DC current interruption device

Abstract

A DC current breaker according to the embodiment includes a plurality of DC transmission lines, a first DC bus, a second DC bus, an interruption and consumption unit, a commutation circuit, and a control unit. Each of DC transmission lines branches, at a predetermined branch point, to a first auxiliary line provided with a first mechanical contact and a second auxiliary line provided with a second mechanical contact. The plurality of first auxiliary lines are connected to the first DC bus. The plurality of second auxiliary lines are connected to the second DC bus. The interruption and consumption unit has a semiconductor breaker capable of interrupting a current flowing through the DC transmission line and an energy-consuming element that consumes energy at least between the two ends of the semiconductor breaker. The commutation circuit commutates the current flowing through the DC transmission line to the interruption and consumption unit. The control unit controls the first mechanical contact, the second mechanical contact, the semiconductor breaker, and the commutation circuit.

Description

Technical Field

[0001] Embodiments of the present invention relate to a DC current interruption device.

Background Art

[0002] A DC current interruption device interrupts the current flowing through a DC transmission line in a DC power transmission system. Compared with a conventional AC power transmission system, when applied to long-distance and high-power power transmission, the DC power transmission system can construct a highly efficient system that can be installed at low cost and has low power loss. However, the DC current transmitted in the DC power transmission system cannot be easily interrupted when a system accident occurs, compared with the AC current transmitted in the conventional AC power transmission system. That is, in the DC power transmission system, it is difficult to interrupt a faulty DC transmission line by a simple mechanical contact type circuit breaker. This is because in an AC current, there are periodically points (current zero points) where the current crosses zero, while in a DC current, there is no current zero point. Therefore, in the DC power transmission system, when an accident occurs in a DC transmission line, in order to be able to interrupt the faulty DC transmission line (faulty line) by the mechanical contact type circuit breaker belonging to this DC transmission line, it is necessary to actively create a current zero point by a DC current interruption device. For this reason, DC current interruption devices with various configurations for actively creating a current zero point in a mechanical contact type circuit breaker have been studied.

[0003] As one form of the DC current interruption device, there is a device configured by combining a mechanical contact type circuit breaker and a semiconductor breaker composed of semiconductor elements. This is called a hybrid type DC current interruption device. In the hybrid type DC current interruption device, the current (fault current) generated and flowing through the mechanical contact type circuit breaker due to an accident is diverted to a semiconductor element capable of self-extinguishing the arc to actively create a current zero point, thereby shifting the mechanical contact type circuit breaker to an electrically interrupted state, and in this state, the semiconductor breaker interrupts the fault current.

[0004] In hybrid DC current interruption devices, mechanical contact type circuit breakers, semiconductor circuit breakers, and commutation circuits (commutation elements) that commutate fault current to semiconductor circuit breakers are installed on DC transmission lines. Therefore, in hybrid DC current interruption devices applied to DC transmission systems with multiple DC transmission lines, the number of mechanical contact type circuit breakers, semiconductor circuit breakers, and commutation circuits will be provided according to the number of DC transmission lines. However, semiconductor components that make up semiconductor circuit breakers and commutation circuits are among the most expensive components in hybrid DC current interruption devices. This is because, in DC transmission systems, the voltage transmitted through DC transmission lines is high, requiring the use of high-voltage semiconductor components that can withstand a voltage higher than that of the DC transmission lines. For this reason, in multi-terminal hybrid DC current interruption devices, a configuration in which semiconductor circuit breakers are shared among multiple DC transmission lines has been considered. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6845333 [Overview of the project] [Problems that the invention aims to solve]

[0006] The problem that this invention aims to solve is to provide a DC current interruption device that can be applied to a multi-terminal DC power transmission system, and that can interrupt a DC power transmission line in the event of a fault, while standardizing semiconductor circuit breakers and commutation circuits. [Means for solving the problem]

[0007] The DC current interruption device of the embodiment includes a plurality of DC transmission lines, a first DC bus, a second DC bus, an interruption consumption unit, a commutation circuit, and a control unit. Each of the plurality of DC transmission lines branches at a predetermined branching point into a first auxiliary line provided with a first mechanical contact and a second auxiliary line provided with a second mechanical contact. The first DC bus is connected to a plurality of the first auxiliary lines. The second DC bus is connected to a plurality of the second auxiliary lines. The interruption consumption unit includes a semiconductor circuit breaker capable of interrupting the current flowing through the DC transmission line and an energy consumption element that consumes energy at least between both ends of the semiconductor circuit breaker. The commutation circuit commutates the current flowing through the DC transmission line to the interruption consumption unit. The control unit controls the open and closed states of the first mechanical contact and the second mechanical contact, the conduction and non-conduction states of the semiconductor circuit breaker, and the states in which current flows through one or more of the paths of the first mechanical contact, the second mechanical contact, and the semiconductor circuit breaker via the commutation circuit, as well as states in which the current is reduced to approximately zero. [Brief explanation of the drawing]

[0008] [Figure 1] A diagram showing an example of the configuration of a DC current interruption device according to the first embodiment. [Figure 2A] This figure shows an example of a modified configuration of the semiconductor circuit breaker and arrester included in the DC current interruption device of the first embodiment. [Figure 2B] This figure shows an example of a modified configuration of the semiconductor circuit breaker and arrester included in the DC current interruption device of the first embodiment. [Figure 2C] This figure shows an example of a modified configuration of the semiconductor circuit breaker included in the DC current interruption device of the first embodiment. [Figure 2D] This figure shows an example of a modified configuration of the semiconductor circuit breaker included in the DC current interruption device of the first embodiment. [Figure 2E] This figure shows an example of a modified configuration of the semiconductor circuit breaker included in the DC current interruption device of the first embodiment. [Figure 3A] This figure shows an example of a modified configuration of the commutation circuit included in the DC current interruption device of the first embodiment. [Figure 3B] This figure shows an example of a modified configuration of the commutation circuit included in the DC current interruption device of the first embodiment. [Figure 3C] This figure shows an example of a modified configuration of the commutation circuit included in the DC current interruption device of the first embodiment. [Figure 3D] This figure shows an example of a modified configuration of the commutation circuit included in the DC current interruption device of the first embodiment. [Figure 3E] This figure shows an example of a modified configuration of the commutation circuit included in the DC current interruption device of the first embodiment. [Figure 4] A diagram illustrating the first operation of the DC current interruption device according to the first embodiment. [Figure 5] A diagram illustrating the first operation of the DC current interruption device according to the first embodiment. [Figure 6] A diagram illustrating the first operation of the DC current interruption device according to the first embodiment. [Figure 7] A diagram illustrating the first operation of the DC current interruption device according to the first embodiment. [Figure 8] A diagram illustrating the first operation of the DC current interruption device according to the first embodiment. [Figure 9] A diagram illustrating the first operation of the DC current interruption device according to the first embodiment. [Figure 10] A diagram illustrating the first operation of the DC current interruption device according to the first embodiment. [Figure 11] A diagram illustrating the first operation of the DC current interruption device according to the first embodiment. [Figure 12] A diagram illustrating the second operation of the DC current interruption device according to the first embodiment. [Figure 13] A diagram illustrating the second operation of the DC current interruption device according to the first embodiment. [Figure 14] A diagram illustrating the second operation of the DC current interruption device according to the first embodiment. [Figure 15]A diagram for explaining the second operation of the DC current interruption device according to the first embodiment. [Figure 16] A diagram for explaining the second operation of the DC current interruption device according to the first embodiment. [Figure 17] A diagram for explaining the third operation of the DC current interruption device according to the first embodiment. [Figure 18] A diagram for explaining the third operation of the DC current interruption device according to the first embodiment. [Figure 19] A diagram for explaining the third operation of the DC current interruption device according to the first embodiment. [Figure 20] A diagram for explaining the third operation of the DC current interruption device according to the first embodiment. [Figure 21] A diagram for explaining the third operation of the DC current interruption device according to the first embodiment. [Figure 22] A diagram for explaining the third operation of the DC current interruption device according to the first embodiment. [Figure 23] A diagram for explaining the third operation of the DC current interruption device according to the first embodiment. [Figure 24] A diagram for explaining the third operation of the DC current interruption device according to the first embodiment. [Figure 25] A diagram showing an example of the configuration of the DC current interruption device according to the second embodiment. [Figure 26A] A diagram showing an example of the configuration of the auxiliary semiconductor breaker included in the DC current interruption device according to the second embodiment. [Figure 26B] A diagram showing an example of the configuration of the auxiliary semiconductor breaker included in the DC current interruption device according to the second embodiment. [Figure 26C] A diagram showing an example of the configuration of the auxiliary semiconductor breaker included in the DC current interruption device according to the second embodiment. [Figure 26D] A diagram showing an example of the configuration of the auxiliary semiconductor breaker included in the DC current interruption device according to the second embodiment. [Figure 27] A diagram showing an example of the configuration of the DC current interruption device according to the third embodiment. [Figure 28] A diagram illustrating the fourth operation in the DC current interruption device of the third embodiment. [Figure 29] A diagram illustrating a fourth operation in the DC current interruption device of the third embodiment. [Figure 30] A diagram illustrating a fourth operation in the DC current interruption device of the third embodiment. [Figure 31] A diagram illustrating the fourth operation in the DC current interruption device of the third embodiment. [Figure 32] A diagram illustrating a fourth operation in the DC current interruption device of the third embodiment. [Figure 33] A diagram illustrating the fourth operation in the DC current interruption device of the third embodiment. [Figure 34] A diagram illustrating the fourth operation in the DC current interruption device of the third embodiment. [Figure 35] A diagram illustrating a fourth operation in the DC current interruption device of the third embodiment. [Figure 36] A diagram illustrating the fourth operation in the DC current interruption device of the third embodiment. [Figure 37] A diagram showing an example of the configuration of a DC current interruption device according to the fourth embodiment. [Figure 38] A diagram showing an example of a modified configuration of a DC current interruption device according to the third embodiment. [Figure 39] A diagram showing an example of a modified configuration of a DC current interruption device according to the fourth embodiment. [Modes for carrying out the invention]

[0009] The DC current interruption device of this embodiment will be described below with reference to the drawings.

[0010] (First Embodiment) Figure 1 is a diagram showing an example of the configuration of a DC current interruption device according to the first embodiment. Figure 1 shows an example of a DC current interruption device 1 that is applied to a multi-terminal DC power transmission system with n lines (where n is a natural number) and is configured at the nodal portions of multiple DC power transmission lines LN (DC power transmission lines LN-1 to LN-n). In the DC current interruption device 1, each DC power transmission line LN is branched into auxiliary lines P and auxiliary lines N at predetermined locations (branching points), and DC current (hereinafter simply referred to as "current") is transmitted between each DC power transmission line LN by a DC bus BP, which is formed by connecting the auxiliary lines P, and / or a DC bus BN, which is formed by connecting the auxiliary lines N.

[0011] The DC current interruption device 1 includes, for example, a plurality of DC reactors 10 (DC reactors 10-1 to 10-n), a plurality of disconnectors 20 (disconnectors 20-P-1 to 20-Pn, and disconnectors 20-N-1 to 20-Nn), a commutation circuit 30, a plurality of semiconductor circuit breakers 40 (semiconductor circuit breakers 40-1 to 40-n), a plurality of arresters 50 (arresters 50-1 to 50-n), an inductor 60, and a control unit 100. The control unit 100 is not limited to being located inside the DC current interruption device 1, as shown in Figure 1. The control unit 100 may be located outside the DC current interruption device 1.

[0012] In Figure 1, a hyphen and a number are added after the respective symbols of the DC reactor 10 and the disconnector 20 of the DC current interruption device 1 to indicate which of the DC transmission lines LN-1 to LN-n they correspond to. Furthermore, in Figure 1, a hyphen and the designation "P" or "N" are added after the respective symbols of the disconnector 20 and the DC bus B of the DC current interruption device 1 to indicate which of the auxiliary lines P or N they correspond to. In the following explanation, if it is not necessary to distinguish which DC transmission line LN or auxiliary line a component corresponds to, the hyphen and the designation or number added to the respective symbol will be omitted.

[0013] In the DC current interruption device 1, a DC reactor 10 is connected in series to each DC transmission line LN, and on the opposite side from the transmission side, it branches into two auxiliary lines (auxiliary line P and auxiliary line N). In the DC current interruption device 1, a disconnector 20 is connected in series to each auxiliary line. For example, in the DC transmission line LN-1, the first end of the DC reactor 10 is connected to the transmission side, and on the second end opposite the first end of the DC reactor 10, it branches into auxiliary line P-1 and auxiliary line N-1. In auxiliary line P-1, the first pole aP-1 of disconnector 20-P-1 is connected to the second end of the DC reactor 10, and the second pole bP-1 of disconnector 20-P-1 is connected to the DC bus BP. On the other hand, in auxiliary line N-1, the second pole dN-1 of disconnector 20-N-1 is connected to the second end of DC reactor 10, and the first pole aN-1 of disconnector 20-N-1 is connected to DC bus BN. The same applies to DC transmission lines LN-2 to LN-n. In normal power transmission with DC current interruption device 1, current flows through the DC reactor 10 belonging to each DC transmission line LN, and further through the disconnector 20 and DC bus B in the auxiliary lines branched from each DC transmission line LN. Auxiliary line P is an example of a "first auxiliary line," and auxiliary line N is an example of a "second auxiliary line." Disconnector 20-P is an example of a "first mechanical contact," and disconnector 20-N is an example of a "second mechanical contact." The DC bus BP is an example of the "first DC bus," and the DC bus BN is an example of the "second DC bus."

[0014] In the DC current interruption device 1, each DC bus B, which is formed by connecting the auxiliary lines branched off from each DC transmission line LN, is connected to each other via a commutation circuit 30, multiple semiconductor circuit breakers 40 and multiple arresters 50, and an inductor 60. In other words, in the DC current interruption device 1, a configuration in which multiple stages (n stages in Figure 1) of parallel circuits of corresponding semiconductor circuit breakers 40 and arresters 50 are connected in series, and a series circuit of the commutation circuit 30 and an inductor 60 is connected in series between the two DC buses B. More specifically, DC bus BP is connected to the first terminal e of the first stage semiconductor circuit breaker 40-1 and the first terminal of the arrester 50-1, and DC bus BN is connected to the second terminal d side of the commutation circuit 30 via an inductor 60. As a result, in the DC current interruption device 1, the two auxiliary lines branched from each DC transmission line LN are connected to each other via the corresponding DC bus B, a parallel circuit of multiple stages of semiconductor circuit breakers 40 and arresters 50, a commutation circuit 30, and an inductor 60. The commutation circuit 30 is an example of a "commutation circuit". The semiconductor circuit breaker 40 is an example of a "semiconductor circuit breaker", and the arrester 50 is an example of an "energy consumption element". The configuration of the semiconductor circuit breaker 40 and the arrester 50 is an example of a "breaking and consumption unit".

[0015] The DC reactor 10 suppresses changes in the current in the corresponding DC transmission line LN when a fault occurs in the DC transmission line LN.

[0016] The disconnector 20 is a mechanical contact type switch. The disconnector 20 is controlled by the control unit 100 to be either open or closed.

[0017] Each of the semiconductor circuit breakers 40-1 to 40-n interrupts the current flowing from the first terminal e to the second terminal f. Each semiconductor circuit breaker 40 comprises, for example, a semiconductor switching element and a diode connected in parallel to each other. More specifically, in each semiconductor circuit breaker 40, the cathode of the diode and the collector of the semiconductor switching element are connected to each other to form the first terminal e, and the anode of the diode and the emitter of the semiconductor switching element are connected to each other to form the second terminal f. The gate of the semiconductor switching element is controlled by the control unit 100 (a control voltage is applied). In other words, the semiconductor switching element is controlled by the control unit 100 to either an ON state (conducting state) or an OFF state (non-conducting state). The semiconductor switching element is, for example, an insulated gate bipolar transistor (IGBT). The semiconductor switching element is not limited to IGBTs, but can be any switching element that is capable of self-extinguishing. Each semiconductor circuit breaker 40, when in the ON state, allows current to flow from the first terminal e to the second terminal f, and when in the OFF state, interrupts this current. The ON state of the semiconductor circuit breaker 40 is an example of a "conducting state," and the OFF state is an example of a "non-conducting state."

[0018] Each of the arresters 50-1 to 50-n is connected in parallel to the corresponding semiconductor circuit breaker 40, and when the semiconductor circuit breaker 40 is controlled to the off state, it consumes (absorbs) the surge energy generated due to the energy of the DC transmission line LN, auxiliary line P, auxiliary line N, semiconductor circuit breaker 40, and the inductance component of the inductor 60.

[0019] In the DC current interruption device 1, the first terminal e of the first-stage semiconductor circuit breaker 40-1 and the first terminal of the first-stage arrester 50-1 are connected to the DC bus BP, and the second terminal d of the commutation circuit 30 is connected to the DC bus BN via the inductor 60. In the DC current interruption device 1, each semiconductor circuit breaker 40 and each arrester 50 are connected in parallel with each other. Therefore, in the DC current interruption device 1, in response to the control unit 100 controlling the semiconductor switching elements of the semiconductor circuit breaker 40 to either an on state or an off state, the device allows or blocks (interrupts) the current flowing from the DC bus BP side to the DC bus BN side, and consumes (absorbs) surge energy when the semiconductor switching elements of the semiconductor circuit breaker 40 are controlled to the off state by the control unit 100.

[0020] The configuration of the semiconductor circuit breaker 40 and arrester 50 in the DC current interruption device 1 is not limited to the configuration in which multiple parallel circuits of the semiconductor circuit breaker 40 and arrester 50 are connected in series, as shown in Figure 1. Figures 2A and 2B show examples of modified configurations of the semiconductor circuit breaker 40 and arrester 50 in the DC current interruption device 1 of the first embodiment.

[0021] Figure 2A shows an example of a configuration in which a semiconductor circuit breaker 40a, which has a series circuit configuration in which multiple semiconductor switch units 41 (only two are shown in Figure 2A) are connected in series in the same direction to one another, is connected in parallel to a single arrester 50. The semiconductor switch units 41 have the same configuration as the single semiconductor circuit breaker 40 shown in Figure 1. Therefore, if the semiconductor circuit breaker 40a has a configuration in which n semiconductor switch units 41 are connected in series, the semiconductor circuit breaker 40a is equivalent to the configuration in which semiconductor circuit breakers 40-1 to 40-n are connected in series as shown in Figure 1. The configuration of the semiconductor circuit breaker 40a and arrester 50a shown in Figure 2A can interrupt the current flowing from the first end e to the second end f of the semiconductor circuit breaker 40a and dissipate (absorb) surge energy, just as the configuration of multiple semiconductor circuit breakers 40 and multiple arresters 50 shown in Figure 1.

[0022] Figure 2B shows an example of a configuration in which a semiconductor circuit breaker 40b, which has a series circuit configuration in which multiple semiconductor switch units 41 (only four are shown in Figure 2B) are connected in series in opposite directions, is connected in parallel with a single arrester 50. In the configuration of the semiconductor circuit breaker 40b and arrester 50 shown in Figure 2B, in addition to interrupting the current flowing from the first end e to the second end f of the semiconductor circuit breaker 40b and consuming (absorbing) surge energy, similar to the configuration of multiple semiconductor circuit breakers 40 and multiple arresters 50 shown in Figure 1, it is also possible to interrupt the current flowing from the second end f to the first end e of the semiconductor circuit breaker 40b and consume (absorbing) surge energy. In other words, in the configuration of the semiconductor circuit breaker 40b and arrester 50 shown in Figure 2B, it is possible to interrupt the current flowing in both directions (fault current) and consume (absorb) surge energy in a DC transmission line LN (fault circuit) where a fault has occurred.

[0023] The semiconductor switch section 41 included in the semiconductor circuit breaker 40a shown in Figure 2A and the semiconductor circuit breaker 40b shown in Figure 2B, as well as the semiconductor circuit breaker 40 shown in Figure 1, can be replaced with a different configuration. Figures 2C to 2E show an example of a modified configuration of the semiconductor circuit breaker 40 (including the semiconductor switch section 41) included in the DC current interruption device 1 of the first embodiment.

[0024] The semiconductor switch section 41a shown in Figure 2C comprises, for example, two leg sections which are series circuits in which one semiconductor switch section and one diode are connected in series, and one capacitor, and these components are connected to each other to form a bridge circuit. The semiconductor switch section 41b shown in Figure 2D comprises, for example, two leg sections which are series circuits in which two semiconductor switch sections are connected in series in the same direction, and one capacitor, and these components are connected to each other to form a bridge circuit. The semiconductor switch sections in semiconductor switch sections 41a and 41b have the same configuration as the semiconductor switch section 41 in the semiconductor circuit breaker 40 shown in Figure 1, the semiconductor circuit breaker 40a shown in Figure 2A, and the semiconductor circuit breaker 40b shown in Figure 2B. If the configuration of the semiconductor circuit breaker 40 is replaced with a semiconductor switch section 41a or a semiconductor switch section 41b, or if the semiconductor switch section 41 in the semiconductor circuit breaker 40a or semiconductor circuit breaker 40b is replaced with a semiconductor switch section 41a or a semiconductor switch section 41b, each semiconductor circuit breaker 40 (including semiconductor circuit breakers 40a and semiconductor circuit breaker 40b) can interrupt the bidirectional fault current flowing between the first terminal e and the second terminal f.

[0025] The semiconductor switch section 41c shown in Figure 2E is, for example, composed of a single capacitor. Even if the configuration of the semiconductor circuit breaker 40 is replaced with the semiconductor switch section 41c, or if the semiconductor switch section 41 in semiconductor circuit breakers 40a and 40b is replaced with the semiconductor switch section 41c, each semiconductor circuit breaker 40 (including semiconductor circuit breakers 40a and 40b) can interrupt the current flowing between the first terminal e and the second terminal f. However, in the semiconductor switch section 41c shown in Figure 2E, the control unit 100 cannot actively control the semiconductor switch section 41c to be on or off, and the arrester 50 consumes (absorbs) this energy after the energy of the fault current stored in the capacitor has saturated, so the speed at which the current flowing between the first terminal e and the second terminal f is interrupted is reduced. However, the configuration of the semiconductor switch section 41c shown in Figure 2E is simpler than that of each semiconductor switch section 41 which has a semiconductor switching element, thus reducing the cost and size when constructing the semiconductor circuit breaker 40, semiconductor circuit breaker 40a, and semiconductor circuit breaker 40b.

[0026] The commutation circuit 30 switches the direction of the current flowing between the first end c and the second end d. This causes the commutation circuit 30 to transfer (commutate) the current flowing through the auxiliary lines P and N, to which the commutation circuit section 20 (controlled to be in an open state) is connected, to the semiconductor circuit breaker 40. At this time, the control unit 100 controls the semiconductor switching element of the semiconductor circuit breaker 40 to either an on state or an off state. The commutation circuit 30 includes, for example, a thyristor and a capacitor connected in parallel. More specifically, in the commutation circuit 30, the anode of the thyristor and the first end of the capacitor (one end on the negative side in Figure 1) are connected to form the first end c, and the cathode of the thyristor and the second end of the capacitor (one end on the positive side in Figure 1) are connected to form the second end d. The gate of the thyristor is controlled (a control voltage is applied) by the control unit 100. In other words, the thyristor allows or blocks the current flowing between its ends in response to the gate control by the control unit 100. As a result, the commutator circuit 30, in response to the gate control of the thyristor by the control unit 100, transfers (commutates) the current flowing through the auxiliary lines P and N to which the commutator circuit section 20, which is controlled to be in an open state, is connected to the semiconductor circuit breaker 40, thereby reducing the current flowing between the first end c and the second end d to approximately zero. The thyristor in the commutator circuit 30 is an example of a "semiconductor switch section," and the capacitor in the commutator circuit 30 is an example of an "energy storage element."

[0027] The configuration of the commutation circuit 30 provided by the DC current interruption device 1 is not limited to the configuration in which a thyristor and a capacitor are connected in parallel, as shown in Figure 1. Figures 3A to 3E show an example of a modified configuration of the commutation circuit 30 provided by the DC current interruption device 1 of the first embodiment.

[0028] The commutator circuit 30a shown in Figure 3A is a bridge circuit comprising, for example, two leg sections which are series circuits in which one semiconductor switch section and one diode are connected in series, and one capacitor, with these components connected to each other. The diode in the leg section of the commutator circuit 30a is an example of a "current rectifier element". The commutator circuit 30b shown in Figure 3B is a bridge circuit comprising, for example, two leg sections which are series circuits in which two semiconductor switch sections are connected in series in the same direction, and one capacitor, with these components connected to each other. The commutator circuit 30c shown in Figure 3C is a parallel circuit comprising, for example, one semiconductor switch section and one capacitor, with these components connected to each other in parallel. The semiconductor switch sections of the commutator circuits 30a, 30b, and 30c each comprise, for example, a semiconductor switching element and a diode connected in parallel to each other, similar to the semiconductor circuit breaker 40 and the semiconductor switch sections 41 of the semiconductor circuit breaker 40a and 40b. More specifically, in the semiconductor switch sections of the commutation circuits 30a, 30b, and 30c, the cathode of the diode and the collector of the semiconductor switching element are connected to each other, and the anode of the diode and the emitter of the semiconductor switching element are connected to each other. The gate of the semiconductor switching element is controlled (a control voltage is applied) by the control unit 100. In other words, the semiconductor switch sections of the commutation circuits 30a, 30b, and 30c are controlled by the control unit 100 to be either on or off, similar to the thyristor in the commutation circuit 30. The semiconductor switching element in the semiconductor switch section of the commutation circuit 30 is, for example, an insulated-gate bipolar transistor (IGBT), similar to the semiconductor switching element in the semiconductor circuit breaker 40 and the semiconductor switch section 41 in the semiconductor circuit breakers 40a and 40b. However, the semiconductor switching elements in the semiconductor switch section of the commutation circuit 30 may have a lower voltage rating than the semiconductor switching elements in the semiconductor circuit breaker 40, or the semiconductor switch section 41 of the semiconductor circuit breaker 40a and semiconductor circuit breaker 40b.The semiconductor switching element in the semiconductor switch section of the commutation circuit 30 is not limited to IGBTs, but can be any switching element that is capable of self-extinguishing. Each of the commutation circuits 30a, 30b, and 30c changes the current value of the current flowing between the first end c and the second end d in response to the control unit 100's control of the semiconductor switch section to either an ON state or an OFF state, thereby causing the current flowing between the first end c and the second end d to be approximately zero.

[0029] The commutator circuit 30d shown in Figure 3D is a series circuit comprising, for example, one reactor, one capacitor, and one semiconductor switch (which may be a mechanical contact type switch) as a semiconductor switch unit, with these components connected in series. The commutator circuit 30e shown in Figure 3E is a series circuit comprising, for example, one reactor, one capacitor, and one thyristor, with these components connected in series. The switch in the commutator circuit 30d and the thyristor in the commutator circuit 30e are controlled by the control unit 100, similar to the thyristor in the commutator circuit 30. That is, the switch in the commutator circuit 30d is controlled by the control unit 100 to be either open or closed, and the thyristor in the commutator circuit 30e is controlled by the control unit 100 to be either on or off. In both the commutator circuit 30d and the commutator circuit 30e, a zero current point is generated by the resonance between the reactor and the capacitor. As a result, both the commutation circuit 30d and the commutation circuit 30e, in response to the control unit 100's control to either state, transfer (commutate) the current flowing through the auxiliary lines P and N to which the commutation circuit section 20 controlled to the open state is connected to the semiconductor circuit breaker 40, thereby reducing the current flowing between the first end c and the second end d to approximately zero.

[0030] The inductor 60 prevents the capacitors in the corresponding commutation circuits 30 (including commutation circuits 30a to 30e) from being damaged in the event of a fault in the DC transmission line LN.

[0031] The control unit 100 controls the disconnection and conduction of the DC transmission line LN in the DC current interruption device 1 by controlling the disconnector 20, the commutation circuit 30, and the semiconductor circuit breaker 40. The control unit 100 implements control functions that control the operation of each component by having a hardware processor, such as a CPU (Central Processing Unit), execute a program (software). Some or all of the control functions of the control unit 100 may be implemented by hardware (including circuitry) such as an LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), or GPU (Graphics Processing Unit), or by the cooperation of software and hardware. Some or all of the control functions of the control unit 100 may be implemented by a dedicated LSI. Here, the program (software) may be stored in advance in a ROM (Read Only Memory), RAM (Random Access Memory), flash memory or other semiconductor memory element, or in a storage device (a storage device equipped with a non-transient storage medium) provided by the control unit 100, or it may be stored in a removable storage medium (a non-transient storage medium) such as a DVD or CD-ROM, and installed in the storage device provided by the control unit 100 when the storage medium is mounted on the DC current interruption device 1 or the drive device provided by the control unit 100.

[0032] With this configuration, the DC current interruption device 1 can standardize the semiconductor circuit breaker 40 and commutation circuit 30, which would otherwise be costly due to the need to use high-voltage semiconductor components, across all DC transmission lines LN. In the event of a fault in any of the DC transmission lines LN, it can interrupt that DC transmission line LN. In other words, the DC current interruption device 1 can interrupt a faulty DC transmission line LN while reducing the number of high-voltage semiconductor components used (reducing the number of components).

[0033] [First operation of the DC current interruption device 1 to interrupt the DC transmission line LN] Here, referring to Figures 4 to 11, we will describe the first operation in which the control unit 100 shuts off the DC transmission line LN where a fault has occurred. In the following description, we will assume that the DC current interruption device 1 has three circuits (n=3). In the DC current interruption device 1, for example, DC transmission lines LN-1 to LN-3 are each connected to each other via DC bus BP and DC bus BN, and current is flowing from DC transmission line LN-3 to DC transmission lines LN-1 and DC transmission lines LN-2. When a fault occurs in DC transmission line LN-1, we will describe an example in which the control unit 100 shuts off DC transmission line LN-1 as the first operation. Figures 4 to 11 show the current flow in the DC current interruption device 1 when each component is controlled by the control unit 100.

[0034] In the steady-state power transmission (initial state) where DC transmission lines LN-1 to LN-3 are connected to each other via DC buses BP and BN and transmitting power, all disconnectors 20 are in the closed state. The commutator circuit 30 is in the off state, and the semiconductor circuit breakers 40 are in the off state. More specifically, the thyristors in the commutator circuit 30 are in the off state (i.e., the commutator circuit 30 is in a state where it commutates the current flowing between the first end c and the second end d), and all the semiconductor switching elements in the semiconductor circuit breakers 40 are in the off state (i.e., each semiconductor circuit breaker 40 is in a state where it is interrupting the current flowing from the first end e to the second end f). In this case, as shown in Figure 4, current is flowing from DC transmission line LN-3 to DC transmission lines LN-1 and LN-2 via DC buses BP and BN, respectively, in the DC current interruption device 1.

[0035] Here, let's assume that fault X occurs in DC transmission line LN-1, as shown in Figure 5. In this case, the control unit 100 shuts off DC transmission line LN-1 where fault X has occurred by controlling the open state, closed state, on state, and off state of each component in the following procedure. In the following explanation, DC transmission line LN-1 where fault X has occurred will also be called the "fault line," and DC transmission lines LN other than DC transmission line LN-1 (fault line) where fault X has occurred, that is, DC transmission lines LN-2 and DC transmission lines LN-3 where fault X has not occurred, will also be called "healthy lines."

[0036] (Procedure 1-1): First, the control unit 100 opens the disconnector 20-P-1 belonging to auxiliary line P-1 of DC transmission line LN-1 (fault line) where fault X occurred. Furthermore, the control unit 100 opens the disconnector 20-N-2 belonging to auxiliary line N-2 of DC transmission line LN-2 (healthy line) where fault X did not occur, and the disconnector 20-N-3 belonging to auxiliary line N-3 of DC transmission line LN-3 (healthy line). In other words, the control unit 100 opens the mechanical contact type switches belonging to the fault line in auxiliary line P, and opens the mechanical contact type switches belonging to the healthy line in auxiliary line N. Even in this case, as shown in Figure 6, the DC current interruption device 1 is in a state where current (fault current) is flowing from the DC transmission line LN-3 to the DC transmission lines LN-1 and LN-2 via the DC buses BP and BN, respectively. This is because simply opening the disconnectors 20, which are mechanical contact type switches, does not electrically interrupt the DC transmission lines LN (the interrupted state) due to the arc A generated between the contacts of the disconnectors 20 that are in the open state.

[0037] (Procedure 1-2): Next, the control unit 100 operates the semiconductor circuit breakers 40 to the ON state. More specifically, the control unit 100 turns on all the semiconductor switching elements of the semiconductor circuit breakers 40 (that is, each semiconductor circuit breaker 40 is not interrupting the current flowing from the first terminal e to the second terminal f). As a result, the commutation circuit 30 discharges the charge from its capacitor and applies a negative voltage to the DC bus BN with the DC bus BP as the reference. Figure 7 shows the state in which a current CC corresponding to the negative voltage applied by the commutation circuit 30 (hereinafter also referred to as the "commutation current") flows. Due to the commutation current CC flowing in response to the application of the negative voltage to the DC bus BN by the commutation circuit 30, the fault current flowing through the disconnectors 20 (disconnector 20-P-1, disconnector 20-N-2, and disconnector 20-N-3) that were opened in procedure 1-1 becomes approximately zero. This extinguishes the arc A that occurred between the contacts of each disconnector 20 that was opened in step 1-1. However, after opening the disconnectors 20 in step 1-1, depending on the direction of the fault current flow (current flow state), the fault current between the two poles of the disconnector 20 may become approximately zero. In this case, the control unit 100 does not need to operate the commutation circuit 30 in step 1-2.

[0038] When the fault current flowing through each disconnector 20, which was opened in step 1-1, becomes approximately zero due to the commutation current CC that flows in response to the application of a negative voltage to the DC bus BN by the commutation circuit 30, the fault current is commutated to the semiconductor circuit breaker 40.

[0039] (Steps 1-3): Subsequently, if the voltage of the capacitor in the commutation circuit 30 exceeds a specified value, the control unit 100 operates the commutation circuit 30 to the ON state. More specifically, the control unit 100 turns on the thyristor in the commutation circuit 30 (that is, the commutation circuit 30 does not commutate the current flowing between the first terminal c and the second terminal d). As a result, the fault current that has been commutated to the semiconductor circuit breaker 40 flows through the thyristor in the commutation circuit 30, as shown in Figure 8. In other words, the fault current flows without passing through the capacitor in the commutation circuit 30 (hereinafter referred to as the "bypass state").

[0040] (Procedure 1-4): Next, the control unit 100 operates the semiconductor circuit breaker 40 to the OFF state. As a result, the fault current of the DC transmission line LN-1 is interrupted in the DC current interruption device 1 and becomes approximately zero (transitions to approximately zero). After that, the fault current continues to flow for a while in the DC current interruption device 1 due to the surge energy accumulated in the inductance component in the line, but this surge energy is consumed by the arrester 50. Figure 9 shows the state in which the fault current of the DC transmission line LN-1 flows through the arrester 50. Here, the control unit 100 may turn off the thyristor in the commutation circuit 30 in procedure 1-4, or in the next procedure 1-5.

[0041] (Steps 1-5): Next, the control unit 100 opens the disconnector 20-N-1 belonging to the auxiliary line N-1 of the DC transmission line LN-1 where fault X occurred, after the fault current flowing through the DC transmission line LN-1 has become zero (for example, after a period of time has elapsed in which it can be considered that the fault current flowing through the DC transmission line LN-1 has become zero). In other words, the control unit 100 also opens the mechanical contact type switch belonging to the fault circuit in the auxiliary line N-1 of the DC transmission line LN-1 where fault X occurred. Figure 10 shows the state in which the disconnector 20-N-1 is open when the fault current has stopped flowing through the DC transmission line LN-1. As a result, in the DC current interruption device 1, as shown in Figure 10, current flows from the DC transmission line LN-3 to the DC transmission line LN-2 via the DC bus BP. In other words, the DC transmission line LN-1 where accident X occurred is shut off, and although it is only the DC bus BP, the transmission of DC current through a healthy line is maintained.

[0042] (Procedure 1-6): Next, the control unit 100 closes the disconnector 20-N-2 belonging to auxiliary line N-2 of DC transmission line LN-2 where fault X has not occurred, and the disconnector 20-N-3 belonging to auxiliary line N-2 of DC transmission line LN-3. In other words, the control unit 100 returns the mechanical contact type switch belonging to the healthy circuit in auxiliary line N, which was opened in procedure 1-1, back to the closed state. With this, the control unit 100 completes the operation of electrically interrupting DC transmission line LN-1 where fault X has occurred. As a result, the DC current interruption device 1 maintains the transmission of DC current through the healthy circuit. Figure 11 shows the state in which current flows from DC transmission line LN-3, which is a healthy circuit, to DC transmission line LN-2, which is a healthy circuit, via DC bus BP and DC bus BN, respectively.

[0043] Through this procedure, the DC current interruption device 1's control unit 100 controls the disconnector 20-P belonging to the auxiliary line P of the faulty circuit and the disconnector 20-N belonging to the auxiliary line N of the healthy circuit to extinguish the arc A caused by the fault current. Then, after the fault current becomes zero, the control unit 100 controls the disconnector 20-N belonging to the auxiliary line N of the faulty circuit. As a result, the DC current interruption device 1 can interrupt the faulty circuit and maintain power transmission through the healthy circuit.

[0044] In the first operation described above, the control unit 100 controls the disconnector 20-P belonging to the auxiliary line P of the faulty line and the disconnector 20-N belonging to the auxiliary line N of the healthy line to cause the fault current to flow from the first end e to the second end f of the semiconductor circuit breaker 40, thereby interrupting the DC transmission line LN-1 (faulty line). This is because the semiconductor circuit breaker 40 is configured to interrupt the current flowing from the first end e to the second end f. In other words, in the first operation, the control unit 100 controlled the respective components belonging to the auxiliary line P and the auxiliary line N so that the upstream side of the fault current flowing through the faulty line is the first end e of the semiconductor circuit breaker 40, and the downstream side of the fault current is the second end f of the semiconductor circuit breaker 40. However, as described above, the semiconductor circuit breaker 40 can be configured to interrupt bidirectional fault currents by, for example, replacing the semiconductor circuit breaker 40b shown in Figure 2B, or the semiconductor switch unit 41 with the semiconductor switch unit 41a shown in Figure 2C or the semiconductor switch unit 41b shown in Figure 2D. In this case, the DC current interruption device 1 may reverse the control unit 100's control of each component when interrupting a fault circuit for the auxiliary line P and the auxiliary line N. That is, the control unit 100 may interrupt the fault circuit by controlling the disconnector 20-N belonging to the auxiliary line N of the fault circuit and the disconnector 20-P belonging to the auxiliary line P of the healthy circuit. However, even in this case, the concept of the upstream and downstream sides of the fault current remains the same as in the first operation. That is, the control unit 100 controls each component belonging to the fault circuit on the upstream side of the fault current and controls each component belonging to the healthy circuit on the downstream side of the fault current. In this case, the procedure in the control unit 100 should be equivalent to that of the first operation. Therefore, a further detailed explanation of the procedure in the control unit 100 will be omitted.

[0045] [Second operation in DC current interruption device 1: interrupting DC bus B] The first operation described above explains the operation to interrupt a faulty circuit in the DC transmission line LN-1 when a fault occurs in this line. However, faults can also occur inside the DC current interruption device 1, for example. For example, in the configuration of the DC current interruption device 1 shown in Figure 1, a fault may occur in the DC bus BN. In this case, the fault occurring in the DC bus BN will cause fault current to flow from the DC transmission line LN-1 to the DC transmission line LN-3.

[0046] Here, referring to Figures 4 and 12 to 16, a second operation in which the control unit 100 shuts off the DC bus B where a fault has occurred will be described. In the following description, it will be assumed that the DC current interruption device 1 has three circuits (n=3). The second operation will be described as an example in which, for example, DC transmission lines LN-1 to LN-3 are connected to each other via DC buses BP and BN, and current is flowing from DC transmission line LN-3 to DC transmission lines LN-1 and LN-2, and a fault occurs in DC bus BN, causing the control unit 100 to shut off DC bus BN. Figures 12 to 16 show the current flow within the DC current interruption device 1 when each component is controlled by the control unit 100.

[0047] In the steady-state power transmission condition (initial state) where DC transmission lines LN-1 to LN-3 are connected to each other via DC buses BP and BN and transmitting power, all disconnectors 20 are closed, similar to the first operation. The commutation circuit 30 is also off, and the semiconductor circuit breaker 40 is also off (see Figure 4).

[0048] Here, as shown in Figure 12, let's assume that a fault X (for example, a ground fault) occurs in the DC bus BN. In this case, the control unit 100 shuts off the DC bus BN where the fault X occurred by controlling the open state, closed state, on state, and off state of each component in the following procedure. In the following explanation, the auxiliary line N of the DC transmission line LN connected to the DC bus BN where the fault X occurred will also be called the "fault line," and the auxiliary line P of the DC transmission line LN connected to DC bus BP other than the DC bus BN (fault line) where the fault X occurred, that is, the DC bus BP where the fault X did not occur, will also be called the "healthy line."

[0049] (Procedure 2-1): First, the control unit 100 opens each disconnector 20-N (disconnectors 20-N-1 to 20-N-3) belonging to the auxiliary line N of the DC transmission line LN connected to the DC bus BN (fault line) where fault X occurred. In other words, the control unit 100 opens all mechanical contact type switches belonging to the auxiliary line N. Even in this case, as shown in Figure 13, current (fault current) is flowing through the DC bus BN to the auxiliary line N in the DC current interruption device 1. This is because, as in the first operation when fault X occurs in the DC transmission line LN-1, simply opening each disconnector 20-N, which is a mechanical contact type switch, does not electrically interrupt the DC transmission line LN (interruption state) due to the arc A generated between the contacts of each disconnector 20-N that has been opened.

[0050] (Procedure 2-2): Next, the control unit 100 operates each semiconductor circuit breaker 40 to the ON state. As a result, the commutation circuit 30 discharges the charge from the capacitor and applies a negative voltage to the DC bus BN with respect to the DC bus BP. Figure 14 shows the state in which a commutation current CC corresponding to the negative voltage applied by the commutation circuit 30 is flowing. Due to the commutation current CC flowing in response to the application of the negative voltage to the DC bus BN by the commutation circuit 30, the fault current flowing through each disconnector 20-N that was opened in Procedure 2-1 becomes approximately zero. As a result, the arc A that was generated between the contacts of each disconnector 20-N that was opened in Procedure 2-1 is extinguished. Here, in step 2-2, similar to the first operation, if, after opening each disconnector 20-N in step 2-1, the fault current between the poles of each disconnector 20-N becomes approximately zero due to the fault current flow state, the control unit 100 does not need to operate the commutation circuit 30 in step 2-2.

[0051] When the fault current flowing through each disconnector 20-N, which was opened in step 2-1, becomes approximately zero due to the commutation current CC that flows in response to the application of a negative voltage to the DC bus BN by the commutation circuit 30, the fault current is commutated to the semiconductor circuit breaker 40.

[0052] (Step 2-3): Subsequently, if the voltage across the capacitor in the commutation circuit 30 exceeds a specified value, the control unit 100 activates the commutation circuit 30 to the ON state. As a result, the fault current commutated to the semiconductor circuit breaker 40 enters a bypass state, flowing without passing through the capacitor in the commutation circuit 30, as shown in Figure 15.

[0053] (Procedure 2-4): Next, the control unit 100 operates the semiconductor circuit breaker 40 to the OFF state. As a result, the fault current of the DC bus BN is interrupted in the DC current interruption device 1 and becomes approximately zero (transitions to approximately zero). After that, the fault current continues to flow in the DC current interruption device 1 for a while due to the surge energy accumulated in the inductance component in the line, but this surge energy is consumed by the arrester 50. Figure 16 shows the state in which the fault current of the DC bus BN flows through the arrester 50. Here, in the second operation as in the first operation, the control unit 100 may or may not turn off the thyristor in the commutation circuit 30 in procedure 2-4.

[0054] Through this procedure, the control unit 100 of the DC current interruption device 1 controls each disconnector 20-N belonging to all auxiliary lines N connected to the faulty DC bus BN to extinguish the arc A caused by the fault current. As a result, the control unit 100 completes the operation of electrically interrupting the DC bus BN where the fault X occurred. Thus, the DC current interruption device 1 can interrupt the faulty DC bus BN and maintain power transmission through the healthy DC bus BP.

[0055] (Procedure 2-5): After the DC bus BN is no longer a faulty line (for example, after the repair of fault X that occurred on DC bus BN is completed), the control unit 100 closes each disconnector 20-N belonging to all auxiliary lines N connected to DC bus BN. In other words, the control unit 100 returns the mechanical contact type switches that were open on the auxiliary lines N connected to DC bus BN where fault X occurred to the closed state. As a result, the DC current interruption device 1 transmits DC current in the power transmission state (initial state) via DC bus B for both DC bus BP and DC bus BN (see Figure 4).

[0056] Through this procedure, the control unit 100 of the DC current interruption device 1 controls the disconnector 20-N belonging to the auxiliary line N connected to the faulty DC bus BN to extinguish the arc A caused by the faulty current. As a result, the DC current interruption device 1 can interrupt the DC bus BN and maintain power transmission via the DC bus BP. Moreover, in this case, the power flow state of each DC transmission line LN in the steady-state power transmission state (initial state) does not matter. Subsequently, the control unit 100 of the DC current interruption device 1 restores the state of each component to its original state after the DC bus BN is no longer a faulty line.

[0057] The second operation described above explained the case where the DC bus BN becomes a fault circuit. That is, it explained the case where the fault current flows from the first terminal e to the second terminal f of the semiconductor circuit breaker 40. This is because the configuration of the semiconductor circuit breaker 40 is such that it interrupts the current flowing from the first terminal e to the second terminal f. However, even if the DC bus BP becomes a fault circuit, if the fault current flows from the first terminal e to the second terminal f of the semiconductor circuit breaker 40, the DC bus BP can be similarly interrupted, and power transmission via the DC bus BN can be maintained. Furthermore, as described above, the semiconductor circuit breaker 40 can be configured to interrupt fault currents in both directions by, for example, replacing the semiconductor circuit breaker 40b shown in Figure 2B, or the semiconductor switch unit 41 with the semiconductor switch unit 41a shown in Figure 2C or the semiconductor switch unit 41b shown in Figure 2D. In this case, the DC current interruption device 1 can interrupt the DC bus B where fault X occurred, regardless of the direction of the fault current flowing due to fault X, and maintain power transmission via the DC bus B where fault X did not occur. In this case, the procedure in the control unit 100 should be equivalent to the second operation. Therefore, a further detailed explanation of the procedure in the control unit 100 is omitted.

[0058] [Third operation in DC current interruption device 1 to interrupt the DC transmission line LN] The first and second operations described above explained the case where the DC current interruption device 1 has three circuits (n=3). However, the number of circuits in the DC current interruption device 1 is not limited to three circuits; it may have two circuits, four circuits or more.

[0059] Here, referring to Figures 17 to 24, a third operation in which the control unit 100 shuts off the DC transmission line LN where a fault has occurred will be described when the number of circuits in the DC current interruption device 1 is different. In the following description, it will be assumed that the number of circuits in the DC current interruption device 1 is two (n=2). Then, in the DC current interruption device 1, for example, DC transmission lines LN-1 and LN-2 are connected to each other via DC bus BP and DC bus BN, and current is flowing from DC transmission line LN-2 to DC transmission line LN-1, and a fault occurs in DC transmission line LN-1, so the control unit 100 shuts off DC transmission line LN-1 will be described as an example of the third operation. Figures 17 to 24 show the flow of current in the DC current interruption device 1 when each component is controlled by the control unit 100.

[0060] In a steady-state power transmission operation (initial state) where DC transmission lines LN-1 and LN-2 are connected to each other via DC buses BP and BN and transmitting power, all disconnectors 20 are closed, the commutation circuit 30 is off, and the semiconductor circuit breaker 40 is off. In this case, as shown in Figure 17, current is flowing from DC transmission line LN-2 to DC transmission line LN-1 via DC buses BP and BN, respectively, in the DC current interruption device 1.

[0061] Here, as shown in Figure 18, if fault X occurs in DC transmission line LN-1, the control unit 100 shuts off DC transmission line LN-1 where fault X occurred by controlling the open, closed, on, and off states of each component in the following procedure. In the following explanation, DC transmission line LN-1 where fault X occurred will also be referred to as the "fault line," and DC transmission lines other than DC transmission line LN-1 (fault line), that is, DC transmission lines LN-2 where fault X has not occurred, will also be referred to as "healthy lines."

[0062] (Procedure 3-1): First, the control unit 100 opens the disconnector 20-P-1 belonging to the auxiliary line P-1 of the DC transmission line LN-1 (fault line) where fault X occurred, and opens the disconnector 20-N-2 belonging to the auxiliary line N-2 of the DC transmission line LN-2 (healthy line) where fault X did not occur. In this case as well, as shown in Figure 19, an arc A is generated between the contacts of each of the open disconnectors 20 in the DC current interruption device 1, and current (fault current) flows from the DC transmission line LN-2 to the DC transmission line LN-1 via the DC bus BP and DC bus BN, respectively.

[0063] (Procedure 3-2): Next, the control unit 100 operates the semiconductor circuit breaker 40 to the ON state, similar to the first operation. As a result, the commutation circuit 30 discharges the charge from the capacitor and applies a negative voltage to the DC bus BN with respect to the DC bus BP. Figure 20 shows the state in which a commutation current CC corresponding to the negative voltage applied by the commutation circuit 30 is flowing. Due to the commutation current CC flowing in response to the application of the negative voltage to the DC bus BN by the commutation circuit 30, the fault currents flowing through disconnectors 20-P-1 and 20-N-2, which were opened in procedure 3-1, become approximately zero. As a result, the arc A that was generated between the contacts of disconnectors 20-P-1 and 20-N-2, which were opened in procedure 3-1, is extinguished. Here, in step 3-2, similar to the first operation, if, after opening each disconnector 20 in step 3-1, the fault current between the poles of each disconnector 20 becomes approximately zero due to the fault current flow state, the control unit 100 does not need to operate the commutation circuit 30 in step 3-2.

[0064] When the fault current flowing through each disconnector 20, which was opened in step 3-1, becomes approximately zero due to the commutation current CC that flows in response to the application of a negative voltage to the DC bus BN by the commutation circuit 30, the fault current is commutated to the semiconductor circuit breaker 40.

[0065] (Step 3-3): Subsequently, if the voltage across the capacitor in the commutation circuit 30 exceeds a specified value, the control unit 100 turns on the commutation circuit 30, similar to the first operation. As a result, the fault current commutated to the semiconductor circuit breaker 40 enters a bypass state, flowing without passing through the capacitor in the commutation circuit 30, as shown in Figure 21.

[0066] (Procedure 3-4): Next, the control unit 100 operates the semiconductor circuit breaker 40 to the OFF state, similar to the first operation. As a result, the fault current of the DC transmission line LN-1 is interrupted in the DC current interruption device 1, becoming approximately zero (transitioning to a state of approximately zero). Subsequently, in the DC current interruption device 1, the fault current that continues to flow due to the surge energy accumulated in the inductance component in the line is consumed by the arrester 50. Figure 22 shows the state in which the fault current of the DC transmission line LN-1 flows through the arrester 50. Here, in the third operation as well, the control unit 100 may turn off the thyristor in the commutation circuit 30 in procedure 3-4, or in the next procedure 3-5, similar to the first operation.

[0067] (Step 3-5): Next, the control unit 100, similar to the first operation, opens the disconnector 20-N-1 belonging to the auxiliary line N-1 of the DC transmission line LN-1 where fault X occurred, after the fault current flowing through the DC transmission line LN-1 has become zero (for example, after a period of time has elapsed in which it can be considered that the fault current flowing through the DC transmission line LN-1 has become zero). Figure 23 shows the state in which the disconnector 20-N-1 is open when no fault current is flowing through the DC transmission line LN-1. As a result, the DC current interruption device 1, as shown in Figure 23, prevents the current flowing from the DC transmission line LN-2 via the DC bus BP from flowing through the DC transmission line LN-1. In other words, the DC transmission line LN-1 where fault X occurred is interrupted. In other words, in the third operation, because the DC current interruption device 1 has two circuits, the transmission of DC current from the healthy DC transmission line LN-2 is stopped.

[0068] (Procedure 3-6): Next, the control unit 100 closes the disconnector 20-N-2 belonging to the auxiliary line N-2 of the DC transmission line LN-2 where fault X has not occurred. With this, the control unit 100 completes the operation of electrically interrupting the DC transmission line LN-1 where fault X has occurred. Here again, the DC current interruption device 1 maintains a state in which the transmission of DC current from the healthy DC transmission line LN-2 is stopped. Figure 24 shows the state in which the current flowing from the healthy DC transmission line LN-2 through the DC bus BP and DC bus BN respectively no longer flows to the faulty DC transmission line LN-1.

[0069] Through this procedure, even when the number of circuits differs, the DC current interruption device 1 controls the disconnector 20-P belonging to the auxiliary line P of the faulty circuit and the disconnector 20-N belonging to the auxiliary line N of the healthy circuit to extinguish the arc A caused by the fault current. After the fault current becomes zero, the control unit 1 controls the disconnector 20-N belonging to the auxiliary line N of the faulty circuit to interrupt the faulty circuit.

[0070] In the third operation described above, the case in which the control unit 100 interrupts the DC transmission line LN-1 (fault circuit) when the DC current interruption device 1 has two circuits (n=2) was explained. However, the fault circuit can be interrupted similarly even when the DC current interruption device 1 has four or more circuits. In this case, the procedure for controlling the open, closed, on, and off states of each component in the control unit 100 should be equivalent to that of the first, second, and third operations. Therefore, a detailed explanation of the procedure in the control unit 100 when the DC current interruption device 1 has four or more circuits will be omitted.

[0071] As described above, the DC current interruption device 1 of the first embodiment is applicable to multi-terminal DC power transmission systems. The semiconductor circuit breaker 40 and commutation circuit 30, which are costly due to the need to use high-voltage semiconductor components, are made common across all DC power transmission lines LN (reducing the number of high-voltage semiconductor components). In the event of a fault in any of the DC power transmission lines LN or DC bus B, the faulty DC power transmission line LN or DC bus B can be interrupted. Furthermore, if there are DC power transmission lines LN or DC bus B that are not experiencing faults, the DC current transmission through those fault-free DC power transmission lines LN or DC bus B can be maintained.

[0072] Furthermore, in the DC current interruption device 1 of the first embodiment, by configuring the semiconductor circuit breaker 40 to interrupt fault currents in both directions, it is possible to interrupt the fault current flowing through the faulted line regardless of the power flow state of the faulted line, and to maintain power transmission without causing steady power loss during DC power transmission in a healthy line.

[0073] (Second embodiment) The second embodiment will now be described. Figure 25 is a diagram showing an example of the configuration of a DC current interruption device according to the second embodiment. In Figure 25, components having functions common to the DC current interruption device 1 of the first embodiment are denoted by the same reference numerals. Figure 25 shows an example of a DC current interruption device 2 that is applied to a multi-terminal DC power transmission system with n circuits (where n is a natural number) and is configured at the nodal portions of multiple DC power transmission lines LN (DC power transmission lines LN-1 to LN-n).

[0074] The DC current interruption device 2 includes, for example, a plurality of DC reactors 10 (DC reactors 10-1 to 10-n), a plurality of disconnectors 20 (disconnectors 20-P-1 to 20-Pn, and disconnectors 20-N-1 to 20-Nn), a commutation circuit 30, a semiconductor circuit breaker 40, an arrester 50, an inductor 60, a plurality of auxiliary semiconductor circuit breakers 70 (auxiliary semiconductor circuit breakers 70-1 to 70-n), and a control unit 100. Similar to the DC current interruption device 1 of the first embodiment, the DC current interruption device 2 has an additional configuration in which auxiliary semiconductor circuit breakers 70 are added between each auxiliary line N branched off from each DC transmission line LN at a predetermined location (branching point) and the DC bus BN to which the auxiliary lines N are connected.

[0075] Figure 25 shows a DC current interruption device 2 configured such that the semiconductor circuit breakers 40-1 to 40-n in DC current interruption device 1 are combined into a single semiconductor circuit breaker 40, and the arresters 50-1 to 50-n are combined into a single arrester 50. This is merely an example, and the configuration of the semiconductor circuit breakers 40 and arresters 50 in DC current interruption device 2 shown in Figure 25 is intended to facilitate the configuration of DC current interruption device 2 and the following explanation. Therefore, the number of semiconductor circuit breakers 40 and arresters 50 in DC current interruption device 2 may also be multiple, similar to DC current interruption device 1.

[0076] Each of the auxiliary semiconductor circuit breakers 70-1 to 70-n allows or blocks (interrupts) the current flowing between the first terminal g and the second terminal h. The configuration of each auxiliary semiconductor circuit breaker 70 is, for example, the same as the configuration of the semiconductor circuit breaker 40. That is, each auxiliary semiconductor circuit breaker 70 comprises, for example, a semiconductor switching element and a diode connected in parallel to each other. The gate of the semiconductor switching element in the auxiliary semiconductor circuit breaker 70 is controlled (a control voltage is applied) by the control unit 100. That is, the gate of the semiconductor switching element in the auxiliary semiconductor circuit breaker 70 is also controlled by the control unit 100 to either an ON state (conducting state) or an OFF state (non-conducting state). The semiconductor switching element in the auxiliary semiconductor circuit breaker 70 is, for example, a switching element such as an insulated-gate bipolar transistor (IGBT), similar to the semiconductor switching element in the semiconductor circuit breaker 40. However, the semiconductor switching element in the auxiliary semiconductor circuit breaker 70 may have a lower withstand voltage than the semiconductor switching element in the semiconductor circuit breaker 40. The semiconductor switching element in the auxiliary semiconductor circuit breaker 70 is not limited to IGBTs, but can be any switching element that is capable of self-extinguishing. Each auxiliary semiconductor circuit breaker 70, for example, similar to the semiconductor circuit breaker 40, allows current to flow from the first end g to the second end h when it is in the ON state, and blocks (interrupts) this current when it is in the OFF state. The ON state of the auxiliary semiconductor circuit breaker 70 is an example of a "conducting state," and the OFF state is an example of a "non-conducting state." The semiconductor switching element in the auxiliary semiconductor circuit breaker 70 is an example of a "semiconductor element capable of interrupting current flowing between the second auxiliary line and the second DC bus."

[0077] In the DC current interruption device 2, an auxiliary semiconductor circuit breaker 70 is provided between each auxiliary line N and the DC bus BN. Due to the semiconductor elements, such as the semiconductor switching element and diode, in the auxiliary semiconductor circuit breaker 70, the impedance of the auxiliary line N on the DC bus BN side is high. Therefore, in the DC current interruption device 2, regardless of whether the auxiliary semiconductor circuit breaker 70 is in the ON state (i.e., the auxiliary semiconductor circuit breaker 70 is allowing current to flow from the first end g to the second end h) or the OFF state (i.e., the auxiliary semiconductor circuit breaker 70 is blocking (interrupting) current flowing from the first end g to the second end h), current will flow through the auxiliary line P on the DC bus BP side, where the impedance is lower than that of the DC bus BN side. In other words, in the DC current interruption device 2, the current transmitted between each DC transmission line LN flows mainly through the DC bus BP side. Therefore, the DC current interruption device 2 can transmit power in the same way as the DC current interruption device 1 without increasing the steady-state power loss during power transmission due to the provision of an auxiliary semiconductor circuit breaker 70 on the DC bus BN side. Furthermore, in the DC current interruption device 2, since the impedance of the auxiliary line N on the DC bus BN side is high, even if the disconnector 20 is opened in response to a fault occurring in either the DC transmission line LN or DC bus B, the size of the arc generated between the contacts in the disconnector 20 on the DC bus BN side that is opened will be smaller than that of the DC current interruption device 1, making it easier to extinguish the arc.

[0078] The configuration of the auxiliary semiconductor circuit breaker 70 provided in the DC current interruption device 2 is not limited to the configuration comprising the semiconductor switching element and diode described above. Figures 26A to 26D show an example of the configuration of the auxiliary semiconductor circuit breaker 70 provided in the DC current interruption device 2 of the second embodiment.

[0079] The auxiliary semiconductor circuit breaker 70a shown in Figure 26A has a configuration in which, for example, a semiconductor switching element and a diode are connected in parallel with each other. The auxiliary semiconductor circuit breaker 70a is an example of a configuration similar to that of the semiconductor circuit breaker 40 described above. The auxiliary semiconductor circuit breaker 70a can allow or block (interrupt) the current flowing from the first end g to the second end h depending on the control of the control unit 100 to either an ON state or an OFF state.

[0080] The auxiliary semiconductor circuit breaker 70b shown in Figure 26B is, for example, composed of a single diode. In the auxiliary semiconductor circuit breaker 70b, the control unit 100 cannot control it to either an ON state or an OFF state, and it interrupts the current flowing from the first terminal g to the second terminal h. However, because it has a simpler configuration than the auxiliary semiconductor circuit breaker 70a which has a semiconductor switching element, the cost and size of the auxiliary semiconductor circuit breaker 70 can be reduced.

[0081] The auxiliary semiconductor circuit breaker 70c shown in Figure 26C is, for example, composed of a single thyristor. The auxiliary semiconductor circuit breaker 70c can also allow or block (interrupt) the current flowing from the first end g to the second end h, depending on whether it is controlled to an ON or OFF state by the control unit 100. Since the auxiliary semiconductor circuit breaker 70c is composed of a single thyristor, it has a simpler configuration than the auxiliary semiconductor circuit breaker 70a, and the cost and size of the auxiliary semiconductor circuit breaker 70 can be reduced.

[0082] The auxiliary semiconductor circuit breaker 70d shown in Figure 26D is, for example, composed of two thyristors connected in parallel and facing opposite directions. The auxiliary semiconductor circuit breaker 70d is composed of so-called bidirectional thyristors. The auxiliary semiconductor circuit breaker 70d can allow or block (interrupt) bidirectional current flowing between the first end g and the second end h in response to control by the control unit 100 to either an ON state or an OFF state. Because the auxiliary semiconductor circuit breaker 70d is composed of two thyristors (bidirectional thyristors), it is more expensive and larger than the auxiliary semiconductor circuit breaker 70c, but it is easier to construct than the auxiliary semiconductor circuit breaker 70a, thus reducing the cost and size when constructing the auxiliary semiconductor circuit breaker 70.

[0083] [Operation of DC current interruption device 2] In the DC current interruption device 2, as in the DC current interruption device 1, if a fault occurs in either the DC transmission line LN or DC bus B, the control unit 100 controls the open, closed, on, and off states of each component in order to interrupt the faulty circuit. The procedure of the control unit 100 when interrupting the faulty DC transmission line LN or DC bus B in the DC current interruption device 2 should be equivalent to the procedure of the control unit 100 in the DC current interruption device 1 (the procedures for the first, second, and third operations). Therefore, a detailed explanation of the procedure of the control unit 100 in the DC current interruption device 2 is omitted.

[0084] Incidentally, the DC current interruption device 2 is configured to have auxiliary semiconductor circuit breakers 70 between each auxiliary line N and DC bus BN. Therefore, in the DC current interruption device 2, the control unit 100 controls each auxiliary semiconductor circuit breaker 70 to either an ON state or an OFF state. The control unit 100 may keep the auxiliary semiconductor circuit breaker 70 always ON. Furthermore, the control unit 100 does not need to change the state of the auxiliary semiconductor circuit breaker 70 even if a fault occurs in either the DC transmission line LN or DC bus B. In this case, the operation of the DC current interruption device 2 will be equivalent to the operation of the DC current interruption device 1. However, the control unit 100 may also control the ON state and the OFF state of each auxiliary semiconductor circuit breaker 70 according to the direction of the steady current or fault current (current flow state) flowing through the auxiliary line N.

[0085] For example, in the steady-state power transmission state (initial state) of the DC current interruption device 2, the control unit 100 may operate each auxiliary semiconductor circuit breaker 70 in the ON state, and if a fault occurs in any of the DC transmission lines LN or DC bus B, it may change the state of each auxiliary semiconductor circuit breaker 70 in the procedure for interrupting the faulty line. In this case, the control unit 100 operates the auxiliary semiconductor circuit breaker 70 connected to the auxiliary line N to which the disconnector 20-N that was opened in step 1-1, step 2-1, and step 3-1 belongs in the OFF state. Subsequently, when the disconnector 20-N that was opened in step 1-6, step 2-5, and step 3-6 is closed, the control unit 100 operates the auxiliary semiconductor circuit breaker 70 connected to the auxiliary line N to which the disconnector 20-N to be closed belongs in the ON state.

[0086] As an example in this case, let's consider the first operation of the DC current interruption device 1. In the first operation, before the control unit 100 turns on the semiconductor circuit breaker 40 in step 1-2, it turns off the auxiliary semiconductor circuit breaker 70-2 connected to the auxiliary line N-2 to which disconnector 20-N-2 belongs, and the auxiliary semiconductor circuit breaker 70-3 connected to the auxiliary line N-3 to which disconnector 20-N-3 belongs. As a result, in the DC current interruption device 1, the commutation current CC flowed through three paths passing through disconnectors 20-P-1, 20-N-2, and 20-N-3, which were opened in step 1-1, by the commutation circuit 30 applying a negative voltage to the DC bus BN (see Figure 7). However, in the DC current interruption device 2, the commutation current CC flows only through one path passing through disconnector 20-P-1 (the path via auxiliary line N-1 and auxiliary line P-1). As a result, the DC current interruption device 2 can reduce the fault current flowing through the disconnector 20-P-1 to approximately zero more quickly by the commutation current CC that flows in response to the application of a negative voltage to the DC bus BN by the commutation circuit 30. This allows the arc A generated between the contacts of the disconnector 20-P-1 to be extinguished more quickly in the DC current interruption device 2. Moreover, in the DC current interruption device 2, the commutation current CC flows only through the path passing through the disconnector 20-P-1, thereby reducing the load on the commutation circuit 30 when a negative voltage is applied to the DC bus BN. On the other hand, the arc A generated between the contacts of the disconnectors 20-N (disconnectors 20-N-2 and 20-N-3) belonging to the auxiliary line N, which has the auxiliary semiconductor circuit breaker 70 turned off, is extinguished as the auxiliary semiconductor circuit breaker 70 is controlled to the off state. Subsequently, when the control unit 100 closes the disconnectors 20-N-2 and 20-N-3, which were in the open state in step 1-6, it operates the auxiliary semiconductor circuit breakers 70-2 and 70-3 to the ON state. The control unit 100 may also operate the auxiliary semiconductor circuit breakers 70-2 and 70-3 to the ON state when it operates the semiconductor circuit breaker 40 to the OFF state in step 1-4 (for example, at the same time as it operates the semiconductor circuit breaker 40 to the OFF state).

[0087] For example, in the steady-state power transmission state (initial state) of the DC current interruption device 2, the control unit 100 may operate each auxiliary semiconductor circuit breaker 70 in the OFF state, and in the procedure for interrupting the faulty circuit when a fault occurs in either the DC transmission line LN or DC bus B, it may change the state of each auxiliary semiconductor circuit breaker 70. In this case, the control unit 100 operates the semiconductor circuit breaker 40 in the ON state in steps 1-2, 2-2, and 3-2, causing the commutation circuit 30 to apply a negative voltage to the DC bus BN, that is, when the commutation current CC flows through the path passing through the disconnector 20-P which was opened in steps 1-1, 2-1, and 3-1, it operates the auxiliary semiconductor circuit breaker 70 connected to the auxiliary line N of the path to which the disconnector 20-P which was opened belongs, in the ON state. For example, in the first operation, when the commutation current CC flows through the path passing through the disconnector 20-P-1 belonging to the auxiliary line P-1 of the fault circuit that was opened in step 1-1, the auxiliary semiconductor circuit breaker 70-1 connected to the auxiliary line N-1 is activated to the ON state. This ensures that even when the auxiliary semiconductor circuit breaker 70, which is currently in the OFF state, is activated to the ON state, the commutation current CC flows through only one path passing through the disconnector 20-P-1 (the path passing through auxiliary line N-1 and auxiliary line P-1). The commutation current CC then flows to the disconnector 20-P via the ON-state auxiliary semiconductor circuit breaker 70, causing the arc generated between the contacts of the disconnector 20-P to be extinguished more quickly. Moreover, even when the auxiliary semiconductor circuit breaker 70, which is currently in the OFF state, is activated to the ON state, the load on the commutation circuit 30 when a negative voltage is applied to the DC bus BN is reduced, similar to the method of activating the auxiliary semiconductor circuit breaker 70, which is currently in the ON state, to the OFF state. Then, the arc generated between the contacts of the disconnectors 20-N (disconnectors 20-N-2 and 20-N-3 in the first operation) belonging to the auxiliary line N to which the auxiliary semiconductor circuit breaker 70, which is initially in the off state, is connected, is extinguished by the off-state auxiliary semiconductor circuit breaker 70. Subsequently, when the disconnectors 20-N belonging to the auxiliary line N are opened in steps 1-5 and 3-5, the control unit 100 operates the auxiliary semiconductor circuit breaker 70 connected to this auxiliary line N to the off state.The control unit 100 may also turn off the auxiliary semiconductor circuit breaker 70 connected to the auxiliary line N when it turns off the semiconductor circuit breaker 40 in steps 1-4, 2-4, and 3-4 (for example, at the same time as turning off the semiconductor circuit breaker 40).

[0088] With this configuration and procedure, the DC current interruption device 2, like the DC current interruption device 1, can standardize the semiconductor circuit breaker 40 and commutation circuit 30, which would otherwise be costly due to the need to use high-voltage semiconductor components, across all DC transmission lines LN. In the event of a fault in any of the DC transmission lines LN or DC bus B, it can interrupt that DC transmission line LN or DC bus B. As a result, the DC current interruption device 2, like the DC current interruption device 1, can maintain the transmission of DC current through DC transmission lines LN and DC bus B that are not experiencing faults.

[0089] Furthermore, in the DC current interruption device 2, an auxiliary semiconductor circuit breaker 70 is connected between each auxiliary line N and the DC bus BN. As a result, in the DC current interruption device 2, the impedance of the auxiliary line N on the DC bus BN side is increased, and even when the disconnector 20 is opened in response to an accident, it is possible to extinguish the arc generated between the contacts in the disconnector 20 on the DC bus BN side that is in the open state. This also allows for a simpler configuration of the commutation circuit 30 in the DC current interruption device 2.

[0090] As described above, the DC current interruption device 2 of the second embodiment, like the DC current interruption device 1, is applied to multi-terminal DC power transmission systems. The semiconductor circuit breaker 40 and commutation circuit 30, which are costly due to the need to use high-voltage semiconductor components, are made common across all DC transmission lines LN (reducing the number of high-voltage semiconductor components). In the event of a fault in any of the DC transmission lines LN or DC bus B, the faulty DC transmission line LN or DC bus B is interrupted, and the transmission of DC current through the DC transmission lines LN or DC bus B that are not faulty is maintained. Furthermore, in the DC current interruption device 2 of the second embodiment, similar to the DC current interruption device 1, the semiconductor circuit breaker 40 is configured to interrupt fault currents in both directions. This allows for the interruption of fault currents flowing through the faulty line regardless of the power flow state of the faulty line, and enables power transmission to be maintained without causing steady-state power loss during DC power transmission on healthy lines.

[0091] Furthermore, in the DC current interruption device 2 of the second embodiment, by connecting an auxiliary semiconductor circuit breaker 70 between each auxiliary line N and the DC bus BN, the impedance of the auxiliary line N on the DC bus BN side is increased, making it easier to extinguish the arc generated between the contacts in the disconnector 20 on the DC bus BN side, which is opened in response to the occurrence of a fault. As a result, the commutation circuit 30 in the DC current interruption device 2 of the second embodiment can be made simpler, and the cost of the DC current interruption device 2 of the second embodiment can be reduced.

[0092] (Third embodiment) The third embodiment will now be described. Figure 27 is a diagram showing an example of the configuration of a DC current interruption device according to the third embodiment. In Figure 27, components having functions common to the DC current interruption device 1 of the first embodiment or the DC current interruption device 2 of the second embodiment are denoted by the same reference numerals. Figure 27 shows an example of a DC current interruption device 3 that is applied to a multi-terminal DC power transmission system with n circuits (where n is a natural number) and is configured at the nodal portions of multiple DC power transmission lines LN (DC power transmission lines LN-1 to LN-n).

[0093] The DC current interruption device 3 includes, for example, a plurality of DC reactors 10 (DC reactors 10-1 to 10-n), a plurality of disconnectors 20 (disconnectors 20-P-1 to 20-Pn, and disconnectors 20-N-1 to 20-Nn), a commutation circuit 30, a semiconductor circuit breaker 40, an arrester 50, an inductor 60, a disconnector 80, and a control unit 100.

[0094] Figure 27 also shows a DC current interruption device 3, which, like the DC current interruption device 2 of the second embodiment, has a configuration in which the semiconductor circuit breakers 40-1 to 40-n of the DC current interruption device 1 are combined into a single semiconductor circuit breaker 40, and the arresters 50-1 to 50-n are combined into a single arrester 50. However, the number of semiconductor circuit breakers 40 and arresters 50 in the DC current interruption device 3 may also be multiple, similar to the DC current interruption device 1.

[0095] The DC current interruption device 3 has a configuration in which a component that has the function of interrupting a fault circuit that is connected in series between the two DC buses B in the DC current interruption device 1 is connected in parallel between the two DC buses B. For this reason, a disconnector 80 is added to the DC current interruption device 3. More specifically, in the DC current interruption device 3, a parallel circuit of a semiconductor circuit breaker 40 and an arrester 50 is connected between the DC bus BP and the DC bus BN, and a series circuit in which the disconnector 80, a commutator circuit 30, and an inductor 60 are connected in this order is connected between the DC bus BP and the DC bus BN. As a result, in the DC current interruption device 3, the two auxiliary lines that branch off in each DC transmission line LN are connected to each other via the corresponding DC bus B and the parallel circuit of the semiconductor circuit breaker 40 and arrester 50, or the series circuit of the disconnector 80, a commutator circuit 30, and an inductor 60.

[0096] The disconnector 80, like the disconnector 20, is a mechanical contact type switch. Like the disconnector 20, the disconnector 80 is controlled by the control unit 100 to be either open or closed. The disconnector 80 is an example of a "third type of mechanical contact."

[0097] [Fourth operation of the DC current interruption device 3, which interrupts the DC transmission line LN] Here, referring to Figures 28 to 36, a fourth operation in which the control unit 100 shuts off the DC transmission line LN where a fault has occurred will be described. In the following description, similar to the first operation in the DC current interruption device 1, it will be assumed that the number of circuits in the DC current interruption device 3 is three (n=3). And, similar to the first operation, in the DC current interruption device 3, for example, when DC transmission lines LN-1 to LN-3 are each connected to each other via DC bus BP and DC bus BN, and current is flowing from DC transmission line LN-3 to DC transmission lines LN-1 and DC transmission lines LN-2, and a fault occurs in DC transmission line LN-1, the control unit 100 will shut off DC transmission line LN-1 as an example, which will be described as the fourth operation. Figures 28 to 36 show the current flow in the DC current interruption device 3 when each component is controlled by the control unit 100.

[0098] In the steady-state power transmission condition (initial state) where DC transmission lines LN-1 to LN-3 are connected to each other via DC buses BP and BN and transmitting power, all disconnectors 20 are in the closed state, similar to the first operation. In the fourth operation, the commutation circuit 30 is in the off state, and the semiconductor circuit breaker 40 is in the off state. Furthermore, the disconnector 80 is in the closed state. In this case, as shown in Figure 28, current is flowing from DC transmission line LN-3 to DC transmission lines LN-1 and LN-2 via DC buses BP and BN, respectively, in the DC current interruption device 3.

[0099] Here, as shown in Figure 29, if fault X occurs in DC transmission line LN-1, the control unit 100 shuts off DC transmission line LN-1 where fault X occurred by controlling the open, closed, on, and off states of each component in the following procedure. In the following explanation, DC transmission line LN-1 where fault X occurred will also be referred to as the "fault line," and DC transmission lines LN other than DC transmission line LN-1 (fault line) where fault X occurred, that is, DC transmission lines LN-2 and LN-3 where fault X has not occurred, will also be referred to as "healthy lines."

[0100] (Procedure 4-1): First, the control unit 100, similar to the first operation, opens the disconnector 20-P-1 belonging to the auxiliary line P-1 of the DC transmission line LN-1 (fault line) where fault X occurred, and also opens the disconnector 20-N-2 belonging to the auxiliary line N-2 of the DC transmission line LN-2 (healthy line) where fault X did not occur, and the disconnector 20-N-3 belonging to the auxiliary line N-3 of the DC transmission line LN-3 (healthy line). In this case as well, as shown in Figure 30, an arc A is generated between the contacts of each of the open disconnectors 20 in the DC current interruption device 3, and current (fault current) flows from the DC transmission line LN-3 to the DC transmission lines LN-1 and LN-2 via the DC buses BP and BN, respectively.

[0101] (Procedure 4-2): Next, the control unit 100 turns on the commutation circuit 30. As a result, the commutation circuit 30 discharges the charge from its capacitor and applies a negative voltage to the DC bus BN with respect to the DC bus BP. Figure 31 shows the state in which a commutation current CC corresponding to the negative voltage applied by the commutation circuit 30 is flowing. Furthermore, Figure 31 shows that because the disconnector 80 is in a closed state, a fault current is also flowing through the series circuit path between the disconnector 80 connected between the DC bus BP and the DC bus BN, the commutation circuit 30, and the inductor 60 (hereinafter referred to as the "path of the commutation circuit 30"). Due to the commutation current CC flowing in response to the application of a negative voltage to the DC bus BN by the commutation circuit 30, the fault current flowing through the disconnectors 20 (disconnector 20-P-1, disconnector 20-N-2, and disconnector 20-N-3), which were opened in procedure 4-1, becomes approximately zero. This extinguishes the arc A that was generated between the contacts of each disconnector 20 that was opened in step 4-1.

[0102] (Procedure 4-3): Next, the control unit 100 operates the semiconductor circuit breaker 40 to the ON state. As a result, the commutation current CC and fault current that flow in response to the application of a negative voltage to the DC bus BN by the commutation circuit 30 also flow through the semiconductor circuit breaker 40. Figure 32 shows the state in which the commutation current CC and fault current corresponding to the negative voltage applied by the commutation circuit 30 also flow through the semiconductor circuit breaker 40.

[0103] (Procedure 4-4): Subsequently, if the voltage of the capacitor in the commutation circuit 30 exceeds a specified value, the control unit 100 operates the commutation circuit 30 to the OFF state. As a result, the fault current flowing through the path of the commutation circuit 30 becomes approximately zero. The fault current is then commutated to the semiconductor circuit breaker 40, as shown in Figure 33. Hereinafter, after the disconnector 20 is opened in procedure 4-1, depending on the direction of the fault current flow (current flow state), the fault current between the two poles of the disconnector 20 may become approximately zero. In this case, the control unit 100 does not need to operate the commutation circuit 30 in procedure 4-4.

[0104] (Steps 4-5): Next, the control unit 100 operates the semiconductor circuit breaker 40 to the OFF state. As a result, the fault current of the DC transmission line LN-1 is interrupted in the DC current interruption device 3, becoming approximately zero (transitioning to a state of approximately zero). After that, the fault current continues to flow for a while in the DC current interruption device 3 due to the surge energy accumulated in the inductance component in the line, but this surge energy is consumed by the arrester 50. Figure 34 shows the state in which the fault current of the DC transmission line LN-1 flows through the arrester 50.

[0105] (Procedure 4-6): Next, the control unit 100, similar to the first operation, opens the disconnector 20-N-1 belonging to the auxiliary line N-1 of the DC transmission line LN-1 where fault X occurred, after the fault current flowing through the DC transmission line LN-1 has become zero (for example, after a period of time has elapsed in which it can be considered that the fault current flowing through the DC transmission line LN-1 has become zero). Figure 35 shows the state in which the disconnector 20-N-1 is open when no fault current is flowing through the DC transmission line LN-1. As a result, the DC current interruption device 3, as shown in Figure 35, is in a state where current is flowing from the DC transmission line LN-3 to the DC transmission line LN-2 via the DC bus BP. In other words, the DC transmission line LN-1 where fault X occurred is interrupted, and the transmission of DC current by a healthy line is maintained, albeit only through the DC bus BP.

[0106] (Procedure 4-7): Next, the control unit 100 closes the disconnectors 20-N-2 belonging to the auxiliary line N-2 of the DC transmission line LN-2 where fault X has not occurred, and the disconnectors 20-N-3 belonging to the auxiliary line N-2 of the DC transmission line LN-3, respectively, in the same manner as in the first operation. As a result, the control unit 100 completes the operation of electrically interrupting the DC transmission line LN-1 where fault X has occurred. As a result, the DC current interruption device 3 maintains the transmission of DC current through the healthy lines. Figure 36 shows the state in which current flows from the healthy DC transmission line LN-3 to the healthy DC transmission line LN-2 via the DC bus BP and DC bus BN, respectively.

[0107] Through this procedure, the DC current interruption device 3, like the DC current interruption device 1, allows the control unit 100 to control the disconnector 20-P belonging to the auxiliary line P of the faulty circuit and the disconnector 20-N belonging to the auxiliary line N of the healthy circuit to extinguish the arc A caused by the fault current. After the fault current becomes zero, the control unit 100 controls the disconnector 20-N belonging to the auxiliary line N of the faulty circuit to interrupt the faulty circuit and maintain power transmission through the healthy circuit.

[0108] In the fourth operation described above, similar to the first operation in the DC current interruption device 1, the control unit 100 controls the disconnector 20-P belonging to the auxiliary line P of the faulty line and the disconnector 20-N belonging to the auxiliary line N of the healthy line to cause the fault current to flow from the first end e to the second end f of the semiconductor circuit breaker 40, thereby interrupting the DC transmission line LN-1 (faulty line). However, in the DC current interruption device 3, if the semiconductor circuit breaker 40 is replaced with, for example, the semiconductor circuit breaker 40b shown in Figure 2B, or the semiconductor switch unit 41 is replaced with the semiconductor switch unit 41a shown in Figure 2C or the semiconductor switch unit 41b shown in Figure 2D, and the configuration is such that it interrupts fault currents in both directions, then, similar to the DC current interruption device 1, the components controlled by the control unit 100 when interrupting the faulty line may be reversed for the auxiliary line P and the auxiliary line N. In this case, the procedure in the control unit 100 should be equivalent to the fourth operation described above. Therefore, a further detailed explanation of the procedure in the control unit 100 will be omitted.

[0109] [Other interruption operations in DC current interruption device 3] The procedure of the control unit 100 when interrupting DC bus B in the DC current interruption device 3 should be equivalent to the procedure of the control unit 100 for the second operation in the DC current interruption device 1, taking into consideration the fourth operation described above. Therefore, a detailed explanation of the procedure of the control unit 100 when interrupting DC bus B in the DC current interruption device 3 is omitted. Furthermore, the procedure of the interruption operation performed by the control unit 100 when the number of circuits is different in the DC current interruption device 3 should also be equivalent to the procedure of the control unit 100 for the third operation in the DC current interruption device 1, taking into consideration the fourth operation described above. Therefore, a detailed explanation of the procedure of the interruption operation of the control unit 100 when the number of circuits is different in the DC current interruption device 3 is omitted.

[0110] With this configuration and procedure, the DC current interruption device 3, like the DC current interruption device 1, can standardize the semiconductor circuit breaker 40 and commutation circuit 30, which would otherwise be costly due to the need to use high-voltage semiconductor components, across all DC transmission lines LN. In the event of a fault in any of the DC transmission lines LN or DC bus B, it can interrupt that DC transmission line LN or DC bus B. As a result, the DC current interruption device 3, like the DC current interruption device 1, can maintain the transmission of DC current through DC transmission lines LN and DC bus B that are not experiencing faults.

[0111] As described above, the DC current interruption device 3 of the third embodiment, like the DC current interruption device 1, is applied to multi-terminal DC power transmission systems. The semiconductor circuit breaker 40 and commutation circuit 30, which are costly due to the need to use high-voltage semiconductor components, are made common across all DC transmission lines LN (reducing the number of high-voltage semiconductor components). In the event of a fault in any of the DC transmission lines LN or DC bus B, the faulty DC transmission line LN or DC bus B is interrupted, and the transmission of DC current through the DC transmission lines LN or DC bus B that are not faulty is maintained. Furthermore, in the DC current interruption device 3 of the third embodiment, similar to the DC current interruption device 1, the semiconductor circuit breaker 40 is configured to interrupt fault currents in both directions. This allows for the interruption of fault currents flowing through a faulty line regardless of the power flow state of the faulty line, and enables the maintenance of power transmission without causing steady-state power loss during DC power transmission on healthy lines.

[0112] (Fourth embodiment) The fourth embodiment will now be described. Figure 37 is a diagram showing an example of the configuration of a DC current interruption device according to the fourth embodiment. In Figure 37, components having functions common to the DC current interruption device 1 of the first embodiment, the DC current interruption device 2 of the second embodiment, and the DC current interruption device 3 of the third embodiment are denoted by the same reference numerals. Figure 37 shows an example of a DC current interruption device 4 that is applied to a multi-terminal DC power transmission system with n circuits (where n is a natural number) and is configured at the nodal portions of multiple DC transmission lines LN (DC transmission lines LN-1 to LN-n).

[0113] The DC current interruption device 4 includes, for example, a plurality of DC reactors 10 (DC reactors 10-1 to 10-n), a plurality of disconnectors 20 (disconnectors 20-P-1 to 20-Pn, and disconnectors 20-N-1 to 20-Nn), a commutation circuit 30, a semiconductor circuit breaker 40, an arrester 50, an inductor 60, a disconnector 80, a circuit breaker 90, and a control unit 100.

[0114] Figure 37 also shows a DC current interruption device 4, similar to the DC current interruption device 2 of the second embodiment and the DC current interruption device 3 of the third embodiment, in which the semiconductor circuit breakers 40-1 to 40-n of the DC current interruption device 1 are combined into a single semiconductor circuit breaker 40, and the arresters 50-1 to 50-n are combined into a single arrester 50. However, the number of semiconductor circuit breakers 40 and arresters 50 in the DC current interruption device 4 may also be multiple, similar to the DC current interruption device 1.

[0115] The DC current interruption device 4, like the DC current interruption device 3 of the third embodiment, has a configuration in which components that have the function of interrupting a fault circuit connected in series between the two DC buses B in the DC current interruption device 1 are connected in parallel between the two DC buses B, but the way in which they are connected in parallel is different. For this reason, the DC current interruption device 4 has an additional circuit breaker 90 compared to the configuration of the DC current interruption device 3. More specifically, in the DC current interruption device 4, a parallel circuit of a semiconductor circuit breaker 40 and an arrester 50 is connected between the DC buses BP and BN, a disconnector 80 and a circuit breaker 90 are connected in series between the DC buses BP and BN in this order, and a series circuit in which an inductor 60 and a commutator circuit 30 are connected in series in this order is connected in parallel between the ends of the circuit breaker 90. As a result, in the DC current interruption device 4, the two auxiliary lines that branch off in each DC transmission line LN are connected to each other via the corresponding DC bus B and a parallel circuit of semiconductor circuit breaker 40 and arrester 50, or a circuit breaker 90 in which a disconnector 80 and a series circuit of inductor 60 and commutator circuit 30 are connected in parallel.

[0116] The circuit breaker 90, like the disconnectors 20 and 80, is a mechanical contact type switch. Like the disconnectors 20 and 80, the circuit breaker 90 is controlled by the control unit 100 to be either open or closed. The circuit breaker 90 is an example of a "fourth type of mechanical contact."

[0117] [Operation of DC current interruption device 4] In the DC current interruption device 4, as with the DC current interruption device 3, if a fault occurs in any of the DC transmission line LN or DC bus B, the control unit 100 controls the open, closed, on, and off states of each component in order to interrupt the faulty circuit. The procedure of the control unit 100 when interrupting the faulty DC transmission line LN or DC bus B in the DC current interruption device 4 should be equivalent to the procedure of the control unit 100 in the DC current interruption device 3 and DC current interruption device 1 (the fourth operation, and the first, second, and third operations considering the fourth operation). In this case, the control unit 100 should control the circuit breaker 90 in the same way as the disconnector 80. Therefore, a detailed explanation of the procedure of the control unit 100 in the DC current interruption device 4 is omitted.

[0118] With this configuration and procedure, the DC current interruption device 4, like the DC current interruption device 3, can standardize the semiconductor circuit breaker 40 and commutation circuit 30, which would otherwise be costly due to the need to use high-voltage semiconductor components, across all DC transmission lines LN. In the event of a fault in any of the DC transmission lines LN or DC bus B, it can interrupt that DC transmission line LN or DC bus B. As a result, the DC current interruption device 4, like the DC current interruption device 3, can maintain the transmission of DC current through DC transmission lines LN and DC bus B that are not experiencing faults.

[0119] As described above, the DC current interruption device 4 of the fourth embodiment, like the DC current interruption device 3, is applied to multi-terminal DC power transmission systems. The semiconductor circuit breaker 40 and commutation circuit 30, which are costly due to the need to use high-voltage semiconductor components, are made common across all DC transmission lines LN (reducing the number of high-voltage semiconductor components). In the event of a fault in any of the DC transmission lines LN or DC bus B, the faulty DC transmission line LN or DC bus B is interrupted, and the transmission of DC current through the DC transmission lines LN or DC bus B that are not faulty is maintained. Furthermore, in the DC current interruption device 4 of the fourth embodiment, similar to the DC current interruption device 3, the semiconductor circuit breaker 40 is configured to interrupt fault currents in both directions. This allows for the interruption of fault currents flowing through a faulty line regardless of the power flow state of the faulty line, and enables the maintenance of power transmission without the steady-state power loss that occurs during DC power transmission on healthy lines.

[0120] [Variations of DC current interruption device 3 and DC current interruption device 4] In DC current interruption devices 3 and 4, similar to DC current interruption device 2, an auxiliary semiconductor circuit breaker 70 can be connected between each auxiliary line N and the DC bus BN. Figure 38 shows an example of a modified configuration of DC current interruption device 3 according to the third embodiment. Figure 39 shows an example of a modified configuration of DC current interruption device 4 according to the fourth embodiment. Figures 38 and 39 show an example of a DC current interruption device 3a or DC current interruption device 4a that is applied to a multi-terminal DC power transmission system with n lines (where n is a natural number) and configured at the nodal portions of multiple DC power transmission lines LN (DC power transmission lines LN-1 to LN-n). The DC current interruption device 3a shown in Figure 38 is a configuration in which an auxiliary semiconductor circuit breaker 70 is added between each auxiliary line N and the DC bus BN, similar to DC current interruption device 2. The DC current interruption device 4a shown in Figure 39 is configured similarly to the DC current interruption device 2 in that an auxiliary semiconductor circuit breaker 70 is added between each auxiliary line N and the DC bus BN. In Figures 38 and 39, components that have functions common to the DC current interruption device 1, DC current interruption device 2, DC current interruption device 3, and DC current interruption device 4 are denoted by the same reference numerals.

[0121] By changing the configuration of DC current interruption devices 3 and 4 to that of DC current interruption devices 3a and 4a, similar to DC current interruption device 2, the impedance of the auxiliary line N on the DC bus BN side can be increased, making it easier to extinguish the arc generated between the contacts in the disconnector 20 on the DC bus BN side, which is opened in response to an accident. As a result, DC current interruption devices 3a and 4a can have a simpler commutation circuit 30 configuration, similar to DC current interruption device 2, and the cost of DC current interruption devices 3a and 4a can be reduced.

[0122] The procedure of the control unit 100 when shutting off the DC transmission line LN or DC bus B in the DC current interruption device 3a or DC current interruption device 4a in the event of a fault can be easily considered by making it equivalent to the procedure of the control unit 100 in DC current interruption device 1 (the procedure for the first, second, and third operations), taking into account the fourth operation in DC current interruption device 2 described above. Therefore, a detailed explanation of the procedure of the control unit 100 in DC current interruption device 3a or DC current interruption device 4a will be omitted.

[0123] As described above, in the DC current interruption devices of each embodiment, in the DC current interruption devices configured at the node portions of a multi-terminal DC power transmission system, each DC power transmission line LN is branched into auxiliary lines P and N at predetermined locations (branching points), and the DC buses B corresponding to each auxiliary line are connected via common components (commutation circuits, semiconductor circuit breakers, arresters, and inductors) that have the function of interrupting faulty circuits (DC power transmission lines LN and DC buses B) where a fault has occurred. As a result, in the DC current interruption devices of each embodiment, the components (semiconductor circuit breakers and commutation circuits) that have the function of interrupting faulty circuits, which would otherwise be costly due to the need to use high-voltage semiconductor components, can be common to all DC power transmission lines LN (reducing the number of high-voltage semiconductor components). In each embodiment of the DC current interruption device, when a fault occurs in either the DC transmission line LN or DC bus B, the control unit controls the open or closed state of the disconnector 20 belonging to the auxiliary line of the faulty circuit (e.g., auxiliary line P) on the upstream side of the faulty current (e.g., DC bus BP side) and the disconnector 20 belonging to the auxiliary line of the healthy circuit (e.g., auxiliary line N) on the downstream side of the faulty current (e.g., DC bus BN side), thereby controlling the open, closed, on, and off states of the components that have the function of interrupting the faulty circuit, and thereby interrupting the faulty circuit. As a result, in each embodiment of the DC current interruption device, when a fault occurs in either the DC transmission line LN or DC bus B, the faulty circuit is interrupted, and if a healthy circuit exists, power transmission by that healthy circuit can be maintained. In other words, the DC current interruption devices of each embodiment reduce costs by commonizing components that would otherwise be expensive due to the need to employ high-voltage semiconductor components across all DC transmission lines LN, while also enabling interruption of faulty lines and maintenance of normal power transmission through healthy lines.

[0124] According to at least one embodiment described above, a plurality of DC transmission lines (LN) are branched at a predetermined branching point into a first auxiliary line (P) provided with a first mechanical contact (20-P) and a second auxiliary line (N) provided with a second mechanical contact (20-N), a first DC bus (BP) to which the plurality of first auxiliary lines are connected, a second DC bus (BN) to which the plurality of second auxiliary lines are connected, a semiconductor circuit breaker (40) capable of interrupting the current flowing through the DC transmission lines, and an energy consumption element (50) that consumes energy between at least both ends of the semiconductor circuit breaker. The system includes a commutation circuit (30) that commutates the current flowing through the DC transmission line to the interruption consumption unit, a control unit that controls the open and closed states of the first and second mechanical contacts, the conduction state (on state) and non-conduction state (off state) of the semiconductor circuit breaker, and the states in which current flows through one or more of the first mechanical contacts, the second mechanical contacts, and the semiconductor circuit breaker via the commutation circuit (on state) and the state in which the current is reduced to approximately zero (off state). By providing these components, the semiconductor circuit breaker and commutation circuit can be standardized, and the DC transmission line in the event of an accident can be interrupted.

[0125] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0126] 1,2,3,3a,4,4a...DC current interrupter, 10,10-1,10-2,10-3,10-n...DC reactor, 20,20-P-1,20-P-2,20-P-3,20-Pn,20-N-1,20-N-2 ,20-N-3,20-Nn...Disconnector, 30,30a,30b,30c,30d,30e...Commutation circuit, 40,40-1,40-2,40-n,40a,40b...Semiconductor circuit breaker, 41,41a,41b,41c... Semiconductor switch section, 50, 50-1, 50-2, 50-n... Arrester, 60... Inductor, 70, 70-1, 70-2, 70-n, 70a, 70b, 70c, 70d... Auxiliary semiconductor circuit breaker, 80... Disconnector, 90... Circuit breaker, 100... Control unit, LN, LN-1, LN-2, LN-3, LN-n... DC transmission line, B, BP, BN... DC bus, P, P-1, P-2, P-3, Pn, N, N-1, N-2, N-3, Nn... Auxiliary line

Claims

1. Multiple DC transmission lines are branched at a predetermined branching point into a first auxiliary line equipped with a first mechanical contact and a second auxiliary line equipped with a second mechanical contact, A first DC bus to which multiple first auxiliary lines are connected, A second DC bus to which multiple second auxiliary lines are connected, A circuit breaker capable of interrupting the current flowing through the DC transmission line, and an energy consumption unit having an energy consumption element that consumes energy between at least both ends of the semiconductor circuit breaker, A commutation circuit that commutates the current flowing through the DC transmission line to the interruption consumption unit, A control unit that controls the open and closed states of the first mechanical contact and the second mechanical contact, the conduction and non-conduction states of the semiconductor circuit breaker, and the states in which current flows through one or more of the paths of the first mechanical contact, the second mechanical contact, and the semiconductor circuit breaker by the commutation circuit, and states in which the current is reduced to approximately zero. A DC current interruption device equipped with [a specific feature].

2. The interruption and consumption unit and the commutation circuit are connected in series between the first DC bus and the second DC bus. The DC current interruption device according to claim 1.

3. The system further comprises a third mechanical contact capable of interrupting the current flowing between the first DC bus and the second DC bus, The interruption consumption unit is connected between the first DC bus and the second DC bus, The commutation circuit and the third mechanical contact are connected in series between the first DC bus and the second DC bus. The DC current interruption device according to claim 1.

4. A third mechanical contact capable of interrupting the current flowing between the first DC bus and the second DC bus, A fourth mechanical contact capable of interrupting the current flowing between the first DC bus and the second DC bus, Furthermore, The interruption consumption unit is connected between the first DC bus and the second DC bus, The third mechanical contact and the fourth mechanical contact are connected in series between the first DC bus and the second DC bus. The commutation circuit is connected in parallel with the fourth mechanical contact. The DC current interruption device according to claim 1.

5. The control unit, During steady-state operation, all of the first mechanical contacts and the second mechanical contacts are closed. When an accident occurs in any of the aforementioned DC transmission lines, The first mechanical contact belonging to the first auxiliary line of the faulty DC transmission line where the fault occurred is opened. The second mechanical contact belonging to the second auxiliary line of the healthy DC transmission line other than the faulty line is opened. Next, the current flowing through the path passing through the first mechanical contact, which is at least open, is reduced to approximately zero by the commutation circuit and then commutated to the path passing through the interruption consumption unit. After that, the semiconductor circuit breaker is de-conducted, and the energy consumption element causes the current flowing through the path passing through the semiconductor circuit breaker to be reduced to approximately zero, thereby reducing the current flowing through the fault circuit to approximately zero. A DC current interruption device according to any one of claims 1 to 4.

6. The control unit, After the current flowing through the fault circuit becomes nearly zero, the second mechanical contact belonging to the second auxiliary line of the fault circuit is opened. To close the second mechanical contact that was in the open state in the healthy circuit, The DC current interruption device according to claim 5.

7. The control unit, During steady-state operation, all of the first mechanical contacts and the second mechanical contacts are closed. When an accident occurs in either the first DC bus or the second DC bus, The mechanical contact belonging to the auxiliary line connected to the DC bus where the accident occurred is opened. Next, the semiconductor circuit breaker is made to conduct, and the current flowing through the path passing through the mechanical contacts, which are at least in an open state, is reduced to approximately zero by the commutation circuit and commutated to the path passing through the interruption consumption unit. Then, the semiconductor circuit breaker is made to deconduct, and the energy consumption element causes the current flowing through the path passing through the semiconductor circuit breaker to be reduced to approximately zero, thereby reducing the current flowing through the DC bus where the fault has occurred to approximately zero. A DC current interruption device according to any one of claims 1 to 4.

8. Each of the second auxiliary lines is further provided with an auxiliary semiconductor circuit breaker having at least one semiconductor element capable of interrupting the current flowing between the second auxiliary line and the second DC bus. A DC current interruption device according to any one of claims 1 to 4.

9. The control unit, During steady-state operation, all of the first mechanical contacts and the second mechanical contacts are closed. When an accident occurs in any of the aforementioned DC transmission lines, The first mechanical contact belonging to the first auxiliary line of the faulty DC transmission line where the fault occurred is opened. The second mechanical contact belonging to the second auxiliary line of the healthy DC transmission line other than the faulty line is opened. The auxiliary semiconductor circuit breaker belonging to the second auxiliary line of the healthy circuit is activated, Next, the current flowing through the path passing through the first mechanical contact, which is at least open, is reduced to approximately zero by the commutation circuit and then commutated to the path passing through the interruption consumption unit. After that, the semiconductor circuit breaker is de-conducted, and the energy consumption element causes the current flowing through the path passing through the semiconductor circuit breaker to be reduced to approximately zero, thereby reducing the current flowing through the fault circuit to approximately zero. The DC current interruption device according to claim 8.

10. The commutation circuit comprises at least one energy storage element. A DC current interruption device according to any one of claims 1 to 4.

11. The commutation circuit comprises at least one semiconductor switch and at least one energy storage element. A DC current interruption device according to any one of claims 1 to 4.

12. The commutation circuit is a bridge circuit in which a plurality of leg sections, including a semiconductor switch section, and at least one energy storage element are connected in parallel. A DC current interruption device according to any one of claims 1 to 4.

13. The leg section is a series circuit formed by connecting multiple semiconductor switch sections in series. The DC current interruption device according to claim 12.

14. The aforementioned leg section is a series circuit in which at least one semiconductor switch section and at least one current rectifier element are connected in series. The DC current interruption device according to claim 12.

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