JP2015231270A - Digital protection relay device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress influences upon a relay operation in the case where a frequency variation occurs in a power system, by using a relatively simple correction operation.SOLUTION: In a digital protection relay device 10, on the basis of output of an A/D converter 14, a data storage section 24 successively stores a digital value of the quantity of electricity for each sample cycle corresponding to a frequency that is 2×k times ((k) is an integer equal to or greater than 1) as high as a rating frequency. In order to suppress the influences of the frequency variation in the power system, a correction operation section 26 corrects digital data on the quantity of electricity stored in the data storage section 24. When correcting the digital value of the quantity of electricity stored in the data storage section 24 (g) pieces of values before a present time point ((g) is an integer equal to or greater than 1), the correction operation section 26 corrects the digital value by using the digital value of the quantity of electricity stored in the data storage section 24 (g+k) pieces of values before the present time point.

Description

  The present invention relates to a digital protection relay device.

  Generally, a digital protection relay device performs a relay operation using digital data obtained at a sampling frequency that is an integer multiple of a rated frequency. For example, when the sampling frequency is 12 times the rated frequency, data for every 30 ° electrical angle at the rated frequency is used for the relay calculation.

  Therefore, when the frequency of the power system is equal to the rated frequency, data for every electrical angle of 30 ° is accurately used for the relay calculation, but when the system frequency fluctuates, data acquired at a timing different from that for every electrical angle of 30 °. Is used for relay calculation. For example, when the system frequency is increased by 5% from the rated frequency, data obtained at 30 ° × 1.05, that is, every 31.5 ° is used for the relay calculation. For this reason, depending on the applied relay calculation algorithm, an error may occur in the calculation result, which deviates from the standard required for the relay element, and as a result, a problem may occur in the operation of the protection relay device.

  Until now, several methods for correcting an error caused by fluctuations in the system frequency have been proposed. For example, JP-A-1-298914 (Patent Document 1) calculates the amount of cosine even when the input AC frequency fluctuates when the cosine amount of the phase difference between two vectors is used for relay calculation. A correction method capable of reducing the error is disclosed. Japanese Patent Laid-Open No. 2002-186167 (Patent Document 2) extracts a sine component and a cosine component from a fundamental wave of an AC input by a Fourier transform operation, and based on the extracted component, influences of frequency fluctuations of the power system. Execute the calculation to be corrected.

JP-A-1-298914 JP 2002-186167 A

  However, since the correction method described in Patent Document 1 is limited to the case of calculating the cosine amount, it cannot be applied to all the various calculation algorithms applied to the relay calculation. Since the correction method described in Patent Document 2 uses Fourier transform calculation, the load on a CPU (Central Processing Unit) mounted on the digital protection relay device increases. As a result, actual application may be difficult.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide a digital signal capable of suppressing the influence when a frequency fluctuation occurs in the power system by a relatively simple correction calculation. It is to provide a protective relay device.

  The digital protection relay device according to the present invention includes an AD (Analog to Digital) converter, a data storage unit, a correction calculation unit, and a relay calculation unit. The AD converter converts an analog value of current or voltage detected in the power system into a digital value. Based on the output of the AD converter, the data storage unit sequentially outputs a digital value of an electric quantity (current or voltage) for each sampling period corresponding to a frequency 2 × k times (k is an integer of 1 or more) of the rated frequency. Store. The correction calculation unit corrects the digital data of the amount of electricity stored in the data storage unit in order to suppress the influence of frequency fluctuation of the power system. The relay calculation unit performs a relay calculation based on the corrected digital data of the amount of electricity. When correcting the digital value of the electric quantity stored in the data storage unit before g (g is an integer of 1 or more) before the current time, the correction calculation unit stores data (g + k) times before the current time. The digital value of the quantity of electricity stored before g is corrected using the digital value of the quantity of electricity stored in the unit.

  According to this invention, when correcting the digital value of the quantity of electricity stored in the data storage unit before g times, k times before that (k before is 180 degrees before the rated frequency). The correction calculation is executed using the digital value of the electric quantity stored in the data storage unit. As described above, it is not necessary to detect the current frequency of the power system in order to suppress the influence of the frequency fluctuation, and the influence of the frequency fluctuation can be suppressed by a relatively simple correction calculation.

It is a block diagram which shows the structure of the digital protection relay apparatus by 1st Embodiment. It is a figure which shows the correspondence of the time series data before correction | amendment, and the time series data after correction | amendment. It is a voltage vector diagram in case the frequency of the voltage signal input into a digital protection relay apparatus increases from a rated frequency. It is a vector diagram for demonstrating the method of the error calculation at the time of data correction. It is the vector diagram which generalized FIG. It is the figure which showed the calculation result of the phase error and the amplitude error in a table format when the input frequency is shifted by 5% from the rated frequency. It is a flowchart which shows operation | movement of the digital protection relay apparatus by 1st Embodiment (The procedure until the digital data of a voltage and an electric current is stored in the data storage part before correction | amendment is shown). It is a flowchart which shows operation | movement of the digital protection relay apparatus by 1st Embodiment (The procedure which performs a relay calculation using the data stored in the data storage part before correction | amendment is shown). It is a vector diagram for demonstrating the method to determine a correction coefficient in 2nd Embodiment. In the case of 2nd Embodiment, it is the figure which showed the calculation result of the phase error and the amplitude error in a tabular form. It is a block diagram which shows the structure of the digital protection relay apparatus by 3rd Embodiment. It is a vector diagram for demonstrating the method of determining a correction coefficient in 3rd Embodiment. It is a figure which shows the value of the correction coefficient calculated when the input frequency has shifted | deviated 1-5% with respect to the rated frequency in a tabular form. It is a figure which shows the example of the correction table stored in the correction coefficient memory | storage part of FIG. It is a flowchart which shows operation | movement of the digital protection relay apparatus by 3rd Embodiment.

  Hereinafter, each embodiment will be described in detail with reference to the drawings. The same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

<First Embodiment>
[Configuration of digital protection relay device]
FIG. 1 is a block diagram showing the configuration of the digital protection relay device 10 according to the first embodiment.

  Referring to FIG. 1, a digital protection relay device 10 includes a current transformer 2 (CT: Current Transformer) 6 and a voltage transformer (PT: Potential Transformer) 4 installed in a power line 2 of a power system. The instantaneous values of the current and voltage above are detected, and the detected current signal and voltage signal are AD (Analog to Digital) converted into digital data. The digital protection relay device 10 determines whether or not there is a failure in the corresponding protection section (area to be protected) based on the AD-converted digital data, and disconnects the failure section from the power system when a failure is detected. Therefore, an open command is output to a circuit breaker (not shown) installed in the power system. When only one of the current and the voltage is used for the relay calculation, the digital protection relay device 10 may be configured to capture a current or voltage necessary for the relay calculation. In this specification, current and voltage may be collectively referred to as an electric quantity.

  Specifically, the digital protection relay device 10 includes an analog circuit 12, an AD converter 14, an arithmetic processing unit 16, and an output processing unit 18.

  The analog circuit 12 includes an input converter composed of an auxiliary transformer, an antialiasing filter, a sample and hold circuit, and the like. The input converter converts the voltage level of the current signal and the voltage signal respectively input from the current transformer 6 and the voltage transformer 4 into a voltage level that can be processed inside the digital protection relay device 10. The anti-aliasing filter is a low-pass filter for removing aliasing errors during AD conversion. The sample-and-hold circuit samples the current signal and voltage signal after level conversion at a sampling frequency (96 × fn) that is 96 times the rated frequency fn of the power system, for example. The sampled current signal and voltage signal are converted into digital data by the AD converter 14.

  The arithmetic processing unit 16 is configured based on a microcomputer including a CPU, a memory such as a random access memory (RAM) and a read only memory (ROM), and an interface circuit. The arithmetic processing unit 16 performs a relay operation on the AD-converted current signal and voltage signal, determines the presence or absence of a system failure based on the result of the relay operation, and detects a failure in an area to be protected (protection section) Then, a signal for disconnecting the failure section from the power system is output.

  In terms of functionality, the arithmetic processing unit 16 includes a filter processing unit 22, a pre-correction data storage unit 24, a correction calculation unit 26, a correction coefficient storage unit 28, a post-correction data storage unit 30, and a relay calculation unit. 32 and a logic processing unit 34. The functions of these constituent elements are realized by a program stored in the ROM being executed by the CPU.

  The filter processing unit 22 generates voltage and current digital values for each period Ts by averaging the voltage data and current data input from the AD converter 14 for each predetermined sampling period Ts. The generated digital values (voltage value and current value) are sequentially stored in the pre-correction data storage unit 24 in the memory and used for relay calculation.

  The sampling cycle Ts corresponds to a sampling frequency fs (Ks = K × fn) that is K times the rated frequency fn (K is an even number) (Ts = 1 / fs). For example, when K = 12, data for every electrical angle of 30 ° is generated at the rated frequency, and when K = 16, data for every electrical angle of 22.5 ° is generated at the rated frequency. The sampling frequency fs (12 × fn or 16 × fn) is naturally smaller than the sampling frequency (for example, 96 × fn) at the time of AD conversion.

  The pre-correction data storage unit 24 stores voltage data and current data required for relay calculation from the present time to several cycles before (the number of data accumulated by the applied relay calculation is different). For example, the current voltage value (digital value of voltage) is V (m), the voltage value before one sampling period (Ts = 1 / fs) is V (m−1), and the voltage value before two sampling periods is Let V (m−2). Similarly, the voltage value before the n sampling period is assumed to be V (mn). Assuming that voltage values from the present time to n sampling cycles before are necessary for the relay calculation, n + 1 V (m), V (m-1), V (m-2), ..., V (mn). The time-series data including the voltage value is accumulated in the pre-correction data storage unit 24. This time series data is sequentially updated every sampling period Ts. When the latest voltage value V (m) is input, the previous data is sequentially lowered one by one. The same applies to the current data I (m), I (m-1), I (m-2),.

The correction calculation unit 26 uses the time series data V (m), V (m−1),... To correct the time series data V ^* (m−1), V ^* (m−2),. Are generated every sampling period Ts. This correction is performed to suppress the influence of the frequency fluctuation of the current system. Similarly, for the current data, the correction calculation unit 26 uses the time series data I (m), I (m−1),... To correct the time series data I ^* (m−1), I ^* ( m-2),... are generated every sampling period Ts. The corrected time series data is stored in the corrected data storage unit 30.

  FIG. 2 is a diagram illustrating a correspondence relationship between time-series data before correction and time-series data after correction. Hereinafter, a method for correcting voltage data will be described, but current data can also be corrected by a similar method.

As shown in FIG. 2, the time series data V (m), V (m−1),... Generated by the filter processing unit 22 is stored in the pre-correction data storage unit 24. 1 corrects the time series data V (m), V (m−1),... Stored in the pre-correction data storage unit 24 for each sampling period Ts. The corrected time-series data V ^* (m−1), V ^* (m−2),... Are stored in the corrected data storage unit 30. Since the current data V (m) does not need to be corrected, it is stored in the corrected data storage unit 30 as it is.

  Specifically, the voltage value V (m−1) stored in the pre-correction data storage unit 24 one time before the current time is the k-th correction value data storage unit 24 further before V (m−1). Is corrected using the voltage value V (m-1-k) and the correction coefficient P1 stored in. Here, the constant k corresponds to an electrical angle of 180 ° at the rated frequency, and is represented by k = 180 ° / φ, where φ is an electrical angle corresponding to one sampling period at the rated frequency. If the sampling frequency fs is K times the rated frequency fn, there is a relationship of k = K / 2. For example, when K = 12 (that is, when fs = 12 × fn), k = 6 and φ = 30 °.

The specific expression of the corrected voltage value V ^* (m−1) is
V ^* (m-1) = V (m-1) + (V (m-1) + V (m-1-k)) · P1 (1A)
＝ （1 ＋ P1） ・ V (m-1) ＋ P1 ・ V (m-1-k)… (1B)
Represented by Expression (1B) is obtained by rewriting the right side of Expression (1A).

The correction coefficient P1 indicates that the corrected voltage value V ^* (m−1) is a voltage value V (m) that is an electrical angle φ (electrical angle φ corresponds to one sampling period at the rated frequency) before the current time. -Φ). In the case of the first embodiment, the correction coefficient P1 is set to 1 / k (a method for deriving the correction coefficient P1 will be described later with reference to FIG. 3).

The voltage value V (m−2) stored in the pre-correction data storage unit 24 two times before the current time is equal to the voltage value V (m−2) stored k times before V (m−2). -K) and the correction factor P2 (= 2 / k),
V ^* (m-2) = V (m-2) + (V (m-2) + V (m-2-k)) · P2 (2A)
＝ （1 ＋ P2） ・ V (m-2) ＋ P2 ・ V (m-2-k)… (2B)
It is corrected according to. Expression (2B) is obtained by rewriting the right side of Expression (2A).

Similarly, the voltage value V (m−3) three times before the current time is equal to the voltage value V (m−3−k) k times before V (m−3) and the correction coefficient P3 (= 3). / K) and
V ^* (m-3) = V (m-3) + (V (m-3) + V (m-3-k)) · P3 (3A)
＝ （1 ＋ P3） ・ V (m-3) ＋ P3 ・ V (m-3-k)… (3B)
It is corrected according to. Expression (3B) is obtained by rewriting the right side of Expression (3A).

More generally, the voltage value V (m−g) g times before the present time (g is an integer of 1 or more) is the voltage value V (m−g) k times before V (m−g). g−k) and the correction coefficient Pg (= g / k),
V ^* (mg) = V (mg) + (V (mg) + V (mgk)) · Pg (4A)
= (1 + Pg) · V (mg) + Pg · V (mgk) ... (4B)
It is corrected according to. Expression (4B) is obtained by rewriting the right side of Expression (4A).

According to equation (4A), the corrected voltage value V ^* (mg) is obtained by adding a correction term to the uncorrected voltage value V (mg). The correction term is given by a linear combination of the voltage value V (m−g) and V (m−g−k) before correction.

  When the phase relationship with past data is not required for the relay calculation, the correction calculation according to the above equation (4A) may be up to half a cycle before (1 ≦ g <k). As the voltage value after the correction from half cycle to one cycle before (k ≦ g <2k), a voltage value obtained by reversing the sign of the corrected voltage value from the present time to the half cycle before can be used.

Specifically, the sign of the current voltage value V (m) is inverted as the voltage value V ^* (m−k) obtained by correcting the voltage value V (m−k) half a cycle before the current time. Things can be used. Correction after half a cycle as voltage values V ^* (m−k−1), V ^* (m−k−2),..., V ^* (m−2k + 1) after correction from a half cycle to one cycle before Those obtained by inverting the signs of the subsequent voltage values V ^* (m−1), V ^* (m−2),..., V ^* (m−k + 1) can be used. The specific expression is
V ^* (mk) = -V (m) (5)
V ^* (mk-1) = -V ^* (m-1) = -V (m-1)-(V (m-1) + V (m-1-k)) · P1 (6)
V ^* (mk-2) = -V ^* (m-2) = -V (m-2)-(V (m-2) + V (m-2-k)) · P2 (7)
...
V ^* (m- (2k-1)) = -V ^* (m- (k-1))
= −V (m− (k−1)) − (V (m− (k−1)) + V (m− (k−1) −k)) · Pk−1 (8)
Given in.

When past phase data is required, as in the case of determining the direction of the accident point as viewed from the relay installation point in a distance relay or the like, the voltage value is corrected according to the above-described equation (4A). For example, the voltage value V ^* (m−4k) obtained by correcting the voltage value V (m−4k) two cycles ago is the voltage value V (m−5k) 2.5 cycles ago and the correction coefficient P4k (= 4k / k = 4) and
V ^* (m-4k) = V (m-4k) + (V (m-4k) + V (m-5k)) · P4k (9)
It is corrected according to.

  Referring again to FIG. 1, the relay calculation unit 32 executes the relay element calculation using the data stored in the pre-correction data storage unit 24 or the data stored in the post-correction data storage unit 30. Specifically, the relay calculation unit 32 performs relay element calculation using the data stored in the corrected data storage unit 30 in the calculation of the relay element that places importance on the phase characteristic, and calculates the relay element that is not related to the phase characteristic. Then, the relay element calculation is executed using the data stored in the pre-correction data storage unit 24.

  The logic processing unit 34 performs a failure determination as to whether or not there is a failure in the power system by performing a logical operation using the operation result of the relay operation unit 32, and outputs the determination result. When the logic processing unit 34 determines that there is a failure in the power system, the output processing unit 18 outputs an open command to the circuit breaker to disconnect the corresponding protection section from the power system.

[Derivation of correction coefficient]
Next, a method for deriving a correction coefficient (for example, Pg in the above equation (4A)) when correcting voltage data and current data will be described. As a specific example, a case where a voltage value delayed by 90 ° from the current time is required when the sampling period is an electrical angle of 30 ° at the rated frequency will be described. When data correction is not performed, when the frequency of the power system increases by 5% from the rated frequency, a voltage value delayed by 94.5 ° from the current time is used for the relay calculation.

  In the following description, the current voltage value is described as V (m), the voltage value delayed by 90 ° is described as V (m−90 °), and the voltage value delayed by 270 ° is V (m−270 °). The voltage value three times before the sampling cycle (corresponding to 90 ° before the rated frequency) is written as V (m−3), and nine voltage values before the sampling cycle (270 ° before the rated frequency). Is represented as V (m-9). The frequency (hereinafter also referred to as input frequency) of the voltage signal and current signal input to the digital protection relay device 10 is f, and the rated frequency is fn.

  FIG. 3 is a voltage vector diagram when the frequency of the voltage signal input to the digital protection relay device increases from the rated frequency. Referring to FIG. 3, an angle formed between voltage vectors V (m−3) and V (m−90 °) is θ1 (f), and voltage vectors V (m−9) and V (m−270 °) Is defined as θ2 (f). Note that θ1 (f) and θ2 (f) indicate that θ1 and θ2 are functions of the input frequency f. When the input frequency f is equal to the rated frequency fn, θ1 = θ2 = 0.

The angles θ1 (f) and θ2 (f) are obtained by using the input frequency f and the rated frequency fn,
θ1 (f) = 90 ° · (f−fn) / fn (10)
θ2 (f) = 270 ° · (f−fn) / fn = 3 · θ1 (f) (11)
Each is required. Therefore, the difference Δθ (f) between the angles θ2 and θ1 is
Δθ (f) = 2 ・ θ1 (f) (12)
Given in.

  The above equation (3A) (where k = 6) is obtained by converting the angular error θ1 (f) of V (m−3) caused by the frequency shift to a vector (V (m−3) + V (m−9)) × It is corrected by P3. As shown in FIG. 3, the vector (V (m−3) + V (m−9)) is zero when the frequency f is the rated frequency, and when the frequency f changes from the rated frequency (increases in the figure). Is in the direction of correcting the phase shift of V (m−3). Since Δθ is twice as large as θ1, the vector (V (m−3) + V (m−9)) is multiplied by ½ of the reciprocal as a coefficient P3 for correction. When the frequency change from the rated frequency is small and therefore θ1 is small, the error due to correction is small.

  More generally, when the sampling period is the electrical angle φ at the rated frequency, the voltage value is delayed by g × φ from the current time (where g is an integer satisfying 1 ≦ g <k, k = 180 ° / φ). The necessary case will be described. The current voltage value is described as V (m), the voltage value delayed by g × φ is described as V (m−g · φ), and the voltage value delayed by 180 ° from g × φ is expressed as V (m− (G + k) · φ), the voltage value before g in the sampling period is described as V (m−g), and the voltage value before (g + k) in the sampling period is expressed as V (m− (g + k). )).

The angle θ1 (f) formed by the voltage vectors V (m−g) and V (m−g · φ) and the voltage vectors V (m− (g + k)) and V (m− (g + k) · φ) The formed angle θ2 (f) is
θ1 (f) = g · φ · (f−fn) / fn (13)
θ2 (f) = (g + k) · φ · (f−fn) / fn = (1 + k / g) · θ1 (f) (14)
Are given respectively.

Therefore, the difference Δθ (f) between the angle θ2 and the angle θ1 is
Δθ (f) = k / g · θ1 (f) (15)
Given in.

Since the voltage value V (m−g) is corrected using the voltage value V (m− (g + k)) and the correction coefficient Pg according to the above-described equation (4A), the correction coefficient Pg is
Pg = θ1 (f) / Δθ (f) = g / k (16)
Given in.

[Calculation of phase error and amplitude error]
The data V ^* (m−3) corrected according to the above equation (3A) does not completely match V (m−90 °) necessary for the relay calculation, and there is an error between the two. Next, a method for calculating this error (phase error and amplitude error) will be described.

FIG. 4 is a vector diagram for explaining an error calculation method at the time of data correction. The vector diagram of FIG. 4 shows the mutual relationship between the voltage vectors V (m−3), V (m−9), V (m−90 °), and V ^* (m−3) in the above equation (3B). Showing the relationship. Here, the amplitudes of the voltage vectors V (m−3), V (m−9), and V (m−90 °) before correction are set to 1, and the corrected voltage vector V ^* (m−3) Let the amplitude be X. An angle formed by the voltage vector V ^* (m−3) and V (m−3) is θx. In FIG. 4, for the sake of simplicity, the suffix of the correction coefficient P3 is omitted and simply indicated as P.

In FIG. 4, the cosine and sine theorems are applied to the triangle formed by the voltage vectors (1 + P) × V (m−3), P × V (m−9), and V ^* (m−3). By
X ² = (1 + P) ² + P ² −2 ・ (1 + P) ・ P ・ cosΔθ (17)
X / sinΔθ = P / sinθx (18)
Is obtained.

  If the input frequency f is known, Δθ (f) can be calculated according to the above equations (10) and (12), and therefore X and θx can be calculated according to the above equations (17) and (18). Thereby, the phase error θ1-θx and the amplitude error X-1 can be calculated.

FIG. 5 is a vector diagram generalizing FIG. The vector diagram of FIG. 5 shows the voltage vectors V (m−g), V (m−g−k), V (m−g · φ), and V ^* (m−g) in the above equation (4B). Shows the mutual relationship. Here, the amplitudes of the voltage vectors V (m−g), V (m−g−k), and V (m−g · φ) before correction are set to 1, and the corrected voltage vector V ^* (m− Let X be the amplitude of g). An angle formed by the voltage vector V ^* (m−g) and V (m−g) is θx. In FIG. 5, for the sake of simplicity, the suffix of the correction coefficient Pg is omitted and is simply indicated as P.

In FIG. 5, the cosine and sine theorems are applied to a triangle composed of voltage vectors (1 + P) × V (m−g), P × V (m−g−k), and V ^* (m−g). By applying, the relationship of the above-mentioned formulas (17) and (18) is obtained as in the case of FIG. If the input frequency f is known, Δθ (f) can be calculated according to the above equations (13) and (15), and therefore X and θx can be calculated according to the above equations (17) and (18).

  FIG. 6 is a diagram showing the calculation results of the phase error and the amplitude error in a tabular form when the input frequency is shifted by 5% from the rated frequency. Note that the change amount of 5% in frequency is a value that cannot be in a normal operation state, and is the maximum value of the standard defined by JEC (Japanese Electrotechnical Committee).

  Referring to FIG. 6, in order from the leftmost column, the phase angle necessary for the relay calculation, the voltage data before correction, the phase error of the voltage data before correction when the frequency is shifted by 5%, the correction formula, and the correction A coefficient (also referred to as a P value), a phase error of the corrected voltage data, and an amplitude error of the corrected voltage data are shown. The sampling period is a case where the electrical angle is 30 ° at the rated frequency, and corresponds to the above-mentioned k = 6 (K = 12). As apparent from FIG. 6, according to the present embodiment, the improvement of the phase error is remarkable, and even if the amplitude value error is taken into consideration, the level is not problematic for the relay calculation.

[Summary of operation of digital protection relay device]
7 and 8 are flowcharts showing the operation of the digital protection relay device according to the first embodiment. FIG. 7 shows a procedure until voltage and current digital data is stored in the pre-correction data storage unit, and FIG. 8 shows a procedure for performing a relay operation using the data stored in the pre-correction data storage unit. . Hereinafter, the description so far will be summarized with reference to FIG. 1, FIG. 7, and FIG.

  First, the digital protection relay device 10 detects the instantaneous values of the voltage and current of the power line 2 through the voltage transformer 4 and the current transformer 6 (step S100). In the analog circuit 12, analog signal processing such as level conversion and filter processing is performed on the detected voltage signal and current signal (step S110). The voltage signal and current signal after the analog signal processing are AD converted by the AD converter 14 (step S120). The digital data output from the AD converter 14 is subjected to digital filter processing every predetermined period Ts, so that 2 × k times the rated frequency fn (k satisfies k ≧ 1). Voltage data and current data are generated at an integer sampling frequency fs (fs = 1 / Ts) (S130). The generated voltage data and current data are stored in the pre-correction data storage unit 24 (step S140).

  Next, the correction calculation unit 26 corrects the data stored in the pre-correction data storage unit 24 (step S300). Specifically, according to the above-described formula (4A), the digital value (voltage value or current value) of the electrical quantity g before the current time is the digital value (k + k) of the electrical quantity (k + k) before the current time. Is equivalent to 180 ° before the rated frequency) and the correction coefficient Pg expressed by the equation (16). The corrected data is stored in the corrected data storage unit 30 (step S310).

  Next, the relay computing unit 32 performs relay element computation using the data stored in the pre-correction data storage unit 24 or the data stored in the post-correction data storage unit 30 (step S320). In the calculation of the relay element in which the phase characteristics are important, the data stored in the corrected data storage unit 30 is used for the relay calculation.

  Subsequently, the logic processing unit 34 determines a failure in the protection section based on the relay calculation result (step S330). The output processing unit 18 outputs a breaker open command to disconnect the failure section from the power system (step S340).

[Effect of the first embodiment]
As is apparent from FIG. 6, according to the digital protection relay device of the first embodiment, it is possible to reduce the phase angle error to a level at which there is no problem as a characteristic of the protection relay device, and the effect that the frequency characteristic can be improved. There is.

  Further, as shown in the above equation (4A), the digital value before g and the digital value before (g + k) are used as correction terms for correcting the digital value (voltage value or current value) before g at the present time. A value obtained by multiplying the addition result of the value (k before is equivalent to 180 degrees before the electrical angle at the rated frequency) is used. Therefore, the value of the correction term when there is no difference between the input frequency and the rated frequency is zero, and the relay calculation result is not affected. As described above, even when the input frequency is unknown, the digital value (voltage value and current value) of the electric quantity necessary for the relay calculation can be corrected with a simple correction formula.

<Second Embodiment>
In the first embodiment, by setting the correction coefficient Pg to a value given by the above equation (16), the phase error is reduced to a level that does not cause any problem as a characteristic of the protection relay device. In the second embodiment, in order to further reduce the phase error, the correction coefficient Pg is set to a value different from that of the first embodiment so that the phase error becomes zero at a predetermined input frequency f. is there.

  FIG. 9 is a vector diagram for explaining a method of determining the correction coefficient Pg in the second embodiment. The vector diagram of FIG. 9 corresponds to the vector diagram of FIG. However, in FIG. 9, the correction coefficient Pg is determined such that the phase error (that is, θ1 (f) −θx in FIG. 5) becomes zero at a predetermined input frequency f. In FIG. 9, the suffix g of the correction coefficient Pg is omitted.

Specifically, when the input frequency f increases by 5% from the rated frequency fn, the phase error becomes zero, that is, the direction of the voltage vector V (m−g · φ) in FIG. ^{* The} correction coefficient P is determined so that the direction of (mg) coincides. The magnitude (X) of the voltage vector V ^* (mg) is different from the magnitude (here, 1) of the voltage vector V (mg−φ).

To determine the correction factor P, a sine with respect to the triangle constituted by the voltage vector (1 + P) × V (m−g), P × V (m−g−k), and V ^* (m−g) Apply the theorem. by this,
X / sinΔθ (f) = P / sinθ1 (f) = (1 + P) / sin (180 ° −θ1 (f) −Δθ (f)) (19)
Is obtained.

  Here, when the input frequency is set to be 5% higher than the rated frequency fn, θ1 (f) and Δθ (f) can be calculated according to the above-described equations (13) and (15). Therefore, X and Pg can be calculated by the above equation (17) and the above equation (19).

  FIG. 10 is a diagram showing the calculation results of the phase error and the amplitude error in a table format in the case of the second embodiment. FIG. 10 shows the calculation results of the phase error and the amplitude error when the input frequency f is shifted by 5% from the rated frequency and when it is shifted by 3%. The sampling period Ts at the rated frequency is 30 °. That is, it corresponds to the case of k = 6.

  As shown in FIG. 10, according to the digital protection relay device of the second embodiment, the frequency at which the phase error is zero is determined (in the above example, the frequency that is the maximum deviation of the necessary frequency band is 5%). By setting the phase error to zero), the phase error can be further reduced in the required frequency band, and the frequency characteristics can be further improved.

  Hereinafter, the effect of the second embodiment will be further described by taking as an example a case where the phase of the voltage value or current value two cycles before is required for the relay calculation. Assuming that the input frequency f is shifted by 5% with respect to the rated frequency fn, in the voltage data or current data before correction, the phase angle error of the voltage value or current value before two cycles is 720 ° × 0. 05 = 36 °.

  In the first embodiment, the correction coefficient Pg is given by Expression (16). Therefore, the correction coefficient Pg when correcting the voltage value or current value two cycles before is set to g = 4k, and Pg = 4k / k = 4. Therefore, when error calculation is performed according to the equations (17) and (18), the phase error is 5.2 ° and the amplitude error is 22%. Thus, the phase error exceeds 5 ° and becomes an angle that cannot be ignored.

  On the other hand, in the second embodiment, when the phase error becomes 0 when the input frequency f is shifted by 5% with respect to the rated frequency fn, the correction coefficient P when g = 4k is 4.926. Become. In this case, the amplitude error increases to 31%, but the phase angle error is zero. When the input frequency f is shifted by 3% with respect to the rated frequency fn, the phase error is 2.4 ° and the amplitude error is 12.2%. Reduced to

<Third Embodiment>
In the second embodiment, when the input frequency f deviates by a predetermined frequency from the rated frequency fn (for example, deviates by 5%), a correction method that can improve the frequency characteristics of the protection relay device is shown. . In the third embodiment, the value of the input frequency f is calculated from the input voltage data or current data, and optimal correction is performed according to the calculated input frequency f. Hereinafter, specific description will be given with reference to the drawings.

  FIG. 11 is a block diagram showing a configuration of a digital protection relay device 10A according to the third embodiment. The arithmetic processing unit 16A in FIG. 11 is different from the arithmetic processing unit 16A in FIG.

The frequency calculation unit 36 performs frequency calculation by a known method based on the voltage data or current data stored in the pre-correction data storage unit 24. For example, the frequency calculation unit 36
A = {V (m-3) ・ V (m-6) −V (m) ・ V (m-9)}
/ {V (m-3) ・ V (m-3) −V (m) ・ V (m-6)}… (20)
f ＝ {cos ^-1 (A) / 2)} ・ 2 ・ fn / π (21)
To calculate the input frequency f. In the formula (21), π represents a circumference ratio.

  Note that the frequency of the power system usually does not change abruptly even when a system failure occurs. Therefore, under the situation where there is no system failure, it is not necessary to perform the above frequency calculation every sampling cycle Ts (= 1 / fs).

When correcting the voltage value V (m−g) before g times from the current time, the correction calculation unit 26 further calculates the voltage value V (m−g−k) before k times and the correction coefficients Pf1 and Pf2. make use of,
V ^* (mg) = V (mg) + V (mg) · Pf1 + V (mgk) · Pf2 (22)
Correct according to That is, the correction term for correcting the voltage value V (m−g) is obtained by linear combination of the voltage value V (m−g) and the voltage value V (m−g−k).

  The correction coefficients Pf1 and Pf2 of the above equation (22) are stored in advance in the correction coefficient storage unit 28 corresponding to various input frequencies f. Correction coefficients Pf1 and Pf2 corresponding to the input frequency f calculated by the frequency calculation unit 36 are read from the correction coefficient storage unit 28 and used for the correction calculation.

  Other points in FIG. 11 are the same as those in FIG. 1, and therefore, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

FIG. 12 is a vector diagram for explaining a method of determining correction coefficients Pf1 and Pf2 in the third embodiment. The vector diagram of FIG. 12 corresponds to the vector diagrams of FIG. 5 and FIG. However, in the case of FIG. 12, the correction coefficient Pf1 multiplied by the voltage value V (m−g) and the correction coefficient Pf2 multiplied by the voltage value V (m−g−k) are provided separately. Further, the correction coefficients Pf1 and Pf2 are determined so that the phase error and the amplitude error of the corrected voltage value V ^* (m−g) are both zero at the calculated input frequency f. That is, in FIG. 12, the voltage vector V ^* (mg) coincides with the voltage vector V (mg−φ).

To determine the correction factors Pf1, Pf2, for a triangle composed of voltage vector (1 + Pf1) × V (m−g), Pf2 × V (m−g−k), and V ^* (m−g) Apply the sine theorem. by this,
1 / sinΔθ (f) = Pf2 / sinθ1 (f)
= (1 + Pf1) / sin (180 ° −θ1 (f) −Δθ (f)) (23)
Is obtained.

  Here, if the input frequency f is known, θ1 (f) and Δθ (f) can be calculated according to the above-described equations (13) and (15). Therefore, the correction coefficients Pf1 and Pf2 can be determined by using the above equation (23).

  FIG. 13 is a table showing the values of correction coefficients Pf1 and Pf2 calculated when the input frequency f is shifted by 1 to 5% with respect to the rated frequency fn. In the table of FIG. 13, the electrical angle φ corresponding to the sampling period Ts at the rated frequency is set to 30 ° (ie, k = 6), and the voltage value V (m−3) three times before the current time is corrected. The calculation results of the correction coefficients Pf1 and Pf2 for (that is, g = 3) are shown.

  FIG. 14 is a diagram showing an example of a correction table stored in the correction coefficient storage unit 28 of FIG. The correction table of FIG. 14 is created based on the calculation result of the correction coefficient shown in FIG. By referring to the correction table of FIG. 14, correction coefficients Pf1 and Pf2 corresponding to the calculated input frequency f are determined when φ = 30 ° (k = 6) and g = 3. Correction tables corresponding to other values of φ and g are similarly created and stored in the correction coefficient storage unit 28 of FIG.

  In the example of FIG. 14, new correction coefficients Pf1 and Pf2 are set every time the input frequency is shifted by 1%, but the step size of the input frequency is changed according to the degree of error required for the relay calculation. It doesn't matter.

  FIG. 15 is a flowchart showing the operation of the digital protection relay device according to the third embodiment. The flowchart of FIG. 15 corresponds to the flowchart of FIG. 8, but differs from the flowchart of FIG. 8 in that steps S200 and S210 are further provided.

  With reference to FIG. 11 and FIG. 15, in the third embodiment, the frequency calculation unit 36 calculates the current input frequency f using voltage data or current data stored in the pre-correction data storage unit 24. (Step S200). Correction coefficients Pf1 and Pf2 corresponding to the calculated input frequency f are determined based on the correction table stored in the correction coefficient storage unit 28 (step S210). Since the frequency of the power system does not change abruptly, the frequency may not be calculated every sampling period Ts.

  Next, the correction calculation unit 26 corrects the data stored in the pre-correction data storage unit 24 using the determined correction coefficients Pf1 and Pf2 (step S300A). Since the subsequent steps are the same as those in FIG. 8, the same or corresponding steps are denoted by the same reference numerals, and description thereof will not be repeated.

  As described above, according to the digital protection relay device according to the third embodiment, since the correction coefficients Pf1 and Pf2 are selected according to the frequency f of the power system, the phase when correcting voltage data or current data is selected. The error and the amplitude error can be made substantially zero, and the frequency characteristics of the protection relay device can be further improved.

  Each embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  2 Electrical lines, 4 Voltage transformer, 6 Current transformer, 10, 10A Digital protective relay device, 12 Analog circuit, 14 AD converter, 16, 16A Arithmetic processing unit, 18 Output processing unit, 22 Filter processing unit, 24 Correction Pre-data storage unit, 26 correction calculation unit, 28 correction coefficient storage unit, 30 post-correction data storage unit, 32 relay calculation unit, 34 logic processing unit, 36 frequency calculation unit.

Claims (7)

An AD (Analog to Digital) converter that converts an instantaneous value of the amount of electricity detected from the power system into a digital value;
A data storage unit that sequentially stores the digital value of the electric quantity for each sampling period corresponding to a frequency of 2 × k times (k is an integer of 1 or more) of a rated frequency based on the output of the AD converter;
In order to suppress the influence of frequency fluctuations of the power system, a correction calculation unit that corrects digital data of the amount of electricity stored in the data storage unit,
A relay operation unit that performs a relay operation based on the corrected digital data of the amount of electricity,
When correcting the digital value of the electric quantity stored in the data storage unit before g (g is an integer of 1 or more) before the current time, the correction calculation unit is (g + k) before the current time. A digital protection relay device configured to correct the digital value of the quantity of electricity stored in the previous g using the digital value of the quantity of electricity stored in the data storage unit. The correction calculation unit is configured to correct the digital value of the electrical quantity stored before g times by adding a correction term to the digital value of the electrical quantity stored before g times.
The digital correction according to claim 1, wherein the correction term is represented by a linear combination of the digital value of the quantity of electricity stored before g and the digital value of the quantity of electricity stored before (g + k). Protection relay device.   The correction term is obtained by multiplying a value obtained by adding the digital value of the quantity of electricity stored before g and the digital value of the quantity of electricity stored before (g + k) times by a correction coefficient. The digital protection relay device according to claim 2.   The digital protection relay device according to claim 3, wherein the correction coefficient is equal to g / k.   When the amount of frequency shift of the power system is a predetermined value, the phase error of the value obtained by correcting the digital value of the quantity of electricity stored before g is zero. The digital protection relay device according to claim 3, wherein a correction coefficient is defined. The digital protection relay device further includes a frequency calculation unit that calculates the frequency of the power system based on digital data of the amount of electricity stored in the data storage unit,
The correction term includes a second correction value obtained by multiplying the digital value of the electrical quantity stored before g times by a first correction coefficient and the digital value of the electrical quantity stored before (g + k) times. Obtained by adding the value multiplied by the coefficient,
The digital protection relay device according to claim 2, wherein the first and second correction coefficients are determined according to the calculated frequency of the power system.   The digital protection relay device according to claim 1, further comprising a correction data storage unit for storing digital data of the amount of electricity corrected by the correction calculation unit.

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