A hybrid switch device for power grid

Abstract

The present disclosure relates to a hybrid switch device for a power grid. A switch device for a power grid includes: first and second electrical terminals, electrically connected to corresponding power grid parts; a first electrical branch, including a plurality of switch devices, which have electrical contacts that can be mechanically coupled or separated to conduct or block current; a second electrical branch, including a solid-state switch device, which includes a semiconductor switch component, the switch device is suitable for switching between on and off, and the first and second electrical branches are connected in parallel between the first and second electrical terminals; the first electrical branch includes: a first switch device, which can switch between closing and opening, and switches from closing to opening when driven by current without receiving an external control signal or power supply, and switches from closing to opening when the current exceeds a threshold or the current change rate exceeds a threshold or a combination thereof; a second switch device, which is connected in series with the first switch device and can switch between closing and opening, and switches between closing and opening when receiving an input control signal.

Description

Technical Field

[0001] The present invention relates to the field of power grids. More specifically, the present invention relates to a hybrid switchgear for providing a circuit protection function in a power grid (eg, a DC power grid). Background Art

[0002] DC grids are widely used in various 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 power line, many electrical components electrically connected to the power line may aggravate the electrical fault.

[0004] Obviously, this can lead to disastrous consequences, especially when power generation systems (e.g., photovoltaic panels) or energy storage systems (e.g., batteries) are installed in the grid.

[0005] To prevent this possibility, DC grids typically include a plurality of switchgear configured to allow for selective disconnection of portions of the grid when a fault event occurs.

[0006] Some switchgears of the prior art include electromechanical circuit breakers.

[0007] In general, these devices have the advantage of ensuring galvanic isolation between disconnected grid sections. In addition, they are relatively cheap to implement at an industrial level.

[0008] However, due to their operating principle, these devices usually do not provide satisfactory interruption levels. For example, at relatively high voltages (e.g. up to 1.5 kV DC or higher), the disconnection time can be quite long. Therefore, the arc that is usually generated between the separated mechanical contacts can last for a relatively long time. Obviously, this fact may bring about relevant problems in terms of reliability and maintenance costs.

[0009] Other switching devices of the prior art include solid-state type switching devices which include switching components based on semiconductor materials.

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

[0011] In addition, these devices operate quickly and have significantly shorter interruption times compared to electromechanical switchgear.

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

[0013] In order to alleviate the above-mentioned problems, hybrid switchgear that adopts both electromechanical switchgear and solid-state switchgear has been developed. Examples of these protection devices are disclosed in WO2017 / 186262 and WO2011 / 057675.

[0014] In general, in particular in the event of a short circuit, known switching devices of this type cannot intervene as quickly as devices which employ solely solid-state switching devices, since a relatively long time is required to commutate the current from the electromechanical switching devices employed to the solid-state devices.

[0015] Furthermore, they are often bulky and relatively expensive to manufacture at an industrial level, particularly as the solid-state switching devices employed must be designed to withstand relatively high currents for relatively long periods of time. Summary of the invention

[0016] The main object of the present invention is to provide a hybrid switchgear for an electrical network, such as a DC network, which allows to overcome or mitigate the above mentioned key problems.

[0017] More particularly, it is an object of the present invention to provide a hybrid switching device which ensures the performance of the interrupting rating in the event of an electrical fault, in particular in the presence of a short-circuit current.

[0018] As a further object, the invention aims at providing a hybrid switchgear in which cheaper and smaller sized solid-state switchgear can be used with respect to corresponding solutions of the prior art.

[0019] Yet another object of the invention is to provide a hybrid switchgear which can be easily manufactured at industrial level and at a cost competitive with respect to prior art solutions.

[0020] In order to achieve these goals and objectives, the present invention provides a switch device as follows.

[0021] According to the present invention, the hybrid switch device comprises:

[0022] - first and second electrical terminals for electrical connection to corresponding power grid parts;

[0023] - a first electrical branch comprising a plurality of switching devices of electromechanical type, each switching device having electrical contacts that are mechanically coupled or separated to respectively conduct or interrupt an electric current;

[0024] - a second electrical branch comprising one or more switching devices of solid-state type, each comprising one or more switching components based on semiconductor material. Each solid-state switching device is suitable for switching between an on-state in which the switching device conducts current and an off-state in which the switching device blocks current.

[0025] The above-mentioned second electrical branch is electrically connected in parallel with the first electrical branch between the first electrical terminal and the second electrical terminal.

[0026] According to the invention, the first electrical branch of the switching arrangement comprises a first switching device of electromechanical type which is reversibly switchable between a closed state in which the first switching device conducts current and an open state in which the first switching device blocks current.

[0027] The first switching device is a self-acting switching device capable of rapidly switching from the closed state to the open state when driven by a current flowing along the switching device without receiving an external control signal or an external power supply.

[0028] The first switching device switches from the closed state to the open state when the current flowing along the switching device exceeds a corresponding predefined threshold or when the rate of change of the current flowing along the switching device exceeds a corresponding predefined threshold or a combination of these conditions.

[0029] According to the invention, the first electrical branch of the switching arrangement comprises a second switching device of electromechanical type which is electrically connected in series with the first switching device and is suitable for switching between a closed state in which the second switching device conducts current and an open state in which the second switching device blocks current.

[0030] The second switching device is reversibly switchable between the closed state and the open state upon receiving a corresponding input control signal.

[0031] According to one aspect of the present invention, the first switching device includes a first actuator, which can use the electric force generated by the circulation of current along the switching device to actuate the electrical contacts of the first switching device, thereby switching the first switching device from the closed state to the open state.

[0032] Preferably, the first actuator comprises a Thomson coil actuation device operably connected to electrical contacts of the first switching device.

[0033] According to an aspect of the invention, the second switching device comprises a second actuator of the electromechanical type capable of actuating the electrical contacts of the second switching device upon receipt of a corresponding input control signal.

[0034] According to one aspect of the invention, the second electrical branch of the switching device comprises a current blocking circuit adapted to block the current flowing along the second electrical branch. The blocking circuit comprises a third switching device of solid-state type comprising one or more switching components based on semiconductor material and a first electronic circuit electrically connected in parallel with the third switching device. The third switching device can be arranged in a unidirectional or bidirectional type, i.e. capable of carrying and interrupting current flowing in one direction only in a DC network, or capable of carrying and interrupting current in any direction in a DC or AC network.

[0035] According to a variant embodiment, the third switching device comprises a pair of switching components based on semiconductor material, arranged according to an anti-parallel or anti-series configuration. In operation, the semiconductor switching components conduct current alternately to allow controlling a bidirectional current flowing along the second electrical branch.

[0036] According to another variant embodiment, the second electrical branch of the switching device comprises a first diode bridge operatively associated to said current-breaking circuit to allow controlling a bidirectional current flowing along said second electrical branch.

[0037] According to one aspect of the invention, the second electrical branch of the switching device comprises a current limiting circuit adapted to limit the current flowing along the second electrical branch. The current limiting circuit is electrically connected in series with the current blocking circuit of the second electrical branch. The current limiting circuit comprises a fourth switching device of a solid-state type and a second electronic circuit electrically connected in parallel with the fourth switching device.

[0038] Furthermore, the fourth switching device may be arranged in a unidirectional or bidirectional type manner.

[0039] According to a variant embodiment, said fourth switching device comprises a pair of switching components based on semiconductor material, arranged according to an anti-parallel or anti-series configuration. In operation, said semiconductor switching components conduct current alternately to allow controlling a bidirectional current bypassing such a second electronic circuit.

[0040] According to another variant embodiment, the second electric branch of the switching device comprises a second diode bridge operatively associated with said current limiting circuit so as to allow control of a bidirectional current flowing along said second electric branch.

[0041] According to other embodiments of the present invention, the second electrical branch of the switching device includes a third diode bridge circuit electrically connected to other components of the second electrical branch (for example, a series component connected to the current blocking circuit, and possibly the current limiting circuit) to allow control of the bidirectional current flowing along the second electrical branch.

[0042] In operation of the switching device, if a short-circuit current flows along the switching device, the first switching device switches from a closed state to an open state.

[0043] In operation of the switching apparatus, if an overload current or a normal current flows along the switching apparatus, the first switching device is not switched from a closed state to an open state.

[0044] In the operation of the switching device, if a short circuit current flows along the switching device, the second switching device is commanded to switch from the closed state to the open state. However, if an overload current or a normal current flows along the switching device, the second switching device may also be commanded to switch from the closed state to the open state.

[0045] In operation of the switching device, during an opening operation of the first switching device, the third switching device is commanded to switch from the on state to the off state after a first time interval has elapsed from the moment the short-circuit current has been commutated from the first electrical branch to the second electrical branch.

[0046] In operation of the switching device, upon disconnection of the second switching device, the third switching device is commanded to switch from the on state to the off state after another time interval has elapsed from the moment when the overload current or the normal current has been commutated from the first electrical branch to the second electrical branch. This third time interval may be different from or identical to the first time interval mentioned above.

[0047] In operation of the switching device, upon an opening operation of the first switching device or the second switching device, the fourth switching device is commanded to switch from the on state to the off state after the current has been commutated from the first electrical branch to the second electrical branch.

[0048] On the other hand, according to the contents described in this application, the present invention also relates to a power grid including at least one switching device of the present invention, a switch group including a switching device of the present invention and an isolating switch electrically connected in series, and a method for protecting a power grid.

[0049] Generally speaking, the electrical grid comprises a plurality of switch groups for electrically connecting or disconnecting different grid parts of the electrical grid.

[0050] Preferably, the power grid comprises a battery energy storage system comprising 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 or disconnecting the battery cells from the DC bus.

[0051] Each switch group includes:

[0052] - a switching device according to the invention, comprising the first blocking circuit and the current limiting circuit and capable of controlling a bidirectional current. The switching device is capable of switching in a closed state in which the switching device conducts current or in an open state in which the switching device blocks current or in a current limiting mode in which the switching device limits the current commutated from the first electrical branch to the second electrical branch;

[0053] A disconnector switch is electrically connected in series with the switchgear. The disconnector switch is switchable in a closed state, in which the disconnector switch conducts current, or in an open state, in which the disconnector switch blocks current.

[0054] Each switch group is capable of switching in a closed state in which the switching device is in a closed state and the disconnecting switch is in a closed state, or in an open state in which the switching device is in an open state and the disconnecting switch is in an open state, or in a current limiting mode in which the switching device is in a current limiting mode and the disconnecting switch is in a closed state.

[0055] The method of the present invention comprises the following steps:

[0056] - if there is an electrical fault in the grid, switching the switch group to a current limiting mode;

[0057] - switching the switch group closest to the electrical fault to an open state and maintaining the remaining switch groups of the power grid in a current limiting mode;

[0058] If the electrical fault is electrically isolated within a predetermined time interval when the switch group closest to the electrical fault is in an open state:

[0059] - maintaining the switch group closest to the electrical fault in an open state and switching the remaining switch groups of the power grid to a closed state;

[0060] If the electrical fault is not electrically isolated within a predetermined time interval when the switch group closest to the electrical fault is in an open state:

[0061] - Switching all switch groups of the power grid to the open state. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Further features and advantages of the invention will emerge from the description of a preferred but non-exclusive embodiment of a contactor according to the invention, a non-limiting example of which is provided in the accompanying drawings, in which:

[0063] Figure 1-6 , Fig. 6A and Figure 7 Some embodiments of the switch device according to the present invention are schematically shown;

[0064] Figure 8 Schematically shows a DC grid comprising a switching device according to the invention;

[0065] Figure 9-16 The operation of a battery energy storage system of a DC grid comprising a plurality of switchgears according to the invention is schematically illustrated. DETAILED DESCRIPTION

[0066] With reference to the cited drawings, the present invention relates to a hybrid switchgear 1 for an electrical network.

[0067] The switchgear of the present invention is particularly suitable for use in low voltage DC grids and will be described below with specific reference to these applications for the sake of brevity only, without intending to limit the scope of the invention in any way.

[0068] In fact, the switchgear of the invention can be successfully used in different types of power systems, such as a low voltage AC grid or a medium voltage AC or DC grid.

[0069] For the purposes of this 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, for example up to 72 kV AC and 100 kV DC.

[0070] The switchgear 1 comprises first and second electrical terminals 11, 12 for electrical connection with corresponding grid parts (not shown), such as a DC link bus and an electrical load.

[0071] Preferably, at one of the electrical terminals 11 - 12 , a disconnector (or another equivalent switchgear) 150 is operatively associated to the switchgear 1 to form a switch group 110 .

[0072] The disconnector 150 is arranged for electrically connecting or disconnecting the switchgear to another circuit part of the electrical network. Thus, the disconnector 150 is able to provide galvanic isolation between different circuit parts, one of which comprises the switchgear 1, whenever required.

[0073] To this end, the disconnector 150 is adapted to be reversibly switched between a closed state, in which it conducts electric current, and an open state, in which it blocks electric current.

[0074] The disconnect switch 150 may or may not be part of the switchgear.

[0075] In general, the disconnector 150 may be of known type. Therefore, its function will be described below only in relation to the aspects of interest to the present invention.

[0076] The switching device 1 comprises a first electrical branch 3 and a second electrical branch 4 which are electrically connected in parallel between electrical terminals 11 , 12 .

[0077] The first electrical branch 3 comprises a pair of electromechanical switching devices 31 , 32 which are electrically connected in series.

[0078] Each electromechanical switching device 31 , 32 of the first electrical branch 3 has electrical contacts which can be mechanically coupled or decoupled to respectively conduct or block an electrical current.

[0079] More specifically, each switching device 31 , 32 of the first electrical branch 3 has one or more fixed contacts and one or more movable contacts that can be coupled or decoupled with the fixed contacts to conduct or block an electric current.

[0080] Each switching device 31 , 32 of the first electrical branch 3 is in a closed state when its electrical contacts are coupled to each other to conduct current, and is in an open state when its electrical contacts are decoupled to each other to block current.

[0081] The switching device 31 of the first electrical branch 3 is of the self-acting type for the execution of an opening operation. In this case, the transition from the closed state to the open state (opening operation) occurs by moving the movable contact or triggering the movement of the movable contact by means of the electric force generated by the circulation of the current along the switching device (for example, along the first electrical branch 3 or at the terminals 11, 12). Therefore, the opening operation of this type of switching device occurs in a very short opening time (fast switching) without receiving an input control signal or an external power supply (uncontrolled opening operation).

[0082] Alternatively, the further switching device 32 of the first electrical branch 3 is of a fully controllable type. In this case, any transition from a closed state to an open state (opening operation) or from an open state to a closed state (closing operation) occurs in response to receiving a suitable input control signal, which causes activation of a drive mechanism, thereby moving a movable contact or triggering movement of said movable contact.

[0083] In general, the switchgear of the first electrical branch 3 can be implemented according to solutions of known type. Therefore, only those aspects of interest to the present invention will be described below.

[0084] According to the invention, the first electrical branch 3 comprises a first switching device 31 of electromechanical type capable of rapid switching between a closed state in which the first switching device conducts current and an open state in which the first switching device blocks current.

[0085] The first switching device 31 is a self-acting switching device that is capable of rapidly switching from a closed state to an open state when driven by the current flowing along the switching device. Therefore, the first switching device 31 can perform an opening operation without receiving an external control signal commanding such an operation or without receiving an external power supply.

[0086] For the sake of clarity, within the scope of the present invention, a switching device is considered to be "fast switching" if it shows an opening time of the electrical contacts that is shorter than 1 ms, more preferably shorter than 500 μs.

[0087] The switching device 31 is suitable for quickly switching from a closed state to an open state (opening operation) when the current flowing along the switching device exceeds a corresponding threshold value (for example, a short-circuit value, typically 10-20 times the nominal value) or when the change in the current rate exceeds a corresponding threshold value (for example, greater than 10kA / ms) or when these last two conditions occur simultaneously.

[0088] Preferably, the first switching device 31 is adapted to be quickly switched from a closed state to an open state (opening operation) whenever a short circuit current flows along the switching device.

[0089] Preferably, the first switching device 31 is adapted not to switch from a closed state to an open state (opening operation) when an overload current or a normal current flows along the switching device.

[0090] For the purpose of this application:

[0091] - "Normal current" is an operating value that is usually about the nominal value or lower (e.g.

[0092] up to 1.1 times the nominal value);

[0093] - "Overload current" is a current that usually has a higher operating value, for example, from 1.1 times the nominal value to 10 times the nominal value;

[0094] - "Short-circuit current" is a current which typically has even higher operating values, for example, from 10 times the nominal value to several tens of times the nominal value.

[0095] Preferably, the switching device 31 comprises a first actuator (not shown) capable of actuating the electrical contacts during an opening operation using the electric force generated by the circulation of the electric current along the switching device.

[0096] Preferably, the switch device 31 comprises a Thomson coil actuation device (not shown) operatively coupled to the electrical contacts (eg via a suitable kinematic chain) so as to actuate said electrical contacts during an opening maneuver.

[0097] The Thomson coil actuation device is adapted to provide sufficient actuation force to separate the electrical contacts of the first switching device 31 when the circulating current exceeds a corresponding threshold value and / or when the rate of change of the current exceeds a corresponding threshold value, in particular when the circulating current is a short circuit current.

[0098] Generally speaking, the Thomson coil actuation device is operatively connected to the electrical contacts of the first switching device 31 (which is arranged along the first electrical branch) through a suitable kinematic chain.

[0099] According to some embodiments of the present invention, the Thomson coil actuation device is electrically connected in series to the above-mentioned first terminal 11 or second terminal 12 of the switching device. As an example, the Thomson coil can be arranged between the first terminal 11 or the second terminal 12 and a common node of the first electrical branch 3 and the second electrical branch 4 (a node where the electrical branches are separated from each other).

[0100] According to other embodiments of the present invention, the Thomson coil actuation device is arranged along the first electrical branch 3 and is electrically connected in series with the electrical contacts of the first switching device 31 .

[0101] According to some embodiments of the invention, the first switching device 31 is adapted to return to the closed state immediately after the opening operation if the current no longer flows along the first electrical branch 3 or if for any reason the current returns to a lower intensity value. To this end, the first switching device 31 may comprise a suitable spring-operated mechanism (not shown) to actuate the electrical contacts during the opening operation by utilizing the stored elastic energy.

[0102] According to other embodiments of the present invention, the first switch device 31 is adapted to maintain the disconnected state once the disconnection operation is performed. To this end, the first switch device 31 may include a suitable latch mechanism (not shown) capable of maintaining the electrical contacts separated and an actuation mechanism (not shown) coupling the electrical contacts after receiving a corresponding input control signal.

[0103] According to an additional variant of the invention (not shown), an electronic circuit (e.g., comprising a snubber circuit, a spark gap, a discharge tube, a metal oxide varistor or a semiconductor component) is electrically connected in parallel with the first switching device 31 to protect the first switching device 31 (e.g., by limiting voltage transients) and / or to dissipate electrical energy when necessary during a disconnection operation of the switching device.

[0104] According to the invention, the first electrical branch 3 comprises a second switching device 32 of the electromechanical type which is electrically connected in series with the first switching device 31 .

[0105] The switching device 32 is fully controllable and reversibly switches between a closed state and an open state upon receipt of a corresponding input control signal commanding the execution of an operation.

[0106] As will be shown below, the control signals for controlling the operation of the switchgear 32 may conveniently be provided by a control unit 90, which may or may not be part of the switchgear.

[0107] Generally speaking, the opening time of the second switching device 32 is much longer than that of the first switching device, such as several milliseconds (eg, approximately 5 to 20 ms).

[0108] Preferably, the second switching device 32 comprises a second actuator of the electromechanical type which actuates the electrical contacts of the second switching device upon receipt of a corresponding input control signal.

[0109] Preferably, whenever the first switching device 31 switches from a closed state to an open state, in particular when a short-circuit current (e.g., a value 10-20 times the nominal value) flows along the first electrical branch 3, the second switching device 32 is commanded to switch from a closed state to an open state.

[0110] However, unlike the first switching device 31, the second switching device 32 can be commanded to switch from the closed state to the open state (opening operation) even when the current circulating along the first electrical branch 3 takes values ​​below the above-mentioned short-circuit value.

[0111] Preferably, if an overload current (eg, having a value 2-3 times the rated value) flows along the first electrical branch 3, the second switching device 32 is commanded to perform a disconnection operation.

[0112] Even when the current flowing along the first electrical branch 3 takes a normal value (e.g., approximately the nominal value or below the nominal value), if a disconnect operation of the hybrid switching device must be performed (e.g., upon request of an operator), the second switching device 32 can be commanded to switch from the closed state to the open state.

[0113] As mentioned above, the first and second switching devices 31 and 32 are electrically connected in series. In this way, these switching devices can control the current circulating along the first electrical branch 3 in a suitable manner depending on the nature of this current.

[0114] For example, if the current circulating along the first electrical branch 3 is a short-circuit current, the first switching device 31 intervenes quickly to perform a disconnection operation and it blocks the current without receiving an input control signal. In this case, the second switching device 32 is also commanded to perform a disconnection operation. However, since it is slower than the first switching device 31, the second switching device 32 will perform this disconnection operation later than the first switching device 31, usually when the current has already commutated on the second electrical branch 4.

[0115] If the current flowing along the first electrical branch 3 is a normal current or an overload current, the first switching device 31 does not intervene and may command the second switching device 32 to perform a disconnection operation to block such current after receiving a suitable control signal input.

[0116] According to the invention, the second electrical branch 4 comprises one or more switching devices 41 , 42 of solid-state type.

[0117] Each switch device 41, 42 includes one or more switch components based on semiconductor materials. Generally speaking, the semiconductor switch components can be conventional types, such as power MOSFET, JFET, insulated gate bipolar transistor ("IGBT"), gate turn-off thyristor (GTO), integrated gate commutated thyristor ("IGCT"), etc.

[0118] In response to receiving a suitable input control signal, each solid-state switching device 41 , 42 of the second electrical branch 4 is reversibly switchable between an on-state in which it conducts current and an off-state in which it blocks current.

[0119] The solid-state switching device turns off when switching from the on state to the off state, and turns on when switching from the off state to the on state.

[0120] As will be shown below, the control signals for controlling the operation of the switchgear 41, 42 may conveniently be provided by a control unit 90, which may or may not be part of the switchgear.

[0121] According to an important aspect of the invention, the second electric branch 4 comprises a current blocking circuit 40A suitable for blocking the electric current circulating along the second electric branch 4 .

[0122] The blocking circuit 40A comprises a third switching device 41 of a solid-state type and a first electronic circuit 48 adapted to protect the third switching device (eg from voltage transients) and dissipate energy when necessary.

[0123] The first electronic circuit 48 is electrically connected in parallel with the third switching device 41 and it may include a snubber circuit, a spark gap, a discharge tube, a metal oxide varistor or a semiconductor component.

[0124] In general, the third switching device 41 is operated depending on the behavior of the current circulating along the second electrical branch 4 and depending on the behavior of the switching devices 31 , 32 of the first electrical branch 3 .

[0125] As will be better seen below, this solution allows operating conditions of overload current or short-circuit current circulation to be managed in an efficient manner.

[0126] Preferably, if the third switching device 41 is in the off state for any reason, the third switching device 41 is commanded to switch to the on state immediately or before the first switching device 31 or the second switching device 32 performs the off operation. In this way, the current circulating along the first electrical branch 3 is allowed to commutate to the second electrical branch 4.

[0127] Preferably, the third switching device 41 is switched off after a first time interval from the moment when the short-circuit current (ie above a predefined short-circuit threshold) is completely commutated from the first electrical branch 3 to the second electrical branch 4 due to the opening operation of the first switching device 31 .

[0128] Preferably, the first time interval mentioned above is calculated according to the minimum time required to restore the dielectric tolerance of the gap between the electrical contacts of the first switching device 31 in order to avoid possible arc reignition (this minimum time is often referred to as the "gap clearing time"). Conveniently, if communication between the switching devices of the network is possible, the first time interval can be modified in order to better coordinate the operation of such switching devices.

[0129] In practice, the first time interval mentioned above is selected to be long enough to prevent a reignition phenomenon between the electrical contacts of the first switching device 31 , and short enough to prevent the third switching device 41 from being damaged by overheating.

[0130] When a short-circuit current flows along the second electrical branch 4 and the fault generating such a short circuit cannot be cleared before the above-mentioned first time interval has elapsed, the third switching device 41 is switched off.

[0131] Since the third switching device 41 is switched off with a certain time delay from the moment when the short-circuit current has completely commutated along the second electrical branch 4 , under certain conditions the third switching device 41 can remain switched on even if a short-circuit current initially exists.

[0132] When the short-circuit current has commutated along the second electrical branch 4 and the fault generating such a short circuit can be cleared in some way before the first time interval mentioned above has elapsed (for example, due to intervention of an external circuit breaker), the third switching device 41 is not switched off and remains in the on state, even if the short-circuit current initially flows along the second electrical branch 4.

[0133] Preferably (but not necessarily as an alternative to the above solution), the third switching device 41 may be commanded to shut down for self-protection purposes if one or more of the following conditions are achieved:

[0134] - the current flowing along the electrical branch 4 exceeds a given threshold current value;

[0135] - the temperature of the third switching device 41 exceeds a given temperature threshold;

[0136] - the voltage across the third switching device 41 exceeds a given threshold voltage value;

[0137] - The electrical power consumed by the third switching device 41 exceeds a given threshold power value.

[0138] Moreover, this solution also provides some significant advantages. For example, when the electrical protection device 1 is reconnected to the power line with the first and second switching devices 31, 32 in the disconnected state and a short-circuit current flows along the second electrical branch 4 due to the presence of an existing fault, the third switching device 41 is turned off as soon as the second time interval (in practice, the time required to detect the presence of the fault by appropriately processing the detection signal indicating the physical quantity mentioned above) has passed, thus preventing overheating damage.

[0139] Preferably, upon a disconnection operation of the second switching device 32 (in this case, the first switching device 31 does not intervene), the third switching device 41 is commanded to shut down after a third time interval has elapsed from the moment when an overload current (i.e., higher than a predefined overload threshold) or a normal current (i.e., having a value approximately the nominal value or less) has been commutated from the first electrical branch 3 to the second electrical branch 4.

[0140] Conveniently, the third time interval mentioned above is calculated based on similar criteria as the first time interval mentioned above, even though the criteria are explicitly with reference to the second switching device 32. In general, the third time interval mentioned above may be different from or the same as the first time interval mentioned above as desired.

[0141] According to another important aspect of the present invention, the second electrical branch 4 further comprises a current limiting circuit 40 , which is suitable for limiting the current flowing along the second electrical branch 4 .

[0142] The current limiting circuit 40 is electrically connected in series with the above-mentioned current limiting circuit 40A.

[0143] The current limiting circuit 40 comprises a fourth switching device 42 of a solid-state type and a second electronic circuit 49 adapted to limit the current, protect the fourth switching device (eg from voltage transients) and, if necessary, dissipate electrical energy.

[0144] The second electronic circuit 49 is electrically connected in parallel with the fourth switching device 42 and it preferably comprises a varistor or a resistive device or both.

[0145] Generally speaking, the fourth switching device 42 operates according to the behavior of the current flowing along the second electrical branch 4 .

[0146] For example, the fourth switching device 42 may be switched on to bypass the second electronic circuit 49 and facilitate commutation of the current from the first electrical branch 3 to the second electrical branch 4 .

[0147] As another example, the fourth switching device 42 may be switched off if the current flowing along the second electrical branch 4 has to be limited. In this way, the fault current may be conducted along the second electrical branch 4 without oversizing of the third switching device 41 being necessary.

[0148] Preferably, if the fourth switching device 42 is in the on state for any reason, immediately or before the first switching device 31 or the second switching device 32 performs the off operation, the fourth switching device 42 is commanded to switch to the on state simultaneously with the third switching device 41. In this way, the current flowing along the first electrical branch 3 can be commutated to the second electrical branch 4.

[0149] Preferably, following the opening actuation of the first switching device 31 , the fourth switching device 42 is switched off after a short-circuit current (ie above a predefined short-circuit threshold) has been commutated from the first electrical branch 3 .

[0150] Preferably, when a short-circuit current flows along the second electrical branch 4 (due to the completion of commutation from the first electrical branch 3) and the fault generating such a short circuit cannot be cleared in any way, the fourth switching device 42 (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.

[0151] Preferably, when a short circuit current flows along the second electrical branch 4 and the fault generating such a short circuit is cleared in some way (e.g. due to intervention of an external circuit breaker), the fourth switching device 42 is initially switched off to provide a current limiting function (as shown above), but once the fault is cleared and the current returns to a lower value, it is switched on again. After reclosing the first switching device 31 and the second switching device 32, the current will commutate back to the first electrical branch 3.

[0152] Conveniently, the fourth switching device 42 can also be commanded to switch off after the overload current has been commutated from the first electrical branch 3 to the second electrical branch 4 according to the opening operation of the second switching device 32 (in this case the first switching device 31 does not intervene).

[0153] Conveniently, when a disconnection operation of the second switching device 42 is performed for any reason, the fourth switching device 42 may also be commanded to switch off after normal current (ie having a value approximately nominal or lower) has been commutated from the first electrical branch 3 to the second electrical branch 4 .

[0154] Figure 1 A possible embodiment of the switching device 1 of the invention is shown.

[0155] In this case, the first electrical branch 3 comprises a first and a second switching device 31 and 32 which are electrically connected in series, whereas the second electrical branch 3 comprises only the current-breaking circuit 40A.

[0156] According to this embodiment of the invention, the switching device 1 normally allows current to circulate between the terminals 11 , 12 (closed state).

[0157] However, when necessary, the switchgear is capable of electrically isolating (disconnecting state) a wide range of currents flowing along the power line.

[0158] The following describes in more detail Figure 1 Operation of the switching device in the embodiment.

[0159] Closed state (normal operation)

[0160] In normal operation (ie, in the presence of current at or below nominal value), the switching devices 31 , 32 are in a closed state, while the third switching device 41 can be in an on state or an off state.

[0161] Even if the third switching device 41 is in the on-state, the current naturally flows mainly along the first electrical branch 3 , since the first electrical branch 3 exhibits a lower equivalent resistance.

[0162] The isolating switch 150 is in a closed state.

[0163] Overload current or interruption of normal current

[0164] It is assumed that the first and second switching devices 31 , 32 are in a closed state.

[0165] In the presence of a normal current or an overload current, the first switching device 31 does not intervene (and thus remains in a closed state) while the second switching device 32 is commanded to perform an opening operation.

[0166] If the third switching device 41 is not already in the on state, the third switching device 41 is commanded to be turned on.

[0167] As soon as the electrical contacts of the second switching device 32 are separated, current starts to flow along the second electrical branch 4. Complete commutation of the current from the first electrical branch 3 to the second electrical branch 4 eliminates arcing between the electrical contacts of the second switching device 32.

[0168] After a third time interval from the moment the current has commutated, the second switching device 32 has sufficient dielectric withstand to avoid arc reignition, the third switching device 41 is commanded to switch off.

[0169] The current is forced to circulate along the first electronic circuit 48 (which dissipates the inductive energy of the grid) until it disappears. It can be seen that the current cannot restart flowing along the first electrical branch 3 when the second switching device 32 is in the open state.

[0170] Conveniently, the disconnector 150 is commanded to perform an opening maneuver, thereby providing galvanic isolation for the portion of the grid that includes the switchgear.

[0171] When interruption of the normal current is requested for any reason, the switching device 1 behaves in substantially the same way.

[0172] Interruption of short-circuit current

[0173] It is assumed that the first and second switching devices 31 , 32 are in a closed state.

[0174] When a short circuit current is present, the first switching device 31 immediately performs a (fast switching) disconnection operation without receiving an input control signal or an external power supply.

[0175] If the third switching device 41 is not already in the on state, the third switching device 41 is commanded to be turned on.

[0176] The second switching device 32 is also commanded to perform a disconnection maneuver. However, the intervention of the first switching device 31 occurs long before the second switching device 32.

[0177] The separation of the electrical contacts of the first switching device 31 commutates the short-circuit current to the second electrical branch 4 .

[0178] Complete commutation of the current from the first electrical branch 3 to the second electrical branch 4 eliminates arcing phenomena between the electrical contacts of the first switching device 31 .

[0179] The current flowing along the second electrical branch 4 flows through the third switching device 41 .

[0180] After the above-mentioned first time interval has elapsed from the time at which the current has been commutated to the second electrical branch 4 , the third switching device should be commanded to switch off.

[0181] However, if the fault generating the short-circuit current is cleared in some way (for example, due to intervention of an external switching device) before the first time interval mentioned above has elapsed, then when the current flowing along the second electrical branch 4 returns to a lower value, the third switching device 41 is not commanded to turn off and it remains in the turned-on state.

[0182] At the same time, the first switching device 31 returns to the closed state, and commands the second switching device 32 to perform a closing operation.

[0183] When the first and second switching devices 31 , 32 finally return to the closed state, the switching arrangement 1 operates again under normal conditions and the current naturally commutates from the second electrical branch 4 to the first electrical branch 3 .

[0184] Alternatively, if the fault generating the short-circuit current is not cleared before the above-mentioned first time interval has elapsed, the third switching device 41 is commanded to turn off.

[0185] The current is forced to circulate along the first electronic circuit 48 until it dies out. As indicated above, the current cannot restart flowing along the first electrical branch 3.

[0186] Subsequently, the disconnector 150 is commanded to perform an opening operation, thereby providing galvanic isolation for the grid portion including the switchgear.

[0187] Reconnecting to power lines

[0188] Since no current flows, the first switching device 31 is assumed to be in a closed state, the second switching device 32 is assumed to be in an open state, and the third switching device 41 is assumed to be in an off state.

[0189] The disconnector 150 is commanded to perform a closing maneuver. As a result, it no longer provides galvanic isolation of the network section comprising the switchgear from another network section (not comprising the switchgear).

[0190] The third switching device 41 is commanded to turn on.

[0191] The current flows along the second semiconductor branch 4 .

[0192] If this current remains within the normal range for a second time interval (the time necessary to check whether a short circuit exists), the second switching device 32 is commanded to perform a closing operation.

[0193] Once the second switching device 32 has completed the closing operation (the first switching device 31 is already in the closed state), the current is naturally commutated to the first electrical branch 3 and the switching device 1 starts to operate under normal conditions.

[0194] Reconnecting to the power line in the event of a short circuit

[0195] Since no current flows, the first switching device 31 is assumed to be in a closed state, the second switching device 32 is assumed to be in an open state, and the third switching device 41 is assumed to be in an off state.

[0196] The disconnector 150 is commanded to perform a closing maneuver. The galvanic isolation of the grid section comprising the switchgear from another grid section (not comprising the switchgear) is no longer ensured.

[0197] The third switching device 41 is commanded to turn on.

[0198] A short-circuit current starts to flow along the second semiconductor branch 4. When the control unit 90 detects a fault, it commands the third switching device 41 to be switched off again within the above-mentioned second time interval.

[0199] The second switching device 32 is not commanded to perform a closing operation and it remains in the open state.

[0200] The current is forced to circulate along the first electronic circuit 48 until it disappears.

[0201] Subsequently, the disconnector 150 is commanded to perform an opening operation, thereby providing galvanic isolation for the grid portion including the switchgear.

[0202] It can be clearly seen from the above that when Figure 1 When the embodiment is arranged, the switching device 1 can be operated in two different states: a closed state in which it conducts current (normal operation), or an open state in which it blocks current (i.e., commutates the current from the first electrical branch 3 to the second electrical branch 4).

[0203] It is further demonstrated how the switch group 110 formed by the switching device 1 and the disconnector 150 electrically connected in series can also be operated according to two different states: a closed state in which the switching device 1 and the disconnector 150 are both in a closed state, or an open state in which the switching device 1 and the disconnector 150 are both in an open state.

[0204] Figure 2 A possible embodiment of the switching device 1 of the invention is shown.

[0205] In this case, the first electrical branch 3 comprises a first and a second switching device 31 , 32 which are electrically connected in series, whereas the second electrical branch 4 comprises a current-breaking circuit 40A and a current-limiting circuit 40 .

[0206] According to this embodiment of the invention, the switching device 1 normally allows current to flow between the terminals 11 , 12 .

[0207] However, whenever necessary, it can provide electrical isolation (disconnected state) for a wide range of currents flowing along the power lines.

[0208] and Figure 1 Different from the embodiments of the present invention, the switching device 1 can also provide a current limiting function (current limiting mode), in particular when a short-circuit current exists.

[0209] The following describes in more detail Figure 2 Operation of the switching device in the embodiment.

[0210] Closed state (normal operation)

[0211] In normal operation (ie, current flow at or below nominal), the switching devices 31 , 32 are in a closed state, while the third and fourth switching devices 41 , 42 may be switched on or off as required.

[0212] The isolating switch 150 is also in the closed state.

[0213] Even if the third and fourth switching devices 41 , 42 are switched on for any reason, the current naturally flows mainly along the first electrical branch 3 , since the first electrical branch 3 exhibits a lower equivalent resistance.

[0214] Overload current or interruption of normal current

[0215] It is assumed that the first and second switching devices 31 , 32 are in a closed state.

[0216] In the presence of an overload current, the first switching device 31 does not intervene (and thus remains in the closed state) while the second switching device 32 is commanded to perform an opening operation.

[0217] If the third and fourth switching devices 41 , 42 are not already in the on state, they are commanded to switch on.

[0218] As soon as the electrical contacts of the second switching device 32 are separated, current starts to flow along the second electrical branch 4. Complete commutation of the current from the first electrical branch 3 to the second electrical branch 4 eliminates arcing between the electrical contacts of the second switching device 32.

[0219] After a third time interval has elapsed from the moment of commutation of the current from the first electrical branch 3 to the second electrical branch 4 (so that the second switching device 32 has sufficient dielectric resistance to avoid arc reignition), the third and fourth switching devices 41, 42 are commanded to switch off. The overload current is forced to circulate along the first and second electronic circuits 48, 49 until it disappears.

[0220] As an alternative, after the current to the second electrical branch 4 has been completely commutated, the fourth switching device 42 is commanded to switch off and the current is forced to circulate along the second electronic circuit 49 and the third switching device 41 .

[0221] In this case, the switch device 1 provides a current limiting function (current limiting mode) of the overload current.

[0222] After the above-mentioned third time interval has elapsed from the time at which the overload current was commutated to the second electrical branch 4 , the third switching device 41 is subsequently commanded to switch off.

[0223] As a further alternative, only the third switching device 41 is commanded to switch off after the third time interval mentioned above has elapsed, after the current to the second electrical branch 4 has been completely commutated. In this case, the current is forced to circulate along the first electronic circuit 48 until it disappears.

[0224] Since the second switching device 32 is in the open state, current cannot resume flowing along the first electrical branch 3 .

[0225] Conveniently, after the current is interrupted, the disconnector 150 is commanded to perform an opening operation, thereby providing galvanic isolation for the portion of the grid comprising the switchgear.

[0226] The switching device behaves in the same manner when a request is made to interrupt the normal current flow for any reason.

[0227] Interruption of short-circuit current

[0228] It is assumed that the first and second switching devices 31 , 32 are in a closed state.

[0229] When a short circuit current is present, the first switching device 31 immediately performs a (fast switching) disconnection operation without receiving an input control signal or an external power supply.

[0230] If the third and fourth switching devices 41 and 42 are not already in the conducting state, they are commanded to switch on.

[0231] Furthermore, the second switching device 32 is commanded to perform a disconnection operation. However, the intervention of the first switching device 31 occurs long before the second switching device 32.

[0232] The separation of the electrical contacts of the first switching device 31 forces the current to be commutated to the second electrical branch 4 .

[0233] Complete commutation of the current from the first electrical branch 3 to the second electrical branch 4 eliminates arcing phenomena between the electrical contacts of the first switching device 31 .

[0234] The short-circuit current commutated to the second electrical branch 4 initially flows through both the third and the fourth switching device 41 , 42 .

[0235] Once the current is fully commutated to the second electrical branch 4 , the fourth switching device 42 is commanded to switch off and the current is forced to circulate along the second electronic circuit 49 and the third switching device 41 .

[0236] In this case, the switching device 1 provides a current limiting function of the short-circuit current (current limiting mode).

[0237] After the above-mentioned first time interval has elapsed from the time at which the short-circuit current was commutated to the second electrical branch 4 , the third switching device 41 should be commanded to switch off.

[0238] However, if the fault generating the short-circuit current is cleared in some way (for example, due to intervention of an external circuit breaker) before the first time interval mentioned above has elapsed, then when the current flowing along the second electrical branch 4 returns to a lower value, the third switching device 41 is not commanded to turn off and it remains in the turned-on state.

[0239] In this case, the fourth switching device 42 may be maintained in an off state.

[0240] As an alternative, the fourth switching device 42 may be newly commanded to be switched on and the current flowing along the electrical branch 4 may newly flow along the third and fourth switching devices 41 , 42 .

[0241] In any case, at the same time, the first switching device 31 returns to the closed state, and commands the second switching device 32 to perform a closing operation.

[0242] When both the first and second switching devices 31 , 32 eventually return to the closed state, the switching arrangement 1 will again operate under normal conditions, with the current naturally commutating from the second electrical branch 4 to the first electrical branch 3 .

[0243] Alternatively, if the fault generating the short-circuit current is not cleared before the above-mentioned first time interval has elapsed, the third switching device 41 is commanded to turn off.

[0244] The current is forced to circulate along the first and second electronic circuits 48, 49 until it dies out. As indicated above, the current cannot restart flowing along the first electrical branch 3.

[0245] Subsequently, the disconnector 150 is commanded to perform an opening operation, thereby providing galvanic isolation for the grid portion including the switchgear.

[0246] Reconnecting to power lines

[0247] It is assumed that the first switching device 31 is already in a closed state, the second switching device 32 is assumed to be in an open state, and the third and fourth switching devices 41 , 42 are assumed to be in an off state.

[0248] The disconnector 150 is commanded to perform a closing maneuver. The galvanic isolation of the grid section comprising the switchgear from another grid section (not comprising the switchgear) is no longer ensured.

[0249] The third switching device 41 is commanded to turn on.

[0250] As an alternative, both the third and fourth switching devices 41 , 42 are commanded to be switched on.

[0251] The current flows along the second semiconductor branch 4 .

[0252] If only the third switching device 41 is switched on, current flows along the second electronic circuit 49 and the third switching device 41 .

[0253] If both the third and fourth switching devices 41 , 42 are switched on, current flows along these two switching devices.

[0254] If no short circuit is detected within a second predefined time interval (necessary to check whether a short circuit exists), the second switching device 32 is commanded to perform a closing operation.

[0255] As mentioned above, the fourth switching device 42 can be either in an on state or in an off state. If the fourth switching device 42 is in an on state, it can be maintained in that state or turned off. If it is in an off state, it can be maintained in that state or turned on.

[0256] Once the second switching device 32 has completed the closing operation (the first switching device 31 is already in the closed state), the switching device 1 starts to operate under normal conditions, and the current is naturally commutated to the first electrical branch 3.

[0257] Reconnecting to the power line in the event of a short circuit

[0258] It is assumed that the first switching device 31 is already in a closed state, the second switching device 32 is assumed to be in an open state, and the third and fourth switching devices 41 , 42 are assumed to be in an off state.

[0259] The disconnector 150 is commanded to perform a closing maneuver. The galvanic isolation of the grid section comprising the switchgear from another grid section (not comprising the switchgear) is no longer ensured.

[0260] The third switching device 41 is commanded to be turned on, while the fourth switching device 42 is maintained in the off state and is turned on later than the third switching device 41 .

[0261] As an alternative, the third and fourth switching devices 41 , 42 are commanded to be switched on simultaneously.

[0262] The short-circuit current initially flows along the second semiconductor branch 4 .

[0263] When only the third switching device 41 is turned on, current flows along the second electronic circuit 49 and the third switching device 41 (current limiting mode). After a first predefined time interval (necessary to identify a short circuit condition), the third switching device 41 is commanded to turn off. The current is forced to circulate along the first electronic circuit 48 until it disappears.

[0264] When the third and fourth switching devices 41, 42 are turned on simultaneously, current flows along the two switching devices. After the first predefined time interval, the third switching device 41 is commanded to turn off, while the fourth switching device 42 can be turned off or maintained in the on state. The current is forced to circulate along the first electronic circuit 48 until it disappears.

[0265] The second switching device 32 is not commanded to perform a closing operation and it remains in the open state.

[0266] Subsequently, the disconnector 150 is commanded to perform an opening operation, thereby providing galvanic isolation for the grid portion including the switchgear.

[0267] It can be clearly seen from the above that when Figure 2 When the embodiment is arranged, the switching device 1 can operate in three different states: a closed state in which it conducts current (normal operation), an open state in which it blocks current (i.e., the current commutated from the first electrical branch 3 to the second electrical branch 4), or a current limiting mode in which it limits the current commutated from the first electrical branch 3 to the second electrical branch 4 (transient condition).

[0268] It is also demonstrated how the switch group 110 formed by the switching device 1 and the disconnector 150 electrically connected in series can be operated according to different states: a closed state in which the switching device 1 is in a closed state and the disconnector 150 is in a closed state, an open state in which the switching device 1 is in an open state and the disconnector 150 is in an open state, or a current limiting mode in which the switching device 1 is in a current limiting mode and the disconnector 150 is in a closed state.

[0269] According to some embodiments of the present invention ( Figure 1-2 ), the switching device 1 comprises a control unit 90 (which may be of known type), which comprises one or more control logics configured to control the operation of the controllable switching devices 32, 41 and (if present) the switching device 42 of the switching device.

[0270] Preferably, the control unit 90 is also capable of controlling the operation of the isolation switch 150 .

[0271] The control unit 90 is adapted to receive a sensing signal S from one or more sensors 93 arranged at suitable locations of the switching device to monitor the behavior of the current and / or other physical quantities along the first electrical branch 3 and the second electrical branch 4 .

[0272] The control unit 90 is adapted to process the sensing signal S provided by the above mentioned sensor 93 and to provide control signals C to operate the second switching device 32 , the third switching device 41 and possibly the disconnector 150 and the fourth switching device 42 according to the above mentioned operation mode.

[0273] The control unit 90 may execute suitable data processing algorithms to process the information provided by the sensors 93 and to check whether certain operating criteria for operating the switching devices 32 , 41 and possibly the switching devices 150 , 42 are met.

[0274] The control unit 90 may provide control signals to operate the switching devices 32 , 41 and possibly the switching devices 150 , 42 when an operator manually requests an operation to be performed or an external operation request is sent to the switching apparatus.

[0275] According to a variant embodiment of the invention (not shown), the control unit 90 is not arranged on the switching device 1 .

[0276] As an example, it may be arranged on a digital relay operatively associated with the switchgear or on another switchgear or on a remote computerized platform. In this case, the switchgear 1 may comprise a communication interface for communicating with the control unit 90 .

[0277] Figure 3-7 Variant embodiments of the invention are shown, in which the switchgear 1 is able to control bidirectional currents. These solutions may be particularly advantageous when the switchgear is installed in an AC power grid.

[0278] Figure 3 Shows Figure 1 A variant solution of the embodiment shown in .

[0279] According to this embodiment, the second electrical branch 4 comprises a first bridge circuit 47 operatively associated with the current-breaking circuit 40A.

[0280] The operation of this embodiment of the present invention is similar to that described above with respect to Figure 1 The operation is the same as described in the embodiment.

[0281] Figure 4 Shows Figure 2 A variant solution of the embodiment shown in .

[0282] According to this embodiment, the second electrical branch 4 comprises a first bridge circuit 45 operatively associated with the current-breaking circuit 40A and a second bridge circuit 46 operatively associated with the current-limiting circuit 40 .

[0283] The operation of this embodiment of the present invention is similar to that described above with respect to Figure 2 The operation is the same as described in the embodiment.

[0284] Figure 5 Shows Figure 3 A variant solution of the embodiment shown in .

[0285] According to this embodiment, the second electrical branch 4 comprises a third bridge circuit 47 operatively associated with the remaining components of the second electrical branch, for example the series circuit formed by the current limiting circuit 40 and the current blocking circuit 40A.

[0286] When the second electrical branch 4 comprises only the current blocking circuit 40A, this embodiment of the present invention is similar to Figure 3 The embodiment shown in FIG.

[0287] The operation of these embodiments of the present invention is similar to that described above with respect to Figure 1 or Figure 2 The same as described in the embodiment.

[0288] Preferably, Figure 3-5 In the embodiment shown, each bridge circuit 45, 46, 47 includes a plurality of diodes arranged according to a Graetz bridge configuration.

[0289] Figure 6 Shows Figure 1 Additional variant solutions to the embodiment shown in .

[0290] According to this embodiment, the third switching device 41 comprises a pair of semiconductor switching components 41A, 41B which are connected to each other according to an anti-parallel configuration.

[0291] For this configuration, each semiconductor switch component 41A, 41B must either be of the reverse blocking type or arranged in series with a diode.

[0292] Depending on the direction of the current flow, only one semiconductor switch component 41A, 41B can be operated at a certain time, while the other semiconductor switch component remains in the off state.

[0293] Both semiconductor switches 41A, 41B are electrically connected in parallel with the first electronic circuit 48 .

[0294] The operation of this embodiment of the present invention is similar to that described above with respect to Figure 1 The operation is the same as described in the embodiment.

[0295] Fig. 6A Shows Figure 1 Additional variant solutions to the embodiment shown in .

[0296] According to this embodiment, the third switching device 41 comprises a pair of semiconductor switching components 41A, 41B which are connected to each other according to an anti-series configuration.

[0297] For this configuration, each semiconductor switch component 41A, 41B must be either of the reverse conducting type or arranged in parallel with a diode.

[0298] The series assembly formed by the semiconductor switch components 41A, 41B is electrically connected in parallel with the first electronic circuit 48 .

[0299] The operation of this embodiment of the present invention is similar to that described above with respect to Figure 1 The operation is the same as described in the embodiment.

[0300] Figure 7 Shows Figure 2 Additional variant solutions to the embodiment shown in .

[0301] According to this embodiment, the current interrupt circuit 40A and the current limiting circuit 40 both include pairs of semiconductor switch components 41A, 41B and 42A, 42B connected to each other in an anti-parallel configuration.

[0302] For this configuration, each semiconductor switch component 41A, 41B and 42A, 42B must be either of the reverse blocking type or arranged in series with a diode.

[0303] Both semiconductor switches 41A, 41B are electrically connected in parallel to a first electronic circuit 48 , while both semiconductor switch components 42A, 42B are electrically connected in parallel to a second electronic circuit 49 .

[0304] The operation of this embodiment of the present invention is similar to that described above with respect to Figure 2 The operation is the same as described in the embodiment.

[0305] According to a further variant embodiment of the invention (not shown), both the third and fourth switching devices 41 , 42 may comprise corresponding pairs of semiconductor switching components which are connected to each other according to an anti-series configuration.

[0306] For this configuration, each semiconductor switch component 41A, 41B and 42A, 42B must be either of the reverse conducting type or arranged in parallel with a diode.

[0307] The operation of this embodiment of the present invention is similar to that described above with respect to Figure 2 The operation is the same as described in the embodiment.

[0308] Figure 8 An example of a DC grid 100 is shown.

[0309] The DC grid comprises a DC bus 101 (DC link) and a plurality of components electrically connected to the DC bus.

[0310] Some components may be formed by electrical loads or devices that need to be fed with electrical power (eg electric motors).

[0311] Other components may be formed by energy storage devices (for example capacitor banks or batteries) or power generation devices (for example photovoltaic plants), so that they are able to provide electrical energy.

[0312] In the DC grid 100, according to the present invention, a plurality of switchgears are suitably employed to manage the electrical connection of the above-mentioned components to the DC electrical busbars.

[0313] Conveniently, as indicated above, each switch device 1 is electrically connected in series with a disconnector 150 to form a switch group 110 .

[0314] As is evident from the above mentioned figures, the DC current circulating through the components linked to the DC bus can be bidirectional.

[0315] In case of an electrical fault, many components of the DC grid may contribute to possible short circuit currents, since reverse currents may flow along them. In the worst case, if an electrical fault occurs on the DC bus, many components may directly feed the electrical fault.

[0316] Employing the switchgear according to the invention in a DC grid allows a fast reaction to possible electrical faults and the implementation of suitable protection and selectivity functions to manage possible electrical faults.

[0317] Furthermore, efficient strategies can be implemented to manage and coordinate circuit protection interventions along different branches of the power grid.

[0318] Figure 9-16 Some examples of strategies that may be implemented to manage electrical faults in a simplified DC grid 100A are shown.

[0319] The DC grid 100A includes a battery energy storage system (BESS) in which a bank of battery cells is electrically connected to a power converter (not shown) via a DC bus 101A.

[0320] Each battery cell is electrically connected to or disconnected from the DC bus 101A by means of a switch group 110 .

[0321] Each switch group 110 includes a switch device 1 according to the present invention (e.g., similar to Figure 2 an embodiment but capable of conducting bidirectional current) and an isolating switch 150 electrically connected in series.

[0322] The DC bus 101A is electrically connected to or disconnected from the above-mentioned power converter via a circuit breaker 160 of, for example, an electromechanical type.

[0323] As an alternative, the DC bus 101A can be electrically connected 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 embodiment is capable of conducting bidirectional current.

[0324] As shown above, since each switch group 110 includes Figure 2 The switching device of the present invention in the embodiment of the present invention can therefore be operated in the following states: a closed state in which the switching device 1 is in a closed state and the disconnecting switch 150 is in a closed state, an disconnecting state in which the switching device 1 is in an disconnecting state and the disconnecting switch 150 is in an disconnecting state, and a current limiting mode in which the switching device 1 is in a current limiting mode and the disconnecting switch 150 is in a closed state.

[0325] When in a closed state, each switch group 110 conducts current, thereby electrically connecting the corresponding battery cell to the DC bus.

[0326] When in the off state, each switch group 110 blocks current flow, thereby electrically disconnecting the corresponding battery cell from the DC bus.

[0327] When it is in the current limiting mode, each switch group 110 provides a current limiting function, thereby limiting the current circulating between the corresponding battery cell and the DC bus.

[0328] 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 between a closed state in which it conducts current and thereby electrically connects the power converter to the DC bus, or an open state in which it blocks current and thereby disconnects the power converter from the DC bus.

[0329] When using include Figure 2 When an additional switch group of the switching device of the present invention (and capable of conducting bidirectional current) in an embodiment of the present invention replaces the circuit breaker 160, the switch group behaves as described above, so that when it is in a closed state, it electrically connects the power converter to the DC bus, when it is in an open state, it electrically disconnects the power converter from the DC bus, or when it is in a current limiting mode, it limits the current circulating between the power converter and the DC bus.

[0330] Normal Operation

[0331] Fig. 9 The operation of the power grid 100A under normal conditions is schematically illustrated.

[0332] In this case, the circuit breaker 160 is in a closed state and each switch group 110 is in a closed state (normal operation). If an additional switch group is used instead of the circuit breaker 160, such switch group will be in a closed state.

[0333] Current I N1 ,I N2 ,I N3 Circulating along the battery cells mentioned above, the current I NC Flows along the electronic converter. Current INC In essence, the current I N1 ,I N2 ,I N3 The sum of .

[0334] All currents flowing into / out of the battery cells and the electronic converter I N1 ,I N2 ,I N3 ,I NC Taking values ​​not exceeding the foreseen nominal current of the battery cell in question and having the same direction, it depends essentially on the operating mode of the battery cell (charging or discharging).

[0335] exist Fig. 9 In the example, it is assumed that the battery cell is in discharge mode. If the battery cell is operated in charge mode, then the current I N1 ,I N2 ,I N3 ,I NC The direction of the power grid will be reversed. However, the operation of the grid will be essentially the same.

[0336] Short circuit in battery cell

[0337] Fig.10 A situation is schematically shown in which a short circuit occurs in a battery cell.

[0338] Short circuit current I S1 Flows to the battery cell affected by the electrical fault. The electrical fault is caused by the short-circuit current I S2 ,I S3 and the short-circuit current I flowing through the power converter SC feed.

[0339] When the power converter is in discharge mode, the short-circuit current I flowing through the power converter SC Relative to the corresponding current I NC have opposite directions.

[0340] like Fig.11 As shown in SC ,I S1 ,I S2 ,I S3 When the current flows in the grid 100A, the switch group 110 operatively associated with the battery unit is switched to the current limiting mode. The circuit breaker 160 is maintained in the closed state to wait for the electrical fault to be cleared.

[0341] If an additional switch bank is used instead of the circuit breaker 160, such a switch bank will also switch in the current limiting mode.

[0342] The result of the intervention of the switch group 110 is that the short-circuit current I S1 .

[0343] Subsequently, due to the short-circuit current I SC ,I S1 ,I S2 ,I S3 The cycle continues in the electrical grid 100 so that the switch group 110 closest to the battery cell affected by the electrical fault is switched to the open state.

[0344] In fact, the switch group 110 closest to the battery cell affected by the electrical fault may remain in the current limiting mode for a shorter time relative to other switch groups because such switch group is affected by the short-circuit current having a larger magnitude.

[0345] Since the corresponding switch group 110 has been switched to the open state, the battery cell affected by the electrical fault is electrically isolated from the rest of the grid.

[0346] In this case, the switch group 110 operatively associated with the other battery cells remains in the current limiting mode and a relatively small current (e.g., having a value even lower than the nominal value) will circulate through the switch group ( Fig.12 ). The circuit breaker 160 is still maintained in the closed state.

[0347] Finally, since the electrical fault has been cleared by operating the switch pack 110 in the open state, the switch pack 110 operably associated with the battery cells not affected by the electrical fault can be switched back to the closed state and operated again under normal conditions ( Fig.13 ).

[0348] If an additional switch group is used instead of the circuit breaker 160, then this switch group will also be switched to the closed state.

[0349] The current circulating in the power grid 100 also takes a normal value I NC ,I N2 ,I N3 and in the same direction. Obviously, the battery cell affected by the electrical fault is galvanically isolated from the rest of the grid 100A. Obviously, the current I flowing through the power converter NC Reduce accordingly.

[0350] If the battery unit is operated in charging mode, the operation of the grid will be essentially the same.

[0351] Short circuit in the DC bus

[0352] Fig.14 A situation is schematically shown in which a short circuit occurs in the DC bus 101A. The short circuit current ISC ,I S1 ,I S2 ,I S3 Flows along the battery cells and electronic converters, causing electrical faults. In this case, the short-circuit current I flowing through the power converter SC Relative to the corresponding current I when the power converter is in discharge mode NC have opposite directions.

[0353] Since the electrical fault is located in the DC bus, the short-circuit current I flows along the battery cell S1 ,I S2 ,I S3 will have the same direction as the short-circuit current I flowing through the power converter SC on the contrary.

[0354] like Fig.15 As shown in SC ,I S1 ,I S2 ,I S3 Cycle in the grid 100, the switch group 110 associated with the battery unit operation is switched to the current limiting mode. The circuit breaker 160 is temporarily maintained in a closed state to wait for the possible removal of the electrical fault. If the switch group 110 is used instead of the circuit breaker 160, then this switch group will also operate in the current limiting mode.

[0355] Since the electrical fault is located in the DC bus, the electrical fault cannot be cleared by operating a single switch group 110 (closest to the electrical fault) to be in an open state.

[0356] Since the fault has not been cleared, after the first time interval mentioned above has passed, all the switch groups 110 and the circuit breakers 160 are switched to the open state.

[0357] If an additional switch group is used instead of the circuit breaker 160, then this switch group will also be switched to the open state.

[0358] As a result of the above, the entire DC grid 100 is cut off ( Fig.16 ).

[0359] If the battery unit is operated in charging mode, the operation of the grid will be essentially the same.

[0360] It is demonstrated that a different type of electrical grid (eg, AC type) typically comprising a plurality of switch banks 110 (configured as described above) for electrically connecting or disconnecting different grid parts of said grid will operate mutatis mutandis substantially as the above-described DC grid 100A.

[0361] It is therefore clear how, in another aspect, the present invention relates to a method for operating an electrical network comprising a plurality of switch groups 110 (configured as described above) for electrically connecting or disconnecting different grid parts of said network.

[0362] The method according to the invention comprises the step of switching the switch group 110 into a current limiting mode if there is an electrical fault (ie a short circuit) in the electrical network.

[0363] The method of the invention then comprises the step of switching the switch group 110 closest to the electrical fault to an open state and maintaining the remaining switch groups of the electrical network in a current limiting mode.

[0364] In fact, the switch group 110 closest to the electrical fault may remain in the current limiting mode for a shorter time relative to other switch groups, since such switch group is affected by the short-circuit current having a larger magnitude.

[0365] If the electrical fault is electrically isolated within a predefined time period (which is substantially consistent with the first time interval mentioned above) by operating the switch group 110 closest to the electrical fault, the method of the present invention comprises the following steps: maintaining the switch group 110 closest to the electrical fault in an open state and switching the remaining switch groups 110 of the power grid back to a closed state.

[0366] If the electrical fault is not electrically isolated by operating the switch group 110 closest to the electrical fault within the predefined time period, the method of the present invention comprises the following step: switching all switch groups 110 of the power grid to an open state.

[0367] like Figure 9-16 As shown in the above example, the method of the present invention is particularly suitable for protecting a DC grid 100A, which includes a battery energy storage system having 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 the battery cells to the DC bus or electrically disconnecting the battery cells from the DC bus.

[0368] In this case, the method according to the invention comprises the following steps: If there is an electrical fault (ie a short circuit) in the energy battery storage system, switching the switch group 110 to a current limiting mode.

[0369] When the DC bus 101A is electrically connected to or disconnected from the above-mentioned power converter via a circuit breaker 160 (eg, electromechanical type), the method of the present invention further comprises the step of maintaining the circuit breaker 160 in a closed state.

[0370] When the DC bus 101A is electrically connected to or disconnected from the above-mentioned power converter via an additional switch group (similar to the switch group 110 ), the method of the present invention further comprises the step of switching the additional switch group to a current limiting mode.

[0371] According to the invention, the method comprises the step of switching the switch group 110 closest to the electrical fault to an open state and maintaining the remaining switch groups 110 of the energy storage system in a current limiting mode.

[0372] If the electrical fault is electrically isolated within a predefined time period (the first time interval mentioned above) by switching the closest switch group 110 to an open state, the method of the present invention includes the steps of maintaining the switch group 110 closest to the electrical fault in an open state and switching the remaining switch groups 110 of the battery energy storage system back to a closed state.

[0373] When the DC bus 101A is electrically connected to or disconnected from the above-mentioned power converter via a circuit breaker 160 (eg, electromechanical type), the method of the present invention further comprises the step of maintaining the circuit breaker 160 in a closed state.

[0374] When the DC bus 101A is electrically connected to or disconnected from the above-mentioned power converter via an additional switch group (similar to the switch group 110 ), the method of the present invention further comprises the step of switching the additional switch group to a closed state.

[0375] If the electrical fault cannot be electrically isolated within said predefined time period by operating the switch group 110 closest to the electrical fault in the open state, the method according to the invention comprises the step of switching all switch groups 110 of the battery energy storage system to the open state.

[0376] When the DC bus 101A is electrically connected or disconnected from the above-mentioned power converter via a circuit breaker 160 (e.g., an electromechanical type) or via an additional switch group (similar to the switch group 110), the method of the present invention also includes a step of switching the circuit breaker 160 or the additional switch group to a disconnected state.

[0377] The method of the invention allows managing electrical faults (ie short circuits) in an electrical network in a selective manner, depending on whether said electrical fault can be electrically isolated or not.

[0378] The method of the invention initially provides for limiting fault currents circulating along various parts of the electrical network.

[0379] If the electrical fault can be cleared within a predefined period of time by operating a particular switch bank 110 (closest to the short circuit) in an open state, the method of the present invention provides for bringing the portion of the grid not involved in the electrical fault back to a normal conduction mode.

[0380] If the electrical fault cannot be cleared within said predefined period of time by operating said specific switch group 110 in the open state, the method of the present invention provides for disconnecting the grid.

[0381] This method allows to improve the flexibility of using the power grid. In addition, it allows to reduce the possible downtime of the power grid when there is a short circuit. In practice, the power grid is only cut off when absolutely necessary, because the electrical fault cannot be cleared in any way.

[0382] The switching device of the invention can have many variations falling within the concept of the claimed invention.

[0383] The switchgear 1 can be industrially implemented as a standalone device or as an additional module, for example for each pole of a mechanical circuit breaker (MCCB).

[0384] According to a further variant, the switching device 1 may comprise an additional commutated booster circuit of known type, such as those disclosed in the above-mentioned patent document WO 2017 / 186262.

[0385] The switching device according to the invention offers significant advantages over similar known solutions from the prior art.

[0386] The switching device according to the invention allows to perform a rapid intervention in order to interrupt a possible short-circuit current when an electrical fault occurs in an electric power line.

[0387] In addition, in some embodiments ( Figure 2 ), it provides a limiting function for the short-circuit current that may flow through solid-state switching devices.

[0388] The above mentioned features allow the use of smaller sized solid-state devices for a given nominal current. Obviously, this allows the size and cost of the switchgear to be significantly limited.

[0389] The switchgear according to the invention allows managing both nominal currents and possible overload currents flowing along a power line in a reliable manner.

[0390] The switchgear according to the invention allows to achieve improved selectivity functionality by exploiting the improved operating conditions of the on-board solid-state switching devices, in particular when the current limiting function is put into practice.

[0391] Furthermore, it allows the implementation of efficient strategies to manage and coordinate circuit protection interventions along different branches of the grid.

[0392] The industrial production and installation of the switchgear according to the invention on site is relatively easy and cheap.

Claims

1. A switch device (1) for a power grid (100), comprising: - a first electrical terminal and a second electrical terminal (11, 12) for electrical connection to a corresponding power grid part; - a first electrical branch (3) comprising a plurality of switching devices (31, 32) of electromechanical type, each having electrical contacts capable of being mechanically coupled or decoupled to respectively conduct or interrupt an electric current; a second electrical branch (4) comprising one or more switching devices (41, 42) of solid-state type, each of which comprises one or more switching components (41A, 41B, 42A, 42B) based on semiconductor material and adapted to switch between an on-state in which the switching device conducts an electric current and an off-state in which the switching device blocks an electric 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 first electrical branch (3) comprises: - a first switching device (31) of electromechanical type, capable of switching between a closed state in which the first switching device conducts current and an open state in which the first switching device blocks current, the first switching device being a self-acting switching device capable of switching from the closed state to the open state when driven by a current flowing along the switching device without receiving an external control signal or an external power supply, the first switching device switching from the closed state to the open state when the current flowing along the switching device exceeds a corresponding predefined threshold value or when the rate of change of the current flowing along the switching device exceeds a corresponding predefined threshold value or when these two conditions are combined; a second switching device (32) of electromechanical type, electrically connected in series with the first switching device, the second switching device being switchable between a closed state in which the second switching device conducts an electric current and an open state in which the second switching device blocks an electric current, Upon receiving a corresponding input control signal, the second switching device switches between the closed state and the open state.

2. The switch device according to claim 1, characterized in that: The first switching device (31) comprises a first actuator capable of actuating electrical contacts of the first switching device using an electric force generated by a current flowing along the switching device, thereby switching the first switching device from the closed state to the open state.

3. The switch device according to claim 2, characterized in that: The first actuator includes a Thomson coil actuation device operably coupled to electrical contacts of the first switching device.

4. The switch device according to claim 1, characterized in that: The second electrical branch (4) comprises a current breaking circuit (40A) suitable for breaking the current flowing along the second electrical branch, the current breaking circuit comprising a third switching device (41) of solid-state type and a first electronic circuit (48) electrically connected in parallel with the third switching device.

5. The switch device according to claim 4, characterized in that: The second electrical branch (4) comprises a current limiting circuit (40) adapted to limit the current flowing along the second electrical branch, the current limiting circuit being electrically connected in series with the current blocking circuit (40A) and comprising a fourth switching device (42) of a solid-state type and a second electronic circuit (49) electrically connected in parallel with the fourth switching device (42).

6. The switch device according to claim 4 or 5, characterized in that: The third switching device (41) comprises a pair of switching components based on semiconductor material, arranged according to an anti-parallel or anti-series configuration to allow controlling a bidirectional current flowing along the second electrical branch (4).

7. The switch device according to claim 4 or 5, characterized in that: The second electrical branch (4) comprises a first diode bridge (45) operatively associated to the current blocking circuit (40A) to allow control of a bidirectional current flowing along the second electrical branch (4).

8. The switch device according to claim 5, characterized in that: The fourth switching device (42) comprises a pair of switching components based on semiconductor material, which are arranged according to an anti-parallel or anti-series configuration to allow controlling a bidirectional current flowing along the second electrical branch (4).

9. The switch device according to claim 5, characterized in that: The second electrical branch (4) comprises a second diode bridge (46) operatively associated to the current limiting circuit (40) to allow control of a bidirectional current flowing along the second electrical branch (4).

10. The switch device according to claim 5, characterized in that: The second electrical branch (4) includes a third diode bridge circuit (47) operatively associated with the current limiting circuit (40) and the current blocking circuit (40A) to allow control of a bidirectional current flowing along the second electrical branch (4).

11. The switch device according to any one of claims 1 to 5, characterized in that: The first switching device (31) is adapted to switch from a closed state to an open state if a short circuit current flows along the switching arrangement.

12. The switch device according to any one of claims 1 to 5, characterized in that The first switching device (31) is adapted not to switch from a closed state to an open state if an overload current or a normal current flows along the switching arrangement.

13. The switch device according to claim 4 or 5, characterized in that: In response to the disconnection operation of the first switching device (31), the third switching device (41) is commanded to switch from the on state to the off state after a period of time has passed since the moment when the short-circuit current has been commutated from the first electrical branch (3) to the second electrical branch (4).

14. The switch device according to claim 4 or 5, characterized in that: According to the disconnection operation of the second switching device (32), the third switching device (41) is suitable for switching from the on state to the off state after a period of time has passed since the moment when the overload current or the normal current has been commutated from the first electrical branch (3) to the second electrical branch (4).

15. The switch device according to claim 5, characterized in that In response to the disconnection operation of the first switching device (31) or the second switching device (32), the fourth switching device (42) is commanded to switch from the on state to the off state after the current has been commutated from the first electrical branch (3) to the second electrical branch (4).

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

17. A switch group (110), comprising a switch device (1) according to any one of claims 1 to 15 and a disconnector (150) electrically connected in series.

18. A method for protecting an electrical network, the electrical network comprising a plurality of switch groups (110) for electrically connecting or disconnecting different grid sections of the electrical network, Each switch group (110) includes: - a switching device (1) according to claim 5 capable of controlling bidirectional currents, The switching device is capable of being switched to a closed state in which the switching device conducts current or an off state in which the switching device blocks the current or a current limiting mode in which the switching device limits the current commutated from the first electrical branch (3) to the second electrical branch (4); - an isolating switch (150) electrically connected in series with the switching device (1), the isolating switch being capable of being switched to a closed state in which the isolating switch conducts current or to an open state in which the isolating switch blocks current; Each switch group (110) is capable of switching to a closed state in which the switch device (1) is in a closed state and the isolating switch (150) is in a closed state, or switching to an open state in which the switch device (1) is in an open state and the isolating switch (150) is in an open state, or switching to a current limiting mode in which the switch device (1) is in a current limiting mode and the isolating switch (150) is in a closed state, It is characterized by comprising the following steps: - if there is an electrical fault in the grid, switching the switch group (110) to a current limiting mode; - switching the switch group (110) closest to the electrical fault to an open state and maintaining the remaining switch groups (110) of the power grid in a current limiting mode; If the electrical fault is electrically isolated within a predefined period of time when the switch group (110) closest to the electrical fault is in an open state: - maintaining the switch group (110) closest to the electrical fault in an open state and switching the remaining switch groups (110) of the power grid back to a 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 an open state: - Switching all switch groups (110) of the power grid to the open state.

19. The method according to claim 18, characterized in that The power grid (100A) includes a battery energy storage system, which includes 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) for electrically connecting the battery cells to or disconnecting them from the DC bus.

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