CN109188088B - A kind of vertical demixing electric resistance of soil nonlinear characteristic test method - Google Patents

Abstract

A test method for non-linear characteristics of vertical layered soil resistance. The inner wall of the soil box of the test platform is provided with a temperature control device, and the left and right walls are provided with a left copper electrode and a right copper electrode; the output end of the impulse current generator is connected to the voltage divider The high-voltage end of the voltage divider is connected to the left copper electrode; the right copper electrode is connected to the ground terminal of the impulse current generator, and the ground terminal is connected to the grounding device; the current acquisition module is used to measure the flow through the left copper electrode and the right The current of the copper electrode; also includes the insulating partition, when the insulating partition is inserted into the soil box, the soil box is divided into two or more spaces from bottom to top. The test method includes steps such as filling the soil and setting the temperature, measuring the voltage and current of the soil sample at the current temperature, and evaluating the non-linear characteristics of the soil resistance. The invention can effectively simulate the working condition of vertical stratification of soil around the grounding system, and accurately evaluate the non-linear characteristics of vertical stratification soil resistance.

Description

A test method for non-linear characteristics of vertical layered soil resistance

technical field

The invention belongs to the field of power system grounding analysis, in particular to a test method for the non-linear characteristic of vertical layered soil resistance.

Background technique

When the transmission line tower is struck by lightning, due to the existence of the grounding resistance of the tower, a high potential will be generated on the tower body. Excessive potential will cause the tower to counterattack the transmission line, which will cause a short circuit of the transmission line and reduce the stability of the power system. reliability. The main function of the transmission line tower grounding device is to effectively discharge the lightning current into the ground when the tower top or the lightning protection line is struck by lightning, so the current flowing through the grounding device is mainly the lightning impulse current. Due to the large amplitude of the lightning current, it is easy to cause local breakdown of the soil around the grounding body, which increases the soil conductance and reduces the soil resistivity. In addition, when the electric field intensity generated by the scattered flow in the soil exceeds the critical breakdown field When it is strong, a spark discharge process similar to air breakdown will occur in the soil around the grounding body. Soil spark discharge will significantly reduce the potential of each point on the grounding body and the potential difference between points of the grounding body, and has a more obvious effect on reducing the potential of the transmission line tower top and the transient potential rise on the grounding network of the power generation and substation. It can be seen that the research on the lightning impulse characteristics of the transmission and distribution tower grounding device is of great significance to the establishment of an advanced and reliable transmission and distribution network and power supply system in the smart grid, and to improve the security and defense system of the power grid.

Since the grounding electrode of the transmission line tower is buried in the soil, its impact characteristics are closely related to the impact characteristics of the soil around the grounding body. At present, domestic research on the nonlinear characteristics of soil resistance mainly uses computer simulation to simulate the process of nonlinear characteristics of soil resistance and the phenomenon of spark discharge, while the nonlinear characteristics of soil resistance under impact currents are affected by many factors, such as: impact current Amplitude, soil composition and structure, soil density, water content, temperature, external electric field strength, etc. These factors make the impact characteristics of soil more complicated under the action of high-frequency and large impact currents, so the nonlinear characteristics of soil resistance are difficult to simulate. Accurate simulation. Therefore, in order to accurately analyze the nonlinear characteristics of soil resistance, it is urgent to establish an intelligent measurement and control device, which can consider the influence of temperature and vertical layering of soil, and has the test and analysis of nonlinear characteristics of vertical layering soil resistance at different temperatures, which can be used to input Safety assessment of power distribution systems.

Contents of the invention

The purpose of the invention is to provide a test method for the non-linear characteristic of vertical layered soil resistance.

The technical scheme that realizes the object of the present invention is as follows, comprises the following steps:

Step 1: Build a test platform for non-linear characteristics of vertical layered soil resistance, including a soil box; the inner wall of the soil box is provided with a temperature control device; the left wall of the soil box is provided with a left copper electrode, and the lateral movement of the left copper electrode is controlled The operating mechanism of the soil box; the right side wall of the soil box is also provided with a right copper electrode; the left copper electrode and the right copper electrode are both vertical and circular; The temperature sensor, the second temperature sensor, the third temperature sensor and the fourth temperature sensor also include an impulse current generator and a voltage divider;

Wherein: the first temperature sensor, the second temperature sensor, the third temperature sensor and the fourth temperature sensor are respectively connected to the input terminals of the temperature analyzer, and the output terminals of the temperature analyzer are respectively connected to the digital controller and the upper computer; the digital controller connected to the temperature control device;

The output end of the impulse current generator is connected to the high-voltage end of the voltage divider, and the high-voltage end of the voltage divider is connected to the left copper electrode through a high-voltage cable and cable joint; the right copper electrode is connected to the ground end of the impulse current generator through a wire, and the ground end Connect to the grounding device; the grounding terminal of the voltage divider is connected to the grounding device, the voltage measurement terminal of the voltage divider is connected to the host computer; the communication terminal of the current acquisition module is connected to the host computer, and the test terminal of the current acquisition module is connected to the wire;

It also includes more than one insulating partition, which can be horizontally inserted into or withdrawn from the soil box; when the insulating partition is inserted into the soil box, the soil box is divided into two or more spaces from bottom to top.

Step 2: Fill the soil and set the temperature: open the left panel of the soil box, and control the distance between the left copper electrode and the right copper electrode through the operating mechanism; according to the thickness ratio of the soil to be tested, layer the soil box with insulating partitions , fill the soil samples in sequence after layering; remove the insulating partitions to make the soil samples stick together; cover the left panel; monitor the temperature through the first temperature sensor, the second temperature sensor, the third temperature sensor and the fourth temperature sensor; Set the test temperature as T, if the measured temperature exceeds the allowable upper limit T _max of the error, the digital controller will enable the cooling mode of the temperature control device to cool down; if the temperature is lower than the allowable lower limit T _min of the error, the digital controller will enable the temperature control device to cool down Heating mode to heat up; control the temperature of the soil sample in the soil box within the allowable range of the test temperature T error;

Step 3: Measure the voltage and current of the soil sample at temperature T1: When the measurement temperature of the soil sample is stable within the allowable range of the test temperature T error, turn on the impulse current generator, and measure the left copper electrode and the right copper electrode through the voltage divider The voltage between them is transmitted to the host computer, and the current flowing through the left copper electrode and the right copper electrode is measured by the current acquisition module and transmitted to the host computer;

Step 4: Evaluate the nonlinear characteristics of soil resistance: obtain the full-time domain R(t) waveform curve of the impact resistance through the voltage and current obtained by the host computer, and extract R(t) _min , R(t) _max , and drop time Δt ₁ and the effective recovery time Δt ₂ , calculate the average decline rate k of the soil under the impact current,

In the formula, R(t) _min is the minimum resistance value in the R(t) waveform curve, R(t) _max is the maximum resistance value in the R(t) waveform curve, and t ₁ means that R(t) changes from the maximum value R(t) ) _max drops to the minimum value R(t) _min time interval;

Calculate the composite evaluation factor q ₁ of R(t) _min and k:

Calculate the compound evaluation factor q ₂ of R(t) _min and t ₁ :

Approximately calculate the minimum radius of curvature γ:

in,

In the formula, t _m ∈[t _a +1,t _b ), t _a is the time corresponding to R(t) _max , t _b is the time corresponding to R(t) _min , the above formula indicates that the calculation of R(t) waveform curve is decreasing In the period of time, from the time t _a + 1, every interval of 0.1 μs, calculate the radius of curvature at each time, so that the smallest radius of curvature can be calculated;

Calculate the correction factor k ₁ considering the temperature and the minimum curvature radius from the minimum curvature radius:

In the formula, T is the test temperature;

Calculate the judgment remainder:

q ₃ =0.03258log(0.26Δt ₁ +0.625Δt ₂ −41.3)

-0.0953log(R(t) _min +1.38)

In the formula, t ₂ represents the time when R(t) rises from R(t) _min to the effective recovery resistance R(t) _eff ; where R(t) _eff =R(t) _min +0.8(R(t) _max - R(t) _min ),R(t) _eff means that R(t) gradually recovers from the minimum resistance value R(t) _min , when the recovery amount is 80%, the maximum drop difference (R(t) _max -R(t) _min ) corresponding to the resistance value;

Based on the above calculations, the soil nonlinear characteristic evaluation factor of the soil under the impact current and temperature is:

q=k ₁ (q ₁ +q ₂ )+q ₃

According to the value range of q, the nonlinear characteristic of resistance is characterized;

Step 5: Non-linear characteristic test of soil resistance at different temperatures: According to the test requirements, set different temperatures, and repeat the third and fourth steps to evaluate the non-linear characteristic of soil resistance in vertical stratification at different temperatures.

The beneficial effect of the present invention is that,

1) The soil is vertically stratified, and the resistance nonlinear characteristics of the vertically stratified soil are measured, which can effectively simulate the vertical stratification of the soil around the grounding system;

2) It can effectively obtain the waveform curve of the full-time variation of the vertical layered soil resistance under the action of the impact current, and the use of the evaluation factor can accurately evaluate the nonlinear characteristics of the vertical layered soil resistance;

3) The main operation and control are completed by the upper computer, combined with the digital controller and temperature control device to realize the precise control of the vertical layered soil temperature, which can effectively measure the non-linear characteristics of the vertically layered soil resistance at different temperatures;

4) The experimental device is easy to operate, safe and reliable, and has universal applicability to vertical multi-layer soil tests.

Description of drawings

Fig. 1 is the overall structural representation of the present invention;

Fig. 2 is the structural representation of soil box of the present invention;

Fig. 3 is the flow chart of test method in the invention;

Figure 4 is an example of the full-time variation waveform of the impact resistance reflecting the dynamic resistance characteristics of the soil.

Detailed ways

The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings. Include the following steps:

Step 1: Build a test platform for the nonlinear characteristics of vertical layered soil resistance

As Fig. 1 and Fig. 2, test platform of the present invention comprises: soil box (06); The inwall of soil box (06) is provided with temperature control device (08); Soil box (06) left side wall is provided with left copper electrode ( 05), and the operating mechanism (04) for controlling the lateral movement of the left copper electrode (05); the right copper electrode (07) is also arranged on the right side wall of the soil box (06); the left copper electrode (05) and the right copper electrode (07 ) are vertical discs; the upper left, upper right, lower left and lower right of the soil box are respectively provided with a first temperature sensor (01a), a second temperature sensor (01b), a third temperature sensor (01c) and The fourth temperature sensor (01d) also includes an impulse current generator (12) and a voltage divider (13).

Wherein: the first temperature sensor (01a), the second temperature sensor (01b), the third temperature sensor (01c) and the fourth temperature sensor (01d) are respectively connected to the input end of the temperature analyzer (14), and the temperature analyzer ( The output terminals of 14) are respectively connected to the digital controller (15) and the host computer (18); the digital controller (15) is connected to the temperature control device (08); the output terminal of the impulse current generator (12) is connected to the voltage divider The high voltage end of (13), the high voltage end of voltage divider (13) is connected to left copper electrode (05) by high voltage cable (19) and cable joint (03); Right copper electrode (07) is connected to by wire (20) The grounding terminal of the impulse current generator (12), the grounding terminal is connected to the grounding device (11); the grounding terminal of the voltage divider (13) is connected to the grounding device (11), and the voltage measuring terminal of the voltage divider (13) is connected to The host computer (18); the communication terminal of the current acquisition module (17) is connected to the host computer (18), and the test terminal of the current acquisition module (17) is connected to the wire (20); The plate (09) can be inserted into or pulled out of the soil box (06) horizontally; when the insulating partition (09) is inserted into the soil box (06), the soil box (06) is divided into two or more spaces from bottom to top, and the number of layers is the finite number of layers of the actual soil, if the actual soil is divided into 3 layers, and each layer has a finite thickness, then the thickness ratio of the soil can be obtained, and the insulating separator (09) divides the soil box (06 ) are separated according to the thickness ratio, and after the soil samples are filled, the insulating partition (09) is pulled out, and each layer of soil is closely attached.

Step 2: Fill the soil and set the temperature

Open the upper panel of the soil box (06), and control the distance between the left copper electrode (05) and the right copper electrode (07) through the operating mechanism (04); The box (06) is layered, and the soil samples are filled in sequence after layering; the insulating partition (09) is removed to make the soil samples stick together.

If the soil in a certain area is vertically stratified, the thickness of the first layer of soil is 7m, the soil resistivity is 200Ω·m, the thickness of the second layer of soil is 20m, the soil resistivity is 1000Ω·m, and the third layer The thickness of the soil is 39m, the soil resistivity is 500Ω·m, and the soil area beyond the third layer of soil is infinite thickness; then the vertical layer thickness ratio is 7:20:39, and the distance between the upper and lower walls of the soil box is s, Then the distance is divided according to the thickness ratio, layered with insulating partitions (09), and soil samples are put in. The soil resistivity of each layer of the soil sample is the same as that of the actual soil layer.

Cover the left panel; monitor the temperature through the first temperature sensor (01a), the second temperature sensor (01b), the third temperature sensor (01c) and the fourth temperature sensor (01d); set the test temperature to T1, and the temperature analyzer The average temperature measured by the four sensors is calculated, and the allowable error of the temperature test is plus or minus ±0.5°C. If the average temperature exceeds the allowable upper limit T _max of the error, the digital controller (15) enables the cooling mode of the temperature control device (08) Cool down; if the average temperature is lower than the allowable lower limit T _min of the error, then the digital controller (15) enables the heating mode of the temperature control device (08) to heat up; control the temperature of the soil sample in the soil box (06) at the test temperature T1 The error is within the allowable range (T _min ~ T _max ).

Step 3: Measure the voltage and current of the soil sample at temperature T1

When the soil sample measurement temperature was stabilized within the allowable range of test temperature T1 error, the impulse current generator (12) was turned on, and the voltage between the left copper electrode (05) and the right copper electrode (07) was measured through the voltage divider (13) and It is transmitted to the host computer (18), and the current flowing through the wire (20) is measured by the current acquisition module (17) and transmitted to the host computer (18).

Step 4: Evaluate Soil Resistive Nonlinearity

Through the voltage and current obtained by the host computer, the full-time domain R(t) waveform curve of the impact resistance is obtained, and the minimum resistance value R(t) _min (unit is Ω), and the maximum resistance value R(t) _max (unit is Ω), falling time Δt ₁ (unit of measurement is μs) and effective recovery time Δt ₂ (unit of measurement is μs), to calculate the average rate of decline k of the soil under the impact current:

In the formula, R(t) _min is the minimum resistance value in the R(t) waveform curve, R(t) _max is the maximum resistance value in the R(t) waveform curve, and Δt ₁ means that R(t) changes from the maximum value R(t) ) _max drops to the minimum value R(t) _min time interval;

Calculate the composite evaluation factor q ₁ of R(t) _min and k:

Calculate the compound evaluation factor q ₂ of R(t) _min and t ₁ :

Approximately calculate the minimum radius of curvature γ:

in,

In the formula, t _m ∈[t _a +1,t _b ), t _a is the time corresponding to R(t) _max , t _b is the time corresponding to R(t) _min , the above formula indicates that the calculation of R(t) waveform curve is decreasing In the period of time, from the time t _a + 1, every interval of 0.1 μs, calculate the radius of curvature at each time, so that the smallest radius of curvature can be calculated;

Calculate the correction factor k ₁ considering the temperature and the minimum curvature radius from the minimum curvature radius:

Calculate the judgment remainder:

q ₃ =0.3258log(0.26Δt ₁ +0.625Δt ₂ −41.3)

-0.0953log(R(t) _min +1.38)

In the formula, t ₂ represents the time when R(t) rises from R(t) _min to the effective recovery resistance R(t) _eff ; where R(t) _eff =R(t) _min +0.8(R(t) _max - R(t) _min ),R(t) _eff means that R(t) gradually recovers from the minimum resistance value R(t) _min , when the recovery amount is 80%, the maximum drop difference (R(t) _max -R(t) _min ) corresponding to the resistance value;

Based on the above calculations, the evaluation factor of the resistance nonlinear characteristics of the soil under the impact current and temperature is:

q=k ₁ (q ₁ +q ₂ )+q ₃

According to the value range of q, the nonlinear characteristic of resistor is characterized.

Step 5: Non-linear characteristic test of soil resistance at different temperatures

According to the test requirements, set different temperatures, repeat the test, and conduct the nonlinear characteristic test of vertical layered soil resistance at different temperatures. If also need to test T2, the non-linear characteristic of soil resistance of vertical layering under T3, then after T1 test finishes, after interval period of time, the setting temperature of setting temperature analyzer (14) is T2, repeats the 3rd the 4th step , to test the nonlinear characteristics of soil resistance at T2 temperature, and after a period of time, test the nonlinear characteristics of soil resistance at T3 temperature.

Claims (1)

1. a vertical layered soil resistance nonlinear characteristic test method, is characterized in that, comprises the following steps: Step 1: Build a test platform for nonlinear characteristics of vertical layered soil resistance, including Soil box (06); the inner wall of the soil box (06) is provided with a temperature control device (08); the left side wall of the soil box (06) is provided with a left copper electrode (05), and a device for controlling the lateral movement of the left copper electrode (05) Manipulating mechanism (04); soil box (06) right side wall is also provided with right copper electrode (07); Left copper electrode (05) and right copper electrode (07) are vertical circular; left upper part of soil box, The upper right part, the lower left part and the lower right part are respectively provided with a first temperature sensor (01a), a second temperature sensor (01b), a third temperature sensor (01c) and a fourth temperature sensor (01d), and also includes an impulse current generator (12) and voltage divider (13); Wherein: the first temperature sensor (01a), the second temperature sensor (01b), the third temperature sensor (01c) and the fourth temperature sensor (01d) are respectively connected to the input end of the temperature analyzer (14), and the temperature analyzer ( 14) the output ends are respectively connected to the digital controller (15) and the host computer (18); the digital controller (15) is connected to the temperature control device (08); The output end of the impulse current generator (12) is connected to the high voltage end of the voltage divider (13), and the high voltage end of the voltage divider (13) is connected to the left copper electrode (05) through the high voltage cable (19) and the cable connector (03) ; The right copper electrode (07) is connected to the ground terminal of the impulse current generator (12) by a lead (20), and the ground terminal is connected to the grounding device (11); the ground terminal of the voltage divider (13) is grounded, and its voltage measurement terminal Connect to the upper computer (18); the communication end of the current acquisition module (17) is connected to the upper computer (18), and the test end of the current acquisition module (17) is connected to the wire (20) for measuring the flow through the left copper electrode (05) and the electric current of the right copper electrode (07); also include more than one insulation partition (09), the insulation partition (09) can be inserted horizontally or extract the soil box (06); when the insulation partition (09) inserts the soil box (06 ), divide the soil box (06) into two or more spaces from bottom to top; The second step: soil filling and temperature setting: open the left panel of the soil box (06), and control the distance between the left copper electrode (05) and the right copper electrode (07) through the operating mechanism (04); Thickness ratio, use the insulating partition (09) to layer the soil box (06) and fill it with soil samples; remove the insulating partition (09) to make the soil samples stick together; cover the left panel; pass the first temperature sensor ( 01a), the second temperature sensor (01b), the third temperature sensor (01c) and the fourth temperature sensor (01d) monitor the temperature; set the test temperature as T, if the measured temperature exceeds the allowable upper limit T _max of the error, the digital controller (15) Enable the cooling mode of the temperature control device (08) to cool down; if the temperature is lower than the allowable lower limit T _min of the error, the digital controller (15) enables the temperature rise mode of the temperature control device (08) to heat up; control the soil box ( 06) The temperature of the soil sample is within the allowable range of the test temperature T error; Step 3: Measure the voltage and current of the soil sample at temperature T: when the measured temperature of the soil sample is stable within the allowable range of the test temperature T error, the impulse current generator (12) is turned on, and the left voltage is measured through the voltage divider (13). The voltage between the copper electrode (05) and the right copper electrode (07) is transmitted to the host computer (18), and the current flowing through the wire (20) is measured by the current acquisition module (17) and transmitted to the host computer (18); Step 4: Evaluate the nonlinear characteristics of soil resistance: obtain the full-time domain R(t) waveform curve of the impact resistance through the voltage and current obtained by the host computer, and extract R(t) _min , R(t) _max , and drop time Δt ₁ and the effective recovery time Δt ₂ , calculate the average decline rate k of the soil under the impact current, In the formula, R(t) _min is the minimum resistance value in the R(t) waveform curve, R(t) _max is the maximum resistance value in the R(t) waveform curve, and Δt ₁ means that R(t) changes from the maximum value R(t) ) _max drops to the minimum value R(t) _min time interval; Calculate the composite evaluation factor q ₁ of R(t) _min and k: Calculate the composite evaluation factor q ₂ of R(t) _min and Δt ₁ : Approximately calculate the minimum radius of curvature γ: in, In the formula, t _m ∈ [t _a +1, tb), t _a is the time corresponding to R(t) _max , t _b is the time corresponding to R(t) _m in, the above formula shows that the calculation of R(t) waveform curve is decreasing In the period of time, from the time t _a + 1, every interval of 0.1 μs, calculate the radius of curvature at each time, so that the smallest radius of curvature can be calculated; Calculate the correction factor k ₁ considering the temperature and the minimum curvature radius from the minimum curvature radius: In the formula, T is the test temperature; Calculate the judgment remainder: q ₃ =0.03258log(0.26Δt ₁ +0.625Δt ₂ −41.3) -0.0953log(R(t) _min +1.38) In the formula, t ₂ represents the time when R(t) rises from R(t) _min to the effective recovery resistance R(t) _eff ; where R(t) _eff =R(t) _min +0.8(R(t) _max - R(t) _min ),R(t) _eff means that R(t) gradually recovers from the minimum resistance value R(t) _min , when the recovery amount is 80%, the maximum drop difference (R(t) _max -R(t) _min ) corresponding to the resistance value; Based on the above calculations, the soil nonlinear characteristic evaluation factor of the soil under the impact current and temperature is: q=k ₁ (q ₁ +q ₂ )+q ₃ According to the value range of q, the nonlinear characteristic of resistance is characterized; Step 5: Non-linear characteristic test of soil resistance at different temperatures: According to the test requirements, set different temperatures, and repeat the third and fourth steps to evaluate the non-linear characteristic of soil resistance in vertical stratification at different temperatures.