Arrangement for electrical monitoring of the switching state of a fuse

Abstract

Arrangement (1) for electrical monitoring of the switching state of a fuse, - with a fuse to be monitored (10), - with a signal generator (20) which is electrically connected in parallel to the fuse (10) and is arranged outside the fuse (10) and has a firing pin indicator (21, 22); - with a sensor element (23) which has a functional connection with a striker pin (22) of the signal transmitter (20), - wherein the signal generator (20) has an internal resistance that is significantly higher than the internal resistance of the fuse (10), so that in the energized state the operating current of the signal generator (20) is significantly lower than the operating current of the fuse (10), - wherein the signal generator (20) is designed as a fuse, characterized in that - the arrangement (1) includes a fuse holder (26) in which the signal transmitter (20) is received and held, and - the sensor element (23) is attached to the fuse holder (26).

Description

[0001] The invention relates to an arrangement for electrically monitoring the switching state of a fuse, for example a semiconductor protection fuse, so-called HLS fuse, a power converter fuse or a low-voltage high-performance fuse, so-called NH fuse.

[0002] Conductors carrying an electric current heat up. Excessively high currents can lead to excessive heating of the conductor and, consequently, melting of the surrounding insulation. This can ultimately result in a cable fire. To prevent this fire hazard, an excessively high electric current, i.e., an overload current or a short circuit, must be interrupted in a timely manner. This is ensured by a so-called overcurrent protection device.

[0003] One possible embodiment of such an overcurrent protection device is a fuse, which interrupts the circuit by melting one or more fusible links when the current in the circuit protected by the fuse exceeds a certain value for a specific period of time. The fuse consists of an insulating body and has at least two electrical terminals that are electrically connected inside the insulating body by a fusible link. Alternatively, multiple fusible links can be used. The fusible link, which has a reduced cross-section compared to the other conductors in the circuit, is heated by the current flowing through it and melts when the relevant rated current of the fuse is significantly exceeded for a predetermined period.

[0004] Fuses are available in various designs. Besides simple appliance fuses, which consist of a simple glass cylinder containing the fusible link, there are also designs where the fuse body is filled with sand – usually quartz sand. In such a sand-filled fuse, the fusible link is surrounded by quartz sand. Due to its good insulating properties, ceramic is most commonly used as the material for the fuse body. The solidified sand, the electrical connections, and the fusible link are all contained within the fuse body. The sand acts as an arc-quenching medium: if the rated current of the fuse is significantly exceeded – for example, due to a high short-circuit current – ​​the fuse will trip, causing the fusible link to first melt and then vaporize due to the high temperature.This process creates an electrically conductive plasma, which initially maintains the current flow between the electrical terminals – an electric arc is formed. As the metal vapor from the vaporized fuse condenses on the surface of the quartz sand grains, the arc cools down. Consequently, the resistance inside the fuse increases to such an extent that the arc finally extinguishes. The electrical circuit protected by the fuse is thus interrupted.

[0005] From the prior art, fuse links such as low-voltage high-performance fuses (NH fuses) and semiconductor protection fuses (HLS fuses), such as those sold under the product name SITOR, are in principle already known - for example from the German patent applications DE 10 2014 205 871 A1, DE 10 2012 210 292 A1 or DE 10 2012 202 059 A1.

[0006] NH fuses typically use one or more fusible links in the form of copper strips. Each of these fusible links has so-called constriction rows for selectively tripping the fuse. Furthermore, at least one or more of the fusible links may have a solder deposit applied to them, which influences the overload characteristics of the fuse: If the fusible link heats up to a temperature above the melting point of the solder due to an electrical overload current, the solder diffuses into the fusible link material and forms an alloy with it. This increases the electrical resistance of the fusible link, leading to further heating. The diffusion process is accelerated until the fusible link in the vicinity of the solder deposit is completely dissolved. When this occurs, the fusible link breaks, interrupting the current flow.In the case of a brief, permissible overcurrent, the NH fuse does not trip prematurely. However, if a short-circuit current occurs, the fusible link ruptures at the narrowing points. This creates several small, electrically connected arcs simultaneously, whose voltages add up and thus lead to a faster tripping of the fuse. NH fuses are used, for example, to protect systems or control cabinets from fire, such as from overheated connecting cables. The let-through energy value I, which is decisive for the tripping behavior of the fuse, is... 2 The current-limiting time (t) of NH fuses is relatively large, which is why they have a slower response characteristic. Semiconductor protection is therefore generally not feasible with NH fuses.

[0007] Semiconductor protection fuses are typically used to protect high-value components, such as power semiconductors, from the damaging effects of a short circuit. Due to their significantly faster tripping characteristics, semiconductor protection fuses are used, for example, in the rectifier section and the DC link of inverters, as well as in UPS (uninterruptible power supply) systems and soft starters for motors. They are generally characterized by higher power dissipation, which is why silver is most commonly used as the fusible link material.

[0008] Fuses are used, for example, for line protection, semiconductor protection, battery protection, or, in the case of photovoltaic systems, for protecting the respective power grid. Fuses therefore have a tripping characteristic adapted to the specific task and react according to their respective operating curve.

[0009] In many applications, it is desirable to indicate the switching state of the fuse(s). Furthermore, some applications require the switching state to be transmitted to a higher-level location, such as a control room or monitoring station. Some fuse designs incorporate a so-called indicator wire for this purpose. This is usually a wire element that is mechanically pre-tensioned and routed through the sand inside the fuse between the fuse terminals. The first end of this wire is led to one of the terminals and attached there. When the fuse blows, the indicator wire, which carries current parallel to the fuse element, breaks, thus visually signaling the blown state of the fuse at the corresponding terminal. However, this does not yet allow for the direct transmission of the switching state to a monitoring station.For standardized fuse designs, integrated solutions are available, for example, in switchgear. However, this is often not the case for power converter fuses, as these usually require special designs. Furthermore, the fuse's mounting position often makes the arrangement and readability of the indicator more difficult.

[0010] Furthermore, so-called firing pin indicators are known. These are used to transmit the triggered switching state to a higher-level control room. For this purpose, the indicator has a firing pin, which is usually spring-loaded and interacts with the indicator wire in such a way that when the fuse is triggered, the movement of the spring-loaded firing pin acts on a microswitch. The microswitch then electrically transmits the fuse triggering information to a control room or other higher-level location.

[0011] From US patent 4,906,963 A, an arrangement for electrically monitoring the switching state of a fuse is known according to the preamble of the arrangement according to the invention. This arrangement comprises a fuse to be monitored and a signal transmitter, which is electrically connected in parallel to the fuse and arranged outside the fuse, and includes a firing pin indicator. Furthermore, the arrangement includes a sensor element that has a functional connection with the firing pin of the signal transmitter. The signal transmitter is designed as a fuse and has an internal resistance that is significantly higher than the internal resistance of the fuse, so that when energized, the operating current of the signal transmitter, i.e., the electrical current flowing through the signal transmitter, is significantly lower than the operating current of the fuse.

[0012] Similar arrangements for electrically monitoring the switching state of a fuse are also known from publications JP H07 - 296 714 A, CN 201 435 368 Y and US 5,319,344 A.

[0013] Furthermore, external indicator attachments are known for selected fuse designs; these are mounted externally on the fuse body. A microswitch can also be mounted on these indicator attachments to electrically transmit the fuse's tripping. However, the use of such indicator attachments is limited to open designs and accessible mounting positions. Another disadvantage of these indicator attachments is that the fuse being monitored can reach temperatures of up to 200°C during operation, which places a high temperature load on the indicator attachment and thus calls its reliability into question.

[0014] The invention is therefore based on the objective of providing an arrangement for the electrical monitoring of a fuse which overcomes or at least improves upon the disadvantages listed above.

[0015] This problem is solved according to the invention by the arrangement for electrical fuse monitoring according to claim 1. Advantageous embodiments are the subject of the dependent claims.

[0016] The arrangement according to the invention for electrically monitoring the switching state of a fuse comprises a fuse to be monitored and a signal transmitter, which is electrically connected in parallel to the fuse and arranged outside the fuse and includes a firing pin indicator. Furthermore, the arrangement includes a sensor element which has a functional connection with the firing pin of the signal transmitter. The signal transmitter is designed as a fuse and has an internal resistance that is significantly higher than the internal resistance of the fuse, so that when energized, the operating current of the signal transmitter, i.e., the electric current flowing through the signal transmitter, is significantly lower than the operating current of the fuse, i.e., the electric current flowing through the fuse.Furthermore, the arrangement includes a fuse holder in which the signal transmitter is received and held, with the sensor element being attached to the fuse holder.

[0017] The signaling device is located outside the fuse body of the fuse being monitored – specifically, at a distance from the fuse body – and is electrically connected in parallel to the fuse being monitored using suitable electrical cables, i.e., in a manner that protects against earth faults and short circuits. This spatial separation of the fuse and the signaling device allows the signaling device to be protected from the high operating temperatures of the fuse. Furthermore, this arrangement significantly improves the accessibility and visibility of the signaling device.

[0018] Under normal operating conditions in the parallel circuit, the electrical current flowing through the signal transmitter is negligibly small due to its high internal resistance compared to the fuse. This effectively prevents damage to and / or unintended tripping of the signal transmitter. The operating current of the monitored electrical line thus flows almost entirely through the fuse being monitored. If the fuse trips due to an overload or a short circuit, the operating current briefly flows completely through the signal transmitter's indicator wire, causing it to break abruptly.The firing pin, mechanically coupled to the indicator wire, acts on the sensor element in such a way that the firing pin's movement can be transmitted to a control system via the sensor element. This triggering of the signal transmitter, indicated mechanically by the firing pin indicator, electrically transmits the tripping of the fuse, for example, to a control room. The firing pin of the signal transmitter is thus designed to act on the sensor element to generate an electrical signal indicating the switching state of the fuse being monitored.

[0019] Designing the signal transmitter as a fuse has the advantage that an existing fuse can be used as the signal transmitter, eliminating the need to develop and provide special designs for the transmitter. However, this requires that the fuse be of high resistance compared to the fuse being monitored, and that its rated current be significantly lower. This approach significantly reduces the manufacturing and development costs for the signal transmitter, as well as the number of components required.

[0020] If the signal transmitter has the form of a fuse, an existing fuse holder for this type and size can be used for mounting the signal transmitter. In this case, the signal transmitter and fuse holder form a single unit; that is, the signal transmitter is permanently but detachably connected to the fuse holder. This connection can be purely frictional or positive-locking. This offers the advantage that the signal transmitter can be easily replaced after both the monitored fuse and the signal transmitter itself have tripped, by removing the defective signal transmitter from the fuse holder and replacing it with a new, functional one. This significantly simplifies the maintenance of the arrangement according to the invention during operation.

[0021] In an advantageous further development of the arrangement, the fuse to be monitored is a non-signal-capable fuse.

[0022] The term "non-signaling capable" means that, due to the design and / or installation position of the fuse, it is not possible to use a conventional, signaling-capable fuse for the given application. Particularly in these cases, it is advantageous to connect a signal transmitter of the type described above electrically in parallel with the fuse to be monitored using suitable electrical wiring, thus enabling the fuse to signal. This can also be done retroactively, so that an installation with a fuse that was originally non-signaling capable can be made signaling capable.

[0023] In a further advantageous embodiment of the arrangement, the sensor element is designed as a microswitch, a light barrier, or a Hall sensor.

[0024] Microswitches, light barriers, and Hall sensors represent different ways of technically implementing the sensor element to generate an electrical signal from the mechanical movement of the firing pin of the signal transmitter. In the case of a microswitch, the "mechanical connection" between the firing pin and the sensor element is therefore a mechanical connection, while in the case of a light barrier or a Hall sensor, it is a coupling via the photoelectric effect or an electromagnetic field, respectively. The term "mechanical connection" is thus to be interpreted broadly and includes any coupling suitable for generating an electrical signal from the mechanical movement of the firing pin of the signal transmitter.

[0025] In a further advantageous embodiment of the arrangement, the fuse holder is adapted to the rated voltage of the signal transmitter with regard to its voltage resistance.

[0026] By adapting the voltage resistance of the fuse holder to the rated voltage of the signal transmitter, the stability - and thus the reliability of the arrangement - is further improved.

[0027] In a further advantageous embodiment of the arrangement, the fuse to be monitored is designed as a power converter fuse, as a semiconductor protection fuse or as a low-voltage high-performance fuse.

[0028] Converter fuses, semiconductor protection fuses, and low-voltage high-performance fuses are common types of fuses. Particularly in the case of converter fuses and semiconductor protection fuses, the arrangement according to the invention for monitoring the switching state of a fuse can eliminate the need for the development and manufacture of expensive special designs with an integrated signal transmitter. Existing installations can also be retrofitted with the arrangement according to the invention and upgraded with regard to the fuse's signaling capability.

[0029] In a further advantageous embodiment of the arrangement, the fuse to be monitored has a rated voltage of up to 1000 volts (AC) or 1500 volts (DC).

[0030] The term "low voltage" generally refers to a voltage range up to 1000 volts (V) alternating current (AC) or 1500 V direct current (DC). The arrangement according to the invention is therefore particularly suitable for use in the low-voltage range, but also for voltage values ​​up to several thousand volts. Rated currents in this range start at approximately 10 amperes, but can also reach several thousand amperes. Within these voltage and current ranges, fuse types are addressed which, due to their size, are generally not equipped with a conventional indicator or retrofittable with a conventional indicator attachment. The device according to the invention represents a suitable solution for enabling the signaling capability of these fuse types, particularly for voltage values ​​between 400 and 1000 volts and rated currents between 100 and 2400 amperes.

[0031] In a further advantageous embodiment of the arrangement, the internal resistance of the signal transmitter is at least 50 times higher than the internal resistance of the fuse.

[0032] The ratio of internal resistances allows conclusions to be drawn about the operating currents of the fuse or signal transmitter during operation: The larger this ratio, the more likely it is that the operating current flowing through the signal transmitter under normal operating conditions is negligibly small compared to the operating current of the fuse being monitored. This effectively protects the signal transmitter from damage caused by excessive electrical currents.

[0033] In a further advantageous development of the arrangement, the fuse to be monitored and the signal transmitter are combined in a fixed but detachable structural unit.

[0034] If the system is being installed for the first time, this method can significantly reduce the installation costs incurred during the initial setup. In the case of retrofitting an existing installation, i.e., upgrading an already installed fuse to include its alarm capability, only the signaling device would need to be installed. This further reduces the installation effort.

[0035] Two exemplary embodiments of the arrangement for electrically monitoring the switching state of a fuse are explained in more detail below with reference to the accompanying figures. The figures show: Fig. 1 a schematic representation of a first embodiment of the arrangement for electrical monitoring of the switching state of a fuse; Fig. 2 a schematic representation of a second embodiment of the arrangement for electrical monitoring of the switching state of a fuse.

[0036] In the various figures of the drawing, identical parts are always marked with the same reference symbol. This description applies to all figures in the drawing in which the corresponding part is also recognizable.

[0037] In Fig. Figure 1 schematically illustrates a first embodiment of an arrangement 1 for electrically monitoring the switching state of a fuse 10. A power supply network 2 and an electrical load circuit 3 are connected to each other via an electrical line 4. To protect against short circuits or electrical overloads, a fuse 10 is installed in the electrical line 4 to interrupt it if necessary. The fuse 10 to be monitored is a non-signaling fuse, i.e., the fuse 10 either does not have an integrated indicator and / or an indicator attachment due to its size and design, or, if an indicator is present, it is not readable due to the installation position of the fuse 10, or the switching state of the fuse 10 cannot be transmitted to a higher-level location – for example, a control room.For electrical monitoring of the switching state of this fuse 10, the arrangement 1 therefore has a signal transmitter 20, which is electrically connected in parallel to the fuse 10 to be monitored by means of suitable electrical connecting lines 24, e.g. in an earth- and short-circuit-proof installation method.

[0038] Since the fuse 10 being monitored can reach temperatures of up to 200 °C on its outer surface under normal load, i.e., when an electric current less than or equal to its rated current is applied, the signal transmitter 20 is located outside the fuse 10. The distance between the signal transmitter 20 and the fuse 10 is chosen to effectively prevent thermal damage to the signal transmitter 20 due to the high operating temperature of the fuse 10 and, if necessary, to ensure the readability of the signal transmitter 20.

[0039] The signal transmitter 20 is designed as a firing pin indicator and has an indicator wire 21 and a firing pin 22 mechanically coupled to the indicator wire 21. If a trigger criterion for the signal transmitter 20 is present, for example, a short-circuit current, this leads to the breaking of the indicator wire 21, whereupon the firing pin 22, which is mechanically coupled to the indicator wire 21, is actuated. Furthermore, the arrangement 1 has a sensor element 23 in the form of a microswitch, which has a mechanical operative connection with the firing pin 22 of the signal transmitter 20. This means that when the firing pin 22 acts on the microswitch 23, an electrical signal is generated, which is transmitted via an electrical signal line 25, which is connected to the microswitch 23, to a higher-level communication device 30, for example, a control room.

[0040] Regarding the electrical design of the arrangement 1, the signal transmitter 20 has an internal resistance that is significantly higher than the internal resistance of the fuse 10. Therefore, when energized, the rated current of the signal transmitter 20 is significantly lower than the rated current of the fuse 10. This results in a negligible current flowing through the signal transmitter during normal operation, i.e., when the electrical current is below the rated current of the fuse 10. This effectively prevents damage to or tripping of the signal transmitter 20. The operating current of the monitored electrical line 4 thus flows almost entirely through the fuse 10 being monitored. If the fuse 10 trips due to an overload or short circuit current, the operating current briefly flows entirely through the indicator wire 21 of the signal transmitter 20.This immediately triggers the signal transmitter 20, as the indicator wire 21 is abruptly interrupted due to the high electrical current. The firing pin 22, mechanically coupled to the indicator wire 21, acts on the microswitch 23. The movement of the firing pin 22, which indicates the triggering of the signal transmitter 20 – and thus of the monitored fuse 10 – is consequently transmitted by the microswitch 23 via the electrical signal line 25 to the communication device 30, for example, a control system or a control room.

[0041] An existing design of a fuse with a firing pin indicator can also be used as the signal transmitter 20, provided that this design is dimensioned accordingly, i.e. it would have to be a fuse with a correspondingly high resistance compared to the fuse 10 to be monitored, whose rated current is significantly smaller than the rated current of the fuse 10 to be monitored, so that the electric current flowing in the electrical line 4 in the normal operating state flows almost exclusively through the fuse 10 to be monitored.

[0042] Fig. Figure 2 schematically shows a second embodiment of the arrangement 1 for electrically monitoring the switching state of a fuse 10. In contrast to the one in Fig.In the first embodiment shown in Figure 1 and described above, the arrangement 1 additionally includes a fuse holder 26 in which the signal transmitter 20 is received and held. This is particularly advantageous if the signal transmitter 20 has the form of a fuse, so that a fuse holder 26 already existing for this form and size can be used for mounting the signal transmitter 20. The signal transmitter 20 and fuse holder 26 form a single structural unit, i.e., the signal transmitter 20 is permanently but detachably connected to the fuse holder 26. This significantly simplifies the replacement of a signal transmitter 20 triggered by a blown fuse with a new, functional signal transmitter 20.

[0043] Both embodiments share the characteristic that, due to the significantly higher internal resistance of the signal transmitter 20 compared to the fuse 10 being monitored, which is electrically connected in parallel to the fuse 10, the signal transmitter 20 carries hardly any current during normal operation. Only when the circuit is switched off, i.e., when the fuse 10 being monitored trips, is the signal transmitter 20 also immediately triggered due to the now very high current it carries. By implementing a signal transmitter 20 as a fuse that has a firing pin indicator but no separate fusible link, the operating range of the arrangement 1 can be significantly extended to higher voltages. Such firing pin indicator fuses without their own fusible link can be very easily manufactured from standard components already available for corresponding fuses.

[0044] The arrangement 1 according to the invention means that fuse monitoring is no longer limited to specific fuse sizes. Furthermore, the effort required to develop special fuses, which are only manufactured in small quantities due to their application-specific characteristics, is eliminated. A flexible installation design is enabled, eliminating the need for special contacts on the fuse 10 being monitored. Moreover, the arrangement 1 according to the invention achieves a high level of display reliability compared to standard fuses with indicator lights or indicator-based indicator attachments. Particularly with power converter fuses, monitoring over a very wide current / voltage range is possible. Reference symbol list 1 arrangement 2 Energy supply network 3 electrical load circuit 4 electrical lines 10 fuse 20 signal transmitters 21 Identification wire 22 firing pins 23 Sensor element / microswitch 24 connection cable 25 Signal line 26 fuse holders 30 Communication device

Claims

[1] Arrangement (1) for electrical monitoring of the switching state of a fuse, - with a fuse to be monitored (10), - with a signal generator (20) which is electrically connected in parallel to the fuse (10) and arranged outside the fuse (10) and has a firing pin indicator (21, 22); - with a sensor element (23) which has an operative connection with a firing pin (22) of the signal generator (20), - wherein the signal generator (20) has an internal resistance which is significantly higher than the internal resistance of the fuse (10), so that in the energized state the operating current of the signal generator (20) is significantly lower than the operating current of the fuse (10), - wherein the signal generator (20) is designed as a fuse, characterized by , that - the arrangement (1) has a fuse holder (26) in which the signal generator (20) is received and held, and - the sensor element (23) is attached to the fuse holder (26). [2] Arrangement (1) according to claim 1, wherein the fuse (10) to be monitored is a non-detectable fuse. [3] Arrangement (1) according to one of the preceding claims, wherein the sensor element (23) is designed as a microswitch or as a light barrier or as a Hall sensor. [4] Arrangement (1) according to one of the preceding claims, wherein the fuse holder (26) is adapted with regard to its dielectric strength to the rated voltage of the signal generator (20). [5] Arrangement (1) according to one of claims 1 to 4, wherein the fuse (10) to be monitored is designed as a converter fuse, as a semiconductor protection fuse or as a low-voltage high-performance fuse. [6] Arrangement (1) according to one of the preceding claims, wherein the fuse (10) to be monitored has a rated voltage of up to 1000 volts (AC) or 1500 volts (DC). [7] Arrangement (1) according to one of the preceding claims, in which the internal resistance of the signal generator (20) is at least 50 times higher than the internal resistance of the fuse (10). [8] Arrangement (1) according to one of the preceding claims, in which the fuse (10) to be monitored and the signal transmitter (20) are fixedly but detachably combined in a structural unit.

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