CN110068735B - Method for measuring and calculating contact resistance between grounding body and soil - Google Patents
Method for measuring and calculating contact resistance between grounding body and soil Download PDFInfo
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- CN110068735B CN110068735B CN201910068292.5A CN201910068292A CN110068735B CN 110068735 B CN110068735 B CN 110068735B CN 201910068292 A CN201910068292 A CN 201910068292A CN 110068735 B CN110068735 B CN 110068735B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/20—Measuring earth resistance; Measuring contact resistance, e.g. of earth connections, e.g. plates
- G01R27/205—Measuring contact resistance of connections, e.g. of earth connections
Abstract
The invention discloses a method for measuring and calculating contact resistance between a grounding body and soil, which comprises the following steps: firstly, placing a grounding body in a test device, filling simulated soil, and connecting a test circuit to form a first test device; measuring the total resistance of a loop in the first testing device and the soil resistance in the first testing device, and calculating the contact resistance of the aluminum plate and the soil; calculating the contact resistance of the aluminum plate and the soil in unit area in the first test device; measuring the total resistance of a loop in the second testing device, substituting the contact resistance of the aluminum plate and the soil in unit area into a thermal power equivalent formula to calculate the contact resistance of the aluminum plate and the soil, obtaining the soil resistance in the second testing device, and calculating the contact resistance of the grounding body and the soil; and calculating the unit area contact resistance of the grounding body and the soil and the equivalent coating resistivity of the contact resistance of the grounding body and the soil. The invention realizes the purpose of measuring the contact resistance of the grounding body and the soil.
Description
Technical Field
The invention belongs to the technical field of grounding resistance testing equipment, and particularly relates to a method for measuring and calculating the contact resistance between a grounding body and soil.
Background
The operation experience of the power system shows that lightning strike is one of the main reasons for tripping the power transmission line, national power grid companies have listed lightning protection as the first of six-protection of the power transmission line, and as the voltage level and the transmission capacity of the power transmission line are continuously improved, higher requirements are put forward on the lightning resistance level of the line.
After the grounding grid is laid, the construction unit usually adopts a backfill tamping mode to improve the joint degree between the grounding body and the soil, but because the elastic modulus of the metal grounding material is higher and the soil is in an amorphous loose form, the contact between the grounding body and the soil is point contact rather than complete contact, which causes the existence of contact resistance. When the soil is acted by external forces such as frost heaving, rheology, settlement and the like, the air gap between the grounding body and the soil is increased, and the most serious condition is that the grounding body is separated from the soil in a large area. Generally, the grounding resistance of a grounding grid mainly includes the body resistance of the grounding grid, the contact resistance between the grounding grid and the soil, and the current spreading resistance of the soil resistance, so that when the air gap between the grounding grid and the soil is increased, the contact resistance between the grounding grid and the soil is increased, and in addition, the contact resistance is also increased due to the corrosion of a metal grounding material in the soil. Therefore, the phenomenon of 'no connection' of the grounding cannot be avoided in the power system, and the increase of the grounding resistance is undoubtedly caused.
The contact resistance between the grounding body and the soil is influenced by the surface characteristics of the grounding body, the soil components, the compactness, the humidity degree and the like, and the dispersibility is large and difficult to estimate. In actual engineering, the design of the grounding grid by adopting grounding design software is based on ideal contact, and the influence of contact resistance is not considered, so that the margin is lack of accurate estimation, which is one of main reasons that the grounding resistance value measured after actual construction is greater than the software design value, and the construction can possibly hardly meet the requirement of the design standard, and the situation is particularly obvious in special soil areas (such as rock areas, frozen soil areas and the like).
therefore, in order to reduce the lightning trip-out rate of the power transmission line tower, design the grounding grid based on the contact resistance correction, accurately estimate the contact resistance margin, and improve the design level of the grounding grid, a method for accurately measuring and calculating the contact resistance between the grounding body and the soil is needed.
disclosure of Invention
the technical problem solved by the invention is as follows: the method for measuring and calculating the contact resistance between the grounding body and the soil is provided to solve the technical problems in the prior art.
The technical scheme adopted by the invention is as follows: a method for measuring and calculating the contact resistance of a grounding body and soil comprises the following steps:
The method comprises the following steps: two aluminum plates and a grounding body are respectively arranged on two sides and the middle part of the organic glass box and filled with simulated soil, and the two aluminum plates are connected with a current meter and a voltmeter and an alternating current source through insulated copper wires to form a first test device;
Step two: measuring total resistance R of loop of test device I1：
In the formula, R1Is the total loop resistance, in Ω; u shape1Is the voltage between the aluminum plates, in units of V; i is1Is the total current flowing through the loop, in units A; r11The contact resistance of the aluminum plate and the soil is expressed by omega; ra1Is the soil resistance, unit omega;
Obtaining contact resistance R of the aluminum plate and soil by the formula (1)11Comprises the following steps:
The current value measured in the test is loaded on the upper surface of the left aluminum plate, and the right surface of the right aluminum plate is taken as a zero potential reference surface, so that the soil resistance Ra1the values of (a) are obtained from the thermal power equivalent:
In the formula I1Is the total current flowing through the loop, in units A; ra1is the soil resistance, unit omega; wiThermal power for the ith soil cell (values can be extracted in ANSYS), in units J;
R is obtained by the formulae (2) and (3)11And Ra1And then, uniformly splitting the left aluminum plate close to the 1mm thick soil into a plurality of units, wherein each unit is a cube with the side length of 1mm, so as to extract the current density j of each unit1iThe remaining part of the soil is divided into sparse units relative to the units of the soil adjacent to the left aluminum plate;
Equivalently calculating the contact resistance R of the aluminum plate and the soil in unit area according to the thermal power01：
Thus:
In the formula i1iThe current flowing out of each unit on the contact surface of the aluminum plate is unit A; j is a function of1iThe current density of each unit on the surface of the aluminum plate is in A/m2；R01contact resistance per unit area of aluminum plate, unit omega m2；S1iIs the area of each unit of the aluminum plate, and the unit m2in the calculation, the average value calculated by the three groups of measured values is used as the contact resistance value of the aluminum plate and the soil in unit area;
Step three: changing the line connection mode of the first test device, connecting the ammeter, the voltmeter and the alternating current source with the grounding body and the single-side aluminum plate or the double-side aluminum plate to form a second test device, and measuring the total loop resistance R of the second test device2：
In the formula, R2To measure the total resistance of the loop, in Ω; u shape2Voltage of the grounding body and the aluminum plate is measured in unit V; i is2is the total current flowing through the loop, in units A; r22The total contact resistance between the grounding body and the soil is in unit omega; r21The contact resistance of the aluminum plate and the soil is expressed by omega; ra2Is the soil resistance, unit omega;
The current value measured in the upper surface loading test of the grounding body takes the right aluminum plate or the aluminum plates at the two sides as a zero potential reference surface, and the soil resistance Ra2The values of (d) are also derived from the thermal power equivalent:
In the formula, WiThermal power for the ith soil cell, unit J;
Contact resistance R of aluminum plate and soil21Calculated from the following formula:
In the formula i2ithe current flowing out of the ith cell of the aluminum plate is unit A; j is a function of2iThe current density of each unit on the surface of the aluminum plate is in A/m2；R01The contact resistance of the aluminum plate and the soil in unit area is omega; s2iIs the area of the ith aluminum plate cell in m2；
So the contact resistance R of the grounding body and the soil22Comprises the following steps:
R22＝R2-Ra2-R21 (9)
To obtain R22then, uniformly dividing soil with the thickness of 1mm outside the ground body into units, and extracting the current density j of each unit3i；
Contact resistance R of unit area between grounding body and soil02The thermal power equivalent yields:
thus:
In the formula i3iAnd j3iRespectively the current and the current density flowing out of the ith cell on the surface of the grounding body; r0Contact resistance per unit area of the grounding body, in omega m2；S3iThe area of the ith cell of the grounding body in m2Contact resistance per unit area R0Equivalent to a conductivity of ρ0Coating of (2):
In the formula, ρ0The equivalent coating resistivity, in Ω · m; r0To connect toContact resistance per unit area of the ground body, unit omega m2；d0The equivalent coating thickness (taking the soil particle size when the soil is uniform and taking the average particle size when the soil is not uniform) in m; the average value calculated by the three groups of measured values is used as the contact resistance value of the grounding body and the soil in unit area in the calculation.
Preferably, the simulated soil is prepared according to different soil types and different particle size combinations.
Preferably, above-mentioned test device one includes upper end open-ended organic glass box, aluminum plate and grounding body and alternating current source, aluminum plate adopts two, install two inside walls departments about the organic glass box respectively, it has the soil horizon to fill in the organic glass box, the vertical soil horizon middle part of pegging graft of grounding body, alternating current source one end is through insulating copper line connection ampere meter, the ampere meter other end is connected in left aluminum plate top, the aluminum plate on right side is through insulating copper line connection at the alternating current source other end, there is the voltmeter through insulating copper line connection between two aluminum plates.
Two testing device include upper end open-ended organic glass box, aluminum plate and grounding body and alternating current source, aluminum plate adopts two, install two inside walls departments about the organic glass box respectively, it has the soil horizon to fill in the organic glass box, the vertical soil horizon middle part of pegging graft of grounding body, alternating current source one end is through insulating copper line connection ampere meter, the ampere meter other end is connected on grounding body top, two aluminum plates all are through insulating copper line connection at the alternating current source other end, there is the voltmeter grounding body and one of them aluminum plate within a definite time through insulating copper line connection.
preferably, the upper end of the grounding body is connected with the insulated copper wire through a metal hoop.
Preferably, the grounding body comprises round steel and graphite, and the diameter of the grounding body is 10 mm-30 mm.
Preferably, the aluminum plate and the organic glass box are equal in side face size and are adhered through insulating glue.
Preferably, the bottom of the organic glass box is provided with a blind hole, and the lower end of the grounding body is inserted into the blind hole.
The invention has the beneficial effects that: compared with the prior art, the invention has the following effects:
(1) According to the invention, by establishing a test device, measuring the resistivity of the soil in the device and the overall resistance of the device, and utilizing a finite element analysis method to calculate the soil resistance, the contact resistance of the aluminum plate and the soil in unit area, and the contact resistance of the grounding body and the soil in unit area, the purpose of measuring the contact resistance of the grounding body and the soil is realized; the method is used in the technical field of electric power lightning protection grounding, and after the contact resistance of a grounding body and soil is equivalent to a coating resistance through a finite element analysis method, the influence of the contact resistance of the grounding body and the soil on power frequency grounding resistance and impact grounding resistance can be further analyzed, and certain reference can be provided for the design work of a design department;
(2) The testing device is suitable for indoor establishment of the testing device to measure the contact resistance of the grounding body and the soil, the testing device can measure the grounding resistance of the grounding body made of the grounding material, the structure is simple, the operation is convenient, the testing is easy, different soil and grounding body materials can be conveniently replaced on the soil layer, the testing flexibility is good, the testing range is wide, and the cost of the testing device made of the grounding material and the contact resistance of the soil is greatly reduced.
drawings
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a schematic structural view of the test apparatus;
FIG. 3 is a schematic diagram of a connection of the test apparatus;
FIG. 4 is a schematic top view of a connection of the assay device;
FIG. 5 is a schematic diagram of a measurement of the test apparatus;
FIG. 6 is an equivalent circuit diagram of the test apparatus;
FIG. 7 shows the right side of the aluminum plate with soil uniformly divided into grid cells;
FIG. 8 is a schematic diagram of the structure of the model integrally mesh-divided unit;
FIG. 9 is a schematic diagram of a single-side measurement of a second testing device;
FIG. 10 is a single-sided equivalent circuit diagram of the test apparatus;
FIG. 11 is a schematic diagram of a double-sided measurement of a second testing apparatus;
FIG. 12 is a diagram of a two-sided equivalent circuit of the test apparatus;
FIG. 13 is a mesh chart of the outer soil layer of the grounding body;
FIG. 14 is a model ensemble subdivision grid diagram.
the device comprises a 1-alternating current source, a 2-ammeter, a 3-voltmeter, a 4-soil layer, a 5-organic glass box, a 6-aluminum plate, a 7-grounding body and an 8-metal hoop.
Detailed Description
The invention is further described with reference to the accompanying drawings and specific embodiments.
example 1: 1-14, a method for measuring and estimating the contact resistance of a ground contact body with soil, the method comprising the steps of:
the method comprises the following steps: two aluminum plates and a grounding body are respectively arranged on two sides and the middle part of the organic glass box and filled with simulated soil, and the two aluminum plates are connected with a current meter and a voltmeter and an alternating current source through insulated copper wires to form a first test device;
Step two: measuring total resistance R of loop of test device I1：
In the formula, R1Is the total loop resistance, in Ω; u shape1Is the voltage between the aluminum plates, in units of V; i is1is the total current flowing through the loop, in units A; r11The contact resistance of the aluminum plate and the soil is expressed by omega; ra1is the soil resistance, unit omega;
Obtaining contact resistance R of the aluminum plate and soil by the formula (1)11Comprises the following steps:
The current value measured in the test is loaded on the upper surface of the left aluminum plate, and the right surface of the right aluminum plate is taken as a zero potential reference surface, so that the soil resistance Ra1The values of (a) are obtained from the thermal power equivalent:
In the formula I1Is the total current flowing through the loop, in units A; ra1Is the soil resistance, unit omega; wiThermal power for the ith soil cell (values can be extracted in ANSYS), in units J;
R is obtained by the formulae (2) and (3)11And Ra1and then, uniformly splitting the left aluminum plate close to the 1mm thick soil into a plurality of units, wherein each unit is a cube with the side length of 1mm, so as to extract the current density j of each unit1iThe remaining part of the soil is divided into sparse units relative to the units of the soil adjacent to the left aluminum plate; the entire model was split as shown in FIG. 7(b), and 193794 cells were co-split.
Equivalently calculating the contact resistance R of the aluminum plate and the soil in unit area according to the thermal power01：
Thus:
in the formula i1iThe current flowing out of each unit on the contact surface of the aluminum plate is unit A; j is a function of1iThe current density of each unit on the surface of the aluminum plate is in A/m2；R01Contact resistance per unit area of aluminum plate, unit omega m2；S1iIs the area of each unit of the aluminum plate, and the unit m2In the calculation, the average value calculated by the three groups of measured values is used as the contact resistance value of the aluminum plate and the soil in unit area;
Step three: changing the line connection mode of the first test device, connecting the ammeter, the voltmeter and the alternating current source with the grounding body and the single-side aluminum plate or the double-side aluminum plate to form a second test device, and measuring the total loop resistance R of the second test device2：
In the formula, R2to measure the total resistance of the loop, in Ω; u shape2voltage of the grounding body and the aluminum plate is measured in unit V; i is2Is the total current flowing through the loop, in units A; r22The total contact resistance between the grounding body and the soil is in unit omega; r21the contact resistance of the aluminum plate and the soil is expressed by omega; ra2Is the soil resistance, unit omega;
The current value measured in the upper surface loading test of the grounding body takes the right aluminum plate or the aluminum plates at the two sides as a zero potential reference surface, and the soil resistance Ra2The values of (d) are also derived from the thermal power equivalent:
In the formula, WiThermal power for the ith soil cell, unit J;
Contact resistance R of aluminum plate and soil21Calculated from the following formula:
In the formula i2iThe current flowing out of the ith cell of the aluminum plate is unit A; j is a function of2ithe current density of each unit on the surface of the aluminum plate is in A/m2；R01The contact resistance of the aluminum plate and the soil in unit area is omega; s2iIs the area of the ith aluminum plate cell in m2；
So the contact resistance R of the grounding body and the soil22comprises the following steps:
R22＝R2-Ra2-R21 (9)
To obtain R22Then, uniformly dividing soil with the thickness of 1mm outside the ground body into units, and extracting the current density j of each unit3i(ii) a The entire model was split into 228880 cells as shown in FIG. 10 (b).
Contact resistance R of unit area between grounding body and soil02the thermal power equivalent yields:
thus:
In the formula i3iAnd j3irespectively the current and the current density flowing out of the ith cell on the surface of the grounding body; r0Contact resistance per unit area of the grounding body, in omega m2；S3iThe area of the ith cell of the grounding body in m2Contact resistance per unit area R0Equivalent to a conductivity of ρ0Coating of (2):
In the formula, ρ0The equivalent coating resistivity, in Ω · m; r0Contact resistance per unit area of the grounding body, in omega m2；d0The equivalent coating thickness (taking the soil particle size when the soil is uniform and taking the average particle size when the soil is not uniform) in m; the average value calculated by the three groups of measured values is used as the contact resistance value of the grounding body and the soil in unit area in the calculation.
Calculating the contact resistance of the grounding body and the soil by utilizing the integral resistance in the testing device and combining finite element software, and equivalently obtaining the unit area contact resistance of the grounding body and the soil and the equivalent layer resistivity of the contact resistance.
Preferably, the simulated soil is prepared according to different soil types and different particle size combinations.
Preferably, above-mentioned test device one includes upper end open-ended organic glass box 5, aluminum plate 6 and grounding body 7 and alternating current power supply 1, aluminum plate 6 adopts two, install two inside walls departments about organic glass box 5 respectively, it has soil horizon 4 to fill in the organic glass box 5, the vertical soil horizon 4 middle part of pegging graft of grounding body 7, 1 one end of alternating current power supply is through insulating copper line connection ampere meter 2, the ampere meter 2 other end is connected in 6 tops of left aluminum plate, aluminum plate 6 on right side is through insulating copper line connection at the 1 other end of alternating current power supply, there is voltmeter 3 through insulating copper line connection between two aluminum plate 6.
Preferably, above-mentioned test device two includes upper end open-ended organic glass box 5, aluminum plate 6 and grounding body 7 and alternating current power supply 1, aluminum plate 6 adopts two, install two inside walls departments about organic glass box 5 respectively, it has soil horizon 4 to fill in the organic glass box 5, the vertical soil horizon 4 middle part of pegging graft of grounding body 7, 1 one end of alternating current power supply is through insulated copper line connection ampere meter 2, the ampere meter 2 other end is connected in 7 tops of grounding body, two aluminum plate 6 all connect at the 1 other end of alternating current power supply through insulated copper line, there is voltmeter 3 through insulated copper line connection between grounding body 7 and one of them aluminum plate 6, soil horizon 4 can cover grounding body test section, machine glass box 5 incasement is long, wide, the height is 300mm x 200mm respectively, thickness 5 mm.
preferably, the upper end of the grounding body 7 of the first test device or the second test device is connected with an insulated copper wire through a metal hoop 8.
Preferably, the grounding body 7 of the first test device or the second test device comprises round steel and graphite, and the diameter of the grounding body is 10 mm-30 mm.
Preferably, the size of the side face of the first test device or the second test device is equal to that of the side face of the organic glass box 5, the length, the width and the thickness of the aluminum plate are respectively 200mm multiplied by 2mm, and the aluminum plate is adhered through insulating glue.
Preferably, the bottom of the organic glass box 5 of the first testing device or the second testing device is provided with a blind hole with the depth of 2mm, the lower end of the grounding body 7 is inserted into the blind hole, the positioning effect can be achieved, and the testing is more accurate.
specific examples are as follows: a method for measuring and calculating the contact resistance of a grounding body and soil comprises the following steps:
Firstly, in order to measure and calculate the contact resistance of the graphite-based flexible grounding body under different soil conditions, a test adopts a stone with an outer diameter phi of 28mmThe ink-based flexible grounding body is a research object, and the related material parameter is the resistivity of the graphite-based flexible grounding body of 3.25 multiplied by 10-5Ω · m, relative permeability μrIs 1, in order to simulate the soil conditions of different soils, different granularities and different combination of granularities, the test measurement is respectively carried out under the condition of eight simulated soils, and the parameters of the eight simulated soils are as follows: all types one are loess; type two is fine sand; type three is all bentonite; type four comprises 50% of loess, 25% of fine sand and 25% of 10mm broken stone; type five is 50% of loess, 25% of fine sand and 25% of 20mm broken stone; the type six comprises 25 percent of loess, 25 percent of bentonite, 25 percent of 10mm broken stone and 25 percent of 20mm broken stone; type seven comprises 40% of fine sand, 20% of bentonite, 20% of 10mm gravel and 20% of 20mm gravel; the type eight is 10mm crushed stone 50 percent and 20mm crushed stone 50 percent.
An organic glass box with the length, width and height of 300mm multiplied by 200mm is designed to be used as a test device for indoor measurement and calculation of contact resistance between a grounding body and soil, and a round hole with the depth of 2mm and the diameter of phi 29mm is arranged in the center of the bottom plate of the organic glass box, so that the arranged grounding body is positioned in the center of the test device. The left side and the right side of the testing device are 200mm multiplied by 2mm aluminum plates which are used as current injection and return electrodes, the grounding bodies for the test are graphite-based flexible grounding bodies with phi 28mm and round steel, the top ends of the graphite-based flexible grounding bodies are fixed on insulated copper wires by adopting hoops, and the design perspective view of the testing device is shown in fig. 2. In the test, alternating current is provided by a TDGC2-1 contact voltage regulator, relevant parameters of the alternating current voltage regulator are TDGC2-1 working voltage 220V, output voltage 0-250V, working frequency 50Hz, output current 0-4A, rated capacity 1kVA and insulation grade A, and voltage and current parameters in the test are measured by a UT51 MULTIMER MULTIMETER.
In order to ensure that the calculation of the contact resistance between the return aluminum plate and the soil and the calculation of the contact resistance between the grounding body and the soil are carried out under the same soil condition, the soil is only filled once in two times of measurement for each type of soil. However, if the soil is backfilled once, the grounding body must be placed in the soil, and the existence of the grounding body in the soil brings errors to the measurement results of the soil resistance and the aluminum plate contact resistance. When the grounding body exists in the test device, the shape of the whole soil body is irregular, and the soil resistance cannot be directly calculated according to a formula, but the thermal power of the soil unit can be extracted by means of ANSYS software, and then the total resistance of the soil can be equivalently calculated according to the thermal power, so that the influence of the existence of the grounding body on the measurement error is analyzed. The error result is between 2% and 3.5%, and the influence of the existence of the grounding body on the resistance of the soil body can be ignored, so that the influence of the existence of the grounding body on the measurement of the contact resistance of the aluminum plate is small.
The schematic diagram of the measurement of the contact resistance between the aluminum plate of the return electrode and the soil is shown in fig. 5, and during measurement, the two aluminum plates are used as the current injection and return electrodes, and the aluminum plates and the soil form a series circuit. The simulation calculation shows that the influence of the existence of the grounding body on the measurement of the contact resistance between the aluminum plate and the soil is small, so that the schematic diagram shown in FIG. 5 can be equivalent to the circuit diagram shown in FIG. 6, wherein R is11is the contact resistance of the aluminum plate and the soil, Ra1The average value of three sets of estimated values of measurement was used as the contact resistance per unit area of the aluminum plate in the test as the resistance of the soil in the test apparatus.
According to the principle shown in figure 5, an alternating current power supply is connected between two aluminum plates, and the measuring ranges of a voltmeter and an ammeter are adjusted to be maximum; after the loop is closed, adjusting the power supply voltage and the measuring range of the voltmeter and the ammeter to an appropriate value, rapidly reading the voltage U and the current I, properly increasing and decreasing the voltage value, continuously measuring for 3 times, and taking the average value of the resistance calculated by three times of measurement as the total resistance of the loop; and (5) dismantling the test wiring, and carrying out subsequent measurement.
The method for estimating the contact resistance of the aluminum plate in unit area comprises the following steps: firstly, according to the equivalent circuit diagram shown in fig. 6, the total resistance of the measurement loop is:
In the formula, R1total loop resistance, Ω; u shape1voltage between the aluminum plates, V; i is1Is the total current flowing through the loop, a; r11the contact resistance between the aluminum plate and the soil is omega; ra1Is the soil resistance, Ω.
Therefore, the contact resistance R of the aluminum plate with the soil1Comprises the following steps:
The current value measured in the test is loaded on the upper surface of the left aluminum plate, and the right surface of the right aluminum plate is taken as a zero potential reference surface, so that the soil resistance Ra1The value of (d) can be derived from the thermal power equivalent:
In the formula I1is the total current flowing through the loop, a; ra1is the soil resistance, Ω; wiThermal power for the ith soil cell (values can be extracted in ANSYS), J.
To obtain R11And Ra1Then, the left aluminum plate is evenly split close to the 1mm thick soil (as shown in fig. 7), each unit is a cube with the side length of 1mm, and therefore the current density j of each unit can be extracted conveniently1iAnd the other units are relatively sparse in subdivision, the whole subdivision of the model is shown in FIG. 8, and 193794 units are obtained by co-subdivision.
the contact resistance R of unit area between the aluminum plate and the soil can be calculated according to equivalent thermal power01：
Thus:
in the formula i1iThe current flowing out of each unit on the contact surface of the aluminum plate is A; j is a function of1iThe current density of each unit on the surface of the aluminum plate is A/m 2; r01Is the contact resistance per unit area of the aluminum plate, omega. m2；S1iIs the area of each unit of the aluminum plate, m2. The average value calculated by three groups of measured values in the calculation is used as the unit surface of the aluminum plate and the soilAnd the contact resistance value is accumulated.
When the contact resistance of the grounding body and the soil is measured, alternating current is injected into the grounding body, the aluminum plates on one side or two sides can be used as the backflow electrodes of the current, schematic diagrams and equivalent circuit diagrams measured by adopting two methods are respectively shown in fig. 10 and fig. 12, the measurement results of the two methods are mutually contrasted, and therefore the accuracy of measurement and calculation can be verified.
the connection of the lines is made first. Connecting a circuit according to a schematic diagram shown in fig. 9, and adjusting a voltmeter and an ammeter to corresponding gears; the reading is then measured. Closing a power switch, adjusting the current to a proper value, reading corresponding voltage and current data, properly increasing and decreasing the input current value, continuously reading the data for three times, recording the data into a table, and disconnecting the power switch; after the steps 1 and 2 are finished, after the soil is recovered to the room temperature within 10 minutes, connecting the lines according to a schematic diagram shown in fig. 11, continuously reading the data for three times and recording the data into a table according to the same method, and finally dismantling the test line.
as shown in fig. 10 and 12, since the test apparatus is strictly symmetrical, the equivalent circuit diagram shown in fig. 12 can always be equivalent to the circuit diagram shown in fig. 8(b) in parallel, and therefore, the total resistance R of the circuit is2Comprises the following steps:
In the formula, R2To measure the total resistance of the loop, Ω; u shape2voltage, V, of the grounding body and the aluminum plate is measured; i is2Is the total current flowing through the loop, a; r22Is the total contact resistance, omega, between the grounding body and the soil; r21The contact resistance between the aluminum plate and the soil is omega; ra2is the soil resistance, Ω.
The current value measured in the upper surface loading test of the grounding body takes the right aluminum plate or the aluminum plates at the two sides as a zero potential reference surface, and the soil resistance Ra2the values of (A) can likewise be derived from the thermal power equivalent:
In the formula, WiThermal power for the ith soil cell, J.
Contact resistance R of aluminum plate and soil21calculated from the following formula:
In the formula i2iThe current flowing out of the ith cell of the aluminum plate is A; j is a function of2iThe current density of each unit on the surface of the aluminum plate, A/m2；R01The contact resistance per unit area of the aluminum plate and the soil is omega; s2iIs the area of the ith aluminum plate cell, m2。
So the contact resistance R of the grounding body and the soil22Comprises the following steps:
R22＝R2-Ra2-R21
to obtain R22Then, the outside of the ground body was divided into 1mm thick soil (as shown in FIG. 13) to extract the current density j of each cell3ithe overall model was split as shown in fig. 14, and 228880 cells were obtained by co-splitting.
Contact resistance R of unit area between grounding body and soil02Can be obtained from the thermal power equivalent:
Thus:
In the formula i3iAnd j3iRespectively the current and the current density flowing out of the ith cell on the surface of the grounding body; r0Contact resistance per unit area of the grounding body, omega. m2；S3iArea of the ith cell of the grounding body, m2. Can make contact with the unit area resistance R0equivalent to a conductivity of ρ0Coating of：
In the formula, ρ0Is the equivalent coating resistivity, Ω · m; r0Contact resistance per unit area of the grounding body, omega. m2；d0The equivalent coating thickness (soil particle size for uniform soil, average particle size for non-uniform soil), m. The average value calculated by the three groups of measured values is used as the contact resistance value of the grounding body and the soil in unit area in the calculation.
The above description is only an example of the specific embodiments of the present invention, and the scope of the present invention is not limited thereto. Those skilled in the art can easily find out the modifications or alterations within the technical scope of the present disclosure, which should be covered by the protection scope of the present disclosure. For this reason, the protection scope of the present invention shall be subject to the protection scope of the appended claims.
Claims (8)
1. A method for measuring and calculating contact resistance between a grounding body and soil is characterized in that: the method comprises the following steps:
the method comprises the following steps: two aluminum plates and a grounding body are respectively arranged on two sides and the middle part of the organic glass box and filled with simulated soil, and the two aluminum plates are connected with a current meter and a voltmeter and an alternating current source through insulated copper wires to form a first test device;
step two: measuring total resistance R of loop of test device I1：
In the formula, R1is the total loop resistance, in Ω; u shape1Is the voltage between the aluminum plates, in units of V; i is1is the total current flowing through the loop, in units A; r11the contact resistance of the aluminum plate and the soil is expressed by omega; ra1Is the soil resistance, unit omega;
the contact electricity of the aluminum plate obtained by the formula (1) and soilresistance R11Comprises the following steps:
The current value measured in the test is loaded on the upper surface of the left aluminum plate, and the right surface of the right aluminum plate is taken as a zero potential reference surface, so that the soil resistance Ra1The values of (a) are obtained from the thermal power equivalent:
In the formula I1is the total current flowing through the loop, in units A; ra1Is the soil resistance, unit omega; wiThermal power for the ith soil cell, unit J;
R is obtained by the formulae (2) and (3)11And Ra1Then, uniformly dividing the left aluminum plate close to the soil with the thickness of 1mm into a plurality of units, wherein each unit is a cube with the side length of 1mm, and extracting the current density j of each unit1iThe remaining part of the soil is divided into sparse units relative to the units of the soil adjacent to the left aluminum plate;
Equivalently calculating the contact resistance R of the aluminum plate and the soil in unit area according to the thermal power01：
thus:
In the formula i1iThe current flowing out of each unit on the contact surface of the aluminum plate is unit A; j is a function of1iThe current density of each unit on the surface of the aluminum plate is in A/m2；R01Contact resistance per unit area of aluminum plate, unit omega m2；S1iIs the area of each unit of the aluminum plate, and the unit m2；
Step three: changing the line connection mode of the first test device, connecting the ammeter, the voltmeter and the alternating current source with the grounding body and the single-side aluminum plate or the double-side aluminum plate to form a second test device, and measuring the total loop resistance R of the second test device2：
In the formula, R2to measure the total resistance of the loop, in Ω; u shape2Voltage of the grounding body and the aluminum plate is measured in unit V; i is2is the total current flowing through the loop, in units A; r22The total contact resistance between the grounding body and the soil is in unit omega; r21the contact resistance of the aluminum plate and the soil is expressed by omega; ra2Is the soil resistance, unit omega;
the current value measured in the upper surface loading test of the grounding body takes the right aluminum plate or the aluminum plates at the two sides as a zero potential reference surface, and the soil resistance Ra2The values of (d) are also derived from the thermal power equivalent:
In the formula, Withermal power for the ith soil cell, unit J;
Contact resistance R of aluminum plate and soil21Calculated from the following formula:
In the formula i2ithe current flowing out of the ith cell of the aluminum plate is unit A; j is a function of2iThe current density of each unit on the surface of the aluminum plate is in A/m2；R01The contact resistance of the aluminum plate and the soil in unit area is omega; s2iIs the area of the ith aluminum plate cell in m2；
So the contact resistance R of the grounding body and the soil22Comprises the following steps:
R22＝R2-Ra2-R21 (9)
to obtain R22then, uniformly dividing soil with the thickness of 1mm outside the ground body into units, and extracting the current density j of each unit3i；
Contact resistance R of unit area between grounding body and soil02The thermal power equivalent yields:
thus:
In the formula i3iAnd j3iRespectively the current and the current density flowing out of the ith cell on the surface of the grounding body; r0Contact resistance per unit area of the grounding body, in omega m2；S3iThe area of the ith cell of the grounding body in m2contact resistance per unit area R0Equivalent to a conductivity of ρ0Coating of (2):
In the formula, ρ0The equivalent coating resistivity, in Ω · m; r0Contact resistance per unit area of the grounding body, in omega m2；d0equivalent coating thickness in m.
2. The method for measuring and estimating the contact resistance of the grounding body and the soil as claimed in claim 1, wherein: the simulated soil is combined and proportioned according to different soil types and different granularity.
3. The method for measuring and estimating the contact resistance of the grounding body and the soil as claimed in claim 1, wherein: test device one includes upper end open-ended organic glass box (5), aluminum plate (6) and grounding body (7) and alternating current power supply (1), aluminum plate (6) adopt two, install two inside walls departments about organic glass box (5) respectively, it has soil horizon (4) to fill in organic glass box (5), grounding body (7) is vertical to be pegged graft soil horizon (4) middle part, alternating current source (1) one end is through insulating copper line connection ampere meter (2), ampere meter (2) other end is connected in left aluminum plate (6) top, aluminum plate (6) on right side are connected at the alternating current source (1) other end through insulating copper line, there are voltmeter (3) through insulating copper line connection between two aluminum plate (6).
4. the method for measuring and estimating the contact resistance of the grounding body and the soil as claimed in claim 1, wherein: test device two includes upper end open-ended organic glass box (5), aluminum plate (6) and grounding body (7) and alternating current power supply (1), aluminum plate (6) adopt two, install two inside walls departments about organic glass box (5) respectively, it has soil horizon (4) to fill in organic glass box (5), grounding body (7) is vertical to be pegged graft soil horizon (4) middle part, alternating current source (1) one end is through insulating copper line connection ampere meter (2), ampere meter (2) other end is connected on grounding body (7) top, two aluminum plate (6) are all connected at the alternating current source (1) other end through insulating copper line, there is voltmeter (3) through insulating copper line connection between grounding body (7) and one of them aluminum plate (6).
5. the method for measuring and calculating the contact resistance of the grounding body and the soil as claimed in any one of claims 3 or 4, wherein: the upper end of the grounding body (7) is connected with an insulated copper wire through a metal hoop (8).
6. The method for measuring and calculating the contact resistance of the grounding body and the soil as claimed in any one of claims 3 or 4, wherein: the grounding body (7) comprises round steel and graphite, and the diameter of the grounding body is 10-30 mm.
7. The method for measuring and calculating the contact resistance of the grounding body and the soil as claimed in any one of claims 3 or 4, wherein: the aluminum plate (6) and the organic glass box (5) are equal in side face size and are adhered through insulating glue.
8. The method for measuring and calculating the contact resistance of the grounding body and the soil as claimed in any one of claims 3 or 4, wherein: the bottom of the organic glass box (5) is provided with a blind hole, and the lower end of the grounding body (7) is inserted into the blind hole.
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