Corona loss prediction method suitable for high-altitude corona cage alternating current multi-split conductor

Abstract

The invention provides a corona loss prediction method suitable for a high-altitude corona cage alternating-current multi-split conductor, and the method comprises the steps: constructing a three-dimensional ion flow field numerical calculation model of an extra-high-voltage corona cage alternating-current split conductor suitable for a high-altitude region based on the size of an actual corona cage, determining input parameters of the three-dimensional ion flow field numerical calculation model of the ultra-high-voltage corona cage alternating-current split conductor, performing altitude correction on discharge parameters, and calculating corona onset and emission of simulated charges based on the three-dimensional ion flow field numerical calculation model of the ultra-high-voltage corona cage alternating-current split conductor. And calculating migration and recombination of space charges based on a numerical calculation model of the three-dimensional ion flow field of the ultra-high voltage corona cage alternating current split conductor, and calculating corona current and corona loss. According to the method, the corona loss of different split conductors of the corona cage in the high-altitude area can be predicted, and a certain reference value is provided for researching the corona loss of a power transmission line in the high-altitude area.

Description

Technical Field

[0001] The present invention relates to the technical field of power transmission and transformation engineering, and particularly relates to a method for predicting corona loss of AC multi-split conductors suitable for high altitude corona cages. Background Art

[0002] With the rapid development of China's power industry, China focuses on the development and large-scale transmission of large-scale clean energies such as hydropower and solar energy in the Qinghai-Tibet Plateau region. The air pressure is low and the air density is small in high altitude areas. Compared with plains, obvious changes will occur in microscopic physical parameters such as ionization, adsorption, and ion mobility during the discharge process, making the corona discharge of the line more intense and the corona loss problem serious. At present, the measurement test of the ultra-high voltage corona cage is the main method to obtain the corona loss of the conductor, but there are still many limitations in the measurement test of studying the corona loss of the prototype conductor based on the ultra-high voltage corona cage, such as the upper limit of the applied voltage, and the long period required for moving the cage body and large transformers between different altitude measurement points. Therefore, it is of great significance to study the corona loss of split conductors in high altitude corona cages by using numerical simulation methods.

[0003] Regarding the numerical simulation problem of corona loss, domestic experts and scholars have conducted a large number of studies. However, most of them are based on the research background of plain areas and cannot realize the prediction of corona loss of multi-split conductors in high altitude corona cages. China will continue to carry out the construction of ultra-high voltage AC transmission line projects in extremely high altitude areas above 4000m in altitude in the future. However, so far, there is a lack of research on the numerical simulation of corona loss of AC multi-split conductors in ultra-high voltage corona cages in high altitude areas in China.

[0004] Therefore, it is very necessary to design a method for predicting corona loss of AC multi-split conductors suitable for high altitude corona cages. Summary of the Invention

[0005] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a method for predicting corona loss of AC multi-split conductors suitable for high altitude corona cages.

[0006] To achieve the above purpose, the present invention provides the following solutions:

[0007] The present invention provides a method for predicting corona loss of AC multi-split conductors suitable for high altitude corona cages, including:

[0008] Constructing a three-dimensional ion flow field numerical calculation model of an ultra-high voltage corona cage AC split conductor suitable for high altitude areas based on the actual corona cage size;

[0009] Determining the input parameters of the three-dimensional ion flow field numerical calculation model of the ultra-high voltage corona cage AC split conductor;

[0010] Performing altitude correction on the discharge parameters.

[0011] Based on the numerical calculation model of the three-dimensional ion flow field of the AC bundled conductors in the UHV corona cage, calculate and simulate the corona inception and emission of charges;

[0012] Based on the numerical calculation model of the three-dimensional ion flow field of the AC bundled conductors in the UHV corona cage, calculate the migration and recombination of space charges;

[0013] Calculate the corona current and corona loss.

[0014] Preferably, determine the input parameters of the numerical calculation model of the three-dimensional ion flow field of the AC bundled conductors in the UHV corona cage, specifically:

[0015] Determine the input parameters of the numerical calculation model of the three-dimensional ion flow field of the AC bundled conductors in the UHV corona cage, including the applied voltage V, the number of conductor bundles, the bundle spacing, the radius of the sub-conductor, and the surface roughness coefficient of the conductor.

[0016] Preferably, perform altitude correction on the discharge parameters, specifically:

[0017] Atmospheric pressure P and ion mobility μ are the main influencing factors of altitude change on corona discharge. Among them, the relationship between altitude and atmospheric pressure is:

[0018]

[0019] In the formula, H is the altitude, P0 is the standard atmospheric pressure, and k is a calculation constant;

[0020] When other variables are constant, the ion mobility μ is inversely proportional to the gas density, and the gas density is directly proportional to the atmospheric pressure. If the ion mobility under standard atmospheric pressure is μ0, then the ion mobility μ at different altitudes is expressed as:

[0021]

[0022] In the formula, P is the atmospheric pressure at altitude H, and μ0 is the mobility of positive and negative ions.

[0023] Preferably, based on the numerical calculation model of the three-dimensional ion flow field of the AC bundled conductors in the UHV corona cage, calculate and simulate the corona inception and emission of charges, specifically:

[0024] Add the contribution of the ring charge to the potential equation and field strength equation of the numerical calculation model of the three-dimensional ion flow field of the AC bundled conductors in the UHV corona cage, which is:

[0025]

[0026] In the formula, P cond and P space are the simulated charges Q of the conductor respectivelycond and the space charge Q space Potential coefficient matrix of each point on the wire surface; P ri-co , P co-ri and P ring are respectively the potential coefficient matrices of the ring charge on the wire surface points, the simulated charge on the ring charge surface points, and the ring charge on the ring charge surface points; U cond and U ring are respectively the voltages of the wire and the grading ring, and their potentials are the same; F cond and F space are respectively the field strength coefficient matrices of the wire simulated charge Q cond and the space charge Q space for each point on the wire surface; F ri-co is the field strength coefficient of the ring charge at each nuclear point inside the cage and the location of the space charge, and is composed of the field strength coefficients in three-dimensional directions;

[0027] Among them, the released space charge Q space is calculated as follows:

[0028] Obtain the simulated charge quantity Q cond corresponding to each point on the wire surface at each time step onset± and the corona inception charge Q cond > Q onset+ or Q cond < Q onset- , then it is judged that corona occurs at this point on the wire surface and the space charge Q space is released. The released space charge and the simulated charge are both finite long line charges, and the space charge quantity is the part exceeding the corona inception charge, that is:

[0029] Q space,k = Q cond,k - Q onset±,k

[0030] Preferably, based on the numerical calculation model of the three-dimensional ion flow field of the UHV corona cage AC bundled conductor, the migration and recombination of space charge are calculated specifically as follows:

[0031] Under the condition that the polarity of the space charge is the same as that of the wire, the space charge will move away from the wire, otherwise it will move towards the wire. When the space charge moves to the wire surface at a certain moment, its charge quantity becomes 0. After a time step Δt, the space charge migrates to a new space point along the electric field line direction, and the migration distance ΔS is expressed as:

[0032] ΔS = μ|E q |Δt

[0033] In the formula, μ is the mobility of the above-mentioned corrected positive and negative ions, |Eq is the modulus of vector E q ;

[0034] Positive and negative space charges will move towards each other under the action of the electric field force and there is a certain recombination probability. This process needs to be completed through charge loss, and its loss rate is closely related to the local charge density. When the space charge density decreases by two orders of magnitude after multiple losses, its influence is ignored. After a time step, a certain space charge Q t after loss, its charge quantity Q t+Δt becomes:

[0035]

[0036] where ρ ± is the charge density in the region where positive and negative space charges are located.

[0037] Preferably, the corona current and corona loss are calculated as follows:

[0038] The corona current on the wire in the corona cage is composed of the displacement current I c generated by the change of simulated charges and the induced current I s generated by the migration movement of space charges on the wire. Among them, the induced current is the main component of the corona current. The displacement current at time t is expressed as:

[0039]

[0040] where ΔQ k,t is the change amount of the k-th simulated charge quantity at time t, ΔQ k,t,null is the change amount of the k-th simulated charge at time t without considering space charges, Δt is the calculation time step, and n is the total number of simulated charges;

[0041] The induced current of the corona cage wire is equal to the sum of the induced currents generated by each simulated charge due to the movement of all space charges, and is expressed as:

[0042]

[0043] where n is the total number of simulated charges, m is the total number of space charges, E kp refers to the electric field intensity vector generated on the space charge q j when a unit voltage is applied to the k-th conductor, and E qj,t refers to the electric field intensity at the space charge q j at time t;

[0044] Perform vector decomposition on the corona current I cor to calculate the corona loss of the wire. Suppose the effective value of the voltage applied to the corona cage wire is U, and the instantaneous power of the corona loss generated on the wire is expressed as:

[0045]

[0046] Wherein, U(t) and I cor (t) are the voltage and corona current vectors respectively, both with power frequency, and θ(t) is the phase angle difference between the voltage and current at time t;

[0047] After stable corona discharge occurs, the instantaneous corona loss power is extended to an AC cycle T, and the corona loss of the corona cage wire in one AC cycle is expressed as:

[0048]

[0049] The effective value of the corona loss power converted to per 1m wire is:

[0050]

[0051] Wherein, L is the length of the wire in the corona cage.

[0052] According to the specific embodiments provided by the present invention, the following technical effects are disclosed:

[0053] The present invention provides a method for predicting corona loss of AC multi - split conductors in a high - altitude corona cage, and the method includes: constructing a three - dimensional ion - flow field numerical calculation model of UHV corona cage AC split conductors applicable to high - altitude areas based on the actual corona cage size, determining the input parameters of the three - dimensional ion - flow field numerical calculation model of UHV corona cage AC split conductors, performing altitude correction on the discharge parameters, calculating and simulating the corona initiation and emission of charges based on the three - dimensional ion - flow field numerical calculation model of UHV corona cage AC split conductors, calculating the migration and recombination of space charges based on the three - dimensional ion - flow field numerical calculation model of UHV corona cage AC split conductors, and calculating the corona current and corona loss. The present invention has the following advantages:

[0054] 1. A three - dimensional AC ion - flow model of split conductors in a large - scale corona cage applicable to high - altitude areas is built. The model considers the influence of the grading rings on both sides of the actual corona cage, the non - uniformity of the surface electric field of the split conductors, and the migration and recombination processes of space charges. The magnitude of the corona current of the wire is calculated based on the Shockley - Ramo rule, and the corona loss of the wire is calculated based on the power factor method. The corona loss obtained by using this method can be directly used for calculating the corona loss of split conductors in a high - altitude corona cage;

[0055] 2. It can realize the prediction of corona loss of split conductors under different weather conditions and different electric field intensities. It can simulate three weather conditions: dry, raining, and humid, and can avoid the trouble of frequent operation of the rain - shower device during corona cage tests;

[0056] 3. Existing corona loss estimation methods are all proposed based on actual corona loss data and are only applicable to areas with an altitude lower than 4000m. Once the altitude is higher, the error of corona loss increases rapidly, and accurate estimation of the corona loss of bundled conductors cannot be achieved. The present invention can predict the corona loss of different bundled conductors in a corona cage at high altitudes, providing certain reference value for studying the corona loss of transmission lines in high-altitude areas;

[0057] 4. It can solve many problems in the measurement of corona loss of prototype conductors based on the study of UHV corona cages, including the upper limit of the applied voltage, the long time required for the movement of the corona cage body and large transformers between different altitude measurement points, etc.;

[0058] 5. Considering the influence of the grading rings on both sides of the bundled conductor on the surface field strength and current density of the bundled conductor, the simulated charge Q of the conductor grading ring ring is added to the existing potential equation and field strength equation without the influence of grading rings. The addition of the simulated charge of the grading ring contributes to the potential of the surface charge of the bundled conductor, suppressing the increase in the simulated charge amount of the end conductor, thereby reducing the end electric field strength and current density of the bundled conductor, and making the calculation of the corona current and corona loss of the bundled conductor more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0060] Figure 1 is the flowchart of the method provided by the embodiment of the present invention;

[0061] Figure 2 is the block diagram of the method provided by the embodiment of the present invention;

[0062] Figure 3 is the structural schematic diagram of the numerical calculation model of the three-dimensional ion flow field of the AC bundled conductor of the UHV corona cage;

[0063] FIG. 4 shows the corona loss values of two kinds of conductors under different weather conditions ( Figure 4a is the corona loss value of the 6×LGJ720 conductor under different weather conditions, Figure 4b is the corona loss value of the 8×LGJ500 conductor under different weather conditions). DETAILED DESCRIPTION OF THE EMBODIMENTS

[0064] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0065] The object of the present invention is to provide a corona loss prediction method applicable to AC multi-split conductors of a high-altitude corona cage, which can realize the prediction of corona losses of different split conductors in a high-altitude corona cage and provides certain reference value for the study of corona losses of transmission lines in high-altitude areas.

[0066] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0067] Figure 1 It is the flowchart of the method provided by the embodiment of the present invention. Figure 2 It is the block diagram of the method provided by the embodiment of the present invention. As Figure 1 and Figure 2 shown, the present invention provides a corona loss prediction method applicable to AC multi-split conductors of a high-altitude corona cage, including:

[0068] Step 100: Construct a three-dimensional ion flow field numerical calculation model of UHV corona cage AC split conductors applicable to high-altitude areas based on the actual corona cage size;

[0069] Step 200: Determine the input parameters of the three-dimensional ion flow field numerical calculation model of UHV corona cage AC split conductors;

[0070] Step 300: Correct the discharge parameters for altitude;

[0071] Step 400: Calculate the corona initiation and emission of simulated charges based on the three-dimensional ion flow field numerical calculation model of UHV corona cage AC split conductors;

[0072] Step 500: Calculate the migration and recombination of space charges based on the three-dimensional ion flow field numerical calculation model of UHV corona cage AC split conductors;

[0073] Step 600: Calculate the corona current and corona loss.

[0074] In step 100, constructing a three-dimensional ion flow field numerical calculation model of UHV corona cage AC split conductors applicable to high-altitude areas based on the actual corona cage size is specifically as follows:

[0075] The three-dimensional ion flow field numerical calculation model of UHV corona cage AC bundled conductors takes into account the influence of the grading rings on both sides of the actual corona cage, the non-uniformity of the surface electric field strength of the bundled conductors, and the migration and recombination processes of space charges. The simulated charge method is used to calculate the magnitude of the corona current of the bundled conductors based on the Shockley-Ramo theorem, and the corona loss of the bundled conductors is calculated based on the power factor method. Its structural schematic diagram is as shown in Figure 3 shown;

[0076] The three-dimensional ion flow field numerical calculation model of UHV corona cage AC bundled conductors mainly refers to the actual dimensions of the corona cage at the high-altitude test base of State Grid Corporation of China in Yangbajing, Tibet (altitude 4300m). The cross-sectional size of the corona cage is 12×12m, and the total length of the corona cage body is 45m. In order to control the corona of the clamping disc and the end fitting, grading rings with a ring diameter of 2m are made of aluminum pipes with a diameter of φ300mm, which are about 2.5m away from both ends of the cage body. The calculation model of the present invention takes into account the finite-length characteristics of the conductors. By segmenting along the conductor direction, the conductors inside the cage are divided into shorter finite-length conductors, and then the bundled conductors are replaced by equal-length simulated line charges. 8 simulated charges are set in each bundled sub-conductor, evenly distributed at 0.7 times the radius of the sub-conductor, and the corresponding potential check points are set on the surface of the sub-conductor.

[0077] In step 200, determine the input parameters of the three-dimensional ion flow field numerical calculation model of UHV corona cage AC bundled conductors, specifically:

[0078] Determine the input parameters of the three-dimensional ion flow field numerical calculation model of UHV corona cage AC bundled conductors, including the applied voltage V, the number of conductor bundles, the bundle spacing, the sub-conductor radius, and the surface roughness coefficient of the conductor, as shown in Table 1 specifically;

[0079] Table 1 Input characteristic parameter table of the three-dimensional ion flow field numerical calculation model of UHV corona cage AC bundled conductors

[0080]

[0081] In step 300, correct the discharge parameters for altitude, specifically:

[0082] Altitude is an important influencing factor for conductor corona loss. As the altitude increases, the air pressure gradually decreases, and the decrease in air density makes the ion mobility μ and the mean free path of electrons increase. The space charges have a faster movement speed under the action of the electric field, making the corona phenomenon more likely to occur and the corona loss increase significantly. The atmospheric pressure P and the ion mobility μ are the main influencing factors of altitude change on corona discharge. Among them, the relationship between altitude and air pressure is:

[0083]

[0084] Wherein, H is the altitude, in km, and the altitude of the Yangbajing high-altitude test base of the present invention is 4.3 km; P0 is the standard atmospheric pressure, 760 Torr (101.3 kPa); k is a calculation constant, generally taken as 10.7;

[0085] When other variables are constant, the ion mobility μ is inversely proportional to the gas density, and the gas density is directly proportional to the atmospheric pressure. If the ion mobility under the standard atmospheric pressure is μ0 (including different polarities), then the ion mobility μ at different altitudes is expressed as:

[0086]

[0087] Wherein, P is the atmospheric pressure at the altitude H, in Torr; μ0 is the mobilities of positive and negative ions, taken as 1.5×10 - 4 m 2 / (Vs) and 1.8×10 -4 m 2 / (Vs).

[0088] In step 400, the corona inception and emission of simulated charges are calculated based on the three-dimensional ion flow field numerical calculation model of the UHV corona cage AC bundled conductors, specifically:

[0089] After considering the grading ring, all points in the space will be affected not only by the wire simulated charge Q cond , but also by the ring charges Q ring on both sides (the ring charges on both sides are equal due to symmetry). Therefore, the contributions of the ring charges are added to the potential equation and field strength equation of the three-dimensional ion flow field numerical calculation model of the UHV corona cage AC bundled conductors, as follows:

[0090]

[0091] Wherein, P cond and P space are the potential coefficient matrices of the wire simulated charge Q cond and the space charge Q space to each point on the wire surface; P ri-co , P co-ri and P ring are the potential coefficient matrices of the ring charge to the point on the wire surface, the simulated charge to the point on the ring charge surface, and the ring charge to the point on the ring charge surface, respectively; U cond and U ring are the voltages of the wire and the grading ring, and their potentials are the same; F cond and F space are the field strength coefficient matrices of the wire simulated charge Q cond and the space charge Q space to each point on the wire surface; Fri-co The field strength coefficients of the ring charge pairs at each nuclear point and the space charge location inside the cage are all composed of the field strength coefficients in three-dimensional directions;

[0092] Among them, the released space charge Q space is calculated as follows:

[0093] Obtain the simulated charge quantity Q corresponding to each point on the wire surface at each time step cond and the corona inception charge Q onset± , and compare them. If a certain point satisfies Q cond >Q onset+ or Q cond <Q onset- , then it is determined that corona inception occurs at this point on the wire surface and space charge Q space is released. The released space charge and the simulated charge are both finite long line charges, and the space charge quantity is the part exceeding the corona inception charge, that is:

[0094] Q space,k =Q cond,k -Q onset±,k

[0095] Step 500: Calculate the migration and recombination of space charges based on the three-dimensional ion flow field numerical calculation model of UHV corona cage AC bundled conductors, specifically:

[0096] Under the condition that the space charge polarity is the same as the wire polarity, the space charge will move away from the wire, otherwise it will move towards the wire. When the space charge moves to the wire surface at a certain moment, its charge quantity becomes 0. After a time step Δt, the space charge migrates along the electric field line direction to a new space point, and the migration distance ΔS is expressed as:

[0097] ΔS = μ|E q |Δt

[0098] In the formula, μ is the corrected positive and negative ion mobilities above, and |E q | is the modulus of the vector E q ;

[0099] Positive and negative space charges will move towards each other under the action of the electric field force and there is a certain recombination probability. This process needs to be completed through charge loss, and its loss speed is closely related to the local charge density. When the space charge density decreases by 2 orders of magnitude after multiple losses, its influence is ignored. After a time step, a certain space charge Q t after loss, its charge quantity Q t+Δt becomes:

[0100]

[0101] In the formula, ρ± is the charge density in the regions where positive and negative space charges are located, and the recombination coefficient γ = 1.5×10 -12 m 2 s -1 。

[0102] In step 600, the corona current and corona loss are calculated, specifically as follows:

[0103] The corona current on the wire in the corona cage is composed of the displacement current I c generated by the change of simulated charges and the induced current I s generated by the migration movement of space charges on the wire. Among them, the induced current is the main component of the corona current. The displacement current at time t is expressed as:

[0104]

[0105] In the formula, ΔQ k,t is the change amount of the k-th simulated charge quantity at time t, ΔQ k,t,null is the change amount of the k-th simulated charge at time t without considering space charges, Δt is the calculation time step, and n is the total number of simulated charges;

[0106] The induced current of the corona cage wire is equal to the sum of the induced currents generated by each simulated charge due to the movement of all space charges, and is expressed as:

[0107]

[0108] In the formula, n is the total number of simulated charges, m is the total number of space charges, E kp refers to the electric field intensity vector generated on the space charge q j when a unit voltage is applied to the k-th conductor, and E qj,t refers to the electric field intensity at the space charge q j at time t;

[0109] The corona loss is the active power loss caused by the corona of the transmission line wire, which is mainly caused by the resistive component of the corona current. In the present invention, through the three-dimensional ion flow field model, the corona current I cor is numerically calculated. However, the calculation result contains multiple harmonics, and vector decomposition is required to calculate the corona loss of the wire. Suppose the effective value of the voltage applied to the corona cage wire is U, and the instantaneous power of the corona loss generated on the wire is expressed as:

[0110]

[0111] In the formula, U(t) and I cor (t) are the voltage and corona current vectors respectively, with the frequency being the power frequency, and θ(t) is the phase angle difference between the voltage and the current at time t;

[0112] After stable corona discharge occurs, the instantaneous power of corona loss is extended to an AC cycle T, and the corona loss of the corona cage wire in one AC cycle is expressed as:

[0113]

[0114] The effective value of the corona loss power converted to per 1 m of wire is:

[0115]

[0116] In the formula, L is the length of the wire in the corona cage

[0117] The present invention provides an embodiment, listing the prediction results of the corona loss of the bundled conductors in the corona cage, as:

[0118] The present invention lists the numerical analysis of the corona loss of two types of bundled conductors, 6×LGJ720 and 8×LGJ500, under rainy, dry, and humid weather conditions. Table 2 shows the comparison between the numerically calculated corona loss and the experimentally measured corona loss of the two types of bundled conductors under the maximum electric field intensity. Figure 4 shows the corona loss values of the two types of bundled conductors under different weather conditions. (a) and (b) are 6×LGJ720 and 8×LGJ500 conductors respectively. The following analysis can be obtained from Table 2 and Figure 4:

[0119] For the 6×LGJ720 conductor, under rainy weather conditions, the corona loss of the conductor increases from 0 W / m to 334.2 W / m as the surface electric field intensity increases. When the surface electric field intensity of the conductor is the largest, the error of the corona loss is 7.4%; under dry weather conditions, the corona loss of the conductor rises from the initial 0 W / m to 228.6 W / m. Under the maximum electric field intensity, the error of the corona loss of the conductor is 5.8%; under humid weather conditions, the corona loss of the conductor can reach up to 311.0 W / m, and the error of the corona loss of the conductor is only 0.8% under the maximum electric field intensity;

[0120] For the 8×LGJ500 conductor, when the surface electric field intensity of the conductor is 17 kV / cm, the corona loss per unit length of the conductor calculated by this method is 321.3, 267.0, and 290.1 W / m respectively under the three weather conditions. When the surface electric field intensity is the largest, the errors between the corona loss of the conductor calculated by this method and the experimentally measured values are 11.9%, 1.5%, and 7.1% respectively;

[0121] As can be seen from Figure 4 and Table 2, the corona losses of the two types of bundled conductors under different weather conditions increase with the increase of the conductor electric field strength, and show an exponential law. When the surface electric field strength of the two types of bundled conductors is the largest, the average errors between the numerically calculated corona loss values and the experimentally measured corona loss values are 4.7% and 6.8% respectively. It can be seen that the accuracy of the established model can be used to predict the corona losses of different bundled conductors.

[0122] Table 2 Comparison table of corona loss simulation and experiment at maximum electric field strength

[0123]

[0124]

[0125] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0126] Specific examples are used in this article to elaborate on the principles and implementation manners of the present invention. The descriptions of the above embodiments are only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A method for predicting corona loss of AC multi - split conductors applicable to a corona cage at high altitude, characterized in that, Including: Construct a three-dimensional ion flow field numerical calculation model of UHV corona cage AC bundled conductors applicable to high altitude areas based on the actual corona cage size; Determine the input parameters of the three-dimensional ion flow field numerical calculation model of UHV corona cage AC bundled conductors; Perform altitude correction on the discharge parameters; Calculate and simulate the corona inception and emission of charges based on the three-dimensional ion flow field numerical calculation model of UHV corona cage AC bundled conductors; Calculate the migration and recombination of space charges based on the three-dimensional ion flow field numerical calculation model of UHV corona cage AC bundled conductors; Calculate the corona current and corona loss.

2. The method according to claim 1, wherein Determine the input parameters of the three-dimensional ion flow field numerical calculation model of UHV corona cage AC bundled conductors, specifically: Determine the input parameters of the three-dimensional ion flow field numerical calculation model of UHV corona cage AC bundled conductors, including the applied voltage V, the number of conductor bundles, the bundle spacing, the radius of the sub-conductor, and the surface roughness coefficient of the conductor.

3. The method according to claim 2, wherein Perform altitude correction on the discharge parameters, specifically: Atmospheric pressure P and ion mobility μ are the main factors affecting corona discharge with the change of altitude. Among them, the relationship between altitude and atmospheric pressure is: In the formula, H is the altitude, P0 is the standard atmospheric pressure, and k is a calculation constant; When other variables are constant, the ion mobility μ is inversely proportional to the gas density, and the gas density is directly proportional to the atmospheric pressure. If the ion mobility under standard atmospheric pressure is μ0, then the ion mobility μ at different altitudes is expressed as: In the formula, P is the atmospheric pressure at altitude H, and μ0 is the mobility of positive and negative ions.

4. The method according to claim 3, characterized in that, Calculate and simulate the corona inception and emission of charges based on the three-dimensional ion flow field numerical calculation model of UHV corona cage AC bundled conductors, specifically: Add the contribution of ring charges to the potential equation and field strength equation of the three-dimensional ion flow field numerical calculation model of UHV corona cage AC bundled conductors, which is: Wherein, P cond and P space are respectively the potential coefficient matrices of the wire analog charges Q cond and the space charges Q space for each point on the wire surface; P ri-co , P co-ri and P ring are respectively the potential coefficient matrices of the ring charge for the points on the wire surface, the analog charge for the points on the ring charge surface, and the ring charge for the points on the ring charge surface; U cond and U ring are respectively the voltages of the wire and the grading ring, and their potentials are the same; F cond and F space are respectively the field strength coefficient matrices of the wire analog charges Q cond and the space charges Q space for each point on the wire surface; F ri-co is the field strength coefficient of the ring charge for each nuclear point in the cage and the location of the space charge, and is composed of the field strength coefficients in three-dimensional directions; Among them, the released space charge Q space is calculated as follows: Obtain the simulated charge quantity Q corresponding to each point on the surface of the wire at each time step cond and the corona onset charge Q onset± , and compare them. If a certain point satisfies Q cond >Q onset+ or Q cond <Q onset- , then it is determined that corona occurs at this point on the wire surface and space charge Q space is released. Both the released space charge and the simulated charge are finite line charges, and the space charge quantity is the part exceeding the corona onset charge, that is: Q space,k = Q cond,k -Q onset±,k 。 5. The method according to claim 4, wherein Calculate the migration and recombination of space charges based on the three-dimensional ion flow field numerical calculation model of UHV corona cage AC bundled conductors, specifically: Under the condition that the polarity of the space charge is the same as that of the conductor, the space charge will move away from the conductor, otherwise it will move towards the conductor. When the space charge moves to the conductor surface at a certain moment, its charge quantity becomes 0. After a time step Δt, the space charge migrates to a new space point along the electric field line direction, and the migration distance ΔS is expressed as: ΔS = μ|E q |Δt where μ is the mobility of positive and negative ions after the above-mentioned correction, and |E q | is the magnitude of the vector E q ; Positive and negative space charges will move towards each other under the action of the electric field force and there is a certain probability of recombination. This process needs to be completed through charge loss, and its loss rate is closely related to the local charge density. When the space charge density decreases by two orders of magnitude after multiple losses, its influence is ignored. After a time step, a certain space charge Q t After loss, its charge quantity Q t+Δt Becomes: where ρ ± is the charge density in the regions where positive and negative space charges are located.

6. The method according to claim 5, characterized in that Calculate the corona current and corona loss, specifically: The corona current on the wire in the corona cage is composed of the displacement current I generated by the change of simulated charges c and the induced current I generated on the wire by the migration motion of space charges. Among them, the induced current is the main component of the corona current. The displacement current at time t is expressed as: s ​ where, ΔQ k,t is the change in the k-th simulated charge quantity at time t, and ΔQ k,t,null is the change in the k-th simulated charge at time t without considering space charge, Δt is the calculation time step, and n is the total number of simulated charges; The induced current of the corona cage conductor is equal to the sum of the induced currents generated by each simulated charge due to the movement of all space charges, which is expressed as: where n is the total number of simulated charges, m is the total number of space charges, and E kp refers to the electric field intensity vector generated on the space charge q j when a unit voltage is applied to the k-th conductor, and E qj,t refers to the electric field intensity at the space charge q j at time t; For the corona current I cor Perform vector decomposition to calculate the corona loss of the wire. Assume that the effective value of the voltage applied to the corona cage wire is U, and the instantaneous power of the corona loss generated on the wire is expressed as: where U(t) and I cor (t) are the voltage and corona current vectors respectively, both with power frequency, and θ(t) is the phase angle difference between the voltage and current at time t; After stable corona discharge occurs, expand the instantaneous power of corona loss to an AC cycle T. The corona loss of the corona cage conductor in one AC cycle is expressed as: Converted to the effective value of the corona loss power per 1m conductor is: In the formula, L is the length of the conductor in the corona cage.

Images