Switchgear with short-circuit protection devices

Abstract

Switchgear (50) for limiting and switching off short-circuit currents in high-energy direct current networks (5, 55), in particular short-circuit currents of high-performance battery systems (51) in submarine direct current networks, with a plurality of parallel-connected protective devices (1) for limiting, preferably also switching off, short-circuit currents in high-energy direct current networks (5, 55), in particular short-circuit currents of high-performance battery systems (51) in submarine direct current networks, the protective devices (1) having - an electrical resistor (9), in particular an ohmic resistor, for guiding and limiting the short-circuit current in the event of a short circuit, - a first switch (10) connected in parallel with the resistor (9) for bridging the resistor (9) when the high-energy direct current network (5, 55) is free of short circuits, - a monitoring and control device (11) for monitoring a current (I) through the first switch (10) and for opening the first switch (10) when the current (I) through the switch (10) exceeds a predetermined limit value and at least one protective device (56) which is connected downstream of these protective devices (1), wherein the resistors (9) of the protective devices (1) are dimensioned such that in the event of a short circuit, a total current I* formed by the sum of the currents flowing through the resistors (9) and flowing through the protective device (56) triggers the protective device (56).

Description

[0001] The invention relates to a switchgear assembly with short-circuit protection devices for limiting, preferably also switching off, short-circuit currents in high-energy direct current networks, in particular short-circuit currents of battery systems in submarine direct current networks.

[0002] Batteries or accumulators are preferred for energy storage in direct current grids. For simplicity, the term "batteries" will be used for both types of energy storage devices. Batteries with low internal resistance, low self-discharge, and high energy density are particularly advantageous. Lithium-based batteries, in particular, meet these requirements based on current state-of-the-art technology, so they are increasingly being used in high-performance direct current grids. A very typical application is in DC island grids, such as those used in vehicles (e.g., submarines).

[0003] For example, EP 1 641 066 A2 and WO 2008 / 055 493 A1 disclose a submarine direct current network with a lithium-based battery. The battery comprises several battery modules connected in parallel, which are connected to the direct current network via connecting conductors. Each battery module comprises one or more parallel strings of high-performance battery cells connected in series, and each of the strings has the mains voltage of the direct current network. A switchgear is used to switch the operating currents and limit the short-circuit currents.

[0004] The low internal resistance of lithium batteries, which is advantageous for high energy storage efficiency, has the disadvantage, however, of very high short-circuit currents occurring in the event of a short circuit in the DC grid. These currents are several times higher than those previously known from other batteries, such as lead batteries. In the case of a submarine DC grid, for example, the prospective short-circuit currents can be 20 kA for a battery string and up to 500 kA per battery.

[0005] The very high short-circuit current is associated with a very rapid rise in this short-circuit current. For example, the time constant of the unaffected short-circuit current is only a few milliseconds.

[0006] The interruption of such a short-circuit current becomes particularly problematic when electromagnetically operated circuit breakers with overcurrent detection are used to monitor and interrupt the short-circuit current, which have an unavoidable response and tripping time. Since the resulting overcurrent detection and interruption time of such circuit breakers is equal to or greater than the time constant of the prospective short-circuit current of the batteries, such a high current already flows at the time of interruption that the circuit breaker is overloaded by the very high interruption energy W ∼ I 2 is overloaded. Serious damage to the circuit breaker itself and / or the components it is designed to protect may result.

[0007] For example, US 2008 / 304 198 A1 discloses a power supply device comprising a current limiting unit connected in series between a power source and a power supply circuit that limits the output current of the power source. A first switch is connected in series with the current limiting unit; a second switch is connected in parallel with the current limiting unit; and a resistor is connected in series between the power source and the current limiting unit. An abnormal current detection unit is connected in parallel with the resistor and detects the current flowing through the resistor and further determines whether the detected current is abnormal or not. A control unit switches the switches accordingly.

[0008] For example, DE 696 04 533 T2 discloses a device for interrupting a direct current in a two-conductor high-voltage line, comprising a first group with a first resistor connected in parallel with a first circuit breaker, at least one second group with a second resistor connected in parallel with a second circuit breaker, and a disconnector. Furthermore, a fault detector is disclosed which, in the event of a fault, issues an opening command to the circuit breaker of the first group, an opening command to the circuit breaker of the second group when the line current, as a lower value, exceeds a first predetermined threshold, and an opening command to the disconnector when the line current, as a lower value, exceeds a second predetermined threshold.

[0009] Further arrangements for switching off high currents are known, for example, from DE 10 2007 004 092 A1, DE 21 37 082 A or DE 12 53 332 A.

[0010] As an alternative or in addition to circuit breakers, fuses can be used in some cases. These fuses must be replaced with new ones after the short-circuit current has been switched off. However, in many cases, such a replacement of fuses after short circuits is not desirable or not possible in a short time. A typical case is a DC island network, e.g., on vehicles such as submarines.

[0011] If the short-circuit current is interrupted virtually instantaneously by a suitable switch, there is the problem that there is not enough time to trip downstream electromagnetically operated circuit breakers. Thus, only limited selectivity can be achieved in the DC network.

[0012] With regard to a submarine direct current network using high-performance energy storage devices, DE 10 2007 053 229 A1 discloses a submarine direct current network with two subnetworks connected via a grid coupling. The battery consists of several battery groups connected in parallel, each consisting of several strings of series-connected high-performance energy storage cells. Each string has a surge-limiting protective device, and a protective device is also provided for the sum of the short-circuit currents of several battery groups.

[0013] It is an object of the present invention to provide a switchgear assembly with protective devices with which it is possible to safely control the short-circuit current occurring in a high-energy direct current network during a short circuit, whereby the problems described above can be avoided.

[0014] This problem is solved by a switchgear according to patent claim 1. Advantageous embodiments of the switchgear are the subject of patent claims 2 to 11.

[0015] A switchgear according to the invention for limiting and switching off short-circuit currents in high-energy direct current networks, in particular short-circuit currents of high-performance battery systems in submarine direct current networks, comprises a plurality of parallel-connected protective devices for limiting, preferably also switching off, short-circuit currents in high-energy direct current networks, in particular short-circuit currents of high-performance battery systems in submarine direct current networks, the protective devices comprising - an electrical resistor, in particular an ohmic resistor, for guiding and limiting the short-circuit current in the event of a short circuit, - a first switch connected in parallel to the resistor for bridging the resistor when the high-energy direct current network is short-circuit-free, and - a monitoring and control device for monitoring the current through the switch and for opening the switch if the current through the switch exceeds a predetermined limit, and at least one protective device connected downstream of these protective devices, wherein the resistors of the protective devices are dimensioned such that, in the event of a short circuit, a total current formed by the sum of the currents flowing through the resistors, which flows through the protective device, triggers the protective device. This enables selectivity in the triggering of different protective devices.

[0016] Such a switchgear assembly is not known from the prior art. While DE 10 2007 053 229 A1 provides several parallel-connected current-rise-limiting protective devices 25 and a protective element 24 or an HTSC current limiter 22, it provides no indication of using current-rise-limiting protective elements, such as those disclosed, for example, in US 2008 / 0 304 198 A1 or DE 696 04 533 T2, instead of or in addition to the HTSC current limiter 22 (see paragraph 58) to limit the total short-circuit currents.

[0017] According to the invention, if the network is short-circuit-free, the current is bypassed by the electrical resistor. However, as soon as the monitoring and control device detects a short-circuit current, it opens the switch and the current is conducted through the resistor. With the help of the resistor, the short-circuit current can be limited in terms of its magnitude, its temporal effectiveness, and, if necessary, its rise (gradient), so that downstream protective devices, such as electromagnetic circuit breakers, can be reliably triggered. This enables the desired selectivity in the triggering of downstream protective devices in the DC network, whereby suitable dimensioning of the resistor can ensure that the permissible breaking currents or energies of these protective devices are not exceeded.

[0018] The total current generated during a short circuit in the DC network is thus limited to a defined overcurrent. Instead of an "uncontrolled short circuit," a "controlled and defined overload" occurs.

[0019] The electrical resistance can consist of a single resistor or of several resistors.

[0020] In principle, with suitable dimensioning and parameterization, the protective device can be used not only to limit short-circuit currents, but also to limit other overcurrents, in particular those caused by operational reasons.

[0021] Particularly fast switching of a short-circuit current to the resistor, and consequently particularly fast limitation of the short-circuit current, is possible because the first switch is designed as a power semiconductor switch. This switch also features contact wear-free operation compared to a mechanical switch.

[0022] The protective device of the switchgear preferably also includes a second switch for disconnecting the current limited by the resistor in the event of a short circuit. This switch can be used to temporarily limit the current flowing through the resistor, thus protecting the resistor and downstream protective devices from overload.

[0023] The second switch can be connected in series with the resistor. Downstream switches can then be switched off in the de-energized state and thus be designed, for example, as contactors.

[0024] Alternatively, the second switch can also be connected in series to the parallel circuit of the resistor and the first switch.

[0025] Preferably, the second switch is also designed as a power semiconductor switch.

[0026] A particularly reliable time limitation of the current conducted through the resistor and thus protection of the resistor and downstream protective devices against overload is possible in that the protective device of the switchgear comprises a monitoring and control device for monitoring the duration of a current through the second switch and for opening the second switch if the duration exceeds a predetermined limit value.

[0027] For use of the switchgear's protective device between a battery and a load, it advantageously comprises a diode connected in parallel with the power semiconductor switch, wherein the diode is polarized such that its forward direction is opposite to the forward direction of the power semiconductor switch. The battery's discharge current can then flow through the power semiconductor switch, and the battery's charging current can flow through the diode.

[0028] The switchgear preferably serves to limit and disconnect short-circuit currents of high-performance battery systems, particularly in high-energy direct current networks of submarines. The high-performance battery comprises several battery modules connected in parallel, which are connected to the high-energy direct current network via connecting conductors. The battery modules each comprise one string or several parallel strings of series-connected high-performance battery cells, wherein the or each of the strings has the mains voltage of the high-energy direct current network. The switchgear comprises one of the protective devices for each of the connecting conductors.

[0029] If the protective device comprises a first switch designed as a power semiconductor switch and a diode which is connected in parallel to the power semiconductor switch, wherein the diode is polarized such that its forward direction is opposite to the forward direction of the power semiconductor switch, the power semiconductor switch is preferably polarized such that it allows the discharge current of the battery module to pass through, and the diode is polarized such that it allows the charging current of the battery module to pass through.

[0030] According to a particularly advantageous embodiment, the protective devices are standardized and of the same type. This makes it possible to design all parallel-connected battery modules and the protective devices connected to them in the same way, so that the "controlled and defined overload" in the event of a short circuit is evenly distributed among all available (intact) battery modules.

[0031] Particularly advantageously, the design and / or parameterization of the protective devices is such that fewer than the nominal number of all battery modules can deliver a sufficiently high overcurrent to trigger downstream protective devices. If any individual battery modules fail, sufficient total overcurrent is still available to ensure the required selectivity in the event of a short circuit in the grid.

[0032] By limiting the short-circuit current to a defined overcurrent according to the invention, the energy released from current-carrying inductances in each battery module or battery string during the shutdown process is significantly smaller than in the unaffected short-circuit situation. With the solution according to the invention, the energy released during the shutdown process can be stored comparatively easily (e.g., transferred to a capacitor) and / or "dissipated," i.e., converted into heat (e.g., in a varistor) due to the now limited overcurrent. This significantly simplifies the dimensioning and / or size of the surge limiters typically required for semiconductor switches.

[0033] Due to the overcurrent limitation according to the invention provided for each battery module or each battery string, the total overcurrent in the DC network is also limited in total, so that downstream protective devices, in particular electromagnetically operated circuit breakers and protective switches, are significantly relieved during their own shutdown process in the course of selective short-circuit clearance.

[0034] The invention is primarily used in direct current networks. However, it can also be used in alternating current networks.

[0035] The invention and advantageous embodiments of the invention are explained in more detail below using exemplary embodiments in the figures, in which: Fig. 1 a schematic diagram of a first embodiment of a protective device of the switchgear according to the invention in short-circuit-free operation; Fig. 2 the protective device of Fig. 1 in case of short circuit; Fig. 3 a schematic diagram of a second embodiment of a protective device of a switchgear according to the invention; Fig. 4 a possible maximum configuration of a protective device; Fig. 5 one compared to Fig. 4 reduced configuration of a protective device; Fig. 6 one to Fig. 4 alternative reduced configuration of a protective device; Fig. 7 a possible minimum configuration of a protective device; Fig. 8 a switchgear according to the invention.

[0036] One in Fig. 1, a short-circuit protection device 1 shown in a schematic diagram is connected in connecting conductors 2, 3 of a battery 4 to a direct current network 5. The protection device 1 comprises a parallel circuit 6 of a first conduction path 7 and a second conduction path 8. The parallel circuit 6 is connected in the connecting conductor 2 with positive potential.

[0037] A preferably constant ohmic resistor 9 is arranged in the first conduction path 7. The resistor 9 serves to guide and limit a short-circuit current in the connecting conductor 2 in the event of a short circuit.

[0038] A first switch 10, preferably designed as a semiconductor power switch, is arranged in the second conduction path 8. The switch 10 serves to bridge the resistance when the network is short-circuit-free.

[0039] A preferably electronic monitoring and control device 11 serves to monitor the current I through the switch 10 and to open the switch 10 when the current I through the switch 10 exceeds a limit value stored in the monitoring and control device 11. Overcurrent detection is carried out by means of a current measuring element 12 connected in series with the first switch 10. The monitoring and control device 11 is connected to the current measuring element 12 via a signal line 13 to record the current measured values ​​and to the first switch 10 via a control line 14 to control the first switch.

[0040] By means of a switch 15 connected in series with the parallel circuit 6 and arranged in the connecting conductor 2 between the protective device 1 and the network 5, i.e., downstream of the protective device 1, a current limited by the resistor 9 can be switched off in the event of a short circuit. The switch 15 is preferably designed as a circuit breaker.

[0041] In the Fig. In the operating state shown in Figure 1, there is no short circuit in network 5. Switch 10 is therefore closed. This bridges resistor 9, and current I flows exclusively through the first switch 10.

[0042] If the current I exceeds the specified limit value in the event of a short circuit in the network 5, the monitoring and control device 11 opens the switch 10 so that the excess current is conducted via the resistor 10 and limited by it (see Fig. 2). The short-circuit current, limited to a defined value by the resistor 10, can then be switched off by the switch 15. A Fig. The protective device 1 shown in Figure 3 differs from that shown in Fig. 1 and Fig. 2 in that it has a second switch 36, designed as a semiconductor power switch, for switching off the overcurrent limited by the resistor 9. The switch 36 is connected in series with the resistor 9 in the first conduction path 7. The downstream switch 15 can then switch off in the de-energized state and can thus be designed, for example, as a contactor. The switch 36 is controlled via a preferably electronic monitoring and control device 37. Alternatively, the switch 36 can also be connected in series with the parallel circuit 6.

[0043] The monitoring and control device 37 serves to monitor the duration of a current through switch 36 and to open the second switch 36 if the duration exceeds a predetermined limit. The monitoring and control device 37 thus determines how long the defined overcurrent flows through resistor 9. If the short circuit in the network 5 cannot be cleared within the predetermined time period, the monitoring and control device 37 opens switch 36, thereby shutting off the current I. The battery 4 can then be galvanically isolated from the network 5 by opening switch 15.

[0044] If the short circuit in the network can be cleared within the specified time period, switch 36 remains closed. When the battery current I then falls below the specified limit again, switch 10 is closed by the monitoring and control device 11, and the battery current I flows again through switch 10, bypassing resistor 9.

[0045] It is also possible, after a defined time has elapsed and before the current limited by resistor 9 is switched off, to close switch 10 again so that it is automatically switched on again by the monitoring and control device 11. If the current through switch 10 then increases again, switch 10 is switched off again by the monitoring and control device 11 (possibly permanently), so that the current flows again through resistor 9. This process can also be repeated several times, or the current can be switched off permanently via switch 36. The battery 4 can then be disconnected from the mains 5 via switch 15 in the de-energized state.

[0046] Fig. 4 shows a possible maximum configuration of a protective device 1. The protective device 1 is designed as a four-pole and is based on the configuration according to Fig. 3. However, in addition to the provisions relating to Fig. 1 - 3 already explained components contactors (or circuit breakers, if applicable) 40 for all-round and all-pole separability of the protective device 1 from the battery 4 and from the mains 5 and emergency fuses 41 for all-round and all-pole emergency protection. A current rise limiter 42 serves to limit the current rise in the direction of the mains 5. On the battery side, the protective device comprises a voltage limiter 43 for the semiconductor switches, connected in parallel to the battery 4 between the connecting conductors 2 and 3. For dynamic decoupling from the mains 5, a freewheeling diode 44 is connected in parallel to the mains 5. If the diode 44 is arranged on the mains side upstream of the contactor / circuit breaker 40, its contacts are relieved during shutdown processes.

[0047] A diode 45 is connected in parallel to the switch 10, which is designed as a power semiconductor switch. The diode 45 is polarized such that its forward direction is opposite to the forward direction of the power semiconductor switch. The power semiconductor switch is polarized such that it allows the discharge current of the battery 4 to pass through, and the diode 45 is polarized such that it allows the charging current of the battery 4 to pass through.

[0048] The protective device 1 further comprises the Fig. 1 - 3 shown control and monitoring devices 11 and 37 with their associated components, which, however, are not shown to simplify the illustration.

[0049] In addition, further voltage limiters can be connected in parallel to the semiconductor switches 10, 36.

[0050] When reconnecting after a short-circuit in network 5 has been cleared, contactor / circuit breaker 40 is reconnected first. Resistor 9 can be used to limit the inrush current if, for example, voltage limiter 43 contains a capacitor (capacitor pre-charging). After switch 36 closes (with current limitation toward network 5), switch 10 is then closed (provided no fault is detected by monitoring and control device 11).

[0051] One in Fig. The reduced configuration shown in Figure 5 differs from that shown in Fig. 4 in that all-pole protection by a contactor 40 and all-pole protection by an emergency fuse 41 is only present on the mains side of the protective device 1.

[0052] One in Fig. The alternative reduced configuration shown in Figure 6 differs from that shown in Fig. The configuration shown in Figure 4 is essentially characterized by the fact that the protective device is designed as a reduced four-pole (three-pole) circuit. A contactor (or possibly a circuit breaker) 40 enables all-side and all-pole disconnection. Protection by emergency fuses 41 is provided only for connecting conductor 2 with positive potential.

[0053] One in Fig. The minimum configuration shown in Figure 7 differs from that shown in Fig. 4 is essentially characterized by the fact that the protective device 1 is essentially designed as a two-pole circuit. The switch 36 is omitted. A switch 46 arranged on the mains side provides only single-pole disconnection from the mains 5. The switch 46 must be designed as a circuit breaker, since it must switch off under load (current-limited by the resistor 9). Protection by an emergency fuse 41 is only provided on the mains side for the connecting conductor 2 with positive potential. The voltage limiter 43 is preferably designed as a varistor.

[0054] The protective devices 1 described above can be designed in a modular manner. The semiconductor components can be arranged on a common heat sink or on separate heat sinks. Depending on the installation conditions and the heat output to be dissipated, cooling can be achieved, for example, by air cooling, water cooling, or forced cooling. For applications in vehicles, a shock-resistant design is advantageous.

[0055] Fig. Figure 8 shows a simplified representation of a switchgear 50 for limiting and switching off short-circuit currents of a high-performance battery system 51 in a submarine direct current network 55. In relation to Fig. 1 - 7, identical components are designated by the same reference numerals. The high-performance battery system 51 comprises several parallel-connected battery modules 54, which are connected to the direct current network 55 via connecting conductors 2 with positive potential. For simplicity, a single-pole representation was chosen, i.e., the connecting conductors with negative potential are not shown.

[0056] The battery modules 54 each comprise one string or several parallel-connected strings of series-connected high-performance battery cells, wherein the or each of the strings has the mains voltage of the direct current network 55.

[0057] The switchgear 50 has for each of the connecting conductors 2 or each of the battery modules 54 a separate protective device 1 according to one of the Fig. 1 - 7, which is connected to the respective connecting conductor 2.

[0058] The monitoring and control devices 11, 37 of all protective devices 1 (see Fig. 1 - 3) can also be centrally combined in a single, higher-level monitoring and control device.

[0059] A protective device 56, e.g. a circuit breaker, is connected downstream of the parallel-connected protective devices 1. The resistors 9 (see Fig. 1 - 7) of the protective devices 1 are dimensioned such that in the event of a short circuit, a total current I*, which flows through the protective device 56 and which is formed by the sum of the currents I flowing through the resistors 9 of the protective devices 1, triggers the protective device 56.

[0060] A diode 45 is connected in parallel to the switch 10 of the protective devices 1, which is designed as a power semiconductor switch (see Fig.1 - 7). The power semiconductor switch is polarized to allow the discharge current of battery 4 to pass through, and diode 45 is polarized to allow the charging current of battery 4 to pass through.

[0061] All protective devices 1 of the switchgear are of the same type. This makes it possible to design all parallel-connected battery modules 54 and the protective devices 1 connected to them in the same way, so that the controlled and defined overload current in the event of a short circuit is evenly distributed among all available (intact) battery modules 54.

[0062] The design and / or parameterization of the protective devices 1 is such that less than the nominal number of all battery modules 54 in total deliver a sufficiently high total overcurrent I* to trigger the protective device 56. In the event of the failure of any individual battery modules 54, sufficient total overcurrent I* is still available to ensure the required selectivity in the event of a short circuit in the network.

Claims

[1] Switchgear (50) for limiting and switching off short-circuit currents in high-energy direct current networks (5, 55), in particular short-circuit currents of high-performance battery systems (51) in submarine direct current networks, with a plurality of parallel-connected protective devices (1) for limiting, preferably also switching off, short-circuit currents in high-energy direct current networks (5, 55), in particular short-circuit currents of high-performance battery systems (51) in submarine direct current networks, the protective devices (1) having - an electrical resistor (9), in particular an ohmic resistor, for guiding and limiting the short-circuit current in the event of a short circuit, - a first switch (10) connected in parallel with the resistor (9) for bridging the resistor (9) when the high-energy direct current network (5, 55) is free of short circuits, - a monitoring and control device (11) for monitoring a current (I) through the first switch (10) and for opening the first switch (10) when the current (I) through the switch (10) exceeds a predetermined limit value and at least one protective device (56) which is connected downstream of these protective devices (1), wherein the resistors (9) of the protective devices (1) are dimensioned such that in the event of a short circuit, a total current I* formed by the sum of the currents flowing through the resistors (9) and flowing through the protective device (56) triggers the protective device (56). [2] Switchgear (50) according to claim 1, characterized by that the first switch (10) is designed as a power semiconductor switch. [3] Switchgear (50) according to claim 1 or 2, characterized by a second switch (36) for switching off the current limited by the resistor (9) in the event of a short circuit. [4] Switchgear (50) according to claim 3, characterized bythat the second switch (36) is connected in series with the resistor (9). [5] Switchgear (50) according to claim 3, characterized by that the second switch (36) is connected in series to the parallel circuit (6) comprising the resistor (9) and the first switch (10). [6] Switchgear (50) according to one or more of claims 3 to 5, characterized by that the second switch (36) is designed as a power semiconductor switch. [7] Switchgear (50) according to one or more of claims 3 to 6, characterized by a second monitoring and control device (37) for monitoring a time duration of a current through the second switch (36) and for opening the second switch (36) when the time duration exceeds a predetermined second limit value. [8] Switchgear (50) according to claim 2, characterized bya diode (45) which is connected in parallel to the first switch (10) designed as a power semiconductor switch, wherein the diode (45) is polarized such that its forward direction is opposite to the forward direction of the first switch (10) designed as a power semiconductor switch. [9] Switchgear (50) according to one of the preceding claims, characterized byin that the switchgear (50) has a high-performance battery system (51), in particular in high-energy direct current networks (5, 55) of submarines, wherein the high-performance battery system (51) comprises a plurality of battery modules (54) connected in parallel, which are connected to the high-energy direct current network (5, 55) via connecting conductors (2), wherein the battery modules (54) each comprise one string or a plurality of parallel-connected strings of series-connected high-performance battery cells, wherein the or each of the strings has the mains voltage of the high-energy direct current network (5, 55), wherein the switchgear (50) has one of the protective devices (1) for each of the connecting conductors (2). [10] Switchgear (50) according to claims 8 and 9, characterized bythat the first switch (10) designed as a power semiconductor switch is polarized such that it allows a discharge current of the battery module (54) to pass through, and that the diode (45) is polarized such that it allows a charging current of the battery module (54) to pass through. [11] Switchgear (50) according to one of the preceding claims, characterized by that the protective devices (1) are standardised and of the same type.

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