DC Circuit Breaker

Abstract

The DC circuit breaker (5) includes a core circuit breaker (51) that breaks a fault current flowing in the DC line (4), a residual current circuit breaker (52) that is a gas circuit breaker that breaks a residual current flowing in the DC line (4), and a control unit (53) that controls the core circuit breaker (51) and the residual current circuit breaker (52). The core circuit breaker (51) includes a main branch (511) that breaks the fault current by mechanical contacts, and a temporary branch (512) that extinguishes an arc generated between the poles of the mechanical contacts. (512) and an energy processing branch (513) that absorbs energy remaining in the DC system including the DC line (4) and attenuates the fault current, and the control unit (53) controls the residual current circuit breaker (52) to interrupt the residual current after completing thermal interruption in which the arc is extinguished and dielectric interruption in which the core circuit breaker (51) withstands an overvoltage generated by the diversion of the fault current to the temporary branch (512) and the energy processing branch (513).

Description

[Technical field]

[0001] The present disclosure relates to a DC circuit breaker applied to a multi-terminal high-voltage DC power transmission system. [Background technology]

[0002] Conventionally, two-terminal high-voltage DC transmission has been used for high-voltage DC transmission, in which two AC / DC converters are connected by at least one of a power transmission cable and an overhead transmission line. A high-voltage DC transmission system in which three or more AC / DC converters are connected is called a multi-terminal high-voltage DC transmission system. As an example, a four-terminal high-voltage DC transmission system is configured by connecting four AC / DC converters in a ring shape by DC lines.

[0003] Due to the rapid expansion of offshore wind power generation worldwide and the need for long-distance electricity transportation from generation areas to demand areas, electricity transmission using multi-terminal high-voltage direct current (DC) transmission systems is attracting increasing attention.

[0004] When an accident occurs in a DC system, the accident can be cleared by stopping the current flowing toward the accident point. In a two-terminal high-voltage DC transmission system in which two AC / DC converters are connected by a single DC line, the accident can be cleared by opening the AC circuit breaker installed in the AC system and stopping the AC / DC converter, thereby stopping the current flowing toward the accident point. However, in the case of a multi-terminal high-voltage DC transmission system, clearing the accident using the same method as a two-terminal high-voltage DC transmission system would mean stopping all power transmission, which would also stop power transmission in healthy sections unrelated to the accident, potentially causing a large-scale blackout.

[0005] For this reason, in multi-terminal high-voltage DC transmission systems, a method is used in which a DC circuit breaker is installed on each DC line that constitutes the DC system, and the fault current is interrupted in the DC line including the fault section.

[0006] A DC circuit breaker is composed of a core circuit breaker that breaks the current and a residual current circuit breaker that breaks the residual current. The residual current circuit breaker generally uses a gas circuit breaker that breaks the current in an insulating gas. Sulfur hexafluoride is widely used as the insulating gas.

[0007] Patent Document 1 discloses a DC circuit breaker including a mechanical switch consisting of a gas circuit breaker and a vacuum circuit breaker connected in series, and a semiconductor switch connected in parallel to the mechanical switch. In the DC circuit breaker disclosed in Patent Document 1, the function of a residual current circuit breaker is incorporated in a gas circuit breaker that is a part of a core circuit breaker, but like a general DC circuit breaker, it breaks the residual current in the insulating gas. By applying the DC circuit breaker to a multi-terminal high-voltage DC transmission system and isolating the fault section from the sound section in the DC system instead of the AC system to break the fault current, it is possible to continue transmitting power in the sound section. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2016 / 047209 Summary of the Invention [Problem to be solved by the invention]

[0009] However, sulfur hexafluoride gas, which is widely used as an insulating gas, is being subject to increasingly stringent emission regulations from the standpoint of protecting the global environment, and is being replaced by alternative gases such as synthetic air.

[0010] In a gas circuit breaker, when the electrodes of the interrupting part in the arc extinguishing chamber are opened, a current flows through the arc generated between the electrodes. When the insulating gas is sulfur hexafluoride, the insulating gas has the property of decomposing once when exposed to the arc but then recombining, so a gas circuit breaker using sulfur hexafluoride as the insulating gas can repeatedly interrupt current without a significant decrease in interrupting performance. On the other hand, when the insulating gas is an alternative gas such as synthetic air, the insulating gas decomposed by exposure to the arc does not easily recombine, so the interrupting performance of a gas circuit breaker using an alternative gas as the insulating gas significantly decreases with repeated interruptions. This problem is particularly noticeable when the arc current is large.

[0011] The DC circuit breaker disclosed in Patent Document 1 interrupts residual current with a gas circuit breaker, and therefore has the same problems as those of a DC circuit breaker that includes a residual current circuit breaker in addition to a core circuit breaker.

[0012] The present disclosure has been made in consideration of the above, and aims to obtain a DC circuit breaker in which the insulating gas inside the gas circuit breaker that interrupts residual current is less likely to deteriorate even when the residual current is repeatedly interrupted. [Means for solving the problem]

[0013] In order to solve the above problems and achieve the object, the DC circuit breaker according to the present disclosure includes a core circuit breaker that breaks a fault current flowing in a DC line, a residual current circuit breaker that is a gas circuit breaker that breaks a residual current flowing in the DC line after breaking the fault current in an insulating gas, and a control unit that controls the core circuit breaker and the residual current circuit breaker. The core circuit breaker includes a main branch that breaks the fault current by a mechanical contact, a temporary branch that forms a current zero point in the mechanical contact and extinguishes an arc generated between the poles of the mechanical contact, and an energy processing branch that absorbs energy remaining in a DC system including the DC line and attenuates the fault current until the current value becomes zero. The main branch, the temporary branch, and the energy processing branch are connected in parallel with each other. The control unit causes the residual current circuit breaker to break the residual current after completing a thermal interruption in which the arc is extinguished and a dielectric interruption in which the core circuit breaker withstands an overvoltage generated by the commutation of the fault current to the temporary branch and the energy processing branch due to the opening of the mechanical contact. Effect of the Invention

[0014] According to the present disclosure, it is possible to obtain a DC circuit breaker in which the insulating gas inside the gas circuit breaker that interrupts a residual current is not easily deteriorated even when the residual current is repeatedly interrupted. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing a configuration of a multi-terminal high-voltage DC transmission system using a DC circuit breaker according to a first embodiment. [Diagram 2] FIG. 1 is a diagram showing a configuration of a DC circuit breaker according to a first embodiment. [Diagram 3] FIG. 1 is a diagram showing a fault current interruption operation of a DC circuit breaker according to the first embodiment. [Figure 4] FIG. 13 is a diagram showing a fault current interruption operation of a DC circuit breaker according to a second embodiment. [Diagram 5] FIG. 13 is a diagram showing a fault current interruption operation of a DC circuit breaker according to a third embodiment. [Figure 6] FIG. 1 is a diagram showing an example of a hardware configuration for implementing a control unit included in a DC circuit breaker according to the first, second, or third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a DC circuit breaker according to an embodiment will be described in detail with reference to the drawings.

[0017] Embodiment 1 FIG. 1 is a diagram showing a configuration of a multi-terminal high-voltage DC transmission system using a DC circuit breaker according to the first embodiment. A multi-terminal high-voltage DC system 80 includes four AC systems 1 and a DC system 2. An AC / DC converter 3 is installed between each of the AC systems 1 and the DC system 2. The DC system 2 includes four DC lines 4. Each of the AC / DC converters 3 is connected in a ring shape by the DC line 4. Therefore, each of the AC systems 1 is connected in a ring shape via the DC line 4 and the AC / DC converter 3. A DC circuit breaker 5 according to the first embodiment is installed on the DC line 4. An AC power source 7 and an AC circuit breaker 6 are installed in the AC system 1.

[0018] FIG. 2 is a diagram showing the configuration of the DC circuit breaker according to the first embodiment. The DC circuit breaker 5 includes a core circuit breaker 51, a residual current circuit breaker 52, and a control unit 53 that controls the core circuit breaker 51 and the residual current circuit breaker 52. The core circuit breaker 51 includes a main branch 511 having a mechanical contact for interrupting a current, a temporary branch 512 that forms a current zero point at the mechanical contact, and an energy processing branch 513 that performs energy processing and attenuation of a fault current. The main branch 511, the temporary branch 512, and the energy processing branch 513 are connected in parallel with each other. A lightning arrester that reduces current resistance when a high voltage is applied can be applied to the energy processing branch 513. The DC circuit breaker 5 is a mechanical DC circuit breaker in which a mechanical contact is applied only to the main branch 511. The residual current circuit breaker 52 is a gas circuit breaker that interrupts a current in an insulating gas. Examples of the insulating gas include sulfur hexafluoride and synthetic air, but a type of gas different from the examples may be applied.

[0019] The control unit 53 outputs an opening command to the core circuit breaker 51 and the residual current circuit breaker 52 based on the fault detection signal input from the protection relay 8. The protection relay 8 is connected to a potential transformer 41 (not shown in FIG. 1) that connects the DC line 4 to the ground, and a current transformer 42 (not shown in FIG. 1) that is installed on the DC line 4. The protection relay 8 outputs a fault detection signal to the control unit 53 based on at least one of the magnitude of the current flowing through the DC line 4 detected via the current transformer 42 and the magnitude of the voltage applied to the DC line 4 detected via the potential transformer 41. The fault detection is performed when the current value of the current flowing through the DC line 4 becomes equal to or exceeds a predetermined threshold value, and when the system voltage U s It can be determined by satisfying at least one of the conditions when the voltage of the power supply becomes equal to or lower than a predetermined threshold value.

[0020] Fig. 3 is a diagram showing a fault current interruption operation of the DC circuit breaker according to embodiment 1. In Fig. 3, hatching slanting downward to the right indicates an opening period during which the core circuit breaker 51 or the residual current circuit breaker 52 is performing an opening operation, and hatching slanting upward to the right indicates an arc period during which an arc is generated in the core circuit breaker 51 or the residual current circuit breaker 52. Also, in Fig. 3, hatching with dots indicates a delay period during which the start of the opening operation in the residual current circuit breaker 52 is delayed.

[0021] In a steady state, a current flows through the main branch 511 and the residual current circuit breaker 52. When a fault occurs in the high-voltage DC transmission system at time T0, a fault current I f is detected by protective relay 8.

[0022] Fault current I f The protection relay 8 that detects the fault outputs a fault detection signal to the control unit 53. The control unit 53 that receives the fault detection signal outputs a fault detection signal for a fault detection time t relay At time T1 after the elapse of time, the core circuit breaker 51 outputs an opening command to the core circuit breaker 51. The core circuit breaker 51, which has received the opening command, starts opening the mechanical contacts applied to the main branch 511.cbop When the mechanical contacts of the main branch 511 open at time T2 after the time has elapsed, an arc is generated between the poles of the mechanical contacts. In addition, when the mechanical contacts applied to the main branch 511 open, the fault current is commutated to the temporary branch 512 and the energy processing branch 513.

[0023] Time T2 to core breaker arc time t cbarc At time T3 after the current has elapsed, a switch (not shown) connected to the temporary branch 512 is turned on, and a current zero point is formed at the mechanical contacts by a current zero point forming circuit provided in the temporary branch 512, and the current flowing through the main branch 511 is interrupted. Time T3 is the timing when the contact gap opens to a distance that can withstand the transient interruption voltage applied between the contacts after the current is interrupted. Interruption of the fault current by the main branch 511 is completed when the arc generated between the contacts of the mechanical contacts is extinguished. Interruption of the fault current by the main branch 511 is generally referred to as "thermal interruption."

[0024] When the mechanical contacts of the main branch 511 interrupt the fault current, the energy handling branch 513 reduces the voltage to a transient interruption voltage U TIV Transient cut-off voltage U TIV is the grid voltage U limited by the energy processing branch 513. s At time T4, the transient cutoff voltage U TIV is the system voltage U s When the peak current I pf The current flowing through the DC circuit breaker 5 during current limiting is called the limiting current I s Transient cutoff voltage U TIV The overvoltage is suppressed according to the voltage-current characteristic set in the energy processing branch 513. Therefore, the transient cutoff voltage U TIV After reaching a peak value at time T5, it starts to decrease. Generally, the peak value of the transient blocking voltage, U TIVpk is the system voltage U s This is about 1.5 to 1.7 times the original amount.

[0025] Current Limiting I s The current I is absorbed by flowing through the energy processing branch 513. The energy absorption in the energy processing branch 513 causes the current limiting I s This reduces the current value of the current limiter I s The absolute value of I is small enough that the decomposition of the insulating gas caused by the arc between the poles of the residual current circuit breaker 52 does not affect the circuit breaking performance. s If the arc generated at the current limiting I is large enough not to affect the interruption performance of the residual current circuit breaker 52, the contacts of the residual current circuit breaker 52 can be opened, and this period is called the residual current circuit breaker opening possible period. s The current value of the fault current decays to zero, and the core breaker 51 generates a transient cutoff voltage U TIV This resistance is commonly referred to as "dielectric blocking."

[0026] The control unit 53 also outputs an opening command to the residual current circuit breaker 52 at time T1, which is the same timing as when the control unit 53 outputs the opening command to the core circuit breaker 51. Upon receiving the opening command, the residual current circuit breaker 52 waits a preset delay time t rcsd The time required for the residual current circuit breaker 52 to perform the opening operation is defined as the residual current circuit breaker opening operation time t rcsop Then, the current limiting I s The current value of becomes zero for the first time after the delay time t rcsd + Residual current circuit breaker opening operation time t rcsop This is time T8 after the passage of time t1 through t4. Therefore, the residual current circuit breaker 52 finishes its opening operation at time T8. Therefore, at time T8, both the thermal cutoff and the dielectric cutoff are achieved, and the interruption of the fault current is completed.

[0027] In addition, current limiting I s The current limiting I sTherefore, the arc period of the residual current circuit breaker 52 can be set to the time T7, which is earlier than the time when the current value of the current limiting I s It is possible to make the time start from time T7, which is earlier than time T8 at which the current value first becomes zero.

[0028] Here, the time required from when the control unit 53 issues an opening command to the core circuit breaker 51 until the core circuit breaker 51 completes dielectric interruption is defined as the interruption time t break In the DC circuit breaker 5 according to the first embodiment, the delay time t rcsd is the cutoff time t break ≦Delay time t rcsd + Residual current circuit breaker opening operation time t rcsop That is, the delay time t rcsd is set so that time T8 when the residual current circuit breaker 52 finishes its opening operation is the same as time T7 when the residual current circuit breaker opening possible period begins or is later than time T7.

[0029] In addition, the residual current circuit breaker opening operation time t rcsop Since is a value specific to the device, if the time T8 at which the residual current circuit breaker 52 finishes the opening operation can be set to the same time as the time T7 at which the residual current circuit breaker opening possible period begins or later than the time T7, the delay time t rcsd may be zero.

[0030] At time T8, the residual current circuit breaker 52 finishes its opening operation, causing an arc to occur between the poles of the residual current circuit breaker 52. However, since the thermal and dielectric interruptions have been completed in the core circuit breaker 51, the residual current flowing through the residual current circuit breaker 52 after time T8 has attenuated to an oscillatory current that can be interrupted by the residual current circuit breaker 52, and the current value of the residual current is kept small. rcsarc At time T9 after the lapse of time, the residual current circuit breaker 52 completes interruption of the residual current, and the fault removal operation by the DC circuit breaker 5 ends.

[0031] The DC circuit breaker 5 according to the first embodiment also inputs an opening command to the residual current circuit breaker 52 at the same timing as the core circuit breaker 51, so that there is no need for complicated calculations to determine the timing of inputting the opening command to the residual current circuit breaker 52. Also, since the time T8 at which the residual current circuit breaker 52 finishes its opening operation is later than the time T7 at which the residual current circuit breaker opening possible period begins, deterioration of the insulating gas can be suppressed even if the residual current circuit breaker 52 repeatedly interrupts the residual current. Also, the delay time t rcsd By setting this in accordance with the characteristics of the residual current circuit breaker 52, the residual current can be interrupted promptly after the start of the period during which the residual current circuit breaker can open contacts.

[0032] Embodiment 2 The configuration of the DC circuit breaker 5 of embodiment 2 is similar to that of the DC circuit breaker 5 of embodiment 1, but the timing at which the control unit 53 outputs an opening command to the residual current circuit breaker 52 differs from that of the DC circuit breaker 5 of embodiment 1.

[0033] Fig. 4 is a diagram showing a fault current interruption operation of the DC circuit breaker according to embodiment 2. In Fig. 4, hatching slanting downward to the right indicates an opening period during which the core circuit breaker 51 or the residual current circuit breaker 52 is performing an opening operation, and hatching slanting upward to the right indicates an arc period during which an arc is generated in the core circuit breaker 51 or the residual current circuit breaker 52. Also, in Fig. 4, hatching with dots indicates a delay period during which the start of the opening operation in the residual current circuit breaker 52 is delayed.

[0034] The operation of the core circuit breaker 51 is similar to that of the DC circuit breaker 5 according to the first embodiment. After the main branch 511 cuts off the current, the control unit 53 controls the transient cutoff voltage U TIV While this is being applied to the core circuit breaker 51, an opening command is output to the residual current circuit breaker 52.

[0035] The control unit 53 detects the current I fm is zero, and the transient cutoff voltage U TIV is a predetermined threshold U thBased on at least one of the above, the fault current I f is cut off and the core breaker 51 receives a transient cut-off voltage U TIV In the example shown in FIG. 4, at time T3, the current I fm When the fault current I f is cut off and the core breaker 51 receives a transient cut-off voltage U TIV Therefore, in the example shown in Fig. 4, the control unit 53 outputs an opening command to the residual current circuit breaker 52 at time T3.

[0036] Upon receiving the opening command, the residual current circuit breaker 52 starts the opening process from time T3 with a preset delay time t rcsd The time required for the residual current circuit breaker 52 to perform an opening operation is defined as a residual current circuit breaker opening operation time t rcsop Then, the current limiting I s The current value of becomes zero for the first time after the delay time t rcsd + Residual current circuit breaker opening operation time t rcsop Therefore, the residual current circuit breaker 52 operates from time T10 until the residual current circuit breaker opening operation time t rcsop The opening operation is completed at time T11 after the elapse of time.

[0037] Here, the delay time t rcsd is the cutoff time t break - Core breaker opening operation time t cbop + Core breaker arc time t cbarc ≦Delay time t rcsd + Residual current circuit breaker opening operation time t rcsop That is, the delay time t rcsd is set so that time T11 when the residual current circuit breaker 52 finishes opening is the same as time T7 when the residual current circuit breaker opening possible period begins or is later than time T7.

[0038] In addition, the residual current circuit breaker opening operation time t rcsopSince is a value specific to the device, if the time T11 at which the residual current circuit breaker 52 finishes the opening operation can be set to the same time as the time T7 at which the residual current circuit breaker opening possible period begins or later than the time T7, the delay time t rcsd may be zero.

[0039] At time T11, the residual current circuit breaker 52 finishes its opening operation, causing an arc to occur in the residual current circuit breaker 52. However, since the core circuit breaker 51 has completed thermal and dielectric interruption, the value of the residual current flowing through the residual current circuit breaker 52 is kept small. rcsarc At time T12 after the lapse of time, the residual current circuit breaker 52 completes interruption of the residual current, and the fault removal operation by the DC circuit breaker 5 ends.

[0040] In this way, in the DC circuit breaker 5 according to the second embodiment, the control unit 53 performs a core circuit breaker opening operation time t cbop and core breaker arc time t cbarc After time T3, and after time T1, the interruption time t break An opening command is output to the residual current circuit breaker 52 until time T7 after the lapse of time, and the residual current circuit breaker 52 completes the opening operation at time T11 which is the same as time T7 or later than time T7.

[0041] In the DC circuit breaker 5 according to the second embodiment, an opening command is input to the residual current circuit breaker 52 after the completion of thermal interruption, which is the reason why DC interruption is more difficult than AC interruption. Therefore, in the DC circuit breaker 5 according to the second embodiment, if the core circuit breaker 51 has a dielectric interruption performance, the fault current I f Therefore, the DC circuit breaker 5 according to the second embodiment can reliably interrupt the fault current I f The probability of failure of interrupting the core circuit breaker 51 is low, and the fault current I f This reduces the risk of damage to the residual current circuit breaker 52 due to a circuit breaker failure.

[0042] Embodiment 3 The configuration of the DC circuit breaker 5 of embodiment 3 is similar to that of the DC circuit breaker 5 of embodiment 1, but the timing at which the control unit 53 outputs an opening command to the residual current circuit breaker 52 differs from that of the DC circuit breaker 5 of embodiment 1.

[0043] Fig. 5 is a diagram showing a fault current interrupting operation of the DC circuit breaker according to embodiment 3. In Fig. 5, hatching slanting downward to the right indicates an opening period during which the core circuit breaker 51 or the residual current circuit breaker 52 is performing an opening operation, and hatching slanting upward to the right indicates an arcing period during which an arc is generated in the core circuit breaker 51 or the residual current circuit breaker 52.

[0044] The operation of the core circuit breaker 51 is similar to that of the DC circuit breaker 5 according to embodiment 1. The control unit 53 outputs an opening command to the residual current circuit breaker 52 after the core circuit breaker 51 has completed thermal and dielectric circuit breaker operations.

[0045] The control unit 53 is a current limiting s is a preset threshold I sth and the transient cut-off voltage U TIV is a predetermined threshold U th Based on at least one of the above, it is determined that the thermal cutoff and the dielectric cutoff are completed. In the example shown in FIG. 5, at time T7, the current limiting I s is a preset threshold I sth When the following occurs, the control unit 53 determines that the thermal cutoff and the dielectric cutoff are completed. Therefore, in the example shown in Fig. 5, the control unit 53 outputs an opening command to the residual current circuit breaker 52 at time T7.

[0046] The residual current circuit breaker 52 that has received the opening command starts the opening operation without delay. The time required for the residual current circuit breaker 52 to perform the opening operation is defined as the residual current circuit breaker opening operation time t rcsop In this case, the residual current circuit breaker 52 completes the opening operation from time T7 to the residual current circuit breaker opening operation time t rcsop After that, time T14 is reached.

[0047] At time T14, the residual current circuit breaker 52 finishes the opening operation, and an arc is generated in the residual current circuit breaker 52. s At time T13 when the current value becomes zero for the first time, the thermal cutoff and dielectric cutoff are completed, so the current value of the residual current flowing through the residual current circuit breaker 52 is kept small. rcsarc At time T15 after the lapse of time, the residual current circuit breaker 52 completes interruption of the residual current, and the fault removal operation by the DC circuit breaker 5 ends.

[0048] Thus, in the DC circuit breaker 5 of embodiment 3, the control unit 53 outputs an opening command to the residual current circuit breaker 52 at the same time as or after time T7 when thermal and dielectric circuit breakers are completed, and the residual current circuit breaker 52 completes the opening operation at a time later than time T7.

[0049] In the DC circuit breaker 5 according to the third embodiment, an opening command is input to the residual current circuit breaker 52 after the core circuit breaker 51 completes thermal and dielectric interruption. Therefore, in the DC circuit breaker 5 according to the third embodiment, the possibility of restrike occurring in the core circuit breaker 51 and failing to interrupt the current is lower than in the DC circuit breaker 5 according to the first and second embodiments, and the fault current I f This can reduce the risk of damage to the residual current circuit breaker 52 due to a failure to break the current.

[0050] Next, a hardware configuration of the control unit 53 will be described. Fig. 6 is a diagram showing an example of a hardware configuration realizing the control unit provided in the DC circuit breaker according to the first, second or third embodiment. The control unit 53 is realized as a computer system by a processing circuit including a processor 91 that executes various processes, a memory 92 that is a main memory, and a storage device 93 that stores information.

[0051] The processor 91 may be a calculation means such as an arithmetic device, a microprocessor, a microcomputer, a CPU (Central Processing Unit), or a DSP (Digital Signal Processor). The memory 92 may be a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable Read Only Memory), or an EEPROM (Electrically Erasable Programmable Read Only Memory). The storage device 93 stores a program for executing a process of outputting an opening command to the core circuit breaker 51 and the residual current circuit breaker 52. The processor 91 reads the program stored in the storage device 93 into the memory 92 and executes it. The processor 91 reads the program stored in the storage device 93 into the memory 92 and executes it, thereby realizing the function of the control unit 53.

[0052] The configurations shown in the above embodiments are merely examples of the contents, and may be combined with other known technologies. Parts of the configurations may be omitted or modified without departing from the spirit of the invention. [Explanation of symbols]

[0053] 1 AC system, 2 DC system, 3 AC / DC converter, 4 DC line, 5 DC circuit breaker, 6 AC circuit breaker, 7 AC power source, 8 protective relay, 41 potential transformer, 42 current transformer, 51 core circuit breaker, 52 residual current circuit breaker, 53 control unit, 80 multi-terminal high voltage DC system, 91 processor, 92 memory, 93 storage device, 511 main branch, 512 temporary branch, 513 energy processing branch.

Claims

1. The system comprises a core circuit breaker that interrupts fault current flowing through a DC line, a residual current circuit breaker which is a gas circuit breaker that interrupts residual current flowing through the DC line in an insulating gas after the fault current has been interrupted, and a control unit that controls the core circuit breaker and the residual current circuit breaker. The core circuit breaker comprises a main branch that interrupts the fault current by mechanical contacts, a temporary branch that forms a current zero point at the mechanical contacts and extinguishes the arc generated between the poles of the mechanical contacts, and an energy processing branch that absorbs residual energy in the DC system including the DC line and attenuates the fault current until the current value becomes zero. The main branch, the temporary branch, and the energy processing branch are connected to each other in parallel. The control unit causes the residual current circuit breaker to interrupt the residual current after the core circuit breaker has completed dielectric interruption, which is performed by thermal interruption in which the arc is extinguished and by the commutation of the fault current to the temporary branch and the energy processing branch due to the opening of the mechanical contacts, thereby preventing the core circuit breaker from interrupting the residual current. The control unit outputs an opening command to the core circuit breaker and the residual current circuit breaker simultaneously. The residual current circuit breaker is a DC circuit breaker characterized in that it performs the opening operation after a preset delay time has elapsed since the opening command was input.

2. A core circuit breaker for interrupting fault current flowing through a DC line, a residual current circuit breaker which is a gas circuit breaker for interrupting residual current flowing through the DC line in an insulating gas after the fault current has been interrupted, and a control unit for controlling the core circuit breaker and the residual current circuit breaker, The core circuit breaker comprises a main branch that interrupts the fault current by mechanical contacts, a temporary branch that forms a current zero point at the mechanical contacts and extinguishes the arc generated between the poles of the mechanical contacts, and an energy processing branch that absorbs residual energy in the DC system including the DC line and attenuates the fault current until the current value becomes zero. The main branch, the temporary branch, and the energy processing branch are connected to each other in parallel. The control unit causes the residual current circuit breaker to interrupt the residual current after the core circuit breaker has completed dielectric interruption, which is performed by thermal interruption in which the arc is extinguished and by the commutation of the fault current to the temporary branch and the energy processing branch due to the opening of the mechanical contacts, thereby preventing the core circuit breaker from interrupting the residual current. The control unit outputs an opening command to the residual current circuit breaker after the completion of the thermal interruption and while the dielectric interruption is being performed by the core circuit breaker. The residual current circuit breaker is a DC circuit breaker characterized in that it performs the opening operation after a preset delay time has elapsed since the opening command was input.

3. The DC circuit breaker according to claim 1 or 2, characterized in that the insulating gas is synthetic air.

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