JP3788883B2 - Motion detection system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fluctuation detection system that detects fluctuations in a power system.
[0002]
[Prior art]
Conventionally, as a fluctuation detection system for detecting fluctuations in an electric power system, as shown in FIG. 17A, when a current from a protection target system is higher than levels L1, L2,... When the current level determining means 1 having a current relay is provided and the output “1” is determined from the overcurrent relays of the levels L1, L2,... L7 of the current level determining means 1 as shown in FIG. The outputs are input to the motion detection signal generators 2a to 2g separately to output a motion detection signal for a predetermined time (for example, 2 sec), and motion detection is performed from the AND gates 3a to 3g via the OR gate 4. There is what I did. In this case, when the current of the protection target system becomes equal to or lower than the levels L1, L2,... L7, the output of the fluctuation detection signal is stopped.
[0003]
[Problems to be solved by the invention]
However, according to such a sway detection system, the sway of the system to be protected can be reliably detected, but the system will operate even when the current suddenly changes due to a system fault, etc. There was a problem that it was impossible to distinguish between accidents and upsets. .
[0004]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fluctuation detection system that can accurately distinguish between a power system accident and a fluctuation and accurately detect only the system fluctuation.
[0005]
[Means for Solving the Problems]
According to the first aspect of the present invention, the amplitude value calculation means for obtaining the amplitude value of the current of the power system, and a plurality of current levels are set in advance, and whether the current amplitude value is equal to or more than the plurality of current levels at predetermined time intervals. Level determination means for determining and outputting a determination result corresponding to each current level; and a fluctuation detection means for detecting system fluctuation when only one determination result corresponding to each current level in the level determination means is changed. It is characterized by comprising.
[0006]
According to a second aspect of the present invention, in the first aspect of the present invention, when the fluctuation detecting means changes a plurality of determination results corresponding to each current level in the level determining means, the fluctuation of the system is detected for a predetermined time. It is characterized by non-operation.
[0007]
According to a third aspect of the present invention, in the first aspect of the present invention, the fluctuation detecting means changes for a predetermined time before and after a period in which only one determination result corresponding to each current level changes in the level determining means. It is characterized by detecting system fluctuations due to the absence of a period.
[0008]
According to a fourth aspect of the present invention, in the first aspect of the present invention, the fluctuation detecting unit includes a plurality of periods in which a single determination result corresponding to each current level in the level determining unit changes within a certain time. It is characterized by detecting system sway by being present twice.
[0009]
According to a fifth aspect of the present invention, in the first aspect of the invention, the fluctuation detection means is configured so that only one determination result corresponding to each current level in the level determination means is changed. When is repeatedly changed, the system fluctuation is not detected.
[0013]
Claim 6 The described invention is characterized in that, in the invention described in claim 1, the amplitude value calculating means obtains the amplitude value by using the positive phase of the current of the power system.
[0014]
As a result, according to the first aspect of the present invention, the system fluctuation is detected when only one determination result corresponding to a plurality of current levels performed every predetermined time is changed. Can accurately distinguish between accidents and upsets.
[0015]
According to the second aspect of the present invention, when a plurality of determination results corresponding to a plurality of current levels are changed, the detection of the system fluctuation is disabled for a certain period of time. It is possible to avoid detecting shaking in advance.
[0016]
According to the third aspect of the present invention, system fluctuation is detected because there is a period that does not change for a certain period of time before and after a period when only one determination result corresponding to a plurality of current levels changes. The system oscillation can be reliably detected even when the system oscillation is caused by a relatively slow current change.
[0017]
According to the fourth aspect of the present invention, since the system fluctuation is detected when the period in which only one determination result corresponding to a plurality of current levels changes is present a plurality of times within a certain period of time, It is possible to distinguish only the system fluctuation from the current change and system fluctuation accompanying the increase / decrease of the load.
[0018]
According to the fifth aspect of the present invention, when only one determination result corresponding to the current level changes and the content of the determination result changes repeatedly, the system oscillation is not detected. It is possible to distinguish only a system fluctuation from a current change accompanying a minute load fluctuation and a system fluctuation.
[0022]
Claim 6 According to the described invention, since the amplitude value is obtained using the positive phase of the current of the power system, if any phase is shaken, the shake can be detected without performing multiphase calculation. it can.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0024]
(First embodiment)
FIG. 1 shows a schematic configuration of a motion detection system to which the present invention is applied.
[0025]
In the figure, 11 is an input unit, and this input unit 11 is configured to receive a detection current from a power system to be protected via a CT (not shown).
[0026]
The input unit 11 is connected in series with an amplitude value calculation unit 12, a level determination unit 13, and a motion detection unit 14. Here, the amplitude value calculation unit 12 calculates the amplitude value of the detected current input to the input unit 11 by calculation. The level determination unit 13 determines whether or not the current amplitude value calculated by the amplitude value calculation unit 12 is equal to or higher than each of a plurality of different current levels set in advance. To do. As shown in FIG. 2, the fluctuation detection unit 14 includes the current determination result recording circuit 14a, the previous determination result recording circuit 14b, the comparison circuit 14c that compares the previous determination result with the current determination result, and the number output from the comparison circuit 14c. And a counter circuit 14d for determining fluctuations. Of these, the current determination result recording circuit 14 a records the result of the level determination unit 13, and the previous determination result recording circuit 14 b displays the result of the level determination unit 13 when the previous shake detection is performed. In this case, after the current fluctuation is detected, the result of the current determination result recording circuit 14a is recorded as it is. The comparison circuit 14c compares the outputs of the current determination result recording circuit 14a and the previous determination result recording circuit 14b for each level. If they are different, the comparison circuit 14c is “1”. "Is output. Then, the counter circuit 14d inputs the result of the comparison circuit 14c, counts the state where the comparison result is “1”, and outputs a fluctuation detection signal if the number of “1” is one, 0 or 2 In the case of more than one, the fluctuation detection signal is not output.
[0027]
Next, the operation of the embodiment configured as described above will be described.
[0028]
Now, when a current is taken into the input unit 11 from a protection target system via a CT (not shown), the amplitude value calculation unit 12 calculates the amplitude value of the current taken in the input unit 11. In this case, the interval at which the amplitude value calculation unit 12 calculates the amplitude value is set to a time sufficiently shorter than the oscillation period of the system.
[0029]
The amplitude value calculated by the amplitude value calculation unit 12 is input to the level determination unit 13. In the level determination unit 13, the current amplitude value calculated by the amplitude value calculation unit 12 is greater than or equal to each of the predetermined current levels (seven levels in the example, L1, L2,... L7). And a determination result corresponding to each current level is output. The current levels here are L1, L2,... L7 from the lowest.
[0030]
The result determined by the level determination unit 13 is given to the motion detection unit 14. The motion detection unit 14 records the determination result of the level determination unit 13 in the current determination result recording circuit 14a, and records the determination result of the level determination unit 13 when the previous motion detection is performed. Together with the output from 14b, the result is output to the comparison circuit 14c. The comparison circuit 14c compares the determination results for the current levels of the current determination result recording circuit 14a and the previous determination result recording circuit 14b. In these comparisons, if the two are different, “1” is the same. If "0" is output, "0" is output. Then, the comparison result in the comparison circuit 14c is sent to the counter circuit 14d, and only the output “1” is counted.
[0031]
Such an operation has a sufficiently short period compared with the oscillation period of the protection target system, and the result of the current determination result recording circuit 14a after the detection of the fluctuation is displayed in the previous determination result recording circuit 14b of the fluctuation detection unit 14. It is executed repeatedly while migrating. Finally, if the count number of the output “1” in the counter circuit 14d is only 1, the oscillation detection signal is output as the system oscillation, while the count number of “1” is 0 or 2 or more. In this case, the fluctuation detection signal is not output as a system fault.
[0032]
FIG. 3 illustrates the operation when an accident occurs in the protection target system. Here, the relationship between the current i from the system and the time t is used, and the current i is the current amplitude in the amplitude value calculation unit 12. The value is shown.
[0033]
Assuming that a system fault occurs between times t1 and t2 and a system fault is removed between times ta1 and ta2, the current amplitude value suddenly changes across multiple levels when the system fault occurs and when the fault is removed. The level determination unit 13 changes from level 2 to level 7 from non-operation to operation at times t1 and t2, and changes from level 7 to level 1 from operation to non-operation at times ta1 and ta2.
[0034]
Then, the fluctuation detection unit 14 compares the recorded contents of the previous determination result recording circuit 14b at time t1 with the recorded contents of the current determination result recording circuit 14a at time t2 by the comparison circuit 14c. It judges that they are different and outputs “1”. Similarly, since the contents of the previous determination result recording circuit 14b at time ta1 and the current determination result recording circuit 14a at time ta2 are also different, “1” is output. As a result, the counter circuit 14d counts two “1” outputs, so that it is determined that there is no system oscillation and the output of the oscillation detection signal is blocked (FIG. 3B).
[0035]
On the other hand, FIG. 4 illustrates the operation when the protection target system is shaken. Here, the relationship between the current i from the system and the time t is used, and the current i is the amplitude value calculation unit 12. The current amplitude value is shown.
[0036]
In this case, the current i changes relatively slowly as compared with the system fault described above, and at time t1 and t2, only level 2 becomes inoperable, and at time ta1 and ta2, only level 3 becomes inoperable. It is operating.
[0037]
Then, the fluctuation detection unit 14 compares the recorded contents of the previous determination result recording circuit 14b at time t1 with the recorded contents of the current determination result recording circuit 14a at time t2 by the comparison circuit 14c. It judges that they are different and outputs “1”. Similarly, the previous determination result recording circuit 14b at the time ta1 and the current determination result recording circuit 14a at the time ta2 are compared. However, since the contents of both are the same, “0” is output. As a result, since only one “1” output is counted in the counter circuit 14d, it is determined that the system is oscillating and an oscillation detection signal is output (FIG. 4B).
[0038]
Therefore, in this way, the amplitude value of the current of the protection target system is obtained by the amplitude value calculation unit 12, and it is determined every predetermined time whether the current amplitude value is equal to or more than a plurality of current levels preset by the level determination unit 13. Then, the determination result corresponding to each current level is output, and the present detection result is compared with the previous determination result by the motion detection unit 14, and the determination corresponding to each current level is performed in this comparison and the previous determination. When only one of the results has changed, it is determined as system oscillation, so that it is possible to accurately distinguish between a system fault and system oscillation, and it is possible to accurately detect only system oscillation.
[0039]
(Second Embodiment)
In this case, since the schematic configuration of the fluctuation detection system to which the second exemplary embodiment of the present invention is applied is the same as that in FIG. 1, the same figure is used here. Further, as shown in FIG. 5, the fluctuation detection unit 14 described with reference to FIG. 2 has a counter / fluctuation detection circuit 14e connected to the comparison circuit 14c.
[0040]
The counter / sway detection circuit 14e has a motion detection circuit including an AND gate 14e1, a delay circuit 14e2 and an inverter 14e3 in addition to the counter body (not shown). The comparison circuit 14c is used to determine the current determination result recording circuit 14a. When the output “1” corresponding to the comparison result for each level of the previous determination result recording circuit 14b is counted and the count number is 1, the oscillation detection signal is output via the AND gate 14e1, and the count number When 2 is detected to be 2 or more (2 or more levels change), the delay circuit 14e2 detects fluctuations on the condition that a certain time has passed. That is, when the level changes suddenly, the fluctuation detection is locked for a certain time.
[0041]
FIG. 6 illustrates the operation when the protection target system is shaken. Here, the relationship between the current i from the system and the time t is used, and the current i is the current amplitude in the amplitude value calculation unit 12. The value is shown.
[0042]
In this case, the amplitude value changes greatly at time t1 when the system fault occurs, but the current amplitude value may change slowly thereafter. This is due to the method of fluctuation of the current i accompanying the occurrence of an accident and the calculation of the current amplitude value. That is, it takes some time for the result of the calculation of the current amplitude value to reach a predetermined level. As shown in FIG. 6, most levels operate immediately after the occurrence of the accident, but the level set as the accident current. May be slightly longer than other levels due to delays in the calculation of the amplitude value of the current i until the level operates. For this reason, comparing the current level of current operation with the previous time, it is considered that the current level was changed due to the influence of the accident itself, although it was one level change.
[0043]
Therefore, in order to avoid malfunctions due to such causes, when multiple levels operate simultaneously, it is determined that there is an accident, and then the motion detection immediately after the accident occurs is locked by locking the shake detection for a certain period of time. Detection of fluctuation is avoided (FIG. 6B). The same applies to accident removal.
[0044]
Accordingly, in this way, in the counter / sway detection circuit 14e of the motion detection unit 14, when a plurality of determination results corresponding to a plurality of current levels change, the system motion detection is disabled for a certain period of time. Therefore, even if the current amplitude value changes greatly immediately after the occurrence of a system fault and the current amplitude value changes slowly thereafter, the system fluctuation is inadvertently detected by the current change at this time. Can be avoided.
[0045]
(Third embodiment)
In this case, since the schematic configuration of the fluctuation detection system to which the third embodiment of the present invention is applied is the same as that shown in FIG. 1, the same figure is used here. Further, as shown in FIG. 7, the fluctuation detecting unit 14 described with reference to FIG. 2 has a counter / fluctuation detecting circuit 14f connected to the comparison circuit 14c.
[0046]
The counter / sway detection circuit 14f has a motion detection circuit including AND gates 14f1, 14f2, OR gate 14f3, delay circuits 14f4, 14f5, 14f6, 14f7, and a flop flop 14f8 in addition to a counter body (not shown). The comparison circuit 14c counts the output “1” corresponding to the comparison result for each level of the current determination result recording circuit 14a and the previous determination result recording circuit 14b, and no level change is after the delay time t1 of the delay circuit 14f4. When one level change occurs until the delay time of the delay circuit 14f6, the flop flop 14f8 is set via the AND gate 14f2, and then there is no level change and no level change is after the delay time t2 of the delay circuit 14f5. If it continues, the motion detection signal is output (FIG. 8B), and the When the delay time of the delay circuit 14f7 elapses after the setting of the drop flop 14f8, the flop flop 14f8 is reset via the OR gate 14f3. That is, the fluctuation detection signal is output when no level change continues for a certain period of time, only one level changes, and then no level change continues for a certain period of time.
[0047]
FIG. 8 illustrates the operation when the protection target system is shaken. Here, the relationship between the amplitude value of the current i and the time t in the amplitude value calculation unit 12 is shown.
[0048]
In this case, if the calculation interval in the amplitude value calculation unit 12 is shortened and the current level is relatively large, the system fluctuation becomes a relatively slow current change. For this reason, the current i changes by one level, and there is a period in which there is no level change before and after the level change. In this case, when the system is shaken, the current may decrease. However, since the current slowly changes as in the case of the rise, the shake can be detected with the same logic.
[0049]
Therefore, in this way, even when the system fluctuation becomes a relatively slow current change by setting the calculation interval in the amplitude value calculation unit 12 to be short and the current level to be relatively large, a plurality of currents By detecting the system fluctuations before and after the period when only one determination result corresponding to the level is changed, the system fluctuations are detected, so that the system fluctuations can be detected reliably.
[0050]
(Fourth embodiment)
In this case, since the schematic configuration of the fluctuation detection system to which the fourth embodiment of the present invention is applied is the same as that shown in FIG. 1, the same figure is used here. Further, as shown in FIG. 9, the fluctuation detecting unit 14 described in FIG. 2 further has a fluctuation detecting circuit 14g connected to the counter / swing detecting circuit 14f described in FIG. 7 of the third embodiment. .
[0051]
The motion detection circuit 14g takes in the motion detection signal 15a from the counter / motion detection circuit 14f and a signal 15b indicating that the level has changed by two or more at a time, and detects the motion detection signal 15a more than once within a predetermined time. The fluctuation detection signal is output on condition that there is no signal 15b that has changed more than two levels at a time in the meantime.
[0052]
FIG. 10 illustrates the operation when the protection target system is shaken. Here, the relationship between the amplitude value of the current i and the time t in the amplitude value calculation unit 12 is shown.
[0053]
In this case, the amplitude value of the current i changes with time t even with a simple increase / decrease of the load, but the change in the current amplitude value is compared with the system fluctuation as a phenomenon before the system instability to be detected here. I am slow. The period of system oscillation is about 1 to 3 s, and when the level changes as the load increases or decreases, the change is in the order of minutes. For this reason, the motion detection signal 15a is output twice or more from the counter / motion detection circuit 14f within a predetermined time (FIG. 10B), and the motion detection signal 14a is detected by the motion detection circuit 14g. By adding to the above, it is possible to discriminate from current changes accompanying normal load fluctuations and system fluctuations, and to detect only system fluctuations (FIG. 10 (c)).
[0054]
(Fifth embodiment)
In this case, since the schematic configuration of the fluctuation detection system to which the fifth embodiment of the present invention is applied is the same as that shown in FIG. 1, the same figure is used here. Further, as shown in FIG. 11, the fluctuation detection unit 14 described in FIG. 2 further has a fluctuation detection circuit 14h connected to the counter / swing detection circuit 14f described in FIG. 7 of the third embodiment.
[0055]
The motion detection circuit 14h is a current detected when the motion detection signal 15a from the counter / motion detection circuit 14f and the signal 15b indicating a change of two levels or more at a time and the motion detection signal 15a are output from the comparison circuit 14c. Level information 15c is taken, and at least two fluctuation detection signals 15a are detected within a predetermined time. At this time, the operated current level is different from the current level information 15c, and the signal 15b that has changed more than two levels at a time. The sway detection signal is output on condition that there is no noise.
[0056]
FIG. 12 illustrates a state in which a load fluctuation has occurred in the protection target system. Here, the relationship between the amplitude value of the current i and the time t in the amplitude value calculation unit 12 is shown.
[0057]
In this case, when the current amplitude value is substantially constant and substantially equal to the set current level, the current amplitude value exceeds or falls below the set current level with only a slight load fluctuation. For this reason, in the method of the third embodiment, there is a possibility that the vibration is detected (FIG. 12B), but in the case of the system fluctuation, the current i increases or decreases as shown in FIG. However, the current i changes across a plurality of levels.
[0058]
For this reason, the current level 15c operated when the fluctuation detection signal 15a is output from the comparison circuit 14c is added as a condition for detecting the fluctuation, so that the current change accompanying the minute load fluctuation is distinguished from the system fluctuation, and only the system fluctuation is detected. can do.
[0059]
(Sixth embodiment)
FIG. 13 shows a schematic configuration of the sixth embodiment of the present invention, and the same parts as those in FIG.
[0060]
In this case, when a motion detection system from the input unit 11 to the motion detection unit 14 is prepared for each phase (R, S, T), and any of the motion detection systems of each phase outputs a motion detection signal. Therefore, it is determined that the system is shaken, and the shake is detected via the OR gate 16.
[0061]
In this way, it is possible to reliably detect system fluctuations.
[0062]
(Seventh embodiment)
FIG. 14 shows a schematic configuration of the seventh embodiment of the present invention, and the same parts as those in FIG.
[0063]
Also in this case, a motion detection system from the input unit 11 to the motion detection unit 14 is prepared for each phase (R, S, T), and the motion detection signal from the motion detection system of each phase is supplied to the delay circuit 17a, 17b and 17c are input to the AND gate 18 and the motion detection signal from the motion detection system of each phase is extended for a certain period of time. To do.
[0064]
Even in this case, since the system oscillation usually occurs in all three phases, it is possible to prevent inadvertent detection of the system oscillation by taking the AND condition of the three phases. In addition, by using the delay circuits 17a, 17b, and 17c, stable operation is possible even when the operation time of each phase varies.
[0065]
(Eighth embodiment)
FIG. 15 shows a schematic configuration of the eighth embodiment of the present invention, and the same parts as those in FIG.
[0066]
Also in this case, a motion detection system from the input unit 11 to the motion detection unit 14 is prepared for each phase (R, S, T), and the motion detection signal from the motion detection system unit of each phase is supplied to the delay circuit 17a. , 17b and 17c are input to the determination circuit 19, and when two of the three phases are operated by the determination circuit 19, it is determined that the system is upset. In this case, the amplitude value calculation of the amplitude value calculation unit 12 is performed by the line current.
[0067]
In this way, system oscillation usually occurs in all three phases, and if oscillation begins during an open-phase accident, all phases cannot be detected, but line voltage is used to detect three-phase oscillation. By detecting that two phases have been operated, it is possible to detect fluctuation during a phase failure accident.
[0068]
(Ninth embodiment)
FIG. 16 shows a schematic configuration of the ninth embodiment of the present invention, and the same parts as those in FIG.
[0069]
Also in this case, a motion detection system from the input unit 11 to the motion detection unit 14 is prepared for each phase (R, S, T). And the amplitude value calculation part 12 of each phase is made to perform a normal phase calculation, when performing an amplitude value calculation.
[0070]
In this way, when the amplitude value calculation unit 12 performs the normal phase calculation of the amplitude value, if any of the three phases is shaken, the shake can be detected without performing the calculation for the three phases. Thus, it is possible to more easily detect the system fluctuation.
[0071]
【The invention's effect】
As described above, according to the present invention, by focusing on the fact that the grid current changes abruptly at the time of an accident and changes relatively slowly at the time of a shake, the grid fault and the shake are accurately distinguished, and the grid fluctuation is The detection signal can be output only at the time, and normal load increase / decrease and system oscillation can be distinguished, and regular load fluctuation and system oscillation can be reliably identified.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a first embodiment of the present invention.
FIG. 2 is a diagram showing a schematic configuration of a fluctuation detecting unit used in the first embodiment.
FIG. 3 is a diagram for explaining the relationship between current and level determination when an accident occurs according to the first embodiment.
FIG. 4 is a diagram for explaining a relationship between current and level determination when fluctuations occur in the first embodiment;
FIG. 5 is a diagram showing a schematic configuration of a fluctuation detecting unit used in a second embodiment of the present invention.
FIG. 6 is a diagram for explaining the relationship between current and level determination when an accident occurs according to the second embodiment.
FIG. 7 is a diagram showing a schematic configuration of a motion detection unit used in a third embodiment of the present invention.
FIG. 8 is a diagram for explaining a relationship between current and level determination when an accident occurs according to a third embodiment.
FIG. 9 is a diagram showing a schematic configuration of a fluctuation detecting unit used in a fourth embodiment of the present invention.
FIG. 10 is a diagram for explaining the relationship between current and level determination when an accident occurs according to the fourth embodiment.
FIG. 11 is a diagram showing a schematic configuration of a fluctuation detecting unit used in a fifth embodiment of the present invention.
FIG. 12 is a diagram for explaining a relationship between a current and a level determination at the time of a minute current change according to the fifth embodiment.
FIG. 13 is a diagram showing a schematic configuration of a sixth embodiment of the present invention.
FIG. 14 is a diagram showing a schematic configuration of a seventh embodiment of the present invention.
FIG. 15 is a diagram showing a schematic configuration of an eighth embodiment of the present invention.
FIG. 16 is a diagram showing a schematic configuration of a ninth embodiment of the present invention.
FIG. 17 is a diagram for explaining a conventional motion detection system;
[Explanation of symbols]
11 ... Input section
12 ... Amplitude value calculator
13 ... Level judgment part
14: Motion detection unit
14a: Current determination result recording circuit
14b ... previous determination result recording circuit
14c: Comparison circuit
14d ... Counter circuit
14e ... oscillation detection circuit
14e1 ... ANDGATE
14e2 ... delay circuit
14e3 ... Inverter
14f ... oscillation detection circuit
14f1.14f2 ... ANDGATE
14f3 ... Or gate
14f4-14f7 ... delay circuit
14f8 ... flop flop
14g. 14h ... oscillation detection circuit
15a ... shaking signal
15b: Signal due to changes of 2 levels or more at a time
15c ... Current level
16 ... Or Gate
17a. 17b. 17c ... Delay circuit
18 ... Andgate
19: Determination circuit

Claims (6)

An amplitude value calculating means for obtaining an amplitude value of the current of the power system;
A plurality of current levels are set in advance, a level determination unit that determines whether the current amplitude value is equal to or higher than the plurality of current levels every predetermined time, and outputs a determination result corresponding to each current level;
A fluctuation detection system comprising: fluctuation detection means for detecting system fluctuation when only one determination result corresponding to each current level in the level determination means is changed.   2. The fluctuation detection unit according to claim 1, wherein the fluctuation detection unit disables the detection of the system fluctuation for a predetermined time when a plurality of determination results corresponding to each current level in the level determination unit change. system.   The fluctuation detection means detects system fluctuation by a period that does not change for a certain time before and after a period when only one determination result corresponding to each current level changes in the level determination means. The motion detection system according to claim 1.   The fluctuation detection means detects the fluctuation of the system when a period in which only one determination result corresponding to each current level in the level determination means changes exists a plurality of times within a predetermined time. Item 3. The motion detection system according to item 1.   The fluctuation detecting means does not detect system fluctuation when the determination result corresponding to each current level in the level determining means changes only one and the content of the determination result changes repeatedly. The motion detection system according to claim 1.   2. The fluctuation detection system according to claim 1, wherein the amplitude value calculation means obtains an amplitude value using a positive phase of a current of a power system.

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