WO2025083282A1 - Switching device for high-voltage dc electric current with secure control - Google Patents

Abstract

The invention relates to a switching device (1) for a high-voltage DC electric current, the device comprising: - a main circuit (16); - a switch module (18) comprising the following branches connected in parallel: - a main branch (24) including a main switching unit (26); - a switch branch (32) comprising a plurality of switch modules (34) in series, wherein each of the switch modules comprises: - a switch capacitor (38) for the flow of current through the switch branch (32); - a switch (41, 42) in series with the switch capacitor (38); - a loop formed by the main branch (24) and the switch branch (32); - a control system (561) for closing the switch and discharging the switch capacitor (38) into the loop; - wherein the switch module (18) comprises a surge suppressor (30) for conduction when the main branch and the switch branch are open.

Description

Description

Title of the invention: Cut-off device for high-voltage direct current with secure control

[0001] The invention relates to a cut-off device for high-voltage direct current. Such devices are intended to be implemented in HVDC networks or network units in the event of the occurrence of an electrical fault generating a fault current in at least one electrical conductor of the network.

[0002] HVDC networks are particularly envisaged as a solution for the interconnection of disparate or non-synchronous electricity production sites. HVDC networks are particularly envisaged for the transmission and distribution of energy produced by offshore wind farms rather than alternating current technologies, due to lower line losses and the absence of the impact of parasitic network capacitances over long distances. Such networks typically have nominal operating voltage levels above 75 kV, particularly in the order of 100 kV and above.

[0003] In the present text, a high DC voltage device is considered to be either a "high voltage A" device, in which the nominal DC operating voltage is greater than 1500 V, but less than or equal to 75,000 V, or a "high voltage B" device when the nominal DC operating voltage is greater than 75,000 V. Thus, the high DC voltage domain includes the "high voltage A" domain and that of "high voltage B".

[0004] Power cuts in such networks are a crucial security issue which directly affects the feasibility and development of such networks.

[0005] The evolution of these networks today tends towards the interconnection of infrastructures to result in meshed networks, that is to say networks comprising several possible paths between two given points of the network. [0006] In an electrical circuit, there is generally at least one voltage source, and at least one voltage user, which may include any device or set of devices or any network having such devices that use electrical energy to transform it into another form of energy. In an electrical circuit, there is generally at least one electrical cut-off device for interrupting the flow of electric current in the circuit, generally between the voltage source and the voltage user, or between the voltage source and ground.

[0007] Different types of electrical cut-off devices are known, intended to be interposed in an electrical conductor of an electrical circuit. For example, circuit breakers are known, which are mechanical devices for cutting off the electrical circuit and which are designed and sized to allow, in particular, opening under load or in fault conditions of the electrical circuit in which they are interposed. Electrical cut-off devices of simpler design are also known, such as disconnectors, which are generally not designed to cut off circuits under load, but rather to ensure, in a circuit where the flow of current is already interrupted by another cut-off device, electrical insulation of a predetermined high level between an upstream portion of a conductor of the circuit, connected for example to the voltage source, and a downstream portion of this conductor of the circuit.

[0008] In a main mechanical type switching device, the current is cut off solely by opening a mechanical switching element. Such a mechanical switching element comprises two conductive contacting parts which are in mechanical and electrical contact when the switching element is closed and which separate mechanically when the switching element is open.

[0009] In the presence of a high DC current and/or voltage, mechanical separation can result in the establishment of an electric arc between the two conductive parts, due to the high energy accumulated in the network that the device protects. As long as the electric arc remains established through the mechanical separation, the mechanical electrical cut-off device does not perform the electrical cut-off since a current continues to flow through the device due to the presence of the arc. Electrical cut-off, in the sense of the effective interruption of the flow of electric current is sometimes particularly difficult to achieve in a context of high voltage direct currents, these conditions tending to maintain the electric arc.

[0010] Cutting off high-voltage DC currents is more complex to achieve than cutting off AC currents. Indeed, when cutting off an AC current, we take advantage of a zero crossing of the current to achieve the electrical cut, which cannot be achieved with a high-voltage DC current.

[0011] Hybrid circuit breakers have been developed to cut off direct current. Thus, hybrid circuit breakers use a main branch crossed by direct current during normal operation and a parallel branch of power electronic components. The main branch usually comprises a vacuum interrupter type switch in series with a switching assistance module. During a fault, the opening of the vacuum interrupter generates an arc voltage. The impedance-increasing switching assistance module increases the impedance in the main branch to force the current to flow through the parallel branch. The power electronic components of the parallel branch then open to interrupt the flow of current.

[0012] A disadvantage of the impedance boost switching assistance module is that it is connected in series to the main branch. It therefore induces Joule effect losses during normal operation and must be cooled.

[0013] In order to limit such losses, document EP3072143 proposes connecting a reverse current injection module as a switching assistance module. A current transformer is then used to inject a reverse current into the main branch at the time of switching.

[0014] Patent FR2103336 proposes a reverse current injection module based on the discharge of a capacitor.

[0015] The invention aims to solve one or more of these drawbacks. The invention thus relates to a cut-off device for high-voltage direct current as defined in the appended claim 1. [0016] The invention also relates to variants of the dependent claims. Those skilled in the art will understand that each of the features of the dependent claims and the description can be independently combined with the features of claim 1, without constituting an intermediate generalization.

[0017] Other characteristics and advantages of the invention will emerge clearly from the description given below, for information purposes only and in no way limiting, with reference to the appended drawings, in which:

[0018] [Fig.1] is a schematic representation of an exemplary embodiment of a cut-off device for high-voltage direct current according to the invention;

[0019] [Fig.2] is a schematic representation of a first example of a switching module of a cut-off device;

[0020] [Fig.3] is a schematic representation of a switching module of a first type for a second example of switching module;

[0021] [Fig.4] is a schematic representation of another exemplary embodiment of an electrical cut-off device according to the invention;

[0022] [Fig.5] illustrates a variant of a switching module associated with a surge protector;

[0023] [Fig.6] illustrates another variant of a switching module associated with a surge protector;

[0024] [Fig.7] further illustrates a variant of a switching module associated with a surge protector;

[0025] [Fig.8] illustrates another variant of a switching module associated with a surge protector;

[0026] [Fig.9] illustrates another variant of a switching module associated with a surge protector.

[0027] In an electrical network, the transmission of electrical power between two given points of the network is done by a power transmission line which generally comprises several electrical conductors, each of which corresponds to an electrical pole of the power transmission line. Thus, in an HVDC network, the transmission of electrical power between two given points of the network is done by a power transmission line which generally has two electrical poles. In this case, the power transmission line therefore has two electrical conductors of different polarities, with, under load, for example, an electrical conductor which is at a positive potential and an electrical conductor which is at a negative or neutral potential.

[0028] Still in an HVDC network unit, the transmission of electrical power between two given points of the network can also be done by a power transmission path with three electrical poles comprising three electrical conductors, with, under load, an electrical conductor which is at a positive potential, an electrical conductor which is at a negative potential, and an electrical conductor which is at a neutral potential. In certain cases, the transmission of electrical power between two given points of the network can be done by a power transmission line with a single electrical pole, with an electrical conductor at the line potential and with an electrical return via the earth.

[0029] Fig. 1 illustrates a first exemplary embodiment of a cut-off device 10 for interrupting a high-voltage direct current flowing in an electrical conductor 11. The electrical conductor 11 may, for example, belong to an electrical power transmission line in an HVDC network unit that operates under a nominal continuous operating voltage greater than 1500 V, or even greater than 75,000 V (75 kV). The cut-off device 10 is therefore interposed in the electrical conductor 11, between a primary point 12 of the device 10 and a secondary point 14 of the device 10. The primary point 12 and the secondary point 14 may be connection terminals of the device 10 respectively. The cut-off device 10 therefore divides the electrical conductor 11 into two sections, a first section 111 which is connected to the primary point 12, and a second section 112 which is connected to the secondary point 14.

[0030] The cut-off device 10 therefore comprises a main circuit 16, between the primary point 12 of the device 10 and the secondary point 14 of the device 10. In a conduction configuration of the cut-off device 10, an operational electric current flows under a high nominal operating voltage of the continuous cut-off device 10. This is the operational electric current flowing in the conductor 11, and the intensity of which is less than or equal to the nominal intensity for the device. Indeed, in the event of an electrical fault, the intensity of the current through the cut-off device may exceed this nominal intensity for a short time.

[0031] The cut-off device 10 is configured to fulfill the role of a circuit breaker, namely that it has the capacity to interrupt a current of intensity lower than its cut-off capacity, therefore either under load at nominal or partial intensity, or in the presence of a fault current.

[0032] The cut-off device 10 comprises at least one cut-off module 18 interposed in the main circuit 16 between a first point 20 and a second point 22. In the example of Fig. 1 (which only comprises a single cut-off module 18), the first point 20 and a second point 22 of the main circuit 16 are points of the main circuit 16 which are respectively at the same electrical potential as, respectively, the primary point 12 and the secondary point 14 of the cut-off device 10 which delimit the main circuit 16 of the cut-off device 10.

[0033] The cut-off device may comprise several cut-off modules which may be electrically arranged in series in the main circuit 16, between the primary point 12 and the secondary point 14 of the cut-off device 10.

[0034] A cut-off module 18 comprises three branches which are electrically in parallel with each other between the first point 20 and the second point 22.

[0035] A cut-off module 18 comprises a main branch 24, between the first point 20 and the second point 22, with at least one main cut-off device 26, which is interposed in the main branch 24 between the first point 20 and the second point 22, and which is of the mechanical type to ensure the electrical cut-off in the main branch 24. The main cut-off device 26 can switch between a closed state, in which it allows the flow of electric current in the main branch 24, and an open state in which it ensures the electrical cut-off in the main branch 24 by interrupting the flow of electric current at the time of a zero crossing of the intensity in the main branch 24. The main branch 24 of the module 18 is that in which the operational current circulates in normal operation of the network when the cut-off device 10 is in its conduction configuration. In normal operation of the network, when the cut-off device 10 is in its conduction configuration, the main cut-off device 26 is therefore crossed by the operational current circulating in the electrical conductor 11, according to a regime which can be permanent, or quasi-permanent.

[0036] The main cut-off device 26 may for example be a disconnector, a load switch, or even a circuit breaker.

[0037] In the main mechanical cut-off device 26, the electrical cut-off is obtained by displacement, in particular by separation, of one or more pairs of electrical contacts. The displacement of the electrical contacts is generally carried out by mechanical, pneumatic, hydraulic or electrical operating members or actuators. This displacement can be controlled electronically, for example by an electronic control unit 100. In the presence of a significant current and/or voltage, the mechanical separation of the electrical contacts can result in the establishment of an electric arc between the two electrical contacts of the device. As long as the electric arc remains established through the mechanical separation, the main cut-off device 26 does not carry out the electrical cut-off since a current continues to flow through the switch due to the presence of the arc.

[0038] As will be seen later, the invention provides means for ensuring electrical cut-off, in the sense of effectively interrupting the flow of electric current. The main cut-off device 26 may consist of a single main cut-off device, or may consist of several main electrical cut-off devices arranged electrically in series and/or in parallel. The main cut-off device 26 may be a so-called "metal-enclosed" device where the electrical contacts are enclosed in a sealed enclosure filled with an insulating fluid, or even, more preferably, a "vacuum" device (sometimes called a "vacuum interrupter") where the electrical contacts are enclosed in a sealed enclosure in which the pressure is lower than atmospheric pressure, in particular lower than 100 millibars, in particular lower than 10 microbars. The main cut-off device 26 will advantageously be capable of interrupting the electric arc of a current exhibiting, at the time of a zero crossing of the intensity, a high speed of variation of intensity (di/dt), typically with a speed of variation of intensity greater than or equal to 100 A per microsecond.

[0039] A cut-off module 18 also comprises an absorption branch 28, which is electrically arranged in parallel with the main branch 24 between the first point 20 and the second point 22 of the cut-off module 18 in question, with at least one general surge protector 30 interposed in the absorption branch 28 between the first point 20 and the second point 22 of the module in question.

[0040] Such a general surge protector 30 makes it possible to limit the amplitude of the potential difference across the terminals of any component or set of components in parallel with which it is arranged. A surge protector is therefore a device that limits the voltage peaks across its terminals. A surge protector generally comprises an electrical component that has a variable resistance depending on the electrical voltage across its terminals. The surge protector acts as a voltage limiter across its terminals over the current range for which it was chosen. It opposes the protection voltage when the highest current for which the surge protector was sized is passed. Below the transition voltage, it tends to prevent the passage of current. Above the transition voltage, it allows the passage of current through the surge protector for a small increase in the voltage across its terminals. As is known, the transition voltage is generally not a precise value but rather corresponds to a transition voltage range. However, in this text, the definition will be taken as the transition voltage of a surge protector is the voltage for which the surge protector allows a current of 1 ampere (A) to pass. The protection voltage is the voltage across the surge protector when it is crossed by the highest current for which it has been sized. Among surge protectors, lightning arresters are known in particular, which may in particular include varistors and "TVS" (Transient Voltage Suppressor) diodes, such as "Transil™" diodes. In particular, in the context of the invention, a surge protector, in particular the general surge protector 30 may comprise a metal oxide varistor (or MOV, meaning "metal oxide varistor").

[0041] In the example illustrated in Figure 1, the absorption branch 28 does not include a switch. Therefore, it is necessary to choose the general surge protector 30 such that its transition voltage is higher than the voltage likely to appear at the terminals of the cut-off module 18 when the cut-off device 10 is in service and in electrical opening configuration under the nominal service voltage of the network. For example, the general surge protector 30 is chosen such that its protection voltage is between 1.2 and 2 times, for example 1.6 times the nominal service voltage of the module 18 which is the voltage under which the cut-off module 18 operates when the cut-off device 10 is in service under the nominal service voltage of the network.

[0042] Due to the presence of the general surge protector 30 interposed in the absorption branch 28, and due to the choice of its transition voltage value, it can be considered that, in normal operation of the network when the cut-off device 10 is in its conduction configuration, no electric current flows in the absorption branch 28.

[0043] A cut-off module 18 according to the invention also comprises a switching branch 32 which is electrically arranged in parallel with the main branch 24 and the absorption branch 28 between the first point 20 and the second point 22 of the cut-off module 18 considered.

[0044] Several switching modules 34 are electrically interposed in series in the switching branch 32, between the first point 20 and the second point 22. The switching modules 34 are controlled by the electronic control unit 100.

[0045] A sufficient number of switching modules 34 is connected in series to enable high currents (for example greater than 500 A, for example of the order of 10000 A) to be interrupted under a direct voltage equal to or greater than 50 kV in the branch 32. The number of switching modules 34 connected in series may also be adapted to enable this high current interruption even if the control or operation of one of the 34 modules were to fail.

[0046] To control the switching modules 34, the electronic control unit 100 allows them to be switched either into their open state or into their closed state.

[0047] As detailed below, the switching modules 34 are intended to be controlled to their closed state only in switching phases of the main cut-off device 26, in particular in a switching phase of the main cut-off device 26 from its closed state to its open state. Outside of these switching phases (in particular in a nominal conduction phase when the main cut-off device 26 is maintained in its closed state or in an isolation phase in which the main cut-off device 26 is maintained in its open state) the switching modules 34 are intended to be maintained in their open state, so that no current flows in the switching branch 32.

[0048] For each switching module 34, a switching capacitor 38 is connected in series with at least one semiconductor switch.

[0049] Figure 2 illustrates an exemplary embodiment of a switching module 34. A switching capacitor 38 is connected in series between unidirectional semiconductor switches 41 and 42. The switching capacitor 38 plays the role of generating an oscillating current in the switching branch 32 to inject a counter-current into the main branch 24, this in order to promote the extinction of the electric arc likely to appear between the electrodes of the main switching device 26 at the time of its opening. The device 1 according to the invention makes it possible to carry out the opening functions of the switch 26 with switching capacitors 38 having a voltage withstand much lower than the nominal operating voltage of the switching module 18, therefore much lower than the nominal operating voltage of the network in which the electrical conductor 11 is inserted.

[0050] Several one-way switches 41 and 42 can be connected in parallel to increase the capacity of the system. [0051] The switching capacitor 38 also acts as a power supply for a control system 561. Due to the use of several modules 34 connected in series, the voltage across the various capacitors 38 can be sufficiently lowered to approach the power supply voltage of the control systems 561. Alternatively, the control system 561 advantageously comprises a pre-charging circuit for the switching capacitor 38. This pre-charging circuit makes it possible to apply a predetermined electrical voltage between the two plates of the switching capacitor 38, before any switching of the main switching device 26. In the example, the pre-charging circuit comprises a DC voltage source 501 selectively applying a voltage across the switching capacitor 38. This voltage is here applied through a resistor 531 and through another resistor 551. The resistors 531, 551 of the pre-charging circuit may have the same resistance value, or may have different values. In practice, only one of the two resistors may be sufficient. The resistor(s) 531, 551 have the role of limiting the charge/discharge current to be supplied by the DC voltage source 501. In order to enable the control system 561 to be powered by its capacitor 38, a DC/DC converter may be interposed between the control system 561 and this capacitor 38 or may be contained in the control system 561.

[0052] The module 34 comprises, electrically in parallel with the switching capacitor 38, a switching surge protector 801. This switching surge protector 801 is connected by its two terminals respectively to two points of the first section of the switching branch 32, on either side of the switching capacitor 38. The switching surge protector 801 makes it possible to limit the voltage across the switching capacitor 38, and thus to use lower voltage capacitors. Such a surge protector 801 is for example of the ZnO type. Typically, in a cut-off device 1 intended for a very high voltage network, the voltage across the switching capacitor 38 can thus be limited by the first switching surge protector 801, to a level dependent on the number of modules 34 connected. in series. For example, we can plan to connect at least 8 34 modules in series.

[0053] The switches 41 and 42 are here of the IGBT (Insulated Gate Bipolar Transistor) type. The IGBTs 41 and 42 are here in opposite directions to each other. The IGBTs 41 and 42 form a bidirectional switch capable of selectively conducting or blocking the current in both directions. The use of two IGBTs 41 and 42 makes it possible to have a bidirectional switch in current and voltage.

[0054] Each IGBT 41, 42 has a freewheeling diode connected in antiparallel to the IGBT. In operation, both IGBTs 41 and 42 are normally open. The IGBTs 41, 42 are driven to their closed state to control the initiation of the discharge of the capacitor 38.

[0055] The IGBTs 41 and 42 are controlled by the control system 561. The control system 561 is dedicated to the module 34 and is powered by the capacitor 38. Such a configuration makes it possible to avoid the problems of a common power supply of the control systems 561 with corresponding galvanic isolation. The control systems 561 are controlled via the electronic control unit 100.

[0056] As detailed below, the generation of a switching current oscillation in the switching branch 32, when the modules 34 are in their closed state, results from a modulation of the current in the loop formed by the main branch 24 and the switching branch 32 of the cut-off module 18. This loop, which notably comprises the switching capacitors 38, necessarily and naturally has, like any loop, a certain inductance so that the loop forms an LC circuit which generates a current ripple in the transient phases. This current ripple is used to interrupt an electric arc likely to be formed in the main cut-off device 26 in its open state.

[0057] The switching inductance may result from the self-inductance of the components which make up the loop, in particular the self-inductance of the main branch 24 and/or the self-inductance of the switching branch 32. However, if the self-inductance of the components is not sufficient, the loop formed by the main branch 24 and the switching branch 32 may comprise a coil 82. This coil is preferably arranged in the switching branch 32. The switching inductance will be dimensioned to limit the rate of variation of current through the main breaking device 26, variation which appears when the switching branch 32 becomes conductive. The rate of variation of current in the loop formed by the switching branch 32 and the main branch 24 must be limited by the components in the switching branch 32 to a value corresponding to the capacity of the main breaking device 26 to interrupt the electric arc. The device is thus dimensioned so that it ensures the interruption of the arc in the main breaking device 26 when the current passing through this main electrical breaking device 26 passes through a zero value.

[0058] The device 1 may comprise or be associated with one or more electronic control unit(s) 100 for controlling/piloting the modules 34. An electronic control unit 100 typically comprises at least one processor and at least one electronic memory, and may comprise or be connected to one or more electronic communication circuits, for example for communication with one or more computer networks, and/or one or more electronic interface circuits, and/or one or more electronic input/output circuits. An electronic control unit 100 may comprise or be associated with one or more displays. An electronic control unit may comprise or be associated with one or more sensors, for example one or more current sensors and/or one or more voltage sensors, configured to measure a value of a physical parameter in the cut-off device 1 or in the electrical installation in which the device 1 is intended to be integrated. The electronic control unit(s) is/are programmed to implement all or part of a method for opening the device as described above. Advantageously, it may be provided that the electronic control unit(s) 100 communicate(s) their control/piloting orders, in particular to the control system(s) 561, by signals galvanically isolated from the high voltage. These signals could be optical signals transported by optical fibers. They could be electrical signals isolated by transformers. These signals may be electromagnetic signals carried by wireless communication links.

[0059] The electrical cut-off device 1 as described above therefore forms a current circuit breaker particularly suitable for currents under high direct voltage, in particular under high direct voltage greater than 75 kV. This device 1 makes it possible to obtain sufficient cut-off performance with components which have, in total, reduced size and cost, with a minimum of energy losses in normal operation.

[0060] The operating sequence of the device 1 in the event of a fault is as follows. In operation, the switches of the modules 34 are open and the switch 26 is closed. When the fault is detected (for example by information or detection at the electronic control unit 100), a command to open the switch 26 is sent by the electronic control unit 100. Due to the presence of an arc when the switch 26 is opened, the current cut-off through this switch 26 is not yet effective. A command to generate a switching operation is sent to the modules 34 synchronously. The switching time of the current from the main branch 24 to the switching branch 32 is equal to a maximum of three-quarters of the oscillation period of the current in the loop formed by the main branch 24 and by the switching branch 32, knowing that this oscillation can be likened to the discharge of the capacitors in an LC or RLC circuit. After a time delay or after having verified the effective cutting of the current through the switch 26, the switches of the modules 34 are opened again. The surge protector 30 then attenuates the fault current and absorbs residual energy from the network.

[0061] The invention advantageously makes it possible to reduce the losses by Joule effect in the main branch 24 while limiting the risks of failure in the switching branch 32. Indeed, due to the presence of several modules 34 connected in series, switching can still be obtained even if the control of one of the modules 34 proves to be faulty. Furthermore, such a device 1 makes it possible to maintain the effective cut-off speed in the main branch 24, which makes it possible to limit the erosion of the electrodes of the switch 26. [0062] The switching module 341 illustrated in Figure 3 is based on the use of symmetrical GTO thyristors, mounted in anti-parallel. The module 341 here includes the components 38, 501, 801, 531 and 551 which will not be detailed further. The control system 561 here drives the gates of GTO thyristors 81 and 83 positioned in opposite directions on either side of the capacitor 38. GTO thyristors 85 and 87 are mounted in anti-parallel respectively to GTO thyristors 81 and 83. The thyristors 85 and 87 are driven respectively by the control circuits 91 and 93. Another block is connected in series with the capacitor 38 and the switch system above. This other block here comprises a capacitor 75. A switching surge protector 77 and a direct voltage source 79 are connected in parallel across the terminals of the capacitor 75. The direct voltage source 79 is connected across the terminals of the capacitor 75 via resistors 71 and 73. The capacitor 75 is notably used to power the control circuit 91 and possibly the control circuit 93. The power supply of the control circuit 93 is not illustrated here for the sake of simplification.

[0063] The operating sequence of the device 1 according to this embodiment in the event of a fault is similar to that of the previous embodiment. In operation, the switches of the modules 34 are open and the switch 26 is closed. When the fault is detected, an order to open the switch 26 is sent by the electronic control unit 100. An order to generate a switching operation is sent to the modules 34 synchronously. After a time delay or after having verified the effective interruption of the current through the switch 26, the switches of the modules 34 are opened again. The surge protector 30 then attenuates the fault current and absorbs residual energy from the network.

[0064] Figure 4 schematically illustrates another embodiment of a cut-off device 1 according to the invention. In this example, the absorption branch 28 is replaced by a set of surge protectors 30. Each surge protector 30 is here connected in parallel with a respective module 34.

[0065] Figure 5 illustrates an example of module 34 dedicated to a parallel connection with a surge protector 30. The module 34 here comprises a coil 80 connected in series with the switch (here including IGBTs 41 and 42) and the capacitor 38. The surge protector is here connected in parallel with the branch of module 34 comprising coil 80, the switch and capacitor 38.

[0066] Figure 8 illustrates another example of module 34. In contrast to the example of Figure 5, the surge protector 30 is here connected in parallel with the switches 41 and 42. A suitable dimensioning of the switching surge protector 801 can be achieved.

[0067] Figure 6 illustrates another example of module 34. In this example, capacitor 38 is not connected between switches 41 and 42.

[0068] Figure 7 illustrates another example of module 34. In this example, module 34 comprises only one switch 41 in series with capacitor 38. This example allows unidirectional operation.

[0069] Each switching surge protector (801 or 77 in the examples) is sized in relation to the voltage of the switching capacitor 38 and has a transition voltage less than or equal to the transition voltage of the general surge protector 30.

[0070] In all of the examples above, it has been seen that the power supply and control of the modules 34 placed in the switching branch 32 is carried out with a control system which does not impose any electrical or electronic component in the main branch 24 of the cut-off module 18. As a result, in the conduction configuration, there is no component belonging to the control system(s) which dissipates electrical energy permanently during normal operation of the network. Thus, no cooling system is necessary to cool such components.

[0071] According to another aspect of the invention illustrated in Figure 9, the surge protector 801 is replaced by a switch 809. The switch 809 may for example be of the thyristor type. Advantageously, a resistor or an impedance 808 is used to protect the capacitor from an overvoltage when the main cut-off device 26 is opened or closed, and to protect the switch 809 from an overcurrent when the main cut-off device 26 is closed. This variant is applicable to the different variants described previously.

Claims

Claims [Claim 1] Device (1) for cutting off high-voltage direct current, characterized in that it comprises: - a main circuit (16), in which circulates, in a conduction configuration of the cutting-off device (10), an electric current under a high nominal continuous operating voltage of the device; - a cutting-off module (18), interposed in the main circuit (16) between a first point (20) and a second point (22) of the main circuit (16), the cutting-off module comprising the following branches connected in parallel between the first point and the second point: - a main branch (24) including a main electrical cut-off device (26) of mechanical type interposed between the first point (20) and the second point (22); - a switching branch (32) comprising several switching modules (34) connected in series, each switching module (34) comprising -a switching capacitor (38) configured to allow current flow in the switching branch (32); -at least one switching switch (41, 42) of the semiconductor type, connected in series with the switching capacitor (38) and configured to selectively authorize or interrupt the flow of current in the switching branch (32); - a loop formed by the main branch (24) and the switching branch (32) of the cut-off module, said loop of the cut-off module having a switching inductance; - a control system (561) of the switching switch (41, 42) and configured to control the closing of the switching switch so as to discharge the switching capacitor (38) in said loop; -the cut-off module (18) comprising at least one surge protector (30) interposed between the first point (20) and the second point (22) of so as to ensure conduction between the first and second points when the main branch and the switching branch are open. [Claim 2] A switching device (1) according to claim 1, wherein said switching switch of each switching module (34) includes at least two transistors (41, 42) connected in series (38). [Claim 3] A switching device (1) according to claim 1 or 2, wherein said switching switch of each switching module (34) comprises a first pair of anti-parallel GTO thyristors and a second pair of anti-parallel GTO thyristors, the first and second pairs being connected in series. [Claim 4] A cut-off device (1) according to any preceding claim, wherein each switching module (34) further comprises another surge protector (801, 77) connected across the switching capacitor (38, 75). [Claim 5] A cut-off device (1) according to claim 4, wherein the sum of the transition voltages of the other surge protectors (801, 77) is lower than the transition voltage of the surge protector (30) of the cut-off module. [Claim 6] A cutting device (1) according to any one of the preceding claims, further comprising an electronic control unit (100) configured to control the control systems (561) of the control modules (34). [Claim 7] A cut-off device (1) according to any one of the preceding claims, wherein the device comprises a pre-charging circuit (501) for the switching capacitor (38). [Claim 8] A switching device (1) according to any preceding claim, further comprising an inductor (82) connected in series with the switching modules (34). [Claim 9] A cut-off device (1) according to any one of claims 1 to 8, wherein each switching module (34) comprises a coil (80) connected in series with the switching switch and the switching capacitor (38). [Claim 10] A cut-off device (1) according to claim 1 to 9, comprising a surge protector (30) for each switching module (34), connected in parallel to the terminals of a respective switching module. [Claim 11] A cut-off device (1) according to any one of the preceding claims, wherein each control system (561) of the switching switch (41, 42) of a cut-off module is electrically powered by the switching capacitor (38) of this cut-off module.