Protection device for interrupting an electrical circuit in the event of an overcurrent

Abstract

The invention relates to a protective device (3) for interrupting a circuit in the event of an overcurrent. The protective device (3) has a current path (4; 5) extending through the protective device (3) from an input terminal of the protective device (3) to an output terminal of the protective device (3), wherein the protective device (3) has in the current path (4; 5) a fuse holder for receiving a fuse link (6) comprising a fusible link and a load break switch (7) connected in series with the fuse holder, the load break switch (7) having mechanically switchable contact elements, wherein the load break switch (7) is coupled to a tripping mechanism (8) such that when the tripping mechanism (8) is triggered, the switchable contact elements of the load break switch (7) are disconnected to interrupt the current path (4;5), wherein the protective device (3) comprises an electronic monitoring device (9), wherein the electronic monitoring device (9) comprises a measuring device configured to detect one or more electrical measurements characteristic of the presence of an overcurrent, wherein the electronic monitoring device (9) comprises evaluation electronics configured to detect the occurrence of an overcurrent in the current path (4; 5) based on the electrical measurements detected by the measuring device, and wherein the monitoring device (9) is configured to trigger the tripping mechanism upon detection of the occurrence of an overcurrent in the current path (4; 5) to interrupt the current path (4; 5) by separating the contacting elements.

Description

[0001] The invention relates to a protective device for interrupting an electrical circuit when an overcurrent occurs. An overcurrent can be, for example, a short-circuit current or an overload current. The protective device is, in particular, a protective device for a direct current circuit.

[0002] A wide variety of protective devices for interrupting a current flow or an electrical circuit in the event of an overcurrent are known from the state of the art. For example, DE 10 2011 089 631 A1 describes a circuit breaker for disconnecting an electrical current in the event that, due to an electrical fault, the magnitude of the current or the temporal progression of the current no longer exhibits the desired properties. This circuit breaker is, in particular, a low-voltage circuit breaker.

[0003] Direct current (DC) applications are becoming increasingly important in various economic sectors. In the industrial sector, DC grids are being developed to supply energy to production halls or entire factories. In addition to economic factors, such as energy savings due to the elimination of conversion losses from DC to AC, the technical advantages of DC grids also play a significant role, such as the avoidance of harmonics. As part of the energy transition, DC plays a key role in energy storage systems, where excess energy is buffered so that it can be used during periods of low power production. Another area of ​​application is uninterruptible power supply systems (UPS systems).Due to the ever-increasing energy demand, the corresponding UPS systems are becoming ever larger and the corresponding energy storage devices ever more powerful, so that ever higher currents and / or voltages occur in such UPS systems.

[0004] DC and AC grids with low frequencies are particularly problematic for various reasons when it comes to reliably protecting against overcurrents, especially short-circuit currents, and safely shutting down when an overcurrent occurs. For example, the increasing performance of battery storage systems is leading to a continuous decrease in the internal resistance of the battery cells. In the event of a short circuit, the reduction in internal resistance leads to very high prospective short-circuit currents. Very short lines between the battery and a protective device for interrupting the circuit also ensure very low inductances, resulting in extremely short time constants. These are regularly less than a millisecond and can, in individual cases, be in the range of several microseconds.The low time constants, combined with the high prospective short-circuit currents, lead to very steep current increases in the event of a short circuit. When the corresponding power grid or circuit is protected by a fuse link with a fusible element, also known as a fuse for short, this can result in the current-limiting effect of the fuse link being delayed or not occurring at all in relation to these time constants. As a result, the current flowing at the time the fuse trips can already be so high that the fuse and / or components are overloaded. In addition, due to the low inductance, the amount of energy stored in the protected circuit is insufficient to generate a sufficiently high countervoltage across the switching arc within the fuse link to completely interrupt the short-circuit current.After the fuse element has actually melted, a current may still flow through the arc channel(s) of the melted fuse element for several milliseconds. With alternating current, such arcs may be extinguished automatically by the current crossing zero. The danger posed by arcs is considerably higher with direct current. Therefore, the use of fuses in direct current applications or AC applications with low frequencies is associated with disadvantages. However, fuses also have significant advantages. For example, fuses exhibit fail-safe behavior, meaning they reliably trigger in the event of an overcurrent and generally interrupt the corresponding circuit.A further advantage of fuse links is that arcs and ionizing gases are not released into the environment when the fuse is triggered, but remain encapsulated within the fuse link housing. Compared to semiconductor circuit breakers, which are also used to protect DC networks, fuse links are also significantly more cost-effective.

[0005] The object of the present invention is to provide a protective device for interrupting an electrical circuit when an overcurrent occurs, which utilizes the advantages of the fuse link with a fusible element and overcomes its aforementioned disadvantages.

[0006] This object is achieved by a protective device having the features of patent claim 1. Advantageous embodiments of the protective device are the subject of the dependent claims.

[0007] The protective device according to the invention serves to interrupt an electrical circuit when an overcurrent occurs. The protective device is preferably used in direct current applications. The protective device has a current path that extends through the protective device from an input terminal of the protective device to an output terminal of the protective device. The protective device has a fuse holder in the current path for receiving a fuse link comprising a fusible element and a load-break switch connected in series with the fuse holder and having mechanically switchable contacting elements. The load-break switch is coupled to a tripping mechanism such that, upon tripping of the tripping mechanism, the switchable contacting elements of the load-break switch are separated to interrupt the current path. The protective device has an electronic monitoring device.wherein the electronic monitoring device comprises a measuring device configured to detect one or more electrical measured variables characteristic of the presence of an overcurrent, wherein the electronic monitoring device comprises evaluation electronics configured to detect the occurrence of an overcurrent in the current path based on the electrical measured variable(s) detected by the measuring device, wherein the monitoring device is configured to trigger the triggering mechanism upon detection of the occurrence of an overcurrent in the current path to interrupt the current path by separating the contacting elements.

[0008] Due to the inventive design, the disadvantages of fuses mentioned above are less or not at all significant in DC applications, since the current path of the protective device is reliably interrupted by opening the switch-disconnector. A further advantage of using the switch-disconnector is that the disconnection point created by the triggered fuse link generally does not meet the requirements for safe isolation, whereas the opened switch-disconnector does. The advantage of using the fuse link is that the current path is reliably interrupted and / or the current flowing through the current path is at least significantly reduced due to the triggered fuse, in order to protect downstream devices and / or persons.By combining the switch-disconnector with the series-connected fuse holder, the switch-disconnector and the tripping mechanism coupled to it do not need to have particularly fast switching characteristics, so the corresponding components can be designed relatively simply. This has a positive effect on the manufacturing costs of the protective device. The particular advantage of the protective device according to the invention compared to a circuit breaker is that the main task of the switching process is still performed by the fuse link. The contacting elements and any other elements for contacting and separating the contacting elements of the switch-disconnector can thus be designed more simply, since, in particular, no particularly high currents need to be switched, since the current intensity is already reduced by the melting of the fuse link.Because the fuse link is connected in series with the load-break switch, a particularly high level of safety is guaranteed should the load-break switch and / or the monitoring device and / or the tripping mechanism malfunction for any reason. This means that system and personnel protection are still ensured to a high degree due to the generally very reliable tripping of the fuse link, even if the load-break switch fails to open.

[0009] Another advantage is that in the event of a short circuit, only the fuse link needs to be replaced to restore the reliable function of the protective device.

[0010] An overcurrent occurs in particular when the fuse link's tripping current causes the fuse element to melt and thus the fuse link to trip. It is conceivable that the tripping current could be exceeded briefly without the fuse element melting. The fuse link's tripping time generally depends on the extent to which the tripping current is exceeded. The tripping current and the tripping time of the fuse link depend on the fuse link's tripping characteristics. The tripping current is usually several times the rated current of the circuit to be protected. Preferably, the tripping current is at least 1.05 times the rated current of the circuit to be protected.

[0011] A fast tripping characteristic of the protective device can be achieved, particularly in DC applications, by using fuse links with the corresponding fast characteristic, for example fuses of the following operating classes: ar fuse, gr fuse, aBat fuse, gBat fuse or gS fuse.

[0012] It is entirely conceivable that the protective device is designed to trigger the tripping mechanism before the fuse element completely melts, in order to interrupt the current path as quickly as possible by separating the contact elements. It is therefore entirely conceivable that an overcurrent may occur in the current path and the fuse element melts, but that the tripping mechanism is triggered during the melting process in order to achieve complete galvanic isolation as quickly as possible by opening the load-break switch, since the tripping mechanism has a certain inertia and requires a certain amount of time to trip.

[0013] To detect an overcurrent, the measuring electronics can be configured to detect certain predefined current and voltage waveforms in the current path based on the electrical measured value(s) acquired by the measuring device, which are characteristic of the occurrence of an overcurrent. For example, an overcurrent could be detected based on a temporal current gradient. A particularly steep current increase is usually an indication of a short circuit and thus an indication of an existing overcurrent.

[0014] Preferably, the switchable contacting elements of the load-break switch can be transferred from a disconnected position, in which the contacting elements are spaced apart from one another and electrical contact between the contacting elements is thereby interrupted, into a contact position, in which the contacting elements contact one another and electrical contact exists between the contacting elements, and vice versa for switching the load-break switch, wherein the triggering mechanism is designed to transfer the contacting elements from the contact position to the disconnected position when the triggering mechanism is triggered.

[0015] The trigger mechanism preferably acts mechanically on the contacting elements.

[0016] It is entirely conceivable that the evaluation electronics are set up to decide, based on a variable limit value for the corresponding electrical measured variable, whether an overcurrent in the current path is imminent, present, or has occurred. In principle, however, it is considered advantageous if the evaluation electronics are set up to record the temporal progression of the measured variable or variables and to infer the presence of an overcurrent based on the temporal progression, for example, based on the gradient of the voltage drop across the fuse link. It is entirely conceivable that, particularly in DC applications, the voltage drop across the fuse link during normal operation will be close to 0 V or only a few volts due to the low internal resistance of the fuse link.If an overcurrent occurs that causes the fuse link to trip, thus melting the fuse element, the voltage drop across the fuse link also increases due to the rising fuse element temperature and the sharply rising current. As soon as the fuse element melts at one or more narrow points, this leads to a further sharp increase in voltage drop due to the subsequent arcs across the melted narrow points and the associated arc impedance. This temporal progression of the voltage drop across the fuse link can be detected by the evaluation electronics and converted into a trigger pulse for the triggering mechanism.The load-break switch then interrupts the remaining (residual) short-circuit current and ensures safe separation of the current path by separating the switchable contacting elements of the load-break switch, in particular by moving the contacting elements into the disconnected position.

[0017] It is considered particularly advantageous if the monitoring device is designed as a fuse monitoring device, wherein the fuse monitoring device is designed to detect a voltage drop across the fuse link.

[0018] In a particularly preferred embodiment, as previously described, the evaluation electronics are configured to detect the occurrence of an overcurrent based on the temporal development of the voltage drop across the fuse link. It is entirely conceivable that a voltage curve characteristic of an overcurrent for the fuse link used is stored in a memory of the evaluation electronics, wherein the evaluation electronics are configured to compare the voltage drop across the fuse link detected by the measuring device with the stored characteristic voltage curve and, based on the result of the comparison, to assess whether an overcurrent is imminent or present, leading to the melting of the fusible element in the fuse link.It is considered particularly advantageous if the evaluation electronics are programmable in order to adapt to different operating conditions, for example to adapt threshold values ​​for the voltage drop and / or voltage curves that characterise the presence of an overcurrent to the fuse link used.

[0019] As already explained, the protective device according to the invention offers particular advantages, particularly in direct current applications, due to the combination of a fuse link with a fusible element and a series-connected load-break switch. Accordingly, it is considered particularly advantageous if the protective device is used in direct current applications or is designed as a direct current protective device.

[0020] In a particularly preferred embodiment, the protective device is designed to be two-pole with a positive current path and a negative current path. Preferably, the respective current path has a fuse holder for receiving a fuse link with a fusible element and a load-break switch connected in series with the fuse holder with mechanically switchable contacting elements, wherein the respective load-break switch is coupled to a triggering mechanism such that, upon triggering of the triggering mechanism, the switchable contacting elements of the load-break switch are separated to interrupt the respective current path, wherein the monitoring device is designed to monitor the positive and / or the negative current path, wherein the monitoring device is designed toupon detection of the occurrence of an overcurrent in the positive and / or negative current path, to trigger at least one of the triggering mechanisms, preferably to trigger the respective triggering mechanism, to interrupt the positive and / or negative current path by separating the contacting elements of the respective load-break switch.

[0021] The spatial arrangement of the components, namely the fuse holder(s) or fuse links and the switch-disconnector(s), can be designed in different ways. It is considered particularly advantageous if the fuse holder(s) or fuse links and the switch-disconnector(s) are housed in one and the same housing.

[0022] It is considered particularly advantageous if the release mechanism has a preloadable mechanical energy storage device. The preloadable mechanical energy storage device is preferably one or more mechanical springs. When the release mechanism is triggered, the force stored in the energy storage device is transferred to the switchable contacting elements via a coupling mechanism, transferring them from the contact position to the disconnected position.

[0023] In principle, it is conceivable for the protective device to have an electric motor, with the electric motor being configured to preload the mechanical energy storage device. However, preloading of the energy storage device is preferably done manually, for example, using a hand-operated rotary lever.

[0024] In a particularly preferred embodiment, the protective device has a mechanically, preferably manually, actuated actuating device for transferring the contacting elements of the load-break switch from the disconnected position to the contact position and vice versa. This actuating mechanism is preferably an assembly independent of the tripping mechanism. This enables the load-break switch to switch, thus enabling the circuit to be interrupted even without an overcurrent and without triggering the tripping mechanism, and thus closing the current path and thus the circuit.

[0025] The actuating device can, for example, have a handle in the form of a switching lever, wherein manual actuation of the switching lever by an operator transfers the contacting elements of the load-break switch from the disconnected position (isolated position), in which the current path is interrupted, to the contact position, in which the current path is closed, and vice versa. It is considered particularly advantageous if the actuating device is an actuating device with an operator-independent switching mechanism. This operator-independent switching mechanism can, for example, be designed in the manner described in EP 0 496 212 81, the content of which is hereby incorporated into this application.

[0026] However, the operating mechanism can also be operated by a motor instead of manually.

[0027] It is considered particularly advantageous if the operating mechanism has a snap-action switch.

[0028] In a particularly preferred embodiment, the protective device comprises a locking element, wherein the locking element is coupled to the energy storage device of the tripping mechanism and interacts with the actuating device in such a way that, when the energy storage device is released, the locking element prevents the switch-disconnector from being transferred from the open to the closed switching position by mechanically blocking the actuating device. This ensures that the switch-disconnector can only be closed or transferred to the contact position when the tripping mechanism is preloaded. This ensures a high level of operational reliability, since switching on is only possible when the energy storage device is preloaded and the tripping mechanism is thus active.

[0029] It is considered particularly advantageous if the actuating device is coupled to the energy storage device of the tripping mechanism in such a way that when the actuating device is actuated to transfer the switchable contacting elements of the load-break switch from the open to the closed switching position, the energy storage device of the tripping mechanism is pretensioned.

[0030] In a particularly preferred embodiment, the measuring device comprises one or more voltage sensors and / or one or more current sensors. The current sensor can be a Rogowski coil, a Hall sensor, or a measuring method using semiconductor sensors. The voltage sensor can be a conventional direct contact or a voltage tap, as known from patent EP 3 671 792 A1, the content of which is hereby incorporated into this application. It is entirely conceivable that the measuring device does not measure absolute values ​​of the current and / or voltage, but merely changes in the current and / or voltage.

[0031] It is considered advantageous if the protective device is a low-voltage protective device and the protective device is suitable for use with a direct voltage in the range of 75 volts to 1500 volts (according to the Low Voltage Directive 2014 / 35 / EU) and with a current in the range of up to 1600A, preferably from 6A to 1600A.

[0032] Preferably, the fuse link has a contact blade.

[0033] In a particularly preferred embodiment, it is provided that the fuse holder(s) are fuse holders for NH fuse links (low-voltage high-performance fuse links).

[0034] In a preferred embodiment, the switchable contacting elements comprise two separate, stationary base elements and a movable contact bridge. The contact bridge contacts the two base elements in the contact position of the load-break switch, thereby electrically connecting them, and is arranged at a distance from the two base elements in the disconnected position. Preferably, the contact bridge is designed as a contact blade, and the respective base element has a receiving slot for the contact blade.

[0035] In a further advantageous embodiment, the contact bridge can be trapezoidal, with the base elements consisting of trapezoidally facing plate contacts, the base elements being designed to accommodate the trapezoidal contact bridge in the contact position. Such a design is described, for example, in patent EP1 439 558 A1, the content of which is hereby incorporated into this application.

[0036] In a further preferred embodiment, it is provided that the switchable contacting elements have two contact elements separated from one another, one of these elements being fixed and the other element being movable, the movable contact element contacting the two contact elements in the contact position of the load-break switch and thereby electrically connecting them to one another, and in the disconnected position the movable contact element being arranged at a distance from the fixed contact element.

[0037] Due to the very low time constants in a DC circuit, closing the switch-disconnector typically results in a very steep current rise. This can lead to arcing between the contacting elements during the switch-disconnector closing process, causing significant material removal on the switchable contacting elements of the switch-disconnector and thus contact wear. The high current flow may even lead to welding of the switchable contacting elements. For example, welding of the movable contact blade and one or both base elements may occur.Accordingly, it is considered particularly advantageous if the switch-disconnector has a contact system in which the largest possible electrical contact area is formed immediately and without any delay at the moment of electrical contact between the contacting elements of the switch-disconnector. This can be achieved, for example, by having several contacting elements arranged electrically parallel to one another close simultaneously. It is also quite conceivable that the arc occurring when the switch-disconnector closes is directed to an area that is deliberately sacrificed to wear.It is considered particularly advantageous if at least one of the switchable contacting elements of the switch-disconnector has a permanent contact and a sacrificial contact. In the contact position, the current flows via the permanent contact, and during a switching operation, the current flows temporarily via the sacrificial contact in order to protect the permanent contact from arcing during switching. The sacrificial contact achieves controlled arc guidance to non-critical surfaces. In an embodiment with a movable bridge contact and fixed base elements, at least one of the base elements has such a sacrificial contact and a permanent contact.

[0038] It is also quite conceivable that during the closing of the switchable contact elements of the load-break switch, i.e. during the switch-on process, a component with an inductance, such as a coil, is inserted into the current path in series with the switchable contact elements in order to limit the current flow due to the then higher inductance in the current path. Immediately after the switch-on process, this inductance can then be bridged by another switch contact.

[0039] In a preferred embodiment, it is provided that at least one of the switchable contacting elements of the load-break switch has a pre-contact, in particular a sacrificial contact, for temporarily conducting current when switching the load-break switch, and a permanent contact for permanently conducting current in the contact position of the load-break switch, wherein the permanent contact and the pre-contact are designed such that during the switching-on process of the load-break switch, thus when the switchable contacting elements are closed, the pre-contact is contacted first and the permanent contact is contacted subsequently.An inductance, for example a coil, is connected in series with the pre-contact, whereby the circuit initially closes via the pre-contact and thus via the inductance during the switching-on process and then the permanent contact closes, whereby in the final contact position the pre-contact is no longer contacted, whereby the inductance is bridged without switching another switching contact.

[0040] In a preferred development, it is provided that the protective device has an electrical circuit for limiting or reducing a current flow when the load-break switch is switched on, this electrical circuit being connected in series with the load-break switch, the electrical circuit having an inductance and an electromagnetic switching contact connected in parallel to the inductance, the electromagnetic switching contact being controlled in such a way that when the load-break switch is closed, the electromagnetic switching contact is in a disconnected position so that the current flows via the inductance connected in parallel, and after the contact position of the load-break switch has been reached, the electromagnetic switching contact is controlled in such a way that the electromagnetic switching contact changes from the disconnected position to the contact position.The electromagnetic switching contact can be controlled, for example, via the monitoring device.

[0041] It is considered advantageous if the protective device has an electrical circuit for limiting or reducing a current flow when the load-break switch is switched on, this electrical circuit being connected in series with the load-break switch, the electrical circuit having an inductance and an electromagnetic switching contact connected in parallel with the inductance, the electromagnetic switching contact being controlled in such a way that when the load-break switch is closed, the electromagnetic switching contact is in a disconnected position so that the current flows via the inductance connected in parallel, and after the contact position of the load-break switch has been reached, the electromagnetic switching contact is controlled in such a way that the electromagnetic switching contact changes from the disconnected position to the contact position.

[0042] It is also conceivable that an inductance is connected in series to the load-break switch, wherein an electromagnetic switching contact is arranged in parallel to the inductance, which is closed as soon as the load-break switch has reached the contact position, wherein the monitoring device immediately after reaching the contact position of the load-break switch applies a voltage to the electromagnetic switching contact, which transfers the electromagnetic switching contact from the disconnected position to the contact position.

[0043] The following figures illustrate the invention in more detail using exemplary embodiments, without being limited to them. They show: Fig. 1 a diagram showing the temporal course of current and voltage at a fuse link in the event of a short circuit, Fig. 2 a circuit diagram of a first embodiment of the protective device according to the invention, Fig. 3 a circuit diagram of a second embodiment of the protective device according to the invention Fig. 4 components of a switchable contact system of a load-break switch of the protective device in a disconnected position of the load-break switch, Fig. 5 components of a switchable contact system of a load-break switch of the protective device in a contact position of the load-break switch.

[0044] When protecting a DC circuit using only a fuse link with a fusible element, special effects occur which are associated with disadvantages. Fig. 1 These effects will be discussed in more detail below using the diagram shown. It should be noted that the DC circuit in the diagram is in the Fig. 1 is not protected by a protective device according to the invention, but only by a fuse. In the diagram of the Fig. 1 Curve 1 shows the time course of the voltage drop across the fuse. Curve 2 shows the time course of the current flowing through the fuse. At time t0, a short circuit occurs in the circuit. Curve 2 rises steeply and then becomes more flat. Curve 1, and thus the voltage drop across the fuse, initially only rises slightly. As soon as the fuse element of the fuse has melted at one or more narrow points, this leads to a further sharp increase in the voltage drop due to the subsequent arcs across the melted narrow points and the associated arc impedance. This begins at time t1. Accordingly, curve 1 rises sharply at time t1.At the same time, the short-circuit current is already reduced by the increasing impedance, which is also reflected in the temporal course of the current by the drop (negative slope) of curve 2 that begins at time t1. As can be seen from the diagram of the . Fig. 1 As can be seen, the current, or rather curve 1, does not immediately drop to 0 when the fuse melts, thus when the fuse is triggered, but remains constant for a certain period of time. Even if the current then finally drops to 0, insofar as the circuit is disconnected, the triggered fuse and the disconnection point of the fuse do not meet the requirements for safe separation.

[0045] These disadvantages are compensated by a protective device 3, as described in Fig. 2 shown, despite the use of a fuse. The protective device 3 is in this case two-pole and has a positive current path 4 and a negative current path 5, wherein the respective current path 4, 5 has a fuse holder for receiving a fuse link 6 with a fuse. A load-break switch 7 is connected in series to the respective fuse holder 6, wherein this load-break switch 7 has mechanically switchable contacting elements which can be transferred from a disconnected position in which the respective current path 4, 5 is interrupted, to a contact position in which the respective current path 4, 5 is closed. The load-break switch 7 is shown in the circuit diagram of Fig. 2 shown only symbolically. The respective load-break switch 7 is coupled to a tripping mechanism 8 such that, upon tripping of the tripping mechanism 8, the switchable contacting elements of the load-break switch 7 are transferred from the contact position to the disconnected position to interrupt the respective current path 4, 5.

[0046] The protective device 3 comprises a monitoring device 9 for each current path 4, 5, wherein this monitoring device 9 is configured to detect the occurrence of an overcurrent in the respective current path 4, 5. For this purpose, the respective monitoring device 9 has a measuring device configured to record the voltage drop across the respective fuse link 6, wherein the monitoring device 9 further comprises evaluation electronics configured to detect the presence of an overcurrent, in particular a short-circuit current, in the respective current path 4, 5 based on the temporal profile of the voltage drop across the respective fuse link 6.The monitoring device 9 is designed to trigger the respective triggering mechanism 8 upon detection of the occurrence of an overcurrent in the respective current path 4, 5 and thereby actuate the contacting elements and thereby interrupt the corresponding current path 4, 5.

[0047] The advantage of the protective device 3 according to the invention for protecting a DC circuit is that the disadvantages associated with the use of a fuse link 6 with a fusible element in a DC circuit are compensated for by the load-break switch 7 connected in series with the fuse link 6. Furthermore, the triggering of the load-break switch 7 creates a safe disconnection point so that no current can flow through the respective current path 4, 5, thereby interrupting the circuit. Since the load-break switch 7 is connected in series with the fuse link 6, it is not necessary for the load-break switch 7 or the triggering mechanism 8 to trigger particularly quickly or swiftly, since this is already achieved by the fusible element. Furthermore, the load-break switch 7 does not have to be designed to switch particularly high currents, since the current intensity is already reduced by the triggering of the fuse.

[0048] The Fig. 3 shows a further embodiment of the protective device 3, which differs from the embodiment according to the Fig. 2 essentially differs in that only in the positive current path 4 there is a load-break switch 7, which is coupled to a tripping mechanism 8 and has a monitoring device 9, and a series-connected fuse holder with a fuse link 6 with a fusible element, whereas the negative current path 5 has only one load-break switch 7 and a series-connected fuse holder with a fuse link 6 with a fusible element. In a further embodiment, this load-break switch 7 in the negative current path can also be mechanically coupled to the load-break switch 7 in the positive current path, so that they are actuated together when the tripping conditions are present in the positive current path.

[0049] The Fig. 4 shows components of a switchable contact system of the load-break switch 7 of the protective device 3. The contact system comprises a first group 10 of switchable contacting elements and a second group 11 of switchable contacting elements. The first group 10 is arranged between an input contact 12 of the fuse holder and the input terminal of the protective device 3, and the second group 11 is arranged between an outgoing contact 13 of the fuse holder and the output terminal of the protective device 3. In this case, a fuse link 6 designed as an NH fuse link is inserted into the fuse holder. The respective group 10, 11 comprises switchable contacting elements, wherein these switchable contacting elements comprise two spatially separated, fixedly arranged base elements 14a, 14b and a contact bridge 16 movable along the double arrow 15.The contact bridge 16 is designed as a contact blade, and the two base elements 14a, 14b have a receiving slot for receiving the contact bridge 16 in the contact position. In the contact position of the load-break switch 7, the contact bridge 16 is retracted into the receiving slots of the two base elements 14a, 14b, and the base elements 14a, 14b are then electrically connected to one another via the contact bridge 16. In the disconnected position, which is shown in the . Fig. 4 As shown, the contact bridge 16 is arranged at a distance from the two base elements 14a, 14b and thus the load-break switch 7 is in the disconnected position. The contact position is in the Fig. 5shown. The respective base element has a permanent contact surface in the region of the slot and a rod-shaped pre-contact 17 that contacts the contact bridge 16 during closing. The pre-contact 17 forms a sacrificial contact to prevent an arc on the permanent contact surface and thus protect the permanent contact surface from arcing during switching. List of reference symbols

[0050] 1Curve 2Curve 3Protection device 4Positive current path 5Negative current path 6Fuse link 7Load-break switch 8Trip mechanism 9Monitoring device 10First group 11Second group 12Input contact 13Output contact 14aBase element 14bBase element 15Double arrow 16Contact bridge 17Pre-contact t0Time t1Time

Claims

1. A protective device (3) for interrupting an electrical circuit when an overcurrent occurs, wherein the protective device (3) has a current path (4; 5) which extends through the protective device (3) from an input terminal of the protective device (3) to an output terminal of the protective device (3), wherein the protective device (3) has, in the current path (4; 5), a fuse holder for receiving a fuse link (6) comprising a fusible element and a load-break switch (7) connected in series with the fuse holder and having mechanically switchable contacting elements, wherein the load-break switch (7) is coupled to a tripping mechanism (8) in such a way that, when the tripping mechanism (8) is triggered, the switchable contacting elements of the load-break switch (7) are separated to interrupt the current path (4;5), wherein the protective device (3) has an electronic monitoring device (9), wherein the electronic monitoring device (9) has a measuring device which is designed to detect one or more electrical measured variables characteristic of the presence of an overcurrent, wherein the electronic monitoring device (9) has evaluation electronics which are designed to detect the occurrence of an overcurrent in the current path (4; 5) based on the electrical measured variable(s) detected by the measuring device, wherein the monitoring device (9) is designed to trigger the triggering mechanism to interrupt the current path (4; 5) by separating the contacting elements upon detection of the occurrence of an overcurrent in the current path (4; 5); 2. Protective device (3) according to claim 1, wherein the monitoring device (9) is designed as a fuse monitoring device, wherein the fuse monitoring device is designed to detect a voltage drop across the fuse link (6).

3. Protective device (3) according to claim 2, wherein the evaluation electronics are configured to detect the occurrence of an overcurrent based on a temporal development of the voltage drop across the fuse link (6).

4. Protective device (3) according to one of claims 1 to 3, wherein the protective device (3) is designed as a direct current protective device.

5. Protective device (3) according to one of claims 1 to 4, wherein the protective device (3) is designed to be two-pole with a positive current path (4) and a negative current path (5), wherein the respective current path (4; 5) has a fuse holder for receiving a fuse link (6) with a fusible element and a load-break switch (7) connected in series with the fuse holder and having mechanically switchable contacting elements, wherein the respective load-break switch (7) is coupled to a triggering mechanism (8) in such a way that when the triggering mechanism (8) is triggered, the switchable contacting elements of the load-break switch (7) are separated to interrupt the respective current path (4; 5), wherein the monitoring device (9) is designed to monitor the positive and / or the negative current path (4;5), wherein the monitoring device (9) is designed to trigger at least one of the triggering mechanisms (8) upon detection of the occurrence of an overcurrent in the positive and / or negative current path (4; 5) in order to interrupt the positive and / or negative current path (4; 5) by separating the contacting elements of the respective load-break switch (7).

6. Protective device (3) according to one of claims 1 to 5, wherein the triggering mechanism (8) has a pre-tensionable mechanical energy accumulator.

7. Protective device (3) according to one of claims 1 to 6, wherein the protective device (3) has a mechanically, preferably manually, operable actuating device for transferring the contacting elements of the load-break switch (7) from the disconnected position to the contact position and vice versa.

8. Protective device (3) according to claim 7, wherein the actuating mechanism comprises a snap-action switch.

9. Protective device (3) according to one of claims 7 or 8, wherein the protective device (3) has a locking element, wherein the locking element is coupled to the energy accumulator of the triggering mechanism (8) and interacts with the actuating device in such a way that, when the energy accumulator is relaxed, the locking element prevents the transfer of the load-break switch (7) from the open to the closed switching position by mechanically blocking the actuating device.

10. Protective device (3) according to one of claims 1 to 9, wherein the measuring device comprises one or more voltage sensors and / or one or more current sensors, for example a Rogowski coil, a Hall sensor or a measuring method using semiconductor sensors.

11. Protective device (3) according to one of claims 1 to 10, wherein the protective device (3) is a low-voltage protective device and the protective device (3) is suitable for use with a DC voltage in the range of 75 volts to 1500 volts and with a current in the range of up to 1600A.

12. Protective device (3) according to one of claims 1 to 11, wherein the fuse holder(s) are fuse holders for NH fuse links.

13. Protective device (3) according to one of claims 1 to 12, wherein the switchable contacting elements have two separate, fixedly arranged base elements (14) and a movable contact bridge (16), wherein the contact bridge (16) in the contact position of the load-break switch (7) contacts the two base elements (14) and thereby electrically connects them to one another and is arranged at a distance from the two base elements (14) in the disconnected position.

14. Protective device (3) according to one of claims 1 to 13, wherein at least one of the switchable contacting elements of the load-break switch (7) has a pre-contact (17) for temporarily conducting current when switching the load-break switch (7), and a permanent contact for permanently conducting current in the contact position of the load-break switch (7), wherein the permanent contact and the pre-contact (17) are designed such that when the switchable contacting elements are closed, the pre-contact (17) is contacted first and the permanent contact is contacted subsequently, wherein an inductance is connected in series with the pre-contact (17).

15. Protective device (3) according to one of claims 1 to 14, wherein the protective device has an electrical circuit for limiting or reducing a current flow when the load-break switch (7) is switched on, wherein this electrical circuit is connected in series with the load-break switch (7), wherein the electrical circuit has an inductance and an electromagnetic switching contact connected in parallel with the inductance, wherein the electromagnetic switching contact is controlled in such a way that when the load-break switch (7) is closed, the electromagnetic switching contact is in a disconnected position so that the current flows via the inductance connected in parallel, wherein after the contact position of the load-break switch (7) is reached, the electromagnetic switching contact is controlled in such a way that the electromagnetic switching contact changes from the disconnected position to the contact position.

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