EP2497098B1 - Overvoltage protection element - Google Patents

Description

The invention relates to an overvoltage protection element having a housing, having at least one overvoltage limiting component arranged in the housing, in particular a varistor or a gas-filled surge arrester, and having at least two connecting elements for electrically connecting the overvoltage protection element to the current or signal path to be protected, wherein in the normal state of Overvoltage protection element, the connection elements are each in electrical contact with a pole of the overvoltage limiting device.

From the DE 42 41 311 A1 is an overvoltage protection element is known, which has a thermal separation device for monitoring the state of a varistor. In this overvoltage protection element, the first connection element is connected via a flexible conductor to a rigid separation element whose end remote from the flexible conductor is connected via a solder joint to a connection lug provided on the varistor. The other connection element is connected via a flexible conductor fixed to the varistor or a terminal lug on the varistor. The separating element is acted upon by a spring system with a force which results in the separating element being linearly moved away from the connecting lug during the separation of the soldering connection, with the result that the varistor is electrically cut off in the event of thermal overloading. By means of the spring system, a remote signaling contact is actuated at the same time during the separation of the solder connection, whereby a remote monitoring of the state of the overvoltage protection element is possible.

Also from the DE 20 2004 006 227 U1 an overvoltage protection element is known, in which the monitoring of the state of a varistor according to the principle of a temperature switch, so that when overheating of the varistor a provided between the varistor and a separator solder joint is separated, resulting in an electrical separation of the varistor. In addition, when separating the solder joint, a plastic element is pushed by the restoring force of a spring from a first position to a second position in which the formed as a resilient metal tongue separating element is thermally and electrically separated from the varistor by the plastic element, so that a possibly between the metal tongue and the contact point of the varistor arcing arc is deleted. Since the plastic element two juxtaposed colored markings In addition, it acts as an optical status indicator, whereby the state of the overvoltage protection element can be read directly on the spot. From the DE 699 04 274 T2 An overvoltage protection element with a thermal cutoff mechanism is also known. In this overvoltage protection element, one end of a rigid spring-loaded slider in the normal state of the overvoltage protection element is soldered both to the first connection element and to a connection lug connected to the varistor. An inadmissible heating of the varistor also leads here to a heating of the solder joint, so that the slider is pulled due to the force acting on it a spring from the junction between the first terminal and the terminal lug, resulting in an electrical separation of the varistor.

The DE 695 03 743 T2 discloses an overvoltage protection element with two varistors, which has two separating means, which can individually separate the varistors at their end of life. The separating means each have a resilient separating tongue, wherein the first end of the separating tongue firmly connected to the first terminal and the second end of the separating tongue is attached in the normal state of the overvoltage protection element via a solder joint to a connecting tongue on the varistor. If there is an inadmissible heating of the varistor, this leads to a melting of the solder joint. Since the separation tongue is deflected in the soldered state (normal state of the overvoltage protection element) from its rest position and thus biased, the free end of the separation tongue springs when softening the solder joint of the connecting tongue of the varistor, whereby the varistor is electrically disconnected. In order to ensure the required insulation and tracking resistance and to erase an emerging when opening the separation point arc, it is necessary that when pivoting the separation tongue as large a distance between the second end of the separation tongue and the connection tongue of the overvoltage limiting component is achieved.

US2009 / 0009921 A1 discloses an overvoltage protection element according to the preamble of claim 1.

The known overvoltage protection elements are generally designed as a "protective plug", which together with a device lower part form an overvoltage protection device. To install such a surge protection device, which is intended to protect, for example, the phase-leading conductors L1, L2, L3 and the neutral conductor N and possibly also the earth conductor PE, in the known surge protective devices on the bottom of the device corresponding terminals for the individual conductors provided. For simple mechanical and electrical contacting of the device base with the respective overvoltage protection element, the connection elements are designed as plug pins in the overvoltage protection element, which are arranged in the lower device part corresponding, connected to the terminals sockets, so that the overvoltage protection element can be easily plugged onto the device base.

In such overvoltage protection devices, the installation and assembly by plugging the surge protection elements is very simple and time-saving feasible. In addition, such overvoltage protection devices partly still have a changeover contact as a signal transmitter for remote signaling of the state of at least one overvoltage protection element as well as an optical status indication in the individual overvoltage protection elements. The status display indicates whether the overvoltage-limiting component arranged in the overvoltage protection element is still functional or not. In particular, varistors are used as overvoltage limiting component, although it is also possible to use gas-filled surge arresters, spark gaps or diodes depending on the intended use of the overvoltage protection element.

The above-described, used in the known overvoltage protection elements, thermal separation devices, which are based on the melting of a solder joint, have to fulfill several tasks. In the normal state of the overvoltage protection element, d. H. in the non-separated state, a secure and good electrical connection between the first connection element and the overvoltage limiting component must be ensured. When a certain limit temperature is exceeded, the separation point must ensure a safe separation of the overvoltage limiting component as well as a permanent insulation resistance and tracking resistance. The problem is, however, that the solder joint is permanently loaded with a shear stress due to the spring force of the spring element or deflected from its rest position separating tongue in the normal state of the overvoltage protection element.

The present invention is therefore based on the object to provide an initially described overvoltage protection element, in which the aforementioned disadvantages are avoided. It should be both a safe and good electrical connection in the normal state as well as a safe separation of a defective overvoltage limiting component to be ensured.

This object is achieved by an overvoltage protection element according to claim 1. Further embodiments emerge from the subclaims. In the overvoltage protection element described above, a heat-expandable, intumescent material is arranged within the housing such that upon thermal overloading of the overvoltage limiting device, the position of the overvoltage limiting device is variable relative to the position of the terminal elements due to expansion of the heat-expandable material such that at least one pole of the overvoltage-limiting device Component is no longer in electrical contact with the corresponding connection element.

The heat-expandable material, which is preferably composed of a low-melting plastic, for example polyethylene (PE) or polypropylene (PP), and a propellant is in the normal state of the overvoltage protection element in a solid state. As the temperature of the heat-expandable material increases due to increased self-heating of the surge limiting component, the heat-expandable material changes state of aggregation and becomes liquid. After exceeding a certain threshold temperature, the heat-expandable material reacts with a large volume increase; the heat-expandable material foams up. This caused by the increase in temperature large increase in volume of the heat-expandable material is used in the overvoltage protection element according to the invention to move the overvoltage limiting component away from the connection elements, so that the overvoltage limiting component is electrically separated.

Since the heat-expandable material is activated only upon a corresponding heating, ie thermal overloading of the overvoltage-limiting component, the electrical contact between the connection elements and the poles of the overvoltage-limiting component in the normal state is not mechanically stressed by the heat-expandable material.

In the overvoltage protection element according to the invention, a shock current carrying plug connection is provided instead of a solder connection. For this purpose, in the normal state of the overvoltage protection element, both poles of the overvoltage limiting component are connected via a respective plug connection to a connection element. In this case, the heat-expandable material arranged inside the housing assumes both the function of a sensor, which detects an inadmissible self-heating of the overvoltage-limiting component, and the function of an actuator, which moves the overvoltage-limiting component away from the connection elements under thermal overload. In contrast, in the known overvoltage protection elements, which are based on the melting of a solder joint, the function of the sensor is taken over by the solder joint and the function of the actuator of the spring or deflected from its rest position release agent.

The overvoltage protection element according to the invention is designed such that, in the case of thermal overloading of the overvoltage limiting component, both poles are disconnected from the connection elements, so that after the separation has taken place, both poles of the overvoltage limiting component are no longer in electrical contact with the connection elements. The formation of two separation points the extinction of a possibly occurring arc is favored because the two separation points form a series connection, so that increases the total arc length and thus the arc voltage by the series connection of the two separation points. It is advantageous if - as previously stated - both poles of Überspannungsbgerenzenden device via a respective connector with a connection element are connected, since then the separation of the electrical connection primarily from the temperature behavior of the heat-expandable material and not (also) of the Separation behavior of a solder joint depends.

According to a further advantageous embodiment of the overvoltage protection element according to the invention, the two poles of the overvoltage limiting component are each electrically connected to a terminal lug or a pin. Due to the design of the connection lugs or pins, both the solder joints and the connections between the poles of the overvoltage limiting component and the connection element can be realized easily. In the first case, the solder joints are each provided between a connecting lug or a connecting pin and a connecting element while, in the case of a plug connection, the connecting elements have plug sockets on the side facing the connecting lugs or the connecting pins. According to an advantageous structural embodiment of the invention, the housing has an outer housing and a housing disposed in the outer housing, on one side open inner housing, wherein the inner housing is displaceable relative to the outer housing. The connection elements are fixedly connected to the outer housing, while the surge-limiting device is disposed within the inner housing. In the normal state of the overvoltage protection element, the hood-shaped inner housing encloses the heat-expandable material in such a way that the inner housing with the overvoltage-limiting component is displaced relative to the outer housing - and thus also to the two connection elements - upon expansion of the heat-expandable material. Due to that thus heating the overvoltage-limiting component-activated heat-expandable material, the inner housing together with the overvoltage-limiting component arranged therein is pushed away from the connection elements so that the poles of the overvoltage-limiting component are no longer in electrically conductive contact with the connection elements.

To ensure that with a displacement of the inner housing and the overvoltage limiting component is moved, this is preferably connected via a holding element with the inner housing. In this case, the retaining element can be configured, for example, in the manner of a web and fastened by its two ends to the inner wall of the housing so that it extends in the transverse direction of the overvoltage-limiting component.

According to a preferred embodiment of an overvoltage protection element according to the invention with an outer housing and an inner housing displaceably arranged in the outer housing, the change in position of the inner housing is used for optical indication of the state of the overvoltage limiting component. For this purpose, the inner housing is arranged in the normal state of the overvoltage protection element in its first position within the outer housing so that the upper side of the inner housing does not protrude beyond the upper side of the outer housing. In thermal overloading of the overvoltage protection element, however, the inner housing is moved due to the expanding material in a second position in which the top of the inner housing protrudes beyond the top of the outer housing. The displacements of the inner housing in case of thermal overload of the overvoltage protection element is thus used to display the functional status of the overvoltage protection element.

According to an alternative constructive embodiment of the overvoltage protection element according to the invention, the housing has two electrically insulated holding elements, wherein in the normal state of the overvoltage protection element, the holding elements are each in electrical contact with a pole or a connecting pin or a connecting lug of the overvoltage limiting component. In this case, the holding elements surround the heat-expandable material, so that the overvoltage-limiting component is displaced relative to the holding elements in the event of an inadmissible heating by the expanding material. The overvoltage limiting component is then no longer with the holding elements in electrically conductive contact and is electrically isolated. In this embodiment variant, the electrically conductive holding elements serve both as a housing for receiving the overvoltage limiting component and the heat-expandable material and as connecting elements for the electrical connection of the poles of the overvoltage-limiting component.

The electrically conductive contact between the poles or connected to the poles connecting tabs or pins of the surge arrester and serving as connecting elements holding elements can be realized both via a solder connection and via a plug connection, wherein in the realization of a connector in the connection region of the holding elements the connector tabs or the connector pins corresponding sockets can be arranged. Such an overvoltage protection element is particularly suitable when using a gas-filled surge arrester as overvoltage limiting component, wherein the surge arrester can be connected via the two holding elements, for example with a printed circuit board.

Depending on the configuration of the holding elements and depending on the arrangement of the overvoltage limiting component and the heat-expandable material between the holding elements, the overvoltage limiting component is pressed by thermal expansion of the expanding material either upwards - perpendicular to its longitudinal extent - or horizontally to the side. Of course, a configuration is possible in which the overvoltage limiting component is pressed by the expanding material both upwards than to the side. In any case, the expansion of the heat-expandable material and the consequent change in position of the overvoltage-limiting device ensure that the poles of the over-voltage limiting device are no longer in electrically conductive contact with the holding elements.

In order to ensure a high insulation and tracking resistance and to erase a resulting when opening the contacts between the poles of the overvoltage limiting component and the connecting elements arc, the largest possible distance between the poles or the terminal straps of the overvoltage limiting component and the Connection elements can be achieved. In the overvoltage protection element according to the invention is provided according to an advantageous embodiment, that the heat-expandable material in case of thermal overload of the overvoltage limiting component in the forming gap between the at least one pole or the connecting tab or the one pin of the overvoltage limiting component and the at least one connecting element penetrates, so that at Cutting the electrical contact resulting arc is suppressed or deleted by the insulating heat-expandable material. Alternatively or additionally, at least one plastic part, for example made of POM, may be arranged in the region of the connection elements, which is gassing when heated. If an arc occurs in the vicinity of the plastic part, it is extinguished by blowing it with an extinguishing gas, which is generated by the dissociation of the plastic part.

According to a not belonging to the present invention embodiment of the overvoltage protection element, which will be briefly mentioned here, alternatively or in addition to the optical state display described above, a fernübertragbare status display is provided, for which a remote signaling contact is disposed within the housing, which is actuated when the Position of the overvoltage limiting device changed by the expanding material.

The heat-expandable, intumescent material used in the overvoltage protection element according to the invention preferably has an activation temperature which is more than 80 ° C. Preferably, the activation temperature of the heat-expandable material, i. H. the temperature at which the material expands, between 120 ° C and 150 ° C. Thus, the activation temperature of the heat-expandable material is optimally adapted to the maximum allowable operating temperature of the overvoltage protection element, which is often about 80 ° C.

As previously stated, the overvoltage limiting device is to be moved away from its first position by the heat expandable material. Thus, a significant expansion of the material is desired when this has reached its activation temperature. The volume increase of the heat-expandable material is preferably at least 200%, ie at least twice the volume of the heat-expandable material before it is activated. Since a rapid separation of the overvoltage limiting component is required in the event of overload, the heat-expandable material is preferably designed such that that it has a response time of less than one second for activation.

To the aforementioned boundary conditions, d. H. to achieve the desired activation temperature, volume increase and reaction time, the heat-expandable material is preferably a support material and a blowing agent. In this case, a thermoplastic polymer which is preferably selected from the group consisting of: acrylonitrile-butadiene-styrene (ABS), polyamides (PA), polylacetate (PLA), polymethylmethacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate can be used as carrier (PET), polyolefins, such as Polyethylene (PE), polypropylene (PP), polyisobutylene (PIB), polybutylene (PB), polystyrene (PS), polyetheretherketone (PEEK), polyvinyl chloride (PVC), polybutylene terephthalate (PBT) and celluloid. Alternatively, an elastomer having a low Shore A hardness can also be used as the carrier material, the Shore A hardness preferably being less than 20.

As blowing agent either a chemically acting blowing agent or a physically acting blowing agent can be used. According to a preferred embodiment, a physically acting blowing agent is used, which consists of smallest hollow bodies filled with gases which are present in liquid phase. Such a blowing agent is also referred to as microsphere. The size of the hollow body is in the one to two-digit micrometer range. The shell of the body is diffusion-tight and rigid below the activation temperature, but elastic when the activation temperature is reached. An increase in temperature causes a phase change of the liquid within the hollow body from liquid to gaseous, which leads to a very strong volume increase. By suitable choice of the liquid or of the gas while the activation temperature is adjustable, so that the blowing agent can be adapted to the particular application.

The proportion of the blowing agent is preferably about 5 to 15% in relation to the carrier material. With such a mixing ratio, a sufficiently good and practical volume increase of the heat-expandable material consisting of the carrier material and the blowing agent is achieved. Overall, such a volume multiplication by a factor of 5 can be achieved.

The support material is selected so that its softening temperature is of the order of the activation temperature of the blowing agent. Also from this point of view, polyethylene (PE) and polypropylene (PP) are particularly suitable as a carrier material. Depending on the application, the carrier material or the blowing agent is chosen so that the activation temperature of the blowing agent is greater or less than the softening temperature of the carrier material. For applications that require the fastest possible separation of a component or the operation of a switch, it is advantageous if the activation temperature of the blowing agent is slightly lower than the softening temperature of the carrier material. This then leads to the fact that the blowing agent already begins with its reaction before the softening temperature of the carrier material is reached. As a result, a bias voltage is built up in the heat-expandable material, which leads to a very rapid volume increase when the softening temperature is reached.

If a carrier material and a blowing agent is selected in which the activation temperature of the blowing agent is greater than the softening temperature of the carrier material, this leads to the carrier material already softening before the blowing agent reacts, so that the increase in volume of the material begins upon reaching the activation temperature and then ends when the maximum increase in volume has been reached or the activation temperature has fallen below again. The process runs much slower than in the case when the activation temperature is lower than the softening temperature. Such a slower course of the process is suitable, for example, for changing an optical status display. In order to change an optical state indication by increasing the volume of a heat-expandable material, a material combination of blowing agents with different activation temperatures can be used, whereby a stepwise change of the status display depending on the temperature that has occurred in each case is possible.

According to an alternative embodiment, the heat-expandable material consists of two components, which are separated from each other in the non-activated state, wherein the components react with each other with an increase in volume when the separation is canceled. The two components may be, for example, sodium bicarbonate on the one hand and an acid, for. As citric acid, on the other hand, which are initially separated from each other by a release layer. If the separation is canceled, for example by mechanical or thermal Exposure, the two components react with each other, whereby gas is released, which leads to an increase in volume. Similar reactions can also be achieved with multicomponent polyurethanes or by means of rapid oxidations, for example when a combustion process is ignited.

Typically, the heat-expandable material is designed so that the volume increase is irreversible. By a suitable selection and arrangement of the blowing agent and the carrier material, however, it can also be achieved that the carrier material is transferred back to its starting state during cooling, so that the volume increase of the material can be reversed.

Since the activation of the heat-expandable material, and in particular the blowing agent, depends on the introduction of heat into the heat-expandable material, good thermal coupling to the over-voltage-limiting component to be monitored is required. In order to increase or improve the heat input into the heat-expandable material, active heating can be provided by additional energy input from outside into the material.

For this purpose, for example, a heating resistor may be embedded in the heat-expandable material, whose own power dissipation results in additional heating of the material. Alternatively, a heat pipe or a conductor with high thermal conductivity, such as copper, be embedded in the material. Finally, additional heating of the heat-expandable material can also be achieved by mixing conductive material such as graphite powder or copper powder into the material. As a result, an intrinsic conductivity of the material is achieved, so that the material is heated in full volume when a voltage is applied through the current flowing through the material. With the increase in volume of the material commencing when the activation temperature is reached, the resistance increases because the number of conductive components per unit volume is reduced. Preferably, this results in a complete cessation of the current flow, whereby the additional heat input is switched off.

Fig. 1

eine Schnittdarstellung eines ersten Ausführungsbeispiels eines Überspannungsschutzelements, im Normalzustand,

Fig. 2

eine Schnittdarstellung des Überspannungsschutzelements gemäß Fig. 1, mit einem abgetrennten Varistor,

Fig. 3

eine weitere Schnittdarstellung eines Überspannungsschutzelements gemäß Fig. 1, mit einem abgetrennten Varistor,

Fig. 4

eine Schnittdarstellung eines zweiten Ausführungsbeispiels eines Überspannungsschutzelements, im Normalzustand,

Fig. 5

eine Draufsicht des Überspannungsschutzelements gemäß Fig. 4, im Normalzustand,

Fig. 6

eine Schnittdarstellung des Überspannungsschutzelements gemäß Fig. 4, mit einem abgetrennten Überspannungsableiter,

Fig. 7

eine Schnittdarstellung eines dritten Ausführungsbeispiels eines Überspannungsschutzelements, im Normalzustand,

Fig. 8

das Überspannungsschutzelement gemäß Fig. 7, in der Draufsicht,

Fig. 9

das Überspannungsschutzelement gemäß Fig. 8, mit einem abgetrennten Überspannungsableiter, in der Draufsicht,

Fig. 10 - 12

drei Varianten des Überspannungsschutzelements gemäß Fig. 6, mit einem abgetrennten Überspannungsableiter

In particular, there are a variety of ways to design and develop the overvoltage protection element according to the invention. Reference is made to both the claims subordinate to claim 1 and to the following description of preferred embodiments in conjunction with the drawings. In the drawing show

Fig. 1

a sectional view of a first embodiment of an overvoltage protection element, in the normal state,

Fig. 2

a sectional view of the overvoltage protection element according to Fig. 1 , with a separate varistor,

Fig. 3

a further sectional view of an overvoltage protection element according to Fig. 1 , with a separate varistor,

Fig. 4

a sectional view of a second embodiment of an overvoltage protection element, in the normal state,

Fig. 5

a plan view of the overvoltage protection element according to Fig. 4 , in the normal state,

Fig. 6

a sectional view of the overvoltage protection element according to Fig. 4 , with a separate surge arrester,

Fig. 7

a sectional view of a third embodiment of an overvoltage protection element, in the normal state,

Fig. 8

the overvoltage protection element according to Fig. 7 , in plan view,

Fig. 9

the overvoltage protection element according to Fig. 8 , with a separate surge arrester, in plan view,

Fig. 10 - 12

three variants of the overvoltage protection element according to Fig. 6 , with a separate surge arrester

The figures show an overvoltage protection element 1 with a housing 2, wherein a surge-limiting component is arranged in the housing 2. In the embodiment according to the Fig. 1 to 3 the overvoltage limiting component is a varistor 3, whereas with the overvoltage protection element 1 according to FIGS 4 to 12 is a gas-filled surge 3 'acts.

The overvoltage protection element 1 according to the Fig. 1 to 3 , which may be formed as a protective plug, has two connection elements 4, 5, which can be inserted into corresponding connection sockets of a device lower part, not shown here. In the normal state of the overvoltage protection element 1, the connection elements 4, 5 are each connected to one pole of the varistor 3, so that the varistor 3 can be connected via the two connection elements 4, 5 to the current or signal path to be protected.

Like from the Fig. 1 . 4 and 7 2, it is apparent that in the normal state of the overvoltage protection element 1, a heat-expandable material 6, which is an intumescent material, is arranged in the housing 2, which is initially solid but changes its state of aggregation and becomes liquid as the temperature increases. When an activation temperature is exceeded, the heat-expandable material 6 reacts with a large volume increase, ie the material 6 foams up and expands. This then causes the position of the varistor 3 or the surge arrester 3 'to change relative to the position of the connection elements 4, 5, since the heat-expandable material 6 pushes the varistor 3 or the surge arrester 3' out of their first position. In the embodiments according to the Fig. 2 and 6 is the varistor 3 and the surge arrester 3 'while upward and in the embodiment according to Fig. 9 pushed away to the side.

The overvoltage protection element 1 according to the Fig. 1 to 3 on the one hand and the overvoltage protection elements 1 according to the 4 to 12 on the other hand differ initially characterized by the fact that in the first embodiment as overvoltage limiting component, a varistor 3 is used, while in the other embodiments, a gas-filled surge arrester 3 'is used. In addition, the overvoltage protection elements 1 still differ by the type of electrical contact between the varistor 3 and the connection elements 4, 5 on the one hand and the surge arrester 3 'and the connection elements 4, 5 on the other.

While in the two embodiments according to the Fig. 4 and 7 In the normal state of the overvoltage protection element 1, the two poles of the surge arrester 3 'via one solder joint 7, 8 are connected to the two connection elements 4, 5, the two poles of the varistor 3 via a plug connection 9, 10 with the two connection elements 4, 5 in electrically conductive contact. In this case, the two poles of the varistor 3 are connected via two connecting lugs 11, 12 to the connecting elements 4, 5, wherein the connecting elements 4, 5 on the connecting tabs 11, 12 facing sides each have a female connector 13, 14. At the in Fig. 4 illustrated embodiment of the overvoltage protection element 1, the two poles of the surge arrester 3 'are each connected to a pin 15, 16, so that the solder joints 7, 8 between the pins 15, 16 and the connecting elements 4, 5 are formed.

In the embodiment of the overvoltage protection element 1 according to the invention according to the Fig. 1 to 3 2, the housing 2 has an outer housing 17 and an inner housing 18, which is displaceably arranged in the outer housing 17. As can be seen from the figures, the underside of the inner housing 18 is open, so that the inner housing 18 encloses the varistor 3 and the heat-expandable material 6 like a hood. If there is a reduction in the impedance of the varistor 3 due to overloading or due to aging of the varistor 3, then an impermissible leakage current flows through the varistor 3, which leads to a heating of the varistor 3. Since the varistor 3 is at least partially surrounded by the heat-expandable material 6, a self-heating of the varistor 3 also leads to a heating of the material 6, so that this greatly expands when a certain activation temperature is exceeded. This results in an increase in pressure within the space enclosed by the outer housing 17 and the inner housing 18, so that the inner housing 18 is pushed upwards by the expanding material 6 when the holding force of the inner housing 18 within the outer housing 17 and the contact force between the terminal lugs 11, 12 and the sockets 13, 14 is exceeded by the force of the expanding material 6.

Thus, with the inner housing 18 and the varistor 3 moves upward, the varistor 3 is connected via a holding element 19 with the inner housing 18, wherein the holding element 19 is disposed below the varistor 3 and in the illustration according to the Fig. 1 to 3 perpendicular to the plane of the drawing, that extends in the transverse direction of the varistor 3. The inner housing 18 is thus performed similar to a piston in the outer housing 17, wherein a not shown in the figures stop ensures that the lifting movement of the inner housing 18 is limited upwards.

How out Fig. 1 it can be seen, the inner housing 18 is in the normal state of the overvoltage protection element 1 in a first position within the outer housing 17, in which the upper side 20 of the inner housing 18 is substantially flush with the upper side 21 of the outer housing 17, so that the upper side 20 of the inner housing 18th does not protrude beyond the outer housing 17. In contrast, the inner housing 18 is in thermal overload of the overvoltage protection element 1 after the electrical separation of the varistor 3 in a - Fig. 2 illustrated - second position in which the top 20 of the inner housing 18 extends beyond the top 21 of the outer housing 17. The position of the inner housing 18 thus serves as an optical status display for displaying the state of the overvoltage protection element 1.

It has previously been stated that the heat-expandable material 6 used is preferably an intumescent material which is solid in the normal state of the overvoltage protection element 1 and initially becomes liquid when the temperature rises. In order to reliably prevent the liquid intumescent material 6 from escaping, a sealing film 22 is arranged in the outer housing 17 above the connecting elements 4, 5, ie opposite the open underside of the inner housing 18, in the illustrated embodiment. Here, the terminal lugs 11, 12 extend in the normal state of the overvoltage protection element 1 through slots provided in the sealing film 22, so that the terminal lugs 11, 12 contacted by the sockets 13, 14 and thus in electrically conductive contact with the connection elements 4, 5.

Fig. 3 shows the overvoltage protection element 1 according to Fig. 1 in which the inner housing 18 is in the second position, so that the varistor 3 is separated. In contrast to the representation according to Fig. 2 is in the illustration according to Fig. 3 However, the varistor 3 or the inner housing 18 has been pushed not by an expansion of the heat-expandable material 6 upwards, but due to an overpressure caused by a bursting of the varistor 3 due to an extreme overload. An extreme overload can cause a varistor 3 abruptly in a low-impedance state, so that in this extreme case, a line-driven current in the size of the short-circuit current can flow through the varistor 3. A current flowing through the varistor 3 in this case can lead to destruction and thus to a bursting of the varistor 3. The resulting pressure is passed through a formed in the arranged under the varistor 3 holding element 19 opening 23 in the space formed by the outer housing 17, the inner housing 18 and the sealing film 22 space 24. The resulting pressure in this space 24 then causes the inner housing 18 is pushed from its first position to its second position upwards, whereby the varistor 3 is moved away from the connection elements 4, 5, so that the connecting lugs 11, 12 not more with the sockets 13, 14 are in electrically conductive contact. The overloaded varistor 3 is thus reliably and quickly separated.

In the in Fig. 3 illustrated position of the inner housing 18, the existing in the space 24 increased pressure escape through the openings formed in the outer housing 17 openings 25. The openings 25 are arranged in the outer housing 17 such that they are closed by the inner housing 18, as long as the inner housing 18 is not yet in its second position.

At the in Fig. 4 illustrated embodiment of the overvoltage protection element 1, the housing 2 is not an outer housing and an inner housing, but of two U-shaped in cross-section holding elements 26, 27 in addition to the inclusion of the heat-expandable material 6 for holding and contacting the pins 15, 16 of the surge arrester. 3 serve in the normal state of the overvoltage protection element 1. In the in the 4 to 12 illustrated embodiments of the overvoltage protection element 1 serve the two mutually insulated, electrically conductive support members 26, 27 thus simultaneously as connection elements 4, 5 for the gas-filled surge arrester 3 '. Out Fig. 4 it can be seen that in the normal state of the overvoltage protection element 1 each have a solder joint 7, 8 between the two pins 15, 16 and the holding elements 26, 27 is formed.

If there is a heating of the surge arrester 3 'in this transitional protection element 1, this also leads to a heating of the heat-expandable material 6 arranged below the surge arrester 3', so that this expands when it reaches its activation temperature. The surge arrester 3 'is then pushed up when the force exerted by the heat-expandable material 6 is greater than the holding force of the softening solder joints 7, 8. In this in Fig. 6 illustrated second position of the surge arrester 3 ', the two pins 15, 16 are no longer in electrically conductive contact with the support members 26, 27, so that the surge 3' is no longer connected to the protected signal path via the support members 26, 27. The electrical connection of the holding elements 26, 27 with the signal path to be protected takes place in the embodiments according to the 4 to 12 in that the holding elements 26, 27 are connected to a printed circuit board 28.

Instead of the solder connection between the pins 15, 16 and the holding elements 26, 27 shown in the figures, in principle, a plug connection according to the Fig. 1 to 3 be provided. In this case, the holding elements 26, 27 would have corresponding plug sockets on the sides facing the connection pins 15, 16.

While in the embodiment according to the 4 to 6 the holding elements 26, 27 are formed and the heat-expandable material 6 is arranged between the holding elements 26, 27 such that upon thermal overload of the surge arrester 3 'it is forced upwards by the expanding material 6, the surge arrester 3' in the exemplary embodiment according to the Fig. 7 to 9 pushed away by the expanding material 6 horizontally to the side.

In principle, when opening an electrical contact via which a current flows, an arc can occur, which in the case of an overvoltage protection element 1 can lead to an impermissible current also flowing in the actually disconnected state of the overvoltage-limiting component via the arc. Such an arc is at the in Fig. 2 illustrated embodiment of the overvoltage protection element 1 is prevented in that the expanding heat-expandable material 6 penetrates upon thermal overload of the varistor 3 in the forming gap between the terminal lugs 11, 12 and the sockets 13, 14. Possible switching arcs are deleted by the foaming of the connecting lugs 11, 12. This also applies to the in Fig. 9 illustrated left pin 15 of the surge arrester 3 '.

In addition, also at the in Fig. 3 illustrated situation of the overvoltage protection element 1 to extinguish an interrupting the electrical connection between the terminal lugs 11, 12 and the sockets 13, 14 pending arc, the two connection elements 4, 5 surrounded by a plastic part 29 that is gassing at a pending arc. In the case of a pending arc, the dissociation of the plastic parts 29 thus produces a blowing out of the arc, as a result of which the arc is extinguished.

The Fig. 10 - 12 show three different variants of an overvoltage protection element 1, each only by the formation of the heat-expandable material 6 from each other and the execution of Fig. 6 differ.

In the embodiment according to Fig. 10 In the heat-expandable material 6 conductive particles 30 are arranged, which may be, for example, graphite powder or copper powder. By the admixture of the conductive particles 30, an intrinsic conductivity of the material 6 is achieved, so that when a voltage is applied, a current flows through the heat-expandable material 6, through which the material 6 is heated to full volume. If the material 6 reaches its activation temperature, there is an increase in volume, which also leads to a reduction in the number of conductive components per unit volume, so that as the volume increases, the conductivity of the material 6 decreases, preferably to such an extent that at maximum Volume increase no current flows through the material 6.

In the embodiments according to FIGS. 11 and 12 is a heat pipe 31 and a resistance wire 32 embedded in the heat-expandable material 6, whereby it also comes to an additional heating of the material 6 when a current flows through the heat pipe 31 and the resistance wire 32. The connections of the heat pipe 31 and the resistance wire 32 can either - as in the FIG. 11 and 12 shown - be led out separately or connected to the connection elements 4, 5. In the second case, the current via the surge arrester 3 'is also used for additional heating of the heat-expandable material 6 by the heat pipe 31 or the resistance wire 32.

It can be seen that the previously described variants or configurations of the heat-expandable material 6 not only in an overvoltage protection element 1 with a gas-filled surge arrester 3 'according to Fig. 6 but also in an overvoltage protection element 1 with a varistor 3 according to Fig. 1 can be used.

Claims (16)

1. An overvoltage protection element with a housing (2), with at least one overvoltage limiting component (3) which is located in the housing (2), especially a varistor or a gas-filled surge arrester, and with two connection elements (4, 5) for electrical connection of the overvoltage protection element (1) to a current or signal path which is to be protected, wherein in the normal state of the overvoltage protection element (1) the connection elements (4, 5) each being in electrically conductive contact with a pole of the overvoltage limiting component (3) at a time,
   wherein there is an intumescent material (6) within the housing (2) such that when the overvoltage limiting component (3, 3') is thermally overloaded the position of the overvoltage limiting component (3, 3') as a result of expansion of the intumescent material (6) can be changed relative to the position of the connection elements (4, 5) such that at least one pole of the overvoltage limiting component (3, 3') is no longer in electrically conductive contact with the corresponding connection element (4, 5)
   characterized in
   that in the normal state of the overvoltage protection element (1) the two poles of the overvoltage limiting component (3, 3') are each connected via a plug connection (9, 10) to one connection element (4, 5).
2. Overvoltage protection element according to claims 1, characterized in that the two poles of the overvoltage limiting component (3, 3') are each electrically connected conductively to a terminal lug (11, 12) or a terminal post (15, 16).
3. Overvoltage protection element according to claim 1 or 2, characterized in that the housing (2) has an outer housing (17) and an inner housing (18) which is open on one side and which is located in the outer housing (17), that the connection elements (4, 5) are connected stationary to the outer housing (17), that the overvoltage limiting component (3, 3') is located within the inner housing (18), that in the normal state of the overvoltage protection element (1) the inner housing (18) surrounds the intumescent material (6), and that the inner housing (18) with the overvoltage limiting component (3, 3') can be shifted when the intumescent material (6) expands relative to the outer housing (17) as a result of the heating of the overvoltage limiting component (3, 3').
4. Overvoltage protection element according to claim 3, characterized in that the overvoltage limiting component (3, 3') is connected to the inner housing (18) via a holding element (19), wherein the holding element (19) is attached with its two ends to the inner wall of the inner housing (18) and extending preferably in the transverse direction of the overvoltage limiting component (3).
5. Overvoltage protection element according to claim 3 or 4, characterized in that the inner housing (18) in the normal state of the overvoltage protection element (1) is in a first position within the outer housing (17) in which the top (20) of the inner housing (18) does not project above the top (21) of the outer housing (17) and wherein in thermal overloading of the overvoltage protection element (1) the inner housing (18) is shifted into a second position in which the top (20) of the inner housing (18) projects above the top (21) of the outer housing (17).
6. Overvoltage protection element according to any one of claims 3 to 5, wherein the two poles of the overvoltage limiting component (3, 3') are each electrically connected conductively to one terminal lug (11, 12), characterized in that on the open side of the inner housing (18) facing the connection elements (4, 5) there is a sealing film (22), wherein in the normal state of the overvoltage protection element (1) the terminal lugs (11, 12) extending through the sealing film (22) so that the terminal lugs (11, 12) are in electrically conductive contact with the connection element (4, 5).
7. Overvoltage protection element according to claim 6, characterized in that in the holding element (19) which is located under the overvoltage limiting component (3, 3') an opening (23) is formed through which the pressure can escape which forms when the overvoltage limiting component (3, 3') is destroyed as a result of an extreme overload so that the position of the inner housing (18) with the overvoltage limiting component (3, 3') changes relative to the outer housing (17) and the poles of the overvoltage limiting component (3, 3') are no longer in electrically conductive contact with the connection elements (4, 5).
8. Overvoltage protection element according to claim 7, characterized in that in the outer housing (17) at least one opening (25) is formed through which the pressure can escape when the inner housing (18) is in the second position.
9. Overvoltage protection element according to claim 1 or 2, characterized in that the housing (2) has two electrically conductive holding elements (26, 27) which are isolated from one another, that in the normal state of the overvoltage protection element (1) the holding elements (26, 27) each are in electrically conductive contact with one pole or one terminal lug (11, 12) or one terminal post (15, 16) of the overvoltage limiting component (3, 3') and surround the intumescent material (6) and that the overvoltage limiting component (3, 3') can be displaced relative to the holding elements (26, 27) when the intumescent material (6) expands due to heating of the overvoltage limiting components (3, 3').
10. Overvoltage protection element according to claim 9, characterized in that the overvoltage limiting component (3, 3') in thermal overloading is forced upward by the expanding intumescent material (6) so that the poles of the overvoltage limiting component (3, 3') are no longer in electrically conductive contact with the holding elements (26, 27).
11. Overvoltage protection element according to claim 9, characterized in that the overvoltage limiting component (3, 3') in thermal overloading is forced horizontally to the side by the expanding intumescent material (6) so that the poles of the overvoltage limiting component (3, 3') are no longer in electrically conductive contact with the holding elements (26, 27).
12. Overvoltage protection element according to any one of claims 1 to 11, characterized in that the intumescent material (6) in thermal overloading of the overvoltage limiting component (3, 3') penetrates into the intermediate space which forms between at least one pole or one terminal lug (11, 12) or one terminal post (15, 16) of the overvoltage limiting component (3, 3') and at least one connection element (4, 5) so that an arc which forms when the electrical contact is broken between at least one pole and at least one connection element (4, 5) is suppressed or extinguished by the insulating intumescent material (6).
13. Overvoltage protection element according to any one of claims 1 to 12, characterized in that in the region of the connection elements (4, 5) there is at least one plastic part (29) which evolves gas when heated.
14. Overvoltage protection element according to any one of claims 1 to 13, characterized in that the intumescent material (6) has a carrier agent, especially a thermoplastic polymer or an elastomer with low Shore hardness, and a propellant, wherein as propellant preferably a physically acting propellant, especially microspheres, are used.
15. Overvoltage protection element according to any one of claims 1 to 14, characterized in that the intumescent material (6) consists of two components which are separated from one another in the unactivated state, wherein the components react with one another as the volume increases when the separation is neutralized.
16. Overvoltage protection element according to any one of claims 1 to 15, characterized in that the activation of the intumescent material (6) is supported by active heating by additional energy delivery from the outside.

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