DEVICE AND METHOD FOR MONITORING A FAULT CURRENT IN AN ELECTROLYSIS PLANT AND ELECTROLYSIS PLANT

Abstract

The application relates to a device (20) for monitoring a fault current (IF) of an electrolysis plant (100), wherein the device has two DC monitoring conductors (22) and an intermediate monitoring circuit (24) with earthing (PE), and each DC monitoring conductor (22) can be connected to a respective DC conductor (DC+, DC-) of the electrolysis plant (100), wherein the monitoring circuit (24, 26, 28) is configured to replicate a potential level of the DC conductors (DC+, DC-) which have an intermediate earthing (ZPE). The application further relates to an electrolysis plant (100), a method for monitoring a fault current (IF) in an electrolysis plant (100) and a use of a device (20) for monitoring a fault current (IF) in an electrolysis plant (100).

Description

TECHNICAL AREA

[0001] The application relates to a device and a method for monitoring a fault current in an electrolysis plant. The application further relates to an electrolysis plant comprising electrolyzers and such a device.

[0002] The application further concerns the use of the device in an electrolysis plant for monitoring a fault current. Monitoring the fault current is pursued primarily for safety reasons. STATE OF THE ART

[0003] DE881826 describes an earth fault monitoring device for electrolysis plants in which the center of a series connection of electrolyzers is kept at earth potential.

[0004] Alkaline electrolyzers for applications such as power-to-gas are known to feature DC grounding with low DC voltage at high DC currents. To increase efficiency and voltage, a series connection with an upside-down configuration and a common grounding base plate is used. In the upside-down configuration, two electrolyzers are connected in series, with the negative terminal of one electrolyzer and the positive terminal of the other connected to the grounded base plate. This shifts the ground potential to the center point of the series connection. The entire electrolysis system thus has a center ground.

[0005] One possible solution for residual current monitoring in electrolysis plants is a GFDI (Ground Fault Detection and Interruption) with current monitoring / disconnection at the grounding point. Such a solution is difficult to implement for electrolysis plants with series connection in an upside-down configuration because, due to the design, the base plate is directly connected to the electrolyzers and this base plate is in turn directly grounded.

[0006] An electrolyzer can comprise an array of multiple cells that work together to convert electrical energy into chemical energy. Such an array of cells in an electrolyzer is called an electrolysis stack. This allows, for example, water to be split into its components – hydrogen and oxygen. Each stack consists of several electrolysis cells connected in series or parallel. Each of these cells contains electrodes where the electrolysis reactions take place, as well as membranes that separate the resulting gases and ions. TASK

[0007] The application is based on the task of providing an improved device and an improved procedure for monitoring the fault current in an electrolysis plant. SOLUTION

[0008] The problem is solved by a device having the features of independent claim 1 and a method having the features of independent claim 12. Advantageous further developments are specified in the dependent claims. DESCRIPTION

[0009] A device for monitoring a fault current in an electrolysis plant has two DC monitoring conductors and an intermediate monitoring circuit with grounding. Each DC monitoring conductor (DC, direct current: direct current / direct voltage) can be connected to a corresponding DC conductor of the electrolysis plant. The monitoring circuit is configured to simulate the potential difference of the DC conductors, which have an intermediate ground. The fault current can, in particular, include a current flowing towards earth via the intermediate ground.

[0010] Of the DC conductors in the electrolysis system, one has a DC+ potential and the other a DC- potential. When a DC monitoring conductor is connected to each DC conductor, the potential of the monitoring conductor then corresponds to the potential of the DC conductor to which it is connected. It can be specifically arranged that the intermediate grounding of the DC conductors is located at the midpoint of the DC conductors' potentials, and that the magnitude of the respective DC+ and DC- potentials is equal. Since the intermediate grounding is located between the DC conductors, the potential of the DC conductors depends on the potential of the intermediate grounding, and vice versa.

[0011] The electrolysis plant has electrolyzers that are supplied with DC current via the DC conductors. The electrolyzers are therefore connected between the DC conductors. In particular, the electrolyzers can be connected in series between the DC conductors. They are supplied with DC power, for example, via a rectifier in the electrolysis plant from an AC network (AC, alternating current).

[0012] The fault current monitored by the system can originate from a fault in at least one of the electrolyzers, causing a potential shift in the electrolyzers relative to the DC conductors and resulting in current flowing through the intermediate ground. This current is fed by the rectifier, a power rectifier, and can become so large that it poses a risk of electric shock upon contact with the electrolysis system and / or can cause damage to the system. Therefore, the fault current flowing through the intermediate ground should be monitored, and appropriate measures should be taken if necessary.

[0013] If the power rectifier has no earth reference on either the DC or AC side, the fault current circuit closes outside the power rectifier and via the intermediate earth of the electrolyzer.

[0014] The monitoring circuit enables the simulation of the intermediate ground's potential, the detection of changes in the output potential, and optionally, the amplification of these changes for improved detection. "Equipotential" refers specifically to the potential of the intermediate ground and thus the potential difference between the DC+ conductor and ground, and between the DC conductor and ground.

[0015] The device enables the monitoring of fault currents, particularly in electrolysis plants that use a power rectifier with a split DC link. The power rectifier can also be a three-level rectifier, and the device can detect fault currents in such cases as well.

[0016] In one embodiment of the device, the monitoring circuit is configured to simulate the potential difference of the DC conductors, with two electrolyzers arranged in series between the DC conductors, and an intermediate ground connection between them. The fault current circuit thus closes via one of the electrolyzers and the intermediate ground connection between the electrolyzers. The monitoring circuit of the device enables the determination of the fault current by detecting the potential difference of the intermediate ground connection.

[0017] In some embodiments, the electrolyzers can be arranged in an upside-down configuration, for example, with a common base plate. Intermediate grounding is then achieved via the base plate. The base plate itself can be difficult to access in the electrolysis system, making direct measurement of the current towards intermediate grounding via the base plate challenging. This design allows for the detection of fault currents via the monitoring circuit. Current measurement at the base plate is therefore unnecessary.

[0018] In one embodiment of the device, the monitoring circuit for simulating the potential difference between the monitoring conductors comprises a series connection of capacitors with an intervening ground connection. The capacitors allow the monitoring circuit to act as a capacitance booster between DC+ and ground and DC- and ground, thus enabling the detection of the fault current.

[0019] To simulate the potential difference between the DC conductors, the monitoring circuit can, in particular, include two capacitors with the ground connection between them. The capacitor values ​​are chosen such that their relative values ​​correspond to the ratio of the input voltages of the electrolyzers above the intermediate ground to those below it. Depending on the position of the intermediate ground relative to the DC conductors, the relative values ​​of the capacitors can then be selected. This allows the monitoring circuit to simulate the potential difference of the intermediate ground relative to the DC conductors.

[0020] In one embodiment of the device, the capacitors are of the same size and configured to replicate a potential symmetrical to ground. It can be provided, in particular, that the electrolyzers are of the same design and that the capacitors are also of the same design and, in particular, of the same size. The monitoring circuit thus enables the detection of ground faults on the DC side by means of compensating currents resulting from a fault-induced asymmetry in the monitoring circuit, especially in the capacitance booster.

[0021] In one embodiment of the device, the monitoring circuit includes an ammeter located between the capacitors and the ground. The ground current detected by the ammeter depends on the fault current. These detected ground currents can be the compensating currents resulting from fault-induced asymmetry in the monitoring circuit, particularly the capacitance booster. Thus, the detected ground currents depend on the fault current via the intermediate ground, and the fault current can be determined from these detected ground currents.

[0022] If there is an earth current, the potential of the intermediate ground is shifted relative to the DC conductors compared to the state before the fault occurred. The potential of the capacitors relative to the monitoring conductors still corresponds to the state before the fault occurred. Consequently, a current, namely the equalizing current, flows through the ammeter to the ground between the capacitors of the monitoring circuit. The ammeter can measure this current. This equalizing current flows at the beginning of the fault. After a certain time, when the potential of the capacitors has adjusted to that of the electrolyzers, the earth current measured by the ammeter drops again, even if the fault current is still flowing through the fault location and the intermediate ground.

[0023] The monitoring of the fault current by the monitoring circuit can, for example, include monitoring whether the current measured by the ammeter rises above a predefined threshold. If this occurs, further measures can be taken, such as switching off the power transformer and / or disconnecting it from the AC network and / or the electrolyzers. A trip threshold can thus be set for the device, above which a fault current is detected. After the fault current is detected, the fault can be signaled and / or further measures can be taken.

[0024] In one embodiment, the monitoring circuit includes an auxiliary rectifier connected to the DC monitoring conductors. The auxiliary rectifier is configured to maintain the potential difference between the DC conductors and the intermediate ground in a predefinable ratio. If the potential difference is symmetrical, the auxiliary rectifier is configured to maintain this symmetrical potential difference.

[0025] If the potential difference in the electrolysis plant deviates from the predefined ratio, the auxiliary rectifier compensates for the deviation by supplying electrical power. The current generated and required for this purpose by the auxiliary rectifier can be measured by the ammeter as ground current.

[0026] The auxiliary rectifier can have a split DC link, with each part of the DC link containing one of the capacitors. This allows for a cost-effective design of the device, since the capacitors of the monitoring circuit can also serve as the DC link.

[0027] The auxiliary rectifier can be designed as an active rectifier. The grounding can be arranged in an auxiliary transformer of the device. The auxiliary transformer can, for example, supply the auxiliary rectifier with AC power from the AC network and be arranged between the AC network and the auxiliary rectifier. In this embodiment, the ammeter can, for example, be designed as a differential ammeter, i.e., a differential current meter between AC phases of an AC network.

[0028] In some embodiments, the device is configured to provide auxiliary functions for the electrolysis plant via the monitoring lines using the auxiliary rectifier. Such auxiliary functions include, for example, supporting systems and components that ensure and optimize the operation of the electrolyzer. In this embodiment, a cost-effective design of the device is possible, since the auxiliary functions required for the operation of the electrolysis plant can also be electrically powered by the device itself.

[0029] In one embodiment of the device, the auxiliary rectifier is designed as a passive rectifier, in particular as a charge pump. The current supplied and generated by the auxiliary rectifier to maintain the predefinable potential can be detected, for example, by an ammeter as earth current, which is arranged between the charge pump and the grounding system.

[0030] Active and passive rectifiers differ in how they rectify current. An active rectifier uses electronic components such as transistors (e.g., MOSFETs or IGBTs) that are clocked to perform the rectification. The components are actively driven by a clock signal to direct the current flow in the desired direction. Active rectifiers can also reverse the direction of power conversion and function as inverters. A passive rectifier uses passive components, particularly diodes. These are conductive in one direction and blocking in the other. Rectification in a passive rectifier is achieved through the properties of the passive components.

[0031] An electrolysis system comprises two DC conductors and a series connection of electrolyzers with intermediate grounding. The electrolysis system further includes the described device for monitoring a fault current. The series connection of the electrolyzers can be configured as an upside-down configuration or may include an upside-down configuration.

[0032] The electrolysis plant can further include a power rectifier to supply the electrolyzers with electrical power from an AC network. The power rectifier can, for example, be designed as a three-level rectifier with a split DC link. The power rectifier can also function as an inverter and feed electrical power into the AC network when needed.

[0033] The electrolysis system features a series connection of electrolyzers with intermediate grounding between the two DC conductors. The series connection can, in particular, include two electrolyzers in an upside-down configuration. A method for monitoring a fault current includes: Monitoring of the fault current using the described device for monitoring a fault current, wherein a respective DC monitoring conductor is connected to a respective DC conductor of the electrolysis system.

[0034] In one embodiment, the method further features: Detecting the fault current when the earth current detected by the ammeter exceeds a predefinable threshold.

[0035] In one embodiment, the method further features: Upon detection of a fault current: Open the AC-side disconnect switches and / or the DC-side disconnect switches of the electrolysis system. The AC-side disconnect switches are designed to disconnect the electrolysis system from the AC network. The DC-side disconnect switches are designed to disconnect the electrolyzers of the electrolysis system from the rectifier of the electrolysis system.

[0036] The described device can be used to monitor a fault current in an electrolysis system that has two DC conductors and a series connection of electrolyzers with intermediate grounding. The monitored fault current can, in particular, include a current flowing through the intermediate grounding. BRIEF DESCRIPTION OF THE FIGURES

[0037] The application is further explained and described below with reference to the embodiments shown in the figures. These show: Fig. 1 schematically an electrolysis plant with a first embodiment of a device for monitoring a fault current; Fig. 2 schematically the electrolysis plant of Fig. 1 in case of error; Fig. 3 schematically the electrolysis plant with a second embodiment of the device for monitoring the fault current; Fig. 4 schematically the electrolysis plant with a third embodiment of the device for monitoring the fault current; Fig. 5 schematically the electrolysis plant of Fig. 4 in case of error; Fig. 6 schematically the electrolysis plant with a fourth embodiment of the device for monitoring the fault current; Fig. 7 schematically the electrolysis plant of Fig. 5 in case of error.

[0038] The same reference symbols are used in the figures for identical or similar elements. Representations in the figures may not be to scale. FIGURE DESCRIPTION

[0039] Fig. Figure 1 schematically shows an electrolysis plant 100 with a first embodiment of a device 20 for monitoring a fault current IF.

[0040] The electrolysis plant 100 has a power rectifier 10, which is connected to an AC network 14 via AC-side disconnect switches 13 and a mains transformer 16. On the DC side, the power rectifier 10 is connected to a DC load 12 via DC conductors DC+ and DC-. The DC conductors DC+ and DC- can be interrupted via DC-side disconnect switches 11. The power rectifier 10 can be disconnected from the DC load 12 via the DC-side disconnect switches 11.

[0041] The DC load 12 comprises two electrolyzers 18, which are connected in series in an upside-down configuration between the DC conductors DC+ and DC-. An intermediate grounding conductor ZPE is arranged between the electrolyzers 18, through which the electrolyzers 18 are grounded. The intermediate grounding conductor ZPE can, for example, be provided via a base plate on which the electrolyzers 18 are mounted.

[0042] In the upside-down configuration, the positive terminal of the first electrolyzer 18 is connected to the positive DC conductor DC+. The negative terminal of the first electrolyzer 18 is connected to the intermediate ground ZPE. The positive terminal of the second electrolyzer 18 is also connected to the intermediate ground ZPE. The negative terminal of the second electrolyzer 18 is connected to the negative DC conductor DC-.

[0043] The electrolyzers can be of identical construction. For such a symmetrical design of the DC load 12, the intermediate ground ZPE is located midway between the electrical potentials of the two DC conductors DC+ and DC- with respect to the electrical potential and can be referred to as a center-ground. During normal operation of the electrolysis system with identical electrolyzers 18, the voltages of the respective DC conductors DC+ and DC- are symmetrical with respect to the intermediate ground ZPE. For example, a basic leakage current of <2 A can flow through the center-ground of a 3500Adc electrolyzer, which is tolerable with regard to fault-free normal operation.

[0044] The power rectifier 10 is configured to supply the DC load 12 with DC electrical power from the AC network 14. For this purpose, the power rectifier 10 provides a DC current IDC, which supplies the electrolyzers 18 of the DC load 12. The power rectifier 10 can, in particular, be configured as a split-circuit power rectifier 10 and, for example, have a 3-level configuration.

[0045] The in Fig. The first embodiment of the device 20, as shown in Figure 1, has two monitoring conductors 22. A first monitoring conductor 22 is electrically connected to the positive DC conductor DC+. A second monitoring conductor 22 is electrically connected to the negative DC conductor DC-. The device 20 has a monitoring circuit 24 with two capacitors, an ammeter 21, a grounding switch 23, and a protective earth (PE). The two capacitors are arranged in series between the monitoring conductors 22. The protective earth (PE) is located between the capacitors. The grounding switch 23 and the ammeter 21 are also arranged between the capacitors and the protective earth.

[0046] The voltage drop U1G across the first capacitor corresponds to the potential difference between the positive DC conductor DC+ and the intermediate ground ZPE. The voltage drop across the second capacitor U2G corresponds to the potential difference between the negative DC conductor DC- and the intermediate ground ZPE. With identical electrolyzer designs 18, the voltages U1G and U2G are equal during normal, ground-fault-free operation.

[0047] Fig. Figure 2 schematically shows the electrolysis plant of Fig. 1 in the event of a fault. An example of a fault circuit with fault current IF in the event of a DC earth fault is shown. In the illustrated example, in the event of an earth fault in the negative DC conductor DC- of the electrolysis system 100, the fault circuit with fault current IF closes via the intermediate earth ZPE of the DC load 12. Similarly, in the event of an earth fault in the positive DC conductor DC+ of the electrolysis system 100, the fault circuit with fault current IF can close via the intermediate earth ZPE of the DC load 12.

[0048] It is possible that the power rectifier 10 has no direct ground reference on either the DC or AC side. In such a case, as described in Fig. Figure 2 shows the fault current circuit with the fault current IF outside the power rectifier 10 and on the direct path to the intermediate earth ZPE of the DC load 12. It is possible that the fault condition or the fault current IF is not detectable by the power rectifier 10. This can lead to the power rectifier 10 continuing to supply the DC current IDC to the electrolyzers 18, thus feeding the DC current IDC into the fault location. For example, if the power rectifier 10 is designed as an active rectifier with a 3-phase, 3-level topology and supplies the DC load 12 via it, the described fault condition or fault current IF is not detectable at the power rectifier 10. The power rectifier 10 can, for example, be an active rectifier with a 3-phase, 3-level topology. This topology is a possible IGBT rectifier topology for high-power rectifiers with >1 MW rated power.

[0049] It is therefore possible that in such a case, power rectifier 10 continues to feed the DC current IDC to the ground short circuit and fails to detect the fault and the fault current IF. If power rectifier 10 is consequently not switched off or is switched off too late, hazards or damage can occur. For example, the undetected ground fault can also generate further hazards, such as explosion, fire, etc.

[0050] Due to the intermediate earthing system (ZPE), an insulation monitor cannot be used. Installing a DI converter that detects the fault current (IF) early and switches off the power rectifier (100) is also difficult, as closing the fault current circuit via the DI converter is physically challenging due to the base plate being part of the intermediate earthing system (ZPE).

[0051] Device 20 provides a solution for detecting the fault current IF. Device 20 includes a monitoring circuit 24 with a capacitance booster. The capacitance booster has a first capacitor between the monitoring conductor 22, which is connected to the positive DC conductor DC+, and the ground PE. The capacitance booster has a second capacitor between the monitoring conductor 22, which is connected to the negative DC conductor DC-, and the ground PE. The capacitance booster then reacts to sudden voltage changes between the positive DC conductor DC+ and the intermediate ground ZPE, and between the negative DC conductor DC- and the intermediate ground ZPE, thus enabling the detection of the ground fault.

[0052] In a symmetrical configuration of the DC load 12, i.e., with identical electrolyzers 18 and an intermediate ground ZPE arranged between them, which is configured as a center ground, the device 20 is synchronized to the voltage of the electrolyzers 18. The voltage U1G corresponds to the voltage between the positive DC conductor DC+ and ground. The voltage U2G corresponds to the voltage between the negative DC conductor DC- and ground. For this symmetrical configuration, the voltages U1G and U2G are equal in fault-free normal operation. Such a device 20 can also be referred to as a Middle-Point Fault Boost GFDI device (GFDI: Ground Fault Detection and Interruption). The device 20 does not interrupt the fault current circuit itself, but can, after detecting the fault current IF, initiate a disconnection of the power rectifier 10 from the AC network 14 via the AC-side disconnect switches 13 and / or from the DC load 12 via the DC-side disconnect switches 11.

[0053] A method for detecting the fault current IF can proceed as follows, for example: • In normal, fault-free operation, the ammeter 21 in the device 20 measures an earth current IFD of 0A to below 2A (a basic leakage current that can be tolerated may, for example, be below 2A). • In the event of a DC earth fault, the fault current circuit closes via the intermediate earthing ZPE of the DC load 12. • The fault current IF in the fault current circuit causes an asymmetry or a change in the ratio of the voltages of the positive DC conductor DC+ to earth and the negative DC conductor DC- to earth. • Since the power rectifier 10 has no direct earth reference on either the DC side or the AC side, the fault current circuit closes outside the power rectifier 10 and on the direct path to the intermediate earth ZPE between the electrolyzers 18. • In the Fig. In example 2, the earth fault in the negative DC line DC- causes a voltage asymmetry between the voltages U1G and U2G across the capacitors. This is shown in Fig. 2 by different lengths of the voltage arrows U1G and U2G. • This change in the voltage ratio drives an earth current IFD in device 20. The maximum value of the earth current IFD in device 20 corresponds in magnitude and direction to the fault current IF at the fault location in the DC conductor DC-. The earth current IFD flows into the PE earthing conductor of device 20. • The earth current IFD in device 20 can be measured by the ammeter 21 of device 20. The earth current IFD measured by the ammeter 21 flattens out with the time constant τ = C * R_Fault, where C: capacitance of one of the capacitors, R_Fault: earth resistance, down to 0 A (or a value below 2 A, with a basic leakage current in fault-free normal operation). • Device 20 detects the change in current and triggers an emergency shutdown of the power rectifier when the earth current IFD measured by ammeter 21 exceeds an adjustable threshold. Alternatively or additionally, the power rectifier can be disconnected from the DC load 12 and / or the AC network 14 via the DC disconnect switches 11 and / or the AC disconnect switches 13. • Optionally, if the threshold is exceeded, the earth reference of the device 20 can also be disconnected, e.g. by an earthing switch 23 ( Fig. 3) be separated.

[0054] The device 20 does not itself interrupt the fault current circuit, but can access the DC disconnect switches 11 in the DC power path to interrupt the fault current circuit. The device can therefore be described as "non-monolithic".

[0055] Fig. Figure 3 schematically shows the connection to Fig. 1 described electrolysis plant 100, which has a second embodiment of the device 20 for monitoring the fault current IF.

[0056] The second embodiment of the device 20 differs from the one described in the Fig. 1 + Fig. In the first embodiment shown in Figure 2, an additional damping resistor 25 and the earthing switch 23 are included. The monitoring circuit 24 comprises the earthing switch 23 and the damping resistor 25. The earthing switch 23 and the damping resistor 25 are connected in series between the earthing PE and the ammeter 21.

[0057] By means of the earthing switch 23, the monitoring circuit 24 can disconnect the capacitors from the earth PE, which can be advantageous, for example, in the event of a detected earth fault.

[0058] The method for detecting the fault current IF corresponds to that used in connection with Fig. 2 described with altered decay behavior of the earth current IFD measured by the ammeter 21 in the device 20: • In normal, fault-free operation, the ammeter 21 in the device 20 measures an earth current IFD of 0A to below 2A (a basic leakage current that can be tolerated may, for example, be below 2A). • In the event of a DC earth fault, the fault current circuit closes via the intermediate earthing ZPE of the DC load 12. • The fault current IF in the fault current circuit causes an asymmetry or a change in the ratio of the voltages of the positive DC conductor DC+ to earth and the negative DC conductor DC- to earth. • Since the power rectifier 10 has no direct earth reference on either the DC side or the AC side, the fault current circuit closes outside the power rectifier 10 and on the direct path to the intermediate earth ZPE between the electrolyzers 18. • In the Fig. In the example shown, a ground fault in one of the DC lines DC+, DC- causes (ground fault in Fig. 3 not shown) a voltage asymmetry of the voltages U1G and U2G across the capacitors. • This change in the voltage ratio drives an earth current IFD in the device 20. The maximum value of the earth current IFD in the device 20 corresponds in direction to the fault current IF at the fault location in the DC conductor. The earth current IFD flows into the earthing PE of the device 20. The magnitude of the earth current IFD is reduced compared to the fault current IF due to the damping resistance 25. • The earth current IFD in the device 20 can be measured by the ammeter 21 of the device 20. The earth current IFD measured by the ammeter 21 flattens out with the time constant τ = C* (R+R_Fault), where C: capacitance of one of the capacitors, R_Fault: earth resistance, R: resistance value of the earth resistor 25, down to 0 A (or a value below 2 A, with a basic leakage current in fault-free normal operation). • Device 20 detects the change in current and triggers an emergency shutdown of the power rectifier when the earth current IFD measured by ammeter 21 exceeds an adjustable threshold. Alternatively or additionally, the power rectifier can be disconnected from the DC load 12 and / or the AC network 14 via the DC disconnect switches 11 and / or the AC disconnect switches 13. • Optionally, if the threshold is exceeded, the earth reference of the device 20 can also be disconnected by an earthing switch 23.

[0059] The embodiment of Fig. 3 offers the advantage that, due to the earth resistance, the earth current IFD measured in the device 20 falls more slowly, and therefore more time remains to detect the fault current IF.

[0060] Fig. Figure 4 schematically shows the electrolysis plant 100 with a third embodiment of the device 20 for monitoring the fault current IF.

[0061] The electrolysis plant 100 features - as in on Fig. As described in Figure 1, the power rectifier 10 is connected to the AC network 14 via the AC-side disconnect switches 13 and the mains transformer 16. On the DC side, the power rectifier 10 is connected to the DC load 12 via the DC conductors DC+ and DC-. The DC conductors DC+ and DC- can be interrupted via the DC-side disconnect switches 11. The power rectifier 10 can be disconnected from the DC load 12 via the DC-side disconnect switches 11.

[0062] The DC load 12 comprises two electrolyzers 18, which are connected in series in an upside-down configuration between the DC conductors DC+ and DC-. An intermediate grounding conductor ZPE is arranged between the electrolyzers 18, through which the electrolyzers 18 are grounded. The intermediate grounding conductor ZPE can, for example, be connected via the base plate on which the electrolyzers 18 are mounted.

[0063] In the upside-down configuration, the positive terminal of the first electrolyzer 18 is connected to the positive DC conductor DC+. The negative terminal of the first electrolyzer 18 is connected to the intermediate ground ZPE. The positive terminal of the second electrolyzer 18 is also connected to the intermediate ground ZPE. The negative terminal of the second electrolyzer 18 is connected to the negative DC conductor DC-.

[0064] Also in the Fig. In the electrolysis system shown in Figure 4, the electrolyzers can be of identical construction. For such a symmetrical design of the DC load 12, the intermediate ground ZPE is located midway between the electrical potentials of the two DC conductors DC+ and DC- with respect to the electrical potential and can be referred to as a center-ground. During normal operation of the electrolysis system with identical electrolyzers 18, the voltages of the respective DC conductors DC+ and DC are symmetrical with respect to the intermediate ground ZPE. For example, a basic leakage current of <2 A can flow through the center-ground of a 3500A DC electrolyzer, which is tolerable with regard to fault-free normal operation.

[0065] The power rectifier 10 is configured to supply the DC load 12 with DC electrical power from the AC network 14. For this purpose, the power rectifier 10 sets the DC current IDC, which supplies the electrolyzers 18 of the DC load 12. The power rectifier 10 can, in particular, be configured as a split-circuit power rectifier 10 and, for example, have a 3-level configuration.

[0066] The in Fig. Figure 4, the third embodiment of the device 20, has two monitoring conductors 22. The first monitoring conductor 22 is electrically connected to the positive DC conductor DC+. The second monitoring conductor 22 is electrically connected to the negative DC conductor DC-. The device 20 includes the monitoring circuit 24 with an active auxiliary rectifier 26. The intermediate circuit of the active auxiliary rectifier 26 is divided and accordingly includes two capacitors. The monitoring circuit 24 further includes a differential ammeter 27, the earthing switch 23, and an auxiliary transformer 29 with the PE earth connection. Each capacitor forms a respective part of the intermediate circuit of the active auxiliary rectifier 26. The capacitors are arranged in series between the monitoring conductors 22 and are earthed via their intermediate tap through the auxiliary transformer 29.The protective earth (PE) is thus located between the capacitors via the auxiliary transformer 29. The earthing switch 23 and the differential ammeter 27 are arranged between the auxiliary rectifier 26 and the auxiliary transformer 29.

[0067] The auxiliary rectifier 26 is configured to convert AC power drawn from the AC network 14 into DC power. In addition to residual current monitoring as part of the unit 20, the auxiliary rectifier 26 can also perform other tasks in the electrolysis plant 100. For example, peripheral devices of the electrolyzers 18, such as the storage unit, pumps, and / or auxiliary units, can optionally be supplied with DC power via the auxiliary rectifier 26.

[0068] The voltage drop U1G across the first capacitor corresponds to the potential difference between the positive DC conductor DC+ and the intermediate ground ZPE. The voltage drop across the second capacitor U2G corresponds to the potential difference between the negative DC conductor DC- and the intermediate ground ZPE. With identical electrolyzer designs 18, the voltages U1G and U2G are (almost) equal during normal, ground-fault-free operation.

[0069] The in Fig. The third embodiment of the device 20, shown in Figure 4, includes the auxiliary rectifier 26, which is provided in the electrolysis plant 100 in addition to the power rectifier 10. The auxiliary rectifier 26 is a second rectifier in the electrolysis plant 100, which is significantly smaller in power rating than the power rectifier 10. The auxiliary rectifier 26 is connected in parallel to the power rectifier 10 via the auxiliary transformer 29. The auxiliary transformer 29 is preferably designed separately from the mains transformer 16. The auxiliary transformer 29 is preferably designed with a neutral point connection.

[0070] The auxiliary rectifier 26, for example, has a 3-level topology and a split DC link. The differential current meter 27 can, for example, be configured as a DI sensor for the AC side. The auxiliary rectifier 26 is designed to keep the voltages U1G and U2G in its two DC link halves nearly symmetrical. By connecting each half of the DC link in parallel to a respective electrolyzer 18, the auxiliary rectifier 26 also keeps the potential of the DC conductors DC+ and DC- symmetrical with respect to ground, i.e., the protective earth (PE) and the intermediate ground (ZPE), respectively.

[0071] If the DC load 12 and, accordingly, the intermediate circuit of the auxiliary rectifier 26 are asymmetrically constructed, the auxiliary rectifier 26 shifts energy between the intermediate circuit parts in order to maintain the set ratio of the voltages U1G, U2G to each other.

[0072] Fig. Figure 5 schematically shows the electrolysis plant 100 from Fig. 4 in case of a fault. The fault circuit with fault current IF in the event of a DC earth fault is shown as an example. In the example shown, in the event of an earth fault in the negative DC conductor DC- of the electrolysis system 100, the fault circuit with fault current IF closes via the intermediate earth ZPE of the DC load 12. Similarly, in the event of an earth fault in the positive DC conductor DC+ of the electrolysis system 100, the fault circuit with fault current IF can close via the intermediate earth ZPE of the DC load 12.

[0073] In the example shown, the power rectifier 10 has no direct ground reference on either the DC or AC side. In such a case, as in Fig. Figure 4 shows the fault current circuit with the fault current IF outside the power rectifier 10 and on the direct path to the intermediate earth ZPE of the DC load 12. It is possible that the fault condition or the fault current IF is not detectable by the power rectifier 10. This can lead to the power rectifier 10 continuing to supply the DC current IDC to the electrolyzers 18, thus feeding the DC current IDC into the fault location. For example, if the power rectifier 10 is designed as an active rectifier with a 3-phase, 3-level topology and supplies the DC load 12 via it, the described fault condition or fault current IF is not detectable at the power rectifier 10. The power rectifier 10 can, for example, be an active rectifier with a 3-phase, 3-level topology. This topology is a possible IGBT rectifier topology for high-power rectifiers with a rated power of >1 MW.

[0074] It is therefore possible that in such a case, power rectifier 10 continues to feed the DC current IDC to the ground short circuit and fails to detect the fault and the fault current IF. If power rectifier 10 is consequently not switched off or is switched off too late, hazards or damage can occur. For example, the undetected ground fault can also generate further hazards, such as explosion, fire, etc.

[0075] The third embodiment of the device 20 shown provides a solution for detecting the fault current IF. For this purpose, the third embodiment of the device 20 includes the monitoring circuit 24 and the active auxiliary rectifier 26.

[0076] In a symmetrical configuration of the DC load 12, i.e., with identical electrolyzers 18 and an intermediate ground ZPE arranged between them, which is configured as a center ground, the device 20 is synchronized to the voltage of the electrolyzers 18. The voltage U1G corresponds to the voltage between the positive DC conductor DC+ and ground. The voltage U2G corresponds to the voltage between the negative DC conductor DC- and ground. For this symmetrical configuration, the voltages U1G and U2G are equal in fault-free normal operation. Such a device 20 can also be referred to as a Middle-Point Fault Boost GFDI device (GFDI: Ground Fault Detection and Interruption). The device 20 does not interrupt the fault current circuit itself, but can, after detecting the fault current IF, initiate a disconnection of the power rectifier 10 from the AC network 14 via the AC-side disconnect switches 13 and / or from the DC load 12 via the DC-side disconnect switches 11.

[0077] Through the in Fig. In the case of the earth fault shown in Figure 5 in the negative DC conductor DC-, the fault current IF flows between the intermediate earth ZPE and the fault location. The fault current IF causes an asymmetry in the voltages of the DC conductors DC+, DC- relative to earth PE, ZPE. The higher the fault current IF, the greater the asymmetry. The auxiliary rectifier 26 now attempts to compensate for this asymmetry by generating an earth current IFD as a DC component in the AC current, which directly reflects the fault current IF.

[0078] This DC component in the AC current of the auxiliary rectifier 26 can now be detected by the differential current meter 27. In this embodiment, the auxiliary rectifier 26, with its DC link balancing, thus functions as a fault current sensor. If the fault current IF detected by the auxiliary rectifier exceeds a predefinable threshold, which is optionally offset by a maximum of 2 A from the base leakage current, a reaction can be initiated. This reaction can, for example, include disconnecting the power rectifier 10 and the auxiliary rectifier 26 from the electrolyzers 18.

[0079] The same applies to asymmetrical intermediate circuits, where an attempt is made to maintain the voltage ratio as specified. If the voltage ratio between the intermediate circuit sections changes, the auxiliary rectifier 26 counteracts this, thereby generating the earth current IFD, which can be measured.

[0080] Fig. Figure 6 schematically shows the electrolysis plant 100 with a fourth embodiment of the device 20 for monitoring the fault current IF. Except for the device 20, the electrolysis plant 100 is identical to the electrolysis plant shown in the preceding figures.

[0081] The fourth embodiment of the device 20 has a passive auxiliary rectifier 28 as an auxiliary rectifier. The passive auxiliary rectifier 28 can, for example, comprise an active voltage balancer in the form of a charge pump.

[0082] For a symmetrical DC load configuration 12, the voltage balancer of the passive rectifier 28 balances the DC voltages U1G, U2G with respect to ground PE, ZPE by transferring energy from one half of the intermediate circuit with the higher voltage to the other half with the lower voltage. Thus, energy is transferred from the capacitor with the higher voltage of U1G, U2G to the capacitor with the lower voltage of U1G, U2G via the passive rectifier 28.

[0083] If the DC load 12 and, accordingly, the intermediate circuit of the auxiliary rectifier 28 are asymmetrically constructed, the auxiliary rectifier 28 shifts energy between the intermediate circuit parts in order to maintain the set ratio of the voltages U1G, U2G to each other.

[0084] Fig. Figure 7 schematically shows the electrolysis plant 100 from Fig.4 in case of a fault. Analogous to the preceding figures, the fault circuit with fault current IF in the event of a DC earth fault is shown as an example.

[0085] In the event of such a ground fault, the auxiliary rectifier 28 attempts the described balancing. If balancing fails, a ground current IFD arises, which is equivalent to the fault current IF. The ground current IFD can be detected by the voltmeter 21, and appropriate action can be taken in response to the detected fault.

[0086] The same applies to asymmetrical intermediate circuits, where an attempt is made to maintain the voltage ratio as specified. If the voltage ratio between the intermediate circuit sections changes, the auxiliary rectifier 28 counteracts this change, thereby generating the earth current IFD, which can be measured. REFERENCE MARK LIST 10 power rectifiers 11 DC-side disconnect switches 12 DC load 13 AC-side disconnect switches 14 AC network 16 Mains transformer 18 Electrolyzer 20 Device for monitoring a fault current 21 electricity meters 22 Supervisors 23 Earthing switches 24 monitoring circuit 25 Damping resistance 26 Active auxiliary rectifier 27 Differential ammeters 28 Passive auxiliary rectifier 29 Auxiliary transformer 100 electrolysis plants IF fault current IFD Earth current in the facility 20 PE protective earth ZPE intermediate grounding DC+, DC- DC conductor IDC rectified current U1G, U2G Simulated potential level QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 881826

[0003]

Claims

[1] Device (20) for monitoring a fault current (IF) of an electrolysis plant (100), wherein the device has two DC monitoring conductors (22) and an intermediate monitoring circuit (24) with earthing (PE) and each DC monitoring conductor (22) can be connected to each DC conductor (DC+, DC-) of the electrolysis plant (100), wherein the monitoring circuit (24, 26, 28) is configured to replicate a potential position of the DC conductors (DC+, DC-) which have an intermediate earthing (ZPE). [2] Device according to claim 1, wherein the monitoring circuit (24) is configured to replicate a potential position of the DC conductors (DC+, DC-), wherein two electrolyzers (18) are arranged in series between the DC conductors (DC+, DC-) and the intermediate earth (ZPE) is arranged between them. [3] Device according to claim 1 or 2, wherein the monitoring circuit (24) for replicating the potential position between the monitoring conductors (22) comprises a series connection of capacitors with an earthing conductor (PE) arranged between them. [4] Device according to claim 3, wherein the capacitors are of the same size and are configured to replicate a potential symmetrical to earth. [5] Device according to claim 3 or 4, wherein the monitoring circuit (24) has an ammeter (21, 27) which is arranged between the capacitors and the earth (PE), wherein the earth current (IFD) detected by the ammeter (21, 27) depends on the fault current (IF). [6] Device according to one of the preceding claims, wherein the monitoring circuit (24) has an auxiliary rectifier (26, 28) which is connected to the DC monitoring conductors (22). [7] Device according to claim 6, wherein the auxiliary rectifier (26, 28) has a split intermediate circuit, wherein each part of the intermediate circuit has one of the capacitors. [8] Device according to claim 6 or 7, wherein the auxiliary rectifier (26) is configured as an active rectifier (26) and the earthing (PE) is arranged in an auxiliary transformer (29) of the device (20). [9] Device according to claim 8, wherein the device (20) is configured to provide auxiliary functions via the monitoring conductors (22) for the electrolysis plant (100) using the auxiliary rectifier (26). [10] Device according to claim 6 or 7, wherein the auxiliary rectifier (28) is designed as a passive rectifier, in particular as a charge pump (28). [11] Electrolysis system comprising two DC conductors (DC+, DC-) and a series connection of electrolyzers (18) with intermediate earthing (ZPE) arranged between them, further comprising a device (20) according to one of the preceding claims. [12] Method for monitoring a fault current (IF) in an electrolysis plant (100) which has a series connection of electrolyzers (18) with intermediate earthing (ZPE) between two DC conductors (DC+, DC-), wherein the method comprises: Monitoring of the fault current (IF) by means of a device (20) connected to the DC conductors (DC+, DC-) according to one of claims 1 to 10. [13] Method according to claim 12, further comprising: Detection of the fault current (IF) when the earth current (IFD) detected by the ammeter (21, 27) exceeds a predefinable threshold. [14] Method according to claim 12 or 13, further comprising: Upon detection of the fault current (IF): Open the AC-side disconnect switches (13) and / or DC-side disconnect switches (11) of the electrolysis system. [15] Use of the device according to any one of claims 1 to 10 for monitoring a fault current (IF) in an electrolysis plant (100) which has two DC conductors (DC+, DC-) and a series connection of electrolyzers with intermediate earthing (ZPE) arranged between them.

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