EP3347911B1 - Load current-carrying fuse comprising an internal switching element - Google Patents

Description

Electrical loads must be secured.

Depending on the type of supply network and depending on the type of load different security elements are used.

The separation is a major problem, especially in DC networks, since, in contrast to alternating current networks, there are no periodic zero crossings, so that possible switching arcs do not easily go out.

For example, from the international patent application WO 2014/065 763 A2 a fuse is known in which a fuse wire is caused by a targeted heating of the neighborhood for melting.

In the past, therefore, many types of fuses have been designed with ingenious arc suppression techniques.

Previous fuses are designed to switch when overcurrent.

However, there is an increasing demand for fuse elements that can be reliably triggered even with a moderate current.

For example, shows the German patent DE 10 2014 215 282 B3 a combined surge protection device with an integrated spark gap and with a series-connected fuse.

Previous fuses switch off reliably only at greatly increased currents. This is due to the triggering behavior. If, in the case of previous fuses, the protection level is set too low, the fuse will trip even in the event of temporary overcurrent, eg when charging capacitive loads or when switching on motors. Therefore, previous backups in terms of overcurrent are rather generous (over-) dimensioned.

On the other hand, there are more and more applications in which there is a continuous slight overload, which is dangerous, but is not recognized as overcurrent.

For networks with limited short circuit currents, e.g. PV systems, where the operating current is only about 10% below the short-circuit current, the currents in a short circuit are so low that normal fuses do not trigger.

In the case of PV and wind power plants, it is aggravating that the currents in part-load operation (for example, light cloud cover, moderate wind) are so far below the maximum current of the system that a short-circuit current then occurring is within the range and below the rated current value of the corresponding fuse.

Object of the invention

It would therefore be desirable to be able to provide a cost-effective load current-carrying fuse, which can allow a reliable turn-off in the said case.

Brief description of the invention

The object is achieved by a load current-carrying fuse with internal switching element. The load-carrying fuse has a protective element, wherein the protective element has a first connection for connection to a first potential of a supply network and a second connection, which can be connected via a device to be protected with a second potential of the supply network. The protective element has a fusible conductor, which connects the first terminal and the second terminal of the protective element, wherein the protective element further comprises a third terminal, which is connectable to the second potential of the supply network and which is adjacent, but electrically isolated to the fusible conductor. The fusible conductor has a constriction in the region of the adjacent connection, wherein the constriction is configured in this way in that the fusible conductor has an electrically conductive flux in the region of the constriction, the flux having a lower softening point than the fusible conductor itself. The fuse element further comprises an internal switching element which internally monitors the protection element and can effect a selective turn-off, the internal switching element being a voltage-sensitive element connected to one terminal to the first terminal and having another terminal adjacent to the overvoltage-sensitive element, but is electrically isolated from the fusible conductor and adjacent but electrically isolated from the third terminal.

Further advantageous embodiments of the invention are specified in the subclaims and the description.

Brief description of the drawings

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

Fig. 1

eine erfindungsgemäße aststromtragende Sicherung mit internem Schaltelement in einer schematischen Darstellung,

Fig. 2a

einen Aspekt der Erfindung,

Fig. 2b

einen weiteren Aspekt der Erfindung,

Fig. 3

noch einen weiteren Aspekt der Erfindung, und

Fig. 4

einen beispielhaften Aufbau von Kontakten und Schmelzleitern gemäß Ausführungsformen der Erfindung.

It shows

Fig. 1

an inventive current-carrying fuse with internal switching element in a schematic representation,

Fig. 2a

an aspect of the invention,

Fig. 2b

another aspect of the invention,

Fig. 3

Yet another aspect of the invention, and

Fig. 4

an exemplary structure of contacts and fuse conductors according to embodiments of the invention.

Detailed description

Hereinafter, the invention will be illustrated in more detail with reference to the figure. It should be noted that different aspects are described, which can be used individually or in combination. That Any aspect may be used with different embodiments of the invention unless explicitly illustrated as a mere alternative.

Furthermore, in the following, for the sake of simplicity, usually only one entity will be referred to. Unless explicitly stated, however, the invention may also have several of the entities concerned. As such, the use of the words "a," "an" and "an" is to be understood merely as an indication that at least one entity is used in a simple embodiment.

Although reference is made in the following to phases N, L of an alternating voltage network, the invention is not limited thereto but can be used in any configuration of an electrical supply network, be it a direct current network, a single-phase or multi-phase alternating voltage network.

In the most general form, a load current-carrying fuse 1 according to the invention with an internal switching element has a protective element F.

The protection element F has a first connection FA1 for connection to a first potential L of a supply network and a second connection FA2, which can be connected via a device Z to be protected to a second potential N of the supply network.

Although reference is now made in the description to a device Z to be protected, this does not necessarily mean an electrical load. Likewise, the device to be protected could also be a power generating device, such as a power plant. be a wind turbine or a solar system.

The protective element F has a fuse D, which connects the first terminal FA1 and the second terminal FA2 of the protective element F, wherein the protective element F further comprises a third terminal FA3, which is connectable to the second potential N of the supply network and the adjacent, but is electrically isolated from the fusible conductor D, wherein the fusible conductor D in the region of the adjacent terminal FA3 has a constriction E, wherein the constriction is configured so that the fusible conductor D in the constriction E a having electrically conductive flux SM, wherein the flux SM has a lower softening point than the fusible conductor D itself.

The load-carrying fuse further has an internal switching element that monitors the protection element F internally and can bring about a targeted shutdown, wherein the internal switching element is a voltage-sensitive element TVS, which is connected to a terminal to the first terminal FA1, and another terminal FA4 of the overvoltage-sensitive element TVS adjacent, but electrically isolated to the fusible conductor D and adjacent, but electrically isolated to the third terminal FA3 is arranged.

By means of the design of the bottleneck, the load-carrying fuse 1 can be designed so that even longer-term overcurrents lead to a safe separation.

If the overcurrent is very high, as in the case of a short circuit, the fuse element in the region of the constriction E will immediately melt and thus trigger.

That the constriction E is thermally overloaded so that the fusible conductor melts at the constriction E and an arc arises, which in turn commutes to the third supplied port FA3 in the vicinity of the constriction E, so that the device to be protected Z is relieved of electricity, the current deletes and the device to be protected Z has disconnected from the network. Thus, the device Z to be protected is relieved of the deletion integral of the protective element F and finally isolated safely isolated from the network.

In the second case of overloading, the amount of overload of the device Z to be protected is in a range in which the device Z to be protected is not destroyed directly, but a change in its electrical properties is to be expected.

For this purpose, the fusible conductor D in the region of the bottleneck on an electrically conductive flux SM. The electrically conductive flux SM diffuses when heated in the Schmelzeiter and reduces its conductivity. Since the electrically conductive flux SM is arranged in the region of the bottleneck, due to the fact that there is now a higher electrical resistance, a correspondingly faster heating is to be expected here.

This technique allows an improved triggering of the protective element F. By suitable dimensioning, choice of material and geometry of the bottleneck as well as a targeted influencing of the exposure time of the temperature, the aging process of the bottleneck E can be suitably adjusted.

That The aging of the constriction E can be used specifically to bring the fuse with low long-lasting overcurrents to trigger.

On the other hand, another triggering option is available via the internal switching element TVS. In this case, the voltage across the fuse element D is evaluated. This results in a conclusion about the current flowing through the fuse element D. If the voltage has reached the characteristic voltage for switching the voltage-sensitive element TVS, an ignition occurs in the region of the bottleneck E, analogously to the case of the overcurrent.

That By means of a suitable selection of the switching voltage, influence on the switching point can be made as before. Thus, overcurrents, which have not yet led to tripping in classic fuse elements, can be used for switching.

As a result, the protection levels can be further reduced without endangering plant availability.

In an advantageous embodiment, which in the FIGS. 2a and 2b is shown, the fusible conductor, at least in the region of the narrowed E - as in Fig. 2a shown - a perforation (or perforation series) P or - as in FIG. 2b shown - several perforations P (or perforation rows) P on. Of course, at other points on the Schmelzeiter D corresponding perforations may be arranged, such as from FIG. 2a seen. The structure of the perforation P is only exemplary circular. It can also assume other forms.

Particularly advantageously, the cage E can have a perforation in which the flux SM is located. As a result, the process of diffusing into the melt conductor D can be accelerated. The in-diffusion leads to a change in the electrical resistance (increase), so that the heat conversion increases locally and favors an early separation.

In the illustration 1 the voltage-sensitive element is shown as Transient Voltage Suppressor Diode (TVS). However, the invention is not on this limited and it can be used any form of a voltage-sensitive element, in particular other electrical / electronic components, such as a thermally non-linearly-variable resistor, such as a NTC (Negative Temperature Coefficient Thermistor) or a PTC (Positive Temperature Coefficient Thermistor) , a suppressor diode, or a gas discharge or even bimetal switch. Of course, these elements may also be provided in any suitable parallel or series connection.

In Figure 3 a further aspect of the invention is shown. Here, in addition to the internal switching element TVS, a time-delaying device is integrated (dead time), which is provided with respect to the internal switching element TVS, for example by low-pass-forming elements, for example a resistor R and a capacitor C.

This may be e.g. Load peaks are intercepted by switching on motors or when loading capacitive loads, i. the currents go back so far within the dead time that the triggering condition no longer exists.

Preferably, the load-carrying fuse 1 is arranged in a pressure-resistant and / or insulating housing.

Although an ignition between the third terminal FA3 and the fusible conductor D is possible with small short-circuit currents, it may happen that the arc then burning is unstable. That it could come to a case in which the arc extinguished without the fusible conductor would be completely interrupted.

The fusible conductor is then often only in a partial area, namely the part which is closest to the third terminal FA3 - i. usually at the bottleneck E - melted. More distant areas are preserved, since the arc can not stably burn until there, due to the increasing length.

This behavior can be explained, in particular in the case of AC networks, by the fact that, with the low short-circuit current values, the energy for melting the fusible conductor D can not be applied within one half-wave.

In order to allow a more stable burning of the arc, especially in AC, a surface approximation of the fuse element D to the third Connection FA3 proposed. As a result, it is first of all ensured that there is a defined distance to the third connection FA3 on the complete width of the fusible conductor D.

In Figure 4 For this purpose, another aspect according to an embodiment is shown.

Here, the fuse element D and the third terminal FA3 of the fuse element in the normal operating state are electrically separated by an insulating material ISO, wherein the third terminal and the insulating material ISO are arranged such that an ignition adjacent to the insulating material ISO to an at least superficial degradation of the insulating material ISO, in such a way that the surface loses its insulating property and allows a current flow between the fuse element D and the third terminal FA3.

Here, the melting time D (shown with longitudinal hatching) without bottleneck E is shown. The fuse wire D is separated from the third terminal FA 3 (shown by oblique hatching) by an insulating material ISO (shown as a white layer). Furthermore, a fourth connection FA4 (illustrated with cross-hatching) is provided, wherein the third contact and the fourth contact FA4 can in turn be separated by an (identical or different) insulating material ISO. The sequence of the fourth contact FA4 and the third contact FA3 may also be chosen differently, i. also the fourth contact FA4 can be arranged adjacent to the fuse element D. The different contacts FA3, FA4 and the fusible conductor D may be made of thin metal foils or plates, for example. The different elements can be embedded in an insulating border (shown in dotted lines).

In the case of triggering by means of the third terminal FA3 or the fourth terminal FA4 (if present), an arc occurs towards the fuse element D, which damages the insulating material ISO (between D and FA3) in the vicinity, so that it now opens Because of its low CTI value (CTI value of FR4 eg about 150 V) and the (local superficial) degradation caused by the arc (eg sooting, charring) now leads to a (small) arc is maintained further (resp. in an AC operation, even after a zero crossing of the phase again re-ignites), which virtually eats away from the point of origin along the interface (in both directions), so that at the end of the fuse element D is separated.

Although here an ignition between FA4 and FA3 is assumed, any ignition, i. also lead an ignition of FA4 to the fuse element D to a corresponding (superficial) degradation of the (previously) insulating material ISO.

In this case, the insulating material ISO a plastic or a composite material with low CTI value, for example, phenolic resin (PF resins), polyetheretherketone (PEEK), polyimide (PI), epoxy resin-filled glass fiber composites such as FR4 or the like. CTI values - also known as tracking resistance - are determined according to IEC 60112, for example. Exemplary materials are assigned to the insulating group IIIa and / or insulating group IIIb.

LIST OF REFERENCE NUMBERS

Load current carrying fuse 1 Protected device Z protection element F device connection ZA1, ZA2 Protection element connection FA1, FA2, FA3, FA4 potential L, N fuse element D bottleneck e flux SM overvoltage-sensitive element TVS insulating material ISO

Claims (8)

1. A load current-bearing fuse with internal switch element having

   • a protective element (F),

   • wherein the protective element (F) has a first contact (FA1) for connecting to a first potential (L) of a supply network and a second contact (FA2) that configured to be connected via a device to be protected (Z) to a second potential (N) of the supply network,

   • wherein the protective element (F) has at least one fuse element (D) that connects the first contact (FA1) and the second contact (FA2),

   • wherein the protective element (F) has a third contact (FA3) configured to be connected to the second potential (N) of the supply network and is arranged so as to be adjacent to, but electrically insulated from, the fuse element (D),

   • wherein the fuse element (D) has a constriction (E) in the proximity of the third contact (FA3), with the constriction (E) being embodied such that the fuse element (D) has an electrically conductive fluxing agent (SM) in the proximity of the constriction (E),

   • wherein the fluxing agent (SM) has a lower fusion point than the fuse element (D) itself,

   • wherein the load current-bearing fuse further comprises an internal switch element that monitors the protective element (F) internally and provides a targeted disconnection,

   • wherein the internal switch element (TVS) is connected with an contact thereof to the first contact (FA1), and wherein another contact (FA4) of the internal switch element (TVS) is so as to be adjacent to, but electrically insulated from, the third contact (FA3),

   • with the internal switch element comprising a voltage-sensitive element or a bimetallic switch or a non-linear thermal varying resistor, or a gas discharge tube or a parallel or series connection thereof.
2. Load current-bearing fuse according to claim 1, wherein the constriction (E) has a perforation in which the fluxing agent (SM) is located.
3. Load current-bearing fuse according to one of the preceding claims, wherein in addition to the internal switch element, a time-delaying device is integrated upstream to the voltage-sensitive element (TVS).
4. Load current-bearing fuse according to one of the preceding claims, wherein the internal switch element (TVS) is arranged in a pressure-tight housing.
5. Load current-bearing fuse according to claim 5, characterized in that the fuse element (D) and the third contact (FA3) are electrically separated in the normal operating state by an insulating material (POM), whereby the third contact (FA3) and the insulating material (ISO) are arranged such that an ignition near the insulating material (ISO) results in an at least superficial degradation of the insulating material (ISO), such that a surface thereof loses its insulating property and allows current to flow between the fuse element (D) and the third contact (FA3).
6. Load current-bearing fuse according to claim 5, characterized in that the insulating material (ISO) comprises a plastic or a composite material with a low CTI value.
7. Load current-bearing fuse according to claim 6, characterized in that the insulating material (ISO) comprises polyether ether ketone (PEEK), polyimide (PI), or epoxy resin-filled glass fiber composite materials.
8. Load current-bearing fuse according to claim 6, characterized in that the insulating material (ISO) comprises FR4.

Images