WO2022149256A1 - 零相電流差動リレー - Google Patents
零相電流差動リレー Download PDFInfo
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- WO2022149256A1 WO2022149256A1 PCT/JP2021/000456 JP2021000456W WO2022149256A1 WO 2022149256 A1 WO2022149256 A1 WO 2022149256A1 JP 2021000456 W JP2021000456 W JP 2021000456W WO 2022149256 A1 WO2022149256 A1 WO 2022149256A1
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- 230000001629 suppression Effects 0.000 claims abstract description 130
- 230000008859 change Effects 0.000 claims abstract description 118
- 238000001514 detection method Methods 0.000 claims abstract description 96
- 238000004364 calculation method Methods 0.000 claims abstract description 83
- 230000007935 neutral effect Effects 0.000 claims abstract description 77
- 238000004804 winding Methods 0.000 claims description 23
- 238000010586 diagram Methods 0.000 description 18
- 230000007257 malfunction Effects 0.000 description 11
- 238000000605 extraction Methods 0.000 description 9
- 238000006243 chemical reaction Methods 0.000 description 8
- 238000000034 method Methods 0.000 description 8
- 230000035945 sensitivity Effects 0.000 description 8
- 229920006395 saturated elastomer Polymers 0.000 description 7
- 230000004048 modification Effects 0.000 description 5
- 238000012986 modification Methods 0.000 description 5
- 230000006870 function Effects 0.000 description 4
- 238000005070 sampling Methods 0.000 description 4
- 230000002265 prevention Effects 0.000 description 3
- 230000000717 retained effect Effects 0.000 description 2
- 230000007704 transition Effects 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 239000000284 extract Substances 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/10—Measuring sum, difference or ratio
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/26—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents
- H02H3/28—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at two spaced portions of a single system, e.g. at opposite ends of one line, at input and output of apparatus
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/04—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for transformers
- H02H7/045—Differential protection of transformers
Definitions
- This disclosure relates to a zero-phase current differential relay.
- the current differential relay protects the section surrounded by the current transformer (CT: Current Transformer) by the current input from the CT in the power equipment such as a transformer and the transmission line.
- CT Current Transformer
- the zero-phase current differential relay uses the zero-phase current to detect ground faults in the protection section with high sensitivity.
- a zero-phase current differential relay for example, a ground fault protection relay using each phase current and a neutral point current of the Y connection winding of a transformer is known.
- the zero-phase current differential relay calculates a differential amount and a suppression amount based on a zero-phase current based on each phase current and a neutral point current.
- the relay calculation unit that determines whether the differential amount and the suppression amount are in the operating range, and determines whether the phase of the neutral point current with respect to the zero-phase current is in the first region including the same phase. It includes a phase determination unit, and an operation determination unit that outputs a protection signal for protecting the three-phase transformer based on the determination result of the relay calculation unit and the determination result of the phase determination unit.
- the zero-phase current differential relay in order to detect a ground fault, it is a condition that the zero-phase current and the neutral point current used for the phase determination flow at a certain value or more.
- the ground fault current flowing to the failure point is the current flowing to the power supply side through the ground and the neutral point current flowing from the neutral point to the three-phase winding. Divided into. Further, the neutral point current is divided into a current flowing from the winding of the faulty phase to the faulty point and a current flowing from the winding of the healthy phase to the power supply. Therefore, the neutral point current is smaller than the ground fault current.
- the neutral point current becomes smaller because the ground fault current itself is small. In this way, if the neutral point current is small when an internal ground fault failure occurs on the power supply side, phase determination cannot be performed.
- Patent Document 1 when a three-phase short-circuit external failure occurs and CT saturation occurs in one of the phases, the zero-phase current flows but the neutral point current does not flow, so even in this case, the phase cannot be determined accurately. Therefore, in Patent Document 1, there is a possibility that the zero-phase current differential relay may malfunction, and there is room for improvement in achieving both high-sensitivity failure detection and malfunction prevention.
- An object in a certain aspect of the present disclosure is to provide a zero-phase current differential relay capable of achieving both high-sensitivity failure detection and malfunction prevention.
- a zero-phase current differential relay is provided to protect a three-phase transformer, including a Y-wire winding.
- the phase currents and neutral point currents of the Y-connected windings are defined so that the directions toward the neutral point are polar to each other.
- the zero-phase current differential relay has a first differential amount calculation unit that calculates the first differential amount based on the zero-phase current and the neutral point current based on each phase current, and detects changes in each phase current. It is provided with a current change detecting unit for calculating a first suppression amount, and a first suppression amount calculation unit for calculating a first suppression amount based on the detection result of the current change detection unit, each phase current, and a neutral point current.
- the first suppression amount calculation unit calculates the subtraction current of each phase current by subtracting the phase current of the cycle before the current cycle from the phase current of the current cycle, and the change of each phase current is detected. In this case, the first maximum value of the effective value of the subtraction current and the effective value of the neutral point current in each phase, or the maximum value of the effective value of the subtraction current in each phase plus the effective value of the neutral point current. 1 The added value is calculated as the first suppression amount.
- the zero-phase current differential relay further includes an operation determination unit that outputs a protection signal for protecting the three-phase transformer when the first differential amount and the first suppression amount are present in the operating range.
- a zero-phase current differential relay is provided to protect a three-phase transformer, including a Y-wire winding.
- the phase currents and neutral point currents of the Y-connected windings are defined so that the directions toward the neutral point are polar to each other.
- the zero-phase current differential relay has a first differential amount calculation unit that calculates the first differential amount based on the zero-phase current and the neutral point current based on each phase current, and each phase current and the neutral point.
- the first suppression amount calculation unit that calculates the first suppression amount based on the scalar sum with the current, and the three-phase transformer are protected when the first differential amount and the first suppression amount are present in the operating range.
- the output control unit is a current change detection unit that detects changes in each phase current, and a second differential quantity calculation unit that calculates the absolute value of the added current between each phase current and the neutral point current as the second differential quantity. And a second suppression amount calculation unit for calculating the second suppression amount based on each phase current and the neutral point current.
- the second suppression amount calculation unit calculates a subtraction current obtained by subtracting the phase current of the cycle before the current cycle from the phase current of the current cycle for each phase current, and calculates the absolute value of the subtraction current in each phase and the subtraction current.
- the maximum value of the absolute values of the neutral point current is calculated as the second suppression amount.
- the output control unit locks the output of the protection signal when a change in each phase current is detected and the second differential amount and the second suppression amount do not exist in the second operating range. It further includes a signal output unit that outputs a lock signal.
- the zero-phase current differential relay According to the zero-phase current differential relay according to the present disclosure, it is possible to achieve both high-sensitivity failure detection and malfunction prevention.
- FIG. It is a timing chart for demonstrating the operation when CT saturation occurs at the time of an external failure in the zero-phase current differential relay according to Embodiment 1.
- FIG. It is a figure for demonstrating the transition of the differential quantity at the time of CT saturation and at the time of CT non-saturation.
- It is a block diagram which shows an example of the functional structure of the zero-phase current differential relay which follows the modification of Embodiment 1.
- FIG. It is a timing chart for demonstrating the operation at the time of an internal ground fault failure in a zero-phase current differential relay according to the modification of Embodiment 1.
- FIG. It is a block diagram which shows the zero-phase current differential relay according to Embodiment 2.
- FIG. It is a figure for demonstrating the functional structure of the external failure detection part according to Embodiment 2.
- FIG. It is an operation characteristic diagram of the area determination part according to Embodiment 2.
- FIG. It is a timing chart for demonstrating the operation at the time of an external ground fault failure in the
- FIG. 1 is an overall configuration diagram including a zero-phase current differential relay and a three-phase transformer.
- the zero-phase current differential relay 40 protects the three-phase transformer 30 including the Y-connection winding.
- the three-phase transformer 30 is a Y- ⁇ connection type three-phase transformer having a primary side winding 31 which is a Y winding and a secondary side winding 32 which is a ⁇ winding.
- the primary winding 31 is composed of a-phase winding 33a, b-phase winding 33b, and c-phase winding 33c.
- the current transformer CTa, CTb, and CTc are provided on the lines of each phase on the primary side of the three-phase transformer 30.
- the current transformer CTa detects the a-phase current Ia flowing through the a-phase line 37a
- the current transformer CTb detects the b-phase current Ib flowing through the b-phase line 37b
- the current transformer CTc detects the b-phase current Ib flowing through the c-phase line 37c.
- the phase current Ic is detected.
- a current transformer CTN is provided on the ground wire 36 connecting the neutral point 34 of the primary winding 31 and the ground electrode 35.
- the current transformer CTN detects the neutral point current In.
- the signal representing these phase currents Ia, Ib, Ic and the signal representing the neutral point current In are input to the zero-phase current differential relay 40.
- the a-phase current Ia, the b-phase current Ib, the c-phase current Ic, and the neutral point current In have the same current directions (for example, positive) toward the neutral point 34 of the three-phase transformer 30. Is defined as.
- the zero-phase current differential relay 40 is composed of, for example, a digital protection relay configured based on a microcomputer.
- the zero-phase current differential relay 40 is not shown in order to disconnect the three-phase transformer 30 from the power system when it is determined that an internal ground fault has occurred based on the differential amount and the suppression amount.
- a protection signal (for example, a trip signal) for protecting the three-phase transformer 30 is output to the circuit breaker.
- the circuit breaker is usually installed closer to the three-phase transformer 30 than the current transformers CTa, CTb, CTc, and CTN. The three-phase transformer 30 is disconnected from the power system by opening the circuit breaker by the protection signal.
- the internal failure is a failure that occurs in the internal protection section surrounded by the current transformers CTa, CTb, CTc, and CTN.
- an external failure is a failure that occurs in an external section of the current transformers CTa, CTb, CTc, and CTN.
- FIG. 2 is a block diagram showing an example of the hardware configuration of the zero-phase current differential relay 40.
- the zero-phase current differential relay 40 has a configuration similar to that of a so-called digital protection relay device.
- the zero-phase current differential relay 40 includes an input conversion unit 100, an A / D conversion unit 110, an arithmetic processing unit 120, and an I / O (Input and Output) unit 130.
- the input conversion unit 100 includes auxiliary transformers 101_1, 101_2, ... For each input channel.
- the input conversion unit 100 receives inputs of a signal representing the phase currents Ia, Ib, and Ic output from the current transformers CTa, CTb, and CTc, respectively, and a signal representing the neutral point current In output from the current transformer CTN. ..
- Each auxiliary transformer 101 converts the current signals from the current transformers CTa, CTb, CTc and CTN into a voltage level signal suitable for signal processing in the A / D conversion unit 110 and the arithmetic processing unit 120.
- the A / D conversion unit 110 includes an analog filter (AF: Analog Filter) 111_1, 111_2, ..., a sample hold circuit (S / H: Sample Hold Circuit) 112_1, 112_2, ..., and a multiplexer (MPX: Multiplexer) 113. , A / D converter 114 and the like.
- the analog filter 111 and the sample hold circuit 112 are provided for each channel of the input signal.
- Each analog filter 111 is a low-pass filter provided for removing a folding error during A / D conversion.
- Each sample hold circuit 112 samples and holds a signal that has passed through the corresponding analog filter 111 at a specified sampling frequency.
- the sampling frequency is, for example, 4800 Hz.
- the multiplexer 113 sequentially selects the voltage signals held in the sample hold circuits 112_11, 112_2, ....
- the A / D converter 114 converts the signal selected by the multiplexer 113 into a digital value.
- the arithmetic processing unit 120 includes a CPU (Central Processing Unit) 121, a RAM (Random Access Memory) 122, a ROM (Read Only Memory) 123, and a bus 124 connecting them.
- the CPU 121 controls the overall operation of the zero-phase current differential relay 40.
- the RAM 122 and the ROM 123 are used as the main memory of the CPU 121.
- the ROM 123 can store a program, a set value for signal processing, and the like.
- the I / O unit 130 includes a digital input (D / I: Digital Input) circuit 132 and a digital output (D / O: Digital Output) circuit 133.
- the digital input circuit 132 and the digital output circuit 133 are interface circuits for communicating between the CPU 121 and an external device.
- the zero-phase current differential relay 40 may be configured by using circuits such as FPGA (Field Programmable Gate Array) and ASIC (Application Specific Integrated Circuit).
- FPGA Field Programmable Gate Array
- ASIC Application Specific Integrated Circuit
- FIG. 3 is a block diagram showing an example of the functional configuration of the zero-phase current differential relay according to the first embodiment.
- the zero-phase current differential relay 40 includes a differential amount calculation unit 210, a suppression amount calculation unit 220, a current change detection unit 230, and an operation determination unit 240 as main functional configurations. .. These configurations are realized, for example, by a processing circuit.
- the processing circuit may be dedicated hardware or may be a CPU 121 that executes a program stored in the internal memory of the zero-phase current differential relay 40.
- the processing circuit is composed of, for example, FPGA, ASIC, or a combination thereof.
- the differential quantity calculation unit 210 calculates the differential quantity ID1 based on the zero-phase current based on each phase current Ia, Ib, and Ic and the neutral point current In.
- the differential quantity calculation unit 210 includes an addition unit 11 and an effective value calculation unit 12.
- three times the zero-phase current I0 may be simply referred to as a zero-phase current.
- the addition unit 11 outputs the addition current Id * of the zero-phase current (that is, 3 ⁇ I0) and the neutral point current In to the effective value calculation unit 12.
- the effective value calculation unit 12 calculates the effective value of the added current Id * as the differential quantity ID1.
- the current change detection unit 230 detects changes in each phase current Ia, Ib, Ic.
- FIG. 4 is a block diagram showing an example of the functional configuration of the current change detection unit 230 according to the first embodiment.
- the current change detection unit 230 includes a current change calculation unit 51 to 53, an addition unit 54, a determination unit 55, and a one-shot timer 56.
- the current change calculation units 51, 52, and 53 calculate the changes ⁇ Ia, ⁇ Ib, and ⁇ Ic of each phase current.
- the change in each phase current is defined by the absolute value of the subtraction value between the absolute value of the instantaneous value at the present time and the absolute value of the instantaneous value ⁇ cycle (for example, 0.5) before the present time.
- ⁇ i / 2
- i is an integer of 1 or more.
- the time T ⁇ is the time corresponding to the ⁇ cycle.
- ⁇ Ia
- ⁇ Ib
- ⁇ Ic
- the determination unit 55 determines whether or not the addition value ⁇ I is equal to or greater than the threshold value J. When the addition value ⁇ I is equal to or greater than the threshold value J, the determination unit 55 outputs a signal indicating that each phase current has changed (for example, a signal having a value “1”), and when the addition value ⁇ I is less than the threshold value J. Outputs a signal (for example, a signal having a value of "0”) indicating that each phase current has not changed.
- the one-shot timer 56 maintains that value for the time T1 and outputs a signal to the suppression amount calculation unit 220, and when the time T1 elapses, the value "0". Is output to the suppression amount calculation unit 220.
- the subtraction value between the absolute value of the instantaneous value at the present time and the absolute value of the instantaneous value before the ⁇ cycle becomes zero, so no current change is detected.
- the subtracted value does not become zero, so that a current change is detected. Therefore, when the current change is detected by the current change detecting unit 230, it can be considered that some kind of failure has occurred. Further, since the current change is defined by an absolute value, the calculation time is short, so that the current change can be detected in a short time after the failure occurs.
- the maximum value of the detection time from the occurrence of the ground fault to the detection of the current change by the current change detection unit 230 is the time corresponding to 0.5 cycle. Since the time corresponding to the ⁇ cycle is set to a time equal to or greater than the maximum value of the detection time, ⁇ is set to a value of 0.5 cycle or more. In this embodiment, for example, ⁇ is set to 0.5.
- the suppression amount calculation unit 220 calculates the suppression amount IR1 based on the detection result of the current change detection unit 230, each phase current Ia, Ib, Ic and the neutral point current In. .. Specifically, the suppression amount calculation unit 220 includes an effective value calculation unit 13, 14, 16, a subtraction unit 15, a selection unit 19, and a maximum value extraction unit 20.
- the effective value calculation unit 13 calculates the effective value IN of the neutral point current In.
- the effective value calculation unit 14 calculates the effective value I1a of the a-phase current Ia, the effective value I1b of the b-phase current Ib, and the effective value I1c of the c-phase current Ic.
- the subtraction currents Ia *, Ib *, and Ic * are currents excluding the influence of the load current. It is assumed that the instantaneous values of the phase currents Ia, Ib, and Ic are sequentially stored in the memory (not shown). Therefore, the instantaneous value n cycles before is acquired from the memory.
- the effective value calculation unit 16 calculates the effective value I2a of the subtraction current Ia *, the effective value I2b of the subtraction current Ib *, and the effective value I2c of the subtraction current Ic *.
- the selection unit 19 selects either the effective value I1a to I1c or the effective value I2a to I2c based on the detection result of the current change detection unit 230, and outputs the selected effective value to the maximum value extraction unit 20. Specifically, the selection unit 19 selects the effective values I1a to I1c when the change of each phase current Ia to Ic is not detected by the current change detection unit 230, and the selection unit 19 selects the change of each phase current Ia to Ic. When is detected, the effective values I2a to I2c are selected. More specifically, the selection unit 19 selects the effective values I1a to I1c during the period when the value "0" is output from the one-shot timer 56 in FIG. 4, and the value "1" is set from the one-shot timer 56. During the output period, the effective values I2a to I2c are selected.
- the maximum value extraction unit 20 extracts the maximum value of the effective value selected by the selection unit 19 and the effective value IN of the neutral point current In, and calculates the maximum value as the suppression amount IR1. More specifically, when the change of each phase current is not detected (that is, when the value "0" is output from the one-shot timer 56), the maximum value extraction unit 20 has effective values I1a to I1c. , IN is calculated as the suppression amount IR1, and when the change of each phase current is detected (for example, when the value "1" is output from the one-shot timer 56), the effective value. The maximum value among I2a to I2c and IN is calculated as the suppression amount IR1.
- the operation determination unit 240 outputs a protection signal for protecting the three-phase transformer 30 when the differential amount ID1 and the suppression amount IR1 are present in the operating range.
- the operation determination unit 240 includes an area determination unit 21 and an operation timer 22.
- the area determination unit 21 determines whether or not the differential amount ID1 and the suppression amount IR1 exist in the operating range according to the following equations (1) and (2).
- K1 is a set value indicating the minimum operating sensitivity (hereinafter referred to as the minimum sensitivity value K1)
- p1 is a ratio set so as not to operate due to a CT error or the like.
- FIG. 5 is an operating characteristic diagram of the zero-phase current differential relay according to the first embodiment.
- the vertical axis of FIG. 5 shows the differential amount ID1, and the horizontal axis shows the suppression amount IR1.
- the zero-phase current differential relay 40 is configured so that the operating range is when both the above equations (1) and (2) are satisfied.
- the area determination unit 21 outputs a signal Sa having a value of “1” when a point (IR1, ID1) indicating the suppression amount IR1 and the differential amount ID1 exists in the operating range.
- the area determination unit 21 outputs a signal Sa having a value of "0" when the point (IR1, ID1) does not exist in the operating area.
- the operation timer 22 outputs the signal Sb of the value “1” when the signal Sa of the value “1” output from the area determination unit 21 continues for the time T2 or more.
- the signal Sb having a value of "1" corresponds to a protection signal for protecting the three-phase transformer 30.
- the operation determination unit 240 outputs a protection signal to the circuit breaker when the differential quantity ID1 and the suppression quantity IR1 are present in the operating range for a time T2 or more, and disconnects the three-phase transformer 30 from the power system.
- the current change detection unit 230 outputs a value “1” in the period from the detection of the change in each phase current to the elapse of the time T1, and the time T1 is set. When it elapses, the value "0" is output.
- the suppression amount calculation unit 220 calculates the maximum value among the effective values I2a to I2c, IN as the suppression amount IR1 during the period from the detection of the change in each phase current to the elapse of the time T1. Further, when the time T1 elapses after the change in each phase current is detected, the suppression amount calculation unit 220 calculates the maximum value among the effective values I1a to I1c and IN as the suppression amount IR1.
- the time T1 is shorter than the time Tn corresponding to the n cycle, and is set to, for example, the time corresponding to the (n— ⁇ ) cycle.
- FIG. 6 is a timing chart for explaining the operation at the time of an internal ground fault failure in the zero-phase current differential relay according to the first embodiment.
- the neutral point current is small when the phase a internal ground fault failure occurs (for example, the case where the internal ground fault failure occurs near the neutral point and the failure current itself is small).
- the waveform 610 is a waveform showing the a-phase current Ia
- the waveform 620 is the waveform showing the subtraction current Ia * of the a-phase.
- the subtraction current Ia * is zero before the occurrence of the internal failure, but corresponds to the a-phase failure current from which the load current is removed after the occurrence of the internal failure.
- the current change detection unit 230 outputs a signal having a value of "1" at time t1 1/4 cycle after time t0. This value "1" is maintained for the time T1 corresponding to the (n- ⁇ ) cycle (that is, 1.5 cycles) from the time t1.
- the detection time of the current change detection unit 230 (that is, the time from time t0 to time t1) is a time corresponding to 1/4 cycle.
- the suppression amount IR1 is the maximum value M2 among the effective values I2a to I2c and IN at time t1. Further, the suppression amount IR1 becomes the maximum value M1 among the effective values I1a to I1c and IN after the time T1 has elapsed from the time t1.
- the maximum value M2 is smaller than the maximum value M1 because it is calculated using the effective values I2a to I2c from which the load current is removed.
- the suppression amount IR1 becomes the maximum value M2 at the time t1, the suppression amount IR1 and the differential amount ID1 exist in the operating range. Therefore, the signal Sa output from the area determination unit 21 has a value of “1”. Subsequently, the value of the signal Sb becomes "1" after the lapse of time T1 from time t1, and the protection signal of the three-phase transformer 30 is output to the circuit breaker. In this way, the current change is detected instantly when a failure occurs, and the value referred to as the suppression amount IR1 is set to the maximum value M2 calculated using the effective values I2a to I2c from which the negative overcurrent is removed. It is understood that the internal failure can be detected with high sensitivity.
- FIG. 7 is a timing chart for explaining the operation of the zero-phase current differential relay according to the first embodiment when CT saturation occurs at the time of an external failure.
- the a-phase current transformer CTa is saturated at the time of an external failure (for example, an external three-phase short-circuit failure) in which the failure current is so large that CT saturation occurs.
- the waveform 710 shows the CT saturation waveform of the a-phase current Ia.
- the waveform 720 is shown as the CT unsaturated waveform of the a-phase current Ia.
- the a-phase current Ia suddenly increases.
- CT saturation occurs at time t2a, and CT saturation is restored at time t3a.
- the a-phase current Ia repeats the generation of CT saturation and the recovery from CT saturation.
- the current change detection unit 230 outputs a signal having a value of "1" at time t1a, which is 1/12 cycle after time t0a.
- the value “1” is maintained for the time T1 corresponding to the (n— ⁇ ) cycle (that is, 1.5 cycles) from the time t1a.
- the detection time of the current change detection unit 230 is a time corresponding to 1/4 cycle.
- the current change detection time of the current change detection unit 230 is a time corresponding to 1/12 cycle (that is, the time from the time t0a to the time t1a), and the detection is more than in the case of FIG. The time is short.
- FIG. 7 assumes an external failure (for example, an external three-phase short-circuit failure) in which the failure current is so large that CT saturation occurs. Specifically, when the failure current is large, the current change is also large and the current change detection time of the current change detection unit 230 is shortened.
- the suppression amount IR1 is the maximum value M2 among the effective values I2a to I2c and IN at time t1a. Further, the suppression amount IR1 becomes the maximum value M1 among the effective values I1a to I1c and IN after the time T1a has elapsed from the time t1a. However, in the case of an external failure in which the failure current is so large that CT saturation occurs, there is no difference between the maximum value M1 and the maximum value M2 because the load current is small with respect to the failure current. Therefore, after the time t2a, the suppression amount IR1 becomes constant at a relatively large value.
- the waveform is greatly disturbed by the saturation of the single-phase current transformer (CTa in this case), but in the present embodiment, the maximum values of each phase current and the neutral point current are suppressed. It is understood that a sufficient amount of suppression can be secured because the maximum value suppression method is adopted.
- the differential amount ID1 is a value larger than zero when CT saturation occurs, and becomes zero when CT is not saturated. Specifically, the differential amount ID1 changes as shown in FIG.
- FIG. 8 is a diagram for explaining the transition of the differential amount at the time of CT saturation and the time of CT non-saturation.
- the differential amount ID1 becomes larger, and when the CT saturation is restored, the differential amount ID1 becomes smaller. Therefore, in the signal Sa of the region determination unit 21, the differential quantity ID1 and the suppression quantity IR1 enter the operating range as the CT saturation progresses, and the differential quantity ID1 and the suppression quantity IR1 exit the operating region when the CT saturation is restored.
- the time that exists in the operating range is short because a sufficient amount of suppression can be secured. That is, the time for maintaining the value of the signal Sa at "1" is short.
- the signal Sb since this time is less than the time T2 of the operation timer 22, the signal Sb does not become the value “1” and the protection signal is not output as shown in FIG. 7. That is, it is understood that the malfunction of the zero-phase current differential relay 40 when an external failure occurs can be prevented.
- FIG. 9 is a block diagram showing an example of the functional configuration of the zero-phase current differential relay according to the modified example of the first embodiment.
- the zero-phase current differential relay 40A has a differential amount calculation unit 210, a suppression amount calculation unit 220A, a current change detection unit 230A, an operation determination unit 240, and a memory as main functional configurations.
- a unit 250, a zero current determination unit 260, and a setting unit 270 are included.
- These configurations are realized, for example, by a processing circuit. Since the configurations of the differential quantity calculation unit 210 and the operation determination unit 240 are the same as those described in FIG. 3, the detailed description thereof will not be repeated.
- the current change detection unit 230A corresponds to the configuration in which the one-shot timer 56 is deleted from the configuration of the current change detection unit 230 in FIG.
- the current change detection unit 230A is a signal indicating that each phase current has changed (for example, a signal having a value "1") or a signal indicating that each phase current has not changed (for example, a value). "0" signal) is output.
- the zero current determination unit 260 determines whether or not at least one of the effective values of the phase currents Ia, Ib, and Ic has become zero. For example, the zero-current determination unit 260 indicates as a determination result a signal indicating that at least one effective value is zero (for example, a signal having a value “1”), or indicating that none of the effective values is zero. A signal (for example, a signal having a value of "0") is output.
- the setting unit 270 outputs a set signal or a reset signal to the memory unit 250 and the subtraction unit 15A based on the detection result of the current change detection unit 230A and the determination result of the zero current determination unit 260.
- the setting unit 270 includes a return timer 63, an operation timer 64, an OR gate 65, and an SR circuit 66.
- the SR circuit 66 holds the set signal and stores the set signal in the memory unit. Output to 250 and subtraction unit 15A.
- the return timer 63 maintains the value for the time Ta. After the time Ta has elapsed, the return timer 63 outputs the value "0".
- the time Ta is set to a time during which the failure is expected to be eliminated after the protection signal is output by the zero-phase current differential relay 40.
- the operation timer 64 outputs the value "1” when the value "1" output from the zero current determination unit 260 continues for the time Tb or more.
- the OR gate 65 performs an OR operation on the value obtained by inverting the logic level of the output of the return timer 63 and the output value of the operation timer 64. Specifically, whether the value "0" is output from the return timer 63 (for example, after a lapse of time Ta after the current change is detected by the current change detection unit 230A), or the value "1" is output from the operation timer 64. If it is output (for example, the value "1" output from the zero current determination unit 260 continues for a time Tb or more), the OR gate 65 outputs a value "1", otherwise. The value "0" is output to.
- the SR circuit 66 When the SR circuit 66 receives the input of the value "1" from the OR gate 65, the SR circuit 66 resets the set signal and outputs the reset signal to the memory unit 250 and the subtraction unit 15A.
- the setting unit 270 outputs a set signal when a change in each phase current is detected by the current change detection unit 230A. Further, when the time Ta has elapsed since the change of each phase current is detected by the current change detection unit 230A (for example, when the value "0" is output from the return timer 63), the setting unit 270 is used. A reset signal is output when the period in which at least one of the effective values of each phase current becomes zero continues for a time Tb or more (for example, when the value "1" is output from the operation timer 64).
- the memory unit 250 sequentially stores the instantaneous values of the phase currents Ia, Ib, and Ic. Specifically, when the memory unit 250 does not receive the set signal from the setting unit 270, each phase current Ia for the latest m cycles (where m is an integer of 1 or more satisfying m ⁇ n). , Ib, Ic are retained. That is, the memory unit 250 holds the instantaneous values of the phase currents Ia, Ib, and Ic from the present time to m cycles before.
- the memory unit 250 stops the sequential storage of the latest phase currents Ia, Ib, and Ic, and starts from the time when the set signal is received (that is, the time when the change in each phase current is detected).
- the instantaneous values of the phase currents Ia, Ib, and Ic up to m cycles before are retained.
- the memory unit 250 receives the reset signal from the setting unit 270, the memory unit 250 resumes the sequential storage of the latest phase currents Ia, Ib, and Ic, and the memory unit 250 resumes the sequential storage of the latest phase currents Ia, Ib, and Ic for the latest m cycles. Holds the instantaneous value of.
- the suppression amount calculation unit 220A includes an effective value calculation unit 13, 16A, a subtraction unit 15A, and a maximum value extraction unit 20A.
- the effective value calculation unit 13 calculates the effective value IN of the neutral point current In.
- the subtraction unit 15A When the subtraction unit 15A does not receive the set signal, the subtraction currents Ia *, Ib *, Ic obtained by subtracting the instantaneous values n cycles before the current time from the current instantaneous values of the phase currents Ia, Ib, Ic. * Calculate.
- the subtraction unit 15A acquires the instantaneous value n cycles before from the memory unit 250.
- each phase current Ia, Ib in the reference cycle indicating one cycle m cycles before the reception time of the set signal (that is, the detection time of the change of each phase current).
- Ic instantaneous value is acquired from the memory unit 250.
- the subtraction unit 15A calculates the current obtained by subtracting the phase current in the reference cycle from the phase current in the current cycle as the subtraction current for each phase current.
- the subtraction unit 15A calculates the current obtained by subtracting the instantaneous value of the reference cycle from the instantaneous value of the current cycle of each phase current Ia, Ib, Ic as the subtraction current Ia *, Ib *, Ic *.
- the data for one cycle m cycles before time t1 (that is, the data of the reference cycle) is applied as the data on the subtraction side (that is, the subtraction side).
- the time corresponding to the m cycle is Tm
- the sampling time is Ts
- the time corresponding to one cycle is Tc
- the subtraction currents Ia *, Ib *, and Ic * are collectively referred to as Isu.
- Isu (t1 + k ⁇ Ts) I (t1) -I (t1-Tm)
- Isu (t1 + Ts) I (t1 + Ts) -I (t1-Tm + Ts)
- Isu (t1 + 2Ts) I ( t1 + 2Ts) -I (t1-Tm + 2Ts).
- Isu (t1 + j ⁇ Tc) I (t1 + Tc) -I (t1-Tm)
- Isu (t1 + Tc + Ts) I (t1 + Tc + Ts) -I (t1-Tm + Ts)
- Isu (t1 + Tc + 2Ts) I (t1 + Tc + 2Ts) -Tm + 2Ts).
- the current value on the subtrahend side at the time (t1 + k ⁇ Ts) and the current value on the subtrahend side at the time (t1 + j ⁇ Tc + k ⁇ Ts) are the same and are I (t1-Tm + k ⁇ Ts).
- the subtraction unit 15A calculates the current obtained by subtracting the phase current in the reference cycle from the phase current in the current cycle as the subtraction current for each phase current. Further, when time Ta has elapsed since the change in each phase current is detected, or when at least one of the effective values of each phase current becomes zero, the subtraction unit 15A performs the current cycle for each phase current. The current obtained by subtracting the phase current n cycles before the current cycle from the phase current is calculated as the subtraction current.
- the effective value calculation unit 16A calculates the effective value I2a of the subtraction current Ia *, the effective value I2b of the subtraction current Ib *, and the effective value I2c of the subtraction current Ic *.
- the maximum value extraction unit 20A calculates the maximum value among the effective values I2a to I2c and IN as the suppression amount IR1.
- the suppression amount calculation unit 220A always calculates the suppression amount IR using the effective values I2a, I2b, I2c of the subtraction currents Ia *, Ib *, and Ic *. Different from 220. If no failure has occurred and no current change has been detected, the subtraction currents Ia *, Ib *, and Ic * are calculated based on the instantaneous value of the current cycle and the instantaneous value n cycles before. If no failure has occurred, each phase current is a load current, so the effective values I2a, I2b, and I2c are zero. Therefore, the zero-phase current differential relay 40A does not operate.
- the subtraction currents Ia *, Ib *, and Ic * are calculated based on the instantaneous value in the current cycle and the instantaneous value in the reference cycle.
- the subtraction current is a current excluding the influence of the load current from the failure current. Therefore, as in the configuration of FIG. 3, the zero-phase current differential relay 40A can detect an internal failure with high sensitivity even when the neutral point current is small.
- the subtraction currents Ia *, Ib *, and Ic * are calculated based on the instantaneous value of the current cycle and the instantaneous value n cycles before. If so, the effective values of the subtraction currents Ia *, Ib *, and Ic * become zero after n cycles have elapsed from the occurrence of the failure. Therefore, if the failure continues after n cycles, the zero-phase current differential relay 40A cannot operate properly. For example, when CT saturation occurs due to an external failure, a sufficient suppression amount cannot be secured and there is a possibility of malfunction.
- each phase current including only the failure current that is not affected by the load current even if the failure continues is calculated.
- the subtraction currents Ia *, Ib *, and Ic * are calculated based on the instantaneous value of each phase current in the current cycle and the instantaneous value of each phase current in the reference cycle m cycles before the detection of the current change. Will be done.
- each phase current (that is, subtraction current) that is not affected by the load current can be obtained by repeatedly using the data in the reference cycle even after n cycles have elapsed from the occurrence of the failure. Therefore, the zero-phase current differential relay 40A can operate appropriately when a failure occurs.
- FIG. 10 is a timing chart for explaining the operation at the time of an internal ground fault failure in the zero-phase current differential relay according to the modification of the first embodiment.
- the neutral point current is small when the internal ground fault of phase a occurs.
- the waveform 810 is a waveform showing the a-phase current Ia
- the waveform 820 is the waveform showing the a-phase current on the subtraction side used in the subtraction unit 15A
- the waveform 830 is the subtraction current Ia *. It is a waveform shown. As shown in the waveform 810, when an internal failure occurs at time t0, the a-phase current Ia becomes large.
- the current change detection unit 230A detects the change in each phase current at time t1 and outputs the value "1".
- the current value on the subtrahend side is the current value n cycles before the change in each phase current is detected.
- the current value on the subtrahend side becomes the current value of the reference cycle. Therefore, as shown in the waveform 830, the subtraction current Ia * becomes zero because the a-phase current Ia is only the load current before the change detection of each phase current is detected.
- the subtraction current Ia * becomes the a-phase failure current in which the load current is removed from the a-phase current Ia.
- the suppression amount IR1 maintains the value calculated using the effective values I2a to I2c from which the load current is removed. From this, even in the modified example of the first embodiment, the current change can be detected instantly when a failure occurs, and the suppression amount IR1 using the effective values I2a to I2c from which the negative overcurrent is removed can be secured, so that the sensitivity is high. It is understood that an internal failure can be detected. Similarly, even when CT saturation occurs at the time of an external failure, a sufficient suppression amount IR1 can be obtained, so that a malfunction of the zero-phase current differential relay can be prevented.
- Embodiment 2 In the second embodiment, a configuration in which a lock function at the time of external failure detection is added to the zero-phase current differential relay 40 according to the first embodiment will be described.
- FIG. 11 is a block diagram showing a zero-phase current differential relay 40B according to the second embodiment.
- the zero-phase current differential relay 40B includes a zero-phase differential relay unit 310 and an output control unit 320.
- the zero-phase differential relay unit 310 corresponds to the zero-phase current differential relay 40 or 40A described in the first embodiment.
- the signal Sb output from the zero-phase differential relay unit 310 is output to the output control unit 320 instead of the circuit breaker.
- the zero-phase current differential relay 40B according to the second embodiment corresponds to a configuration in which an output control unit 320 is added to the zero-phase current differential relay 40 or 40A.
- the zero-phase differential relay unit 310 outputs the signal Sb as described with reference to FIG. 3 or 9. Specifically, when the signal Sb has a value of "1", it indicates that the zero-phase differential relay unit 310 operates and the protection signal of the three-phase transformer 30 is output. On the other hand, when the signal Sb has a value of "0", it indicates that the zero-phase differential relay unit 310 is not operating.
- the output control unit 320 includes an external failure detection unit 322 and an AND gate 324.
- the external failure detection unit 322 detects an external failure and outputs a signal Xc according to the detection result. Specifically, the external failure detection unit 322 outputs a signal Xc having a value of "1" when an external failure is detected, and outputs a signal Xc having a value of "0" when no external failure is detected. do.
- the specific configuration of the external failure detection unit 322 will be described later.
- the AND gate 324 performs an AND operation on the output value of the zero-phase differential relay unit 310 and the value obtained by inverting the logical level of the output of the external failure detection unit 322, and outputs the signal Xs.
- a protection signal eg, a trip signal
- the circuit breaker is opened and the three-phase transformer 30 is separated from the power system.
- the AND gate 324 has a value of “1”. Output the signal Xs. That is, when the zero-phase differential relay unit 310 is operating and no external failure is detected by the external failure detection unit 322, the protection signal from the zero-phase differential relay unit 310 is output as it is.
- the AND gate 324 outputs a signal Xs with a value of "0". Therefore, even if the zero-phase differential relay unit 310 is operating, if an external failure is detected (that is, when the value of the signal Xc of the external failure detection unit 322 is “1”), the zero-phase differential relay unit The operation output by 310 is locked. That is, the output control unit 320 has a function of locking the output of the protection signal by the zero-phase differential relay unit 310 when an external failure occurs.
- FIG. 12 is a diagram for explaining the functional configuration of the external failure detection unit 322 according to the second embodiment.
- the external failure detection unit 322 includes a current change detection unit 230, a differential amount calculation unit 410, a suppression amount calculation unit 420, and a signal output unit 430.
- the current change detection unit 230 in FIG. 12 is the same as the current change detection unit 230 in FIG.
- the differential quantity calculation unit 410 calculates the absolute value of the sum of the phase currents Ia, Ib, Ic and the neutral point current In as the differential quantity ID2.
- the differential quantity calculation unit 410 includes an addition unit 83 and an absolute value calculation unit 84.
- the absolute value calculation unit 84 calculates the absolute value of the added current Id2 * (that is,
- the suppression amount calculation unit 420 calculates the maximum value of the absolute value of the subtraction current and the absolute value of the neutral point current in each phase as the suppression amount IR2. Specifically, the suppression amount calculation unit 420 includes an absolute value calculation unit 85, 87, a subtraction unit 86, and a maximum value extraction unit 88.
- the absolute value calculation unit 85 calculates the absolute value
- the subtraction unit 86 is substantially the same as the subtraction unit 15 in FIG. That is, the subtraction unit 86 calculates the subtraction currents Ia *, Ib *, Ic * by subtracting the instantaneous values n cycles before the current cycle from the instantaneous values of the current cycles of the phase currents Ia, Ib, and Ic.
- the absolute value calculation unit 87 calculates the absolute value
- the maximum value extraction unit 88 calculates the maximum value among the absolute values
- the signal output unit 430 exists when the change in each phase current is detected by the current change detection unit 230, and the differential amount ID2 and the suppression amount IR2 do not exist in the operating range (that is, in the external region). ), Output a lock signal to lock the output of the protection signal.
- the signal output unit 430 includes an area determination unit 89, an AND gate 90, an operation timer 91, and a return timer 92.
- the area determination unit 89 determines whether or not the differential amount ID2 and the suppression amount IR2 exist outside the operating range according to the following equations (3) and (4).
- K2 is a set value indicating the minimum operating sensitivity (hereinafter referred to as the minimum sensitivity value K2)
- p2 is a ratio set so as not to operate due to a CT error or the like.
- FIG. 13 is an operation characteristic diagram of the area determination unit according to the second embodiment.
- the vertical axis of FIG. 13 shows the differential amount ID2, and the horizontal axis shows the suppression amount IR2.
- the area determination unit 89 outputs the signal Xb having the value “1” when the points (IR2, ID2) indicating the suppression amount IR2 and the differential amount ID2 exist in the external area.
- the area determination unit 89 outputs the signal Xb having the value “0” when the point (IR2, ID2) does not exist in the external area.
- the AND gate 90 performs an AND operation between the output value of the current change detection unit 230 and the output value of the area determination unit 89, and outputs the signal Xc.
- the current change is detected by the current change detection unit 230 (that is, when the value of the signal Xa is "1")
- the area determination unit 89 presents a point (IR2, ID2) in the external region.
- the AND gate 90 outputs the signal Xc having the value "1".
- the operation timer 91 outputs the value "1" to the return timer 92 when the value "1" of the signal Xc of the AND gate 90 continues for a time T réellep or more.
- the return timer 92 maintains the value for the time Tre.
- the time Tre is set longer than the time T réellep.
- the signal Xc of the value "1" output from the return timer 92 corresponds to a lock signal that locks the operation output of the zero-phase differential relay unit 310.
- the time T réellep of the operation timer 91 is set so that the operation output of the zero-phase differential relay unit 310 can be locked before CT saturation occurs at the time of an external failure. If the CT saturation progresses too much, the operating output of the zero-phase differential relay unit 310 cannot be locked. Therefore, for example, the lockable time is from the occurrence of the failure to the lapse of 1/4 cycle (that is, the electric angle of 90 °). Let's say it's time. In this case, it is necessary that the total time of the detection time by the current change detection unit 230 and the time T réellep of the operation timer 91 is less than the 1/4 cycle period for a large current failure that causes CT saturation.
- the detection time by the current change detection unit 230 when CT saturation occurs at the time of an external failure is a time corresponding to 1/12 cycle (that is, an electric angle of 30 °).
- the time T NEEDp of the operation timer 91 is set to a time corresponding to 1/12 to 1/6 cycle (that is, an electric angle of 30 ° to 60 °).
- the time T réellep is set to a time corresponding to 1/12 cycle in consideration of a margin.
- the total time of the detection time by the current change detection unit 230 and the time T Desip is a time corresponding to 2/12 cycles (that is, less than 1/4 cycle).
- the time Tre of the return timer 92 is set to be equal to or longer than the time from the occurrence of an external failure to the convergence of CT saturation. Since CT saturation depends on the DC component included in the fault current, the time Tre is set to about the time constant of the DC component (for example, a period of 5 to 20 cycles).
- the time T1 of the one-shot timer 56 of the current change detection unit 230 is set to a longer time than the operation timer T réellep of the external failure detection unit 322.
- the time T1 is set to a time corresponding to one cycle in consideration of a margin.
- the output of the protection signal by the zero-phase differential relay unit 310 can be instantly locked when an external failure occurs.
- a protection signal is output by the zero-phase differential relay unit 310. Therefore, the malfunction of CT saturation by the zero-phase differential relay unit 310 can be prevented more accurately.
- the subtraction currents Ia *, Ib *, and Ic * including only the failure current are used to calculate the suppression amount IR2. This makes it possible to prevent the determination of an external failure despite the internal failure.
- the suppression amount is calculated using the phase currents Ia, Ib, and Ic including the load current and the failure current, when the failure current is larger than the load current when an internal failure occurs, The amount of suppression becomes larger than the amount of differential. In this case, the signal output unit 430 may erroneously determine that an external failure has occurred.
- the differential amount becomes larger than the suppression amount when an internal failure occurs. It is possible to prevent erroneous judgment that a failure has occurred.
- the differential amount ID2 and the suppression amount IR2 used in the signal output unit 430 are calculated not by the effective value calculation but by the absolute value calculation.
- the effective value calculation is adopted, the calculation time of the differential quantity ID2 and the suppression quantity IR2 is delayed, so that it takes time to secure a sufficient differential quantity when an internal failure occurs.
- the suppression amount becomes larger than the differential amount, and there is a possibility that it is erroneously determined that an external failure has occurred when an internal failure occurs.
- the absolute value calculation is adopted, a sufficient differential amount can be immediately secured when an internal failure occurs, so that it is possible to prevent erroneous determination that an external failure has occurred.
- FIG. 14 is a timing chart for explaining the operation at the time of an external failure in the external failure detection unit according to the second embodiment.
- an external failure for example, an external three-phase short-circuit failure
- the current transformer CTN is saturated.
- the current change detection unit 230 detects a change in each phase current at time t1b and outputs a signal Xa having a value of "1".
- the time from the time t0b to the time t1b (that is, the detection time of the current change detection unit 230) is, for example, a time corresponding to 1/12 cycle.
- the area determination unit 89 outputs a signal Xb having a value of "1" because the differential amount ID2 and the suppression amount IR2 exist in the external area other than the operating range before the time t0b before the occurrence of the external failure. Further, even if an external failure occurs at time t0b, the output of the signal Xb having the value “1” is maintained because the differential quantity ID2 and the suppression quantity IR2 exist in the external region until CT saturation occurs. When CT saturation occurs in the current transformer CTN at time t3b, the differential quantity ID2 and the suppression quantity IR2 are present in the operating range, so that the signal Xb having the value “0” is output. After that, the area determination unit 89 outputs the signal Xb having a value of “0” when the CT is saturated, and outputs the signal Xb having a value “1” when the CT is not saturated.
- a state in which the change of each phase current is detected by the current change detection unit 230 and the differential amount ID2 and the suppression amount IR2 are determined to exist in the external region by the region determination unit 89 that is, the signal Xa and the signal Xb.
- a signal Xc having a value of "1" is output at a time t2b in which the value (a state of "1") continues for a time T réellep (for example, a time corresponding to 1/12 cycle) of the operation timer 91.
- the operation output of the zero-phase differential relay unit 310 is locked at the time t2b before the time t3b where the current transformer CTN saturates. Therefore, it is possible to more accurately prevent the malfunction of the zero-phase differential relay unit 310 due to CT saturation.
- the maximum value among the effective values I1a to I1c of each phase current and the effective value IN of the neutral point current is set. It is calculated as the suppression amount IR1, and when a change in each phase current is detected, the maximum value among the effective values I2a to I2c of the subtraction current and the effective value IN of the neutral point current is calculated as the suppression amount IR1.
- the configuration has been described, but the configuration is not limited to this. For example, when the change of each phase current is not detected, the value obtained by adding the effective value IN to the maximum value of the effective values I1a to I1c is calculated as the suppression amount IR1, and the change of each phase current is detected. If so, the configuration may be such that the value obtained by adding the effective value IN to the maximum value among the effective values I2a to I2c is calculated as the suppression amount IR1.
- the suppression amount calculation unit 220 sets the effective value IN to the maximum value of each effective value I1a to I1c, IN, or the maximum value of each effective value I1a to I1c.
- the added value obtained by adding the above may be calculated as the suppression amount IR1.
- the suppression amount calculation unit 220 sets the effective value to the maximum value among the effective values I2a to I2c and IN, or the maximum value of the effective values I2a to I2c.
- the added value obtained by adding IN may be calculated as the suppression amount IR1.
- the absolute value calculation unit 84 may calculate the larger of the current absolute value
- the maximum value extraction unit 88 has the maximum value of each absolute value
- may be configured to calculate the larger of the maximum values as the suppression amount IR2.
- the zero-phase differential relay unit 310 corresponds to the zero-phase current differential relay 40 or 40A in the first embodiment has been described, but the configuration is not limited to this.
- the zero-phase differential relay unit 310 may be a zero-phase differential relay unit that employs a scalar sum method when calculating the suppression amount.
- the zero-phase differential relay unit includes a differential amount calculation unit 210 in FIG. 3, a suppression amount calculation unit that calculates a suppression amount using a scalar sum method, and an operation determination unit 240 in FIG. include.
- the differential quantity calculation unit 210 calculates the differential quantity ID1 based on the zero-phase current based on each phase current Ia, Ib, and Ic and the neutral point current In.
- the suppression amount calculation unit calculates the sum of the effective value of the zero-phase current (3 ⁇ I0) and the effective value of the neutral point current In (that is, the scalar sum) as the suppression amount.
- the operation determination unit 240 outputs a protection signal for protecting the three-phase transformer 30 when the differential amount ID1 and the suppression amount are present in the operation range. The functions of the area determination unit 21 and the operation timer 22 of the operation determination unit 240 will not be repeated.
- the scalar sum method When the scalar sum method is adopted, the influence of the load current can be removed. Therefore, when an internal failure occurs in which the failure current is small with respect to the load current (that is, the neutral point current is small), the suppression amount does not increase, so that highly sensitive internal failure detection becomes possible.
- the suppression amount becomes zero when CT saturation occurs at the time of an external failure.
- the zero-phase differential relay unit may malfunction due to the operation determination unit 240 erroneously determining an internal failure in spite of the external failure.
- the output control unit 320 according to the second embodiment when an external failure occurs, the output of the protection signal by the zero-phase differential relay unit can be instantly locked. Therefore, it is possible to prevent a malfunction of CT saturation due to the zero-phase differential relay unit that employs the scalar sum suppression method.
- the configuration exemplified as the above-described embodiment is an example of the configuration of the present disclosure, can be combined with another known technique, and a part thereof is not deviated from the gist of the present disclosure. It is also possible to change and configure it, such as by omitting it. Further, in the above-described embodiment, the processing and configuration described in the other embodiments may be appropriately adopted and carried out.
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Abstract
Description
<全体構成>
図1は、零相電流差動リレーと三相変圧器とを含む全体構成図である。
図2は、零相電流差動リレー40のハードウェア構成の一例を示すブロック図である。図2を参照して、零相電流差動リレー40は、いわゆるデジタル保護リレー装置と同様の構成を有している。具体的には、零相電流差動リレー40は、入力変換部100と、A/D変換部110と、演算処理部120と、I/O(Input and Output)部130とを含む。
図3は、実施の形態1に従う零相電流差動リレーの機能構成の一例を示すブロック図である。図3を参照して、零相電流差動リレー40は、主たる機能構成として、差動量算出部210と、抑制量算出部220と、電流変化検出部230と、動作判定部240とを含む。これらの構成は、例えば、処理回路により実現される。処理回路は、専用のハードウェアであってもよいし、零相電流差動リレー40の内部メモリに格納されるプログラムを実行するCPU121であってもよい。処理回路が専用のハードウェアである場合、処理回路は、例えば、FPGA、ASIC、またはこれらを組み合わせたもの等で構成される。
ID1>p1×IR1 …(2)
ここで、K1は最小動作感度を示す整定値(以下、最小感度値K1と称する)であり、p1はCTの誤差などで動作しないよう整定される比率である。抑制量IR1がK1/p1以下の場合には式(1)に従って判定が行なわれ、抑制量IR1がK1/p1より大きい場合には式(2)に従って判定が行われる。
(内部故障時)
図6は、実施の形態1に従う零相電流差動リレーにおける内部地絡故障時の動作を説明するためのタイミングチャートである。図6では、a相の内部地絡故障発生時において中性点電流が小さい場合(例えば、内部地絡故障が中性点付近で発生して故障電流自体が小さい場合等)を想定する。また、n=2、α=0.5であるとする。
図7は、実施の形態1に従う零相電流差動リレーにおける、外部故障時にCT飽和が発生した場合の動作を説明するためのタイミングチャートである。図7では、CT飽和が発生するほど故障電流が大きい外部故障(例えば、外部三相短絡故障)時においてa相の電流変成器CTaが飽和した場合を想定する。また、n=2、α=0.5であるとする。
(機能構成)
図9は、実施の形態1の変形例に従う零相電流差動リレーの機能構成の一例を示すブロック図である。図9を参照して、零相電流差動リレー40Aは、主たる機能構成として、差動量算出部210と、抑制量算出部220Aと、電流変化検出部230Aと、動作判定部240と、メモリ部250と、零電流判定部260と、設定部270とを含む。これらの構成は、例えば、処理回路により実現される。なお、差動量算出部210および動作判定部240の構成は、図3で説明したものと同一であるため、その詳細な説明は繰り返さない。
図10は、実施の形態1の変形例に従う零相電流差動リレーにおける内部地絡故障時の動作を説明するためのタイミングチャートである。図10では、a相の内部地絡故障発生時において中性点電流が小さい場合を想定する。また、n=2、m=2であるとする。
実施の形態2では、実施の形態1に従う零相電流差動リレー40に、外部故障検出時におけるロック機能を追加した構成について説明する。
ID2<p2×IR2 …(4)
ここで、K2は最小動作感度を示す整定値(以下、最小感度値K2と称する)であり、p2はCTの誤差などで動作しないよう整定される比率である。
(1)上述した実施の形態において、図5の電流変化検出部230の構成では、変化ΔIa,ΔIb,ΔIcの加算値ΔIに基づいて電流変化を検出する構成について説明したが、当該構成に限られない。例えば、加算値ΔIに中性点電流Inの変化ΔIn(=||In|-|In(t-Tα)||)を加算してもよい。
Claims (7)
- Y結線巻線を含む三相変圧器を保護するための零相電流差動リレーであって、
前記Y結線巻線の各相電流および中性点電流は中性点に向かう方向が互いに同極性となるように定義され、
各前記相電流に基づく零相電流と前記中性点電流とに基づいて、第1差動量を算出する第1差動量算出部と、
各前記相電流の変化を検出する電流変化検出部と、
前記電流変化検出部の検出結果と各前記相電流と前記中性点電流とに基づいて、第1抑制量を算出する第1抑制量算出部とを備え、
前記第1抑制量算出部は、
各前記相電流について、現サイクルの当該相電流から、前記現サイクルよりも前のサイクルの当該相電流を減算した減算電流を算出し、
各前記相電流の変化が検出された場合、各相における前記減算電流の実効値および前記中性点電流の実効値のうちの第1最大値、または各相における前記減算電流の実効値の最大値に前記中性点電流の実効値を加算した第1加算値を前記第1抑制量として算出し、
前記第1差動量および前記第1抑制量が動作域に存在する場合に、前記三相変圧器を保護するための保護信号を出力する動作判定部をさらに備える、零相電流差動リレー。 - 前記第1抑制量算出部は、
各前記相電流について、前記現サイクルの当該相電流から、前記現サイクルよりもnサイクル前(nは1以上の整数)の当該相電流を減算した電流を前記減算電流として算出し、
各前記相電流の変化が検出されてから第1の時間が経過するまでの期間、前記第1最大値または前記第1加算値を前記第1抑制量として算出し、
前記第1の時間は、前記nサイクルに相当する時間よりも短い、請求項1に記載の零相電流差動リレー。 - 各前記相電流の変化が検出されてから前記第1の時間が経過した場合、前記第1抑制量算出部は、各前記相電流の実効値および前記中性点電流の実効値のうちの第2最大値、または各前記相電流の実効値の最大値に前記中性点電流の実効値を加算した第2加算値を前記第1抑制量として算出する、請求項2に記載の零相電流差動リレー。
- 前記第1抑制量算出部は、各前記相電流の変化が検出された場合、各前記相電流について、前記現サイクルにおける当該相電流から、前記変化が検出された時点よりもmサイクル前(mは1以上の整数)の1サイクルを示す基準サイクルにおける当該相電流を減算した電流を前記減算電流として算出する、請求項1に記載の零相電流差動リレー。
- 各前記相電流の変化が検出されてから第2の時間が経過した場合または各前記相電流の実効値のうちの少なくとも1つがゼロになった場合、前記第1抑制量算出部は、各前記相電流について、前記現サイクルの当該相電流から、前記現サイクルよりもnサイクル前(nは、n≦mを満たす1以上の整数)の当該相電流を減算した電流を前記減算電流として算出する、請求項4に記載の零相電流差動リレー。
- 前記動作判定部による前記保護信号の出力をロックする出力制御部をさらに備え、
前記出力制御部は、
各前記相電流と前記中性点電流との加算電流の絶対値を第2差動量として算出する第2差動量算出部と、
各相における前記減算電流の絶対値および前記中性点電流の絶対値のうちの最大値を第2抑制量として算出する第2抑制量算出部と、
各前記相電流の変化が検出された場合であって、かつ前記第2差動量および前記第2抑制量が第2動作域に存在しない場合に、前記保護信号の出力をロックするためのロック信号を出力する信号出力部とを含む、請求項1~請求項5のいずれか1項に記載の零相電流差動リレー。 - Y結線巻線を含む三相変圧器を保護するための零相電流差動リレーであって、
前記Y結線巻線の各相電流および中性点電流は中性点に向かう方向が互いに同極性となるように定義され、
各前記相電流に基づく零相電流と前記中性点電流とに基づいて、第1差動量を算出する第1差動量算出部と、
各前記相電流と前記中性点電流とのスカラー和に基づいて、第1抑制量を算出する第1抑制量算出部と、
前記第1差動量および前記第1抑制量が動作域に存在する場合に、前記三相変圧器を保護するための保護信号を出力する動作判定部と、
前記動作判定部による前記保護信号の出力をロックする出力制御部とを備え、
前記出力制御部は、
各前記相電流の変化を検出する電流変化検出部と、
各前記相電流と前記中性点電流との加算電流の絶対値を第2差動量として算出する第2差動量算出部と、
各前記相電流と前記中性点電流とに基づいて、第2抑制量を算出する第2抑制量算出部とを含み、
前記第2抑制量算出部は、
各前記相電流について、現サイクルの当該相電流から、前記現サイクルよりも前のサイクルの当該相電流を減算した減算電流を算出し、
各相における前記減算電流の絶対値および前記中性点電流の絶対値のうちの最大値を第2抑制量として算出し、
前記出力制御部は、各前記相電流の変化が検出された場合であって、かつ前記第2差動量および前記第2抑制量が第2動作域に存在しない場合に、前記保護信号の出力をロックするためのロック信号を出力する信号出力部をさらに含む、零相電流差動リレー。
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JP2019030073A (ja) * | 2017-07-27 | 2019-02-21 | 三菱電機株式会社 | 零相電流差動リレー |
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