Power grid protection system

Abstract

The present invention is a power grid protection system (100) for protecting a power grid (50) comprising a voltage line (56) through which a current supplied from a transformer secondary-side facility flows, and a grounded neutral line (55), said power grid protection system (100) comprising a circuit breaker (11) installed in the voltage line (56), and a commutator (12) that connects the voltage line (56) and the neutral line (55) on the transformer secondary-side facility side from the breaker (11). When an abnormality occurs in the voltage line (56) due to a short-circuit accident or a ground fault accident, the accident current flowing through the voltage line (56) is commutated to the neutral line (55) via the commutator (12).

Description

Power System Protection System

[0001] The present disclosure relates to a power system protection system that protects a power system when an abnormality occurs due to a short circuit fault or a ground fault.

[0002] Conventionally, in power systems that supply power transformed by substation equipment to loads, mechanical circuit breakers have been used to protect the power system in the event of an abnormality such as a short circuit or ground fault. However, with mechanical circuit breakers, the current interruption is not completed until the arc that occurs when the current is interrupted is extinguished, which takes time to interrupt the current and increases the scope of the accident.

[0003] Patent Document 1 discloses a power system protection system that protects a power system when an abnormality occurs due to a short circuit or a ground fault. The power system protection system disclosed in Patent Document 1 includes a power switch, a bridging circuit installed on the load side of the power switch, and a contactor installed on the load side of the bridging circuit. The power system protection system disclosed in Patent Document 1 includes a magnetically driven switch that closes when an abnormality due to a short circuit or a ground fault occurs, thereby commutating the fault current to a neutral conductor. By commutating the fault current to the neutral conductor, the device disclosed in Patent Document 1 prevents the fault current from flowing to the location of the short circuit or ground fault without using a circuit breaker to interrupt the fault current, thereby preventing the scope of the fault from expanding.

[0004] Special Publication No. 8-508154

[0005] However, the power system protection system disclosed in Patent Document 1 prevents the fault current from flowing through the short-circuit location by diverting the fault current to the neutral conductor. However, since the short-circuit location does not enter a currentless state even after the diverting of the fault current, the contactor cannot be opened to isolate the short-circuit location simply by diverting the fault current. Therefore, the power system protection system disclosed in Patent Document 1 cannot isolate the short-circuit location and resume power transmission unless another device interrupts the fault current after the diverting of the fault current. For this reason, the device disclosed in Patent Document 1 has the problem of requiring a long time from the occurrence of the fault to the resumption of power transmission.

[0006] The present disclosure has been made in consideration of the above, and aims to provide a power system protection system that shortens the time from the occurrence of an abnormality due to a short circuit accident or a ground fault accident to the resumption of power transmission to a load.

[0007] In order to solve the above-mentioned problems and achieve the object, the power system protection system according to the present disclosure is a power system protection system that protects a power system having a voltage line through which current supplied from a secondary equipment of a substation flows and a grounded neutral line, and includes a circuit breaker installed on the voltage line and a commutator that connects the voltage line and the neutral line on the secondary equipment side of the substation equipment rather than the circuit breaker. When an abnormality due to a short circuit or a ground fault occurs in the voltage line, the power system protection system commutates the fault current flowing in the voltage line to the neutral line via the commutator.

[0008] The present disclosure provides an advantage of providing a power system protection system that reduces the time from the occurrence of an abnormality due to a short circuit fault or a ground fault until the resumption of power transmission to a load.

[0009] FIG. 1 is a diagram showing the configuration of a power system protection system according to embodiment 1; FIG. 2 is a functional block diagram of a control unit of the power system protection system according to embodiment 1; FIG. 3 is a schematic configuration diagram of a circuit breaker tripping mechanism of the power system protection system according to embodiment 1; FIG. 4 is a diagram showing the tripping characteristics of a circuit breaker of the power system protection system according to embodiment 1; FIG. 1 is a diagram showing a state in which the semiconductor switch of the commutator is turned off. FIG. 2 is a diagram showing a first example of the transition of the fault current when an abnormality occurs due to a short circuit fault or a ground fault in the power system protection system according to embodiment 1. FIG. 3 is a diagram showing a second example of the transition of the fault current when an abnormality occurs due to a short circuit fault or a ground fault in the power system protection system according to embodiment 1. FIG. 4 is a diagram showing the current limiting unit of the circuit breaker in the power system protection system according to a modified example of embodiment 1. FIG. 5 is a diagram showing the configuration of the power system protection system according to embodiment 2. FIG. 6 is a diagram showing the configuration of the power system protection system according to embodiment 3. FIG. 7 is a diagram showing the configuration of the control unit of the power system protection system according to embodiment 4. FIG. 8 is a diagram showing the hardware configuration of the control unit of the power system protection system according to embodiments 1 to 4.

[0010] Hereinafter, a power system protection system according to an embodiment will be described in detail with reference to the drawings.

[0011] Embodiment 1. Figure 1 is a diagram showing the configuration of a power system protection system according to embodiment 1. The power system protection system 100 according to embodiment 1 is a system that protects a power system 50 that supplies power transformed by a substation to a load 53. The power system 50, which is the target of protection by the power system protection system 100, includes a transformer 51, which is a secondary-side facility of the substation, a voltage line 56, and a neutral line 55. The transformer 51 steps down the power supplied from a primary-side facility of the substation (not shown), and supplies the power to the voltage line 56. The voltage line 56 includes a main system 52 connected to the transformer 51, a plurality of branch lines 54 branching from the main system 52 and connected to each load 53, and a grounding line 58 connecting each load 53 to ground 57. The power system protection system 100 includes a plurality of circuit breakers 11, commutators 12 installed upstream of the plurality of circuit breakers 11, a control device 13 having a control unit 80 that controls the circuit breakers 11 and the commutators 12, and relays 14 and instrument transformers 15 installed in each of the circuit breakers 11. The circuit breakers 11 include a main circuit breaker 111 installed in the main system 52 and subordinate circuit breakers 112 provided in each branch line 54. The power system 50 and the power system protection system 100 constitute a DC distribution system that supplies DC power to a load 53.

[0012] The circuit breaker 11 and the commutator 12 included in the power system protection system 100 are installed in the same switchboard.

[0013] The commutator 12 includes a plurality of semiconductor switches 121 connected in series or in parallel, and connects the main system 52 and the neutral conductor 55. Connecting a plurality of semiconductor switches 121 in parallel increases the current that can flow through the commutator 12. Connecting a plurality of semiconductor switches 121 in series increases the withstand voltage of the commutator 12. The main circuit breaker 111 and the subordinate circuit breakers 112 are mechanical circuit breakers. When a fault current greater than the rated current flows in the event of an abnormality due to a short circuit or ground fault, the relay 14 sends an abnormality detection signal to the control unit 80. The instrument transformer 15 reduces the voltage and current of the current flowing through the main system 52 or the branch line 54 and outputs it.

[0014] 2 is a functional block diagram of the control unit of the power system protection system according to embodiment 1. The control unit 80 includes an abnormality detection signal receiving unit 81 that receives an abnormality detection signal output by the relay 14 when the relay 14 detects the occurrence of an abnormality due to a short circuit fault or a ground fault, a commutation completion detecting unit 82 that detects the completion of commutation based on the magnitude of the current output by the instrument transformer 15, a semiconductor switch control unit 83 that controls the semiconductor switch 121 of the commutator 12, and a circuit breaker control unit 84 that controls the circuit breaker 11.

[0015] 3 is a schematic diagram of the circuit breaker tripping mechanism of the power system protection system according to Embodiment 1. The circuit breaker 11 includes a heating resistor 31, a bimetal 32 attached to the heating resistor 31, an electromagnet 33 having a fixed core 331 and a movable core 332, a tripping rod 34 fixed to the movable core 332, a molded case 35, and a common tripping shaft 37 rotatably supported by a support arm 36 inside the molded case 35. The tripping mechanism 40 also includes a latch 38 protruding from the common tripping shaft 37 and a roller trigger 39 engaging with the latch 38. The circuit breaker 11 tripping mechanism 40 is a thermal-electromagnetic type that performs thermal tripping using the bimetal 32 and electromagnetic tripping using the electromagnet 33.

[0016] When an overcurrent flows, Joule heat is generated in the heating resistor 31, causing the temperature of the bimetal 32 to rise, causing the bimetal 32 to bend in the direction of arrow A, causing the common tripping shaft 37 to rotate in the direction of arrow B. When the common tripping shaft 37 rotates in the direction of arrow B, the latch 38 and the roller trigger 39 are disengaged, causing the circuit breaker 11 to trip.

[0017] Furthermore, when a large current such as a short-circuit current flows as an overcurrent, current flows through the movable core 332, and the movable core 332 is attracted to the fixed core 331. At this time, the tripping rod 34 fixed to the movable core 332 comes into contact with a protrusion on the common tripping shaft 37, causing the common tripping shaft 37 to rotate in the direction of arrow B. Rotation of the common tripping shaft 37 in the direction of arrow B disengages the latch 38 from the roller trigger 39, causing the circuit breaker 11 to trip. The circuit breaker 11 used as the subordinate circuit breaker 112 is equipped with a detection unit (not shown) that detects a fault current flowing due to a short-circuit or ground fault, and the circuit breaker 11 detects the occurrence of the fault and performs an electromagnetic tripping operation. The circuit breaker 11 used as the main circuit breaker 111 is not equipped with a detection unit that detects a fault current flowing due to a short-circuit or ground fault, and performs an electromagnetic tripping operation upon receiving a trip command output from the circuit breaker control unit 84. In addition, a circuit breaker 11 equipped with a detection unit (not shown) that detects fault current flowing due to a short circuit or ground fault may be used as the main circuit breaker 111, in which case the control unit 80 may be configured to omit the circuit breaker control unit 84.

[0018] 4 is a diagram showing the tripping characteristics of the circuit breaker of the power system protection system according to embodiment 1. When the magnitude of the overcurrent is equal to or less than current I1, circuit breaker 11 performs thermal tripping using a bimetal, and when the magnitude of the overcurrent exceeds current I1, it performs electromagnetic tripping using an electromagnet. Thermal tripping is performed by the transfer of Joule heat generated in heating resistor 31 to bimetal 32, and therefore has a longer operating time than electromagnetic tripping.

[0019] FIG. 5 is a flowchart showing the flow of the electromagnetic tripping operation of the circuit breaker of the power system protection system according to the first embodiment. In step S1, a short-circuit or ground fault occurs, causing a fault current to flow. In step S2, current flows through the movable core 332, initiating electromagnetic tripping. In step S3, the tripping rod 34 fixed to the movable core 332 rotates the common tripping shaft 37, thereby performing a trip latch operation that disengages the latch 38 from the roller trigger 39. In step S4, the trip latch operation rotates the roller trigger 39, and the movable contact (not shown) begins to separate from the fixed contact (not shown). At this time, an arc is generated between the movable contact and the fixed contact. In step S5, the movable contact moves to a predetermined position, completing the separation of the movable contact and the fixed contact, and the arc is extended. In step S6, the extended arc is extinguished, completing the current interruption. In the above operation, the time from when a short circuit or ground fault occurs until the contacts start to open in step S4 is the contact opening time.

[0020] FIG. 6 is a diagram illustrating a state in which an abnormality due to a short circuit or a ground fault occurs in a branch path of the power system that is the protection target of the power system protection system according to the first embodiment. Note that FIG. 6 illustrates only a portion of the power system protection system 100, and the relay 14 and the potential transformer 15 are not shown. When an abnormality due to a short circuit or a ground fault occurs in one of the branch paths 54, current flows without passing through the load 53, and a fault current 22, which is a current greater than the rated current 21, flows in the branch path 54 where the abnormality due to the short circuit or the ground fault occurs. When the relay 14 detects the fault current 22, it notifies the control unit 80 of the occurrence of the abnormality due to the short circuit or the ground fault. Furthermore, the lower-level circuit breaker 112 installed in the branch path 54 where the abnormality due to the short circuit or the ground fault occurs detects the short circuit or the ground fault and performs an electromagnetic tripping operation.

[0021] The control unit 80, upon receiving notification of the occurrence of an abnormality due to a short circuit or a ground fault, outputs a command to the commutator 12 to turn on the semiconductor switch 121. For example, when the control unit 80 detects that the circuit breaker 11 has opened due to a short circuit or a ground fault, the control unit 80 outputs a command to the commutator 12 to turn on the semiconductor switch 121. FIG. 7 is a diagram showing a state in which the semiconductor switch of the commutator of the power system protection system according to embodiment 1 is turned on. Note that FIG. 7 illustrates only a portion of the power system protection system 100, and the relay 14, the instrument transformer 15, and the like are not shown. When commutating the fault current to the neutral conductor 55 (not shown in FIG. 7), the commutator 12 is turned on when at least the circuit breaker 11 detects the occurrence of a short circuit or a ground fault. For example, when commutating the fault current to the neutral conductor 55, the commutator 12 is turned on when at least the circuit breaker 11 has opened. Because the semiconductor switch 121 has a faster operating speed than a mechanical switch, even if the control unit 80 simultaneously outputs commands to the commutator 12 and the lower-level circuit breaker 112, the operation of turning on the semiconductor switch 121 of the commutator 12 is performed before the tripping operation of the lower-level circuit breaker 112. In other words, when the tripping operation of the lower-level circuit breaker 112 is performed, the semiconductor switch 121 of the commutator 12 is already in the on state, the fault current 22 is commutated to the neutral conductor 55, and the current flowing in the branch path 54 is smaller than the fault current 22. Therefore, when the tripping operation of the lower-level circuit breaker 112 is performed, no arc or only a weak arc is generated. This makes it possible to suppress deterioration of the lower-level circuit breaker 112 due to the tripping operation.

[0022] After the tripping of the lower-level circuit breaker 112 is completed, the control unit 80 turns off the semiconductor switch 121 of the commutator 12. FIG. 8 is a diagram showing a state in which the semiconductor switch of the commutator of the power system protection system according to embodiment 1 is turned off. Note that FIG. 8 illustrates only a portion of the power system protection system 100, and the relay 14 and the potential transformer 15 are not shown. Because the lower-level circuit breaker 112 installed in the branch path 54 in which an abnormality due to a short circuit or ground fault has occurred is in a tripped state, no current flows through the branch path 54 in which an abnormality due to a short circuit or ground fault has occurred. As a result, the rated current 21 flows only through the branch path 54 and the main system 52 in which no abnormality due to a short circuit or ground fault has occurred.

[0023] The time from when the relay 14 detects the fault current to when it outputs a command to turn on the semiconductor switch 121 of the commutator 12 is preferably less than ¼ cycle of the frequency of the current flowing through the power system 50. Figure 9 is a diagram showing a first example of the progression of the fault current when an abnormality occurs due to a short circuit or a ground fault in the power system protection system according to embodiment 1. In Figure 9 , the solid line indicates the current flowing through the circuit breaker 11 installed in the main system 52 or the branch line 54 where an abnormality occurs due to a short circuit or a ground fault, the dashed-dotted line indicates the current flowing through the semiconductor switch 121 of the commutator 12, and the dashed line indicates the current flowing through the circuit breaker when the fault current is interrupted in a power system protection system that interrupts the fault current with a mechanical circuit breaker. In the first example shown in Figure 9 , the time from when the relay 14 detects the fault current to when it outputs a command to turn on the semiconductor switch 121 of the commutator 12 is more than ¼ cycle of the frequency of the current flowing through the power system 50. When an abnormality due to a short circuit or ground fault occurs at time t11, the lower-level circuit breaker 112 detects the occurrence of the short circuit or ground fault and initiates an electromagnetic tripping operation at time t12a. At time t12b, the control unit 80 outputs a command to the commutator 12 to turn on the semiconductor switch 121. As a result, from time t12b onwards, the current flowing through the semiconductor switch 121 increases and the current flowing through the lower-level circuit breaker 112 decreases. The tripping operation of the lower-level circuit breaker 112 is completed at time t13. The instrument transformer 15, which detects that no current is flowing through the lower-level circuit breaker 112, notifies the control unit 80 that the commutation of the fault current is complete. As a result, at time t14, the control unit 80 outputs a command to the commutator 12 to turn off the semiconductor switch 121. As a result, the current flowing through the semiconductor switch 121 decreases from time t14 onwards. At time t15, when the current increases, the operation to turn off the semiconductor switch 121 is completed. Since the lower-level circuit breaker 112 has tripped, even if the semiconductor switch 121 of the commutator 12 is turned off, no current flows to the location where the abnormality due to the short circuit fault or ground fault has occurred.

[0024] 9, if the time from when the relay 14 detects the fault current to when it outputs a command to turn on the semiconductor switch 121 of the commutator 12 is equal to or longer than ¼ cycle of the frequency of the current flowing through the power system 50, the current flowing through the lower-level circuit breaker 112 will reach its maximum before the commutation of the fault current begins. Therefore, if the time from when the relay 14 detects the fault current to when it outputs a command to turn on the semiconductor switch 121 of the commutator 12 is equal to or longer than ¼ cycle of the frequency of the current flowing through the power system 50, a circuit breaker with the same breaking capacity as that of a lower-level circuit breaker in a power system protection system without a commutator must be used as the lower-level circuit breaker.

[0025] FIG. 10 illustrates a second example of the transition of a fault current when an abnormality due to a short circuit or a ground fault occurs in the power system protection system according to the first embodiment. In FIG. 10 , a solid line indicates the current flowing through the circuit breaker 11 installed in the main system 52 or the branch line 54 where an abnormality due to a short circuit or a ground fault occurs. A dashed-dotted line indicates the current flowing through the semiconductor switch 121 of the commutator 12. A dashed line indicates the current flowing through the circuit breaker when a fault current is interrupted in a power system protection system that interrupts fault currents using a mechanical circuit breaker. When an abnormality due to a short circuit or a ground fault occurs at time t1, the lower-level circuit breaker 112 detects the occurrence of the short circuit or the ground fault at time t2 and initiates a trip operation by electromagnetic tripping. The control unit 80 also outputs a command to the commutator 12 to turn on the semiconductor switch 121. As a result, after time t2, the current flowing through the semiconductor switch 121 increases and the current flowing through the lower-level circuit breaker 112 decreases. At time t3, the tripping operation of the lower-level circuit breaker 112 is completed. The instrument transformer 15, which detects that no current is flowing through the lower-level circuit breaker 112, notifies the control unit 80 that the commutation of the fault current is complete, and at time t4, the control unit 80 outputs a command to the commutator 12 to turn off the semiconductor switch 121. As a result, the current flowing through the semiconductor switch 121 decreases after time t4. At time t5, when the current increases, the operation to turn off the semiconductor switch 121 is completed. Because the lower-level circuit breaker 112 has tripped, turning off the semiconductor switch 121 of the commutator 12 does not cause current to flow to the location where the abnormality due to the short-circuit fault or ground fault has occurred. As a result, power transmission is resumed normally in the branch paths 54 other than the branch path 54 where the abnormality due to the short-circuit fault or ground fault has occurred. In the power system protection system 100 according to embodiment 1, the maximum value of the current flowing through the lower circuit breaker 112 is smaller than the maximum value of the current flowing through the lower circuit breaker in a power system protection system that does not have a commutator, and therefore a smaller circuit breaker with a lower breaking capacity can be used than in a power system protection system that does not have a commutator.

[0026] The commutators 12 can aggregate the breaking capacities of the individual circuit breakers 11, and the breaking capacity of the entire power system protection system 100 can be easily adjusted by changing the number of parallel-series connections of the commutators 12. Furthermore, since the power system protection system 100 does not require circuit breakers 11 with high breaking capacities, the number of circuit breaker 11 models can be reduced by standardizing the model of the circuit breakers 11. Standardizing the model of the circuit breakers 11 eliminates the need for model selection of the circuit breakers 11, making it possible to standardize the panel design. Furthermore, when increasing the breaking capacity of the power system protection system 100, it is not necessary to replace all of the circuit breakers 11; it is only necessary to adjust the number of parallel-series connections of only the commutators 12, so the breaking capacity of the entire power system protection system 100 can be easily increased.

[0027] In the above explanation, an example was given of an abnormality caused by a short circuit or a ground fault in the branch line 54. However, if an abnormality caused by a short circuit or a ground fault occurs in the main system 52, when the relay 14 installed in the main system 52 detects the occurrence of an abnormality caused by a short circuit or a ground fault, the control unit 80 trips the main circuit breaker 111 and turns on the semiconductor switch 121 of the commutator 12, thereby commutating the fault current and isolating the location where the short circuit occurred.

[0028] In addition, when multiple power systems 50 are provided corresponding to each phase of the three-phase AC, the control unit 80 turns on the semiconductor switches 121 of the commutators 12 of the power systems 50 corresponding to the two phases in which the short-circuit accident occurred in the case of a two-phase short circuit, and turns on the semiconductor switches 121 of the commutators 12 of the power systems 50 corresponding to the three phases in the case of a three-phase short circuit, thereby making it possible to commutate the fault current and isolate the location where the short circuit occurred only in the phase in which the short-circuit accident occurred.

[0029] Because the operating speed of the semiconductor switch 121 is faster than that of a mechanical switch, the power system protection system 100 according to the first embodiment can prevent the fault current from flowing to the abnormality location more quickly than when a mechanical circuit breaker is used, thereby preventing the extent of the fault from expanding. Furthermore, after the fault current is commutated, the location where the short-circuit fault occurred can be isolated by interrupting the rated current with the lower-level circuit breaker 112 installed in the branch path 54 where the abnormality due to the short-circuit fault or ground fault occurred. Since the main circuit breaker 111 and the lower-level circuit breaker 112 do not need to interrupt the fault current and only need to interrupt the rated current, the power system protection system 100 can be made smaller by using small circuit breakers with low interrupting capacity. Furthermore, because the main circuit breaker 111 and the subordinate circuit breaker 112 do not interrupt the fault current, it is easy to comply with the protection coordination stipulated in IEC 60947-1, Coordination of the components of the motor circuit, type 2, a standard established by the International Electrotechnical Commission, which states that "there shall be no damage except for slight welding of the electromagnetic contactor, and it shall be possible to continue using it without replacement."

[0030] Furthermore, the semiconductor switch 121 of the commutator 12 is normally in the OFF state and is turned ON only when an abnormality such as a short circuit or a ground fault occurs, so there is no need to provide any cooling equipment.

[0031] In the power system protection system 100 according to embodiment 1, after the commutation of the fault current is completed, the circuit breaker 11 installed in the main system 52 or the branch line 54 where the abnormality due to the short circuit or ground fault has occurred can cut off the current flowing to the location where the abnormality has occurred, and therefore, power transmission to the load 53 can be resumed in a short time after the occurrence of the abnormality due to the short circuit or ground fault.

[0032] In the above explanation, the commutator 12 using the semiconductor switch 121 is used as an example, but the commutator 12 can also be configured using a mechanical switch that can operate at a speed faster than 1 / 4 cycle of the frequency of the current flowing through the power system 50.

[0033] The circuit breaker 11 may also include a current limiting unit that limits a fault current that flows when a short-circuit fault or a ground fault occurs. FIG. 11 is a schematic diagram of a current limiting unit of a circuit breaker in a power system protection system according to a modification of the first embodiment. The current limiting unit 60 includes a grid 61 disposed around a fixed contact 72 provided on a fixed contactor 71, and a protrusion 62 provided on the fixed contactor 71. The grid 61 is configured by a plurality of insulating members arranged at close intervals. When a fault current flows in the event of a short-circuit fault or a ground fault, an electromagnetic repulsive force acts between the movable contactor 73 and the fixed contactor 71, causing the movable contactor 73 to rotate in the direction of arrow C, separating the movable contactor 74 provided on the movable contactor 73 from the fixed contactor 72. This generates an arc between the movable contactor 74 and the fixed contactor 72 as shown by line X in FIG. 11 . The arc generated between the movable contactor and the fixed contactor is attracted to the grid 61 as shown by line Y in FIG. 11 , forcibly reducing the arc spot and narrowing the arc column. 11, the arc spot of the fixed contact 72 is rapidly commutated to the protrusion 62, and the arc is cooled by the grid 61. Thereafter, the circuit breaker 11 body trips, completing the circuit breaker operation.

[0034] When the circuit breaker 11 is equipped with the current limiting unit 60, the control unit 80 may detect the automatic opening of the current limiting unit 60 and issue an ON command to the commutator 12. In this case, compared to the case where the opening of the circuit breaker 11 is detected, the commutator 12 can be turned ON at an earlier timing, and the effect of the current limiting unit 60 makes it possible to shorten the time required for commutation and breaking.

[0035] Embodiment 2. Fig. 12 is a diagram showing the configuration of a power system protection system according to embodiment 2. The power system protection system 100 according to embodiment 2 differs from the power system protection system 100 according to embodiment 1 in that a control unit 80 is provided in a commutator 12. Other than this, the power system protection system 100 according to embodiment 2 is the same as the power system protection system 100 according to embodiment 1, and therefore, redundant explanations will be omitted.

[0036] In the power system protection system 100 according to the second embodiment, the control unit 80 is provided in the commutator 12, and therefore the signal line connecting the control unit 80 and the semiconductor switch 121 is short, and there is little delay when a command to turn on or off the semiconductor switch 121 is transmitted from the control unit 80 to the semiconductor switch 121. This makes it possible to shorten the time required from the occurrence of an abnormality due to a short-circuit fault or a ground fault to the commutation of the fault current.

[0037] Third Embodiment Fig. 13 is a diagram showing the configuration of a power system protection system according to a third embodiment. The power system protection system 100 according to the third embodiment differs from the power system protection system 100 according to the first embodiment in that a control unit 80 is provided in a relay 14. The control unit 80 is provided in a relay 14 installed in the main system 52 or the branch line 54 where a short circuit fault or a ground fault is likely to occur among the voltage lines 56. In the third embodiment, the control unit 80 is provided in the relay 14 installed in the main system 52. The rest of the configuration is the same as the power system protection system 100 according to the first embodiment, and therefore a duplicated description will be omitted.

[0038] In the power system protection system 100 according to the third embodiment, the control unit 80 is provided in the relay 14, and therefore the signal line connecting the control unit 80 and the relay 14 is short, and there is little delay in transmitting the fault detection signal from the relay 14 to the control unit 80. As a result, the time required from the occurrence of an abnormality due to a short-circuit fault or a ground fault to the commutation of the fault current can be shortened.

[0039] Embodiment 4. Fig. 14 is a diagram showing the configuration of a control unit of a power system protection system according to embodiment 4. The power system protection system 100 according to embodiment 4 differs from the power system protection system 100 according to embodiment 1 in that the control unit 80 includes a commutation count storage unit 85. Other than this, the power system protection system 100 according to embodiment 4 is the same as the power system protection system 100 according to embodiment 1, and therefore, repeated explanations will be omitted.

[0040] The commutation count storage unit 85 stores the number of times that a command to turn on the semiconductor switch 121 has been output to the commutator 12 .

[0041] If an abnormality occurs due to a short circuit or ground fault and a fault current flows in the voltage line 56, a large current exceeding the rated current will flow, which may cause deterioration of the main system 52 and the branch line 54, deterioration of the load 53, deterioration of the circuit breaker 11, the relay 14, and the instrument transformer 15, etc.

[0042] When a fault current is interrupted using a mechanical circuit breaker, traces such as melting of a portion of the circuit breaker contacts due to an arc generated when the current is interrupted are left, making it possible to recognize after the fact that the circuit breaker has interrupted the fault current. Therefore, users of power system protection systems using mechanical circuit breakers can find traces of the fault current during maintenance of the power system protection system and replace voltage wires 56, etc., even if it is not immediately after the occurrence of an abnormality due to a short circuit or a ground fault. In contrast, in the power system protection system 100 according to embodiment 3, the commutator 12 commutates the fault current to the neutral conductor 55, so the fault current is not interrupted by the circuit breaker 11 and no trace of the fault current remains on the circuit breaker 11. However, in the power system protection system 100 according to the third embodiment, the number of times that a command to turn on the semiconductor switch 121 has been output to the commutator 12 is stored in the commutation count storage unit 85, and therefore a user of the power system protection system 100 can recognize after the fact that an abnormality due to a short circuit fault or a ground fault has occurred in the voltage line 56 by checking the number of times stored in the commutation count storage unit 85. Therefore, a user of the power system protection system 100 according to the third embodiment can find traces of a fault current during maintenance of the power system protection system 100 and replace the voltage line 56, etc., even if it is not immediately after the occurrence of a short circuit fault or a ground fault fault.

[0043] 15 is a diagram showing the hardware configuration of a control unit of the power system protection system according to Embodiments 1 to 4. The control unit 80 is realized by a computer system including a processor 91 that executes various processes, a memory 92 that is a main memory, and a storage device 93 that stores information.

[0044] The processor 91 may be a computing means 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 a program for executing a process for controlling the commutator 12 and the circuit breaker 11.

[0045] The computer system described above realizes the functions of the control device 13 by having the processor 91 read into the memory 92 programs stored in the storage device 93 and corresponding to the processing of each component, and executes the programs. The memory 92 is also used as a temporary memory for each process executed by the processor 91. The programs executed by the processor 91 may be provided in a state stored in a storage medium, or may be provided via a network.

[0046] 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.

[0047] REFERENCE SIGNS LIST 11 circuit breaker, 12 commutator, 13 control device, 14 relay, 15 instrument transformer, 21 rated current, 22 fault current, 31 heating resistor, 32 bimetal, 33 electromagnet, 34 tripping rod, 35 molded case, 36 support arm, 37 common tripping shaft, 38 latch, 39 roller trigger, 40 tripping mechanism, 50 power system, 51 transformer, 52 main system, 53 load, 54 branch path, 55 neutral line, 56 voltage line, 57 ground, 58 earthing line, 60 current limiting unit, 61 grid, 62 protrusion, 71 fixed contact, 72 fixed contact, 73 moving contact, 74 moving contact, 80 control unit, 81 abnormality detection signal receiving unit, 82 commutation completion detection unit, 83 semiconductor switch control unit, 84 Circuit breaker control unit, 85 Commutation count storage unit, 91 Processor, 92 Memory, 93 Storage device, 100 Power system protection system, 111 Main circuit breaker, 112 Sub-circuit breaker, 121 Semiconductor switch, 331 Fixed core, 332 Moving core.

Claims

1. A power system protection system for protecting a power system having a voltage line through which current supplied from a secondary equipment of a substation flows and a grounded neutral line, comprising: a circuit breaker installed on the voltage line; and a commutator that connects the voltage line and the neutral line on the secondary equipment side of the substation rather than the circuit breaker, wherein when an abnormality due to a short circuit or ground fault occurs in the voltage line, the power system protection system commutates the fault current flowing in the voltage line to the neutral line via the commutator.

2. The power system protection system according to claim 1, characterized in that the commutator is turned on at least when the circuit breaker detects the occurrence of a short circuit fault or a ground fault when commutating the fault current to the neutral line.

3. The power system protection system according to claim 2, characterized in that the commutator is turned on when it detects that at least the circuit breaker has opened when commutating the fault current to the neutral line.

4. The power system protection system according to claim 2, wherein the commutator starts commutating the fault current to the neutral line before the circuit breaker opens.

5. A power system protection system as claimed in any one of claims 1 to 4, characterized in that the commutator commutates the fault current to the neutral line within a time period less than 1 / 4 cycle of the frequency of the current flowing through the voltage line after an abnormality due to the short circuit fault or the ground fault occurs in the voltage line.

6. A power system protection system as described in any one of claims 1 to 5, characterized in that the voltage line has a main system connected to the secondary equipment of the substation equipment and a plurality of branch paths branching off from the main system, the circuit breaker has a main circuit breaker installed in the main system and subordinate circuit breakers installed in each of the branch paths, and the commutator connects the main system and the neutral line on the secondary equipment side of the substation equipment rather than the main circuit breaker.

7. The power system protection system according to any one of claims 1 to 6, characterized in that the commutator comprises a plurality of semiconductor switches connected in parallel or in series.

8. The power system protection system according to any one of claims 1 to 7, further comprising a commutation completion detection unit that detects completion of commutation of the fault current to the neutral line.

9. The power system protection system according to any one of claims 1 to 8, further comprising a control unit for controlling the commutator and the circuit breaker.

10. The power system protection system according to claim 9, further comprising a relay for monitoring a current flowing through the voltage line, wherein the control unit is provided in the relay.

11. The power system protection system according to any one of claims 1 to 10, further comprising a commutation count memory unit that stores the number of times the commutator has commutated the fault current to the neutral line.

12. The power system protection system according to any one of claims 1 to 11, characterized in that the circuit breaker and the commutator are installed in the same substation.

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