Protection device for DC power grid

Abstract

The invention relates to a protection device for a DC power grid. The protection device includes a first terminal for coupling to a first branch portion of the power grid and a second terminal for coupling to a second branch portion of the power grid. The protection device further includes a switch assembly including one or more switch devices and a magnetic device electrically connected in series with the switch assembly between the first and second terminals of the protection device. The magnetic device has an inductance value that can vary in operation as a function of a current flowing through the protection device.

Description

Technical Field

[0001] This invention relates to the field of power grids. More specifically, this invention relates to protection devices for DC power grids that provide improved circuit protection and greatly facilitate the selective disconnection of portions of the power grid in the event of a fault. Background Technology

[0002] DC power grids are widely used in various applications, such as photovoltaic systems, naval systems, and battery-powered energy storage systems.

[0003] As is known, when a fault event (such as a short circuit) occurs in a DC power line, many electrical components electrically connected to the line can feed this electrical fault. This can obviously lead to catastrophic consequences, especially when power generation systems (such as photovoltaic panels) or energy storage systems (such as batteries) are installed in the power grid.

[0004] To prevent such accidents, DC power grids typically include protective devices configured to disconnect portions of the grid when necessary. These protective devices usually include solid-state or hybrid types of switching devices.

[0005] The main challenge in managing DC power grids is to selectively disconnect these circuits in such a way that only the faulty part of the grid is disconnected, while allowing the remaining parts of the grid to continue operating normally.

[0006] These problems stem from the fact that DC power grids are essentially power systems with distributed capacitance. This means that fault currents (e.g., short-circuit currents) typically have similar values ​​in any part of the grid and can peak within a short time (~several μs).

[0007] Therefore, protection devices located in different parts of the power grid intervene almost simultaneously when a fault event occurs, even if their size and configuration differ to intervene based on different fault thresholds. Consequently, it is virtually impossible to selectively disconnect potentially faulty sections of the power grid.

[0008] There is a great need for innovative solutions in DC power grids that allow for a high level of selectivity when disconnecting different parts of the grid, preventing unnecessary downtime for the still-operating parts of the grid when electrical fault events occur in this manner. Summary of the Invention

[0009] To meet this need, the present invention provides a protection device for a DC power grid according to claim 1 and related dependent claims.

[0010] In summary, the protection device of the present invention includes a first terminal for coupling to a first branch portion of the power grid and a second terminal for coupling to a second branch portion of the power grid.

[0011] The protection device also includes a switching assembly and a magnetic device. The switching assembly includes one or more switching devices, and the magnetic device is electrically connected in series with the switching assembly between the first and second terminals of the protection device.

[0012] Preferably, the control device is included in or operatively coupled to the protection device. The control device is configured to control one or more switching devices of the switching assembly, such that the switching devices selectively switch between a closed state and an open state.

[0013] According to the present invention, the protection device includes a magnetic device having an inductance value that is selected during operation based on the current flowing through the protection device.

[0014] Preferably, the magnetic device of the protective device has:

[0015] - First inductance value, if the current flowing through the protection device is lower than or equal to the characteristic threshold;

[0016] - The second inductance value is determined if the current flowing through the protection device exceeds a characteristic threshold.

[0017] Preferably, the first inductance value is lower than the second inductance value.

[0018] Preferably, the magnetic device of the protection device has an inductance value, which is selected according to the location of the protection device in the power grid for a given current flowing through the protection device.

[0019] According to some embodiments of the present invention, the switching assembly of the protection device includes one or more solid-state type switching devices.

[0020] According to other embodiments of the present invention, the switching assembly of the protection device includes one or more electromechanical switching devices.

[0021] According to one aspect of the invention, the magnetic device of the protective device includes:

[0022] - A magnetic circuit, which includes a magnetic body and one or more permanent magnets, one or more of which are coupled to the magnetic body and feed a corresponding magnetic flux to the magnetic body when the permanent magnet is in a magnetized state;

[0023] - One or more excitation coils, which are adapted to be fed with current flowing through the protection device, each excitation coil feeds a corresponding magnetic flux to the magnet when the excitation coil is energized.

[0024] One or more permanent magnets generate magnetic flux, saturating the magnets without current feeding one or more excitation coils.

[0025] At least one excitation coil is wound around the magnet in such a way that it generates a magnetic flux in the opposite direction to the magnetic flux generated by the permanent magnet. Attached Figure Description

[0026] Further features and advantages of the invention will become more apparent from the description of preferred, but not exclusive, embodiments shown in the accompanying drawings, which are illustrated purely by way of example and not by limitation, in which:

[0027] Figure 1 2, 3A-3D schematically illustrate the power grid according to the present invention;

[0028] Figure 4-8 This is a diagram schematically illustrating the behavior of the protective device of the present invention;

[0029] Figure 9-10 This is a schematic diagram illustrating the protective device of the present invention according to various embodiments. Detailed Implementation

[0030] Referring to the accompanying drawings, the present invention relates to a protection device P for a DC power grid.

[0031] Figure 1 A DC power grid 100 for low-voltage or medium-voltage applications is shown.

[0032] Within the framework of this invention, the term "low voltage" refers to an operating voltage of up to 1.5 kV DC (and can even be extended to 3 kV), while the term "medium voltage" generally refers to an operating voltage of more than 2.5 kV DC, up to tens of kV, such as an operating voltage of up to 100 kV DC.

[0033] Grid 100 can be used in industrial, commercial, and residential buildings or factories. As an example, its characteristics can be an average power consumption level in the range of 0.05MW to 10MW.

[0034] Power grid 100 includes multiple electrical nodes N1, N2, N3, N4, ..., N P One or more electrical branches B1, B2, B3, ..., B connected to an electrical node R .

[0035] The power grid 100 can be electrically connected to one or more electrical loads EL1, EL2, EL3, ..., EL TEach of these electrical loads is fed a certain amount of electrical power from the power grid. As needed, the electrical loads can be electrically connected to various branches of the power grid.

[0036] In principle, electrical loads can be of any type, depending on the requirements. For example, they can be electric motors, electrical systems, electrical equipment, etc. Generally speaking, an electrical load can be any device or system that consumes a certain amount of electrical power during operation.

[0037] The power grid 100 can be electrically connected to one or more power sources EG1, EG2, ..., EG Q Each of these power sources feeds a certain amount of electrical power into the power grid. As needed, the power sources can be electrically connected to various branches of the power grid.

[0038] In principle, a power source can be of any type. For example, it can be a solar panel power plant, a wind turbine power plant, a combined heat and power (CHP) system, a ship power generation system, a diesel power generation system, a geothermal or biomass power generation system, an energy storage system, etc. Generally speaking, a power source can be any device or system that generates a certain amount of electrical power during operation.

[0039] The power grid 100 can be electrically connected to other electrical systems 101, 102 as needed. These other electrical systems can be of any type and, depending on their operating conditions, can be equivalent electrical loads or equivalent power sources.

[0040] During the operation of power grid 100, DC current flows through the aforementioned electrical branches and electrical nodes.

[0041] DC current can always flow in the same direction. This can happen, for example, when grid 100 is electrically connected to a separate power source (e.g., another electrical system) and one or more electrical nodes.

[0042] Alternatively, DC current can flow in the opposite direction. This can happen, for example, when grid 100 is electrically connected to multiple power sources and / or to an electrical system whose behavior (as an electrical load or power source) can be altered according to its operating conditions.

[0043] Power grid 100 includes multiple protection devices P1, P2, P3, P4, ..., P S It is used to electrically disconnect or connect electrical loads, power sources and / or electrical branches from the rest of the power grid.

[0044] Figure 2 The protective device P according to the present invention is shown schematically.

[0045] The protection device P includes a corresponding first branch section B for coupling to the power grid. A First terminal TA and the second branch section B used for coupling to the power grid B The second terminal T B .

[0046] The protection device P includes a switching assembly SD, which includes components electrically connected to the first and second terminals T. A T B One or more switching devices.

[0047] According to some embodiments of the present invention, the switching assembly SD includes one or more solid-state type switching devices. Figure 3A Solid-state switching devices (SSDs) are based on semiconductor materials. Typically, SSDs can be conventional types, such as MOSFETs, JFETs, IGBTs, GTOs, and IGCTs.

[0048] In response to receiving an appropriate input control signal, each solid-state switch can reversibly switch between a closed state (on state) and an open state (off state). In the closed state, the solid-state switch conducts current, and in the open state, the solid-state switch blocks current.

[0049] The solid-state switch disconnects when switching from the on state to the off state and connects when switching from the off state to the on state.

[0050] Preferably, each solid-state type switching device is electrically connected in parallel to a protection circuit (not shown) adapted to protect the switching device (e.g., from voltage transients) and dissipate energy when needed. The protection circuit can be integrated with the associated switching device and can include, for example, a buffer, spark gap, discharge tube, metal oxide rheostat, or suitable semiconductor component.

[0051] When DC current can flow through the protection device in a single direction, the switching assembly SD may include a single solid-state type switching device or multiple solid-state type switching devices connected in series.

[0052] When DC current can flow through the protection device P in the opposite direction, the switching assembly SD advantageously includes multiple solid-state type switching devices arranged according to anti-parallel or anti-series configurations.

[0053] According to some embodiments of the present invention, the switching assembly SD includes at least an electromechanical type switching device, which is connected in series with one or more of the aforementioned solid-state type switching devices. Figure 3B ).

[0054] Each electromechanical type of switching device has electrical contacts that can be mechanically coupled or disengaged to conduct or block current respectively.

[0055] Each type of electromechanical switching device is in a closed state to conduct current when its electrical contacts are coupled together, and in an open state to block current when its electrical contacts are decoupled together.

[0056] One or more electromechanical switching devices may be of the automatic type, used to perform disconnection operations. In this case, the transition from the closed state to the open state (disconnection operation) occurs by utilizing the electrodynamic force generated by the circulation of current through the protection device.

[0057] Alternatively, one or more electromechanical switching devices may be of a fully controllable type. In this case, in response to receiving an appropriate input control signal, any transition from a closed state to an open state (disconnection operation) or from an open state to a closed state (closed operation) results in the activation of the drive mechanism, causing the movable contact to move or causing the movement of the movable contact to trip.

[0058] The arrangement of one or more additional electromechanical switching devices connected in series with one or more solid-state type switching devices ensures that when a protection device intervenes to interrupt the current passing through it, the electrical terminal T... A T B Current separation between them.

[0059] According to another embodiment of the invention, the switching assembly SD includes one or more electromechanical switching devices, preferably a single electromechanical switching device. Figure 3C ).

[0060] Each electromechanical type of switching device has electrical contacts that can be mechanically coupled or disengaged to conduct or block current respectively.

[0061] Each type of electromechanical switching device is in a closed state to conduct current when its electrical contacts are coupled together, and in an open state to block current when its electrical contacts are decoupled together.

[0062] According to these embodiments of the invention, at least one of the one or more electromechanical switching devices of the switching assembly SD is of a fully controllable type. Possible additional electromechanical switching devices may be of an automatic type or a fully controllable type.

[0063] According to another embodiment of the invention, the switching assembly SD includes one or more solid-state switching devices electrically connected in parallel with one or more electromechanical switching devices. Figure 3D ).

[0064] Typically, the switching devices included in the protection system of the power grid 100 can be implemented using known types of solutions. Therefore, they will be described below only with respect to aspects of interest to the present invention.

[0065] Preferably, the protection device P includes or is operatively coupled to the control device CD.

[0066] The control device CD is configured to control one or more switching devices of the switching assembly SD to selectively switch the switching devices between a closed state and an open state. For this purpose, the control device CD is configured to send appropriate control signals to the controlled switching devices.

[0067] Preferably, the control device CD is configured to receive appropriate detection signals from one or more sensors arranged to monitor the behavior of current, voltage and / or other physical quantities, and is configured to process these detection signals to generate control signals required to operate the controlled switching device.

[0068] Preferably, the control device CD is configured to process the detection information provided by the aforementioned sensors and check whether specific criteria for operating the controlled switching device are met. More specifically, the control device CD is configured to: when such a control device determines that the current flowing through the protection device exceeds a fault threshold set for the protection device, cause one or more switching devices of the protection device P to switch from a closed state to an open state to interrupt the current flowing through the protection device.

[0069] In other words, the control device CD is configured to cause the protection device P to interrupt the current flowing through it if it determines that the current is a fault current (e.g., a short-circuit current).

[0070] Preferably, the control device CD calculates a current value indicating the current flowing through the associated protection device based on the received detection information, and compares the calculated current value with a fault threshold set for the protection device. If the calculated current value exceeds the current threshold, the control device CD generates an appropriate control signal to switch one or more switching devices of the protection device to the open state, thereby interrupting the current flowing through the protection device.

[0071] The control device CD can obviously perform functions other than those described above. For example, upon receiving appropriate input signals from an HMI or a remote computerized device, a given control device can provide control signals to operate one or more switching devices of an associated protection device.

[0072] According to the present invention, the protective device P includes first and second terminals T A T B The magnetic device MD is connected in series with the switching assembly SD.

[0073] The magnetic device MD of the protection device is advantageously formed by an inductor comprising a magnet and one or more excitation windings wound around the magnet. The one or more excitation windings are electrically connected in series with each other and electrically connected to the switching assembly SD. In this way, they can be fed with current through the protection device.

[0074] According to the present invention, the magnetic device MD has an inductance value that can vary according to the current flowing through the protection device.

[0075] Preferably, if the current flowing through the protection device is less than or equal to the characteristic threshold I0, the magnetic device MD adopts a first inductance value L. A If the current flowing through the protection device is higher than the characteristic threshold I0, then the magnetic device MD adopts the second inductance value L. B .

[0076] Advantageously, the aforementioned first inductance value L A Lower than the second inductance value L mentioned above B .

[0077] Figure 4 The magnetization curve of the magnetic device MD arranged according to the last embodiment of the present invention is shown. Figure 5 In this example, the first magnetization curve is compared with the first magnetization curve (dashed line) of a conventional magnetic device used in protection devices for DC power grids. It is evident how the magnetization curve of the magnetic device exhibits different rates of change (inductance value) depending on the current circulating along the excitation winding of the magnetic device.

[0078] Figure 6 The behavior of a protective device equipped with a magnetic device MD arranged according to the last embodiment of the invention is shown.

[0079] Under normal circumstances, it has a nominal value I. n The current flows through the protection device. If at fault time t f When an electrical fault occurs (such as a short circuit), a fault current flows through the protection device. Initially, the fault current increases with time at a high rate of change because the magnetic device MD has a low inductance L for currents below the characteristic current threshold I0. A Once the characteristic current threshold I0 is exceeded, the fault current increases at a low rate of change because the magnetic device MD has a high inductance value L. B .

[0080] It can be noted that by appropriately selecting different inductance values ​​L that characterize the magnetization curve of the magnetic device MD... A L B It can adjust the behavior of the protection device when an electrical fault occurs.

[0081] Preferably, the magnetic device MD has an inductance value, which is selected for a given current flowing through the protection device P based on the location of the protection device in the power grid where it will be installed.

[0082] According to this scheme, the magnetic device MD has a magnetization curve that can be selected based on the location of the protection device in the power grid.

[0083] By appropriately selecting the structural parameters of the magnetic device (e.g., the geometric parameters of the magnet and one or more excitation coils) that affect the magnetic behavior of the magnetic device, the magnetic device MD can be designed to have a certain magnetization curve.

[0084] Preferably, for a given current flowing along the current path of the power grid in a given direction, the magnetic device MD of the protection device arranged upstream along the current path has a lower inductance value than the magnetic device of another protection device arranged downstream along the current path.

[0085] For clarity, the relative terms "upstream position" and "downstream position" refer to the direction of current along the current path as considered.

[0086] When the magnetic device MD has different inductance values ​​L depending on the current passing through the protection device A L B hour( Figure 4-6 These inductance values ​​can be advantageously selected based on the location of the protection device within the power grid 100.

[0087] refer to Figure 1 As an example, we consider a current path extending along branches B1, B2, and B6 of the power grid. Along this current path, protection devices P1 and P3 are positioned upstream and downstream, respectively (assuming the current is directed to the electrical load E). L1 ).

[0088] Arranged in different locations, the magnetic devices MD of protective devices P1 and P3 have different magnetization curves Z1 and Z3. Figure 7 These magnetization curves are configured in such a way that the first and second inductance values ​​L of the magnetic device MD of the first protection device P1 are... A1 L B1 The first and second inductance values ​​L of the magnetic device MD, which are respectively lower than those of the third protection device P3, are also lower than those of the third protection device P3. A3 L B3 .

[0089] The solution provided by the claimed invention allows for the management of protection devices for DC power grids with an improved level of selectivity. Therefore, when a fault event occurs, a specific portion of the power grid can be disconnected while allowing the remaining portions to continue normal operation.

[0090] In summary, how to appropriately select different inductance values ​​L to characterize the magnetization curve of a magnetic device MD is a key factor in understanding this concept. A L B It is obvious that the behavior of the protection device P should be adjusted when an electrical fault occurs.

[0091] As an example, let's consider again the current paths extending along branches B1, B2, B6 of the power grid ( Figure 1 ).

[0092] Because the magnetic devices MD of protection devices P1 and P3 have different magnetization curves Z1 and Z3, the behavior of the fault current depends more on the location of the electrical fault relative to protection devices P1 and P3. Figure 8 ).

[0093] If the electrical fault occurs downstream of protection devices P1 and P3, the fault current rises more slowly (curve C3) because the magnetic device MD of the third protection device P3 has a higher inductance value.

[0094] If the electrical fault occurs downstream of protection device P1 and upstream of protection device P3, the fault current rises faster (curve C1) because the magnetic device MD of the first protection device P1 has a lower inductance value.

[0095] The behavior (i.e., slope) of the fault current that feeds an electrical fault is therefore a kind of "signature" that allows the location of the electrical fault to be identified.

[0096] Employing magnetic devices with highly differentiated magnetization profiles allows for more effective differentiation of fault current behavior based on the location of the electrical fault. This enables more efficient identification of the latter, allowing for a higher level of selectivity in disconnecting different sections of the power grid.

[0097] Figure 9 and 10 Different variations of the magnetic device MD implemented according to these final embodiments of the invention are shown.

[0098] The magnetic device MD includes a magnetic circuit 10 configured to form one or more magnetic loops.

[0099] The magnetic circuit 10 includes a magnet 11, which may be made of, for example, a ferromagnetic iron or other material with suitable magnetic properties.

[0100] The magnet 11 can be implemented according to known solutions in the prior art. For example, it can be formed from a single-shaped sheet of magnetic material or from different sheets of magnetic material joined together.

[0101] according to Figure 9A variant of the magnet 11 includes a first branch 111 and a second branch 112 forming a single magnetic circuit.

[0102] according to Figure 10 In a variant, magnet 11 includes a first branch 111, a second branch 112, and a third branch 113. The first and second branches 111 and 112 are arranged on opposite sides of the third branch 113. Magnetic circuit 10 includes a first magnetic loop formed by the first and second branches 111 and 112 and a second magnetic loop formed by the second and third branches 112 and 113.

[0103] Preferably, the opposing first and second branches 111, 112 are arranged such that the magnet 11 has an overall symmetrical configuration.

[0104] Advantageously, in Figure 9-10 In both variants, magnet 11 may include one or more air gaps (not shown), which may be located at one or more branches of the magnet.

[0105] The magnetic circuit 10 also includes one or more permanent magnets 12, which are coupled to the magnet 11 and arranged such that when the permanent magnets are magnetized, a magnetic flux Φ1 with a predetermined direction is fed to them. For this purpose, the permanent magnets 12 are preferably sandwiched between opposing facing portions of the magnet 11, such as... Figure 9-10 As shown.

[0106] exist Figure 9-10 In the two embodiments shown, the permanent magnet 12 is coupled to the second branch 112 of the magnet 11.

[0107] The magnetic device MD also includes one or more excitation coils 13, 13a, 13b, which are adapted to be fed with current flowing through a protection device in which the magnetic device is arranged. Therefore, the one or more excitation coils 13, 13a, 13b are connected to the first and second terminals T of the protection device. A T B It is electrically connected in series with the switching component SD.

[0108] Each excitation coil 13, 13a, 13b is wound on a magnet 11 to feed corresponding magnetic fluxes Φ0, Φ2, and Φ3 to the magnet when the excitation coil is fed with current through the protection device.

[0109] exist Figure 9 In one embodiment, the magnetic device MD includes a single excitation coil 13 wound around a first branch 111 of a magnet, while Figure 10In one embodiment, the magnetic device MD includes first and second excitation coils 13a, 13b wound on first and third branches 111, 113 of a magnet. The first and second excitation coils 13a, 13b are arranged such that currents with opposite directions flow along the excitation coils.

[0110] A first important aspect of these embodiments of the invention is that the permanent magnet 12 is arranged in a manner that generates a magnetic flux Φ1, which is high enough to saturate the magnetic circuit 10.

[0111] Another important aspect of these embodiments of the invention is that at least one excitation coil 13, 13a is wound around the magnet 11 in such a way that when the excitation coil is fed with current flowing through the protection device, it generates a corresponding magnetic flux in the opposite direction to the magnetic flux Φ1 generated by the permanent magnet 12.

[0112] exist Figure 9 In one embodiment, a single excitation coil 13 generates a magnetic flux Φ1, which has a direction opposite to that of the magnetic flux Φ1 generated by the permanent magnet. Figure 10 In the embodiments, it is conventionally assumed that the current fed to the excitation coils 13a and 13b has such a direction that the first excitation coil 13a generates a magnetic flux Φ2 in the opposite direction to the magnetic flux Φ1 generated by the permanent magnet, and the second excitation coil 13b generates a magnetic flux Φ3 in the same direction as the magnetic flux Φ1 generated by the permanent magnet. Obviously, the magnetic fluxes Φ2 and Φ3 generated by the excitation coils 13a and 13b can typically have opposite directions, depending on the direction of the current fed to the excitation coils.

[0113] The above scheme allows the magnetic circuit 10 to be in a saturated or linear state depending on the current flowing through the protection device and feeding one or more excitation coils. This, in turn, allows for obtaining the magnetization curve of the magnetic device, based on which the magnetic device can employ different inductance values ​​depending on the current flowing through the protection device.

[0114] refer to Figure 9 The embodiments are explained in more detail to illustrate the operation of the magnetic device MD.

[0115] As described above, when no current is fed to the excitation coil 13 of the magnetic device, the permanent magnet 12 generates a magnetic flux Φ1 that saturates the magnetic circuit 10.

[0116] If the current flowing through the protection device and feeding the excitation coil 13 is lower than or equal to the characteristic threshold I0, the magnetic circuit 10 remains in saturation because the magnetic flux Φ1 generated by the permanent magnet 12 is still higher than the magnetic flux Φ0 generated by the excitation coil 13.

[0117] The magnetic device MD has a relatively low first inductance value LA ( Figure 4 ).

[0118] Therefore, by appropriately designing the geometric parameters of the magnet 11, the excitation coil 13, and the possible air gap in the magnet 11, the first inductance value L can be achieved. A How to adjust it according to needs.

[0119] When the current flowing through the protection device and feeding the excitation coil 13 exceeds the characteristic threshold I0, the magnetic circuit 10 enters a linear state because the magnetic flux Φ1 generated by the permanent magnet 12 becomes lower than the magnetic flux Φ0 generated by the excitation coil 13.

[0120] The magnetic device MD now uses a second inductance value L B It is higher than the first inductance value L A ( Figure 4 Furthermore, by appropriately designing the geometric parameters of the magnet 11, the excitation coil 13, and the possible air gap in the magnet 11, the second inductance value L can be adjusted as needed. B .

[0121] Clearly, if the current flowing through the protection device and fed to the excitation coil 13 continues to increase, the magnetic circuit 10 will again become saturated, because the magnetic flux Φ0 generated by the excitation coil 13 will be high enough to saturate the magnetic circuit. However, the current will exceed the fault threshold set for the protection device, which will intervene to interrupt it.

[0122] Therefore, the magnetic device MD can only operate as described above when the current flowing through the protection device and feeding the excitation coil 13 takes a predetermined direction. Figure 9 In its variant, the magnetic device MD actually has an overall asymmetrical configuration.

[0123] When according to Figure 10 When the variant is implemented, the operation of the magnetic device MD is basically the same.

[0124] In this case, depending on the direction of the current flowing along the excitation coil, the magnetic flux Φ2 generated by the excitation coil 13a or the magnetic flux Φ3 generated by the excitation coil 13b has the opposite direction to the magnetic flux Φ1 generated by the permanent magnet 12.

[0125] Whether the magnetic circuit 10 is in a saturated or linear state depends on whether the magnetic flux Φ1 generated by the permanent magnet 12 is higher or lower than the sum of magnetic fluxes Φ2 and Φ3, which are generated by excitation coils 13a and 13b and have the opposite direction to magnetic flux Φ1.

[0126] Therefore, it can be seen that the magnetic device MD operates independently of the direction of the current flowing through the protection device and feeding the excitation coils 13a and 13b, as described above. In fact, in Figure 10 In the variant, the magnetic device MD has an overall symmetrical configuration.

[0127] Magnetic device MD can be based on Figure 9 and 10 Other variations that operate similarly to the variant shown are implemented.

[0128] In principle, the magnet 11 can have any shape as long as one or more magnetic circuits are formed. Furthermore, the permanent magnet 12 and the excitation coils 13, 13a, 13b can be coupled to any part of the magnet 11. Additionally, any possible air gaps in the magnet 11 can be arranged at any location along the magnet 11.

[0129] The protective device according to the present invention provides relevant technical advantages.

[0130] The protection device according to the invention is equipped with a magnetic device that is electrically connected in series with a switching assembly and has a different inductance value depending on the current flowing through the protection device.

[0131] A key advantage of this solution is that by appropriately adjusting the inductance value of the onboard magnetic device, the energy dissipated during protection intervention can be reduced. This allows for a reduction in the size and manufacturing cost of the switching devices on the protection system.

[0132] Another advantage is that the ripple of the current flowing through the protection device can be avoided or limited by appropriately adjusting the inductance value of the onboard magnetic device. This allows for a significant reduction in the harmonic content introduced into the power grid.

[0133] Another advantage is that the magnetization curves of the magnetic devices in the protection devices of the power grid can be more easily distinguished. As a result, an improved level of selectivity can be achieved when disconnecting parts of the power grid.

[0134] As mentioned above, different inductance values ​​for the magnetic devices can be selected based on the location of the protection equipment in the power grid. Selection criteria similar to those commonly used in AC power grids can be employed. This greatly facilitates power grid management.

[0135] Therefore, the power grid can be managed in a robust and efficient manner, thereby avoiding or reducing unnecessary over-shedding interventions in the normally operating parts of the power grid when a fault event occurs.

[0136] Compared to conventional protective devices of the prior art, the protective device according to the present invention is relatively easy to manufacture at an industrial level at a competitive cost.

Claims

1. A protection device (P) for a DC electrical network (100), wherein said protection device comprises: - a first terminal (T A ) for coupling to a first branch portion (B A ) of the electrical grid and a second terminal (T B ) for coupling to a second branch portion (B B ) of the electrical grid; - a switching assembly (SD) comprising one or more switching devices; - a magnetic device (MD) electrically connected in series with said switching assembly between said first terminal (T A ) and said second terminal (T B ). characterized in that said magnetic device (MD) has an inductance value which is able to vary in operation as a function of the current flowing through said protection device.

2. The protection device according to claim 1, characterized in that said magnetic device (MD) has: - a first inductance value (L A ), if the current flowing through the protection device (P) is lower than or equal to a characteristic threshold value (I0); - a second inductance value (L B ), if the current flowing through the protection device (P) is higher than the characteristic threshold (I0); wherein said first inductance value (L A ) is lower than said second inductance value (L B ).

3. Protection device according to any of the preceding claims, characterized in that Said magnetic device (MD) has an inductance value (L A , L B ) selected as a function of the position of the protection device in the electrical network for a given current flowing through said protection device.

4. Protection device according to any of the preceding claims, characterized in that said switching assembly (SD) of said protection device (P) comprises one or more switching devices of solid-state type.

5. The protection device according to claim 4, characterized in that said switching assembly (SD) comprises a pair of switching devices of solid-state type arranged according to an anti-parallel or anti-series configuration to control a bidirectional current flowing through said protection device.

6. The protection device according to any one of claims 4 to 5, characterized in that, said switching assembly (SD) of said protection device (P) comprises a switching device of electromechanical type electrically connected in series with said one or more switching devices of solid-state type.

7. The protection device according to any one of claims 1 to 3, characterized in that said switching assembly (SD) of said protection device (P) comprises one or more switching devices of electromechanical type.

8. The protection device according to claim 7, characterized in that said switching assembly (SD) of said protection device (P) comprises one or more switching devices of solid-state type electrically connected in parallel with said one or more switching devices of electromechanical type.

9. Protection device according to any of the preceding claims, characterized in that said magnetic device (MD) comprises: - a magnetic circuit (10) comprising a magnet (11) and one or more permanent magnets (12) coupled to said magnet and feeding said magnet with a corresponding magnetic flux (Φ1) when said permanent magnets are in a magnetized state; - one or more excitation coils (13, 13a, 13b) adapted to be fed with a current flowing through said protection device, each excitation coil being wound on said magnet to feed said magnet with a corresponding magnetic flux (Φ0, Φ2, Φ3) when said excitation coil is fed; wherein said one or more permanent magnets (12) generate a magnetic flux (Φ1) which, in the absence of a current feeding said one or more excitation coils, brings said magnetic circuit (10) into a saturated state, wherein at least an excitation coil (13, 13a, 13b) generates a magnetic flux (Φ0, Φ2) having an opposite direction compared to the direction of the magnetic flux (Φ1) generated by said permanent magnets (12) when said excitation coil is fed.

10. The protection device according to claim 9, characterized in that Said magnetic device (MD) comprises a single excitation coil (13) electrically connected in series between said first terminal (T A ) and said second terminal (T B ) of said protection device (P) to said switching assembly (SD) of said protection device (P).

11. The protection device of claim 9, wherein The magnetic device (MD) comprises a plurality of excitation coils (13a, 13b) electrically connected in series to each other between the first terminal (T A ) and the second terminal (T B ) of the protection device and electrically connected to the switching assembly (SD) of the protection device (P).

12. The protection device according to any one of claims 9 to 11, characterized in that, said magnet (11) comprises one or more air gaps.

13. The protection device according to any one of claims 9 to 12, characterized in that, said magnet (11) comprises a first branch (111) and a second branch (112) forming a single magnetic circuit.

14. The protection device according to any one of claims 9 to 12, characterized in that, said magnet (11) comprises a first branch (111), a second branch (112) and a third branch (113), wherein said magnetic circuit comprises a first magnetic circuit formed by said first branch (111) and said second branch (112) and a second magnetic circuit formed by said second branch (112) and said third branch (113).

15. The protection device according to claim 10 or 13, characterized in that said excitation coil (13) is wound on said first branch (111) and said one or more permanent magnets (12) are coupled to said second branch (112).

16. The protection device according to claim 11 or 14, characterized in that A first excitation coil (13a) is wound on the first branch (111), a second excitation coil (13b) is wound on the third branch (112), and the one or more permanent magnets (12) are coupled to the second branch (112), wherein the first excitation coil and the second excitation coil are arranged such that electric currents with opposite directions flow along the first excitation coil and the second excitation coil.

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