EP1523792B1 - Protective element for arresting overvoltages and the use thereof - Google Patents

Abstract

A protective element is provided for reliably arresting overvoltages and is comprised of a parallel circuit consisting of a varistor and of an overvoltage arrester. In order to reduce the capacitance of the protective element, the varistor is provided in the shape of a disk and is placed between a contact pin (KS) and the overvoltage arrester. An electric insulation between the contact pin and the varistor is ensured by an electrically insulating intermediate piece inside of which openings are provided for electrical contact elements for connecting the varistor to the can and the contact pin to the overvoltage arrester. The overvoltage arrester and the intermediate piece are mounted, preferably with positive engagement, inside the can.

Description

A protective element for dissipating electrical surges, for example, the DE 43 31 215 A1 known. It consists of a parallel connection of a surge arrester, an air spark gap and a varistor, which are arranged in a cup-shaped metallic sleeve. The varistor is ring-shaped and sits directly on the surge arrester. Through the opening of the annular varistor, a contact pin is guided, which is contacted with the upper electrode of the surge arrester. Lower electrode of the surge arrester and upper electrode of the varistor are connected to the cup-shaped sleeve.

Such a protective element of parallel-connected varistor and surge arrester has the advantage that with steeply increasing overvoltages, the ignition delay of the surge arrester is bridged with the aid of the prematurely responding varistor. In this way, the protective effect of the protective element is improved during the response time of the surge arrester.

A disadvantage of the known protective element, however, is that the annular varistor has a high intrinsic capacity. This determines the damping behavior of the protective element when it is used in high-frequency circuits. A higher capacity leads to higher attenuation, which in turn reduces the line length that can be realized with such a protective element.

However, in high frequency telecommunications systems such as ADSL, VDSL, and others, there is a need for overvoltage protection elements that can bridge the surge arrestor response time and at the same time have a low attenuation and are therefore particularly suitable for the high-frequency systems.

The object of the invention is therefore to provide such a protective element which avoids the mentioned disadvantages of known protective elements.

This object is achieved with a protective element according to claim 1. Advantageous embodiments of this protective element and advantageous uses can be found in further claims.

In the protective element according to the invention a varistor and a surge arrester are arranged one above the other in an electrically conductive cup and electrically connected in parallel between the cup and a contact pin. The varistor is disk-shaped and sits directly on a first electrode of the surge arrester. The second electrode of the surge arrester sits on the bottom of the cup and contacts it electrically. The upper electrode of the varistor is electrically connected to the cup. The contact pin is electrically conductively connected to the first electrode of the surge arrester and is at least partially guided in the space between the varistor and the cup. Between varistor and contact pin an insulating intermediate piece is arranged.

Preferably, varistor and surge arrester are rotationally symmetrical and arranged concentrically or coaxially with each other in the cup. The diameter of the cup is determined by the diameter of the surge arrester. Preferably, the cross-section of the cup in the region of the surge arrester on a step-like extension, so that the cup is spaced in the region of the upper electrode of the surge arrester thereof.

Preferably, the upper electrode of the varistor is mechanically and electrically connected to a spreader, which has at least two arms which are spread against the inner wall of the cup and electrically connect the upper electrode of the varistor with the cup. This has the advantage that both a centered orientation of the varistor and a secure hold of the varistor in the cup is achieved. Also advantageous is a spreading with more than two arms, which are offset evenly over a circular arc against each other. This creates an optimal spreading.

Preferably, the contact pin has at least two feet, which are guided laterally between the varistor and the inner wall of the cup to the first electrode of the surge arrester. These feet are then offset against the arms of the expansion element, or are passed between them.

The electrically insulating intermediate piece is preferably formed elastically and has such a shape that it can firmly abut the inner wall of the cup in the manner of a rubber stopper. The intermediate piece has openings through which the feet of the contact pin are guided. The arms of the expansion element are preferably bent upwards on the cup wall, whereby openings in the intermediate piece are advantageously also provided for the upwardly bent ends of the arms of the expansion element. Number of feet and arms of the expansion element preferably correspond to each other and are then arranged in pairs or alternately. In an advantageous embodiment, the spreader element has three arms and the contact pin has three feet.

In a further advantageous embodiment of the invention, the intermediate piece on a disk-shaped base body having in the middle on at least one side of a recess which is adapted to the diameter of the contact pin and / or the varistor, wherein the contact pin and / or varistor are at least partially sunk in the recess of the intermediate piece.

In one embodiment of the invention, the intermediate piece forms the upper end of the cup, wherein the contact pin projects beyond the cup wall and the intermediate piece. The arms of the expansion element terminate below the upper cup rim and can be completely covered in an advantageous embodiment of the upper portion of the intermediate piece.

Cup and contact pin are advantageously formed of brass.

The varistor is advantageously designed as a known metal oxide varistor.

Also, the surge arrester can be chosen arbitrarily and is known in its exact configuration per se. Advantageously, gas-filled surge arresters are used, which have a priming line and can form a gas discharge to a discharge electrode in the event of overvoltage.

Figur 1

zeigt ein erfindungsgemäßes Schutzelement im sche- matischen Querschnitt

Figur 2

zeigt eine weitere Ausführungsform eines Schutzele- ments im schematischen Querschnitt (Figur 2a) bzw. in der Draufsicht (Figur 2b)

Figur 3

zeigt in perspektivischer Explosionszeichnung Ein- zelteile eines erfindungsgemäßen Bauelements

Figur 4

zeigt die Teile von Figur 3 in zusammengesetzter Form

Figur 5

zeigt das Ausführungsbeispiel von Figur 4 innerhalb eines Bechers.

In the following the invention will be explained in more detail with reference to embodiments and the accompanying figures. The figures show, in partial not to scale and schematic representation, various embodiments of the invention.

FIG. 1

shows a protective element according to the invention in the schematic cross section

FIG. 2

shows a further embodiment of a protection element in schematic cross section ( FIG. 2a ) or in plan view ( FIG. 2b )

FIG. 3

shows in perspective exploded view of individual parts of a device according to the invention

FIG. 4

shows the parts of FIG. 3 in composite form

FIG. 5

shows the embodiment of FIG. 4 inside a mug.

FIG. 1 shows on the basis of a schematic cross section through a protective element according to the invention the basic structure of such. The protective element is arranged in a cup B, which consists of a substantially cylindrical cup wall BW and a cup bottom BB. Within the cup B, a surge arrester UA, a varistor V, an intermediate piece ZS and above a contact pin KS are arranged one above the other. The surge arrester UA is seated on the cup bottom BB and is electrically connected thereto via its second electrode E2. The varistor V is seated on the surge arrester UA and is connected via its lower electrode to the first electrode E1 of the surge arrester. The intermediate piece is arranged in a form-fitting manner between the contact pin and the varistor and electrically insulates them from each other. The upper electrode of the varistor is connected to the cup wall BW via an electrical connection EV. The contact pin KS is connected via a foot to the first electrode E1 of the surge arrester. In this way, an electrical parallel connection of the two protective components of the protective element results between the contact pin KS and the cup B.

In a preferred use of the protective element, this is held by a spring tension between two contacts which are in communication with the contact pin KS and the cup bottom BB. In this way, an additional mechanical fixation of the individual parts of the protective element is not required. But it is possible that individual parts of the protective element are positively inserted in the cup B and are fixed in this way mechanically with this. there It makes sense to fit the surge arrester as the volume-largest component of the protective element form fit into the cup. Likewise, the intermediate piece may be positive, in particular since this is preferably made of an elastic material, such as rubber or silicone rubber. Another fixation can take place via the electrical connection EV, which is formed in one embodiment as a spreading element, which has at least two arms that can be braced against the inner cup wall BW. The foot F of the contact pin KS is performed as shown by the intermediate piece ZS. However, it is also possible to design the electrically insulating intermediate piece with a smaller diameter, the foot then being guided past the intermediate piece to the surge arrester UA.

FIG. 2a shows a specific embodiment of the invention, which the in FIG. 1 obeyed principle. More detailed here is the structure of the surge arrester UA. This consists essentially of a ceramic sleeve KH and two electrodes E1, E2, which form a spark gap in the interior of the gas-filled cavity of the ceramic sleeve KH.

The varistor V sits on the first electrode E1 and is arranged here in a depression of the first electrode E1. As a result, the height of the entire protection element can be reduced. Within the recess, the varistor is arranged on a mesa-like flattened elevation, so that only a central region of the lower electrode of the varistor contacts the first electrode E1 of the surge arrester UA. This ensures that only the metallization of the varistor is contacted and unwanted current paths are avoided over the lateral surfaces of the disc-shaped varistor.

The upper electrode of the varistor V is connected to a metallic expansion element SE, of which in the figure one of the present in particular in triplicate arms is shown in section. These consist for example of metallic strips which are bent upwards at the end and can be fitted in a form-fitting manner in the cup as a whole. About the varistor V and the associated with this expansion element SE an electrically insulating intermediate piece is arranged. This has in the region of the cup wall on a continuous or blind hole-like opening, through which the bent end of the expansion element SE is guided and abuts there against the cup wall BW. On the intermediate piece ZS sits on the contact pin, which has at least one foot F, which is passed through a further opening of the intermediate piece down and electrically connected to the first electrode E1 of the surge arrester UA. The electrical connection can be designed as a contact.

Contact pin and cup as well as the feet and the spreading element SE are made of brass in particular. The electrical connection between the contact pin KS and its foot F is preferably designed as a solder joint, as well as the connection between the upper electrode of the varistor and the expansion element SE. The electrical connection between the lower electrode of the varistor and the upper electrode E1 of the surge arrester is likewise electrically conductive, for example a soldered connection or else designed as an electrically conductive adhesive connection. However, it is also possible to carry out this electrical connection as a press contact.

Another beneficial detail of in FIG. 2a illustrated protective element is a step-like extension ST of the cross section of the cup, which leads above the step-like extension ST to a larger inner diameter. This has the consequence that forms an air gap between the outer edge region of the first electrode E1 of the surge arrester UA and the cup wall, on the one hand this electrode E1 of the cup wall BW electrically insulated and on the other hand provides an additional air spark gap. This allows a second current path, which leads in the unlikely event of a total failure of the surge arrester (eg in case of leakage) to safely dissipate this overvoltage by means of sparkover to the cup wall.

FIG. 2b shows the device of FIG. 2a in the plan view. From the plan view it is clear that the protective element is preferably formed rotationally symmetrical with a central axis of symmetry A, which here has a threefold symmetry. This symmetry relates in particular to the number and arrangement of the arms of the expansion element SE or the feet F of the contact pin KS. From the top view it is also clear that the arms of the expansion element and the feet are alternately offset from each other and are guided by spaced openings of the intermediate piece ZS- Between the openings, the intermediate piece ZS preferably concludes positively with the inner cup wall BW. The contact pin KS is preferably fitted in a recess of the intermediate piece, which thus has a smaller thickness in the interior than between the openings.

FIG. 3 shows an exploded perspective view of a contact pin KS with feet F, an intermediate piece ZS and connected to a spreader SE varistor V. From the figure it is clear that varistor and spreader form a preferably connected by a solder joint LV unit, as well as contact pin KS and the with this connected via a solder joint LV feet.

The plate shape of the basic shape formed intermediate piece has openings in the edge region through which the feet F and the arms of the expansion element SE can be pushed through from different sides.

FIG. 4 shows in a perspective view the three in FIG. 3 shown components in assembled form, as they are arranged in the finished protective element. From this representation, it is clear that the intermediate piece ZS is used for electrical insulation between the contact pin and the varistor, or for electrical insulation of the feet F against the arms of the expansion element SE. The feet F are also spaced from the varistor, as are the arms of the expansion element SE from the contact pin.

FIG. 5 shows in a perspective plan view, as the in FIG. 4 represented part in the cup B is fitted form-fitting. From the figure it is clear that the intermediate piece ZS concludes positively with the cup B. It is also clear that the arms of the expansion element SE are braced against the cup wall and thus establish an electrical contact to this.

Although the invention has been explained by way of example only, it is not limited to this. Since it essentially represents the arrangement and interconnection of varistor and contact pin by means of electrically insulating intermediate piece, feet and spreading element, the exact design of the surge arrester UA and the varistor V for the invention without meaning. It is only important that the varistor is disc-shaped, wherein the upper and lower major surface are metallized and thus represent upper and lower electrode. Such a varistor has a low capacitance and allows the use of the protective element in high-frequency systems, in particular for high-frequency communication systems such as ADSL, VDSL, etc. The invention is characterized by the low space requirements, the simple structure and secure cohesion on the specific geometric design out. Further possible variations of the invention result from the selection of different types of surge arresters, different materials for the individual components as well as a deviating from the illustrated spatial configuration geometric design.

LIST OF REFERENCE NUMBERS

B

cups

V

varistor

UA

Surge arresters

KS

pin

E1, E2

first and second electrode of the surge arrester

BB

Bottom of the mug

BW

cup wall

ZS

electrically insulating intermediate piece

EV

electrical connection of the upper electrode of the varistor with the cup

SE

spreader

F

Feet of the contact pin

A

axis of symmetry

LV, LV '

solder

KH

Ceramic sleeve

ST

Step-like extension of the cup wall

Claims (13)

1. Protection element for arresting overvoltages having an electrically conductive cup (B), in which a varistor (V) and a surge arrester (UA) are arranged one above the other and are connected electrically in parallel between the cup and a contact pin (KS),
   in which the lower electrode of the varistor is seated directly on a first electrode (E1) of the surge arrester,
   in which the contact pin makes contact with the first electrode of the surge arrester,
   in which the second electrode (E2) of the surge arrester is seated on the bottom (BB) of the cup, having an electrical connection (EV) of the upper electrode of the varistor to the cup, characterized in that
   an electrically insulating intermediate piece (ZS) is arranged between the varistor and the contact pin,
   the varistor is in the form of a disc and has a smaller diameter than the surge arrester, and
   the contact pin is arranged at least partially in the space between the cup and the varistor.
2. Element according to Claim 1,
   in which the upper electrode of the varistor (V) is connected to a spreading element (SE), which has at least two arms which are spread in the cup (B) and are used as the electrical connection to the cup.
3. Element according to Claim 1 or 2,
   in which the contact pin (KS) has at least two feet (F) which pass by the varistor (V) at the side.
4. Element according to Claim 2 or 3,
   in which the intermediate piece (ZS) is matched to the internal diameter of the cup (B) and has openings, which are separated from one another, for the feet (F) of the contact pin (KS) or for the feet of the contact pin and the arms of the spreading element (SE).
5. Element according to one of Claims 1 to 4,
   in which the intermediate piece (ZS) has a depression in the centre, in which depression the contact pin (KS) is partially recessed.
6. Element according to one of Claims 1 to 4,
   in which the intermediate piece (ZS) has a depression in the centre,
   in which depression the varistor (V) is partially recessed.
7. Element according to one of Claims 1 to 6,
   in which the varistor (V), the surge arrester (UA) and the cup (B) are rotationally symmetrical, and in which the contact pin (KS), the intermediate piece (ZS), the varistor (V) and the surge arrester (UA) are arranged coaxially and concentrically with respect to the centre axis (A) of the cup.
8. Element according to one of the preceding claims, in which the cross section of the cup (B) has a step-like widened area (ST) in the area of the surge arrester (UA), such that the cup is separated from the surge arrester in the area of the first electrode (E1) of the surge arrester.
9. Element according to one of the preceding claims, in which the cup (B) and the contact pin (KS) are formed from brass.
10. Element according to one of the preceding claims, in which the intermediate piece (ZS) is formed from rubber or silicone.
11. Element according to one of the preceding claims, in which the operating voltage of the varistor (V) is chosen such that it is above the operating voltage of the surge arrester (UA).
12. Use of the element, according to one of the preceding claims, for protection of telecommunications facilities.
13. Use of the element, according to one of the preceding claims, for protection of assemblies in radio-frequency telecommunications systems.

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