Multi-terminal transmission system protection system

Abstract

To provide a protection system that does not stop power transmission line protection even when a protection section is changed. [Solution] In a protection system for a multi-terminal power transmission system, a switching state acquisition unit (40) acquires information on the switching state of each of one or more switches (SX) provided in the multi-terminal power transmission system. A fault section determination unit (60) determines whether an internal fault has occurred in any section of the multi-terminal power transmission system using a current differential method, based on detected values ​​of terminal currents at each terminal of the multi-terminal power transmission system and the switching state of each of the one or more switches. The fault section determination unit (60) determines that an internal fault has occurred in a partial section defined by the switching states of one or more switches (SX) when the absolute value of the sum of the terminal currents at each terminal of the partial section exceeds a first threshold value and the absolute value of the sum of the terminal currents at each terminal constituting the entire section exceeds a second threshold value.

Description

[Technical Field]

[0001] The present disclosure relates to a protection system for a multi-terminal power transmission system. [Background technology]

[0002] Japanese Patent Publication No. 2021-136707 (Patent Document 1) discloses a protection system for protecting a multi-terminal power transmission system in which the protection section changes by changing the open / closed state of multiple switches, using a current differential method.

[0003] Specifically, this protection system includes a plurality of protective relays connected to each other via communication. Each protective relay includes a protection zone identification unit that identifies a protection zone based on information on the changed switch states when the switch states of the plurality of switches are changed, and a protection relay calculation unit that performs protection relay calculation using a current differential method based on current values ​​sampled at each terminal of the identified protection zone (see the abstract of Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-136707 Summary of the Invention [Problem to be solved by the invention]

[0005] In the case of the protection system described in the above-mentioned JP 2021-136707 A (Patent Document 1), it is considered necessary to stop the protection of the power transmission line by the protective relay during the opening and closing operation of the switch, as well as before and after the opening and closing operation of the switch. The reason for this is as follows.

[0006] Normally, the energization state of a switch is detected based on the opening and closing of the auxiliary contacts, but the opening and closing timing of the main contacts and the auxiliary contacts do not necessarily coincide. If protective relay calculations using the current differential method are performed based on erroneous opening and closing state information, the protective relay will malfunction. Therefore, when changing the protected section in the protection system of Patent Document 1, it is considered necessary to stop transmission line protection by the protective relay.

[0007] The present disclosure has been made in consideration of the above-mentioned problems, and an object of the present disclosure is to provide a protection system for protecting a multi-terminal power transmission system using a current differential method, in which the protection zone changes depending on the open / closed states of multiple switches, and which does not stop transmission line protection even when the protection zone changes. [Means for solving the problem]

[0008] In one embodiment, a protection system for a multi-terminal power transmission system is provided. The multi-terminal power transmission system includes four or more terminals and one or more switches. By opening at least one of the one or more switches, the entire section of the multi-terminal power transmission system is divided into a plurality of sub-sections, each of which includes two or more terminals. The protection system includes a current transformer, a switching status acquisition unit, and a fault section determination unit. The current transformer is provided at each terminal of the multi-terminal power transmission system and detects the terminal current of the terminal. The switching status acquisition unit acquires information on the switching status of each of the one or more switches. The fault section determination unit determines whether an internal fault has occurred in the entire section or any of the sub-sections of the multi-terminal power transmission system using a current differential method, based on the detected value of the terminal current at each terminal of the multi-terminal power transmission system and the switching status of each of the one or more switches. The fault section determination unit determines that an internal fault has occurred in a partial section when the absolute value of the sum of the terminal currents of each terminal in the partial section determined by the open / closed state of the one or more switches exceeds a first threshold value and the absolute value of the sum of the terminal currents of each terminal in the entire section exceeds a second threshold value. [Effects of the Invention]

[0009] According to the above embodiment, if the absolute value of the sum of the terminal currents of each terminal in a partial section determined by the open / closed state of the one or more switches exceeds a first threshold value and the absolute value of the sum of the terminal currents of each terminal in the entire section exceeds a second threshold value, it is determined that an internal fault has occurred in the partial section, so that a protection system can be provided that does not stop power line protection even when the protection section is changed. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating a configuration example of a protection system according to a first embodiment and a multi-terminal power transmission system protected thereby. [Figure 2] FIG. 2 is a block diagram showing an example of a hardware configuration of a protection relay. [Figure 3] 2 is a block diagram showing an example of a hardware configuration of a switch controller shown in FIG. 1. FIG. [Figure 4] FIG. 2 is a block diagram for explaining the protective operation of each protective relay in FIG. 1. [Figure 5] FIG. 5 is a block diagram showing a modified example of FIG. 4. [Figure 6] FIG. 10 is a diagram illustrating a configuration example of a protection system according to a second embodiment and a multi-terminal power transmission system protected thereby. [Figure 7] FIG. 7 is a diagram illustrating an example of a network configuration of the protection system of FIG. 6. [Figure 8] FIG. 2 is a block diagram illustrating an example of a hardware configuration of a common control device. [Figure 9] FIG. 8 is a block diagram for explaining an example of the operation of the common control device of FIGS. 6 and 7. [Figure 10] FIG. 10 is a block diagram showing the operation of each merging unit when a section protection command is received from the common control device. [Figure 11] FIG. 10 is a block diagram showing a modified example of FIG. 9. [Figure 12] 10 is a block diagram showing the operation of each merging unit when a terminal protection command is received from the common control device. FIG. [Figure 13]FIG. 10 is a diagram illustrating a configuration example of a protection system according to a third embodiment and a multi-terminal power transmission system protected thereby. [Figure 14] FIG. 14 is a diagram illustrating an example of a network configuration of the protection system of FIG. [Figure 15] FIG. 15 is a block diagram for explaining an example of the operation of the common control device of FIGS. 13 and 14. [Figure 16] FIG. 15 is a block diagram for explaining an example of the operation of the common control device of FIGS. 13 and 14. [Figure 17] FIG. 16 is a diagram showing a modification of the block diagram of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] Each embodiment will be described in detail below with reference to the drawings. The same or corresponding parts will be denoted by the same reference characters and description thereof will not be repeated.

[0012] Embodiment 1 [Example of a protection system configuration for a multi-terminal power transmission system] Fig. 1 is a diagram showing an example of the configuration of a protection system 1 according to the first embodiment and a multi-terminal power transmission system 7 protected thereby. For the purpose of explanation, the multi-terminal power transmission system 7 in Fig. 1 is a simplified version of an actual multi-terminal power transmission system, and has four terminals: A terminal, B terminal, C terminal, and D terminal.

[0013] 1, the multi-terminal power transmission system 7 includes a transmission line L1 that connects a bus B1 of the A-end substation and a bus B4 of the D-end substation, and transmission lines L2 and L3 that branch off from branch points J1 and J2 on the path of the transmission line L1. The transmission line L2 connects branch point J1 and a bus B2 of the B-end substation, and the transmission line L3 connects branch point J2 and a bus B3 of the C-end substation.

[0014] Furthermore, the multi-terminal power transmission system 7 includes a switch SX provided between branch points J1 and J2 on the path of the power transmission line L1, and a switch controller CNTL_X that controls the opening and closing of the switch SX in accordance with commands from a higher-level computer in a control center (not shown). When the switch SX is open, the entire section of the multi-terminal power transmission system 7 is divided into a first section including terminals A and B, and a second section including terminals C and D.

[0015] Protection system 1 includes a circuit breaker CB1 and a current transformer CT1 provided on transmission line L1 near bus B1 of the A-end substation, a circuit breaker CB2 and a current transformer CT2 provided on transmission line L2 near bus B2 of the B-end substation, a circuit breaker CB3 and a current transformer CT3 provided on transmission line L3 near bus B3 of the C-end substation, and a circuit breaker CB4 and a current transformer CT4 provided on transmission line L1 near bus B4 of the D-end substation. In the following description, circuit breakers CB1 to CB4 will be referred to collectively or any one of them will be referred to as circuit breaker CB, and current transformers CT1 to CT4 will be referred to collectively or any one of them will be referred to as current transformer CT.

[0016] 1 shows one transmission line for ease of illustration, but in the case of a three-phase transmission line, there are actually three transmission lines. Also, although each of the circuit breaker CB, current transformer CT, and switch SX is actually provided for each phase, in this disclosure the three phases are collectively shown as one circuit breaker CB, current transformer CT, and switch SX.

[0017] Furthermore, the protection system 1 includes a protective relay RY_A provided in the A-end substation, a protective relay RY_B provided in the B-end substation, a protective relay RY_C provided in the C-end substation, and a protective relay RY_D provided in the D-end substation. In the following description, the protective relays RY_A to RY_D will be referred to collectively or any one of them will be referred to as a protective relay RY.

[0018] Each protective relay RY is connected to the circuit breaker CB and current transformer CT at its own end. Furthermore, the protective relays RY_A to RY_D are connected to one another via a communication line 2. The communication line 2 may be wired or wireless. Furthermore, each protective relay RY is connected to a switch controller CNTL_X via the communication line 2 and acquires the open / closed state of the switch SX.

[0019] Each protection relay RY detects the current flowing in its own transmission line via its own current transformer CT. In this case, the current sampling timing of each protection relay RY is synchronized with each other.

[0020] Various methods can be used for sampling synchronization. For example, the Precision Time Protocol (PTP) of the IEEE 1588 standard using Ethernet (registered trademark) may be used. Another method is to synchronize the clocks provided in each protection relay RY using a GPS (Global Positioning System) signal. Alternatively, timing flags may be transmitted from the protection relay RY of the own terminal and the protection relay RY of the other terminal to each other via a dedicated line, and the sampling timing may be synchronized based on the time difference between the transmission time and reception time of the timing flag at both the own terminal and the other terminal.

[0021] Each protective relay RY determines whether a fault has occurred in the protection section including its own end using a current differential method based on the current value detected at its own end, the current detection value of the other terminal received via communication line 2, and the switch SX open / close information. If each protective relay RY determines that a fault has occurred in the corresponding protection section including its own end, it outputs a trip signal to trip the circuit breaker CB of the corresponding protection section. Note that the protection section is the entire section when the switch SX is in the closed state, and a partial section, i.e., the first and second sections bounded by the switch SX, when the switch SX is in the open state. Details of the fault determination method will be described later with reference to Figure 4 or Figure 5.

[0022] [Example of hardware configuration for protective relays] An example in which the protection relay RY in Fig. 1 is configured based on a microcomputer will be described below. Unlike the example described below, at least a part of the protection relay RY may be configured using an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), or a combination of these. Note that the hardware configuration of the merging unit MU described in embodiments 2 and 3 is also similar to the hardware configuration of the protection relay RY shown in Fig. 2.

[0023] Fig. 2 is a block diagram showing an example of a hardware configuration of a protection relay RY. Referring to Fig. 2, the protection relay RY includes one or more input converters 10, one or more analog filters (AF) 11, one or more sample-and-hold circuits (S / H) 12, a multiplexer (MUX) 13, an A / D (Analog to Digital) converter 14, an arithmetic processing unit 20, a communication circuit 26, one or more digital output circuits (D / O: Digital Output) 27, and one or more digital input circuits (D / I: Digital Input) 28. The protection relay RY further includes a bus 24 connecting the A / D converter 14, the arithmetic processing unit 20, the communication circuit 26, the digital output circuit 27, and the digital input circuit 28.

[0024] The protective relay RY has a plurality of channels for signal input, and receives the current signals of each phase output from a current transformer provided at its own end via some of the plurality of channels. Furthermore, the protective relay RY may be configured to receive the voltage signals of each phase output from a voltage transformer (not shown) provided at its own end and the current signals of each phase output from another current transformer (not shown) provided at its own end.

[0025] The input converter 10 has an auxiliary transformer for each input channel, which converts the output signal from the current or voltage transformer into a signal with a voltage level suitable for subsequent signal processing.

[0026] An analog filter 11 is provided for each input converter 10. The analog filter 11 is a low-pass filter or a band-pass filter used to remove aliasing errors during A / D conversion.

[0027] A sample-and-hold circuit 12 is provided for each corresponding input converter 10 and analog filter 11. The sample-and-hold circuit 12 samples and holds, at a specified sampling frequency, a signal (i.e., a voltage signal or a current signal) that is output from the corresponding input converter 10 and that represents an electrical quantity that has passed through the corresponding analog filter 11.

[0028] The multiplexer 13 sequentially selects the signals held in the plurality of sample-and-hold circuits 12. The A / D converter 14 converts the signal selected by the multiplexer 13 into a digital value. Note that by providing a plurality of A / D converters 14, A / D conversion may be performed in parallel on detection signals of a plurality of input channels.

[0029] The arithmetic processing unit 20 includes a CPU (Central Processing Unit) 21, a RAM (Random Access Memory) 22, and a ROM (Read Only Memory) 23. These elements, the A / D converter 14, the communication circuit 26, the digital output circuit 27, and the digital input circuit 28 are interconnected via a bus 24. The arithmetic processing unit 20 may include an electrically rewritable non-volatile memory such as a flash memory.

[0030] The RAM 22 and the ROM 23 are used as main memories of the CPU 21. The CPU 21 controls the overall operation of the protection relay RY and executes protection relay calculations in accordance with programs stored in the ROM 23 and the non-volatile memory. Typically, the processing of the protection relay RY described below is executed by the calculation processing unit 20.

[0031] The communication circuit 26 communicates with the communication circuits 26 of the other protection relays RY and the communication circuit 36 ​​of the switch controller CNTL in accordance with a specified protocol. Typically, the communication circuit 26 has multiple communication ports depending on the application. For example, the communication circuit 26 includes one or more transmission ports for transmitting data and one or more reception ports for receiving data. The communication circuit 26 receives, via the reception ports, signals representing current values ​​detected by the other protection relays RY and receives switching information of the switch SX from the switch controller CNTL_X.

[0032] The digital output circuit 27 is an interface circuit for outputting a signal to an external device. For example, the digital output circuit 27 outputs a trip signal to a corresponding circuit breaker CB provided at its own end in accordance with a command from the CPU 21.

[0033] The digital input circuit 28 is an interface circuit for receiving signals from external devices. For example, the digital input circuit 28 receives switching information indicating the open / closed state of a corresponding circuit breaker CB provided at its own end.

[0034] [Example of hardware configuration for a switch controller] Fig. 3 is a block diagram showing an example of a hardware configuration of the switch controller CNTL_X of Fig. 1. Referring to Fig. 3, the switch controller CNTL_X includes an arithmetic processing unit 30, a communication circuit 36, a digital output circuit 37, and a digital input circuit 38. The arithmetic processing unit 30 includes a CPU 31, a RAM 32, and a ROM 33. The arithmetic processing unit 30 may include an electrically rewritable non-volatile memory such as a flash memory. The above components are connected to each other via a bus 34.

[0035] The RAM 32 and the ROM 33 are used as main memories for the CPU 31. The CPU 31 operates in accordance with programs stored in the ROM 33 and the nonvolatile memory, thereby controlling the overall operation of the switch controller CNTL_X.

[0036] The communication circuit 36 ​​communicates with a host computer in a control center (not shown) and with the communication circuit 26 of each protection relay RY in accordance with a specified protocol. Typically, the communication circuit 36 ​​has multiple communication ports depending on the application. For example, the communication circuit 36 ​​includes one or more transmission ports for transmitting data and one or more reception ports for receiving data. The communication circuit 36 ​​transmits a signal indicating the open / closed state of the switch SX to the communication circuit 26 of each protection relay RY via the transmission port.

[0037] The digital output circuit 37 is an interface circuit for outputting a signal to an external device. For example, the digital output circuit 37 outputs an open / close signal to a corresponding switch SX in accordance with a command from a host computer in a control center (not shown).

[0038] The digital input circuit 38 is an interface circuit for receiving signals from external devices. For example, the digital input circuit 38 receives, from the corresponding switch SX, opening and closing information indicating the opening and closing state of the switch SX.

[0039] At least a part of the configuration of the switch controller CNTL_X may be configured by an FPGA, an ASIC, or a combination of these.

[0040] [Protection system protection operation] Next, a detailed operation of the protection system 1 in Fig. 1 will be described. Fig. 4 is a block diagram for explaining the protection operation of each protection relay RY in Fig. 1. In Fig. 4, the function of the arithmetic processing unit 20 of each protection relay RY is shown as a logic circuit. The function of this logic circuit may be realized by a computer program, may be realized by an FPGA, or may be realized by a logic circuit of another configuration having equivalent functions.

[0041] Referring to Figure 4, the calculation processing unit 20 of each protection relay RY includes a switch open / close state acquisition unit 40, a protection relay calculation unit 50, a fault section determination unit 60, a section protection command generation unit 70, and an interruption command generation unit 80.

[0042] The switch open / close state acquisition unit 40 includes a first open / close state acquisition unit 41 that acquires information on the open / close state of the switch SX from the switch controller CNTL_X. The first open / close state acquisition unit 41 outputs a logical value of "1" when the switch SX is in a closed state, and outputs a logical value of "0" when the switch SX is in an open state.

[0043] The protection relay calculation unit 50 performs protection relay calculations using a current differential relay method for each protection section determined according to the open / closed state of the switch SX. Specifically, the protection relay calculation unit 50 includes a first section calculation unit 51 that performs protection relay calculations for the first section, a second section calculation unit 52 that performs protection relay calculations for the second section, and a full section calculation unit 59 that performs protection relay calculations for all sections.

[0044] The first interval calculation unit 51 outputs a logical value "1" if the absolute value Id1 of the sum of the detected current I1 at terminal A and the detected current I2 at terminal B included in the first interval is greater than the threshold Tap1, and outputs a logical value "0" otherwise.

[0045] The second interval calculation unit 52 outputs a logical value "1" if the absolute value Id2 of the sum of the detected current I3 at the C terminal and the detected current I4 at the D terminal included in the second interval is greater than the threshold Tap2, and outputs a logical value "0" if not.

[0046] The total interval calculation unit 59 outputs a logical value of "1" if the absolute value of the sum of the terminal currents for all intervals, i.e., the absolute value Idall of I1+I2+I3+I4, is greater than the threshold Tapall, and outputs a logical value of "0" otherwise. The thresholds Tap1, Tap2, and Tapall may all be different, all the same, or any two of them may be the same.

[0047] The fault section determination unit 60 determines whether or not there is a fault section in which an internal fault has occurred, based on the information on the open / close state of the switch SX output from the open / close state acquisition unit 40 and the protective relay calculation results for each section output from the protective relay calculation unit 50. Specifically, as shown in Fig. 4, the fault section determination unit 60 includes a logic gate A1 for making an internal fault determination for all sections, a logic gate A2 for making an internal fault determination for the first section, and a logic gate A3 for making an internal fault determination for the second section.

[0048] The logic gate A1 outputs the logical product of the output of the first opening / closing state acquisition unit 41 and the output of the all-section calculation unit 59. Therefore, when the switch SX is in the closed state and the absolute value Idall of the sum of the terminal currents in all sections is greater than the threshold Tapall, the logic gate A1 determines that the all sections are internal fault sections and outputs the logical value "1."

[0049] The logic gate A2 outputs the negation of the output of the first opening / closing state acquisition unit 41, the logical product of the output of the first interval calculation unit 51, and the output of the all interval calculation unit 59. Therefore, when the switch SX is in the open state, the absolute value Id1 of the sum of the terminal currents in the first interval is greater than the threshold value Tap1, and the absolute value Idall of the sum of the terminal currents in all intervals is greater than the threshold value Tapall, the logic gate A2 determines that the first interval is an internal fault interval and outputs a logical value of "1."

[0050] The logic gate A3 outputs the logical product of the negation of the output of the first opening / closing state acquisition unit 41, the output of the second interval calculation unit 52, and the output of the all interval calculation unit 59. Therefore, when the switch SX is in the open state, the absolute value Id2 of the sum of the terminal currents in the second interval is greater than the threshold value Tap2, and the absolute value Idall of the sum of the terminal currents in all intervals is greater than the threshold value Tapall, the logic gate A3 determines that the second interval is an internal fault interval and outputs a logical value of "1."

[0051] In the above, when determining an internal fault in a partial section such as the first or second section, the determination conditions include not only the current differential relay calculation results based on the terminal currents in the partial section, but also the current differential relay calculation results based on the terminal currents in all sections. This prevents malfunction of the protective relay during the opening and closing of the switch SX and the periods before and after, which has the advantage of allowing the transmission line to continue being protected even when the protection section is switched.

[0052] For example, consider the case where, when the switch SX is open, the auxiliary contacts are open but the main contacts are still closed. In this case, the switch SX open / closed state information output from the switch controller CNTL_X is based on the state of the auxiliary contacts and therefore indicates an open state, so the output of the first open / closed state acquisition unit 41 is "0." However, because the main contacts are closed, the sum of the terminal currents in the first section does not become zero. Therefore, if the presence or absence of a fault in the first section is determined based only on the output of the first open / closed state acquisition unit 41 and the output of the first section calculation unit 51, an erroneous determination will occur. In the case of the protection system 1 of this embodiment, the presence or absence of a fault in the first section is determined based on the output result of the all-section calculation unit 59 as well, so that an erroneous determination can be prevented.

[0053] Furthermore, when the switch SX is opened, after both the auxiliary contacts and the main contacts have opened, if no internal fault has occurred in either the first or second section, the current differential relay calculation results for all sections will naturally indicate that there is no internal fault. Therefore, even if the internal fault judgment conditions for the entire section are included in the internal fault judgment for the partial section, it does not affect the fault judgment results.

[0054] The section protection command generator 70 generates a protection command for each minimum section divided by all switches (therefore, each minimum section does not include a switch inside), if the minimum section is included in the fault section. In the case of the multi-terminal power transmission system 7 to which the protection system 1 of the first embodiment is applied, the minimum sections are the first section and the second section.

[0055] Specifically, the section protection command generator 70 includes a logic gate O1 for generating a protection command for the first section and a logic gate O2 for generating a protection command for the second section. The logic gate O1 outputs a logical sum of the outputs of the logic gates A1 and A2. The logic gate O2 outputs a logical sum of the outputs of the logic gates A1 and A3.

[0056] Therefore, when the output of logic gate A1 is "1", i.e., when all sections of multi-terminal power transmission system 7 are internal fault sections, the outputs of both logic gates O1 and O2 are "1". When the output of logic gate A2 is "1" and the output of logic gate A3 is "0", i.e., when the first section is an internal fault section, the output of logic gate O1 is "1" and the output of logic gate O2 is "0". When the output of logic gate A2 is "0" and the output of logic gate A3 is "1", i.e., when the second section is an internal fault section, the output of logic gate O1 is "0" and the output of logic gate O2 is "1".

[0057] The trip command generating unit 80 determines whether or not to output a trip command (i.e., a trip signal) to the circuit breaker CB of its own terminal. Specifically, the trip command generating unit 80 includes registers 81 and 82 in which terminal information of its own terminal is set, and logic gates A4, A5, and O3.

[0058] If the own terminal is included in the first section (i.e., if it is end A or end B), register 81 is set to "1" and register 82 is set to "0". If the own terminal is included in the second section (i.e., if it is end C or end D), register 81 is set to "0" and register 82 is set to "1". Logic gate A4 outputs the logical product of the output of logic gate O1 and the set value of register 81. Logic gate A5 outputs the logical product of the output of logic gate O2 and the set value of register 82. Logic gate O3 outputs the logical sum of the output of logic gate A4 and the output of logic gate A5.

[0059] According to the configuration of the tripping command generating unit 80 described above, when the output of the logic gate O1 is "1" (i.e., a protection command for the first section is generated) and the own end is included in the first section, "1" is output from the logic gate A4, and therefore the final logic gate O3 outputs a logical value of "1", i.e., a tripping command 83 for the circuit breaker CB of the own end. Alternatively, when the output of the logic gate O2 is "1" (i.e., a protection command for the second section is generated) and the own end is included in the second section, "1" is output from the logic gate A5, and therefore the final logic gate O3 outputs a logical value of "1", i.e., a tripping command 83 for the circuit breaker CB of the own end.

[0060] Figure 5 is a block diagram showing a modification of Figure 4. In the protection relay calculation unit 50 of Figure 4, protection relay calculation is performed for all sections and all partial sections. In contrast, in the protection relay calculation unit 50 of Figure 5, protection relay calculation is performed only for all sections and partial sections that include the own end. This simplifies the logic circuit configuration.

[0061] Specifically, referring to FIG. 5(A), when the local end is the A-end or the B-end, the protection relay calculation unit 50 includes the first section calculation unit 51 and the all-section calculation unit 59, but does not include the second section calculation unit 52. In this case, the fault section determination unit 60 includes a logic gate A1 that outputs a logical product of the output of the first switching state acquisition unit 41 and the output of the all-section calculation unit 59, and a logic gate A2 that outputs a logical product of the negation of the first switching state acquisition unit 41, the output of the first section calculation unit 51, and the output of the all-section calculation unit 59, but does not need to include the logic gate A3 of FIG. 4. The section protection command generation unit 70 includes a logic gate O1 that outputs a logical sum of the output of the logic gate A1 and the output of the logic gate A2, but does not need to include the logic gate O2 of FIG. 4. Furthermore, when the output of the logic gate O1 is “1” (i.e., when a protection command for the first section is generated), a tripping command 83 can be immediately output to the circuit breaker CB of the local end, so the tripping command generation unit 80 of FIG. 4 is not required.

[0062] Similarly, referring to FIG. 5(B), when the local end is the C-end or the D-end, the protection relay calculation unit 50 includes the second section calculation unit 52 and the all-section calculation unit 59, but does not include the first section calculation unit 51. In this case, the fault section determination unit 60 includes a logic gate A1 that outputs a logical product of the output of the first switching status acquisition unit 41 and the output of the all-section calculation unit 59, and a logic gate A3 that outputs a logical product of the negation of the first switching status acquisition unit 41, the output of the second section calculation unit 52, and the output of the all-section calculation unit 59, but does not need to include the logic gate A2 of FIG. 4. The section protection command generation unit 70 includes a logic gate O2 that outputs a logical sum of the output of the logic gate A1 and the output of the logic gate A3, but does not need to include the logic gate O1 of FIG. 4. Furthermore, when the output of the logic gate O2 is “1” (i.e., when a protection command for the second section is generated), a tripping command 83 can be immediately output to the circuit breaker CB of the local end, so the tripping command generation unit 80 of FIG. 4 is not required.

[0063] [Summary of the first embodiment] As described above, in the protection system 1 for the multi-terminal power transmission system 7 according to the first embodiment, the multi-terminal power transmission system 7 includes four or more terminals (terminal A, terminal B, terminal C, and terminal D) and one or more switches SX. By opening at least one of the one or more switches SX, the entire section of the multi-terminal power transmission system 7 is divided into a plurality of partial sections (first section, second section), each including two or more terminals. The protection system 1 includes a current transformer CT, a switch switching state acquisition unit 40, and a fault section determination unit 60. The current transformer CT is provided at each terminal of the multi-terminal power transmission system 7 and detects the terminal current of the terminal. The switch switching state acquisition unit 40 acquires information on the switching state of each of the one or more switches SX. The fault section determination unit 60 determines, using a current differential method, whether an internal fault has occurred in the entire section or any of the partial sections of the multi-terminal power transmission system 7, based on the detected value of the terminal current at each terminal of the multi-terminal power transmission system 7 and the switching state of each of the one or more switches SX. The fault section determination unit 60 determines that an internal fault has occurred in a partial section (first section or second section) when the absolute value (Id1, Id2) of the sum of the terminal currents of each terminal of the partial section (first section or second section) determined by the open / closed state of one or more switches SX exceeds a first threshold value (Tap1, Tap2) and the absolute value (Idall) of the sum of the terminal currents of each terminal constituting the entire section exceeds a second threshold value (Tapall).

[0064] According to the above configuration, even if the fault section determination unit 60 continues to determine whether or not there is an internal fault before or after an opening or closing operation is performed on any of the one or more switches SX, the protection system 1 can be prevented from malfunctioning.

[0065] More specifically, the protection system 1 of the first embodiment includes a plurality of protective relays RY connected to each other via a communication line 2. Each of the plurality of protective relays RY is provided individually corresponding to each terminal of the multi-terminal power transmission system 7, and acquires the value of the terminal current of its own terminal from the current transformer CT of its own terminal, and also acquires the values ​​of the terminal current of other terminals from the other protective relays RY via the communication line 2. Each of the plurality of protective relays RY includes the above-described open / close state acquisition unit 40 and fault section determination unit 60, and outputs a trip signal to open the circuit breaker CB provided at its own terminal when the fault section determination unit 60 determines that an internal fault has occurred in the entire section or a partial section including its own terminal.

[0066] Embodiment 2 In the protection system 3 of embodiment 2, a case will be described in which the protection relay RY provided for each terminal in the protection system 1 of embodiment 1 is separated into a merging unit MU and a common control device 92 connected to each merging unit MU via a network 90.

[0067] [Example of a protection system configuration for a multi-terminal power transmission system] Fig. 6 shows an example of the configuration of a protection system 3 according to the second embodiment and a multi-terminal power transmission system 7 protected thereby. The multi-terminal power transmission system 7 in Fig. 6 is similar to that in Fig. 1, and therefore description thereof will not be repeated.

[0068] Protection system 3 includes circuit breakers CB (CB1 to CB4) and current transformers CT (CT1 to CT4) provided for the respective terminals. These configurations are the same as those in the first embodiment shown in Fig. 1, and therefore description thereof will not be repeated.

[0069] Furthermore, the protection system 3 includes a merging unit MU_A provided in the A-end substation, a merging unit MU_B provided in the B-end substation, a merging unit MU_C provided in the C-end substation, and a merging unit MU_D provided in the D-end substation. In the following description, the merging units MU_A to MU_D will be referred to collectively as a merging unit MU or any one of them will be referred to as a merging unit MU.

[0070] Each merging unit MU is connected to a circuit breaker CB and a current transformer CT at its own end. Furthermore, each merging unit MU is connected to a common control device 92 via a network 90.

[0071] Each merging unit MU detects the current flowing in its own transmission line via its own current transformer CT, converts the detected current into a digital value, and transmits the digital current detection value to a common control device 92 via a network 90.

[0072] In the above case, the current sampling timings in each merging unit MU are synchronized with each other. In this second embodiment, as will be described in the following Fig. 7, PTP (Precision Time Protocol) synchronization of the IEEE1588 standard using Ethernet is used for timing synchronization. However, the timing synchronization method is not limited to PTP synchronization.

[0073] Each merging unit MU is also connected to a number of other current transformers and voltage transformers (not shown) provided at its own end. Each merging unit MU converts the current and voltage signals detected by these current and voltage transformers into digital signals, and transmits the resulting digital signals as aggregated data to the common control device 92.

[0074] The common control device 92 determines whether a fault has occurred in any of the protection sections based on the current detection values ​​of each terminal received from each merging unit MU and the open / closed state of the switch SX received from the switch controller CNTL_X, using a current differential method. Here, the protection section is the entire section when the switch SX is in the closed state, and is a partial section of the first section and the second section when the switch SX is in the open state. Details of the fault determination method will be described later with reference to Figures 9 to 12.

[0075] When the common control device 92 detects a fault in any section, it outputs a protection command for the faulty section to each merging unit MU. A merging unit MU that receives this protection command outputs a tripping command to its own end's circuit breaker CB if its own end is included in the faulty section. Alternatively, when the common control device 92 detects a fault in any section, it outputs a protection command for a terminal included in the faulty section. A merging unit MU that receives this protection command outputs a tripping command to its own end's circuit breaker CB if its own end is a terminal to be protected.

[0076] The common control device 92 may perform a protective relay calculation other than that of the current differential method based on the detection signals of the other current transformers and voltage transformers received from each merging unit MU.

[0077] [Example of network configuration for protection system] Fig. 7 is a diagram showing an example of a network configuration of the protection system 3 of Fig. 6. Referring to Fig. 7, the protection system 3 further includes network switches SW_A to SW_D, SW_X, and a synchronization master 91, in addition to the merging units MU_A to MU_D and common control device 92 described in Fig. 6. The network switches SW_A to SW_D, SW_X will be referred to collectively or any one of them will be referred to as network switch SW.

[0078] The network switch SW is an Ethernet switch with IEEE-1588 functionality, such as a Layer 3 switch.

[0079] The synchronization master 91 provides synchronization messages necessary for each merging unit MU acting as a slave device and the common control device 92 to correct their clocks. The clocks of each merging unit MU and the common control device 92 are synchronized by exchanging messages containing timestamps between the synchronization master 91 and each slave device.

[0080] As shown in Fig. 7, network switches SW_A to SW_D, and SW_X are connected to one another via a ring-type network 90. ​​Merging units MU_A to MU_D and switch controller CNTL_X are individually connected to the network switches SW_A to SW_D, and SW_X, respectively. A synchronization master 91 and a common control device 92 are each connected to one of the plurality of network switches SW. In the example of Fig. 7, the synchronization master 91 is connected to the network switch SW_B together with the merging unit MU_B, and the common control device 92 is connected to the network switch SW_D together with the merging unit MU_D.

[0081] Each merging unit MU acquires, at predetermined timing, a current signal from a current transformer CT provided at its own terminal and signals representing electrical quantities (current and voltage) from numerous other detectors (current transformers and voltage transformers, not shown) also provided at its own terminal, and converts them into digital electrical quantity data. Each merging unit MU transmits a frame including the electrical quantity data to the network 90 via the corresponding network switch SW, thereby transmitting it to the common control device 92. The frame is data that aggregates the electrical quantity data obtained at its own terminal.

[0082] The common control device 92 determines whether a fault has occurred in any of the protection sections by a current differential method using the current data sampled at the same time by each merging unit MU and the switching information of the switch SX obtained from the switch controller CNTL_X. In the case of the multi-terminal power transmission system 7 in Fig. 6, the protection section is the entire section when the switch SX is in the closed state, and is a partial section of the first section and the second section when the switch SX is in the open state.

[0083] When the common control device 92 determines that a fault has occurred in any of the protection sections, it outputs a protection command to shut off the corresponding circuit breaker CB to the network 90 via the corresponding network switch SW_D. As a result, the protection command is transmitted to the merging unit MU provided at the terminal included in the fault section.

[0084] In order to avoid frame collisions, the communication path between the network switch SW_A and the network switch SW_X is in a dormant state in the network 90 of Fig. 7. When a communication path between other network switches SW becomes unavailable due to a failure, the dormant communication path is used.

[0085] According to the above-described configuration of the network 90, a single merging unit MU is connected to each network switch SW. This reduces the number of devices that transmit or receive data, making it easier to manage the timing of frame transmission to the network 90. ​​Furthermore, data can be sent and received normally via the network 90 without placing a load on each network switch SW that exceeds its specifications.

[0086] [Example of hardware configuration for merging units] The hardware configuration of the merging unit MU in Figures 6 and 7 is similar to the hardware configuration of the protection relay RY described with reference to Figure 2. Figure 2 shows an example in which the merging unit MU is configured based on a microcomputer. Unlike the example in Figure 2, at least a part of the configuration of the merging unit MU may be configured using an FPGA, an ASIC, or a combination of these.

[0087] 2, the merging unit MU includes one or more input converters 10, one or more analog filters (AF) 11, one or more sample-and-hold circuits (S / H) 12, a multiplexer (MUX) 13, an A / D (Analog to Digital) converter 14, a processing unit 20, a communication circuit 26, one or more digital output circuits (D / O: Digital Output) 27, and one or more digital input circuits (D / I: Digital Input) 28. The merging unit MU further includes a bus 24 that connects the A / D converter 14, the processing unit 20, the communication circuit 26, the digital output circuit 27, and the digital input circuit 28. These components are basically the same as those of the protection relay RY, so only the differences will be described below.

[0088] The CPU 21 of the arithmetic processing unit 20 controls the entire merging unit MU in accordance with programs stored in the ROM 23 and nonvolatile memory. Typically, the functions of the merging unit MU described above are executed by the arithmetic processing unit 20.

[0089] The communication circuit 26 communicates via the network 90 in accordance with a specified protocol. Typically, the communication circuit 26 has multiple communication ports depending on the application. For example, the communication circuit 26 includes one or more transmission ports for transmitting data and one or more reception ports for receiving data. The communication circuit 26 transmits frames including electrical quantity data to the common control device 92 via the transmission ports and receives protection commands from the common control device 92 via the reception ports.

[0090] The digital output circuit 27 outputs a trip signal (also referred to as a trip command) to the corresponding circuit breaker CB in accordance with, for example, a protection command from the common control device 92. The digital input circuit 28 receives, for example, from the corresponding circuit breaker CB, opening / closing information indicating the opening / closing state of the circuit breaker CB.

[0091] [Example of common control device hardware configuration] 8 is a block diagram showing an example of a hardware configuration of the common control device 92. Referring to FIG. 8, the common control device 92 includes an arithmetic processing unit 100 and a communication circuit .

[0092] The arithmetic processing unit 100 includes a CPU 101, a RAM 102, and a ROM 103. These elements and a communication circuit 106 are connected to each other via a bus 104. The arithmetic processing unit 100 may include an electrically rewritable non-volatile memory such as a flash memory.

[0093] The RAM 102 and the ROM 103 are used as the main memory of the CPU 101. The CPU 101 controls the entire common control device 92 and executes protection relay calculations in accordance with programs stored in the ROM 103 and the non-volatile memory. Typically, the operations of the common control device 92 described above are executed by the calculation processing unit 100.

[0094] The communication circuit 106 performs network communication according to a specified protocol via the corresponding network switch SW_D. Typically, the communication circuit 106 has multiple communication ports depending on the application. For example, the communication circuit 106 includes one or more transmit ports for transmitting data and one or more receive ports for receiving data. The communication circuit 106 receives frames containing electrical quantity data from each merging unit MU via the receive ports and transmits protection commands to the merging unit MU provided at the terminal of the faulty section via the transmit ports.

[0095] [Protection system protection operation] Next, detailed operation of the protection system 3 of Figures 6 and 7 will be described. Figure 9 is a block diagram for explaining an example of operation of the common control device 92 of Figures 6 and 7. In Figure 9, the function of the arithmetic processing unit 100 of the common control device 92 is shown as a logic circuit. The function of this logic circuit may be realized by a computer program, may be realized by an FPGA, or may be realized by a logic circuit of another configuration having equivalent function.

[0096] 9, the calculation processing unit 100 of the common control device 92 includes a switch open / close state acquisition unit 40, a protection relay calculation unit 50, a fault section determination unit 60, and a section protection command generation unit 70. This configuration is basically the same as the configuration of the protection relay RY in FIG. 4 except for the tripping command generation unit 80, and therefore the same or corresponding parts are given the same reference symbols and description thereof will not be repeated.

[0097] The section protection command generation unit 70 generates a protection command for each minimum section divided by all switches (therefore, each minimum section does not include a switch inside), if the minimum section is included in the fault section, and transmits the generated protection command to each merging unit MU via the network 90.

[0098] In the case of the multi-terminal power transmission system 7 of the second embodiment, the minimum sections are the first section and the second section. Specifically, when the first section is included in the fault section, the logic gate O1 transmits a protection command 71 for the first section to each merging unit MU. When the second section is included in the fault section, the logic gate O2 transmits a protection command 72 for the second section to each merging unit MU.

[0099] Fig. 10 is a block diagram showing the operation of each merging unit MU when a section protection command is received from the common control device 92. In Fig. 10, the function of the arithmetic processing unit 20 of each merging unit MU is shown as a logic circuit. The function of this logic circuit may be realized by a computer program, an FPGA, or a logic circuit of another configuration having equivalent functions.

[0100] 10, the arithmetic processing unit 20 of each merging unit MU includes a tripping command generating unit 80 having a configuration similar to that of the protection relay RY of FIG.

[0101] Specifically, the trip command generator 80 includes registers 81 and 82 in which terminal information of the own terminal is set, and logic gates A4, A5, and O3. If the own terminal is included in the first section (i.e., if it is the A terminal or the B terminal), "1" is set in the register 81 and "0" is set in the register 82. If the own terminal is included in the second section (i.e., if it is the C terminal or the D terminal), "0" is set in the register 81 and "1" is set in the register 82.

[0102] Logic gate A4 outputs the logical product of protection command 71 for the first section received from common control device 92 and the set value of register 81. Logic gate A5 outputs the logical product of protection command 72 for the second section received from common control device 92 and the set value of register 82. Logic gate O3 outputs the logical sum of the output of logic gate A4 and the output of logic gate A5.

[0103] According to the configuration of the tripping command generating unit 80 described above, when a protection command 71 for the first section is received from the common control device 92 and the own end is included in the first section, "1" is output from the logic gate A4, and therefore the final logic gate O3 outputs a logical value of "1", i.e., a tripping command 83 for the circuit breaker CB of the own end. Alternatively, when a protection command 72 for the second section is received from the common control device 92 and the own end is included in the second section, "1" is output from the logic gate A5, and therefore the final logic gate O3 outputs a logical value of "1", i.e., a tripping command 83 for the circuit breaker CB of the own end.

[0104] Fig. 11 is a block diagram showing a modification of Fig. 9. In the example shown in Fig. 9, the common control device 92 is configured to output a protection command for the smallest section included in the fault section to each merging unit MU. In the modification shown in Fig. 11, the common control device 92 is configured to output a protection command for a terminal included in the fault section to each merging unit MU. The configuration of the modification of the common control device 92 will be described in detail below.

[0105] As shown in FIG. 11, the calculation processing unit 100 of the modified common control device 92 includes a switch opening / closing state acquisition unit 40, a protection relay calculation unit 50, a fault section determination unit 60, a section protection command generation unit 70, and a terminal protection command generation unit 110.

[0106] In Figure 11, the configurations of the switch opening / closing state acquisition unit 40, protection relay calculation unit 50, fault section determination unit 60, and section protection command generation unit 70 are the same as in Figure 9, so the same or corresponding parts are given the same reference numerals and description will not be repeated. As described with reference to Figure 9, a protection command 71 for the first section is output from logic gate O1 of section protection command generation unit 70, and a protection command 72 for the second section is output from logic gate O2 of section protection command generation unit 70.

[0107] The terminal protection command generation unit 110 generates a protection command for each terminal (terminal A to terminal D) that constitutes the multi-terminal power transmission system 7 in Fig. 1. As shown in Fig. 11, the terminal protection command generation unit 110 includes registers 111 to 118 for setting information about which minimum section each terminal is included in, and logic gates A11 to A18 and O11 to O14.

[0108] Register 111 is set to "1" if end A is included in the first section, and is set to "0" if not. Register 112 is set to "1" if end A is included in the second section, and is set to "0" if not.

[0109] Similarly, register 113 is set to "1" if end B is included in the first section, and is set to "0" if not. Register 114 is set to "1" if end B is included in the second section, and is set to "0" if not.

[0110] Register 115 is set to "1" if the C end is included in the first section, and is set to "0" if not. Register 116 is set to "1" if the C end is included in the second section, and is set to "0" if not.

[0111] Register 117 is set to "1" if terminal D is included in the first section, and is set to "0" if not. Register 118 is set to "1" if terminal D is included in the second section, and is set to "0" if not.

[0112] Therefore, in the configuration of the multi-terminal power transmission system 7 shown in FIG. 1, the registers 111, 113, 116, and 118 are set to "1," and the registers 112, 114, 115, and 117 are set to "0."

[0113] Logic gate A11 outputs the logical product of the output of logic gate O1 and the set value of register 111. Logic gate A12 outputs the logical product of the output of logic gate O2 and the set value of register 112. Therefore, when a fault occurs in the first section, logic gate A11 outputs a logical value of "1" and logic gate A12 outputs a logical value of "0". Since logic gate O11 outputs the logical sum of the output of logic gate A11 and the output of logic gate A12, when a fault occurs in the first section, logic gate O11 transmits a logical value of "1" as a protection command 121 at the A end to each merging unit MU via network 90.

[0114] Similarly, logic gate A13 outputs the logical product of the output of logic gate O1 and the setting value of register 113. Logic gate A14 outputs the logical product of the output of logic gate O2 and the setting value of register 114. Therefore, when a fault occurs in the first section, logic gate A13 outputs a logical value of "1" and logic gate A14 outputs a logical value of "0". Since logic gate O12 outputs the logical sum of the output of logic gate A13 and the output of logic gate A14, when a fault occurs in the first section, logic gate O12 transmits a logical value of "1" as a protection command 122 for end B to each merging unit MU via network 90.

[0115] Logic gate A15 outputs the logical product of the output of logic gate O1 and the setting value of register 115. Logic gate A16 outputs the logical product of the output of logic gate O2 and the setting value of register 116. Therefore, when a fault occurs in the second section, logic gate A15 outputs a logical value of "0" and logic gate A16 outputs a logical value of "1". Logic gate O13 outputs the logical sum of the output of logic gate A15 and the output of logic gate A16, so when a fault occurs in the second section, logic gate O13 transmits a logical value of "1" as a protection command 123 at the C end to each merging unit MU via network 90.

[0116] Logic gate A17 outputs the logical product of the output of logic gate O1 and the set value of register 117. Logic gate A18 outputs the logical product of the output of logic gate O2 and the set value of register 118. Therefore, when a fault occurs in the second section, logic gate A17 outputs a logical value of "0" and logic gate A18 outputs a logical value of "1". Logic gate O14 outputs the logical sum of the output of logic gate A17 and the output of logic gate A18, so when a fault occurs in the second section, logic gate O14 transmits a logical value of "1" as a protection command 124 for the D terminal to each merging unit MU via network 90.

[0117] Fig. 12 is a block diagram showing the operation of each merging unit MU when a terminal protection command is received from the common control device 92. In (A) to (D) of Fig. 12, the functions of merging units MU_A to MU_D are shown as logic circuits. The functions of these logic circuits may be realized by a computer program, an FPGA, or a logic circuit of another configuration having equivalent functions.

[0118] 12(A), the arithmetic processing unit 20 of the merging unit MU_A provided at the A-end includes a register 126A in which the A-end is set as the terminal information of its own terminal, and a logic gate A21. The logic gate A21 receives a protection command 121 for the A-end from the common control device 92, and when the A-end is set as the terminal information in the register 126A, outputs a trip command 83A for the circuit breaker CB1 at the A-end, which is its own terminal.

[0119] 12(B), the arithmetic processing unit 20 of the merging unit MU_B provided at the B end includes a register 126B in which the B end is set as the terminal information of its own terminal, and a logic gate A22. The logic gate A22 receives a protection command 122 for the B end from the common control device 92, and when the B end is set as the terminal information in the register 126B, outputs a trip command 83B for the circuit breaker CB2 at the B end, which is its own end.

[0120] 12(C), the arithmetic processing unit 20 of the merging unit MU_C provided at the C-end includes a register 126C in which the C-end is set as the terminal information of its own terminal, and a logic gate A23. The logic gate A23 receives a protection command 123 for the C-end from the common control device 92, and when the C-end is set as the terminal information in the register 126C, outputs a trip command 83C for the circuit breaker CB3 at the C-end, which is its own terminal.

[0121] 12(D), the arithmetic processing unit 20 of the merging unit MU_D provided at the D terminal includes a register 126D in which the D terminal is set as the terminal information of its own terminal, and a logic gate A24. The logic gate A24 receives a protection command 124 for the D terminal from the common control device 92, and when the D terminal is set as the terminal information in the register 126D, outputs a trip command 83D for the circuit breaker CB4 at the D terminal, which is its own terminal.

[0122] [Summary of the second embodiment] As described above, the protection system 3 of the second embodiment includes a plurality of merging units MU and a common controller 92. The plurality of merging units MU and the common controller 92 are connected to each other via a communication line 90. Each of the plurality of merging units MU is provided corresponding to a respective terminal of the multi-terminal power transmission system 7, acquires a terminal current value from the current transformer CT of its own terminal, and transmits the acquired terminal current value to the common controller 92 via the communication line 90. The common controller 92 includes the same switching state acquisition unit 40 and fault section determination unit 60 as in the first embodiment. When the fault section determination unit 60 determines that an internal fault has occurred in the entire section or any partial section, the common controller 92 transmits protection commands 71, 72, 121 to 124 to each merging unit MU via the communication line 90 to protect the multi-terminal power transmission system 7.

[0123] As one example, the protection commands 71 ​​and 72 include information for identifying the fault section in which an internal fault has occurred. When the received protection commands 71 ​​and 72 indicate that the own terminal is included in the fault section, each merging unit MU outputs a trip signal for opening the circuit breaker CB provided at the own terminal. As another example, the protection commands 121 to 124 include information for identifying a terminal included in the fault section in which an internal fault has occurred. When the received protection commands 121 to 124 indicate that the own terminal is included in the fault section, each merging unit MU outputs a trip signal for opening the circuit breaker CB provided at the own terminal.

[0124] The protection system 3 of embodiment 2 also has a fault section determination unit 60 configured in the same manner as in embodiment 1, so that when any of the switches is opened or closed, the fault section determination unit 60 will not malfunction even if it continues to determine whether or not an internal fault has occurred.

[0125] Embodiment 3 In the third embodiment, a case will be described in which a multi-terminal power transmission system 8 having six terminals is divided into partial sections by two switches SX and SY. As in the second embodiment, the following describes a case in which the protection system 4 includes a merging unit MU provided for each terminal and a common control device 92. However, as explained in the first embodiment, a protection system for protecting the multi-terminal power transmission system 8 can also be configured using a protection relay RY provided for each terminal.

[0126] [Example of a protection system configuration for a multi-terminal power transmission system] Fig. 13 is a diagram showing an example of the configuration of a protection system 4 according to the third embodiment and a multi-terminal power transmission system 8 protected thereby. For the purpose of explanation, the multi-terminal power transmission system 8 in Fig. 13 is a simplification of an actual multi-terminal power transmission system, and has six terminals: A terminal, B terminal, C terminal, D terminal, E terminal, and F terminal.

[0127] 13, multi-terminal transmission system 8 includes transmission line L1 connecting bus B1 of the A-end substation and bus B6 of the F-end substation, and transmission lines L2, L3, L4, and L5 branching off from branch points J1, J2, J3, and J4 that are arranged on the path of transmission line L1 from the side closest to bus B1. Transmission line L2 connects branch point J1 to bus B2 of the B-end substation, transmission line L3 connects branch point J2 to bus B3 of the C-end substation, transmission line L4 connects branch point J3 to bus B4 of the D-end substation, and transmission line L5 connects branch point J4 to bus B5 of the E-end substation.

[0128] Furthermore, the multi-terminal transmission system 7 includes a switch SX provided between branch points J1 and J2 on the path of the transmission line L1, a switch controller CNTL_X that controls the opening and closing of the switch SX, a switch SY provided between branch points J3 and J4 on the path of the transmission line L1, and a switch controller CNTL_Y that controls the opening and closing of the switch SY. The switch controllers CNTL_X and CNTL_Y control the opening and closing of the corresponding switches SX and SY, respectively, in accordance with commands from a higher-level computer in a control center (not shown).

[0129] When switch SX and switch SY are both open, the entire section of multi-terminal power transmission system 8 is divided into a first section including terminals A and B, a second section including terminals C and D, and a third section including terminals E and F. When switch SX is closed and switch SY is open, the entire section of multi-terminal power transmission system 8 is divided into a fourth section including terminals A, B, C, and D, and a third section including terminals E and F. When switch SX is open and switch SY is closed, the entire section of multi-terminal power transmission system 8 is divided into a first section including terminals A and B, and a fifth section including terminals C, D, E, and F. Each of the first, second, and third sections is the smallest section that does not include switches SX and SY within itself.

[0130] The protection system 4 includes circuit breakers CB (CB1 to CB6) and current transformers CT (CT1 to CT6) provided on the transmission lines near each terminal, merging units MU (MU_A to MU_F) provided for each terminal, and a common control device 92. The merging units MU, the common control device 92, and the switch controllers CNTL_X and CNTL_Y are connected to each other via a network 90.

[0131] The hardware configuration and function of each merging unit MU and the common control device 92 are generally the same as those described in embodiment 2, and therefore will not be described repeatedly. The hardware configuration and function of the switch controllers CNTL_X and CNTL_Y are generally the same as those described in embodiment 1, and therefore will not be described repeatedly.

[0132] [Example of network configuration for protection system] Figure 14 is a diagram showing an example of a network configuration of the protection system 4 of Figure 13. The protection system 4 of Figure 13 differs from the case of Figure 7 in that it further includes network switches SW_E and SW_F connected to a network 90, and merging units MU_E and MU_F connected to the network switches SW_E and SW_F, respectively. The protection system 4 shown in Figure 14 also differs from the case of Figure 7 in that a common control device 92 is connected to the network switch SW_F instead of the network switch SW_D. Since the other points in Figure 14 are the same as those in Figure 7, the same or corresponding parts are designated by the same reference numerals and description thereof will not be repeated.

[0133] [Protection system protection operation] Figures 15 and 16 are block diagrams for explaining an example of the operation of the common control device 92 of Figures 13 and 14. In Figures 15 and 16, the function of the arithmetic processing unit 100 of the common control device 92 is shown as a logic circuit. The function of this logic circuit may be realized by a computer program, an FPGA, or a logic circuit of another configuration having equivalent functions.

[0134] The block diagrams in Figures 15 and 16 are extensions of the block diagram in Figure 11, which is applied to the multi-terminal power transmission system 7 in Figure 1, so that it is applied to the multi-terminal power transmission system 8 in Figure 13. Therefore, as in the case of Figure 11, the calculation processing unit 100 of the common control device 92 includes a switch opening / closing state acquisition unit 40, a protection relay calculation unit 50, a fault section determination unit 60, a section protection command generation unit 70, and a terminal protection command generation unit 140. Figure 15 shows specific configuration examples of the switch opening / closing state acquisition unit 40, the protection relay calculation unit 50, the fault section determination unit 60, and the section protection command generation unit 70, and Figure 16 shows a specific configuration example of the terminal protection command generation unit 140.

[0135] Unlike the above, the block diagram of FIG. 9 applied to the multi-terminal power transmission system 7 of FIG. 1 can be extended to be applied to the multi-terminal power transmission system 8 of FIG. 13, and it is also possible to protect the multi-terminal power transmission system 8 of FIG. 13 by a protective relay RY provided for each terminal as described in the first embodiment.

[0136] 15, the switch open / close state acquisition unit 40 includes a first open / close state acquisition unit 41 that acquires information on the open / close state of the switch SX from the switch controller CNTL_X, and a second open / close state acquisition unit 42 that acquires information on the open / close state of the switch SY from the switch controller CNTL_Y. The second open / close state acquisition unit 42 outputs a logical value of "1" when the switch SY is in the closed state, and outputs a logical value of "0" when the switch SY is in the open state.

[0137] The protection relay calculation unit 50 performs protection relay calculations using a current differential relay method for each protection zone determined according to the open / closed states of the switches SX and SY. Specifically, the protection relay calculation unit 50 includes a first zone calculation unit 51 that performs protection relay calculations for the first zone, a second zone calculation unit 52 that performs protection relay calculations for the second zone, a third zone calculation unit 53 that performs protection relay calculations for the third zone, a fourth zone calculation unit 54 that performs protection relay calculations for the fourth zone, a fifth zone calculation unit 55 that performs protection relay calculations for the fifth zone, and a full zone calculation unit 59 that performs protection relay calculations for all zones.

[0138] The first interval calculation unit 51 outputs a logical value "1" if the absolute value Id1 of the sum of the detected current I1 at terminal A and the detected current I2 at terminal B included in the first interval is greater than the threshold Tap1, and outputs a logical value "0" otherwise.

[0139] The second interval calculation unit 52 outputs a logical value "1" if the absolute value Id2 of the sum of the detected current I3 at the C terminal and the detected current I4 at the D terminal included in the second interval is greater than the threshold Tap2, and outputs a logical value "0" if not.

[0140] The third interval calculation unit 53 outputs a logical value “1” if the absolute value Id3 of the sum of the detected current I5 at terminal E and the detected current I6 at terminal F included in the third interval is greater than the threshold Tap3, and outputs a logical value “0” otherwise.

[0141] The fourth interval calculation unit 54 outputs a logical value of "1" if the absolute value of the sum of the terminal currents of terminals A, B, C, and D included in the fourth interval, i.e., the absolute value of I1+I2+I3+I4, is greater than a threshold Tap4, and outputs a logical value of "0" otherwise.

[0142] The fifth interval calculation unit 55 outputs a logical value of "1" if the absolute value of the sum of the terminal currents of terminals C, D, E, and F included in the fifth interval, i.e., the absolute value of I3+I4+I5+I6, is greater than a threshold Tap5, and outputs a logical value of "0" otherwise.

[0143] The total interval calculation unit 59 outputs a logical value of "1" if the absolute value of the sum of the terminal currents for all intervals, i.e., the absolute value Idall of I1+I2+I3+I4+I5+I6, is greater than the threshold Tapall, and outputs a logical value of "0" if not. The above thresholds Tap1, Tap2, Tap3, Tap4, Tap5, and Tapall may all be different, may all be the same, or any two or more may be the same.

[0144] The fault section determination unit 60 determines whether or not there is a fault section in which an internal fault has occurred, based on the information on the open / close states of the switches SX and SY output from the open / close state acquisition unit 40 and the protective relay calculation results for each section output from the protective relay calculation unit 50. Specifically, as shown in Fig. 15, the fault section determination unit 60 includes a logic gate A31 for making an internal fault determination for all sections, a logic gate A32 for making an internal fault determination for the first section, a logic gate A33 for making an internal fault determination for the second section, a logic gate A34 for making an internal fault determination for the third section, a logic gate A35 for making an internal fault determination for the fourth section, and a logic gate A36 for making an internal fault determination for the fifth section.

[0145] The logic gate A31 outputs the logical product of the output of the first opening / closing state acquisition unit 41, the output of the second opening / closing state acquisition unit 42, and the output of the entire section calculation unit 59. Therefore, when the switch SX is in the closed state, the switch SY is in the closed state, and the absolute value Idall of the sum of the terminal currents in all sections is greater than the threshold Tapall, the logic gate A31 determines that the entire section is an internal fault section and outputs the logical value "1."

[0146] The logic gate A32 outputs the logical product of the negation of the output of the first opening / closing state acquisition unit 41, the output of the first interval calculation unit 51, and the output of the all interval calculation unit 59. Therefore, when the switch SX is in the open state, the absolute value Id1 of the sum of the terminal currents in the first interval is greater than the threshold value Tap1, and the absolute value Idall of the sum of the terminal currents in all intervals is greater than the threshold value Tapall, the logic gate A32 determines that the first interval is an internal fault interval and outputs a logical value of "1."

[0147] The logic gate A33 outputs a logical product of the negation of the output of the first opening / closing state acquisition unit 41, the negation of the output of the second opening / closing state acquisition unit 42, the output of the second interval calculation unit 52, and the output of the all interval calculation unit 59. Therefore, when the switch SX is in the open state, the switch SY is in the open state, the absolute value Id2 of the sum of the terminal currents in the second interval is greater than the threshold value Tap2, and the absolute value Idall of the sum of the terminal currents in all intervals is greater than the threshold value Tapall, the logic gate A33 determines that the second interval is an internal fault interval and outputs a logical value "1".

[0148] The logic gate A34 outputs the logical product of the negation of the output of the second opening / closing state acquisition unit 42, the output of the third interval calculation unit 53, and the output of the all interval calculation unit 59. Therefore, when the switch SY is in the open state, the absolute value Id3 of the sum of the terminal currents in the third interval is greater than the threshold value Tap3, and the absolute value Idall of the sum of the terminal currents in all intervals is greater than the threshold value Tapall, the logic gate A34 determines that the third interval is an internal fault interval and outputs a logical value of "1."

[0149] The logic gate A35 outputs the logical product of the output of the first opening / closing state acquisition unit 41, the negation of the output of the second opening / closing state acquisition unit 42, the output of the fourth section calculation unit 54, and the output of the all section calculation unit 59. Therefore, when the switch SX is in the closed state, the switch SY is in the open state, the absolute value Id4 of the sum of the terminal currents in the fourth section is greater than the threshold value Tap4, and the absolute value Idall of the sum of the terminal currents in all sections is greater than the threshold value Tapall, the logic gate A35 determines that the fourth section is an internal fault section and outputs the logical value "1".

[0150] The logic gate A36 outputs the logical product of the negation of the output of the first opening / closing state acquisition unit 41, the output of the second opening / closing state acquisition unit 42, the output of the fifth interval calculation unit 55, and the output of the all interval calculation unit 59. Therefore, when the switch SX is in the open state, the switch SY is in the closed state, the absolute value Id5 of the sum of the terminal currents in the fifth interval is greater than the threshold value Tap5, and the absolute value Idall of the sum of the terminal currents in all intervals is greater than the threshold value Tapall, the logic gate A36 determines that the fifth interval is an internal fault interval and outputs a logical value of "1".

[0151] In the above, as in the cases of the first and second embodiments, when an internal fault is judged in a partial section from section 1 to section 5, not only the current differential relay calculation result based on the terminal current of the partial section but also the current differential relay calculation result based on the terminal current of all sections are included in the judgment conditions. This makes it possible to prevent malfunction of the protective relay during the opening and closing of the switch SX and during the periods before and after, which has the advantage of enabling the transmission line to continue being protected even when the protection section is switched.

[0152] The section protection command generating unit 70 generates a protection command for each minimum section divided by all switches (therefore, each minimum section does not include a switch inside), if the minimum section is included in the fault section. In the case of the multi-terminal power transmission system 8 to which the protection system 4 of the third embodiment is applied, the minimum sections are the first section, the second section, and the third section.

[0153] Specifically, the section protection command generation unit 70 includes a logic gate O21 for generating a protection command 131 for the first section, a logic gate O22 for generating a protection command 132 for the second section, and a logic gate O23 for generating a protection command 133 for the third section.

[0154] The logic gate O21 outputs the logical sum of the output of the logic gate A31, the output of the logic gate A32, and the output of the logic gate A35. Therefore, when all sections, the first section, or the fourth section is a fault section, the logic gate O21 outputs a logical value of "1" as a protection command 131 for the first section, which is the smallest section.

[0155] The logic gate O22 outputs the logical sum of the outputs of the logic gates A31, A33, A35, and A36. Therefore, when all sections, the second section, the fourth section, or the fifth section is a fault section, the logic gate O22 outputs a logical value of "1" as a protection command 132 for the second section, which is the smallest section.

[0156] The logic gate O23 outputs the logical sum of the output of the logic gate A31, the output of the logic gate A34, and the output of the logic gate A36. Therefore, when all sections, the third section, or the fifth section is a fault section, the logic gate O23 outputs a logical value of "1" as a protection command 133 for the third section, which is the smallest section.

[0157] 15, terminal protection command generation unit 140 generates a protection command for each terminal (terminal A to terminal F) constituting multi-terminal power transmission system 8 of Fig. 13 based on protection commands 131 to 133 for each minimum section output from section protection command generation unit 70. As shown in Fig. 16, terminal protection command generation unit 140 includes registers 141 to 149, 151 to 159 for setting information regarding which minimum section each terminal is included in, and logic gates A41 to A49, A51 to A59, and O31 to O36.

[0158] Register 141 is set to "1" if end A is included in the first section, and is set to "0" if not. Register 142 is set to "1" if end A is included in the second section, and is set to "0" if not. Register 143 is set to "1" if end A is included in the third section, and is set to "0" if not.

[0159] Similarly, register 144 is set to "1" if end B is included in the first section, and is set to "0" if not. Register 145 is set to "1" if end B is included in the second section, and is set to "0" if not. Register 146 is set to "1" if end B is included in the third section, and is set to "0" if not.

[0160] Register 147 is set to "1" if the C end is included in the first section, and is set to "0" if not. Register 148 is set to "1" if the C end is included in the second section, and is set to "0" if not. Register 149 is set to "1" if the C end is included in the third section, and is set to "0" if not.

[0161] Register 151 is set to "1" if terminal D is included in the first section, and is set to "0" if not. Register 152 is set to "1" if terminal D is included in the second section, and is set to "0" if not. Register 153 is set to "1" if terminal D is included in the third section, and is set to "0" if not.

[0162] Register 154 is set to "1" if end E is included in the first section, and is set to "0" if not. Register 155 is set to "1" if end E is included in the second section, and is set to "0" if not. Register 156 is set to "1" if end E is included in the third section, and is set to "0" if not.

[0163] Register 157 is set to "1" if the F terminal is included in the first section, and is set to "0" if not. Register 158 is set to "1" if the F terminal is included in the second section, and is set to "0" if not. Register 159 is set to "1" if the F terminal is included in the third section, and is set to "0" if not.

[0164] Therefore, in the case of the multi-terminal power transmission system 8 shown in FIG. 13, the registers 141, 144, 148, 152, 156, and 159 are set to "1," and the other registers are set to "0."

[0165] Logic gate A41 outputs the logical product of protection command 131 for the first section output from logic gate O21 and the setting value ("1") of register 141. Logic gate A42 outputs the logical product of protection command 132 for the second section output from logic gate O22 and the setting value ("0") of register 142. Logic gate A43 outputs the logical product of protection command 133 for the third section output from logic gate O23 and the setting value ("0") of register 143. Logic gate O31 outputs the logical sum of logic gate A41, logic gate A42, and logic gate A43. Therefore, when the first section is included in the fault section in the multi-terminal power transmission system 8 of FIG. 13, logic gate O31 transmits a logical value of "1" as protection command 161 at the A end to each merging unit MU via network 90.

[0166] Similarly, logic gate A44 outputs the logical product of protection command 131 for the first section output from logic gate O21 and the setting value (“1”) of register 144. Logic gate A45 outputs the logical product of protection command 132 for the second section output from logic gate O22 and the setting value (“0”) of register 145. Logic gate A46 outputs the logical product of protection command 133 for the third section output from logic gate O23 and the setting value (“0”) of register 146. Logic gate O32 outputs the logical sum of logic gates A44, A45, and A46. Therefore, when the first section is included in the fault section in the multi-terminal power transmission system 8 of FIG. 13 , logic gate O32 transmits a logical value “1” as protection command 162 at end B to each merging unit MU via network 90.

[0167] Logic gate A47 outputs the logical product of protection command 131 for the first section output from logic gate O21 and the setting value (“0”) of register 147. Logic gate A48 outputs the logical product of protection command 132 for the second section output from logic gate O22 and the setting value (“1”) of register 148. Logic gate A49 outputs the logical product of protection command 133 for the third section output from logic gate O23 and the setting value (“0”) of register 149. Logic gate O33 outputs the logical sum of logic gate A47, logic gate A48, and logic gate A49. Therefore, when the second section is included in the fault section in the multi-terminal power transmission system 8 of FIG. 13 , logic gate O33 transmits a logical value “1” as the C-end protection command 163 to each merging unit MU via network 90.

[0168] Logic gate A51 outputs the logical product of protection command 131 for the first section output from logic gate O21 and the setting value (“0”) of register 151. Logic gate A52 outputs the logical product of protection command 132 for the second section output from logic gate O22 and the setting value (“1”) of register 152. Logic gate A53 outputs the logical product of protection command 133 for the third section output from logic gate O23 and the setting value (“0”) of register 153. Logic gate O34 outputs the logical sum of the outputs of logic gate A51, logic gate A52, and logic gate A53. Therefore, when the second section is included in the fault section in the multi-terminal power transmission system 8 of FIG. 13 , logic gate O34 transmits a logical value “1” as protection command 164 at the D terminal to each merging unit MU via network 90.

[0169] Logic gate A54 outputs the logical product of protection command 131 for the first section output from logic gate O21 and the setting value (“0”) of register 154. Logic gate A55 outputs the logical product of protection command 132 for the second section output from logic gate O22 and the setting value (“0”) of register 155. Logic gate A56 outputs the logical product of protection command 133 for the third section output from logic gate O23 and the setting value (“1”) of register 156. Logic gate O35 outputs the logical sum of logic gate A54, logic gate A55, and logic gate A56. Therefore, when the third section is included in the fault section in the multi-terminal power transmission system 8 of FIG. 13 , logic gate O35 transmits a logical value “1” as E-end protection command 165 to each merging unit MU via network 90.

[0170] Logic gate A57 outputs the logical product of protection command 131 for the first section output from logic gate O21 and the setting value (“0”) of register 157. Logic gate A58 outputs the logical product of protection command 132 for the second section output from logic gate O22 and the setting value (“0”) of register 158. Logic gate A59 outputs the logical product of protection command 133 for the third section output from logic gate O23 and the setting value (“1”) of register 159. Logic gate O36 outputs the logical sum of the outputs of logic gate A57, logic gate A58, and logic gate A59. Therefore, when the third section is included in the fault section in the multi-terminal power transmission system 8 of FIG. 13 , logic gate O36 transmits a logical value “1” as protection command 166 at the F end to each merging unit MU via network 90.

[0171] When each merging unit MU receives a protection command for its own end from the common control device 92 via the network 90, it outputs a breaker command to the circuit breaker CB at its own end.

[0172] [Variations] Fig. 17 is a diagram showing a modification of the block diagram of Fig. 15. In the case of Fig. 15, the protection relay calculation unit 50 performs protection relay calculation for all sections from section 1 to section 5, regardless of the open / close states of the switches SX and SY. In contrast, in the case of Fig. 17, the sections for which protection relay calculation is performed are limited depending on the open / close states of the switches SX and SY, so the amount of calculation performed can be reduced. This will be explained in detail below with reference to Fig. 17.

[0173] As shown in Fig. 17, the calculation processing unit 100 of the modified common control device 92 includes a switch opening / closing state acquisition unit 40, a fault section determination unit 170, a section protection command generation unit 70, and the terminal protection command generation unit 140 of Fig. 16. The configuration of the switch opening / closing state acquisition unit 40 is the same as in Fig. 15, so the same or corresponding parts are given the same reference symbols and descriptions will not be repeated.

[0174] The fault section determination unit 170 determines whether or not there is a fault section in which an internal fault has occurred, based on the information on the open / close states of the switches SX and SY output from the open / close state acquisition unit 40 and the protective relay calculation results for each section by the protective relay calculation unit 50. As shown in FIG. 17 , the fault section determination unit 170 includes a protective section identification unit 171, a protective relay calculation unit 50, and a fault section identification unit 172.

[0175] The protection section specification unit 171 determines the protection section that is currently set as the target of the current differential relay calculation based on the information on the open / close states of the switches SX and SY output from the open / close state acquisition unit 40. Specifically, the protection section specification unit 171 includes logic gates A61 to A66.

[0176] The logic gate A61 outputs the logical product of the output of the first opening / closing state acquisition unit 41 and the output of the second opening / closing state acquisition unit 42. Therefore, the logic gate A61 outputs a logical value of "1" when the entire section of the multi-terminal power transmission system 8 is set as the protection section.

[0177] The logic gate A62 outputs the negation of the output of the first opening / closing state acquisition unit 41. Therefore, the logic gate A62 outputs a logical value of "1" when the first section is set as the protection section by opening the switch SX.

[0178] The logic gate A63 outputs the logical product of the negation of the output of the first opening / closing state acquisition unit 41 and the negation of the output of the second opening / closing state acquisition unit 42. Therefore, the logic gate A63 outputs a logical value of "1" when the second section is set as the protection section by opening both of the switches SX and SY.

[0179] The logic gate A64 outputs the negation of the output of the second opening / closing state acquisition unit 42. Therefore, the logic gate A64 outputs a logical value of "1" when the third section is set as the protection section by opening the switch SY.

[0180] Logic gate A65 outputs the logical product of the output of first opening / closing state acquisition unit 41 and the negation of the output of second opening / closing state acquisition unit 42. Therefore, logic gate A65 outputs a logical value of "1" when switch SX is closed and switch SY is opened, thereby setting the fourth zone as the protection zone.

[0181] Logic gate A66 outputs the logical product of the negation of the output of first opening / closing state acquisition unit 41 and the output of second opening / closing state acquisition unit 42. Therefore, logic gate A66 outputs a logical value of "1" when switch SX is opened and switch SY is closed, thereby setting the fifth section as the protection section.

[0182] The protection relay calculation unit 50 basically has the same configuration as in Fig. 15, and includes a first section calculation unit 51, a second section calculation unit 52, a third section calculation unit 53, a fourth section calculation unit 54, a fifth section calculation unit 55, and a whole section calculation unit 59. However, each calculation unit performs protection relay calculation only when the corresponding section is set as a protection section.

[0183] Specifically, when logic gate A62 outputs a logical value of "1," first interval calculation unit 51 calculates the absolute value Id1 of the sum of terminal A detection current I1 and terminal B detection current I2 included in the first interval, and outputs a logical value of "1" if the calculation result is greater than threshold Tap1, and outputs a logical value of "0" otherwise. When logic gate A62 outputs a logical value of "0," first interval calculation unit 51 outputs a logical value of "0" without performing a relay calculation.

[0184] When logic gate A63 outputs a logical value of "1", second interval calculation unit 52 calculates the absolute value Id2 of the sum of C-terminal detection current I3 and D-terminal detection current I4 included in the second interval, and outputs a logical value of "1" if the calculation result is greater than threshold Tap2, and outputs a logical value of "0" otherwise. When logic gate A63 outputs a logical value of "0", second interval calculation unit 52 outputs a logical value of "0" without performing a relay calculation.

[0185] When logic gate A64 outputs a logical value of "1", third interval calculation unit 53 calculates the absolute value Id3 of the sum of E-terminal detection current I5 and F-terminal detection current I6 included in the third interval, and outputs logical value "1" if the calculation result is greater than threshold Tap3, and outputs logical value "0" otherwise. When logic gate A64 outputs a logical value of "0", third interval calculation unit 53 outputs logical value "0" without performing relay calculation.

[0186] When logic gate A65 outputs a logical value of "1", fourth interval calculation unit 54 calculates the absolute value of the sum of the terminal currents at terminals A, B, C, and D included in the fourth interval, i.e., the absolute value of I1+I2+I3+I4, and outputs a logical value of "1" if the calculation result is greater than threshold Tap4, and outputs a logical value of "0" otherwise. When logic gate A65 outputs a logical value of "0", fourth interval calculation unit 54 outputs a logical value of "0" without performing a relay calculation.

[0187] When logic gate A66 outputs a logical value of "1", fifth interval calculation unit 55 calculates the absolute value of the sum of the terminal currents of terminals C, D, E, and F included in the fifth interval, i.e., the absolute value of I3+I4+I5+I6, and outputs a logical value of "1" if the calculation result is greater than threshold Tap5, and outputs a logical value of "0" otherwise. When logic gate A66 outputs a logical value of "0", fifth interval calculation unit 55 outputs a logical value of "0" without performing a relay calculation.

[0188] The all-section calculation unit 59 calculates the absolute value of the sum of the terminal currents of all sections, i.e., the absolute value Idall of I1+I2+I3+I4+I5+I6, regardless of the open / closed state of the switches SX and SY, and outputs the logical value "1" if the calculation result is greater than the threshold Tapall, and outputs the logical value "0" if not.

[0189] The fault section identification unit 172 identifies whether each of the first to fifth sections and all sections is a fault section based on the output from the protection relay calculation unit 50, and outputs information about the fault section. As shown in Fig. 17, the fault section identification unit 172 includes logic gates A71 to A76.

[0190] The logic gate A71 outputs the logical product of the output of the logic gate A61 and the output of the logic gate A59. Therefore, when the switches SX and SY are both in the closed state and the absolute value Idall of the sum of the terminal currents in all sections is greater than the threshold Tapall, the logic gate A71 determines that the entire section is an internal fault section and outputs a logical value of "1."

[0191] The logic gate A72 outputs a logical product of the output of the first interval calculation unit 51 and the output of the full interval calculation unit 59, thereby outputting a logical value of "1" if the first interval is an internal fault interval. The logic gate A73 outputs a logical product of the output of the second interval calculation unit 52 and the output of the full interval calculation unit 59, thereby outputting a logical value of "1" if the second interval is an internal fault interval. The logic gate A74 outputs a logical product of the output of the third interval calculation unit 53 and the output of the full interval calculation unit 59, thereby outputting a logical value of "1" if the third interval is an internal fault interval. The logic gate A75 outputs a logical product of the output of the fourth interval calculation unit 54 and the output of the full interval calculation unit 59, thereby outputting a logical value of "1" if the fourth interval is an internal fault interval. The logic gate A76 outputs a logical product of the output of the fifth interval calculation unit 55 and the output of the full interval calculation unit 59, thereby outputting a logical value of "1" if the fifth interval is an internal fault interval.

[0192] In the above, as in the case of Fig. 15, when internal fault judgment is performed on the partial sections from Section 1 to Section 5, not only the current differential relay calculation result based on the terminal current of the partial section but also the current differential relay calculation result based on the terminal current of the entire section are included in the judgment conditions. This has the advantage that malfunction of the protective relay can be prevented even during the opening and closing of the switch SX and the periods before and after, so that the transmission line can be continuously protected even when the protection section is switched.

[0193] 15, the section protection command generation unit 70 includes a logic gate O21 for generating a protection command 131 for the first section as the minimum section, a logic gate O22 for generating a protection command 132 for the second section as the minimum section, and a logic gate O23 for generating a protection command 133 for the third section as the minimum section. The protection commands 131 to 133 for each section are input to the terminal protection command generation unit 140 of FIG.

[0194] Specifically, logic gate O21 outputs the logical sum of the output of logic gate A71, the output of logic gate A72, and the output of logic gate A75. Therefore, when all sections, the first section, or the fourth section is a fault section, logic gate O21 outputs a logical value of "1" as protection command 131 for the first section, which is the smallest section.

[0195] The logic gate O22 outputs the logical sum of the outputs of the logic gates A71, A73, A75, and A76. Therefore, when all sections, the second section, the fourth section, or the fifth section is a fault section, the logic gate O22 outputs a logical value of "1" as a protection command 132 for the second section, which is the smallest section.

[0196] The logic gate O23 outputs the logical sum of the output of the logic gate A71, the output of the logic gate A74, and the output of the logic gate A76. Therefore, when all sections, the third section, or the fifth section is a fault section, the logic gate O23 outputs a logical value of "1" as a protection command 133 for the third section, which is the smallest section.

[0197] [Summary of the third embodiment] In the third embodiment, a protection system 4 applied to a multi-terminal power transmission system 8 having a more complicated configuration than those in the first and second embodiments has been described.

[0198] Furthermore, in the third embodiment, a modified example of the fault section determination unit 60 has been described. Specifically, the fault section determination unit 170 includes a protection section identification unit 171, a protection relay calculation unit 50, and a fault section identification unit 172. The protection section identification unit 171 identifies the entire section or a partial section that is currently the target of current differential relay calculation as a protection section based on the open / close state of each of one or more switches SX and SY included in the multi-terminal power transmission system 8. The protection relay calculation unit 50 performs current differential relay calculation using terminal currents in the entire section, and also performs current differential relay calculation for each protection section when the protection section is a partial section. The fault section identification unit 172 identifies a protection section that has an internal fault based on the result of the current differential relay calculation by the protection relay calculation unit. As described above, the fault section identification unit 172 determines that an internal fault has occurred in a partial section determined by the open / closed states of the switches SX and SY included in the multi-terminal power transmission system 8 when the absolute value of the sum of the terminal currents of each terminal in the partial section exceeds a first threshold value and the absolute value of the sum of the terminal currents of each terminal in the entire section exceeds a second threshold value.

[0199] The fault section determination unit 170 having the above configuration can be combined with either the first or second embodiment.

[0200] Various aspects of the present disclosure are summarized below as appendices. (Appendix 1) 1. A protection system for a multi-terminal power transmission system, comprising: the multi-terminal power transmission system includes four or more terminals and one or more switches, and at least one of the one or more switches is opened, thereby dividing an entire section of the multi-terminal power transmission system into a plurality of subsections, each of which includes two or more terminals; The protection system comprises: a current transformer provided at each terminal of the multi-terminal power transmission system for detecting a terminal current at the terminal; an opening / closing state acquisition unit that acquires information on the opening / closing state of each of the one or more switches; a fault section determination unit that determines whether an internal fault has occurred in the entire section or any partial section of the multi-terminal power transmission system using a current differential method based on the detected values ​​of terminal currents at each terminal of the multi-terminal power transmission system and the open / closed state of each of the one or more switches, A protection system for a multi-terminal power transmission system, wherein the fault section determination unit determines that an internal fault has occurred in a partial section when the absolute value of the sum of the terminal currents of each terminal of the partial section determined by the open / closed state of the one or more switches exceeds a first threshold value and the absolute value of the sum of the terminal currents of each terminal of the entire section exceeds a second threshold value.

[0201] (Appendix 2) 2. A protection system for a multi-terminal power transmission system as described in Appendix 1, wherein the fault section determination unit continues to determine whether or not an internal fault exists before and after an opening or closing operation is performed on any of the one or more switches.

[0202] (Appendix 3) The protection system includes a plurality of protection relays connected to each other via a communication line; each of the plurality of protective relays is provided corresponding to a terminal of the multi-terminal power transmission system, and acquires a terminal current value from the current transformer of its own terminal, and acquires terminal current values ​​of other terminals from other protective relays via the communication line; 3. The protection system for a multi-terminal power transmission system according to claim 1, wherein each of the plurality of protection relays includes the open / close state acquisition unit and the fault section determination unit, and outputs a trip signal to open a circuit breaker provided at the own terminal when the fault section determination unit determines that an internal fault has occurred in the entire section or a partial section including the own terminal.

[0203] (Appendix 4) The protection system includes a plurality of merging units and a common control device; the plurality of merging units and the common control device are connected to each other via a communication line; Each of the plurality of merging units is provided corresponding to a terminal of the multi-terminal power transmission system, acquires a terminal current value from the current transformer of the terminal, and transmits the acquired terminal current value to the common control device via the communication line; The protection system for a multi-terminal power transmission system according to claim 1 or 2, wherein the common control device includes the opening / closing state acquisition unit and the fault section determination unit, and when the fault section determination unit determines that an internal fault has occurred in the entire section or any partial section, transmits a protection command to each merging unit via the communication line to protect the multi-terminal power transmission system.

[0204] (Appendix 5) the protection command includes information for identifying a fault section in which an internal fault has occurred, A protection system for a terminal power transmission system as described in Appendix 4, wherein each merging unit outputs a trip signal to open a circuit breaker provided at its own terminal when its own terminal is included in the fault section based on the received protection command.

[0205] (Appendix 6) the protection command includes information for identifying a terminal included in a fault section in which an internal fault has occurred, A protection system for a terminal power transmission system as described in Appendix 4, wherein each merging unit outputs a trip signal to open a circuit breaker provided at its own terminal when its own terminal corresponds to a terminal included in the fault section based on the received protection command.

[0206] (Appendix 7) The fault section determination unit a protection section identification unit that identifies, based on the open / closed state of each of the one or more switches, the entire section or a partial section that is currently the target of current differential relay calculation as a protection section; a protection relay calculation unit that performs a current differential relay calculation using terminal currents of all sections and, when the protection section is a partial section, performs a current differential relay calculation for each protection section; A protection system for a multi-terminal power transmission system according to any one of appendices 1 to 6, including a fault section identification unit that identifies a protection section having an internal fault based on the result of the current differential relay calculation by the protection relay calculation unit.

[0207] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of this application is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0208] 1, 3, 4 Protection system, 2 Communication line, 7, 8 Multi-terminal power transmission system, 10 Input converter, 11 Analog filter, 12 Sample-and-hold circuit, 13 Multiplexer, 14 Converter, 20, 30, 100 Processing unit, 22, 32, 102 RAM, 23, 33, 103 ROM, 24, 34, 104 Bus, 26, 36, 106 Communication circuit, 27, 37 Digital output circuit, 28, 38 Digital input circuit, 40 Switching status acquisition unit, 41 First switching status acquisition unit, 42 Second switching status acquisition unit, 50 Protection relay calculation unit, 51 First section calculation unit, 52 Second section calculation unit, 53 Third section calculation unit, 54 Fourth section calculation unit, 55 Fifth section calculation unit, 59 Total section calculation unit, 60, 170 Fault section determination unit, 70 Section protection command generation unit, 71, 72, 121 to 124, 131 to 133, 161 to 166 protection command, 80 tripping command generation unit, 81, 82, 111 to 118, 126A to 126D, 141 to 149, 151 to 159 register, 83 tripping command, 90 network (communication line), 91 synchronization master, 92 common control device, 110, 140 terminal protection command generation unit, 171 protection section identification unit, 172 fault section identification unit, A1 to A5, A11 to A18, A21 to A24, A31 to A36, A41 to A49, A51 to A59, A61 to A66, A71 to A76 logic gate (AND circuit), O1 to O3, O11 to O14, O21 to O23, O31 to O36 Logic gate (OR circuit), B~B6 busbars, CB circuit breaker, CNTL switch controller, CT current transformer, I1~I6 terminal current, Id1~Id5, Idall absolute value of the sum of terminal currents, J1~J4 branch points, L1~L5 transmission lines, MU merging unit, RY protection relay, SX, SY switches, SW network switch, Tap1~Tap5, Tapall threshold value.

Claims

1. 1. A protection system for a multi-terminal power transmission system, comprising: the multi-terminal power transmission system includes four or more terminals and one or more switches, and at least one of the one or more switches is opened, thereby dividing an entire section of the multi-terminal power transmission system into a plurality of subsections, each of which includes two or more terminals; The protection system comprises: a current transformer provided at each terminal of the multi-terminal power transmission system for detecting a terminal current at the terminal; an opening / closing state acquisition unit that acquires information on the opening / closing state of each of the one or more switches; a fault section determination unit that determines whether an internal fault has occurred in the entire section or any partial section of the multi-terminal power transmission system using a current differential method based on the detected values ​​of terminal currents at each terminal of the multi-terminal power transmission system and the open / closed state of each of the one or more switches, A protection system for a multi-terminal power transmission system, wherein the fault section determination unit determines that an internal fault has occurred in a partial section when the absolute value of the sum of the terminal currents of each terminal of the partial section determined by the open / closed state of the one or more switches exceeds a first threshold value and the absolute value of the sum of the terminal currents of each terminal of the entire section exceeds a second threshold value.

2. The protection system for a multi-terminal power transmission system according to claim 1 , wherein the fault section determination unit continues to determine whether or not an internal fault exists before and after an opening operation or a closing operation is performed in any of the one or more switches.

3. The protection system includes a plurality of protection relays connected to each other via a communication line; each of the plurality of protective relays is provided corresponding to a terminal of the multi-terminal power transmission system, and acquires a terminal current value from the current transformer of its own terminal, and acquires terminal current values ​​of other terminals from other protective relays via the communication line; 3. The protection system for a multi-terminal power transmission system according to claim 1, wherein each of the plurality of protective relays includes the open / close state acquisition unit and the fault section determination unit, and when the fault section determination unit determines that an internal fault has occurred in the entire section or a partial section including the own terminal, outputs a trip signal to open a circuit breaker provided at the own terminal.

4. The protection system includes a plurality of merging units and a common control device; the plurality of merging units and the common control device are connected to each other via a communication line; Each of the plurality of merging units is provided corresponding to a terminal of the multi-terminal power transmission system, acquires a terminal current value from the current transformer of the terminal, and transmits the acquired terminal current value to the common control device via the communication line; 3. The protection system for a multi-terminal power transmission system according to claim 1 or 2, wherein the common control device includes the opening / closing state acquisition unit and the fault section determination unit, and when the fault section determination unit determines that an internal fault has occurred in the entire section or any partial section, transmits a protection command to each merging unit via the communication line to protect the multi-terminal power transmission system.

5. the protection command includes information for identifying a fault section in which an internal fault has occurred, 5. The protection system for a terminal power transmission system according to claim 4, wherein each merging unit outputs a trip signal for opening a circuit breaker provided at its own terminal when its own terminal is included in the fault section based on the received protection command.

6. the protection command includes information for identifying a terminal included in a fault section in which an internal fault has occurred, 5. The protection system for a terminal power transmission system according to claim 4, wherein each merging unit outputs a trip signal to open a circuit breaker provided at its own terminal when its own terminal corresponds to a terminal included in the fault section based on the received protection command.

7. The fault section determination unit a protection section identification unit that identifies, based on the open / closed state of each of the one or more switches, the entire section or a partial section that is currently the target of current differential relay calculation as a protection section; a protection relay calculation unit that performs a current differential relay calculation using terminal currents of all sections and, when the protection section is a partial section, performs a current differential relay calculation for each protection section; 3. The protection system for a multi-terminal power transmission system according to claim 1, further comprising: a fault section identification unit that identifies a protection section having an internal fault based on a result of the current differential relay calculation by the protection relay calculation unit.

Images