JP5380318B2 - Digital protection control device and abnormality detection method thereof - Google Patents

Description

  The present invention relates to a digital protection control apparatus, and more particularly to a digital protection control apparatus suitable for performing defect detection with high accuracy and an abnormality detection method thereof.

  In the conventional technique, for example, as described in Patent Document 1, a plurality of analog input signals are switched by a multiplexer, the signals are multiplexed, and the multiplexed signals are time-divisionally used as one A / D. A digital type protection control device for converting to a digital quantity by conversion has been proposed, and it has been adopted as a mainstream configuration for a protection device for a substation.

  The above-mentioned device detects the presence or absence of a system fault by performing digital arithmetic processing on the A / D converted data by a digital arithmetic means such as a microcomputer based on a predetermined program, and issues a trip command to the circuit breaker. It is something that is emitted.

  In such a protection control device, as described in Patent Document 2, for example, as a circuit monitoring of the analog input unit, harmonics are superimposed on an input stage of an analog low-pass filter that is generally applied, and the signal of the harmonic component is detected. Is detected, and the fluctuation of the attenuation characteristic of the filter is monitored.

  Further, for monitoring the A / D converter, a dedicated input channel for applying a known reference DC voltage to the input A / D converter is provided separately from the input signal fetched from the power system as described in Non-Patent Document 1. A method of checking the data after digital conversion and monitoring the accuracy is standardly adopted.

Japanese Patent No. 3186735 JP 2003-37928 A

Electric Cooperative Research Vol. 50 No. 1 2nd Generation Digital Relay

  In the case where A / D conversion is performed by switching a plurality of analog signals in a time division manner using a multiplexer as in the prior art, there is a limit to further increase the speed while maintaining high A / D conversion accuracy.

  That is, in the method of A / D conversion by multiplexing analog input signals by applying a multiplexer, it is necessary to wait until the transient state of the signal after multiplexer switching is stabilized, ensuring accuracy and speeding up sampling. To do is a contradiction, and naturally has its limits. The reason why the speed cannot be increased is that the stray capacitance is generated in the signal line, and the waveform is dull due to the relation with the ON resistance of the multiplexer.

  In addition, due to the switching time of the multiplexer and the ringing phenomenon, which is a transient phenomenon when switching the signal waveform, it takes time until the waveform stabilizes. It was difficult to perform higher-speed sampling after securing.

  To solve this problem, it is conceivable to increase the speed by providing A / D conversion means with a plurality of channels in parallel. However, in the conventional monitoring technique described above, it is necessary to provide a dedicated input channel for applying a known monitoring reference DC voltage corresponding to the A / D conversion means in order to check the A / D conversion accuracy essential as a protection control device. For this reason, means for switching the input signal and the monitoring signal are required for the A / D conversion means. Therefore, in order to satisfy these functions, it is necessary to add a circuit, and there is a problem that the circuit scale becomes large and the switching control becomes complicated.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a digital protection control device capable of monitoring defects with a simple configuration while realizing high-speed sampling, and an abnormality detection method thereof.

  The above problem is a harmonic generator that generates a harmonic signal having a frequency higher than the analog AC electric quantity of the power system, and a signal obtained by superimposing the analog AC electric quantity and the harmonic signal taken from the power system. A plurality of analog filters that perform the filtering process, and at least the same number or more A / D converters as the plurality of analog filters, and the amplitude value and phase of the superimposed harmonic signal component from the output of the A / D converter It is solved by providing a Fourier transform means for calculating.

  With the above-described configuration, the phase deviation and amplitude deviation from a predetermined reference value are obtained from the phase and amplitude value calculated by the Fourier transform means, and the phase deviation is large from the characteristic that the analog filter changes phase due to component deterioration. Accordingly, the problem is solved by specifying the defective part.

  That is, when the phase deviation is equal to or less than a predetermined value, the A / D converter abnormality detection process is performed, and when the phase deviation is larger than the predetermined value, the analog filter abnormality is detected. Furthermore, by making each monitoring level different, it becomes possible to make a flexible determination according to changes in characteristic deterioration due to component deterioration.

  According to the digital protection control apparatus of the present invention, the A / D accuracy check and the harmonic superposition monitoring can be performed with a simple configuration while realizing high-speed sampling, so that the circuit can be reduced in size and cost.

The block structural example of the protection control apparatus of this invention. The signal processing block structural example of a protection control apparatus. Analog filter circuit example for preventing folding error with signal addition function. The characteristic example of the analog filter shown in FIG. Input / output waveform example when the analog filter is abnormal. An example of an oversampling digital filter circuit configuration. 7 is an example of total gain characteristics of the filters shown in FIGS. 3 and 6. Waveform example and twiddle factor example when filter characteristics deteriorate. The processing block example which shows the monitoring method of this invention. An X-R characteristic vector diagram example when the input circuit is normal and abnormal. The processing flow example of this invention. The gain error-phase error relative characteristic example of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing an embodiment of a digital protection control apparatus of the present invention. In FIG. 1, the digital protection control device of the present invention includes an input converter (auxiliary CT / auxiliary PT) 1a for converting a plurality of voltage / current signals from the power system into an analog voltage signal of full scale ± 10V, and an addition function. An analog filter 1b for preventing aliasing by sampling, a plurality of A / D converters 1c for converting an analog signal into a digital quantity, a plurality of hardware digital filters 1d provided for each channel, and for decimation Sampling frequency rate converter (decimator) 1e, buffer memory 1f, CPU 11, work memory 1 i, nonvolatile memory 1 j, and I / O interface 1 k.

  Also, the entire operation is performed in a cycle in which each circuit is synchronized by a control timing signal from the OSC 1h through the timing control circuit 1g. Further, with respect to the harmonic signal to be superimposed on the analog filter, the signal from the timing control is received, and the D / A converter 1m uses a harmonic of a frequency n times (n is a natural number) a predetermined frequency of the power system. A wave superposition signal is generated and applied to the aliasing error preventing analog filter 1b.

  Further, the harmonic superposition signal is configured to be directly applied to the A / D converter 1c without going through the analog filter in order to detect the characteristic deterioration of the analog filter and the failure of the digital filter DF1.

FIG. 2 functionally describes the configuration of FIG. In FIG. 2, 1b, 1c, 1d, and 1e are the same as those in FIG. 1, and this portion indicated by 20a represents a circuit block from the input filter to the sampling rate conversion circuit, and all operates as hardware.
On the other hand, 20b is a block in the range to be implemented by the arithmetic processing by the CPU 11 and is executed by software in the arithmetic unit shown by the CPU 11 described above. 2h shows a processing configuration for carrying out a protection operation, and a low-order harmonic removal digital filter (DF2) 2e for removing low-order harmonic components contained in a system signal fetched from the power system, A second sampling frequency rate converter (decimator) 2f for converting the data rate of the digital filter 2e is provided, and the data is sent to the protection arithmetic processing unit 2g with the sampling rate lowered (lowered).

  The protection calculation processing unit 2g receives this input signal, performs a protection calculation, and determines whether there is a system fault. At this time, the harmonic superposition signal taken into 20a is removed by the low-order harmonic removal digital filter (DF2) 2e so that the protection calculation is not affected.

On the other hand, FIG. 2-2l represents circuit blocks from 2i to 2k, and is a block that extracts a harmonic superposition signal taken in 20a and obtains an amplitude value and a phase deviation to perform analog monitoring. The output signal 20a is input, only the harmonic superimposed signal component is passed through the digital filter (DF3) 2i, and the magnitude and phase of the superimposed signal component are obtained by the DFT (Discrete Fourier Transformer) processing means 2j. The monitoring operation unit 2k of the analog circuit unit operates to receive the DFT processing result, detect a failure of the analog circuit including the A / D converter and characteristic deterioration due to element variation, and issue an alarm output. It is.

  In the above, it is needless to say that the DFT function can be realized without providing the digital filter (DF3) 2i, and can be configured as one modification.

  FIG. 3 shows an example of the circuit configuration of the analog filter for preventing aliasing error due to sampling shown in FIG. 1-1B. In FIG. 3, 3a, 3b, 3c and 3e are resistors, 3d is a capacitor, and 3f is an operational amplifier (op amp).

  The analog filter shown in FIG. 3 is a low-pass filter having a first-order lag element, and attenuates a signal in a high frequency region. In addition, this circuit has a function of adding a signal acquired from the power system and a harmonic signal for superimposing a harmonic signal for detecting characteristic deterioration of the analog filter.

  The transfer function G for the harmonic signal Vn of the analog filter can be expressed by the following equation (1).

  In formula (1), R3b and R3c represent 3b and 3c shown in FIG. 3, and C3d represents 3d shown in FIG.

  FIG. 4 shows an example of frequency-gain characteristics and an example of frequency-phase characteristics when the harmonic signal of the analog filter shown in FIG. 3 is superimposed. In FIG. 4, (a) shows an example in which the characteristic variation of only the gain is caused by the characteristic deterioration of the element, and (b) shows an example in which the characteristic fluctuation of the gain and the phase is caused by the characteristic deterioration of the element. It is.

  The element deterioration factors shown in FIG. 4A are the gain error of the A / D converter 1c provided in the previous stage of the filter circuit shown in FIG. 3 and the resistance 3b of the filter circuit shown in FIG. In this case, the gain difference ε1 fluctuates as in the frequency-gain characteristic example 4b when the A / D converter is abnormal, and the phase difference is different from the frequency-gain characteristic example 4a of the analog filter in which only the gain characteristic is initial. It can be seen that the difference (θ1) between the frequency-phase characteristic example 4c of the initial analog filter and the frequency-phase characteristic example 4d when the A / D converter is abnormal hardly occurs. This gain error directly affects the input signal. For example, if the gain has an error of 5%, the influence of the error of 5% appears regardless of the frequency of the input signal. Means.

  On the other hand, the element deterioration factor shown in FIG. 4B is the resistor 3c or the capacitor 3d of the filter circuit shown in FIG. In this case, the gain characteristic is the same as the initial analog filter frequency-gain characteristic example 4e, but the phase characteristic is also the initial analog characteristic together with the fluctuation of the gain difference ε2 as in the frequency-gain characteristic example 4f when the analog filter characteristic is deteriorated. A phase difference (θ2) is generated with respect to the filter frequency-phase characteristic example 4g as in the case of the frequency-phase characteristic example 4h when the analog filter characteristic is deteriorated. By performing such a phase difference detection, it is possible to calculate the fluctuation of the above-described phase characteristic with respect to the initial value and specify the characteristic deterioration factor.

  Generally, the monitoring level of the protection control device is determined so that an abnormality is determined when the A / D conversion accuracy check monitoring deviates from a known ± 5%, and the harmonic superposition monitoring is a known ± 10% to 20%. The judgment values are different. This is because it is set in consideration of the influence of the fundamental wave (50 Hz or 60 Hz), and the A / D conversion accuracy check monitoring generates an error of the fluctuation regardless of the input frequency, and the harmonic superposition is performed. For the monitoring, the above-described value is set as the monitoring level for the reason of being equivalent to ± 5% when converted as the fundamental wave.

  Therefore, the gain fluctuation is monitored at a level suitable for each error factor by dividing into A / D conversion accuracy monitoring: ± 5% or less and harmonic superposition monitoring: ± 10-20% or less depending on the magnitude of the phase fluctuation. It is possible to monitor with high accuracy without excessive detection.

  In the above description, when the resistance 3c changes, the gain also changes as shown in the equation (1). This is because the characteristic fluctuation is caused by using the same lot of resistance (surface mount product). Since the same tendency can be made, this variation can be ignored by preventing both resistances from varying at different rates.

  In addition, it goes without saying that, by applying parts such as a resistance module in which a plurality of resistance elements are provided on the same chip, similarly, it is possible to further suppress that both resistance values vary differently. This is an example of a possible application development.

  FIG. 5 shows a waveform example when the above-mentioned analog filter has deteriorated characteristics.

FIG. 5A illustrates an abnormal state when the gain fluctuates. 5a is an example of the harmonic signal voltage waveform superimposed on the analog filter, Vfn, 5b is an example of an initial analog filter output waveform when normal, and 5c is an example of a filter output voltage waveform when the A / D converter is abnormal.
As shown in this figure, when only the gain fluctuates, an amplitude deviation of 5d occurs, but no phase deviation of 5b and 5c occurs.

  FIG. 5B shows a waveform example when the A / D converter, the analog filter circuit, and the digital filter circuit completely fail. In this case, both the amplitude and the phase deviate greatly from the initial values, and the failure can be easily detected.

  FIG. 5C illustrates an abnormal state at the time of phase fluctuation. 5f in the figure shows an example of an output voltage waveform when the analog filter has deteriorated characteristics, and it can be understood that the phase deviation shown in 5g is generated together with the gain deviation.

  As described above, it is possible to grasp the failure or characteristic deterioration of the analog input circuit as the deviation from the theoretical value of the output signal from the A / D converted analog filter output. Similarly, it is possible to detect a failure of a digital filter provided after A / D conversion.

FIG. 6 shows a circuit configuration example of a digital filter implemented after A / D conversion.
In FIG. 6, 6a to 6e are 1-sample delay circuits, 6l to 6r are multiplication circuits, and 6f to 6k are addition circuits.

  FIG. 7 shows an example of gain characteristics of the digital filter shown in FIG. In FIG. 7, the fundamental frequency component of the system signal is almost 0 dB, and there is no attenuation, and the sampling frequency component of the digital filter DF2 for removing lower harmonics shown in FIG. 2-2e is greatly attenuated. . This is to prevent aliasing errors due to sampling of the digital filter DF2.

  Similar to the analog filter and A / D converter described above, even in the digital filter, it is possible to detect that the circuit is not operating normally by obtaining the gain and the phase deviation in the subsequent stage.

  In this way, it is possible to monitor deterioration and failure of the circuit in a consistent manner from the analog filter to the digital filter after A / D conversion.

  Next, it was shown that A / D conversion abnormality or analog filter abnormality can be detected by obtaining the above gain deviation and phase deviation. Next, how to calculate the gain deviation and phase deviation? Explain what you want.

FIG. 8A shows an input / output waveform example of the harmonic superposition monitoring signal and an example of calculation timing. 8a is a harmonic superposition monitoring signal, 8b is a signal that has passed through analog and digital filters, 8c is an example of a calculation cycle of the digital filter (DF3) 2i, and 8d is a DFT (Discrete Fourier Transformer) processing means 2j for detecting a harmonic signal. An example of the calculation timing is shown below. As shown in the figure, it is desirable that 8c and 8d operate in synchronization with timing, but it is not always necessary to synchronize. Further, the protection calculation processing unit 2g can be configured to perform the protection calculation in accordance with the timing of the DFT processing unit 2j.

  The processing of the DFT (Discrete Fourier Transformer) processing means 2j can be expressed by the following equation.

  In this embodiment, the DFT operation is performed for one period of the superimposed harmonic signal. Therefore, from this calculation, the fundamental component (F1) of the DC component (F0) and the harmonic component is obtained by the calculation formula shown by the following formula.

  However,

FIG. 8B shows the periodicity of the twiddle factor W expressed by equation (6). That is, 80 a corresponds to W ⁰ , 80 b corresponds to W ¹ , 80 c corresponds to W ² , 80 d corresponds to W ³ , 80 e corresponds to W ⁴ , 80 f corresponds to W ⁵ , 80 g corresponds to W ⁶ , and 80 h corresponds to W ⁷ .

  In this way, the fundamental component of the DC component and the harmonic signal can be obtained by calculating Equations (4) and (5).

  The real part R and the imaginary part X can be obtained from the equation (5), and the phase arg (F1) based on the amplitude value | F1 | and the COS waveform can be obtained from the following equation.

  FIG. 9 shows a processing flow for judging abnormality of the A / D converter and the analog filter / digital filter circuit from the amplitude value and the phase obtained above. In FIG. 9, reference numeral 90a represents a calculation block for a harmonic signal acquired without passing through the analog filter 1b, and 90b represents a calculation block for a harmonic signal acquired through the analog filter 1b.

In FIG. 9, 9a and 9e are real part R calculating parts, 9b and 9f are imaginary part X calculating parts, 9c and 9g are amplitude value calculating calculating parts, and 9d and 9h are phase calculating calculating parts. From the amplitude and phase obtained as described above, the amplitude ratio calculation unit 9i and the phase difference calculation unit 9m obtain the amplitude ratio and the phase difference, respectively.
With respect to this value, the deviation between the initial gain value 9j and the initial phase value 9n previously obtained and stored is obtained by the adders 9k and 9o, and the gain deviation εg from the initial values indicated by 9l and 9p is obtained. Processing is performed so as to obtain the phase deviation εθ from the initial value.

  Since this calculation process can detect a variation with respect to the initial value, the variation of the initial value can be canceled, so that only the variation can be obtained with high accuracy.

  FIG. 10A shows an example of the vector display of the harmonic signal acquired without passing through the analog filter 1b indicated by 90a, and FIG. 10B shows an example of the vector display of the harmonic signal acquired through the analog filter 1b.

  10a and 10e are the initial imaginary part X vector and the imaginary part X vector when the filter characteristics are deteriorated, 10b and 10f are the initial real part R vector and the real part R vector when the filter characteristics are deteriorated, and 10c and 10g are the initial values. The amplitude value vector and the amplitude value vectors 10d and 10h when the filter characteristics are deteriorated represent the initial phase and the phase when the filter characteristics are deteriorated, respectively.

  FIG. 11 is a diagram for determining whether the accuracy of the A / D converter is abnormal or the abnormality due to the failure of the analog filter and the digital filter from the gain deviation εg9l with the initial value shown in FIG. 9 and the phase deviation εθ9p between the initial value. It is a processing flow. In FIG. 11, the deviation data is taken in the processing block 11a for obtaining the gain deviation / phase deviation from the initial value, and the phase deviation determination processing unit 11b first determines whether the phase difference εθ is equal to or smaller than the set value α1.

  In the following cases, the gain deviation determination processing unit 11c determines whether the gain deviation εg is equal to or larger than the set value β. When the value is equal to or larger than the set value β, it is determined that the phase deviation does not occur and the gain deviation is large as an accuracy abnormality of the A / D converter, and an alarm is output from the A / D accuracy check abnormality alarm output processing unit 11d.

  Further, if the phase difference εθ is equal to or larger than the set value α1 in the phase deviation determination processing unit 11b, there is a possibility that the characteristics of the analog filter may be deteriorated. If it is larger than the second set value α2, if it is larger, the harmonic superposition monitoring abnormality alarm output processing unit 11f performs an alarm output as a harmonic superposition monitoring abnormality due to a change in filter characteristics.

  FIG. 12 illustrates the processing flow shown in FIG. 11 in relation to the gain deviation εg and the phase deviation εθ. That is, in FIG. 12, the zone 1 where the phase deviation is α1 or less and the gain deviation is larger than β is an area where the A / D conversion accuracy check is abnormal, and when the phase deviation εθ is α2 or more, the characteristics of the filter fluctuate. Can be detected as a harmonic superposition monitoring abnormality.

  In this way, it is possible to monitor at different gain deviation levels when the A / D conversion accuracy check is abnormal and when the harmonic monitoring is abnormal, suppressing excessive detection, and from the analog filter to the A / D converter And proper analog monitoring of the digital filter can be realized.

  Further, the detection value stored in the nonvolatile memory for storing setting data is written in the nonvolatile memory 1j for storing the setting data shown in FIG. 1 at each detection time. From the data, it is possible to obtain fluctuations over time and grasp the degree of characteristic deterioration. In addition, it is easy to understand from the series of explanations of the present invention that the future characteristic deterioration can be grasped in advance from the inclination of the detected data so that it can be effectively used for preventive maintenance. .

Summarizing the present embodiment as described above, by having the following points as configurations, it is possible to separately monitor abnormality of the A / D converter and characteristic deterioration of the analog filter with a simple configuration.
(1) The multiplexer is removed and an A / D converter is provided for each of the plurality of input channels. (2) A harmonic signal is applied to the input filter and superimposed on the input signal. configuring the filter to operate at 2 ⁿ times oversampling (4) DFT signal frequency of the harmonic superimposed monitoring as a basic cycle (Discrete Fourier Transformer) calculating (5) the amplitude ratio between the reference signal channel and the monitoring channel (6) A / D conversion accuracy is obtained from the amplitude ratio, and harmonic superposition monitoring is obtained from the magnitude of the phase difference. Thus, according to the digital protection control device of the present invention, To improve the accuracy of conversion data by noise compression effect by high-speed sampling and to use both A / D accuracy check and harmonic superposition monitoring As a result, the circuit can be significantly reduced in size and cost.

  In addition, the time axis resolution can be improved and the accuracy can be improved simultaneously by increasing the sampling speed, and the analog input filter can be further simplified, the failure rate can be reduced, and the characteristics can be stabilized by increasing the sampling speed.

1a Input converter (auxiliary CT / auxiliary PT)
1b Analogue filter 1c for aliasing error prevention 1c A / D converter 1d Hardware digital filter 1e Sampling frequency rate converter (decimator)
1f Buffer memory 1g Timing control circuit 1h Oscillator circuit (oscillator)
1i Work memory 1j Non-volatile memory 1k I / O interface 1l CPU
1m D / A converter 2e Digital filter for removing lower harmonics (DF2)
2f Second sampling frequency rate converter (decimator)
2g protection operation processing unit 2h 2e to 2g circuit block 2i digital filter (DF3)
2j DFT (Discrete Fourier Transformer) processing means 2k Analog circuit unit monitoring arithmetic unit 2l 2i to 2k circuit blocks 3a, 3b, 3c, 3e Resistor 3d Capacitor 3f Operational amplifier (op amp)
4a, 4e Example of initial analog filter frequency-gain characteristics 4b Example of frequency-gain characteristics when A / D converter malfunctions 4c, 4g Example of initial analog filter frequency-phase characteristics 4d Frequency of A / D converter malfunctions -Phase characteristic example 4f Frequency when analog filter characteristic is degraded-Gain characteristic example 4h Frequency-phase characteristic example when analog filter characteristic is degraded 5a Harmonic signal voltage waveform example 5b superimposed on analog filter Initial analog filter output waveform example 5c A Filter output voltage waveform example 5e when the A / D converter is abnormal Analog filter waveform example 5f when the A / D converter completely fails Output voltage waveform examples 6a to 6e when the analog filter has deteriorated characteristics 1 sample delay circuit 6f ~ 6k adder circuit 6l ~ 6r multiplier circuit 8a harmonic superposition monitoring signal 8b analog and digital signal Signal 8c passed through filter 8c Operation period example of digital filter (DF3) 2i 8d Operation timing example 9a, 9e of real DFT (Discrete Fourier Transformer) processing means 2j Real part R operation part 9b, 9f Imaginary part X operation part 9c, 9g Amplitude value calculation calculation unit 9d, 9h Phase calculation calculation unit 9i Amplitude ratio calculation unit 9m Phase difference calculation unit 9j Initial gain value 9n Initial phase value 9k, 9o Addition unit 9l Gain deviation εg from initial value
9p Phase deviation from initial value εθ
10a initial imaginary part X vector 10b initial real part R vector 10c initial amplitude value vector 10d initial phase 10e imaginary part X vector 10f when filter characteristics are degraded real part R vector 10g when filter characteristics are degraded Amplitude value vector 10h Phase 11a when filter characteristic is deteriorated Processing blocks 11b and 11e for obtaining gain deviation / phase deviation from initial value Phase deviation determination processing unit 11c Gain deviation determination processing unit 11d A / D accuracy check abnormality alarm output processing unit 11f Harmonic superposition monitoring abnormality alarm output processing unit 20a Circuit block 20b from input filter to sampling rate conversion circuit Block 80a to 80h in the range to be implemented by arithmetic processing by CPU 1l Rotation factor on S plane

Claims (11)

A harmonic generator that generates a harmonic signal having a frequency higher than the analog AC electricity quantity of the power system;
A plurality of analog filters that perform an acquisition filter process by superimposing the analog alternating current electric quantity and the harmonic signal acquired from the power system;
A plurality of A / D converters provided for each of the plurality of analog filters, for converting an output of the analog filter into a digital electric quantity;
Fourier transform means for calculating the amplitude value and phase of the superimposed harmonic signal from the outputs of the plurality of A / D converters,
A phase deviation and an amplitude deviation are obtained from the phase and amplitude values calculated by the Fourier transform means, and when the phase deviation is equal to or less than a predetermined value, abnormality detection processing of the A / D converter is performed, and the phase deviation is the predetermined value. Monitoring means for performing an abnormality detection process of the analog filter if greater than the value;
A digital protection control device comprising: In Claim 1, the monitoring means comprises:
A digital protection control device, wherein when the phase deviation is equal to or smaller than the predetermined value and the amplitude deviation is equal to or larger than a second predetermined value, it is determined that the A / D converter is abnormal. In claim 2, the monitoring means comprises:
The digital protection control device, wherein the analog filter is determined to be abnormal when the phase deviation is equal to or greater than a third predetermined value that is set to a value greater than the predetermined value. In Claim 1, the monitoring means comprises:
Amplitude ratio and phase difference between amplitude value and phase value of the harmonic signal input through the analog filter and amplitude value and phase value of the harmonic signal input without passing through the analog filter And calculating an amplitude deviation and a phase deviation from an initial value stored in advance to determine an abnormality. Further in claim 1,
A digital protection control device comprising: a frequency rate converter that converts a sampling frequency to a frequency lower than the A / D conversion frequency with respect to an output of the A / D converter. In claim 1,
The Fourier transform means calculates an amplitude value and a phase value in accordance with a period of the harmonic signal, and calculates together with a protection control calculation of the power system using the digital quantity of electricity. apparatus. Further in claim 5,
A digital filter that extracts the superimposed harmonic signal from the output of the A / D converter and outputs it to the Fourier transform means;
2. The digital protection control apparatus according to claim 1, wherein the digital filter extracts a harmonic signal at a period of 1 / ²ⁿ (n is an integer) of the period of the protection control calculation. Further in claim 1,
And a memory for storing amplitude deviation and phase deviation of the harmonic signal calculated by the Fourier transform means for each calculation time. Further in claim 8,
A digital protection control device comprising: deterioration prediction means for calculating a change with time from an amplitude deviation and a phase deviation for each calculation time stored in the memory and predicting deterioration. A harmonic signal having a frequency higher than that of the analog AC electricity amount is superimposed on the analog AC electricity amount taken from the power system,
Performs a filter process for attenuating the frequency in a specific region with respect to the analog AC electric quantity on which the harmonic signal is superimposed,
A / D conversion of the filtered signal into a digital signal;
Calculating a phase deviation and an amplitude deviation of the superimposed harmonic signal from the A / D converted signal;
Comparing the phase deviation with a first predetermined value;
When the phase deviation is equal to or less than a first predetermined value, the amplitude deviation is compared with a second predetermined value;
An abnormality detection method for a digital protection control device that outputs an abnormality signal indicating that the A / D conversion is abnormal when the amplitude deviation is equal to or greater than a second predetermined value. In claim 10,
If the phase deviation is larger than a first predetermined value, the phase deviation is compared with a third predetermined value determined to be larger than the first predetermined value;
An abnormality detection method for a digital protection control device that outputs an abnormality signal indicating that the filter processing is abnormal when the phase deviation is equal to or greater than a third predetermined value.

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