Power system protection system, power system protection device, and power system protection method

Abstract

A power-system protection system (90) comprises: a system breaker (40) that is installed on a power line (20) connecting a power generator (10) and a load (60) to which power is supplied from the power generator (10), and that shuts off current flowing through the power line (20) when the power line (20) has experienced an abnormality; and a commutator (51) that is connected to ground (80), insulates the power line (20) and the ground (80) when in an OFF state, and creates conduction through the power line (20) and the ground (80) when in an ON state. When an accident due to a ground fault or short circuit occurring in the power line (20) is sensed, the commutator (51) is turned on before the system breaker (40) shuts off the current flowing through the power line (20), thus causing the current flowing through the power line (20) to be commutated to the ground.

Description

[Technical Field]

[0001] The present disclosure relates to a power system protection system, a power system protection device, and a power system protection method that protect a power system when an accident such as a ground fault or a short circuit occurs in a power transmission line. [Background technology]

[0002] Conventionally, in a power transmission system that transmits power generated by a generator to a load, a circuit breaker and a relay as disclosed in Patent Document 1 are installed in a power transmission line in preparation for the occurrence of an accident such as a short circuit or a ground fault. When a ground fault occurs in a power transmission line due to the influence of a lightning strike or the like, the relay detects the accident and sends a break command to the circuit breaker. The circuit breaker, upon receiving the break command from the relay, opens its contacts, thereby interrupting the current flowing in the power transmission line. After the arc is extinguished by interrupting the current flowing in the power transmission line, the circuit breaker is closed, and the power transmission system returns to a state in which power can be transmitted normally. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-281302 Summary of the Invention [Problem to be solved by the invention]

[0004] It is known that the insulation performance of the space around the ground fault in a power line recovers in a time equivalent to a maximum of two AC cycles after the arc has extinguished. Therefore, if a ground fault occurs on a 60 Hz AC power line, the insulation performance of the space around the ground fault will recover 30 ms after the arc has extinguished.

[0005] During the open circuit breaker period, the transmission line is in a no-voltage power outage state, increasing the impedance of the power system and reducing the stability of the power system. Therefore, it is desirable to resume power transmission as soon as possible after the arc is extinguished. Circuit breakers open and close by physically moving the moving contact, so there is a limit to how fast they can be operated. Therefore, it takes approximately 300 ms to 1 second from the time the arc is extinguished by the circuit breaker interrupting the current flowing through the transmission line to the time the circuit breaker closes and restores normal power transmission. Thus, if an arc is extinguished by interrupting the current with a circuit breaker installed on the transmission line, the circuit breaker's operating speed becomes a bottleneck, making it difficult to shorten the time until power transmission resumes.

[0006] The present disclosure has been made in consideration of the above, and aims to provide a power system protection system that can restore the power transmission system to a state in which power is transmitted normally in a short time after an arc is extinguished. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, the power system protection system according to the present disclosure includes a system circuit breaker that is installed on a transmission line connecting a generator and a load to which power is supplied from the generator and that interrupts the current flowing through the transmission line when an abnormality occurs in the transmission line, and a commutator that is connected to a portion of the transmission line between the system circuit breaker and the load and to ground and that insulates the transmission line from ground in an off state and conducts the transmission line from ground in an on state. When the power system protection system detects an accident due to a ground fault or short circuit occurring in the transmission line, it turns on the commutator to commutate the current flowing through the transmission line to ground before the system circuit breaker interrupts the current flowing through the transmission line. [Effects of the Invention]

[0008] The present disclosure provides an advantageous effect of providing a power system protection system that can restore the power transmission system to a state in which power is transmitted normally in a short time after an arc is extinguished. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a configuration of a power transmission system according to a first embodiment. [Figure 2] Functional block diagram of a relay of a power system protection device according to the first embodiment [Figure 3] 1 is a flowchart showing the flow of operation of the power system protection device according to the first embodiment. [Figure 4] FIG. 1 is a diagram showing a state in which a ground fault occurs in the power transmission system according to the first embodiment. [Figure 5] FIG. 1 is a diagram showing a state in which a mechanical switch of a commutator of a power system protection device according to a first embodiment is turned on. [Figure 6] FIG. 1 is a diagram showing a state in which a semiconductor switch of a commutator of a power system protection device according to a first embodiment is turned on. [Figure 7] FIG. 1 is a diagram showing a state in which a semiconductor switch of a commutator of a power system protection device according to a first embodiment is turned off. [Figure 8] FIG. 10 is a diagram showing a configuration of a power transmission system according to a second embodiment. [Figure 9] FIG. 10 is a diagram showing a configuration of a power transmission system according to a third embodiment. [Figure 10] FIG. 10 is a diagram showing a configuration of a power transmission system according to a fourth embodiment. [Figure 11] FIG. 10 is a diagram showing the hardware configuration of a control unit of a relay in a power system protection device according to first and second embodiments and a control unit of a control device according to third and fourth embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A power system protection system, a power system protection device, and a power system protection method according to embodiments will be described in detail below with reference to the accompanying drawings.

[0011] Embodiment 1 FIG. 1 is a diagram illustrating a configuration of a power transmission system according to a first embodiment. The power transmission system 100 is a power system that transmits power generated by a generator 10 to a load 60. A transformer 30, a system circuit breaker 40, and a power system protection device 50 are installed on a power transmission line 20. The power system protection device 50 includes a commutator 51 and a relay 52. ​​The commutator 51 is connected to a portion of the power transmission line 20 between the system circuit breaker 40 and the load 60 and to ground 80. In an OFF state, the commutator 51 insulates the power transmission line 20 from the ground 80, and in an ON state, the commutator 51 conducts power between the power transmission line 20 and the ground 80. The commutator 51 includes a semiconductor switch 511 and a mechanical switch 512 connected in series with the semiconductor switch 511. The power system protection device 50 is installed so as to connect the power transmission line 20 to the ground 80 via the commutator 51. The commutator 51 is installed so that the mechanical switch 512 is on the power transmission line 20 side and the semiconductor switch 511 is on the ground 80 side.

[0012] The semiconductor switch 511 is configured by connecting multiple switching elements in series or in parallel. Increasing the number of parallel-connected switching elements increases the current that can be passed through the semiconductor switch 511. Increasing the number of serial-connected switching elements also increases the withstand voltage of the semiconductor switch 511.

[0013] 2 is a functional block diagram of a relay of the power system protection device according to the first embodiment. Relay 52 includes a fault detection unit 521 that detects the occurrence of an abnormality due to an accident such as a short circuit or a ground fault in power transmission line 20 based on the voltage value of the current flowing through power transmission line 20, and a control unit 522 that controls commutator 51 and system breaker 40. When a ground fault occurs in power transmission line 20 due to a lightning strike or the like, fault detection unit 521 detects the occurrence of the fault and notifies control unit 522. Control unit 522 includes counter 523. In the following description, it is assumed that the initial value of count value N of counter 523 is 1.

[0014] In normal operation when no fault occurs on the power transmission line 20, both the semiconductor switch 511 and the mechanical switch 512 are turned off.

[0015] FIG. 3 is a flowchart showing a flow of operations of the power system protection device according to the first embodiment. In step S1, the control unit 522 determines whether or not the fault detection unit 521 has notified the control unit 522 of the occurrence of an accident. FIG. 4 is a diagram showing a state in which a ground fault has occurred in the power transmission system according to the first embodiment. In FIG. 4, the solid arrow indicates the path of the current transmitted from the generator 10. When a ground fault has occurred in the power transmission line 20, the voltage value of the current flowing through the power transmission line 20 becomes an abnormal value, the fault detection unit 521 detects the occurrence of an accident, and the fault detection unit 521 notifies the control unit 522 of the occurrence of the accident. If the fault detection unit 521 has notified the control unit 522 of the occurrence of the accident, the result of step S1 is Yes, and the control unit 522 proceeds to step S2. If the fault detection unit 521 has not notified the control unit 522 of the occurrence of an accident, the result of step S1 is No, and the control unit 522 repeats the process of step S1.

[0016] In step S2, the control unit 522 transmits a closing command to the mechanical switch 512 to turn on the mechanical switch 512. Fig. 5 is a diagram showing a state in which the mechanical switch of the commutator of the power system protection device according to embodiment 1 is turned on. In Fig. 5, the solid arrow indicates the path of the current transmitted from the generator 10. When the mechanical switch 512 is turned on, the semiconductor switch 511 remains off, and therefore the current flowing through the transmission line 20 continues to flow through the transmission line 20 without being commutated to the commutator 51.

[0017] In step S3, the control unit 522 sends a command to the semiconductor switch 511 to turn it on. Fig. 6 is a diagram showing a state in which the semiconductor switch of the commutator of the power system protection device according to embodiment 1 is turned on. In Fig. 6, the solid arrow indicates the path of the current transmitted from the generator 10. When the mechanical switch 512 and the semiconductor switch 511 are both turned on, the commutator 51 is turned on, and current flows from the transmission line 20 to the ground 80 via the commutator 51. Current no longer flows in the fault location, and the arc is extinguished.

[0018] In step S4, the control unit 522 waits for a time period equivalent to (N+1) cycles of the AC current flowing through the power transmission line 20. Here, N is the count value of the counter 523.

[0019] In step S5, the control unit 522 sends a command to the semiconductor switch 511 to turn it off. FIG. 7 is a diagram showing a state in which the semiconductor switch of the commutator of the power system protection device according to embodiment 1 is turned off. In FIG. 7, the solid arrow indicates the path of the current transmitted from the generator 10. When the semiconductor switch 511 is turned off, the commutator 51 is turned off, and no current flows through the commutator 51, but instead, current flows through the transmission line 20.

[0020] In step S6, control unit 522 determines whether or not an accident has occurred from accident detection unit 521. If an accident has occurred from accident detection unit 521, the result of step S6 is Yes, and control unit 522 proceeds to the process of step S7. If an accident has not occurred from accident detection unit 521, the result of step S6 is No, and control unit 522 proceeds to the process of step S9.

[0021] In the case of a ground fault, if no current flows through transmission line 20 for two cycles of the AC period flowing through transmission line 20 as described above, the arc that occurred in the space at the fault location will have extinguished, and the result in step S6 is expected to be No.

[0022] In step S7, control unit 522 determines whether count value N of counter 523 has reached a preset number. If count value N of counter 523 has not reached the preset number, the result of step S7 is No, and control unit 522 proceeds to step S8. If count value N of counter 523 has reached the preset number, the result of step S7 is Yes, and control unit 522 proceeds to step S10.

[0023] In step S8, control unit 522 increments count value N of counter 523 by 1. After step S8, control unit 522 advances the process to step S3.

[0024] In step S9, the control unit 522 sends a shutoff command to the mechanical switch 512 to turn off the mechanical switch 512. Since power transmission to the power transmission line 20 has resumed at the time when the semiconductor switch 511 is turned off in step S5, the mechanical switch 512 may be turned off at any timing. After step S9, the control unit 522 ends the process.

[0025] In step S10, the control unit 522 sends a break command to the system breaker 40 to turn off the system breaker 40 and break the current. After step S10, the control unit 522 ends the process.

[0026] In the above operation, when the occurrence of an accident is notified to control unit 522 in step S6, if count value N of counter 523 has not reached a preset number, count value N of counter 523 is incremented by 1 in step S8, semiconductor switch 511 is turned on in step S3, and after waiting for a time equivalent to (N+1) cycles of the AC period in step S4, semiconductor switch 511 is turned off in step S5. That is, if the result in step S6 is Yes, the determination of whether the occurrence of an accident has been notified is repeated while extending the time for which semiconductor switch 511 is turned off. Therefore, even if the arc is not extinguished for some reason while semiconductor switch 511 is turned on the first time, the arc can be extinguished during the time period while semiconductor switch 511 is turned off from the second time onwards.

[0027] In the case of a short-circuit fault, the cause of the short circuit is not eliminated even if the time for which semiconductor switch 511 is turned on is extended, and therefore, the fault will occur repeatedly if a current flows through power transmission line 20. In this case, in step S7, when count value N of counter 523 reaches a preset number, system breaker 40 is turned off and no current flows through power transmission line 20, so that work can be done to remove the cause of the short circuit at the fault location.

[0028] In this way, the power system protection device 50 according to the first embodiment prevents current from flowing to the fault location by commutating the current to the commutator 51, and when the semiconductor switch 511 of the commutator 51 is turned off, the current is no longer commutated to the commutator 51, and power supply to the transmission line 20 is resumed. Therefore, the power transmission system 100 using the power system protection device 50 according to the first embodiment can reduce the time required to restore normal power transmission after an arc is extinguished, compared to a power transmission system that uses a circuit breaker to interrupt the current in the transmission line.

[0029] JEC-2300, an AC circuit breaker standard established by the Institute of Electrical Engineers of Japan, and IEEE37.09-2018, an AC circuit breaker standard established by the Institute of Electrical and Electronics Engineers of America, stipulate that the standard operating duty of a high-speed reclosing circuit breaker is to perform a closing operation and an opening operation at a standard voltage-free time interval of 0.3 seconds. When interrupting a current flowing through a power transmission line with a circuit breaker, it is difficult to perform a closing operation and an opening operation at intervals of less than 0.3 seconds. However, the power system protection device 50 according to the first embodiment opens and closes the power transmission line 20 by turning on and off the semiconductor switch 511. This allows the power system protection device 50 to close and open the power transmission line 20 at time intervals shorter than 0.3 seconds, thereby complying with the JEC-2300 and IEEE37.09-2018 standards.

[0030] Embodiment 2 8 is a diagram illustrating a configuration of a power transmission system according to embodiment 2. The power transmission system 100 according to embodiment 2 differs from the power transmission system 100 according to embodiment 1 in that a power transmission line 20 branches downstream of a transformer 30 into a branch path 20a connected to a load 60a, a branch path 20b connected to a load 60b, and a branch path 20c connected to a load 60c, and that system circuit breakers 40a, 40b, and 40c and power system protection devices 50a, 50b, and 50c are installed in the branch paths 20a, 20b, and 20c, respectively. The power system protection devices 50a, 50b, and 50c are similar to the power system protection device 50 provided in the power transmission system 100 according to embodiment 1.

[0031] In the power transmission system 100 of embodiment 2, if an accident occurs in one of the branch paths 20a, 20b, and 20c, power transmission can be continued in the branch paths 20a, 20b, and 20c where no accident has occurred, thereby improving the stability of the power system.

[0032] Embodiment 3 FIG. 9 is a diagram showing the configuration of a power transmission system according to the third embodiment. The power transmission system 100 according to the third embodiment includes a control device 70 that controls a commutator 51 and a grid circuit breaker 40. The commutator 51 and the grid circuit breaker 40 may be connected to the control device 70 via a network or via a dedicated line. The relay 52 includes a fault detection unit 521, similar to the relay 52 of the power transmission system 100 according to the first embodiment shown in FIG. 2, but does not include a control unit 522. Instead, the control unit 71 is provided in the control device 70. The fault detection unit 521 notifies the control unit 71 of the control device 70 of the occurrence of a fault. The grid circuit breaker 40, the power system protection device 50, and the control device 70 form a power system protection system 90 that protects the power transmission system 100, which is a power system.

[0033] The operation of the power system protection system 90 according to the third embodiment is similar to the operation of the power system protection device 50 according to the first embodiment, except that the commutator 51 and the system breaker 40 are controlled by the control unit 71 of the control device 70.

[0034] As with the power system protection device 50 according to the first embodiment, the power system protection system 90 according to the third embodiment prevents current from flowing to the fault location by commutating the current to the commutator 51, and therefore, when the semiconductor switch 511 of the commutator 51 is turned off, the current is no longer commutated to the commutator 51, and power supply to the transmission line 20 is resumed. Therefore, the power transmission system 100 using the power system protection system 90 according to the third embodiment can reduce the time required to restore normal power transmission after an arc is extinguished, compared to a power transmission system that uses a circuit breaker to interrupt the current in the transmission line.

[0035] Embodiment 4 10 is a diagram illustrating the configuration of a power transmission system according to embodiment 4. In the power transmission system 100 according to embodiment 4, a power transmission line 20 branches downstream of a transformer 30 into a branch line 20a connected to a load 60a, a branch line 20b connected to a load 60b, and a branch line 20c connected to a load 60c, and system circuit breakers 40a, 40b, and 40c and power system protection devices 50a, 50b, and 50c are installed in the branch lines 20a, 20b, and 20c, respectively, and the system circuit breakers 40a, 40b, and 40c, the power system protection devices 50a, 50b, and 50c, and the control device 70 form a power system protection system. The control device 70 is connected to the relays 52a, 52b, and 52c of the power system protection devices 50a, 50b, and 50c of the branch paths 20a, 20b, and 20c, respectively, and when notified of the occurrence of a fault by any of the relays 52a, 52b, and 52c, controls the commutators 51a, 51b, and 51c of the power system protection devices 50a, 50b, and 50c that are the same as the relays 52a, 52b, and 52c that notified the occurrence of the fault. The rest is the same as the power transmission system 100 according to the third embodiment.

[0036] In the power transmission system 100 of embodiment 4, if an accident occurs in one of the branch paths 20a, 20b, and 20c, power transmission can be continued in the branch paths 20a, 20b, and 20c where no accident has occurred, thereby improving the stability of the power system.

[0037] Although the configuration described here is such that one control device 70 centrally controls the system circuit breakers 40a, 40b, and 40c and the commutators 51a, 51b, and 51c, the system circuit breaker 40a and the commutator 51a, the system circuit breaker 40b and the commutator 51b, and the system circuit breaker 40c and the commutator 51c may be controlled by separate control devices 70.

[0038] The hardware configuration of the control unit 522 of the power system protection devices 52a, 52b, and 52c of the power system protection devices 50, 50a, 50b, and 50c according to the first and second embodiments and the control unit 71 of the control device 70 according to the third and fourth embodiments will be described.

[0039] 11 is a diagram illustrating the hardware configuration of the control unit of the relay of the power system protection device according to the first and second embodiments and the control unit of the control device according to the third and fourth embodiments. The control unit 522, 71 is realized by a processor 91 that executes various processes, a memory 92 that is a main memory, and a storage device 93 that stores information.

[0040] The processor 91 may be a computing device such as an arithmetic unit, a microprocessor, a microcomputer, a central processing unit (CPU), or a digital signal processor (DSP). The memory 92 may be a non-volatile or volatile semiconductor memory such as a random access memory (RAM), a read-only memory (ROM), a flash memory, an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM). The storage device 93 stores programs for controlling the system circuit breakers 40, 40a, 40b, and 40c and the power system protection devices 50, 50a, 50b, and 50c. The processor 91 reads the programs stored in the storage device 93 into the memory 92 and executes them. The processor 91 reads the programs stored in the storage device 93 into the memory 92 and executes them, thereby realizing the functions of the control units 522 and 71.

[0041] 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. [Explanation of symbols]

[0042] 10 generator, 20 transmission line, 20a, 20b, 20c branch, 30 transformer, 40, 40a, 40b, 40c system circuit breaker, 50, 50a, 50b, 50c power system protection device, 51, 51a, 51b, 51c commutator, 52, 52a, 52b, 52c relay, 60, 60a, 60b, 60c load, 70 control device, 71, 522 control unit, 80 ground, 90 power system protection system, 91 processor, 92 memory, 93 storage device, 100 power transmission system, 511 semiconductor switch, 512 mechanical switch, 521 fault detection unit, 523 counter.

Claims

1. a system breaker that is installed on a transmission line connecting a generator and a load to which power is supplied from the generator, and that cuts off a current flowing through the transmission line when an abnormality occurs in the transmission line; a commutator connected to a portion of the transmission line between the system breaker and the load and to ground, the commutator insulating the transmission line from the ground in an off state and connecting the transmission line to the ground in an on state; a control unit that controls on / off of the commutator and the system breaker, When detecting a ground fault or short circuit occurring in the transmission line, the system breaker turns on the commutator to commutate the current flowing through the transmission line to ground before the system breaker interrupts the current flowing through the transmission line, The control unit determines whether the fault has been resolved based on the result of a fault resolution confirmation operation that turns on the commutator if the fault is detected when the commutator is turned off after a preset time has elapsed since the commutator was turned on.

2. 2. The power system protection system according to claim 1, wherein the control unit turns off the system breaker if the fault is not resolved even after performing the fault resolution confirmation operation a preset number of times.

3. 2. The power system protection system according to claim 1, wherein the control unit extends the time for which the commutator is turned on in the fault clearance confirmation operation each time the fault clearance confirmation operation is performed.

4. the commutator includes a mechanical switch and a semiconductor switch connected in series to the mechanical switch, and is installed such that the mechanical switch is on the power transmission line side and the semiconductor switch is on the ground side; The control unit When turning on the commutator, the mechanical switch is turned on and then the semiconductor switch is turned off; 2. The power system protection system according to claim 1, wherein when the commutator is turned off, the semiconductor switch is turned off and then the mechanical switch is turned off.

5. 5. The power system protection system according to claim 4, wherein the semiconductor switch comprises a plurality of semiconductor elements connected in parallel or in series with each other.

6. the power transmission line includes a plurality of branches; 6. The power system protection system according to claim 1, wherein the system breaker and the commutator are installed in each of the plurality of branch paths.

7. A system circuit breaker that is installed on a transmission line connecting a generator and a load to which power is supplied from the generator, and that cuts off the current flowing through the transmission line when an abnormality occurs in the transmission line; a commutator connected to a portion of the transmission line between the system breaker and the load and to ground, the commutator insulating the transmission line from the ground in an off state and connecting the transmission line to the ground in an on state; a control unit that controls on / off of the commutator and the system breaker, When detecting a ground fault or short circuit occurring in the transmission line, the system breaker turns on the commutator to commutate the current flowing through the transmission line to ground before the system breaker interrupts the current flowing through the transmission line, the commutator includes a mechanical switch and a semiconductor switch connected in series to the mechanical switch, and is installed such that the mechanical switch is on the power transmission line side and the semiconductor switch is on the ground side; The control unit When turning on the commutator, the mechanical switch is turned on and then the semiconductor switch is turned off; The power system protection system is characterized in that, when turning off the commutator, the semiconductor switch is turned off and then the mechanical switch is turned off.

8. A power system protection device that is installed in a portion of a power transmission line connecting a generator and a load to which power is supplied from the generator, between a system breaker and the load, a commutator connected to a portion of the transmission line between the system breaker and the load and to ground, the commutator insulating the transmission line from the ground in an off state and connecting the transmission line to the ground in an on state; a control unit that controls on / off of the commutator, When a fault due to a ground fault or a short circuit occurring in the transmission line is detected, the commutator is turned on to commutate the current flowing in the transmission line to the ground; The control unit determines whether the fault has been resolved based on the result of a fault resolution confirmation operation that turns on the commutator if the fault is detected when the commutator is turned off after a preset time has elapsed since the commutator was turned on.

9. 9. The power system protection device according to claim 8, wherein the control unit extends the time for which the commutator is turned on in the fault clearance confirmation operation each time the fault clearance confirmation operation is performed.

10. the commutator includes a mechanical switch and a semiconductor switch connected in series to the mechanical switch, and is installed such that the mechanical switch is on the power transmission line side and the semiconductor switch is on the ground side; The control unit When turning on the commutator, the mechanical switch is turned on and then the semiconductor switch is turned off; 10. The power system protection device according to claim 8, wherein when the commutator is turned off, the semiconductor switch is turned off and then the mechanical switch is turned off.

11. 11. The power system protection device according to claim 10, wherein the semiconductor switch comprises a plurality of semiconductor elements connected in parallel or in series with each other.

12. A power system protection device installed in a portion of a power transmission line connecting a generator and a load to which power is supplied from the generator, between a system breaker and the load, comprising: a commutator connected to a portion of the transmission line between the system breaker and the load and to ground, the commutator insulating the transmission line from the ground in an off state and connecting the transmission line to the ground in an on state; a control unit that controls on / off of the commutator, When a fault due to a ground fault or a short circuit occurring in the transmission line is detected, the commutator is turned on to commutate the current flowing in the transmission line to the ground; the commutator includes a mechanical switch and a semiconductor switch connected in series to the mechanical switch, and is installed such that the mechanical switch is on the power transmission line side and the semiconductor switch is on the ground side; The control unit When turning on the commutator, the mechanical switch is turned on and then the semiconductor switch is turned off; The power system protection device is characterized in that, when turning off the commutator, the semiconductor switch is turned off and then the mechanical switch is turned off.

13. A power system protection method using a power system protection system including: a system breaker installed on a power transmission line connecting a generator and a load to which power is supplied from the generator; and a commutator connected to a portion of the power transmission line between the system breaker and the load and to ground, the commutator insulating the power transmission line from the ground in an off state and conducting the power transmission line from the ground in an on state, determining whether a fault due to a ground fault or a short circuit has occurred in the power transmission line; when it is determined that the fault has occurred, turning on the commutator to commutate the current flowing through the power transmission line to ground; and if the fault is detected when the commutator is turned off after a preset time has elapsed since the commutator was turned on, determining whether the fault has been resolved based on the result of a fault resolution confirmation operation that turns on the commutator.

14. 14. The power system protection method according to claim 13, further comprising turning off the system breaker if the fault is not resolved even after the fault resolution confirmation operation is performed a preset number of times.

15. 14. The power system protection method according to claim 13, wherein the time period for which the commutator is turned on in the fault clearance confirmation operation is extended each time the fault clearance confirmation operation is performed.

16. the commutator includes a mechanical switch and a semiconductor switch connected in series to the mechanical switch, and is installed such that the mechanical switch is on the power transmission line side and the semiconductor switch is on the ground side; When turning on the commutator, the mechanical switch is turned on and then the semiconductor switch is turned off; 16. The power system protection method according to claim 13, wherein when the commutator is turned off, the semiconductor switch is turned off and then the mechanical switch is turned off.

17. A method for protecting a power system using a power system protection system including a system circuit breaker installed on a transmission line connecting a generator and a load to which power is supplied from the generator, and a commutator connected to a portion of the transmission line between the system circuit breaker and the load and to ground, the commutator insulating the transmission line from the ground in an off state and conducting the transmission line from the ground in an on state, determining whether a fault due to a ground fault or a short circuit has occurred in the power transmission line; and when it is determined that the fault has occurred, turning on the commutator to commutate the current flowing through the power transmission line to ground, the commutator includes a mechanical switch and a semiconductor switch connected in series to the mechanical switch, and is installed such that the mechanical switch is on the power transmission line side and the semiconductor switch is on the ground side; When turning on the commutator, the mechanical switch is turned on and then the semiconductor switch is turned off; A power system protection method, characterized in that, when turning off the commutator, the semiconductor switch is turned off and then the mechanical switch is turned off.

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