CN107728024B - Large-scale grounding grid impact characteristic testing method utilizing grounding grid backflow - Google Patents

Large-scale grounding grid impact characteristic testing method utilizing grounding grid backflow Download PDF

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CN107728024B
CN107728024B CN201711021516.4A CN201711021516A CN107728024B CN 107728024 B CN107728024 B CN 107728024B CN 201711021516 A CN201711021516 A CN 201711021516A CN 107728024 B CN107728024 B CN 107728024B
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current
impact
point
ground
injection point
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CN107728024A (en
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张波
蒙泳昌
王森
李志忠
何金良
余占清
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Tsinghua University
Electric Power Research Institute of State Grid Shaanxi Electric Power Co Ltd
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Tsinghua University
Electric Power Research Institute of State Grid Shaanxi Electric Power Co Ltd
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/12Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant

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Abstract

The invention discloses a method for testing impact characteristics of a large grounding grid by utilizing grounding grid backflow, which comprises the following steps: selecting the positions of a current injection point and a current backflow point on the ground screen, wherein the current injection point is connected with the positive electrode of the impact power supply, and the current backflow point is connected with the negative electrode of the impact power supply; selecting a voltage reference point on a connecting line of the current injection point and the current return point; when the high-voltage probe is used for measuring the potential difference between the current injection point and the voltage reference point when the impact current is injected into the ground grid, reading the peak value of the potential difference, namely the impact ground potential rise of the injection point; measuring a peak value of the impact current by using a current probe; and calculating the impulse grounding impedance of the grounding grid according to the impulse ground potential rise and the current. The current return electrode is arranged on the grounding grid to be detected, so that the current return electrode does not need to be laid outside the grounding grid to be detected again, the impedance of a loop is reduced, and the detection of the impact characteristic of the grounding grid is facilitated.

Description

Large-scale grounding grid impact characteristic testing method utilizing grounding grid backflow
Technical Field
The invention relates to the technical field of high voltage, in particular to a method for testing impact characteristics of a large grounding grid by utilizing grounding grid backflow.
Background
For operation and safety in power systems, it is often necessary to connect some parts of the power system and its electrical equipment to ground, which is ground. In order to ensure reliable grounding of the transformer substation, a grounding grid needs to be buried underground of the transformer substation, and the size of the grounding grid can be equivalent to the area of the transformer substation.
At present, the main index for checking the performance of the grounding network is the power frequency grounding resistance of the grounding network, the related detection method is very complete, the newly-built grounding network and the grounding network used for a period of time need to be subjected to power frequency grounding resistance measurement in practice, and the performance of the grounding network is evaluated according to the size of the power frequency grounding resistance.
Short circuit to ground and lightning strike are common accidents in power systems, and the impact current which is generally mainly composed of high-frequency components and is injected into a grounding grid during the lightning strike. The impact characteristic of the grounding grid is greatly different from the power frequency characteristic, under impact, due to the inductance effect of the grounding conductor, impact current is difficult to uniformly diffuse on the grounding grid, but is concentrated on the grounding conductor near a current injection point to diffuse, and the effective area of the diffused current is small. Therefore, under the impact current injection, a great transient potential difference occurs between the injection point and other areas of the grounding grid. The diagonal length of the grounding grid of the newly-built extra-high voltage transformer substation can generally reach hundreds of meters, and the power frequency grounding resistance of the large-area grounding grid is very small. However, since the problem of effective area exists in the inrush current dissipation, even if the power frequency ground resistance of the ground grid is small, the inrush current is injected into the ground grid, which may still cause dangerous inrush transient ground potential rise. Therefore, it is necessary to examine the impact characteristics of the grounding grid. However, at present, the impact characteristics of the grounding grid are rarely considered in engineering, which undoubtedly leaves a great safety hazard.
The DL/T266-2012 grounding device impact characteristic parameter test guide provides a method for measuring the impact characteristic of the grounding device with reference to the power frequency characteristic measurement method, which is a conventional three-pole method, as shown in fig. 1. According to the requirements of DL/T266-2012, the current return pole (labeled C in FIG. 1) should be 2-3D away from the edge of the ground grid (D is the maximum diagonal length of the grounding device). The small-sized grounding device has smaller diagonal length, and can easily meet the requirement. However, the length of the diagonal line of the grounding grid of the extra-high voltage transformer substation can reach hundreds of meters, and the position of a reflux point meeting the requirement is often within one kilometer or even several kilometers. The impact current generated by the impact test is generally high in amplitude, a thick copper wire is required to be selected as a current lead, the current lead is difficult to arrange in a long distance, and the field workload is huge; and the overlong lead has larger inductance, so that the impact current is greatly hindered. Meanwhile, the laid return electrode can only be simply arranged due to the limitation of field conditions, and the grounding resistance is very large. The inductance of the long lead and the grounding resistance of the return electrode cause the impedance of the whole loop to be larger, the amplitude of the output impact current is severely limited, the waveform of the impact current can be seriously distorted, and the impact current meeting the requirements cannot be obtained.
Disclosure of Invention
Aiming at the defects in the problems, the invention provides a method for testing the impact characteristic of a large grounding grid by utilizing the backflow of the grounding grid.
In order to achieve the above object, the present invention provides a method for testing impact characteristics of a large-scale grounding grid by using grounding grid backflow, comprising:
step 1, selecting positions of a current injection point and a current backflow point on a ground screen, wherein the current injection point is connected with a positive electrode of an impact power supply, and the current backflow point is connected with a negative electrode of the impact power supply;
step 2, selecting a voltage reference point on a connecting line of the current injection point and the current backflow point;
step 3, measuring the potential difference between the current injection point and a voltage reference point when the impact current is injected into the ground grid by using the high-voltage probe, and reading the peak value of the potential difference, namely the impact ground potential rise of the injection point;
step 4, measuring the peak value of the impact current by using a current probe;
and 5, calculating the impact grounding impedance of the ground network according to the impact ground potential rise and the current.
As a further improvement of the present invention, in step 1, the current injection point and the current flowing point are grounded downleads, and the distance between the current injection point and the current flowing point is greater than 100 m.
As a further improvement of the present invention, in step 2, the distance between the current injection point and the current flowing point is L, and the distance between the current injection point and the voltage reference point is 0.618L.
As a further improvement of the present invention, in step 3, the positive terminal of the high voltage probe is connected to the current injection point, the negative terminal of the high voltage probe is connected to the voltage reference point through a metal wire, the data terminal of the high voltage probe is connected to an oscilloscope or a data acquisition card to record the waveform of the potential difference, and the peak value Um of the potential difference is read, i.e. the impulse ground potential rise of the injection point.
As a further improvement of the invention, a current probe is used for measuring the peak value Im of the impact current, and the impact grounding impedance of the grounding grid is calculated according to Um and Im.
As a further improvement of the invention, the method also comprises the following steps: measuring the ground potential rise near the current injection point;
during measurement, the positive end of the high-voltage probe is connected to the grounding down lead near the injection point, and the negative end of the high-voltage probe is connected to a voltage reference point through a metal wire.
Compared with the prior art, the invention has the beneficial effects that:
according to the invention, the current return electrode is arranged on the grounding grid to be detected, so that the current return electrode does not need to be laid outside the grounding grid to be detected again, the impedance of a loop is reduced, and the detection of the impact characteristic of the grounding grid is facilitated;
the testing method only needs to lay a current lead wire of about 100m, greatly reduces the measuring workload, and can compensate the influence of a reflux point, so that the measuring result is more accurate.
Drawings
FIG. 1 is a schematic diagram of a conventional tripolar process;
fig. 2 is a flowchart of a method for testing impact characteristics of a large-scale grounding grid using ground grid backflow according to an embodiment of the present invention;
FIG. 3 is a diagram of the arrangement of current injection points and current return points on the earth mat according to one embodiment of the present invention;
FIG. 4 is a layout diagram of voltage reference points disclosed in one embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it should also be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
The invention is described in further detail below with reference to the attached drawing figures:
in fact, when the impact current is injected into the earth screen, the impact current is concentrated on the injection point and the nearby area for scattering. From the injection point outwards, the ground network ground potential rise decays rapidly, which is very different from the low frequency, so for extra-high voltage substations the return point does not need to be as far as recommended in the standard. The reasonable position of the reflux point can even be in the ground net to be tested, at the moment, because the longitudinal inductance of the ground net under impact is larger, most of current scatters to flow into the ground, and does not flow back to the power supply through a ground net conductor. According to the thought, the invention provides the method for testing the impact characteristic of the large grounding grid by utilizing the return current of the grounding grid.
As shown in fig. 2, the present invention provides a method for testing impact characteristics of a large-scale grounding grid using ground grid backflow, wherein a current injection point and a current backflow point are simultaneously disposed in the ground grid to be tested; the method specifically comprises the following steps:
s101, as shown in figure 3, selecting the positions of a current injection point and a current return point on a to-be-detected grounding grid (a grid shown in figure 3), wherein the current injection point is generally a grounding down lead of important equipment or a lightning rod, and the current return point selects the grounding down lead which has a certain distance (more than 100 m) from the current injection point; after the positions of the current injection point and the current backflow point are selected, the positive electrode of the impact power supply is connected with the current injection point grounding down lead, the negative electrode of the impact power supply is connected with the current backflow point grounding down lead, and impact current is generated through the impact power supply.
S102, as shown in the figure 4, selecting a voltage reference point on a connecting line of a current injection point and a current return point; the distance between the current injection point and the current flowing point is L, and the distance between the current injection point and the voltage reference point is 0.618L.
S103, measuring the potential difference between a current injection point and a voltage reference point when the impact current is injected into the ground grid by using a high-voltage probe; the positive end of the high-voltage probe is connected with a current injection point, the negative end of the high-voltage probe is connected with a voltage reference point through a metal wire, a data connector of the high-voltage probe is connected with an oscilloscope or a data acquisition card to record the waveform of the potential difference, and the peak value Um of the potential difference is read, namely the impulse ground potential rise of the injection point.
S104, measuring a peak value Im of the impact current by using a current probe;
and S105, calculating the impact grounding impedance of the earth screen according to the impact ground potential rise Um and the current Im.
The invention can also use the high-voltage probe to measure the ground potential rise near the injection point; during measurement, the positive end of the high-voltage probe is connected to the grounding down lead near the injection point, and the negative end of the high-voltage probe is connected to a voltage reference point through a metal wire.
Different from the traditional three-pole method that the current return electrode needs to be laid outside the grounding grid to be detected again, the current return electrode is arranged on the grounding grid to be detected, the current return electrode does not need to be laid outside the grounding grid to be detected again, the impedance of a loop is reduced, and the detection of the impact characteristic of the grounding grid is facilitated; the testing method only needs to lay a current lead wire of about 100m, greatly reduces the measuring workload, and can compensate the influence of a reflux point, so that the measuring result is more accurate.
To super large-scale ground net, also can lay the backward flow utmost point near the department outside the ground net, but the position of backward flow utmost point need not to be as far as 2 ~ 3D apart from the ground net edge that requires in the standard, can lay the backward flow utmost point even at ground net edge.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (6)

1. A large-scale grounding grid impact characteristic test method utilizing grounding grid backflow is characterized by comprising the following steps:
step 1, selecting positions of a current injection point and a current backflow point on a ground screen, wherein the current injection point is connected with a positive electrode of an impact power supply, and the current backflow point is connected with a negative electrode of the impact power supply;
step 2, selecting a voltage reference point on a connecting line of the current injection point and the current backflow point;
step 3, measuring the potential difference between the current injection point and a voltage reference point when the impact current is injected into the ground grid by using the high-voltage probe, and reading the peak value of the potential difference, namely the impact ground potential rise of the injection point;
step 4, measuring the peak value of the impact current by using a current probe;
and 5, calculating the impact grounding impedance of the ground network according to the impact ground potential rise and the current.
2. A large ground net impact characteristic test method using ground net backflow according to claim 1, wherein in step 1, the current injection point and the current backflow point are ground down lines, and the distance between the current injection point and the current backflow point is more than 100 m.
3. The method for testing the impact characteristics of a large grounding grid using ground grid return current of claim 1, wherein in step 2, the distance between the current injection point and the current return point is L, and the distance between the current injection point and the voltage reference point is 0.618L.
4. The method for testing the impact characteristics of the large-scale grounding grid using the ground grid backflow as claimed in claim 1, wherein in step 3, the positive end of the high voltage probe is connected to a current injection point, the negative end of the high voltage probe is connected to a voltage reference point through a metal wire, the data connector of the high voltage probe is connected to an oscilloscope or a data acquisition card to record the waveform of the potential difference, and the peak value Um of the potential difference is read, namely the impact ground potential rise of the injection point.
5. A large grounding grid impact characteristic test method using grounding grid backflow as claimed in claim 4, characterized in that a current probe is used to measure the peak value Im of the impact current, and the impact grounding resistance of the grounding grid is calculated according to Um and Im.
6. A method for testing the impact characteristics of a large ground grid using ground grid reflow as set forth in claim 1, further comprising: measuring the ground potential rise near the current injection point;
during measurement, the positive end of the high-voltage probe is connected to the grounding down lead near the injection point, and the negative end of the high-voltage probe is connected to a voltage reference point through a metal wire.
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CN110412355A (en) * 2018-04-28 2019-11-05 武汉市康达电气有限公司 A kind of earth loop impedance test instrument
CN108761175B (en) * 2018-05-18 2021-03-12 云南电网有限责任公司电力科学研究院 Ground potential rise detection system and power transmission line lightning stroke condition determination method
CN109991468B (en) * 2019-03-21 2022-12-20 中国电力科学研究院有限公司 Method and device for testing disturbance voltage of secondary system of extra-high voltage transformer substation

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