JP2011030306A - Method of detecting isolated operation and detector - Google Patents

Abstract

An object of the present invention is to prevent unnecessary detection of a single operation of a distributed power source to suppress simultaneous stop of the distributed power source, to suppress generation of reactive power, and to perform a single operation of the distributed power source at high speed. Makes it possible to detect.
In a frequency shift method combined with a frequency change rate detection method that is a passive method for detecting a single operation of a distributed power source in a power conditioner for a distributed power source linked to a distribution line, the power conditioner The gain value is set to a level at which reactive power does not occur when the system frequency fluctuates due to internal oscillator control, and the difference between the short-term moving average value and long-term moving average value of the system frequency is When the difference range is exceeded, the gain value is increased to accelerate the change in the system frequency, and the difference is distributed when the difference between the short-term moving average value and the long-term moving average value of the system frequency exceeds a predetermined threshold. The single operation of the power source was detected.
[Selection] Figure 1

Description

  The present invention relates to an isolated operation detection method and a detection apparatus. More specifically, the present invention relates to a technique for detecting that a distributed power source such as a residential solar power generation system linked to a low-voltage distribution line has shifted to a single operation state.

(1) Conventional isolated operation detection method In the case of distributed power sources such as residential solar power generation connected to low-voltage distribution lines, when the distribution lines are disconnected from the distribution system at substations etc. There is a possibility that the operation is continued with the distribution line charged (that is, the distribution line is stopped). Such an operation of the distributed power source is referred to as an isolated operation, and the stability of the system is impaired, so it must be prevented. For this reason, in the grid connection regulations (Non-patent Document 1), an isolated operation detection function is provided for low-voltage interconnected distributed power sources such as residential solar power generation in order to prevent reliable isolated operation when the distribution line stops. As for the active method and the passive method, it is supposed to equip each one or more types.

(1-1) Passive method Independent operation detection The passive method monitors and detects changes in frequency and voltage phase that occur during independent operation, and is broadly divided into a phase jump detection method and a frequency change rate detection method. There are two types of methods. The frequency change rate detection method that is detected based on the integrated value of the phase change is often used because it can be said that the detection reliability is superior.

  As shown in FIG. 3, the basic configuration of the frequency change rate detection system is that the system voltage 5 is received by the calculator 5A and the long-term moving average value fl of the system frequency is calculated by the calculator 5A. A moving average value fs is calculated, and a difference | fs-fl | between both moving average values is calculated by the isolated operation detection comparator 6, and the difference is determined in advance (hereinafter referred to as an isolated operation detection threshold fd). Is exceeded, the isolated operation of the distributed power source is detected, and the output stop signal Ss is output to the disconnector (not shown) of the distribution line via the counter 7.

(1-2) Active system As an independent operation detection active system, a frequency shift system, which is a system that does not easily interfere with each other even when a plurality of distributed power sources are operated in parallel, is often used. The frequency shift method detects the grid frequency from moment to moment, calculates the difference between the grid frequency and the standard frequency at all times, and changes the phase of the output current of the distributed power source in proportion to the difference, during single operation Control is performed so that the change in frequency increases.

  Specifically, the frequency shift method detects a change from a normal standard value of the system frequency generated during the single operation according to Equation 1 and is distributed power sources such as residential solar power generation in proportion to the change. This is a method for increasing the phase of the output signal Ib in the power conditioner model (FIG. 4). The gain is the rate of change of the output current with respect to the frequency difference.

(Equation 1) Ib '= Ib.exp [jAsign (f-f0)]
Where Ib ′: output signal of the phase modulator,
Ib: output signal,
A: coefficient (gain),
f: System frequency during single operation,
f0: standard frequency at normal time,
j: represents an imaginary unit.
Further, sign () is a function for extracting the sign of + or − in ().

  The positive / negative change direction of the phase in the frequency shift method is a bidirectional type that expands in the direction changed first at the time of shifting to the single operation. As a result, a positive feedback loop is formed during the single operation, and the frequency diverges in the positive or negative direction.

(2) Unnecessary stop characteristics during frequency fluctuations in the conventional islanding detection method The above-mentioned islanding detection passive method generally enables detection at a higher speed than the active method, This method unnecessarily detects changes in the frequency and voltage phase of the distribution system even during system disturbances that are different from single operation such as when a system frequency fluctuation occurs due to a large-capacity generator dropping due to an earthquake disaster, etc. It is possible to mistakenly detect a system disturbance that is not a result of single operation), resulting in a simultaneous stop of the distributed power supply, which may greatly impair the stability of the entire system when a large number of distributed power supplies are introduced. There is a problem.

Table 1 shows the stop time characteristics when the system frequency fluctuates (specifically decreases) in the frequency change rate detection method (see FIG. 3) which is a conventional passive operation detection passive method. In addition, the premise of examination here regarding a stop time characteristic is as follows.
1) The normal system frequency is 50 Hz.
2) The number of long-term frequency moving average sampling cycles in the calculator 5A:
500 cycles (hence long-time frequency moving average length X = 10 seconds)
3) Number of sampling cycles of short-time frequency moving average in the arithmetic unit 5B:
2 cycles (hence, short-time frequency moving average length Y = 0.04 seconds)
4) Change rate of the system frequency for detecting the isolated operation in the isolated operation detection comparator 6:
0.3% (independent operation detection threshold fd = ± 0.15 Hz with reference frequency = 50 Hz)
5) Time period (ie, comparator output duration required for final detection):
4 cycles (= 0.08 seconds)
As a result, the isolated operation of the distributed power source is detected when the frequency change rate obtained above continues more than twice the short-time frequency moving average cycle number and deviates from the isolated operation detection threshold.

  From Table 1, it can be seen that in the conventional method, when the long-term frequency moving average length X = 10 seconds, unnecessary stop is caused by a slight frequency fluctuation with a frequency change rate of less than 0.1 Hz / second.

  As a measure to improve the above situation, although it is considered effective to reduce the detection sensitivity by reducing the value of the long-term frequency moving average length X, the single operation of the distributed power source is detected by the decrease in the detection sensitivity. This may cause a problem that the time required for the operation (hereinafter referred to as the isolated operation detection time) increases. Note that the increase in the isolated operation detection time means that the time for which the isolated operation state of the distributed power source continues becomes longer, which is not preferable for system operation management.

  Here, the relationship between the long-term frequency moving average length X and the isolated operation duration (that is, the isolated operation detection time) when the gain of the frequency shift method is 0.2, which is generally employed, is shown in FIG. Shown in The parameter is an unbalance rate (P, Q) between the effective component P and the ineffective component Q between the generated power just before the distribution line stops and the load amount.

  FIG. 5 shows that the isolated operation detection time becomes particularly long when P = 0 and Q = 0 are completely balanced, but when the long-time frequency moving average length X is greater than about 0.5 seconds, the isolated operation detection time is reached. It can be seen that the effect does not appear.

  Based on these results, assuming that 0.5 seconds, which is the minimum value in the range that does not affect the isolated operation detection time, is adopted as the long-term frequency moving average length X, the frequency shown in Table 1 indicates that there is no unnecessary stop frequency. It can be seen that the rate of change can be increased to about 0.5 Hz / second. However, when dealing with a frequency change rate higher than that, it is necessary to further reduce the value of the long-term frequency moving average length X and increase the gain of the frequency shift method.

(3) Effect of gain increase in frequency shift method of conventional isolated operation detection passive method Next, as an example of increasing the gain of the frequency shift method, the gain is set to 0.4 and the isolated operation is performed. FIG. 6 shows the relationship between the value of the long-term frequency moving average length X and the isolated operation continuation time (that is, the isolated operation detection time) when the change rate of the system frequency to be detected is set to 0.3%. Compared with the results shown in FIG. 5, the stop time when P = 0 and Q = 0 is significantly reduced from 0.26 seconds to 0.16 seconds and the long-term frequency moving average length X is reduced to 0.3 seconds. It can be seen that there is no effect on the isolated operation detection time.

NEC Corporation: Grid Connection Regulations, JEAC9701-2006

  However, when looking at the power conditioner output reactive power value when the system frequency fluctuates when the gain of the frequency shift method is used as a parameter (FIG. 7), the gain increases while it hardly occurs when the gain is 0.2. As a result, it will increase significantly. For example, when the gain is 0.4, the reactive power is generated at about 1 kVar, which is significantly increased as compared with the case where the gain is 0.2. This is because when the gain is small, the control of the internal oscillator (PLL circuit) 11 of the power conditioner in FIG. 4 follows, and as a result, the phase difference between the current and the voltage does not increase.

  From the above, while increasing the gain of the frequency shift method, it is possible to decrease the detection sensitivity of the passive operation detection passive method and enhance the suppression of unnecessary stop when the system frequency fluctuates during system disturbance. Thus, the reactive power increases with respect to changes in the system frequency when the system is disturbed, and the stability of the system is impaired. Therefore, it is understood that the method of simply increasing the gain is not appropriate for the stable operation of the system.

  Therefore, the present invention can prevent unnecessary detection of the isolated operation of the distributed power source when the system frequency fluctuation occurs, thereby suppressing simultaneous stop of the distributed power source and suppressing generation of reactive power. An object of the present invention is to provide an isolated operation detection method and detection apparatus capable of detecting isolated operation of a power source at high speed.

  In order to achieve this object, the islanding operation detection method according to claim 1 is a frequency change rate which is a passive system for detecting islanding operation of a distributed power source in a power conditioner for a distributed power source connected to a distribution line. In the frequency shift method combined with the detection method, the gain value is set to a level where no reactive power is generated due to fluctuations in the system frequency during system disturbance by controlling the internal oscillator of the power conditioner, and the short-time moving average value of the system frequency When the difference between the value and the long-term moving average value exceeds the range of the difference at the time of the system disturbance, the gain value is increased to accelerate the change in the system frequency, and the short-time moving average value and the long-term moving average value of the system frequency The single operation of the distributed power source is detected when the difference between and exceeds a predetermined threshold.

  Further, the isolated operation detection device according to claim 2 is combined with a frequency change rate detection method which is a passive method for detecting the isolated operation of the distributed power source in the power conditioner for the distributed power source connected to the distribution line. An isolated operation detection device that implements a frequency shift method, by means of calculating a short-term moving average value of a system frequency, means for calculating a long-term moving average value of a system frequency, and control of an internal oscillator of the power conditioner The difference between the short-term moving average value and the long-term moving average value of the system frequency exceeds the range of the difference at the time of the system disturbance. And the difference between the short-term moving average value and the long-term moving average value of the system frequency exceeds a predetermined threshold value. So that and means for detecting operating.

  Therefore, according to the islanding operation detection method and the detection device according to claims 1 and 2, unnecessary detection of the islanding operation of the distributed power source at all times and at the time of system disturbance is prevented and generation of reactive power is suppressed.

  According to the isolated operation detection method and detection apparatus of the present invention, it is possible to prevent unnecessary detection of isolated operation of the distributed power source at all times and during disturbances of the system, thereby suppressing simultaneous stop of the distributed power source and suppressing generation of reactive power. Therefore, stable operation of the system can be performed.

It is a flowchart explaining the isolated operation detection method of embodiment. It is a functional block diagram of the isolated operation detection apparatus which implements the isolated operation detection method of embodiment. It is a functional block diagram explaining the conventional frequency change rate detection system of a single operation detection passive system. It is a functional block diagram explaining the example of the conventional isolated operation detection system. It is a figure explaining the relationship between the long-time frequency moving average length and the independent operation continuation time in the conventional frequency shift system (gain: 0.2). It is a figure explaining the relationship between the long-time frequency moving average length and the independent operation continuation time in the conventional frequency shift system (gain: 0.4). It is a figure explaining the relationship between the system frequency change rate in a conventional frequency shift system, and a power conditioner output reactive power value. It is a figure explaining the relationship between the system frequency change rate in Example 1, and the difference of a long and short-time frequency moving average value. It is a figure explaining the relationship between the system frequency change rate at the time of gain switching in the frequency shift system of Example 1, and an independent operation continuation time.

  Hereinafter, the configuration of the present invention will be described in detail based on an example of an embodiment shown in the drawings.

  1 and 2 show an example of an embodiment of the isolated operation detection method and detection apparatus of the present invention. The isolated operation detection method of the present embodiment is a frequency shift method combined with a frequency change rate detection method which is a passive method for detecting the isolated operation of a distributed power source in a power conditioner for a distributed power source connected to a distribution line. In this case, the gain value is set to a level at which no reactive power is generated when the system frequency fluctuates during the system disturbance by controlling the internal oscillator of the power conditioner, and the short-time moving average value and the long-time moving average value of the system frequency are When the difference exceeds the range of the difference at the time of system disturbance, the gain value is increased to accelerate the change of the system frequency, and the difference between the short-term moving average value and the long-term moving average value of the system frequency is a predetermined threshold value When the value exceeds the value, the isolated operation of the distributed power source is detected.

  The isolated operation detection method is realized as the isolated operation detection device of the present invention. The isolated operation detection device of the present embodiment is a frequency shift method combined with a frequency change rate detection method that is a passive method for detecting the isolated operation of a distributed power source in a power conditioner for a distributed power source connected to a distribution line. A system for detecting a short-time moving average value of a system frequency, a means for calculating a long-time moving average value of a system frequency, and control of an internal oscillator of the power conditioner during a system disturbance. The gain value set to a level at which reactive power does not occur due to fluctuations in the grid frequency increases when the difference between the short-term moving average value of the grid frequency and the long-term moving average value exceeds the range of the difference during grid disturbance When the difference between the short-term moving average value and the long-term moving average value of the system frequency exceeds a predetermined threshold, the distributed power source is operated alone. And means for output.

  As shown in FIG. 2, the isolated operation detection device of the present invention is a kind of isolated operation detection system equipped in a power conditioner for a distributed power source such as a residential solar power generation connected to a low voltage distribution line. Compared with a conventional configuration (for example, FIG. 4) for implementing a certain frequency change rate detection method and frequency shift method, a gain switching comparator 8 and a gain switching device 9 are further provided.

  It should be noted that the frequency change rate detection method and the frequency shift method as the isolated operation detection method, and the equipment configuration for carrying out the processing relating to these methods, the conventional configuration shown in FIG. 4 and the present invention shown in FIG. Since the configuration common to these configurations is a well-known technique, a detailed description thereof will be omitted here (for example, refer to the Japan Electric Association: Grid Connection Regulations, JEAC9701-2006).

  In carrying out the present invention, first, the voltage detector 3 detects the voltage at the connection point with the distribution line 1 and outputs the system voltage V (S1).

  Next, the frequency detector 15 receives the input of the signal of the system voltage V, detects the system frequency, and outputs the value of the system frequency (S2).

  On the other hand, the arithmetic unit 5A receives the input of the system voltage V signal, calculates the long-term moving average value fl of the system frequency and outputs the value of the moving average value fl, and the arithmetic unit 5B outputs the system voltage V. The short-time moving average value fs of the system frequency is calculated in response to the input of the signal, and the value of the moving average value fs is output (S3).

  Next, the isolated operation detection comparator 6 receives the values of both moving average values fl and fs, calculates a difference | fs−fl | between the moving average values, and calculates the difference and the isolated operation detection threshold fd. The size is compared (S4).

  The value of the isolated operation detection threshold fd is set to a value that is outside the management range of the system frequency and is very close to or equivalent to the management frequency in accordance with the recommended value of the grid interconnection regulations (NEC); The The value of the isolated operation detection threshold fd is set in advance and stored in the isolated operation detection comparator 6.

  When the difference | fs−fl | between the moving average values is larger than the isolated operation detection threshold fd (S4; Yes), the isolated operation detection comparator 6 outputs the isolated operation detection signal Sd. Then, when the output stop signal Ss output from the counter 7 receiving the isolated operation detection signal Sd is input, the disconnector 1a of the distribution line 1 cuts the circuit and the output of the inverter 2 stops (S6). .

  On the other hand, when the value of the difference between the moving average values | fs−fl | is equal to or less than the isolated operation detection threshold fd (S4; No), the gain switching comparator 8 sets the values of the moving average values fl and fs. The difference between the moving average values | fs−fl | is calculated and the threshold value (hereinafter referred to as gain switching threshold value) fg for determining the switching between the difference and the gain value is calculated. Comparison is performed (S5).

  The value of the gain switching threshold value fg, which is a setting value peculiar to the present invention, is determined by the largest value among the values obtained for the predetermined isolated operation detection time in each gain value before and after switching. Note that the value of the gain switching threshold fg is preset and stored in the gain switching comparator 8.

  If the difference | fs-fl | between the moving average values is equal to or less than the gain switching threshold fg (S5; No), the processing returns to S3 and the subsequent processing is repeated.

  On the other hand, when the difference | fs−fl | between the two moving average values is larger than the gain switching threshold fg (S5; Yes), the command signal output from the gain switching comparator 8 is received. Then, the gain switch 9 outputs the frequency shift type gain value after switching (S7).

  The gain value of the frequency shift method in the present invention is always set to a level at which reactive power is not generated, and is increased when an isolated operation is detected. The value of the gain for normal use and the value of the gain after switching (that is, for detection of isolated operation) are not limited to specific values, and no reactive power is generated at all times and the isolated operation detection time after switching. May be set as appropriate by the operator so that is sufficiently short. Specifically, for example, it is conceivable that the gain value is set to about 0.2 at all times and about 0.4 after switching. The gain value after switching is preset and stored in the gain switch 9.

  Next, the phase modulator 10 performs phase modulation of the signal output from the phase locked loop circuit 11 by the frequency shift method (S8).

  Specifically, the phase-locked loop circuit 11 receives the signal of the system voltage V, extracts the difference between the system voltage waveform and the waveform output by itself (that is, the feedback waveform of the circuit output), and the difference is The phase of the output waveform of the transmitter inside the circuit is changed in a direction approaching zero, and the signal Ib having the waveform with the phase changed is output. As a result, an output waveform having the same phase and frequency as the system voltage waveform is obtained.

  The phase modulator 10 outputs the value of the system frequency f output from the frequency detector 15 by the process of S2, the gain after switching output from the gain switcher 9 by the process of S7, and the phase-locked loop circuit 11 The phase difference from the output signal Ib of the phase-locked loop circuit 11 is increased in proportion to the difference between the system frequency value f and the standard frequency value f0 according to Equation 1. The obtained signal Ib ′ is obtained and the signal Ib ′ is output.

  Here, as processing related to the APR (that is, AC power regulator) related to the next processing of S9, the current detector 4 detects the output current of the inverter 2 linked to the distribution line 1 and outputs the output current I. To do.

  Then, the AC output calculator 12 receives the signal of the system voltage V and the signal of the inverter output current I, detects the phase difference θ between the system voltage V and the inverter output current I, and generates AC by P = V · Icos θ. The output power P is calculated and the value of P is output.

  The AC output setting unit 13 outputs the reference AC output power P0 of the inverter 2 manually or automatically by a schedule program or the like input in advance.

  Then, the APR controller 14 receives the input of the AC output power P from the AC output calculator 12 and the reference AC output power P0 from the AC output setter 13 and calculates the difference Ps = P−P0 between the two. The gain A is output by changing ΔA of gain A = A0−ΔA, which is an arithmetic expression inside the controller, in the direction in which the difference Ps approaches zero. A0 is an initial value of gain A that is arbitrarily given.

  Then, the multiplier 16 receives the input of the signal Ib ′ output from the phase modulator 10 and the gain A output from the APR controller 14 in the process of S8, and multiplies the inverter output current command value Io. And the value of Io is output. Thus, the absolute value and phase of the output current of the inverter 2 are adjusted based on the output from the multiplier 16 (S9).

  Through the above processing, the voltage and frequency of the distribution line 1 are adjusted (S10).

  Then, the isolated operation detection device returns to the process of S1 and repeats the subsequent processes.

  According to the isolated operation detection method and detection apparatus of the present invention having the above-described configuration, unnecessary detection of isolated operation of the distributed power source during normal and system disturbances is prevented, and simultaneous stop of the distributed power source is suppressed and disabled. Since generation of electric power can be suppressed, it becomes possible to perform stable operation of the system. More specifically, the range for preventing the unnecessary stop of the distributed power source with respect to the frequency change can be made wider than the conventional method while satisfying the isolated operation detection time condition required for stable operation of the system. Therefore, in the case of a system disturbance that is not caused by a single operation, the system disturbance is caused by a single operation even if the distributed power source wants to continue operation in order to ensure the stability of the system. It is possible to prevent erroneous detection and stop of the distributed power supply.

  In addition, although the above-mentioned form is an example of the suitable form of this invention, it is not limited to this, A various deformation | transformation implementation is possible in the range which does not deviate from the summary of this invention.

  The Example which examined the setting reference | standard of the various setting values which concern on the isolated operation detection method of this invention, and the validity of the said method is demonstrated using FIG.8 and FIG.9.

  First, referring to the result shown in FIG. 7, in the present embodiment, the gain value of the frequency shift method is set to 0.2, which is a level at which reactive power is not always generated, and is set to 0.4 after switching. I did it.

  Further, in order to examine the value of the gain switching threshold fg, the frequency shift is performed for a long time in 0.3 seconds, which is an appropriate value at a gain = 0.4, which has been clarified in the above-mentioned examination by the present inventors (see FIG. 6). The result shown in FIG. 8 was obtained by setting the average length and organizing the relationship between the rate of change of the system frequency and the difference between the short-time moving average value fs of the system frequency and the long-time moving average value fl. . FIG. 8 shows the isolated operation detection threshold fd = 0.15 Hz when the rate of change of the system frequency is set to 0.3%. Note that 0.3% related to the change rate of the system frequency is a ratio to the reference frequency (specifically, 50 Hz or 60 Hz), and the long-time moving average value and the short-time moving average value of the frequency in the frequency change rate detection method. Is a threshold value for detecting the isolated operation of the distributed power source when the difference exceeds the value, and is defined as a recommended value in the grid interconnection regulations (NEC Association; supra).

  From the results shown in FIG. 8, for example, the frequency shift gain is maintained at 0.2 until the actual rate of change of the actual system frequency is 0.8 Hz / second, and the rate of change of the system frequency is 0.8 Hz / s. It was found that the gain switching threshold value fg should be set to 0.11 Hz when the gain is switched when the second is exceeded.

  Further, in order to verify the isolated operation continuation time of the distributed power source, the long-term frequency moving average length is set to 0.3 seconds, the rate of change of the system frequency for detecting the isolated operation is set to 0.3%, and the gain is set to 0. When switching from 2 to 0.4, when the effective amount P and the ineffective amount Q between the generated power and the load amount are balanced, the value of the gain switching threshold fg and the isolated operation duration time of the distributed power source The results shown in FIG.

  From the results shown in FIG. 9, assuming that the frequency change rate for determining switching of the gain value of the frequency shift method is 0.8 Hz / second (that is, gain switching threshold fg = 0.11 Hz), the value of the frequency change rate is obtained. As a result, the reactive power is not noticeably generated even when the frequency increases up to 0.8 Hz / second, and the result of the case where the isolated operation detection time is fixed to 0.4 with the gain value of the frequency shift method shown in FIG. It was confirmed that the time can be reduced to about 0.17 seconds, which is almost the same as the above.

  From the above results, the islanding operation detection method of the present invention prevents unnecessary detection of the islanding operation of the distributed power source at the time of occurrence of system frequency fluctuation, suppresses simultaneous suspension of the distributed power source, and reactive power. It has been confirmed that it is effective for suppressing generation and detecting single operation of a distributed power source at high speed.

DESCRIPTION OF SYMBOLS 1 Distribution line 2 Inverter 3 Voltage detector 4 Current detector 5A, 5B Arithmetic unit 6 Comparator for independent operation detection 7 Counter 8 Comparator for gain switching 9 Gain switching device 10 Phase modulator 11 Phase locked loop circuit 12 AC output calculation 13 AC output setting device 14 APR controller 15 Frequency detector 16 Multiplier

Claims (2)

  Control of the internal oscillator of the power conditioner in the frequency shift method combined with the frequency change rate detection method that is a passive method for detecting the isolated operation of the distributed power source in the power conditioner for the distributed power source connected to the distribution line Thus, the gain value is set to a level where no reactive power is generated when the system frequency changes during system disturbance, and the difference between the short-time moving average value and long-time moving average value of the system frequency When it exceeds, the gain value is increased to accelerate the change of the system frequency, and when the difference between the short-term moving average value of the system frequency and the long-term moving average value exceeds a predetermined threshold, the distributed power source alone An isolated operation detection method characterized by detecting an operation.   An independent operation detection device that implements a frequency shift method combined with a frequency change rate detection method that is a passive method for detecting the isolated operation of a distributed power source in a power conditioner for a distributed power source connected to a distribution line. Reactive power is generated when the system frequency fluctuates when the system is disturbed by the means for calculating the short-term moving average value of the system frequency, the means for calculating the long-time moving average value of the system frequency, and the control of the internal oscillator of the power conditioner Means for increasing the gain value set to a level that is not activated when the difference between the short-term moving average value of the system frequency and the long-term moving average value exceeds the range of the difference at the time of system disturbance, and the short-term movement of the system frequency And means for detecting isolated operation of the distributed power source when the difference between the average value and the long-term moving average value exceeds a predetermined threshold value. Isolated operation detecting apparatus.

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