JP2020508557A - Safety fuse for low voltage applications - Google Patents

Abstract

The present invention comprises at least one fuse element located between two contacts and located in a protective housing, and a short-circuit auxiliary contact having an internal insulation distance to a fusible conductor, and to a power supply system. The invention relates to connectable devices, in particular safety fuses for low voltage applications to protect overvoltage arresters such as spark gaps or varistors. According to the present invention, an externally operable switching device for overcoming an insulation distance is embodied in a protective housing to create a low impedance or short circuit involving impedance, wherein the switching device comprises an insulation distance. And the insulating element undergoes a change of state by the exothermic activator, the activator being connected to at least one control connection. [Selection diagram] FIG.

Description

  The invention comprises at least one fusible conductor arranged between two contacts in a fuse housing, and a short-circuit auxiliary contact having an internal insulation distance to the fusible conductor, which can be connected to a supply network. The invention is based on a safety fuse for low voltage applications according to claim 1 for protecting surge protection devices such as spark gaps or varistors.

  Conventional fuses are used in large numbers and in many applications to provide protection against overcurrent or short circuits for cables and wiring and connected equipment.

  Furthermore, fuses are used in so-called cross branches as backup protection for surge arresters. Here, suitable fuses must ensure protection in the event of a short circuit.

  As renewable energy sources are increasingly used and integrated into supply networks, increasingly volatile short circuit values are occurring at equipment installation sites, depending on the feed-in situation. This can result in the required fuse or switch-off integration having to be varied over a wide range. In certain circumstances, the selected fuse can no longer provide protection under all possible feed-in conditions.

  To a very limited extent, the problem of volatile short-circuit values can be solved using the "short-circuit" method. Rather, the "short circuit" method converts the undefined impedance of the surge protector to a defined impedance in the event of a fault. This can be understood similarly to a short circuit connected in parallel for surge protection. In the case of a low-impedance metal connection, the fuse can be provided with a mains short-circuit current, which is only turned off in a defined manner if it is large enough. This is not always the case for networks with volatile short-circuit currents.

  In the case of a low resistance short circuit, the maximum short circuit current available to the fuse is provided. In the case of a short circuit involving impedance, the current load on the fuse is reduced, making switch-off at low currents suspicious. Arcing or arc erosion of the fusible conductor has effects such as impedance limiting current. This can result in delays in interrupting, or only local damage to the fusible conductors, resulting in extremely long arc times, or the extension of the arc can destroy the fuse and thus leave the fuse open. Risk increases.

  In principle, the use of circuit breakers with trip characteristics is an alternative here, but these switches are considerably more expensive than fuses and are not suitable for all applications for cost reasons .

  The special properties of the fuse mean that there is little room for changing or adjusting the protection range of the fuse.

  It has already been proposed to cut the current conductor of the electric fuse element with the help of a cutting device operated by pyrotechnics so that the application area of the fuse can be adjusted and extended. DE 42 11 079 A1 discloses a pyrotechnic when the current flowing through a fusible conductor and the current detected by a current detection device has an intensity greater than a predetermined threshold. Shows such a solution in which is ignited.

  DE 102 08 047 256 A1 discloses a high-voltage fuse with a controllable drive for a shear rod breaking some bottlenecks. Actuation can be performed from another controller depending on the fault current.

  DE 10 2014 215 279 A1 discloses a fuse for a device to be protected which is connected in series with the fuse.

With regard to the dimensions of the fuse, DE 10 2014 215 279 A1 refers to the fuse integral I ² t. Thus, the melting of the fusible conductor is determined by its material and shape characteristics, and depending on the material and / or shape of the fusible conductor, a respective amount of heat Q is required for evaporation of the fusible conductor.

  If the device protected by the fuse is a surge protection device, this can carry large currents in a short time without tripping the fuse, and at the same time occurs, for example, in the case of damage to the surge protection device, or Special requirements apply because they are also intended to be turned off early in case of short-term fault currents that can occur as follower currents. The first of these requirements often leads to an increase in the rated current value of the fuse. The second of the above requirements can only be achieved with a low nominal current value.

  In view of this problem, DE 10 2014 215 279 A1 discloses a trigger contact in which additional contacts are provided, one of the additional contacts causing, directly or indirectly, the melting of the fusible conductor. The further development of fuses in such a way as to exhibit In addition, the fusible conductor may have a predetermined breaking point in the area of one of the other contacts. In one embodiment, the fusible conductor is at least partially surrounded by a fire extinguishing medium, in particular sand.

  An electric arc is ignited between the additional contact and the fusible conductor, causing current to flow in an auxiliary path parallel to the device to be protected. This parallel path reduces the load on the device to be protected and increases the current load on the fusible conductor. This leads to faster interruption of the current by the fuse. The effect here is similar to that of a known individual short circuit. In contrast to short circuits, the impedance of the path is increased, inter alia, by relatively long arcs bridging the insulation distance between the auxiliary contact and the fusible conductor, and thus the effectiveness of the current increase is still limited . Therefore, it is impossible to guarantee that the fuse is blown under all conditions.

  DE 102013005783 A1 shows a device for generating a safe and low-impedance electrical short circuit independent of the operating voltage. This device is based on two electrical connection parts having different potentials, in particular plate-like connection parts. An insulating part exists between the connecting parts. A short circuit can be achieved by at least partially penetrating or breaking the insulation path.

  According to the solution described above, the connecting parts are closely adjacent and are arranged with the inclusion of insulation. The insulation is designed as an insulating foil or foil-like coating. In addition, a heating mass is present in the immediate vicinity of the insulation and, when energy is applied, releases the heating energy, causing the insulation to melt or deform, thus eliminating the potential gap between the connecting components and the desired A short circuit occurs.

  The device with the internal short-circuit function according to DE 102013005783A1 requires a separate external surge protection device arranged to break the short circuit.

  From the above, it is an object of the present invention to specify a device which can be connected to the supply network, in particular a further developed safety fuse for low voltage applications for protecting surge protection devices. The safety fuse comprises at least one fusible conductor located between two contacts in a fuse housing, and a short-circuit auxiliary contact having an internal insulation distance to the fusible conductor. The specified safety fuse should be realized in a space-saving and cost-effective manner and have the possibility of tripping short-circuit currents via auxiliary connections or auxiliary contacts. The use of external short-circuitable switches should be omitted.

  The object of the invention is to be solved by a safety fuse according to a combination of the features of claim 1, the dependent claims including at least a suitable configuration and further developments.

  The fuse according to the invention is intended in particular for use in cross branches in combination with surge protection devices. The possibility of active activation of the short-circuit auxiliary path is achieved by destroying the insulation element, in particular the insulation foil, ie by using an exothermic reaction.

  No additional external switching devices are required, since the insulating elements used, in particular the insulating foil, fulfill the electrical requirements for the insulating paths for use in cross branches.

  According to the present invention, a low impedance short circuit of metal between the fusible conductor and the auxiliary contact, and a short circuit with impedance and spark formation can be realized.

  In an embodiment of the invention, the insulating element is protected from thermal damage caused by impulse loading due to heating of the fusible conductor.

  In order to ensure that the short-circuit path of the safety fuse responds under normal function, the requirements for the insulation distance are fulfilled according to the present description without requiring the use of external short-circuitable switches.

  The safety fuse according to the invention can have one or more parallel fusible conductors. The fusible conductor may be surrounded by a fire extinguishing medium in the fuse housing.

  The fusible conductor can have a conventional constriction. Alternatively or additionally, the constriction is modified, i.e. the same, so that a short melting time can be achieved with a small overcurrent, thus resulting in an advantageous reduction in the rated current of a fuse having the same pulse carrying capacity. It is possible to increase the length of the constricted portion of the fusible conductor having a cross section.

  In addition, it is possible to design the safety fuse according to the invention as a triggerable safety fuse, in which the trigger device has a controlled disconnection of the fusible conductor in the event of a fault or overload of the respectively connected device. Work for. In this regard, for example, a portion of the fusible conductor may be formed exposed within the fuse housing, and the mechanical isolation element may be configured to have at least one fusible conductor defined as its fusible integral, depending on the trigger device. Irrespective of mechanical destruction, it can be introduced via access in the housing into a fire-free area.

  Such a separating element can be designed as a blade or cutting edge. It is also possible to drive the separating element in the direction of the fusible conductor by means of a bridge igniter.

  In this regard, the at least one fusible conductor can have a number of known electrical constrictions designed for the rated load of each fuse, as described above. In addition, additional geometric constrictions can be provided that can be cut by tearing when exposed to tensile stress in response to the trigger unit.

  In this regard, briefly summarized, at least one externally actuable switching device for overcoming the insulation distance is provided within the fuse housing of the fuse according to the present invention in order to cause a short circuit involving low impedance or impedance. Designed to.

  The switching device has an insulation element forming an insulation distance, the insulation element undergoing a change of state by the heating activator, the activator being connected to at least one control connection.

  The insulating element can be designed as an insulating foil.

  The exothermic activator can also be realized as a foil, here as a reaction foil, which is connected to an ignition device.

  The heating activator can have a bridge igniter that directly or indirectly destroys the insulating element.

  The bridge igniter can also drive the conductive elements to overcome the insulation distance, thereby creating the desired short circuit.

  The ignition device preferably has an ignition element that heats up when a current flows, the ignition element being connected to at least one control connection.

  A plurality of fusible conductors may be formed parallel to one another in the fuse housing, the plurality of fusible conductors being guided by a disk, the disk being located in the housing and supported by the fuse housing. The switching device can then be located on the disk or on the disk.

  The fusible conductor has a reduced area and / or section in each linear extent. However, the switching device according to the invention is arranged outside these reduced areas and / or sections of the cross section.

  In cylindrical fuse housings, cap-shaped contacts are preferably used at the end faces, the auxiliary short-circuit contacts being guided through one of the cap-shaped contacts. In this case, insulated isolation regions can be formed in the respective caps to form auxiliary contacts. Furthermore, it is also possible to guide at least one control connection via one of the cap-shaped contacts. This can be done via also insulated contact parts, or a bush can be provided to accommodate the control line connection cable.

The invention is explained in more detail below by way of example embodiments and figures.
FIG. 3 shows a top view of a fusible conductor for a capsule fuse having a constriction. FIG. 2 shows a cross-sectional view of a safety fuse with a cap-shaped contact and an integrated switching device. Figure 2 shows a further developed fusible conductor for a capsule fuse having a constriction and an additional surface for arranging a switching device according to the invention. Figure 3 shows a detailed view of the switching device according to the invention in a stacked arrangement, with the fuse housing and the connection cap omitted for clarity. 1 shows an exemplary embodiment of an igniter with ignition elements A; B heated by electric current. A further embodiment of a fuse according to the invention comprising two essentially parallel fusible conductors guided by a disk and having a switching device arranged on the disk is shown in principle in a longitudinal section. I have. In a configuration comprising two fusible conductors, together with a disk for guiding the fusible conductors, having a fuse housing and a cap-like connecting contact, the bridge igniter destroys the insulating element and makes the conductive movable Fig. 3 shows a further embodiment of a fuse according to the invention used as an activator for causing a short-circuit condition by a component, showing the normal state of the switching device before closing. In a configuration comprising two fusible conductors, together with a disk for guiding the fusible conductors, having a fuse housing and a cap-like connecting contact, the bridge igniter destroys the insulating element and makes the conductive movable Fig. 3 shows a further embodiment of a fuse according to the invention used as an activator for causing a short-circuit condition by a component, showing the state of the switching device after closure, i.e. in case of a short-circuit.

  It is known that surge protection devices or elements use spark gaps or varistors, suppressor diodes, gas arresters, capacitors, non-linear resistors, and combinations thereof. These known elements generally have a non-linear response or characteristic. If the surge protection element responds frequently or is overloaded due to overvoltage or overcurrent that is too large or too long, the corresponding surge protection device may gradually deteriorate or be destroyed. is there.

  The causes of such overloads are manifold and are often specific to each type of protection device.

  If a varistor is used as a surge protection element, there is the risk that it will be destroyed for a long time in gradual degradation by very small leakage currents. Known thermal cutting devices are used as protection against such loads.

  Thermal cutting devices can provide sufficient protection within their respective switching capacities for small leakage currents in the range of milliamps to several amps and the nominal voltage range of the varistor. If a varistor is subjected to a pulse current that exceeds its capacity, or a very high current and voltage gradient, the varistor can fail or be beaten. If exposed to transient overvoltages or mains frequency overvoltages for extended periods of time, the varistors may be thermally damaged or defeated after a period of tens of milliseconds. Such a fault condition cannot be controlled by a typical thermal cutting device having a response time of several seconds.

  For this reason, it is known to operate varistors in series with conventional electric fuses or switchgear.

Varistor manufacturers often specify a maximum rated current value for the backup fuse for adequate protection. Conventional safety fuses generally respond at a rated current load that is significantly lower than the theoretical adiabatic fuse integral. However, if a short but large pulse current is applied to the varistor, the load limit of the varistor is already well above the theoretical value of the fuse and thus far above the actual maximum. This means that the backup fuse can be destroyed even with a single pulse value that the varistor can easily pull out. For this reason, varistor manufacturers often recommend the use of larger and stronger fuses. However, this is in case of failure, because although a larger I ^{2 t} load resulting trip too slowly occurs, can lead to significant damage to the device.

  Design the fuse or blower in such a way that the fuse is used in a cross-branch, ie there is no continuous current load, so that the rated current of the fuse can be significantly reduced despite the same pulse carrying capacity. As a result, the scope of protection has already been greatly expanded.

  Fuses with current ratings in the range of less than 100A for passive operation cannot provide full protection of the surge protector. When considering fire or arc hazards, currents from a few milliamps up to the maximum short-circuit current must be safely and quickly interrupted or short-circuited. The driving mains voltage may even be higher than the mains voltage. The aforementioned problems are often circumvented or solved by a combination of different protection devices. However, some combinations of protection devices require functional adjustment and require additional space. If the protection device is active outside its switching capacity or if two different protection devices respond simultaneously, it is often not possible to safely eliminate the danger to the environment.

  For this reason, the use of triggerable fuses has already been proposed. In order to ensure that the fuse has the highest possible insulation strength after shutdown, arcing is required at several narrow points that typically occur in short-circuit current shutdowns. This can be achieved in a device with a suitable short circuit by means of a known fuse with an auxiliary connection for short-circuiting the device to be protected.

  According to an example embodiment, the proposed solution is based on one or more parallel fusible conductors, preferably arranged in a fire-extinguishing medium. The fusible conductor has narrow points in series, the number corresponding to the usual design of the corresponding rated voltage of the fuse.

  The fuse according to the invention has a third connection through which a short-circuit current guided radially or axially to the outside can flow. A switching device according to the invention, which can be operated actively and optionally also passively, is located inside the fuse.

  This switching device meets the requirements regarding insulation strength for use in cross-branches. The insulation strength corresponds at least to the protection level of the arrester to be protected in normal operation.

  The switching device is preferably designed in such a way that a metal short circuit is realized between the auxiliary connection and the main fusible conductor.

  According to a first embodiment, the switch is designed for a short reaction time as a short circuit, based on the use of an exothermic reaction foil or a bridge igniter. The approaches of these solutions minimize the effort and energy demands for operation.

  If parallel fusible conductors are used, an internal shorting bridge allows the use of a single switch. The shorting bridge may have a low impedance or may include an impedance.

  The highest requirement for the short-circuit carrying capacity of the short-circuit auxiliary contact when used with a surge protector relates to the required pulse carrying capacity of the fusible conductor, where the blowing of the fuse in the fusible conductor is not achieved.

  The size of the fusible conductor also determines the time / current characteristics. The auxiliary contacts of the fuse, and thus the entire short-circuit path, also have a current carrying capacity which satisfies this characteristic curve at least in the range of the expected short-circuit current.

  The pulse current load of the varistor based arrester is lower than the pulse current load of the spark gap based arrester. In general, a maximum load of 100 kA 10/350 μs is achieved with the lightning rod. This implies a load of 25 kA 10/350 μs for each spark gap in a conventional AC network. The fusible conductor of the fuse must meet the above requirements for the above applications.

  In a standard NH fuse, this requirement roughly corresponds to a fuse with a rated current of 315A. With respect to the rated voltage of the fuse, the voltage is selected within the range of the coupling voltage of the network in which the arrester is used. This makes the fuse suitable for a voltage of 400 V in a standard 230/400 V mains supply.

  When a short circuit that turns off the fuse occurs, it is advantageous to lower the rated current of the fuse or to design a flat time / current characteristic. This can improve selectivity to the upstream surge protection device, especially with limited short-circuit current. In addition, arc erosion between the fusible conductor and the auxiliary contact can be used to achieve a sufficient separation distance faster, especially at low currents.

  FIG. 1 shows a conventional fusible conductor for a safety fuse designed as a strip-shaped fusible conductor 1 with a constriction 2 which leads to a reduction in area or cross section in the corresponding area.

  The constriction 2 shown in principle by FIG. 1 is already longer in the longitudinal direction of the fusible conductor 1 compared to the known constriction. This results in an advantageous reduction in the rated current of a fuse having the same pulse carrying capacity.

  Next, FIG. 2 shows a longitudinal section of a safety fuse having a fuse housing 6 and a cap-shaped connection contact 9. An externally operable switching device according to the invention is arranged in the fuse housing 6.

  The fusible conductor 1 shown shows the constriction 2 already described in a part of its longitudinal extension.

  In the portion of the fusible conductor 1 not occupied by the constriction, one auxiliary short-circuiting contact 3 is located below the fusible conductor and another auxiliary short-circuiting contact 3 is located above the fusible conductor 1. I have.

  Further, a sandwich structure composed of an insulating foil 4 and an exothermic reaction foil 5 is arranged inside the housing 6 of the fuse.

  The exothermic reaction foil 5 is connected to an ignition device 7 that can be controlled via one or more control lines 8. In addition, a passive ignition possibility (not shown) may be provided.

  In the case shown in FIG. 2, the ignition takes place by means of an ignition element which is overloaded at low current intensities and forms an arc (see FIG. 4b). Ignition can be provided by a flashover in the spark gap, a transformer, or the like, or can be provided by a thermal heating circuit.

  The externally accessible part of the short-circuit auxiliary contact 3 is located on the wall part of the housing 6, but as shown in FIGS. 6a and 6b, in the area of one of the connection caps 9 And may be drawn out insulated.

  The switching device according to FIG. 2 above the fusible conductor 1 envisages a reaction foil 5 in almost direct contact with the fusible conductor 1. This arrangement ensures that the reaction foil 5 does not operate unintentionally or is damaged when the fusible conductor 1 is heated during an impulse load.

  If this is not possible due to the load or the given design, or is only possible to a limited extent, using a typical arrangement below the fusible conductor 1 with a conductive component 10 that also optionally includes impedance , An excessive temperature load can be avoided.

  The insulating foil 4 is dimensioned in such a way that the normal function of the mains operating voltage and surge protection does not cause a flashover due to a catastrophic discharge. Short-term temperature loads, such as, for example, impulse loads, do not cause thermal damage to the insulating foil and thus do not initiate an exothermic reaction. However, at higher loads, and thus higher or longer temperature rises, ignition is certainly desired. For this purpose, the stack arrangement "insulating foil-reaction foil" can be exchanged.

  In order to reduce the thermal load on the insulating foil 4 when arranged according to FIG. 2 above the fusible conductor 1, the foil 4 is placed in the area of the unreduced cross section of the fusible conductor (as shown). Can be applied. However, the fusible conductor can also have additional cooling surfaces, for example in the form of extensions.

  Furthermore, it is possible to arrange between the fusible conductor and the insulating foil further materials forming a thermal barrier.

  FIG. 3 shows a strip-shaped fusible conductor 1 having a constriction 2 similar to that of FIG.

  The further developed fusible conductor 1 has a region enlarged portion 11. This makes it possible in this region 11 to fix the switching device according to the invention to the fusible conductor.

  FIG. 4a shows a side view of the fusible conductor 1 with the switching device according to the invention without the fuse housing and the connection cap.

  As shown in FIG. 4a, the switching device is designed as a stacked arrangement.

  In this case, the reaction foil 5 is arranged above the insulating foil 4 and is connected in a suitable manner by an ignition device 7 triggered via a connection 8.

  The arrangement of the element 10 between the fusible conductor 1 and the insulating foil 4 protects the insulating foil 4 from thermal overload.

  In addition, a minimum gap range 12 can be provided between the fusible conductor 1 and the insulating foil 4 or the component 10. The design of the gap range may be such that the gap range 12 is passively arced when the switch is activated.

  The embodiment according to FIG. 4 a also makes it possible in principle to arrange the switching device in the immediate vicinity of one of the constrictions 2.

  FIG. 4b shows in a different view a variant of the design of the ignition device with the ignition element A or B.

  The ignition element A can be realized, for example, as a soluble conductor by printing on a printed circuit board. In the lower view of FIG. 4b, the ignition element B is arranged as a wire in a cutout of the printed circuit board and is heated when an electric current flows, so that an exothermic reaction of the reaction foil can be started.

  The variant shown in FIG. 4b with the arrangement and configuration of the ignition device 7 on a printed circuit board allows a very simple integration in a preferred sandwich structure of the switch device according to the invention.

  The diagram according to FIG. 5 assumes a safety fuse with a housing 6 and a cap-shaped contact 9, in which two parallel fusible conductors 1 are present.

  The fusible conductor 1 is guided through a common disc 13 made of a material having good conductivity or impedance. The disc 13 is in contact with the inner wall of the fuse housing 6.

  The switching device according to the present invention is arranged on the disk 13 or is arranged on the disk 13.

  When the switching device is closed, current flows through both fusible conductors 1 to the auxiliary contacts 3.

  In the case of high-impedance materials, an additional arc can occur in the feedthrough area between the disc 13 and the fusible conductor 1, especially when the material is mounted in a small area. May increase damage. The disk 13 may be made of metal, but may be made of conductive ceramic or graphite.

  In addition to the switching device with the exothermic reaction foil in a sandwich arrangement, a switching device using a bridge igniter is also possible, as shown in FIGS. 6a and 6b.

  If a bridge igniter 17 is used, gas expansion due to heating upon ignition is used to bring the metal part 16 into contact with the fusible conductor 1 or the disk 13.

  In this case, the metal part 16 bridges the distance to the auxiliary contact 3 or through the insulating foil between the parts mentioned above.

  6a and 6b show the foil insulator 14 in this regard.

  In the fuses shown in FIGS. 6 a and 6 b, the auxiliary contact 3 and the control line 8 can be inserted axially through one of the connection caps 9.

  For example, the auxiliary contact 3 is electrically insulated from the cap 9 by the insulating component 15. Inside the fuse, there is an area near the disk 13 that is not filled with the extinguishing agent. In this area, an insulating foil 14 insulated from the disk 13 by the auxiliary contact 3 is attached.

  In the area of the auxiliary contact 3, the above-described movable part 16 in which the electric bridge igniter is arranged as an actuator 17 is incorporated.

  In operation, part 16 moves in the direction of wheel 14 and disc 13. Thereby, the insulating foil 14 is destroyed.

  In this regard, not only the component 13, ie, the disk, but also the conductive component 16, can be provided with a notching device in order to cut the insulating foil 14 quickly and safely.

  The movement of the component 16 stops on the disk 13. The disk 13 is conductively connected to the auxiliary connection part 3 via the metal part 16. This connection can be supported as a positive connection. Further improvements in the connection are possible if the targeted deformation of the metal part 16 occurs or is supported.

  The current carrying capacity of this embodiment follows the desired time / current characteristics and fuse for short circuit current.

  FIG. 6a shows the normal state of the switching device and the fuse before the short circuit, and FIG. 6b shows the state of the switch or the switching device in the case of a short circuit.

  However, it is also possible to operate the switching device using shape memory alloys or other materials that change shape, configuration or volume.

  If the fuse is activated by a shape memory alloy or a bridge igniter or a reaction foil in connection with a short circuit, this can be done via a proportional current. This current can be generated from an adjacent grid or another energy storage device. However, in a bridge igniter, it is also possible to provide the required energy in a manner that is electrically separated by a transformer.

Claims (11)

Consisting of at least one fusible conductor located between the two contacts and arranged in the fuse housing, and a short-circuit auxiliary contact having an internal insulation distance with respect to the fusible conductor, connectable to a supply network Safety fuses for low voltage applications to protect sensitive devices, especially surge protection devices such as spark gaps or varistors,
An externally operable switching device for overcoming the insulation distance is formed in the fuse housing to create a low impedance or short circuit including impedance, the switching device forming the insulation distance. A safety fuse, characterized in that the activator has an insulating element that undergoes a state change in the external activator, said activator being connected to at least one control connection.   2. The safety fuse according to claim 1, wherein the insulating element is designed as an insulating foil.   3. The safety fuse according to claim 1, wherein the exothermic activator is formed as a reaction foil connected to the ignition device.   The safety fuse according to claim 1 or 2, wherein the heating activator comprises a bridge igniter that directly or indirectly destroys the insulating element.   The safety fuse of claim 4, wherein the bridge igniter drives a conductive element to overcome the insulation distance.   The ignition device has an ignition element (A; B) that heats when a current flows, and the ignition element (A; B) is connected to the control connection (8). The safety fuse according to claim 3.   A plurality of fusible conductors (1) are formed in parallel with each other in the fuse housing (6), and the plurality of fusible conductors (1) are guided by a disk supported in the fuse housing (6). 7. The safety fuse according to claim 1, wherein the switching device is arranged on the disk (13) or on the disk (13).   The fusible conductor (1) has a reduced area and / or a reduced cross section in each of its length ranges, and the switching device is reduced on the front and / or cross section side. The safety fuse according to any one of claims 1 to 7, wherein the safety fuse is located at a portion where the safety fuse is not provided.   9. A safety fuse according to any one of the preceding claims, characterized in that it is arranged in a cross-branch associated with a surge protection device.   In the case of a substantially cylindrical housing (6) having a cap-shaped contact (9) on the end face, the short-circuit auxiliary contact (3) extends beyond one of the cap-shaped contacts (9). The safety fuse according to claim 1, wherein the safety fuse is guided.   A safety fuse according to claim 10, wherein the at least one control connection (8) is guided via one of the cap-shaped contacts (9).

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