Dry-type hollow smoothing reactor turn-to-turn insulation thickness design method, medium and system

Abstract

The invention discloses a dry-type hollow smoothing reactor turn-to-turn insulation thickness design method, medium and system, and the method comprises the steps: building a reactor finite element simulation model in simulation software, and applying a DC voltage or a higher harmonic current to the reactor finite element simulation model in a normal operation state; calculating an electric field intensity extreme value, a hot spot temperature and a stress extreme value under different turn-to-turn insulation thicknesses; quantizing the electric field intensity extreme value, the hot spot temperature and the stress extreme value to obtain a quantized value of the electric field intensity extreme value, a quantized value of the hot spot temperature and a quantized value of the stress extreme value; drawing a first curve in which the quantized value of the electric field intensity extreme value changes along with the turn-to-turn insulation thickness, a second curve in which the quantized value of the hot spot temperature changes along with the turn-to-turn insulation thickness, and a third curve in which the quantized value of the stress extreme value changes along with the turn-to-turn insulation thickness; and determining the turn-to-turn insulation thickness corresponding to the intersection point of the first curve, the second curve and the third curve as the final turn-to-turn insulation thickness. According to the invention, the optimal turn-to-turn insulation thickness can be accurately determined.

Description

Technical Field

[0001] This invention relates to the field of dry-type air-core smoothing reactor technology, and in particular to a method, medium and system for designing the inter-turn insulation thickness of a dry-type air-core smoothing reactor. Background Technology

[0002] Smoothing reactors are one of the main pieces of equipment in high-voltage direct current (HVDC) transmission projects. They not only limit overcurrents that cause voltage collapse on the inverter side, but also smooth out ripples in the transmitted DC current. Furthermore, they effectively prevent overvoltages that intrude along the DC line into the converter station from affecting the insulation of the converter valves. Currently, dry-type air-core reactors are widely used as smoothing reactors in ultra-high-voltage direct current (UHVDC) projects due to their advantages such as simple structure, light weight, low noise, no oil leakage, and simple maintenance.

[0003] However, in actual operation, the voltage applied across the terminals of indoor dry-type air-core smoothing reactors is primarily DC, but this DC voltage is mixed with a large number of high-order harmonic voltages. Due to their high frequency and steepness, these harmonics easily cause uneven electric field distribution between turns and layers of the reactor, severely damaging the inter-turn insulation. Uneven electric field distribution is considered one of the main causes of discharge phenomena in reactors, and in severe cases, it can lead to reactor combustion, threatening the safe operation of the DC field. Therefore, the impact of high-order harmonics on the electric field of the reactor windings must be carefully considered when designing the inter-turn insulation thickness of dry-type air-core smoothing reactors.

[0004] For dry-type air-core smoothing reactors, due to their special importance in DC power transmission, the inter-turn insulation thickness of smoothing reactors needs to be adjusted according to the harmonic characteristics that appear in the power system, and the frequency and amplitude of the harmonics need to be considered. Summary of the Invention

[0005] This invention provides a method, medium, and system for designing the inter-turn insulation thickness of a dry-type air-core smoothing reactor, in order to solve the problem that the prior art does not consider the influence of higher harmonics, resulting in inaccurate design of the inter-turn insulation thickness of the dry-type air-core smoothing reactor.

[0006] Firstly, a method for designing the inter-turn insulation thickness of a dry-type air-core smoothing reactor is provided, including:

[0007] After establishing a finite element simulation model of a dry-type hollow smoothing reactor in the simulation software, DC voltage or high-order harmonic current is applied to the finite element simulation model of the dry-type hollow smoothing reactor under normal operating conditions. The control equations of different physical fields are called to calculate the extreme values ​​of electric field intensity, hot spot temperature and stress under different inter-turn insulation thicknesses.

[0008] The extreme values ​​of electric field intensity, hot spot temperature, and stress under different inter-turn insulation thicknesses were quantified to obtain the quantified values ​​of the extreme values ​​of electric field intensity, hot spot temperature, and stress under different inter-turn insulation thicknesses.

[0009] Plot the first curve of the quantized value of the electric field intensity extremum as a function of the inter-turn insulation thickness, the second curve of the quantized value of the hot spot temperature as a function of the inter-turn insulation thickness, and the third curve of the quantized value of the stress extremum as a function of the inter-turn insulation thickness, all in the same coordinate system.

[0010] The inter-turn insulation thickness corresponding to the intersection of the first curve, the second curve, and the third curve is determined as the final inter-turn insulation thickness.

[0011] In a second aspect, a computer-readable storage medium is provided, wherein computer program instructions are stored on the computer-readable storage medium; when the computer program instructions are executed by a processor, they implement the method for designing the inter-turn insulation thickness of a dry-type air-core smoothing reactor as described in the embodiment of the first aspect.

[0012] Thirdly, a system for designing the inter-turn insulation thickness of a dry-type air-core smoothing reactor is provided, comprising: a computer-readable storage medium as described in the embodiments of the second aspect.

[0013] Thus, this embodiment of the invention focuses on the influence of higher harmonics on the potential distribution of dry-type air-core smoothing reactors. Furthermore, considering the combined effect of the coupling between electric field, temperature field, and stress field for different insulating materials, the optimal thickness of the inter-turn insulation of the dry-type air-core smoothing reactor can be accurately determined so that the thickness can meet the requirements of the inter-turn insulation of the dry-type air-core smoothing reactor. It also helps to maximize the performance of the insulating material and effectively save the cost of the insulating material. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a flowchart of the design method for the inter-turn insulation thickness of a dry-type hollow smoothing reactor according to an embodiment of the present invention;

[0016] Figure 2 This is a schematic diagram of the finite element simulation model of the dry hollow smoothing reactor according to an embodiment of the present invention;

[0017] Figure 3This is a diagram showing the coupling relationship during the simulation of a dry-type air-core smoothing reactor under DC operation.

[0018] Figure 4 This is a schematic diagram of a rectifier circuit simulation model according to a specific embodiment of the present invention;

[0019] Figure 5 This is a schematic diagram of high-order harmonic currents obtained by Fourier analysis according to a specific embodiment of the present invention.

[0020] Figure 6 This is a schematic diagram of a finite element simulation model of a ±500kV dry-type hollow smoothing reactor according to a specific embodiment of the present invention.

[0021] Figure 7 This is a schematic diagram of the simulation results of the electric field, temperature field and stress field of a specific embodiment of the present invention. Detailed Implementation

[0022] 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, not all, of the embodiments of the present invention. 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.

[0023] This invention discloses a method for designing the inter-turn insulation thickness of a dry-type air-core smoothing reactor. Dry-type air-core smoothing reactors are mainly used in DC circuits after rectification to suppress ripple in the rectified voltage, making the output DC close to ideal DC. By using multiple turns of coil within the same enclosure and multiple enclosures, the dry-type air-core smoothing reactor can meet the requirements for high current carrying capacity under series operation. Figure 1 As shown, the method of this embodiment of the invention includes the following steps:

[0024] Step S101: After establishing the finite element simulation model of the dry-type hollow smoothing reactor in the simulation software, apply DC voltage or high-order harmonic current to the finite element simulation model of the dry-type hollow smoothing reactor under normal operating conditions, call the control equations of different physical fields, and calculate the extreme values ​​of electric field intensity, hot spot temperature and stress under different inter-turn insulation thicknesses.

[0025] The simulation software can be COMSOL, which comes with control equations for various physical fields for use.

[0026] To accurately simulate the inter-turn insulation of the reactor, a two-dimensional axisymmetric finite element simulation model of the dry-type air-core smoothing reactor is established based on its dimensions, with each unit turn as the smallest unit. Each winding layer consists of several circular surfaces, with one circular surface representing one turn. The circular surfaces of one winding layer are connected in series with single-conductor coil groups to simulate the connection method of one winding layer. For example, this invention selects a ±660kV dry-type air-core smoothing reactor from a converter station as an example and establishes a reactor model with each unit turn as the smallest unit, as shown in the figure below. Figure 2 As shown.

[0027] By adding circuit modules, each layer of the reactor windings is connected in parallel. This model is used to calculate the electric field distribution of the reactor under DC and higher harmonic loads, as well as the electro-thermal-stress coupling field under DC load, by applying different physical field boundary conditions.

[0028] To perform simulation calculations, it is necessary to determine the applied DC voltage. Therefore, the process of obtaining the applied DC voltage for the finite element simulation model of the dry-type air-core smoothing reactor is as follows:

[0029] Assuming that the voltage of each winding of the dry-type air-core smoothing reactor is linearly distributed, the voltage difference between adjacent coil turns is calculated under the rated current. The product of the voltage difference between adjacent coil turns and the number of coil turns is calculated to obtain the voltage applied to the finite element simulation model of the dry-type air-core smoothing reactor.

[0030] Under DC conditions, due to the inherent resistance of the conductor, the voltage difference ∆U between adjacent turns of the winding can be calculated using the following formula:

[0031] (1)

[0032] (2)

[0033] Where I is the current flowing through the wire, and R... DC Let ρ be the DC resistance of the conductor, ρ be the resistivity of the conductor, r be the radius of the conductor, and l be the length of the coil.

[0034] To perform simulation calculations, it is also necessary to determine the applied higher harmonic currents. The specific process for obtaining the applied higher harmonic currents to the finite element simulation model of the dry-type hollow smoothing reactor is as follows:

[0035] A model of the actual converter station where the dry-type hollow smoothing reactor is located was built using Matlab / Simulink. The frequency and amplitude of the high-order harmonic current flowing through the dry-type hollow smoothing reactor under normal operating conditions were obtained by Fourier analysis.

[0036] The above process is existing technology and will not be described in detail here.

[0037] For example, the higher harmonic currents obtained by Fourier analysis include the 12th harmonic current, the 24th harmonic current, and the 36th harmonic current, and then the frequency and amplitude of the three harmonic currents are obtained.

[0038] In actual operation, dry-type air-core smoothing reactors primarily operate under direct current (DC), with a small amount of higher harmonics affecting the electric field distribution of the windings. The heating and stress displacement of the windings are mainly caused by heating under DC conditions. Therefore, the electric field analysis in this embodiment of the invention needs to comprehensively consider both DC and harmonic scenarios. The temperature and stress analysis primarily considers the DC scenario. Based on the calculation of different eigenvalues, different excitations are applied, and different physical field equations are invoked, as detailed below:

[0039] 1. When calculating the extreme values ​​of the electric field intensity, a DC voltage is applied to the finite element simulation model of the dry-type hollow smoothing reactor, and the physical field is an electrostatic field.

[0040] Under DC current, the electric field of the windings within the enclosure of a dry-type air-core smoothing reactor is controlled by an electrostatic field. Gauss's law in dielectrics states that the flux of the electric displacement vector through a closed surface in an electric field is equal to the algebraic sum of the charges enclosed by that surface. Specifically, the governing equations of the electrostatic field include the following equations:

[0041] (3)

[0042] (4)

[0043] (5)

[0044] (6)

[0045] Where E is the electric field intensity vector, D is the electric displacement vector passing through a closed surface in the electric field, ρ is the charge density, V is the electrostatic potential, l is the length, and s is the area. This is the gradient operator.

[0046] For a homogeneous medium Then we have the following Poisson equation for the electrostatic field:

[0047] (7)

[0048] Where φ is the potential and ε is the dielectric constant of the dielectric.

[0049] Solving for the case where there is no charge in the domain, i.e., when ρ=0, we obtain the following Laplace equation for the electrostatic field:

[0050] (8)

[0051] It should be understood that in the above equation for calculating the extreme value of the electric field strength, the electric field strength E can be calculated by inputting the inter-turn insulation thickness into the simulation software, where the maximum calculated electric field strength is denoted as E0. max This refers to the extreme value of the electric field strength described in the embodiments of the present invention.

[0052] 2. When calculating the extreme values ​​of the electric field intensity, a high-order harmonic current is applied to the finite element simulation model of the dry-type hollow smoothing reactor, and the physical field is the electromagnetic field.

[0053] The electric field distribution between turns of the winding within the enclosure of a dry-type air-core smoothing reactor under the influence of high-order harmonic currents is affected by the electromagnetic field. Under the influence of high-order harmonic currents, electromagnetic induction occurs between the windings of the dry-type air-core smoothing reactor, resulting in an oscillation process within the windings. Specifically, the governing equations of the electromagnetic field include the following equations:

[0054] (9)

[0055] (10)

[0056] (11)

[0057] (12)

[0058] Where E is the electric field intensity vector, H is the magnetic field intensity vector, J is the current density vector, B is the magnetic induction intensity, ρ is the charge volume density, v is the electric potential, and J e Let A be the externally injected current density, A be the vector magnetomotive force, and t be the magnetic flux.

[0059] It should be understood that in the above equation for calculating the extreme value of the electric field intensity, the extreme value E of the electric field intensity can be calculated by inputting the inter-turn insulation thickness into the simulation software. The maximum electric field intensity obtained from the calculation is denoted as E. max This refers to the extreme value of the electric field strength described in the embodiments of the present invention.

[0060] 3. When calculating the hot spot temperature, apply a DC voltage to the finite element simulation model of the dry-type hollow smoothing reactor, and the physical field is the temperature field.

[0061] When a dry-type air-core smoothing reactor is encapsulated under DC voltage, the current flowing through the windings generates heat, causing the winding temperature to rise. This leads to varying degrees of thermal expansion in the windings and insulation materials, i.e., thermal stress. Therefore, it is generally necessary to first calculate the hot spot temperature and then calculate the stress extreme value.

[0062] Based on the above analysis, the coupling relationship of the dry-type air-core smoothing reactor encapsulation in the simulation process under DC operation is as follows: Figure 3 As shown.

[0063] The heat inside the insulation material of a dry-type air-core smoothing reactor mainly comes from the heating of the conductor, that is, the Joule heating generated when current passes through the conductor. The specific governing equations for the temperature field include the following:

[0064] (13)

[0065] (14)

[0066] (15)

[0067] Where U is the voltage across the conductor, Q is the Joule heat generated by the conductor, Q0 is the Joule heat per unit volume, I is the current flowing through the conductor, R is the resistance of the conductor, t is the energizing time of the dry-type air-core smoothing reactor winding, d is the thickness of the insulation material of the dry-type air-core smoothing reactor, p is the density of the insulation material of the dry-type air-core smoothing reactor, and c is the current through the conductor. p Let T be the constant-voltage heat capacity of the insulation material of the dry-type air-core smoothing reactor, k be the thermal conductivity of the insulation material of the dry-type air-core smoothing reactor, h be the surface heat transfer coefficient of the insulation material of the dry-type air-core smoothing reactor, and T be the constant-voltage heat capacity of the insulation material of the dry-type air-core smoothing reactor. ext The reference temperature is T, which is the temperature at a certain location of the insulation material of the dry-type hollow smoothing reactor.

[0068] It should be understood that in the above equation for calculating the hot spot temperature, the temperature T can be calculated by inputting the inter-turn insulation thickness into the simulation software, and the highest temperature calculated is denoted as T. max This refers to the hotspot temperature described in the embodiments of the present invention.

[0069] 4. When calculating the stress extrema, apply a DC voltage to the finite element simulation model of the dry-type hollow smoothing reactor, and the physical field is the stress field.

[0070] As mentioned earlier, the heat generated by the windings leads to thermal stress. Specifically, the governing equations of the stress field include the following equations:

[0071] (16)

[0072] (17)

[0073] (18)

[0074] (19)

[0075] (20)

[0076] Where p is the density of the insulation material of the dry-type hollow smoothing reactor, λ is the Lamé constant of the insulation material of the dry-type hollow smoothing reactor, u is the displacement, s is the stress tensor, s0 is the initial value of the stress tensor, and F v Let ϵ be the volume force, ϵ be the strain tensor, and ϵ0 be the initial value of the strain tensor. th Let C be the thermal strain tensor, C be the specific heat capacity, E be Young's modulus, v be Poisson's ratio, α be the coefficient of thermal expansion, and T be the temperature. ref The reference temperature is t, and t is the energizing time of the dry-type air-core smoothing reactor winding.

[0077] It should be understood that in the above equation for calculating the stress extremum, the stress tensor s can be calculated by inputting the inter-turn thickness into the simulation software, where the maximum calculated stress tensor is denoted as s0. max This refers to the stress extreme value described in the embodiments of the present invention.

[0078] It should be understood that in the above calculation process, the maximum voltage level and operating current that the dry-type air-core smoothing reactor can withstand are used as boundary conditions; during the calculation process, if the calculated physical quantities meet the pre-set convergence conditions, the COMSOL simulation software will stop the calculation. These convergence conditions can be set according to the actual situation.

[0079] In summary, under DC voltage conditions, the circuit module applies a DC voltage to the reactor winding, sets different inter-turn insulation thicknesses, and calculates the effects of different inter-turn insulation thicknesses on the electric field, temperature field, and stress field of the reactor winding. Under high-order harmonic current conditions, the circuit module applies different high-order harmonic currents with different characteristics obtained in the aforementioned analysis (e.g., 12th, 24th, and 36th characteristic harmonic currents) to the reactor model, and calculates the electric field distribution of the reactor encapsulated winding under different characteristic harmonic currents and different inter-turn insulation thicknesses.

[0080] Step S102: Quantify the extreme values ​​of electric field intensity, hot spot temperature, and stress under different inter-turn insulation thicknesses to obtain quantified values ​​of the extreme values ​​of electric field intensity, hot spot temperature, and stress under different inter-turn insulation thicknesses.

[0081] The specific steps are as follows:

[0082] 1. Using the electric field breakdown strength of the dry-type hollow smoothing reactor as the benchmark value, calculate the quotient of the electric field strength extremum and the electric field breakdown strength to obtain the quantized value of the electric field strength extremum.

[0083] It should be understood that the extreme value of the electric field intensity is the sum of the extreme values ​​of the electric field intensity corresponding to each higher harmonic current and the extreme value of the electric field intensity corresponding to the DC voltage. For example, the extreme value of the electric field intensity is the sum of the extreme values ​​of the electric field intensity corresponding to the 12th characteristic harmonic current, the 24th characteristic harmonic current, and the 36th characteristic harmonic current, plus the extreme value of the electric field intensity corresponding to the DC voltage, to obtain the final extreme value of the electric field intensity.

[0084] 2. Using the maximum withstand temperature of the dry-type air-core smoothing reactor as the benchmark, calculate the quotient of the hot spot temperature and the maximum withstand temperature to obtain the quantified value of the hot spot temperature.

[0085] 3. Using the maximum tensile strength that the dry-type hollow smoothing reactor can withstand as the benchmark value, calculate the quotient of the stress extremum and the maximum tensile strength to obtain the quantified value of the stress extremum.

[0086] Among them, the electric field breakdown strength, the highest withstand temperature, and the maximum tensile strength can be obtained by looking up information such as the inter-turn insulation material and the encapsulation filling material of the dry-type hollow smoothing reactor.

[0087] This step involves de-normalization to achieve quantization, allowing for plotting within the same coordinate system.

[0088] Step S103: Plot the first curve of the quantized value of the electric field intensity extremum as a function of the inter-turn insulation thickness, the second curve of the quantized value of the hot spot temperature as a function of the inter-turn insulation thickness, and the third curve of the quantized value of the stress extremum as a function of the inter-turn insulation thickness, all in the same coordinate system.

[0089] The horizontal axis of this coordinate system represents the inter-turn insulation thickness, and the vertical axis represents the quantified value.

[0090] Step S104: Determine the inter-turn insulation thickness corresponding to the intersection of the first curve, the second curve and the third curve as the final inter-turn insulation thickness.

[0091] It should be understood that, while ensuring insulation margin and conductor manufacturing quality, the calculated inter-turn insulation thickness can be pre-calculated to retain a certain number of decimal places.

[0092] Furthermore, embodiments of the present invention also provide a computer-readable storage medium storing computer program instructions; when the computer program instructions are executed by a processor, they implement the inter-turn insulation thickness design method for dry-type hollow smoothing reactors as described in the above embodiments.

[0093] Furthermore, embodiments of the present invention also provide a system for designing the inter-turn insulation thickness of a dry-type hollow smoothing reactor, comprising: a computer-readable storage medium as described in the above embodiments.

[0094] The technical solution of the present invention will be further described below with reference to a specific embodiment.

[0095] Taking a ±500kV DC transmission project's 12-pulse rectifier circuit as an example, this paper analyzes the harmonic current characteristics generated by the converter valve, specifically the harmonic current characteristics flowing through the dry-type air-core smoothing reactor. The rectifier circuit simulation model is as follows: Figure 4 As shown, the Fourier analysis results of the obtained waveform are as follows: Figure 5 As shown.

[0096] Depend on Figure 5 It can be seen that the current flowing through the smoothing reactor is mainly direct current, which also contains a small amount of harmonic components. Among these harmonic components, even harmonics are more abundant, and the 12th, 24th, 36th and 48th harmonics are more abundant.

[0097] Taking a ±500kV dry-type hollow smoothing reactor at a converter station as a calculation example, model LKGKL-110-328.25-413.95W, the reactor uses polyester film as the inter-turn insulation material. This reactor has nine windings, an inner diameter of 1775mm, an outer diameter of 2400mm, and a coil height of 2990mm. Due to the complex structure of the reactor, the model is appropriately simplified while retaining its computational characteristics. A two-dimensional axisymmetric finite element model with a single turn as the smallest unit is established based on the actual dimensions of the reactor. The model diagram is shown below. Figure 6 As shown.

[0098] Based on the above scheme, the reactor is subjected to excitation to realize the numerical calculation of the reactor's electric field, temperature field and stress field.

[0099] By establishing a two-dimensional overall model of the reactor and changing the inter-turn insulation thickness through parametric scanning, the extreme values ​​of electric field intensity, hot spot temperature, and stress extreme values ​​under different inter-turn insulation thicknesses can be obtained. Consulting relevant data on polyester film, its electric breakdown strength is 54 kV / mm, its maximum withstand temperature is 120℃, and its maximum tensile strength is 1300 N / m. 2 Using the above values ​​as a baseline, the simulation values ​​were de-normalized. A coordinate system was established to obtain the variation of simulation values ​​with inter-turn insulation thickness under different fields, as shown below. Figure 7 As shown.

[0100] Depend on Figure 7 Based on the simulation results of the combined electric field, temperature field, and stress field, the optimal value for the inter-turn insulation thickness is 0.60091 mm. To ensure insulation margin and maintain the quality of conductor manufacturing processes, the optimal inter-turn insulation thickness is chosen to be 0.61 mm.

[0101] In summary, the embodiments of the present invention focus on the influence of higher harmonics on the potential distribution of dry-type air-core smoothing reactors. Furthermore, considering the comprehensive effect of the coupling between electric field, temperature field, and stress field for different insulating materials, the optimal thickness of the inter-turn insulation of the dry-type air-core smoothing reactor can be accurately determined so that the thickness can meet the requirements of the inter-turn insulation of the dry-type air-core smoothing reactor. It also helps to maximize the performance of the insulating material and effectively save the cost of the insulating material.

[0102] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for designing the inter-turn insulation thickness of a dry-type hollow smoothing reactor, characterized in that, include: After establishing a finite element simulation model of a dry-type hollow smoothing reactor in the simulation software, DC voltage or high-order harmonic current is applied to the finite element simulation model of the dry-type hollow smoothing reactor under normal operating conditions. The control equations of different physical fields are called to calculate the extreme values ​​of electric field intensity, hot spot temperature and stress under different inter-turn insulation thicknesses. The extreme values ​​of electric field intensity, hot spot temperature, and stress under different inter-turn insulation thicknesses were quantified to obtain the quantified values ​​of the extreme values ​​of electric field intensity, hot spot temperature, and stress under different inter-turn insulation thicknesses. Plot the first curve of the quantized value of the electric field intensity extremum as a function of the inter-turn insulation thickness, the second curve of the quantized value of the hot spot temperature as a function of the inter-turn insulation thickness, and the third curve of the quantized value of the stress extremum as a function of the inter-turn insulation thickness, all in the same coordinate system. The inter-turn insulation thickness corresponding to the intersection of the first curve, the second curve, and the third curve is determined as the final inter-turn insulation thickness.

2. The method for designing the inter-turn insulation thickness of a dry-type hollow smoothing reactor according to claim 1, characterized in that, The steps for obtaining the quantized values ​​of the electric field intensity extrema, the hot spot temperature, and the stress extrema under different inter-turn insulation thicknesses include: Using the electric field breakdown strength of the dry-type hollow smoothing reactor as the benchmark value, the quotient of the extreme value of the electric field strength and the electric field breakdown strength is calculated to obtain the quantized value of the extreme value of the electric field strength. Using the maximum withstand temperature of the dry-type air-core smoothing reactor as a benchmark, the quotient of the hot spot temperature and the maximum withstand temperature is calculated to obtain the quantified value of the hot spot temperature. Using the maximum tensile strength that the dry-type hollow smoothing reactor can withstand as a benchmark value, the quotient of the stress extreme value and the maximum tensile strength is calculated to obtain the quantified value of the stress extreme value.

3. The method for designing the inter-turn insulation thickness of a dry-type hollow smoothing reactor according to claim 1, characterized in that: When calculating the extreme value of the electric field intensity, a DC voltage is applied to the finite element simulation model of the dry-type hollow smoothing reactor, and the physical field is an electrostatic field. or, When calculating the extreme value of the electric field intensity, a high-order harmonic current is applied to the finite element simulation model of the dry-type hollow smoothing reactor, and the physical field is an electromagnetic field.

4. The method for designing the inter-turn insulation thickness of a dry-type hollow smoothing reactor according to claim 1, characterized in that: When calculating the hot spot temperature, a DC voltage is applied to the finite element simulation model of the dry-type hollow smoothing reactor, and the physical field is the temperature field.

5. The method for designing the inter-turn insulation thickness of a dry-type hollow smoothing reactor according to claim 1, characterized in that: When calculating the stress extremum, a DC voltage is applied to the finite element simulation model of the dry-type hollow smoothing reactor, and the physical field is the stress field.

6. The method for designing the inter-turn insulation thickness of a dry-type hollow smoothing reactor according to claim 1, characterized in that: The extreme value of the electric field intensity is the sum of the extreme values ​​of the electric field intensity corresponding to each of the higher harmonic currents and the extreme value of the electric field intensity corresponding to the DC voltage.

7. The method for designing the inter-turn insulation thickness of a dry-type hollow smoothing reactor according to claim 1, characterized in that, The process of obtaining the DC voltage applied to the finite element simulation model of the dry-type air-core smoothing reactor includes: assuming that the voltage of each winding of the dry-type air-core smoothing reactor is linearly distributed, calculating the voltage difference between adjacent coil turns under rated current, and then calculating the product of the voltage difference between adjacent coil turns and the number of coil turns to obtain the voltage applied to the finite element simulation model of the dry-type air-core smoothing reactor.

8. The method for designing the inter-turn insulation thickness of a dry-type hollow smoothing reactor according to claim 1, characterized in that, The process of obtaining the high-order harmonic current applied to the finite element simulation model of the dry-type hollow smoothing reactor includes: building a model of the actual converter station where the dry-type hollow smoothing reactor is located based on Matlab / Simulink, and analyzing the frequency and amplitude of the high-order harmonic current flowing through the interior of the dry-type hollow smoothing reactor under normal operating conditions using Fourier analysis.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer program instructions; when the computer program instructions are executed by a processor, they implement the method for designing the inter-turn insulation thickness of a dry-type hollow smoothing reactor as described in any one of claims 1 to 8.

10. A design system for inter-turn insulation thickness of a dry-type hollow smoothing reactor, characterized in that, include: The computer-readable storage medium as described in claim 9.

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