EP2876653B1 - Multi-contact element for a varistor - Google Patents

Description

The invention relates to a multi-contact element for a varistor.

Varistors provide a voltage dependent resistor in electrical circuits. Varistors are therefore used in many applications, typically to dissipate overvoltages above a certain threshold voltage so as to prevent overloading or damaging a subsequent device. Therefore, varistors are often synonymous as a surge protection device called. An example of such overvoltage is a voltage that can be caused by lightning. If such an overvoltage event occurs, the task of the varistor is to divert the current past the respective electrically downstream consumer and thus to limit the voltage at the electrical load.

In this case, the varistor generally has as its material a granular metal oxide, e.g. Zinc oxide and / or bismuth oxide and / or manganese oxide and / or chromium oxide and / or silicon carbide, which is introduced as a rule as a (sintered) ceramic between two planar electrodes as supply elements.

Typically, the individual grains have a different conductivity. In this case, at the respective grain boundaries, i. at the points of contact of the grains, barrier layers. It can be seen that with increasing thickness, the number of grain boundaries increases and thus the limit voltage. When a voltage is applied to the lead elements, an electric field is formed. Depending on the voltage while the barrier layers are now degraded and the resistance decreases.

Due to the material properties of the varistor, both the current distribution and the overcoming of the barrier layers are not a uniform process, but rather local current paths are formed which come into the conducting state at different rates.

Due to the material properties and as a result of using the varistor occur leakage currents. Although these leakage currents are usually low, but may lead to significant heating of the device and therefore there is a risk of fire. To counteract here typically a temperature sensor is used, which operates a switch when a certain temperature is exceeded. However, temperature sensors can only be used to detect slow events. Rapid heating, as occurs, for example, when applying a high voltage, leads to a greatly delayed due to the necessary and known slow heat conduction temperature rise at the temperature sensor, so that the varistor would be destroyed as a rule. Also, the separation ability is usually limited here, i. only small currents can be switched off.

Such an energy input may e.g. arise because over an extended period of time an overvoltage occurs, which leads to a switching of the varistor and now the short-circuit current of the network is derived via the varistor. In this case, significant heating of the varistor occurs and there is a risk of fire. Furthermore, the varistor can be damaged so far that the varistor breaks down explosively.

Typically, varistors are therefore provided with an upstream fuse element.

So far, this classic fuses were used, which were upstream of the respective surge protection device. However, two contradictory boundary conditions had to be considered: While in the event of an overvoltage event, a high current flows in the short term, which should not lead to a tripping of the fuse, a safe tripping must be provided if the overvoltage protection device is damaged with the lowest possible current.

In other words, in order to ensure rapid disconnection in the event of a fault of the overvoltage protection device, ie at low residual currents, a fuse having a small nominal value would have to be used. However, such a fuse carries only low pulse currents due to the associated I ² t value. Conversely, however, in order to derive a large pulse current, the fuse must have a large nominal value.

Nevertheless, damage to varistors that can not be detected by the aforementioned elements occurs repeatedly, i. There are currents that can not be separated by the separation capacity of the thermal shutdown, but are too low for an upstream fuse element.

Against this background, it is the effort to minimize the fuse rating of the upstream fuse element, but still maintain the maximum surge current capability.

So far, this problem could only be solved inadequately.

A first approach to solve this problem was in DE 10 2012 011 241.6 described. Here, a distribution of the currents is proposed in parallel paths, so as to reduce the nominal value of the individual fuses.

Although the solution presented fulfills its task, it would be desirable to find a solution that is easily adjustable and also allows smaller sizes and also easy to manufacture.

The invention is based on the object to provide a contact element for a varistor, which circumvents one or more of these disadvantages.

This object is solved by the features of claim 1. Advantageous developments are also the subject of the dependent claims.

The invention will be explained in more detail with reference to the accompanying drawings with reference to preferred embodiments.

Fig. 1

ein Prinzip-Ersatzschaltbild eines Aspektes der Erfindung,

Fig. 2

einen Schnitt durch eine beispielhafte Anordnung gemäß Ausführungsformen der Erfindung,

Fig. 3

ein Prinzip-Ersatzschaltbild eines weiteren Aspektes der Erfindung,

Fig. 4

einen Schnitt durch eine weitere beispielhafte Anordnung gemäß Ausführungsformen der Erfindung,

Fig. 5

Prinzipdarstellungen äquivalenter Schaltungen gemäß eines Aspektes der Erfindung,

Fig. 6

ein Prinzip-Ersatzschaltbild noch eines weiteren Aspektes der Erfindung,

Fig. 7

einen Schnitt durch eine weitere beispielhafte Anordnung gemäß Ausführungsformen der Erfindung,

Fig. 8

einen Schnitt durch eine weitere beispielhafte Anordnung gemäß Ausführungsformen der Erfindung,

Fig. 9

ein Prinzip-Ersatzschaltbild und eine hierzu korrespondierende quasiräumliche Anordnung gemäß eines weiteren Aspektes der Erfindung,

Fig. 10

ein Prinzip-Ersatzschaltbild in quasi-räumliche Anordnung gemäß eines weiteren Aspektes der Erfindung,

Fig. 11

einen Schnitt durch eine weitere beispielhafte Anordnung gemäß Ausführungsformen der Erfindung,

Fig. 12

einen Schnitt durch eine weitere beispielhafte Anordnung gemäß Ausführungsformen der Erfindung, und

Fig. 13

eine Draufsicht auf Fig. 12.

Show it

Fig. 1

a principle equivalent circuit diagram of an aspect of the invention,

Fig. 2

a section through an exemplary arrangement according to embodiments of the invention,

Fig. 3

a principle equivalent circuit diagram of a further aspect of the invention,

Fig. 4

a section through a further exemplary arrangement according to embodiments of the invention,

Fig. 5

Schematic representations of equivalent circuits according to one aspect of the invention,

Fig. 6

a principle equivalent circuit diagram of yet another aspect of the invention,

Fig. 7

a section through a further exemplary arrangement according to embodiments of the invention,

Fig. 8

a section through a further exemplary arrangement according to embodiments of the invention,

Fig. 9

a principle equivalent circuit diagram and a corresponding thereto Quasiräumliche arrangement according to another aspect of the invention,

Fig. 10

a principle equivalent circuit diagram in a quasi-spatial arrangement according to a further aspect of the invention,

Fig. 11

a section through a further exemplary arrangement according to embodiments of the invention,

Fig. 12

a section through a further exemplary arrangement according to embodiments of the invention, and

Fig. 13

a top view Fig. 12 ,

The invention takes advantage of the fact that a breakdown of a varistor is usually first of all a local phenomenon, which is only then a phenomenon relating to the entire varistor.

Therefore, the invention proposes the division of the fuse into individual fuse elements 1, 2,... N as in FIG FIG. 1 shown in parallel contact a varistor. A corresponding exemplary structure is shown in FIG FIG. 1 shown. In this case, a multicontact element MKE is used for a varistor VAR, wherein the multicontact element MKE has a sandwich structure. In this case, the sandwich structure has in a lowermost layer US two or more contact elements KE1, KE2 for contacting the varistor VAR and in a topmost layer OS at least one common connection electrode A for contacting a consumer network to be protected.

Between the lowermost layer US and the uppermost layer OS, a first intermediate layer ZS1 of an electrically insulating material layer is provided at least in sections. Such an electrically insulating material layer can be used, for example, by a board material, a glass fiber mat soaked with epoxy resin, for example FR4, or else polymers, ceramics or glass.

In the first intermediate layer ZS1 are now the individual fuse elements DK1, DK2, which are designed so that they can carry a specified surge current, the specified surge current per fuse element is less than the specified surge current of the varistor VAR. That Although the nominal value of the individual fuse elements is small, the necessary separation capacity can be provided by the parallel connection of the fuse elements, while at the same time ensuring that due to the low nominal value of the individual fuse elements a quick shutdown in the local fault current event and thus in total global fault current case is made available.

In this case, the securing elements DK1, DK2 are designed as plated-through holes within the first intermediate layer ZS1. As a result, a low height is possible.

For this purpose, the fuse elements DK1, DK2 in the first intermediate layer are in direct electrical contact with the common connection electrode A.

Each of the fuse elements DK1, DK2 is in direct or indirect electrical contact with a subset of the contact elements KE1, KE2. That is, in the embodiment of the FIG. 2 the contact element KE1 is in direct contact with the securing element DK1 and the contact element KE2 is in direct contact with the securing element DK2.

In the event of a fault, the securing elements DK1, DK2 have blow-out channels AK in the first intermediate layer ZS1, so that in the event of thermal overloading of a securing element DK1, DK2 of the first intermediate layer ZS1, the affected securing element DK1 can evaporate through the blow-off channel and thus establish the electrical connection to the underlying ( Part-) varistor is interrupted. That The plasma produced in the separation case can pass via blow-off channels AK into a possibly existing surrounding extinguishing medium LM and the plasma is cooled there.

Goods in the embodiment of FIG. 1 and FIG. 2 each contact element KE assigned exactly one securing element DK, the advantageous division can also be carried out with respect to a contact element or, if for example it is not possible to achieve a desired nominal value with a securing element, this by a parallel connection of several m fuse elements a ₁ , b ₁ , ..., m ₁ Representing a first fuse element 1, a parallel connection of a plurality of fuse elements a ₂ , b ₂ , ..., m ₂ representative of a second fuse element 2, etc. to achieve, as in FIG. 3 compared to FIG. 1 is clarified.

Ie in FIG. 4 Each of the fuse elements DK1, DK2, DK3, DK4 is in direct or indirect electrical contact with a subset of the contact elements KE1, KE2. That is, in the embodiment of the FIG. 4 the contact element KE1 is in direct contact with the security elements DK1 ₁ and DK1 ₂ , while the contact element KE2 is in direct contact with the security elements DK2 ₁ and DK2 ₂ .

In a further embodiment of the invention, as in FIG. 7 8 and 8, at least in sections, between the lowermost layer US and the first intermediate layer ZS1, a second intermediate layer ZS2 is provided from an electrically insulating material layer. Such an electrically insulating material layer can, for example, in turn be used by a circuit board material, a glass fiber mat impregnated with epoxy resin, for example FR4, or else polymers, ceramics or glass. Particularly advantageous here, in addition to individual material layers and combination products such as multi-layer boards or the like can be used.

Again, in the second intermediate layer ZS2 there are fuse elements DK3, DK4, which are designed so that they can carry a specified surge current, wherein the specified surge current per fuse element is less than the specified surge current of the varistor VAR. That Although the nominal value of the individual fuse elements is small, the necessary separation capacity can be provided by the parallel connection of the fuse elements, while at the same time ensuring that due to the low nominal value of the individual fuse elements a quick shutdown in the local fault current event and thus in total global fault current case is made available.

In this case, the securing elements DK3, DK4 are designed as plated-through holes within the second intermediate layer ZS2. As a result, a low height is possible.

The fuse elements DK3, DK4 in the second intermediate layer are in turn in electrical contact via at least one plated-through hole DK1, DK2 of the first intermediate layer ZS1 with the common terminal electrode A.

Each of the fuse elements DK3, DK4 of the second intermediate layer ZS2 is in direct electrical contact with a subset of the contact elements KE1, KE2. That is, in the embodiment of the FIG. 7 the contact elements KE1 is in direct contact with the securing elements DK3 and the contact elements KE2 are in direct contact with the securing element DK4. In the embodiment of the FIG. 8 is the contact elements KE1 in direct contact with the security elements DK2 and DK3 and the contact elements KE2 in direct contact with the security elements DK4 and DK5.

In the event of a fault, the securing elements DK3, DK4 have blow-out channels AK in the second intermediate layer ZS2, so that in the event of thermal overloading of a securing element DK3, DK4 of the second intermediate layer ZS2, the affected securing element DK3, DK4 can evaporate through the blow-off channel and thus establish the electrical connection to the underlying (part) varistor is interrupted. That The plasma produced in the separation case can pass via blow-off channels AK into a possibly existing surrounding extinguishing medium LM and the plasma is cooled there.

In FIGS. 7 and 8 are doing the Figures 5 corresponding variants of a series connection of a fuse element of a first intermediate layer realized with a parallel circuit of fuse elements of a second intermediate layer. In this case, the arrangement is not limited to these forms of series circuits, but it can of course also be provided that in each case parallel circuits are provided in both the first intermediate layer and in the second intermediate layer, which are connected in series. These measures allow the nominal value of the individual fuse elements as well as the nominal value provided by the circuit to be set very precisely. In general, this principle is in FIG. 9 again clarified, where in the lower part of the FIG. 9 a possible quasi-spatial alternating arrangement is shown, as it can be realized by way of example with an intermediate layer. Again, as in FIG. 10 indicated, a single fuse element can be realized as a parallel circuit of fuse elements.

An exemplary meander-shaped arrangement of such a multi-contact element is shown in FIG FIG. 11 shown. There is a possible current path illustrated by the dashed arrow. In this case, a (partial) current of the varistor VAR occurs at the contact element KE1 and is passed through the via through a third intermediate layer ZS3, which is shown by way of example as insulation to the varistor, and through a second intermediate layer ZS2. Subsequently, in a conductor track position between the first intermediate layer ZS1 and the second intermediate layer ZS2, which may likewise be configured in the manner of a securing element, a contact to a second through-connection to the right is produced. Subsequently, in a second interconnect layer between the third intermediate layer ZS3 and the second intermediate layer ZS2, which may likewise be designed in the form of a fuse element, a contact to a third via right next to it is produced. This process can be provided as many times as necessary to achieve the desired rating or voltage. Of course, it can also be provided that here several fuse elements are connected in parallel, this would, for example, in the illustrated cut perspective simply possible that in a further underlying layer the same arrangement is repeated, at a suitable location, a compound of the levels is provided on Leiterbahneben.

As in the Figures 2 . 4 . 7 and 8 2, at least some of the plated-through holes DK1, DK2 of the first intermediate layer ZS1 are connected to the terminal electrode A via strip conductors. By suitable dimensioning and / or shaping of the strip conductors, the strip conductors can also be designed as further securing elements.

In order to provide additional protection for the case of an error, provision may additionally be made for at least part of the exhaust channels AK above the first intermediate layer ZS1 to be surrounded by an electrically insulating extinguishing medium LM. For example, polyoxymethylene (POM) or quartz sand can be used as an electrically insulating extinguishing agent.

In a particularly preferred embodiment, the securing elements DK1, DK2 of the first intermediate layer ZS1 and, if present, also the securing elements DK3, DK4 of the second intermediate layer ZS2 are designed to have a nominal value of up to 10 A, preferably 1 A. Further advantageously, the surge current capability is designed so that currents up to 1 kA, in particular up to 2 kA or more can be worn short term

As in FIG. 12 it can also be provided that at least one of the securing elements DK1, DK2; DK3, DK4 is machined by means of a bore in such a way that the flow-throughable diameter is reduced and the blow-out duct is enlarged. As a result, for example, backup values can be set precisely by post-processing a via. In addition, it can be provided that, for example, through holes targeted connections to a connection electrode A are interrupted and so the nominal value can be subsequently adjusted. For example, can be removed by drilling a fuse element of a parallel circuit of fuse elements.

To set the nominal value very precisely, e.g. be provided that the bore is eccentric.

The invention is not limited to the multi-contact element, but also includes a varistor VAR, which has at least one multi-contact element MKE. It can even be provided that both terminals of a varistor are equipped by means of the multi-contact elements according to the invention. Also in more recently available multi-contact varistors, i. Varistors with one or more center taps, the invention is equally applicable to all connections.

The connection between the multicontact element MKE and the varistor ceramic VAR preferably takes place via a pressure contact. Alternatively or additionally, a soldering, adhesive or clamping connection may be provided.

Preferably, the varistor VAR and the multi-contact element MKE are then in a housing G, in particular when an extinguishing agent LM is still used.

As a result, an arrangement is proposed in which the fuse elements are arranged substantially parallel to the varistor surface. The fuse elements can be manufactured particularly easily in printed circuit board technology. Particularly advantageous multi-layer printed circuit boards can be used for this purpose.

Instead of a multi-layer printed circuit board and a printed circuit board can be used, which has at the bottom of the contact elements, which are connected by vias to the conductor on the top. A second circuit board, which has no copper coating on the bottom and the recesses and holes is fixed on the lower circuit board, so that the recesses are aligned substantially over the (fuse) traces and the holes at the end. Through the holes, wires can be bonded, soldered or welded to the end of the fuse tracks, which can then be attached to the top of the top board.

For higher voltage levels, multiple vias can be connected in series. In the case of large short-circuit currents, these disconnect almost simultaneously, whereby a sufficient countervoltage for disconnection is achieved. <U> REFERENCE LIST </ u> Multi contact element MKE varistor VAR contact elements KE1, KE2 top layer OS common connection electrode A lowest layer US first intermediate layer ZS1 fuse element DK1, DK2, DK3, DK4 blow-out AK second intermediate layer ZS2 electrically insulating extinguishing agent LM

Claims (13)

1. A multi-contact element (MKE) for connection with a varistor (VAR),

   • wherein the multi-contact element (MKE) has a sandwich structure,

   • wherein the sandwich structure has two or more contact elements in a lowermost layer (US), and wherein the sandwich structure has at least one common connection electrode (KE1, KE2) in an uppermost layer (OS),

   • wherein a first intermediate layer (ZS1) made of an electrically insulating layer of material is provided between the lowermost layer (US) and the uppermost layer (OS) at least in segments,

   • wherein fuses (DK1, DK2) are located in the first intermediate layer (ZS1) that are configured such that they can sustain a specified surge current, the specified surge current per fuse being less than the specified surge current of the varistor (VAR),

   • wherein the fuses (DK1, DK2) are embodied as vias within the first intermediate layer (ZS1),
   wherein the fuses in the first intermediate layer are in direct electrical contact with the common connection electrode,

   • wherein each of the fuses (DK1, DK2) is in direct or indirect electrical contact with a subset of the contact elements,

   • wherein the fuses (DK1, DK2) provide blow-out channels in the first intermediate layer (ZS1) so that in the event of a thermal overloading of a fuse (DK1, DK2) of the first intermediate layer (ZS1), the affected fuse (DK1) can vaporize through the blow-out channel.
2. The multi-contact element as set forth in claim 1, characterized in that a second intermediate layer (ZS2) made of an electrically insulating layer of material is provided at least in segments between the lowermost layer (US) and the first intermediate layer (ZS1),

   • wherein further fuses (DK3, DK4) are located in the second intermediate layer (ZS2) that are configured such that they can sustain a specified surge current, the specified surge current per fuse being less than the specified surge current of the varistor (VAR),

   • wherein the further fuses (DK3, DK4) are embodied as vias within the second intermediate layer (ZS2),

   • wherein the further fuses (DK3, DK4) in the second intermediate layer are in electrical contact with the common connection electrode (A) by means of at least one fuse (DK1, DK2) of the first intermediate layer (ZS1),

   • wherein each of the further fuses (DK3, DK4) of the second intermediate layer is in direct electrical contact with a subset of the contact elements (KE1, KE2),

   • wherein the further fuses (DK3, DK4) provide blow-out channels in the first intermediate layer (ZS1) and in the second intermediate layer (ZS2) so that in the event of a thermal overloading of a further fuse (DK3, DK4) of the second intermediate layer (ZS2), the affected fuse (DK3) can vaporize through the blow-out channel.
3. The multi-contact element (MKE) as set forth in claim 2, wherein the second intermediate layer (ZS2) has a circuit board material.
4. The multi-contact element (MKE) as set forth in one of the preceding claims, wherein the first intermediate layer (ZS1) has a circuit board material.
5. The multi-contact element (MKE) as set forth in one of the preceding claims, wherein at least a portion of the vias (DK1, DK2) of the first intermediate layer (ZS1) is connected to the connection electrode (A) by means of conductive paths, the conductive paths being configured as fuses.
6. The multi-contact element (MKE) as set forth in one of the preceding claims 1, wherein at least a portion of the blow-out channels (AK) is surrounded above the first intermediate layer (ZS1) by an electrically insulating extinguishing agent (LM).
7. The multi-contact element (MKE) as set forth in one of the preceding claims, wherein at least a portion of the blow-out channels (AK) is surrounded above the first intermediate layer (ZS1) by polyoxymethylene or quartz sand as an electrically insulating extinguishing agent (LM).
8. The multi-contact element (MKE) as set forth in one of the preceding claims, wherein the fuses (DK1, DK2; DK3, DK4) have a rating of up to 10 A, preferably 1 A.
9. The multi-contact element (MKE) as set forth in one of the preceding claims, wherein a plurality of fuses (DK1, DK2; DK3, DK4) are connected in parallel.
10. The multi-contact element as set forth in one of the preceding claims, wherein at least one of the fuses is machined by boring such that the aperture through which current can flow is reduced and the blow-out channel is enlarged.
11. The multi-contact element as set forth in claim 10, wherein the bore is eccentric.
12. Varistor (VAR) having at least one multi-contact element (MKE) as set forth in one of the preceding claims.
13. The varistor (VAR) as set forth in claim 12, wherein the multi-contact element (MKE) and the varistor (VAR) are arranged in a housing (G).

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