CN114221327B - Interconnected direct-current path equivalent modeling method based on transformer substation bias - Google Patents
Interconnected direct-current path equivalent modeling method based on transformer substation bias Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
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Abstract
The method comprises the steps of projectively transforming spherical geodetic coordinates into plane rectangular coordinates based on longitude and latitude of a transformer substation, setting wide area power system soil as a non-uniform medium finite block to determine soil resistivity, and establishing a transformer substation direct current path model based on the plane rectangular coordinates, the soil resistivity and geomagnetic storm parameters, wherein the transformer substation direct current path model comprises a main transformer neutral point, a winding and transformer substation outgoing line model and a neutral point magnetic bias suppression element model which are sequentially arranged, simulating conductors among transformer substations, forming a transformer substation interconnection direct current path model based on the transformer substation direct current path model equivalent modeling, and calculating transformer substation magnetic bias to simulate and optimize the transformer substation interconnection direct current path model.
Description
Technical Field
The application relates to the technical field of transformer substations, in particular to an interconnection direct current path equivalent modeling method based on transformer substation magnetic bias.
Background
The dc bias phenomenon is an abnormal operation state of the transformer, that is, a dc component occurs in the exciting current of the transformer, and half-wave saturation occurs. When DC magnetic bias occurs, the exciting current of the transformer can generate a large amount of harmonic waves, the harmonic waves can cause the problems of temperature rise, vibration, noise and the like of the transformer, and in addition, the DC magnetic bias can influence the normal operation of equipment such as relay protection equipment, a capacitor bank, a current transformer and the like. The transformer windings flow into the dc component for a number of reasons and can be divided into the following 2 main aspects:
(1) Dc power transmission monopolar earth return mode operation for a two-terminal dc system for remote power transmission, typically in bipolar mode. However, in the initial stage of construction of the direct current transmission system, in order to improve economic benefit, a pole is often built and then put into operation, the single pole operation mode of direct current transmission often uses the earth as a reflux circuit, namely the earth serves as another wire of the direct current transmission line, the current flowing through the earth is the working current of the direct current transmission project, at this time, the current up to several kiloamperes is injected into the earth from the direct current grounding pole, and the current of the extra-high voltage direct current transmission grounding pole is even larger than 4kA.
(2) The potential gradient on the earth surface is caused by the change of geomagnetic field of 'geomagnetic storm' generated by the interaction of the dynamic change of solar plasma wind and the geomagnetic field. When severe geomagnetic storm occurs, the potential gradient of the area with small ground conductivity can reach several volts per kilometer to hundreds of volts, the duration is from minutes to hours, when the low-frequency electric field with a certain duration acts on the transformer with the neutral point grounded in the power grid, the Geomagnetic Induction Current (GIC) is generated in the winding, the frequency is between 0.001 and 1HZ, the frequency can be approximately regarded as direct current, and the value can reach more than 80 to 100A. Serious geomagnetic storm affects power and communication systems, direct current magnetic bias caused by the magnetic storm enables a transformer iron core to be seriously saturated, harmonic wave is increased, relay protection misoperation is caused, a large number of capacitors are out of operation, and system voltage collapses.
The damage to the two conditions is frequent in the power system of China. Therefore, research on the DC magnetic bias influence of the transformer by the domestic and foreign electric power scientific research institutions is continuously carried out, and the research mainly comprises the following aspects of firstly evaluating the DC magnetic bias influence of the transformer by installing a DC measuring device at the neutral point of the transformer and secondly researching the earth surface potential and the current density when the DC system operates in the monopolar earth or the solar magnetic storm occurs. According to the research, the establishment of the transformer substation interconnection direct current path model of the large-scale power system is not realized at present, the region of China is wide, and the power system is huge, so that equivalent modeling of the transformer substation bias calculation interconnection direct current path is necessary, and the follow-up power system can safely operate.
The above information disclosed in the background section is only for enhancement of understanding of the background of the application and therefore may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.
Disclosure of Invention
In order to overcome the defect of modeling in the existing transformer substation direct current magnetic biasing process, the equivalent modeling method for the interconnected direct current paths based on transformer substation magnetic biasing is provided, so that the direct current paths of a large-scale power system can be accurately established, the influence of transformer direct current magnetic biasing can be evaluated, and the stable operation of the power system is ensured.
In order to achieve the above purpose, the application provides a technical scheme that the interconnected direct current path equivalent modeling method based on transformer substation bias magnetism comprises the following steps:
based on longitude and latitude of the transformer substation, the spherical geodetic coordinates are projected and transformed into plane rectangular coordinates;
setting the soil of the wide area power system as a non-uniform medium finite block to determine the soil resistivity;
establishing a transformer substation direct current path model based on the plane rectangular coordinates, the soil resistivity and geomagnetic storm parameters, wherein the transformer substation direct current path model comprises a main transformer neutral point, a winding, a transformer substation outgoing line model and a neutral point magnetic bias suppression element model which are sequentially arranged;
simulating conductors among substations, and forming a substation interconnection direct current path model based on equivalent modeling of the substation direct current path model, wherein transformer outgoing lines are connected among the substations of the substation direct current path model through lines to form the substation interconnection direct current path model;
and calculating the magnetic bias of the transformer substation to simulate and optimize the transformer substation interconnection direct current path model.
In the equivalent modeling method of the interconnected direct current path based on transformer substation magnetic bias,
and further establishing a direct current path model of the transformer substation based on the grounding electrode parameters.
In the equivalent modeling method of the interconnected direct current path based on transformer substation magnetic bias,
and when the calculated magnetic bias of the transformer substation is larger than a threshold value required by the transformer substation, the transformer substation direct current path model suppresses the magnetic bias element model through the neutral point to optimize the transformer substation interconnection direct current path model.
In the equivalent modeling method of the interconnected direct current path based on transformer substation magnetic bias,
when the studied power grid comprises at least two substations, the inter-station surface potential V of two adjacent substations on the power grid is:
wherein ,hi H is the thickness of the ith layer of the soil 0 Is the thickness of the soil surface layer; z is the soil depth; r is the distance from the ground electrode; ρ i The resistivity of the soil of the corresponding layer; g is a direct current grounding electrode, the ground potential is assumed to be V, the current in the upper soil is I, and the ground current of the grounding electrode g is I 0 ，J 0 (lambda r) is a zero-order Bessel function of the first class, ai (lambda), bi (lambda) are coefficients of a surface potential function solution, wherein lambda is a Bessel constant and is determined by boundary conditions:
when z approaches infinity, the surface potential is zero: v (r, z) | z→∞ =0; when the potentials at the soil interfaces are equal:
v is the earth potential, h i The thickness of the ith layer of the soil, z is the depth of the soil, r is the distance from the grounding electrode, ρ i The resistivity of the soil of the corresponding layer;
further, the magnetic bias change trend of the transformer substation can be inspected based on the earth surface potential.
In the equivalent modeling method of the interconnected direct current path based on transformer substation magnetic bias,
when the network under investigation comprises only a single substation, or when simplified calculation of the ground potential is required, the ground potential of the substationThe method comprises the following steps:
wherein ,hi The thickness of the ith layer of the soil; epsilon is the complex dielectric constant of soil 0 For the complex dielectric constant of the soil at the grounding electrode epsilon r The complex permittivity of the soil at a distance r from the grounding electrode; z is the soil depth and sigma is the soil conductivity;
further, the magnetic bias change trend of the transformer substation can be inspected based on the earth surface potential.
In the technical scheme, the interconnection direct current path equivalent modeling method based on transformer substation magnetic bias has the following beneficial effects: the interconnection direct current path equivalent modeling method based on transformer substation bias can conduct direct current path equivalent modeling on a large-scale complex power system, solves the limitation of building a direct current bias model of the transformer substation interconnection system, and can evaluate the bias level of a transformer of the power system, so that stable and safe operation of the power system is guaranteed.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments described in the present application, and other drawings may be obtained according to these drawings for a person having ordinary skill in the art.
FIG. 1 is a schematic flow chart of the present application.
Fig. 2 is a schematic diagram of converting longitude and latitude of a substation according to an embodiment of the present application.
Fig. 3 is a schematic view of an actual net rack of the device according to the embodiment of the present application.
FIG. 4 is a schematic illustration of a finite block of any inhomogeneous medium of the soil according to an embodiment of the application.
Fig. 5 is a substation grounding grid diagram according to an embodiment of the present application.
Fig. 6 is a main transformer position diagram in an embodiment of the application.
Fig. 7 is a schematic diagram of a transformer high-medium voltage winding distribution in an embodiment of the application.
Fig. 8 is a schematic diagram of a neutral grounding mode of a transformer according to an embodiment of the application.
Fig. 9 is a schematic diagram of neutral point bias suppression of a transformer according to an embodiment of the present application.
Fig. 10 shows the variation of bias current of each station with 1, 2, 3, 4 and 5 ohm resistors added after the bias current of 16.46A flows into the 500kV transformer substation according to the embodiment of the application.
Fig. 11 shows the variation of bias current of each station with 1, 2, 3, 4 and 5 ohm resistors added after the bias current of 14.85A flows into the 500kV transformer substation according to the embodiment of the application.
Note that, the light gray background and the grid thereof in fig. 5 to 9 represent reference lines of the related drawings, and are not limited in any way to any substantial limitation in fig. 5 to 9.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present application more apparent, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, based on the embodiments of the application, which are apparent to those of ordinary skill in the art without inventive faculty, are intended to be within the scope of the application.
Thus, the following detailed description of the embodiments of the application, as presented in the figures, is not intended to limit the scope of the application, as claimed, but is merely representative of selected embodiments of the application. All other embodiments, based on the embodiments of the application, which are apparent to those of ordinary skill in the art without inventive faculty, are intended to be within the scope of the application.
It should be noted that: like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further definition or explanation thereof is necessary in the following figures.
In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings are merely for convenience in describing the present application and simplifying the description, and do not indicate or imply that the apparatus or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present application.
Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present application, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.
In the present application, unless explicitly specified and limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally formed; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art according to the specific circumstances.
In the present application, unless expressly stated or limited otherwise, a first feature "above" or "below" a second feature may include both the first and second features being in direct contact, as well as the first and second features not being in direct contact but being in contact with each other through additional features therebetween. Moreover, a first feature being "above," "over" and "on" a second feature includes the first feature being directly above and obliquely above the second feature, or simply indicating that the first feature is higher in level than the second feature. The first feature being "under", "below" and "beneath" the second feature includes the first feature being directly under and obliquely below the second feature, or simply means that the first feature is less level than the second feature.
In order to make the technical scheme of the present application better understood by those skilled in the art, the present application will be further described in detail with reference to the accompanying drawings.
In one embodiment, the application discloses an interconnection direct current path equivalent modeling method based on transformer substation magnetic bias, which comprises the following steps:
converting longitude and latitude of the transformer substation, performing projection transformation on spherical geodetic coordinates, converting the spherical geodetic coordinates into plane rectangular coordinates required by modeling,
setting the soil resistivity, setting the soil of the wide area power system as a non-uniform medium finite block so as to improve the accuracy of the model,
establishing a transformer substation direct current path model based on the plane rectangular coordinates, the soil resistivity and geomagnetic storm parameters, wherein the transformer substation direct current path model comprises a main transformer neutral point, a winding, a transformer substation outgoing line model and a neutral point magnetic bias suppression element model which are sequentially arranged; in other words, when the transformer substation model is built, models such as a main transformer neutral point, a winding, a transformer substation outgoing line and the like can be sequentially set, and accurate model building can be performed on whether the main transformer is grounded, a neutral point magnetic bias suppression element and the like;
simulation of conductors between stations is realized, and equivalent modeling of the interconnected direct current paths is realized through bias calculation of the transformer substation of the power system: specifically, simulating conductors among substations, and forming a substation interconnection direct current path model based on equivalent modeling of the substation direct current path model, wherein transformer outgoing lines are connected among transformer stations of the substation direct current path model through lines to form the substation interconnection direct current path model; it can be appreciated that the transformer outlet, the primary of the transformer substation outlets described above;
further, substation bias is calculated to simulate and optimize the substation interconnection direct current path model.
In a further embodiment of the present application,
in the equivalent modeling method of the interconnected direct current path based on transformer substation magnetic bias,
and further establishing a direct current path model of the transformer substation based on the grounding electrode parameters. It can be appreciated that this helps to more quickly and to simulate the degree of simulation more closely to that required by an actual substation.
The sources of the soil resistivity, geomagnetic storm parameters, grounding electrode parameters and the like are local historical original data or actual measurement on site if necessary. In addition, the direct current path model of each transformer substation can be established on the cdegs software by utilizing the parameters.
In another embodiment, see fig. 1, wherein,
establishing a direct current path model of the transformer substation based on the plane rectangular coordinates, the soil resistivity, the grounding electrode parameters and the geomagnetic storm parameters;
after the direct current path model of the transformer substation is built, further checking whether the model is defect-free, and if so, returning to build the direct current path model of the transformer substation again; if no defect exists, the transformer substation bias is calculated through simulation, namely bias current calculation is carried out on the interconnected direct current system;
when the deviation between the simulation value of the bias current calculated by the model and the actual field measurement value is less than 5%, the current model is matched with the actual field situation, but the bias is higher, and a suppression measure can be added to the transformer with larger neutral point current, for example, the bias of the current interconnected direct current channel model is suppressed by the neutral point suppression bias element model in the previous embodiment. It can be understood that the smaller the bias is, the better, and therefore, the neutral point suppression bias element model is set by default in the modeling method described in the present application. When the deviation between the simulation value of the bias current calculated by the model and the actual field value is less than 5%, the current model is not fit with the actual field situation, so that in order to refine, the interconnection direct current parameters of the transformer substation are required to be adjusted to adjust the interconnection direct current path model, and the simulation value of the bias current is calculated again based on the adjusted interconnection direct current path model and compared with the deviation of the actual field value until the simulation value meets the following requirements: when the deviation between the calculated bias current simulation value and the field actual measurement value is less than 5%, the current model is matched with the field actual condition, the bias is higher, and then the suppression measure is added to the transformer with larger bias current.
Thus, for the purposes of the present application, as is generic,
and when the calculated magnetic bias of the transformer substation is larger than a threshold value required by the transformer substation, the transformer substation direct current path model suppresses the magnetic bias element model through the neutral point to optimize the transformer substation interconnection direct current path model.
In one embodiment, after finishing the collected data of each transformer substation and the grounding electrode in the study, the data are converted into plane coordinates through Gauss-Gauss transformation, and as shown in fig. 2, the longitude and latitude of the geodetic coordinates are converted into plane rectangular coordinates. For example, for the entire Shandong, the difference in longitude of ωeast is 13.4 ° and the difference in latitude is 4.0166 °. Without the sphere to plane conversion, the longitude in the eastern Shandong region would cause a distance error of 1232.8kmm and the latitude would cause a distance error of 349.4442 km. The influence of spherical coordinates on the calculation result is not negligible.
In the equivalent modeling method of the interconnected direct current path based on transformer substation magnetic bias,
when the studied power grid comprises at least two substations, the inter-station surface potential V of two adjacent substations on the power grid is:
wherein ,hi H is the thickness of the ith layer of the soil 0 Is the thickness of the soil surface layer; z is the soil depth; r is the distance from the ground electrode; ρ i The resistivity of the soil of the corresponding layer; g is a direct current grounding electrode, the ground potential is assumed to be V, the current in the upper soil is I, and the ground current of the grounding electrode g is I 0 ，J 0 (lambda r) is a zero-order Bessel function of the first class, ai (lambda), bi (lambda) are coefficients of a surface potential function solution, wherein lambda is a Bessel constant and is determined by boundary conditions:
when z approaches infinity, the surface potential is zero: v (r, z) | z→∞ =0; when the potentials at the soil interfaces are equal:
v is the earth potential, h i The thickness of the ith layer of the soil, z is the depth of the soil, r is the distance from the grounding electrode, ρ i The resistivity of the soil of the corresponding layer;
further, the magnetic bias change trend of the transformer substation can be inspected based on the earth surface potential.
By now it can be appreciated that on the basis of the above calculation of bias, the main purpose of further calculating the surface potential is to: and (5) inspecting the magnetic bias change trend of the transformer substation.
For this embodiment, the following is described: the interconnection direct current path model, as the name implies, relates to the interconnection of substations, and precisely to two adjacent substations on a power grid, which are naturally electrically connected on the power grid. Just as the interconnection of the two is involved, the main object of the application is: the network under investigation comprises a situation of at least two substations. However, if the studied power grid comprises only one substation, the core concept of the technical scheme of the application can still be expanded.
Therefore, in one embodiment, in the interconnected direct current path equivalent modeling method based on transformer substation magnetic bias,
when the network under investigation comprises only a single substation, or when a simplified calculation of the surface potential is required for the previous embodimentThe method comprises the following steps:
wherein ,hi The thickness of the ith layer of the soil; epsilon is the complex dielectric constant of soil 0 For the complex dielectric constant of the soil at the grounding electrode epsilon r The complex permittivity of the soil at a distance r from the grounding electrode; z is the soil depth and sigma is the soil conductivity;
further, the magnetic bias change trend of the transformer substation can be inspected based on the earth surface potential.
In fact, in another embodiment, when the electric network under study includes only a single substation, the inventive concept of the present application can be generalized to obtain the following method for modeling the equivalent of the interconnected dc paths based on the bias of the substation, including the following steps:
when the studied power grid comprises one or more substations, based on the longitude and latitude of each substation, the spherical geodetic coordinates are projectively transformed into plane rectangular coordinates,
the wide area power system soil is set as a finite block of non-uniform medium to determine soil resistivity,
establishing each transformer substation direct current path model on cdegs software based on the plane rectangular coordinates, the soil resistivity, the grounding electrode parameters and the geomagnetic storm parameters, wherein the transformer substation direct current path model comprises a main transformer neutral point and a winding which are sequentially arranged, and whether a transformer substation outgoing line is included or not is an option;
simulating conductors among all substations, and forming a substation interconnection direct current path model between two adjacent substations on a power grid based on equivalent modeling of the substation direct current path model, wherein transformer outgoing lines are connected between transformer substations of the substation direct current path model through lines to form the substation interconnection direct current path model-it can be understood that when only one substation exists in the researched power grid, the conductors among all substations do not exist, and therefore the step does not need to be executed;
and finally, calculating the magnetic bias of each transformer substation to judge whether the magnetic bias inhibition of the neutral point is needed to be passed so as to optimize the transformer substation direct current path model corresponding to each transformer substation.
The application will be further described with reference to the drawings and examples. In the embodiment, two 500kV substations and two 220kV substations form a power system grid for case analysis, as shown in fig. 3, and the accuracy of the equivalent modeling method of the transformer substation bias calculation interconnection direct current path under the two conditions of the grounding electrode and the grounding magnetic storm is analyzed by setting different excitation sources.
On the one hand, the normal operation mode of the transformer is influenced by the grounding electrode as follows:
when the DC transmission engineering runs in a monopolar mode, the grounding electrode injects DC current into the ground to form an electric field in the ground, DC potential difference exists between the two transformer stations, the DC current flows into an AC system through the grounding neutral point of the transformer, the DC magnetic bias phenomenon of the transformer is caused, and the ground surface potential and the soil structure have great correlation, so that the DC magnetic bias phenomenon is very important for calculating the magnetic bias current of the transformer substation. At present, the direct current bias current calculation adopts a field coupling principle, the ground potential and the ground resistance are separately and independently discussed, the ground potential is calculated by using a soil model, the potential difference between two transformer stations is obtained, and then the direct current bias current is calculated according to a circuit method. In the direct current magnetic bias research, a horizontal soil layering model, h, is generally adopted for analyzing the earth surface potential in a large range i H is the thickness of the ith layer of the soil 0 Is the thickness of the soil surface layer; z is the soil depth; r is the distance from the ground electrode; ρ i The resistivity of the soil of the corresponding layer; g is a direct current grounding electrode. Assuming that the ground potential is V, the current in the upper soil is I, and the earth-entering current of the grounding electrode g is I 0 。
Solving the earth surface potential distribution problem is to solve the green function of the horizontal multi-layer soil model, and the earth surface potential function is as follows:
in the above formula: j (J) 0 (lambda r) is a first zero-order Bessel function, ai (lambda) and Bi (lambda) are coefficients of a surface potential function solution, and the coefficients are determined by boundary conditions:
when z approaches infinity, the surface potential is zero:
V(r，z)| z→∞ ＝0
when the potentials at the soil interfaces are equal:
in the actual ground engineering, the earth potential is of interest, and thus if the earth potential is calculated in a simplified manner, the earth potential may be:
the circuit method for the topological structure of the ground alternating current network frame comprises the following steps:
R b I b ＝B T U m
I m ＝-B T I b
I b ＝G b U b
I m ＝-B T G b BU m
wherein: m is the number of substations, b is the number of independent grounded neutral points, U m and In Column vectors of main transformer neutral point direct current potential and bias current respectively; u (U) b and Ib The column vectors are respectively the branch voltage and the branch direct current of the branch connected with each transformer substation; g b Is a branch admittance matrix; b is an n×m incidence matrix.
Then for the entire grid model, given the grid topology, the following equation can be obtained:
in the formula ：RM Is a mutual resistance matrix between transformer substations; r is R N Is a mutual resistance matrix between the transformer substation and the grounding electrode.
Equations (8) and (9) are combined to obtain the ground potential and DC magnetic bias current of the transformer substation, and the magnetic bias change trend is inspected.
On the other hand, geomagnetic storms affect the normal operation of the transformer as follows:
when a geomagnetic storm occurs, the geomagnetic field caused by the space current can be assumed to be a plane wave vertically downward because the high-energy particle flow is very far from the earth's surface. The electromagnetic field induced in the earth is assumed to be the same as the z-axis direction by using a rectangular coordinate system, the x-direction is north, the y-direction is east, and the z-direction is vertically downward, and the earth's soil conductivity sigma is considered to be uniform and unchanged. The method can obtain:
let g=db/dt, when the low frequency phenomenon is:
the inverse Fourier transform can be used to obtain the time-domain relation between the induction electric field and the geomagnetic field change rate
E (omega) is a time-harmonic electromagnetic field, mu 0 Is vacuum permeability, σ is soil conductivity. E (t) is the induction electric field component, g (t) is the change rate of the geomagnetic field. Can be used forThe ground induced potential is calculated according to this formula.
The transformer substation model is positioned by adopting standard plane rectangular coordinates, and all simulation results are carried out aiming at soil with a plane and a certain depth. The coordinates provided by the current converter station, the grounding electrode and each transformer substation are longitude and latitude. Longitude and latitude become Geodetic Coordinates (GCS) in mapping professions. The reference plane of the geodetic coordinates is the sphere of the earth, so projection transformation is necessary in the calculation of a large range (tens of square kilometers) to obtain more accurate plane rectangular coordinates.
In the embodiment of the application, the soil adopts any finite block of heterogeneous medium as shown in fig. 4, and for a large-scale power system, only horizontal or vertical layering is far from sufficient, so that a plurality of finite soil blocks are required to be designated, and soil characteristics and soil block coordinates are defined. The number of soil pieces is first specified (20 soil pieces are defined in this example), and the surrounding soil resistivity is defined at the natural soil resistivity. For each block, it is necessary to input any two coordinates of the opposing block surface X, Y, Z, each plane being defined by the coordinates of the four vertices and arranged in either a clockwise or counterclockwise direction.
The embodiment of the application establishes a theoretical model of the transformer substation, and the power frequency grounding resistance of each transformer substation is set to be 0.1 omega. In order to reduce the calculation scale, according to the earlier research, the transformer substation grounding network is simplified into a square conductor grid composed of 6 conductors, the buried depth is 1.5m, the side length of the conductor grid is 63.3m as shown in fig. 5, 7 main transformers of each transformer substation are tentatively set in the simulation process, the main transformers are sequentially distributed at the middle positions of the grounding network of each transformer substation as shown in fig. 6, high-voltage ABC three-phase windings are horizontally arranged at each station, medium-voltage ABC three-phase windings are horizontally arranged at the position of 5m of the high-voltage windings along the positive direction of the Y axis, a small section of the main transformer neutral point bus is arranged for appearance, and the windings are respectively connected with the corresponding main transformer as shown in fig. 7.
In the embodiment, the 220kV transformer substation model adopts two transformers, wherein one transformer neutral point is grounded, and the other transformer neutral point is not grounded, so that the 220kV transformer substation adopts the model shown in fig. 8, and different operation modes of the transformers can be distinguished.
In this example, the adding point of the transformer inhibition measure is shown in fig. 9, and the bias magnetic inhibition element can be added below the connecting point of the neutral point and the winding of the transformer substation, so as to achieve the comprehensiveness of the model establishment.
By modeling the equivalent of the transformer substation bias calculation interconnection direct current path, different excitations are applied, and individual spread direct current bias current distribution can be obtained as shown in table 1. By comparing the simulation value with the actual measurement value which is smaller than 5%, the accuracy of the model is verified.
Table 1 dc bias current statistics for each station
| ID | Voltage level (KV) | DC bias current |
| Sa | 500 | 16.46 |
| Sb | 500 | 14.85 |
| Sc | 220 | 6.08 |
| Sd | 220 | 4.57 |
From the statistics of the dc bias current, it is known that the Sa Sb station needs to be treated. The parameters of the resistance type restraining device are important, if the resistance value is too large, the overvoltage of a neutral point is high, and the protection is also greatly influenced; the selected resistance value is smaller, and the direct current inhibition effect is affected. According to the condition of the power grid, in order to select a proper resistance value, after 1, 2, 3, 4 and 5 ohm resistors are added in a 500kV Sa station and a 500kV Sb station respectively in the model, the change condition of bias current of each station is shown in figures 10 and 11.
As can be seen from the results of fig. 10 and 11, the suppression effect shows a tendency to gradually saturate as the resistance value increases, and the dc amplitude decreases significantly as the resistance value increases when the resistance value is smaller; when the resistance value is large, the proportion of the decrease of the direct current amplitude value along with the increase of the resistance value is smaller. From the above calculation, it is appropriate to select the 4Q resistance value at Sa and Sb stations only from the viewpoint of the magnitude of the decrease in the direct-current bias current.
In practice, multiple geological conditions such as mountains, rivers, faults and the like require multiple soils to perform block modeling, in one embodiment, wide area power system soil refers to performing model building and calculation on a power grid GIC, and the composite soil model resistivity is more fit to reality, so that the accuracy of calculation can be improved.
Finally, it should be noted that: the described embodiments are intended to be illustrative of only some, but not all, of the embodiments of the present application and, based on the embodiments herein, all other embodiments that may be made by those skilled in the art without the benefit of the present disclosure are intended to be within the scope of the present application.
While certain exemplary embodiments of the present application have been described above by way of illustration only, it will be apparent to those of ordinary skill in the art that modifications may be made to the described embodiments in various different ways without departing from the spirit and scope of the application. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive of the scope of the application, which is defined by the appended claims.
Claims (3)
1. The interconnection direct current path equivalent modeling method based on transformer substation bias is characterized by comprising the following steps of:
based on longitude and latitude of the transformer substation, the spherical geodetic coordinates are projected and transformed into plane rectangular coordinates;
setting the soil of the wide area power system as a non-uniform medium finite block to determine the soil resistivity;
establishing a transformer substation direct current path model based on the plane rectangular coordinates, the soil resistivity and geomagnetic storm parameters, wherein the transformer substation direct current path model comprises a main transformer neutral point, a winding, a transformer substation outgoing line model and a neutral point magnetic bias suppression element model which are sequentially arranged;
simulating conductors among substations, and forming a substation interconnection direct current path model based on equivalent modeling of the substation direct current path model, wherein transformer outgoing lines are connected among the substations of the substation direct current path model through lines to form the substation interconnection direct current path model;
calculating transformer substation bias to simulate and optimize the transformer substation interconnection direct current path model;
in addition, in the equivalent modeling method of the interconnected direct current path based on transformer substation magnetic bias,
when the studied power grid comprises at least two substations, the inter-station surface potential V of two adjacent substations on the power grid is:
，
wherein ,h0 Is the thickness of the soil surface layer; z is the soil depth; r is the distance from the ground electrode;the resistivity of the soil corresponding to the i layer; assuming g as a direct current grounding electrode, the current in the upper soil is I, and the earth-entering current of the grounding electrode g is I 0 ，/>Is the firstZero-order Bessel function A i (λ)、B i (λ) is the coefficient of the earth potential function solution, where λ is the Bezier constant, determined by the boundary conditions:
when z approaches infinity, the surface potential is zero:；
when the potentials at the soil interfaces are equal:
，
h i the thickness of the ith layer of the soil;
when the network under investigation comprises only a single substation, or when simplified calculation of the ground potential is required, the ground potential of the substationThe method comprises the following steps:
，
wherein ,for the complex dielectric constant of the soil at the grounding electrode, < + >>The complex permittivity of the soil at a distance r from the grounding electrode; sigma is the soil conductivity;
and (5) researching the magnetic bias change trend of the transformer substation based on the earth surface potential.
2. The substation bias-based interconnection direct current path equivalent modeling method according to claim 1, wherein a substation direct current path model is built based on grounding electrode parameters.
3. The method for modeling the equivalent of the interconnected direct current path based on magnetic biasing of a transformer substation according to claim 1, wherein the method comprises the steps of,
and when the calculated magnetic bias of the transformer substation is larger than a threshold value required by the transformer substation, the transformer substation direct current path model suppresses the magnetic bias element model through the neutral point to optimize the transformer substation interconnection direct current path model.
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