Ultra-high altitude wire alternating current corona loss calculation method considering outer layer strand structure

Abstract

The invention provides an ultra-high altitude wire alternating current corona loss calculation method considering an outer layer strand structure. The method comprises the following steps: based on a Kaptzov hypothesis, defining corona loss, judging whether a wire has corona at each position of a strand, if so, calculating charge consumption, and calculating the corona loss according to the charge consumption. According to the method, the influence of the ultrahigh altitude condition and the wire outer layer strand structure on the corona loss is fully considered, the calculation precision is remarkably improved, the calculation time is shortened to about 1 / 4 of that of an original method by optimizing the simulation charge number and the calculation process, reliable theoretical support is provided for design and operation of a high-altitude power transmission line, power transmission loss can be reduced, and the method is suitable for popularization and application. The economical efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of power transmission and transformation engineering, and in particular to a method for calculating the AC corona loss of a conductor taking into account an outer strand structure at ultra-high altitudes. Background Art

[0002] Ultra-high altitude covers the range of 3500 to 5500m. At present, the influence of altitude factors on the AC corona characteristics of transmission lines is mainly below 2000m, and the conductors are treated as smooth steel pipes. Their macroscopic characteristics are studied, such as the main analysis of the influence of altitude on parameters such as corona inception voltage, corona loss, and radio interference. However, there is a lack of research on their microscopic characteristics. For example, it is necessary to study the outer strand structure of the conductor under different air pressure conditions and study the theoretical calculation model of the corona loss characteristics of the conductor at ultra-high altitude.

[0003] In order to effectively reduce the error introduced when calculating the corona loss by treating the conductor as a smooth steel pipe and ensure the safe, economical and reliable operation of the transmission line, it is necessary to accurately evaluate the corona characteristics of the outer strand structure of the stranded wire and establish a calculation model for the AC corona loss of the conductor considering the outer strand structure at ultra-high altitudes. This has great theoretical significance and engineering value, but related research is still blank. Therefore, it is very necessary to design a calculation method for the AC corona loss of the conductor considering the outer strand structure at ultra-high altitudes. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art, the object of the present invention is to provide a method for calculating the AC corona loss of a conductor at ultra-high altitudes taking into account the structure of the outer strand.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] The present invention provides a method for calculating AC corona loss of a conductor at ultra-high altitudes taking into account the structure of an outer strand, comprising:

[0007] Based on Kaptzov hypothesis, corona loss is defined;

[0008] At each position of the strand, determine whether the conductor is dizzy, and if dizzy, calculate the charge consumption;

[0009] Corona losses are calculated based on charge consumption.

[0010] Preferably, it is determined at each position of the strand whether the conductor is dizzy, and if dizzy, the charge consumption is calculated, specifically:

[0011] According to the conductor simulation charge model and the calculation method of the corona initiation field strength, the conductor corona initiation field strength is obtained, and the conductor simulation charge at this time is calculated, which is used as the corona initiation charge criterion Qcri+ or Qcri- at ​​each point of the conductor, and the voltage of the conductor at a certain moment is obtained as U app =Umax ·sin(ω·t), calculate the simulated charge Q at this time cond , the simulated charge Q cond Compare with the corona charge criterion Qcri+ or Qcri- at ​​each point of the conductor, analyze whether the conductor corona occurs at each position of the strand, and simulate the charge Q after the conductor corona starts. cond The part exceeding the corona onset charge criterion Qcri+ or Qcri- at ​​each point of the conductor will be emitted from the charge emission point on the conductor surface in the form of space charge. After the corona occurs at a certain position, the simulated charge at that position becomes the corona onset charge criterion Qcri+ or Qcri- at ​​each point of the conductor, that is, the corona starting charge.

[0012] Among them, there are two processes involving charge consumption, namely the charge consumption caused by the recombination of positive and negative ions and the charge consumption caused by the movement of opposite-sign charges to the surface of the wire. The total charge consumption is calculated, where the positive and negative charge densities n ± and space charge q ± The relationship between them is:

[0013]

[0014] Where ΔV is the control volume of the line charge, and e is the electron charge, e=1.6×10 -19 C, after time Δt, the space charge decreases to:

[0015]

[0016] Where, γ = 1.5 × 10 -12 m 3 / s, q' is the charge after time Δt has passed.

[0017] Preferably, the corona loss is calculated based on the charge consumption, specifically:

[0018] Assume that the movement distance of the space charge in the two coordinate axis directions is Δd ix and Δd iy , the corona loss within the Δt time is:

[0019] W i =q i ·E ix ·Δd ix +q i ·E iy ·Δd iy

[0020] The corona loss of the conductor in a corresponding calculation cycle is:

[0021]

[0022] Where N sc is the space charge number within the time Δt;

[0023] The corresponding corona loss power per unit length of conductor is:

[0024] P=fW

[0025] Where f is 50Hz. When the corona loss error in two adjacent power frequency cycles is less than a specific value, the calculation is considered to be stable and the calculation is stopped.

[0026] Preferably, the migration distance of the space charge under the action of the electric field force within the time Δt is calculated as:

[0027] Δd=μ×E×Δt

[0028] Where μ is the mobility of positive and negative ions, and E is the electric field strength at the location of the space charge.

[0029] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0030] The present invention provides a method for calculating the AC corona loss of a conductor at ultra-high altitudes taking into account the structure of an outer strand. The method comprises: based on the Kaptzov hypothesis, defining the corona loss, judging whether the conductor is coronaing at various positions of the strand, and if coronaing, calculating the charge consumption, and calculating the corona loss according to the charge consumption. The present invention fully considers the influence of ultra-high altitude conditions and the structure of the outer strand of the conductor on the corona loss, significantly improves the calculation accuracy, and by optimizing the simulated charge number and the calculation process, shortens the calculation time to about 1 / 4 of the original method, providing reliable theoretical support for the design and operation of high-altitude transmission lines, helping to reduce power transmission losses and improve economic efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0032] Figure 1 is the trajectory diagram of positive ion movement;

[0033] Figure 2 It is the trajectory diagram of negative ion movement;

[0034] Figure 3 Schematic diagram of the effect of simulated charge number on calculation results;

[0035] Figure 4The schematic diagram of the calculation results of corona loss of three types of conductors;

[0036] Figure 5 This is the trajectory diagram of ion movement in AC corona discharge;

[0037] Figure 6 This is a schematic diagram of the calculation results of corona loss of different split conductors under high altitude conditions;

[0038] Figure 7 A flow chart of a method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] The purpose of the present invention is to provide a method for calculating the AC corona loss of a conductor at ultra-high altitudes taking into account the outer strand structure, which fully considers the influence of ultra-high altitude conditions and the outer strand structure of the conductor on the corona loss, significantly improves the calculation accuracy, and shortens the calculation time to about 1 / 4 of the original method by optimizing the simulated charge number and the calculation process, providing reliable theoretical support for the design and operation of high-altitude transmission lines, helping to reduce power transmission losses and improve economy.

[0041] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] Figure 7 A flow chart of a method provided by an embodiment of the present invention, such as Figure 7 As shown, the present invention provides a method for calculating the AC corona loss of a conductor at ultra-high altitudes taking into account the outer strand structure, comprising:

[0043] Step 100: Based on the Kaptzov hypothesis, define corona loss;

[0044] Step 200: determining whether the conductor is dizzy at each position of the strand, and if dizzy, calculating the charge consumption;

[0045] Step 300: Calculate the corona loss according to the charge consumption.

[0046] In step 100, based on the Kaptzov hypothesis, the corona loss is defined as:

[0047] The present invention abandons the Deutsch hypothesis, that is, the positive and negative ions generated by corona discharge will not only change the magnitude of the original electric field, but also change the direction of the electric field; adopts the Kaptzov hypothesis, that is, after corona discharge occurs, the surface electric field strength of the wire remains at the corona inception field strength, and this is used as the basis for calculating the corona inception charge. The power frequency period is discretized into several time steps. At each time point, the simulated charge quantity of the wire is calculated according to the instantaneous value of the applied voltage and compared with the corona inception charge quantity. After corona inception, the part of the simulated charge quantity exceeding the corona inception charge quantity is emitted into the surrounding space in the form of space charge. The space charge moves under the action of the electric field force. During the movement of the charge, the charge consumption caused by the recombination of positive and negative ions and the charge consumption caused by the movement of opposite-sign charges to the wire surface are considered. The loss generated by the movement of positive and negative ions around the wire under the action of the alternating electric field is the corona loss.

[0048] In step 200, at each position of the strand, it is judged whether the wire starts to corona. If it starts to corona, the charge consumption is calculated, specifically:

[0049] According to the wire simulated charge model and the corona inception field strength calculation method, the corona inception field strength (voltage) of the wire is obtained, and the simulated charge quantity of the wire at this time is calculated, and it is used as the corona inception charge criterion Qcri+ or Qcri- of each point of the wire (that is, the corona inception charge quantity described above). Assume that the voltage of the wire at a certain moment is U app = U max ·sin(ω·t), calculate the simulated charge quantity Q at this time cond , and compare the simulated charge quantity Q cond with the corona inception charge criterion Qcri+ or Qcri- of each point of the wire. At each position of the strand, it is analyzed whether the wire starts to corona. If Q cond > Qcri+ or Q cond < Qcri-, then the wire starts to corona. After the wire corona inception, the part of the simulated charge quantity Q cond exceeding the corona inception charge criterion Qcri+ or Qcri- of each point of the wire will be emitted from the wire surface charge emission point in the form of space charge, and the emission quantity is Q cond - Qcri+ or Q cond - Qcri-. After corona occurs at a certain position, the simulated charge quantity at that place becomes the corona inception charge criterion Qcri+ or Qcri- of each point of the wire;

[0050] Among them, there are two processes involving charge consumption, namely the charge consumption caused by the recombination of positive and negative ions and the charge consumption caused by the movement of opposite-sign charges to the wire surface. Calculate the total charge consumption. Among them, the relationship between the positive and negative charge densities n ± and the space charge quantity q ± is:

[0051]

[0052] Where ΔV is the control volume of the line charge, and e is the electron charge, e=1.6×10 -19 C, after time Δt, the space charge consumption is:

[0053]

[0054] Where, γ = 1.5 × 10 -12 m 3 / s, q' is the charge after time Δt has passed.

[0055] In step 300, the corona loss is calculated according to the charge consumption, specifically:

[0056] Assume that the movement distance of the space charge in the two coordinate axis directions is Δd ix and Δd iy , the corona loss within the Δt time is:

[0057] W i =q i ·E ix ·Δd ix +q i ·E iy ·Δd iy

[0058] Among them, q i is the i-th space charge emitted into space, and the corona loss of the conductor in a corresponding calculation cycle is:

[0059]

[0060] Where N sc is the space charge number within the time Δt;

[0061] The corresponding corona loss power per unit length of conductor is:

[0062] P=fW

[0063] Where f is 50Hz. When the corona loss error in two adjacent power frequency cycles is less than a specific value, the calculation is considered to be stable and the calculation is stopped.

[0064] It should be noted that the migration distance of space charge under the action of electric field force within Δt time is calculated as:

[0065] Δd=μ×E×Δt

[0066] Where μ is the mobility of positive and negative ions. The ion mobility at different altitudes adopts the measured values ​​of ion mobility at different simulated altitudes, see Table 1. The ion mobility values ​​at other intermediate altitudes can be obtained by interpolation. E is the electric field strength at the location of the space charge, which can be obtained by the simulated charge method.

[0067] Table 1 Positive and negative ion mobility values ​​at different simulated altitudes

[0068]

[0069] The present invention provides an embodiment, for a small corona cage with a cross-section of 1.8m×1.8m, three types of conductors LGJ300-40, LGJ400-35 and LGJ630-45 are used in the calculation to verify the feasibility and accuracy of the conductor AC corona loss method of the present invention, and the small corona cage test is carried out at an altitude of 14m.

[0070] After the cage wall is replaced by 100 simulated charges, the number of simulated charges and the number of space charges in the calculation process will be greatly reduced. Table 2 compares the changes in program running time when calculating the AC corona loss of the LGJ300-40 conductor using a primary image and replacing the cage wall with simulated charges. It can be seen that the calculation time is greatly shortened and the calculation efficiency is greatly improved.

[0071] Table 2 Program running time comparison table

[0072]

[0073] Figure 1 and Figure 2 The figure is a diagram of the movement trajectory of positive and negative ions. It can be seen that the outermost ions of each strand appear earlier and end later. Generally, only emission points 8, 9 and 10 can reach the corona initiation field strength and cause corona discharge. This shows that the improved calculation model of AC corona loss of conductors considering the outer strand structure is more in line with physical reality.

[0074] The selection of the simulated charge number has a great influence on the calculation results of the corona loss. If the selected simulated charge is too small, the gradual process of the conductor corona onset cannot be reflected, and the calculation result error is relatively large. At this time, only the outermost end of the strand can produce corona discharge. When the selected simulated charge number increases, the corresponding calculation time also increases significantly. The final selection of the simulated charge number should be considered from these two aspects. Figure 4 The influence of the simulated charge number of the LGJ400-35 conductor strand on the calculation results of corona loss can be seen from the figure. The calculation results tend to be stable after the simulated charge number reaches 15, and increasing the simulated charge number has little effect on the calculation results of corona loss. The calculation results of other types of conductors are consistent with the calculation results of LGJ400-35 conductors, and the simulated charge number of the strands finally selected is 17.

[0075] The overall roughness coefficients of the three conductors in the calculation are 0.92, 0.88 and 0.87 respectively. Figure 4 As shown in the figure, from the calculation results of corona loss, the calculation results of the improved conductor corona loss calculation model are more consistent with the experimental measurement results at the beginning of corona, and the turning point is relatively smooth, which is consistent with the gradual development process of conductor corona.

[0076] Figure 5 This is the ion emission and motion trajectory diagram of the LGJ630 eight-split wire at an air pressure of 83.29kpa (corresponding to an altitude of 2000m). Similar to the results of a single wire, the outermost ions of each wire appear earlier and end later, which is consistent with the process of wire corona occurrence and development.

[0077] The AC corona loss test of LGJ630 eight-split conductor, LGJ720 eight-split conductor and LGJ720 ten-split conductor was carried out in the UHV corona cage in Xining, Qinghai, and compared with the calculated results. The results are as follows: Figure 6 shown.

[0078] The overall roughness coefficient of the split conductor in the calculation is 0.8. From the calculation results of corona loss, it is consistent with the calculation results of a single conductor. The calculation results of the improved conductor corona loss calculation model are in good agreement with the experimental measurement results at the beginning of corona, and the inflection point is relatively smooth, which is consistent with the gradual development process of conductor corona.

[0079] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0080] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for calculating AC corona loss of conductors at ultra-high altitudes taking into account the outer strand structure, characterized in that: include: Based on Kaptzov hypothesis, corona loss is defined; At each position of the strand, determine whether the conductor is dizzy, and if dizzy, calculate the charge consumption; Corona losses are calculated based on charge consumption.

2. The method according to claim 1, characterized in that At each position of the strand, determine whether the conductor is dizzy. If dizzy, calculate the charge consumption, specifically: According to the conductor simulation charge model and the calculation method of the corona initiation field strength, the conductor corona initiation field strength is obtained, and the conductor simulation charge at this time is calculated, which is used as the corona initiation charge criterion Qcri+ or Qcri- at ​​each point of the conductor, and the voltage of the conductor at a certain moment is obtained as U app =U max ·sin(ω·t), calculate the simulated charge Q at this time cond , the simulated charge Q cond Compare with the corona charge criterion Qcri+ or Qcri- at ​​each point of the conductor, analyze whether the conductor corona occurs at each position of the strand, and simulate the charge Q after the conductor corona starts. cond The part exceeding the corona onset charge criterion Qcri+ or Qcri- at ​​each point of the conductor will be emitted from the charge emission point on the conductor surface in the form of space charge. After the corona occurs at a certain position, the simulated charge at that position becomes the corona onset charge criterion Qcri+ or Qcri- at ​​each point of the conductor, that is, the corona starting charge. Among them, there are two processes involving charge consumption, namely the charge consumption caused by the recombination of positive and negative ions and the charge consumption caused by the movement of opposite-sign charges to the surface of the wire. The total charge consumption is calculated, where the positive and negative charge densities n ± and space charge q ± The relationship between them is: Where ΔV is the control volume of the line charge, and e is the electron charge, e=1.6×10 -19 C, after time Δt, the space charge decreases to: Where, γ = 1.5 × 10 -12 m 3 / s, q' is the charge after time Δt has passed.

3. The method according to claim 2, characterized in that The corona loss is calculated based on the charge consumption, specifically: Assume that the movement distance of the space charge in the two coordinate axis directions is Δd ix and Δd iy , the corona loss within the Δt time is: W i =q i ·E ix ·Δd ix +q i ·E iy ·Δd iy The corona loss of the conductor in a corresponding calculation cycle is: Where N sc is the space charge number within the time Δt; The corresponding corona loss power per unit length of conductor is: P=fW Where f is 50Hz. When the corona loss error in two adjacent power frequency cycles is less than a specific value, the calculation is considered to be stable and the calculation is stopped.

4. The method according to claim 3, characterized in that The migration distance of space charge under the action of electric field force within Δt time is calculated as: Δd=μ×E×Δt Where μ is the mobility of positive and negative ions, and E is the electric field strength at the location of the space charge.

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