JP2017005868A - Distance relay device and transmission line protection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance relay device capable of detecting short circuit fault in single line of a two parallel line transmission line and different-phase ground fault across both lines more accurately.SOLUTION: A distance relay device for protecting a polyphase two parallel line transmission line including a first transmission line and a second transmission line comprises a calculation unit for calculating the line voltage and line current of the first transmission line, based on a voltage and a current detected on the first transmission line, a current generation unit capable of generating a composite current by adding the zero-phase current of the first transmission line to the line current, an impedance calculation unit capable of calculating the impedance value based on the composite current and line voltage, and a fault detector for detecting a short circuit fault occurring between respective phases of the first transmission line, and a fault occurring across the first and second transmission lines, based on the impedance value calculated by the impedance calculation unit and a predetermined setting.SELECTED DRAWING: Figure 4

Description

  The present disclosure relates to a distance relay device and a transmission line protection method, and more particularly, to a distance relay device and a transmission line protection method for protecting a parallel two-line transmission line.

  Conventionally, a distance relay device has been widely used as a protective relay device that detects and protects against a short circuit accident in a power transmission line of an electric power system. Since the distance relay device can detect accidents by inputting its own voltage and current, its configuration as a protective relay device is relatively simple and highly reliable. Widely used as electrical equipment.

  The distance relay device is an instrument transformer (VT: Voltage Transformer) in which the current taken from the current transformer (CT: Current Transformer) placed on the transmission line and the bus line to which the transmission line is connected are placed. Based on the voltage taken in, the impedance to the accident point is calculated. The distance relay device determines whether the protection range is inside or outside by comparing the impedance value and the settling value. And a distance relay apparatus opens the circuit breaker arrange | positioned at the power transmission line at the time of internal determination, and disconnects the said power transmission line from a system | strain.

  A short-circuit distance relay device that detects a short-circuit accident of a transmission line to be protected is mainly used when detecting a three-phase short-circuit and a two-phase short-circuit accident of a transmission line. This short-circuit distance relay device can correctly calculate the impedance up to the accident point by using the line voltage and line current of the transmission line as the amount of electricity used for calculating the impedance.

  Here, considering the case where a short-circuit distance relay device is used for two parallel transmission lines in an ineffective grounding power system, the line voltage and line current can be used for a short-circuit accident on one line. It is possible to calculate the impedance correctly. However, when a two-phase ground fault occurs in different phases on both lines (hereinafter also referred to as a different-phase ground fault), the impedance cannot be calculated correctly even though the entire system is equivalent to a two-phase short-circuit fault. In this case, there is a problem that the distance relay device installed in each line does not operate, and a technique for improving this has been proposed.

  For example, Japanese Patent Laid-Open No. 8-205387 (Patent Document 1) discloses a phase current type distance protection relay device for a multiphase balanced two-line power transmission line having a first line and a second line. This device is considering that it is possible to detect a fault even when a ground fault occurs in different phases of one line and two lines.

JP-A-8-205387

  However, the phase current type short-circuit distance relay device disclosed in Patent Document 1 calculates the impedance by dividing the line voltage by twice the phase current. Therefore, when a two-phase short-circuit accident occurs in one of the parallel two-line transmission lines, the device calculates an impedance that is half of the impedance up to the actual fault point (that is, accurately calculates the impedance up to the fault point). Cannot be calculated). From this, the phase current short-circuit distance relay device according to Patent Document 1 may erroneously detect an internal accident even though a short-circuit accident has occurred outside the protection range.

  The present disclosure has been made in view of the problems as described above, and an object in one aspect is to detect a short-circuit accident in one line of a parallel two-line power transmission line and an out-of-phase ground fault across both lines more accurately. A distance relay device and a transmission line protection method that can be performed.

  According to an embodiment, a distance relay device for protecting a multiphase parallel two-line power transmission line including a first power transmission line and a second power transmission line is provided. The distance relay device is configured to calculate a line voltage and a line current of the first power transmission line based on the voltage and current detected in the first power transmission line; A current generation unit capable of generating a combined current obtained by adding phase currents, an impedance calculation unit capable of calculating an impedance value based on the combined current and the line voltage, and an impedance value calculated by the impedance calculation unit And an accident detection unit that detects a short-circuit accident that occurs between the phases of the first transmission line and an accident that occurs across the first transmission line and the second transmission line based on the settling value.

  According to another embodiment, a transmission line protection method for protecting a multiphase parallel two-line transmission line including a first transmission line and a second transmission line is provided. The transmission line protection method includes a step of calculating a line voltage and a line current of the first transmission line based on the voltage and current detected in the first transmission line, and a zero phase of the first transmission line as the line current. A step of generating a combined current obtained by adding the current, a step of calculating an impedance value based on the combined current and the line voltage, a first impedance based on the calculated impedance value and a predetermined settling value. Detecting a short-circuit accident that occurs between the phases of the transmission line and an accident that occurs across the first transmission line and the second transmission line.

  According to the present disclosure, it is possible to more accurately detect a short-circuit accident in one line of parallel two-line transmission lines and an out-of-phase ground fault across both lines.

It is a figure which shows the parallel 2 line power transmission line with which the distance relay apparatus according to Embodiment 1 is applied. It is a figure which shows the structure of the distance relay apparatus according to Embodiment 1. It is a figure for demonstrating the specific structure of an auxiliary transformer. 3 is a block diagram showing a functional configuration of an arithmetic processing unit according to the first embodiment. FIG. It is a figure for demonstrating operation | movement of the distance relay apparatus at the time of the two-phase short-circuit accident in the one line side. It is a vector diagram showing each impedance when a two-phase short circuit accident occurs. It is a figure for demonstrating operation | movement of the distance relay apparatus at the time of the occurrence of a different-phase ground fault across both lines. It is a vector diagram which showed each impedance calculated by the distance relay apparatus according to a comparative example when a different-phase ground fault occurs. FIG. 6 is a vector diagram showing impedances calculated by the distance relay device according to the first embodiment when an out-of-phase ground fault occurs. 3 is a flowchart showing a processing procedure of an arithmetic processing unit according to the first embodiment. FIG. 11 is a block diagram showing a functional configuration of an arithmetic processing unit according to the second embodiment. 6 is a flowchart showing a processing procedure of an arithmetic processing unit according to the second embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

[Embodiment 1]
<Overall configuration>
FIG. 1 is a diagram showing a parallel two-line power transmission line to which the distance relay device according to the first embodiment is applied. Referring to FIG. 1, a parallel two-line transmission line of an ineffective grounding system is provided with a transmission line L <b> 1 (No. 1 line) and a transmission line L <b> 2 (No. 2 line) on bus line 3 connected to AC power supply 7. . The AC power supply 7 is, for example, a three-phase AC power supply supplied from a power company's substation equipment. A neutral point grounding device 17 is connected to the neutral point of the AC power source 7. The power transmission lines L1 and L2 constitute one line and two lines of 3-phase alternating current, respectively. Each of power transmission line L1 and power transmission line L2 includes three (a phase, b phase, c phase) power transmission lines.

  Instrument current transformers CT1 and CT2 are arranged on transmission lines L1 and L2, respectively, and detect each phase current of the corresponding transmission line. The distance relay devices 100 and 100A take in currents from the current transformers CT1 and CT2, respectively. Specifically, the distance relay device 100 takes in the phase currents of the a-phase, b-phase, and c-phase of the transmission line L1 from CT1. The distance relay device 100A takes in the phase currents of the a-phase, b-phase, and c-phase of the power transmission line L2 from the instrument current transformer CT2.

  In addition, the instrument transformer VT is connected to the bus 3 and detects each phase voltage of the transmission lines L1 and L2. The distance relay devices 100 and 100A take in the phase voltages of the a-phase, b-phase, and c-phase of the transmission line from the instrument transformer VT.

  The distance relay devices 100 and 100A perform computations necessary to protect the power system such as relay computations using the captured system electricity (current and voltage), respectively, and detect the occurrence of a system fault. Typically, distance relay devices 100 and 100A are digital-type protective relay devices for protecting power transmission lines L1 and L2, respectively.

<Configuration of distance relay device>
FIG. 2 is a diagram showing the configuration of the distance relay device according to the first embodiment. The configuration of the distance relay device 100A is the same as the configuration of the distance relay device 100.

  Referring to FIG. 2, distance relay device 100 includes an auxiliary transformer 10, an AD (Analog to Digital) conversion unit 20, and an arithmetic processing unit 30.

  The auxiliary transformer 10 takes in the grid electricity quantity from the instrument current transformer CT1 and the instrument transformer VT, converts it into a smaller electricity quantity, and outputs it. Specifically, the auxiliary transformer 10 takes in the grid electricity as shown in FIG.

  FIG. 3 is a diagram for explaining a specific configuration of the auxiliary transformer 10. Referring to FIG. 3, auxiliary transformer 10 includes an auxiliary transformer 11 and an auxiliary current transformer 12.

  The instrument transformer VT converts the primary side voltages V1a, V1b, and V1c of each phase into secondary side voltages V2a, V2b, and V2c. The auxiliary transformer 11 converts the secondary voltage V2a, V2a, V2c of each phase into each phase voltage Va, Vb, Vc suitable for the distance relay device 100, and outputs it to the AD converter 20.

  The instrument current transformer CT1 is configured to be able to measure a zero-phase current transformation together with each phase current of the transmission line L1. Specifically, instrument current transformer CT1 includes a current circuit (secondary circuit) for detecting each phase current and a residual circuit for detecting a zero-phase current that is a feedback circuit thereof. The instrument current transformer CT1 converts the primary currents I1a, I1b, and I1c of each phase into secondary currents I2a, I2b, and I2c. Further, the instrument current transformer CT1 converts the primary-side zero-phase current into the secondary-side zero-phase current I20.

  The auxiliary current transformer 12 converts the secondary currents I2a, I2b, I2c of each phase and the zero-phase current I20 of the secondary side to the respective phase currents Ia, Ib, Ic and zero-phase current suitable for the distance relay device 100, respectively. The data is converted to I0 and output to the AD converter 20.

  Referring again to FIG. 2, the AD conversion unit 20 is connected to the grid electricity quantity (phase voltages Va, Vb, Vc, phase currents Ia, Ib, Ic and zero-phase current I0) output from the auxiliary transformer 10. Is converted to digital data. Specifically, the AD conversion unit 20 includes filters 21 and 23, sample and hold (SH) circuits 24 and 25, a multiplexer 26, and an AD converter 27.

  The filters 21 and 23 are analog filters and remove high frequency noise components from the current and voltage waveform signals output from the auxiliary transformer 10. The outputs of the filters 21 and 23 are input to the SH circuits 24 and 25, respectively.

  The SH circuits 24 and 25 sample current and voltage waveform signals output from the filters 21 and 23, respectively, at a predetermined sampling period. Based on the timing signal input from the arithmetic processing unit 30, the multiplexer 26 sequentially switches the waveform signals input from the SH circuits 24 and 25 in time series and inputs the waveform signals to the AD converter 27.

  The AD converter 27 converts the waveform signal input from the multiplexer 26 from analog data to digital data. The AD converter 27 outputs the digitally converted waveform signal (digital data) to the arithmetic processing unit 30.

  The arithmetic processing unit 30 is mainly composed of a microcomputer. Specifically, the arithmetic processing unit 30 includes a CPU (Central Processing Unit) 32, a ROM (Read Only Memory) 33, a RAM (Random Access Memory) 34, a DO (Digital Output) circuit 36, and a DI (Digital Input) circuit 37. These are connected by a bus 31.

  CPU32 controls the operation | movement of the distance relay apparatus 100 by reading and running the program previously stored in ROM33 as a control part. The CPU 32 is, for example, a microprocessor. The hardware may be an FPGA (Field Programmable Gate Array) other than the CPU, an ASIC (Application Specific Integrated Circuit), a circuit having other arithmetic functions, or the like.

  Specifically, the CPU 32 takes in digital data from the AD conversion unit 20 via the bus 31. The CPU 32 executes a relay operation using the captured digital data in accordance with a program stored in the ROM 33. CPU32 determines the presence or absence of the accident of a protection area (area | region which should be protected) based on a relay calculation result. When the CPU 32 detects an accident (for example, when the impedance value is lower than the settling value), the circuit breaker connected to the power system to disconnect the accident section from the power system via the DO circuit 36. A shutoff command is output to CB.

  The DI circuit 37 receives, for example, a contact signal that is a signal indicating switching information of the switch. In addition to the contact signal from the circuit breaker CB, a contact signal indicating opening / closing information of a disconnector (not shown) may be input to the DI circuit 37.

<Functional configuration>
FIG. 4 is a block diagram showing a functional configuration of arithmetic processing unit 30 according to the first embodiment. Referring to FIG. 4, arithmetic processing unit 30 includes a line current calculation unit 102, a line voltage calculation unit 104, a current generation unit 106, an impedance calculation unit 108, and an accident detection unit 110. Note that the functional configuration shown in FIG. 4 mainly represents the function of the short-circuit distance relay element in the arithmetic processing unit 30.

  The line current calculation unit 102 is based on the phase currents Ia, Ib, and Ic output from the AD conversion unit 20, and the line currents Iab (= Ia−Ib), Ibc (= Ib−Ic), Ica (= Ic−Ia) is calculated. The line current calculation unit 102 outputs the line currents Iab, Ibc, and Ica to the current generation unit 106.

  The line voltage calculation unit 104 is based on the phase voltages Va, Vb, Vc output from the AD conversion unit 20, and the line voltages Vab (= Va-Vb), Vbc (= Vb-Vc) between the two phases. Vca (= Vc−Va) is calculated. The line voltage calculation unit 104 outputs the line voltages Vab, Vbc, Vca to the impedance calculation unit 108.

  The current generator 106 adds the zero-phase current I0 output from the AD converter 20 to the line currents Iab, Ibc, and Ica, and combines the currents Iab0 (= Iab + I0), Ibc0 (= Ibc + I0), Ica0 (= Ica + I0). ) Is generated. Current generation unit 106 outputs combined currents Iab0, Ibc0, and Ica0 to impedance calculation unit 108.

  The impedance calculation unit 108 determines the impedance Zab (= Vab / Iab0) between the two phases based on the combined currents Iab0, Ibc0, Ica0 corresponding to the two phases and the line voltages Vab, Vbc, Vca between the two phases. , Zbc (= Vbc / Ibc0), Zca (= Vca / Ica0). The impedance calculation unit 108 outputs the impedances Zab, Zbc, Zca to the accident detection unit 110.

  The accident detection unit 110 detects an accident based on the impedances Zab, Zbc, Zca and a predetermined settling impedance. Although details will be described later, the accident detection unit 110 can detect a short-circuit accident that occurs between the phases of the transmission line L1 and a different-phase ground fault that occurs across the transmission line L1 and the transmission line L2. When the accident detection unit 110 detects these accidents, it outputs a break command to the circuit breaker CB.

<Operation example>
Next, a specific operation of the distance relay device 100 when an accident occurs will be described. Hereinafter, the operation of the distance relay device 100 when a two-phase short-circuit accident occurs on one line side and when a different-phase ground fault occurs across both lines will be described.

(Operation at the time of two-phase short-circuit accident on one line side)
FIG. 5 is a diagram for explaining the operation of the distance relay device when a two-phase short-circuit accident occurs on one line side. In the example of FIG. 5, a case where a two-phase short-circuit accident occurs between the b-phase and the c-phase of the transmission line L1 will be described.

  Here, the accident current is determined by the magnitude of the voltage of the AC power source 7 and the impedance up to the accident point. This impedance has a resistance component and a reactance component, but the reactance component is dominant for the transmission line. Therefore, when the voltage of the AC power supply 7 is used as a reference, the phase of the accident current is delayed by 60 ° to 90 °. On the other hand, on the basis of the accident current, the voltage phase of the AC power supply 7 advances by 60 ° to 90 °.

  Note that a load current flows through an actual transmission line, but usually the magnitude of the accident current is sufficiently larger than the load current. Therefore, for convenience of explanation, the load current is ignored in the example of FIG. 5 (that is, the load current is zero). In addition, since the distance relay device calculates the impedance up to the accident point based on the voltage and current at the installation point, the impedance on the AC power source 7 side does not affect the calculation in principle. Therefore, the impedance of the bus 3 on the side of the AC power supply 7 is ignored. Furthermore, since a current does not flow through the neutral point grounding device 17 in the case of a two-phase short circuit accident, it is assumed that the current In is zero.

  Referring to FIG. 5, when a two-phase short-circuit accident occurs between the b-phase and c-phase of transmission line L1, no current flows in the a-phase of transmission line L1, and a positive fault current flows in b-phase. Flows, a negative fault current flows in the c phase, and no current flows in the neutral point. When the fault current is If, the phase currents Ia, Ib, and Ic are Ia = 0, Ib = If, and Ic = −If, respectively. The zero-phase current I0 is I0 = 0.

  Therefore, the above-described combined currents Iab0, Ibc0, and Ica0 are expressed as the following formulas (1) to (3).

Iab0 = Ia−Ib + I0 = 0−If + 0 = −If (1)
Ibc0 = Ib−Ic + I0 = If − (− If) + 0 = 2If (2)
Ica0 = Ic−Ia + I0 = −If−0 + 0 = −If (3)
Therefore, when the equations (1) to (3) are used, the impedances Zab, Zbc and Zca described above are expressed as the following equations (4) to (6).

Zab = Vab / Iab0 = Vab / (− If) (4)
Zbc = Vbc / Ibc0 = Vbc / 2If (5)
Zca = Vca / Ica0 = Vca / (− If) (6)
When the impedances Zab, Zbc, and Zca calculated as shown in the above equations (4) to (6) are expressed by vectors, they are shown as in FIG.

  FIG. 6 is a vector diagram showing each impedance when a two-phase short circuit accident occurs. In order to represent the characteristics of the distance relay device, an RX diagram as shown in FIG. 6 is used. The RX diagram shows the impedance as a polar coordinate vector. In FIG. 6, the horizontal axis R represents the resistance component, and the vertical axis X represents the reactance component. Further, Xs indicating a predetermined range in the positive direction from the origin of the vertical axis X is a settling value of the reactance element X.

  Referring to FIG. 6, a case is assumed where a short circuit accident occurs in two phases of bc phase at accident point F. The impedance bc of the bc phase is the correct impedance up to the accident point F. Note that the ab-phase impedance Zab and the ca-phase impedance Zca do not indicate the correct impedance up to the accident point, but this is a characteristic of the operation principle of the distance relay device using the line voltage and line current. There is no problem. Specifically, the distance relay device includes a reactance element having a distance measurement characteristic for measuring an electrical distance to the accident point F and a direction element having a direction characteristic for determining the direction of the accident point F (in FIG. 6). This is because it is realized by combining a plurality of basic characteristic elements such as the circle 600). Therefore, it is important that the impedance of the accident phase (in this case, the impedance Zbc) is correctly calculated.

(Operation at the time of different-phase ground fault across both lines)
FIG. 7 is a diagram for explaining the operation of the distance relay device when a different-phase ground fault occurs across both lines. In the example of FIG. 7, a case where a ground fault occurs in the b phase of the transmission line L1 and the c phase of the transmission line L2 at the same point will be described.

  Referring to FIG. 7, the b phase of power transmission line L1 and the c phase of power transmission line L2 are conducted with a low impedance such as a steel tower or the ground. Therefore, the accident current flowing from the AC power source 7 to the fault point F of the power transmission line L1 returns to the AC power source 7 via the fault point F of the power transmission line L2. Further, in the non-effective grounding system, a current determined by the impedance value may flow through the neutral point grounding device 17 in the event of a ground fault. However, since this current is sufficiently smaller than the accident current, it is ignored.

  Here, the distance relay device according to the first embodiment and the distance relay device according to the comparative example are compared, and the superiority of the distance relay device according to the first embodiment will be described. First, the operation of the distance relay device according to the comparative example when an out-of-phase ground fault as shown in FIG. 7 occurs will be described. Unlike the distance relay device 100 according to the first embodiment, the distance relay device according to the comparative example employs a method of calculating the impedance by dividing the line voltage by the line current. That is, the distance relay device according to the comparative example does not have the function of the current generation unit 106 described above.

  Referring to FIG. 7, when a different-phase ground fault occurs between the b phase of transmission line L1 and the c phase of transmission line L2 at the same point, current flows in the a phase and c phase of transmission line L1. In the b phase, a positive fault current flows. If the fault current is If, the phase currents Ia, Ib, and Ic are Ia = 0, Ib = If, and Ic = 0, respectively.

  Therefore, the line currents Iab, Ibc, Ica are expressed as the following formulas (7) to (9).

Iab = Ia−Ib = 0−If = −If (7)
Ibc = Ib-Ic = If-0 = If (8)
Ica = Ic−Ia = 0−0 = 0 (9)
Therefore, when the equations (7) to (9) are used, the impedances Zab, Zbc, Zca are expressed as the following equations (10) to (12).

Zab = Vab / Iab = Vab / (− If) (10)
Zbc = Vbc / Ibc = Vbc / If (11)
Zca = Vca / Ica = Vca / 0 = ∞ (12)
When the impedances Zab, Zbc, and Zca calculated as shown in the above equations (10) to (12) are represented by vectors, they are shown as in FIG.

  FIG. 8 is a vector diagram showing impedances calculated by the distance relay device according to the comparative example when a heterogeneous ground fault has occurred.

  Referring to FIG. 8, a case is assumed where a ground fault has occurred in phase b of power transmission line L1 at fault point F and a ground fault has occurred in phase c of power transmission line L2. In this case, the correct impedance up to the accident point F needs to be calculated as Vbc / 2If (impedance Zf in FIG. 8). However, the bc-phase impedance Zbc calculated by the distance relay device according to the comparative example is Vbc / If, as shown in the equation (11) and FIG. 8, and is twice the correct impedance Zf. That is, the distance relay device according to the comparative example cannot accurately determine the distance to the accident point F, and operates depending on the distance to the accident point F (for example, the accident point where the reactance element X is greater than 0.5Xs). There are cases where it is not possible.

  Next, the operation of the distance relay device according to the first embodiment when an out-of-phase ground fault as shown in FIG. 7 occurs will be described. Referring to FIG. 7, when an out-of-phase ground fault occurs at the same point between phase b of transmission line L1 and phase c of transmission line L2, assuming that the fault current is If, each phase current Ia, Ib, Ic and zero-phase current I0 are Ia = 0, Ib = If, Ic = 0, and I0 = If, respectively.

  Therefore, the above-described combined currents Iab0, Ibc0, and Ica0 are expressed as the following formulas (13) to (15).

Iab0 = Ia−Ib + I0 = 0−If + If = 0 (13)
Ibc0 = Ib-Ic + I0 = If-0 + If = 2If (14)
Ica0 = Ic−Ia + I0 = 0−0 + If = If (15)
Therefore, when the equations (13) to (15) are used, the impedances Zab, Zbc and Zca described above are expressed as the following equations (16) to (18).

Zab = Vab / Iab0 = Vab / 0 = ∞ (16)
Zbc = Vbc / Ibc0 = Vbc / 2If (17)
Zca = Vca / Ica0 = Vca / If (18)
When the impedances Zab, Zbc, Zca calculated as shown in the above formulas (16) to (18) are represented by vectors, they are shown as in FIG.

  FIG. 9 is a vector diagram showing impedances calculated by the distance relay device according to the first embodiment when a different-phase ground fault occurs.

  Referring to FIG. 9, a case is assumed where a ground fault has occurred in phase b of power transmission line L1 at fault point F and a ground fault has occurred in phase c of power transmission line L2. In this case, the bc-phase impedance Zbc calculated by the distance relay device 100 of the transmission line L1 is the correct impedance up to the accident point F.

  Similarly, on the transmission line L2 side, no current flows in the a-phase and b-phase of the transmission line L2, and a negative fault current flows in the c-phase. Therefore, the distance relay device 100A of the transmission line L2 calculates the current. The ca phase impedance Zca is the correct impedance up to the accident point F.

<Processing procedure>
FIG. 10 is a flowchart showing a processing procedure of the arithmetic processing unit according to the first embodiment. Referring to FIG. 10, arithmetic processing unit 30 calculates a line current and a line voltage based on the amount of electricity (voltage and current) of power transmission line L <b> 1 captured by auxiliary transformer 10 (step S <b> 100). . The arithmetic processing unit 30 adds the zero-phase current to the line current to generate a combined current (step S120). The arithmetic processing unit 30 calculates the impedance between the two phases based on the combined current and the line voltage (step S140).

  The arithmetic processing unit 30 determines whether or not an accident has occurred in the protection range based on the calculated impedance and the set value (settling impedance) (step S160). Specifically, the arithmetic processing unit 30 performs a short-circuit accident between the phases (two-phase short-circuit, three-phase short-circuit accident) within the protection range of the transmission line L1, and a different-phase ground fault that spans the transmission line L1 and the transmission line L2. It is determined whether any of them has occurred. If the accident has not occurred (NO in step S160), arithmetic processing unit 30 ends the process. When the accident has occurred (YES in step S160), arithmetic processing unit 30 outputs a cutoff command to circuit breaker CB installed in power transmission line L1 (step S180), and ends the process.

<Advantages>
According to the first embodiment, in a parallel two-line transmission line of an ineffective grounding system, a short-circuit accident between each phase of a single line (a two-phase short-circuit accident and a three-phase short-circuit accident) can be accurately detected as before. At the same time, it is possible to accurately detect an out-of-phase ground fault across both lines. That is, the out-of-phase ground fault protection performance can be improved without affecting the protection performance of the two-phase short circuit and the three-phase short circuit of the parallel two-line power transmission line. Moreover, since the accident can be detected with high accuracy by a simple configuration, the cost reduction of the distance relay device can be realized.

[Embodiment 2]
In Embodiment 1, the structure which detects the short circuit accident of the transmission line of protection object by the short circuit distance relay element in the distance relay apparatus 100 was demonstrated. Since the short-circuit distance relay element is a set of two phases, the impedance up to the accident point cannot be detected correctly in the case of a one-wire ground fault. Therefore, the distance relay device used in the ineffective grounding system includes the short-circuit distance relay element and a ground fault overvoltage relay element for detecting a one-line ground fault of the transmission line to be protected.

  In the resistance grounding method among the ineffective grounding methods, the accident current that flows at the time of a one-wire ground fault is considerably smaller than the accident current that flows at the time of a short-circuit accident, for example, about 1/50. Therefore, when the fault current flowing at the time of one-line ground fault in the resistance grounding method is sufficiently smaller than the short-circuit fault current, the short-circuit distance relay element does not operate even if a one-line ground fault occurs.

  However, in the compensated reactor grounding method among the ineffective grounding methods, the zero-phase current that flows at the time of a one-wire ground fault is relatively large. For this reason, the influence of this zero-phase current cannot be ignored, and if the zero-phase current is added to the line-to-line current, the calculation accuracy of the impedance of the short-circuit distance relay element is reduced at the time of a one-wire ground fault and malfunctions. There is a possibility. Therefore, in the second embodiment, a configuration will be described in which a zero-phase current is not added to the line current when a one-line ground fault is detected.

  Since <overall configuration> and <configuration of distance relay device> in the second embodiment are the same as those in the first embodiment, detailed description thereof will not be repeated.

  FIG. 11 is a block diagram showing a functional configuration of the arithmetic processing unit according to the second embodiment. Referring to FIG. 11, arithmetic processing unit 30A of distance relay device 100 according to the second embodiment includes line current calculation unit 102A, line voltage calculation unit 104A, current generation unit 106A, and impedance calculation unit 108A. And an accident detection unit 110A and a ground fault detection unit 112A. The arithmetic processing unit 30A corresponds to the arithmetic processing unit 30 illustrated in FIG. 2, but for the sake of distinction from the first embodiment, an additional code such as “A” is attached for convenience.

  Line current calculation unit 102A, line voltage calculation unit 104A, and accident detection unit 110A are the same as line current calculation unit 102, line voltage calculation unit 104, and accident detection unit 110 in FIG. 4, respectively.

  The ground fault accident detection unit 112A detects a one-line ground fault of the power transmission line L1 based on the voltage detected in the power transmission line L1. Specifically, the ground fault detection unit 112A detects a one-wire ground fault (ground fault phase) based on the phase voltages Va, Vb, Vc and the zero phase voltage. Specifically, the ground fault detection unit 112A is based on the magnitudes of the phase voltages Va, Vb, Vc and the zero phase voltage, and the phase relationship between the phase voltages Va, Vb, Vc and the zero phase voltage. Detect a one-line ground fault. That is, the ground fault detection unit 112A functions as a ground fault protection relay element (such as a ground fault overvoltage relay) that can detect the ground fault phase of the one-wire ground fault. The zero-phase voltage may be calculated based on each phase voltage (calculated from the sum of the respective phase voltages) or may be configured to be taken in by a grounded instrument transformer (not shown). The ground fault detection unit 112A outputs the detection result to the current generation unit 106A.

  When a one-line ground fault is not detected by the ground fault detecting unit 112A, the current generating unit 106A generates a combined current obtained by synthesizing the zero-phase current with the line current. In this case, the current generation unit 106A outputs the generated combined currents Iab0, Ibc0, and Ica0 to the impedance calculation unit 108A.

  On the other hand, when a one-line ground fault is detected by the ground fault detecting unit 112A, the current generating unit 106A does not generate a combined current obtained by combining the zero-phase current with the line current. In this case, the current generator 106A outputs the line currents Iab, Ibc, and Ica to the impedance calculator 108A. That is, the current generation unit 106A outputs the line currents Iab, Ibc, Ica received from the line current calculation unit 102A to the impedance calculation unit 108A as they are. Therefore, when a one-line ground fault is detected by the ground fault detection unit 112A, the line currents Iab, Ibc, Ica calculated by the line current calculation unit 102A are passed through the current generation unit 106A. Instead, the configuration may be such that the impedance is directly output to the impedance calculation unit 108A.

  When the combined current is not generated by the current generator 106A, the impedance calculator 108A determines the impedance Zab (= Vab) between the two phases based on the line currents Iab, Ibc, Ica and the line voltages Vab, Vbc, Vca. / Iab), Zbc (= Vbc / Ibc), Zca (= Vca / Ica). When the combined current is generated by the current generator 106A, the impedance calculator 108A determines the impedance between the two phases based on the combined currents Iab0, Ibc0, Ica0 and the line voltages Vab, Vbc, Vca. Zab (= Vab / Iab0), Zbc (= Vbc / Ibc0), and Zca (= Vca / Ica0) are calculated.

<Processing procedure>
FIG. 12 is a flowchart showing a processing procedure of the arithmetic processing unit according to the second embodiment. Referring to FIG. 12, arithmetic processing unit 30A calculates a line current and a line voltage based on the amount of electricity of power transmission line L1 taken in by auxiliary transformer 10 (step S200). The arithmetic processing unit 30A determines whether or not a one-wire ground fault has occurred based on the amount of electricity of the power transmission line L1 (step S210).

  If a one-line ground fault has not occurred (NO in step S210), arithmetic processing unit 30A adds a zero-phase current to the line current to generate a combined current (step S220), The impedance between each two phases is calculated based on the line voltage (step S240). When a one-line ground fault has occurred (YES in step S210), arithmetic processing unit 30A calculates an impedance between the two phases based on the line current and the line voltage (step S215).

  Next, arithmetic processing unit 30A determines whether or not a short circuit accident or an out-of-phase ground fault has occurred in the protection range based on the calculated impedance and the set value (step S260). Specifically, when a one-line ground fault has occurred, the arithmetic processing unit 30A determines the occurrence of the accident using the impedance calculated in step S240. When the one-line ground fault has not occurred, the arithmetic processing unit 30A determines the occurrence of the accident using the impedance calculated in step S215. If the accident has not occurred (NO in step S260), arithmetic processing unit 30A ends the process. When the accident has occurred (YES in step S260), arithmetic processing unit 30A outputs a cutoff command to circuit breaker CB installed in power transmission line L1 (step S280), and ends the process.

  When it is determined in step S210 that a one-line ground fault has occurred using the ground fault protection relay element, the arithmetic processing unit 30A outputs a trip signal to a circuit breaker or the like provided in the ground fault phase. May be.

<Advantages>
According to the second embodiment, when a one-line ground fault is detected, the process of adding the zero-phase current to the line current is not performed. Therefore, even if the distance relay device is applied to a grounding system in which a relatively large zero-phase current flows when a one-wire ground fault occurs, malfunction of the short-circuit distance relay element can be reliably prevented.

[Other embodiments]
In the above-described embodiment, the distance relay device 100 has been described with respect to the configuration in which the zero-phase current is detected using the residual circuit of the secondary circuit of the current transformer for the instrument. However, the configuration is not limited thereto. The distance relay device 100 may be configured to calculate the zero-phase current I0 based on the phase currents Ia, Ib, and Ic taken from the phase current transformers included in the instrument current transformer. Specifically, the zero-phase current I0 is calculated using an equation of I0 = Ia + Ib + Ic. In this case, for example, the line-current calculating unit 102 in FIG. 4 calculates the zero-phase current I0 using each phase current Ia, Ib, Ic and the above equation, and outputs it to the current generating unit 106. According to this configuration, it is not necessary to provide a residual circuit, and the zero-phase current can be calculated by software processing.

  The configuration illustrated as the above-described embodiment is an example of the configuration of the present invention, and can be combined with another known technique, and a part of the configuration is omitted without departing from the gist of the present invention. It is also possible to change the configuration.

  In the above-described embodiment, the processing and configuration described in the other embodiments may be adopted as appropriate.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  3 Busbars, 7 AC Power Supply, 10 Auxiliary Transformer, 11 Auxiliary Transformer, 12 Auxiliary Current Transformer, 17 Neutral Point Grounding Device, 20 AD Converter, 21, 23 Filter, 24, 25 SH Circuit, 26 Multiplexer, 27 Converter, 30, 30A arithmetic processing unit, 31 bus, 32 CPU, 33 ROM, 34 RAM, 36 DO circuit, 37 DI circuit, 100, 100A distance relay device, 102, 102A line current calculation unit, 104, 104A Line voltage calculation unit, 106, 106A Current generation unit, 108, 108A Impedance calculation unit, 110, 110A Accident detection unit, 112A Ground fault detection unit, CB breaker, CT1, CT2 Current transformer, L1, L2 Transmission line, transformer for VT instrument.

Claims (5)

A distance relay device for protecting a multiphase parallel two-line power transmission line including a first power transmission line and a second power transmission line,
A calculation unit that calculates a line voltage and a line current of the first power transmission line based on the voltage and current detected in the first power transmission line;
A current generator capable of generating a combined current obtained by adding the zero-phase current of the first transmission line to the line current;
An impedance calculator capable of calculating an impedance value based on the combined current and the line voltage;
Based on the impedance value calculated by the impedance calculation unit and a predetermined settling value, a short-circuit accident that occurs between the phases of the first transmission line, and the first transmission line and the second transmission line A distance relay device comprising: an accident detection unit that detects an accident that occurs across the board.   The distance relay device according to claim 1, wherein the zero-phase current of the first transmission line is detected by a residual circuit of a current transformer provided in the first transmission line.   The distance relay device according to claim 1, wherein the zero-phase current of the first power transmission line is calculated based on each phase current detected by a current transformer provided in the first power transmission line. Further comprising a ground fault detection unit for detecting a one-line ground fault of the first power transmission line based on the voltage and current detected in the first power transmission line;
When the one-line ground fault is detected by the ground fault detector, the current generator does not generate the combined current,
The impedance calculation unit calculates an impedance value based on the line current and the line voltage when the combined current is not generated by the current generation unit. The distance relay device according to item 1. A transmission line protection method for protecting a multiphase parallel two-line transmission line including a first transmission line and a second transmission line,
Calculating a line voltage and a line current of the first power transmission line based on the voltage and current detected in the first power transmission line;
Generating a combined current obtained by adding a zero-phase current of the first power transmission line to the line current;
Calculating an impedance value based on the combined current and the line voltage;
Based on the calculated impedance value and a predetermined settling value, a short circuit accident that occurs between the phases of the first power transmission line and the first power transmission line and the second power transmission line occurs. A method for protecting a transmission line, comprising the step of detecting an accident.

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