DC circuit breaker

Abstract

A DC circuit breaker (5) is provided with: a core circuit breaker (51) that cuts off an accidental current flowing through a DC line (4); a residual current circuit breaker (52) that is a gas circuit breaker that cuts off a residual current flowing through 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) is provided with: a main branch (511) that cuts off the accidental current by means of a mechanical contact; a temporary branch (512) that extinguishes an arc generated between the poles of the mechanical contact; and an energy processing branch (513) that absorbs energy remaining in the DC system including the DC line (4) to attenuate the accidental current. The control unit (53) causes the residual current circuit breaker (52) to cut off the residual current after the completion of thermal cutoff in which the arc is extinguished and dielectric cutoff in which the core circuit breaker (51) withstands an overvoltage that occurs due to commutation of the accidental current to the temporary branch (512) and the energy processing branch (513).

Description

DC circuit breaker

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

[0002] Conventionally, two-terminal high-voltage DC transmission systems have 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 that connects three or more AC / DC converters is called a multi-terminal high-voltage DC transmission system. For example, a four-terminal high-voltage DC transmission system is configured by connecting four AC / DC converters in a ring shape with DC lines.

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

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

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

[0006] A DC circuit breaker consists of a core circuit breaker that interrupts the current and a residual current circuit breaker that interrupts the residual current. Residual current circuit breakers are generally gas circuit breakers that interrupt 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 disconnecting switch and a vacuum circuit breaker connected in series, and a semiconductor switch connected in parallel to the mechanical switch. The DC circuit breaker disclosed in Patent Document 1 incorporates the residual current circuit breaker function into a gas circuit breaker that is part of a core circuit breaker, but interrupts residual current in the insulating gas, just like a general DC circuit breaker. By applying the DC circuit breaker to a multi-terminal high-voltage DC transmission system, the fault section is separated from the sound section in the DC system, not the AC system, and the fault current is interrupted, allowing power transmission to continue in the sound section.

[0008] International Publication No. 2016 / 047209

[0009] However, sulfur hexafluoride gas, which is widely used as an insulating gas, is being increasingly restricted in terms of emissions from the perspective of protecting the global environment, and replacement with alternative gases such as synthetic air is being promoted.

[0010] In a gas circuit breaker, when the electrodes in the arc extinguishing chamber are parted, current flows through the arc that occurs between the electrodes. When the insulating gas is sulfur hexafluoride, the insulating gas decomposes when exposed to the arc but then recombines. This allows gas circuit breakers using sulfur hexafluoride to 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 gas circuit breakers using alternative gases will experience a significant decrease in interrupting performance with repeated interruptions. This problem is particularly pronounced when the arc current is large.

[0011] The DC circuit breaker disclosed in Patent Document 1 interrupts residual current using a gas circuit breaker, and therefore suffers from the same problems as DC circuit breakers that include a residual current circuit breaker separate from a core circuit breaker.

[0012] The present disclosure has been made in consideration of the above, and aims to provide 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.

[0013] To solve the above-mentioned problems and achieve the object, the DC circuit breaker according to the present disclosure includes a core circuit breaker that interrupts a fault current flowing in a DC line, a residual current circuit breaker that is a gas circuit breaker that interrupts a residual current flowing in the DC line after interrupting the fault current within 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 interrupts the fault current using mechanical contacts, a temporary branch that forms a current zero point in the mechanical contacts and extinguishes an arc that occurs between the mechanical contacts, 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 reaches zero. The main branch, temporary branch, and energy processing branch are connected in parallel. The control unit controls the residual current circuit breaker to interrupt the residual current after completing thermal interruption (in which the arc is extinguished) and dielectric interruption (in which the core circuit breaker withstands an overvoltage generated by commutation of the fault current to the temporary branch and the energy processing branch due to the opening of the mechanical contacts).

[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 residual current is less likely to deteriorate even when the residual current is repeatedly interrupted.

[0015] FIG. 1 is a diagram showing the configuration of a multi-terminal high-voltage DC transmission system using a DC circuit breaker according to embodiment 1. FIG. 2 is a diagram showing the configuration of a DC circuit breaker according to embodiment 1. FIG. 3 is a diagram showing the fault current interruption operation of a DC circuit breaker according to embodiment 1. FIG. 4 is a diagram showing the fault current interruption operation of a DC circuit breaker according to embodiment 2. FIG. 5 is a diagram showing the fault current interruption operation of a DC circuit breaker according to embodiment 3. FIG. 6 is a diagram showing an example of a hardware configuration realizing a control unit provided in a DC circuit breaker according to embodiment 1, embodiment 2 or embodiment 3.

[0016] 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 the configuration of a multi-terminal high-voltage DC transmission system using a DC circuit breaker according to embodiment 1. 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 lines 4. Therefore, each of the AC systems 1 is connected in a ring shape via the DC lines 4 and the AC-DC converters 3. A DC circuit breaker 5 according to embodiment 1 is installed on the DC lines 4. An AC power source 7 and an AC circuit breaker 6 are installed in the AC system 1.

[0018] FIG. 2 illustrates the configuration of a 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 with mechanical contacts that interrupt current, a temporary branch 512 that forms a current zero point at the mechanical contacts, and an energy processing branch 513 that processes energy and attenuates fault current. The main branch 511, the temporary branch 512, and the energy processing branch 513 are connected in parallel. 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 mechanical contacts are applied only to the main branch 511. The residual current circuit breaker 52 is a gas circuit breaker that interrupts current in an insulating gas. Examples of insulating gases include sulfur hexafluoride and synthetic air, but other types of gases may also be used.

[0019] The control unit 53 outputs an opening command to the core circuit breaker 51 and the residual current circuit breaker 52 based on a 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. A fault is detected when the current value of the current flowing through the DC line 4 exceeds a predetermined threshold, 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 the fault current interruption operation of the DC circuit breaker according to embodiment 1. In Fig. 3, hatching sloping 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 sloping upward to the right indicates an arc period during which an arc is occurring in the core circuit breaker 51 or the residual current circuit breaker 52. In Fig. 3, dotted hatching 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 the protection 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 from time T0 to the fault detection time t ｒｅｌａｙ At time T1 after the elapse of time T, an opening command is output to the core circuit breaker 51. Upon receiving the opening command, the core circuit breaker 51 starts opening the mechanical contacts applied to the main branch 511. From time T1, a core circuit breaker opening operation time t ｃｂｏｐWhen the mechanical contacts of the main branch 511 are opened at time T2 after the time t has elapsed, an arc is generated between the mechanical contacts. Also, when the mechanical contacts applied to the main branch 511 are opened, the fault current is commutated to the temporary branch 512 and the energy processing branch 513.

[0023] From time T2 to core breaker arc time t ｃｂａｒｃ At time T3 after the fault, a switch (not shown) connected to the temporary branch 512 is turned on, and a current zero forming circuit included in the temporary branch 512 forms a current zero at the mechanical contacts, thereby interrupting the current flowing through the main branch 511. 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. The 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. The interruption of the fault current by the main branch 511 is generally referred to as "thermal interruption."

[0024] When the mechanical contact of the main branch 511 interrupts the fault current, the energy processing 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 value I ｐｆ Here, the current flowing through the DC circuit breaker 5 during current limiting is defined as the limiting current I ｓ Transient cutoff voltage U ＴＩＶ The overvoltage is suppressed in accordance with the voltage-current characteristic set by the energy processing branch 513. ＴＩＶ Generally, the peak value of the transient blocking voltage, U, reaches a peak value at time T5 and then starts to decrease. ＴＩＶｐｋ is the system voltage U ｓ It is about 1.5 to 1.7 times the original value.

[0025] Current Limiting I ｓis absorbed by flowing through the energy processing branch 513. By absorbing energy in the energy processing branch 513, the current limiting I ｓ This reduces the current limiting value I ｓ The absolute value of the current limiting I is small enough that the decomposition of the insulating gas due to the arc generated 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 current decays to zero, and the core circuit 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 referred to as the residual current circuit breaker opening operation time t ｒｃｓｏｐ Then, the limiting current 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 At time T8, the residual current circuit breaker 52 completes its contact opening operation. Therefore, at time T8, both thermal and dielectric interruption are achieved, and the interruption of the fault current is completed.

[0027] In addition, current limiting I ｓ The current limiting I is attenuated to a level where the decomposition of insulating gas due to the arc generated between the poles of the residual current circuit breaker 52 does not affect the interruption performance. ｓ Therefore, the arc period of the residual current circuit breaker 52 can be set to time T7, which is earlier than the time when the current value of the current limiting I ｓIt is possible to set the timing to start at time T7, which is earlier than time T8 when the current value of (1) 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 shutoff 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 is a value specific to the device, so if the time T8 at which the residual current circuit breaker 52 completes the opening operation can be set to the same time as or later than the time T7 at which the residual current circuit breaker opening possible period begins, the delay time t ｒｃｓｄ may be zero.

[0030] At time T8, the residual current circuit breaker 52 completes its contact opening operation, causing an arc to occur between the contacts of the residual current circuit breaker 52. However, since the core circuit breaker 51 has completed thermal and dielectric interruption, 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 elapse 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 is completed.

[0031] The DC circuit breaker 5 according to the first embodiment inputs an opening command to the residual current circuit breaker 52 at the same timing as the core circuit breaker 51, eliminating the need for complex calculations to determine the timing of inputting the opening command to the residual current circuit breaker 52. Furthermore, since the time T8 at which the residual current circuit breaker 52 completes its opening operation is later than the time T7 at which the residual current circuit breaker opening possible period begins, it is possible to suppress deterioration of the insulating gas even if the residual current circuit breaker 52 repeatedly interrupts the residual current. 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 according to embodiment 2 is similar to that of the DC circuit breaker 5 according to embodiment 1, but differs from that of the DC circuit breaker 5 according to embodiment 1 in the timing at which the control unit 53 outputs an opening command to the residual current circuit breaker 52.

[0033] Fig. 4 is a diagram showing the fault current interruption operation of the DC circuit breaker according to embodiment 2. In Fig. 4, hatching sloping 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 sloping upward to the right indicates an arc period during which an arc is occurring in the core circuit breaker 51 or the residual current circuit breaker 52. In Fig. 4, dotted hatching 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 the same as 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 is applied to the core circuit breaker 51, an opening command is output to the residual current circuit breaker 52.

[0035] The control unit 53 controls the current I flowing through the main branch 511. ｆｍ is zero, and the transient cut-off voltage U ＴＩＶ is a predetermined threshold U ｔｈ Based on at least one of the above, the fault current I ｆis cut off, and the transient cut-off voltage U ＴＩＶ In the example shown in FIG. 4, at time T3, the current I ｆｍ becomes zero, the control unit 53 detects the fault current I ｆ is cut off, and the 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 predetermined 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 limiting current I ｓ The current value of becomes zero for the first time after the time T3 with a 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 contact opening operation is completed at time T11 after the elapse of time.

[0037] Here, the delay time t ｒｃｓｄ is the shutoff 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 the time T11 when the residual current circuit breaker 52 finishes opening contacts is the same as or later than the time T7 when the residual current circuit breaker opening possible period begins.

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

[0039] At time T11, the residual current circuit breaker 52 completes 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 elapse 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 is completed.

[0040] In this way, in the DC circuit breaker 5 according to the second embodiment, the control unit 53 controls the core circuit breaker opening operation time t ｃｂｏｐ and core breaker arc time t ｃｂａｒｃ After time T3, and after time T1, the disconnection time t ｂｒｅａｋ An opening command is output to the residual current circuit breaker 52 by time T7 after the time has elapsed, 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 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 in the core circuit breaker 51, compared to the DC circuit breaker 5 according to the first embodiment. ｆ The possibility of failure in interrupting 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 according to embodiment 3 is similar to that of the DC circuit breaker 5 according to embodiment 1, but differs from that of the DC circuit breaker 5 according to embodiment 1 in the timing at which the control unit 53 outputs an opening command to the residual current circuit breaker 52.

[0043] 5 is a diagram showing the fault current interruption operation of the DC circuit breaker according to embodiment 3. In Fig. 5, hatching sloping downward to the right indicates an opening period in which the core circuit breaker 51 or the residual current circuit breaker 52 is performing an opening operation, and hatching sloping upward to the right indicates an arc period in 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 the same as 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 determines the 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 thermal shutdown and dielectric shutdown 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 Then, 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 the time has elapsed, time T14 is reached.

[0047] At time T14, the residual current circuit breaker 52 completes the opening operation, and an arc is generated in the residual current circuit breaker 52. ｓAt 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 elapse 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 is completed.

[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 breaking is 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 has completed thermal interruption 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 reduces the risk of damage to the residual current circuit breaker 52 due to a failure to break the power supply.

[0050] Next, a description will be given of the hardware configuration of the control unit 53. Fig. 6 is a diagram showing an example of a hardware configuration realizing the control unit provided in the DC circuit breaker according to embodiment 1, embodiment 2, or embodiment 3. 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 computing 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 functions of the control unit 53.

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

[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 Protection 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. A DC circuit breaker comprising: a core circuit breaker that interrupts a fault current flowing in a DC line; a residual current circuit breaker which is a gas circuit breaker that interrupts, in insulating gas, a residual current flowing in the DC line after interrupting the fault current; and a control unit that controls the core circuit breaker and the residual current circuit breaker, wherein the core circuit breaker comprises: a main branch that interrupts the fault current with mechanical contacts; a temporary branch that forms a current zero point at the mechanical contacts and extinguishes an arc generated between the poles of the mechanical contacts; and an energy processing branch that absorbs energy remaining in a DC system including the DC line and attenuates the fault current until its current value becomes zero, wherein the main branch, the temporary branch, and the energy processing branch are connected in parallel with each other, and the control unit causes the residual current circuit breaker to interrupt the residual current after completing thermal interruption, in which the arc is extinguished, and dielectric interruption, in which the core circuit breaker withstands an overvoltage generated by commutation of the fault current to the temporary branch and the energy processing branch due to the opening of the mechanical contacts.

2. The DC circuit breaker according to claim 1, characterized in that the control unit outputs an opening command to the core circuit breaker and the residual current circuit breaker simultaneously, and the residual current circuit breaker performs an opening operation after a preset delay time has elapsed since the opening command was input.

3. The DC circuit breaker according to claim 1, characterized in that the control unit outputs an opening command to the residual current circuit breaker after the core circuit breaker has completed the thermal breaking and while the dielectric breaking is being performed, and the residual current circuit breaker performs an opening operation after a preset delay time has elapsed since the opening command was input.

4. The DC circuit breaker according to claim 1, characterized in that the control unit outputs an opening command to the residual current circuit breaker after the core circuit breaker has completed the thermal interruption and the dielectric interruption, and the residual current circuit breaker performs an opening operation without delay when the opening command is input.

5. A DC circuit breaker according to any one of claims 1 to 4, characterized in that the insulating gas is synthetic air.

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