A double-terminal ground loop resistance and ground grid resistance measuring device and measuring method

Abstract

The present invention discloses a device and method for measuring the resistance of a two-terminal ground loop and a ground grid resistance, wherein the device comprises a measuring device for outputting a constant current to a measuring loop, wherein the measuring loop comprises a measured branch, a grounding bar and a ground grid connected in series, wherein a sampling fixture for measuring a voltage signal of the grounding bar is provided on the grounding bar, and the output end of the sampling fixture is connected to the input end of the measuring device; wherein the method comprises using the sampling fixture and the measuring device to measure the voltage of the grounding bar to obtain a shunt ratio by a voltage ratio, and then calculating the resistance of the measured branch. The present invention can accurately measure the actual current value flowing through each branch without removing the grounding wire, and then more accurately measure the loop resistance or ground grid resistance of each branch, thereby improving the accuracy of detection and work efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of power supply detection, in particular to a device and method for measuring double-terminal grounding loop resistance and ground grid resistance. Background Art

[0002] With the promotion of GIS (gas insulated substation), disconnectors and circuit breakers will automatically enter the double-terminal grounding state during power outages and maintenance. Due to the presence of multiple current loops, the traditional loop resistance measurement will result in excessive errors. In the measurement of ground grid resistance with multiple grounding points, multiple current branches will also be formed, resulting in similar situations.

[0003] For the loop resistance or grounding resistance of double-end grounding, double-end grounding leads to multiple branches in parallel. To measure the resistance value of each branch, the key is to obtain the current value of each branch. There are currently two solutions: 1) Use large current measurement: This method is suitable for parallel branches with a difference of at least 1 order of magnitude. Using 300A or even larger current, the measurement result will be close to the resistance of the branch being measured; it is difficult to judge whether its application conditions are met, and there are always errors in the measurement results, which limits its application scope. 2) Use AC and DC current clamps to measure the current of one or more branches, so as to obtain the actual current value of the branch being measured, and then calculate the resistance value; its measurement accuracy is limited by the measurement accuracy of the current clamp. Some sites cannot even provide the current clamp measurement location, or there are too many branches, and the current clamp simultaneous measurement becomes complicated and difficult to achieve. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a two-terminal grounding loop resistance and ground grid resistance measuring device and measurement method, which can accurately measure the actual current value flowing through each branch without removing the grounding wire, and then more accurately measure the loop resistance or ground grid resistance of each branch, thereby improving the detection accuracy and work efficiency.

[0005] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows.

[0006] A device for measuring double-terminal grounding loop resistance and ground grid resistance comprises a measuring device for outputting a constant current to the measuring loop, the measuring loop comprises a measured branch, a grounding bar and a ground grid connected in series, the grounding bar is provided with a sampling fixture for measuring the grounding bar voltage signal, and the output end of the sampling fixture is connected to the input end of the measuring device.

[0007] The above-mentioned two-terminal grounding loop resistance and ground grid resistance measuring device comprises a microcontroller, a constant current source, a current acquisition module and a voltage acquisition module; the output end of the microcontroller is connected to the input end of the constant current source, and the two current output clamps of the constant current source are respectively clamped at one end of the measured branch and the middle of the grounding bar; the output ends of the current acquisition module and the voltage acquisition module are respectively connected to the input end of the microcontroller, and the microcontroller calculates the resistance of the measured branch according to the output constant current, the collected voltage at both ends of the measured branch and the actual current value in the measuring loop.

[0008] The above-mentioned two-terminal ground loop resistance and ground grid resistance measuring device further comprises a human-computer interaction module composed of a liquid crystal screen and a keypad, and the human-computer interaction module communicates with the microcontroller.

[0009] The above-mentioned two-terminal grounding loop resistance and ground grid resistance measuring device, the sampling fixture includes a shell, a magnet is fixedly arranged on the bottom end surface of the shell for easy adsorption on the grounding bar, a retractable probe is respectively arranged on the bottom end surface of the shell on both sides of the magnet, a circuit board with an input end connected to the retractable probe and used for signal conversion is arranged in the shell, and the output end of the circuit board is connected to a voltage signal line with one end fixed on the shell.

[0010] A method for measuring a two-terminal ground loop resistance and a ground grid resistance is implemented based on the above-mentioned measuring device and specifically comprises the following steps:

[0011] A. The measured branch, ground bar and ground grid are connected in series to form a measurement loop;

[0012] B. Clamp the two current output clamps of the measuring host at one end of the measured branch and the middle of the ground bar respectively, attach the sampling fixture to the ground bar, and connect the voltage signal line to the measuring device;

[0013] C. The measuring device outputs a constant current to the measuring loop, and collects the current value of the measured branch, the voltage value at both ends of the measured branch, the voltage value from the current injection point on the grounding bar to the end point of the measured branch, and the voltage value from the current injection point on the grounding bar to the end point of the grounding network;

[0014] D. Calculate the resistance of the branch under test based on the data collected in step C.

[0015] In the above-mentioned method for measuring the resistance of a two-terminal ground loop and the ground grid resistance, in step B, two sampling fixtures are used to respectively collect the voltages of the upper and lower parts of the grounding bar, or one fixture is used to respectively measure the voltages of the upper and lower parts to obtain the shunt ratio.

[0016] Due to the adoption of the above technical scheme, the technical progress achieved by the present invention is as follows.

[0017] The present invention is used to measure the loop resistance of a double-terminal grounding and the ground grid resistance of a double-terminal grounding. It can accurately measure the actual current value flowing through each branch without removing the grounding wire and without using multiple times large current or current clamps, and then more accurately measure the loop resistance or ground grid resistance of each branch, greatly improving the detection accuracy and work efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a principle block diagram of the present invention;

[0019] Figure 2 It is a framework diagram of the testing device of the present invention;

[0020] Figure 3 It is the measurement principle diagram of the present invention;

[0021] Figure 4 A schematic diagram of current flow during the measurement process of the present invention;

[0022] Figure 5 It is a structural schematic diagram of the sampling fixture of the present invention;

[0023] Figure 6 This is a schematic diagram of current flow when two sampling fixtures are used to measure and verify the calibration coefficient in the present invention.

[0024] Among them: 1. measured loop resistance, 2. sampling fixture, 21. shell, 22. magnet, 23. retractable probe, 24. voltage signal line, 3. measuring device, 4. ground grid, 5. ground bar. DETAILED DESCRIPTION

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] A two-terminal grounding loop resistance and grounding network resistance measuring device, comprising a measuring device 3 and a sampling fixture 2, wherein the measuring device is used to output a constant current to the measuring loop, and the measuring loop comprises a measured branch 1, a grounding bar 5 and a grounding network 4 connected in series, such as Figure 1 As shown, the sampling fixture 2 is adsorbed on the grounding bar to measure the voltage signal of the grounding bar, and the output end of the sampling fixture 2 is connected to the input end of the measuring device.

[0027] The structure of the measuring device is as follows Figure 2As shown, it includes a microcontroller, a constant current source, a current acquisition module, a voltage acquisition module and a human-computer interaction module, and the human-computer interaction module is composed of a liquid crystal screen and a keypad. Among them, the output end of the microcontroller is connected to the input end of the constant current source, and the two current output clamps of the constant current source are clamped at one end of the measured branch and the middle of the ground bar respectively; the output ends of the current acquisition module and the voltage acquisition module are respectively connected to the input end of the microcontroller, and the microcontroller calculates the resistance of the measured branch according to the output constant current and the collected voltages at both ends of the measured branch and the actual current value in the measurement loop; the human-computer interaction module communicates with the microcontroller, the keypad inputs control instructions to the microcontroller, and the liquid crystal screen is used to display the measurement results.

[0028] The structure of the sampling fixture is as follows: Figure 5 As shown, it includes a shell 21, a magnet 22 is fixedly arranged on the bottom surface of the shell for easy adsorption on the grounding bar, a retractable probe 23 is respectively arranged on the bottom surface of the shell on both sides of the magnet, a circuit board is arranged in the shell, the input end of the circuit board is connected to the retractable probe for signal conversion, and the output end of the circuit board is connected to a voltage signal line 24 one end of which is fixed on the shell.

[0029] The present invention proposes a method for measuring the resistance of a two-terminal ground loop and a ground grid. The method is implemented based on the above-mentioned measuring device, wherein the ground bar is used as a sampling resistor, and the length and voltage of the ground bar on both sides of the current injection point are measured respectively to obtain the magnitude of the current flowing to the two ends. The principle is as follows Figure 3 As shown in the figure, Rx is the resistance of the branch under test, Rg is the resistance of the ground grid and its connected branches, Rw is the resistance of the grounding bar of the branch under test, and Ux is the voltage of the branch under test.

[0030] The grounding bar on site is usually made of iron or copper, with constant resistivity and cross-sectional area. The current is applied to the middle of the grounding bar, such as Figure 4 As shown, take two sections with lengths of L1 and L2 at the upper and lower parts of the application point and measure their voltages u1 and u2 respectively. Assuming that their resistance values ​​are R1 and R2, then,

[0031] It is known that I = I1 + I2,

[0032] u1=I1*R1=I1*ρL1 / S,

[0033] u2=I2*R2=I2*ρL2S,

[0034] So, Right now

[0035]

[0036] Substituting the above formula into I=I1+I2, we can get,

[0037]

[0038] Among them, L1, L2, u1 and u2 are measured respectively.

[0039] I1 is the current value of a grounding bus connected to the branch under test, that is, the current value flowing through the branch under test in the measurement loop can be obtained, and then the resistance of the branch under test can be calculated based on the measured branch voltage Ux.

[0040] The method for measuring the branch resistance to be measured by using two sampling fixtures of the present invention specifically comprises the following steps.

[0041] A. The measured branch 1, two grounding bars 5 and ground grid 4 are connected in series to form a measurement circuit. Figure 1 shown.

[0042] B. Clamp the two current output clamps of the measuring host at one end of the measured branch and the middle of the grounding bar connected to the other end of the measured branch, and use two sampling clamps to adsorb them on the upper and lower parts of the grounding bar, that is, one current output clamp of the measuring host is located on the grounding bar between the two sampling clamps; and connect the voltage signal line to the measuring device.

[0043] When two sampling fixtures are used for measurement, since there is a certain difference between the two sampling fixtures, it is necessary to calculate the calibration coefficients of the two sampling fixtures. The specific method is: place the sampling fixture on the side of the ground bus current injection point, such as Figure 6 As shown, the calibration coefficient k of the two sampling fixtures is calculated.

[0044]

[0045] Among them, L 10 , L 20 are the lengths of the two sampling fixtures, u 10 and u 20 The voltage collected by the two sampling fixtures.

[0046] C. The measuring device outputs a constant current to the measuring circuit, and collects the current value of the measured branch, the voltage value at both ends of the measured branch, the voltage value from the current injection point on the grounding bus to the end point of the measured branch, and the voltage value from the current injection point on the grounding bus to the end point of the grounding grid.

[0047] D. Based on the data collected in step C, calculate the actual current i flowing into the branch under test x :

[0048]

[0049] Use the following formula to calculate the measured branch resistance Rx:

[0050]

[0051] When the present invention uses a sampling fixture to measure the branch resistance to be measured, there is no fixture calibration situation. The voltage values ​​on the upper and lower grounding bars of the current injection point are directly measured twice (equivalent to the calibration coefficient k being 1), and then the branch current and the branch resistance to be measured are calculated.

[0052] The core of the present invention is to use a ground bus to measure the shunt resistance, including but not limited to the above two measurement methods; the method of using one or more sampling fixtures or any other voltage measuring device to measure the ground bus voltage once or multiple times to obtain the shunt ratio by voltage ratio all falls within the scope of this method.

Claims

1. A two-terminal ground loop resistance and ground grid resistance measuring device, characterized in that: The invention comprises a measuring device for outputting a constant current to a measuring circuit, wherein the measuring circuit comprises a branch circuit (1) to be measured, a grounding bar (5) and a grounding grid (4) connected in series, wherein a sampling fixture (2) for measuring a voltage signal of the grounding bar is arranged on the grounding bar, and an output end of the sampling fixture (2) is connected to an input end of the measuring device; The measuring device comprises a microcontroller, a constant current source, a current acquisition module and a voltage acquisition module; the output end of the microcontroller is connected to the input end of the constant current source, and two current output clamps of the constant current source are respectively clamped at one end of the measured branch and the middle of the ground bar; the output ends of the current acquisition module and the voltage acquisition module are respectively connected to the input end of the microcontroller, and the microcontroller calculates the resistance of the measured branch according to the output constant current, the collected voltages at both ends of the measured branch and the actual current value in the measuring loop; Select the middle of the grounding bar to apply current, take two sections with lengths of L1 and L2 at the upper and lower parts of the application point, and measure their voltages u1 and u2 respectively. According to the formula Calculate I1; Where, I is the constant current value output by the microcontroller, that is, the current value of the input grounding bar; L1 is the length of the grounding bar above the application point, L2 is the length of the grounding bar below the application point, u1 is the voltage value of the grounding bar above the application point, u2 is the voltage value of the grounding bar above the application point, and I1 is the current value of the grounding bar above the application point; I1 is the current value of a grounding bus connected to the branch under test, that is, the current value flowing through the branch under test in the measurement loop can be obtained, and then the resistance of the branch under test can be calculated based on the measured branch voltage Ux.

2. A two-terminal ground loop resistance and ground grid resistance measuring device according to claim 1, characterized in that: The measuring device also includes a human-machine interaction module composed of a liquid crystal screen and a keypad, and the human-machine interaction module communicates with the microcontroller.

3. A two-terminal ground loop resistance and ground grid resistance measuring device according to claim 1, characterized in that: The sampling fixture comprises a shell (21), a magnet (22) is fixedly arranged on the bottom end surface of the shell for facilitating adsorption on a grounding bar, a retractable probe (23) is respectively arranged on the bottom end surface of the shell on both sides of the magnet, a circuit board for signal conversion is arranged in the shell, the input end of which is connected to the retractable probe, and the output end of the circuit board is connected to a voltage signal line (24) one end of which is fixed on the shell.

4. A method for measuring two-terminal ground loop resistance and ground grid resistance, characterized in that: The method is implemented based on the measuring device according to any one of claims 1 to 3, and specifically comprises the following steps: A. The measured branch (1), the grounding bar (5) and the grounding grid (4) are connected in series to form a measurement loop; B. Clamp the two current output clamps of the measuring host at one end of the branch to be measured and the middle of the ground bar respectively, adsorb the sampling fixture on the ground bar, and connect the voltage signal line to the measuring device; C. The measuring device outputs a constant current to the measuring loop, and collects the current value of the measured branch, the voltage value at both ends of the measured branch, the voltage value from the current injection point on the grounding bar to the end point of the measured branch, and the voltage value from the current injection point on the grounding bar to the end point of the grounding network; D. Calculate the resistance of the branch under test based on the data collected in step C.

5. A method for measuring a two-terminal ground loop resistance and a ground grid resistance according to claim 4, characterized in that: In step B, two sampling fixtures are used to respectively collect the voltages of the upper and lower parts of the grounding bar, or one voltage sampling fixture is used to respectively measure the voltages of the upper and lower parts of the grounding bar, and then the shunt ratio is calculated.

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