JP7309450B2 - Protection device for DC power transmission system - Google Patents

Description

Embodiments of the present invention relate to protection devices for DC power transmission systems.

In recent years, as a power transmission system suitable for long-distance high-power transmission, a high-efficiency direct-current power transmission system with lower equipment costs and less power transmission loss than conventional three-phase alternating current power transmission systems has attracted attention. In such a DC power transmission system, power conversion devices such as a converter that converts the generated AC power into DC for DC power transmission and an inverter that converts the transmitted DC into AC for urban use are required. That is, a pair of power converters are connected to the AC power transmission lines of the pair of AC power transmission systems, respectively, and the DC power transmission system is configured by these power converters and the DC power transmission lines connected therebetween.

Here, practical use of a modular multilevel converter (MMC: Modular Multilevel Converter) is being promoted as a converter used in a power converter. The MMC can output a voltage waveform close to a sine wave so that harmonics associated with switching of the converter and inverter do not flow out to the AC system. A power converter using such an MMC is applied to a high-voltage DC power transmission system (HVDC), which is a long-distance high-power transmission system.

International publication WO2016/013053

In the DC transmission system as described above, the DC transmission line may include an overhead line section. An accident that has occurred in a DC power transmission system may be a transient accident caused by a lightning strike on an overhead line section or the like. In such a case, the energy stored in the capacitor inside the MMC is used to temporarily turn off all the switching elements of the MMC into a gate block (GB) state, and then open the AC circuit breaker to remove the fault current. . After the fault current is removed, there is a demand to turn on the AC circuit breaker again to quickly restart the power converter.

On the other hand, there are also cases of accidents inside power converters, ground faults within the premises of converter stations where power converters are installed, and ground faults in cable sections of DC transmission lines. When such an accident occurs on the side of one of the power conversion devices, in the conventional separately-excited power conversion device, the side of the power conversion device detects this, stops the power conversion device, and opens the AC circuit breaker. was doing

However, on the side of the other power converter, the accident on the side of one power converter cannot be detected. For this reason, a communication facility is provided between both power converters, an accident on one power converter side is transmitted to the other power converter side, and the other power converter is stopped and the AC circuit breaker is opened. was doing

However, when an accident occurs, it is necessary to quickly and reliably separate the accident occurrence point. However, when communication delays or failures occur in communication equipment, prompt processing becomes impossible. Moreover, when both power converters are installed in remote locations, the influence of communication delays in communication equipment becomes greater.

An object of the present embodiment is to provide a protection device for a DC power transmission system using a self-commutated power converter, which is capable of removing fault current at high speed.

The protection device of the DC power transmission system of the present embodiment includes a pair of self-commutated power conversion devices connected between a pair of AC power transmission lines including an AC circuit breaker and both ends of the DC power transmission line, and both power conversion devices. A current value detected by a detector on either one of the power conversion devices provided in a DC power transmission system having a detector that detects the current value, provided on the device side at a location where an overcurrent flows due to an accident. Based on, when an overcurrent due to an accident on the one power converter side or an accident on the other power converter side is detected, the one power converter is stopped and the AC circuit breaker is opened. and a block instruction unit for blocking the AC power transmission line and the one power conversion device , and the detection unit is provided at a plurality of locations on the AC power transmission line and the DC power transmission line, and the plurality of detection units A differential current detection unit that detects the differential current caused by the fault based on the detected current value, and an accident section determination unit that determines the fault section, which is the section where the fault occurred, based on the detected differential current. and a restart instruction unit that instructs re-closing of the AC circuit breaker and restart of the power conversion device according to the determination result of the fault section after the interruption by the interruption instruction unit.

The block diagram which shows the DC power transmission system of embodiment 1 is a block diagram showing a protective device according to an embodiment; FIG. Flowchart showing the processing procedure of the embodiment FIG. 3 is a logic block diagram showing control logic of Modification 1 of the embodiment; 4 is a flowchart showing a processing procedure of modification 1 of the embodiment; FIG. 11 is a logic block diagram showing control logic of modification 2 of the embodiment; 4 is a flow chart showing a processing procedure of modification 2 of the embodiment; FIG. 11 is a logic block diagram showing control logic of Modification 3 of the embodiment; 10 is a flow chart showing a processing procedure of modification 3 of the embodiment; Explanatory drawing which shows the example of transmission of the accident detection signal of embodiment Explanatory drawing which shows the example of transmission of the accident detection signal of embodiment

[composition]
The configuration of the embodiment will be described with reference to FIGS. 1 and 2. FIG. A DC power transmission system S to which the present embodiment is applied includes a pair of power conversion devices C1 and C2, DC power transmission lines D1 and D2, detection units M3 to M8, protection devices 11α and 11β, control devices 12α and 12β, and a transmission device 13α. , 13β. The power converters C1 and C2 are connected between both ends of the DC transmission lines D1 and D2 and a pair of AC transmission lines A1 and A2 including AC circuit breakers SW9 and SW10, respectively. In the following description, one side of the DC transmission lines D1 and D2 is the power conversion device C1 side, and the other side is the power conversion device C2 side. Similar devices are arranged on the power conversion device C1 side and the power conversion device C2 side, respectively. M, the protection device 11, the control device 12, the transmission device 13, the AC transmission line A, and the AC circuit breaker SW.

The power converters C1 and C2 are composed of self-excited converters capable of mutually converting AC power and DC power. A self-excited converter is a converter using a self-extinguishing switching element. In this embodiment, a modular multi-level converter (MMC) with a high breakdown voltage is used in which a plurality of cell converters each including an IGBT as a switching element, a diode as a rectifying element, and a capacitor as an energy storage element are cascade-connected.

A pair of power converters C1 and C2 each have a similar structure, one of which functions as a converter that converts alternating current to direct current, and the other functions as an inverter that converts direct current to alternating current, but these functions are alternated. It is possible. Moreover, the power converters C1 and C2 enter a gate block state for overcurrent protection by turning off all the switching elements.

DC transmission lines D1, D2 include overhead lines and cables. The overhead line referred to here is a direct current transmission line suspended in the air by a support such as a steel tower. Cables are DC transmission lines other than overhead lines. In the following description, an overhead line section is called an overhead line section, and a cable section is called a cable section. However, in this embodiment, one of the features is that an accident in an overhead line section is handled separately from other accidents, so for convenience, the DC transmission lines D1 and D2 correspond to the overhead line section. described as a thing. A DC power transmission line D1 is a main line, and D2 is a ground potential return line.

The AC transmission lines A1 and A2 are connected to separate AC transmission systems. The AC power transmission system is a system that supplies power from the three-phase AC power sources P1 and P2, and can exchange power with each other via the DC power transmission system S of the present embodiment.

The AC transmission lines A1 and A2 are provided with AC circuit breakers SW9 and SW10 and transformers T1 and T2, respectively. The AC circuit breakers SW9 and SW10 are circuit breakers that disconnect the power converters C1 and C2 from the AC system by opening according to an accident. The transformers T1 and T2 adjust the voltage of the AC power from the AC system and output it to the power conversion devices C1 and C2, or adjust the voltage of the AC power from the power conversion devices C1 and C2 to supply the AC power to the AC system. output to

The detection units M3 to M8 are devices for detecting current. The detectors M3 to M6 are DC current detectors provided at both ends of the DC transmission lines D1 and D2, respectively. DC current transformers can be used as the detection units M3 to M6. The detectors M7 and M8 are AC current detectors provided in the AC power transmission lines A1 and A2, respectively. AC current transformers can be used as the detectors M7 and M8.

The protective devices 11α and 11β are devices that perform various judgment processes for protecting the DC power transmission system S. That is, the protective devices 11α and 11β perform various arithmetic processing for controlling the power converter C and the AC circuit breaker SW according to the current value detected by the detector M, and output the results. Detectors M3, M4, M5 and M7 are connected to the protective device 11α, and detectors M3, M4, M6 and M8 are connected to the protective device 11β. is omitted.

The protection device 11 can be configured by a hardware circuit such as an ASIC (application specific integrated circuit) or a processor such as a PLD (programmable logic device) that executes a program. The protective device 11, as shown in FIG. It functions as part 140 . Note that such a program and a recording medium recording the program are also aspects of the embodiments.

Based on the current value detected by the detection unit M of one of the power converters C, the shutdown instructing unit 110 detects an overload due to an accident on the side of one power converter C or an accident on the side of the other power converter C. When the current is detected, the AC transmission line A and the power converter C are cut off by stopping one of the power converters C and opening the AC circuit breaker SW. Overcurrent detection is performed based on comparison with a threshold preset in a memory or the like.

That is, the cutoff instruction unit 110 of the protection device 11α stops the power conversion device C1 and cuts off the AC when overcurrent is detected from the current values detected by the detection units M3, M5, and M7 on the power conversion device C1 side. switch SW9 is opened. When an overcurrent is detected from the current values detected by the detection units M4, M6, and M8 on the side of the power converter C2, the shutdown instruction unit 110 of the protection device 11β stops the power converter C2, and the AC circuit breaker SW10 open up.

In the self-commutated power converters C1 and C2, an overcurrent flows to the self-end even if an accident occurs on either side. In this embodiment, when an overcurrent is detected, regardless of whether the fault is on the counterpart end side, the power converters C1 and C2 are stopped and disconnected from the AC transmission lines A1 and A2. The accident includes, for example, an internal accident of the power converter C, a ground fault on the premises of the conversion station where the power converter C is installed, and an overhead line ground fault of the DC transmission line D. In any case of these accidents, an overcurrent flows, so that the shutdown instruction unit 110 stops the power converters C1 and C2 and disconnects them from the AC transmission lines A1 and A2. The shutdown instruction unit 110 functions as a protective relay in relation to the AC circuit breaker SW.

The differential current detector 120 detects a differential current due to an accident based on current values detected by the plurality of detectors M. FIG. The fault current flowing into the fault point due to the occurrence of a ground fault has a different direction with the fault point as a boundary. Shows different behavior than time. Therefore, the differential current detected by the differential current detection unit 120 enables detection of an accident.

The fault section determination unit 130 determines the fault section, which is the section in which the fault occurred, based on the detected differential current. For example, the fault zone determination unit 130 of the protection device 11α detects the fault in the zone between any of the detection units M3, M5, and M7 based on the differential current detected by any one of the detection units M3, M5, and M7. It is determined that In this case, the accident section determination unit 130 outputs an accident detection signal indicating an internal accident of the power converter C1 or a ground fault on the premises. Further, the accident section determination unit 130 of the protective device 11α determines that there is an accident in the section between the detection units M3 and M4 based on the differential current detected by the detection units M3 and M4. In this case, the accident section determination unit 130 outputs an accident signal indicating an overhead line ground fault.

On the other hand, the fault zone determination unit 130 of the protective device 11β detects the fault in the zone between any one of the detection units M4, M6, and M8 based on the differential current detected by any one of the detection units M4, M6, and M8. It is determined that In this case, the fault zone determination unit 130 of the protective device 11β outputs a fault detection signal indicating an internal fault or ground fault fault in the power conversion device C2. Further, the fault section determination unit 130 of the protective device 11β determines that there is an accident in the section between the detection units M4 and M3 based on the differential current detected by the detection units M4 and M3. In this case, the accident section determination unit 130 outputs an accident signal indicating an overhead line ground fault.

After the interruption by the interruption instruction section 110, the restart instruction section 140 instructs the AC circuit breaker SW to be turned on again and the power conversion device C to be restarted according to the determination result of the fault section. When the restart instruction unit 140 of the present embodiment receives an accident detection signal indicating that the fault section determined by the fault section determination unit is an overhead transmission line, the AC circuit breaker SW is re-closed and power conversion is performed. Instruct to restart the device. On the other hand, when the restart instruction unit 140 receives an accident detection signal indicating that the fault section determined by the fault section determination unit is an internal fault of the power converter C or an on-site ground fault, the AC circuit breaker Re-insertion of SW and restart of power converter C are not allowed. That is, even if it is determined as an overhead line ground fault, if an internal fault of the power conversion device C or a ground fault within the premises has occurred, the AC circuit breaker SW is turned on again and the power conversion device Stop the system without rebooting.

For example, even if an overhead line ground fault is detected, the restart instruction unit 140 of the protective device 11α may restart the AC circuit breaker SW9 if an internal fault of the power conversion device C1 or a ground fault in the premises has occurred. Re-insertion and restart of the power conversion device C1 are not allowed. Further, even if an overhead line ground fault is detected, the restart instructing unit 140 of the protection device 11β may restart the AC circuit breaker SW10 if an internal fault of the power conversion device C2 or a ground fault within the premises has occurred. Do not turn on the power again and restart the power conversion device C2.

The control device 12 is a device that controls the operation of the power converter C. As shown in FIG. The control device 12 of this embodiment controls the stop and start of the power conversion device C based on the instruction signal from the protection device 11 . That is, the control device 12α stops the power conversion device C1 based on the stop instruction signal from the protection device 11α. Also, based on the restart instruction signal from the protective device 11α, the power electronics device C1 is restarted. The control device 12β stops the power conversion device C2 based on the stop instruction signal from the protection device 11β. Also, based on the restart instruction signal from the protective device 11β, the power conversion device C2 is restarted.

The transmission device 13 transmits an accident detection signal via the transmission line when the differential current detection unit 120 detects the differential current. The transmission device 13 and the transmission line are communication facilities for transmitting and receiving an accident detection signal between the power conversion device C1 side and the power conversion device C2 side. In other words, when the accident section determination unit 130 of the protection device 11α outputs an accident detection signal indicating an internal fault of the power conversion device C1 or a ground fault on the premises, the fault detection signal is transmitted by the transmission device 13 to the protection device 11β. sent to. Further, when the accident section determination unit 130 of the protection device 11β outputs an accident detection signal indicating an internal fault of the power conversion device C2 or a ground fault on the premises, the fault detection signal is transmitted by the transmission device 13 to the protection device. 11α. In this way, when the protection devices 11α and 11β receive the accident detection signal from the other party, the AC circuit breaker SW is not turned on again and the power conversion device C is not restarted, and the system is stopped.

[motion]
(basic action)
The basic operation of this embodiment as described above will be described with reference to the flowchart of FIG. Note that the flowcharts shown below show the flow of processing executed by each unit that configures the system, and therefore include portions where processing blocks are parallel. A method of protecting the DC power transmission system S by the following procedure and control logic is also one aspect of the embodiment. The cut-off instruction unit 110 monitors whether overcurrent has occurred based on the current value from the detection unit M (step S101). In parallel with this, the differential current detector 120 monitors the differential current based on the current value from the detector M (step S102). When the interruption instruction unit 110 detects an overcurrent due to the occurrence of an accident (YES in step S103), the AC circuit breaker SW is opened to stop the power converter C (step S104).

On the other hand, based on the detection of the differential current by the differential current detection unit 120 (YES in step S105), the fault section determination unit 130 determines the fault section (step S106). If the fault section is only the overhead line section (YES in step S107), based on the differential current detected by the differential current detection unit 120, the restart is performed on the condition that the fault current is removed. The instruction unit 140 restarts the power converter C and turns on the AC circuit breaker SW (steps S108 and S109).

If the accident section is a converter internal accident or a ground fault on the premises (NO in step S107), the restart instruction unit 140 restarts the power converter C and does not turn on the AC circuit breaker SW. Stop the system (step S110).

(Modification 1)
The control logic of Modification 1 of the above aspect will now be described with reference to the logic block diagram of FIG. That is, if there is at least one output from overcurrent detection B1, differential current detection B2, and differential current detection B3, 1 is output from the OR gate, power converter C is stopped, and AC circuit breaker SW is opened. (B4). Differential current detection B2 indicates differential current detection due to converter internal faults and ground faults within the premises. Differential current detection B3 indicates differential current detection due to a ground fault in an overhead line section. Then, the output of the differential current detection B2 becomes a system stop B5, resulting in a restart-impossible sequence. Also, the output of the differential current detection B3 is the restart B6 sequence.

An example of operation by such control logic will be described with reference to the flow chart of FIG. First, the operations of steps S201 to S206 are the same as steps S101 to S106 in the flow chart of FIG. However, even if the differential current is detected (YES in step S205), the AC circuit breaker SW is opened to stop the power converter C (step S204). If the fault section determined by the fault section determination unit 130 is a converter internal fault or a ground fault within the premises (YES in step S207), the restart instruction unit 140 restarts the power converter C and interrupts the AC. The system is stopped without turning on the device SW (step S208). If the fault section determined by the fault section determination unit 130 is an overhead line section (YES in step S209), the restart instruction unit 140 instructs restart on the condition that the fault current has been removed ( Step S210), the power converter C is restarted, and the AC circuit breaker SW is turned on (step S211).

(Modification 2)
The control logic of Modification 2 of the above aspect will now be described with reference to the logic block diagram of FIG. In other words, even if a ground fault occurs in an overhead line section, if a fault inside the power converter or a ground fault on the premises occurs simultaneously or continues, the system will be stopped first and restart will not be allowed. is required. Therefore, in Modification 2, the output of the differential current detection B2 is input to the AND gate with the differential current detection B3 via the NOT gate. Therefore, even if there is the differential current detection B3, if the output of the differential current detection B2 is ON, the sequence does not proceed to the restart B6. A restart occurs when the differential current detection B3 is output while the differential current detection B2 is in an OFF state with no output.

An example of operation by such control logic will be described with reference to the flow chart of FIG. First, the operations of steps S301 to S306 are the same as steps S201 to S206 in the flow chart of FIG. However, only when the fault section discriminated by the fault section discriminating unit 130 is not the power converter internal fault or the premises ground fault (NO in step S307), and only when it is the overhead line section ground fault (step YES in S309), the restart instruction unit 140 instructs restart (step S310), the power conversion device C is restarted, and the AC circuit breaker SW is turned on (step S311).

(Modification 3)
The control logic of Modification 3 of the above aspect will now be described with reference to the logic block diagram of FIG. That is, in Modification 3, an off-delay timer is set for the output of the differential current detection B2. The off-delay timer turns on the output when the input turns on, but even if the input turns off, the output turns off after a certain period of time has elapsed. Therefore, when the differential current detection B2 is detected, the output is continued for a certain period of time. Therefore, even if the differential current detection B3 is detected, the system is not immediately restarted, and system stop is prioritized. The off-delay time t may be sufficient for the fault current to be removed. That is, the AC circuit breaker SW is turned off, and the remaining energy is all released, and the time is sufficient for the fault current in the DC transmission line D1 to disappear. For example, it is conceivable to set it to about 300 ms, but it is not limited to this.

An example of operation by such control logic will be described with reference to the flow chart of FIG. First, the operations of steps S401 to S406 are the same as steps S201 to S206 in the flow chart of FIG. However, when the differential current detection unit 120 detects the differential current after the time t has elapsed (YES in step S407), the restart instruction unit 140 restarts the power conversion device C, the AC circuit breaker The system is stopped without turning on the SW (step S408). When the differential current detection 120 no longer detects the differential current after the time t has elapsed (NO in step S407), the restart instruction unit 140 instructs restart (step S409), and the power converter C It is restarted and the AC circuit breaker SW is turned on (step S410).

(signal transmission)
Next, a protection operation performed by transmitting an accident detection signal between the power electronics device C1 and the power electronics device C2 will be described with reference to FIGS. 10 and 11. FIG. In addition, in FIG.10 and FIG.11, a part of DC power transmission system S and a part of control logic are shown, and others are abbreviate|omitted.

FIG. 10 shows a case where a ground fault occurs between the power converter C2 and the detector M4 as an example of the power converter internal accident and the premises ground fault. At this time, the protective device 11α on the power conversion device C1 side detects the overcurrent from the detection unit M3 as described above, stops the power conversion device C1, and shuts off the AC circuit breaker SW9. The protective device 11β on the power conversion device C2 side detects the overcurrent from the detection unit M4, stops the power conversion device C2, and shuts off the AC circuit breaker SW10.

In parallel with this, when the differential current detection unit 120 detects the differential currents of the detection units M4, M6, and M8, the fault detection signal output from the fault section determination unit 130 is transferred to the transmission device 13β. transmits to the transmission device 13α. As a result, the protective device 11α on the side of the power conversion device C1 can also stop the system as described above, assuming that there is an accident inside the power conversion device or a ground fault on the premises.

FIG. 11 shows a case where a ground fault occurs between the detector M3 and the detector M4 as an example of a ground fault in an overhead line section. At this time, the protective device 11α on the power conversion device C1 side detects the overcurrent from the detection unit M3 as described above, stops the power conversion device C1, and shuts off the AC circuit breaker SW9. The protective device 11β on the power conversion device C2 side detects the overcurrent from the detection unit M4, stops the power conversion device C2, and shuts off the AC circuit breaker SW10.

In parallel with this, when the differential current detection unit 120 detects the differential current between the detection unit M3 and the detection unit M4, the transmission device 13β transmits an accident detection signal output from the accident section determination unit 130. Send to the device 13α. As a result, the protection device 11α on the power conversion device C1 side can also be restarted as an overhead line section ground fault, as described above.

[Effect]
(1) The present embodiment as described above includes a pair of self-commutated power converters C connected between a pair of AC transmission lines A including AC circuit breakers SW and both ends of a DC transmission line D, On both power converters C side, provided in a DC power transmission system S having a detection unit M that is provided at a location where an overcurrent flows due to an accident and detects a current value, and one of the power converters C side When an overcurrent due to an accident on the side of one power converter C or an accident on the side of the other power converter C is detected based on the current value detected by the detection unit M, one power converter C is stopped. , and a break instruction unit 110 for breaking the AC transmission line A and the power converter C by opening the AC circuit breaker SW.

Therefore, even if an accident occurs in any power conversion device C side, the AC power transmission line A and the power conversion device C are cut off due to the detection of overcurrent, thereby being affected by the signal transmission delay. The fault current can be removed at high speed without

Here, in the DC power transmission system using the self-commutated power conversion device C, when a ground fault occurs on the DC side of the power conversion device C, the energy of the capacitor is discharged toward the fault point. In this case, if the power converter C is gate-blocked, the discharge of the capacitor is stopped and the energy inside the capacitor can be saved. However, even if the power converter C is gate-blocked, the fault current flows from the AC side to the fault point through the diodes at both ends because the power converter C becomes a passive circuit while the ground fault occurs. continue. Therefore, after the occurrence of the ground fault, it is necessary to open the AC circuit breaker SW and disconnect the power converter C from the AC side at high speed.

On the other hand, in separately-commutated power converters, the fault current on one power converter side does not flow to the other power converter side, so mutual faults cannot be detected unless a communication means is provided. In the case of the self-commutated power conversion device C, when an accident occurs on one power conversion device C side, the fault current also flows in the other power conversion device C side. Therefore, in the present embodiment, a detection unit M is provided at a location where an overcurrent flows, and when an overcurrent is detected, the system is stopped regardless of whether the accident is on the side of any power conversion device C. This makes it possible to eliminate fault currents at high speed without being affected by transmission delays.

(2) The detection units M are provided at a plurality of locations in the AC transmission line A and the DC transmission line D, and based on the current values detected by the plurality of detection units M, a differential current for detecting a differential current due to an accident. A detection unit 120, an accident section discrimination unit 130 that discriminates an accident section, which is a section in which an accident occurred, based on the detected differential current, and after interruption by the interruption instruction unit 110, according to the identification result of the accident section , and a restart instruction unit 140 for instructing re-throwing of the AC circuit breaker SW and restarting of the power converter C.

For this reason, regardless of any accident, first, after disconnecting the power converter C from the AC transmission line A and removing the fault current, depending on the fault section, if there is a need for restarting, restart according to this. can be activated.

(3) When the fault section determined by the fault section determination unit 130 is an overhead line section included in the DC transmission line D, the restart instruction unit 140 causes the AC circuit breaker SW to be reclosed and the power converter C to let it reboot. For this reason, after the fault current due to the ground fault is removed, the overhead line section can be restarted if there is no problem even if it is restarted.

(4) When at least one of the ground fault in the overhead line section and the internal fault of the power converter C and the ground fault in the converter station where the power converter C is installed occurs, the restart instruction unit 140 prevents the AC circuit breaker SW from being turned on again and the power converter C from being restarted. Therefore, in the case of an accident that should not be restarted, the system can be stopped to prevent restart.

(5) The fault section determination unit 130 outputs both or one of a fault detection signal indicating a power converter internal fault or ground fault on the premises and a fault detection signal indicating a ground fault in an overhead line section. An off-delay timer is set for the output of an accident detection signal from the fault section discriminating unit 130 indicating an internal fault of the power converter or a ground fault within the premises. Therefore, even after the ground fault in the overhead line section has been removed, it is possible to prevent restarting in the event of an internal power conversion device accident or a ground fault in the premises.

(6) Having a transmission device 13 that transmits a signal notifying this to the other power conversion device C side when the differential current detection unit 120 on the side of one of the power conversion devices C detects a differential current. . Therefore, the pair of power converters C can perform restart or system stop by transmitting signals to each other. Since cutoff due to overcurrent has already been performed, there is no problem even if transmission delay occurs.

[Other embodiments]
Each of the above embodiments are presented herein by way of example and are not intended to limit the scope of the invention. That is, it can be embodied in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

In addition, in the DC transmission lines D1 and D2, a detection unit is provided between the overhead line section and the cable section, and the differential current detected by this detection unit and the other detection units M3 and M4 detects the fault section. The determination unit 130 may determine whether the accident occurred in an overhead line section or in a cable section. In the case of an accident in a cable section, the restart instructing unit 140 does not restart, as in the case of an internal power conversion device accident and an on-site ground fault. That is, if at least one of an internal accident of the power converter C, a ground fault in the converter station where the power converter C is installed, and an accident in the cable section is detected, the system is stopped without being restarted.

11, 11α, 11β protection device 12, 12α, 12β control device 13, 13α, 13β transmission device 110 cut-off instruction unit 120 differential current detection unit 130 fault section determination unit 140 restart instruction unit A, A1, A2 AC transmission line C , C1, C2 Power converters D, D1, D2 DC power transmission lines M, M3, M4, M5, M6, M7, M8 Detectors P1, P2 Three-phase AC power supply S DC power transmission system SW, SW9, SW10 AC circuit breaker T1 , T2 transformer

Claims (5)

a pair of self-excited power converters connected between a pair of AC transmission lines including an AC circuit breaker and both ends of the DC transmission line;
A detection unit that is provided at a location where an overcurrent flows due to an accident and detects a current value on both power conversion device sides;
provided in a DC power transmission system having
Based on the current value detected by the detection unit of one of the power converters, when an overcurrent due to an accident on the one power converter side or an accident on the other power converter side is detected, a shutdown instruction unit that shuts off the AC power transmission line and the one power conversion device by stopping the power conversion device and opening the AC circuit breaker ;
The detection unit is provided at a plurality of locations on the AC power transmission line and the DC power transmission line,
a differential current detection unit that detects a differential current due to an accident based on the current values detected by the plurality of detection units;
an accident section discriminating unit that discriminates an accident section, which is a section in which an accident has occurred, based on the detected differential current;
After the interruption by the interruption instruction unit, a restart instruction unit that instructs re-insertion of the AC circuit breaker and restart of the power conversion device according to the determination result of the fault section;
A protective device for a DC power transmission system having a When the fault section determined by the fault section determination unit is an overhead line section included in the DC power transmission line, the restart instruction unit restarts the AC circuit breaker and restarts the power converter. The protection device for a DC power transmission system according to claim 1 , wherein When at least one of an internal fault of the power conversion device and a ground fault within the power conversion station where the power conversion device is installed has occurred together with the ground fault in the overhead line section, the restart instruction unit 3. A protective device for a DC power transmission system according to claim 2, wherein said AC circuit breaker is not re-closed and said power conversion device is not restarted. The fault section discriminating unit detects both or one of a fault detection signal indicating an internal fault of the power converter or the ground fault on the premises and a fault detection signal indicating a ground fault in the overhead line section. is set to output
4. A protection device for a DC power transmission system according to claim 3 , wherein an off-delay timer is set for output of an accident detection signal indicating an internal fault of said power conversion device or said ground fault within said premises from said fault section discriminating unit. . 5. The apparatus according to any one of claims 2 to 4 , further comprising a transmission device for transmitting a signal notifying said differential current to the other power conversion device when said differential current detector on one of the power conversion devices detects a differential current. A protection device for a direct current power transmission system according to any one of the above.

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