Hybrid switchgear for power networks

Abstract

A switching device for an electric power network comprises: - first and second electrical terminals; - a first electrical branch; - a second electrical branch comprising a plurality of switching devices of the solid-state type, each of said plurality of switching devices comprising one or more switching components based on a semiconductor material. Said second electrical branch is electrically connected in parallel with the first electrical branch between the first and second electrical terminals. The switching device comprises a current blocking circuit adapted to block the current flowing along said second electrical branch. Said current blocking circuit comprises a first switching device of the solid-state type and a first electronic circuit electrically connected in parallel to said first switching device of the solid-state type. The switching device further comprises a current limiting circuit adapted to limit the current flowing along said second electrical branch. The current limiting circuit is electrically connected in series with the current blocking circuit and it comprises a second switching device of the solid-state type and a second electronic circuit electrically connected in parallel to said second switching device of the solid-state type.

Description

Technical Field

[0001] The present invention relates to the field of power grids. The present invention more particularly relates to a hybrid switching device for providing circuit protection functionality in a power grid, such as a DC power grid. Background Art

[0002] DC power grids are widely used in a variety of applications, such as photovoltaic systems, naval systems, battery-based energy storage systems (BESS), etc.

[0003] As is known, when a fault event (such as an overload or a short circuit) occurs in a DC wire, many electrical components electrically connected to the wire can potentially feed this electrical fault.

[0004] Obviously, this can lead to catastrophic consequences, especially when a power generation system (such as a photovoltaic panel) or an electrical energy storage system (such as a battery) is installed in the power grid.

[0005] To prevent such contingencies, DC power grids typically include a plurality of switching devices configured in such a way as to allow selectively disconnecting parts of the power grid when a fault event occurs.

[0006] Some switching devices of the prior art include switching means of the electromechanical type, i.e., switching means having electrical contacts (such as a circuit breaker) that can be coupled or separated to conduct or block current, respectively.

[0007] Generally speaking, these switching means have the advantage of ensuring current isolation between the disconnected parts of the power grid. Additionally, they are relatively inexpensive to implement at the industrial level.

[0008] However, due to their operating principle, electromechanical switching means generally do not provide a satisfactory interrupt rating. For example, at higher voltages (such as up to 1.5 kV DC or above), Open the time can be quite long. The arc that typically strikes between the electrical contacts under separation can thus last for a long time. Obviously, this fact can Cause pose relevant problems in terms of reliability and maintenance costs.

[0009] Other switching devices of the prior art include switching means of the solid-state type, i.e., switching means including switching components based on semiconductor materials.

[0010] The main advantage of solid-state switching means is that they potentially have infinite electrical durability due to their arc-free switching operation.

[0011] Furthermore, these devices are fast-operating and have an interruption time significantly shorter than that of electromechanical switching means.

[0012] However, when in a closed state, they generally require intensive cooling to remove the heat generated by the current.

[0013] To mitigate the above problems, hybrid switch devices that employ both electromechanical switch devices and solid-state switch devices have been developed. Examples of such protection devices are disclosed in WO2017 / 186262 and WO2011 / 057675.

[0014] Generally, and especially in the case of a short circuit, this type of known switch device is not able to properly manage the current from the electromechanical switch device Commutation to the solid-state switch device.

[0015] For example, due to the long time required to commutate the current from one electrical branch to another, they are not able to intervene as quickly as a device that employs only solid-state switch devices.

[0016] In addition, the solid-state switch devices must be designed to withstand high currents for a long time. Therefore, they are generally bulky and have a high manufacturing cost at the industrial level. Summary of the Invention

[0017] A main object of the present invention is to provide a hybrid switch device for an electric power network (such as a DC power network), which allows overcoming or mitigating the above criticalities.

[0018] A more particular object of the present invention is to provide a hybrid switch device that ensures a performant interrupt rating in the case of an electrical fault, especially in the presence of a short-circuit current.

[0019] As a further object, the present invention aims to provide a hybrid switch device in which a less expensive and smaller-sized solid-state switch device can be employed relative to corresponding solutions of the prior art.

[0020] Yet another object of the present invention is to provide a hybrid switch device that can be easily manufactured at the industrial level at a competitive cost relative to solutions of the prior art.

[0021] To meet these goals and objects, the present invention provides a switch device as described in claim 1 and related dependent claims below.

[0022] The hybrid switch device according to the present invention comprises:

[0023] - a first electrical terminal and a second electrical terminal for electrical connection to a corresponding network section;

[0024] - A first electrical branch, which includes one or more switching devices of electromechanical type, each of the one or more switching devices having electrical contacts that are mechanically coupled or separated to conduct or block current respectively;

[0025] - A second electrical branch, which includes a plurality of switching devices of solid-state type, each of the plurality of switching devices including one or more switching components based on semiconductor materials. Each solid-state switching device is adapted to switch between a conducting state and a non-conducting state, in the conducting state, the switching device conducts current, and in the non-conducting state, the switching device blocks current.

[0026] The second electrical branch as described above is connected in parallel with the first electrical branch Short circuit connection between the first electrical terminal and the second electrical terminal.

[0027] According to the present invention, the switching device includes a current blocking circuit, which is adapted to block the current flowing along the second electrical branch. The current blocking circuit includes a first switching device of solid-state type and a first electronic circuit connected in parallel electrically to the first switching device of solid-state type.

[0028] According to the present invention, the switching device includes Current limit a circuit, a current limiting circuit, which is adapted to limit the current flowing along the second electrical branch. The current limiting circuit is connected in series electrically with the current blocking circuit, and it includes a second switching device of solid-state type and a second electronic circuit connected in parallel electrically to the second switching device of solid-state type.

[0029] According to some embodiments of the present invention, the first electrical branch of the switching device includes a single switching device of electromechanical type, which is capable of reversibly switching between a closed state and an open state, in the closed state, the first switching device conducts current, and in the open state as described above, the first switching device blocks current.

[0030] According to some embodiments of the present invention, the first electrical branch of the switching device includes a first switching device of electromechanical type and a second switching device of electromechanical type connected in series electrically.

[0031] The first switching device of electromechanical type is capable of switching between a closed state and an open state, in the closed state, the first switching device of electromechanical type conducts current, and in the open state, the first switching device of electromechanical type blocks current.

[0032] The first switching device of the electromechanical type is a self-acting switching device that can switch from the closed state to the open state when driven by the current flowing through the switching device and without receiving an external control signal or an external power supply.

[0033] In operation, when the current flowing through the switching device exceeds a corresponding predefined threshold, or when the rate of change of the current flowing through the switching device exceeds a corresponding predefined threshold, or in a combination of these two conditions, the first switching device of the electromechanical type switches from the closed state to the open state.

[0034] The second switching device of the electromechanical type can be switched between a closed state and an open state. In the closed state, the second switching device of the electromechanical type conducts current, and in the open state, the second switching device of the electromechanical type blocks current.

[0035] In operation, when receiving a corresponding input control signal, the second switching device of the electromechanical type switches between the closed state and the open state.

[0036] Preferably, the first switching device of the electromechanical type includes a first actuator that can use the electrodynamic force generated by the flow of current along the switching device to actuate the electrical contact portion of the first switching device of the electromechanical type, thereby switching the first switching device of the electromechanical type from the closed state to the open state.

[0037] Preferably, the first actuator includes a Thomson coil actuating device that is operatively coupled to the electrical contact portion of the first switching device of the electromechanical type.

[0038] Preferably, the second switching device of the electromechanical type includes a second actuator that actuates the electrical contact portion of the second switching device of the electromechanical type when receiving a corresponding input control signal.

[0039] The first switching device of the solid-state type can be arranged in such a way: either of the unidirectional or bidirectional type, that is, it can carry and interrupt the current flowing in only one direction in a DC network, or it can carry and interrupt the current in any direction in a DC or AC network.

[0040] According to some embodiments of the present invention, the first switching device of the solid-state type includes a pair of switching components based on semiconductor materials, and the pair of switching components are arranged in an anti-parallel or anti-series configuration to allow control of the bidirectional current flowing along the second electrical branch.

[0041] According to some embodiments of the present invention, the second ElectronThe branch circuit includes a first diode bridge, which is operatively associated with the current blocking circuit to allow control of the bidirectional current flowing along the second electrical branch circuit.

[0042] Moreover, the second switching device of the solid state type can be arranged in such a way: either of the unidirectional or bidirectional type.

[0043] According to some embodiments of the present invention, the second switching device of the solid state type includes a pair of switching components based on semiconductor materials, and the pair of switching components are arranged in an antiparallel or antiserial configuration to allow control of the bidirectional current flowing along the second electrical branch circuit.

[0044] According to some embodiments of the present invention, the second electronic branch circuit includes a second diode bridge, which is operatively associated with the current limiting circuit to allow control of the bidirectional current flowing along the second electrical branch circuit.

[0045] According to some embodiments of the present invention, the second electrical branch circuit includes a third diode bridge circuit, which is arranged in such a way: allowing control of the bidirectional current.

[0046] Preferably, the above-mentioned first switching device of the electromechanical type is suitable for switching from the closed state to the open state when a short-circuit current flows along the switching device.

[0047] Preferably, the above-mentioned first switching device of the electromechanical type is not suitable for switching from the closed state to the open state when an overload current or a normal current flows along the switching device When from to the open state.

[0048] Preferably, the above-mentioned second switching device of the electromechanical type is suitable for switching from the closed state to the open state when a short-circuit current flows along the switching device. However, if an overload current or a normal current flows along the switching device, the second switching device of the electromechanical type can also be commanded to switch from the closed state to the open state.

[0049] Preferably, the above-mentioned first switching device of the solid state type is suitable for switching from the conducting state to the off state after a first time interval has elapsed since the moment when the short-circuit current has commutated from the first electrical branch circuit to the second electrical branch circuit.

[0050] Preferably, the above-mentioned first switching device of the solid state type is suitable for switching from the conducting state to the off state after a third time interval has elapsed since the moment when an overload current or a normal current has commutated from the first electrical branch circuit to the second electrical branch circuit.

[0051] Preferably, the above-mentioned second switching device of the solid state type is suitable for switching from the conducting state to the off state after the current has commutated from the first electrical branch circuit to the second electrical branch circuit.

[0052] In a further aspect, the present invention relates to a method for protecting an electric power network as described in claim 18 below and the related dependent claims.

[0053] Generally, the electric power network includes a plurality of switch groups for electrically connecting or disconnecting different network sections of the electric power network.

[0054] Preferably, the electric power network includes: a battery energy storage system including a plurality of battery cells; a DC bus for electrically connecting the battery cells to a power converter; and a plurality of switch groups for electrically connecting the battery cells to the DC bus or disconnecting the battery cells from the DC bus.

[0055] Each switch group includes:

[0056] - a switching device of the present invention capable of controlling bidirectional current. The switching device can Switch to a closed state in which the switching device conducts current, or an open state in which the switching device blocks current, or a current limiting mode in which the switching device limits the current commuting from the first electrical branch to the second electrical branch;

[0057] - an isolator electrically connected in series with the switching device. The isolator can be switched to a closed state in which the isolator conducts current or an open state in which the isolator blocks current.

[0058] Each switch group can be switched to a closed state in which the switching device is in the closed state and the isolator is in the closed state, or switched to an open state in which the switching device is in the open state and the isolator is in the open state, or switched to a current limiting mode in which the switching device is in the current limiting mode and the isolator is in the closed state.

[0059] The method of the present invention includes the following steps:

[0060] - If there is an electrical fault in the electric power network, switch the switch group to the current limiting mode;

[0061] - Switch the switch group closest to the electrical fault to the open state and keep the remaining switch groups of the electric power network in the current limiting mode;

[0062] If the electrical fault is electrically isolated within a predefined time interval when the switch group closest to the electrical fault is in the open state, then:

[0063] - Keep the switch group closest to the electrical fault in the open state and switch the remaining switch groups of the power grid to the closed state;

[0064] If the electrical fault is not electrically isolated within a predefined time interval when the switch group closest to the electrical fault is in the open state, then:

[0065] - Switch all switch groups of the power grid to the open state. Description of the Drawings

[0066] According to the description of a preferred but non-exclusive embodiment of the contactor according to the present invention, further features and advantages of the present invention will become apparent. Non-limiting examples of the present invention are provided in the drawings, wherein:

[0067] - Figure 1-7 Schematically shows some embodiments of the switching device according to the present invention;

[0068] - Figure 8 Schematically shows a DC power grid including a switching device according to the present invention;

[0069] - Figure 9-16 Schematically shows an operating example of a DC power grid according to the present invention, the DC power grid including a battery energy storage system, the battery energy storage system including a plurality of switch groups, each of the switch groups including a switching device. Detailed Description

[0070] Referring to the accompanying drawings, the present invention relates to a hybrid switching device 1 for a power grid.

[0071] The switching device of the present invention is particularly suitable for use in low-voltage DC power grids, and will be described hereinafter with particular reference to these applications only for the sake of brevity, and is not intended to limit the scope of the present invention in any way.

[0072] The switching device of the present invention can actually be successfully used in different types of power systems (such as low-voltage AC power grids or medium-voltage AC or DC power grids).

[0073] For the purposes of the present application, the term "low voltage" (LV) relates to operating voltages below 1 kV AC and 1.5 kV DC, while the term "medium voltage" (MV) relates to operating voltages above 1 kV AC and 1.5 kV DC up to several tens of kV (e.g., up to 72 kV AC and 100 kV DC).

[0074] The switching device 1 includes first and second electrical terminals 11, 12 for electrical connection to corresponding grid sections (not shown) (such as a DC link bus and an electrical load).

[0075] Preferably, at one of the electrical terminals 11 - 12, an isolator (or another equivalent switching device) 150 is operatively associated with the switching device 1 to form a switching group 110.

[0076] The isolator 150 is arranged to electrically connect or disconnect the switching device from another circuit portion of the power grid. Thus, the isolator 150 can provide electrical insulation between different circuit portions (one of which includes the switching device 1) whenever necessary.

[0077] For this purpose, the isolator 150 is adapted to reversibly switch between a closed state in which it conducts current and an open state in which it blocks current.

[0078] The isolator 150 may or may not be an integral part of the switching device.

[0079] Generally, the isolator 150 can be of a known type. Therefore, its functionality will only be described hereinafter with respect to aspects of interest of the present invention.

[0080] The switching device 1 includes a first electrical branch 3 and a second electrical branch 4 electrically connected in parallel between the electrical terminals 11, 12.

[0081] The first electrical branch 3 includes one or more switching devices 30, 31, 32 of the electromechanical type, i.e., switching devices having electrical contacts that can be coupled or separated upon the application of appropriate mechanical or electromechanical forces.

[0082] Each electromechanical switching device 30, 31, 32 of the first electrical branch 3 has electrical contacts that can be mechanically coupled or separated to conduct or block current, respectively.

[0083] Each electromechanical switching device 30, 31, 32 of the first electrical branch 3 more particularly has one or more fixed contacts and one or more movable contacts, the movable contacts being able to be coupled or decoupled from the fixed contacts to conduct or block current.

[0084] Each electromechanical switching device 30, 31, 32 of the first electrical branch 3 is in a closed state when its electrical contacts are coupled to conduct current and in an open state when its electrical contacts are decoupled to block current.

[0085] Generally, one or more switching devices 30, 31, 32 of the first electrical branch 3 can be implemented according to known type solutions. Therefore, they will only be described hereinafter with respect to aspects of interest of the present invention.

[0086] According to some embodiments of the present invention ( Figure 1 、 Figure 3 、 Figure 5 、Figure 6 ),the first electrical branch 3 includes a single switching device 30 of electromechanical type, which is capable of switching between a closed state in which the switching device conducts current and an open state in which the switching device blocks current.

[0087] Preferably, the switching device 30 switches from the closed state to the open state (open operation) or from the open state to the closed state (closed operation) in response to receiving an appropriate input control signal, which causes activation of the drive mechanism to move the movable contact or to cut off (trip) the movement of the movable contact.

[0088] As illustrated below, the control signal for controlling the operation of the switching device 30 can be conveniently provided by a control unit 90, which may or may not be part of the switching equipment.

[0089] In operation, when a normal current, overload current or short - circuit current flows through the switching equipment, the switching device 30 can be commanded to switch from the closed state to the open state as required.

[0090] For the sake of brevity, it is stipulated for the purposes of the present application that:

[0091] - A "normal current" is a current that typically has an operating value around the nominal value (e.g., up to 1.1 times the nominal value or less);

[0092] - An "overload current" is a current that typically has a higher operating value (e.g., from 1.1 times the nominal value up to 10 times the nominal value);

[0093] - A "short - circuit current" is a current that typically has an even higher operating value (e.g., from 10 times the nominal value up to dozens of times the nominal value).

[0094] According to other embodiments of the present invention ( Figure 2 , Figure 4 , Figure 5A , Figure 7 ), the first electrical branch 3 includes a first switching device 31 of electromechanical type and a second switching device 32 of electromechanical type connected in series.

[0095] The switching device 31 is a self - acting switching device, which is capable of quickly switching from the closed state to the open state when it is driven by the current flowing through the switching equipment. Thus, the switching device 31 is capable of performing an open operation without receiving an external control signal commanding such an operation or without receiving an external power supply.

[0096] For the sake of brevity, within the scope of the present invention, a switching device of the electromechanical type is considered "fast" when it exhibits an opening time of the electrical contact that is less than 1 ms, and more preferably less than 500 μs. Switch ".

[0097] When the current flowing through the switching device exceeds a corresponding threshold (e.g., the short - circuit value, typically 10 - 20 times the nominal value), or when the rate of change of the current exceeds a corresponding threshold (e.g., greater than 10 kA / ms), or when a combination of events occurs, the switching device 31 is adapted to quickly switch from the closed state to the open state (opening operation). These two bars ".

[0098] Preferably, the switching device 31 is adapted to quickly switch from the closed state to the open state (opening operation) whenever a short - circuit current flows through the switching device, and it is not adapted to switch from the closed state to the open state (opening operation) when an overload current or a normal current flows through the switching device.

[0099] Preferably, the switching device 31 includes a first actuator (not shown) that is capable of using the electrodynamic force generated by the circulation of the current flowing through the switching device during an opening operation to actuate the electrical contact.

[0100] Preferably, the switching device 31 includes Thomson coil actuating means (not shown) that is operatively coupled to the electrical contact (e.g., via a suitable kinematic chain) in order to actuate the electrical contact during an opening operation.

[0101] When the circulating current exceeds a corresponding threshold and / or when the rate of change of the current exceeds a corresponding threshold, especially when the circulating current is a short - circuit current, the Thomson coil actuating means is adapted to provide sufficient actuating force to separate the electrical contact of the switching device 31.

[0102] Generally, the Thomson coil actuating means is operatively connected to the electrical contact of the first switching device 31 of the electromechanical type via a suitable kinematic chain, and it is arranged along the first electrical branch.

[0103] According to some embodiments of the present invention, the Thomson coil actuating means is serially electrically connected to the above - mentioned first terminal 11 or second terminal 12 of the switching device. More particularly, the Thomson coil can be arranged between the first terminal 11 or second terminal 12 and the common node of the first electrical branch 3 and the second electrical branch 4 (at this common node, the electrical branches are separated from each other).

[0104] According to other embodiments of the present invention, the Thomson coil actuating means is arranged along the first electrical branch 3, and it is serially electrically connected to the electrical contact of the first switching device 31 of the electromechanical type.

[0105] According to some embodiments of the present invention, if the current no longer flows along the first electrical branch 3 or if the current returns to a lower density value for any reason, the first switching device 31 of electromechanical type is adapted to return to the closed state immediately after an opening operation. To this end, the first switching device 31 includes a suitable spring-operating mechanism (not shown), which actuates the electrical contacts by using the elastic energy stored during the opening operation.

[0106] According to other embodiments of the present invention, once the opening operation has been performed, the first switching device 31 of electromechanical type is adapted to remain in the open state. To this end, the first switching device 31 of electromechanical type may include a suitable latching mechanism (not shown) capable of keeping the electrical contacts separated and an actuating mechanism (not shown) for coupling the electrical contacts when receiving a corresponding input control signal.

[0107] According to an additional variant of the present invention (not shown), an electronic circuit (e.g., including a buffer circuit, a spark gap, a discharge tube, a metal oxide varistor, or a semiconductor component) is electrically connected in parallel to the first switching device 31 in order to protect the first switching device 31 (e.g., by limiting voltage transients) and / or dissipate electrical energy during the opening operation of the switching device whenever necessary.

[0108] According to the above embodiments of the present invention ( Figure 2 、 Figure 4 、 Figure 5A 、 Figure 7 ), the first electrical branch 3 includes a second switching device 32 of electromechanical type, which is electrically connected in series with the first switching device 31 of electromechanical type.

[0109] The switching device 32 of electromechanical type is fully controllable and it reversibly switches between the closed state and the open state when receiving a corresponding input control signal for the execution of a command operation.

[0110] As illustrated below, the control signal for controlling the operation of the switching device 32 of electromechanical type can be conveniently provided by a control unit 90, which may or may not be part of the switching device.

[0111] Generally, the switching device 32 of electromechanical type has a considerably long opening time compared to the first switching device, e.g., several Millisecond (e.g., approximately 5 to 20 ms).

[0112] Preferably, the switching device 32 of electromechanical type includes a second actuator of electromechanical type, which actuates the electrical contacts of the second switching device when receiving a corresponding input control signal.

[0113] Preferably, whenever the first switching device 31 switches from the closed state to the open state, especially when a short-circuit current (for example, a value 10 - 20 times the nominal value) flows along the first electrical branch 3, the switching device 32 of electromechanical type is commanded to switch from the closed state to the open state.

[0114] However, unlike the first switching device 31 of electromechanical type, even when the current circulating along the first electrical branch 3 takes a value lower than the above short-circuit value, the second switching device 32 of electromechanical type can also be commanded to switch from the closed state to the open state (opening operation).

[0115] Thus, if an overload current (for example, a value 2 - 3 times the nominal value) flows along the first electrical branch 3, or even when the current flowing along the first electrical branch 3 takes a normal value (for example, around or below the nominal value), if the opening operation of the hybrid switchgear must be performed, for example, at the request of an operator, the second switching device 32 of electromechanical type can be commanded to perform the opening operation.

[0116] As described above, the first and second switching devices 31, 32 of electromechanical type are connected in series electrically. In this way, these switching devices can control the current circulating along the first electrical branch 3 in an appropriate manner according to the nature of such current.

[0117] For example, if the current circulating along the first electrical branch 3 is a short-circuit current, the first switching device 31 of electromechanical type intervenes quickly to perform the opening operation, and it blocks the current without receiving an input control signal. In this case, the second switching device 32 of electromechanical type is also commanded to perform the opening operation. However, since it is slower than the first switching device 31, the second switching device 32 of electromechanical type will perform this opening operation later than the first switching device 31, usually when the current has switched To the place to the second electrical branch 4.

[0118] If the current flowing along the first electrical branch 3 is a normal current or an overload current, the first switching device 31 of electromechanical type does not intervene, and the second switching device 32 of electromechanical type can be commanded to perform the opening operation when receiving an appropriate control signal in the input to block such current.

[0119] According to the present invention, the second electrical branch 4 includes a plurality of switching devices 41, 42 of solid-state type.

[0120] Each switching device 41, 42 of solid-state type includes one or more switching components based on semiconductor materials. Generally speaking, the semiconductor switching components can be of a conventional type, such as power MOSFET, JFET, insulated gate bipolar transistor ("IGBT"), gate turn-off thyristor (GTO), integrated gate-commutated thyristor ("IGCT"), etc.

[0121] In response to receiving an appropriate input control signal, each solid-state switching device 41, 42 of the second electrical branch 4 can be reversibly switched between its on-state in which it conducts current and its off-state in which it blocks current.

[0122] The solid-state switching devices 41, 42 turn off when it switches from the on-state to the off-state, and turn on when it switches from the off-state to the on-state.

[0123] As illustrated below, the control signal for controlling the operation of the solid-state type switching devices 41, 42 can be conveniently provided by a control unit 90, which may or may not be part of the switching device.

[0124] According to the present invention, the second electrical branch 4 includes a current blocking circuit 40A, which is suitable for blocking the current circulating along the second electrical branch 4.

[0125] The blocking circuit 40A includes a first switching device 41 of solid-state type and a first electronic circuit 48, which is suitable for protecting the first switching device of solid-state type (e.g., against voltage transients) and dissipating electrical energy whenever necessary.

[0126] The first electronic circuit 48 is electrically connected in parallel to the switching device 41 of solid-state type, and may include a buffer circuit, a spark gap, a discharge tube, a metal oxide varistor or a semiconductor component.

[0127] Generally, the first switching device 41 of solid-state type is operated according to the behavior of the current circulating along the second electrical branch 4 and according to the behavior of the switching devices 30 or 31, 32 of the first electrical branch 3.

[0128] As will be better apparent hereinafter, this solution allows to manage in an effective way the operating conditions in which an overload current or a short-circuit current circulates.

[0129] Preferably, if for any reason it is in the off-state, an electromechanical type switching device 30 or the first switching device 31 or the second switching device 32 performs an opening operation or before it, the first switching device 41 of solid-state type is commanded to switch to the on-state. In this way, the current circulating along the first electrical branch 3 is allowed to commutate to the second electrical branch 4.

[0130] Preferably, the first switching device 41 of solid-state type turns off after a first time interval has elapsed since the short-circuit current (i.e., higher than a predefined short-circuit threshold) has completely commutated from the first electrical branch 3 to the second electrical branch 4 due to an opening operation performed by the electromechanical type switching device 30 or the first switching device 31.

[0131] Preferably, the first time interval is calculated based on the minimum time requested for restoring the dielectric tolerance of the gap between the electrical contacts of the electromechanical type switch device 30 or the first switch device 31 in order to avoid possible arc reignition (this minimum time is usually referred to as the "gap clearing time"). Conveniently, if communication between the switchgears of the power grid is possible, the first time interval can be changed in order to better coordinate the operation of such switchgears.

[0132] In fact, the first time interval is selected to be long enough to prevent the phenomenon of arc reignition between the electrical contacts of the electromechanical type switch device 30 or the first switch device 31, and short enough to prevent overheating damage to the first switch device 41 of the solid state type.

[0133] When the short-circuit current flows along the second electrical branch 4 and the fault generating such a short circuit cannot be cleared before the above first time interval has elapsed, the first switch device 41 of the solid state type turns off.

[0134] Since it turns off with a certain time delay from the moment when the short-circuit current has completely commutated along the second electrical branch 4, in some conditions, the first solid state switch device 41 can remain conducting even if the short-circuit current was initially present.

[0135] When the short-circuit current has commutated along the second electrical branch 4 and the fault generating such a short circuit can be removed in some way (for example, due to the intervention of an external circuit breaker) before the above first time interval has elapsed, the first switch device 41 of the solid state type is not turned off but remains in the conducting state even if the short-circuit current initially flowed along the second electrical branch 4.

[0136] Preferably (but not necessarily as an alternative to the above solution), if one or more of the following conditions are met, the first switch device 41 of the solid state type can be commanded to turn off for self-protection purposes:

[0137] - The current flowing along the electrical branch 4 exceeds a given current threshold;

[0138] - The temperature of the switch device 41 exceeds a given temperature threshold;

[0139] - The voltage across the switch device 41 exceeds a given voltage threshold;

[0140] - The electric power consumed by the switch device 41 exceeds a given power threshold.

[0141] Moreover, this solution offers some significant advantages. For example, when the electrical protection device 1 is reconnected to the electrical wire while the switching device 30 of the electromechanical type or the switching devices 31, 32 are in the open state and a short-circuit current flows along the second electrical branch 4 due to the presence of a pre-existing fault, the first switching device 41 of the solid-state type is turned off as soon as a second time interval has elapsed (which is actually the time required to detect the presence of the fault by appropriately processing the detection signal indicating the above-mentioned physical quantity), so as to prevent overheating damage.

[0142] Preferably, after a third time interval has elapsed since the moment when an overload current (i.e., higher than a predefined overload threshold) or a normal current (i.e., having a value around or below the nominal value) has switched from the first electrical branch 3 to the second electrical branch 4 during the opening operation of the switching device 3 0 or the switching device 32 (the switching device 31 does not intervene in this case), the first switching device 41 of the solid-state type is also commanded to turn off.

[0143] Conveniently, the above-mentioned third time interval is calculated based on a criterion similar to the above-mentioned first time interval. Generally speaking, as required, the above-mentioned third time interval may be different from or equal to the above-mentioned first time interval.

[0144] According to the present invention, the second electrical branch 4 further includes a current limiting circuit 40, which is suitable for limiting the current flowing along the second electrical branch 4.

[0145] The current limiting circuit 40 is electrically connected in series with the above-mentioned current blocking circuit 40A.

[0146] The current limiting circuit 40 includes a second switching device 42 of the solid-state type and a second electronic circuit 49, which is suitable for limiting the current whenever necessary, protecting the switching device 42 (for example, against voltage transients) and dissipating electrical energy.

[0147] The second electronic circuit 49 is electrically connected in parallel to the switching device 42, and it preferably includes a varistor or a resistive device or both.

[0148] Generally speaking, the second switching device 42 of the solid-state type is operated according to the behavior of the current flowing along the second electrical branch 4.

[0149] For example, the second switching device 42 of the solid-state type can be turned on to bypass the second electronic circuit 49 and facilitate the commutation of the current from the first electrical branch 3 to the second electrical branch 4.

[0150] As another example, if the current flowing along the second electrical branch 4 must be limited, the second switching device 42 of the solid state type can be turned off. In this way, the fault current can be conducted along the second electrical branch 4 without having to oversize the first switching device 41 of the solid state type.

[0151] Preferably, if, for any reason, it is in the on state, the switching device 30 of the electromechanical type or the first switching device 31 or the second switching device 32 commands the second switching device 42 of the solid state type to switch to the on state simultaneously with the switching device 41 of the solid state type as soon as an opening operation is performed or before it. In this way, the current flowing along the first electrical branch 3 can be commutated to the second electrical branch 4.

[0152] Preferably, the second switching device 42 of the solid state type is turned off after the short - circuit current (i.e., higher than a predefined short - circuit threshold) has been commutated from the first electrical branch during the opening operation of the switching device 30 of the electromechanical type or the first switching device 31.

[0153] Preferably, when the short - circuit current is flowing along the second electrical branch 4 (because the commutation from the first electrical branch 3 is complete) and the fault that generated such a short - circuit cannot be cleared in any way, the second switching device 42 of the solid state type (which bypasses the second electronic circuit 49) is turned off to force the current to flow along the second electronic circuit 49 and limit the current.

[0154] Preferably, when the short - circuit current is flowing along the second electrical branch 4 and the fault that generated such a short - circuit is cleared in some way (e.g., due to the intervention of an external circuit breaker), the second switching device 42 of the solid state type is initially turned off to provide current - limiting functionality (as illustrated above), but it is turned on again once the fault is cleared and the current returns to a lower value. After the electromechanical type switching device 30 or the first switching device 31 or the second switching device 32 is re - closed, the current will be commutated back to the first electrical branch 3.

[0155] Conveniently, after the overload current has been commutated from the first electrical branch 3 to the second electrical branch 4 during the opening operation performed by the electromechanical type switching device 30 or the second switching device 32 (the first switching device 31 is not involved in this case), the second switching device 42 of the solid state type is also commanded to turn off.

[0156] Conveniently, after the normal current (i.e., a value around or below the nominal value) has been commutated from the first electrical branch 3 to the second electrical branch 4 during the opening operation of the electromechanical type switching device 30 or the second switching device 32 for any reason, the second switching device 42 of the solid state type can also be commanded to turn off.

[0157] Figure 1Shows a possible embodiment of the switching device 1 of the present invention.

[0158] In this case, the first electrical branch 3 includes a single switching device 30 of electromechanical type, and the second electrical branch 4 includes a current interruption circuit 40A and a current limiting circuit 40.

[0159] According to this embodiment of the present invention, the switching device 1 generally allows current to flow between the terminals 11, 12.

[0160] However, whenever necessary, it is capable of providing electrical isolation (open state) for a wide range of currents flowing along the wire.

[0161] The switching device 1 is also capable of providing current limiting functionality (current limiting mode), especially when a short-circuit current is present.

[0162] The operation of the switching device in the embodiment described in more detail below Figure 1 is described.

[0163] Closed state (normal operation)

[0164] In normal operation (i.e., in the presence of currents around or below the nominal value), the switching device 30 of electromechanical type is in the closed state, while the first and second switching devices 41, 42 of solid state type can be switched on or off as required.

[0165] Moreover, the isolator 150 is in the closed state.

[0166] Even if the switching devices 41, 42 of solid state type are switched on for any reason, the current will naturally mainly flow along the first electrical branch 3 because the first electrical branch presents a lower equivalent resistance.

[0167] Interruption of overload or normal current

[0168] The switching device 30 of electromechanical type should be in the closed state.

[0169] In the presence of an overload current, the switching device 30 is commanded to perform an opening operation.

[0170] If they are not already in the conducting state, the first and second switching devices 41, 42 of solid state type are commanded to switch on.

[0171] As soon as the electrical contacts of the switching device 30 separate, the current starts to flow along the second electrical branch 4. The complete commutation of the current from the first electrical branch 3 to the second electrical branch 4 eliminates the arcing phenomenon between the electrical contacts of the switching device 30.

[0172] After a third time interval has elapsed since the moment when the current has commutated from the first electrical branch 3 to the second electrical branch 4 (such that the switching device 30 has sufficient dielectric tolerance to avoid reignition of the arc), the switching devices 41, 42 of the solid-state type are commanded to turn off. The overload current is forced to circulate along the first and second electronic circuits 48, 49 until it is eliminated.

[0173] As an alternative, after the complete commutation of the current to the second electrical branch 4, the switching device 42 of the solid-state type is commanded to turn off, and the current is forced to circulate along the second electronic circuit 49 and the first switching device 41 of the solid-state type.

[0174] In both cases, the switching device 1 provides current limiting functionality (current limiting mode) for the overload current.

[0175] Then, after the above-mentioned third time interval has elapsed since the moment when the overcurrent has been commutated to the second electrical branch 4, the switching device 41 of the solid-state type is commanded to turn off.

[0176] As another alternative, after the complete commutation of the current to the second electrical branch 4, only the switching device 41 of the solid-state type is commanded to turn off (open state) after the above-mentioned third time interval has elapsed. In this case, the current is forced to circulate along the first electronic circuit 48 until it is eliminated.

[0177] The current cannot restart flowing along the first electrical branch 3 because the switching device 30 of the electromechanical type is in the open state.

[0178] Conveniently, after the current interruption, the disconnector 150 is commanded to perform an opening operation, thereby providing current insulation for the power grid part including the switching device.

[0179] The switching device behaves in the same way as when the normal current is requested to be interrupted for any reason.

[0180] Interruption of short-circuit current

[0181] The switching device 30 of the electromechanical type should be in the closed state.

[0182] In the presence of a short-circuit current, the switching device 30 performs an opening operation, preferably without receiving an input control signal or an external power supply.

[0183] The first and second switching devices 41, 42 of the solid-state type are commanded to turn on when they are not already in the conducting state.

[0184] The separation of the electrical contacts of the switching device 30 forces the current to commutate to the second electrical branch 4.

[0185] The complete commutation of the current from the first electrical branch 3 to the second electrical branch 4 eliminates the arcing phenomenon between the electrical contacts of the switching device 30 of the electromechanical type.

[0186] The short-circuit current commuted to the second electrical branch 4 initially flows through both the first and second switching devices 41, 42 of the solid-state type.

[0187] As soon as the current is completely commuted to the second electrical branch 4, the second switching device 42 of the solid-state type is commanded to turn off, and the current is forced to circulate along the second electronic circuit 49 and the first switching device 41 of the solid-state type.

[0188] In this situation, the switching device 1 provides the current limiting functionality (current limiting mode) of the short-circuit current.

[0189] After the above-mentioned first time interval has elapsed since the moment when the short-circuit current is commuted to the second electrical branch 4, the switching device 41 should be commanded to turn off.

[0190] However, if the fault generating the short-circuit current is cleared in some way (for example, due to the intervention of an external circuit breaker) before the above-mentioned first time interval has elapsed, the switching device 41 is not commanded to turn off, but remains in the conducting state because the current flowing along the second electrical branch 4 returns to a lower value.

[0191] In this case, the second switching device 42 of the solid-state type can remain in the off state.

[0192] As an alternative, the second switching device 42 of the solid-state type can be commanded to turn on again, and the current flowing along the electrical branch 4 can flow again along the first and second switching devices 41, 42 of the solid-state type.

[0193] In any case, the switching device 30 of the electromechanical type is commanded to perform a closing operation simultaneously.

[0194] When the switching device 30 finally returns to the closed state, the switching device 1 will operate again under normal conditions because the current naturally commutes from the second electrical branch 4 to the first electrical branch 3.

[0195] Conversely, if the fault generating the short-circuit current is not cleared before the above-mentioned first time interval has elapsed, the first switching device 41 of the solid-state type is commanded to turn off.

[0196] The current is forced to circulate along the first and second electronic circuits 48, 49 until it is eliminated. As shown above, the current cannot start flowing again along the first electrical branch 3.

[0197] Subsequently, the isolator 150 is commanded to perform an opening operation, thereby providing current insulation for the power grid part including the switching device.

[0198] Reconnection to the wire

[0199] The switching device 30 of the electromechanical type should be in the open state, while the first and second switching devices 41, 42 of the solid-state type should be in the off state.

[0200] Command the isolator 150 to perform a closing operation. The current isolation between the power grid part including the switching device and other power grid parts (excluding the switching device) is no longer ensured.

[0201] Command the switching device 41 of the solid-state type to turn on.

[0202] As an alternative, command the switching devices 41, 42 of the solid-state type to turn on.

[0203] The current flows along the second semiconductor branch 4.

[0204] If only the switching device 41 of the solid-state type is turned on, the current flows along the second electronic circuit 49 and the switching device 41.

[0205] If both the switching devices 41, 42 of the solid-state type are turned on, the current flows along these switching devices.

[0206] If no short circuit is detected within the second predefined time interval (required to check for the presence of a short circuit), command the switching device 30 to perform a closing operation.

[0207] As described above, the fourth switching device 42 can be in the conducting state or the off state. If the fourth switching device 42 is in the conducting state, it can remain in that state or be turned off. If it is in the off state, it can remain in that state or be turned on.

[0208] The second switching device 42 of the solid-state type can be held in the conducting state or turned off.

[0209] Once the switching device 30 has completed the closing operation, the switching device 1 starts to operate under normal conditions, and the current naturally commutates to the first electrical branch 3.

[0210] Reconnection to the wire in the presence of a short-circuit fault

[0211] The switching device 30 of the electromechanical type should be in the open state, while the first and second switching devices 41, 42 of the solid-state type should be in the off state.

[0212] Command the isolator 150 to perform a closing operation. The current isolation between the power grid part including the switching device and other power grid parts (excluding the switching device) is no longer ensured.

[0213] Command the solid-state type switching device 41 to turn on, while keeping the switching device 42 off, and it turns on later than the switching device 41.

[0214] As an alternative, command the solid-state type switching devices 41, 42 to turn on simultaneously.

[0215] The short-circuit current initially flows along the second semiconductor branch 4.

[0216] When only the third switching device 41 is turned on, the current flows along the second electronic circuit 49 and the third switching device 41 (current limiting mode). After the first predefined time interval (necessary for identifying the short-circuit condition), command the third switching device 41 to turn on. Force the current to circulate along the first electronic circuit 48 until it is eliminated.

[0217] When the third and fourth switching devices 41, 42 are turned on simultaneously, the current flows through these two switching devices. After the first predefined time interval, command the third switching device 41 to turn off, while the fourth switching device 42 can be turned off or remain in the conducting state. Force the current to circulate along the first electronic circuit 48 until it is eliminated.

[0218] The switching device 30 is not commanded to perform a closing operation, and it remains in the open state.

[0219] Subsequently, command the isolator 150 to perform an opening operation, thereby providing current insulation for the power grid section including the switching equipment.

[0220] It is obvious from the above that the switching equipment 1 can operate in three different states when arranged according to the Figure 1 embodiment: the closed state (normal operation); the open state, in which it blocks the current commuting from the first electrical branch 3 to the second electrical branch 4; or operate in the current limiting mode (transient condition), in which it limits the current commuting from the first electrical branch 3 to the second electrical branch 4.

[0221] It is also demonstrated how the switch group 110 formed by the switching equipment 1 and the isolator 150 connected in series electrically can operate in different states: the closed state, in which the switching equipment 1 is in the closed state and the isolator 150 is in the closed state; the open state, in which the switching equipment 1 is in the open state and the isolator 150 is in the open state; or the current limiting mode, in which the switching equipment 1 is in the current limiting mode and the isolator 150 is in the closed state.

[0222] Figure 2 Show a possible embodiment of the switching equipment 1 of the present invention.

[0223] In this case, the first electrical branch 3 includes first and second switching devices 31, 32 of electromechanical type connected in series electric connection, and the second electrical branch 4 includes a current blocking circuit 40A and a current limiting circuit 40.

[0224] According to this embodiment of the invention, the switching device 1 generally allows the flow of current between the terminals 11, 12.

[0225] However, whenever necessary, it is capable of providing electrical isolation (open state) for a wide range of currents flowing along the wire.

[0226] Moreover, in this case, the switching device 1 is also capable of providing current limiting functionality (current limiting mode), especially when a short-circuit current exists.

[0227] The operation of the switching device in the embodiment described in more detail below Figure 2 will be described.

[0228] Closed state (normal operation)

[0229] In normal operation (i.e., in the presence of currents around or below the nominal value), the first and second switching devices 31, 32 of electromechanical type are in the closed state, while the first and second switching devices 41, 42 of solid-state type can be switched on or off as required.

[0230] Moreover, the isolator 150 is in the closed state.

[0231] Even if the switching devices 41, 42 of solid-state type are switched on for any reason, the current will naturally mainly flow along the first electrical branch 3 because the first electrical branch presents a lower equivalent resistance.

[0232] Interruption of overload or normal current

[0233] The first and second switching devices 31, 32 of electromechanical type should be in the closed state.

[0234] In the presence of overload or normal current, the switching device 31 of electromechanical type does not intervene (thus remaining in the closed state), while the switching device 32 of electromechanical type is commanded to perform an opening operation.

[0235] If they are not yet in the conducting state, the first and second switching devices 41, 42 of solid-state type are commanded to be switched on.

[0236] As soon as the electrical contact of the second switching device 32 of electromechanical type separates, the current starts to flow along the second electrical branch 4. The complete commutation of the current from the first electrical branch 3 to the second electrical branch 4 eliminates the arcing phenomenon between the electrical contacts of the second switching device 32 of electromechanical type.

[0237] After a third time interval has elapsed since the moment when the current commutes from the first electrical branch 3 to the second electrical branch 4 (such that the switching device 32 of electromechanical type has sufficient dielectric tolerance to avoid reignition of the arc), the switching devices 41, 42 of solid state type are commanded to turn off (open state). The overload current is forced to circulate along the first and second electronic circuits 48, 49 until it is eliminated.

[0238] As an alternative, after complete commutation of the current to the second electrical branch 4, the switching device 42 of solid state type is commanded to turn off, and the current is forced to circulate along the second electronic circuit 49 and the switching device 41.

[0239] In both cases, the switching device 1 provides current limiting functionality (current limiting mode) for the overload current.

[0240] After a third time interval has elapsed since the moment when the overcurrent is commuted to the second electrical branch 4, the switching device 41 of solid state type is commanded to turn off.

[0241] As a further alternative, after complete commutation of the current to the second electrical branch 4, only the switching device 41 of solid state type is commanded to turn off (open state) after the above-mentioned third time interval has elapsed. In this case, the current is forced to circulate along the first electronic circuit 48 until it is eliminated.

[0242] The current cannot start flowing again along the first electrical branch 3 because the second switching device 32 of electromechanical type is in the open state.

[0243] Conveniently, after the current interruption, the disconnector 150 is commanded to perform an opening operation, thereby providing current insulation for the grid part including the switching device.

[0244] The switching device behaves in the same way as when normal current interruption is requested for any reason.

[0245] Interruption of short-circuit current

[0246] The first and second switching devices 31, 32 of electromechanical type should be in the closed state.

[0247] In the presence of a short-circuit current, the switching device 31 of electromechanical type immediately performs (fast switching) an opening operation without receiving an input control signal or an external power supply.

[0248] The first and second switching devices 41, 42 of solid state type are commanded to turn on when they are not already in the conducting state.

[0249] Moreover, the second switching device 32 of electromechanical type is commanded to perform an opening operation. However, the intervention of the switching device 31 of electromechanical type occurs earlier than that of the switching device 32.

[0250] The separation of the electrical contact part of the switching device 31 of electromechanical type forces the current to commutate to the second electrical branch 4.

[0251] The complete commutation of the current from the first electrical branch 3 to the second electrical branch 4 eliminates the arcing phenomenon between the electrical contact parts of the switching device 31 of electromechanical type.

[0252] The short - circuit current commutated to the second electrical branch 4 initially flows through both the first and second switching devices 41, 42 of solid - state type.

[0253] As soon as the current is completely commutated to the second electrical branch 4, the switching device 42 of solid - state type is commanded to turn off, and the current is forced to circulate along the second electronic circuit 49 and the switching device 41.

[0254] In this situation, the switching device 1 provides the current - limiting functionality (current - limiting mode) of the short - circuit current.

[0255] After the above - mentioned first time interval has elapsed since the moment when the short - circuit current is commutated to the second electrical branch 4, the switching device 41 of solid - state type should be commanded to turn off.

[0256] However, if the fault generating the short - circuit current is cleared in some way (for example, due to the intervention of an external circuit breaker) before the above - mentioned first time interval has elapsed, the switching device 41 of solid - state type is not commanded to turn off, but remains in the conducting state because the current flowing along the second electrical branch 4 returns to a lower value.

[0257] In this case, the second switching device 42 of solid - state type can remain in the off state.

[0258] As an alternative, the second switching device 42 of solid - state type can be re - commanded to turn on, and the current flowing along the electrical branch 4 can flow again along the first and second switching devices 41, 42 of solid - state type.

[0259] In any case, simultaneously, the switching device 31 of electromechanical type returns to the closed state, and the switching device 32 is commanded to perform a closing operation.

[0260] When the switching devices 31, 32 of electromechanical type both finally return to the closed state, the switching device 1 will operate again under normal conditions because the current naturally commutates from the second electrical branch 4 to the first electrical branch 3.

[0261] Conversely, if the fault generating the short-circuit current has not been cleared before the above-mentioned first time interval has elapsed, the solid-state type switching device 41 is commanded to turn off (open state).

[0262] Force the current to circulate along the first and second electronic circuits 48, 49 until it is eliminated. As shown above, the current cannot restart flowing along the first electrical branch 3.

[0263] Subsequently, the isolator 150 is commanded to perform an opening operation, thereby providing current insulation for the grid section including the switching equipment.

[0264] Reconnection to the wire

[0265] The first switching device 31 of the electromechanical type should already be in the closed state, the second switching device 32 of the electromechanical type should be in the open state, while the first and second switching devices 41, 42 of the solid-state type should be in the off state.

[0266] Command the isolator 150 to perform a closing operation. The current isolation of the grid section including the switching equipment from other grid sections (excluding the switching equipment) is no longer ensured.

[0267] Command the switching device 41 to turn on.

[0268] As an alternative, command the solid-state type switching devices 41, 42 to turn on.

[0269] The current flows along the second semiconductor branch 4.

[0270] If only the solid-state type switching device 41 is turned on, the current flows along the second electronic circuit 49 and the switching device 41.

[0271] If both the solid-state type switching devices 41, 42 are turned on, the current flows through these switching devices.

[0272] If no short-circuit is detected within the second predefined time interval (necessary to check for the presence of a short-circuit), command the second switching device 32 to perform a closing operation.

[0273] As described above, the fourth switching device 42 can be in the conducting state or the off state. If the fourth switching device 42 is in the conducting state, it can remain in that state or turn off. If it is in the off state, it can remain in that state or turn on.

[0274] Once the electromechanical type switching device 32 has completed the closing operation (the electromechanical type switching device 31 is already in the closed state), the switching equipment 1 starts operating under normal conditions, and the current naturally commutates to the first electrical branch 3.

[0275] Reconnection to the wire in the presence of a short-circuit fault

[0276] The first switching device 31 of electromechanical type should already be in the closed state, the second switching device 32 of electromechanical type should be in the open state, and at the same time the first and second switching devices 41, 42 of solid-state type should be in the off state.

[0277] Command the isolator 150 to perform a closing operation. The current isolation between the power grid part including the switching device and other power grid parts (excluding the switching device) is no longer ensured.

[0278] Command the switching device 41 of solid-state type to turn on, while the switching device 42 remains off and it turns on later than the switching device 41.

[0279] As an alternative, command the switching devices 41, 42 of solid-state type to turn on simultaneously.

[0280] The short-circuit current initially flows along the second semiconductor branch 4.

[0281] When only the third switching device 41 is turned on, the current flows along the second electronic circuit 49 and the third switching device 41 (current limiting mode). After the first predefined time interval (necessary for identifying the short-circuit condition), command the third switching device 41 to turn on. Force the current to circulate along the first electronic circuit 48 until it is eliminated.

[0282] When the third and fourth switching devices 41, 42 are turned on simultaneously, the current flows through these two switching devices. After the first predefined time interval, command the third switching device 41 to turn off, while the fourth switching device 42 can be turned off or remain in the conducting state. Force the current to circulate along the first electronic circuit 48 until it is eliminated.

[0283] The second switching device 32 of electromechanical type is not commanded to perform a closing operation and it remains in the open state.

[0284] Subsequently, command the isolator 150 to perform an opening operation, thereby providing current insulation for the power grid part including the switching device.

[0285] It is obvious from the above that the switching device 1 can operate in three different states when arranged according to the Figure 2 embodiment: the closed state (normal operation); the open state, in which it blocks the current commuting from the first electrical branch 3 to the second electrical branch 4; or operate in the current limiting mode (transient condition), in which it limits the current commuting from the first electrical branch 3 to the second electrical branch 4.

[0286] It has also been demonstrated how the switch group 110 formed by the switchgear 1 and the isolator 150 connected in series can be operated in different states: a closed state, in which the switchgear 1 is in the closed state and the isolator 150 is in the closed state; an open state, in which the switchgear 1 is in the open state and the isolator 150 is in the open state; or a current limiting mode, in which the switchgear 1 is in the current limiting mode and the isolator 150 is in the closed state.

[0287] According to some embodiments of the present invention ( Figure 1-2 ), the switchgear 1 includes a control unit 90 (which may be of a known type), and the control unit 90 includes one or more control logics configured to control the operation of the electromechanical type switch device 30 or the second switch device 32 and the operation of the first and second switch devices 41, 42 of the solid state type.

[0288] Preferably, the control unit 90 is also capable of controlling the operation of the isolator 150.

[0289] The control unit 90 is adapted to receive the sensing signal S from one or more sensors 93 arranged at appropriate positions of the switchgear to monitor the behavior of the current and / or other physical quantities along the first electrical branch 3 and the second electrical branch 4.

[0290] The control unit 90 is adapted to process the sensing signal provided by the above-mentioned sensors 93 and provide a control signal C to operate the electromechanical type switch device 30 or the second switch device 32, the first and second switch devices 41 and 42 of the solid state type, and possibly operate the isolator 150 according to the operation modes described above.

[0291] The control unit 90 can execute appropriate data processing algorithms to process the information provided by the sensors 93 and check whether a certain operation criterion for operating the switch devices 30, 32, 41, 42 and possibly operating 150 is met.

[0292] When the operator manually requests the execution of an operation or an external request for an operation is sent to the switchgear, the control unit 90 can provide a control signal to operate the switch devices 30, 32, 41 and 42 and possibly operate 150.

[0293] According to a variant embodiment of the present invention (not shown), the control unit 90 is not arranged on the switchgear 1.

[0294] As an example, it can be arranged on a digital relay operating in association with the switchgear or on another switchgear or on a remote computerized platform. In this case, the switchgear 1 can include a communication interface for communicating with the control unit 90.

[0295] Figure 3-7 Shows a variant embodiment of the present invention, in which the switching device 1 is capable of controlling bidirectional current. These solutions can be particularly advantageous when the switching device is installed in an AC power grid.

[0296] Figure 3 Shows Figure 1 variant solutions of the embodiment shown in

[0297] According to this embodiment, the second electrical branch 4 includes: a first bridge circuit 45, which is operatively associated with the current interruption circuit 40A; and a second bridge circuit 46, which is operatively associated with the current limiting circuit 40.

[0298] The operation of this embodiment of the present invention is the same as that described above for the embodiment of Figure 1

[0299] Figure 4 Shows Figure 2 variant solutions of the embodiment shown in

[0300] Moreover, in this embodiment, the second electrical branch 4 includes: a first bridge circuit 45, which is operatively associated with the current interruption circuit 40A; and a second bridge circuit 46, which is operatively associated with the current limiting circuit 40.

[0301] The operation of this embodiment of the present invention is the same as that described above for the embodiment of Figure 2

[0302] Figure 5 Shows Figure 3 variant solutions of the embodiment shown in

[0303] According to this embodiment, the second electrical branch 4 includes a third bridge circuit 47, which is operatively associated with the remaining components of the second electrical branch (such as the series circuit formed by the current limiting circuit 40 and the current interruption circuit 40A).

[0304] The operation of these embodiments of the present invention is the same as that described above for the embodiment of Figure 1

[0305] Figure 5A Shows Figure 4 variant solutions of the embodiment shown in

[0306] Moreover, in this case, the second electrical branch 4 includes a third bridge circuit 47, which is operatively associated with the remaining components of the second electrical branch (such as the series circuit formed by the current limiting circuit 40 and the current interruption circuit 40A).

[0307] The operation of these embodiments of the present invention is the same as that described above for Figure 2 the embodiment.

[0308] Preferably, in the embodiment illustrated in Figure 3-5A each of the bridge circuits 45, 46, 47 includes a plurality of diodes arranged in a Grez bridge configuration.

[0309] Figure 6 Shows Figure 1 an additional variant solution of the embodiment shown in

[0310] According to this embodiment, both the current interruption circuit 40A and the current limiting circuit 40 include pairs of semiconductor switch assemblies 41A, 41B and 42A, 42B, which are interconnected in an antiparallel configuration.

[0311] For this configuration, each semiconductor switch assembly must have a reverse blocking type or be arranged in series with a diode.

[0312] The semiconductor switch assemblies 41A, 41B are electrically connected in parallel to the first electronic circuit 48, while the semiconductor switch assemblies 42A, 42B are both electrically connected in parallel to the second electronic circuit 49.

[0313] The operation of this embodiment of the present invention is the same as that described above for Figure 1 the embodiment.

[0314] According to a further variant embodiment of the present invention (not shown), the first and second switching devices 41, 42 of the solid state type may each include corresponding pairs of semiconductor switch assemblies, which are interconnected in an anti-series configuration. For this configuration, each semiconductor switch assembly must have a reverse conducting type or be arranged in parallel with a diode.

[0315] Figure 7 Shows Figure 2 an additional variant solution of the embodiment shown in

[0316] Moreover, in this case, both the current interruption circuit 40A and the current limiting circuit 40 include pairs of semiconductor switch assemblies 41A, 41B and 42A, 42B, which are interconnected in an antiparallel configuration.

[0317] For this configuration, each semiconductor switch assembly must have a reverse blocking type or be arranged in series with a diode.

[0318] The semiconductor switch assemblies 41A, 41B are electrically connected in parallel to the first electronic circuit 48, while the semiconductor switch assemblies 42A, 42B are both electrically connected in parallel to the second electronic circuit 49.

[0319] The operation of this embodiment of the present invention is the same as that described above forFigure 2 The operation is the same as that described in the embodiments.

[0320] According to a further variant embodiment of the present invention (not shown), both the first and second switching devices 41, 42 of the solid-state type may include corresponding pairs of semiconductor switching assemblies, which are interconnected in an anti-series configuration.

[0321] For this configuration, each semiconductor switching assembly must be of the reverse-conduction type or arranged in parallel with a diode.

[0322] Figure 8 An example of a DC power grid 100 is shown.

[0323] The DC power grid includes a DC bus 101 (DC link) and a plurality of components electrically connected to the DC bus.

[0324] Some components may be formed by electrical loads or devices (such as electric motors) that need to be electrically fed.

[0325] Other components may be formed by energy storage devices (such as capacitor banks or batteries) or power generation devices (such as photovoltaic power plants), which are thus capable of providing electrical energy.

[0326] In the DC power grid 100, a plurality of switching devices according to the present invention are suitably employed to manage the electrical connection of the above components to the DC power bus.

[0327] Conveniently, as illustrated above, each switching device 1 is electrically connected in series with an isolator 150 to form a switching group 110.

[0328] As is apparent from the above figures, the DC current circulating through the components linked to the DC bus can be bidirectional.

[0329] In the case of an electrical fault, many components of the DC power grid can contribute to the possible short-circuit current because reverse current may flow through them. In the worst case, if an electrical fault occurs on the DC bus, many components can directly intensify the electrical fault.

[0330] The use of the switching device according to the present invention in the DC power grid allows for a rapid response to possible electrical faults and enables the implementation of appropriate protection and selection functionality for managing possible electrical faults.

[0331] In addition, an effective strategy for managing and coordinating circuit protection interventions along different branches of the power grid can be implemented.

[0332] Figure 9-16 Some examples of strategies capable of being implemented to manage electrical faults in the simplified DC power grid 100A are shown.

[0333] The DC power grid 100A includes a battery energy storage system (BESS), in which a set of battery cells is electrically connected to a power converter (not shown) via a DC bus 101A.

[0334] Each battery cell is electrically connected to or disconnected from the DC bus 101A by means of a switch group 110.

[0335] Each switch group 110 includes: a switching device 1 according to the present invention, which is capable of conducting bidirectional current; and an isolator 150 connected in series electrically.

[0336] The DC bus 101A is electrically connected to or disconnected from the above-mentioned power converter by means of a circuit breaker 160 of, for example, the electromechanical type.

[0337] As an alternative, the DC bus 101A can be electrically connected to or disconnected from the above-mentioned power converter by means of an additional switch group, which includes Figure 2 the switching device of the present invention in the embodiments of

[0338] As illustrated above, since it includes the switching device of the present invention, each switch group 110 can operate in the following states: a closed state, in which the switching device 1 is in the closed state and the isolator 150 is in the closed state; an open state, in which the switching device 1 is in the open state and the isolator 150 is in the open state; and a current limiting mode, in which the switching device 1 is in the current limiting mode and the isolator 150 is in the closed state.

[0339] When it is in the closed state, each switch group 110 conducts current, thereby electrically connecting the corresponding battery cell to the DC bus.

[0340] When it is in the open state, each switch group 110 blocks current, thereby electrically disconnecting the corresponding battery cell from the DC bus.

[0341] When it is in the current limiting mode, each switch group 110 provides current limiting functionality, thereby limiting the current circulating between the corresponding battery cell and the DC bus.

[0342] When the circuit breaker 160 is used to electrically connect or disconnect the power converter from the DC bus 101A, the circuit breaker can be switched to the closed state, in which it conducts current and thus electrically connects the power converter to the DC bus, or to the open state, in which it blocks current and thus electrically disconnects the power converter from the DC bus.

[0343] When an additional switch group of the present invention capable of conducting bidirectional current is used to replace the circuit breaker 160, the switch group behaves as described above, thus electrically connecting the power converter to the DC bus when it is in the closed state, disconnecting the power converter from the DC bus when it is in the open state, or limiting the current circulating between the power converter and the DC bus when in the current limiting mode.

[0344] Normal operation

[0345] Figure 9 Schematically shows the operation of the power grid 100A under normal conditions.

[0346] In this situation, the circuit breaker 160 is in the closed state, and each switch group 110 is in the closed state (normal operation). If an additional switch group is used to replace the circuit breaker 160, then this switch group is in the closed state.

[0347] Current I N1 、I N2 、I N3 circulates along the above battery cells, while current I NC flows along the electronic converter. Current I NC is substantially the sum of currents I N1 、I N2 、I N3 .

[0348] All currents I N1 、I N2 、I N3 、I NC flowing to and from the battery cells and the electronic converter take values not exceeding the nominal current predicted for the battery cells and have the same direction, which basically depends on the operating mode (charging or discharging) of the battery cells.

[0349] In the Figure 9 example, the battery cells should be in the discharge mode. Currents I N1 、I N2 、I N3 、I NC will have the opposite direction when the battery cells are operating in the charging mode. However, the operation of the power grid will be substantially the same.

[0350] Short circuit in the battery cell

[0351] Figure 10 Schematically shows a situation where a short circuit occurs in the battery cells.

[0352] Short - circuit current I S1flows to the battery cell affected by the electrical fault. The electrical fault is enhanced by the short-circuit current I S2 、I S3 flowing from other battery cells and by the short-circuit current I SC flowing through the power converter.

[0353] When the power converter is in the discharge mode, the short-circuit current I SC flowing through the power converter has an opposite direction with respect to the corresponding current I NC .

[0354] As Figure 11 illustrated, the short-circuit currents I SC 、I S1 、I S2 、I S3 flowing in the power grid 100A, the switch group 110 operationally associated with the battery cell switches to the current limit mode. The circuit breaker 160 remains in the closed state to wait for the possible clearance of the electrical fault.

[0355] If an additional switch group is used instead of the circuit breaker 160, such a switch group will also switch to the current limit mode.

[0356] The intervention of the switch group 110 results in restricting the short-circuit current I S1 that intensifies the electrical fault.

[0357] Subsequently, due to the short-circuit currents I SC 、I S1 、I S2 、I S3 continuing to circulate in the power grid 100, the switch group 110 closest to the battery cell affected by the electrical fault switches to the open state.

[0358] In fact, the switch group 110 closest to the battery cell affected by the electrical fault can remain in the current limit mode for a shorter time relative to other switch groups because this switch group is affected by the short-circuit current with a larger magnitude.

[0359] Since the corresponding switch group 110 has switched to the open state, the battery cell affected by the electrical fault is electrically insulated from the rest of the power grid.

[0360] In this situation, the switch group 110 operationally associated with other battery cells remains in the current limit mode, and a smaller current (e.g., having a value even lower than the nominal value) will circulate through the switch group ( Figure 12 ). The circuit breaker 160 remains in the closed state.

[0361] Finally, since the electrical fault has been cleared by operating the switch group 110 in the open state, the switch group 110 operationally associated with the battery cells not affected by the electrical fault can be switched back to the closed state and operate again under normal conditions( Figure 13 ).

[0362] If an additional switch group is used to replace the circuit breaker 160, this switch group is also switched to the closed state.

[0363] The current circulating in the power grid 100 again takes on the normal values I NC , I N2 , I N3 and the same direction. Obviously, the battery cells affected by the electrical fault remain current-insulated from the rest of the power grid 100A. Obviously, the current I NC flowing through the power converter is correspondingly reduced.

[0364] If the battery cells operate in the charging mode, the operation of the power grid will be substantially the same.

[0365] Short circuit in the DC bus

[0366] Figure 14 Schematically shows a situation where a short circuit occurs in the DC bus 101A. The short-circuit currents I SC , I S1 , I S2 , I S3 flow along the battery cells and the electronic converter to intensify the electrical fault. Moreover, in this case, when the power converter is in the discharge mode, the short-circuit current I SC flowing through the power converter has the opposite direction with respect to the corresponding current I NC .

[0367] Since the electrical fault is located in the DC bus, the short-circuit currents I S1 , I S2 , I S3 flowing along the battery cells will have the same direction, which is opposite to the short-circuit current I SC flowing through the power converter.

[0368] As Figure 15 illustrated, as soon as the short-circuit currents I SC , I S1 , I S2 , I S3 circulate in the power grid 100, the switch group 110 operationally associated with the battery cells is switched to the current-limiting mode. The circuit breaker 160 remains temporarily closed to wait for the possible clearance of the electrical fault. If the switch group 110 is used to replace the circuit breaker 160, this switch group also operates in the current-limiting mode.

[0369] Since it is located in the DC bus, it is not possible to clear an electrical fault by operating a single switched group 110 (closest to the electrical fault) in the open state.

[0370] Since the fault has not been cleared, after the above-mentioned first time interval has elapsed, all switched groups 110 and the circuit breaker 160 are thus switched to the open state.

[0371] If an additional switched group is used in place of the circuit breaker 160, such a switched group is also switched to the open state.

[0372] As a result of the above, the entire DC power grid 100 is shut down ( Figure 16 ).

[0373] If the battery unit is operating in the charging mode, the operation of the power grid will be substantially the same.

[0374] It has been shown that different types (e.g., AC type) of power grids generally including a plurality of switched groups 110 (configured as described above) for electrically connecting or disconnecting different grid sections of the power grid operate substantially as the above-mentioned power grid 100A with appropriate modifications.

[0375] Thus, it is apparent that in a further aspect, how the present invention relates to a method of operating a power grid including a plurality of switched groups 110 (configured as described above) for electrically connecting or disconnecting different grid sections of the power grid.

[0376] The method according to the present invention includes the following steps: if there is an electrical fault (i.e., a short circuit) in the power grid, the switched group 110 is switched to the current limiting mode.

[0377] The method of the present invention then includes the following steps: the switched group 110 closest to the electrical fault is switched to the open state, while the remaining switched groups of the power grid are maintained in the current limiting mode.

[0378] In fact, the switched group 110 closest to the electrical fault can remain in the current limiting mode for a shorter time relative to other switched groups because such a switched group is affected by a short circuit current with a larger amplitude.

[0379] If the electrical fault is electrically isolated within a predefined time period (which is substantially the same as the above-mentioned first time interval) by operating the switched group 110 closest to the electrical fault, the method of the present invention includes the following steps: the switched group 110 closest to the electrical fault is maintained in the open state, while the remaining switched groups 110 of the power grid are switched back to the closed state.

[0380] If the electrical fault is not electrically isolated within the predefined time period by operating the switch group 110 closest to the electrical fault, the method of the present invention includes the step of switching all the switch groups 110 of the power grid to the open state.

[0381] As Figure 9-16 Illustrated in the above example of, the method of the present invention is particularly suitable for protecting the DC power grid 100A, which includes: a battery energy storage system including a plurality of battery cells; a DC bus 101A for electrically connecting the battery cells to a power converter; and a plurality of switch groups 110 (configured as described above) for electrically connecting or disconnecting the battery cells from the DC bus.

[0382] In this case, the method according to the present invention includes the following steps: if there is an electrical fault (i.e., a short circuit) in the energy battery storage system, switch the switch group 110 to the current limiting mode.

[0383] When the DC bus 101A is electrically connected to or disconnected from the above-mentioned power converter through a circuit breaker 160 of, for example, the electromechanical type, the method of the present invention further includes the step of keeping the circuit breaker 160 in the closed state.

[0384] When the DC bus 101A is electrically connected to or disconnected from the above-mentioned power converter through an additional switch group (similar to the switch group 110), the method of the present invention further includes the step of switching the additional switch group to the current limiting mode.

[0385] The method according to the present invention includes the following steps: switch the switch group 110 closest to the electrical fault to the open state, while keeping the remaining switch groups 110 of the energy storage system in the current limiting mode.

[0386] If the electrical fault is electrically isolated within the predefined time period (the above-mentioned first time interval) by switching the switch group 110 closest to the open state, the method of the present invention includes the following steps: keep the switch group 110 closest to the electrical fault in the open state, while switching the remaining switch groups 110 of the battery energy storage system back to the closed state.

[0387] When the DC bus 101A is electrically connected to or disconnected from the above-mentioned power converter through a circuit breaker 160 of, for example, the electromechanical type, the method of the present invention further includes the step of keeping the circuit breaker 160 in the closed state.

[0388] When the DC bus 101A is electrically connected to or disconnected from the above-mentioned power converter through an additional switch group (similar to the switch group 110), the method of the present invention further includes the step of switching the additional switch group to the closed state.

[0389] If an electrical fault cannot be electrically isolated within the predefined time period by operating the switch group 110 in the open state that is closest to the electrical fault, the method according to the invention includes the step of switching all the switch groups 110 of the battery energy storage system to the open state.

[0390] When the DC bus 101A is electrically connected to or disconnected from the above-mentioned power converter through, for example, a circuit breaker 160 of the electromechanical type or through an additional switch group (similar to the switch group 110), the method according to the invention further includes the step of switching the circuit breaker 160 or the additional switch group to the open state.

[0391] The method according to the invention allows the management of electrical faults (i.e., short circuits) in the power grid in a selective manner according to whether the electrical fault can be electrically isolated.

[0392] The method according to the invention initially provides for limiting the fault current circulating along various parts of the power grid.

[0393] If the electrical fault can be cleared within the predefined time period by operating a specific switch group 110 in the open state (closest to the short circuit), the method according to the invention provides for restoring the part of the power grid not involved in the electrical fault to the normal conduction mode.

[0394] If the electrical fault cannot be cleared within the predefined time period by operating the specific switch group 110 in the open state, the method according to the invention provides for shutting down the power grid.

[0395] The method allows for improving the flexibility in the use of the power grid. Additionally, it allows for reducing the possible downtime of the power grid in the presence of a short circuit. In fact, the power grid is shut down only when strictly necessary because the electrical fault cannot be cleared in any way.

[0396] The switching device according to the invention provides significant advantages over similar known solutions of the prior art.

[0397] The switching device 1 can be subject to a plurality of variants that fall within the concept of the claimed invention.

[0398] The switching device 1 can be industrially implemented as an independent device or as an additional module for each electrode of, for example, a molded case circuit breaker (MCCB).

[0399] According to a further variant, the switching device 1 can include an additional commutation booster circuit of a known type, such as the circuit disclosed in the above-mentioned patent document WO2017 / 186262.

[0400] The switching device according to the invention allows for providing a limiting functionality for the short-circuit current that may flow through the solid-state switching device.

[0401] In addition, in some embodiments ( Figure 2 ), when an electrical fault occurs in the wire, the switching device according to the invention allows for rapid intervention to interrupt a possible short-circuit current.

[0402] The above features allow for the use of smaller-sized solid-state devices for a given nominal current. Obviously, this allows for a significant reduction in the size and cost of the switching device.

[0403] The switching device according to the invention allows for the management of the nominal current and possible overload currents flowing along the wire in a reliable manner.

[0404] The switching device according to the invention allows for the implementation of improved selection functionality by taking advantage of improved operating conditions of the on-board solid-state switching device, especially when implementing the current-limiting functionality.

[0405] In addition, it allows for the implementation of an effective strategy for managing and coordinating circuit protection interventions along different branches of the power grid.

[0406] The switching device according to the invention is relatively easy and inexpensive to industrially produce and install on-site.

Claims

1. A switching device (1) for an electric power network (100), comprising: - a first electrical terminal and a second electrical terminal (11, 12) for electrical connection to a corresponding network section; - a first electrical branch (3) including one or more switching devices (30, 31, 32) of electromechanical type, each switching device (30, 31, 32) having an electrical contact portion that can be mechanically coupled or separated to conduct or block current respectively; - a second electrical branch (4) including a plurality of switching devices (41, 42) of solid-state type, each switching device (41, 42) including one or more switching components (41A, 41B, 42A, 42B) based on semiconductor material and adapted to switch between a conducting state and a non-conducting state, in the conducting state the switching device conducts current, and in the non-conducting state the switching device blocks current, the second electrical branch being electrically connected in parallel with the first electrical branch between the first electrical terminal and the second electrical terminal; characterized in that the second electrical branch (4) comprises: - a current blocking circuit (40A) adapted to block current flowing along the second electrical branch, the current blocking circuit including a first switching device (41) of solid-state type and a first electronic circuit (48) electrically connected in parallel to the first switching device of solid-state type; - a current limiting circuit (40) adapted to limit current flowing along the second electrical branch, the current limiting circuit being electrically connected in series with the current blocking circuit (40A) and including a second switching device (42) of solid-state type and a second electronic circuit (49) electrically connected in parallel to the second switching device (42) of solid-state type, wherein the switching device is configured to operate in a closed mode, an open mode of the first electronic circuit of the current blocking circuit, and a current limiting mode of the second electronic circuit of the current limiting circuit.

2. The switching device according to claim 1, characterized in that the first electrical branch (3) includes a single switching device (30) of electromechanical type, the single switching device (30) being able to switch between a closed state and an open state, in the closed state the switching device conducts current, and in the open state the switching device blocks current.

3. The switching device according to claim 1, characterized in that the first electrical branch (3) includes: - A first switching device (31) of electromechanical type, which is capable of switching between a closed state and an open state. In the closed state, the first switching device of electromechanical type conducts current, and in the open state, the first switching device of electromechanical type blocks current. The first switching device of electromechanical type is a self-acting switching device, which is capable of switching from the closed state to the open state when driven by the current flowing through the switching device and without receiving an external control signal or an external power supply. The first switching device of electromechanical type switches from the closed state to the open state when the current flowing through the switching device exceeds a corresponding predefined threshold, or when the rate of change of the current flowing through the switching device exceeds a corresponding predefined threshold, or when a combination of these two conditions occurs; - A second switching device (32) of electromechanical type, which is electrically connected in series with the first switching device of electromechanical type. The second switching device of electromechanical type is capable of switching between a closed state and an open state. In the closed state, the second switching device of electromechanical type conducts current, and in the open state, the second switching device of electromechanical type blocks current. The second switching device of electromechanical type switches between the closed state and the open state when receiving a corresponding input control signal.

4. The switching device according to claim 3, characterized in that, the first switching device (31) of electromechanical type includes a first actuator, and the first actuator can use the electrodynamic force generated by the flow of current through the switching device to actuate the electrical contact portion of the first switching device of electromechanical type, thereby switching the first switching device of electromechanical type from the closed state to the open state.

5. The switching device according to claim 4, characterized in that, the first actuator includes a Thomson coil actuating device, and the Thomson coil actuating device is operatively coupled to the electrical contact portion of the first switching device of electromechanical type.

6. The switching device according to any one of claims 1 to 5, characterized in that, the first switching device (41) of solid state type includes a pair of switching components based on semiconductor materials, and the pair of switching components are arranged in an anti-parallel or anti-series configuration to allow control of the bidirectional current flowing through the second electrical branch (4).

7. The switching device according to any one of claims 1 to 5, characterized in that, the second electronic branch (4) includes a first diode bridge (45), and the first diode bridge (45) is operatively associated with the current blocking circuit (40A) to allow control of the bidirectional current flowing through the second electrical branch (4).

8. The switching device according to any one of the foregoing claims 1 to 5, characterized in that, the second switching device (42) of solid state type includes a pair of switching components based on semiconductor materials, and the pair of switching components are arranged in an anti-parallel or anti-series configuration to allow control of the bidirectional current flowing through the second electrical branch (4).

9. The switching device according to any one of claims 1 to 5, characterized in that, the second electronic branch (4) includes a second diode bridge (46), and the second diode bridge (46) is operatively associated with the current limiting circuit (40) to allow control of the bidirectional current flowing along the second electrical branch (4).

10. The switching device according to any one of claims 1 to 5, characterized in that, the second electrical branch (4) includes a third diode bridging circuit (47), and the third diode bridging circuit (47) is operatively associated with the current limiting circuit (40) and the current blocking circuit (40A) to allow control of the bidirectional current.

11. The switching device according to any one of claims 3 to 5, characterized in that, the first switching device (31) of the electromechanical type is adapted to switch from a closed state to an open state when a short-circuit current flows along the switching device.

12. The switching device according to any one of claims 3 to 5, characterized in that, the first switching device (31) of the electromechanical type is not adapted to switch from a closed state to an open state when an overload current or a normal current flows along the switching device.

13. The switching device according to any one of claims 1 to 5, characterized in that, the first switching device (41) of the solid-state type is adapted to switch from a conducting state to a non-conducting state after a time interval has elapsed since the moment when a short-circuit current has commuted from the first electrical branch (3) to the second electrical branch (4).

14. The switching device according to any one of claims 1 to 5, characterized in that, the first switching device (41) of the solid-state type is adapted to switch from a conducting state to a non-conducting state after a time interval has elapsed since the moment when an overload current or a normal current has commuted from the first electrical branch (3) to the second electrical branch (4).

15. The switching device according to any one of claims 1 to 5, characterized in that, the second switching device (42) of the solid-state type is adapted to switch from a conducting state to a non-conducting state after current has commuted from the first electrical branch (3) to the second electrical branch (4).

16. A power grid (100) comprising at least the switching device (1) according to any one of claims 1 to 15.

17. A switch group (110) comprising the switching device (1) according to any one of the foregoing claims 1 to 15 and an isolator (150) connected in series electrically.

18. A method for protecting a power grid, the power grid including a plurality of switch groups (110) for electrically connecting or disconnecting different grid sections of the power grid, wherein each switch group (110) comprises: - The switching device (1) as claimed in any one of claims 1 to 15, which is capable of controlling bidirectional current, and the switching device can be switched to a closed state in which the switching device conducts current, or an open state in which the switching device blocks current, or a current limiting mode in which the switching device limits the current commuting from the first electrical branch (3) to the second electrical branch (4); - An isolator (15), which is electrically connected in series with the switching device (1), and the isolator can be switched to a closed state in which the isolator conducts current or an open state in which the isolator blocks current; wherein each switch group (110) can be switched to a closed state in which the switching device (1) is in the closed state and the isolator (150) is in the closed state, or an open state in which the switching device (1) is in the open state and the isolator (150) is in the open state, or a current limiting mode in which the switching device (1) is in the current limiting mode and the isolator (150) is in the closed state, characterized by comprising the following steps: - If there is an electrical fault in the power grid, switch the switch group (110) to the current limiting mode; - Switch the switch group (110) closest to the electrical fault to the open state, and keep the remaining switch groups (110) of the power grid in the current limiting mode; If the electrical fault is electrically isolated within a predefined time period when the switch group (110) closest to the electrical fault is in the open state, then: - Keep the switch group (110) closest to the electrical fault in the open state, and switch the remaining switch groups (110) of the power grid back to the closed state; If the electrical fault is not electrically isolated within the predefined time period when the switch group (110) closest to the electrical fault is in the open state, then: - Switch all the switch groups (110) of the power grid to the open state.

19. The method as claimed in claim 18, characterized in that, the power grid (100A) comprises: a battery energy storage system, which comprises a plurality of battery cells; a DC bus (101A), which is used for electrically connecting the battery cells to a power converter; and a plurality of the switch groups (110), which are used for connecting the battery cells to the DC bus electrically or disconnecting the battery cells from the DC bus.

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