Protection relay system, disassembly determination device, disassembly determination method, and program

Abstract

To provide a protection relay system that rapidly disassembles dispersion power supply from a power system to which the dispersion power supply is connected when short circuit fault occurs in the power system.SOLUTION: A protection relay system 1 controls disassembly of a dispersion power supply 6 in a power system 2 to which dispersion power supplies 5, 6 are connected, the system comprising: a first undervoltage relay device 11 that operates when a voltage drop width of the system voltage of the power system 2 is a first setting value or more; a second undervoltage relay device 12 that operates when the voltage drop width of the system voltage is a second setting value or more, the second setting value being set to be a value lower than the first setting value; and a disassembly determination device 105 that determines whether to disassemble the dispersion power supply 6 on the basis of the operation state of the first undervoltage relay device 11 and second undervoltage relay device 12.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a protective relay system for an electric power system. [Background technology]

[0002] When an accident occurs in a power grid, it is essential to quickly determine that it is an accident, minimize its spread, and work toward early restoration. Generally, power systems are equipped with protective relay devices, and when a system fault is determined to have occurred, a circuit breaker associated with the fault point is activated to quickly isolate the fault point from the power system to ensure safety (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-258145 A Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, as a measure against global warming, many distributed power sources that utilize renewable energy such as solar, wind, and hydroelectric power have been connected to power grids. Of these, distributed power sources such as solar and wind power are easily affected by weather conditions such as sunlight and wind, and are therefore prone to fluctuations in power output.

[0005] These distributed power sources are often connected to power grids of 110 kV or less because of the ease of connection to the power grid. For this reason, the power output of the distributed power sources can be relatively large compared to the transmission capacity of the power grid, and the impact of power output fluctuations of these distributed power sources on the power grid can be relatively large. In this way, in the case of a short circuit or other accident on a transmission line in a power system to which distributed power sources are connected, the distributed power sources may affect the voltage fluctuation and stable operation of the power system at the time of the accident. For this reason, in addition to isolating the accident point, it is necessary to quickly isolate the distributed power sources from the power system as well.

[0006] Conventionally, a distributed power source is disconnected when, for example, an AND condition is satisfied between a main protection relay that determines an accident based on the system current and an undervoltage relay that determines an accident based on the voltage drop of the system voltage. However, since the voltage drop of the system voltage when a short circuit accident occurs in a power system to which a distributed power source is connected is smaller than when the distributed power source is not connected, the conventional accident detection method cannot determine an accident using the undervoltage relay, and there is a risk that the distributed power source cannot be disconnected from the power system.

[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a protective relay system that can quickly disconnect a distributed power source from a power system in the event of a short-circuit accident in the power system to which the distributed power source is connected. [Means for solving the problem]

[0008] One aspect of the present invention is a protective relay system that controls the disconnection of a distributed power source in a power system to which the distributed power source is connected, and includes a first relay means that detects an accident when a voltage drop in the system voltage of the power system is equal to or greater than a first set value, a second relay means that detects an accident when the voltage drop in the system voltage is equal to or greater than a second set value that is set to a value smaller than the first set value, and a disconnection determination means that determines whether to disconnect the distributed power source based on the accident detection status of the first relay means and the second relay means. Effect of the Invention

[0009] In the event of a short-circuit accident in the power system to which the distributed power source is connected, the distributed power source can be quickly disconnected from the power system. [Brief description of the drawings]

[0010] [Figure 1] 1 is an overall configuration diagram showing an example of the configuration of a power system including a protective relay according to an embodiment of the present invention; [Diagram 2] FIG. 1 is a diagram for explaining the need to disconnect a distributed power source when a short-circuit fault occurs in a power grid. [Diagram 3] FIG. 2 is a functional configuration diagram showing an example of functions provided in a parallel-off determination device according to an embodiment of the present invention. [Figure 4] FIG. 2 is a timing chart showing signals output from each component of the protective relay system according to one embodiment of the present invention. [Diagram 5] 2 is a diagram showing an example of an operating state of a circuit breaker when a fault occurs in the power system shown in FIG. 1. [Figure 6] 1 is a diagram for explaining a voltage drop in a system voltage when a fault occurs in a case where a plurality of distributed power sources are connected to a power system; [Figure 7] FIG. 1 is a diagram showing a comparison of changes in system voltage in the first and second sections at the moment a short circuit accident occurs when a distributed power source is not connected to the power system and when it is connected to the power system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A protective relay system according to an embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is an overall configuration diagram showing an example of the configuration of a power system 2 including a protective relay system 1 according to this embodiment. Fig. 1 shows, as an example, a power system 2 with two-circuit transmission having a first line 3 and a second line 4.

[0012] The power system 2 is, for example, a power system of 110 kV or less. In FIG. 1, the symbols Ass, Bss, and Dss all indicate substations. A plurality of distributed power sources 5 and 6 are connected to the power system 2. Here, the distributed power source 5 is equipped with a system for detecting and independently disconnecting the power system when an accident or the like occurs in the power system and the power system goes into an isolated operation state. The distributed power source 6 is also configured to be disconnected from the power system based on a disconnection signal from a protective relay system 1, which will be described later. A distributed power source 5 is connected to a power transmission line L1 that connects Line 1 3 and substation Dss, and a distributed power source 6 is connected to a power transmission line L2 that connects Line 2 4 and substation Dss. Note that, although Fig. 1 illustrates an example in which two distributed power sources 5, 6 are connected to the power system 2, the number of connected distributed power sources is not limited to this and may be one, or three or more.

[0013] A plurality of circuit breakers 8a, 8b are installed on line 1 3 of power system 2 to separate the accident point from power system 2 when an accident occurs, and similarly, circuit breakers 8c, 8d are installed on line 2 4. Furthermore, circuit breaker 8e is installed on transmission line L1 to separate line 1 3 from substation Dss, and circuit breaker 8f is installed on transmission line L2 to separate line 2 4 from substation Dss. Furthermore, circuit breaker 9a is installed to separate distributed power source 5 from transmission line L1, and circuit breaker 9b is installed to separate distributed power source 6 from transmission line L2.

[0014] The protective relay system 1 includes a fault detection device 101 and a parallel-off determination device (parallel-off determination means) 105. The protective relay system 1 may further include main protection relays (third relay means) 102, 103, and a short-circuit distance relay (fourth relay means) (not shown). The parallel-off determination device 105 is configured to be able to communicate with the accident detection device 101, the main protection relays 102, 103, and the short-circuit distance relay, and by obtaining information from these devices, determines whether or not the distributed power source 6 needs to be parallel-off.

[0015] The fault detection device 101 detects the system voltages (bus voltages) of Line 1 3 and Line 2 4, and detects the occurrence of a short circuit fault on Line 1 3 and Line 2 4 based on the detected system voltages. The fault detection device 101 includes, for example, a first undervoltage relay (first relay means) 11 and a second undervoltage relay (second relay means) 12.

[0016] The first undervoltage relay 11 detects an accident when the voltage drop of the system voltage, which is the bus voltage of the power system 2, is equal to or greater than a first set value. Specifically, the first undervoltage relay 11 outputs a first operation detection signal S1 indicating the occurrence of an accident to the parallel-off determination device 105 when the voltage drop of the system voltage is equal to or greater than the first set value. Here, the first set value of the first undervoltage relay 11 is set to a value within a range of more than 5% and not more than 15% of the nominal voltage of the power system 2, for example.

[0017] The second undervoltage relay 12 detects an accident when the voltage drop of the grid voltage is equal to or greater than a second set value that is set to a value smaller than the first set value. Specifically, the second undervoltage relay 12 outputs a second operation detection signal S2 indicating the occurrence of an accident to the parallel-off determination device 105 when the voltage drop of the grid voltage is equal to or greater than the second set value. The second set value of the second undervoltage relay 12 is set to a value within a range of 3% to 5% of the nominal voltage of the power grid, for example.

[0018] Here, the configuration of the accident detection device 101 is not limited to the above configuration. For example, it may be configured by one undervoltage relay that detects an accident based on a plurality of different set values ​​(for example, a first set value and a second set value). Furthermore, the accident detection device 101 may be configured as one or more digital relays that combine an undervoltage setting function with a plurality of relay setting functions.

[0019] The main protection relays 102, 103 are, for example, AC overcurrent relays that detect a fault when the system current (transmission current) of the power system 2 is equal to or greater than a predetermined set value. For example, the main protection relay 102 detects the system current flowing in the No. 1 line 3, and when the detected system current is equal to or greater than a predetermined set value, determines that an accident has occurred and outputs a shutoff command to the circuit breakers 8a and 8b. This causes the circuit breakers 8a and 8b to open, and the accident point is separated from the power system 2. Furthermore, when the main protection relay 102 determines that an accident has occurred, it outputs a third operation detection signal S3 indicating the occurrence of an accident to the parallel-off determination device 105.

[0020] The main protection relay 103 detects, for example, the system current flowing in the No. 2 line 4, and when the detected system current is equal to or greater than a predetermined set value, determines that an accident has occurred and outputs a tripping command to the circuit breakers 8c and 8d. This causes the circuit breakers 8c and 8d to open, and the accident point is separated from the power system 2. Furthermore, when the main protection relay 103 determines that an accident has occurred, it outputs a third operation detection signal S3 indicating the occurrence of an accident to the parallel-off determination device 105.

[0021] In the present embodiment, the main protection relays 102, 103 detect the occurrence of an accident based on the system current, but the present invention is not limited to this. For example, the main protection relays 102, 103 may determine the occurrence of an accident based on the system voltage (bus voltage), or may determine the occurrence of an accident based on the system voltage and the system current. Also, a known technique may be appropriately adopted as a method of determining the occurrence of an accident. For example, the occurrence of an accident may be determined when a current (difference current) obtained by adding a current flowing through the first line 3 and a current flowing through the second line 4 in opposite phases is equal to or greater than a predetermined value. Further, in the present embodiment, the case where two main protection relays 102, 103 are provided has been described as an example, but the number of installed main protection relays is merely an example and is not limited to this.

[0022] In addition, a short circuit distance relay (not shown) calculates impedance based on the system voltage and system current, and detects an accident when the calculated impedance is within a preset value range. Specifically, the short circuit distance relay outputs a fourth operation detection signal S4 indicating the occurrence of an accident when the impedance is within the preset value range. Since the impedance has a correlation with the distance to the accident point, it becomes possible to identify the section where the accident occurred. Note that short circuit distance relays are generally known as devices for detecting accidents in power systems, and therefore details will be omitted. The protective relay system 1 may be equipped with a short circuit distance relay that can be set to identify multiple sections.

[0023] The parallel-off determination device 105 determines whether or not to parallel-off the distributed power source based on, for example, the fault detection state by the first undervoltage relay 11, the second undervoltage relay 12, the main protection relays 102 and 103, and the short-circuit distance relay. Specifically, the parallel-off determination device 105 determines whether or not to parallel-off the distributed power source based on the first operation detection signal S1 output from the first undervoltage relay 11, the second operation detection signal S2 output from the second undervoltage relay 12, the third operation detection signal S3 output from the main protection relays 102 and 103, and the fourth operation detection signal S4 output from the short-circuit distance relay. More specifically, the parallel-off determination device 105 parallel-offs the distributed power source connected to the power system 2 when at least one of the first operation detection signal S1 and the second operation detection signal S2 is input, and at least one of the third operation detection signal S3 and the fourth operation detection signal S4 is input. When multiple dispersed power sources are connected to the power grid 2, the parallel-off determination device 105 may parallel-off one or multiple dispersed power sources according to a preset algorithm.

[0024] Next, the necessity for disconnecting the distributed power sources when a short-circuit fault occurs in the power system 2 will be described with reference to FIG. For example, as shown in FIG. 2, consider a case where a short circuit occurs near substation Bss on line 1 3. In this case, the system current increases while the system voltage decreases. When the system current increases and reaches a current value equal to or greater than the set value of the main protection relay 102, the main protection relay 102 detects the short circuit and outputs a cutoff command to the circuit breakers 8a and 8b installed on line 1 3 and the circuit breaker 8e of the transmission line L1 connected to line 1 3. As a result, the circuit breakers 8a, 8b, and 8e are activated, and the entire line 1 3 including the accident point is isolated from the power system 2. In addition, the distributed power source 5 connected to the transmission line L1 is in isolated operation, so it detects this by itself and outputs a cutoff command to the circuit breaker 9a by itself. As a result, the distributed power source 5 is also disconnected from the power system 2.

[0025] When the entire Line 1 3 including the accident point is disconnected from the power system 2, the power system 2 is limited to Line 2 4. If it is assumed that the distributed power source 6 is kept connected to the power system 2, for example, as shown in FIG. 2, in Line 2 4, a part of the power Pcg generated by the distributed power source 6 is supplied to the substation Bss of Line 2 4, and the remaining power Pcg-Pc is supplied to the substation Ass of Line 2 4. If the output power Pcg of the distributed power source 6 is significantly larger than the load at the substation Bss, the thermal capacity of the transmission line may be exceeded in Section A of Line 2 (the section from the substation Ass to the branch point of the substation Dss). Therefore, in order to ensure the safety of the power system 2, it is necessary to disconnect the distributed power source 6 when an accident occurs in the power system 2. Therefore, in the event of an accident in the power system 2, a parallel-off determination device 105 is installed so that the distributed power sources 6 can be quickly parallel-off from the power system 2.

[0026] FIG. 3 is a functional configuration diagram showing an example of functions provided in the parallel-off determination device 105. As shown in FIG. For example, the parallel-off determination device 105 is a computer, and includes, for example, a CPU (Central Processing Unit: processor), a main memory, a secondary storage, and the like. A series of processes for realizing various functions described below is stored in the secondary storage or the like in the form of a program, and the CPU (processor) reads this program into the main storage and executes information processing and arithmetic processing to realize various functions. The program may be installed in the secondary storage in advance, provided in a state stored in a non-transient computer-readable storage medium, or distributed via a wired or wireless communication means. Examples of the non-transient computer-readable storage medium include a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, and a semiconductor memory. In this embodiment, the following functions are realized by software processing, but the present invention is not limited to this. The parallel-off determination device 105 may be configured as an analog electronic circuit, for example, and there is no particular limitation on the detailed configuration as long as the device is realized as having the following functions.

[0027] The parallel-off determination device 105 includes, for example, a first holding circuit 21 that holds the first operation detection output signal S5 (ON state) for a predetermined period when the first operation detection signal S1 is input, and a second holding circuit 22 that holds the second operation detection output signal (ON state) S6 for a predetermined period when the second operation detection signal S2 is output. The parallel-off determination device 105 also includes a first delay circuit 23 that outputs a third operation detection output signal S7 when a state in which the third operation detection signal S3 is output is maintained for a predetermined period, and a second delay circuit 24 that outputs a fourth operation detection output signal S8 when a state in which the fourth operation detection signal S4 is output is maintained for a predetermined period.

[0028] The parallel-off determination device 105 includes a determination unit 20 that determines to parallel-off the distributed power source when the first operation detection output signal S5 or the second operation detection output signal S6 is input and the third operation detection output signal S7 or the fourth operation detection output signal S8 is input. More specifically, the determination unit 20 includes an OR circuit (logical sum circuit) 25 that outputs a fifth operation detection output signal S9 when the first operation detection output signal S5 or the second operation detection output signal S6 is input, an OR circuit (logical sum circuit) 26 that outputs a sixth operation detection output signal S10 when the third operation detection output signal S7 or the fourth operation detection output signal S8 is input, and an AND circuit (logical product circuit) 27 that outputs a parallel-off determination signal S11 in a state in which the fifth operation detection output signal S9 and the sixth operation detection output signal S10 are input. In addition, a third holding circuit 28 that outputs a transfer cutoff signal S12 that holds the parallel-off determination signal S11 for a predetermined period is provided downstream of the AND circuit 27. As a result, when the parallel-off determination signal S11 is output, the transfer cutoff signal S12 is output for a certain period, so that the transfer cutoff signal S12 can be reliably transmitted to the circuit breaker 9b that disconnects the distributed power source 6 identified from the accident point, and the circuit breaker 9b can be opened.

[0029] Next, the operation of the protective relay system 1 according to this embodiment will be described with reference to Fig. 4. Fig. 4 is a timing chart showing signals output from each component included in the protective relay system 1.

[0030] For example, as shown in Figures 2 and 4, if a short circuit occurs near substation Bss on Line 1 3 at time T0 and the system current reaches a current value equal to or greater than the set value of main protection relay 102, as described above, main protection relay 102 detects the short circuit and outputs a shutoff command to circuit breakers 8a, 8b, and 8e. This disconnects the accident point from the power system 2. As a result, the distributed power source 5 enters isolated operation, so it detects this by itself and outputs a shutoff command to circuit breaker 9a by itself. This also disconnects the distributed power source 5 from the power system 2.

[0031] Furthermore, when an overcurrent is detected by the main protection relay 102, the main protection relay 102 outputs a third operation detection signal (ON signal) S3 indicating the occurrence of an accident to the parallel-off determination device 105. Furthermore, when the occurrence of the short-circuit accident causes the voltage drop in the system voltage to be equal to or greater than the second set value of the second undervoltage relay 12, the second undervoltage relay 12 detects the accident, and outputs a second operation detection signal (ON signal) S2 indicating the occurrence of the accident to the parallel-off determination device 105. The second holding circuit 22 of the parallel-off determination device 105 receives the second operation detection signal S2 and outputs a second operation detection output signal (ON signal) S6.

[0032] Although details will be described later, it is assumed here that the power drop in the system voltage does not increase to or exceed the first setting value of the first undervoltage relay 11. For this reason, the first undervoltage relay 11 does not operate, and therefore the first operation detection signal S1 indicates a state in which it is not being output, i.e., an off signal.

[0033] Next, at time T1, which is a predetermined period after the third operation detection signal S3 is output from the main protection relay 102, the first delay circuit 23 outputs a third operation detection output signal (ON signal) S7. As a result, at time T1, the AND circuit 27 outputs a parallel-off determination signal S11. As a result, the third holding circuit 28 outputs a transfer cutoff signal S12 that holds the parallel-off determination signal S11 for a predetermined period. This transfer cutoff signal S12 is transmitted to the circuit breaker 9b for disconnecting the distributed power source 6 from the power system 2. As a result, the circuit breaker 9b is activated, and the distributed power source 6 is disconnected from the power system 2 (see FIG. 5), making it possible to eliminate the overload in Section A of Line 2 4 (see FIG. 2).

[0034] Thereafter, when the short-circuit fault is resolved and the system voltage and system current return to their normal values ​​at time T2, the operation detection condition of the main protection relay 102 is no longer satisfied. As a result, the main protection relay 102 no longer outputs the third operation detection signal S3 to the parallel-off determination device 105. In other words, the third operation detection signal S3 changes from the ON state to the OFF state. Similarly, the second undervoltage relay 12 no longer satisfies the operation detection condition, and therefore the second operation detection signal S2 is no longer output to the parallel-off determination device 105. In other words, the second operation detection signal S2 changes from the ON state to the OFF state.

[0035] As a result, the parallel-off determination signal S11 output from the AND circuit 27 also becomes OFF. Here, even if the parallel-off determination signal S11 changes to the OFF state, the third holding circuit 28 holds the transfer cutoff signal S12 for a predetermined period. As a result, the transfer cutoff signal S12 continues to be output even after the accident is resolved, so that, for example, it is possible to reliably operate the circuit breaker 9b of the distributed power source 6 to maintain the open state. As a result, it is possible to continue cutting off the distributed power source 6 from the power system 2, and the stability of the power system 2 can be ensured.

[0036] Next, in a case where a distributed power source 5 is connected to the first line 3 of the power system 2, a distributed power source 6 is connected to the second line 4, and the distributed power sources 5 and 6 are connected near Dss, immediately after an accident occurs, the circuit breakers 8a, 8b, 8e, and 9a (Ass, Bss, Dss, E PS The voltage drop of the system voltage before the switch 11 is opened will be described with reference to FIG. As described above, for example, it is assumed that a short circuit occurs near substation Bss on line 1 3 of power system 2. In this case, on line 1 3, the first section is from substation Ass to branch point P1 of substation Dss, and the second section is from branch point P1 to the accident point, with the impedance of the first section being Zb1 and the impedance of the second section being Zb2. Also, on line 2 4, the first' section of the line from substation Ass to branch point P2 of substation Dss is also approximately equivalent to the first section, and the second' section of the line from branch point P2 to the accident point is also approximately equivalent to the second section because the accident point is near Bss, and they are approximately equivalent to the impedance Zb1 of the first section and the impedance Zb2 of the second section, respectively. In this case, the fault current Igf flows from the distributed power sources 5, 6 toward branch points P1, P2 at Igf / 2 on L1 and L2, respectively. For example, if the fault current flowing from Ass to the first section and the first section of each of Line 1 3 and Line 2 4 of power system 2 is If / 2, the fault current flowing to the second section of Line 1 3 and the second section of Line 2 4 of power system 2 will be (If+Igf) / 2.

[0037] As a result, the system voltage of the bus, assuming the voltage at the fault point to be 0V, will be as follows:

[0038] V=(Zb1×If / 2)+{Zb2×(If+Igf) / 2} ={(Zb1+Zb2)×If / 2}+(Zb2×Igf / 2) (1)

[0039] FIG. 7 is a diagram showing a comparison of changes in system voltage in the first section (section 1') and the second section (section 2') when an accident occurs when the distributed power sources 5, 6 are connected to the power system 2 and when they are not connected to the power system 2. In FIG. 7, the dotted line is a graph showing the voltage change of the system voltage when the distributed power sources 5, 6 are not connected to the power system 2, and the solid line is a graph showing the voltage change of the system voltage when the distributed power sources 5, 6 are connected to the power system 2. When the distributed power sources 5, 6 are connected, the voltage rises at the branch point P1 (P2), and from the rise, the voltage drops at a constant rate toward the accident point. The voltage rise amount ΔVp (=Zb2×Igf / 2) caused by the distributed power sources 5, 6 depends on the fault current Igf flowing from the distributed power sources 5, 6 to the power system 2. In other words, the voltage rise amount ΔVp takes a larger value as the power generated by the distributed power sources 5, 6 is larger. Furthermore, the amount of voltage drop ΔV of the system voltage also increases or decreases according to the amount of voltage rise ΔVp, in other words, according to the power generated by the distributed power sources 5 and 6 connected to the power system 2 .

[0040] For the above reasons, it is advisable to adopt an undervoltage relay for the second undervoltage relay 12 that can detect operation under conditions that take into consideration the power generated by all distributed power sources that can be connected to the power grid 2, and the impedance of the power grid 2. Specifically, it is preferable that the undervoltage relay is set to a value between 3% and 5% of the nominal voltage of the power grid 2.

[0041] As described above, the protective relay system 1 of this embodiment includes a first undervoltage relay 11 that detects an accident when the voltage drop width of the system voltage of the power system 2 is equal to or greater than a first set value, a second undervoltage relay 12 that detects an accident when the voltage drop width of the system voltage is equal to or greater than a second set value that is set to a value smaller than the first set value, and a disconnection determination device 105 that determines whether or not to disconnect the distributed power source 6 based on the accident detection states of the first undervoltage relay 11 and the second undervoltage relay 12. In addition, the second set value may be set based on the power generated by the distributed power sources connected to the power system 2 and the impedance of the power system 2, and specifically, may be set to a value between 3% and 5% of the nominal voltage of the power system 2.

[0042] With this configuration, if an accident occurs in the power system 2, it becomes possible to quickly disconnect the distributed power sources connected to the power system 2, regardless of whether the distributed power sources are connected to the power system 2. In addition, because it is only necessary to provide two undervoltage relays with different settings, it becomes possible to determine the disconnection of the distributed power sources with a simple configuration.

[0043] Furthermore, when the number of distributed power sources connected to the power system 2 increases or decreases, the setting values ​​of at least one of the first undervoltage relay 11 and the second undervoltage relay 12 can be updated to an appropriate value in consideration of the output of the distributed power sources, etc. In this way, the protective relay system 1 according to this embodiment can flexibly respond to an increase or decrease in the number of distributed power sources.

[0044] Furthermore, according to this embodiment, the parallel-off determination device 105 determines to parallel-off the distributed power source when at least one of the first undervoltage relay 11 and the second undervoltage relay 12 detects an accident and at least one of the main protection relays 102, 103 or the short-circuit distance relay detects an accident. In this way, since the parallel-off of the distributed power source is determined based on changes in both the system voltage and the system current, it is possible to reduce erroneous determinations and improve the determination accuracy.

[0045] According to this embodiment, the parallel-off determination device 105 includes a first holding circuit 21 that holds the first operation detection output signal S5 for a predetermined period when the first undervoltage relay 11 detects an accident, in other words, when the first operation detection signal S1 is input, and a second holding circuit 22 that holds the second operation detection output signal S6 for a predetermined period when the second undervoltage relay 12 detects an accident, in other words, when the second operation detection signal S2 is input. The parallel-off determination device 105 further includes a first delay circuit 23 that outputs a third operation detection output signal S7 when the state in which the main protection relay 102 or 103 detects an accident is maintained for a predetermined period, in other words, when the third operation detection signal S3 is input for a predetermined period, and a second delay circuit 24 that outputs a fourth operation detection output signal S8 when the state in which the short-circuit distance relay detects an accident is maintained for a predetermined period, in other words, when the fourth operation detection signal S4 is input for a predetermined period. Then, the parallel-off determination device 105 determines to parallel-off the distributed power source when the first operation detection output signal S5 or the second operation detection output signal S6 is input and the third operation detection output signal S7 or the fourth operation detection output signal S8 is input.

[0046] In this way, by providing the first holding circuit 21 and the second holding circuit 22, it is possible to detect even a momentary voltage drop, and it is possible to improve the sensitivity of the operation detection. In addition, by using the first delay circuit 23 and the second delay circuit 24, an overcurrent is detected when an overcurrent state is maintained for a certain period of time. This makes it possible to suppress erroneous determination of an accident.

[0047] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. Various modifications or improvements can be made to the above embodiments without departing from the gist of the invention, and the forms in which such modifications or improvements are made are also included in the technical scope of the present invention. In addition, the above embodiments may be combined as appropriate. [Explanation of symbols]

[0048] 1: Protective relay system 2: Power system 5, 6: Distributed power supply 8a~8f: Circuit breaker 9a~9b: Circuit breaker 11: First undervoltage relay (first relay means) 12: Second undervoltage relay (second relay means) 21: 1st holding circuit 22:Second holding circuit 23: First delay circuit 24: Second delay circuit 25, 26: OR circuit (logical sum circuit) 27: AND circuit (logical product circuit) 28:Third holding circuit 101: Accident detection devices 102, 103: Main protection relay (third relay means) 105: Disconnection determination device (disconnection determination means) Ass: Substation Bss: Substation Dss: Substation L1: Power line L2: Power line S1: First operation detection signal S2: Second operation detection signal S3: Third operation detection signal S4: 4th operation detection signal S5: First operation detection output signal S6: Second operation detection output signal S7: Third operation detection output signal S8: 4th operation detection output signal S9: 5th operation detection output signal S10: 6th operation detection output signal S11: Queue removal judgment signal S12: Transfer interrupt signal

Claims

1. A protective relay system for controlling parallel-off of a distributed power source in a power system to which the distributed power source is connected, comprising: a first relay means for detecting a fault when a voltage drop in a system voltage of the power system is equal to or greater than a first set value; a second relay means for detecting a fault when a voltage drop in the system voltage is equal to or greater than a second set value that is set to a value smaller than the first set value; a disconnection determination means for determining whether or not to disconnect the distributed power source based on a fault detection state of the first relay means and the second relay means; A protective relay system comprising:

2. 2. The protective relay system according to claim 1, wherein the second set value is set to a value equal to or greater than 3% and equal to or less than 5% of a nominal voltage of the power system.

3. 2. The protective relay system according to claim 1, wherein the first set value is set to a value greater than 5% and equal to or less than 15% of a nominal voltage of the power system.

4. 2. The protective relay system according to claim 1, which protects a power system of 110 kV or less to which distributed power sources are connected.

5. a third relay means for detecting a fault when a system current or a system voltage of the power system satisfies a predetermined operating condition; a fourth relay means for calculating an impedance based on a system voltage and a system current, and detecting a fault when the calculated impedance is within a preset value range; 2. The protective relay system according to claim 1, wherein the disconnection determination means determines to disconnect the distributed power source when an accident is detected by at least one of the first relay means and the second relay means, and an accident is detected by at least one of the third relay means and the fourth relay means.

6. a first holding circuit for holding a first operation detection output signal for a predetermined period of time when the first relay means detects an operation; a second holding circuit for holding a second operation detection output signal for a predetermined period of time when the second relay means detects an operation; a first delay circuit that outputs a third operation detection output signal when a state in which the third relay means detects an operation is maintained for a predetermined period of time; a second delay circuit that outputs a fourth operation detection output signal when a state in which the fourth relay means detects an operation is maintained for a predetermined period of time; Equipped with 6. The protective relay system according to claim 5, wherein the disconnection determination means determines to disconnect the distributed power source when the first operation detection output signal held in the first holding circuit or the second operation detection output signal held in the second holding circuit is output, and the third operation detection output signal output from the first delay circuit or the fourth operation detection output signal output from the second delay circuit is output.

Images