KR100593791B1 - Earth Intrinsic Impedance Measurement Device Using Variable Frequency Current - Google Patents

Abstract

The present invention provides a measurement current generating unit for generating a measurement current of varying frequency; First and second auxiliary electrodes; A current-applying wire connecting the first and second auxiliary electrodes to each other and vertically intersecting the potential detecting installation wire; A detection transformer CT for detecting a measurement current; Third and fourth auxiliary electrodes for measuring ground potential; Potential detection cable; A potential rise detection unit measuring a ground potential; Insulation separator; Analog / digital (A / D) converters; Bandpass filter; A subtractor for detecting a phase difference; Waveform size detector; It relates to a ground intrinsic impedance measurement apparatus using a variable frequency, including; earth resistance / reactance calculator. According to the present invention, it is possible to measure the grounding high impedance combined with the capacitance component and the resistance component of the actual equivalent circuit, and can be used as an important basic data for designing and supplementing a grounding system to be installed in the future.

High impedance, variable frequency, measurement

Description

A device for measuring the Soil Resistivity Using Variable Frequency Currents

1 is a view showing an electrical equivalent model of the earth,

Figure 2a is a view showing a horizontal two-layer structure site model,

FIG. 2b shows a ρ-a curve of the earth shown in FIG. 2a, FIG.

Figure 2c is a view showing a horizontal three-layer structure site model,

FIG. 2D shows a ρ − a curve of the site shown in FIG. 2C, FIG.

3 is a diagram illustrating a four-pole electrode method of Wener

Figure 4 is a view showing the configuration of a high ground impedance measurement apparatus according to the present invention,

5A is a diagram showing the configuration of the inverter shown in FIG. 4;

5B is a diagram illustrating a configuration of the inverter controller shown in FIG. 4;

6 is a view showing the shapes of a current-applied laid wire and a potential detecting laid wire;

7A and 7B show measurement waveforms of ground potential with and without chain link flux;

8 is a view showing the configuration of the high high impedance measuring unit;

9A and 9B show an applied current and a ground potential waveform of an A / D converter;

10A and 10B are diagrams illustrating a measurement current and a ground potential waveform output from the filter unit;

11A is a diagram showing the earth resistivity;

11b is a diagram showing the phase of the high-impedance impedance;

11C and 11D are diagrams illustrating a resistance component and a reactance component of the earth resistivity, respectively;

12 is a flowchart illustrating a process of measuring earth intrinsic impedance using a variable frequency in the present invention.

The present invention relates to an earth inherent impedance measuring apparatus using a variable frequency, and more particularly, to add a concept of frequency conversion to an applied current to measure earth inherent impedance, and to filter and analyze the earth inherent impedance. A measuring device for measuring intrinsic impedance.

The most important point when designing a grounding system is the ground parameter. Ground parameters refer to the type and thickness of the layers and their resistivity. Soil is not very well electricity when it is completely dry. However, due to the nature of silicic acid (SiO ₂ ) or aluminum oxide (Al ₂ O ₃ ), the earth's resistivity decreases rapidly. Therefore, the earth resistivity of a specific earth is measured according to the type of earth, the moisture content, etc., and the grounding system is designed based on the data.

Conventionally, before constructing a substation or a large-scale grounding system, the ground resistivity, that is, only the resistance component of the ground is measured to design and install the grounding system of the grounded object. The grounding system installed in this way has a problem in that it cannot cope with the problem of various aspects of the grounding impedance in a lightning surge or a large-scale grounding system including a high frequency component. In other words, the resistance, capacitive and inductive characteristics of the ground impedance were difficult to interpret clearly with only high resistance.

1 is a diagram showing an electrical equivalent model of the earth. As shown in FIG. 1, an equivalent model of the earth is known to consist of a series of parallel arrangements of a resistance component and a capacitance component. As in the equivalent model, an error occurs when the earth parameter is measured only by resistance. When the grounding system was installed with the earth resistivity including the error, there was a problem in that it did not properly play the role of grounding expected in the design.

 Recently, there have been many developments in the shape and construction technique of the ground electrode, instead of simply connecting the grounded object and the ground electrically. In particular, the purpose of grounding is to diversify the purpose of grounding, from discharging the fault current of the power system to equipotentiality of all systems, to prevent electric shock and device damage, to stabilize the control measurement system, and to safely discharge the brain current. Due to the diversification of the grounding system, the grounding system includes various complex frequency components. However, when designing and evaluating the grounding system, only the result of a specific frequency around 50 ~ 200Hz is used, which causes a problem of failing to achieve the expected safety and characteristics of the grounding system.

The land is a collection of soils with various earth resistivities, which are composed of several layers. There are horizontal layers, sloped layers, and curved layers.

2A is a diagram illustrating a horizontal two-layer structure site model.

FIG. 2B is a view showing a ρ − a curve of the earth shown in FIG. 2A.

As shown in FIG. 2A, a case in which the upper resistivity ρ ₁ , the thickness d ₁ , and the lower layer have a horizontal two-layer structure of ρ ₂ and d ₂ is shown. Depending on the size of ρ ₁ and ρ ₂ , the ρ-a curve of the earth is where (a) is ρ ₁ <ρ ₂ , and (b) is ρ ₁ > ρ ₂ . In the case of the structure as shown in (a), since the lower layer has a large ρ ₂ , the ground resistance does not decrease even when the electrode is deeply drilled. In this case, it is better to use the upper ground, and to adopt the parallel grounding method. On the other hand, in the ground as shown in (b), it is advantageous to reduce the ground resistance by deeply constructing the ground electrode.

2C is a diagram illustrating a horizontal three-layer structure site model.

FIG. 2D is a diagram illustrating a p − a curve of the site shown in FIG. 2C.

On the other hand, in the case of the horizontal three-layer structure as shown in Figure 2c, according to the values of the earth resistivity ρ ₁ , ρ ₂ , ρ ₃ of each layer (a) ρ ₁ <ρ ₂ > ρ ₃ , (b) ρ ₁ ρ-a curve is obtained when> ρ ₂ <ρ ₃ , which is shown based on ρ ₂ of the intermediate layer for easy comparison. (a) is a case where ρ ₂ is larger than ρ ₁ and ρ ₂ , and (b) is a case where ρ ₂ is small.

 3 is a diagram illustrating a four-pole electrode method of Wener.

Wener's four-electrode method is the most widely used method for measuring earth resistivity. This is a method of estimating the earth resistivity by measuring the current I flowing between the ground electrodes and the voltage V applied between the ground electrodes with four ground electrodes installed on the ground. The power is connected between the two ground electrodes C ₁ and C ₂ on the outer side. The ground resistance R can be obtained from V / I by applying a current to the ground and measuring the potential difference between the two inner ground electrodes P ₁ and P _{2. If} the distance between the ground electrodes is a [m], the ground resistivity ρ [Ω · m] can be calculated as follows. First, assuming that a ground electrode is installed on a ground having a ground resistivity ρ, and a current I flows into the ground electrode, it is assumed that the current flows radially from the ground electrode to the surrounding ground.

      V = (ρI) / (2πr) (1-1)

Becomes In Figure ₁ C 3, P _1, P _2, if the electrodes of the C ₂ is provided, the potential difference V ₁ generated between electrodes P ₁ and P ₂ by a current flowing into C ₁ is

V ₁ = (ρI) / (2πa)-(ρI) / (4πa) = (ρI) / (4πa) (1-2)

to be. Similarly, the potential difference V ₂ by a current flowing to the C ₂ occurring between electrodes P ₁ and P ₂ are

V ₂ =-(ρI) / (4πa) + (ρI) / (2πa) = (ρI) / (4πa) (1-3)

to be. Since the potential difference V generated between the electrodes P ₁ and P ₂ can be obtained by the sum of V ₁ and V ₂ , equations (1-2) and (1-3)

V = V ₁ + V ₂ = (ρI) / (2πa) (1-4)

to be. Therefore, if we find ρ from equation (1-4),

   ρ = 2πa V / I (1-5)

Thus, the earth resistivity ρ can be obtained.

According to the above equation, when calculating ρ, the distance a between electrodes must be much larger than the depth to which the electrodes are buried. In other words, the conditions for approximating the shape of the electrode to hemispherical shape should be satisfied.

  In the conventional earth resistance analysis by the earth resistivity, since the earth is assumed to be a simple resistor, there is a problem in analyzing the actual earth property as shown in FIG. 1. In addition, with the recent development and spread of various electronic / communication devices, the frequency band of the ground current flowing into the grounding system has been diversified, and it is necessary to analyze the ground-high impedance for the fault current having a fast rise time such as a surge.

Accordingly, an object of the present invention is to provide an earth intrinsic impedance measuring apparatus using a variable frequency that can reduce the error of the earth intrinsic impedance measurement by applying a high measurement current.

Another object of the present invention is to provide an earth intrinsic impedance measurement apparatus using a variable frequency that can reduce the error of the earth intrinsic impedance measurement due to the magnetic coupling generated in the overlapping loop of the current auxiliary electrode and the potential auxiliary electrode.

Another technical problem to be achieved by the present invention is to provide an earth intrinsic impedance measurement apparatus using a variable frequency capable of analyzing the earth intrinsic impedance including not only the resistance component but also the capacitance component.

In order to achieve the above technical problem, the present invention provides a measurement current generation unit for generating a measurement current of a variable frequency; First and second auxiliary electrodes for applying the measurement current to the ground; A current-applying wire connecting the first and second auxiliary electrodes; A measurement current detector for detecting a measurement current from the current-applied laid wire; Third and fourth auxiliary electrodes positioned between straight lines formed by the first and second auxiliary electrodes and configured to measure the ground potential by the measurement current; A potential detecting installation wire connected to the third and fourth auxiliary electrodes in a straight line; A potential rise detector configured to measure a ground potential from the potential detection laid wire by the applied measurement current; An insulation separator which insulates the signal measured by the measurement current detector and the potential rise detector; A grounding impedance measurement unit configured to obtain a ground impedance by receiving the measurement current and the ground potential detected by the measurement current detector and the potential rise detection unit through the insulation separator; The auxiliary electrodes are connected to each other in the form of needles (d), and the wires at positions parallel to the lines formed by the first and second auxiliary electrodes are separated by a distance between the first and third auxiliary electrodes. It is characterized in that it is vertically intersecting the midpoint of the potential detection installation wire and connected in the shape of a needle.
DETAILED DESCRIPTION Hereinafter, a detailed description of a preferred embodiment of the present invention will be described with reference to the accompanying drawings. In the following description of the present invention, detailed descriptions of well-known functions or configurations will be omitted if it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention.

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4 is a diagram showing the configuration of a high ground impedance measurement apparatus according to the present invention.

Work of the present invention Examples of the high-impedance impedance measuring apparatus includes auxiliary electrodes 11, 12, 13, and 14, current-applied installation wires 20, voltage-measuring installation wires 30, measurement current generators 40, measurement currents, and potential rise detection units. 51 and 55, an insulation separator 60, and a ground high impedance measurement unit 300.

The measurement current is applied to the ground through the auxiliary electrode 11, and the current is fed back to the auxiliary electrode 12. The ground potential rise due to the measurement current is measured through the auxiliary electrodes 13 and 14.

FIG. 5A is a diagram illustrating a configuration of the inverter shown in FIG. 4.

The measurement current generator 40 includes an inverter 41 for applying a measurement current to the ground electrode to be measured and an inverter controller 43 for variably applying a square wave having a predetermined frequency. The inverter 41 for applying the measurement current is composed of two Insulated Gate Bipolar Transistor (IGBT) modules, a rectifier and a capacitor.

The inverter 41 has a capacity capable of applying an output current of 0.1A to 10A. The variable current when using a constant load uses a method of varying the voltage. The output current is determined by the ratio of the applied voltage and the load impedance, and the voltage is varied using the slidax.

FIG. 5B is a diagram illustrating a configuration of the inverter controller shown in FIG. 4.

The inverter controller (Voltage-Frequency Converter circuit) 43 has the capability to variably apply a square wave having a frequency of 10 Hz to 500 kHz using the AD654 Chip of Analog Device. The maximum oscillation frequency is determined by the oscillation capacitor Ct, and the potential Et varies when the variable resistor VR1 is varied, so that the frequency of the IGBT drive signal can be adjusted within the maximum oscillation frequency range.

In order to detect the measurement current I _T , a measurement current detector (CT) 51 is connected to the current-applied installation wire 20 on the ground. In addition, a potential rise detection unit (voltage probe) 55 is provided on the potential detection installation wire 30 on the ground for measuring the rise of the ground potential.

Fig. 6 is a diagram showing the shapes of the current-applied laid wires and the potential detecting laid wires. This is how wires are laid on the ground. The current-applied laid wire 20 is connected in a shape of a needle having a current-applied auxiliary electrode 11 and a current feedback auxiliary electrode 12 as both ends. The potential detecting installation wire 30 is connected to two potential measuring auxiliary electrodes 13 and 14 in a straight line.

As shown in FIG. 6, the distance between each auxiliary electrode 11, 13, 14, 12 is a and lies in a straight line. The current-applied laid wire 20 extends in a straight line by a distance (possibly a distance or more) perpendicular to the line formed by the auxiliary electrodes 11, 13, 14, and 12 in the auxiliary electrode 11. The auxiliary electrodes 11, 13, 14, and 12 are extended in parallel with each other, and then bent to cross vertically at the center point between the potential measuring auxiliary electrodes 13 and 14, and extend in the opposite direction. The auxiliary electrodes 11, 13, 14, and 12 are bent 90 degrees again at a point away from the line formed by the distance a. The folded current applying wire 20 is extended in parallel with the line formed by the auxiliary electrodes 11, 13, 14, and 12, and is then bent at 90 degrees to be connected to the auxiliary electrode 12.

6 shows a preferred example in which the current-applied laying wire 20 and the potential detecting laying wire 30 cross each other vertically. Therefore, the wires cross each other vertically even though they have various shapes such as a curved line as well as a needle shape.

When measuring the earth resistivity, a is analyzed by the earth resistivity change graph for a while changing within an appropriate range according to the soil structure. Therefore, as a increases, the distance between measuring lines increases accordingly.

In this way, the influence of the magnetic coupling between the current-applied laid wire 20 and the potential detecting laid wire 30 can be eliminated. In other words, by applying a loop that crosses at right angles, a part of the magnetic flux to be bridged is canceled, thereby greatly reducing an error that occurs largely during high frequency measurement.

7A and 7B show measurement waveforms of ground potentials depending on the presence of a linkage flux. FIG. 7A shows the waveform of the ground potential measured when the linkage flux is present, and FIG. 7B shows the waveform of the ground potential measured when the linkage flux is canceled. It can be seen that the waveform shown in FIG. 7B has a significantly reduced error component compared to the waveform shown in FIG. 7A.

 An insulation separator 60 is used to insulate the signal detected by the measurement current detector (CT) 51 and the potential rise detector (voltage probe) 55. The insulation separator 60 insulates the measurement current generator 40 and the high impedance measuring unit 300 to improve the accuracy of the measurement.

The measurement current I _T detected by the measurement current detector 51 and the ground potential detected by the potential rise detector 55 are applied to the high impedance measurement unit through the insulation separator 60. Is sent to 300.

The high high impedance measurement unit 300 includes an A / D converter 310, a filter unit 320, and a high high impedance analysis unit 330.

8 is a diagram illustrating the configuration of the high ground impedance measuring unit 300.

The waveform of the measurement current I _T and the waveform of the ground potential V _EP applied to the A / D converter 310 are converted into digital signals, and then digital band pass filters 322 and 324 through different channels. Is applied.

9A and 9B illustrate an applied current and a ground potential waveform of the A / D converter 310. The waveform shown in FIG. 8A shows the applied current displayed by the A / D converter 310, and the waveform shown in FIG. 9B shows the measured potential displayed by the A / D converter 310.

The filter unit 320 using the software filter algorithm devised in the present invention filters the digitally converted signal to the detected frequency. The software filter algorithm refers to an algorithm in which the low pass and high pass cutoff frequencies of the bandpass filter are set constant from the measured frequency of the applied current. In this case, since the frequency is variable, the cutoff frequency is reset to have a certain selectivity (preferably selectivity = 2) according to the variable frequency.

A band-pass filter (322, 324) is a low-side cutoff frequency (f _CL) and a high-side cutoff frequency (f _CH), the input and Butterworth filters receive, the low-side cutoff frequency (f _CL) and a high-side cutoff frequency (f _CH ) Is calculated by the filter driver 328 using the output frequency f of the A / D converter 310 detected by the frequency detector 326. The filter driver 328 drives the band pass filters 322 and 324 using the calculated cutoff frequencies f _CL and f _CH . In this case, the selectivity of the band pass filters 322 and 324 is preferably 2. At this time, the waveforms of the current and the voltage which are output after being filtered by the band pass filters 322 and 324 respectively become sine waves.

10A and 10B are diagrams illustrating a measurement current and a ground potential waveform output from the filter unit 320. The waveform shown in FIG. 10A shows the measured measurement current for application displayed by the filter unit 320, and the waveform shown in FIG. 10B shows the ground potential displayed by the filter unit 320.

The phase detector 331 detects the phase θ ₁ of the current sine wave output from the band pass filter 322, and the phase detector 332 receives the phase θ ₂ of the voltage sine wave output from the band pass filter 324. Is detected. The subtractor 333 obtains the difference θ between the detected two phases and outputs the difference θ to the phase indicator 338, which displays the phase on the screen as shown in FIG. 11B. Fig. 11B is a diagram showing the phase of the ground high impedance. Phase changes as the frequency changes.

The waveform magnitude detector 334 detects the magnitude (Amplitude and RMS) of the current sine wave output from the bandpass filter 322, and the waveform magnitude detector 335 measures the magnitude of the voltage sine wave (output) from the bandpass filter 324. Amplitude, rms) is detected. The ground high impedance calculator 336 divides the magnitude of the detected voltage sine wave by the size of the current sine wave to obtain the ground impedance Z, and outputs the ground impedance Z to the ground high impedance calculator 336-2. The ground high impedance calculator 336-2 calculates the ground resistivity ρ by using the distance a between the auxiliary electrodes 11 and 13 and the ground impedance Z received from the electrode space input unit 336-1. . The impedance indicator 339 displays the calculated frequency characteristic graph of the earth resistivity on a screen as shown in FIG. 11A. 11A is a diagram showing the earth resistivity. Earth resistivity changes as the frequency changes.

The earth resistance / reactance calculator 337 uses the phase difference (θ) of the current and voltage calculated by the subtractor 333 and the earth resistivity (ρ) calculated by the high earth impedance calculator 336-2 to calculate the resistance component (R =). ρcosθ) and the reactance component (X = ρsinθ) are calculated and then output to the ground resistance / reactance indicator 340. The ground resistance / reactance indicator 340 separates the resistance component and the reactance component from the ground resistivity, respectively, and is represented graphically as shown in FIGS. 11C and 11D, and the phase change at this time is also represented graphically. 11C and 11D are diagrams showing the resistance component and reactance component of the earth resistivity, respectively. These change as the frequency changes.

In addition, since the high impedance measurement unit 300 of the present invention is made on a PC basis, the high impedance measurement unit 300 stores the result detected and analyzed by the high impedance measurement unit 300 in a hard disk (database) and remotely using a LAN or the like. It also allows remote monitoring.

12 is a flowchart illustrating a process of measuring earth intrinsic impedance using a variable frequency.

The measurement current having a variable frequency through the current-applying wire 20 is applied from the measurement current generator 40 to the ground through the two auxiliary electrodes 11 and 12 (step 710).

The measurement current is detected by the measurement current detector 51 (step 720).

The potential rise detection unit 55 measures the ground potential due to the applied measurement current from the potential detection installation wire 30 perpendicularly intersecting the current application installation wire 20 (step 730).

The measured current and the ground potential are separated from the insulation separator 60 (step 740).

The isolated measurement current and ground potential are converted by the A / D converter 310 into digital signals (step 750).

The converted measurement current and the ground potential are filtered by the filter unit 320 using the low cutoff frequency and the high cutoff frequency and output as a waveform (step 760).

The phase difference between the measured current and the ground potential is detected by the subtractor 333 (step 770).

The ground resistivity is calculated using the distance between the ground impedance and the first and third auxiliary electrodes 11 and 13 obtained by dividing the magnitude of the ground potential waveform by the magnitude of the measurement current waveform. Obtained (Step 780)

Earth resistance and earth reactance are calculated by the earth resistance / reactance calculator 337 using the phase difference and the earth resistivity (step 790).

As described above, according to the present invention, it is possible to measure the grounding high impedance combined with the capacitive component and the resistance component of the actual equivalent circuit, and can be used as an important basic data for designing and supplementing the grounding system to be installed in the future. .

According to the present invention, by applying a large measurement current of up to 10A, it is possible to minimize the error of the measurement of intrinsic impedance due to stray noise in a downtown area or near a power line. In other words, the general earth resistivity measuring device applies a current of several tens of mA, so the S / N ratio is small, which is likely to cause measurement error. In contrast, in the present invention, the applied current of several [A] improves the accuracy of the measurement due to the clear waveform of the potential rise.

In order to reduce the error of the measured value due to the magnetic coupling generated in the overlapping loop of the current auxiliary electrode and the potential auxiliary electrode which are generally used in the conventional measuring method, a loop crossing at right angles at a specific portion is applied. As a result, a part of the magnetic flux to be bridged is canceled to significantly reduce a large error in high frequency measurement.

In the equivalent circuit of the actual earth, not only the resistance component but also the capacitance component known in the art (the reactance component in FIG. 6D represents the capacitive and inductive components in the imaginary part of the impedance, and the capacitive characteristics can be confirmed by the phase graph in FIG. 6B). )do. In addition, the grounding system based on the existing Wenner four-electrode earth resistivity can reduce the safety and characteristics expected in the design due to the inductance caused by the long grounding conductor in the large-scale grounding system. By designing a grounding system based on the system, it can be a countermeasure against weaknesses in high frequency components that occur during actual operation.

The present invention can be used as an important data before observing the characteristics of the earth and installing the grounding system by observing the change of the earth's inherent impedance according to various land condition changes such as winter freezing or rainy weather during the summer.

Claims (6)

A measurement current generator for generating a measurement current having a variable frequency; First and second auxiliary electrodes for applying the measurement current to the ground; A current-applying wire connecting the first and second auxiliary electrodes; A measurement current detector for detecting a measurement current from the current-applied laid wire; Third and fourth auxiliary electrodes positioned between straight lines formed by the first and second auxiliary electrodes and configured to measure the ground potential by the measurement current; A potential detecting installation wire connected to the third and fourth auxiliary electrodes in a straight line; A potential rise detection unit configured to measure a ground potential by the applied measurement current from the potential detection laid wire; An insulation separator which insulates the signal measured by the measurement current detector and the potential rise detector; A grounding impedance measurement unit configured to obtain a ground impedance by receiving the measurement current and ground potential detected by the measurement current detector and the potential rise detector through the insulation separator; The current-applied laid wire connects the needles in the shape of needles with the first and second auxiliary electrodes at both ends, and between the wires parallel to the line formed by the first and second auxiliary electrodes. And a distance between the third auxiliary electrodes and vertically intersecting an intermediate point of the potential detecting installation wire, and connected in a needle shape to form a ground intrinsic impedance measurement device using a variable frequency current. The method of claim 1, wherein the high impedance measurement unit A ground resistance / reactance calculator for calculating a ground resistance component and a reactance component from the ground resistivity obtained by using the distance between the ground impedance and the first and third auxiliary electrodes. Measuring device. delete The method of claim 1, wherein the measurement current generating unit Earth-specific impedance measurement apparatus using a variable frequency, characterized in that it comprises an inverter for generating a measuring current that varies from 0.1A to 10A and an inverter controller for varying the frequency of the measured current from 10Hz to 500kHz. delete delete

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