KR100232764B1 - Apparatus and method for measuring impedance of a digital distance relay - Google Patents

Abstract

According to the present invention, when an accident occurs in a transmission line for transmitting electric power, the distance to the accident occurrence point is measured to separate the transmission line from the accident from the normal transmission line, thereby preventing transmission of the transmission line. An apparatus and method for measuring impedance of a digital distance relay.

The impedance measuring device for a digital distance relay as described above includes an analog filtering unit 101 for analogly filtering waveforms of an input voltage and a current, and a sample / hold for sampling and holding a signal output from the analog filtering unit 101. The unit 102, an analog / digital converter 103 for converting a signal held in the sample / hold unit 102 into a digital signal, and a signal output from the analog / digital converter 103. By removing the various harmonic components included, the measurement error generated during analog / digital conversion and the exponentially decreasing DC component generated in the transient state of the system, and extracting the real and imaginary components from the components of the output signal, It consists of a digital calculating part 104 which measures an impedance by complex calculation using these complex components.

Description

Apparatus and method for measuring impedance of digital distance relay

The present invention relates to an apparatus and method for measuring impedance of a digital distance relay, and in particular, when an accident occurs in a transmission line for transmitting power, the distance to an accident occurrence point is measured to separate an accidental transmission line from a normal transmission line. The present invention relates to an impedance measuring apparatus and a measuring method of a digital distance relay for protecting a transmission line that can prevent the spread of an accident.

In general, digital distance relay is a device that not only checks the abnormality of the transmission line that is transmitting power by measuring voltage and current, but also measures the distance to the accident occurrence point when the transmission accident occurs. Very high reliability and stability are required. Therefore, accurate and fast impedance measurement capability is essential for digital distance relays.

1 is a block diagram of an impedance measuring device of a conventional digital distance relay. Referring to FIG. 1, an impedance measuring apparatus of a conventional digital distance relay analog-filters waveforms of an input voltage (V) and an input current (I) detected through a voltage transformer and a current transformer provided in a transmission line, respectively. Analog Filter 11A, 11B, Sample / Holder (S / H) 12A, 12B for sampling the signal output from the Analog Filter 11A, 11B, and the Sample / Holder 12, respectively. Analog-to-digital converters (A / D) 13A and 13B for converting and outputting the output signals of the digital signal into digital signals, and digital filters 14A for filtering signals output from the analog-to-digital converters 13A and 13B, respectively. And 14B) and an impedance calculation unit 15 for calculating and outputting impedance using the signals output from the digital filters 14A and 14B.

Operation of the impedance measuring device of the conventional digital distance relay configured as described above is as follows.

As shown in FIG. 3, the power generated at the power generation stage S1 of the power system flows into the bus BUS 21 of the substation 25 through a plurality of paths, and consumes an allocated load. Then, it transmits to the power receiver 27 again. At this time, in order to determine whether there is an abnormality in the transmission line, a voltage converter (PT) 23 and a current converter (CT) 24 are installed in each transmission line to convert the primary-converted current and voltage signals (V, I). Detect. The signal waveforms of these voltages and currents V and I are input to the analog filters 11A and 11B, respectively, in order to prevent aliasing errors occurring in frequency bands of ½ or more of the sampling frequency during analog / digital conversion. At this time, since the analog filters 11A and 11B generally use a low-pass filter, the analog filters 11A and 11B have a side effect of removing high-frequency harmonics. The signals passing through the analog filters 11A and 11B are respectively input to the samples / holders 12A and 12B for sampling at the same time in order to prevent an error in impedance calculation due to the phase change of the signal generated when a time error occurs during the sampling process. The signals held in the samples / holders 12A and 12B are converted to digital through the analog / digital converters (A / D) 13A and 13B. At this time, the digital conversion method is to use a multiplexer (MultiFlexer) to sequentially switch the holding signal, the digital value converted in this process is input to the digital filter (14A, 14B). The digital filters 14A and 14B include errors caused in performing the characteristics of the digital relay, transient phenomena caused by overloads, inrush currents generated by transformers, etc., noise or surge generated by switch operation, and the like. It removes various harmonics components and DC offset components that are included in the current signal input when an accident occurs and decrease exponentially.

Therefore, the signals passing through the analog / digital converters 13A and 13B pass through the digital filters 14A and 14B, respectively, and extract only the voltage and current signals of the power frequency component. The impedance calculator 15 calculates impedance by using sampling values of voltage and current of power frequency components passing through the digital filters 14A and 14B. The conventional digital distance relay then performs operation determination of each relay element according to a preset program using the measured impedance for the analysis of the transient state of the power system.

4 shows a sampling time point of an input signal (voltage and current). In the present invention, it is assumed that 12 samples are taken during one cycle of a commercial frequency.

Subscripts (n), (n-1), (n-2),... , (n-12) indicates a sampling time point, and means that the sampling time points (n) and (n-1) are separated by one sampling interval (θs) or by 1/12 times of one period. At this time, the digital filters 14A and 14B are the sampled value S (n) at the present time of the input signal (voltage and current) S _T and the sample values S (n-1) stored in the previous state. Each sampling time, using the data S (n), S (n-1), ..., S (n-3) accumulated during the predetermined period Wc of S (n-12). Each time, various harmonics included in the input signal are removed. An example of this removal method is as follows.

[Equation 1]

Where S (n), S (n-4) and S (n-6) are sample values of the input signal (voltage and current) at each sample time, and S '(n) is the nth sample time. It means the signal from which harmonic component of is removed. On the other hand, the method of formula (1a) removes three times harmonics, six times harmonics and direct current components of the commercial frequency (f ₀ ) included in the input signal, and the method of formula (1b) doubles harmonics, four times harmonics 6 times harmonics and direct current components are removed.

5 shows an example in which equation (1a) is applied, (a) is a commercial frequency input signal, (b) is a triple harmonic input signal, (c) is a six times harmonic input signal, and (d) is a direct current. Each component value (S (n), S (n-1), ..., S (n-4)) represents a generic term for the input signals at each sampling time point. Here, 3, 6 times harmonics based on the nth sampling time point, and 3 times harmonics when the sample values (S3 (n), S (n-4)) from the DC component input are applied to Equation (1a), respectively. In the case of the input signal b and the six times harmonic input signal c, the input value S (n) at time point n and the input value S (n-4) at n-4 coincide. Removed by 1a). In addition, in the case of the DC component input signal d, since the value is constant regardless of the change in the sampling time point and removed as described above, it can be seen that the DC component and the harmonic component are removed regardless of the change in the calculation time point. .

On the other hand, the signal (voltage and current) from which components other than the commercial frequency (power frequency) are removed is a vector value input at every sampling time point, and in order to measure impedance, a complex operation must be performed using the vector value of voltage and current. This is a general fact, but for quickness and convenience of operation, it is common to measure the equivalent conversion without taking a complex operation, and an example thereof is as follows.

[Equation 2]

Where V (t) and I (t) represent the sampled voltage and current values at time t, R and L represent impedance measurements, and di / dt represent the amount of change in current at time t. The impedances R and L can be measured by approximating the amount of current change (di / dt), i.

FIG. 6 shows an example in which Equation (2) is applied, and the subscript t indicates a reference sampling time point, and t-1, t-2,... , t-6 represents 1, 2,... from the reference time point t, respectively. , Time points separated by 6 sampling intervals, and I (t), I (t-1),... , I (t-6) is t, t-1,... , represents the sampled current value at time t-6. At this time, the differential amount of the current in equation (2) at the reference time point t is the time point t with respect to the difference between the current amount I (t) at time point t and the current amount I (t-1) at t-1. Can be approximated as shown by 6a of FIG. 6 by the ratio of and t-1, and by using the approximate derivative of Eq. (1a), the solution is obtained by solving the equation at time points t and t-1. Measure the impedance (R, L) at t.

FIG. 7 is a characteristic diagram used in a conventional digital distance relay, and shows quadrilateral characteristics in which three relay elements of reactance elements RE1, RE2, RE3, direction element DE1, and blinder elements BE1, BE2 are combined. have.

FIG. 8 is a logic circuit diagram showing the logic operation when obtaining the relay output according to the operation of FIG. Referring to FIG. 8, the relay element Ry is output by combining the AND products AND1, AND2, AND3, the OR circuit OR1, and the time limit circuits TD1, TD2.

However, in the conventional impedance measuring apparatus of the conventional digital distance relay, there are some problems as follows.

First, there is a problem that it is difficult to accurately measure impedance due to a mismatch in sampling time and measurement error occurring in characteristics of relay hardware during analog / digital conversion.

배 증폭되는 특성을 나타내었다.Second, in the conventional harmonic removal, in the frequency characteristic (9a of the waveform of FIG. 9) with respect to equation (1a), 3, 6 times harmonic components are removed, and in frequency characteristic 9b with respect to equation (1b), 2 , 4 and 6 times harmonic components are removed, but other frequency components are not removed. In particular, in the case of the power frequency (h1), 5 times harmonic (h2) component, the frequency characteristic (9b) of the formula (1b)

It showed a characteristic to be amplified fold.

That is, as shown in FIG. 9, the frequency characteristics of the harmonic elimination methods of the formulas (1a) and (1b), the waveforms 9a and 9b represent the frequency characteristics of the formulas (1a) and (1b). When the method of equations (1a) and (1b) is used, assuming that the magnitude of each component of the frequency after the harmonics is removed and the horizontal axis represents the distribution of the frequency, that is, the ratio with respect to the commercial frequency (power frequency) component In addition to the power frequency components, 5 times harmonic components are further amplified. In addition, in order to measure an accurate power frequency component of an input signal, a division operation is inevitable, and thus a truncation error is easily generated by digital calculation, and an accurate impedance measurement using only a power frequency component is difficult.

Third, the conventional harmonic rejection method is defined by the assumption that the input signal (voltage and current) is a time-invariant periodic signal, so it is limited in application in a transient state such as a power system accident that cannot guarantee the periodicity of the signal. There is. In particular, since the exponentially decreasing direct current component included in the current waveform that occurs in an accident that occurs when the voltage phase angle of the line is near 0 degrees changes with time, it cannot be removed by the conventional method. The impedance measurement method as shown in (2) has a problem of generating an error caused by approximating the differential amount of current with respect to time.

Accordingly, the present invention has been made in view of the above problems, and a main object of the present invention is to extract a complex element from an input signal, and to generate a DC that is non-periodic, time-varying, and exponentially reduced in addition to the power frequency component included in the input component. The present invention provides an impedance measuring device for a digital distance relay that removes components to measure an accurate impedance.

Another main object of the present invention is to remove the measurement error, harmonic components and exponentially decreasing direct current offset components included in the digital input signals in the steady state and transient states of the power system, thereby including voltage and current containing only the power frequency components. The present invention provides an impedance measuring method for a digital distance relay that measures an impedance using a signal.

1 is a block diagram of an impedance measuring device of a conventional digital distance relay.

2 is a block diagram of an impedance measuring device of a digital distance relay according to the present invention.

3 is a general power schematic.

4 is a timing chart showing sampling points of input signals (voltage and current).

5 is a timing chart showing an application of equation (1a).

6 is a timing chart showing the application of equation (2).

7 is a characteristic diagram for explaining the characteristics of a general distance relay.

FIG. 8 is a logic circuit diagram for explaining the logic operation of the distance relay by the characteristic shown in FIG.

9 is a frequency response characteristic diagram of equations (1a) and (1b).

10 is a frequency response characteristic diagram of Equation (11).

* Explanation of symbols for main parts of the drawings

101: filtering unit 101A, 101B: analog filter

102: sample / hold section 102A, 102B: sample / holder

103: analog / digital converter 103A, 103B: analog / digital converter

104: digital calculating section 105A, 105B: real section digital filter section

106A, 106B: Imaginary part digital filter part 107: Voltage real part component

108: voltage imaginary part component 109: current real part component

110: imaginary imaginary component 111: impedance calculator

112: digital filter coefficient unit AND1-AND3: AND gate

TD1, TD2: Timer OR1: Ora Gate

According to the technical idea of the present invention for achieving the above object, the analog filtering unit 101 for analog filtering the waveform of the input voltage and current; A sample / hold unit 102 for sampling and holding a signal output from the analog filtering unit; An analog / digital converter 103 for converting a signal held in the sample / hold unit into a digital signal; A digital filter coefficient unit 112 for modeling voltage, current, and line constant of a power transmission line to set filter coefficients; The digital calculation unit 104 performs a digital filtering operation for removing noise components included in the signal output from the analog / digital converter using the filter coefficients, and then extracts real and imaginary components to measure impedance through a complex operation. ).

According to the technical idea of the present invention for achieving the above another object, a) modeling the measurement signal of the voltage and current of the transmission line, and select the appropriate model order M to obtain the digital filter coefficient H (i: M) B) sampling current and voltage data on the transmission line, c) digitally converting the voltage and current data, and d) using the obtained digital filter coefficients. Performing a digital filtering operation to remove various noise components and extracting the real and imaginary components of the fundamental wave components, respectively, and e) the magnitude and phase of the impedance using the real and imaginary components. Calculating the resistance and reactance at the same time.

Further objects and advantages of the present invention will become apparent from the following detailed description.

Hereinafter, with reference to the accompanying drawings will be described the configuration, operation and effect of the present invention.

2 is a block diagram of an impedance measuring apparatus for a digital distance relay according to the present invention. Referring to FIG. 2, the impedance measuring apparatus of the digital distance relay according to the present invention includes an analog filtering unit 101 for analogly filtering waveforms of an input voltage and an input current, and a signal output from the analog filtering unit 101. A sample / hold unit 102 for sampling and holding a signal, an analog / digital converter 103 for converting a signal held in the sample / hold unit 102 into a digital signal, and an analog / digital converter. The analog / digital converter 103 removes various harmonic components included in the signal output from the 103, measurement errors occurring during the analog / digital conversion, and exponentially decreasing direct current components generated in the transient state of the system. A real component and an imaginary component are extracted from the component of the signal output from the digital signal, and the impedance is measured by a complex operation using these complex components. It is composed of a digital computing unit 104.

The digital calculating section 104 further comprises: a real section digital filter section (RDF) for extracting a real section component from a complex component from signals output from the analog / digital converters 103A and 103B of the analog / digital converter 103; 105A and 105B, an imaginary part digital filter part (IDF) 106A and 106B for extracting an imaginary part component, and an impedance calculation part 111 for measuring impedance by a complex operation using a complex component signal, respectively, It consists of a digital filter coefficient unit 112 for modeling the voltage, current and line constant of the transmission line of the filter coefficients used for digital filtering.

The digital filtering method in the impedance measuring device for the digital distance relay configured as described above is as follows.

As in the prior art, power generated in a power plant of a power system flows into a busbar of a substation through various paths, consumes an allocated load, and is transmitted to a power receiver again. At this time, the voltage converter and the voltage signals (V, I) converted by the voltage converter and current converters provided in each transmission line prevent the error of occurrence occurring in the frequency band ½ or more of the sampling frequency during analog / digital conversion. To be input to the analog filters 101A and 101B, respectively. At this time, since the analog filters 101A and 101B generally use a low-pass filter, even the side effect of removing the high-frequency harmonics (Higi Frequency Harmonics) is obtained. The signals passing through the analog filters 101A and 101B are respectively input to the samples / holders 102A and 102B for simultaneous sampling in order to prevent an error in impedance calculation due to the phase change of the signal generated when a time error occurs in the sampling process. The signals held in the samples / holders 102A and 102B are digitally converted while going through the analog / digital converters (A / D) 103A and 103B.

At this time, the digital filter coefficient unit 112 performs digital filtering using predetermined filter coefficients for each transmission line, and the equation for obtaining the filter coefficient is as shown in Equation (3) (see FIG. 11, ST1).

[Equation 3]

In equation (3), H (k, M) denotes filter coefficients for the imaginary part and the real part of voltage and current, respectively, and the subscripts A and C are the same as equations (4) and (5).

[Equation 4]

[Equation 5]

As can be seen from equations (4) and (5) above, the values of the matrix A for calculating the digital filter coefficients of voltage and current are different. That is, modeling of Γ _P to remove the exponentially decreasing direct current component included in the fault current is added to the matrix Ai for obtaining the digital filter coefficient of the current. In addition, since all components other than the power frequency components are modeled as noise components, accurate voltage and current of the power frequency components can be obtained.

By using the filter coefficients obtained by the digital filter coefficient unit 112, exponentially decreasing various noise components included in the analog / digital converters (A / D) 103A and 103B and steady state currents included in the transient state. The current and voltage data are sampled on the transmission line to remove the direct current component (see FIG. 11, ST2).

Subsequently, the sampled signals are input to the digital real part filters 105A and 105B and the digital imaginary part filters 106A and 106B to perform a digital filtering operation using the following equation (6) (ST3).

[Equation 6]

(i ; M)가 구해진다. 첨자 M은 주기당 샘플링 수를 의미한다.The voltage signal and current signal Z (k) passing through the analog-to-digital converter (A / D) in Equation (6) are various noise components using H (i, k; M) obtained by Equation (3). This has been removed

(i; M) is obtained. Subscript M means the number of samples per cycle.

At this time, the real part component 107 of the voltage and current using a voltage signal and a current signal including only the power frequency components passing through the digital real part filters 105A and 105B and the digital imaginary part filters 106A and 106B. 109) and the imaginary component (108, 110), which is expressed as follows (see FIG. 11, ST4).

[Equation 7]

As can be seen from the above equation (7), the real part components 107 and 109 and the imaginary part component are obtained by obtaining the magnitudes of voltage and current Mv (i), Mc (i) and phases Φv (i) and Φc (i). (108, 110).

Using the complex components of the imaginary part components 108 and 110 and the real part components 107 and 109 of the voltage and current including only the obtained power frequency components, the impedance calculation part 111 complexes using the following equation (8): A complex component for calculating the magnitude and phase of the impedance is extracted by the calculation (see FIG. 11, ST5).

[Equation 8]

Subsequently, the resistance component R and the reactance component X are finally calculated using the following equation (9).

[Equation 9]

FIG. 10 shows an example of the frequency response characteristic of the digital filtering method, which represents the case where M = 12 in Equation (6), and it can be seen that each harmonic component other than the fundamental frequency component is removed. In this case, 10a represents the frequency response characteristic of the real part component, 10b represents the frequency response characteristic of the imaginary part component, and 10c represents the overall frequency response characteristic.

As described above, various noise components, non-harmonic components, harmonic components, and exponentially decreasing DC offset components included in the fault current other than the voltage signal and the current path inputted by the digital filtering means are removed. Then, the correct impedance can be measured by the complex calculation by the formulas (3) and (7). Therefore, when an accident occurs in a transmission line for transmitting electric power, the distance to the accident occurrence point is measured, thereby separating the accidental transmission line from the normal transmission line, thereby preventing the spread of the accident.

Claims (7)

An impedance measuring device for a digital distance relay, comprising: an analog filtering unit (101) for analog filtering a waveform of an input voltage and a current; A sample / hold unit 102 for sampling and holding a signal output from the analog filtering unit; An analog / digital converter 103 for converting a signal held in the sample / hold unit into a digital signal; A digital filter coefficient unit 112 for modeling voltage, current, and line constant of a power transmission line to set filter coefficients; A digital filtering operation is performed to remove noise components included in the signal output from the analog / digital converter by using the filter coefficients, and then digital realization is performed by extracting real and imaginary components to measure impedance through a complex operation. Impedance measuring device for a digital distance relay comprising a calculation unit (104). The digital calculating unit (104) according to claim 1, further comprising: a real part digital filter (105A, 105B) for extracting a real part component of a complex component from an output signal of the analog / digital converter; An imaginary part digital filter part (106A, 106B) for extracting the analog / digital converting part and the imaginary part component; Impedance measuring unit for measuring the impedance by a complex operation using the signal of the complex component Impedance measuring device for a digital distance relay, characterized in that it comprises a. An impedance measurement method for a digital distance relay, comprising: a first step of modeling a measurement signal of a voltage and a current of a transmission line, and selecting an appropriate model order M to obtain a digital filter coefficient H (i; M); Sampling current and voltage data on the transmission line; Digital converting the voltage and current data; A digital filtering operation is performed to remove various noise components included in the output signal passing through the third step by using the digital filter coefficients obtained in the first stage, and the real and imaginary components of the fundamental wave components are extracted, respectively. Performing a fourth step; And a fifth step of calculating the magnitude and phase of the impedance using the real part component and the imaginary part component, and calculating the resistance component and the reactance component. The impedance measuring method for a digital distance relay according to claim 3, wherein the digital filter coefficient H in the first step is obtained by the following equation.

4. The impedance measuring method for a digital distance relay according to claim 3, wherein the filtering operation in the fourth step is performed by the following equation.

The method of claim 3, wherein the extraction of the real part component and the imaginary part component in the fourth step comprises the magnitude of the fundamental wave voltage, the magnitude of the fundamental wave current, the phase of the fundamental wave voltage, and the fundamental wave current obtained by the following equation. Impedance measurement method for a digital distance relay, characterized in that derived through the phase.

The impedance measuring method for a digital distance relay according to claim 3, wherein in the fifth step, the magnitude, phase, resistance, and reactance of the impedance are performed by the following equation.

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