WO1987006399A1

WO1987006399A1 - Device for protecting a surge arrester against overheating

Info

Publication number: WO1987006399A1
Application number: PCT/EP1987/000194
Authority: WO
Inventors: Gerhard Keller
Original assignee: Schaltbau Gesellschaft Mbh
Priority date: 1986-04-09
Filing date: 1987-04-09
Publication date: 1987-10-22
Also published as: EP0264409A1

Abstract

A device (17) for protecting a surge arrester (2, 3) against overheating consists of a thermostatic bimetal and, after unacceptable heating of the surge arrester to be protected (2, 3), adopts a monostable switching position in which electrodes (4, 5) of the surge arrester are connected to one another by the contact element (17).

Description

Device for protecting a surge arrester against thermal overload

Description

The present invention relates to a device for protecting a surge arrester against thermal overload according to the respective preamble of claims 1, 3 and 6.

Surge arresters which are used in the field of telecommunications are generally designed as so-called two-section surge arresters, which have an essentially ring-shaped, essentially ring-shaped ground electrode and a voltage electrode spaced from the ground electrode. Gas spark gaps between the voltage electrodes and the ground electrode are used to derive the overvoltage. In the event of an overvoltage, an arc arises in the gas spark gap in each case, which can lead to the overvoltage arrester heating up and ultimately to thermal destruction of the overvoltage arrester and the overvoltage arrester magazine receiving it.

^ To protect surge arresters of this type against thermal overload, it is already known from DE-PS 33 23 687 to provide a contact element resiliently abutting the surge arrester or a clip resiliently abutting the surge arrester, one leg of which is connected to a voltage electrode of the surge arrester, while the other leg is held at a distance from the ground electrode via a solder pill. If the surge arrester is inadmissibly heated, the solder pill softens, so that the other leg of the clamp or of the contact element, which is biased against the ground electrode, engages with the ground electrode. The contact elements of the known device for protecting the surge arrester against thermal overload can indeed be used as retrofit protective elements in already existing magazines with surge arresters for their thermal protection, but have the disadvantage that the S- or L-shaped structure of the contact elements is relative is bulky to ensure the necessary contact pressure after melting the solder pill and passing through the contact path. Furthermore, the S- or L-shaped contact elements of the known device for the thermal protection of surge arresters are clamped between the surge arresters and their magazines, which results in a relatively complex assembly of the contact elements. In addition, the assembly of the contact elements in the magazines on the surge arresters is relatively complex because of the contact elements which are already strongly pre-stressed in the cold state.

Compared to this prior art, the object of the present invention is to provide a Direction to protect a surge arrester of the type mentioned in such a way that with a compact design of the device for protecting the surge arrester, a simple assembly of the device is achieved.

This object is achieved in a device according to the preamble of claims 1, 3 and 6 by the features specified in the characterizing part of these claims.

According to a first aspect of the present invention, in a device of the type mentioned at the outset for protecting an overvoltage arrester against thermal overload, the clip consists of two layers of thermobimetal, one above the other and at least partially in contact with the overvoltage arrester, which are arranged with respect to the overvoltage arrester are that when the overvoltage arrester is heated, the inner layer tends to stand out from the latter and the outer layer tends to lie against the latter, the layers of the clamp at their free end being in engagement with one another with a monostable snap element which, when heated to a certain extent the layers come out of engagement and do not engage again even when the layers cool, the clip bridging the electrodes when the snap element is engaged.

This solution according to the invention offers the advantage that even after the device for thermal protection has responded, it is ready for operation again Can be brought into a state in which the monostable snap element is in turn engaged by hand or by means of a tool.

According to the advantageous development specified in claim 2, the surge arrester is a two-way arrester which consists of two surge arresters connected to one another with a common ground electrode and two spaced voltage electrodes, in which the device for thermal protection is designed in such a way that the clamp on the two-way arrester is arranged at the level of the ground electrode and only connected to it in an electrically conductive manner and consists of a thermal bimetallic strip bent up to 180 ° and placed around the surge arrester, so that the inner position adjacent to the surge arrester is at its location free end has a nose bent out against the outer layer, that the outer layer has at its free end both an elongated recess, which together with the nose forms the snap element, the edge of which is directed toward the free end and has a bulge outwards that are so dimensio niert is that with a certain heating of the layers, the free end of the inner layer can pass through this recess, as well as is provided on both sides with widening which in passing through the free end of the inner layer through the recess of the outer layer with the two voltage electrodes Touch comes. This configuration of the device according to the invention for the thermal protection of the double-line surge arrester can be achieved with little effort from a suitably punched and bent thermistor. Produce mobile metal strips and can be pushed onto the two-way surge arrester without further holding devices.

According to a second aspect of the present invention, with which claim 3 is concerned, it is provided in a device for the thermal protection of a two-way surge arrester of the type mentioned at the outset that the contact element consists of a thermobimetal strip, and that the contact element is designed in such a way that it essentially follows a jacket surface surrounding the essentially cylindrical two-section surge arrester, that the contact element has two arms extending circumferentially around the ground electrode and one in the axial direction from one voltage electrode to the other Has voltage electrode extending longitudinal section, and that the longitudinal section of the contact element is spaced from the two-way surge arrester by the spacer which softens in the event of inadmissible heating of the two-way surge arrester. This device for protecting the surge arrester against thermal overload holds onto the surge arrester by means of the arms and is attracted to the surge arrester by the action of the thermobimetal when it heats up, thereby increasing the flattening of the spacer which softens when heated. In this way, a secure contact of the longitudinal section of the contact element against the voltage electrodes is achieved. Nevertheless, no support of the contact element against a housing is required. According to the development specified in claim 4, the spacer consists of a thermoplastic or a metal alloy that melts at a relatively low temperature.

Preferably, as stated in claim 5, the ends of the arms are provided with beads which, after the spacer part has softened, come into contact with the voltage electrodes. In this way, contact is achieved even if the spacer cannot be flattened completely.

According to a third aspect of the present invention, in a device for protecting an overvoltage arrester against thermal overloading of the type mentioned at the outset, it is provided that the contact element consists of a thermobimetal that it also bears against a guide link which is designed in such a way that the Contact element during its deformation due to the heating of the contact element in response to the heating of the overvoltage arrester on the guide link moved from a first to a second position, from which the contact element cannot return to the first position even after cooling, whereby the contact element in the second layer connects the electrodes to one another. The contact element forms, together with the guide link, a monostable switching element which, after responding to excessive heating of the surge arrester, can also be brought back into the operational position using a tool or by hand. According to the development specified in claim 7, the guide link has a step, via which the contact element moves on its way from the first position to the second position.

In the embodiment described in claim 8 when used on a two-way surge arrester, the contact element has arms which extend in the circumferential direction and a longitudinal section which extends in the axial direction of the surge arrester and bears against the guide link, the latter in the first position of the Voltage electrodes is spaced and is in the second layer on these.

According to the embodiment described in claim 9, the arms encompass the ground electrode in each case by approximately 180 °, the ends of the arms facing away from the longitudinal section tapering. This configuration of the ends of the arms achieves a particularly suitable spring characteristic of the arms, with which the arms of the contact element can also easily be placed over the surge arrester.

Preferred embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. Show it:

1 shows a surge arrester;

FIG. 2 shows a clip for thermal protection of the surge arrester according to FIG. 1; 3 and FIG. 4 are side views of the overvoltage arrester with a clamp in a first or second

Switching position;

5 shows a perspective illustration of the surge arrester provided with the clamp according to FIGS. 1 to 4;

Fig. 6 is a perspective view of a

Surge arrester and a contact element;

7 shows a side view of the surge arrester shown in FIG. 6 with a cross-sectional view of the contact element in its unactuated position;

8 shows a representation corresponding to FIG. 7, in which the contact element has assumed its actuated position;

9 shows a side view of an overvoltage arrester with a cross-sectional view of a further contact element in its unactuated position; and

Fig. 10 is a representation corresponding to FIG. 9, in which the further contact element has assumed its actuated position. 1 shows a double-line arrester 1, which consists of two surge arresters 2, 3 connected to one another. Between the overvoltage arresters 2, 3 there is a common, substantially annular ground electrode for both overvoltage arresters

4. A voltage electrode 5, 6 is assigned to each surge arrester 2, 3. A clip 7 consisting of a thermal bimetallic strip is bent at its apex 8 by 180 °. The bimetallic strip has a bore 9 through which a connection of the ground electrode 4 extends. Due to the mechanical tension of the bimetallic strip, it is connected to the connection of the ground electrode 4 in the region of the bore 9. The at least two-layer thermobimetal strip has an inner layer 10 and an outer layer 12. The inner layer 10 of the clamp 7, which is adjacent to the surge arrester 2, 3, due to the material selection of the thermobimetal strip and its dimensions, tends to stand out from the surge arrester 2, 3 when heated. At its free end facing away from the apex .8, the inner layer has a nose 11 which is bent out against the outer layer 12. When heated, the outer layer 12 strives to bear against the surge arresters 2, 3. It has at its free end facing away from the apex 8 a recess 13, the edge of which is directed towards the free end and shows a bulge 14 towards the outside. Furthermore, the free end of the outer layer 12 has widenings 15, 16 which are connected to the voltage electrodes

5, 6 when the device for thermal protection of the surge arrester responds, such as this can be seen in Fig. 5.

FIG. 3 shows a side view of the overvoltage arrester with clip 7 attached, in its rest position, which is maintained, for example, up to a temperature of 140.degree. In the rest position, the clip 7 plugged onto the double-track conductor 1 is only conductively connected to the ground electrode. During heating, the inner layer 10 strives to stand out from the surge arresters 2, 3, while the outer layer 12 strives to contact the surge arresters 2, 3. When heated, the nose 11 therefore moves under the bulge 14 in the direction of the recess 13. At a temperature of approximately 140 ° C., the nose 11 with the free end of the inner layer 10 passes through the recess 13. The outer layer 12 can therefore contact the surge arresters 2, 3 by the widenings 15, 16 making electrical contact with the voltage electrodes 5, 6 and thus short-circuiting the surge arresters 2, 3. This switching position results from FIGS. 4 and 5.

When the two-way diverter 1 has cooled, the clamp 7 can be returned with a tool guided between the bulge 14 and the nose 11 from the position shown in FIG. 4 to the position shown in FIG. 3 and brought into its operating state without this the clamp 7 must be removed from the two-section diverter 1. In the exemplary embodiments shown in FIGS. 6 to 10, identical reference symbols designate identical or similar parts.

Fig. 6 is a perspective view of the two-way arrester 1, which corresponds in structure to the two-way arrester shown in Fig. 1, with a perspective view of a contact element 17- The contact element 17 is in its working position above the two-way arrester 1 and is only for reasons vividness separated from this. shown. The contact element 17 consists of a bimetallic strip which essentially has the shape of a lateral surface enveloping the cylindrical double-line arrester 1. The contact element 17 has two arms 18, 19 which extend around the ground electrode 4 in the circumferential direction and a longitudinal section 20 which extends in the axial direction from one voltage electrode 5 to the other voltage electrode 6. The longitudinal section narrows starting from the arms 18, 19 to its bead-shaped ends 21, 22, which are provided for making contact with the voltage electrodes 5, 6. The arms 18, 19 of the essentially jacket-shaped contact element 17 have tapering arm end sections 23, 24. Each arm 18, 19 surrounds the two-section arrester 1 with a wrap angle of more than 180 ° in the region of the arm end sections 23, 24.

As can be seen in particular from the illustration according to FIG. 7, the contact element 17 is spaced in the middle of its longitudinal section 20 by a spacer part from the two-way arrester 1. The spacer 25 consists of thermoplastic material or of a metal alloy that melts at a relatively low temperature. In this . Due to the spacing part 25 of the position of the contact element 17 spaced apart from the two-way arrester 1, its arm end sections 23, 24 are spaced apart from the voltage electrodes 5, 6.

If inadmissible heating of the two-way conductor 1 occurs, as is the case in FIG. 8, the spacer softens and flattens out under the action of the force which the thermobimetal strip exerts on the spacer 25 when heated. The layer sequence of the bimetallic strip of the contact element 17 is selected such that the contact element 17, when heated, pulls its arms 18, 19 towards the two-way arrester 1. The flattened, softened spacer 25 'enables contacting of the contact element 17 with the arm end sections 23, 24 on the voltage electrodes 5, 6 in order to connect them to the ground electrode 4 via the arms 18, 19.

In the modified embodiment according to FIGS. 9 and 10, no spacer 25 is required, as is the case with the embodiment according to FIGS. 7 and 8. The contact element 17 'has two relatively long support parts 27, 28 which rest on a step-shaped guide link.

The contact element 17 ^f likewise consists of thermal bimetal and, like the contact element 17 shown in FIGS. 7 and 8, has a longitudinal section 20 'and two arms 18', 19 '. The poor Even in the idle state, strive to attract the longitudinal section 20 'against the two-section diverter 1, the contact element 17', however, being held in its position at a distance from the two-section diverter 1 by the supporting parts 27, 28.

In the event of inadmissible heating of the two-way arrester 1, the contact element 17 'also heats up via the heat conduction caused by the arms 18', 19 ', and deforms due to its thermobimetal structure in such a way that the support parts 27, 28 to move. At the same time, the arms 18 ', 19' increasingly pull the contact element 17 'against the two-way arrester 1. Here, the support parts 27, 28 snap over the step 29 in the link 26, whereupon the support parts 27, 28 or the longitudinal section 20' with the Contact voltage electrodes 5, 6. In this state, the voltage electrodes 5, 6 are conductively connected to the ground electrode 4.

After the two-way diverter 1 and thus the contact element 17 'have cooled, the support parts 27, 28 strive to move apart again, but the support parts 27, 28 remain in position on the step 29 of the guide link 26. The contact element 17 'thus remains in connection with the voltage electrodes 5, 6 and the ground electrode 4. However, the support parts 27, 28 can be raised again to the step 29 of the guide link 26 by means of a tool, in order to make the two-way arrester 1 operational again to move. The described embodiments of the device for protecting a surge arrester against thermal overload are designed symmetrically, since the shown embodiments of the surge arrester are designed as two-section surge arresters. However, asymmetrical configurations of the devices for protecting an overvoltage arrester can also be used above all if the overvoltage arrester is merely a one-way surge arrester.

Claims

-I -Device for protecting a surge arrester against thermal overload

1. Device for protecting an overvoltage arrester against thermal overload, which has at least two electrodes (4, 5, 6) spaced apart from one another, with a clip (7) which responds to heating of the overvoltage arrester by connecting the electrodes ,

characterized,

that the clamp consists of two, consisting of a thermal bimetal, arranged one above the other and at least partially resting on the surge arrester - 1 -

Layers (10, 12),

that the layers are arranged in relation to the surge arrester such that the inner layer (10) tends to stand out from the surge arrester when it is heated and the outer layer (12) tends to contact it, and

that the layers of the clamp (7) are in engagement with one another at their free end with a monostable snap element (11, 14) which disengages when the layers (10, 12) are heated to a certain extent and also when they cool down the layers do not engage again, and that the clip bridges the electrodes (4, 5, 6) when the snap element is disengaged.

2. Device according to claim 1,

in which the overvoltage arrester is a two-section arrester (1) which consists of two overvoltage arresters (2, 3) connected to one another with a common ground electrode (4) and two spaced-apart voltage electrodes (5, 6),

characterized ,

that the clamp (7) is arranged on the two-way arrester (1) at the level of the ground electrode (4) and only connected to it in an electrically conductive manner and consists of a bimetallic strip which is bent up to 180 ° and is arranged around the overvoltage arrester (2, 3) ,

that the inner surge arresters (2, 3) adjacent layer (10) has at its free end a nose (11) which is bent out towards the outer layer (12),

that the outer layer (12) has at its free end both an elongated recess (13), which together with the nose (11) forms the snap element (11, 14), the edge of which is directed towards the free end and has a bulge (14 ) which is dimensioned such that when the layers (10, 12) are heated to a certain extent, the free end of the inner layer (10) can pass through this recess (13), and also with widenings (15, 16) on both sides can be seen which come into contact with the two voltage electrodes (5, 6) when the free end of the inner layer (10) passes through the recess (13) of the outer layer (12).

3. Device for protecting an essentially cylindrical two-way surge arrester against thermal overload,

which has a ground electrode (4) and two voltage electrodes (5, 6) spaced from the ground electrode,

with a contact element (17) with which a certain connection of the two-way surge arrester (1) can be used to establish a conductive connection between the voltage electrodes (5, 6) and the ground electrode (4) if there is a contact between the contact element (17 ) and the two-way surge arrester (1) arranged spacer (25) softens due to inadmissible heating of the two-way surge arrester, characterized,

that the contact element (17) consists of a bimetallic strip, and

that the contact element (17) is designed such

that it essentially follows a circumferential surface surrounding the essentially cylindrical two-section surge arrester (1),

that the contact element (17) two to the ground electrode (4) in the circumferential direction er¬ stretching arms (18, 19) and in the axial ^'direction from the trode a Spannungselek¬ extending to the other voltage electrode (6) longitudinal portion (5) (20), and

that the longitudinal section (20) of the contact element (17) is spaced from the two-way surge arrester (1) by the spacer (25) which softens when the two-way surge arrester (1) heats up inadmissibly.

4. Device according to claim 3,

characterized,

that the spacer (25) consists of a thermoplastic or a metal alloy melting at a relatively low temperature. - 13 -

5. The device according to claim 3 or 4,

characterized,

that the ends of the arms (18, 19) are provided with beads (21, 22) which, after the distance part (25) has softened, make contact with the voltage electrodes (5, 6).

6. Device for protecting an overvoltage arrester against thermal overload,

which has at least two spaced electrodes (4, 5, 6),

with a contact element (17 ') which responds to heating of the surge arrester (1) by connecting the electrodes (4, 5; 4, 6),

characterized,

that the contact element (17 ') consists of a thermobimetal,

that the contact element bears against a guide link (26) which is designed in such a way

that the contact element (17 '), when deformed due to the heating of the contact element in response to the heating of the surge arrester (1) on the guide link (26), moves from a first to a second position, from which the contact element also after cooling cannot return to the first position, and that the contact element in the second position connects the electrodes (4, 5; 4, 6) to one another.

7. The device according to claim 6,

characterized,

that the guide link (26) has a step (29) over which the contact element moves as it moves from the first position to the second position.

8. The device according to claim 6 or 7,

in which the overvoltage arrester is a substantially cylindrical two-way surge arrester (1) which has a ground electrode (4) and two voltage electrodes (5, 6) spaced from the ground electrode,

characterized,

that the contact element has two arms (18 ', 19') which extend in the circumferential direction around the ground electrode (4) and a longitudinal section (20 ') which extends in the axial direction beyond the voltage electrodes (5, 6) and which protrudes against the Bearing guide (26) is present, which is spaced from the voltage electrodes (5, 6) in the first position and which bears against these (5, 6) in the second position.

9. Device according to one of claims 3 to 5 and 8, -ZI -

characterized,

that the arms (18, 19; 18 ', 19') the ground electrode

(4) grasp each by approximately 180 °, and

that the ends (23, 24) of the arms facing away from the longitudinal section (20; 20 ') taper.