Protection device for interrupting a circuit in the event of an overcurrent and method for protecting a direct current circuit against overcurrent

Abstract

The invention relates to a protective device (3) for interrupting a current 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 current path (4;5) is a main current path, 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 quantities 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 quantities detected by the measuring device, and wherein the monitoring device (9) is configured, upon detection of the occurrence of an overcurrent in the current path (4; 5), to trigger the tripping mechanism 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 in the event of an overcurrent. 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. Furthermore, the invention relates to a method for protecting a direct current circuit against an overcurrent.

[0002] Various protective devices for interrupting a current flow or a circuit in the event of an overcurrent are known from the prior art. For example, DE 10 2011 089 631 A1 discloses a circuit breaker for switching off an electric current if, due to an electrical fault, the magnitude or time course of the current no longer exhibits the desired characteristics. This circuit breaker is specifically designed for low voltage applications.

[0003] DE 10 2014 004 912 discloses a protective device comprising a microswitch connected in series with a fuse or a circuit breaker. US 5 426 406 A, FR 3 021 465 A1, EP 3 840 008 A1 and EP 3 724 909 A1 disclose further prior art.

[0004] Direct current (DC) applications are gaining increasing importance in various economic sectors. In the industrial sector, DC networks are being developed to supply energy to production halls or entire factories. Besides economic factors, such as energy savings due to the elimination of conversion losses from DC to AC, the technical advantages of DC networks also play a significant role, for example, the avoidance of harmonics. Within the context of the energy transition, DC plays a crucial role in energy storage systems, where excess energy is buffered for use during periods of low electricity production. Another application is in uninterruptible power supply (UPS) systems.Due to the ever-increasing energy demand, the corresponding UPS systems are also becoming larger and the corresponding energy storage systems more powerful, resulting in ever higher currents and / or voltages in such UPS systems.

[0005] DC and low-frequency AC networks present significant challenges regarding reliable overcurrent protection, particularly short-circuit protection, and safe disconnection in the event of an overcurrent, for several reasons. For instance, the increasing power output of battery storage systems leads to a continuous decrease in the internal resistance of the battery cells. In the event of a short circuit, this reduction in internal resistance results in very high prospective short-circuit currents. Furthermore, very short conductors between the battery and a protective device for interrupting the circuit result in very low inductances, leading to extremely low time constants. These are typically less than one millisecond and, in some cases, can be on the order of a few microseconds.The low time constants, in conjunction with the high prospective short-circuit currents, lead to very steep current rises in the event of a short circuit. When protecting the corresponding power grid or circuit with a fuse link, also known simply as a fuse, this can result in the current-limiting effect of the fuse link being delayed or not occurring at all relative to these time constants. At the point when the fuse trips, such a high current may already be flowing that the fuse and / or components are overloaded. Furthermore, due to the low inductance, the amount of energy stored in the protected circuit is insufficient to generate a sufficiently high back EMF across the switching arc within the fuse link to completely interrupt the short-circuit current.After the actual melting of the fuse element, current may continue to flow through the arc channels of the melted element for several milliseconds. With alternating current, such arcs may be extinguished by the current zero crossing. The danger posed by arcs is considerably higher with direct current. Therefore, it must be noted that the use of fuses in direct current applications or low-frequency alternating current applications has disadvantages. However, fuses also offer significant advantages. For example, fuses exhibit fail-safe behavior, meaning they reliably trip in the event of an overcurrent and always interrupt the corresponding circuit.Another advantage of fuse links is that, in the event of a fuse blowing, no arcs or ionizing gases are emitted into the environment, as these remain contained 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.

[0006] The object of the present invention is to create a protective device for interrupting an electrical circuit in the event of an overcurrent, which utilizes the advantages of the fuse insert with fusible link and overcomes its aforementioned disadvantages.

[0007] This problem is solved by a protective device having the features of claim 1. Advantageous embodiments of the protective device are the subject of the dependent claims.

[0008] The protective device according to the invention serves to interrupt a current circuit in the event of an overcurrent. 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, wherein the protective device has in the current path a fuse holder for receiving a fuse link comprising a fusible link and a load break switch with mechanically switchable contact elements connected in series with the fuse holder, wherein the load break switch is coupled with a tripping mechanism such that when the tripping mechanism is triggered, the switchable contact elements of the load break switch are disconnected to interrupt the current path, wherein the current path is a main current path.wherein the protective device comprises an electronic monitoring device, wherein the electronic monitoring device comprises a measuring device configured to detect one or more electrical quantities characteristic 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 quantity(ies) detected by the measuring device, and wherein the monitoring device is configured to trigger the tripping mechanism upon detection of the occurrence of an overcurrent in the current path, interrupting the current path by separating the contacting elements.

[0009] Since the current path is the main current path, and the fuse link inserted into the fuse holder is therefore located in the main current path, the fuse element of the fuse link is live even during normal operation, i.e., even without an overcurrent. In other words, the fuse link is permanently supplied with the operating current of the circuit due to its location in the main current path. Because of this design—namely, the placement of the fuse holder and thus the fuse link inserted within it in the main current path—the circuit is always protected by the fuse link inserted in the fuse holder. Therefore, the main current path is always interrupted when the fuse link cannot conduct current, e.g.,if the fusible link of the fuse insert has melted through due to an overcurrent, or if the fusible link of the fuse insert has been cut for other reasons, or if there is no fuse insert in the fuse holder at all.

[0010] Due to the design according to the invention, the aforementioned disadvantages of fuse links are less pronounced or eliminated in DC applications, since opening the load break switch reliably interrupts the current path of the protective device. A further advantage of using the load break switch is that the disconnect point created by the tripped fuse link typically does not meet the requirements for safe isolation, whereas the open load break switch 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 tripped fuse, in order to protect downstream equipment and / or persons.By combining the load break switch with the series-connected fuse holder, the load break switch and its coupled tripping mechanism do not need to have a particularly fast switching characteristic, allowing the corresponding components to be designed relatively simply. This has a positive effect on the manufacturing costs of the protective device. A further advantage of the protective device according to the invention compared to a circuit breaker is that the main task of the disconnection process is still performed by the fuse link. The contacting elements and any other elements for contacting and disconnecting the contacting elements of the load break switch can therefore be designed more simply, since, in particular, no particularly high currents need to be switched, as the current is already reduced by the melting of the fuse link.Since the fuse link is connected in series with the load break switch, a particularly high level of safety is ensured should a malfunction of the load break switch and / or the monitoring device and / or the tripping mechanism occur for any reason. Thus, the protection of the system and personnel is still guaranteed to a high degree, even if the load break switch fails to open, due to the generally very reliable tripping of the fuse link, which is primarily due to thermal factors.

[0011] Furthermore, there is the advantage that in the event of a short circuit, only the fuse element needs to be replaced to restore the reliable function of the protective device.

[0012] An overcurrent occurs, in particular, when the fuse's tripping current is high enough to melt the fusible link and thus trigger the fuse. It is conceivable that the tripping current can be exceeded briefly without the fusible link melting. The tripping time of the fuse generally depends on the extent to which the tripping current is exceeded. The tripping current and tripping time of the fuse depend on the fuse's tripping characteristics. The tripping current is typically several times the rated current of the circuit being protected. Preferably, the tripping current is at least 1.05 times the rated current of the circuit being protected.

[0013] It is considered particularly advantageous if current can only flow from the input terminal to the output terminal via the current path. Specifically, the protective device does not have a bypass path connected parallel to the current path or sectionally parallel to the current path. This ensures that the circuit is interrupted if the current path is broken. In this way, fail-safe behavior is guaranteed, as current flow between the input and output terminals is reliably prevented when the fuse trips. If a bypass path existed, for example, one that bypassed the fuse, current could still flow from the input terminal to the output terminal via the bypass path if the fuse element were to melt.This would mean that the fail-safe behavior of the fuse would not be effective in protecting the current flow from the input terminal to the output terminal due to the current flow via the bypass path.

[0014] It is intended that the protective device, in particular the monitoring device, and / or the fuse link, are designed such that, in the event of an overcurrent, the fusible link is at least partially melted before the tripping mechanism is triggered. This is advantageous because a lower current needs to be switched when the contact elements are activated. This can, for example, reduce contact erosion of the contact elements.

[0015] A fast tripping characteristic of the protective device can be achieved, especially in DC applications, by using fuse links with a correspondingly fast characteristic, for example, fuses of the following operating classes: ar-fuse, gr-fuse, aBat-fuses, gBat-fuses or gS-fuses.

[0016] It is quite conceivable that the protective device is designed to trigger the tripping mechanism even before the fusible link has completely melted, in order to achieve the fastest possible interruption of the current path by separating the contact elements. Thus, it is quite possible that an overcurrent may occur in the current path and the fusible link may melt, but the tripping mechanism is triggered even during the melting process to achieve complete galvanic isolation by opening the load break switch as quickly as possible, especially if the tripping mechanism has a certain inertia or requires a tripping time.

[0017] To detect an overcurrent, the measuring electronics can be configured to recognize certain predefined current and voltage waveforms in the current path, based on the electrical parameters measured by the measuring device. These waveforms are characteristic of an overcurrent. For example, an overcurrent could be detected based on a time gradient of the current. A particularly steep current rise is generally an indication of a short circuit and thus a sign of an existing overcurrent.

[0018] Preferably, the switchable contact elements of the load break switch can be moved from a disconnected position, in which the contact elements are spaced apart and thus an electrical contact between the contact elements is interrupted, to a contact position, in which the contact elements contact each other and an electrical contact exists between the contact elements, and vice versa for switching the load break switch, wherein the release mechanism is configured to move the contact elements from the contact position to the disconnected position when the release mechanism is triggered.

[0019] The triggering mechanism preferably acts mechanically on the contacting elements.

[0020] It is quite conceivable that the evaluation electronics are configured to decide, based on a variable threshold for the corresponding electrical measurement, whether an overcurrent is imminent, present, or has occurred in the current path. However, it is generally considered advantageous if the evaluation electronics are configured to record the time course of the measurement(s) and, based on this time course, to infer the presence of an overcurrent, for example, by analyzing the gradient of the voltage drop across the fuse link. It is quite conceivable that, particularly in DC applications, the voltage drop across the fuse link will be close to 0 V or only a few volts during normal operation due to the low internal resistance of the fuse link.If an overcurrent occurs, causing the fuse to trip and the fusible link to melt, the voltage drop across the fuse increases due to the rising fusible link temperature and the rapidly increasing current. Once the fusible link has melted through at one or more points, the resulting arcs across these points, and the associated arc impedance, lead to a further sharp increase in the voltage drop. This temporal progression of the voltage drop across the fuse can be detected by the evaluation electronics and converted into a tripping pulse for the tripping mechanism.The load break switch then interrupts the remaining (residual) short-circuit current and ensures a safe separation of the current path by separating the switchable contact elements of the load break switch, in particular by moving the contact elements into the disconnect position.

[0021] It is considered particularly advantageous if the monitoring device is designed as a fuse monitoring device, wherein the fuse monitoring device is configured to detect a voltage drop across the fuse link.

[0022] In a particularly preferred embodiment, as previously described, the evaluation electronics are configured to detect the occurrence of an overcurrent based on the time-dependent development of the voltage drop across the fuse link. It is quite conceivable that a voltage curve characteristic of an overcurrent for the fuse link used is stored in a memory of the evaluation electronics. 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 that would lead to the melting of the fusible link 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 adjust threshold values ​​for voltage drop and / or voltage curves that characterize the presence of an overcurrent to the fuse used.

[0023] As already explained, the protective device according to the invention offers particular advantages, especially in DC applications, due to the combination of a fuse link with a fusible link and a load break switch connected in series. Accordingly, it is considered particularly advantageous when the protective device is used in DC applications or is designed as a DC protective device.

[0024] In a particularly preferred embodiment, the protective device is designed as a two-pole device with a positive current path and a negative current path, wherein the positive current path is a positive main current path and the negative current path is a negative main current path. Preferably, each current path has a fuse holder for receiving a fuse link with a fusible link and a load break switch with mechanically switchable contact elements connected in series with the fuse holder. The load break switch is coupled to a tripping mechanism such that, upon tripping, the switchable contact elements of the load break switch are disconnected to interrupt the respective current path. The monitoring device is configured to monitor the positive and / or the negative current path.wherein the monitoring device is configured to trigger at least one of the tripping mechanisms, preferably the respective tripping mechanism, upon detection of the occurrence of an overcurrent in the positive and / or the negative current path, to interrupt the positive and / or negative current path by separating the contacting elements of the respective load break switch.

[0025] The spatial arrangement of the components, namely the fuse holder(s) or fuse links and the load break switch(es), can be configured in various ways. It is considered particularly advantageous if the fuse holder(s) or fuse links and the load break switch(es) are integrated into the same housing.

[0026] It is considered particularly advantageous if the release mechanism incorporates a pre-tensioned mechanical energy storage device. This pre-tensioned mechanical energy storage device preferably consists of one or more mechanical springs. When the release mechanism is triggered, the force stored in the energy storage device is transferred via a coupling mechanism to the switchable contact elements, thereby transitioning them from the contact position to the disconnect position.

[0027] In principle, it is conceivable that the protective device includes an electric motor, which is configured to pre-tension the mechanical energy storage device. Preferably, however, the pre-tensioning of the energy storage device is carried out manually, for example by means of a hand-operated rotary lever.

[0028] In a particularly preferred embodiment, the protective device has a mechanically, preferably manually, actuating device for moving the contacting elements of the load break switch from the disconnected position to the contacted position and vice versa. This actuating mechanism is preferably an assembly independent of the tripping mechanism. This allows the load break switch to be switched, thus interrupting the circuit and closing the current path and therefore the circuit, even without an overcurrent and without triggering the tripping mechanism.

[0029] The actuating device can, for example, have a handle in the form of a switching lever, wherein, by manual actuation of the switching lever by an operator, the contacting elements of the load break switch are moved from the disconnected position (disconnect 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 B1.

[0030] However, the actuation mechanism can also be operated by a motor instead of manually.

[0031] It is considered particularly advantageous if the actuating mechanism has a snap-action switch.

[0032] In a particularly preferred embodiment, the protective device has a locking element, wherein the locking element is coupled to the energy storage device of the release mechanism and interacts with the actuating device in such a way that, when the energy storage device is relaxed, the locking element prevents the load break switch from being moved from the open to the closed switching position by mechanically blocking the actuating device.

[0033] This ensures that the load break switch can only be closed, or moved into the contact position, when the tripping mechanism is pre-tensioned. This guarantees a high level of operational reliability, as switching on is only possible with a pre-tensioned energy storage device and thus an active tripping mechanism.

[0034] It is considered particularly advantageous if the actuating device is coupled to the energy storage device of the release mechanism in such a way that, when the actuating device is actuated to move the switchable contacting elements of the load break switch from the open to the closed switching position, the energy storage device of the release mechanism is pre-tensioned.

[0035] In a particularly preferred embodiment, the measuring device comprises one or more voltage sensors and / or one or more current sensors. The current sensor may be a Rogowski coil, a Hall sensor, or a measurement method using semiconductor sensors. The voltage sensor may be a conventional direct contact or a voltage tap as known from patent EP 3 671 792 A1. It is entirely conceivable that the measuring device does not measure absolute values ​​of the current and / or voltage, but only changes in the current and / or voltage.

[0036] It is considered advantageous if the protective device is a low-voltage protective device and is suitable for use with a DC voltage in the range of 75 volts to 1500 volts (according to Low Voltage Directive 2014 / 35 / EU) and with a current in the range of up to 1600A, preferably from 6A to 1600A.

[0037] Preferably, the safety insert has a contact blade.

[0038] In a particularly preferred embodiment, the fuse holder(s) are designed for NH fuse links (low-voltage high-performance fuse links). In a preferred embodiment, the switchable contacting elements comprise two separate, fixed base elements and a movable contact bridge. In the contact position of the load break switch, the contact bridge connects the two base elements, thereby electrically connecting them. In the disconnect position, the contact bridge is spaced apart from the two base elements. Preferably, the contact bridge is designed as a contact blade, and each base element has a receiving slot for the contact blade.

[0039] In a further advantageous embodiment, the contact bridge can be trapezoidal, wherein the base elements consist of trapezoidal plate contacts facing each other, the design of the base elements being such that they accommodate the trapezoidal contact bridge in the contact position. Such a design is described, for example, in patent EP1 439 558 A1.

[0040] In a further preferred embodiment, the switchable contacting elements have two separate contact elements, one of which is stationary and the other movable, wherein the movable contact element contacts the two contact elements in the contact position of the load break switch and thereby electrically connects them, and in the disconnect position the movable contact element is arranged spaced apart from the stationary contact element.

[0041] Due to the very low time constants in a DC circuit, closing a load break switch typically results in a very steep current rise. This can lead to arcing between the contact elements during the switch-on process, causing significant material erosion on the switchable contact elements and thus contact wear. In some cases, the high current flow can even cause the switchable contact elements to weld together. For example, the movable contact blade and one or both base elements can weld together.Accordingly, it is considered particularly advantageous if the load break switch has a contact system in which, at the moment of electrical contact between the contacting elements of the load break switch, the largest possible electrical contact area is formed immediately without any delay. This can be achieved, for example, by having several electrically parallel contacting elements close simultaneously. It is also quite conceivable that the arc occurring when the load break switch closes is directed to an area that is deliberately exposed to wear.It is considered particularly advantageous if at least one of the switchable contacting elements of the load break switch has a permanent contact and a sacrificial contact, wherein, 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 ensures 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.

[0042] It is also quite conceivable that during the closing process of the switchable contact elements of the load break switch, i.e., during the switch-on process, a component with an inductance, for example a coil, is introduced into the current path in series with the switchable contact elements in order to limit the current flow through the resulting higher inductance in the current path. Immediately after the switch-on process, this inductance can then be bridged by another switching contact.

[0043] 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, i.e. when closing the switchable contacting elements, the pre-contact is contacted first and the permanent contact is contacted subsequently.The pre-contact is connected in series with an inductor, for example a coil, whereby the circuit is initially closed via the pre-contact and thus via the inductor during the switching process, and then the permanent contact closes, whereby in the final contact position the pre-contact is no longer contacted, thus bridging the inductor without switching another switching contact.

[0044] In a preferred embodiment, the protective device for limiting or reducing current flow when the load break switch is switched on comprises an electrical circuit, wherein this electrical circuit is connected in series with the load break switch, wherein the electrical circuit comprises an inductor and an electromagnetic switching contact connected in parallel to the inductor, wherein the electromagnetic switching contact is controlled such that when the load break switch is closed, the electromagnetic switching contact is in a disconnected position, so that the current flows through the parallel-connected inductor, wherein after reaching the contact position of the load break switch, the electromagnetic switching contact is controlled such that the electromagnetic switching contact transitions from the disconnected position to the contact position.The electromagnetic switching contact can be controlled, for example, via the monitoring device.

[0045] It is considered advantageous if the protective device has an electrical circuit for limiting or reducing current flow when the load break switch is switched on, wherein this electrical circuit is connected in series with the load break switch, wherein the electrical circuit has an inductor and an electromagnetic switching contact connected in parallel to the inductor, wherein the electromagnetic switching contact is controlled such that when the load break switch is closed the electromagnetic switching contact is in a disconnected position, so that the current flows through the parallel-connected inductor, wherein after reaching the contact position of the load break switch the electromagnetic switching contact is controlled such that the electromagnetic switching contact changes from the disconnected position to the contact position.

[0046] It is also conceivable that an inductor is connected in series with the load break switch, with an electromagnetic switching contact arranged in parallel to the inductor, which is closed as soon as the load break switch has reached the contact position, wherein the monitoring device applies a voltage to the electromagnetic switching contact immediately after the load break switch has reached the contact position, which transfers the electromagnetic switching contact from the disconnect position to the contact position.

[0047] Method for protecting a direct current circuit against an overcurrent, wherein the protective device according to the invention or one of the previously described embodiments of the protective device is used to protect the direct current circuit against an overcurrent.

[0048] The following figures explain the invention in more detail with reference to exemplary embodiments, without being limited to these. They show: Fig. 1 a diagram showing the time course of current and voltage at a fuse link during 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.

[0049] When a DC circuit is protected solely by a fuse link with a fusible link, special effects occur that are associated with disadvantages. Based on the [reference to the following text] Fig. 1 The effects shown in the diagram will be discussed in more detail below. It should be noted that the direct current circuit in the diagram is shown in the Fig. 1 It is not protected by a protective device according to the invention, but merely by a fuse. In the diagram of the Fig. 1 Curve 1 shows the voltage drop across the fuse over time. Curve 2 shows the current flowing through the fuse over time. At time t0, a short circuit occurs in the circuit. Curve 2 rises steeply and then flattens out. Curve 1, and thus the voltage drop across the fuse, initially rises only slightly. As soon as the fuse's conductor melts at one or more points, the subsequent arcing across these points and the resulting arc impedance cause a further sharp increase in the voltage drop. This begins at time t1. Accordingly, Curve 1 shows a sharp rise at time t1.At the same time, the short-circuit current is already reduced by the increasing impedance, which is also evident in the current's time course based on the drop (negative slope) of curve 2 that begins at time t1. As shown in the diagram of the... Fig. 1 As can be seen, when the fuse melts, and thus when the fuse trips, the current, or curve 1, does not drop immediately to zero, but remains constant for a certain period. Even if the current eventually drops to zero, provided the circuit is broken, the tripped fuse and the point of separation of the fuse do not meet the requirements for a safe separation.

[0050] These disadvantages are eliminated by a protective device 3, as described in the Fig. 2 The protective device 3 is shown to be two-pole and has a positive main current path 4, hereinafter referred to as positive current path 4, and a negative main current path 5, hereinafter referred to as negative current path 5, wherein each current path 4, 5 has a fuse holder for receiving a fuse link 6 with a fuse element. A load break switch 7 is connected in series with each fuse holder 6, wherein this load break switch 7 has mechanically switchable contact elements that can be moved 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 the Fig. 2 The diagram is shown for symbolic purposes only. The respective load break switch 7 is coupled to a tripping mechanism 8 such that, upon tripping of the tripping mechanism 8, the switchable contact elements of the load break switch 7 are moved from the contact position to the disconnect position to interrupt the respective current path 4, 5. Current can only flow from a positive input terminal associated with the positive current path 4 to a positive output terminal associated with the positive current path 4 via the positive current path 4. In particular, the protective device 3 does not have a positive bypass path connected in parallel to the positive current path 4 or sectionally in parallel to the positive current path 4, through which current could flow from the positive input terminal to the positive output terminal, for example, if the positive current path 4 is interrupted.Current can only flow from the positive input terminal to the positive output terminal via the positive current path 4. This ensures that if the positive current path 4 is interrupted, for example by moving the load break switch 7 from the contact position to the disconnect position and / or by the fuse blowing, no current can flow from the positive input terminal to the positive output terminal. The same applies to the negative current path 5.

[0051] 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 which is configured to detect the voltage drop across the respective fuse link 6, wherein the monitoring device 9 further comprises evaluation electronics which are configured to detect the presence of an overcurrent, in particular a short-circuit current, in the respective current path 4, 5 based on the time course of the voltage drop across the respective fuse link 6.The monitoring device 9 is designed to trigger the respective tripping mechanism 8 when an overcurrent is detected in the respective current path 4, 5, thereby actuating the contacting elements and interrupting the corresponding current path 4, 5.

[0052] 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 link in a DC circuit are compensated by the load break switch 7 connected in series with the fuse link 6. Furthermore, the tripping of the load break switch 7 creates a reliable disconnect point, so that no current can flow through the respective current path 4, 5, thus 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 tripping mechanism 8 to trip particularly quickly or rapidly, as this is already achieved by the fusible links. Moreover, the load break switch 7 does not need to be designed to switch particularly high currents, since the current is already reduced by the tripping of the fuse.

[0053] The Fig. 3 shows a further embodiment of the protective device 3, which differs from the embodiment according to the Fig. 2 The main difference is that only the positive current path 4 has a load break switch 7 coupled to a tripping mechanism 8 and equipped with a monitoring device 9, and a series-connected fuse holder with a fuse link 6 with a fusible link, while the negative current path 5 has only a load break switch 7 and a series-connected fuse holder with a fuse link 6 with a fusible link. 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 in the positive current path are met.

[0054] The Fig. 4 Figure 1 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 contact elements and a second group 11 of switchable contact 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 output contact 13 of the fuse holder and the output terminal of the protective device 3. A fuse link 6, designed as an NH fuse link, is inserted into the fuse holder. Each group 10, 11 comprises switchable contact elements, wherein these switchable contact elements include 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 inserted into the receiving slots of the two base elements 14a, 14b, and the base elements 14a, 14b are then electrically connected to each other via the contact bridge 16. In the disconnect position, which is in the . Fig. 4 As shown, the contact bridge 16 is arranged at a distance from the two base elements 14a, 14b, thereby placing the load break switch 7 in the disconnect position. The contact position is shown in the Fig. 5The respective base element has a permanent contact surface in the area of ​​the slot and a rod-shaped pre-contact 17 that precedes the contact bridge 16 when closing. The pre-contact 17 forms a sacrificial contact to prevent an arc from reaching the permanent contact surface and thus protect the permanent contact surface from arcing during switching. Reference symbol list

[0055] 1 Curve 2 Curve 3 Protective device 4 Positive current path 5 Negative current path 6 Fuse link 7 Load break switch 8 Trip mechanism 9 Monitoring device 10 First group 11 Second group 12 Input contact 13 Output contact 14a Base element 14b Base element 15 Double arrow 16 Contact bridge 17 Pre-contact t0 time t1 time

Claims

1. Protective device (3) for interrupting a circuit in the event of an overcurrent, wherein the protective device (3) has a current path (4; 5), which extends through the protective device (3) from an input connection of the protective device (3) to an output connection of the protective device (3), wherein, in the current path (4; 5), the protective device (3) has a fuse receptacle for receiving a fuse link (6) comprising a fusible element, and a switch disconnector (7) that is connected in series with the fuse receptacle and comprises mechanically switchable contacting elements, wherein the switch disconnector (7) is coupled to a tripping mechanism (8) such that, when the tripping mechanism (8) is tripped, the switchable contacting elements of the switch disconnector (7) are separated so as to interrupt the current path (4; 5), wherein the current path (4; 5) is a main current path, wherein the protective device (3) has an electronic monitoring apparatus (9), wherein the electronic monitoring apparatus (9) has a measuring apparatus that is configured to capture one or more electrical measurement variables that are characteristic of the presence of an overcurrent, wherein the electronic monitoring apparatus (9) has evaluation electronics that are configured to detect the occurrence of an overcurrent in the current path (4; 5) on the basis of the electrical measurement variable or the electrical measurement variables captured by the measuring apparatus, wherein the monitoring apparatus (9) is configured to trip the tripping mechanism so as to interrupt the current path (4; 5) by separating the contacting elements when the occurrence of an overcurrent in the current path (4; 5) is detected, wherein a fuse link (6) is received in the fuse receptable, characterized in that the protective device (3) and the fuse link (6) are designed in such a way that, in the event of an overcurrent, the fusible element is at least partially melted before the tripping mechanism is tripped.

2. Protective device (3) according to Claim 1, wherein a flow of current from the input connection to the output connection is possible exclusively via the current path (4; 5).

3. Protective device (3) according to Claim 1 or 2, wherein the protective device (3) is configured to trip the tripping mechanism even before the fusible element is completely melted.

4. Protective device (3) according to Claim 3, wherein the protective device (3) is configured such that the fusible element melts in the event of an overcurrent in the current path (4, 5), wherein the tripping mechanism trips during the melting.

5. Protective device (3) according to one of Claims 1 to 4, wherein the monitoring apparatus (9) is in the form of a fuse monitoring apparatus, wherein the fuse monitoring apparatus is configured to detect a voltage drop across the fuse link (6).

6. Protective device (3) according to Claim 5, wherein the evaluation electronics are configured to detect the occurrence of an overcurrent on the basis of a development of the voltage drop across the fuse link (6) over time.

7. Protective device (3) according to one of Claims 1 to 6, wherein the protective device (3) is in the form of a DC protective device.

8. Protective device (3) according to one of Claims 1 to 7, wherein the protective device (3) has a bipolar design with a positive current path (4) and a negative current path (5), wherein the positive current path (4) is a positive main current path, and wherein the negative current path (5) is a negative main current path, wherein the respective current path (4; 5) has a fuse receptacle for receiving a fuse link (6) comprising a fusible element, and a switch disconnector (7) that is connected in series with the fuse receptacle and comprises mechanically switchable contacting elements, wherein the respective switch disconnector (7) is coupled to a tripping mechanism (8) such that, when the tripping mechanism (8) is tripped, the switchable contacting elements of the switch disconnector (7) are separated so as to interrupt the respective current path (4; 5), wherein the monitoring apparatus (9) is configured to monitor the positive and / or the negative current path (4; 5), wherein the monitoring apparatus (9) is configured to trip at least one of the tripping mechanisms (8) so as to interrupt the positive and / or negative current path (4; 5) by separating the contacting elements of the respective switch disconnectors (7) when the occurrence of an overcurrent in the positive and / or the negative current path (4; 5) is detected.

9. Protective device (3) according to one of Claims 1 to 8, wherein the tripping mechanism (8) has a pretensionable mechanical energy store.

10. Protective device (3) according to one of Claims 1 to 9, wherein the measuring apparatus has 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 a semiconductor sensor system.

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 at a DC voltage in the range of 75 volts to 1500 volts in terms of absolute value and at a current intensity in the range of up to 1600 A in terms of absolute value.

12. Protective device (3) according to one of Claims 1 to 11, wherein the fuse receptacle or the fuse receptacles are fuse receptacles for NH fuse links.

13. Protective device (3) according to one of Claims 1 to 12, wherein the switchable contacting elements have two base elements (14), which are separate from one another and are arranged in a stationary manner, and a movable contact bridge (16), wherein the contact bridge (16), in the contact position of the switch disconnector (7), makes contact with the two base elements (14) and thereby electrically connects them to one another, and, in the disconnected position, is arranged in a manner spaced apart from the two base elements (14).

14. Method for protecting a DC circuit against an overcurrent, wherein the protective device (3) according to one of Claims 1 to 13 is used to protect the DC circuit against an overcurrent.

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