JP6570476B2 - Current differential protection relay device - Google Patents

Description

  The present disclosure relates to a current differential protection relay device for protecting a power system.

  2. Description of the Related Art Conventionally, a protective relay device that detects an accident or abnormality that has occurred in a power system has been used to operate the power system safely. For example, a representative example of the protective relay device is a digital current differential protective relay device for power transmission line protection.

  The digital current differential protection relay device measures the terminal current at each terminal, sends and receives digital data to each other via the transmission line, detects the system fault in the protection section from the difference current, and eliminates the accident To do.

  Conventionally, the transmission path used in this case employs a method of cyclically transmitting data at a predetermined cycle, for example, at a transmission rate of 54 kbps, 1.5 Mbps, or the like.

  As a technique employing the cyclic transmission method, for example, Japanese Patent Application Laid-Open No. 2004-260885 (Patent Document 1) discloses a current differential protection relay device. In this current differential protection relay device, a standard communication device can be used to realize a reduction in transmission speed when cyclic transmission is performed at a predetermined transmission interval (for example, electrical angle of 30 °). Are considering.

JP 2004-260885 A

Electric Cooperative Research Vol. 71, No. 1, Published by Electric Cooperative Research Society, July 6, 2015

  In the differential current protection relay device, the differential current is derived from the instantaneous value of the current at each terminal in order to detect a system fault. Therefore, the measurement timing of the terminal current at each terminal is accurately synchronized (sampling synchronization control). It is necessary to let Conventionally, this synchronization has been realized by using a communication device adopting the above-mentioned cyclic transmission method and a current differential protection relay device. Therefore, there is a problem that the system is complicated and expensive.

  Therefore, it is considered to use a general-purpose transmission method such as Ethernet (registered trademark) that has a large capacity, is inexpensive, and is highly available. However, the general-purpose transmission system has a larger transmission delay time difference between upstream and downstream and fluctuations in transmission delay time than the conventional cyclic transmission system using a dedicated line. There was a problem that the configuration of the relay device was further complicated.

  The present disclosure has been made in view of the above-described problems, and an object in one aspect thereof is a current differential protection relay device that can accurately determine an accident in a power system with a simple configuration. Is to provide.

  According to an embodiment, a current differential protection relay device for protecting a power system is provided. The current differential protection relay device performs data communication with another current differential protection relay device via a current input unit that receives the input of the first current on the end side of the protected section of the power system, and the transmission line. A transmission unit to be executed. The transmission unit receives data of the second current on the other end side of the protected section from another current differential protection relay device. The current differential protection relay device includes an effective value calculation unit that calculates an effective value of the first current and an effective value of the second current, and whether or not a phase difference between the first current and the second current is less than a reference threshold value. A phase determination unit that determines whether or not, a suppression current calculation unit that calculates a suppression current based on the effective value of the first current and the effective value of the second current, the determination result of the phase determination unit, and the effective value of the first current And a differential current calculation unit that calculates a differential current based on the value and the effective value of the second current. When the phase difference is less than the reference threshold, the differential current calculation unit calculates an addition value of the effective value of the first current and the effective value of the second current as the differential current. The differential current calculation unit calculates a subtraction value between the effective value of the first current and the effective value of the second current as the differential current when the phase difference is equal to or greater than the reference threshold value. The current differential protection relay device further includes an accident determination unit that performs an accident determination based on the differential current calculated by the differential current calculation unit and the suppression current.

  According to the present disclosure, it is possible to accurately determine an accident in the power system with a simple configuration.

It is a figure which shows the structural example of the protection relay system according to this Embodiment. It is a figure which shows an example of the hardware constitutions of the protection relay apparatus according to this Embodiment. It is a figure for demonstrating the sampling synchronous control system employ | adopted in the conventional current differential protection relay apparatus. It is a figure which shows the accident electric current in each electric station when an accident generate | occur | produces in the protection area of a power transmission line. It is a figure which shows the accident electric current in each electric station when an accident generate | occur | produces outside the protection area of a power transmission line. It is a figure which shows the ratio differential characteristic according to this Embodiment. It is a schematic diagram which shows the function structure of the protective relay apparatus according to this Embodiment. It is a figure for demonstrating the phase determination system according to this Embodiment. It is a figure which shows the process sequence of the protection relay apparatus according to this Embodiment.

  Hereinafter, the present embodiment will be described with reference to the drawings. Note that the same or corresponding portions are denoted by the same reference numerals, and the description thereof may not be repeated.

<System configuration>
FIG. 1 is a diagram showing a configuration example of a protective relay system 1000 according to the present embodiment.

  Referring to FIG. 1, a protection relay system 1000 uses a current differential protection relay device (hereinafter also simply referred to as “protection relay device”) to transmit a power line between two electrical stations (protected section). It is a system for protecting. Specifically, the protective relay system 1000 includes an electric station (substation) 1A, an electric station (substation) 1B, a transmission line TL connecting the electric station 1A and the electric station 1B, and a transmission path 40. including.

  For example, an Ethernet (registered trademark) network, which is a general-purpose transmission method, is used as the transmission path 40, but an IP network-compatible network that employs another packet communication transmission form may be used. In other words, the transmission line 40 is not a power dedicated communication network adopting a cyclic transmission method, but a standard network that can change the transmission delay time at any time.

  The electric station 1A includes a protective relay device 10A, a circuit breaker 20A that disconnects the power transmission line in the event of an accident in the power transmission line TL, and a current transformer 30A that detects current information of the power transmission line TL. The electric station 1B includes a protective relay device 10B, a circuit breaker 20B that disconnects the power transmission line in the event of an accident in the power transmission line TL, and a current transformer 30B that detects current information of the power transmission line TL. The power transmission line TL is connected to the bus bar 3A via the circuit breaker 20A, and is connected to the bus bar 3B via the circuit breaker 20B. The bus 3A is connected to the power source 5A behind the electric station 1A, and the bus 3B is connected to the power source 5B behind the electric station 1B.

  Protective relay devices 10A and 10B (hereinafter also collectively referred to as “protective relay device 10”) are typically digital-type current differential protective relay devices that employ a ratio differential system. The protective relay device 10A takes in the current information of the power transmission line TL via the secondary circuit of the current transformer 30A, converts this current information into a digital signal, and then connects the communication device (not shown) such as a router and the transmission path 40. Current information is exchanged with the protective relay device 10B.

  Specifically, the protective relay device 10A transmits the current information to the protective relay device 10B via a downlink transmission path (a transmission path from the protective relay device 10A to the protective relay device 10B) in the transmission path 40. Transmit to. The protective relay device 10A passes through the upstream transmission path (the transmission path from the protective relay apparatus 10B to the protective relay apparatus 10A) in the transmission path 40 at the electric station 1B transmitted from the protective relay apparatus 10B. Receive current information.

  The protective relay device 10A performs a current differential calculation based on the current information on the own end side (point A side in FIG. 1) and the current information on the other end side (point B side in FIG. 1) of the transmission line TL. And the accident determination of the power transmission line TL is performed based on a predetermined threshold value. When the protective relay device 10A detects an accident (internal accident) that occurs in the protection section (for example, point 500) of the transmission line TL between the electric station 1A and the electric station 1B, the protective relay device 10A Trip signal) is output.

  In addition, since the same processing as that of the protective relay device 10A is executed in the protective relay device 10B, the description thereof will not be repeated here.

<Hardware configuration>
FIG. 2 is a diagram showing an example of a hardware configuration of protection relay device 10A according to the present embodiment. Referring to FIG. 2, protective relay device 10 </ b> A includes an auxiliary transformer 50, an AD (Analog to Digital) conversion unit 60, and an arithmetic processing unit 70.

  The auxiliary transformer 50 is connected to the secondary circuit of the current transformer 30A, takes in the electric quantity (current) of the transmission line TL, converts it into a smaller electric quantity, and outputs it.

  The AD converter 60 takes in the electric quantity (analog quantity) output from the auxiliary transformer 50 and converts it into digital data. Specifically, the AD conversion unit 60 includes an analog filter 61, a sample hold (SH) circuit 63, a multiplexer 65, and an AD converter 67.

  The analog filter 61 removes high-frequency noise components from the current waveform signal output from the auxiliary transformer 50. The output of the analog filter 61 is input to the sample hold circuit 63.

  The sample and hold circuit 63 samples the waveform signal of the current output from the analog filter 61 at a predetermined sampling period. Typically, an integer multiple (for example, 12 times or 16 times) of the rated frequency of the protection system is selected as the sampling frequency, and is set to a frequency required in the relay operation.

  The multiplexer 65 sequentially switches the waveform signal input from the sample hold circuit 63 in time series based on the timing signal input from the arithmetic processing unit 70 and inputs the waveform signal to the AD converter 67. Normally, since the protective relay device handles three-phase alternating current, there are three or more sets of the current transformer 30A, the filter 61, and the sample hold circuit 63, and these are connected in parallel to the multiplexer 65. It becomes a form. FIG. 2 shows a simplified diagram for ease of explanation.

  The AD converter 67 converts the waveform signal input from the multiplexer from analog data to digital data. The AD converter 67 outputs the digitally converted waveform signal to the arithmetic processing unit 70.

  The arithmetic processing unit 70 includes a central processing unit (CPU) 72, a read only memory (ROM) 73, a random access memory (RAM) 74, a human machine interface (HMI) 75, and an output interface (I / F) 76. And an input interface (I / F) 77 and a communication interface (I / F) 78. These are connected by a bus 71.

  The CPU 72 controls the operation of the protective relay device 10 by reading and executing a program stored in advance in the ROM 73. The ROM 73 stores various information used by the CPU 72. The CPU 72 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.

  The CPU 72 takes in digital data from the AD conversion unit 60 via the bus 71. The CPU 72 executes a relay operation using the acquired digital data in accordance with a program stored in the ROM 73. The CPU 72 outputs a break command to the breaker 20A via the output interface 76 based on the relay calculation result.

  Further, the CPU 72 is connected to the transmission line 40 via the communication interface 78 and transmits / receives various information to / from the other protective relay device 10. The input interface 77 is typically a switch for various settings or the like, and accepts various setting operations from the system operator.

  Note that the hardware configuration of the protective relay device 10B is the same as the hardware configuration of the protective relay device 10A described above, and thus detailed description thereof will not be repeated.

<About sampling synchronization control>
As described above, since the conventional current differential protection relay device calculates the difference current from the instantaneous value of the current at each terminal in order to detect a system fault, it is necessary to execute the sampling synchronous control with high accuracy.

  Here, in order to understand the present embodiment, sampling synchronization in the conventional protective relay device when it is assumed that the uplink and downlink transmission delay times are the same (that is, when the cyclic transmission method is adopted). The principle of control will be described.

  FIG. 3 is a diagram for explaining a sampling synchronization control method employed in a conventional current differential protection relay device. Referring to FIG. 3, from the sampling timing of the first protective relay device (corresponding to “first device” in FIG. 3), the second protective relay device (“second device” in FIG. 3) is changed. The time until the data reception at the sampling timing of (corresponding) is TQ. In addition, the time from the sampling timing of the second protective relay device to the reception of the sampling timing data of the first protective relay device is defined as TG. Further, the transmission delay time of transmission from the second protection relay device to the first protection relay device is Td1, and the transmission delay time of transmission from the first protection relay device to the second protection relay device is Let Td2 and the sampling synchronization error be ΔT.

  In this case, TQ = Td1−ΔT and TG = ΔT + Td2. Here, assuming that the transmission delay times Td1 and Td2 of the upstream and downstream transmission lines are the same, in order to set the sampling synchronization error ΔT to 0 (synchronize), the sampling timing is set so that TQ = TG. It can be seen that control is required. For example, the time TQ measured by the first protective relay device is transmitted to the second protective relay device. The second protection relay device shifts the sampling timing so that the measured time TG is the same as the received time TQ. Thereby, sampling (sampling synchronization) at the same time can be realized.

  However, in this embodiment, the transmission path 40 is not a power-dedicated communication network adopting a conventional cyclic transmission system, but a general-purpose transmission system in which transmission delay time fluctuations may occur due to sharing with other external devices, etc. Network is adopted. Therefore, the uplink and downlink transmission delay times from the start of data transmission to the completion of data reception vary (that is, the transmission delay time Td1 and the transmission delay time Td2 vary). Even if the synchronization control method is used, the synchronization error cannot be corrected, the difference current error becomes large, and an accurate accident determination cannot be performed.

<Outline of accident determination method>
The protective relay device 10 according to the present embodiment performs an accident determination without executing the sampling synchronization control as described above even when a general-purpose transmission network is employed. Here, an outline of the accident determination method in the protective relay device 10 will be described.

  FIG. 4 is a diagram illustrating an accident current at each electric station when an accident occurs in the protection section of the transmission line TL. When an accident occurs at a point 500 in the protection section of the transmission line TL (see FIG. 1), an accident current flows through the current transformer 30A from the rear power source 5A of the electric station 1A toward the point 500. A current waveform 600A in FIG. 4 shows the current waveform of the accident current measured by the current transformer 30A. On the other hand, the fault current flows from the power source 5B behind the electric station 1B toward the point 500 in the current transformer 30B. A current waveform 600B in FIG. 4 shows the current waveform of the accident current measured by the current transformer 30B.

  In the power system, a plurality of power sources are generally linked, and each power source is operated in a synchronized state. Specifically, the back power supply 5A and the back power supply 5B in FIG. 1 are almost synchronized (phase). In FIG. 1, the bus voltage of the rear power supply 5A is Vs, the bus voltage of the rear power supply 5B is Vr, the phase difference between Vs and Vr is δ, the reactance of the transmission line between point A and point B is X, and from point A to point B Assuming that the effective power flowing is P, P = Vs × Vr × sinδ / X. In order to generate active power, it is necessary to set δ> 0. However, if this value is increased, the stability of the system is lowered, so that the phase difference δ is usually less than a certain value (about ± 15 °). System operation. Therefore, when it is assumed that the protection relay device 10A and the protection relay device 10B have the same sampling timing (no sampling time difference), as shown in FIG. The current waveform 600A measured at 30A and the current waveform 600B measured by the current transformer 30B on the other end side are substantially in phase.

  Specifically, when an internal accident occurs, the phase difference Δθ between the accident current measured on the own end side (current waveform 600A) and the accident current measured on the other end side (current waveform 600B) is the same phase direction. (For example, | Δθ | <θth = 90 °). Here, θth is a reference threshold for the phase difference of each terminal current measured at each end (own end and other end), and is set to 90 °, for example.

  FIG. 5 is a diagram illustrating an accident current at each electric station when an accident occurs outside the protection section of the transmission line TL. Here, when an accident occurs at a point 510 outside the protection section of the transmission line TL (see FIG. 1), the current transformer 30A and the current transformer 30B have an accident from the power source 5A behind the electric station 1A toward the point 510. Current flows. The current waveform 610A in FIG. 5 shows the current waveform of the fault current measured by the current transformer 30A, and the current waveform 610B shows the current waveform of the fault current measured by the current transformer 30B.

  Therefore, when it is assumed that the sampling timings of the protective relay device 10A and the protective relay device 10B are the same, as shown in FIG. 5, the current waveform 610A and the current waveform 610B are substantially in reverse phase. . Specifically, when an external accident occurs, the phase difference Δθ between the accident current measured on the own end side (current waveform 610A) and the accident current measured on the other end side (current waveform 610B) is reversed. It can be said that the phase direction is (for example, | Δθ | ≦ 90 °).

  However, since a sampling time difference actually occurs, it is necessary to consider the time difference when making an accident determination. Further, since the protective relay device 10 performs the accident determination based on the current on the own end side and the current on the other end side transmitted from the other protective relay device 10, the protective relay device 10 It is also necessary to consider the transmission delay time to the device itself.

  First, it is assumed that the sampling time difference between the protective relay device 10A and the protective relay device 10B is Tsp, and an internal accident occurs. In this case, referring to FIG. 4, due to the influence of sampling time difference Tsp, the fault current waveform measured by current transformer 30B is represented as current waveform 600B1. Further, in consideration of the transmission delay time Td of upstream transmission from the protective relay device 10B to the protective relay device 10A, the current data on the other end side received by the protective relay device 10A of the electric station 1A from the protective relay device 10B. The current waveform based on is expressed as 600B2. That is, the phase of current waveform 600B2 is delayed from the phase of current waveform 600A by a phase corresponding to sampling time difference Tsp and transmission delay time Td.

  Next, assume that an external accident occurs. In this case, referring to FIG. 5, due to the influence of sampling time difference Tsp, the fault current waveform measured by current transformer 30B is represented as current waveform 610B1. A current waveform based on the current data on the other end side received by the protective relay device 10A from the protective relay device 10B is expressed as 610B2. That is, the phase of current waveform 610B2 is delayed from the phase of current waveform 610A by a phase corresponding to sampling time difference Tsp and transmission delay time Td.

  Here, the sampling time difference Tsp and the transmission delay time Td are considered. For example, when the sampling frequency is 12 times the rated frequency, the sampling time difference Tsp is a time corresponding to an electrical angle of 30 ° at the maximum. Further, in Chapter 4 of Non-Patent Document 1, transmission delay time in a two-terminal one-line model is examined. According to the examination result, the maximum transmission delay time is estimated to be about 1.55 ms. The time is a time corresponding to an electrical angle of about 28 ° when the rated frequency is 50 Hz, and a time corresponding to an electrical angle of about 33 ° when the rated frequency is 60 Hz. From this, it can be said that the transmission delay time is within the electrical angle of about 30 ° at the maximum.

  From this, it is considered that the sampling time difference Tsp and the transmission delay time Td may cause a phase difference of about 60 ° in electrical angle at the maximum in each terminal current (own end current and other end current). Since this electrical angle is within the above-described reference threshold (90 °), it does not affect the determination result of whether each terminal current is in the in-phase direction or in the opposite phase direction. Specifically, even if it is affected by the phase difference due to the sampling time difference Tsp and the transmission delay time Td, if an internal accident occurs, the protective relay device 10 determines that the reference threshold Using the phase of the current and the phase of the fault current on the other end side, each fault current can be determined to be in the same phase direction. That is, the protective relay device 10 is not erroneously determined to be in the reverse phase direction when an internal accident occurs. Similarly, the protective relay device 10 is not erroneously determined to be in the same phase direction when an external accident occurs.

  As described above, the protective relay device 10 accurately determines the direction (in-phase direction or reverse-phase direction) of each terminal current based on the phase difference between the terminal currents on the own end side and the other end side and the reference threshold value. Can be calculated well. The protective relay device 10 changes the calculation method of the differential current according to the determination result of the direction of each terminal current. Specifically, the protective relay device 10A determines the differential current as the sum of the effective values of the terminal currents when the terminal currents are in the same phase direction (when an internal fault may have occurred). When each terminal current is in the opposite phase direction, the subtraction value of the effective value of each terminal current is calculated as a differential current. Then, when the suppression current and the differential current satisfy a predetermined relationship, the protective relay device 10 determines that an internal accident has occurred and outputs a cutoff command. Typically, as the suppression current, the larger of the effective value of the local current or the effective value of the other-end current is used.

  FIG. 6 shows a ratio differential characteristic according to the present embodiment. In FIG. 6, the vertical axis indicates the differential current Id, and the horizontal axis indicates the suppression current Ir. Referring to FIG. 6, the ratio differential characteristic includes a small current region characteristic represented by a straight line 80 and a large current region characteristic represented by a straight line 81. The small current region characteristic is a characteristic for enabling detection even when the accident current is small at the time of an internal accident. The large current characteristic is a characteristic for preventing an operation with an error current caused by an increase in the error of the current transformer due to the large current when a large current passes during an external accident.

  A point (Ir, Id) indicating the suppression current Ir and the differential current Id is present in the operation region 82 (region above the straight line 80 and above the straight line 81) in both the small current region characteristic and the large current property. In the case (when the suppression current and the differential current satisfy a predetermined relationship), the protective relay device 10 performs a relay operation (output of a cutoff command). For example, when (Ir, Id) exists at point 95, it is normal (no accident occurrence), and when it exists at point 96, it is determined that an internal accident has occurred. When (Ir, Id) exists at the point 97, it is determined that there is a high possibility that an external accident has occurred because the differential current is small and the suppression current is large.

  Here, in the present embodiment, as described above, when each terminal current is in the in-phase direction, the differential current increases, and when each terminal current is in the opposite phase direction, the differential current decreases. (It becomes almost 0). Therefore, when an internal accident occurs and each terminal current is in the same phase direction (when the differential current is large), the shutoff command is output satisfying the above relationship, but no internal accident has occurred and each terminal When the current is in the reverse phase direction (when the differential current is approximately 0), the above relationship is not satisfied, and therefore the cutoff command is not output.

  As described above, the protective relay device 10 according to the present embodiment sets the reference threshold (set to approximately 90 °) in consideration of the phase difference that may occur due to the sampling time difference Tsp and the transmission delay time Td. The direction of each terminal current (in-phase direction or opposite-phase direction) can be calculated with high accuracy. Further, the protective relay device 10 calculates an appropriate differential current according to the calculated direction of each terminal current, and executes an accident determination using the differential current and the suppression current. Further, since the effective value is used instead of the instantaneous value of each terminal current when calculating the differential current, the magnitude of the differential current is not affected by the sampling time difference Tsp and the transmission delay time Td. Absent. Therefore, even when a general-purpose transmission network that can cause transmission delay is employed, accident determination can be performed with a simple configuration with high accuracy.

<Functional configuration>
FIG. 7 is a schematic diagram showing a functional configuration of the protective relay device 10 according to the present embodiment. Referring to FIG. 7, the protective relay device 10 includes a current input unit 110, a transmission unit 120, an effective value calculation unit 130, a phase determination unit 140, a suppression current calculation unit 150, and a differential current calculation unit. 160 and the accident determination part 170 are included. Each of these functions is realized, for example, when the CPU 72 of the arithmetic processing unit 70 executes a program stored in the ROM 73. Note that some or all of these functions may be implemented by hardware.

  The current input unit 110 receives input of digital data (own end current Ia) of current (self end current) measured by the current transformer 30A provided on the own end side of the transmission line TL for each sampling period. Current input unit 110 outputs self-end current Ia to effective value calculation unit 130 and phase determination unit 140.

  The transmission unit 120 performs data communication with the other protective relay device 10 via the transmission line 40. In this embodiment, a general-purpose transmission system network (for example, an Ethernet network) is used as the transmission path 40. Therefore, typically, the transmission unit 120 performs data communication according to a standard that can change the transmission delay time at any time.

  The transmission unit 120 receives the digital data (the other end current Ib) of the current (the other end current Ib) measured by the current transformer 30B provided on the other end side of the transmission line TL from the protective relay device 10B. The transmission unit 120 outputs the received other-end current Ib to the effective value calculation unit 130 and the phase determination unit 140. In addition, the transmission part 120 may transmit the self-terminal current Ia received by the current input part 110 to the protective relay device 10B.

  The effective value calculation unit 130 calculates the effective value Iea of the local current Ia and the effective value Ieb of the other-end current Ib. Various known methods can be used as the effective value calculation method. For example, the effective value Iea is calculated using the following equation (1) by the amplitude square method.

Iea = {Ia ² (t) + Ia ² (t-90 °)} ^1/2 ... (1)
Note that the effective value Ieb is calculated in the same manner using the equation (1). The effective value calculation unit 130 outputs the effective value Iea and the effective value Ieb to the phase determination unit 140, the suppression current calculation unit 150, and the differential current calculation unit 160.

  Phase determination unit 140 includes a phase reference setting unit 142 and a phase discrimination unit 144. The phase reference setting unit 142 sets the current corresponding to the larger effective value of the effective value Iea and the effective value Ieb as the phase reference current Is. For example, when the effective value Iea is larger than the effective value Ieb, the phase reference setting unit 142 sets the self-terminal current Ia to the phase reference current Is. This is because setting the current corresponding to the larger effective value to the phase reference current Is increases the detection accuracy of the phase difference than setting the current corresponding to the smaller effective value to the phase reference current Is. Because it can. When both the effective value Iea and the effective value Ieb are equal to or higher than a certain value and a certain detection accuracy is maintained, the self-terminal current Ia or the other-end current Ib is set as the phase reference current Is. May be. The phase reference setting unit 142 outputs the phase reference current Is to the phase discrimination unit 144.

  FIG. 8 is a diagram for describing a phase determination method according to the present embodiment. Here, it is assumed that the reference threshold θth is set to 90 °. Referring to FIG. 8, the phase discriminating unit 144 calculates the phase difference between the local end current Ia and the other end current Ib based on the phase reference current Is. For example, when the phase reference current Is corresponds to the self-terminal current Ia, the phase difference of the other-end current Ib (corresponding to Ii in the drawing) with respect to the self-terminal current Ia is calculated. Various known methods can be used as the phase difference calculation method. For example, the phase difference θ is calculated using the following equation (2) by the right-angle 2-sample calculation method.

Iea × Ieb × cоsθ = Ia (t) × Ib (t) + Ia (t-90 °) × Ib (t-90 °) (2)
The phase discriminating unit 144 determines whether or not the calculated phase difference is less than the reference threshold θth. For example, when the phase difference of the other current Ii with respect to the phase reference current Is is θ1, the phase discriminating unit 144 determines that the phase difference is less than the reference threshold θth. In this case, the phase discriminating unit 144 may determine that the own-end current Ia and the other-end current Ib are in the same phase direction, or may determine that an internal accident may have occurred. On the other hand, when the phase difference is θ2, the phase discriminating unit 144 determines that the phase difference is greater than or equal to the reference threshold θth. In this case, the phase discriminating unit 144 may determine that the own-end current Ia and the other-end current Ib are in opposite phases, and at least an internal accident has not occurred (the possibility of an external accident has occurred). May be determined).

  If no current is flowing from one of the power sources for some reason, the effective value of the other current Ii becomes 0 (or extremely small) even if an internal accident occurs. Therefore, as an exception, when the effective value of the other current Ii is extremely small, even if it is equal to or greater than the reference threshold θth (corresponding to the region G), it may be determined that an internal accident may have occurred. Good.

  Again referring to FIG. 7, phase discriminating unit 144 outputs the determination result as described above to differential current calculating unit 160.

  The suppression current calculation unit 150 calculates the suppression current Ir based on the effective value Iea and the effective value Ieb. Specifically, when the maximum value control method is used, the suppression current calculation unit 150 compares the effective value Iea and the effective value Ieb, and calculates the larger effective value as the suppression current Ir. When using the scalar suppression method, the suppression current calculation unit 150 may be configured to calculate the scalar sum of the effective value Iea and the effective value Ieb as the suppression current Ir. The suppression current calculation unit 150 outputs the suppression current Ir to the accident determination unit 170.

  The differential current calculation unit 160 calculates the differential current Id based on the determination result of the phase determination unit 140, the effective value Iea, and the effective value Ieb. Specifically, the differential current calculation unit 160 includes an addition unit 162, a subtraction unit 164, and a differential current selection unit 166.

  The adder 162 outputs an addition value Iad (= Iea + Ieb) of the effective value Iea and the effective value Ieb to the differential current selection unit 166. The subtraction unit 164 outputs a subtraction value Isb (= | Iea−Ieb |), which is an absolute value of a difference between the effective value Iea and the effective value Ieb, to the differential current selection unit 166.

  When the phase determination unit 140 determines that the phase difference is less than the reference threshold θth, the differential current selection unit 166 selects (calculates) the added value Iad as the differential current. The differential current selection unit 166 selects (calculates) the subtraction value Isb as the differential current when the phase determination unit 140 determines that the phase difference is equal to or greater than the reference threshold θth. The differential current selection unit 166 outputs the selected (calculated) differential current Id to the accident determination unit 170.

  The accident determination unit 170 performs an accident determination based on the differential current Id calculated (selected) by the differential current calculation unit 160 and the suppression current Ir. Specifically, based on the characteristic diagram shown in FIG. 6, the accident determination unit 170 determines that an internal accident has occurred when a point (Ir, Id) indicating the suppression current Ir and the differential current Id exists in the operating region 82. It is determined that it has occurred. In this case, the accident determination unit 170 outputs a cutoff command to the circuit breaker via the output interface 76.

<Processing procedure>
FIG. 9 is a diagram showing a processing procedure of the protective relay device 10A according to the present embodiment. Typically, each step shown in FIG. 9 is executed by the arithmetic processing unit 70 of the protective relay device 10A. The following steps are executed every predetermined sampling period.

  Referring to FIG. 9, protective relay device 10A acquires self-end current Ia that is a digital value of the current measured by current transformer 30A (step S10). The protective relay device 10A transmits the self-terminal current Ia to the protective relay device 10B via the transmission path 40 (step S12). The protective relay device 10A receives the other-end current Ib from the protective relay device 10B via the transmission line 40 (step S14).

  The protective relay device 10A calculates the effective value Iea of the self-terminal current Ia and the effective value Ieb of the other-end current Ib (step S16). The protective relay device 10A calculates the suppression current Ir based on the effective value Iea and the effective value Ieb (step S18). The protective relay device 10A sets the phase reference current Is based on the effective value Iea and the effective value Ieb (step S20).

  The protective relay device 10A determines whether or not the phase difference of the other current Ii with respect to the phase reference current Is is less than the reference threshold θth (step S22). When the phase difference is less than the reference threshold θth (YES in step S22), the effective value Iea and the added value Iad of the effective value Ieb are calculated as the differential current Id (step S24). On the other hand, when the phase difference is equal to or larger than the reference threshold θth (NO in step S22), the effective value Iea and the subtraction value Isb of the effective value Ieb are calculated as the differential current Id (step S26).

  The protective relay device 10A determines whether or not an internal accident has occurred based on the suppression current Ir and the differential current Id (step S28). If no internal accident has occurred (NO in step S28), protective relay device 10A ends the process. When an internal accident has occurred (YES in step S28), protective relay device 10A outputs a break command to breaker 20A (step S30), and ends the process.

<Advantages>
According to the present embodiment, the accident determination can be performed with high accuracy even when the sampling timing does not match and when it is affected by the transmission delay time. Further, even when a general-purpose transmission network is employed, sampling synchronous control is not executed, so that it is not necessary to introduce an expensive device or employ a complicated configuration for the control. As a result, the cost of the apparatus can be reduced.

  In addition, if a general-purpose network is adopted for a conventional current differential protection relay device, sampling synchronous control cannot be performed accurately due to the effect of transmission delay time fluctuations, so the ratio differential characteristic shown in FIG. 5 needs to be reviewed. It becomes. Specifically, since it is necessary to secure a large margin between the maximum differential current that can be generated at the maximum value of the load current (differential current in a normal state) and the operation region 82, the slope of the straight line 80 is conventionally set. It is necessary to reduce the operation sensitivity by setting a larger value.

  On the other hand, according to the present embodiment, since the differential current is calculated using the effective value instead of the instantaneous value of each terminal current, the sampling time difference Tsp and the transmission delay time Td are calculated for the magnitude of the differential current. It will not be affected. Therefore, it is not necessary to review the ratio differential characteristic, and it is not necessary to lower the operation sensitivity. Thereby, even if it is a case where a general purpose network is employ | adopted, a more accurate accident determination can be implement | achieved.

<Other embodiments>
(1) In the above-described embodiment, when the sampling frequency is 12 times the rated frequency and the maximum transmission delay time is about 1.55 ms (Chapter 4 of Non-Patent Document 1), the sampling time difference Tsp and It has been explained that the transmission delay time Td may cause a phase difference of about 60 ° electrical angle at the maximum. Therefore, it has been explained that, under the above conditions, if the reference threshold value θth is set to about 90 °, the direction of each terminal current (in-phase direction and reverse-phase direction) will not be erroneously determined.

  Here, for example, when the sampling time difference and the transmission delay time can be grasped in advance, the above determination can be made more accurately by setting a reference threshold in consideration of the phase difference of each terminal current that can be generated by these. It is thought that it can be performed. Regarding this point, it is difficult to grasp the sampling time difference in advance, but the sampling interval time (for example, 30 °) is the maximum. Further, in a general-purpose transmission system network, the transmission delay time fluctuates all the time, so that it is difficult to fully grasp. However, the transmission delay time can be divided into a variable part and a fixed part, and the fixed part can be grasped in advance. Specifically, the fixed transmission delay time is a transmission delay time generated as a fixed value in a device such as a switch constituting the IP network, and can be calculated based on the number and specifications of the device.

  Therefore, the reference threshold value θth used in the protective relay device 10A may be set based on a phase corresponding to a fixed transmission delay time among the transmission delay times of uplink transmission. Specifically, when it is assumed that the transmission delay time of uplink transmission and the transmission delay time of downlink transmission are the same, the system operator sets the threshold value (temporary reference threshold value) of each terminal current to θt (for example, , 90 °). In this case, the reference threshold value θth is set to a value (for example, 110 °) obtained by adding a phase (for example, 20 °) corresponding to a fixed transmission delay time to the temporary reference threshold value θt (90 °).

  According to this, since the indeterminate element that generates the phase difference is only the sampling time difference and the fluctuation of the transmission delay time, even if the fluctuation of the transmission delay time increases for some reason than the above condition, A more accurate accident determination can be executed.

  (2) In the above-described embodiment, the configuration in which the protection relay device 10 is a current differential protection relay device for protecting the transmission line of the power system has been described, but the configuration is not limited thereto. For example, the protective relay device 10 may be used to protect other power system devices.

  (3) In the above-described embodiment, the configuration in which the protective relay device 10 is used to protect the power transmission line between two electrical stations has been described, but the configuration is not limited thereto. For example, the protective relay device 10 may be used to protect a transmission line interconnecting three or more electrical stations.

  (4) The configuration exemplified 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 thereof does not depart from the gist of the present invention. It is also possible to change and configure such as omitting. In the above-described embodiment, the process 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.

  1A, 1B Electric Power Station, 3A, 3B Busbar, 5A, 5B Rear Power Supply, 10A, 10B Protection Relay, 20A, 20B Breaker, 30A, 30B Current Transformer, 40 Transmission Line, 50 Auxiliary Transformer, 60 AD Conversion Unit, 61 analog filter, 63 sample hold circuit, 65 multiplexer, 67 AD converter, 70 arithmetic processing unit, 71 bus, 72 CPU, 73 ROM, 75 HMI, 76 output interface, 77 input interface, 78 communication interface, 110 current Input unit, 120 transmission unit, 130 effective value calculation unit, 140 phase determination unit, 142 phase reference setting unit, 144 phase discrimination unit, 150 suppression current calculation unit, 160 differential current calculation unit, 162 addition unit, 164 subtraction unit, 166 Differential current selection unit, 170 Accident determination unit, 100 Protective relay system, TL transmission line.

Claims (5)

A current differential protection relay device for protecting a power system,
A current input unit for receiving an input of the first current on the end side of the protected section of the power system;
A transmission unit that performs data communication with another current differential protection relay device via a transmission line;
The transmission unit receives data of the second current on the other end side of the protected section from the other current differential protection relay device,
An effective value calculator for calculating an effective value of the first current and an effective value of the second current;
A phase determination unit that determines whether or not a phase difference between the first current and the second current is less than a reference threshold;
A suppression current calculator that calculates a suppression current based on the effective value of the first current and the effective value of the second current;
A differential current calculation unit that calculates a differential current based on a determination result of the phase determination unit and an effective value of the first current and an effective value of the second current;
The differential current calculator is
When the phase difference is less than the reference threshold, the sum of the effective value of the first current and the effective value of the second current is calculated as a differential current,
When the phase difference is equal to or greater than the reference threshold, a subtraction value between the effective value of the first current and the effective value of the second current is calculated as a differential current,
A current differential protection relay device further comprising an accident determination unit that performs an accident determination based on the differential current calculated by the differential current calculation unit and the suppression current.   The phase determination unit calculates a phase difference between the first current and the second current using a current corresponding to a larger effective value of the effective value of the first current and the effective value of the second current as a phase reference. The current differential protection relay device according to claim 1 to calculate.   The current differential protection relay device according to claim 1, wherein the transmission unit performs data communication according to a standard that can change a transmission delay time at any time.   The reference threshold is set based on a phase corresponding to a fixed transmission delay time among transmission delay times of the first transmission from the other current differential protection relay device to the current differential protection relay device. The current differential protection relay device according to any one of claims 1 to 3. The reference threshold is assumed that the transmission delay time of the first transmission is the same as the transmission delay time of the second transmission from the current differential protection relay device to the other current differential protection relay device. 5. The current differential protection relay device according to claim 4, wherein the current differential protection relay device is a value obtained by adding a phase corresponding to the fixed transmission delay time to a temporary threshold value of the phase difference that is set in the case of.

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