clip (3) which is attached to the further electrode (1) and presses against the metal plate (5c).
22. Surge arrester according to one of Claims 17 to 21, in which the spring is formed as a folded leaf spring, the folds of the leaf spring being respectively prestressed in a resilient manner by the mass (6).
23. Surge arrester according to one of Claims 1 to 22, which is embedded in a gel.
24. Surge arrester according to one of Claims 1 to 23, having two outer electrodes (2),
    the further electrode (1) being a centre electrode.

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