Protective relay device

Abstract

To provide a protective relay device that does not malfunction when an inrush current occurs, and can quickly operate when an accident occurs.SOLUTION: A protective relay device comprises: a first effective value calculation unit that calculates a first effective value of a fundamental wave component of a difference current; a second effective value calculation unit that calculates a second effective value of a second harmonic component of the difference current; a third effective value determination unit that calculates a third effective value of the second harmonic component of the difference current by using a calculation method different from the second effective value calculation unit; a first determination unit that determines whether a first condition is established where a first ratio of the second effective value to the first effective value is equal to or more than a first threshold; a second determination unit that determines whether a second condition is established where a second ratio of the third effective value to the first effective value is equal to or more than a second threshold; and a lock processing unit that, when at least one of the first condition and the second condition is established, executes lock processing for locking output of a protection signal.SELECTED DRAWING: Figure 13

Description

[Technical Field]

[0001] The present disclosure relates to a protective relay device. [Background technology]

[0002] Biased differential relays have been known as protective relays for protecting equipment that constitutes a power system. Biased differential relays detect the occurrence of internal faults in the protected equipment (e.g., a transformer) using currents taken from current transformers (CTs) installed in the lines connected to the primary and secondary sides of the protected equipment.

[0003] For example, Japanese Patent Laid-Open Publication No. 11-299081 (Patent Document 1) discloses a current differential relay that includes a minimum operation determination means that outputs a signal when the differential current is equal to or greater than a certain level, a ratio determination means that outputs a signal when the differential current is equal to or greater than a certain ratio, a comparison means that performs operation comparison after both the minimum operation determination means and the ratio determination means have operated, and a locking means that locks or unlocks the signal output after operation comparison. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-299081 Summary of the Invention [Problem to be solved by the invention]

[0005] When the protected equipment is a transformer, a magnetizing inrush current (hereinafter referred to as "inrush current") occurs when the transformer is charged or when a transmission line connected to the transformer is reclosed. Inrush current can cause bias differential relays to malfunction. Therefore, as a countermeasure to malfunction, a second harmonic locking method is generally adopted, which takes advantage of the fact that inrush current contains a certain amount of second harmonic components.

[0006] A normal transformer's internal fault current contains almost no second harmonic components, but when a system fault occurs and the current increases suddenly, the ratio of the second harmonic component to the fundamental component (hereinafter also referred to as "content") rises transiently due to the filter circuit of the protective relay and the calculation of the effective value of the second harmonic component at the timing of the current surge. When this happens, the second harmonic lock is activated transiently because the content exceeds the set value, delaying the operation of the protective relay.

[0007] In Patent Document 1, in order to enable quick relay operation in the event of a grid fault, a configuration is adopted in which operation check is performed after both the minimum operation determination means and the ratio operation determination means have operated, and the signal output after operation check is locked. With this configuration, operation check can be started even during a false lock during a grid fault, so operation after unlocking can be shortened. However, the technology disclosed in Patent Document 1 essentially delays protective relay operation until locking is released due to transient detection of the second harmonic component, so there is room for improvement in terms of protective relay operation delay.

[0008] An object of one aspect of the present disclosure is to provide a protective relay device that does not malfunction when an inrush current occurs and that can operate quickly when a fault occurs. [Means for solving the problem]

[0009] According to one embodiment, there is provided a protective relay device for protecting a protected device, the protective relay device including: a first effective value calculation unit that calculates a first effective value of a fundamental component of a difference current calculated from a primary current and a secondary current of the protected device; a second effective value calculation unit that calculates a second effective value of a second harmonic component of the difference current; a third effective value calculation unit that calculates a third effective value of the second harmonic component of the difference current using a calculation method different from that used by the second effective value calculation unit; a first determination unit that determines whether a first condition is satisfied, that is, a first ratio of the second effective value to the first effective value is equal to or greater than a first threshold; a second determination unit that determines whether a second condition is satisfied, that is, a second ratio of the third effective value to the first effective value is equal to or greater than a second threshold; and a lock processing unit that executes lock processing to lock output of a protection signal for protecting the protected device when at least one of the first condition and the second condition is satisfied. [Effects of the Invention]

[0010] According to the present disclosure, there is provided a protective relay device that does not malfunction when an inrush current occurs and that can operate quickly when an accident occurs. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram showing a power system to which a protective relay device according to an embodiment of the present invention is applied; [Figure 2] 1 is a diagram illustrating an example of a hardware configuration of a protection relay device according to an embodiment of the present invention. [Figure 3] FIG. 2 is a block diagram showing a functional configuration of the protection relay device according to the first embodiment. [Figure 4] FIG. 2 is a diagram for explaining a determination method of a determination unit. [Figure 5] FIG. 4 is a diagram showing changes over time in various calculated values according to the first embodiment when an accident occurs. [Figure 6] FIG. 10 shows an example of changes over time in various calculated values according to the first embodiment when an inrush current occurs. [Figure 7]FIG. 10 is a diagram showing another example of changes over time in various calculated values according to the first embodiment when an inrush current occurs. [Figure 8] FIG. 10 is a diagram showing yet another example of changes over time in various calculated values according to the first embodiment when an inrush current occurs. [Figure 9] 5 is a timing chart for illustrating an example of operation of the protective relay device according to the first embodiment when a fault occurs. [Figure 10] 5 is a timing chart for illustrating an example of an operation of the protective relay device according to the first embodiment when an inrush current is applied. [Figure 11] 10 is a timing chart for illustrating another example of the operation of the protective relay device according to the first embodiment when an inrush current is applied. [Figure 12] 10 is a timing chart for illustrating still another example of the operation of the protective relay device according to the first embodiment when an inrush current is applied. [Figure 13] FIG. 10 is a block diagram showing a functional configuration of a protection relay device according to a second embodiment. [Figure 14] FIG. 10 is a diagram showing changes over time in various calculated values according to the second embodiment when an accident occurs. [Figure 15] FIG. 10 is a diagram showing an example of changes over time in various calculated values according to the second embodiment when an inrush current occurs. [Figure 16] FIG. 10 is a diagram showing another example of changes over time in various calculated values according to the second embodiment when an inrush current occurs. [Figure 17] FIG. 10 is a diagram illustrating yet another example of changes over time in various calculated values according to the second embodiment when an inrush current occurs. [Figure 18] 10 is a timing chart for illustrating an example of operation of the protective relay device according to the second embodiment when a fault occurs. [Figure 19] 10 is a timing chart for illustrating an example of an operation of the protective relay device according to the second embodiment when an inrush current is applied. [Figure 20]10 is a timing chart for illustrating another example of the operation of the protective relay device according to the second embodiment when an inrush current is applied. [Figure 21] 10 is a timing chart for illustrating still another example of the operation of the protective relay device according to the second embodiment when an inrush current is applied. [Figure 22] FIG. 11 is a block diagram showing a functional configuration of a protection relay device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, the present embodiment will be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals. The names and functions of these components are also the same. Therefore, detailed description thereof will not be repeated.

[0013] [Configuration underlying each embodiment] <Overall structure> Fig. 1 is a diagram showing a power system to which a protective relay device according to this embodiment is applied. Referring to Fig. 1, the power system includes a transformer 6, which is a protected facility, a circuit breaker 31 installed on the primary side (e.g., high-voltage side) of the transformer 6, a circuit breaker 32 installed on the secondary side (e.g., low-voltage side) of the transformer 6, current transformers 21 and 22, a protective relay device 10, an AC power supply 41 on the high-voltage side, and an AC power supply 42 on the low-voltage side. The AC power supplies 41 and 42 are, for example, three-phase (e.g., a-phase, b-phase, and c-phase) AC power supplies.

[0014] Current transformer 21 detects a primary current (e.g., a high-voltage side current) I1 flowing in a primary line connected to the primary winding of transformer 6. Current transformer 22 detects a secondary current (e.g., a low-voltage side current) I2 flowing in a secondary line connected to the secondary winding of transformer 6. When AC power sources 41, 42 are three-phase AC power sources, current transformer 21 is provided on each of the a-phase line, b-phase line, and c-phase line on the primary side, and current transformer 22 is provided on each of the a-phase line, b-phase line, and c-phase line on the secondary side.

[0015] Current transformer 21 corresponding to phase a detects primary current I1a flowing in the a-phase line, current transformer 21 corresponding to phase b detects primary current I1b flowing in the b-phase line, and current transformer 21 corresponding to phase c detects primary current I1c flowing in the c-phase line. Similarly, current transformer 22 corresponding to phase a detects secondary current I2a flowing in the a-phase line, current transformer 22 corresponding to phase b detects secondary current I2b flowing in the b-phase line, and current transformer 22 corresponding to phase c detects secondary current I2c flowing in the c-phase line. Primary current I1 collectively refers to primary currents I1a, I1b, and I1c, and secondary current I2 collectively refers to secondary currents I2a, I2b, and I2c.

[0016] When the protective relay device 10 detects an internal fault FI (e.g., a ground fault or a short-circuit fault) within the protection range surrounded by the current transformers 21 and 22 using the primary current I1 received from the current transformer 21 and the secondary current I2 received from the current transformer 22, it outputs an opening command (e.g., a trip signal TR) to the circuit breakers 31 and 32 installed on both ends of the transformer 6. This causes the circuit breakers 31 and 32 to open, and the fault location (here, the transformer 6) is isolated from the power system. Typically, the protective relay device 10 performs ratio differential relaying calculations based on the primary current I1 and the secondary current I2.

[0017] <Hardware configuration> 2 is a diagram showing an example of a hardware configuration of a protection relay device according to the present embodiment. Referring to FIG. 2, protection relay device 10 includes auxiliary transformer 51, signal conversion unit 52, and calculation processing unit 70.

[0018] Auxiliary transformer 51 receives the current detected by current transformers 21 and 22, converts it into a voltage signal suitable for signal processing in the relay's internal circuitry, and outputs it. Signal converter 52 receives the voltage signal output from auxiliary transformer 51 and converts it into digital data. Specifically, signal converter 52 includes an analog filter, a sample-and-hold circuit, a multiplexer, and an A / D (Analog to Digital) converter.

[0019] The analog filter removes high-frequency components from the current waveform signal output from auxiliary transformer 51. The sample-and-hold circuit samples the current waveform signal output from the analog filter at a predetermined sampling period. Based on a timing signal input from arithmetic processing unit 70, the multiplexer sequentially switches the waveform signals input from the sample-and-hold circuit in time series and inputs them to the A / D converter. The A / D converter converts the waveform signals input from the multiplexer from analog data to digital data. The A / D converter outputs the digitally converted waveform signal (i.e., digital data) to arithmetic processing unit 70.

[0020] The arithmetic processing unit 70 is mainly configured with a microcomputer, and includes a CPU (Central Processing Unit) 72, a ROM 73, a RAM 74, a digital input (DI) circuit 75, a digital output (DO) circuit 76, and an input interface (I / F) 77. These are connected by a bus 71.

[0021] The CPU 72 controls the operation of the protection relay device 10 by reading and executing a program previously stored in the ROM 73. The RAM 74 as a volatile memory and the ROM 73 as a non-volatile memory are used as the main memory of the CPU 72. The ROM 73 stores programs, setting values for signal processing, and the like. The CPU 72 is, for example, a microprocessor.

[0022] The CPU 72 receives digital data from the signal conversion unit 52 via the bus 71. The CPU 72 executes relay calculations using the received digital data in accordance with a program stored in the ROM 73. The CPU 72 determines whether or not an accident has occurred (i.e., detects an accident) based on the results of each relay calculation.

[0023] When the CPU 72 detects a fault, it outputs a signal to the outside via the digital output circuit 76. For example, the digital output circuit 76 outputs a trip signal TR to the circuit breakers 31 and 32. The CPU 72 receives a signal from the outside via the digital input circuit 75. The input interface 77 is typically made up of various buttons and the like, and accepts various setting operations from the system operator.

[0024] At least a part of the protective relay device 10 may be configured using circuits such as an FPGA (Field Programmable Gate Array) and an ASIC (Application Specific Integrated Circuit). At least a part of the protective relay device 10 may also be configured using analog circuits.

[0025] Embodiment 1 <Functional configuration> 3 is a block diagram showing a functional configuration of protection relaying device 10 according to the first embodiment. Referring to FIG. 3, protection relaying device 10 includes, as main functional components, a ratio differential relaying unit 105, a difference current calculation unit 110, a first effective value calculation unit 121, a second effective value calculation unit 122, a determination unit 130, a lock processing unit 140, an unlocking unit 150, and an output control unit 160. These functions are realized, for example, by CPU 72 of protection relaying device 10 executing a program stored in a memory (for example, ROM 73, RAM 74). Some or all of these functions may be configured to be realized by hardware.

[0026] The ratio differential relay unit 105 and the difference current calculation unit 110 accept inputs of the primary current I1 and the secondary current I2. The primary current I1 and the secondary current I2 input to these units are currents that have undergone gain matching based on the CT winding ratio and the transformation ratio of the transformer 6, and phase matching based on the winding configuration, so that a difference current does not occur in the relay calculation even if a through current flows through the transformer 6 due to an accident outside the protection range, etc.

[0027] Based on the result of the bias differential relay calculation, the bias differential relay unit 105 outputs a protection signal (for example, a signal S having a value of "1") for protecting a protected device (for example, a transformer 6). The protection signal corresponds to, for example, an opening command for opening the circuit breakers 31 and 32.

[0028] Specifically, the bias differential relay unit 105 performs filtering on the matched primary current I1 and secondary current I2 to extract fundamental wave components of the power grid (e.g., grid voltage and grid current), and calculates the difference current Idx and the suppression current Irx using the filtered primary current I1x and secondary current I2x. For example, the bias differential relay unit 105 calculates the effective value of the vector sum of the primary current I1x and the secondary current I2x as the difference current Idx. The bias differential relay unit 105 calculates the scalar sum of the effective value of the primary current I1x and the effective value of the secondary current I2x as the suppression current Irx. Note that although the present disclosure uses effective values for explanation, because the "effective value" can be converted into "amplitude value / √2," all effective values may be converted into amplitude values. The subscript "x" in "I1x", "I2x", "Idx", and "Irx" indicates any one of the three phases (for example, a phase, b phase, and c phase).

[0029] The biased differential relay unit 105 performs a biased differential relay calculation based on the suppression current Irx and the difference current Idx calculated from the primary current I1 and the secondary current I2. The biased differential relay unit 105 determines whether the relationship holds, for example, that the difference current Idx is equal to or greater than the suppression current Irx multiplied by a constant α and equal to or greater than a constant β (Idx≧α×Irx and Idx≧β). If the suppression current Irx and the difference current Idx satisfy the above relationship, the biased differential relay unit 105 outputs a protection (operation) signal. If the biased differential relay unit 105 outputs a protection signal (i.e., if the relay operates), it outputs a signal S with a value of “1,” and if the relay does not operate, it outputs a signal S with a value of “0.”

[0030] The difference current calculation unit 110 calculates the difference current Id from the primary current I1 and the secondary current I2. Specifically, the difference current calculation unit 110 calculates the vector sum of the matched primary current I1 and secondary current I2 as the difference current Id. The difference current Id is input to the first effective value calculation unit 121 and the second effective value calculation unit 122.

[0031] The first effective value calculation unit 121 calculates an effective value Id1f_r of the fundamental component of the difference current Id calculated from the primary current I1 and the secondary current I2. Specifically, the first effective value calculation unit 121 performs filtering on the difference current Id using a first filter that extracts the fundamental component of the power grid, and calculates an effective value Id1f_r of the fundamental component of the difference current Id that has passed through the first filter. The first filter is configured as a filter having frequency characteristics that pass the fundamental component of the power grid and block other components, such as a DC component, second harmonic component, third harmonic component, and fourth harmonic component.

[0032] The second effective value calculation unit 122 calculates the effective value Id2f_r of the second harmonic component of the difference current Id. Specifically, the second effective value calculation unit 122 performs filtering on the difference current Id using a second filter that extracts the second harmonic component of the power grid, and calculates the effective value Id2f_r of the second harmonic component of the difference current Id that has passed through the second filter. The second filter is configured as a filter having frequency characteristics that pass the second harmonic component of the power grid and block other components, such as the DC component, fundamental component, third harmonic component, and fourth harmonic component.

[0033] The determination unit 130 receives the effective value Id1f_r and the effective value Id2f_r at a certain time t, and calculates the ratio of the effective value Id2f_r to the effective value Id1f_r (i.e., Id2f_r / Id1f_r) as the second harmonic content rate R2. The determination unit 130 determines whether or not a condition P1 is met, that is, whether the second harmonic content rate R2 is equal to or greater than a threshold value K (e.g., 10% to 15%). The condition P1 is "(Id2f_r / Id1f_r)≧K".

[0034] The determination unit 130 also determines whether a condition P1a is satisfied, that is, whether the ratio of the effective value Id2f_r to the rated current Ira of the transformer 6 (i.e., Id2f_r / Ira) is equal to or greater than a threshold k1 (e.g., 2%). The condition P1a is "(Id2f_r / Ira)≧k1". The determination unit 130 also determines whether a condition P1b is satisfied, that is, whether the ratio of the effective value Id1f_r to the rated current Ira (i.e., Id1f_r / Ira) is equal to or greater than a threshold k2 (e.g., 10%). The condition P1b is "(Id1f_r / Ira)≧k2". If the minimum operating value (e.g., constant β) of bias differential relay unit 105 is 20% of the rated current and the minimum value of threshold K in condition P1 is 10%, then the minimum value (i.e., threshold k1) required to lock the output of the protection signal (i.e., signal S with a value of "1") is 2% (=20%×10%).From the above, threshold k2 only needs to be less than the minimum value of constant β, so in this case it is set to 10%, which is less than 20%.

[0035] 4A and 4B are diagrams for explaining the determination method of the determination unit. Referring to Fig. 4A, a line 301 is a line expressed by "(Id2f_r / Id1f_r)=K" (i.e., a line related to condition P1), and a line 302 is a line expressed by "(Id2f_r / Ira)=k1" (i.e., a line related to condition P1a). Referring to Fig. 4B, a line 303 is a line expressed by "(Id1f_r / Ira)=k2" (i.e., a line related to condition P1b).

[0036] In one aspect, the judgment unit 130 outputs a signal A1 with a value of "1" when the condition P1 and the condition P1a are satisfied (i.e., the coordinates (Id1f_r, Id2f_r) are in the shaded area of Figure 4(a)), and outputs a signal A1 with a value of "0" otherwise.

[0037] In another aspect, the judgment unit 130 outputs a signal A1 with a value of "1" when the conditions P1 and P1b are met (i.e., the coordinates (Id1f_r, Id2f_r) are in the shaded area in Figure 4(b)), and outputs a signal A1 with a value of "0" otherwise.

[0038] In still another aspect, determination unit 130 outputs signal A1 of value "1" if condition P1, condition P1a, and condition P1b are all satisfied, and outputs signal A1 of value "0" otherwise.

[0039] 3 again, when at least condition P1 is satisfied, lock processing unit 140 executes lock processing to lock the output of a protection signal (e.g., signal S with a value of "1") for protecting a protected device (e.g., transformer 6). Specifically, lock processing unit 140 includes an operation timer 141, a recovery timer 142, and an AND circuit 143.

[0040] When the value "1" of the signal A1 output from the determination unit 130 continues for a period Ta or longer, the operation timer 141 outputs the value "1" to the recovery timer 142. The period Ta is set to, for example, an electrical angle of 30° (i.e., 1 / 12 cycle). In this embodiment, one cycle corresponds to an electrical angle of 360°.

[0041] When the output value of the operation timer 141 changes from "0" to "1", the recovery timer 142 immediately sets its own output value (i.e., the value of the signal A2) to "1". When the output value of the operation timer 141 changes from "1" to "0" and the "0" state continues for a certain period (e.g., period Tb) or more, the recovery timer 142 sets its own output value to "0". Specifically, the recovery timer 142 outputs the signal A2 with a value of "0" after the period Tb has elapsed from the point when the output value of the operation timer 141 changed from "1" to "0". The period Tb is set to, for example, an electrical angle of 120° (i.e., 1 / 3 cycle).

[0042] The AND circuit 143 performs an AND operation on the output value of the recovery timer 142 and a value obtained by inverting the logical level of the output of the lock release unit 150. Specifically, when the output value of the recovery timer 142 is "1" and the output value of the lock release unit 150 is "0" (i.e., when the lock release unit 150 has not output a release signal for releasing the lock), the AND circuit 143 outputs a signal D with a value of "1" (for example, a lock signal for locking the output of a protection signal). The output process of the signal D with a value of "1" corresponds to a lock process for locking the output of a protection signal.

[0043] The unlocking unit 150 releases the locking process performed by the locking unit 140 based on the determination result of the determination unit 130 and the rate of change of the effective value Id2f_r. Specifically, the unlocking unit 150 includes a one-shot timer 151, a rate of change determination unit 152, an AND circuit 153, an operation timer 154, and a recovery timer 155.

[0044] When the determination unit 130 outputs a signal A1 with a value of "1", the one-shot timer 151 continuously outputs a signal B1 with a value of "1" to the AND circuit 153 for a period Tc. When the period Tc has elapsed, the one-shot timer 151 outputs a signal B1 with a value of "0" to the AND circuit 153. The period Tc is set to, for example, an electrical angle of 270° (i.e., 3 / 4 cycle).

[0045] The change rate determination unit 152 uses the following equation (1) to determine whether the effective value Id2f_r of the second harmonic component has changed by a certain value or more. "Ts" in equation (1) is, for example, an electrical angle of 30°. In equation (1), the change rate of the effective value Id2f_r is calculated by dividing the difference between the current effective value Id2f_r(t) and the effective value Id2f_r(t-Ts) time Ts ago by the current effective value Id2f_r(t).

[0046] {Id2f_r(t)-Id2f_r(t-Ts)} / Id2f_r(t)≧ε …(1) The left side of equation (1) is the rate of change ΔId2f_r of the effective value Id2f_r. In this case, the rate of change determination unit 152 outputs a signal B2 with a value of "1" when the rate of change ΔId2f_r is equal to or greater than a reference value ε (e.g., 1% to 50%) (i.e., ΔId2f_r≧ε). The rate of change determination unit 152 outputs a signal B2 with a value of "0" when the rate of change ΔId2f_r is less than the reference value ε (i.e., ΔId2f_r<ε).

[0047] The AND circuit 153 performs an AND operation on the output value of the one-shot timer 151 and a value obtained by inverting the logical level of the output of the change rate determination unit 152. Specifically, the AND circuit 153 outputs a signal C1 with a value of "1" when the output value of the one-shot timer 151 is "1" and the output value of the change rate determination unit 152 is "0" (i.e., when the effective value Id2f_r has not changed by more than a certain value).

[0048] When the value "1" of the signal B1 output from the AND circuit 153 continues for a period Td or longer, the operation timer 154 outputs the value "1" to the recovery timer 155. The period Td is set to, for example, an electrical angle of 150° (i.e., 5 / 12 cycles).

[0049] When the output value of the operation timer 154 changes from "0" to "1", the recovery timer 155 immediately sets its own output value (i.e., the value of the signal C2) to "1". When the output value of the operation timer 154 changes from "1" to "0" and the "0" state continues for a period Te or more, the recovery timer 155 outputs a signal C2 with a value of "0". The period Te is set to, for example, an electrical angle of 210° (i.e., 7 / 12 cycles). The signal C2 with a value of "1" corresponds to an unlock signal for releasing the locking process by the locking process unit 140.

[0050] As described above, the unlocking unit 150 outputs an unlocking signal if the state in which the rate of change ΔId2f_r is less than the reference value ε continues for a period Td or more within the period Tc after the judgment unit 130 judges that at least condition P1 is satisfied.

[0051] The output control unit 160 outputs a protection signal for protecting the transformer 6 based on the result of the ratio differential relay calculation by the ratio differential relay unit 105 and whether or not the locking process is being performed by the locking process unit 140. Specifically, when the ratio differential relay unit 105 is operating and the locking process is not being performed by the locking process unit 140 (for example, the locking process is released), the output control unit 160 determines that an internal accident has occurred in the protected device (for example, the transformer 6) and outputs a protection signal. On the other hand, even if the ratio differential relay unit 105 is operating, when the locking process is being performed by the locking process unit 140 (for example, a lock signal is being output), the output control unit 160 locks the output of the protection signal (i.e., locks the output of the signal S with a value of "1").

[0052] The output control unit 160 is configured as, for example, an AND circuit. The output control unit 160 performs an AND operation on the output value of the bias differential relay unit 105 and a value obtained by inverting the logical level of the output of the lock processing unit 140 (specifically, the AND circuit 143). The output control unit 160 outputs a value of "1" when the output value of the bias differential relay unit 105 is "1" and the output value of the lock processing unit 140 is "0". In other words, the output control unit 160 outputs a protection signal from the bias differential relay unit 105.

[0053] On the other hand, even if the output value of the bias differential relay unit 105 is "1", if the output value of the lock processing unit 140 is "1" (i.e., lock processing is being performed even when the bias differential relay unit 105 is operating), the output control unit 160 outputs the value "0". In other words, the output control unit 160 does not output a protection signal from the bias differential relay unit 105.

[0054] <Changes in various calculated values over time> FIG. 5 is a diagram showing changes over time in various calculated values according to the first embodiment when an accident occurs. The vertical axis of FIG. 5 represents the second harmonic content R2 (corresponding to "2f / 1f" in the diagram), which is the ratio of the effective value Id2f_r to the effective value Id1f_r, and the horizontal axis of FIG. 5 represents time. Referring to FIG. 5, when an accident occurs, the current of the fundamental wave component increases sharply, and the amplitude of the fundamental wave component of the difference current corresponding to the "difference current (1f component)" in the diagram increases. The effective value Id1f_r of the fundamental wave component corresponding to the "1f effective value" in the diagram gradually increases due to the influence of the filter for extracting the fundamental wave component and the data length used in calculating the effective value.

[0055] During this transient period of current fluctuation, a few milliseconds after the fault occurs, the effective value Id2f_r of the second harmonic component, which corresponds to the "2f effective value" in the figure, becomes almost constant. The length of the transient period depends on the filter used in the protective relay device 10 to extract the second harmonic component and the data length used to calculate the effective value. In the example of Figure 5, the transient period lasts for about one cycle after the sudden current change. After the transient period has elapsed, the difference current does not contain the second harmonic component, so the effective value Id2f_r becomes zero.

[0056] Here, during the period when the effective value Id1f_r of the fundamental wave component is small, the second harmonic content R2 (corresponding to "2f / 1f" in the figure) becomes large, and it is determined that the current waveform contains a second harmonic component. In this way, even in a fault current waveform that does not contain a second harmonic component, the operation of the protective relay device 10 is locked by detecting the second harmonic component. The longer the locking time, the longer the delay in opening the circuit breaker.

[0057] Next, we will explain how various calculated values change over time when an inrush current occurs. The international standard for transformer protection relays, IEC 60255-187-1, requires that transformer protection relays not malfunction due to inrush currents, and as defined in the standard, it is necessary to confirm that they do not malfunction when the inrush current conduction angle α is 60°, 90°, or 120°. Therefore, below we will explain how various calculated values change over time when an inrush current occurs with conduction angles α of 60°, 90°, or 120° (for example, when a simulated inrush current is applied).

[0058] FIG. 6 is a diagram showing an example of how various calculated values change over time when an inrush current occurs according to the first embodiment. The vertical and horizontal axes in FIG. 6 represent the second harmonic content R2 and time, respectively. Referring to FIG. 6, the "difference current (1f component)" in the diagram represents the inrush current when the conduction angle α is 60°. A notable difference compared to the example of a fault in FIG. 5 is that the effective value Id2f_r is not constant but changes during the transient period when the current fluctuates. Eventually, the effective value Id2f_r settles to a constant value.

[0059] FIG. 7 is a diagram showing another example of changes over time in various calculated values according to the first embodiment when an inrush current occurs. The vertical and horizontal axes in FIG. 7 represent the second harmonic content R2 and time, respectively. Referring to FIG. 7, the "difference current (1f component)" in the diagram represents the inrush current when the conduction angle α is 90°. In the example of FIG. 7, the effective value Id2f_r is almost constant during a period Tp1 (e.g., 5 ms) during the transient period during current fluctuation. However, as in the example of FIG. 6, the effective value Id2f_r changes during other periods of the transient period. Eventually, the effective value Id2f_r settles to a constant value.

[0060] FIG. 8 is a diagram showing yet another example of changes over time in various calculated values according to the first embodiment when an inrush current occurs. The vertical and horizontal axes in FIG. 8 represent the second harmonic content R2 and time, respectively. Referring to FIG. 8, the “difference current (1f component)” in the diagram represents the inrush current when the conduction angle α is 120°. As with the examples in FIGS. 6 and 7, the effective value Id2f_r changes during the transient period of current fluctuation. Eventually, the effective value Id2f_r settles to a constant value. Note that during a period Tp2 (e.g., 4 ms) within the transient period, the effective value Id2f_r temporarily decreases, and therefore the second harmonic content R2 also decreases. The period Tp2 is a period during which the condition P1 “(Id2f_r / Id1f_r)≧K” set by the determination unit 130 is not met when K=15%. Therefore, it is necessary to extend the period of the recovery timer 142 so that the output of the lock signal (for example, signal D with a value of "1") continues (that is, so that the output of the lock signal is not interrupted).

[0061] From the above, as shown in Fig. 5, the effective value Id2f_r becomes constant during the transient period when the current fluctuates due to the occurrence of a fault, and eventually the effective value Id2f_r settles to zero. On the other hand, as shown in Fig. 6 to Fig. 8, during the transient period when the current fluctuates due to the occurrence of an inrush current, the effective value Id2f_r changes relatively greatly (or the time during which the effective value Id2f_r remains constant is shorter than the time during which the effective value Id2f_r remains constant when a fault occurs), and eventually the effective value Id2f_r settles to a constant value.

[0062] In the first embodiment, by utilizing the above characteristics, the unlocking unit 150 in Fig. 3 is configured to unlock the locking process by the locking processing unit 140 (i.e., stop outputting the lock signal) when the amount of change ΔId2f_r in the effective value Id2f_r within the period Tc is equal to or greater than the reference value ε after the second harmonic content R2 is determined to be equal to or greater than the threshold K and the operation of the protective relay device 10 is locked. This suppresses the operation time delay caused by second harmonic locking during the transient period when the fault current fluctuates.

[0063] <Example of operation> An example of the operation of the protective relay device 10 when a fault occurs and when an inrush current occurs will be described.

[0064] Fig. 9 is a timing chart for explaining an example of operation of the protective relay device according to the first embodiment when a fault occurs. Signals A1, A2, B1, B2, C1, C2, and D in Fig. 9 correspond to signals A1, A2, B1, B2, C1, C2, and D in Fig. 3, respectively. This also applies to Figs. 10 to 12 below.

[0065] 9, an accident occurs at time t1, causing the amplitude of the differential current Id to increase. At time t2, the determination unit 130 determines that the differential current Id contains a second harmonic component equal to or greater than a certain level (for example, conditions P1 and P1a are satisfied), and outputs a signal A1 with a value of "1." Also at time t2, the one-shot timer 151 outputs a signal B1 with a value of "1." Furthermore, at time t2, the rate of change ΔId2f_r of the effective value Id2f_r becomes equal to or greater than the reference value ε, and therefore the rate of change determination unit 152 outputs a signal B2 with a value of "1."

[0066] At time t3, as the value "1" of signal A1 continues for the period Ta or more, operation timer 141 outputs the value "1", and as a result, recovery timer 142 outputs signal A2 with the value "1". At this time, the value of signal C2 is "0", so lock processing unit 140 (specifically, AND circuit 143) outputs signal D with the value "1". As a result, the output of the protection signal from bias differential relay unit 105 is locked, and time t3 becomes the lock start time. In this way, lock processing unit 140 executes locking processing when a state in which the difference current Id contains a second harmonic component of a certain level or more (for example, condition P1 is established) continues for the period Ta or more.

[0067] At time t4, the effective value Id2f_r becomes substantially constant and the rate of change ΔId2f_r becomes less than the reference value ε, so the rate of change determination unit 152 outputs a signal B2 with a value of “0.” This causes the AND circuit 153 to output a signal C1 with a value of “1.”

[0068] At time t5, as the value "1" of signal C1 continues for the period Td or longer, operation timer 154 outputs the value "1", and as a result, recovery timer 155 outputs signal C2 with the value "1". That is, an unlock signal is output from unlock unit 150. As a result, lock processing unit 140 outputs signal D with the value "0" (that is, the lock processing of lock processing unit 140 is released). Time t5 is the unlock time when the lock on the output of the protection signal from bias differential relay unit 105 is released.

[0069] At time t6, when a period Tc has elapsed since time t2, the one-shot timer 151 outputs a signal B1 with a value of "0." As a result, the value of the signal C1 becomes "0."

[0070] At time t7, the determination unit 130 determines that the difference current Id does not contain a second harmonic component equal to or greater than a certain level (for example, condition P1 is not satisfied), and outputs a signal A1 with a value of "0." At time t8, which is a period Tb after time t7, the recovery timer 142 outputs a signal A2 with a value of "0." Thereafter, at time t9, which is a period Te after time t6, the recovery timer 155 outputs a signal C2 with a value of "0." In this way, the unlocking unit 150 stops outputting the unlock signal after the period Te has elapsed since the end of the period Tc.

[0071] Here, in a conventional configuration in which the protection signal is locked when the second harmonic content is equal to or greater than a specified value and the protection signal is unlocked when the second harmonic content falls below the specified value, the locking start time is time t3 and the unlocking time is time t8. On the other hand, in the first embodiment, as described above, the locking start time is time t3 and the unlocking time is time t5. Therefore, the first embodiment can unlock the protection signal earlier by the period Tx (i.e., t8 - t5) than the conventional configuration. Therefore, it is possible to suppress delays in relay operation time due to second harmonic locking in fault currents.

[0072] FIG. 10 is a timing chart for illustrating an example of the operation of the protective relay device according to the first embodiment when an inrush current is applied.

[0073] 10, at time t11, an inrush simulation current with a conduction angle of 60° is applied. At time t12, the determination unit 130 determines that the difference current Id contains a second harmonic component equal to or greater than a certain level, and outputs a signal A1 with a value of "1." Also at time t12, the one-shot timer 151 outputs a signal B1 with a value of "1." Furthermore, at time t12, the rate of change ΔId2f_r becomes equal to or greater than the reference value ε, and therefore the rate of change determination unit 152 outputs a signal B2 with a value of "1."

[0074] At time t13, as the value "1" of signal A1 continues for period Ta or longer, operation timer 141 outputs the value "1", and as a result, recovery timer 142 outputs signal A2 with the value "1". At this time, the value of signal C2 is "0", so lock processing unit 140 outputs signal D with the value "1". As a result, the output of the protection signal from bias differential relay unit 105 is locked, and time t13 becomes the lock start time.

[0075] After time t12, the effective value Id2f_r is not constant but is changing, so the rate of change ΔId2f_r fluctuates around the reference value ε. As a result, the value of signal B2 alternates between "0" and "1." Accordingly, the value of signal C1 alternates between "1" and "0." Because the value "1" of signal C1 does not continue for the period Td or longer, the value of signal C2 remains "0."

[0076] At time t14, the value of signal C1 becomes "1" and remains in this state for a certain period of time, but at time t15, after a period Tc has elapsed since time t12, the one-shot timer 151 outputs signal B1 with a value of "0." As a result, the value of signal C1 becomes "0."

[0077] As a result, the value of signal D remains at "1" after time t13. Therefore, when an inrush current occurs at a conduction angle of 60°, the second harmonic is not unlocked, and the protection signal output from bias differential relay unit 105 remains locked.

[0078] FIG. 11 is a timing chart for illustrating another example of the operation of the protective relay device according to the first embodiment when an inrush current is applied.

[0079] 11, at time t21, a simulated inrush current having a conduction angle of 90° is applied. At time t22, signal A1 having a value of "1" is output, signal B1 having a value of "1" is output, and signal B2 having a value of "1" is output.

[0080] At time t23, signal A1 continues to have the value "1" for the period Ta or longer, so signal A2 with the value "1" is output, and as a result, signal D with the value "1" is output. This causes the protection signal output from bias differential relay unit 105 to be locked, so time t23 becomes the lock start time.

[0081] During a period after time t24 (for example, the period Tp1 in FIG. 7), the effective value Id2f_r becomes substantially constant, so the rate of change ΔId2f_r becomes less than the reference value ε, and the value of signal B2 becomes "0." Accordingly, the value of signal C1 becomes "1" during the period Tp1. However, since the period Tp1 is shorter than the period Td of the operation timer 154, the value of signal C2 remains "0."

[0082] Then, at time t25, when a period Tc has elapsed since time t22, the one-shot timer 151 outputs the signal B1 with a value of "0." As a result, the value of the signal C1 becomes "0."

[0083] As a result, the value of signal D remains at "1" after time t23. Therefore, when an inrush current occurs at a conduction angle of 90°, the second harmonic is not unlocked, and the protection signal output from bias differential relay unit 105 remains locked.

[0084] FIG. 12 is a timing chart for illustrating yet another example of the operation of the protective relay device according to the first embodiment when an inrush current is applied.

[0085] 12, at time t31, a simulated inrush current having a conduction angle of 120° is applied. At time t32, signal A1 having a value of "1" is output, signal B1 having a value of "1" is output, and signal B2 having a value of "1" is output.

[0086] At time t33, signal A1 continues to have a value of "1" for a period Ta or longer, so that signal A2 having a value of "1" is output, and as a result, signal D having a value of "1" is output. This causes the protection signal output from bias differential relay unit 105 to be locked, so time t33 becomes the locking start time.

[0087] For a certain period after time t34, the effective value Id2f_r becomes approximately constant, so the value of signal B2 becomes "0" and the value of signal C1 becomes "1." However, the period during which the value of signal C1 is "1" is shorter than the period Td of the operation timer 154, so the value of signal C2 remains "0."

[0088] Furthermore, the effective value Id2f_r decreases for a certain period from time t35 (for example, period Tp2 in FIG. 8). However, since period Tp2 is shorter than period Tb of the recovery timer 142, the value of signal A2 remains "1."

[0089] At time t36, when a period Tc has elapsed since time t32, the one-shot timer 151 outputs the signal B1 with a value of "0." As a result, the value of the signal C1 becomes "0."

[0090] As a result, the value of signal D remains at "1" after time t33. Therefore, when an inrush current occurs at a conduction angle of 120°, the second harmonic is not unlocked, and the protection signal output from bias differential relay unit 105 remains locked.

[0091] Next, a method for setting the above-mentioned period Ta to Te will be described in more detail. First, when an inrush current occurs, the period Ta of the operation timer 141 is set to a short time (for example, an electrical angle of 0° or more and 60° or less) so that the presence of a second harmonic component at a certain ratio or more relative to the fundamental wave component can be detected and the output of the protection signal can be locked earlier than the output of the protection signal by the ratio-differential relay unit 105 in Fig. 3. In the first embodiment, the period Ta is set to an electrical angle of 30°.

[0092] The period Tb of the recovery timer 142 is set taking into consideration the period Tp2 (see FIG. 8) during which the effective value Id2f_r temporarily decreases when an inrush current occurs. As shown in FIG. 12, the signal A1 may temporarily recover (i.e., its value becomes "0" during the period Tp2). Therefore, in order to reliably perform second harmonic locking, the period Tb must be longer than the period Tp2. For example, since the period Tp2 is about 4 ms (e.g., about an electrical angle of 90°), the period Tb is set to an electrical angle of 120° or more.

[0093] The period Tc of the one-shot timer 151 is set to be sufficiently longer than the period Td of the operation timer 154, but not too longer than the data length used in the filter that extracts the second harmonic component and in calculating the RMS value of the second harmonic component. This is because the RMS value Id2f_r stabilizes after a transient period in the RMS calculation. If the period Tc is longer than the data length, the second harmonic may be unlocked after the transient period has elapsed. For example, the period Tc is set to an electrical angle of 270° or more and 360° or less.

[0094] The period Td of the operation timer 154 is set to be longer than the period Tp1 (see FIG. 7) during which the effective value Id2f_r becomes substantially constant when an inrush current occurs. As shown in FIG. 11, the value of the signal C1 becomes "1" during the period Tp1, but since the period Tp1 is shorter than the period Td, the value of the signal C2 does not become "1". For example, since the period Tp1 is about 5 ms (for example, an electrical angle of about 120°), the period Td is set to an electrical angle of 150° or more.

[0095] 9, the period Te of the recovery timer 155 is set based on the condition that, after the signal A1 becomes ON (for example, the value is "1"), the ON state of the signal C2 continues longer than the ON state of the signal A2. Assuming that the signal B2 is OFF (for example, the value is "0"), the period Te is set to satisfy the condition "ON state duration of the signal A1 + period Tb" < "period Tc + period Te". In other words, it is necessary to satisfy the condition "period Te > ON state duration of the signal A1 + period Tb - period Tc". For example, if the ON state duration of the signal A1 is 360° electrical angle, the period Tb is 120° electrical angle, and the period Tc is 270° electrical angle, the period Te is set to 210° or more.

[0096] In summary, for example, the periods Ta, Tb, Tc, Td, and Te are set to electrical angles of 30°, 120°, 270°, 150°, and 210°, respectively.

[0097] <Advantages> According to the first embodiment, even if the output of the protection signal is locked by the second harmonic locking method when a fault occurs, the lock can be released earlier than conventional methods (for example, earlier by the period Tx in FIG. 9). This allows the operation of the protection relay device 10 to be speeded up. Furthermore, since the lock is maintained when an inrush current occurs, it is possible to prevent the protection relay device 10 from malfunctioning.

[0098] Embodiment 2 In the above-described first embodiment, a configuration was described in which the operation of the protection relay device is accelerated by unlocking the output of the protection signal by the second harmonic locking method, focusing on the rate of change of the effective value of the second harmonic component. In the second embodiment, a configuration is described in which the operation of the protection relay device is accelerated by using two types of harmonic filters with different characteristics in the second harmonic component locking method, thereby shortening the period of the recovery timer used in the second harmonic locking method.

[0099] <Functional configuration> Fig. 13 is a block diagram showing a functional configuration of a protection relaying device 10A according to embodiment 2. The protection relaying device 10A corresponds to the protection relaying device 10 in Fig. 1, but is denoted by the symbol "A" for convenience in order to distinguish it from the protection relaying device 10 according to embodiment 1. This is also true for embodiment 3.

[0100] 13, protective relay device 10A includes, as main functional components, ratio differential relaying unit 105, difference current calculation unit 110, first effective value calculation unit 121, second effective value calculation unit 122, third effective value calculation unit 123, first determination unit 131, second determination unit 132, output control unit 160A, and lock processing unit 170. The functional components of ratio differential relaying unit 105 and difference current calculation unit 110 are similar to the functional components described in FIG.

[0101] The first effective value calculation unit 121 calculates the effective value Id1f_r of the fundamental wave component of the difference current Id, and the second effective value calculation unit 122 calculates the effective value Id2f_r of the second harmonic component of the difference current Id.

[0102] The third effective value calculation unit 123 calculates the effective value Idmf_r of the second harmonic component of the difference current Id using a calculation method different from that of the second effective value calculation unit 122. Specifically, the third effective value calculation unit 123 performs filtering on the difference current Id using a third filter different from the second filter used in the second effective value calculation unit 122. The third effective value calculation unit 123 calculates the effective value Idmf_r of the second harmonic component of the difference current Id that has passed through the third filter.

[0103] Typically, the third filter is configured as a filter having frequency characteristics that pass the second harmonic component of the power system and block the passage of other components such as the DC component, fundamental wave component, third harmonic component, fourth harmonic component, etc., by employing an arithmetic expression different from that of the second filter. This third filter has frequency characteristics (e.g., gain of the frequency that passes) different from that of the second filter, and the arithmetic expression of the third effective value calculation unit 123 that uses the third filter is different from the arithmetic expression of the second effective value calculation unit 122 that uses the second filter.

[0104] Alternatively, the third filter is configured as a filter having frequency characteristics that remove the fundamental wave component and the DC component, pass the second harmonic component, and pass other harmonic components, such as the third harmonic component and the fourth harmonic component, to a certain extent. This third filter has a shorter data length than the second filter and different frequency characteristics from the second filter. In particular, the difference current Id filtered using this third filter mainly contains the second harmonic component, and also contains other harmonic components to a certain extent.

[0105] The first determination unit 131 is substantially the same as the determination unit 130 in Fig. 3. Specifically, the first determination unit 131 calculates the ratio of the effective value Id2f_r to the effective value Id1f_r as the second harmonic content R2. The first determination unit 131 outputs a signal E1 with a value of "1" based on whether the above-mentioned conditions P1, P1a, and P1b are satisfied. The signal E1 corresponds to the signal A1 output from the determination unit 130 in Fig. 3.

[0106] The second determination unit 132 receives the effective value Id1f_r and the effective value Idmf_r at a certain time t, and calculates the ratio of the effective value Idmf_r to the effective value Id1f_r (i.e., Idmf_r / Id1f_r) as the harmonic content rate Rm. The second determination unit 132 determines whether a condition Pm is met that the harmonic content rate Rm is equal to or greater than a threshold value Km. The condition Pm is "(Idmf_r / Id1f_r)≧Km." The threshold value Km may be the same as the threshold value K.

[0107] The second determination unit 132 determines whether a condition Pma is satisfied, that is, whether the ratio of the effective value Idmf_r to the rated current Ira (i.e., Idmf_r / Ira) is equal to or greater than a threshold k1. The condition Pma is "(Idmf_r / Ira)≧k1". Furthermore, the second determination unit 132 determines whether the above-mentioned condition P1b is satisfied. The condition P1b is "(Idmf_r / Ira)≧k2".

[0108] The second determination unit 132 outputs a signal E2 with a value of "1" if the conditions Pm and Pma are satisfied, and outputs a signal E2 with a value of "0" otherwise. In another aspect, the second determination unit 132 outputs a signal E2 with a value of "1" if the conditions Pm and P1b are satisfied, and outputs a signal E2 with a value of "0" otherwise. In yet another aspect, the second determination unit 132 outputs a signal E2 with a value of "1" if the conditions Pm, Pma, and P1b are all satisfied, and outputs a signal E2 with a value of "0" otherwise.

[0109] From the above, in order for the signal E2 with a value of "1" to be output, at least the condition Pm must be satisfied.

[0110] When at least one of the condition P1 and the condition Pm is satisfied, the lock processing unit 170 executes a lock processing for locking the output of a protection signal (for example, a signal S having a value of "1") for protecting a protected device (for example, a transformer 6). Specifically, the lock processing unit 170 includes a one-shot timer 171, an AND circuit 172, an OR circuit 173, an operation timer 174, and a recovery timer 175.

[0111] When the second determination unit 132 outputs a signal E2 with a value of "1," the one-shot timer 171 continuously outputs a signal F with a value of "1" to the AND circuit 172 for a period Tg. When the period Tg has elapsed, the one-shot timer 171 outputs a signal F with a value of "0" to the AND circuit 172. The period Tg is the time until the calculation of the effective value Id2f_r is completed, and is set to, for example, an electrical angle of 270° or more and 360° or less.

[0112] The AND circuit 172 performs an AND operation on the output value of the second judgment unit 132 and the output value of the one-shot timer 171. Specifically, when the output value of the second judgment unit 132 is "1" and the output value of the one-shot timer 171 is "0", the AND circuit 172 outputs a signal G with a value of "1". This means that the judgment of the harmonic content rate Rm by the second judgment unit 132 (for example, the judgment of the condition Pm) is understood to be limited to the period Tg of the one-shot timer 171. Specifically, the condition Pm is invalidated after the period Tg has elapsed since it was determined that the condition Pm was met.

[0113] The OR circuit 173 performs an OR operation on the output value of the first determination unit 131 and the output value of the AND circuit 172. Specifically, the OR circuit 173 outputs a signal H1 with a value of "1" when the output value of the first determination unit 131 is "1" or the output value of the AND circuit 172 is "1."

[0114] When the value "1" of the signal H1 output from the OR circuit 173 continues for a period Th or longer, the operation timer 174 outputs the value "1" to the recovery timer 175. The period Th is set to, for example, an electrical angle of 30°. Typically, the period Th is the same as the period Ta in FIG. 3.

[0115] When the output value of the operation timer 174 changes from "0" to "1", the recovery timer 175 outputs a signal H2 with a value of "1". The output process of the signal H2 with a value of "1" corresponds to a lock process for locking the output of the protection signal. Furthermore, the recovery timer 175 outputs a signal H2 with a value of "0" after a period Ti has elapsed since the output value of the operation timer 174 changed from "1" to "0". This ends the lock process. The period Ti is set to, for example, an electrical angle of 60° (i.e., 1 / 6 cycle).

[0116] According to the above configuration, the locking processor 170 executes the locking process when a state in which at least one of the signals E1 and E2 has a value of "1" (for example, at least one of the conditions P1 and Pm is satisfied) continues for a period of time Th or more. Furthermore, the locking processor 170 ends the locking process (for example, outputs the signal H2 with a value of "0") after a period of time Ti has elapsed since the end of the above state.

[0117] Output control unit 160A performs an AND operation on the output value of ratio differential relay unit 105 and a value obtained by inverting the logical level of the output of lock processing unit 170 (specifically, recovery timer 175). Output control unit 160A outputs the value "1" when the output value of ratio differential relay unit 105 is "1" and the output value of lock processing unit 170 is "0" (i.e., ratio differential relay unit 105 is operating and lock processing is not being executed). In other words, output control unit 160A outputs a protection signal by ratio differential relay unit 105.

[0118] <Changes in various calculated values over time> FIG. 14 is a diagram showing changes over time in various calculated values according to the second embodiment when an accident occurs. The vertical axis of FIG. 14 represents the second harmonic content R2 or the harmonic content Rm, and the horizontal axis of FIG. 14 represents time. Specifically, in addition to the graphs shown in FIG. 5, FIG. 14 also shows a graph of the "harmonic effective value" corresponding to the effective value Idmf_r and a graph of "mf / 1f" corresponding to the harmonic content Rm. Referring to FIG. 14, the effective value Idmf_r increases to a value greater than the effective value Id2f_r and eventually becomes zero. In conjunction with this, the harmonic content Rm also increases and eventually becomes zero.

[0119] Fig. 15 is a diagram showing an example of changes over time in various calculated values according to the second embodiment when an inrush current occurs. The vertical axis of Fig. 15 represents the second harmonic content rate R2 or the harmonic content rate Rm, and the horizontal axis of Fig. 15 represents time. In Fig. 15, a graph of "harmonic effective value" and a graph of "mf / 1f" are shown in addition to the graphs shown in Fig. 6.

[0120] If the third filter is a filter that uses an arithmetic formula different from that of the second filter and has frequency characteristics that allow the second harmonic component to pass and block other components such as the DC component, fundamental wave component, third harmonic component, and fourth harmonic component from passing through, the effective value Idmf_r will constantly change and then settle at a constant value.

[0121] On the other hand, if the third filter has frequency characteristics that remove the fundamental wave component and DC component, pass the second harmonic component, and pass other harmonic components such as the third harmonic component and the fourth harmonic component to a certain extent, the third harmonic component, the fourth harmonic component, and higher harmonic components thereafter are included in the inrush current, and the effective value Idmf_r changes depending on these harmonic components. However, because the operation of the AND circuit 172 is limited by the period Tg of the one-shot timer 171, the behavior after the period Tg does not affect the operation of the output control unit 160A.

[0122] Fig. 16 is a diagram showing another example of changes over time in various calculated values according to the second embodiment when an inrush current occurs. The vertical axis of Fig. 16 represents the second harmonic content rate R2 or the harmonic content rate Rm, and the horizontal axis of Fig. 16 represents time. In addition to the graphs shown in Fig. 7, Fig. 16 also shows a graph of "harmonic effective value" and a graph of "mf / 1f." The effective value Idmf_r changes and then settles at a constant value.

[0123] FIG. 17 shows another example of changes over time in various calculated values according to the second embodiment when an inrush current occurs. The vertical axis of FIG. 17 represents the second harmonic content rate R2 or the harmonic content rate Rm, and the horizontal axis of FIG. 17 represents time. In addition to the graphs shown in FIG. 8, FIG. 17 also shows a graph of "harmonic effective value" and a graph of "mf / 1f." During the period Tp2, the effective value Id2f_r temporarily decreases, but the effective value Id2f_r increases. Accordingly, during the period Tp2, the second harmonic content rate R2 temporarily decreases, but the harmonic content rate Rm remains equal to or greater than the inrush current detection threshold Km (e.g., 15%). Therefore, at least one of the conditions P1 and Pm remains true.

[0124] The time period during which the second harmonic content rate R2 decreases (i.e., period Tp2) varies depending on the filter calculation formula of the second filter, the data length used for the calculation, etc. The filter calculation formula of the third filter is configured so that the decrease in the second harmonic content rate R2 during period Tp2 can be complemented by the harmonic content rate Rm (for example, so that the harmonic content rate Rm is equal to or greater than the threshold value Km during period Tp2).

[0125] <Example of operation> An example of the operation of the protective relay device 10A when a fault occurs and when an inrush current occurs will be described.

[0126] Fig. 18 is a timing chart for explaining an example of the operation of the protective relay device according to the second embodiment when a fault occurs. Signals E1, E2, F, G, H1, and H2 in Fig. 18 correspond to signals E1, E2, F, G, H1, and H2 in Fig. 13, respectively. This also applies to Figs. 19 to 21 below.

[0127] 18, an accident occurs at time t51, causing the amplitude of the difference current Id to increase. At time t52, the first determination unit 131 determines that the difference current Id contains a second harmonic component equal to or greater than a certain level, and outputs a signal E1 with a value of "1." Also at time t52, the OR circuit 173 outputs a signal H1 with a value of "1."

[0128] At time t53, as the value "1" of the signal E1 continues for the period Th or longer, the operation timer 174 outputs the value "1", and as a result, the recovery timer 175 outputs the signal H2 with the value "1". That is, the lock processing unit 170 outputs a lock signal. As a result, the output of the protection signal from the bias differential relay unit 105 is locked, and time t53 becomes the lock start time.

[0129] At time t54, the second determination unit 132 determines that the difference current Id contains a certain amount of harmonic components or more, and outputs a signal E2 with a value of "1." Also at time t54, the one-shot timer 171 outputs a signal F with a value of "1." As a result, the AND circuit 172 outputs a signal G with a value of "1."

[0130] At time t55, when a period Tg has elapsed since time t54, the one-shot timer 171 outputs a signal F with a value of "0." Shortly before time t55, the second determination unit 132 determines that the difference current Id does not contain a certain amount of harmonic components or more, and outputs a signal E2 with a value of "0." As a result, the value of the signal G also becomes "0."

[0131] At time t56, the first determination unit 131 determines that the difference current Id does not contain a second harmonic component equal to or greater than a certain level, and outputs a signal E1 with a value of 0. At this point, the value of the signal G is 0, so the value of the signal H1 also becomes 0.

[0132] At time t57, which is a period Ti after time t56, the recovery timer 175 outputs a signal H2 with a value of "0." This unlocks the output of the protection signal. Therefore, time t57 becomes the unlock time.

[0133] FIG. 19 is a timing chart for illustrating an example of the operation of the protective relay device according to the second embodiment when an inrush current is applied.

[0134] 19, at time t61, an inrush simulation current with a conduction angle of 60° is applied. At time t62, first determination unit 131 determines that difference current Id contains a second harmonic component equal to or greater than a certain level, and outputs signal E1 with a value of "1." Also at time t62, OR circuit 173 outputs signal H1 with a value of "1."

[0135] At time t63, as the value "1" of the signal E1 continues for the period Th or longer, the operation timer 174 outputs the value "1", and as a result, the recovery timer 175 outputs the signal H2 with the value "1". As a result, the output of the protection signal from the bias differential relay unit 105 is locked, and time t63 becomes the lock start time.

[0136] At time t64, the second determination unit 132 determines that the difference current Id contains a certain amount of harmonic components or more, and outputs a signal E2 with a value of "1." Also at time t64, the one-shot timer 171 outputs a signal F with a value of "1." As a result, the AND circuit 172 outputs a signal G with a value of "1."

[0137] At time t65, when a period Tg has elapsed since time t64, the one-shot timer 171 outputs the signal F with a value of "0." As a result, the value of the signal G also becomes "0."

[0138] As a result, the value of signal H2 remains at "1" after time t63. Therefore, when an inrush current occurs at a conduction angle of 60°, the protection signal output from bias differential relay unit 105 remains locked.

[0139] FIG. 20 is a timing chart for illustrating another example of the operation of the protective relay device according to the second embodiment when an inrush current is applied.

[0140] 20, at time t71, a simulated inrush current having a conduction angle of 90° is applied. At time t72, signal E1 having a value of "1" is output, and signal H1 having a value of "1" is also output.

[0141] At time t73, signal E1 has maintained a value of "1" for a period of time Th or longer, so that signal H2 with a value of "1" is output. This causes the protection signal output from bias differential relay unit 105 to be locked, and time t73 becomes the lock start time. At time t74, signal E2 with a value of "1" is output, and signal F with a value of "1" is output. This causes signal G with a value of "1" to be output.

[0142] At time t75, when a period Tg has elapsed since time t74, signal F with a value of "0" is output, causing signal G to also have a value of "0".

[0143] As a result, the value of signal H2 remains at "1" after time t73. Therefore, when an inrush current occurs at a conduction angle of 90°, the protection signal output from bias differential relay unit 105 remains locked.

[0144] FIG. 21 is a timing chart for illustrating yet another example of the operation of the protective relay device according to the second embodiment when an inrush current is applied.

[0145] 21, at time t81, a simulated inrush current is applied at a conduction angle of 120°. At time t82, signal E1 having a value of "1" is output, and signal H1 having a value of "1" is also output.

[0146] At time t83, signal E1 has maintained the value "1" for a period of time Th or longer, so that signal H2 with a value of "1" is output. This causes the protection signal output from bias differential relay unit 105 to be locked, and time t83 becomes the lock start time. At time t84, signal E2 with a value of "1" is output, and signal F with a value of "1" is output. This causes signal G with a value of "1" to be output.

[0147] During a period Tp2 (corresponding to, for example, the period Tp2 in FIG. 17) after time t84, the effective value Id2f_r decreases, causing the second harmonic content R2 to fall below the threshold K, and the value of signal E1 becomes "0." However, during the period Tp2, the effective value Idmf_r remains large, and the harmonic content Rm is equal to or greater than the threshold Km, so the value of signal E2 remains "1." As a result, the value of signal H2 remains "1." In other words, the protection signal output from the bias differential relay unit 105 remains locked.

[0148] At time t85, when a period Tg has elapsed since time t84, signal F with a value of "0" is output, causing signal G to also have a value of "0".

[0149] As a result, the value of signal H2 remains at "1" after time t83. Therefore, when an inrush current occurs at a conduction angle of 120°, the protection signal output from bias differential relay unit 105 remains locked.

[0150] As described above, after an inrush current occurs, there may be a period (e.g., period Tp2) during which the second harmonic content rate R2 is less than the threshold value K. Therefore, when the output of the protection signal is locked using only the second harmonic content rate R2, the lock may be temporarily released. To prevent this, the period of the recovery timer related to the determination of the second harmonic content rate R2 must be set relatively long. For example, referring to FIG. 12, the period Tb of the recovery timer 142 in the first embodiment is set longer than the period Tp2 (e.g., set to an electrical angle of 120°), so the value of the signal A2 remains at “1” (i.e., the protection signal output is not unlocked). The period Tb is the same period as the period of the recovery timer used in the conventional second harmonic locking method.

[0151] On the other hand, in the second embodiment, as explained in FIG. 21, even if there is a period (e.g., period Tp2) in which the second harmonic content rate R2 is less than the threshold value K, the harmonic content rate Rm is equal to or greater than the threshold value Km during that period, and therefore the protection signal output lock is not released. Therefore, there is no need to set the period of the recovery timer related to the determination of the second harmonic content rate R2 long. Therefore, the period Ti of the recovery timer 175 shown in FIGS. 13 and 18 can be set shorter than the period of the recovery timer (e.g., period Tb) used in the conventional second harmonic locking method, and can be set to, for example, an electrical angle of 60°.

[0152] As a result, the second embodiment can shorten the reset timer period compared to the conventional embodiment, and as a result, the protection signal can be unlocked more quickly. Therefore, delays in relay operation time due to second harmonic locking in the fault current can be suppressed.

[0153] <Advantages> According to the second embodiment, even if the output of the protection signal is locked by the second harmonic locking method when a fault occurs, the lock can be released earlier (for example, earlier by the shortened time of the recovery timer) than with the conventional second harmonic locking method. This allows for faster operation of the protection relay device. Furthermore, since the lock is maintained when an inrush current occurs, it is possible to prevent malfunction of the protection relay device.

[0154] Embodiment 3 The third embodiment has a configuration corresponding to a combination of the first and second embodiments. Fig. 22 is a block diagram showing a functional configuration of a protection relay device 10B according to the third embodiment. The protection relay device 10B includes, as main functional components, a ratio differential relaying unit 105, a difference current calculation unit 110, a first effective value calculation unit 121, a second effective value calculation unit 122, a third effective value calculation unit 123, a first determination unit 131, a second determination unit 132, an unlocking unit 150, an output control unit 160B, and a locking processing unit 170B. Of these, the configuration other than the output control unit 160B and the locking processing unit 170B is as described in Fig. 3 or 13 .

[0155] The lock processing unit 170B has a configuration in which an AND circuit 176 is added to the lock processing unit 170 of Fig. 13. The AND circuit 176 performs an AND operation on the output value of the recovery timer 175 and a value obtained by inverting the logical level of the output of the lock release unit 150. Specifically, when the output value of the recovery timer 175 is "1" and the output value of the lock release unit 150 is "0" (i.e., when the lock release unit 150 has not output a release signal for releasing the lock), the AND circuit 176 outputs a signal J with a value of "1" (for example, a lock signal for locking the output of a protection signal). The output process of the signal J with a value of "1" corresponds to the lock process for locking the output of a protection signal.

[0156] The output control unit 160B is configured as, for example, an AND circuit. The output control unit 160B performs an AND operation on the output value of the bias differential relay unit 105 and a value obtained by inverting the logical level of the output of the lock processing unit 170B (specifically, the AND circuit 176). The output control unit 160B outputs the value "1" when the output value of the bias differential relay unit 105 is "1" and the output value of the lock processing unit 170B is "0" (i.e., the bias differential relay unit 105 is operating and the locking process is not being executed). That is, the output control unit 160B outputs a protection signal by the bias differential relay unit 105.

[0157] On the other hand, even if the output value of the bias differential relay unit 105 is "1", if the output value of the lock processing unit 170B is "1" (i.e., lock processing is being performed even when the bias differential relay unit 105 is operating), the output control unit 160B outputs the value "0". In other words, the output control unit 160B does not cause the bias differential relay unit 105 to output a protection signal.

[0158] The third embodiment provides the advantages of the first and second embodiments. Specifically, when the fault current contains almost no harmonic components such as the second harmonic component, the fault current can be distinguished from the inrush current due to the existence of a period in which the second harmonic effective value is constant. Therefore, in the third embodiment, like the first embodiment, the lock can be released quickly at the timing of time t5 in Fig. 9.

[0159] On the other hand, if the fault current contains harmonic components of higher orders than the fundamental wave component, this may affect the second harmonic effective value, which may delay the unlocking. Even in this case, in the third embodiment, the recovery timer period for determining the second harmonic content rate R2 can be shortened as in the second embodiment, so that the locking can be released as quickly as possible.

[0160] Other embodiments. (1) In the above embodiment, the second harmonic locking system is incorporated in a bias differential relay device for transformer protection. However, the second harmonic locking system may also be incorporated in an overcurrent relay used as backup protection for a transformer to prevent malfunction due to inrush current. In this case, too, the same system as above can be used to achieve faster protective relay operation.

[0161] (2) In the above-described embodiment, the protective relay device 10 is described as a protective relay device for protecting a transformer, but the present invention is not limited to this configuration. For example, the protective relay device 10 may be applied as a ratio differential relay device for protecting a power transmission line, etc.

[0162] The configurations exemplified as the above-described embodiments are examples of the configurations of the present disclosure, and may be combined with other known technologies, or may be modified, such as by omitting some parts, within the scope of the gist of the present disclosure. Furthermore, the above-described embodiments may be implemented by appropriately adopting the processes and configurations described in other embodiments.

[0163] <Additional Notes> Various aspects of the present disclosure are summarized below as appendices.

[0164] (Appendix 1) A protective relay device for protecting a protected device, comprising: a first effective value calculation unit that calculates a first effective value of a fundamental wave component of a difference current calculated from a primary current and a secondary current of the protected device; a second effective value calculation unit that calculates a second effective value of a second harmonic component of the difference current; a third effective value calculation unit that calculates a third effective value of the second harmonic component of the difference current using a calculation method different from that used by the second effective value calculation unit; a first judgment unit that judges whether a first condition is met, that is, a first ratio of the second effective value to the first effective value is equal to or greater than a first threshold; a second judgment unit that judges whether a second condition is met, that is, a second ratio of the third effective value to the first effective value is equal to or greater than a second threshold; and a lock processing unit that executes a lock processing to lock the output of a protection signal for protecting the protected device when at least one of the first condition and the second condition is met.

[0165] (Appendix 2) 2. The protection relay device according to claim 1, further comprising an unlocking unit that releases the locking process based on the determination result of the first determination unit and the rate of change of the second effective value, wherein if a state in which the rate of change is less than a reference value continues for a second period or more within a first period after it is determined that the first condition is satisfied, the unlocking unit outputs a release signal to release the locking process.

[0166] (Appendix 3) 3. The protective relay device of claim 2, wherein the first period is longer than the second period.

[0167] (Appendix 4) 4. The protective relay device according to claim 2, wherein the unlocking unit stops outputting the unlock signal after a third period has elapsed since the end of the first period.

[0168] (Appendix 5) 5. The protective relay device of claim 4, wherein the third period is shorter than the first period and longer than the second period.

[0169] (Appendix 6) The protection relay device according to any one of Supplementary Note 1 to Supplementary Note 5, wherein the locking processing unit executes the locking processing when a state in which at least one of the first condition and the second condition is satisfied continues for a fourth period or more, and terminates the locking processing after a fifth period has elapsed since the state in which at least one of the first condition and the second condition is satisfied has ended.

[0170] (Appendix 7) 7. The protective relay device according to claim 1, wherein the second condition is invalidated after a sixth period has elapsed since it was determined that the second condition is satisfied.

[0171] (Appendix 8) 8. The protective relay device according to any one of Supplementary Note 1 to Supplementary Note 7, wherein the protected device is a transformer, and further comprises: a relay unit that performs a ratio differential relay calculation based on a suppression current calculated from the primary current and the secondary current and the difference current; and an output control unit that outputs the protection signal based on a result of the ratio differential relay calculation and whether or not the locking process has been performed.

[0172] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0173] 6 Transformer, 10, 10A, 10B Protection relay device, 21, 22 Current transformer, 31, 32 Circuit breaker, 41, 42 AC power supply, 51 Auxiliary transformer, 52 Signal conversion unit, 70 Processing unit, 71 Bus, 72 CPU, 73 ROM, 74 RAM, 75 Digital input circuit, 76 Digital output circuit, 77 Input interface, 105 Bias differential relay unit, 110 Difference current calculation unit, 121 First effective value calculation unit, 122 Second effective value calculation unit, 123 Third effective value calculation unit, 130 Judgment unit, 131 First judgment unit, 132 Second judgment unit, 140, 170, 170B Lock processing unit, 141, 154, 174 Operation timer, 142, 155, 175 Recovery timer, 143, 153, 172, 176 AND circuit, 150 unlocking unit, 151, 171 one-shot timer, 152 rate of change determination unit, 160, 160A, 160B output control unit, 173 OR circuit.

Claims

1. A protective relay device for protecting a protected device, a first effective value calculation unit that calculates a first effective value of a fundamental wave component of a difference current calculated from the primary current and the secondary current of the protected device; a second effective value calculation unit that calculates a second effective value of a second harmonic component of the difference current; a third effective value calculation unit that calculates a third effective value of the second harmonic component of the difference current by a calculation method different from that of the second effective value calculation unit; a first determination unit that determines whether a first condition is satisfied, that is, a first ratio of the second effective value to the first effective value is equal to or greater than a first threshold value; a second determination unit that determines whether a second condition is satisfied, that is, whether a second ratio of the third effective value to the first effective value is equal to or greater than a second threshold value; a lock processing unit that executes a lock process to lock the output of a protection signal for protecting the protected device when at least one of the first condition and the second condition is satisfied.

2. further comprising an unlocking unit that unlocks the locking process based on a determination result of the first determination unit and a rate of change of the second effective value; 2. The protective relay device according to claim 1, wherein, when a state in which the rate of change is less than a reference value continues for a second period or more within a first period after it is determined that the first condition is satisfied, the unlocking unit outputs an unlock signal to release the locking process.

3. The protective relay device according to claim 2 , wherein the first period is longer than the second period.

4. The protective relay device according to claim 2 or 3, wherein the unlocking unit stops outputting the unlock signal after a third period has elapsed since the end of the first period.

5. The protective relay device according to claim 4 , wherein the third period is shorter than the first period and longer than the second period.

6. The lock processing unit executes the locking process when a state in which at least one of the first condition and the second condition is satisfied continues for a fourth period or more; The protection relay device according to any one of claims 1 to 3, wherein the locking process is terminated after a fifth period has elapsed since a state in which at least one of the first condition and the second condition is satisfied has ended.

7. The protective relay device according to any one of claims 1 to 3, wherein the second condition is invalidated after a sixth period has elapsed since it was determined that the second condition was satisfied.

8. the protected device is a transformer, a relay unit that performs a ratio differential relay calculation based on a suppression current calculated from the primary current and the secondary current and the difference current; The protection relay device according to any one of claims 1 to 3, further comprising an output control unit that outputs the protection signal based on the result of the ratio differential relay calculation and whether or not the locking process is executed.

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