Transformer substation grounding grid state rapid imaging method based on transient electromagnetic method

Abstract

The invention discloses a transformer substation grounding grid state rapid imaging method based on a transient electromagnetic method. The state of the grounding grid needs to be diagnosed, the defects of the grounding grid are found in time, and the problem of larger faults caused by accumulative effects is avoided. According to the invention, with the help of a true grounding grid model device, a transient electromagnetic transmitting device and a transient electromagnetic receiving device, electromagnetic waves transmitted by the transient electromagnetic transmitting device pass through a simulated true grounding grid model and then are received by the transient electromagnetic receiving device, and then data processing and comparison are carried out, so that the structure state of the grounding grid is imaged. According to the invention, the electromagnetic transmitting-receiving device is adopted to actively generate an electromagnetic field signal, so that transient electromagnetic rapid imaging is realized, and the defect position of the grounding grid can be rapidly diagnosed.

Description

Technical Field

[0001] The invention belongs to the technical field of substation grounding grid state monitoring, and in particular relates to a method for fast imaging of substation grounding grid state based on transient electromagnetic method. Background Art

[0002] Laying a grounding grid in a substation is an important measure to ensure the safe and stable operation of the power grid. The grounding grid can provide a common reference ground for various electrical equipment in the station, and can quickly discharge fault current when the power system fails, preventing the ground potential increase (TEV) from endangering the normal operation of secondary equipment. Therefore, the guarantee of the normal grounding function of the grounding grid is directly related to the personal safety of the staff in the power station and the safe and normal operation of the electrical equipment in the station.

[0003] In recent years, with the rapid expansion of the scale and capacity of power systems, many ground short-circuit currents have become increasingly large, which has put forward higher requirements for the safety and reliability of grounding grids. The material used for laying grounding grids is mainly flat steel. Poor welding during construction, soil corrosion, and the electrodynamic effect of grounding short-circuit currents have led to corrosion and fracture of flat steel and grounding flat steel, which has reduced the grounding performance and affected the normal operation of substations. However, it is unrealistic and very uneconomical to frequently excavate the grounding grid and check the status of the grounding conductor. Therefore, it is necessary to diagnose the status of the grounding grid, discover the defects of the grounding grid in time, and avoid the cumulative effect to cause greater fault problems. Summary of the invention

[0004] In order to make up for the shortcomings of the prior art, the present invention provides a method for rapid imaging of the substation grounding grid status based on the transient electromagnetic method, which can be applied to the research on substation grounding grid defect diagnosis and detection. Different geological targets can be identified according to the collected magnetic field strength values, and a method for testing the grounding grid status by building a measurement system is proposed.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for rapid imaging of substation grounding grid status based on transient electromagnetic method, characterized by:

[0007] By means of a real grounding grid model device, a transient electromagnetic transmitting device, and a transient electromagnetic receiving device, the electromagnetic waves emitted by the transient electromagnetic transmitting device pass through the simulated real grounding grid model and are received by the transient electromagnetic receiving device, and then data processing and comparison are performed to image the structural state of the grounding grid; the following steps are included:

[0008] Step 1: Establish a transient electromagnetic emission system near the grounding grid and arrange transient electromagnetic emission devices;

[0009] Step 2: Establish a transient electromagnetic receiving device according to the grounding grid structure and arrange equally spaced measuring lines;

[0010] Step 3: The transient electromagnetic transmitting device outputs current, and the transient electromagnetic receiving device is used to record the magnetic field strength;

[0011] Step 4: Rapidly image the acquired data to diagnose the grounding grid status.

[0012] Furthermore, the transient electromagnetic transmitting device transmits an output current which is a continuous trapezoidal wave.

[0013] Furthermore, a center-loop transient electromagnetic method is used.

[0014] Furthermore, the arrangement of the central loop transient electromagnetic method is specifically as follows:

[0015] A small receiving loop is placed at the center of a large transmitting coil, and the receiving loop detects and records the rate of change of the vertical component of the magnetic induction intensity over time.

[0016] Furthermore, in step 4, the collected data is rapidly imaged based on the smoke ring theory.

[0017] Further, step 4 is specifically as follows:

[0018] The induced electromotive force received by the transmitting coil on the ground is:

[0019]

[0020] Where: a——radius of transmitting coil;

[0021] I——emission current value;

[0022] σ——electrical conductivity of underground medium;

[0023] u——transient electromagnetic field parameters;

[0024] erf(u)——Error control function

[0025] For the central loop device, the transient electromagnetic field parameter u can be expressed as:

[0026]

[0027] Using (1) and (2), we can build a function about parameter u:

[0028]

[0029] Iterative calculation solves the equation F(u)=0 to obtain the transient electromagnetic field parameter u;

[0030] According to formula (3), the reciprocal of conductivity, namely the apparent resistivity value ρ, can be expressed as:

[0031]

[0032] According to the smoke ring theory, the speed v and depth d of the "smoke ring" spreading downward are:

[0033]

[0034]

[0035] Where: t——sampling time;

[0036] u——magnetic permeability of medium;

[0037] The speed v of the "smoke ring" spreading downward is written as the difference quotient of the diffusion depth and the sampling time as follows:

[0038]

[0039] Where: t i+1 and t i ——two consecutive sampling moments;

[0040] d i+1 and d i ——Diffusion depth value at two consecutive sampling moments.

[0041] According to formula (5), the apparent resistivity value ρ r Another expression, written according to the diffusion rate:

[0042]

[0043] Substituting equation (6) into equation (8), the apparent resistivity value calculated by parameter u according to equation (4) is;

[0044] The empirical formula for calculating the apparent depth value is:

[0045]

[0046] Using the calculated apparent resistivity value ρ r And the apparent depth value H r , transient electromagnetic rapid imaging can be achieved.

[0047] Beneficial effects of the present invention:

[0048] 1) The present invention combines the transient electromagnetic method with the actual test grounding grid entity to achieve rapid transient electromagnetic imaging, which is convenient for rapid diagnosis of the defect location of the grounding grid;

[0049] 2) The present invention adopts an electromagnetic transmitting-receiving device to actively generate electromagnetic field signals, thereby avoiding interference problems in traditional grounding grid status diagnosis. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a schematic diagram of a transient electromagnetic method on-site testing method of a method for rapid imaging of a substation grounding grid state based on the transient electromagnetic method of the present invention;

[0051] Figure 2 It is a layout diagram of a grounding grid breakpoint diagnosis experiment in a method for rapid imaging of a substation grounding grid state based on a transient electromagnetic method of the present invention;

[0052] Figure 3 The invention relates to a method for rapid imaging of the state of a substation grounding grid based on a transient electromagnetic method, which uses a transmitting-receiving system to record the magnetic field intensity value at a measuring point above the grounding grid;

[0053] Figure 4 It is a grounding grid structure and structure detection experimental survey line setting diagram of a method for rapid imaging of substation grounding grid status based on transient electromagnetic method of the present invention;

[0054] Figure 5 The invention discloses a 3D surface imaging diagram of apparent resistivity of a grounding grid of a substation according to a method for rapid imaging of the grounding grid state based on a transient electromagnetic method. DETAILED DESCRIPTION

[0055] The present invention is described in detail below in conjunction with specific implementation modes.

[0056] According to Faraday's law of electromagnetic induction, an almost identical magnetic field is induced underground to prevent the change in the magnetic field caused by the transmitting current. Due to Ohm loss, the induced ground current gradually decreases, and the induction field it generates also gradually weakens, thereby forming eddy currents in the underground medium. The current rings that continue to expand and diffuse downward in the underground medium are like expanding smoke rings. The magnetic field generated by the eddy current is collected by the receiving coil in the form of induced voltage (change in magnetic field flux over time). Underground targets with different electrical conductivity have different induced magnetic field values, so different geological targets can be identified based on the collected magnetic field values.

[0057] The present invention uses transient electromagnetic method and smoke ring theory to calculate and process the signal captured by the electromagnetic field receiving device to obtain its 3D apparent resistance map, thereby achieving the purpose of rapid imaging of the grounding grid, matching the imaging view with the actual structure of the grounding grid, and timely discovering the abnormalities and defects of the substation grounding grid to maintain the stable operation of the substation; the present invention includes the following steps:

[0058] Step 1: Establish a transient electromagnetic transmitting system near the grounding grid and arrange the transmitting device; the output current of the transient electromagnetic transmitting device should be a continuous trapezoidal wave;

[0059] Step 2: Establish a transient electromagnetic receiving system according to the grounding grid structure and arrange equally spaced measuring lines;

[0060] Step 3: The transmitter outputs current and the receiver records the magnetic field strength;

[0061] Step 4: Use the loop transient electromagnetic method to record the magnetic field value at the center of the transmitting coil on the ground through the receiving coil, and quickly image the collected data based on the smoke ring theory to assist in diagnosing the grounding grid status.

[0062] There are different transmitting and receiving combination devices in transient electromagnetic method. The present invention uses the center loop transient electromagnetic method. This arrangement places a small receiving loop at the center of a large transmitting coil, and the receiving loop detects and records the time-varying rate of change of the vertical component of the magnetic induction intensity.

[0063] The induced electromotive force received by the transmitting coil on the ground is:

[0064]

[0065] Where: a——radius of transmitting coil;

[0066] I——emission current value;

[0067] σ——electrical conductivity of underground medium;

[0068] u——transient electromagnetic field parameters;

[0069] erf(u)——Error control function

[0070] For the central loop device, the transient electromagnetic field parameter u can be expressed as:

[0071]

[0072] Using (1) and (2), we can build a function about parameter u:

[0073]

[0074] Iterative calculation solves the equation F(u) = 0 to obtain the transient electromagnetic field parameter u. According to formula (3), the reciprocal of conductivity, that is, the apparent resistivity value ρ, can be expressed by u as:

[0075]

[0076] According to the smoke ring theory, the speed v and depth d of the "smoke ring" spreading downward are:

[0077]

[0078] Where: t——sampling time;

[0079] u——magnetic permeability of medium;

[0080] The speed v of the "smoke ring" spreading downward is written as the difference quotient of the diffusion depth and the sampling time as follows:

[0081]

[0082] Where: t i+1 and t i ——two consecutive sampling moments;

[0083] d i+1 and d i ——Diffusion depth value at two consecutive sampling moments.

[0084] According to formula (5), the apparent resistivity value ρ r Change the expression. Write it according to the diffusion rate:

[0085]

[0086] Substituting equation (6) into equation (8), the apparent resistivity value is calculated from parameter u according to equation (4).

[0087] The empirical formula for calculating the apparent depth value is:

[0088]

[0089] Using the calculated apparent resistivity value ρ r And the apparent depth value H r , transient electromagnetic rapid imaging can be achieved.

[0090] The specific embodiments are as follows:

[0091] The present invention builds a small-scale real-type grounding grid experimental field and installs a transient electromagnetic transmitting-receiving system to carry out testing, and a small grounding grid model is used as an example for explanation.

[0092] Step 1: Establish a small-scale real grounding grid test site on the open ground and bury the grounding grid structure as follows: Figure 2 As shown. The grounding grid has 9 conductors in the X-axis direction, each conductor is 10.5m long, and 7 conductors in the Y-axis direction, each conductor is 14m long (some conductors are not drawn in the figure). The conductor material is galvanized flat steel. The grounding grid is buried 0.65m deep, and the size of all meshes surrounded by the grounding grid conductors is 1.75m×1.75m. During the construction of the grounding grid, a 0.02m wide break was set in the conductor CD segment;

[0093] Step 2: Transient magnetic field transmitting and receiving system layout

[0094] A measuring line is set up with 25 measuring points, with an interval of 0.35m between adjacent measuring points. The 13th measuring point is located directly above the grounding grid break. A transient electromagnetic transmitting-receiving system is used to carry out the experiment and record the ground magnetic field strength value. The transmitter is self-developed and can continuously output trapezoidal current without interruption. It is connected to the transmitting coil with a radius of 0.3m. The receiving coil has a radius of 0.17m and is connected to the receiver. The magnetic field data is received in the form of induced voltage and converted into magnetic field strength values ​​in subsequent data processing.

[0095] Step 3: Calculate and analyze the magnetic field strength above the grounding grid. Figure 3 The figure shows the magnetic field intensity values ​​recorded at 25 measuring points. The magnetic field intensity at the measuring points directly above the grounding grid conductor (such as measuring points 3 and 23) is still the local minimum, but the situation at measuring points 8, 13, and 18 has changed. The magnetic field intensity values ​​between measuring points 8 and 18 have become smaller overall. This phenomenon indicates that there is serious corrosion or fracture in the grounding grid conductor below these measuring points. In addition, the expected local maximum magnetic field intensity did not appear at the center of the grounding grid meshes ACDB and CEFD. Instead, an unexpected local maximum magnetic field intensity appeared at measuring point 13 directly above the grounding conductor CD. This shows that meshes ACDB and CEFD are likely to have gaps, while the large mesh AEFB is intact. Since measuring points 8 to 18 span two meshes ACDB and CEFD, and conductor CD is shared by both meshes, it can be inferred that the defect point appears on conductor CD. The defective conductor segment CD weakens the electromagnetic coupling between the transmitting coil and meshes ACDB and CEFD, resulting in a decrease in the magnetic field intensity value at the upper measuring point. At this point, we can conclude that there is a breakpoint on the grounding grid conductor CD.

[0096] Step 4: Redraw the small-scale grounding grid Figure 4 In. Figure 4 As shown in the figure, three measuring lines are set in the X and Y directions. The Y-axis coordinate values ​​of the three measuring lines (L1, L2, and L3) in the X direction are 0.875m, 2.625m, and 4.375m respectively, and the X-axis coordinate values ​​of the three measuring lines (L4, L5, and L6) in the Y direction are 0.875m, 2.625m, and 4.375m respectively. 20 measuring points are set on each measuring line. One measuring line is taken in the X and Y directions. Taking L1 and L4 as examples, the measuring point numbers are marked on Figure 4 The measuring points on other measuring lines are also numbered in sequence, and the distance between adjacent measuring points is 0.35m. After the transmitting current is turned off, the magnetic field strength values ​​on the six measuring lines are recorded, with a sampling interval of 2μs, and then the apparent resistivity values ​​are calculated based on the measured magnetic field strength values. The apparent resistivity value at the 500th sampling time is used to image the grounding grid structure, and the apparent resistivity 3D surface imaging of the grounding grid is obtained as shown in the figure. Figure 5As shown. From the figure, it can be clearly seen that meshes ABCD, BEHC, DCKJ and CHOK are crossed by two measuring lines in two directions (for example, mesh ABCD is crossed by measuring lines L2 and L5), while only a part of meshes EFGH, HGPO, JKMN and KOQM that are crossed by only one measuring line in one direction can be vaguely seen. Taking mesh EFGH as an example, the grounding grid conductors EH and FG can be clearly seen from the 3D surface imaging map of the grounding grid apparent resistivity, while conductors EF and GH are not shown in the figure.

[0097] There are measuring points distributed directly above the conductors EH and FG of the grounding grid. The apparent resistivity values ​​directly above the conductors are larger than those at other points. Therefore, the conductors EH and FG can be clearly displayed in the apparent resistivity 3D surface diagram. However, there are no measuring points distributed above the conductors EF and GH of the grounding grid, so naturally they cannot be displayed in the apparent resistivity 3D surface diagram. In addition, the apparent resistivity value at the center of the grounding grid mesh is lower than that at other points. Therefore, the complete meshes ABCD, BEHC, DCKJ and CHOK can be clearly seen from the apparent resistivity 3D surface diagram, while only part of the meshes EFGH, HGPO, JKMN and KOQM can be seen. In summary, Figure 5 The grounding grid structure under the six measuring lines is clearly drawn. If more measuring lines are set, the entire grounding grid can be imaged for fault diagnosis.

[0098] The content of the present invention is not limited to the embodiments listed, and any equivalent changes made to the technical solution of the present invention by ordinary technicians in this field after reading the description of the present invention are covered by the claims of the present invention.

Claims

1. A method for rapid imaging of substation grounding grid status based on transient electromagnetic method, characterized by: With the help of a real grounding grid model device, a transient electromagnetic transmitting device and a transient electromagnetic receiving device, the electromagnetic waves emitted by the transient electromagnetic transmitting device pass through the simulated real grounding grid model and are then received by the transient electromagnetic receiving device. After that, data processing and comparison are performed to achieve imaging of the structural status of the grounding grid.

2. According to claim 1, a method for rapid imaging of substation grounding grid status based on transient electromagnetic method is characterized by: The following steps are involved: Step 1: Establish a transient electromagnetic emission system near the grounding grid and arrange transient electromagnetic emission devices; Step 2: Establish a transient electromagnetic receiving device according to the grounding grid structure and arrange equally spaced measuring lines; Step 3: The transient electromagnetic transmitting device outputs current, and the transient electromagnetic receiving device is used to record the magnetic field strength; Step 4: Rapidly image the acquired data to diagnose the grounding grid status.

3. The method for rapid imaging of substation grounding grid status based on transient electromagnetic method according to claim 2 is characterized by: The transient electromagnetic emission device emits an output current which is a continuous trapezoidal wave.

4. The method for rapid imaging of substation grounding grid status based on transient electromagnetic method according to claim 3 is characterized by: The center-loop transient electromagnetic method is used.

5. The method for rapid imaging of substation grounding grid status based on transient electromagnetic method according to claim 4 is characterized by: The arrangement of the central loop transient electromagnetic method is specifically as follows: A small receiving loop is placed at the center of a large transmitting coil, and the receiving loop detects and records the rate of change of the vertical component of the magnetic induction intensity over time.

6. A method for rapid imaging of substation grounding grid status based on transient electromagnetic method according to claim 5, characterized in that: In step 4, the collected data is rapidly imaged based on the smoke ring theory.

7. A method for rapid imaging of substation grounding grid status based on transient electromagnetic method according to claim 6, characterized in that: Step 4 is as follows: The induced electromotive force received by the transmitting coil on the ground is: Where: a——radius of transmitting coil; I——emission current value; σ——electrical conductivity of underground medium; u——transient electromagnetic field parameters; erf(u)——Error control function For the central loop device, the transient electromagnetic field parameter u can be expressed as: Using (1) and (2), we can build a function about parameter u: Iterative calculation solves the equation F(u)=0 to obtain the transient electromagnetic field parameter u; According to formula (3), the reciprocal of conductivity, namely the apparent resistivity value ρ, can be expressed as: According to the smoke ring theory, the speed v and depth d of the "smoke ring" spreading downward are: Where: t——sampling time; u——magnetic permeability of medium; The speed v of the "smoke ring" spreading downward is written as the difference quotient of the diffusion depth and the sampling time as follows: Where: t i+1 and t i ——two consecutive sampling moments; d i+1 and d i ——Diffusion depth value at two consecutive sampling moments. According to formula (5), the apparent resistivity value ρ r Another expression, written according to the diffusion rate: Substituting equation (6) into equation (8), the apparent resistivity value calculated by parameter u according to equation (4) is; The empirical formula for calculating the apparent depth value is: Using the calculated apparent resistivity value ρ r And the apparent depth value H r , transient electromagnetic rapid imaging can be achieved.

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