CN108075380B - Converter station grounding grid design method capable of replacing direct current grounding electrode and grounding grid - Google Patents

Converter station grounding grid design method capable of replacing direct current grounding electrode and grounding grid Download PDF

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Publication number
CN108075380B
CN108075380B CN201611013545.1A CN201611013545A CN108075380B CN 108075380 B CN108075380 B CN 108075380B CN 201611013545 A CN201611013545 A CN 201611013545A CN 108075380 B CN108075380 B CN 108075380B
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grounding
converter station
potential difference
grounding grid
network
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CN108075380A (en
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童雪芳
董晓辉
谭波
谢惠藩
潘卓洪
王湘汉
何慧雯
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State Grid Corp of China SGCC
Wuhan University WHU
China Electric Power Research Institute Co Ltd CEPRI
China Southern Power Grid Co Ltd
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State Grid Corp of China SGCC
Wuhan University WHU
China Electric Power Research Institute Co Ltd CEPRI
China Southern Power Grid Co Ltd
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    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02BBOARDS, SUBSTATIONS, OR SWITCHING ARRANGEMENTS FOR THE SUPPLY OR DISTRIBUTION OF ELECTRIC POWER
    • H02B5/00Non-enclosed substations; Substations with enclosed and non-enclosed equipment
    • H02B5/01Earthing arrangements, e.g. earthing rods

Abstract

The invention discloses a converter station grounding grid design method capable of replacing a direct current grounding electrode and a grounding grid. A, arranging a first feeder cable to be connected to a converter station grounding network from a valve hall grounding point; B. calculating the corrosion thickness of the grounding grid conductor under the conditions of monopolar earth running current and bipolar unbalanced current, and determining the section size of the grounding grid conductor; calculating to obtain the contact potential difference of the grounding grid, if the contact potential difference exceeds a preset contact potential difference limit value under the condition that the direct current transmission earth returns the running current, adding a grounding grid conductor at the position where the contact potential difference exceeds the limit value, and reducing the contact potential difference to be within the contact potential difference limit value; C. and establishing connection between the grounding equipment of the converter station grounding network and the converter station grounding network by using a second feeder cable. The converter station grounding grid established by the invention can simultaneously bear the functions of the traditional converter station grounding grid and the direct current grounding electrode, and has the advantages of safety, reliability, low cost and high benefit.

Description

Converter station grounding grid design method capable of replacing direct current grounding electrode and grounding grid
Technical Field
The invention relates to the technical field of direct current transmission, in particular to a converter station grounding grid design method capable of replacing a direct current grounding electrode and the converter station grounding grid.
Background
The direct current grounding electrode is an important link of direct current transmission engineering, directly transmits power for a system as a part of a loop when a single pole operates, and clamps the neutral point potential of a converter station (a rectifier valve) when a double pole operates, so that the damage to equipment caused by unbalance of voltage of two poles to ground is avoided. The ultrahigh voltage direct current transmission project in China is rapidly developed, and the site selection of the direct current grounding electrode is more and more difficult. In the actual engineering construction and construction process, the grounding electrode cannot be put into operation as expected due to external reasons such as land acquisition and site selection, the bipolar smooth operation of the direct-current transmission engineering is influenced, and the economic benefit and the social benefit of large-capacity and long-distance electric energy transmission are seriously hindered. At present, few scholars, research institutions or equipment manufacturers at home and abroad develop researches on other grounding devices capable of replacing the direct current grounding electrode, and the researches on the grounding devices are definitely prospective and practical.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a converter station grounding grid design method capable of replacing a direct current grounding electrode and a converter station grounding grid, which can fully utilize the existing converter station grounding grid to realize the direct current grounding electrode in an extra-high voltage direct current transmission project, reduce the construction investment of the grounding grid as much as possible and ensure the safe and reliable operation of a power grid.
In order to solve the technical problem, the invention provides a converter station grounding grid design method capable of replacing a direct current grounding electrode, which comprises the following steps:
A. a first feeder cable is arranged to be connected to a converter station grounding network from a valve hall grounding point;
B. calculating the corrosion thickness of the grounding grid conductor under the monopolar earth running current and the bipolar unbalanced current, and determining the section size of the grounding grid conductor according to the corrosion thickness;
calculating to obtain the contact potential difference of the grounding network according to the structural size of the grounding network of the converter station, the size of the section of the conductor and the surveyed resistivity model of the soil at the pole site of the converter station;
if the contact potential difference under the return running current of the direct current transmission ground exceeds a preset contact potential difference limit value, adding a grounding grid conductor at the position where the contact potential difference exceeds the limit value, and reducing the contact potential difference to be within the contact potential difference limit value;
C. and establishing connection between the grounding equipment of the converter station grounding network and the converter station grounding network by using a second feeder cable.
Furthermore, the number of the first feeder cables is four, one end of each first feeder cable is connected to four corners of the converter station grounding network, and the other end of each first feeder cable is connected to the valve hall grounding point.
Further, still include:
the maximum potential difference within the network is calculated,
and if the superposition value of the maximum in-network potential difference exceeds the preset potential difference limit value in the equipment safety network under the conditions of alternating current short-circuit fault earth-entering current and direct current earth-entering current, laying a conductive medium in the cable trench in which the secondary cable is buried.
Further, still include:
setting a single-pole allowable operation time limit value by combining a temperature rise condition according to a preset potential difference limit value in the equipment safety network;
calculating the maximum current density J at a monopolar earth operating currentmAnd a grounding resistor R, and further calculating the allowable unipolar running time t by combining the maximum allowable temperature risem
When t ismArranging a conductor connected with the grounding net of the converter station at the periphery of the grounding net of the converter station, and laying coke near the conductor to enable t to be smaller than the set allowable operating time limit of the monopolemThe required monopolar allowed run time is reached.
Further, the contact potential difference limit is 50V under monopolar earth operating current.
Further, the potential difference limit value in the device security network is as follows: the limit value of the potential difference of the secondary equipment in the network is not more than 2.8 kV.
Further, the monopole allowed operation time limit is 5 h.
Further, the method for laying the conductive medium in the cable trench in which the secondary cable is buried comprises the following steps:
adding a preset number of conductive media in the transverse middle, the longitudinal middle and the middle of the peripheral outer side grids of the grounding grid;
and calculating the potential difference in the maximum network again, and if the superposed value of the potential differences in the maximum network still exceeds the preset potential difference limit value in the equipment safety network, continuing to add a group of conductive media between the adjacent grids of the conductive media added last time until the potential difference in the network is smaller than the preset potential difference limit value in the equipment safety network.
Further, the conductive medium laid in the cable trench is electrically connected with the grounding grid, and the cross-sectional dimension of the conductive medium is not less than 220mm2
Further, the coke laid around the conductor has a cross-sectional size in the range of 0.1m x 0.1m to 1m x 1m, wherein the coke is laid with a size proportional to the current density of the conductor.
The invention also provides a converter station grounding grid, which comprises: a grounding grid body, a first feeder cable, a second feeder cable, a grounding device and a conductive medium, wherein,
the first feeder cable is used for connecting the valve hall grounding point and the grounding grid body;
the second feeder cable is used for connecting grounding equipment of the converter station grounding grid with the grounding grid body;
the first calculation module is used for calculating the corrosion thickness of the grounding grid conductor under the conditions of monopolar earth running current and bipolar unbalanced current, and determining the section size of the grounding grid conductor according to the corrosion thickness;
the second calculation module is used for calculating and obtaining the contact potential difference of the grounding network according to the structural size of the grounding network of the converter station, the size of the section of the conductor and the surveyed resistivity model of the soil at the electrode site of the converter station;
and the grounding grid conductor is laid at the position where the electric shock potential difference exceeds the limit value and is connected with the grounding grid body.
Further, still include:
the third calculation module is used for calculating the potential difference in the maximum network;
and the conductive medium is laid in a cable trench in which the secondary cable is buried when the superposition value of the maximum in-network potential difference exceeds the preset potential difference limit value in the equipment safety network under the conditions of alternating current short-circuit fault earth-entering current and direct current earth-entering current.
Further, still include:
a fourth calculation module for calculating the maximum current density J at a unipolar earth operating currentmAnd a grounding resistor R, and further calculating the allowable unipolar running time t by combining the maximum allowable temperature risem
Conductor for when tmWhen the time limit value is less than the set single-pole allowable operation time limit value, the time limit value is arranged at the periphery of the converter station grounding grid and is connected with the converter station grounding grid;
coke laid around the conductor.
The invention introduces the current of the valve hall into the ground through the converter station grounding grid through the first feeder cable, introduces the current of each device in the original converter station grounding grid into the ground through the second feeder cable, and increases the grounding grid conductor according to the set contact potential difference limit value, thereby establishing the converter station grounding grid and simultaneously playing the functions of the traditional converter station grounding grid and the direct current grounding electrode. The grounding grid makes full use of the existing grounding grid, saves additional land acquisition and construction projects of a direct current grounding electrode, ensures the safety of personnel and equipment in a converter station, has obvious economic and social benefits, and can be used for high-voltage direct current transmission projects.
Drawings
Fig. 1 is a flow chart of a converter station grounding grid design method of the invention, which can replace a direct current grounding electrode.
Figure 2 is a schematic view of the connection point of a first feeder cable to a ground grid according to the present invention.
Figure 3 is an enlarged partial view of the connection point of the first feeder cable to the ground grid shown in figure 2.
Fig. 4 is a schematic diagram of a modification of a grounding grid and an encrypted grounding grid thereof according to an embodiment of the present invention.
Figure 5 is a diagram of the potential difference calculation network node numbers in the network according to the embodiment of the invention.
Fig. 6 is a schematic diagram of embedding a copper strip in a secondary cable trench according to an embodiment of the present invention.
Fig. 7 is a schematic diagram of increasing the area of the grounding grid of the converter station according to the embodiment of the invention.
FIG. 8 is a schematic illustration of coke bed laying down of the ground net edge conductors according to an embodiment of the present invention.
Detailed Description
The present invention is further described below in conjunction with the following figures and specific examples so that those skilled in the art may better understand the present invention and practice it, but the examples are not intended to limit the present invention.
The inventor notices in the process of invention that:
although the direct current grounding electrode has larger ground current, the single-pole ground operation time of the current direct current transmission project is shorter and shorter, and the current operation mode is mainly the operation mode under the conditions of faults and maintenance. The converter station grounding grid is usually established in a place with lower soil resistivity, has the characteristics of large floor area, large number of conductors and the like, has strong through-current capability, and can be researched to have the function of circulating direct current at the same time by a design method of the converter station grounding grid, so that a direct current grounding electrode is replaced, the construction of an additional direct current grounding electrode is cancelled, and remarkable economic benefits are achieved. At present, the design of a grounding network of a converter station is mainly used for ensuring the safety of personnel and equipment under the working condition of system fault, circulating lightning stroke and fault short-circuit current and providing grounding for shells of primary equipment and secondary equipment and the like. The design control indexes of the device mainly comprise grounding resistance, contact potential difference under the maximum short-circuit current and step potential difference level. The grounding grid is designed without considering the condition of providing a large-current return path as direct current, so that a plurality of problems are caused if the grounding grid of the converter station is directly adopted to replace the bipolar operation of the grounding electrode.
In addition, in the case of replacing a direct current grounding electrode, when a single pole operates, a strong direct current flows through the grounding electrode and is injected into a grounding grid, and when two poles operate, unbalanced current can flow through the grounding grid for a long time. When direct current flows through the grounding grid and disperses, the pole address ground potential is raised, the problems of step potential difference, contact potential difference, soil heating and the like under the direct current condition occur, and the neutral point grounding transformer in the range of the grounding pole current field generates direct current magnetic bias to influence the safe operation of the power grid. Meanwhile, the buried grounding grid conductor will be corroded to a certain degree due to the direct current invasion.
Therefore, it is necessary to design the grounding grid scientifically to ensure that the above problems do not affect the safe operation of the system, and do not threaten the safety of people and animals, the safe operation of the electrical facilities around the grounding grid, the underground metal pipeline facilities, and the like, and at the same time, to reduce the construction investment of the grounding grid as much as possible.
The invention discloses a converter station grounding grid design method capable of replacing a direct current grounding electrode, which is shown in figure 1 and also shown in figures 2 and 3. The parameters of conductor corrosion thickness, contact potential difference, in-network potential difference, monopole allowed running time controlled by maximum allowed temperature rise and the like of the grounding network of the check converter station are calculated through a computer processing program with a current field calculation function and a related formula, measures of increasing the section size of a grounding network conductor, arranging an encrypted conductor, connecting a copper strip, increasing the conductor on the periphery to enlarge the area of the grounding network, laying coke on the periphery of the conductor, arranging a feeder cable down lead and the like are adopted according to corresponding parameter limit values, and thus the grounding network of the converter station capable of replacing a direct current grounding electrode is obtained.
The method comprises the following steps:
(1) the first feeder cable 202 is arranged to be connected from the valve hall ground to the converter station ground network,
preferably, four first feeder cables 202 are arranged, one ends of the first feeder cables 202 are respectively connected to four corners 201 of the converter station grounding network, and the other ends of the first feeder cables 202 are connected to the valve hall grounding points;
in the prior art, an overhead bare conductor comes out of a valve hall, is connected to a grounding electrode line, and is connected to a grounding electrode through a bus bar; the first feeder cable replaces an overhead bare conductor, a grounding electrode line, a bus bar and a grounding electrode in the prior art, and the existing grounding grid can be used for grounding a valve hall, so that the construction cost is saved.
(2) Setting a contact potential difference limit value according to personal safety requirements based on the existing regulations, operation experience and actual conditions;
calculating the corrosion thickness of the grounding grid conductor under the monopolar earth running current and the bipolar unbalanced current, and determining the section size of the grounding grid conductor of the converter station according to the corrosion thickness; the size of the cross section is usually larger than that of the original grounding grid conductor, and the electrolytic corrosion problem of the direct current can be solved by increasing the size of the cross section of the grounding grid conductor;
establishing a grounding grid model by adopting a computer processing program according to parameters such as the structural size of the grounding grid of the converter station, the size of the section of the conductor, a surveyed converter station electrode site soil resistivity model and the like, and operating and calculating to obtain the contact potential difference of the grounding grid; if the contact potential difference exceeds the preset contact potential difference limit value under the return running current of the direct current transmission earth, adding a grounding grid conductor at a place with larger contact potential difference, and then calculating the contact potential difference again until the contact potential difference is reduced to be within the preset contact potential difference limit value; the personal safety problem of personnel in the station can be solved by encrypting the grounding grid conductor;
(3) and establishing connection between the grounding equipment of the converter station grounding network and the converter station grounding network by using a second feeder cable.
Wherein, the maximum in-network potential difference can be calculated by adopting a model formed by the operation of a computer processing program, and if the alternating current short-circuit fault ground-in current and the direct current ground-in current are in use, the superposition value of the maximum in-network potential difference exceeds the preset valueFor limiting the potential difference in the safety net of the equipment, as shown in fig. 6, at least one cable trench 601 in which a secondary cable is buried has a cross-sectional size of not less than 220mm2The conductive medium 602.
The method for laying the conductive medium 602 in the cable trench in which the secondary cable is buried includes:
adding a preset number of conductive media in the transverse middle, the longitudinal middle and the middle of the peripheral outer side grids of the grounding grid;
and calculating the potential difference in the maximum network again, and if the superposed value of the potential differences in the maximum network still exceeds the preset potential difference limit value in the equipment safety network, continuing to add a group of conductive media between the adjacent grids which are added with the conductive media at the last time until the contact potential difference is smaller than the preset potential difference limit value in the equipment safety network.
The conductive medium is preferably a copper strip or a copper wire, and the copper strip or the copper wire is preferably electrically connected with a grounding grid at intervals; the problem of potential difference in the network, which causes insulation breakdown of secondary equipment, can be solved by laying connecting copper wires or copper strips in a cable trench in which the secondary cable is buried.
In addition, the maximum current density J under the condition of monopolar earth operating current can be calculated by adopting a model formed by the operation of a computer processing program according to the preset potential difference limit value in the equipment safety net and the temperature rise conditionmAnd a ground resistance R, and further calculating the allowable unipolar running time t in combination with the maximum allowable temperature risemWhen t ismWhen the operating time limit of the single pole large land is less than the set operating time limit of the single pole large land, conductors connected with the grounding net of the original convertor station are arranged on the periphery of the grounding net of the convertor station according to the electrode address condition of the grounding net of the actual convertor station to enlarge the area of the grounding net, coke with the thickness of 0.1m to 1m is laid near the conductors, and then the operation is carried out to calculate the tmUp to tmUntil the required monopolar allowed run time is reached; the temperature rise of the grounding grid is controlled by increasing the area of the grounding grid of the converter station, laying a coke bed and other measures, the monopole allowable operation time of a monopole ground operation mode is prolonged, and the temperature rise problem of the grounding down lead can be solved by arranging the down lead of the current-feeding cable.
The contact potential difference can be set to be not more than 50V according to the requirement of personal safety, the limit value of the potential difference in the secondary equipment bearing network can be set to be not more than 2.8kV according to the requirement of equipment safety, and the allowable operation time limit value of the grounding network monopole is 5h in order to meet the fault and maintenance requirements of a direct current transmission system.
As shown in fig. 2-4, in combination with fig. 6 and 7, the grounding grid for a converter station of the present invention includes a grounding grid body, a first feeder cable 202, a second feeder cable, a grounding device, and a conductive medium, wherein:
the first feeder cable 202 is used for connecting the valve hall grounding point and the grounding grid body;
the second feeder cable is used for connecting the grounding equipment of the converter station grounding network with the grounding network body;
the first calculation module is used for calculating the corrosion thickness of the grounding grid conductor under the conditions of monopolar earth running current and bipolar unbalanced current, and determining the section size of the grounding grid conductor according to the corrosion thickness;
the second calculation module is used for calculating and obtaining the contact potential difference of the grounding network according to the structural size of the grounding network of the converter station, the size of the section of the conductor and the surveyed resistivity model of the soil at the electrode site of the converter station;
and the grounding grid conductor is laid at the position where the electric shock potential difference exceeds the limit value and is connected with the grounding grid body.
In addition, the converter station grounding grid of the invention further comprises:
the third calculation module is used for calculating the potential difference in the maximum network;
and the conductive medium is laid in a cable trench in which the secondary cable is buried when the superposition value of the maximum in-network potential difference exceeds the preset potential difference limit value in the equipment safety network under the conditions of alternating current short-circuit fault earth-entering current and direct current earth-entering current.
In addition, the converter station grounding grid of the invention further comprises:
a fourth calculation module for calculating the maximum current density J at a unipolar earth operating currentmAnd a grounding resistor R, and further calculating the allowable unipolar running time t by combining the maximum allowable temperature risem
Conductor 701 for when tmWhen the time limit value is less than the set single-pole allowable operation time limit value, the time limit value is arranged at the periphery of the converter station grounding grid and is connected with the converter station grounding grid;
coke, laid around the conductor 701.
The grounding grid with the grounding grid size of 200m x 200m and the mesh size of 10m x 10m is taken as an example of the grounding grid of the original converter station, and fig. 4 to 8 are specific applications of the invention on the grounding grid of the original converter station.
1. Calculation of corrosion thickness of grounding grid
From the operating condition of direct current transmission, the corrosion of the grounding grid can be divided into electrolytic corrosion caused by unbalanced operating current and electrolytic corrosion caused by monopolar earth operating fault current. The amount of corrosion G per ampere of current flowing through the iron anode was:
the unbalanced current of the DC transmission project within one year is the upper limit value of the regulation, namely 1% rated current, and the maximum local corrosion G of the grounding grid is calculated according to the current DC transmission project with 3000A-level rated current
Wherein y is the design operation time limit, k is the current non-uniformity coefficient, L1 and L2 are the width and height of the flat steel of the grounding grid conductor respectively, the corrosion thickness is obtained, and L is the total length of the conductor. Substituting the relevant data of the grounding grid conductor to obtain the corrosion thickness of the grounding grid conductor of about 3-6 mm under the design age of 30-50 years of the grounding grid of the converter station.
2. Contact potential difference calculation check
Since the contact potential difference is usually more serious than the step potential difference, the criterion of personal safety can be checked by the contact potential difference. As shown in FIG. 4, on the basis of the grounding grid (FIG. 4a) of the original converter station, the size of the cross section of the conductor of the grounding grid is increased by 3mm to offset the influence of electrolytic corrosion. According to parameters such as size and shape of the grounding grid, a grounding grid model of the converter station is established through an MALZ module of grounding analysis software CDEGS, the soil resistivity of a grounding grid electrode site is 100 omega-m, the grounding grid contact potential difference under the grounding current running in the single-pole ground is obtained through calculation, the maximum contact potential difference is 107.5V, and the larger value of the contact potential difference mainly appears around and at the corners of the grounding grid. 6 pieces of 32 x 3.5mm are arranged in the middle and at the center of the four-side grid with higher contact potential2Copper tape 401 encrypts the ground grid (as shown in fig. 4 b). Modeling is carried out on the encrypted grounding grid again, the contact potential difference is calculated and checked, the maximum contact potential difference is reduced to 46.3V, and the maximum contact potential difference is within the requirement of personal safety limit value (namely contact potential difference limit value).
3. Potential difference calculation check in network
And modeling the grounding network formed in the step by adopting an MALZ module of grounding analysis software CDEGS, calculating the in-network potential difference under the alternating current short-circuit fault grounding current, directly taking the upper limit value of the in-network potential difference of the unipolar grounding current to be 50V, and not calculating in the model.
As shown in fig. 5, the calculation conditions are: 50kA power frequency fault current flows in from a 40 point, 20kA flows in from a 22 point to represent 500kV line shunt, 15kA flows in from a 400 point to represent 220kV line shunt, and the maximum in-network potential difference is calculated to be 3153V.
Because the superposition value of the potential difference between the AC and DC lower networks exceeds 2.8kV, as shown in figure 6, a 38 mm-6 mm copper strip (or a copper stranded wire with an equal section) is laid in a cable trench in which the secondary cable is buried, and the copper strip is welded with the grounding network every 20 m. After the copper strip is laid, the potential difference in the network under the alternating current short circuit fault grounding current is calculated again, and is 1739V which is within the requirement of the safety limit value of the equipment.
The potential difference between the two ends of the secondary cable is smaller than the potential difference in the maximum network, and when the potential difference in the maximum network meets the safety requirement of equipment, the potential difference between the two ends of the secondary cable is necessarily within the range of the safety limit value.
4. Maximum unipolar allowed run time calculation check
In practical engineering, the ground pole monopolar earth return operation time does not exceed 5 hours per year, so the monopolar allowable operation time for monopolar earth operation is set to 5 hours.
Modeling the grounding grid formed in the step by adopting an MALZ module of grounding analysis software CDEGS, and calculating to obtain the maximum current density J under the condition of monopole earth ground running grounding currentm=15.9A/m2The ground resistance R is 0.197 Ω, and the allowable operating time t is calculated in combination with the maximum allowable temperature risem. To obtain tmAbout 0.79 h.
Wherein the running time t is allowedmCalculated according to equations (2) to (4):
in the formula, TrIs a time constant; tau ismTaking 60 ℃ for the maximum allowable temperature rise; tau isωThe steady-state temperature rise of the grounding grid is achieved; i is the current injected into the grounding grid, unit A; r is grounding resistance of a grounding grid, and the unit omega is; lambda is the thermal conductivity coefficient and has the unit of W/m DEG C; gamma is specific heat coefficient, and the unit is J/kg DEG C; rho is the resistivity of the soil and has the unit of omega m; l is the total length of the conductor, and is m; s is the conductor cross-sectional area in m2;JmIs the maximum current density in units of A/m2
As shown in fig. 7 and 8, the grounding grid is modified by expanding 200m by 200m grounding grid to 240m by 240m, laying 0.1m by 0.1m coke 801 around the two outermost circles of grounding grid conductors 701, and modifying t after modificationmCarrying out calculation and check again to obtain tmThe time is 22.8h, and the requirement of the running time limit is met.
5. Ground down lead arrangement
And arranging a second feeder cable as a grounding down lead of each device in the grounding network of the original converter station, wherein the size of the second feeder cable is determined according to DL/T5224-2014.
The above-mentioned embodiments are merely preferred embodiments for fully illustrating the present invention, and the scope of the present invention is not limited thereto. The equivalent substitution or change made by the technical personnel in the technical field on the basis of the invention is all within the protection scope of the invention. The protection scope of the invention is subject to the claims.

Claims (11)

1. A method for designing a converter station grounding grid capable of replacing a direct current grounding electrode is characterized by comprising the following steps:
A. a first feeder cable is arranged to be connected to a converter station grounding network from a valve hall grounding point;
B. calculating the corrosion thickness of the grounding grid conductor under the monopolar earth running current and the bipolar unbalanced current, and determining the section size of the grounding grid conductor according to the corrosion thickness;
calculating to obtain the contact potential difference of the grounding network according to the structural size of the grounding network of the converter station, the size of the section of the conductor and the surveyed resistivity model of the soil at the pole site of the converter station;
if the contact potential difference under the return running current of the direct current transmission ground exceeds a preset contact potential difference limit value, adding a grounding grid conductor at the position where the contact potential difference exceeds the limit value, and reducing the contact potential difference to be within the contact potential difference limit value;
C. establishing connection between grounding equipment of the converter station grounding grid and the converter station grounding grid body by using a second feeder cable, and setting the second feeder cable as a grounding down lead of each equipment in the original converter station grounding grid;
further comprising:
setting a single-pole allowable operation time limit value by combining a temperature rise condition according to a preset potential difference limit value in the equipment safety network;
calculating the maximum current density J at a monopolar earth operating currentmAnd a grounding resistor R, and further calculating the allowable unipolar running time t by combining the maximum allowable temperature risem
When t ismLess than set monopolar letAllowing the operation time limit, arranging a conductor connected with the grounding grid of the converter station at the periphery of the grounding grid of the converter station, laying coke near the conductor, and enabling the operation time limit to be tmThe required monopolar allowed run time is reached.
2. The method for designing a grounding network of a converter station capable of replacing a direct current grounding electrode according to claim 1, wherein the number of the first feeder cables is four, one end of each first feeder cable is connected to four corners of the grounding network of the converter station, and the other end of each first feeder cable is connected to a valve hall grounding point.
3. The method for designing a grounding grid of a converter station capable of replacing a direct current grounding electrode according to claim 1, further comprising:
the maximum potential difference within the network is calculated,
and if the superposition value of the maximum in-network potential difference exceeds the preset potential difference limit value in the equipment safety network under the conditions of alternating current short-circuit fault earth-entering current and direct current earth-entering current, laying a conductive medium in the cable trench in which the secondary cable is buried.
4. A method for designing a grounding grid for a converter station instead of a dc earthing pole according to claim 1, characterized in that said contact potential difference limit is 50V at monopolar earth operation current.
5. The method for designing the grounding grid of the converter station capable of replacing the direct current grounding electrode according to claim 3, wherein the potential difference limit value in the equipment safety grid is as follows: the limit value of the potential difference of the secondary equipment in the network is not more than 2.8 kV.
6. A method for designing a converter station grounding network in place of a dc earthing pole according to claim 1, characterized in that said monopole allowed run time limit is 5 h.
7. The method for designing the grounding grid of the converter station capable of replacing the direct current grounding electrode according to claim 3, wherein the method for laying the conductive medium in the cable trench for burying the secondary cable comprises the following steps:
adding a preset number of conductive media in the transverse middle, the longitudinal middle and the middle of the peripheral outer side grids of the grounding grid;
and calculating the potential difference in the maximum network again, and if the superposed value of the potential differences in the maximum network still exceeds the preset potential difference limit value in the equipment safety network, continuing to add a group of conductive media between the adjacent grids of the conductive media added last time until the potential difference in the network is smaller than the preset potential difference limit value in the equipment safety network.
8. The method for designing a grounding grid of a converter station capable of replacing a direct current grounding electrode according to claim 3, wherein a conductive medium laid in the cable trench is electrically connected with the grounding grid, and the cross-sectional dimension of the conductive medium is not less than 220mm2
9. The method of claim 1, wherein the coke deposited around the conductor has a cross-sectional dimension in the range of 0.1m x 0.1m to 1m x 1m, wherein the coke size is proportional to the current density of the conductor.
10. A converter station grounding grid, comprising: a grounding grid body, a first feeder cable, a second feeder cable, a grounding device and a conductive medium, wherein,
the first feeder cable is used for connecting the valve hall grounding point and the grounding grid body;
the second feeder cable is used for connecting the grounding equipment of the converter station grounding grid with the grounding grid body and is used as a grounding down lead of each equipment in the original converter station grounding grid;
the first calculation module is used for calculating the corrosion thickness of the grounding grid conductor under the conditions of monopolar earth running current and bipolar unbalanced current, and determining the section size of the grounding grid conductor according to the corrosion thickness;
the second calculation module is used for calculating and obtaining the contact potential difference of the grounding network according to the structural size of the grounding network of the converter station, the size of the section of the conductor and the surveyed resistivity model of the soil at the electrode site of the converter station;
the grounding grid conductor is laid at the position where the contact potential difference exceeds the limit value and is connected with the grounding grid body;
further comprising:
a fourth calculation module for calculating the maximum current density J at a unipolar earth operating currentmAnd a grounding resistor R, and further calculating the allowable unipolar running time t by combining the maximum allowable temperature risem
Conductor for when tmWhen the time limit value is less than the set single-pole allowable operation time limit value, the time limit value is arranged at the periphery of the converter station grounding grid and is connected with the converter station grounding grid;
coke laid around the conductor.
11. The converter station grounding grid according to claim 10, further comprising:
the third calculation module is used for calculating the potential difference in the maximum network;
and the conductive medium is laid in a cable trench in which the secondary cable is buried when the superposition value of the maximum in-network potential difference exceeds the preset potential difference limit value in the equipment safety network under the conditions of alternating current short-circuit fault earth-entering current and direct current earth-entering current.
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