Method and system for parallel rod inception determination considering photon transport under composite voltage

Abstract

The present application relates to a kind of parallel rod takes out the determination method and system of halo under composite voltage considering photon transmission, comprising: the two wall bushings used in converter station valve hall are simplified into two parallel rod electrodes, and the halo model of the parallel rod electrode is constructed;Under AC composite voltage, the area factor of positive corona and the area factor of negative corona considering photon transmission path are calculated based on the halo model of the parallel rod electrode respectively;According to the area factor of positive corona and the starting halo criterion of positive corona, positive corona is determined;According to the area factor of negative corona and the starting halo criterion of negative corona, negative corona is determined.By constructing the halo model of the parallel rod electrode and combining photon transmission path, the area factor of positive corona and negative corona of the parallel rod electrode is determined, so that the halo of the parallel rod electrode is accurately determined.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of corona onset determination, in particular to a parallel rod corona onset determination method and system considering photon transport path under AC-DC composite voltage. BACKGROUND

[0002] In recent years, the demand for electricity in China is growing rapidly, and the distribution of energy centers and load centers in China is unbalanced. Therefore, it is necessary to vigorously develop large-capacity long-distance power transmission systems. High-voltage direct current transmission has the advantages of high economic benefit, saving transmission corridor, etc. in long-distance power transmission, but it cannot be dropped in the middle, and needs to be converted into alternating current at the receiving end to inject into the receiving end power grid. The converter station can realize the conversion of AC and DC. The wall bushing is used to introduce and export high voltage in the valve hall of the converter station. There are 3 wall bushings on the AC side of the valve hall and 2 DC wall bushings on the DC side. The bushings on the DC side and the AC side are opposite, and the bushings on the same side are parallel. In order to prevent corona discharge from occurring at the end of the wall bushing, it is necessary to study the corona onset characteristics of the bushing end under AC-DC composite voltage. To this end, the present application provides a parallel rod corona onset determination method and system considering photon transport path under AC-DC composite voltage. SUMMARY

[0003] The purpose of the present application is to provide a parallel rod corona onset determination method and system considering photon transport path under composite voltage, which determines the area factor of positive and negative corona of parallel rod electrodes by constructing a corona model of parallel rod electrodes for wall bushings and combining photon transport path, thereby accurately determining the corona of parallel rod electrodes.

[0004] To achieve the above purpose, the present application provides the following scheme:

[0005] A parallel rod corona onset determination method considering photon transport under composite voltage, comprising:

[0006] simplifying two wall bushings used in the valve hall of the converter station into two parallel rod electrodes, and constructing a corona model of the parallel rod electrodes;

[0007] Under AC-DC composite voltage, based on the corona model of the parallel rod electrodes, the area factor of positive corona and the area factor of negative corona considering photon transport path are calculated respectively;

[0008] positive corona determination is performed according to the area factor of positive corona and the starting corona criterion of positive corona;

[0009] negative corona determination is performed according to the area factor of negative corona and the starting corona criterion of negative corona.

[0010] Optionally, the construction of the corona model of the parallel rod electrodes specifically comprises:

[0011] The interval value of the two parallel rod electrodes, the length of the parallel rod electrodes and the air domain of the parallel rod electrodes are set, and the end of the parallel rod electrodes is set as a hemisphere, and a geometric model of the parallel rod electrodes is constructed;

[0012] The AC-DC composite voltage is applied to the parallel rod electrodes in the geometric model, and the boundary and boundary condition of the geometric model in the equivalent positive corona and the equivalent negative corona are set respectively; the boundary of the geometric model includes the boundary 1 and the boundary 2 located at the parallel rod electrodes respectively and the boundary of the air domain.

[0013] Optionally, the area factor of the positive corona considering the photon transmission path based on the corona initiation model of the parallel rod electrodes specifically includes:

[0014] The center of the hemisphere of the end of the parallel rod electrodes is defined as point O, and the point of maximum surface field strength of the hemisphere of the end of the parallel rod electrodes is defined as point M;

[0015] The total number N of photons emitted from point M is calculated pr ;

[0016] The radial cross section containing the line segment OM of the end of the parallel rod electrodes is obtained, and the number N of photons emitted from point M to a distance of r is calculated by combining the photon transmission path pr1 ;

[0017] The radial component of the positive corona area factor of the end of the parallel rod electrodes is calculated according to the total number N pr and the number N of photons pr1 ; the radial component of the positive corona area factor is the same as the axial component of the positive corona area factor;

[0018] The area factor of the positive corona is calculated according to the radial component of the positive corona area factor and the axial component of the positive corona area factor.

[0019] Optionally, the expression of the area factor of the positive corona is:

[0020]

[0021]

[0022]

[0023] In the formula, g r (r) is the radial component of the positive corona area factor; g a (r) is the axial component of the positive corona area factor; r0 is the distance from the hemispherical surface of the end of the anode electrode rod to the center of the sphere; μ is the absorption coefficient of air to photons; θ1 ∈ [0, 2π].

[0024] Optionally, the area factor of the negative corona considering the photon transmission path is calculated based on the corona inception model of the parallel rod electrode, and specifically includes:

[0025] The line connecting point O and point M is constructed and extended, and the intersection point of the extended line and the boundary of the ionization region is recorded as point S;

[0026] According to the proportion of the photons on the line segment MS reaching the surface of the parallel rod electrode, the photons on the line segment MS are divided into the photons on the line segment MN and the photons on the line segment NS; the photons on the line segment MN can only reach the surface of the end hemisphere of the parallel rod electrode; the photons on the line segment NS can reach both the surface of the end hemisphere of the parallel rod electrode and the surface of the cylinder of the parallel rod electrode;

[0027] The line segment MN area factor is calculated according to the photons on the line segment MN in combination with the photon transmission path;

[0028] The line segment NS area factor is calculated according to the photons on the line segment NS in combination with the photon transmission path; the area factor of the negative corona includes the line segment MN area factor and the line segment NS area factor.

[0029] Optionally, the line segment NS area factor is calculated according to the photons on the line segment NS in combination with the photon transmission path, and specifically includes:

[0030] The spherical area factor is calculated according to the photons on the line segment NS reaching the surface of the end hemisphere of the parallel rod electrode in combination with the photon transmission path;

[0031] The cylindrical area factor is calculated according to the photons on the line segment NS reaching the surface of the cylinder of the parallel rod electrode in combination with the photon transmission path;

[0032] The line segment NS area factor is calculated according to the spherical area factor and the cylindrical area factor.

[0033] Optionally, the expression of the line segment MN area factor is:

[0034]

[0035] In the formula, θ3 is the included angle between the line segment PH and the line segment OP, wherein point P is any point on the line segment MN, the photon is emitted from point P to the anode surface to reach the anode surface H point, and the length of the line segment PH is λ.

[0036] Optionally, the expression of the line segment NS area factor is:

[0037]

[0038]

[0039] wherein g sph (r) is a spherical area factor; g col (r) is a cylindrical area factor; θ5 is an angle between line segment OP' and line segment P'h, wherein a photon is emitted from point P' to anode surface to reach point h on the anode surface, and the length of line segment P'h is λ; θ6 is an angle between line segment P'h' in the horizontal direction, wherein a photon is emitted from point P' to anode surface to reach point h' on the anode surface, and the length of line segment P'h' is λ; point P' is an arbitrary point on line segment NS; δ is an angle between line segment OM and line segment OA, point A is an intersection point between a plane where line segment OM and an axis of the parallel rod electrode are located and a maximum radial cross section of a hemispherical end of the parallel rod electrode, and line segment OA is perpendicular to line segment AN; and L is a length of a cylinder of the parallel rod electrode.

[0040] Optionally, an expression of the starting corona criterion of the positive corona is:

[0041]

[0042] An expression of the starting corona criterion of the negative corona is:

[0043]

[0044] wherein f1 is a probability of one electron collision ionization to generate a photon; f2 is a probability of one photoionization to generate one electron; r i is a distance between a boundary position of an ionization region and a center of a sphere; α is a collision ionization coefficient, η is an electron adsorption coefficient, and r' is a virtual integral variable.

[0045] A parallel rod corona initiation system considering photon transmission under composite voltage comprises:

[0046] A corona initiation model construction module is configured to simplify two wall bushings used in a valve hall of a converter station into two parallel rod electrodes, and construct a corona initiation model of the parallel rod electrodes.

[0047] An area factor calculation module is configured to calculate an area factor of a positive corona and an area factor of a negative corona considering a photon transmission path based on the corona initiation model of the parallel rod electrodes under AC-DC composite voltage.

[0048] A positive corona determination module is configured to determine the positive corona according to the area factor of the positive corona and a starting corona criterion of the positive corona.

[0049] A negative corona determination module is configured to determine the negative corona according to the area factor of the negative corona and a starting corona criterion of the negative corona.

[0050] According to the embodiments of the present application, the following technical effects are provided:

[0051] The present application relates to a parallel rod corona inception determination method and system considering photon transmission under composite voltage, comprising: simplifying two wall bushings used in a valve hall of a converter station into two parallel rod electrodes, and constructing a corona inception model of the parallel rod electrodes; under AC-DC composite voltage, calculating an area factor of positive corona and an area factor of negative corona considering a photon transmission path based on the corona inception model of the parallel rod electrodes; determining positive corona according to the area factor of positive corona and a starting corona criterion of positive corona; and determining negative corona according to the area factor of negative corona and a starting corona criterion of negative corona. By constructing the corona inception model of the parallel rod electrodes and combining the photon transmission path, the area factors of positive and negative corona of the parallel rod electrodes are determined, so that the corona inception of the parallel rod electrodes is accurately determined. BRIEF DESCRIPTION OF DRAWINGS

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings described below only show some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0053] Figure 1 A flow chart of a parallel rod corona inception determination method considering photon transmission under composite voltage is provided for the embodiment 1 of the present application.

[0054] Figure 2 A geometric model of a parallel rod electrode is provided for the embodiment 1 of the present application.

[0055] Figure 3 A nominal electric field diagram of a parallel rod electrode is provided for the embodiment 1 of the present application.

[0056] Figure 4 A positive corona area factor diagram is provided for the embodiment 1 of the present application.

[0057] Figure 5 A negative corona area factor zoning diagram is provided for the embodiment 1 of the present application.

[0058] Figure 6 A negative corona MN segment area factor diagram is provided for the embodiment 1 of the present application.

[0059] Figure 7 A negative corona NS segment sphere area factor diagram is provided for the embodiment 1 of the present application.

[0060] Figure 8 A negative corona NS segment column area factor diagram is provided for the embodiment 1 of the present application.

[0061] Figure 9This is a schematic diagram of the calculation results of the corona criterion provided in Embodiment 1 of the present invention. Detailed Implementation

[0062] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0063] The purpose of this invention is to provide a method and system for determining the corona initiation of a parallel rod electrode under a composite voltage, taking into account the photon transmission path. By constructing a corona initiation model of the parallel rod electrode on a through-wall bushing and combining it with the photon transmission path, the area factor of the positive and negative corona of the parallel rod electrode is determined, thereby accurately determining the corona initiation of the parallel rod electrode.

[0064] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0065] Example 1

[0066] like Figure 1 As shown, this embodiment provides a method for determining the corona formation of a parallel rod considering photon transmission under a composite voltage, including:

[0067] Step S1: Simplify the two through-wall bushings used in the converter station valve hall into two parallel rod electrodes, and construct the corona initiation model of the parallel rod electrodes.

[0068] Step S1 includes:

[0069] Set the spacing value between the two parallel rod electrodes, the length of the parallel rod electrodes, and the air domain of the parallel rod electrodes, and set the end of the parallel rod electrodes to be hemispherical to construct the geometric model of the parallel rod electrodes;

[0070] The AC / DC composite voltage is applied to the parallel rod electrode in the geometric model, and the boundaries and boundary conditions of the geometric model are set under the equivalent positive corona condition and the equivalent negative corona condition, respectively; the boundaries of the geometric model include boundary 1 and boundary 2 located at the parallel rod electrode and each boundary of the air domain.

[0071] Electric field simulation of the through-wall bushing shows that the maximum electric field strength occurs at the end of the copper conductor rod. Treating the ends of the two through-wall bushing conductor rods as a pair of parallel rod electrodes, a corona initiation model of the parallel rod electrodes under AC / DC voltages is established. The geometric model parameters, equations, composite voltage settings, boundary condition settings, and corona initiation criteria are clarified to explore the variation of the corona initiation voltage of the parallel rod electrodes.

[0072] For the geometric model parameters: two parallel wall bushings are simplified as parallel rod electrodes, as shown in Figure 2 . The length of the parallel rod electrodes is 40 cm, the head is a hemisphere with a radius of 2 mm, and the distance between the parallel rods is 10 cm. The air domain is set to 0.5 mm x 1.0 m.

[0073] A composite AC-DC voltage is applied to the parallel rod electrodes:

[0074] In terms of voltage setting, the composite AC-DC voltage U hybrid is applied to rod 1, and rod 2 is grounded. Since a complete power frequency AC cycle is 20 ms, but the α, η, β processes of micro-particles change in the order of ns, if the entire AC cycle is calculated in steps of ns, the calculation time is too long. Considering the segmented voltage U h to represent the composite AC-DC voltage U hybrid , as shown in equation (1):

[0075]

[0076] where U AC is the amplitude of the AC voltage; N1 is the total number of segments in a complete AC cycle; U DC is the DC voltage; and T0 is a step time.

[0077] Boundary and boundary conditions of the parallel rod electrode geometric model:

[0078] As shown in Figure 2 , the potential of boundary 1 is set to U h , and the potentials of boundaries 2-6 are all set to 0, which is the first type of boundary condition. Boundaries 3-6 are the boundaries of the air domain. When the sum of the AC voltage peak value and the DC voltage is greater than 0, i.e., U AC + U DC > 0, it is called equivalent positive corona, and when the sum of the AC voltage peak value and the DC voltage is less than 0, i.e., U AC + U DC < 0, it is called equivalent negative corona. Table 1 shows the boundary condition settings for the equivalent positive corona, and Table 2 shows the boundary condition settings for the equivalent negative corona.

[0079] Table 1 Boundary condition settings for equivalent positive corona

[0080]

[0081]

[0082] Table 2 Boundary condition settings for equivalent negative corona

[0083]

[0084] The geometric model of the parallel rod electrode is set in the simulation software, the AC-DC composite voltage is applied, the boundary and boundary conditions are set, the parallel rod electrode generates an electric field, and charged particles perform various movements in the electric field. The parallel rod electrode model under AC-DC composite voltage is established based on the charge continuity equation (equation 2-4) and Poisson equation (equation 5-6), considering the migration, diffusion, collision ionization, adsorption, recombination, photoionization and cathode secondary electron emission of charged particles. The motion equation of the charged particles is:

[0085]

[0086]

[0087]

[0088]

[0089]

[0090] wherein N represents the number density; D is the diffusion coefficient; W represents the migration velocity; a represents the collision coefficient of electrons; η represents the adsorption coefficient of electrons; the subscripts e, p and n respectively represent electrons, positive ions and negative ions; β ep is the combination rate of electrons and positive ions; β np represents the combination rate of positive ions and negative ions; is the electric potential; e is the unit charge; ε0 is the vacuum permittivity; E is the electric field strength.

[0091] Step S2: calculating the area factor of the positive corona and the area factor of the negative corona considering the photon transmission path based on the corona inception model of the parallel rod electrode under the AC-DC composite voltage.

[0092] Many photon transport analysis calculations are involved in the criterion of starting glow: the main factor of maintaining positive glow is photoionization, and the main factor of maintaining positive glow is the secondary emission of cathode after absorbing photons. However, due to the blocking effect of the electrode on the photons, the photons generated by the primary electron avalanche cannot be completely absorbed, so the area factor g(r) is usually introduced in the criterion to describe the proportion of the absorbed photons in the total photon amount. The photon transport path of parallel rod electrodes is different from the electrodes commonly used to analyze the starting glow (rod-plate, wire-plate electrodes). For rod-plate electrodes and wire-plate electrodes, a composite alternating current voltage is generally applied to the rod electrode and the wire electrode, and the plate electrode is grounded. At this time, the maximum field strength under the nominal electric field exists at the point on the rod electrode closest to the plate electrode and the point on the axis of the two wires. Therefore, in the analysis of the photon propagation path in the starting glow criterion, the rod-plate electrode only needs to consider the hemispherical surface of the head of the rod electrode, and the wire-plate electrode only needs to consider the cylindrical surface of the wire electrode. In parallel rod electrodes, the composite voltage is applied to rod 1, and rod 2 is set to ground. The maximum field strength on the electrode surface under the nominal electric field does not occur at the top of rod 1, but at a position deviating from the top and close to rod 2, as shown in FIG. 1. Therefore, under positive and negative glow, the photon transport path changes, especially for negative glow, the influence of both the end hemispherical and cylindrical surfaces needs to be considered to obtain the area factor of the parallel rod electrode, and thus the starting glow criterion. Figure 3

[0093] (1) The area factor determination method for positive glow in step S2 is as follows:

[0094] Step S201: Defining the center of the end hemispherical surface of the parallel rod electrode as point O, and the maximum field strength point of the end hemispherical surface of the parallel rod electrode as point M.

[0095] Step S202: Calculating the total number of photons emitted from point M N pr .

[0096] Step S203: Obtaining the radial cross section of the end of the parallel rod electrode containing line segment OM, and calculating the number of photons emitted from point M to a distance of r N pr1 .

[0097] Step S204: Calculating the radial component of the positive glow area factor of the end of the parallel rod electrode according to the total number N pr and the number of photons N pr1 ; the radial component of the positive glow area factor is the same as the axial component of the positive glow area factor.

[0098] Step S205: Calculating the area factor of the positive glow according to the radial component of the positive glow area factor and the axial component of the positive glow area factor.

[0099] ​The derivation process of the positive corona area factor for parallel rod electrodes is detailed below:

[0100] Positive corona criterion:

[0101] An electron originates from a position r away from the center of the hemisphere at the end of the electrode. Figure 4 During the process of a photon originating from point T and reaching the anode surface, it collides with neutral molecules, ionizing them and generating a large number of excited-state particles. These particles release photons during de-excitation. Since the ionization coefficient is proportional to the electric field strength, photons are considered to be emitted from the electrode surface. As photons propagate through the air, they are absorbed and photoionized, generating secondary electrons, which then develop into a secondary electron avalanche, producing new photons. When the number of photons generated by the secondary electron avalanche is greater than or equal to the number of photons generated by the primary electron avalanche, the positive corona discharge is self-sustaining. Therefore, the initiation criterion for a positive corona discharge is...

[0102]

[0103] Where f1 is the probability of an electron producing a photon through a single collision ionization; f2 is the probability of an electron being produced after a photon undergoes photoionization; r0 is the distance from the hemispherical surface at the end of the anode rod to the center of the sphere; r i α is the distance between the boundary of the ionization region and the center of the sphere; r is the distance between any position (point T) within the ionization region and the center of the sphere; α is the collision ionization coefficient; η is the electron adsorption coefficient; r′ is the virtual integral variable; μ is the absorption coefficient of air for photons; g(r) is the area factor considering the blocking effect of electrodes.

[0104] The area factor g(r) describes the proportion of photons capable of photoionization out of the total number of photons, and can usually be divided into a radial component g. r (r) and axial component g a (r) Multiply the area factor components on the two perpendicular sections, i.e.

[0105] g(r) = g r (r)·g a (r) (8)

[0106] The positive corona area factor describes the proportion of photons that, due to the influence of the electrodes, travel from the electrode surface to any location within the ionization region, relative to the total number of photons. For example... Figure 4 As shown, Figure 4 In the figure, Figure (a) shows a schematic diagram of the head of the rod electrode; Figure (b) shows a schematic diagram of the radial section cutting process of the rod electrode; Figure (c) shows a schematic diagram of the axial section cutting process of the rod electrode; Figure (d) shows the radial section; Figure (e) shows the axial section; Figure (f) shows the calculation of the radial component considering the influence of the electrode; Figure (g) shows the calculation of the axial component considering the influence of the electrode.

[0107] The center of the hemisphere at the head of the rod electrode is point O, and M is the point where the electric field strength on the rod electrode is at its maximum. Photons are emitted from point M, and the number of photons reaching position r with each tiny propagation angular increment dθ1 is... When the effect of electrodes on photon propagation is not considered, θ1∈[0,2π], then the total number of photons N pr (r) is

[0108]

[0109] Including line segment OM The cross-section is the radial cross-section of the rod electrode head, and the cutting process is as follows: Figure 4 As shown in (b) Indicates the angle between line segment OM and line segment Oz. The direction of change; This indicates the direction of change of line segment OM; for example... Figure 4 As shown in (a). Similarly. This indicates the direction of change of the angle θ between line segment OM′ and line segment Ox; point M′ is the projection of point M onto the xoy plane.

[0110] A schematic diagram of photon propagation is shown below. Figure 4 As shown in (f). The distance from M to any point T within the ionization region at a distance r is... The number of photons N that can reach a radial position at a distance r is then... pr1 (r) is

[0111]

[0112] Then the component g r (r) is

[0113]

[0114] Similarly, those containing OM The cross-section is the axial cross-section of the rod electrode head, such as... Figure 4 (e) The extraction process is as follows: Figure 4 As shown in (c), the propagation of photons is as follows: Figure 4 As shown in (g). From Figure 5 (fg) Comparison shows that g a (r)=g r (r), therefore the area factor of the positive corona is

[0115]

[0116] In ΔOMT, we can obtain the law of cosines.

[0117]

[0118]

[0119] (2) The area factor determination method for the negative corona in step S2 is as follows:

[0120] Step S211: A line connecting point O and point M is constructed and extended, and the intersection point of the extended line and the ionization region boundary is recorded as point S.

[0121] Step S212: According to the proportion of photons on line segment MS reaching the surface of the parallel rod electrode, the photons on line segment MS are divided into photons on line segment MN and photons on line segment NS; the photons on line segment MN can only reach the surface of the hemispherical end of the parallel rod electrode; the photons on line segment NS can reach both the surface of the hemispherical end of the parallel rod electrode and the surface of the cylindrical body of the parallel rod electrode.

[0122] Step S213: The area factor of line segment MN is calculated according to the photons on line segment MN and the photon transmission path.

[0123] Step S214: The area factor of line segment NS is calculated according to the photons on line segment NS and the photon transmission path; the area factor of the negative corona includes the area factor of line segment MN and the area factor of line segment NS.

[0124] Step S214 specifically includes:

[0125] The spherical area factor is calculated according to the photons reaching the surface of the hemispherical end of the parallel rod electrode among the photons on line segment NS and the photon transmission path.

[0126] The cylindrical area factor is calculated according to the photons reaching the surface of the cylindrical body of the parallel rod electrode among the photons on line segment NS and the photon transmission path.

[0127] The area factor of line segment NS is calculated according to the spherical area factor and the cylindrical area factor.

[0128] The derivation process of the area factor of the negative corona of the parallel rod electrode will be described in detail below

[0129] Negative corona criterion:

[0130] When an electron starts from the cathode surface in the parallel rod electrode and reaches a position with a distance r from the center of the sphere, it will collide with air molecules and ionize to produce photons. After the photons are absorbed by the cathode, there is a probability that they can produce electrons, thereby producing a new electron avalanche. When the number of secondary electrons is greater than the number of initial electrons, the negative corona can sustain discharge. Therefore, the starting corona criterion of the negative corona is

[0131]

[0132] where γ is the secondary electron emission coefficient.

[0133] The negative corona area factor describes the proportion of the total number of photons that reach the cathode surface from the ionization region under the influence of the electrode. As shown in FIG. 1, point A is the intersection of the line segment OM and the plane of the axis of the parallel rod electrode and the maximum radial cross-section of the hemispherical end of the parallel rod, and the line segment OA is perpendicular to the line segment AN. Figure 6

[0134] The maximum field strength on the spherical surface is M, and the line connecting the center of the sphere O and M is extended to the boundary of the ionization region, i.e., point S. In order to facilitate the derivation of the subsequent calculation formula, the proportion of photons on MS that can reach the electrode surface is considered. The photons on the line segment MN can only reach the spherical surface. The photons on the line segment NS can not only reach the spherical surface but also reach the cylindrical surface. Therefore, the calculation of the area factor can be divided into MN and NS two parts to calculate, and the condition for negative corona self-sustaining discharge changes to

[0135]

[0136] When the photon is in the MN segment, the radial cross-section and the axial cross-section are consistent with the positive corona area factor. The total number of photons reaching the position with a distance r from the center of the sphere is

[0137]

[0138] The radial cross-section considers the blocking of the electrode to the photon motion. The photon starts from point P, which is an arbitrary point on the line segment MN; the farthest point on the circular arc that can be reached is the tangent point B and C, i.e., the range of the photon reaching the electrode surface is as shown in FIG. 2(a). The total number of photons that can reach the surface of the rod electrode is Figure 6

[0139] As shown in FIG. 2(a), θ3 is the included angle between the line segment PH and the line segment OP, where the photon is emitted from point P to the anode surface to reach the anode surface H point, and the length of the line segment PH is λ.

[0140] Figure 6 The radial area factor is

[0141]

[0142] The distance of the photon transmission to the cathode is λ, and by the cosine theorem, we can get

[0143] λ 2 +r 2 -r0 2 = 2λ·r·cosθ3 (20)

[0144] λ 2 +r 2 -r0 2 = 2λ·r·cosθ3 (20)

[0145]

[0146] Since the photon arrives at the cathode surface with a certain angle with the normal, the cathode cannot completely absorb the energy, and the radial and axial area factors need to be multiplied by the cosine value of the angle between the line segment and the normal, cosξ1 and cosξ2.

[0147] From Figure 6 (a-b), we can see that Figure 6 The calculation of the radial area factor is shown in Fig. (a), and the calculation of the axial area factor is shown in Fig. (b). The results of the radial area factor and the axial area factor are consistent, as shown in Fig. (c). Figure 7 (b), considering the blocking of the electrode on the photon motion, the photon starts from P and can reach the tangent points D and E on the circular arc, i.e., the range of the photon reaching the electrode surface is on Therefore, the area factor of the MN segment is

[0148]

[0149] When the photon is in the NS segment, the photon can not only reach the spherical surface but also reach the cylindrical surface, g NS (r) is the sum of the spherical area factor g sph (r) and the cylindrical area factor g col (r), i.e.,

[0150] g NS (r) = g sph (r) + g col (r) (23)

[0151] When the photon propagates to the spherical surface part, it is shown in Figure 7 (a) that since points A and B are not symmetric about OP', P' is an arbitrary point on the line segment NS; therefore, the expression is different:

[0152]

[0153] where λ is consistent with equation (22). Where ψ can be derived from the sine theorem of ΔOP'A

[0154]

[0155] where δ is known as the angle between OM and OA in (a). Solving the above equation gives Figure 7

[0156]

[0157] From Figure 8 (b), we can see that the axial component of the NS segment is equal to the axial component of the MN segment, so the spherical area factor is​

[0158]

[0159] When the photon propagates to the cylindrical part, it can be divided into radial and axial components. The radial cross section is the xOy cross section of the cylinder. The radial cross section is the yOz cross section containing the axis, as shown in Figure 8 .

[0160] Figure 8 The schematic diagram of the negative corona NS segment cylindrical area factor is shown in FIG. 4, wherein Figure 9 FIG. (a) is the cylindrical part of the rod electrode; FIG. (b) is a schematic diagram of the radial cross section of the cylinder; FIG. (c) is a schematic diagram of the axial cross section of the cylinder; FIG. (d) is the calculation of the radial component considering the influence of the electrode; points F and G are the maximum positions where the photon reaches the electrode surface; and FIG. (e) is the calculation of the axial component considering the influence of the electrode.

[0161]

[0162]

[0163] wherein θ5 is the included angle of the line segment OP' and the line segment P'h, wherein the photon is emitted from the point P' to the anode surface to reach the anode surface h point, and the length of the line segment P'h is λ; θ6 is the horizontal included angle of the line segment P'h', wherein the photon is emitted from the point P' to the anode surface to reach the anode surface h' point, and the length of the line segment P'h' is λ; and L is the length of the cylindrical body of the parallel rod electrode.

[0164] Considering the cosine values cosχ1 and cosχ2 of the included angle of the line segment in the radial and axial incident direction and the normal of the cylinder surface, the NS segment cylindrical area factor is

[0165]

[0166] Therefore, the area factor of the NS segment is

[0167]

[0168] Step S3: positive corona determination according to the area factor of the positive corona and the starting corona criterion of the positive corona.

[0169] Step S4: negative corona determination according to the area factor of the negative corona and the starting corona criterion of the negative corona.

[0170] When the equivalent positive corona area factor and the equivalent negative corona area factor of the parallel rod electrode are obtained, the starting corona criterion of the positive corona and the negative corona can be obtained according to formula (8) and formula (17). When the starting corona criterion is greater than 1, as shown in ​ , it can be determined that the corona discharge occurs.

[0171] In the embodiment, a parallel rod electrode-based AC-DC composite voltage corona initiation model is described. In the model, geometric model parameters, equations, boundary condition settings, composite voltage settings, and corona initiation criteria are specified. The corona initiation criteria involve many photon transport analysis calculations: the maximum point of the field strength on the surface of the parallel rod electrode under the composite voltage is not on the intersection of the rod electrode axis and the surface or the central axis of the two electrodes, but deviates from the top end of the rod electrode and is close to the other rod electrode, thereby being different from the commonly used rod-plane electrode and wire-plane electrode in the analysis of the photon transport path, considering the influence of the head hemisphere and the cylinder on the area factor, thereby obtaining a calculation formula of the area factor in the corona initiation criteria of the parallel rod electrode, which can accurately determine the corona initiation of the parallel rod electrode.

[0172] Embodiment 2

[0173] A parallel rod corona initiation system considering photon transport under composite voltage includes:

[0174] A wall bushing corona initiation model construction module is configured to simplify two wall bushings used in a valve hall of a converter station into two parallel rod electrodes, and construct a corona initiation model of the parallel rod electrodes.

[0175] An area factor calculation module is configured to calculate an area factor of positive corona and an area factor of negative corona considering photon transport paths based on the corona initiation model of the parallel rod electrodes under AC-DC composite voltage.

[0176] A positive corona initiation module is configured to determine positive corona according to the area factor of positive corona and a positive corona initiation criterion.

[0177] A negative corona initiation module is configured to determine negative corona according to the area factor of negative corona and a negative corona initiation criterion.

[0178] In the present specification, each embodiment focuses on the difference from other embodiments, and the same or similar parts between the embodiments can be referred to each other. For the system disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the relevant part can be referred to the method part.

[0179] In the present specification, the principles and implementation modes of the present application are described by using specific examples, and the above embodiment description is only used to help understand the method of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed. In view of the above, the content of the present specification should not be understood as a limitation of the present application.

Claims

1. A method for determining the corona inception in parallel rods considering the photon transport at complex voltages, characterized by, The method comprises the following steps: Two wall bushings used in a valve hall of a converter station are simplified into two parallel rod electrodes, and a corona inception model of the parallel rod electrodes is constructed; Under an AC-DC composite voltage, area factors of positive and negative coronas considering photon transmission paths are calculated based on the corona inception model of the parallel rod electrodes; Positive corona judgment is performed according to the area factor of the positive corona and a positive corona inception criterion; Negative corona judgment is performed according to the area factor of the negative corona and a negative corona inception criterion; The calculation of the area factor of the positive corona considering the photon transmission path based on the corona inception model of the parallel rod electrodes specifically comprises the following steps: a center of a hemispherical end of the parallel rod electrode is defined as point O, and a point of maximum surface field strength of the hemispherical end of the parallel rod electrode is defined as point M; The total number N of photons emitted from point M is calculated pr ; Obtaining a radial cross-section of the parallel-plate electrode end portion containing the line segment OM, and combining a photon transport path calculation to determine the number of photons N emitted from the point M to a distance r pr1 ; According to the total number N pr and the number of photons N pr1 calculating a positive corona area factor radial component of the parallel rod electrode end; the positive corona area factor radial component is the same as a positive corona area factor axial component; the area factor of the positive corona is calculated according to the radial component of the positive corona area factor and the axial component of the positive corona area factor; The calculation of the area factor of the negative corona considering the photon transmission path based on the corona inception model of the parallel rod electrodes specifically comprises the following steps: a line connecting point O and point M is constructed and extended, and an intersection point of the extended line and a boundary of an ionization region is recorded as point S; photons on the line segment MS are divided into photons on the line segment MN and photons on the line segment NS according to a proportion of the photons on the line segment MS reaching a surface of the parallel rod electrode; the photons on the line segment MN can only reach the surface of the hemispherical end of the parallel rod electrode; the photons on the line segment NS can reach both the surface of the hemispherical end of the parallel rod electrode and a cylindrical surface of the parallel rod electrode; a line segment MN area factor is calculated according to the photons on the line segment MN in combination with the photon transmission path; a line segment NS area factor is calculated according to the photons on the line segment NS in combination with the photon transmission path; the area factor of the negative corona comprises the line segment MN area factor and the line segment NS area factor.

2. The method of claim 1, wherein, The construction of the corona inception model of the parallel rod electrodes specifically comprises the following steps: a distance between the two parallel rod electrodes, a length of the parallel rod electrodes and an air region of the parallel rod electrodes are set, and the ends of the parallel rod electrodes are set as hemispherical shapes to construct a geometric model of the parallel rod electrodes; the geometric model is applied with the AC-DC composite voltage, and boundaries and boundary conditions of the geometric model under equivalent positive corona and equivalent negative corona are respectively set; the boundaries of the geometric model comprise boundaries 1 and 2 respectively located at the parallel rod electrodes and boundaries of the air region.

3. The method of claim 2, wherein, An expression of the area factor of the positive corona is as follows: where g r (r) is the positive corona area factor radial component; g a (r) is the positive corona area factor axial component; r0is the distance from the hemispherical surface of the anode electrode rod end to the sphere center; μ is the absorption coefficient of air for photons; θ1∈ [0, 2π].

4. The method of claim 3, wherein, The calculation of the line segment NS area factor according to the photons on the line segment NS in combination with the photon transmission path specifically comprises the following steps: a spherical surface area factor is calculated for the photons on the line segment NS reaching the hemispherical surface of the parallel rod electrode end in combination with the photon transmission path; a cylindrical surface area factor is calculated for the photons on the line segment NS reaching the cylindrical surface of the parallel rod electrode in combination with the photon transmission path; the line segment NS area factor is calculated according to the spherical surface area factor and the cylindrical surface area factor.

5. The method of claim 4, wherein, An expression of the line segment MN area factor is as follows: In the formula, θ3 is an angle between line segment PH and line segment OP, wherein point P is an arbitrary point on line segment MN, a photon is emitted from point P to anode surface H, and the length of line segment PH is λ.

6. The method of claim 5, wherein, An expression of an area factor of the line segment NS is: wherein g sph (r) is a spherical area factor; g col (r) is a cylindrical area factor; θ5 is the angle between the line segment OP' and the line segment P'h, wherein the photon is emitted from the point P' to the anode surface to reach the point h on the anode surface, and the length of the line segment P'h is λ; θ6 is the horizontal angle of the line segment P'h', wherein the photon is emitted from the point P' to the anode surface to reach the point h' on the anode surface, and the length of the line segment P'h' is λ; the point P' is any point on the line segment NS; δ is the angle between the line segment OM and the line segment OA; the point A is the intersection of the plane where the line segment OM and the axis of the parallel rod electrode are located and the maximum radial cross section of the hemispherical end of the parallel rod electrode, and the line segment OA is perpendicular to the line segment AN; and L is the length of the cylinder of the parallel rod electrode.

7. The method of claim 6, wherein, An expression of a starting corona criterion of the positive corona is: An expression of a starting corona criterion of the negative corona is: where f1 is the probability of one photoelectron production by one electron impact ionization; f2 is the probability of one electron production by one photoionization; r i is the distance between the ionization region boundary position and the sphere center; α is the impact ionization coefficient, η is the electron adsorption coefficient, and r' is a virtual integration variable.

8. A system based on the method according to any one of claims 1 to 7, characterized in that, The method comprises the steps of: a bushing corona model construction module, configured to simplify two bushings used in a valve hall of a converter station into two parallel rod electrodes, and construct a corona model of the parallel rod electrodes; an area factor calculation module, configured to calculate an area factor of the positive corona and an area factor of the negative corona considering a photon transmission path based on the corona model of the parallel rod electrodes under AC-DC composite voltage; a positive corona determination module, configured to determine the positive corona according to the area factor of the positive corona and a starting corona criterion of the positive corona; a negative corona determination module, configured to determine the negative corona according to the area factor of the negative corona and a starting corona criterion of the negative corona.

Images