Protective relay device

Abstract

This invention provides a protective relay device that can accurately detect CT wire breakage using a simple method. [Solution] The protective relay device includes a current acquisition unit that acquires a first instantaneous current value from a first current transformer and a second instantaneous current value from a second current transformer; a current differential relay unit that determines whether or not a fault has occurred in the protected object based on the operating amount and suppression amount calculated from the first instantaneous current value and the second instantaneous current value; and a wire break detection unit that determines that a wire break has occurred in the first current transformer when a specified condition is met. The wire break detection unit calculates the vector sum of the differential currents of each phase as the first vector, calculates the vector sum of the currents of each phase flowing to the first end as the second vector, and calculates the sum of the first vector and the inverse vector of the second vector as the third vector. The specified condition includes a first condition that the effective value of the third vector is less than a first threshold.

Description

Technical Field

[0001] This disclosure relates to a protective relay device.

Background Art

[0002] Conventionally, the following methods are known as methods for detecting disconnection of the secondary cable of a current transformer (CT: Current Transformer) connected to a differential current relay (i.e., CT disconnection).

[0003] Japanese Patent Application Laid-Open No. 2005-39956 (Patent Document 1) considers preventing unnecessary operation of a differential protection relay by detecting a CT circuit failure at high speed and controlling the output of the protection device when a CT circuit failure occurs during normal operation.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Document 1 discloses a method for detecting CT disconnection using a virtual current obtained from the current vectors of terminals that detect unbalance of three-phase currents. Specifically, when the CT of one phase (for example, phase A) is disconnected, a virtual current is created from the currents of the other two phases excluding the phase A current. Also, when the CTs of two phases (for example, phases B and C) are disconnected, virtual currents that are advanced by 120 degrees and delayed by 120 degrees are created for the phase A current excluding the phase B and phase C currents. Thus, there is a problem in that complicated processing for creating different virtual currents according to disconnection of one phase or two phases of the CT is required.

[0006] One objective of this disclosure is to provide a protective relay device that can accurately detect CT wire breakage using a simple method. [Means for solving the problem]

[0007] A protective relay device according to one embodiment includes a current acquisition unit that acquires a first instantaneous current value from a first current transformer provided on each phase at the first end of the power system to be protected, and a second instantaneous current value from a second current transformer provided on each phase at the second end of the power system to be protected; a current differential relay unit that determines whether or not a fault has occurred in the protected system based on an operating amount and a suppression amount calculated from the first instantaneous current value and the second instantaneous current value; and a wire break detection unit that determines that a wire break has occurred in the first current transformer when a specified condition is met. The wire break detection unit calculates the vector sum of the differential currents of each phase of the power system as a first vector based on the first instantaneous current value and the second instantaneous current value, calculates the vector sum of the currents of each phase flowing on the first end as a second vector based on the first instantaneous current value, and calculates the sum of the first vector and the inverse vector of the second vector as a third vector. The specified condition includes a first condition that the effective value of the third vector is less than a first threshold.

[0008] A protective relay device according to another embodiment includes a current acquisition unit that acquires a first instantaneous current value from a first current transformer provided on each phase at the first end of the power system to be protected, and a second instantaneous current value from a second current transformer provided on each phase at the second end of the power system to be protected; a current differential relay unit that determines whether or not a fault has occurred in the protected system based on an operating amount and a suppression amount calculated from the first instantaneous current value and the second instantaneous current value; and a wire break detection unit that determines that a wire break has occurred in the first current transformer when a specified condition is met. The wire break detection unit calculates the vector sum of the differential currents of each phase of the power system as a first vector based on the first instantaneous current value and the second instantaneous current value, identifies one or more phases corresponding to the vectors of the differential currents of each phase that have an effective value less than a first threshold, calculates the vector sum of the currents of one or more phases flowing at the first end as a second vector based on the first instantaneous current value, and calculates the sum of the first vector and the inverse vector of the second vector as a third vector. The predefined conditions include a first condition that the effective value of the third vector is less than the first threshold. [Effects of the Invention]

[0009] According to this disclosure, the objective is to provide a protective relay device that can accurately detect CT wire breakage using a simple method. [Brief explanation of the drawing]

[0010] [Figure 1] This diagram shows a power system to which a protective relay device according to this embodiment is applied. [Figure 2] This figure shows an example of the hardware configuration of a protective relay device according to this embodiment. [Figure 3] This is a block diagram showing an example of the functional configuration of a protective relay device. [Figure 4] This shows the relationship between the current vector and the differential current vector when a single-phase CT circuit is disconnected. [Figure 5] This shows the relationship between the current vector and the differential current vector when a two-phase CT circuit is broken. [Figure 6]This shows the relationship between the current vector and the differential current vector during a single-phase ground fault in a single-ended power supply. [Figure 7] This shows the relationship between the current vector and the differential current vector during a single-phase ground fault in a power supply at both ends. [Figure 8] This figure shows an example of the functional configuration of the CT wire break detection unit according to Embodiment 1. [Figure 9] This figure shows an example of the functional configuration of the CT wire break detection unit according to Embodiment 2. [Figure 10] This figure shows another example of the functional configuration of the CT wire break detection unit according to Embodiment 2. [Modes for carrying out the invention]

[0011] This embodiment will be described below with reference to the drawings. In the following description, identical parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions of them will not be repeated.

[0012] [Basic configuration of each embodiment] <Overall Structure> Figure 1 shows a power system to which a protective relay device according to this embodiment is applied. Referring to Figure 1, the power system is equipped with AC power sources 11 and 12, current transformers 21 and 22, circuit breakers 31 and 32, a protected object 50, and a protective relay device 10 for protecting the protected object 50. The number of circuit breakers and current transformers will vary depending on the number of terminals on the protected object, but for the sake of simplicity, the case where the protected object has two terminals will be described.

[0013] The protected items 50 include busbars, transformers, and transmission lines. The AC power sources 11 and 12 are three-phase (e.g., A-phase, B-phase, C-phase) AC power sources. Circuit breaker 31 is installed on the first end side of the protected items 50 (e.g., AC power source 11 side). Circuit breaker 32 is installed on the second end side of the protected items 50 (e.g., AC power source 12 side).

[0014] The current transformer 21 detects the alternating current I1 flowing through the line on the first end side. The current transformer 22 detects the alternating current I2 flowing through the line on the second end side. Specifically, since the AC power supplies 11 and 12 are three-phase AC power supplies, current transformers 21 are provided for each of the A-phase line, B-phase line, and C-phase line on the first end side, and current transformers 22 are provided for each of the A-phase line, B-phase line, and C-phase line on the second end side.

[0015] The current transformer 21 corresponding to the A phase detects the A-phase current Ia1 flowing through the A-phase line, the current transformer 21 corresponding to the B phase detects the B-phase current Ib1 flowing through the B-phase line, and the current transformer 21 corresponding to the C phase detects the C-phase current Ic1 flowing through the C-phase line. Similarly, the current transformer 22 corresponding to the A phase detects the A-phase current Ia2 flowing through the A-phase line, the current transformer 22 corresponding to the B phase detects the B-phase current Ib2 flowing through the B-phase line, and the current transformer 22 corresponding to the C phase detects the C-phase current Ic2 flowing through the C-phase line. The alternating current I1 is a general term for the A-phase current Ia1, B-phase current Ib1, and C-phase current Ic1. The alternating current I2 is a general term for the A-phase current Ia2, B-phase current Ib2, and C-phase current Ic2.

[0016] When the protection relay device 10 detects an internal accident (for example, a ground fault accident or a short circuit accident) within the protection range surrounded by the current transformers 21 and 22 by using the alternating current I1 received from the current transformer 21 and the alternating current I2 received from the current transformer 22, it outputs an opening command (for example, a trip signal TR) to the circuit breakers 31 and 32 installed at both ends of the protected object 50. As a result, the circuit breakers 31 and 32 are opened, and the protected object 50 is disconnected from the power system.

[0017] The protection relay device 10 performs a current differential relay operation based on the alternating current I1 and the alternating current I2, and detects an accident within the protection section based on the operation result. The relay element that performs the current differential relay operation detects an accident within the protection section by the differential current. Therefore, when a disconnection occurs in the secondary side cable of the current transformer connected to the protection relay device 10 (hereinafter, also simply referred to as "CT disconnection") in a state where there is a load current equal to or greater than the operating value of the relay element, the protection relay device 10 may malfunction because the differential current becomes equal to the load current. The protection relay device 10 according to the present embodiment has a CT disconnection detection function for detecting such a CT disconnection and locking the operating output of the relay element.

[0018] In the example of FIG. 1, the configuration in which the AC power supply 12 exists on the second end side has been described. However, the second end side may be a load end (that is, a non-power source). Also, for ease of explanation, when the load current flows from the AC power supply 11 to the AC power supply 12, the alternating currents I1 and I2 input from the current transformers 21 and 22 to the protection relay device 10 are of the same magnitude, and the phase of the alternating current I1 and the phase of the alternating current I2 are opposite phases. After the alternating currents I1 and I2 are input to the protection relay device 10, through filter processing and the like necessary to remove harmonics from the alternating currents I1 and I2, they are converted into digital time-series data by A / D conversion processing, and processing such as current differential relay operation is performed.

[0019] When the protection target 50 is a transmission line, the distance between the current transformer 21 and the current transformer 22 installed at both ends of the protection target 50 is large. Therefore, the two protection relay devices 10 installed at both ends perform A / D conversion processing on the currents acquired from the corresponding current transformers, take in the current data of the opposite end through the transmission device, and execute various processes. In this case, since the current data is transmitted through the transmission device, the current differential relay operation is performed using the data of the currents at both ends after the synchronization process, together with processes corresponding to sampling synchronization, transmission delay, and the like. Hereinafter, for ease of explanation, the protection target 50 is assumed to be, for example, a two-terminal bus.

[0020] <Hardware Configuration> Figure 2 shows an example of the hardware configuration of a protective relay device according to this embodiment. Referring to Figure 2, the protective relay device 10 includes an auxiliary transformer 51, a signal conversion unit 52, and an arithmetic processing unit 70.

[0021] The auxiliary transformer 51 takes in the current detected by the current transformers 21 and 22, converts it into a voltage signal suitable for signal processing in the relay's internal circuitry, and outputs it. The signal conversion unit 52 takes in the voltage signal output from the auxiliary transformer 51 and converts it into digital data. Specifically, the signal conversion unit 52 includes an analog filter, a sample-and-hold circuit, a multiplexer, and an A / D (Analog to Digital) converter.

[0022] The analog filter removes high-frequency components from the current waveform signal output from the auxiliary transformer 51. The sample-and-hold circuit samples the current waveform signal output from the analog filter at a predetermined sampling period. The multiplexer sequentially switches the waveform signals input from the sample-and-hold circuit in time series based on the timing signal input from the arithmetic processing unit 70 and inputs them to the A / D converter. The A / D converter converts the waveform signal input from the multiplexer from analog data to digital data. The A / D converter outputs the digitally converted waveform signal (i.e., digital data) to the arithmetic processing unit 70.

[0023] The arithmetic processing unit 70 is mainly composed of a microcomputer and includes a CPU (Central Processing Unit) 72, ROM 73, RAM 74, a digital input circuit 75 (corresponding to the DI (digital input) circuit in the figure), a digital output circuit 76 (corresponding to the DO (Digital output) circuit in the figure), and an input interface (I / F) 77. These are connected by a bus 71.

[0024] The CPU 72 controls the operation of the protective relay device 10 by reading and executing a program pre-stored in the ROM 73. The RAM 74, which is volatile memory, and the ROM 73, which is non-volatile memory, are used as the main memory of the CPU 72. The ROM 73 stores programs and setting values ​​for signal processing, etc.

[0025] The CPU 72 acquires digital data from the signal conversion unit 52 via the bus 71. The CPU 72 performs relay calculations using the acquired digital data according to the program stored in the ROM 73. Based on the results of each relay calculation, the CPU 72 determines whether or not there is a fault (i.e., detects a fault).

[0026] When the CPU 72 detects a fault, it outputs a signal to the outside via the digital output circuit 76. For example, the digital output circuit 76 outputs a trip signal TR to the circuit breakers 31 and 32. The CPU 72 receives signals from the outside via the digital input circuit 75. The input interface 77 is typically a set of buttons, etc., and accepts various setting operations from the system operator.

[0027] Furthermore, at least a portion of the protective relay device 10 may be configured using circuits such as FPGA (Field Programmable Gate Array) and ASIC (Application Specific Integrated Circuit). Also, at least a portion of the protective relay device 10 may be configured using analog circuits.

[0028] <Functional Configuration> Figure 3 is a block diagram showing an example of the functional configuration of a protective relay device. Referring to Figure 3, the protective relay device 10 includes, as its main functional configuration, a current acquisition unit 110, a current differential relay unit 120, a CT disconnection detection unit 130, and an output control unit 140. These functions are realized, for example, by a processing circuit included in the protective relay device 10. The processing circuit may be dedicated hardware, or it may be a CPU 72 that executes a program stored in the internal memory (e.g., ROM 73) of the protective relay device 10. If the processing circuit is dedicated hardware, it may be composed of, for example, an FPGA, an ASIC, or a combination thereof.

[0029] The current acquisition unit 110 acquires instantaneous current values ​​from current transformers 21 provided on each phase at the first end of the protected device 50, and instantaneous current values ​​from current transformers 22 provided on each phase at the second end of the protected device 50. Specifically, the current acquisition unit 110 acquires time-series instantaneous values ​​(i.e., instantaneous current values) sampled from each phase current (e.g., A phase current, B phase current, C phase current) flowing at the first end, which are detected by the current transformers 21 provided on each phase. The current acquisition unit 110 also acquires instantaneous current values ​​sampled from each phase current flowing at the second end, which are detected by the current transformers 22 provided on each phase.

[0030] The sampling and A / D conversion described above are performed by the signal conversion unit 52 described above. For example, the time-series instantaneous value data of the current I from time (tn) to time (t) is I(tn), ....I(t-1), I(t). Here, n represents the number of samples corresponding to the number of positive integer cycles. For example, if the number of positive integer cycles is 2 cycles, then n is the number of samples corresponding to the period of those 2 cycles. If the number of samples corresponding to 1 cycle is "12", then "n=24".

[0031] Assuming the current time is "t", the instantaneous current value from current transformer 21 is "AC current I1(t)", and the instantaneous current value from current transformer 22 is "AC current I2(t)". ​​Furthermore, the instantaneous current values ​​of each phase current flowing on the first end are expressed as A-phase current Ia1(t), B-phase current Ib1(t), and C-phase current Ic1(t), and the instantaneous current values ​​of each phase current flowing on the second end are expressed as A-phase current Ia2(t), B-phase current Ib2(t), and C-phase current Ic2(t).

[0032] The current differential relay unit 120 receives inputs of AC current I1 and AC current I2. The AC currents I1 and I2 input to these units are assumed to be of the same magnitude and in opposite phase to each other when the load is active. The current differential relay unit 120 determines whether a fault has occurred in the protected object 50 based on the operating amount and suppression amount calculated from the instantaneous values ​​of AC current I1 and AC current I2.

[0033] Specifically, the current differential relay section 120 calculates the operating amount and suppression amount for each of the three phases (A phase, B phase, and C phase), and performs fault detection for each phase. For example, the operating amount IOP(t) at time t is expressed as "IOP(t)=|I1(t)+I2(t)|". The suppression amount IRE(t) at time t is expressed as "IRE(t)=|IP(t)|+|IQ(t)|". Here, |X| represents the effective value of vector X.

[0034] Generally, if the condition “IOP(t)≧C1×IRE(t)+C2” is met, it is determined that a fault has occurred in protected device 50. “C1” is the ratio setting value (e.g., less than 0.5), and “C2” is the minimum setting value (e.g., 30% of the rated current value).

[0035] The CT disconnection detection unit 130 determines whether a CT disconnection has occurred in the current transformers 21 and 22 based on the instantaneous value of the AC current I1 and the instantaneous value of the AC power supply 12. The CT disconnection detection unit 130 outputs the determination result to the output control unit 140 and the CT disconnection alarm unit 150. The detailed operation of the CT disconnection detection unit 130 will be described later.

[0036] The output control unit 140 receives the determination result of an internal fault by the current differential relay unit 120 and the determination result of CT disconnection by the CT disconnection detection unit 130. In the example of FIG. 3, the output control unit 140 is composed of an AND gate. Specifically, when it is determined by the current differential relay unit 120 that an internal fault has occurred (i.e., the output value of the current differential relay unit 120 is “1”) and it is determined by the CT disconnection detection unit 130 that no CT disconnection has occurred (the output value of the CT disconnection detection unit 130 is “0”), the output control unit 140 outputs an opening command to the circuit breakers 31 and 32.

[0037] When it is determined by the CT disconnection detection unit 130 that CT disconnection has occurred, the output of the current differential relay unit 120 is blocked. That is, the CT disconnection detection unit 130 has a locking function for locking the output of an opening command for protecting the protected object 50 when CT disconnection occurs.

[0038] When it is determined by the CT disconnection detection unit 130 that CT disconnection has occurred, the CT disconnection alarm unit 150 issues an alarm by sound, light, or screen display, etc. Note that the CT disconnection alarm unit 150 may be a functional configuration included in the protection relay device 10 or a functional configuration realized by a device separate from the protection relay device 10.

[0039] Embodiment 1. <CT Disconnection Detection Method> (During single-phase CT disconnection) FIG. 4 shows the relationship between the current vector and the differential current vector during single-phase CT disconnection. In the example of FIG. 4, the relationship between the current vector and the differential current vector when CT disconnection occurs in the current transformer 21 of one phase (for example, phase A) when there is a three-phase balanced load current is shown. Specifically, FIG. 4(a) shows the relationship between the current vectors of each phase on the first terminal side and the zero-phase current (i.e., 3I01) vector. FIG. 4(b) shows the relationship between the current vectors of each phase on the second terminal side. FIG. 4(c) shows the relationship between the differential current vectors of each phase.

[0040] The protection relay device 10 (CT disconnection detection unit 130) calculates 3I01(t), which is the vector sum of the A-phase current Ia1(t), B-phase current Ib1(t), and C-phase current Ic1(t) flowing through the first end side. Here, since a CT disconnection has occurred in the current transformer 21 provided in the A-phase, "Ia1(t)=0". Therefore, 3I01(t) is represented by the following equation (1).

[0041] 3I01(t)=Ia1(t)+Ib1(t)+Ic1(t)=0+Ib1(t)+Ic1(t)=-Ia1e(t)…(1) As shown in FIG. 4(a), the vector 3I01 corresponds to the inverse vector "-Ia1e" of the A-phase current vector Ia1e when it is assumed that the above CT disconnection has not occurred (or before the CT disconnection). The effective value of the vector 3I01 during CT disconnection becomes the effective value IL of the load current. Only the alternating current I2 (here, corresponding to the load current) is input to the protection relay device 10 for the CT disconnection phase. Therefore, for the operating quantity IOP and the restraining quantity IRE used in the above operation determination formula, "IOP=IL" and "IRE=IL" hold. Therefore, since "IL≧C1×IL+C2" becomes the operating condition, the current differential relay unit 120 operates when the load current satisfies "IL≧C2 / (1-C1)".

[0042] From this, it is necessary to detect CT disconnection using a threshold value Kz that is less than "C2 / (1-C1)". When the effective value IL of the load current is greater than the threshold value Kz, "|3I01|≧Kz" holds. The threshold value Kz is, for example, a value indicating about 40% of the rated value. Also, since the effective value of the disconnected A-phase current vector Ia1(t) becomes almost zero, "|Ia1|<Ki" holds. The threshold value Ki is, for example, a value indicating about 10% of the rated value and is smaller than the threshold value Kz.

[0043] The CT disconnection detection unit 130 calculates 3I02(t), which is the vector sum of the A-phase current Ia2(t), B-phase current Ib2(t), and C-phase current Ic2(t) flowing through the second end side.

[0044] Here, no CT disconnection has occurred in the current transformers 22 of each phase. The current transformers 22 are connected to the protection relay device 10 with the opposite polarity to the current transformer 21 for current differential relay operation. Therefore, the effective value of the vector Ia2 is the same as the effective value of the vector Ia1e before CT disconnection, and the phase of the vector Ia2 is the opposite phase to the vector Ia1e before CT disconnection. Also, the effective value of the vector Ib2 is the same as the effective value of the vector Ib1, and the phase of the vector Ib2 is the opposite phase to the vector Ib1. The effective value of the vector Ic2 is the same as the effective value of the vector Ic1, and the phase of the vector Ic2 is the opposite phase to the vector Ic1. Therefore, 3I02(t) is represented by the following equation (2).

[0045] 3I02(t)=Ia2(t)+Ib2(t)+Ic2(t)=0…(2) Therefore, as shown in Fig. 4(b), since the effective value of the vector 3I02 becomes almost zero, “|3I02|<Ki” holds.

[0046] The CT disconnection detection unit 130 calculates the differential current Ida(t) of the A phase, the differential current Idb(t) of the B phase, and the differential current Idc(t) of the C phase based on the A-phase current Ia1(t), B-phase current Ib1(t), C-phase current Ic1(t) flowing on the first end side and the A-phase current Ia2(t), B-phase current Ib2(t), C-phase current Ic2(t) flowing on the second end side. The differential currents Ida(t), Idb(t), Idc(t) of each phase are represented by the following equations (3), (4), and (5), respectively.

[0047] Ida(t)=Ia1(t)+Ia2(t)=Ia2(t)…(3) Idb(t)=Ib1(t)+Ib2(t)=Ib1(t)+(-Ib1(t))=0…(4) Idc(t)=Ic1(t)+Ic2(t)=Ic1(t)+(-Ic1(t))=0…(5) The CT disconnection detection unit 130 calculates the vector sum of the differential currents Ida(t), Idb(t), and Idc(t) of each phase. Referring to Figure 4(c), it can be seen that the vector "Ida+Idb+Idc" representing this vector sum and vector 3I01 have the same magnitude and phase. In this case, vector 3I01 is the same as the inverse vector "-Ia1e" of vector Ia1e before the CT disconnection, and this inverse vector "-Ia1e" is the same as vector Ia2. Therefore, the following equation (6) holds.

[0048] |Ida(t)+Idb(t)+Idc(t)-3I01(t)|=|Ia2(t)+0+0-Ia2(t)|=0…(6) From this, it can be understood that when a single-phase CT is disconnected, the effective value of the vector sum of the vector "Ida + Idb + Idc" and the inverse vector of vector 3I01, "-3I01", becomes zero and is below the threshold Ki. Also, as shown in Figure 4(c), the effective value of the differential current Ida of the disconnected phase A is greater than or equal to the threshold Kz. The effective values ​​of the differential currents Idb and Idc of the non-disconnected phases B and C are almost zero and are below the threshold Ki.

[0049] (When a two-phase current transformer is disconnected) Figure 5 shows the relationship between current vectors and differential current vectors when a two-phase CT breaks. In the example in Figure 5, the relationship between current vectors and differential current vectors is shown when a CT break occurs in a two-phase (e.g., phase A and phase B) current transformer 21 while there is a three-phase balanced load current. Specifically, Figure 5(a) shows the relationship between the current vectors and 3I01 vectors of each phase at the first end. "Ia1e" and "Ib1e" in Figure 5(a) represent the phase A current vector and phase B current vector, respectively, assuming that the above CT break did not occur (or before the CT break). Figure 5(b) shows the relationship between the current vectors of each phase at the second end. Figure 5(c) shows the relationship between the differential current vectors of each phase.

[0050] Here, since CT disconnection has occurred in the current transformers 21 provided for the A-phase and B-phase, “Ia1(t) = 0” and “Ib1(t) = 0” hold. Therefore, 3I01(t) is expressed by the following equation (7).

[0051] 3I01(t)=Ia1(t)+Ib1(t)+Ic1(t)=0+0+Ic1(t)=Ic1(t)…(7) Therefore, as shown in Fig. 5(a), the effective value and phase of the vector 3I01 are the same as the effective value and phase of the vector Ic1, respectively. Thus, when the effective value of the load current is greater than the threshold value Kz, the effective value of the vector 3I01 becomes greater than or equal to the threshold value Kz, and “|3I01|≧Kz” holds. Also, since the effective values of the A-phase current vector Ia1(t) and the B-phase current vector Ib1 corresponding to the disconnected phase are almost zero, “|Ia1|<Ki” and “|Ib1|<Ki” hold.

[0052] Since CT disconnection has not occurred in the current transformers 22 for each phase, the effective value of the vector Ia2 is the same as the effective value of the vector Ia1e before CT disconnection, and the vector Ia2 is in the reverse phase to the vector Ia1e before CT disconnection. The effective value of the vector Ib2 is the same as the effective value of the vector Ib1e before CT disconnection, and the vector Ib2 is in the reverse phase to the vector Ib1e before CT disconnection. The effective value of the vector Ic2 is the same as the effective value of the vector Ic1, and the vector Ic2 is in the reverse phase to the vector Ic1. 3I02(t) is shown by the following equation (8).

[0053] 3I02(t)=Ia2(t)+Ib2(t)+Ic2(t)=0…(8) Therefore, as shown in Fig. 5(b), since the effective value of the vector 3I02 is almost zero, “|3I02|<Ki” holds.

[0054] The differential currents Ida(t), Idb(t), Idc(t) for each phase are expressed by the following equations (9), (10), and (11), respectively.

[0055] Ida(t)=Ia1(t)+Ia2(t)=Ia2(t)…(9) Idb(t)=Ib1(t)+Ib2(t)=Ib2(t)…(10) Idc(t)=Ic1(t)+Ic2(t)=Ic1(t)+(-Ic1(t))=0…(11) The CT break detection unit 130 calculates the vector sum of the differential currents Ida(t), Idb(t), and Idc(t) of each phase. Referring to Figure 5(c), it can be seen that the vector “Ida+Idb+Idc” representing this vector sum and vector 3I01 have the same effective value and phase. Also, as shown in Figure 5(a), vector 3I01 is the same as vector Ic1. Therefore, the following equation (12) holds.

[0056] |Ida(t)+Idb(t)+Idc(t)-3I01(t)|=|Ia2(t)+Ib2(t)+0-Ic1(t)|=|Ia2(t)+Ib2(t)+Ic2(t)|=0…(12) From this, it can be understood that, similar to the case of a single-phase CT disconnection, in the case of a two-phase CT disconnection, the effective value of the vector sum of the vector "Ida + Idb + Idc" and the inverse vector of vector 3I01 "-3I01" is zero and is below the threshold Ki. Furthermore, as shown in Figure 5(c), the effective values ​​of the differential currents Ida and Idb of the disconnected phases A and B are above the threshold Kz. The effective value of the differential current Idc of the non-disconnected phase C is almost zero and is below the threshold Ki.

[0057] (In case of a ground fault: power supply at both ends) Next, the relationship between the current vector and the differential current vector during a ground fault will be described. Here, as shown in FIG. 1, it is assumed that AC power supplies 11 and 12 are provided at both ends of the protected object 50. In this case, during a ground fault in the protection zone, the fault current flows from the AC power supply 11 and the AC power supply 12. Therefore, the effective values of the vector 3I01 and the vector 3I02 do not become zero, and for example, "|3I01|≧Kz" and "|3I02|≧Kz" are established. As understood from FIGS. 4 and 5, when one or two-phase CTs are disconnected, only one of the vectors 3I01 and 3I02 becomes greater than or equal to the threshold value Kz. Therefore, when "|3I01|≧Kz" and "|3I02|≧Kz" are established, the CT disconnection detection unit 130 does not determine that a CT disconnection has occurred.

[0058] In a configuration where the AC power supply 12 is a weak power source (for example, when the impedance between the protected object 50 and the AC power supply 12 is much larger than the impedance between the protected object 50 and the AC power supply 11 and the fault current from the AC power supply 12 is small), "|3I02|<Kz" may be established. However, even in this case, "|3I02|≧Ki" is established. Here, the vector sum of the differential currents Ida(t), Idb(t), Idc(t) of each phase is represented by the following equation (13). Therefore, the following equation (14) is established.

[0059] Ida(t)+Idb(t)+Idc(t)=3I01(t)+3I02(t)…(13) |Ida(t)+Idb(t)+Idc(t)-3I01(t)|=|3I01(t)+3I02(t)-3I01(t)|=|3I02(t)|≧Ki…(14) From this, it is understood that the effective value of the vector sum of the vector "Ida + Idb + Idc" and the reverse vector "-3I01" of the vector 3I01 does not become zero and becomes greater than or equal to the threshold value Ki. That is, since the above-described CT disconnection determination condition "|Ida(t)+Idb(t)+Idc(t)-3I01(t)|<Ki" is not established, the CT disconnection detection unit 130 does not determine that a CT disconnection has occurred.

[0060] (In case of ground fault: one - end power supply) Here, it is assumed that an AC power supply exists only at one end of the protected object 50, and no AC power supply exists at the other end of the protected object 50 (that is, only a load exists). That is, in FIG. 1, the AC power supply 11 exists, but the AC power supply 12 does not exist.

[0061] In this case, when a ground fault occurs in the protection zone, the fault current is shunted into a part that flows through the ground to the AC power supply 11 and a part that returns to the AC power supply 11 as a zero - phase current via the neutral point of a transformer (not shown) at the load end. Therefore, there may be a case where the effective value of the vector 3I02 becomes greater than or equal to the threshold value Ki (that is, |3I02(t)|≧Ki). However, as described above, in this case, the determination condition for CT disconnection is not satisfied. Therefore, the case where "|3I02|<Ki" holds will be considered.

[0062] FIG. 6 shows the relationship between the current vector and the differential - current vector during a single - phase ground fault at one - end power supply. In the example of FIG. 6, the relationship between the current vector and the differential - current vector when a ground fault occurs in phase A is shown. Specifically, FIG. 6(a) shows the relationship between the current vectors of each phase and the 3I01 vector on the first - end side. FIG. 6(b) shows the relationship between the current vectors of each phase on the second - end side. FIG. 6(c) shows the relationship between the differential - current vectors of each phase. Note that "Va" in FIG. 6(a) indicates the A - phase voltage vector.

[0063] Referring to FIG. 6(a), the A - phase current vector Ia1 is represented by the vector sum of the load - current vector ILa1 flowing in phase A and the fault - current vector IFa1. The B - phase current vector Ib1 is the same as the load - current vector ILb1 flowing in phase B, and the C - phase current vector Ic1 is the same as the load - current vector ILc1 flowing in phase C. In this case, the vector sum of the load - current vectors ILa1, ILb1, ILc1 of each phase is zero. Therefore, the following formula (15) holds.

[0064] 3I01(t) = Ia1(t) + Ib1(t) + Ic1(t) = ILa1(t) + IFa1(t) + ILa1(t) + ILc1(t) = IFa1(t) …(15) That is, the vector 3I01 is identical to the fault current vector IFa1 of phase A.

[0065] Referring to Fig. 6(b), since it is a ground fault accident at a single-ended power source, the vectors Ia2, Ib2, and Ic2 are identical to the load current vectors ILa2, ILb2, and ILc2, respectively. Therefore, since the effective value of the vector 3I02 is almost zero, "|3I02| < Ki" holds.

[0066] Referring to Fig. 6(c), before the occurrence of the ground fault accident, the load current flowing through the first end and the load current flowing through the second end are in opposite phases. Therefore, for the differential current vector Ida, "Ida = Ia1 + Ia2 = ILa1 + IFa1 + ILa2 = IFa1" holds. The differential current vectors Idb and Idc are zero. From Fig. 6(a), the vector 3I01 during the ground fault accident and the fault current vector IFa1 are in the same phase and have the same magnitude. That is, the vector 3I01 and the differential current vector Ida of phase A are in the same phase and have the same magnitude. Therefore, the determination condition for CT disconnection, "|Ida + Idb + Idc - 3I01| < Ki", may hold.

[0067] Here, when one-phase or two-phase CT disconnection occurs, as described above, the effective value of the disconnected phase current vector is almost zero (i.e., less than the threshold value Ki). That is, during CT disconnection, the determination condition that any one of the effective values of each phase current vector is less than the threshold value Ki holds. On the other hand, when the load current is flowing from before the occurrence of the ground fault accident, as shown in Fig. 6(a), the effective values of the vectors Ia1, Ib1, and Ic1 of each phase current are not all zero and are above the threshold value Ki. Therefore, during the ground fault accident, the above determination condition does not hold.

[0068] Furthermore, if a fault current flows in the same magnitude as the load current but in the opposite phase (for example, if the fault current flows toward the fault point in the opposite phase to the load current), the effective value of the phase current vector may be nearly zero. However, such a case is impossible when the power system is composed of a single-ended power source, and is limited to cases where the power system is composed of a double-ended power source. This is because, in current transformers 21 and 22, a fault current flows behind the load current when the load current is flowing in front only if there are AC power sources on the first and second ends of the protected object 50. Therefore, even if a ground fault occurs when a load current is flowing with a single-ended power source, it is inconceivable that the phase current would become zero in one or two phases.

[0069] Furthermore, we will consider a case where, when a ground fault occurs while load current is flowing through the power supply at both ends, the phase current in one phase becomes zero.

[0070] Figure 7 shows the relationship between the current vector and the differential current vector during a single-phase ground fault at both ends of the power supply. Specifically, Figure 7(a) shows the relationship between the current vector and the 3I01 vector for each phase at the first end. Figure 7(b) shows the relationship between the current vectors for each phase at the second end. Figure 7(c) shows the relationship between the differential current vectors for each phase. Note that "Va" in Figure 7(a) represents the A-phase voltage vector.

[0071] Referring to Figure 7(a), the A-phase current vector Ia1 is represented by the vector sum of the load current vector ILa1 flowing through the A-phase and the fault current vector IFa1. Here, it is assumed that the effective values ​​of the load current and the fault current are the same and are in opposite phase, so that the A-phase current Ia1 during a fault is zero. In addition, during an A-phase ground fault, fault currents also flow into the B-phase and C-phase due to zero-sequence current leakage (for example, zero-sequence current flows into the healthy phase via the neutral point of a transformer (not shown) at the far end of the protected object 50), but these are considerably smaller than the A-phase current and are therefore ignored.

[0072] In this case, the B-phase current vector Ib1 is almost identical to the load current vector ILb1 flowing through the B-phase, and the C-phase current vector Ic1 is almost identical to the load current vector ILc1 flowing through the C-phase. Therefore, with respect to the vector sum of each phase current vector (i.e., 3I01), the following holds: "3I01 = Ia1 + Ib1 + Ic1 = ILa1 + IFa1 + ILb1 + ILc1 = IFa1". Thus, if the effective value of the fault current from the AC power supply 11 (i.e., the effective value of the fault current vector IFa1) is greater than the threshold Kz, the effective value of vector 3I01 will be greater than or equal to the threshold Kz.

[0073] Referring to Figure 7(b), the A-phase current vector Ia2 is represented by the vector sum of the load current vector ILa2 flowing through the A-phase and the fault current vector IFa2. If we ignore the zero-sequence current leakage current during a ground fault, the B-phase current vector Ib2 is approximately the same as the load current vector ILb2 flowing through the B-phase, and the C-phase current vector Ic2 is approximately the same as the load current vector ILc2 flowing through the C-phase. Therefore, with respect to the vector sum of each phase current vector (i.e., 3I02), the following holds: "3I02 = Ia2 + Ib2 + Ic2 = ILa2 + IFa2 + ILb2 + ILc2 = IFa2". Thus, if the effective value of the fault current from the AC power supply 12 (i.e., the effective value of the fault current vector IFa2) is greater than the threshold Kz, the effective value of vector 3I02 will be greater than or equal to the threshold Kz.

[0074] Note that fault current vectors IFa1 and IFa2 have different magnitudes because their background impedances are different. Although the phases of fault current vectors IFa1 and IFa2 are almost inverted, current transformers 21 and 22 have opposite polarities. Therefore, as shown in Figure 7, fault current vectors IFa1 and IFa2 are in almost the same direction.

[0075] Referring to Figure 7(c), the differential current vector Ida of phase A is given by "Ida = Ia1 + Ia2 = ILa1 + IFa1 + ILa2 + IFa2 = ILa2 + IFa2". The effective values ​​of the differential currents Idb and Idc of phases B and C are approximately zero.

[0076] Therefore, depending on the magnitudes of the fault current and load current from each of the AC power sources 11 and 12, the determination condition for CT disconnection "|Ida + Idb + Idc - 3I01| = |ILa2 + IFa2 - IFa1| < Ki" may hold. However, as shown in FIGS. 7(a) and 7(b), since |3I01| ≥ Kz and |3I02| ≥ Kz hold, the determination condition for CT disconnection is not satisfied. The same applies when the phase current becomes zero in two phases during a ground fault accident. Therefore, even when a ground fault accident occurs while load current flows in a two-terminal power supply and the phase current becomes zero in one phase, the CT disconnection detection unit 130 does not erroneously determine that CT disconnection has occurred.

[0077] (Summary) The determination conditions for CT disconnection using current vectors and differential current vectors are summarized. First, as described using the vector diagrams of FIGS. 4 and 5, the condition P1 "|Ida + Idb + Idc - 3I01| < Ki" holds during CT disconnection. Also, during CT disconnection, since the effective value of the differential current in the disconnected phase increases, the condition P2 that any one of the effective values of the differential currents Ida, Idb, Idc of each phase is equal to or greater than the threshold value Kz holds.

[0078] Conditions for more accurately distinguishing CT disconnection and ground fault accidents are required. Specifically, as described in FIG. 6, during a ground fault accident, the effective values of the phase current vectors flowing on the first terminal side and the second terminal side do not all become zero, but during CT disconnection, the phase current corresponding to the disconnected phase becomes zero. Therefore, as a determination condition for CT disconnection, the condition P3 that any one of the effective values of the phase current vectors is less than the threshold value Ki is adopted. Specifically, since the condition P3 does not hold during a ground fault accident and the condition P3 holds during CT disconnection, CT disconnection and ground fault accidents can be more accurately distinguished.

[0079] Also, as described in FIGS. 6 and 7, during a ground fault, both |3I01| and |3I02| increase and do not become zero. On the other hand, during a CT disconnection, only one of |3I01| and |3I02| becomes greater than or equal to the threshold value Kz, and the other is less than at least the threshold value Kz.

[0080] Therefore, as a determination condition for CT disconnection, a condition P4 is adopted that the effective value of the vector sum of the phase current vectors on one end side (for example, |3I01|) is greater than or equal to the threshold value Kz, and the effective value of the vector sum of the phase current vectors on the other end side (for example, |3I02|) is less than the threshold value Kz. Typically, the effective value of the vector sum of the phase current vectors on the other end side is less than the threshold value Ki. Therefore, instead of condition P4, a condition P4_1 may be adopted that the effective value of the vector sum of the phase current vectors on one end side is greater than or equal to the threshold value Kz, and the effective value of the vector sum of the phase current vectors on the other end side is less than the threshold value Ki. When condition P4_1 is adopted, the reliability of distinguishing between CT disconnection and ground fault is improved.

[0081] During a ground fault, condition P4 (or P4_1) does not hold, and during a CT disconnection, condition P4 (or P4_1) holds. Therefore, for example, in a configuration where the AC power supply 12 is a weak power supply, CT disconnection and ground fault can be distinguished more accurately.

[0082] <Functional Configuration of CT Disconnection Detection Unit> FIG. 8 is a diagram showing a functional configuration example of a CT disconnection detection unit according to Embodiment 1. Referring to FIG. 8, the CT disconnection detection unit 130 includes determination units 41 to 48, determination units 61 to 63, determination units 81 to 88, determination units 91 and 92, AND circuits 201 to 208, and OR circuits 251 to 255.

[0083] The determination unit 41 determines whether the effective value of the A-phase current vector Ia1 at time (tn) is greater than or equal to the threshold Kz (i.e., |Ia1(tn)|≧Kz). For example, if the number of positive integer cycles is 2, then n is the number of samples corresponding to the period of those 2 cycles. The determination unit 42 determines whether the effective value of the B-phase current vector Ib1 at time (tn) is greater than or equal to the threshold Kz. The determination unit 43 determines whether the effective value of the C-phase current vector Ic1 at time (tn) is greater than or equal to the threshold Kz. The determination units 41 to 43 output the value "1" if the corresponding effective value is greater than or equal to the threshold Kz, and output the value "0" if the corresponding effective value is less than the threshold Kz.

[0084] The determination unit 44 determines whether the effective value of the time (tn) vector 3I01 is less than the threshold Ki. The determination unit 44 outputs the value "1" if the effective value is less than the threshold Ki, and outputs the value "0" if the effective value is equal to or greater than the threshold Ki.

[0085] The determination unit 45 determines whether the effective value of the vector 3I01 at time t is greater than or equal to the threshold Kz. The determination unit 45 outputs the value "1" if the effective value is greater than or equal to the threshold Kz, and outputs the value "0" if the effective value is less than the threshold Kz.

[0086] The AND circuit 201 performs an AND operation on the output values ​​of the determination units 41 to 45. Specifically, the AND circuit 201 outputs a signal S1 of value "1" if all the values ​​output from the determination units 41 to 45 are "1", and outputs a signal S1 of value "0" otherwise. The determination units 41 to 45 and the AND circuit 201 are provided to prevent erroneous detection of CT disconnection in the event of a ground fault when there is no load current.

[0087] Specifically, when a ground fault occurs without load current, the vector sum of the differential currents of each phase (i.e., "Ida + Idb + Idc") and the vector sum of the currents of each phase (i.e., "Ia + Ib + Ic = 3I0") will have the same magnitude and the same phase. Also, no current will flow in the healthy phases where no ground fault has occurred. Therefore, when |3I01| greater than or equal to the threshold Kz is detected, among the determination conditions for CT disconnection detection, there may be cases where condition P1 of "|Ida + Idb + Idc - 3I01| < Ki" and condition P3 that any of the effective values of the phase current vectors is less than the threshold Ki are satisfied. In this case, there is a possibility of misjudging as CT disconnection despite a ground fault.

[0088] To avoid this, when |3I01| greater than or equal to the threshold Kz is detected, it is necessary that a three-phase balanced load current was flowing before the detection. Specifically, the value "1" of signal S1 indicates that condition P5, that a three-phase balanced load current was flowing at a time (t - n) earlier than time t when |3I01| greater than or equal to the threshold Kz is detected at time t, is satisfied.

[0089] The determination unit 46 determines whether the effective value of the phase A current vector Ia1 at time t is less than the threshold Ki. The determination unit 47 determines whether the effective value of the phase B current vector Ib1 at time t is less than the threshold Ki. The determination unit 48 determines whether the effective value of the phase C current vector Ic1 at time t is less than the threshold Ki. The determination units 46 to 48 output the value "1" when the corresponding effective value is less than the threshold Ki, and output the value "0" when the corresponding effective value is greater than or equal to the threshold Ki.

[0090] The OR circuit 251 performs an OR operation on the output values of the determination units 46 to 48. Specifically, when at least one of these output values is "1", the OR circuit 251 outputs a signal S2 with the value "1", and when not, outputs a signal S2 with the value "0".

[0091] The determination units 46-48 and the OR circuit 251 are configured to address condition P3, which is that the effective value of any of the phase current vectors is less than the threshold Ki. Specifically, a value of "1" for signal S2 indicates that condition P3 is met, and a value of "0" for signal S2 indicates that condition P3 is not met.

[0092] The determination unit 61 determines whether the effective value of the differential current vector Ida of the A phase at time t is greater than or equal to the threshold Kz. The determination unit 62 determines whether the effective value of the differential current vector Idb of the B phase at time t is greater than or equal to the threshold Kz. The determination unit 63 determines whether the effective value of the differential current vector Idc of the C phase at time t is greater than or equal to the threshold Kz. The determination units 61 to 63 output the value "1" if the corresponding effective value is greater than or equal to the threshold Kz, and output the value "0" if the corresponding effective value is less than the threshold Kz.

[0093] The OR circuit 252 performs an OR operation on the output values ​​of the determination units 61 to 63. Specifically, if at least one of these output values ​​is "1", the OR circuit 252 outputs a signal S3 with the value "1", and otherwise outputs a signal S3 with the value "0".

[0094] The determination units 61-63 and the OR circuit 252 are configured to address condition P2, which is that any of the effective values ​​of the differential currents Ida, Idb, and Idc of each phase are greater than or equal to the threshold Kz. Specifically, a value of signal S3 "1" indicates that condition P2 is met, and a value of signal S3 "0" indicates that condition P2 is not met.

[0095] The AND circuit 202 performs an AND operation with the value of signal S1 from AND circuit 201, the value of signal S2 from OR circuit 251, the value of signal S3 from OR circuit 252, and the value obtained by inverting the logic level of the output of the determination unit 85. Here, the determination unit 85 determines whether the effective value of the vector sum of the currents of each phase flowing to the second end side (i.e., |3I02(t)|) is greater than or equal to the threshold Kz at time t. The determination unit 85 outputs the value "1" if the effective value is greater than or equal to the threshold Kz, and outputs the value "0" if the effective value is less than the threshold Kz.

[0096] Therefore, when all the values of signals S1 to S3 are "1" and the value output from the determination unit 85 is "0", the AND circuit 202 outputs a signal S4 with the value "1", and otherwise outputs a signal S4 with the value "0".

[0097] Here, the output value "0" from the determination unit 85 indicates that "|3I02(t)| < Kz" holds, and the value "1" of the signal S1 indicates that at least "|3I01(t)| ≧ Kz" holds. Therefore, the value "1" of the signal S1 and the output value "0" from the determination unit 85 indicate that the condition P4 that |3I01| is greater than or equal to the threshold value Kz and |3I02| is less than the threshold value Kz holds. Also, as described above, the value "1" of the signal S1 indicates the establishment of the condition P5, the value "1" of the signal S2 indicates the establishment of the condition P3, and the value "1" of the signal S3 indicates the establishment of the condition P2. As a result, the value "1" of the signal S4 of the AND circuit 202 indicates that all of the conditions P2 to P5 are established.

[0098] The determination unit 91 is a configuration for determining the presence or absence of the establishment of the condition P1. Here, a vector represented by the sum of the vector sum of the differential currents of each phase, "Ida + Idb + Idc", and the inverse vector of the vector 3I01, "-3I01", is defined as "ID1". That is, the vector ID1(t) at time t is represented by "ID1(t) = Ida(t) + Idb(t) + Idc(t) - 3I01(t)".

[0099] The determination unit 91 determines whether the effective value of the vector ID1(t) is less than the threshold value Ki. When the effective value is less than the threshold value Ki, the determination unit 91 outputs a signal S5 with the value "1", and when the effective value is greater than or equal to the threshold value Ki, the determination unit 91 outputs a signal S5 with the value "0". From this, the value "1" of the signal S5 indicates the establishment of the condition P1, and the value "0" of the signal S5 indicates the non - establishment of the condition P1.

[0100] <0The AND gate 203 performs an AND operation between the value of signal S4 and the value of signal S5. Specifically, the AND gate 203 outputs the value "1" if the values ​​of signals S4 and S5 are both "1", and outputs the value "0" otherwise.

[0101] The OR circuit 253 performs an OR operation between the output value from the AND circuit 203 and the output value from the AND circuit 204. Specifically, if at least one of these output values ​​is "1", the OR circuit 253 outputs a signal CT1 with the value "1", otherwise it outputs a signal CT1 with the value "0". A signal CT1 with the value "1" indicates that a CT break has been detected in the current transformer 21.

[0102] The AND circuit 204 performs an AND operation between the value from the determination unit 45 and the value of the signal CT1 from the OR circuit 253. Specifically, the AND circuit 204 outputs the value "1" if the value from the determination unit 45 is "1" and the value of the signal CT1 is "1", and outputs the value "0" otherwise. Now, let's explain why the AND circuit 204 is provided.

[0103] As described above, when the value of signal S1 is "1", it indicates that a three-phase balanced load current was flowing at a time (tn) prior to the time t when |3I01| above the threshold Kz was detected. If conditions P1 to P5 are met, a signal CT1 with a value of "1" is output (i.e., a CT break in the current transformer 21 is detected). For example, if a CT break is detected at time t1 and the CT break persists for time n or more, the current state at time (t1-n) will be that of a CT break. Therefore, condition P5 is not met, and the signal from the AND circuit 203 becomes "0". If the AND circuit 204 is not provided, the value of the signal CT1 from the OR circuit 253 will also be "0", so the CT break will not be detected even though the CT break is still present.

[0104] Therefore, once conditions P1 to P5 are met and a CT disconnection is detected, it is necessary to output a CT disconnection detection signal (i.e., a signal CT1 with a value of "1") as long as "|3I01|≧Kz" is met. When the OR circuit 253 receives a signal of value "1" from the AND circuit 203 when conditions P1 to P5 are met, it outputs a signal CT1 with a value of "1".

[0105] When the AND circuit 204 receives the input signal CT1 with the value "1", if the value of the determination unit 45 is "1" (i.e., "|3I01|≧Kz" is true), it outputs a signal with the value "1". When the OR circuit 253 receives the signal "1" from the AND circuit 204, it outputs a signal CT1 with the value "1".

[0106] Thus, even if condition P5 is not met and the signal value from AND circuit 203 becomes "0", as long as "|3I01|≧Kz" is true, the signal value from AND circuit 204 will be "1". Therefore, the value of the signal CT1 output from OR circuit 253 will also be "1", and the state of detecting a CT break will continue as long as "|3I01|≧Kz" is true.

[0107] The functions of the determination units 81-88 regarding the current on the second end correspond to the functions of the determination units 41-48 regarding the current on the first end, respectively. The function of the determination unit 92 regarding the current on the second end corresponds to the function of the determination unit 91 regarding the current on the first end. The functions of the AND circuits 205-208 regarding the current on the second end correspond to the functions of the AND circuits 201-204 regarding the current on the first end, respectively. The functions of the OR circuits 254 and 255 regarding the current on the second end correspond to the functions of the OR circuits 251 and 253 regarding the current on the first end, respectively. Therefore, a brief description follows.

[0108] The determination unit 81 outputs a signal of value "1" if the effective value of the A-phase current vector Ia2 at time (tn) is greater than or equal to the threshold Kz. The same applies to determination units 82 and 83. The determination unit 84 outputs a signal of value "1" if the effective value of the vector 3I02 at time (tn) is less than the threshold Ki. The determination unit 85 outputs a signal of value "1" if the effective value of the vector 3I02 at time t is greater than or equal to the threshold Kz. The AND circuit 205 outputs a signal S5 of value "1" if all the values ​​output from determination units 81 to 85 are "1". The value "1" of signal S5 indicates that when |3I02| greater than or equal to the threshold Kz is detected at time t, condition Q1, which states that a three-phase balanced load current was flowing at a time (tn) prior to time t, is met.

[0109] The determination unit 86 outputs a signal of value "1" if the effective value of the A-phase current vector Ia2 at time t is less than the threshold Ki. The same applies to determination units 87 and 88. The OR circuit 254 outputs a signal S6 of value "1" if at least one of the output values ​​of determination units 86 to 88 is "1". The value "1" of signal S6 indicates that condition Q2, which states that the effective value of any of the phase current vectors at the second end is less than the threshold Ki, has been met.

[0110] The AND circuit 206 performs an AND operation with the value of signal S3, the value of signal S5, the value of signal S6, and the value obtained by inverting the logic level of the output of the determination unit 45. The AND circuit 206 outputs a signal S7 with the value "1" if the values ​​of signals S3, S5, and S6 are all "1" and the value output from the determination unit 45 is "0".

[0111] Here, a value of "1" for signal S5 and an output value of "0" from the determination unit 45 indicates that condition Q3 is met, which is that |3I02| is greater than or equal to the threshold Kz and |3I01| is less than the threshold Kz. Therefore, a value of "1" for signal S7 indicates that all conditions P2, Q1 to Q3 are met.

[0112] Define a vector "ID2" as the sum of "Ida + Idb + Idc" and the negative vector of vector 3I02, "-3I02". When the effective value of vector ID2(t) is less than the threshold Ki, the determination unit 92 outputs a signal S8 with a value of "1". From this, the value "1" of signal S8 indicates that the condition Q4 of "|Ida + Idb + Idc - 3I02| < Ki" is satisfied.

[0113] The AND circuit 207 outputs a value of "1" when the values of signals S7 and S8 are both "1". When at least one of the value from the AND circuit 207 and the value from the AND circuit 208 is "1", the OR circuit 253 outputs a signal CT2 with a value of "1". The signal CT2 with a value of "1" indicates that a CT disconnection has been detected in the current transformer 22.

[0114] The AND circuit 208 outputs a signal with a value of "1" when both the value from the determination unit 85 and the value of the signal CT2 from the OR circuit 255 are "1".

[0115] Note that the CT disconnection detection unit 130 may further include a determination unit Y1 that determines whether |3I02(t)| is less than the threshold Ki at time t. The determination unit Y1 outputs "1" when |3I02(t)| is less than the threshold Ki, and outputs "0" when |3I02(t)| is greater than or equal to the threshold Ki. In this case, instead of the value with the logic level of the output of the determination unit 85 inverted, the output value of the determination unit Y1 is input to the AND circuit 202. Also, the CT disconnection detection unit 130 may further include a determination unit Y2 that outputs "1" when |3I01(t)| is less than the threshold Ki at time t, and outputs "0" when |3I01(t)| is greater than or equal to the threshold Ki. In this case, instead of the value with the logic level of the output of the determination unit 45 inverted, the output value of the determination unit Y2 is input to the AND circuit 206.

[0116] (Summary) The functions of the CT break detection unit 130 according to Embodiment 1 are summarized below. The CT break detection unit 130 calculates a vector "Ida(t)+Idb(t)+Idc(t)" which represents the vector sum of the differential currents of each phase of the power system, based on the instantaneous current values ​​from the current transformer 21 (for example, the instantaneous value of the AC current I1) and the instantaneous current values ​​from the current transformer 22 (for example, the instantaneous value of the AC current I2).

[0117] The CT break detection unit 130 calculates a vector "Ia1(t)+Ib1(t)+Ic1(t)" (i.e., vector 3I01(t)) which represents the vector sum of the phase currents flowing on the first end side, based on the instantaneous value of the alternating current I1. The CT break detection unit 130 also calculates a vector "Ida(t)+Idb(t)+Idc(t)-3I01(t)" (i.e., vector ID1(t)) which represents the sum of the vector "Ida(t)+Idb(t)+Idc(t)" and the inverse vector of vector 3I01(t).

[0118] The CT disconnection detection unit 130 determines that a disconnection has occurred in the current transformer 21 when the specified conditions are met. The specified conditions include the condition that the effective value of vector ID1(t) is less than the threshold Ki (for example, condition P1). Condition P1 is an essential condition for determining whether a disconnection has occurred in the current transformer 21.

[0119] The specified conditions further include the condition (e.g., condition P2) that any of the RMS values ​​of the differential current vectors of each phase (i.e., |Ida(t)|, |Idb(t)|, |Idc(t)|) is greater than or equal to a threshold Kz. The specified conditions further include the condition P3 that any of the RMS values ​​of the current vectors of each phase flowing to the first end (i.e., |Ia1(t)|, |Ib1(t)|, |Ic1(t)|) is less than a threshold Ki.

[0120] The CT break detection unit 130 calculates a vector "Ia2(t)+Ib2(t)+Ic2(t)" (i.e., vector 3I02(t)) that represents the vector sum of the phase currents flowing to the second end side, based on the instantaneous value of the AC current I2. The specified conditions further include the condition (e.g., condition P4) that the effective value of vector 3I01 is greater than or equal to the threshold Kz, and the effective value of vector 3I02(t) is less than the threshold Kz. The specified conditions may also include, instead of condition P4, the condition (e.g., condition P4_1) that the effective value of vector 3I01(t) is greater than or equal to the threshold Kz, and the effective value of vector 3I02(t) is less than the threshold Ki.

[0121] The CT break detection unit 130 calculates a vector "Ia2(tn)+Ib2(tn)+Ic2(tn)" (i.e., vector 3I01(tn)) which represents the vector sum of the phase currents that flowed to the first end side before the specified cycle, based on the instantaneous value of the AC current I1 acquired before the specified cycle (for example, two cycles before).

[0122] The specified conditions further include the condition (e.g., condition P5) that the effective value of vector 3I01 is greater than or equal to the threshold Kz, the effective values ​​of the vectors of each phase current that flowed to the first end before the specified cycle (e.g., |Ia1(tn)|, |Ia1(tn)|, |Ia1(tn)|) are all greater than or equal to the threshold Kz, and the effective value of vector 3I01(tn) is less than the threshold Ki.

[0123] If the CT break detection unit 130 determines that a break has occurred in the current transformer 21, it identifies an effective value (for example, |Ia1(t)|) among the effective values ​​of the vectors of the phase currents flowing to the first end side that is less than the threshold Ki. The CT break detection unit 130 determines that a break has occurred in the current transformer 21 provided in the phase (for example, phase A) corresponding to the vector having the identified effective value.

[0124] <Advantages> According to Embodiment 1, regardless of whether it is a single-phase or two-phase CT disconnection, the CT disconnection can be detected under the same determination condition (for example, condition P1). Further, by further determining conditions P2 to P5, the ground fault and the CT disconnection can be distinguished more accurately.

[0125] Embodiment 2. In Embodiment 2, a configuration using another condition instead of condition P1 used in Embodiment 1 will be described.

[0126] <CT disconnection detection method> In Embodiment 2, among the differential current vectors of each phase, the phase corresponding to the vector having an effective value less than the threshold value Ki is specified. Then, at the time of CT disconnection, the vector sum “Ida + Idb + Idc” of the differential current vectors of each phase and the vector sum of the current vectors of the specified phase are of the same magnitude and in the same phase are utilized.

[0127] Referring to FIG. 4, at the time of single-phase (for example, phase A) CT disconnection, |Ida(t)|≧Kz, |Idb(t)|<Ki, and |Idc(t)|<Ki hold. Typically, |Idb(t)| and |Idc(t)| are zero. The phases corresponding to the vectors having an effective value less than the threshold value Ki are phase B and phase C. The vector sum of the current vectors of phase B and phase C is “Ib1(t) + Ic1(t)”.

[0128] The vector sum of the differential current vectors of each phase is “Ida(t) + Idb(t) + Idc(t)”. Since “Idb(t)=0” and “Idc(t)=0”, “Ida(t) + Idb(t) + Idc(t)” becomes “Ia1(t) + Ia2(t)”.

[0129] The vector “Ib1(t) + Ic1(t)” corresponds to the inverse vector of the vector Ia1e before CT disconnection. Also, the inverse vector corresponds to the vector Ia2(t). Therefore, at the time of single-phase CT disconnection, the following equation (16) holds.

[0130] |Ida(t) + Idb(t) + Idc(t) - (Ib1(t) + Ic1(t))| = |Ia1(t) + Ia2(t) - Ia2(t)| = |0 + Ia2(t) - Ia2(t)| = 0 < Ki…(16) Referring to FIG. 5, when a CT open circuit occurs in two phases (for example, phase A and phase B), |Ida(t)| ≥ Kz, |Idb(t)| ≥ Kz, and |Idc(t)| < Ki hold. Typically, |Idc(t)| is zero. The phase corresponding to the vector having an effective value less than the threshold Ki is phase C.

[0131] Since “Idc(t) = 0”, “Ida(t) + Idb(t) + Idc(t)” becomes “Ia1(t) + Ia2(t) + Ib1(t) + Ib2(t)”.

[0132] The vector Ic1(t) is the inverse vector “-Ic2(t)” of the vector Ic2(t). Also, “Ia2(t) + Ib2(t) + Ic2(t) = 3I02(t) = 0” holds. Therefore, when a CT open circuit occurs in two phases, the following equation (17) holds.

[0133] |Ida(t) + Idb(t) + Idc(t) - Ic1(t)| = |Ia1(t) + Ia2(t) + Ib1(t) + Ib2(t) - Ic1(t)| = |0 + Ia2(t) + 0 + Ib2(t) + Ic2(t)| = 0 < Ki…(17) Define the vector sum of one or more phase current vectors corresponding to the differential current vector having an effective value less than the threshold Ki as the vector Ik. In this case, when a CT open circuit occurs, the condition R1 of “|Ida + Idb + Idc - Ik| < Ki” holds.

[0134] In a configuration where AC power sources exist at both ends, when a ground fault occurs while a three-phase balanced load current flows above the threshold Kz, fault current flows toward the ground fault point. Therefore, for the two current transformers 21, 22, the conditions of “|3I01| ≥ Kz” and “|3I02| ≥ Kz” hold. Since this condition does not hold during a CT open circuit, a ground fault and a CT open circuit can be distinguished.

[0135] Also, when a ground fault occurs in a configuration where an AC power supply exists only at one end, as described in FIG. 6, only one of |3I01| and |3I02| may exceed the threshold Kz. However, as shown in FIG. 6, the vector 3I01 has a different phase from the vector sum “Ib1 + Ic1” of the current vectors of two phases (here, the B phase and the C phase) corresponding to the differential current vector having an effective value less than the threshold Ki. The vector 3I01 corresponds to the differential current Ida of the A phase. The differential current Ida and the vector sum “Ib1 + Ic1” of the current vectors of the healthy phases have different phases. Therefore, the vector sum of the differential current vectors of each phase and the sum of the current vectors of the healthy phases do not have the same magnitude and the same phase. That is, since neither Equation (16) nor Equation (17) holds, a ground fault and a CT disconnection can be distinguished. Therefore, in Embodiment 2, the condition P3 that any one of the effective values of the phase current vectors used in Embodiment 1 is less than the threshold Ki is unnecessary.

[0136] <Functional Configuration of CT Disconnection Detection Unit> FIG. 9 is a diagram showing a functional configuration example of a CT disconnection detection unit according to Embodiment 2. Referring to FIG. 9, the CT disconnection detection unit 130 includes a determination unit 45, determination units 61 to 63, a determination unit 85, determination units 95 and 96, AND circuits 301 to 304, and an OR circuit 252. The functions of the determination units 45, 61 to 63, 85, and the OR circuit 252 are the same as the functions described in FIG. 8.

[0137] As described above, in Embodiment 2, the condition P3 is unnecessary. Further, in Embodiment 2, since the vector sum of the phases where the differential current cannot be detected (i.e., the healthy phases) is used as the CT disconnection determination condition, an erroneous determination of CT disconnection does not occur even when there is no load current. Further, in Embodiment 2, since the state before a specified cycle (e.g., 2 cycles) is not used as the CT disconnection determination condition, the AND circuit 204 shown in FIG. 8 is unnecessary.

[0138] The AND circuit 301 performs an AND operation between the value from the determination unit 45, the value of signal S3, and the value obtained by inverting the logic level of the output of the determination unit 85. Specifically, the AND circuit 301 outputs a signal S11 with the value "1" if the value from the determination unit 45 is "1", the value of signal S3 is "1", and the value from the determination unit 85 is "0", and outputs a signal S11 with the value "0" otherwise.

[0139] Here, a value of "1" for signal S3 indicates that condition P2 is met, which is that any of the RMS values ​​of the differential currents Ida, Idb, and Idc of each phase are greater than or equal to the threshold Kz. A value of "1" from the determination unit 45 and a value of "0" from the determination unit 85 indicates that condition P4 is met, which is that |3I01(t)| is greater than or equal to the threshold Kz and |3I02(t)| is less than the threshold Kz. Therefore, a value of "1" for signal S11 of the AND circuit 301 indicates that conditions P2 and P4 are both met.

[0140] The determination unit 95 is configured to determine whether or not condition R1 is met. Here, the vector "IDx1" is defined as the sum of the vector sum of the differential currents of each phase, "Ida + Idb + Idc", and the inverse vector of the vector "Ia1(t)*Ka + Ib1(t)*Kb + Ic1(t)*Kc". That is, the vector IDx1(t) at time t is expressed as "ID1x(t) = Ida(t) + Idb(t) + Idc(t) - (Ia1(t)*Ka + Ib1(t)*Kb + Ic1(t)*Kc)".

[0141] Figure 10 shows another example of the functional configuration of the CT wire break detection unit according to Embodiment 2. Referring to Figure 10, the CT wire break detection unit 130 includes determination units 351 to 353 and coefficient output units 361 to 363.

[0142] The determination unit 351 determines whether |Ida(t)| is less than the threshold value Ki. Specifically, when |Ida(t)| is less than the threshold value Ki, the determination unit 351 outputs the value "1", and when |Ida(t)| is greater than or equal to the threshold value Ki, the determination unit 351 outputs the value "0". The determination unit 352 outputs the value "1" when |Idb(t)| is less than the threshold value Ki, and outputs the value "0" when |Idb(t)| is greater than or equal to the threshold value Ki. The determination unit 353 outputs the value "1" when |Idc(t)| is less than the threshold value Ki, and outputs the value "0" when |Idc(t)| is greater than or equal to the threshold value Ki.

[0143] When the input value of the coefficient output unit 361 is "1", it outputs the coefficient Ka with the value "1", and when the input value is "0", it outputs the coefficient Ka with the value "0". Similarly, when the input value of the coefficient output unit 362 is "1", it outputs the coefficient Kb with the value "1", and when the input value is "0", it outputs the coefficient Kb with the value "0". When the input value of the coefficient output unit 363 is "1", it outputs the coefficient Kc with the value "1", and when the input value is "0", it outputs the coefficient Kc with the value "0".

[0144] Referring to FIG. 9 again, the determination unit 95 receives the inputs of the coefficients Ka to Kc. For example, assume that Ka = 0, Kb = 1, and Kc = 1. In this case, |Ida(t)| ≥ Ki, |Idb(t)| < Ki, and |Idc(t)| < Ki are satisfied.

[0145] The determination unit 95 calculates the vector IDx1(t). Specifically, "IDx(t)=Ida(t)+Idb(t)+Idc(t)-(Ib1(t)+Ic1(t))". The determination unit 95 determines whether the effective value of the vector IDx1(t) is less than the threshold value Ki. When the effective value is less than the threshold value Ki, the determination unit 95 outputs the signal S12 with the value "1", and when the effective value is greater than or equal to the threshold value Ki, the determination unit 95 outputs the signal S12 with the value "0". Therefore, the value "1" of the signal S12 indicates the establishment of the condition R1, and the value "0" of the signal S12 indicates the non - establishment of the condition R1.

[0146] The AND circuit 303 performs an AND operation between the value of signal S11 and the value of signal S12. Specifically, the AND circuit 303 outputs a signal CT1 with the value "1" if the values ​​of signals S11 and S12 are both "1", and outputs a signal CT1 with the value "0" otherwise. A signal CT1 with the value "1" indicates that a CT break has been detected in the current transformer 21.

[0147] The AND circuit 302 outputs a signal S13 with the value "1" if the value from the determination unit 85 is "1", the value of signal S3 is "1", and the value from the determination unit 45 is "0", and outputs a signal S13 with the value "0" otherwise. The value "1" of signal S13 from the AND circuit 303 indicates that all conditions Q3, which states that |3I02| is greater than or equal to the threshold Kz and |3I01| is less than the threshold Kz, and condition P2 are all met.

[0148] We define "IDx2" as the vector obtained by adding the vector sum of the differential currents of each phase, "Ida + Idb + Idc", and the inverse vector of the vector "Ia²*Ka + Ib²*Kb + Ic²*Kc". That is, the vector IDx2(t) at time t is expressed as "ID2x(t) = Ida(t) + Idb(t) + Idc(t) - (Ia²(t)*Ka + Ib²(t)*Kb + Ic²(t)*Kc)".

[0149] The determination unit 96 accepts the input of coefficients Ka to Kc. For example, let's assume Ka=0, Kb=1, and Kc=1. The determination unit 96 calculates the vector IDx2(t). Specifically, "IDx2(t)=Ida(t)+Idb(t)+Idc(t)-(Ib2(t)+Ic2(t))". The determination unit 96 outputs a signal S14 with the value "1" if the effective value of the vector IDx2(t) is less than the threshold Ki, and outputs a signal S14 with the value "0" if the effective value is greater than or equal to the threshold Ki.

[0150] The AND circuit 304 performs an AND operation between the value of signal S13 and the value of signal S14. Specifically, the AND circuit 304 outputs a signal CT2 with the value "1" if the values ​​of signals S13 and S14 are all "1". A signal CT2 with the value "1" indicates that a CT break has been detected in the current transformer 22.

[0151] Furthermore, the CT disconnection detection unit 130 according to Embodiment 2 may further include the determination units Y1 and Y2 described in Embodiment 1. Specifically, instead of the inverted logic level of the output of determination unit 85, the output value of determination unit Y1 may be input to the AND circuit 301. Also, instead of the inverted logic level of the output of determination unit 45, the output value of determination unit Y2 may be input to the AND circuit 302.

[0152] (summary) The functions of the CT break detection unit 130 according to Embodiment 2 are summarized below. The CT break detection unit 130 calculates a vector "Ida(t)+Idb(t)+Idc(t)" which represents the vector sum of the differential currents of each phase of the power system. The CT break detection unit 130 identifies one or more phases corresponding to differential current vectors having an effective value less than the threshold Ki, and calculates a vector Ik which represents the vector sum of the currents of that one or more phases flowing to the first end side, based on the instantaneous value of the AC current I1. The CT break detection unit 130 calculates a vector (for example, vector IDx1(t)) which represents the sum of the vector "Ida(t)+Idb(t)+Idc(t)" and the inverse vector of vector Ik(t).

[0153] The CT disconnection detection unit 130 determines that a disconnection has occurred in the current transformer 21 when the specified conditions are met. The specified conditions include the condition that the effective value of the vector IDx1(t) is less than the threshold Ki (for example, condition R1). Condition R1 is an essential condition for determining whether a disconnection has occurred in the current transformer 21.

[0154] The specified conditions further include the condition (e.g., condition P2) that any of the RMS values ​​of the differential current vectors of each phase (i.e., |Ida(t)|, |Idb(t)|, |Idc(t)|) is greater than or equal to a threshold Kz.

[0155] Based on the instantaneous value of the alternating current I2, the CT disconnection detection unit 130 calculates a vector “Ia2(t) + Ib2(t) + Ic2(t)” (that is, vector 3I02(t)) indicating the vector sum of the phase currents flowing through the second terminal side. The specified conditions further include the condition (for example, condition P4) that the effective value of vector 3I01 is greater than or equal to the threshold value Kz and the effective value of vector 3I02(t) is less than the threshold value Kz. Instead of condition P4, the specified conditions may include the condition (for example, condition P4_1) that the effective value of vector 3I01(t) is greater than or equal to the threshold value Kz and the effective value of vector 3I02(t) is less than the threshold value Ki.

[0156] <Advantages> According to the second embodiment, it has the same advantages as the first embodiment.

[0157] Other embodiments. (1) In the above-described embodiments, in conditions P1 and condition R1, the configuration using the vector sum of the differential currents of each phase has been described, but the present invention is not limited to this configuration. When a CT is disconnected, the effective value of the differential current vector of the phases other than the disconnected phase becomes almost zero. Therefore, the vector sum of the differential currents of each phase is substantially the same as the vector sum of the differential current vectors having an effective value greater than or equal to the threshold value Kz. Therefore, in conditions P1 and condition R1, instead of the vector sum of the differential currents of each phase, the vector sum of the differential current vectors having an effective value greater than or equal to the threshold value Kz may be used. Specifically, the CT disconnection detection unit 130 identifies one or more differential vectors having an effective value greater than or equal to the threshold value Kz, and calculates a vector Idx indicating the vector sum of the one or more differential current vectors. For example, instead of condition P1, the CT disconnection detection unit 130 uses the condition “|Idx - 3I01| < Ki”. Also, instead of condition R1, the CT disconnection detection unit 130 uses the condition “|Idx - Ik| < Ki”.

[0158] ​​​(2) The configurations described above as embodiments are examples of the configurations of the Disclosure and can be combined with other known technologies, and can be modified, such as by omitting parts, without departing from the gist of the Disclosure. Furthermore, in the embodiments described above, processes and configurations described in other embodiments may be adopted as appropriate.

[0160] <Note> The various aspects of this disclosure are summarized below as an appendix.

[0161] (Note 1) A protective relay device comprising: a current acquisition unit that acquires a first instantaneous current value from a first current transformer provided on each phase at the first end of the protected object in a power system, and a second instantaneous current value from a second current transformer provided on each phase at the second end of the protected object; a current differential relay unit that determines whether or not a fault has occurred in the protected object based on an operating amount and a suppression amount calculated from the first instantaneous current value and the second instantaneous current value; and a wire break detection unit that determines that a wire break has occurred in the first current transformer when a specified condition is met, wherein the wire break detection unit calculates the vector sum of the differential currents of each phase of the power system as a first vector based on the first instantaneous current value and the second instantaneous current value, calculates the vector sum of the currents of each phase flowing at the first end as a second vector based on the first instantaneous current value, calculates the sum of the first vector and the inverse vector of the second vector as a third vector, and the specified condition includes a first condition that the effective value of the third vector is less than a first threshold.

[0162] (Note 2) The protective relay device according to Appendix 1, wherein the aforementioned specified conditions further include a second condition that any of the effective values ​​of the differential current vectors of each phase is greater than or equal to a second threshold which is greater than the first threshold.

[0163] (Note 3) The wire break detection unit calculates the vector sum of the phase currents flowing to the second end side as a fourth vector based on the second instantaneous current value, and the specified condition further includes a third condition that the effective value of the second vector is greater than or equal to the second threshold, and the effective value of the fourth vector is less than the second threshold, as described in Appendix 2, the protective relay device.

[0164] (Note 4) The protective relay device according to any one of the appendices 1 to 3, wherein the aforementioned specified conditions further include a fourth condition that any of the effective values ​​of the vectors of the phase currents flowing to the first end side is less than the first threshold.

[0165] (Note 5) The wire break detection unit calculates the vector sum of the phase currents that flowed to the first end side before the specified cycle as a fifth vector based on the first instantaneous current value obtained before the specified cycle, and the specified condition further includes a fifth condition that the effective value of the second vector is greater than or equal to the second threshold, the effective values ​​of the vectors of the phase currents that flowed to the first end side before the specified cycle are all greater than or equal to the second threshold, and the effective value of the fifth vector is less than the first threshold, as described in Appendix 2 or Appendix 3.

[0166] (Note 6) The protective relay device according to any one of the appendices 1 to 5, wherein the wire break detection unit determines that a wire break has occurred in the first current transformer, identifies an effective value among the effective values ​​of the vectors of the phase currents flowing to the first end side that is less than the first threshold, and determines that a wire break has occurred in the first current transformer provided in the phase corresponding to the vector having the identified effective value.

[0167] (Note 7) The wire break detection unit identifies one or more vectors from among the differential current vectors of each phase that have an effective value greater than or equal to a second threshold, which is greater than the first threshold, and calculates the vector sum of the one or more vectors as the first vector instead of the vector sum of the differential currents of each phase of the power system, as described in any of the appendices 1 to 6.

[0168] (Note 8) The power system includes a current acquisition unit that acquires a first instantaneous current value from a first current transformer provided on each phase at the first end of the protected power system and a second instantaneous current value from a second current transformer provided on each phase at the second end of the protected power system; a current differential relay unit that determines whether or not a fault has occurred in the protected power system based on an operating amount and a suppression amount calculated from the first instantaneous current value and the second instantaneous current value; and a wire break detection unit that determines that a wire break has occurred in the first current transformer when a specified condition is met, wherein the wire break detection unit acquires the first instantaneous current value and the second instantaneous current value. A protective relay device that, based on instantaneous current values, calculates the vector sum of the differential currents of each phase of the power system as a first vector, identifies one or more phases corresponding to the vectors of the differential currents of each phase that have an effective value less than a first threshold, calculates the vector sum of the currents of the one or more phases flowing to the first end side as a second vector based on the first instantaneous current values, calculates the sum of the first vector and the inverse vector of the second vector as a third vector, and the specified condition includes a first condition that the effective value of the third vector is less than the first threshold.

[0169] (Note 9) The protective relay device according to Appendix 8, wherein the aforementioned specified conditions further include a second condition that any of the effective values ​​of the differential current vectors of each phase is greater than or equal to a second threshold greater than the first threshold.

[0170] (Note 10) The wire break detection unit calculates the vector sum of the phase currents flowing to the second end side as a fourth vector based on the second instantaneous current value, and the specified condition further includes a third condition that the effective value of the second vector is greater than or equal to the second threshold, and the effective value of the fourth vector is less than the second threshold, as described in Appendix 9, the protective relay device.

[0171] (Note 11) The wire break detection unit identifies one or more vectors from among the differential current vectors of each phase that have an effective value greater than or equal to a second threshold greater than the first threshold, and calculates the vector sum of the one or more vectors as the first vector instead of the vector sum of the differential currents of each phase of the power system, as described in any of the appendices 8 to 10.

[0172] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended. [Explanation of Symbols]

[0173] 10 Protective relay device, 11,12 AC power supply, 21,22 Current transformer, 50 Protected object, 31,32 Circuit breaker, 51 Auxiliary transformer, 52 Signal conversion unit, 70 Arithmetic processing unit, 71 Bus, 73 ROM, 74 RAM, 75 Digital input circuit, 76 Digital output circuit, 77 Input interface, 110 Current acquisition unit, 120 Current differential relay unit, 130 CT wire break detection unit, 140 Output control unit, 150 Wire break alarm unit.

Claims

1. A current acquisition unit that acquires the instantaneous value of the first current from the first current transformer provided on each phase at the first end of the power system to be protected, and the instantaneous value of the second current from the second current transformer provided on each phase at the second end of the power system to be protected, A current differential relay unit that determines whether or not a fault has occurred in the protected object based on the operating amount and suppression amount calculated from the first instantaneous current value and the second instantaneous current value, The system includes a wire break detection unit that determines that a wire break has occurred in the first current transformer when a specified condition is met, The wire break detection unit is, Based on the first instantaneous current value and the second instantaneous current value, the vector sum of the differential currents of each phase of the power system is calculated as the first vector. Based on the instantaneous value of the first current, the vector sum of the phase currents flowing on the first end side is calculated as the second vector. The sum of the first vector and the inverse vector of the second vector is calculated as the third vector. A protective relay device in which the aforementioned specified conditions include a first condition that the effective value of the third vector is less than a first threshold.

2. The protective relay device according to claim 1, wherein the aforementioned specified condition further includes a second condition that any of the effective values ​​of the differential current vectors of each phase is greater than or equal to a second threshold greater than the first threshold.

3. The wire break detection unit calculates the vector sum of the phase currents flowing to the second end side as the fourth vector based on the instantaneous value of the second current, The protective relay device according to claim 2, wherein the aforementioned specified conditions further include a third condition that the effective value of the second vector is greater than or equal to the second threshold, and the effective value of the fourth vector is less than the second threshold.

4. The protective relay device according to any one of claims 1 to 3, wherein the aforementioned specified condition further includes a fourth condition that any of the effective values ​​of the vectors of the phase currents flowing to the first end side is less than the first threshold.

5. The wire break detection unit is, Based on the instantaneous value of the first current obtained before the specified cycle, the vector sum of the phase currents that flowed to the first end before the specified cycle is calculated as the fifth vector. The protective relay device according to claim 2 or 3, wherein the prescribed conditions further include a fifth condition that the effective value of the second vector is greater than or equal to the second threshold, the effective values ​​of all phase current vectors that flowed to the first end side before the prescribed cycle are greater than or equal to the second threshold, and the effective value of the fifth vector is less than the first threshold.

6. The wire break detection unit is, If it is determined that a break has occurred in the first current transformer, the effective value of the vector of each phase current flowing to the first end that is less than the first threshold value is identified. A protective relay device according to any one of claims 1 to 3, which determines that a break in the circuit has occurred in the first current transformer provided in the phase corresponding to the vector having the specified effective value.

7. The wire break detection unit is, Among the differential current vectors of each phase, one or more vectors having an effective value greater than or equal to a second threshold, which is greater than the first threshold, are identified. The protective relay device according to any one of claims 1 to 3, wherein instead of calculating the vector sum of the differential currents of each phase of the power system, the vector sum of one or more vectors is used as the first vector.

8. A current acquisition unit that acquires the instantaneous value of the first current from the first current transformer provided on each phase at the first end of the power system to be protected, and the instantaneous value of the second current from the second current transformer provided on each phase at the second end of the power system to be protected, A current differential relay unit that determines whether or not a fault has occurred in the protected object based on the operating amount and suppression amount calculated from the first instantaneous current value and the second instantaneous current value, The system includes a wire break detection unit that determines that a wire break has occurred in the first current transformer when a specified condition is met, The wire break detection unit is, Based on the first instantaneous current value and the second instantaneous current value, the vector sum of the differential currents of each phase of the power system is calculated as the first vector. From the differential current vectors of each phase, one or more phases corresponding to the vectors having an effective value less than the first threshold are identified. Based on the instantaneous value of the first current, the vector sum of the currents of the one or more phases flowing on the first end side is calculated as the second vector. The sum of the first vector and the inverse vector of the second vector is calculated as the third vector. A protective relay device in which the aforementioned predefined conditions include a first condition that the effective value of the third vector is less than the first threshold.

9. The protective relay device according to claim 8, wherein the aforementioned specified condition further includes a second condition that any of the effective values ​​of the differential current vectors of each phase is greater than or equal to a second threshold greater than the first threshold.

10. The wire break detection unit calculates the vector sum of the phase currents flowing to the second end side as the fourth vector based on the instantaneous value of the second current, The protective relay device according to claim 9, wherein the aforementioned specified conditions further include a third condition that the effective value of the second vector is greater than or equal to the second threshold, and the effective value of the fourth vector is less than the second threshold.

11. The wire break detection unit is, Among the differential current vectors of each phase, one or more vectors having an effective value greater than or equal to a second threshold, which is greater than the first threshold, are identified. The protective relay device according to any one of claims 8 to 10, wherein instead of calculating the vector sum of the differential currents of each phase of the power system, the vector sum of one or more vectors is used as the first vector.

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