EP4169138A1

EP4169138A1 - Method for insulating a conductor of a continuous high voltage power drive line

Info

Publication number: EP4169138A1
Application number: EP21740595.0A
Authority: EP
Inventors: Pascal TORWELLE; bertrand Raison; Alberto BERTINATO; Marc Petit; Trung Dung LE
Original assignee: Centre National de la Recherche Scientifique CNRS; Universite Grenoble Alpes; SuperGrid Institute SAS; Universite Paris Saclay; CentraleSupelec
Current assignee: Centre National de la Recherche Scientifique CNRS; Universite Grenoble Alpes; SuperGrid Institute SAS; Universite Paris Saclay; CentraleSupelec
Priority date: 2020-06-22
Filing date: 2021-06-17
Publication date: 2023-04-26
Also published as: WO2021260298A1; FR3111747A1

Abstract

The invention relates to a method for insulating a first conductor (21) of a first continuous high voltage power drive line connected to at least one link node in question comprising at least three distinct links each associated with at least one cut-off device, characterised in that the method comprises, according to an item of information on the criticality of the fault relative to the link node in question: - either, for a targeted opening operation, moving the electrical cut-off device (28.11) from its closed state to its open state, while maintaining each of the second (28.12, 29.1b) and the third (28.13; 18.1; 29.1) electrical cut-off devices in their closed state; - or, to fully open the node in question, interrupting all the power flows in all of the links of the node.

Description

Title of the invention: Method of insulating a conductor of a high voltage direct current power transmission line

Technical area

The invention relates to the field of electric current transmission and / or distribution infrastructure comprising at least one high voltage direct current electric current (HVDC) network unit. In particular, the invention relates to the strategies for power failure in such an HVDC network unit in the event of an electrical fault occurring in an electrical conductor of this network unit.

HVDC network units are in particular envisaged as a solution to the interconnection of disparate or non-synchronous electricity production sites, in particular to increase the capacity of energy transmission between countries (interconnections between countries), via what are called energy highways. HVDC grid units are particularly considered for the transmission and distribution of energy produced by wind farms rather than alternating current technologies, due to lower line losses and no incidence of parasitic capacitances in the network unit over long distances. Such HVDC network units typically have voltage levels on the order of 100 kV and above.

In the present text, for a DC voltage device, a high voltage device is considered to be a "high voltage A" device, in which the nominal operating voltage is continuous and greater than 1500 V, but less than or equal to 75000 V (75kV), ie a “high voltage B” device when the nominal operating voltage is continuous and greater than 75000 V (75kV). Thus, the domain of direct high voltage includes the domain of "high voltage A" and that of "high voltage B".

[0004] Cutting the current under high voltage direct in such networks or network units is a crucial issue directly conditioning the feasibility and development of such networks. The evolution of electricity transmission and / or distribution infrastructure today tends towards the interconnection of network units to lead to mesh networks, which involves HVDC network units comprising several possible paths between two terminals through which the network unit in question is connected to other network units. Thus, starting from a terminal, a network unit can have two or more electrical conductors which electrically connect two other separate points of the same HVDC network unit, so that the network unit has a link node, which can in this case be qualified as an external electrical node, since it is also connected to another network unit. Even within a network unit, there can be a link node having at least three distinct links, all the links of this link node being connected to equipment or to electrical conductors belonging to the network unit considered. We can then refer to such a link node under the name of internal link node.

Generally, in the field of high alternating voltages, at each of the two ends of an electrical conductor, there is an electrical cut-off device capable of cutting off the flow of electrical current in the conductor, whether the current is the nominal current , which is the maximum current that the conductor is likely to conduct in steady state, or a fault current, which can exceed this nominal current. The cutting of electric currents under high direct voltage (HVDC) is more complex to achieve than that of currents under alternating voltage (AC). Indeed, when cutting an alternating current, we take advantage of a zero crossing of the current to achieve the power cut, which we cannot benefit from with a current under direct voltage, in particular HVDC. In the event of a fault, the electrical network is designed to implement a network fault elimination strategy, aimed at interrupting the current in the faulty electrical conductor. Prior art

[0007] Different types of protection strategies are known. As part of the European project “PROgress on Meshed HVDC Offshore Transmission Networks”, a document “D4.2 - Broad comparison of fault clearing strategies for DC grids” was made available, with a date of October 4, 2017, which defines different types of strategies.

[0008] Some defect elimination strategies are said to be "non-selective". They are defined by CIGRE WG B4 / B5-59 considering an entire HVDC network unit as forming a single protection zone for fault elimination, i.e. without any selectivity for interrupting the fault current in the HVDC network. In the event of a fault in the HVDC grid unit, the entire HVDC grid unit is de-energized upon detection of the fault. With the use of “non-selective” fault suppression strategies, the requirements on protective components, especially electrical disconnecting devices, are lower. Consequently, the components allowing the implementation of these networks are less expensive. However, all electrical power flows through the entire network unit must be interrupted whenever a fault occurs in the network unit.

[0009] The most effective defect elimination strategies are said to be "fully selective". CIGRE WG B4 / B5-59 defines “fully selective” fault suppression as implementing protection zones that are defined to individually protect each electrical conductor and each link node under direct voltage. Slightly more broadly, this category includes strategies which aim to minimize the impact of faults on the AC network by generally allowing some continuity of operation of the HVDC network unit in the event of a fault. To do this, each conductor (and ideally each link node) must be individually protected. In the context of a fault occurring on an electrical conductor, this implies being able to isolate the fault by opening only the breaking devices located at the ends of the faulty conductor, leaving the other breaking devices closed in order to maintain other power flows in the network unit. This requires that the breaking devices be made in the form of fast-acting DC voltage circuit breakers, such as hybrid type circuit breakers, and generally also to put protective inductors in series at each end of the circuit. conductor in order to limit the speed of rise in the intensity of the current in the conductor when the fault appears. However, such components are considered expensive. It is also possible to implement “fully selective” defect elimination strategies with mechanical breaking devices, but this then requires placing, at each end of the conductors of the transmission lines, protective inductors having a very high value. high inductance, for example greater than or equal to 200 milli-henrys.

Intermediate, so-called "partially selective" strategies have also been proposed in which the HVDC network unit is divided into several protection zones. If an electrical fault occurs in a zone, which therefore becomes a fault zone, the loss of the entire HVDC network unit is avoided by quickly isolating the healthy areas from the faulty zone.

By limiting the impact of a fault to only part of the HVDC grid unit, the impact of a fault is reduced compared to a non-selective strategy.

However, an entire area of the network unit must be taken out of service, which can be detrimental to adjacent network units connected to that out-of-service area of the network unit where the fault occurs. In document WO2012123015, it is proposed to delimit at least two protection zones in the same HVDC network unit by interposing current limiters in all the conductors connecting these two zones. The document ”DC fault protection strategy considering DC network partition” by M. Rahman, L. Xu, L.

Yao in IEEE PES GM, Boston, 2016, studies the partition of a multi-terminal HVDC network unit. Fast-acting circuit breakers or fault-blocking DC-DC converters can be configured in strategic locations to allow the entire multi-terminal HVDC system to be operated interconnected but partitioned into network zones. In the event of a fault event in one of the zones of the network unit, the disconnecting devices or DC-DC converters of the strategic cable connections that connect the different zones of the HVDC network unit are opened or blocked so that the faulty area of the HVDC network unit is quickly isolated from the rest of the HVDC network unit. Thus, the healthy part of the HVDC network unit can remain operational or recover quickly to restore power transmission. Each zone of the network unit HVDC can be protected using either selective or non-selective type fault elimination strategies.

Most of the currently planned HVDC network units will use, as electrical conductors, buried or submarine cables, because the right of way for overhead conductors is difficult to obtain. However, the overhead conductors of existing overhead lines, intended for the circulation of alternating currents, could be upgraded and subsequently used in HVDC grid units as electrical conductors, which would be an attractive solution due to the both of its simplicity and its profitability.

Each of these two types of electrical conductors may, in service, experience electrical faults. The occurrence of an electrical fault in an electrical conductor of a power transmission line often results in a short-circuit to earth situation, which causes the flow, in the electrical conductor, of a fault current. which very quickly exceeds, in a few milliseconds or less, the rated current for which the conductor and the elements adjacent to the conductor are sized.

However, by comparing the relevant electrical characteristics in the event of a fault, on the one hand buried or submarine cables and on the other hand overhead conductors, significant differences can be identified in particular in terms of characteristic impedance, propagation speed and mutual coupling. However, other characteristics, which are not directly related to the conductor, can also be taken into account in the event of an electrical fault, such as for example the probability of occurrence of an electrical fault, the persistence of the electrical fault and the resistance. default. Usual values of these characteristics are listed in table 1, on the one hand for buried or submarine cables, and on the other hand for overhead conductors, each time dimensioned for use in a network unit under high continuous voltage.

[0014] [Table 1]

[0015] The values given for the characteristic impedance and the propagation speed of an overhead conductor represent the overhead mode. For the return to ground mode of a multi-conductor overhead line, a propagation speed of 263 km / s and a characteristic impedance of 685 W can be considered. The return to ground mode represents the interactions of the driver with the ground while the aerial mode represents the interactions between the drivers.

[0016] The characteristic high impedance of an overhead conductor leads, in the event of an electrical fault occurring in the overhead conductor, to a slower increase in current and to a lower discharge current of the adjacent conductors. The probability of fault occurrence is higher for overhead conductors, especially due to their exposure to harsh weather conditions, such as lightning strikes or pollution, which cannot fail to affect the cut-off rate of the vehicle. entire HVDC network unit when applying a non-selective fault elimination strategy. This leads to more frequent shutdown of the relevant HVDC grid unit.

[0017] The fault resistance of a buried or submarine cable is estimated to be very low, because it is mainly characterized by a dielectric breakdown of the insulation of the conductor. On the other hand, the electrical faults likely to occur in an overhead conductor can have multiple reasons, some of which lead to a higher fault resistance.

It is understood that, in an HVDC network unit implementing one or more electrical conductors comprising an overhead conductor, the adoption a "non-selective" type fault elimination strategy, which requires the complete stopping of power flows in the network unit in the event of a fault, can be very penalizing due to the more frequent occurrence faults in overhead conductors. The same applies, albeit to a lesser degree, in the case of the implementation of partially selective type strategies in which a network unit is divided into several protection zones with means for interrupting or limiting the current between them. different areas. And, we saw above that the implementation of “fully selective” strategies necessitated the generalization of fast-acting cut-off devices, which are particularly expensive.

Document US-2019/199089 describes an isolation strategy "from the outside"", in the sense that it is the external switching devices, connected to a converter, which are opened as a priority. However, this document deals more particularly with the hypothesis in which one of the N external cut-off devices does not operate correctly and does not open. Because of this strategy of favoring insulation "from the outside", this document provides that, in normal operation, the line breaking devices linked to the conductors are not used to interrupt the current. Line disconnecting devices linked to conductors are only used to interrupt the current in the event of a malfunction of an external disconnecting device. In addition, only the line cut-off devices linked to the faulty conductor are likely to be opened, not the others. In general, for a link node considered, it is therefore either the external breaking device which is open, or, in the event of its malfunction, it is the line breaking device linked to the faulty conductor. which is open. Any other cut-off device other than these two is never opened. In this document, the current in the faulty line can be monitored to determine the moment at which the opening will be triggered, while waiting for the decrease in the current caused by the opening of the external cut-off devices to have its effect. In all cases, whatever the opening moment that will be determined by this monitoring, the action taken will be the same: it will consist of opening the cut-off device attached to the faulty conductor. Document CN105896488 describes a method which, in principle, implements a selective defect elimination strategy. However, in this context, this document is interested in the lapse of time between the detection that a fault appears and the identification of the driver in which this fault has appeared. If this period of time is long, that is to say it takes time to identify which of the conductors of the network is faulty, then the method sets up a non-selective cut-off procedure for the whole. from the network, by opening all the disconnecting devices of the network simultaneously. Indeed, this criterion of duration of identification of the faulty conductor can in no case be linked to a link node considered since, in principle, during this period, it is not known in which conductor the fault is located, and that 'it is therefore not possible in any case to determine the impact of this criterion with respect to a link node considered. This has the effect of forcing a complete shutdown of power flows throughout the network unit. The aim of this method is therefore, in a selective fault elimination strategy, to urgently compensate for a delay in the identification of the driver in which this fault has appeared.

The object of the invention is therefore to provide a method for isolating a first conductor of a first power transmission line, in a considered HVDC electrical network unit, which makes it possible to limit the frequency of occurrence. complete shutdowns of the network unit, without requiring the generalization of fast-acting cut-off devices throughout the HVDC network unit, even if the HVDC network unit includes overhead transmission lines power, comprising electrical conductors incorporating at least one overhead conductor.

Disclosure of the invention

To this end, the invention provides a method of isolating a first conductor of a first power transmission line in a considered electrical network unit, the considered electrical network unit operating at a voltage of single nominal service which is a direct high voltage, in which the considered electrical network unit comprises at least one considered link node, comprising at least three separate links connected electrically between them continuously, with:

- a first link which is electrically connected to a proximal end of the first electrical conductor of the electrical network unit considered, with the interposition of a first electrical cut-off device associated with the first link, which has an open state and a closed state in which it allows the circulation of a first flow of power between the link node in question and the first conductor;

- a second link which is electrically connected to another electrical network unit or to a second electrical conductor of the electrical network unit considered to allow the passage of a second flow of electrical power through the second connection which is controlled by at least one second electrical cut-off device, associated with the second link, which has an open state and a closed state;

- a third link which is electrically connected to another electrical network unit or to a third electrical conductor of the considered electrical network unit to allow the passage of a third flow of electrical power through the third connection which is controlled by at least a third electrical cut-off device, associated with the third link, which has an open state and a closed state. [0023] The method further comprises the monitoring of at least monitored parameter relating to the current and / or to the electric potential in the first electric conductor.

The method comprising a step of detecting the appearance of a defect in the first electrical conductor. The method comprises, in addition to the step of detecting the appearance of a fault in the first electrical conductor, at least one step of determining the level of criticality of the fault, with respect to the node of link considered, returning information on the level of criticality of the fault.

In the presence of a fault presence information in the first electrical conductor, the method proceeds, depending on the fault criticality information vis-à-vis the link node considered:

- or, in a targeted opening action, when the first control device passes through electrical disconnection from its closed state to its open state, maintaining the second and third electrical disconnecting devices each in their closed state;

- or, in an action of total opening of the node considered, with the interruption of all the power flows in all the links of the node.

[0027] The method according to the invention can further include the following optional features, taken alone or in combination.

In a total opening action of the node considered, the first electrical cut-off device can be brought from its closed state to its open state after all the electrical power flows through the other links of the link node considered, other than the first link, have been discontinued.

The step of determining the level of criticality vis-à-vis the link node considered may include a comparison of at least one parameter monitored with respect to a fault criticality criterion. The fault criticality criterion may have been determined in advance.

[0031] The step of detecting the appearance of a fault in the first electrical conductor may include a comparison of at least one monitored parameter against a conductor fault criterion.

The step of detecting the appearance of a fault in the first electrical conductor and the step of determining the level of criticality with respect to the link node considered can be carried out as a function of the value d 'the same monitored parameter. Conversely, the step of detecting the appearance of a fault in the first electrical conductor and the step of determining the level of criticality with respect to the link node considered can be carried out as a function of the value of two different monitored parameters.

The fault criticality information can be determined according to a prediction of the evolution of the current in the first electrical conductor following the appearance of the fault and according to the capacity of the first electrical switching device to cut this current. Said at least one monitored parameter can be selected from among the intensity of the current in the first conductor, the derivative with respect to the time of the intensity of the current in the first conductor, the electric potential of the first conductor, and the time derivative of the electric potential of the first conductor, or combinations thereof.

Said at least one monitored parameter may be a value of the derivative, with respect to time, of the electric potential of the first conductor.

The second and / or the third link can be electrically connected to an electrical power converter to another electrical network unit, by means of a second, respectively third, electrical current cutting device under direct voltage .

The second and / or the third link can be electrically connected to an electrical power converter to another electrical network unit, the power converter also forming the second, respectively third, electrical switching device.

The second and / or the third link can be electrically connected to an electrical power converter to another electrical network unit, the second, respectively third, electrical cut-off device being interposed between the electrical power converter and said other electrical network unit. In this case, if the other network unit is operating at an alternating nominal operating voltage, the second, respectively third, electrical cut-off device, interposed between the electrical power converter and said other electrical network unit, is a switching device. electric current cut off under alternating voltage.

The link node considered may include at least one other link, which is distinct from the first link, and which is electrically connected to a second electrical conductor of the electrical network unit considered by means of at least a second electrical cut-off device which is associated with said other link and which has an open state and a closed state.

The electrical network unit considered may include at least one other link node, separate from the first link node and comprising at least three separate links electrically connected to each other continuously, with:

- a first link which is electrically connected to a distal end of the first electrical conductor of the electrical network unit considered, with the interposition of a first electrical cut-off device associated with the first link, which has an open state and a closed state in which it allows the circulation of a first power flow between this other link node;

- a second link which is electrically connected to another electrical network unit or to another electrical conductor of the electrical network unit considered to allow the passage of a second flow of electrical power through the second connection of this other link node, this second flow being controlled by at least one second electrical cut-off device, associated with the second link of this other link node, which has an open state and a closed state;

- a third link which is electrically connected to another electrical network unit or to another electrical conductor of the electrical network unit considered to allow the passage of a third flow of electrical power through the third connection of this other link node, this third flow being controlled by at least a third electrical cut-off device, associated with the third link of this other link node, which has an open state and a closed state.

In the presence of such another link node, the method may include at least one step of determining the level of criticality of the fault with respect to this other link node, returning information on the level of criticality of the fault. default vis-à-vis this other link node; and, depending on the fault criticality information with respect to this other link node, the method can proceed:

- or, in a targeted opening action, when the first electrical cut-off device of this other link node goes from its closed state to its open state, while maintaining, in this other link node, the second and third devices electrical shutdown of this other node each in their closed state;

- or, in an action of total opening of this other link node, the interruption of all the power flows in all the links of this other link node, which may in particular include the passage of the first electrical cut-off device of this other link node from its closed state to its open state. In such a case, for the same electrical fault in the first conductor, the step of determining the level of criticality of the fault with respect to the link node considered and the step of determining the level of criticality of the fault. fault vis-à-vis the other link node can be distinct and can return information on the level of criticality of the fault which can be different, leading to the possibility of having, for a given electrical fault, an opening action total for one of the two nodes, and a targeted opening action for the other of the two nodes.

In general, the method can advantageously be implemented when the first electrical conductor comprises an overhead electrical conductor.

Brief description of the drawings

[0044] [Fig. 1] Figure 1 is a general schematic view of an electricity transmission and distribution infrastructure comprising an HVDC current network unit.

[0045] [Fig. 2] Figure 2 shows a somewhat more detailed view, while remaining schematic, of part of the infrastructure 10, illustrating the environment of a considered link node of the HVDC network unit of FIG. 1.

[0046] [Fig. 3] Fig. 3 is a schematic view of the HVDC network unit of Fig. 1, if a non-selective strategy is implemented at the HVDC network unit level.

[0047] [Fig. 4A] Fig. 4A shows a schematic view of the HVDC network unit of Fig. 1, in case of implementation of a full opening action vis-à-vis the link node shown in Fig. 2.

[0048] [Fig. 4B] Fig. 4B shows a schematic view of the HVDC network unit of Fig. 1, in the event of implementation, in the context of a method according to the invention, of a targeted opening action vis-à-vis the link node illustrated in FIG. 2.

[0049] [Fig. 5] Figure 5 is a flow chart schematically illustrating an example of part of an insulation process according to the invention. [0050] [Fig. 6] FIG. 6 represents the diagram of a modeling with concentrated parameters of an electrical conductor in electrical fault with a view to the estimated calculation of certain parameters characteristic of this fault.

[0051] [Fig. 7] FIG. 7 represents a map indicating the criticality of a fault as a function of certain characteristic parameters of this fault.

[0052] [Fig. 8] Figure 8 shows the diagram of a distributed parameter modeling of an electrical conductor in electrical fault for the estimated calculation of the voltage change in the conductor at the time of the appearance of the fault.

[0053] [Fig. 9] FIG. 9 represents the diagram of a modeling of a link node and of its environment with a view to its modeling, to calculate a threshold for the evolution of the derivative of the voltage in an electrical conductor connected to this node of connection, at the time of the appearance of the fault in this electrical conductor.

[0054] [Fig. 10] FIG. 10 represents a map grouping together the threshold values for the evolution of the derivative of the voltage in an electrical conductor, making it possible to determine the criticality of a fault as a function of certain characteristic parameters of this fault.

[0055] [Fig. 11 A] FIG. 11 A represents a schematic view of an infrastructure for the transmission and distribution of electric current comprising an HVDC current network unit, if implemented, within the framework of a method according to the invention. , a targeted opening action vis-à-vis the two connecting nodes of the HVDC power grid unit.

[0056] [Fig. 11 B] FIG. 11 B shows a schematic view of the infrastructure for the transmission and distribution of electric current of FIG. 11 A, in the event of implementation, within the framework of a method according to the invention, of a total opening action vis-à-vis one of the connection nodes of the current network unit HVDC, and a targeted opening action vis-à-vis the other of the two connecting nodes of the HVDC power grid unit.

Description of the embodiments [0057] FIG. 1 shows an example of an infrastructure 10 for the transmission and distribution of electric current comprising a unit of a high-voltage direct current electric current network, hereinafter referred to as the HVDC network unit 12. In this example, the HVDC network unit 12 has 4 terminals, in this case a first terminal 14.1, a second terminal 14.2, a third terminal 14.3 and a fourth terminal 14.4. The HVDC network unit 12 includes, to electrically connect these 4 terminals, electrical conductors 21, 22, 23, 24, electrical buses 26.1, 26.2, 26.3, 26.4, cut-off devices, etc ... which all operate at a single nominal operating voltage which is a continuous high voltage, for example a “high voltage B” in which the nominal operating voltage is continuous and greater than 75,000 V.

[0058] FIG. 11 A represents another example of an infrastructure 10 for the transmission and distribution of electric current comprising an HVDC network unit 12. In this second example, the HVDC network unit 12 has 2 pairs of terminals, in this case one first pair comprising two terminals 14.1 and 14.1b which are at the same electrical potential, and a second pair of terminals 14.2 and 14.2b which are at the same electrical potential. The HVDC network unit 12 comprises, for electrically connecting these 4 terminals, an electric conductor 21 of a single electric power transmission line which extends electrically between two electric buses 26.1, 26.2, cut-off devices, etc. .. all of which operate at a single nominal operating voltage which is a high continuous voltage, for example a “high voltage B” in which the rated operating voltage is continuous and above 75,000 V.

In an electrical network, the transmission of electrical power between two given points of the network is effected by a power transmission line which generally comprises several conductors, each of which corresponds to an electrical pole of the power transmission line. In all cases, within the meaning of the present text, an electrical conductor can be in the form of a single electrical conductor which extends between two distinct points of a network unit considered, or in the form of a set of electrical conductors which run in electrically parallel between two distinct points of a network unit considered, all the conductors of the set being, at all times, at the same electric potential.

Thus, in an HVDC network unit, the transmission of electrical power between two given points of the network is done by a power transmission line which, in many cases, has two electrical poles, each pole comprising an electrical conductor which extends between the two given points of the network. In this case, the power transmission line therefore comprises two electrical conductors of different polarities, with, in charge, for example an electrical conductor which is at a positive potential and an electrical conductor which is at a negative or neutral potential. Still in an HVDC network unit, the transmission of electrical power between two given points of the network can also be done by a three-pole electrical power transmission path 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 some cases, the transmission of electric power between two given points of the network can be done by a single electric pole power transmission line, with an electric conductor at the potential of the line and with an electric return through the earth.

In the figures, there is shown by a single line a power transmission line between two distinct points of a network unit, in particular in the HVDC network unit 12, in order to clearly show the topology of the network without having to go into technical details. Likewise, where an electric bus 26.1, 26.2, 26.3, 26.4 has been represented at a given point of the network unit, in reality there will be as many electric buses as the number of poles, therefore as many buses electrical as the number of electrical conductors in the transmission lines that start from the point in question. For example, it can be assumed that in HVDC network unit 12 only electrical conductors and electrical buses corresponding to a positive pole have been shown.

All power converters will be considered ideal converters. Only the entrances and exits are indicated and all Technical details of the internal topology, including possible intermediate voltage levels, are not described. Very short electrical conductors are not described. Thus, two electric buses directly connected by a very short electric conductor are considered to form only one electric bus.

In each of its 4 terminals, the HVDC network unit 12 is connected to another network unit 16.1, 16.2, 16.3, 16.4. In the example, each of these other grid units 16.1, 16.2, 16.3, 16.4 is an AC grid unit, so each of the 4 terminals 14.1, 14.2, 14.3 and 14.4 is actually connected to the DC side d 'an AC-DC power converter 18.1, 18.2, 18.3, 18.4. The same arrangement is found in the installation of Figs. 11 A and 11 B. However, one or more of these other network units 16.1, 16.2, 16.3, 16.4, could be of another nature, and could for example be another HVDC network unit . Two HVDC network units can thus be electrically connected at a common terminal via a DC-DC power converter. In the example of Fig. 1, the network units 16.2 and 16.4 each comprise a field of electric generators, for example a field of wind turbines. In the example of Fig. 1, network units 16.1 and 16.3 represent units of electricity transmission and distribution networks.

In particular, it will be possible to consider that two network units are distinct if they can operate simultaneously:

- one under direct voltage, the other under alternating voltage; Where

- one under a first DC voltage, and the other under a second DC voltage of a value different from the first DC voltage; Where

- at the same voltage, but with galvanic isolation or with the interposition of a power converter.

In the example illustrated in FIG. 1, the HVDC network unit 12 comprises several link nodes, in this case 3 link nodes, here made in the form of electric buses 26.1, 26.3 and 26.4, each of which has at least three separate links which are electrically connected between them continuously, that is to say without the possibility of an electrical cut between the links. In the example illustrated in FIG. 11A, the HVDC network unit 12 includes 2 link nodes, here also made in the form of electric buses

26.1, 26.2. One of these link nodes 26.1 of the example of FIG. 1 is illustrated more particularly in FIG. 2. This link node 26.1 illustrated in FIG. 2 presents 4 links 26.11, 26.12, 26.13 and 26.14. The connecting nodes 26. 3 and 26.4 visible in FIG. 1 have only 3 bonds. It should also be noted that, in the example of FIG. 1, the electric bus forming the link node 26.2 has only two links, and can therefore be considered as a simple connection point.

[0066] In the example of FIG. 1, we notice that the 4 connection nodes 26.1,

26.2, 26.3 and 26.4 can each be qualified as an external link node insofar as at least one of the links of the node in question is electrically connected to another electrical network unit 16.1, 16.2, 16.3, 16.4 through a electric power converter. In the example of Fig. 1, it is noted that the link nodes 26.1, 26.2 can also each be qualified as an external link node insofar as, for each, two of the links of the node considered are electrically connected to at least one other electrical network unit 16.1, 16.2, 16.3, 16.4 through an electric power converter. In the example of Fig. 1, the connection to the electric power converter is made by means of an electric cut-off device. In the example of Fig. 11 A, the connection to the electrical power converter is made without a specific electrical cut-off device, that is to say without the presence of a component separate from the electrical power converter which could act as an electrical cut-off device.

However, a network unit within the meaning of the invention could also comprise at least one link node which would be qualified as internal, in the form of a point of the network unit comprising three or more distinct links. which would all be electrically connected to each other in a continuous manner and which would each be connected to other distinct points or devices (for example electrical conductors) of the same network unit.

The link node 26.1 illustrated in Figs. 1 and 2 is made in the form of an electrical bus and has a first link 26.11 which is electrically connected to a proximal end of a first electrical conductor 21 of a first power transmission line of the network unit electrical considered, with the interposition of a first electrical switching device 28.11, associated with the first link 26.11, which has an open state and a closed state. The same arrangement is found for the first link node 26.1 of the example of Figs. 11 A and 11 B. In its closed state, the first electrical cut-off device 28.11 allows the circulation of a first power flow P26.11 between the link node in question and the first conductor 21, in the first link 26.11. This first power flow P26.11 corresponds, in normal service and the absence of a fault, to that which circulates in the first conductor 21. In its open state, the first electrical cut-off device 28.11 interrupts the flow of any electrical power between the link node considered and the first conductor 21, in the first link 26.11.

In the present text, an electrical cut-off device may comprise one or more power cut-off devices, arranged in parallel and / or in series between an entry point of the device and an exit point of the device. In the open state, an electrical disconnect device prevents current flow through the device. In a closed state, an electrical cut-off device allows electric current to flow through the device. An electrical breaking device may include one or more circuit breaker type devices, optimized to interrupt an established current, and / or one or more disconnector type devices, optimized to maintain electrical isolation between its two terminals when it is in a state. open. Such devices can be mechanical, electronic or hybrid devices.

Preferably, the first electrical cut-off device 28.11 is of the mechanical type, in which the electrical cut corresponds to a mechanical separation of two electrodes.

[0071] In FIG. 1, it can be seen that this first electrical conductor 21 is connected, by its distal end, to the fourth terminal 14.4 of the HVDC network unit 12, here by means of a fourth electrical bus 26.4 of the HVDC network unit 12. In this example, an electrical switching device 28.41 is interposed between the distal end of the first electrical conductor 21 and a link 26.41 of the fourth electrical bus 26.4. Preferably, in particular for reasons of reduced cost, the electrical cut-off device 28.41 which ensures the interruption of the power flow in the fourth link of the node of the third electrical bus 26.3 is an electrical cut-off device of the mechanical type. Thus, the first electrical conductor 21 is capable of being fully insulated, at each of its two ends, by means of an electrical switching device of mechanical type which ensures the interruption of the flow of power between the first electrical conductor. 21 and the rest of the infrastructure. In the particular example of FIG. 1, the fourth terminal 14.4 is electrically connected to a fourth further electrical network unit 16.4.

Therefore, link node 26.4 is an external link node. In the example, but this is optional, an electrical cut-off device 28.43 is interposed between the fourth electrical bus 26.4 and the fourth terminal 14.4.

Although not shown in FIG. 1, it is possible to provide, at the ends of this first conductor 21, for example at each end of this first conductor, a protective inductance which can be produced in the form of a dedicated inductive component, such as a coil. Such protective inductions play the role of inductive type current limiter, and could be provided in particular if the first conductor 21 in itself has a low equivalent inductance. In a manner known per se, other parameters can be taken into account to determine the need for the presence of such a protection inductor, such as for example the type and / or the number of adjacent conductors connected to other connections of the node considered, and / or the number and / the power of the electrical power converter (s) connected to other links of the node considered.

The link node 26.1 illustrated in Figs. 1 and 2 comprises a second link 26.12 which, in this example, is electrically connected to a second electrical conductor 22, belonging to a second power transmission line of the HVDC network unit 12. In other embodiments, such as that of FIG. 11, the second link 26.12 could be electrically connected to another electrical network unit, for example in the manner described in relation to the third link of the example of FIG. 1, or in the manner which will be described in relation to the example of FIGS. 11 A and 11 B. In both cases, the passage of a second flow of electrical power P26.12 is allowed through the second link 26.12. This second flow of power P26.12 is controlled by at least a second electrical cut-off device 28.12, associated with the second link 26.12, which has an open state and a closed state. In the example of FIG. 1, the second electrical cut-off device 28.12 is interposed between the second link 26.12 and the second electrical conductor 22.

[0074] In the example of FIG. 1, it can be seen that this second electrical conductor 22 is connected, by its distal end, to the third terminal 14.3 of the HVDC network unit 12, here by means of a third electrical bus 26.3 of the HVDC network unit 12. In this example, an electrical switching device 28.31 is interposed between the distal end of the second electrical conductor 22 and a link 26.31 of the third electrical bus 26.3. In the particular example, the third terminal 14.3 is electrically connected to a third other electrical network unit 16.3. Therefore, the third electric bus 26.3 is an external link node. An electrical cut-off device 28.33 is interposed between the third electrical bus 26.3 and the third terminal 14.3.

It is possible to provide, at the ends of this second conductor 22, for example at each end of this second conductor, a protective inductance which can be produced in the form of a dedicated inductive component, such as a coil .

The link node 26.1 illustrated in Figs. 1 and 2 also includes a third link 26.13. In this example, the third link 26.13 is electrically connected to another power grid unit. In other embodiments, the third link 26.13 could be electrically connected to another conductor of another electric power transmission line, for example as described above in relation to the second link. In both cases, the passage of a third flow of electrical power P26.13 is allowed through the third link 26.13. This third power flow P26.13 is controlled by at least a third electrical cut-off device 28.13, associated with the third link, which has an open state and a closed state. In the particular example of Figs. 1 and 2, the third link 26.13 is electrically connected to a first among the other electrical network units 16.1, at the level of the first terminal 14.1. Therefore, link node 26.1 is an external link node. In this example, the third link 26.13 is therefore electrically connected to an electric power converter 18.1 to another electrical network unit. It can therefore be qualified as an external link. In the example of FIG. 1, the third electrical cut-off device 28.13 is produced in the form of a DC voltage current cut-off device which is interposed between the third link 26.13 and the electrical power converter 18.1. The third electrical cut-off device 28.13 here comprises at least one electrical cut-off device separate from the electrical power converter 18.1. The same arrangement has been illustrated for all other external link nodes of the HVDC network unit 12 of FIG. 1.

However, for one or the other, or more of these external link nodes, or all, provision could be made for an external link to be electrically connected to an electric power converter to another electrical network unit. , without a DC voltage current cutting device interposed between the external link, for example the third link 26.13, and the electric power converter 18.1. In such a case, the power converter can also form the electrical cut-off device associated with the external link in question, here the third electrical cut-off device. In other words, in such a variant, the power converter would be structured so as to be able to perform the power cut function, without it then being necessary to provide a separate device.

[0079] Such a case is found in the example of Figs. 11 A and 11 B.

[0080] In the example of FIG. 1, and also in the embodiment of FIG.

11 A, we note that a current cut-off device 29.1, which will be termed an external cut-off device with respect to the HVDC network unit 12 considered, is electrically arranged between the electric power converter 18.1 towards the first other power grid unit 16.1 and this same other power grid unit 16.1 strictly speaking. If the other outdoor unit is an AC voltage network, the control device external cut-off 29.1 is an AC voltage cut-off device. As will be seen later, the external cut-off device 29.1 can also be used to control the power flow P26.13 in the external link of the link node considered, therefore here in the third link of the first link node. This could in particular be implemented for cases where it is desired to be able to do without a DC voltage current cutting device in the external link of a link node, here the third link 26.13.

However, we note that the link node 26.1 could be an internal link node for which the third link 26.3 would be electrically connected to another electrical conductor of the electrical network unit considered, with in reality all the connections of the link node which would be connected to electrical conductors or electrical buses of the HVDC network unit 12 considered. In such a case, the third link 26.3 would not be considered as an external link, but as an internal link of the link node considered.

The link node 26.1 illustrated in Figs. 1 and 2 has a fourth link 26.14 which is electrically connected to a third electrical conductor 23 of the HVDC network unit 12. The passage of a fourth flow of electrical power P26.14 is allowed through the fourth link 26.14. This fourth power flow P26.14 is controlled by at least a fourth electrical cut-off device 28.14, associated with the fourth link 26.14, which has an open state and a closed state. In the example of FIG. 1, the fourth electrical switching device 28.14 is interposed between the fourth connection 26.14 and the third electrical conductor 23. In the example, it can be seen that this third electrical conductor 23 is connected, by its distal end, to the second terminal 14.2 of the HVDC network unit 12, here via a second electrical bus 26.2 of the HVDC network unit 12. In this example, the distal end of the third electrical conductor 23 is connected to a link 26.21 of the second bus electric 26.2, without the interposition of an electric cut-off device. On the other hand, the second electric bus 26.2 also comprises a link 26.22 electrically connected to a second other electrical network unit 16.2, with the interposition of an electrical cut-off device. 28.22. Therefore, the second electric bus 26.2 is also an external link node. It is possible to provide, at the ends of this third conductor 23, for example at each end of this third conductor, a protective inductance which can be produced in the form of a dedicated inductive component, such as a coil.

Preferably, in particular for reasons of reduced cost, each of the electrical cut-off devices which ensures the interruption of the power flow in each link of the node in question is an electrical cut-off device of the mechanical type.

[0084] In the example illustrated in FIG. 1, it can be seen that the second terminal 14.2 is connected, within the HVDC network unit 12, only to the first terminal 14.1 and the HVDC network unit 12, here by the third electrical conductor 23.

On the contrary, in the example illustrated in FIG. 1, the HVDC network unit 12 has a further electrical conductor 24 which is connected, at a first end, to the third terminal 14.3 of the HVDC network unit 12, here via the third electrical bus 26.3. In this example, an electrical switching device 28.32 is interposed between the first end of this other electrical conductor 24 and a link 26.32 of the third electrical bus 26.3. This other electrical conductor 24 is connected, by its second end, to the fourth terminal 14.4 of the HVDC network unit 12, here via the fourth electrical bus 26.4. In this example, an electrical switching device 28.42 is interposed between the second end of this other electrical conductor 24 and a link 26.42 of the fourth electrical bus 26.4.

Similarly, it is possible to provide, at the ends of this other conductor 24, for example at each end, a protective inductor which can be produced in the form of a dedicated inductive component, such as a coil.

In the example of Figs 11 A and 11 B, the two link nodes have an identical arrangement. Taking for example the first link node 26.1 illustrated in Figs. 11 A and 11 B, it can be seen that it has a second link 26.12 and a third link 26.13 which are each electrically connected respectively to one 16.1, 16.1b of the other electrical network units, each by its own electric power converter 18.1, 18.1b. From this indeed, link node 26.1 is an external link node. In this example each of the second link and of the third external link is an external link which is electrically connected to the electric power converter.

18.1, 18.1b associated without a DC voltage current cutting device interposed between the external link and the associated power converter. The latter can form an electrical cut-off device associated with the external link in question. In other words, in such a variant, the power converter can advantageously be structured to be able to perform the power cut function, without it then being necessary to provide a separate device. However, in this example it is noted that a current cut-off device 29.1, 29.1 b, which will be referred to as an external cut-off device with respect to the HVDC network unit 12 considered, is electrically arranged in each of the other units. from the electrical network 16.1, 16.1b, between the electrical power converter 18.1, 18.1b to the electrical network unit

16.1, 16.1b and this same other electrical network unit 16.1, 16.1b itself. In the event that the other external unit 16.1, 16.1b is an AC voltage network, the external switching device 29.1 is an AC voltage switching device. Thus, the external cut-off device 29.1, 29.1b can also be used to control the flow of power in each of the two external links of the link node considered, therefore here respectively in the second 26.12 and the third link 26.13 of the first link node . This eliminates the need for a DC voltage current cutting device in these two external links 26.12, 26.13 of the first link node 26.1.

[0087] In FIG. 2, it has been illustrated that the electrical cut-off device 28.11, associated with the first link 26.11 of the first link node, is controlled by an electronic control system 30. In the example, the electronic control system 30 is arranged to control several cut-off devices belonging in particular to several separate connection nodes of the HVDC network unit 12. In certain embodiments, the electronic control system 30 will be arranged to control all the cut-off devices of the HVDC network unit 12 In some embodiments, the electronic control system 30 will be arranged to control, in addition, other equipment of the HVDC network unit 12, for example electric power converters. In certain embodiments, the electronic control system 30 will be arranged to communicate with other electronic control systems, for example electronic control systems providing control of other network units, and / or a general control system. network electronics.

In the example illustrated, the electronic control system 30 comprises several electronic control units 30.1, 30.2, 30.3, 30.4, each of which is for example dedicated to a link node of the HVDC network unit 12, at the meaning that it controls the electrical equipment associated with this link node, including for example the breaking device (s) associated with this node. Each electronic control unit 30.1, 30.2, 30.3, 30.4 can advantageously be located in the immediate vicinity of the link node to which it is dedicated. In the example, an electronic control unit 30.1, 30.2, 30.3, 30.4 is dedicated to a single link node, but provision can be made for an electronic control unit to be dedicated to a grouping of several link nodes, for example a grouping of connecting nodes geographically close to each other.

In the example, the electronic control unit 30.1 can comprise several electronic control sub-units 30.11, 30.12, 30.13, 30.13, for example each dedicated to an item of equipment, for example each to an electrical cut-off device of the link node to which the electronic control unit 30.1 is dedicated. Each electronic control sub-unit 30.11, 30.12, 30.13, 30.14 can advantageously be located in the immediate vicinity of the switching device 28.11, 28.12, 28.13, 28.14 to which it is unbound. A control sub-unit 30.11, 30.12, 30.13, 30.14, and therefore a fortiori an electronic control unit, and therefore a fortiori the electronic control system 30, can comprise one or more computer processors, computer memory, inputs / computer outputs, one or more wired or wireless computer communication channels (for example serial links, parallel links, computer communication buses, etc.). A control sub-unit 30.11, 30.12, 30.13, 30.14, and therefore a fortiori an electronic control unit, and therefore a fortiori the system electronic control 30, may include and / or be connected to electrical relays, to sensors, in particular electrical sensors such as voltmeters or ammeters, to actuators, etc. A control sub-unit 30.11, 30.12 , 30.13, 30.14 and therefore a fortiori an electronic control unit, and therefore a fortiori the electronic control system 30, can include and / or be connected to man / machine interfaces, such as: display screens, indicator lights, keyboards , buttons, switches, pointers, etc ...

[0090] It is therefore noted that the HVDC network unit 12 of FIG. 1 is a network unit which is meshed, in the sense that it has at least two points, here two terminals, which are electrically connected by two electrical paths which are at least in part distinct. In this case, the first terminal 14.1 and the fourth terminal 14.4 are connected by two separate electrical paths. A first electrical path comprises the first electrical conductor, which here directly connects the first electrical bus 26.1 to the fourth electrical bus. A second electrical path indirectly connects the first electrical bus 26.1 to the fourth electrical bus via the third electrical bus 26.3 and comprises the second electrical conductor 22 and the other electrical conductor 24 of the HVDC network unit 12. The first, the third and fourth electric buses are therefore the vertices of an electric mesh of the HVDC network unit 12.

In this way, it is understood that, in the example of FIG. 1, in normal operation of the HVDC network unit 12, electrical power can be transmitted between two terminals, here the first terminal 14.1 and the fourth terminal 14.4, along two electrical paths which are at least in part distinct. Thus, in the event of failure in a part of one of these two paths which is not common with the other path, it remains possible to transmit electrical power between the two terminals via this other path. electrical, subject to being able to electrically isolate the part of the path which is faulty.

However, the HVDC network unit can take other configurations, for example a star network unit, or even, as in the example of Figs. 11 A and 11 B, take the form of a point-to-point network unit. In Figs. 3, 4A and 4B, three configurations of the HVDC network unit 12 have been illustrated corresponding to different cut-off states of the HVDC network unit 12 in the event of a fault the first electrical conductor 21. It is noted here that it is by arbitrary choice that one chooses to describe the situation of a fault in the first electrical conductor 21, and that one could similarly describe the situation of a fault in one of the other electrical conductors of the unit of HVDC network 12, for example in the second electrical conductor 22.

In Figs 1 to 4B, as well as in Figs. 11 A and 11 B, the various breaking devices have been illustrated either in their closed state, letting the current flow, in which case they are represented in the form of a solid rectangle, or in their open state, interrupting the flow of current , in which case they are represented as a hollowed-out rectangle. In Fig. 1, the HVDC network unit 12 is in its nominal operating state and all disconnecting devices are in their closed state. [0095] In FIG. 2, the power flows at the level of the first link node 26.1 have been illustrated in the event of the appearance of an electrical fault of the earth leakage type somewhere in the first electrical conductor 21. Such a fault can for example take the form of a short-circuit between the first electrical conductor 21 and the earth, or of a short-circuit between the first electrical conductor 21 and another conductor, for example another conductor of the first power transmission line to which belongs the first electrical conductor 21. At the time of the appearance of this fault, the first electrical conductor 21 is connected to this link node 26.1 by means of the associated electrical cut-off device 28.11 which is in its closed state allowing the passage of the running. At least one other of the links of the link node is connected to another part of the network by means of the associated electrical cut-off device which is in its closed state allowing current to flow. In the example illustrated in FIG. 1, all the other links of the link node are connected to another part of the network (electrical conductor, power converter, etc.) via the associated electrical cut-off device which is in its closed state allowing current to flow . This or these other part (s) of the network are under the nominal operating voltage of the HVDC electrical network unit 12. In this way, due to the appearance of the electrical fault in the first electrical conductor 21, for example an electrical fault of the short-circuit type with the earth, all the electrical power circulating in these other parts of networks, and / or all the energy accumulated in these other parts of the network, for example under inductive form or in capacitive form, is likely to be diverted to follow the path of least electrical resistance through the first electrical conductor 21 to be evacuated through the fault that appeared in the first electrical conductor 21. To avoid this, it is therefore necessary to electrically insulate the first electrical conductor, by interrupting the current by opening certain cut-off devices.

We have seen that certain strategies for eliminating faults provide, in such a case, the opening of all the cut-off devices of the HVDC network unit 12 which connect the HVDC network unit 12 to other network units, which interrupts all current flow through the HVDC network unit 12. This configuration, shown in FIG. 3, causes the cut-off of all transmission of electric power between the other network units which are connected to each of the terminals of the HVDC network unit 12, therefore is very penalizing. It can in fact be seen that all the cut-off devices 28.13, 28.22, 28.33 and 28.43 associated with external links, of all the external link nodes of the HVDC network unit 12, are open. In addition, the cut-off devices 28.11 and 28.41 at both ends of the faulty conductor are also open. In other words, such a strategy applies the same type of action at the level of each of the nodes of the HVDC network unit 12, in any case at least of each of the external nodes of the HVDC network unit 12. It is therefore non-selective at the level of the HVDC network unit 12. A so-called “partially selective” strategy, in which the HVDC network unit is separated into several protection zones, would apply the same type of action at the level of each of the nodes of the protection zone of the HVDC network unit, in which the fault has appeared, in any case at least of each of the nodes external to this protection zone.

On the contrary, the invention proposes a fault isolation method which makes it possible, at least in certain cases, to implement a targeted opening action without requiring the use of fast-acting switching devices or oversized in relation to the breaking capacity that would be necessary for the isolation of the majority of faults.

First of all, the fault isolation method which will be described below ensures a differentiated management of the opening actions at the level of different link nodes of the HVDC network unit, in particular at the level of different external link nodes of the HVDC network unit, in the form of opening actions of potentially different type at the level of different nodes, or even of potentially different type at the level of each node. Preferably, the fault isolation method which will be described below ensures a differentiated management of the opening actions at the level of each external link node of the HVDC network unit, or even at the level of each link node. of the HVDC network unit, in the form of potentially different type of opening actions at each node. This differentiated management corresponds to the capacity of the fault isolation process to trigger opening actions of different types at the level of different link nodes, including at the level of two link nodes connected to two opposite ends of the same one. an electrical conductor exhibiting an electrical fault, for example by triggering a full opening action at one link node and a targeted opening action at another link node of the same HVDC network unit, including included when the two connecting nodes are each connected respectively to one of the two opposite ends of the same electrical conductor exhibiting an electrical fault. Of course, this differentiated management does not prevent, for a given fault, the method leading to the implementation of opening actions of the same type, that is to say total opening actions or targeted opening actions, at the level of two different connecting nodes of the HVDC network unit, including at the level of two connecting nodes respectively each connected to one of the two opposite ends of the same electrical conductor having a electrical fault, or even at more than two different link nodes, or even at all link nodes of the HVDC network unit.

This is illustrated in FIG. 4A where we see for example that all the breaking devices associated with the fourth link node 26.4 are maintained in their closed state, except that which is associated with the link to which is connected the faulty electrical conductor, which represents a targeted opening action at the level of this fourth link node, while the fault isolation process has triggered a full opening action at the level of the first link node 26.1, in causing an opening of a breaking device for each of the links of the node. Such an isolation method therefore comprises local processes which each determine, for a given link node, the type of opening action to be implemented at the level of this link node. Two local processes can of course be linked, one being able for example to have an influence on the other. However, provision could be made for the two processes to be independent of each other as regards the determination of the type of cut to be implemented at their respective link nodes.

[0100] In a strategy for eliminating faults according to the invention, the implementation of each of the local processes, at the level of each of the nodes, can lead, depending in particular on the characteristics of the fault, to the fact that, overall , this results in an opening action of the same type, total or targeted, at all the link nodes which are affected by the fault. In such a strategy, provision can be made not to interrupt the current at the level of the other link nodes, not directly affected by the fault, which is illustrated in FIG. 4A where we see for example that the breaking devices associated with the third link node are maintained in their closed state, while the fault isolation method has triggered a total opening action at the first link node 26.1.

[0101] However, the most favorable situation, in the event of a fault appearing in the first electrical conductor, is that of a selective cut-off as illustrated in FIG. 4B in which it can be seen that the fault in the first conductor is isolated by opening only the two switching devices 28.11, 28.41 arranged at both ends of the faulty electrical conductor. This is implemented in each of the two link nodes which are arranged at both ends of the conductor in which the electrical fault has arisen, in the form of a targeted protective action in which, in each of the two nodes, only the flow power in the link which is connected to the faulty conductor is interrupted. However, the implementation of such a targeted opening action, as envisioned in the prior art, required the implementation fast-acting or oversized breaking devices in relation to the breaking capacity that would be necessary for the isolation of the majority of faults, and therefore expensive.

[0102] We will therefore now describe in more detail an example of a method of insulating the first conductor 21 of the first power transmission line in the HVDC electrical network unit 12 considered.

At the level of a link node considered, to which the first conductor is connected, the method comprises the monitoring of at least one monitored parameter relating to the current and / or to the electric potential in the first conductor 21. In the example which will be described, the link node considered is the first link node 26.1. We note here that we are interested in the first electrical conductor 21 which is connected to the first link 26.11 of this first link node 26.1. This follows from the arbitrary choice to consider that it is in the first electrical conductor 21 that an electrical fault appears. If we had chosen to deal with the case of a fault in the second electrical conductor 22, we would provide for the monitoring of at least the monitored parameter relating to the current and / or the electrical potential in the second electrical conductor 22.

In addition, it will advantageously be provided that what is described here for the first link node is also implemented for the opposite link node to which the faulty electrical conductor is connected, namely, in the example, the third link node.

Of course, provision can advantageously be made that what is described here for the first link node is also implemented in yet other nodes of the HVCD network unit 12, in particular the nodes to which at least one conductor is connected in which a fault is likely to occur.

Preferably, provision will be made for what is described here for the first link node is also implemented for all the nodes of the HVCD network unit 12, external and internal, to which at least one electrical conductor is connected in which a fault is likely to occur.

The method firstly comprises a step of detecting the appearance of a fault in the first electrical conductor which is here taken as an example. Various known methods can be used, for example methods as described in the document I. Jahn, N. Johannesson and S. Norrga, "Survey of methods for selective DC fault detection in MTDC grids", 13th IET International Conférence on AC and DC Power Transmission (ACDC 2017), Manchester,

2017, pp. 1-7, doi: 10.1049 / cp.2017.0041. The method may for example include a first comparison of the at least one monitored parameter against a first conductor fault criterion for this monitored parameter. Typically, the step of detecting the appearance of a fault in the first electrical conductor returns at least one item of information on the presence of a fault or the absence of a fault in this first conductor 21. The information on the presence of a fault or d The absence of fault can be binary. However, we will see that it can have more than two levels.

[0108] The step of detecting the appearance of a fault in the first electrical conductor makes it possible to determine whether a cutting action must be implemented. Typically, the step of detecting the appearance of a fault in the first electrical conductor makes it possible to determine whether at least the electrical breaking device 28.11 which associated with the first link 26.11 of the first link node 26.1 must be brought into its open state.

The method further comprises, in addition to the step of detecting the appearance of a fault in the first electrical conductor, at least one step of determining the level of criticality with respect to the link node. considered, here the first link node 26.1. The purpose of this step is to determine which of at least two different opening actions should be implemented at the node in question. This step returns information on the level of criticality of the fault with respect to the link node considered, that is to say information relating to the criticality of the fault with respect to the link node considered. The fault criticality information may be binary (eg critical or non-critical) or may have more than two levels of criticality.

The criticality level determination step is a step which is associated with a link node to which the faulty electrical conductor is connected, and it can therefore form part of a process specific to this link node. The step of determining the level of criticality can comprise a comparison of at least one monitored parameter with respect to a fault criticality criterion.

Generally, the fault criticality criterion can be determined in advance rather than during operation of the installation. We will see that there are different ways of determining this fault criticality criterion, for example by analytical methods, by simulation methods, by experimental methods or by analysis of pre-existing data.

The step of detecting the appearance of a fault in the first electrical conductor and the step of determining the level of criticality are implemented by computer, preferably in the electronic control system, for example in the 30.1 electronic control unit associated with the first link node 26.1. The step of detecting the appearance of a fault in the first electrical conductor and / or the step of determining the level of criticality can for example be implemented by computer both, or both. or the other, in the electronic control sub-unit 30.11 associated with the electrical cut-off device 28.11 which is associated with the first link 26.11 of the first link node 26.1. In one embodiment, one of the step of detecting the occurrence of a defect in the first electrical conductor or the step of determining the criticality level may be implemented by computer in the electronic subunit. control 30.11 associated with the electrical cut-off device 28.11 which is associated with the first link 26.11 of the first link node 26.1, while the other of the two steps can be implemented by computer in the electronic control unit 30.1 associated with the first link node 26.1, or even in the electronic control system 30, outside the electronic control sub-unit 30.11 associated with the electrical cut-off device 28.11 which is associated with the first link 26.11 of the first link node 26.1.

[0114] The fault criticality criterion may therefore be part of computer data recorded by computer in the electronic control system 30, or accessible to this system. The step of detecting the appearance of a fault in the first electrical conductor, and the step of determining the level of criticality with respect to the link node considered can be carried out as a function of the value. of the same monitored parameter. As an alternative, the step of detecting the appearance of a fault in the first electrical conductor, and the step of determining the level of criticality can be carried out as a function of the value of two different monitored parameters. In practice, for one or the other of the stages, or for one and the other of the stages, the monitored parameter can be selected from among the intensity of the current in the first conductor 21, the derivative with respect to time of the intensity of the current in the first conductor 21, the electric potential of the first conductor 21, and the derivative with respect to time of the electric potential of the first conductor 21, or their combinations. The electrical potential of the first conductor 21 can typically be taken into account through the voltage between this first conductor 21 and the earth, or through the voltage between this first conductor 21 and another conductor, in particular another conductor of the same electric power transmission line.

[0116] Typically, the monitored parameter is measured, or determined from a measurement. Thus, as shown, the first electrical conductor 21 is preferably fitted with a measuring device 32.11 delivering a measurement result used for determining the monitored parameter. The measuring device may in particular include a voltmeter and / or an ammeter. Note that, in some cases, the monitored parameter for the first conductor 21 can be measured or be determined from a measurement of the first link 26.11 to which it is connected. This will for example be possible in cases in which the first conductor is not equipped with protective inductors at its ends.

In the case where the step of detecting the appearance of a fault in the first electrical conductor and the step of determining the level of criticality are carried out as a function of the value of the same monitored parameter, they can each include a comparison with two threshold levels for that parameter. Likewise in this case, the two steps can return common information, the information then preferably having three levels or more than three levels, for example at least the following levels: absence of fault, non-critical fault and critical fault, or which can be interpreted in the form of three such levels.

It is noted that the step of detecting the appearance of a fault in the first electrical conductor, and the step of determining the level of criticality can be successive steps, the step of determining the level of criticality being implemented after the step of detecting the appearance of a fault in the first electrical conductor. For example, in some embodiments, the criticality level determination step is performed only after the step of detecting the occurrence of a fault in the first electrical conductor has returned fault presence information in the first electrical conductor. the first electrical conductor. Alternatively, the step of detecting the occurrence of a fault in the first electrical conductor, and the step of determining the criticality level may be parallel steps.

Depending on the fault criticality information returned, with respect to the link node, by the criticality level determination step, the method implements either a targeted opening action, or full opening action, as described below.

[0120] In certain cases, in the presence of a fault considered critical, the method triggers the triggering, at the level of the link node in question, of a total opening action of the link node in question.

In an action of total opening of the node considered, the method is not satisfied, at the level of the link node considered, here the first link node 26.1, to open the electrical cut-off device associated with the first link , therefore associated with the electrical conductor which has the defect. Rather, in a link node comprising three links, the method causes all power flows in all links of the node to be interrupted.

In the example illustrated in FIG. 4A, in an action of total opening of the link node considered, all the electrical cut-off devices 28.11, 28.12, 28.13, 28.14 associated with a link 26.11, 26.12, 26.13, 26.14 of the link node 26.1 considered are brought from their state closed to their open state. [0122] In the example illustrated in FIG. 11 B, the action of total opening of the link node considered is carried out by causing the opening of the electrical cut-off device 28.11 associated with the first link 26.11, but also by causing the opening of the electrical cut-off devices 29.1, 29.1 b associated with each of the other two links 26.12, 26.13 of the link node 26.1 considered.

Advantageously, provision will be made for, in a total opening action of the node considered, the first electrical cut-off device 28.11, therefore the one which is interposed between the link node considered and the electrical conductor in which the fault occurs, is brought from its closed state to its open state after the electric power flows P26.12, P26.13, P26.24 through the other links of the link node under consideration, other than the first link 26.11, have been interrupted. This makes it possible in particular to go in the direction of reducing the current which will have to be cut in the first electrical switching device 28.11, which will no longer be supplied by the other links of the link node 26.1 considered.

[0124] Preferably, in a total opening action of the node in question, the first electrical cut-off device 28.11 is brought from its closed state to its open state after all the other electrical cut-off devices 28.12, 28.13, 28.14 associated with a link of the link node other than the first link 26.11 have been brought from their closed state to their open state. For example, provision could be made for the method not to trigger the opening of the first electrical breaking device 28.11, which is the one interposed between the link node in question and the electrical conductor in which the fault occurs, only after the interruption. electric current in all other links of the link node other than the first link. The interruption of the electric current in a link can be measured, for example by an ammeter arranged in the link. As a variant, provision could be made for the method to trigger the opening of the first electrical switching device 28.11 only after the expiration of a time period, for example between 2 and 50 milliseconds, preferably between 5 and 15 milliseconds. , following the triggering of the opening of all the other electrical cut-off devices associated with a link of the link node other than the first link. The goal is, in such an action of total staged opening of the node considered, to first interrupt any current flow in all the links other than the first link before triggering the opening of the first electrical cut-off device.

[0125] However, the step of determining the fault criticality may return non-critical or weakly critical fault information. In such a case, the method can then trigger, at the level of the link node considered, a targeted opening action, in which the method causes the passage of the first electrical breaking device 28.11 from its closed state to its open state, in order to electrically isolating the fault with respect to the link node considered, while maintaining at least the second and the third electrical cut-off device each in their closed state. In the example of Fig. 1, this leads in particular to making it possible to maintain the second power flow P26.12 and the third power flow P26.13 respectively in the second and in the third link of the link node considered. In a link node comprising more than three links, the method can thus maintain in their closed state all the electrical cut-off devices 28.12, 28.13, 28.14 which are associated with a link 26.11, 26.12, 26.13, 26.14 of the link node 26.1 considered. , other than the link of this link node considered to which the faulty electrical conductor is connected.

[0126] In the example illustrated in FIG. 11 A, the targeted opening action is performed by causing, at the link node considered, only the opening of the electrical cut-off device 28.11 associated with the first link 26.11, but without causing the opening of the electrical cut-off devices 29.1 , 29.1b associated with each of the other two links 26.12, 26.13 of the link node 26.1 considered. In this configuration, the targeted opening action therefore makes it possible to respectively maintain each of the other electrical network units 16.1, 16.1b which are connected to this node in electrical connection with the AC stage of the electric power converter 18.1, 18.1b that is associated with it. This makes it possible to limit the disturbances which are induced in these other electrical network units 16.1, 16.1b.

[0127] The flowchart of FIG. 5 is an illustration which describes the main steps of an example of a part of a method of insulating a first conductor of a first power transmission line in a considered electrical network unit. In step 100, the process can start with the step of determining the presence of a fault in an electrical conductor of the HVDC network unit 12. In step 110, the method may include a step of determining the electrical conductor in which the fault has appeared. The combination of these two steps forms the step of detecting the appearance of a defect in the first electrical conductor as described above. In fact, it is possible to consider arbitrarily, for the fault considered, that the electrical conductor in which the fault has appeared is the first electrical conductor 21 within the meaning of the above description. When another fault appears in another conductor connected to the same node, this other conductor would then be considered as the first electrical conductor.

The method then comprises step 120 which is a step of determining the level of criticality of the defect with respect to the link node considered. As seen above, this step 120 can be carried out, optionally in parallel, for several connection nodes, in particular for the connection nodes which are for example at each end of the electrical conductor in which the fault has appeared. For the link node considered in this graph, this step 120 therefore returns fault criticality information with respect to the link node considered. If this information leads to consider that the fault is not critical, the method can then continue at step 130 by triggering, at the level of the node considered, a targeted opening action in which, for the node considered, only the breaking device which is associated with the link to which the faulty conductor is connected, is brought from its closed state to its open state. Once this action has taken place, the isolation process can be considered to have been completed for the link node considered, which leads to the end step 140. If, on the contrary, step 120 returns fault criticality information which leads to consider that the defect is critical with respect to the link node considered, the method can then continue by triggering in step 150 a total opening action of the node considered, as described above. As seen above, this step 150 may include a first step in which the method triggers the interruption of all the power flows in all the links of the link node considered other than the first link, for example by opening all of them. other electrical cut-off devices associated with a link of the link node considered other than the first link to which is connected the electrical conductor in which the fault appeared, then a second step in which the opening of the first electrical breaking device 26.11 which is the one which is triggered is triggered. is interposed between the link node considered and the electrical conductor in which the fault occurs. A time delay can be provided between these steps.

At the end of this action of total opening of the node in question, in step 150, it can be considered that the electrical conductor in which the fault has appeared is isolated from the rest of the HVDC network unit 12, and that the flow of a fault current has been interrupted. However, due to the total nature of the opening action at the considered link node, the electric power flows in the HVDC network unit 12 may have been significantly disturbed. Now, since the electrical conductor in which the fault has appeared is isolated, provision can be made for the method, in a step 170, to close all the other electrical cut-off devices associated with a link of the link node considered other than the first link to which is connected the electrical conductor in which the fault appeared. This possibly allows the electrical conductors or other network elements that are not affected by the fault to be put back into service. Before proceeding to this step 170 of reclosing the other electrical cut-off devices, it may be preferable to provide a timing step 160, the duration of which may be for example between 20 and 500 milliseconds, for example between 40 and 200. milliseconds. This timing step makes it possible to ensure that the first breaking device, associated with the faulty conductor, has operated correctly. In addition, this time delay can be useful to allow the breaking device to be ready for a possible reopening after closing in the event of non-isolation of the fault. Once this step 170 of re-closing the other electrical cut-off devices has been carried out, the isolation process can be considered to have been completed for the link node considered, which leads to the end step 140. It is further noted that that the criticality information and / or the type of opening action which results from it, total or targeted, can be taken into account by other elements of the infrastructure, in particular by power converters associated with the nodes external links. For example a converter which would have been brought to a blocking situation can be released more or less quickly depending on the criticality information and / or the type of opening action that results from it. This information can circulate through the electronic control system 30.

[0130] When an opening action, total or targeted, is triggered at a connecting node to which a faulty electrical conductor is connected, therefore at one end of the conductor, the method also causes the opening of at least one device. electrical cutoff at the other end of the faulty electrical conductor. If this other end of the faulty electrical conductor is connected to another link node, the same process as that described above can be applied, but to this other node. Thus, depending on fault criticality information for this other node, we can trigger at this other node, a targeted opening action, or a total opening action of this other node. This is what is illustrated in Figs. 4A and 4B. It is illustrated in FIG. 4A the case of a fault which appears in the first electrical conductor at a point which is close to the first link node and remote from the fourth link node and which, for this reason in particular, may be a critical fault with respect to of the first link node and not critical to the fourth link node. In this case, the isolation process therefore led to a full open action at the first link node, and, at the fourth link node, to a targeted open action. A similar situation is illustrated in Fig. 11 B in which the isolation process resulted in a full open action at the first link node, and, at the second link node, a targeted open action.

[0131] It has been illustrated in FIG. 4B the case of a fault which appears in the first electrical conductor at a point which both far from the first link node and far from the fourth link node (for example substantially in the middle of a very long overhead conductor) and which , for this reason in particular, can be considered as a non-critical defect both vis-à-vis the first link node and vis-à-vis the fourth link node, leading, at the level of these two link nodes, to a targeted opening action. It is noted that, in both cases, the isolation process kept the breaking devices closed at the level of the other connecting nodes to which the electrical conductor presenting the fault is not connected, thus maintaining the flow of electrical power in these link nodes.

[0132] A similar situation is illustrated in FIG. 11 A in which the isolation process led at the first and second link node to a targeted opening action in which the isolation process kept closed the external cut-off devices 29.1, 29.1b associated with the connection to which the electrical conductor exhibiting the defect is not connected, these other connections being external connections.

The fault criticality information returned by the fault criticality determination step, with respect to a link node considered, can be determined as a function of a prediction, from the monitored parameter. , of the evolution of the current through the first electrical cut-off device following the appearance of the fault and of the capacity of the first electrical cut-off device to cut this current. Indeed, according to the nature of the fault, in particular according to its fault resistance, and according to the fault position in the electrical conductor, with respect to the link node considered, it is possible to calculate that the evolution of the current in the first link, and in particular the rate of change of the current in this first link will be different. Thus, for two electrical faults in a given electrical conductor, which are assumed to be at the same location of the electrical conductor, a fault with a higher fault resistance will cause a slower current variation than a fault with a comparatively fault resistance. weaker. Likewise, for two electrical faults in a given electrical conductor, which are assumed to have the same fault resistance, a fault located further from the link node considered will cause a slower current variation than a fault located comparatively less far away. of the link node considered.

[0134] In certain embodiments, said at least one monitored parameter is a value of the derivative, with respect to time, of the electric potential of the first conductor. Preferably, said at least one monitored parameter is a value of the derivative, with respect to time, of the electrical potential of the first conductor at the proximal end of this first conductor, that is to say at that which is the most close to the link node considered. This electric potential of the first conductor 21 can typically be taken into account by means of the voltage between this first conductor 21 and the earth, or through the voltage between this first conductor 21 and another conductor, in particular another conductor of the same electric power transmission line.

In certain embodiments, it may be considered that an electrical fault in an electrical conductor, the electrical fault being for example characterized by the combination of the location of the fault and of the fault resistance, is highly critical with regard to with respect to a link node if it leads to the generation, in the electrical conductor in question, of a fault current which exceeds the capacity of the electrical breaking device which is interposed between the electrical conductor and the node link considered. The breaking capacity of the electrical breaking device can be defined as depending on a maximum value of the intensity of the current that this breaking device can interrupt, and on an operating time of the device. In fact, in particular when the breaking device is a mechanical breaking device, it takes a certain time for the breaking device to reach its open state in which it is effectively capable of breaking a current having this maximum intensity. Typically, a mechanical cut-off device reaches its open state in which it is effectively capable of cutting a current having this maximum intensity within a period, called the operating time, which is for example between 5 and 50 milliseconds, preferably between 5 and 50 milliseconds. and 15 milliseconds after triggering to switch from its closed state to its open state. Typically, following the appearance of a fault in the conductor, the current through the cut-off device will tend to increase rapidly. In the initial state when the fault appears, it can be assumed that the electric current in the first conductor, therefore through the breaking device, is equal to the nominal current in the conductor. If the intensity of the current through the breaking device is caused, by the appearance of the fault, to increase, it must be checked that the increase will not be so rapid that the value of the current exceeds, within this time. operation of the electrical cut-off device, maximum value of the intensity of the current that this cut-off device can interrupt. In order to be sure of being able to cut an increasing current, it is therefore necessary to be able to predict whether, before the end of the operating time of this electrical cut-off device, the intensity of the current at the through the breaking device remains below the maximum value of the intensity of the current that this breaking device can interrupt. It should be noted that one does not need to know the operating time in an exact manner since in practice, an increased value can be taken into account, for safety reasons. An estimated value of the operating time can thus be determined for example by empirical tests or by simulation and this estimated value can then be assigned a safety coefficient and / or increased by a safety margin to take into account in the method as described. Such a safety margin may be of the order of a few milliseconds. Thus, in practice, in the field of direct high voltage, for an electrical cut-off device of the mechanical type, in which the electrical opening corresponds to the spacing of two electrodes movable relative to each other, it is can take into account an operation time between 10 to 25 milliseconds for example.

Thus, in a method according to the invention, the rule can be implemented according to which, if the fault criticality determination step returns fault criticality information signifying that the electrical fault detected is highly critical for a node link considered, the method will implement, at the level of this link node, a total opening action, of the type described above. On the other hand, all the faults leading to the generation, in the electrical conductor in question, of a fault current which, in the operating time of this electrical breaking device, does not exceed the maximum value of the current of the current that can be interrupted by the electrical breaking device which is interposed between the electrical conductor and the node considered, could be considered as weakly critical or non-critical faults for the link node considered. Thus, in a method according to the invention, the rule can be implemented according to which, if the fault criticality determination step returns fault criticality information signifying that the detected electrical fault is non-critical for a link node considered , the method will implement, at this link node, a targeted opening action of the type described above.

A possible approach will now be described for determining the criticality of a fault in an electrical conductor, with respect to a link node. considered, with the assumption that an electrical fault has been detected in the first electrical conductor 21.

As indicated above, this approach comprises the step of predicting, from the parameter monitored at the time of the appearance of the fault or immediately after, whether, before the end of the operating time of this electrical switching device , the intensity of the current through the first breaking device remains less than the maximum value of the intensity of the current that this breaking device can interrupt.

[0139] First, it is possible to determine a law of evolution of the current flowing through the breaking device 28.11 just after the appearance of the fault. This determination is made upstream, for example during the design of the HVDC 12 network unit.

[0140] This approach is described here for the case where the electrical conductor is an overhead conductor or essentially consists of an overhead conductor. Therefore the first electrical conductor 21 can be modeled as a conductor having a linear resistivity r'21 and a linear inductance G21. We assume that an electrical fault appears at a fault point df21 of the first electrical conductor which is located at a distance Ddf21 from the electrical breaking device 28.11 which is associated with the link 26.11 of the first link node 26.1. The electrical fault can be modeled as the closing of an earth connection through a fault resistor Rdf, the closure corresponding to the closing of an Sdf switch at the time of the appearance of the fault.

[0141] Under these assumptions, it is considered that the portion of the first electrical conductor has in itself an equivalent resistance R21df = Ddf21 x r'21, and an equivalent inductance L21df = Ddf21 x G21. We are therefore working here in the context of a modeling in concentrated parameters.

If the electrical conductor 21 exhibited a significant capacitance, it could be taken into account. This would be the case, for example, for a conductor formed from an underground cable or comprising a section formed from an underground cable. In the example illustrated, we have chosen to ignore the capacitance of the electrical conductor 21, which is acceptable for the case where it is an overhead conductor. FIG. 6 illustrates the case where one would have arranged, at the end of the electrical conductor which is connected to the link node 26.1, a protective inductor Lp in order to limit the variations of current in the conductor. In the absence of such an induction of protection, we will therefore have Lp = 0.

In the proposed model, we model all the other elements which are connected to the first link node 26.1 by an ideal voltage source VS, which delivers a voltage Udc which is the nominal voltage of the network unit 12, therefore for example a high continuous voltage greater than 75,000 volts.

With such a model, when the fault appears, the voltage source VS therefore delivers its voltage to earth through a system which has an equivalent resistance R = R21df + Rdf and an equivalent inductance L = L21df + Lp .

It is noted that in this part of the modeling, it is possible to ignore the propagation of the wave in the conductor, in particular thanks to the fact that the characteristic impedance Zc of an overhead conductor is sufficiently high so that l 'one can consider, in this part of the modelization, that the current wave is not very important.

In this way, the current i (t) which circulates through the breaking device 28.11 follows the following law of evolution, as a function of time t: i (t) = iO + (Udc / R) x ( 1 -e ^L (- (R / L) xt)) where iO is the current before the fault.

When we consider the technical specifications of the electrical breaking device 28.11, such as its operating time Te and its current breaking capacity Imax, it is possible to check whether the condition for successful opening, namely the effective interruption of the current flowing in the first electrical conductor 21, is validated for different values of the torques (Ddf21, Rdf) associating on the one hand the distance Ddf21 between the fault point df21 and the breaking device 28.11 and d on the other hand the fault resistor Rdf. By scanning the different pairs of possible values for, on the one hand, the distance Ddf21 between the fault point DF21 and electrical breaking device 28.11 and on the other hand the fault resistance Rdf, we can, by a calculation implementing the law evolution of the above current, determine for each pair of values whether or not the electrical breaking device 28.11 is capable of cutting the fault current which settles in the first electrical conductor 21. For example, it can be ensured that, at the instant corresponding to the breaking time Te, the current i (Tc) in the illustrated circuit is less than the current breaking capacity Imax of the electrical breaking device 28.11. This determination is made upstream, for example during the design of the HVDC network unit 12.

[0149] FIG. 7 is an example of a map, in the plane defined by on the one hand the distance Ddf21 between the fault point df21 and the electrical breaking device 28.11 and on the other hand the fault resistor Rdf, which illustrates two zones C and NC separated by a border curve (Ddf21, Rdf) min. The boundary curve (Ddf21, Rdf) min is formed from all the pairs of values (Ddf21, Rdf) for which the electrical breaking device 28.11 is at the maximum of its current breaking capacity. This mapping is established upstream, for example during the design of the HVDC network unit 12. Of course, it can be enriched and / or specified with experimental data, possibly acquired during the operation of the. HVDC network unit 12.

[0150] The NC zone is the locus of all the pairs of values (Ddf21, Rdf) for which the electrical cut-off device 28.11 is able to cut the fault current which settles in the first electrical conductor 21 following the appearance of the fault. For all the pairs of values (Ddf21, Rdf) in the NC zone, the defects characterized by the pair of values (Ddf21, Rdf) can therefore be considered as not being critical with respect to the first link node, which will therefore make it possible, for such defects, to implement, at the level of the first link node, a targeted opening action. It can be seen that the faults exhibiting a large distance Ddf21 between the fault point df21 and the electrical breaking device 28.11, or exhibiting a large fault resistance Rdf, can be considered as being non-critical faults with respect to the first node. link.

On the contrary, the zone C is the locus of all the pairs of values (Ddf21, Rdf) for which the electrical breaking device 28.11 is not able to cut the fault current which settles in the first. electrical conductor 21 following the appearance of the fault. For all the pairs of values (Ddf21, Rdf) in zone C, the faults characterized by the pair of values (Ddf21, Rdf) can therefore be considered as being critical with respect to the first link node. It can be seen that the faults exhibiting a small distance Ddf21 between the fault point df21 and electrical breaking device 28.11 and also exhibiting a low fault resistance Rdf, can be considered as being critical faults with respect to the first link node , for which it is preferable to implement, at the level of the first link node, a total opening action.

[0152] On the border curve (Ddf21, Rdf Ddf21) min, one can note a minimum value Rdfmin of the fault resistance Rdf beyond which the faults can be considered as being non-critical faults with respect to the first link node. Likewise, on the border curve (Ddf21, Rdf) min, one can note a minimum value Ddf21min of the distance Ddf21 between the fault point df21 and electrical breaking device 28.11 beyond which the faults can be considered as being non-critical faults with respect to the first link node. These two values Rdfmin and Ddf21min will be used in the next step to define an appropriate threshold for the monitored parameter.

[0153] In fact, the step of determining the level of criticality can comprise the comparison of at least one monitored parameter with respect to a fault criticality criterion. In the example which will be described, the monitored parameter is the derivative, with respect to time, of the voltage of the first link with respect to the earth.

This derivative with respect to time of the voltage can be evaluated from the measurement of the voltage in the first electrical conductor 21, near the first link node 26.11, for example with the voltmeter 32.11 illustrated in FIG. 2. In the case where the first electrical conductor 21 is provided with a protective inductor Lp at its proximal end via which it is connected to the link node in question, the voltage of the first conductor 21 will preferably be monitored upstream of the. protection inductance in the direction going from the first conductor 21 to the link node considered. In this same case where the first electrical conductor 21 is provided with a protective inductor Lp at its proximal end via which it is connected to the link node considered, we can choose to monitor the voltage between the two terminals of the protection inductor Lp.

First of all, the method can calculate at each instant an instantaneous derivative value with respect to the time of the voltage, from the measurement of the voltage V32, for example by using a Savitzki-Golay filter ( SGF) whose standard equation would then be: dV32 / dt (k) = ((- 4) V32 (k-8) + (- 3) V32 (k-7)

+ (- 2) V32 (k-6) + (- 1) V32 (k- 5) + 0 V32 (k-4)

+ V32 (k-3) + 2 V32 (k-2) + 3 V32 (k-1)

+ 4 V32 (k) / 60) / AT, with k: the sequence number of a V32 (k) measurement of voltage V32 at a given time

DT: the time difference between two successive measurements V32 (k) and

V32 (k + 1).

The calculation of the derivative by using a Savitzki-Golay filter has advantages in terms of noise elimination and reliability. However, other methods of evaluating the instantaneous value of the derivative could be used instead.

The calculation of the derivative of the voltage V32 is therefore done in real time in the installation, for example in the electronic control system 30, for example in the electronic control unit 30.1, dedicated to the first link node 26.1, possibly in an electronic control sub-unit 30.11 dedicated to the first electrical switching device 28.11.

When designing the HVDC network unit 12, it is possible to establish a rule making it possible to determine a link between the instantaneous value, at the time of the appearance of the fault or immediately after, that is to say in the few milliseconds which follow the appearance of the fault, of the monitored parameter, and the capacity that the first breaking device will have to cut this current which is in the process of appearing.

[0159] The document "Nonunit Protection of HVDC Grids With Inductive DC Cable Termination", by Willem Leterme, Jef Beerten, and Dirk Van Hertem, published in IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 31, NO. 2, APRIL 2016, confirms that the most stringent requirement for a selective fault elimination strategy in a DC high voltage network is operating speed, with fault elimination times typically on the order of several milliseconds. This is due to the characteristics of the fault currents under direct voltage, which show a high rate of rise and large value in steady state. The fault must therefore be isolated very quickly. It also confirms that the protection inductors can be arranged in series with the devices to extend the time available to manage to isolate the fault. However, even under these conditions, the delay remains a few milliseconds or at best a few tens of milliseconds. To obtain the required operating speed, the detection and discrimination of the faults are advantageously carried out during the transient phase which immediately follows the appearance of a fault in the electrical conductor. The detection and discrimination of the faults are advantageously carried out in a period of time which is less than 3 ms, preferably less than 2 ms, for example in a period of one millisecond after the appearance of the first initial overvoltage wave. at the measuring point. This transitional phase is characterized by the presence and circulation of traveling waves.

[0160] According to one example, we can determine a law of evolution of the derivative, with respect to time, of the voltage by an analytical approach. To do this, the system can be modeled as illustrated in FIG. 8. In this FIG. 8, the first electrical conductor 21 has been modeled when a fault occurs at point df21. An initial overvoltage Vf (0+) at the location of the fault can be described by the following equation, where Zc (s) represents the characteristic impedance, as a function of the frequency s in the Laplace domain, of the first electrical conductor 21 in which the fault appeared, Rdf the fault resistance and Vf (O-) is the voltage at point df21 just before the appearance of the fault:

Vf (0+) = [Zc (s) / (Zc (s) +2 Rdf)] x Vf (0-)

[0161] It can be recalled that the characteristic impedance Zc (s) can be defined, if the resistivity of the conductor is neglected, as being given by the relation

Zc (s) = square_root (G21 (s) / c'21 (s)) where 21 (s) is the linear inductance of the first conductor 21 and c'21 (s) its linear capacitance, as a function of the frequency s in the area of Laplace. By moving along the first electrical conductor towards the end of the first electrical conductor which is connected to the link node considered, the initial overvoltage undergoes an attenuation, defined by a propagation function Y (s). The initial overvoltage displacement wave Vi (l, s) in the Laplace domain is described by the following equation, where I is the distance between the fault and the conductor terminal and s the Laplace variable:

Vi (l, s) = (- Vf (0+) / s) e ^A (- Y (S) I)

In the example, the possibility of the presence of a protection inductor Lp has been taken into account, in which case the reflection at the level of the inductor LP can also be taken into account, this reflection being able to be described by a reflection coefficient K (s) which, in the Laplace domain, can be of the following form:

K (s) = (s Lp - Zc (s)) / (s Lp + Zc (s))

[0164] Of course, as illustrated in FIG. 8, other endings are possible which could be taken into account in determining the reflection coefficient. For example, we can take into account the characteristic impedance Zadj of other adjacent conductors which are connected to the same link node considered, as well as their possible protection inductances Ladj. Likewise, the characteristic impedance Zconv of the converter (s) connected to the same link node considered can be taken into account, thus giving another value of the reflection coefficient K (s). This reflection coefficient depends on the characteristic impedance Zb of the assembly which is connected to the considered end of the electrical conductor 21 in which the fault has appeared. Here, this set therefore includes the other adjacent conductors which are connected to the same link node considered, their possible protection inductors Ladj, and the converter (s) linked to the same link node considered. In this case, the reflection coefficient K (s) can be written:

K (s) = (Zb (s) - Zc (s)) / (Zb (s) + Zc (s))

[0165] In the example of FIG. 8, we can thus have:

Zb (s) = s Lp + {Zconv (s) x (s Ladj + Zadj (s))} / {Zconv (s) + s Ladj + Zadj (s)}

With this formulation, the voltage at the end of the first electrical conductor is the superposition of the initial surge wave and its reflection, and can therefore be written, always in the domain of Laplace:

V32 (I, s) = Vi (l, s) x [1 + K (s)]

Therefore, the derivative of the voltage V32 at the end of the first conductor can therefore be written: d / dt (V32 (I, s)) = sx Vi (l, s) x [1 + K ( s)]

Therefore, the derivative of the voltage V32 at the end of the first conductor can therefore be written, in the time domain, by applying an inverse Laplace transformation L ¹ to the above expression: d / dt (V32 (I, t)) = L ¹ {sx Vi (l, s) x [1 + K (s)]}

By calculating this expression for l = Ddf21 min and by taking the value Rdfmin as the fault resistance value in the calculation of Vf (0+) above, we thus end up with a limit curve, as a function of the time elapsed since the appearance of the fault, of the derivative of the voltage V32 of the first conductor with respect to the earth. If the moment of measurement of the derivative of the voltage V32 is fixed with respect to the moment of appearance of the fault, one ends up, for l = Ddf21 min and by taking the value Rdfmin as the value of fault resistance, to a threshold value of the derivative of the voltage V32.

If the derivative of the voltage V32, determined by the measurement at a given instant after the appearance of the fault, exceeds the limit curve or the threshold value thus defined, the method can determine, very quickly after the appearance of the fault. fault, that the fault is a critical fault which requires a total opening action at the level of the link node considered.

On the contrary, if the derivative of the voltage V32, determined by the measurement at a given instant after the appearance of the fault, does not exceed the limit curve or the threshold value thus defined, the method can determine, very quickly after the appearance of the fault, that the fault is a non-critical fault with respect to the link node considered, here the first link node, which allows the method to implement, at the link node level considered, a targeted opening action.

The limit curve and / or the threshold value defined above are therefore examples of a fault criticality criterion used as an element of comparison in a step of determining the level of criticality with respect to the link node considered.

It is noted that the method described below is a method in which one establishes, indirectly, a prediction of the evolution of the current in the first conductor following the appearance of the fault and of the capacity of the first device. power cut to cut this current. Indeed, the way of constructing the limit curve is based among other things on the equation of evolution of the current in the first conductor.

The analytical method described above for determining the fault criticality criterion makes it possible to obtain a fine fault criticality criterion, which makes it possible to approach the real limit of the breaking capacity of the electrical breaking device, and therefore to make the best use of the performance of the electrical breaking device to maximize the possibility of implementing a targeted opening action rather than having to resort to a total opening action at the node considered. However, in certain cases, it will be possible to use a less precise fault criticality criterion, which would still make it possible to have the assurance that the implementation of a targeted opening action guarantees an effective interruption of the system. current by the cut-off device considered (in the example, the first cut-off device considered).

[0175] For example, in certain cases, it will be possible to determine a given value of the monitored parameter for which we are sure to obtain an effective cut-off. It will be recalled that the monitored parameter can consist of a combination of values representative of the current and / or of the voltage, and / or of their derivative with respect to time, in the first conductor.

As an alternative to the analytical approach, an approach based on modeling can be used to define a threshold of the value of the derivative of the voltage with respect to time making it possible to discriminate critical faults from non-critical faults. Therefore, the system including the electrical conductor in which the fault occurred can be represented by a wideband model or by a frequency dependent model in an electromagnetic transient (EMT) program taking into account of the attenuation and distortion of the front modeling wave during its propagation in the transmission conductor. A voltage sensor template is placed at one end of the conductor. In addition, the adjacent conductors as well as a possible power converter and possible protection inductors will advantageously be taken into account in the model in order to sufficiently represent the configuration of the link node 26.1. The architecture of the model is shown in Fig. 9.

[0177] Once the model has been obtained, the peak value of the derivative of the voltage of the first traveling wave can be recorded during parametric simulations with variation of the fault resistance Rdf and of the fault distance I. In this way , it is possible to establish a map, as illustrated in fig. 10, which can be used to define the threshold of the derivative of the voltage V32 according to the values Rdfmin and Ddf21min that can be obtained according to the method explained above.

[0178] Other ways of defining the fault criticality criterion are still possible, based for example on test campaigns, or on analyzes of data drawn from the operation of an identical or similar HVDC network unit. We can cite for example the work described in “Transient-based fault identification algorithm using parametric models for meshed HVDC grids” by P.Verrax, A.Bertinato, M.Kieffer, and B.Raisonac, https://doi.Org/ 10.1016 / j.epsr.2020.106387.

In the above examples, the definition of the fault criticality criterion aims to take into account an estimate of the fault resistance Rdf and of the fault distance I. However, it could be provided that the definition of the criterion of Fault criticality aims to take into account an estimate of only one of these two fault parameters. For example the fault criticality criterion could be based instead on an estimate of the fault distance I. In this case, one could use a method such as that described in the document by MKK Nanayakkara, AD Rajapakse and R. Wachal, " Traveiing-Wave-Based Line Fault Location in Star-Connected Multiterminal HVDC Systems, "appeared in" IEEE Transactions on Power Delivery ", vol. 27, no. 4, pp. 2286-2294, Oct. 2012, doi: 10.1109 / TPWRD.2012.2202405. The method described is particularly advantageous in the context of an electrical conductor which is an overhead conductor or which comprises a section formed of an overhead conductor. Indeed, due to the characteristics of an overhead conductor, the probability that the fault is weakly critical or not critical, to the point of allowing a targeted opening action even with electrical cut-off devices whose action would not be particularly fast, becomes sufficiently high. Likewise, the nature of the electrical conductor and of the faults which are likely to occur therein is frequently non-critical. Thus, the method described above makes it possible to carry out cutting strategies of a selective nature, on a single electrical conductor, without requiring the use of rapid electrical cutting devices. In particular, the invention can be implemented with a first electrical cut-off device 28.11 of mechanical type, in which the electrical cut-off is carried out by mechanical spacing of two electrodes, and this although this type of electrical cut-off device is generally considered as having a high operating time, in particular compared to electronic or hybrid type switching devices. Of course, the invention can be implemented in an HVDC network unit in which the interruption of the power flow in each link of the node considered is operated by an electrical cut-off device of mechanical type,

Claims

[Claim 1] A method of insulating a first conductor (21) of a first power transmission line in a considered electrical network unit (12), the considered electrical network unit operating at a nominal operating voltage single which is a direct high voltage, in which the electrical network unit considered comprises at least one considered link node (26.1), comprising at least three distinct links (26.11, 26.12, 26.13) electrically connected to each other in a continuous manner, with :

- a first connection (26.11) which is electrically connected to a proximal end of the first electrical conductor of the electrical network unit in question, with the interposition of a first electrical switching device (28.11), associated with the first connection, which has an open state and a closed state in which it allows the circulation of a first power flow (P26.ll) between the link node in question and the first conductor;

- a second link (26.12) which is electrically connected to another electrical network unit (16.2; 16.1b) or to a second electrical conductor (22) of the electrical network unit considered to allow the passage of a second flow of electric power (P26.12) through the second link which is controlled by at least one second electric cut-off device (28.12, 29.1b), associated with the second link, which has an open state and a closed state;

- a third link (26.13) which is electrically connected to another electrical network unit (16.1) or to a third electrical conductor of the electrical network unit considered to allow the passage of a third flow of electrical power (P26. 13) through the third link which is controlled by at least a third electrical cut-off device (28.13; 18.1; 29.1), associated with the third link, which has an open state and a closed state; the method further comprising the monitoring of at least monitored parameter relating to the electric current and / or potential in the first electric conductor; and the method comprising a step of detecting the appearance of a fault in the first electrical conductor; characterized in that the method comprises, in addition to the step of detecting the appearance of a fault in the first electrical conductor (21), at least one step of determining the level of criticality of the fault, with respect to screw of the link node considered, returning information on the level of criticality of the fault; in that, in the presence of information on the presence of a fault in the first electrical conductor, the method proceeds, as a function of the information on the criticality of the fault with respect to the link node considered:

- or, in a targeted opening action, when the first electrical cut-off device (28.11) goes from its closed state to its open state, while maintaining the second (28.12, 29.1b) and the third (28.13; 18.1;

29.1) electrical cut-off devices each in their closed state;

[Claim 2] A method according to claim 1, characterized in that, in a fully opening action of the node under consideration, the first electrical cut-off device (28.11) is brought from its closed state to its open state after all the flows electrical power through the other links of the link node in question, other than the first link, have been interrupted.

[Claim 3] Method according to any one of the preceding claims, characterized in that, the step of determining the level of criticality with respect to the link node considered comprises a comparison of at least one parameter monitored with respect to to a fault criticality criterion.

[Claim 4] A method according to claim 3, characterized in that the fault criticality criterion is determined in advance. [Claim 5] A method according to any one of the preceding claims, characterized in that the step of detecting the appearance of a fault in the first electrical conductor (21) comprises a comparison of at least one parameter monitored by in relation to a driver fault criterion.

[Claim 6] A method according to any one of the preceding claims, characterized in that the step of detecting the occurrence of a defect in the first electrical conductor, and the step of determining the level of criticality with respect to -vis of the link node considered are carried out as a function of the value of the same monitored parameter.

[Claim 7] A method according to any one of claims 1 to 5, characterized in that the step of detecting the occurrence of a fault in the first electrical conductor (21), and the step of determining the level criticality with respect to the link node considered are performed as a function of the value of two different monitored parameters.

[Claim 8] A method according to any one of the preceding claims, characterized in that the fault criticality information is determined as a function of a prediction of the evolution of the current in the first electrical conductor (21) following the appearance of the fault and depending on the capacity of the first electrical cut-off device to cut this current.

[Claim 9] A method according to any one of the preceding claims, characterized in that said at least one monitored parameter is selected from the intensity of the current in the first conductor, the derivative with respect to time of the intensity of the current in the first conductor, the electric potential of the first conductor, and the time derivative of the electric potential of the first conductor, or combinations thereof.

[Claim 10] A method according to any one of the preceding claims, characterized in that said at least one monitored parameter is a value of the derivative, with respect to time, of the electric potential of the first conductor. [Claim 11] A method according to any one of the preceding claims, characterized in that the second (26.12) and / or the third link (26.13) is electrically connected to an electric power converter (18.1, 18.2, 18.1b) to another electrical network unit (16.1, 16.2, 16.1b), via a second (28.12), respectively third (28.13), device for cutting the current under direct voltage.

[Claim 12] A method according to any one of the preceding claims, characterized in that the second (26.12) and / or the third (26.13) link is electrically connected to an electric power converter (18.1, 18.2, 18.1b) to another electrical network unit (16.1, 16.2, 16.1b), the power converter also forming the second, respectively third, electrical cut-off device.

[Claim 13] A method according to any one of the preceding claims, characterized in that the second (26.12) and / or the third (26.13) link is electrically connected to an electric power converter (18.1, 18.1b) to another electrical network unit (16.1, 16.1b), the second (29.1), respectively third (29.1b), electrical cut-off device being interposed between the electrical power converter (18.1, 18.1b) and said other electrical network unit ( 16.1, 16.1b).

[Claim 14] A method according to claim 13, characterized in that the other network unit (16.1, 16.1b) operates under an alternating nominal operating voltage, the second (29.1), respectively third (29.1b), electrical cut-off, interposed between the electrical power converter and said other electrical network unit, being an electrical current cut-off device under alternating voltage.

[Claim 15] Method according to any one of the preceding claims, characterized in that the link node considered comprises at least one other link (26.12, 26.14), which is distinct from the first link, and which is electrically connected to a second electrical conductor (22, 23) of the considered electrical network unit (12) through at least a second electrical cut-off device (28.12, 28.14) which is associated with said other link and which has an open state and a closed state.

[Claim 16] Method according to any one of the preceding claims, characterized in that the electrical network unit considered comprises at least one other link node (26.4), distinct from the first link node (26.1) and comprising at least three separate links (26.41, 26.42, 26.43) electrically connected to each other continuously, with:

- a first link (26.41) which is electrically connected to a distal end of the first electrical conductor (21) of the electrical network unit in question, with the interposition of a first electrical switching device (28.41), associated with the first connection , which has an open state and a closed state in which it allows the circulation of a first flow of power between this other link node (26.4) and the first conductor (21);

- a second link (26.42) which is electrically connected to another electrical network unit or to another electrical conductor (24) of the electrical network unit considered to allow the passage of a second flow of electrical power through the second link of this other link node (26.4), this second flow being controlled by at least one second electrical cut-off device (28.42), associated with the second link of this other link node (26.4), which has a state open and a closed state;

- a third link (26.43) which is electrically connected to another electrical network unit (16.4) or to another electrical conductor of the electrical network unit considered to allow the passage of a third flow of electrical power through the third link of this other link node (26.4), this third flow being controlled by at least one third electrical cut-off device (28.43), associated with the third link of this other link node (26.4), which has a state open and a closed state; in that the method comprises at least one step of determining criticality level of the fault with respect to this other link node (26.4), returning information on the criticality level of the fault with respect to this other link node; and in that, the method proceeds, as a function of the fault criticality information with respect to this other link node:

- or, in a targeted opening action, when the first electrical cut-off device (28.41) of this other link node (26.41) passes from its closed state to its open state, while maintaining in this other link node the second (28.12, 29.1b) and the third (28.13; 18.1; 29.1) electrical cut-off devices of this other node each in their closed state;

- or, in a total opening action of this other link node (26.4), the interruption of all the power flows in all the links of this other link node (26.4).

[Claim 17] A method according to claim 16, characterized in that, for the same electrical fault in the first conductor (21), the step of determining the level of criticality of the fault with respect to the link node considered ( 26.1) and the step of determining the level of criticality of the fault vis-à-vis the other link node (26.4) are distinct and return information on the level of criticality of the fault which may be different, leading to the possibility of '' have, for a given electrical fault, a total opening action for one of the two nodes (26.1, 26.4), and a targeted opening action for the other of the two nodes (26.1, 26.4).

[Claim 18] Method according to one of the preceding characteristics, characterized in that the first electrical conductor (21) comprises an overhead electrical conductor.