Power transformer comprehensive weight reduction design method suitable for low-frequency power transmission system

Abstract

The invention relates to a power transformer comprehensive weight reduction design method suitable for a low-frequency power transmission system, and the method comprises the steps: determining original technical data according to a design task book; determining a reference scheme of transformer design according to the original technical data; carrying out magnetic circuit design optimization aiming at the reference scheme; carrying out conductive design optimization on the scheme after the magnetic circuit design optimization; and carrying out insulation design optimization on the scheme after the conductive design optimization to obtain a final design scheme of the transformer. Compared with the prior art, the comprehensive weight reduction of the transformer can be reliably realized by optimally considering the iron core material, the winding design, the insulation design, the heat dissipation system, the leakage reactance and the leakage flux design.

Description

Technical Field

[0001] The invention relates to the technical field of transformer design, and in particular to a comprehensive weight reduction design method for a power transformer suitable for a low-frequency power transmission system. Background Art

[0002] With the depletion of fossil energy and the gradual deterioration of the global environment and climate, the low-carbon transformation of the energy structure has become a general trend, and the development and utilization of new energy has become an important development direction. Among them, offshore wind power generation has the advantages of high power generation hours, no land occupation and little environmental impact, and is an important part of the current development of renewable energy power generation. In recent years, a large number of offshore wind farms have been planned and put into operation, resulting in increasingly tight resources in offshore waters. The development of offshore wind power in deep seas is an important direction for the future.

[0003] At present, there are three main technologies for deep-sea wind power transmission that have attracted widespread attention, namely: High Voltage Alternating Current (HVAC), High Voltage Direct Current (HVDC), and Low Frequency Alternating Current (LFAC). Among them, HVAC and HVDC have been widely used in offshore wind power transmission scenarios, but both have some technical defects: HVAC technology is limited by the transmission limit of long-distance submarine cables, and HVDC technology has the problem of difficult fault current switching. Therefore, some scholars pointed out that LFAC technology (Fractional Frequency Transmission System, FFTS, also known as fractional frequency transmission technology), which draws on the idea of ​​frequency change of DC transmission and takes advantage of the zero-point disconnection of AC transmission, may provide a more economical and effective solution for large-scale deep-sea wind power grid connection. Flexible low-frequency AC transmission technology is a new and efficient AC transmission technology that uses power electronics technology to flexibly select a suitable frequency between 0 and 50 Hz to improve the transmission capacity and flexible regulation capability of the power grid.

[0004] Although the theoretical research and application of low-frequency AC transmission technology has developed rapidly, for example, some low-frequency transmission demonstration projects have been built in China, including the 220kV Zhongbu-Tingshan flexible low-frequency transmission demonstration project in Hangzhou, Zhejiang for urban power grids, and the State Grid Zhejiang Taizhou 35kV flexible low-frequency transmission demonstration project for low-frequency wind turbines. However, there are still many obstacles to the engineering application of low-frequency AC transmission technology in the scenario of long-distance and large-capacity offshore wind power transmission. Low frequency, high voltage level and large capacity have brought difficulties to the research and development and selection of offshore main transformers. If only the conventional idea of ​​increasing the core cross-section and the number of winding turns is adopted to transform the transformer, the weight and volume of the offshore low-frequency main transformer will increase significantly, which will bring huge challenges to the load and layout of the offshore substation and the economy of the overall offshore wind power low-frequency transmission plan. In addition, the degree of optimization of the transformer volume and weight is also extremely limited if only the design method is adjusted. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a comprehensive weight reduction design method for power transformers suitable for low-frequency power transmission systems. The method optimizes the core material, winding design, insulation design, heat dissipation system, leakage reactance and leakage magnetic design, so as to reliably achieve the comprehensive weight reduction of the transformer.

[0006] The object of the present invention can be achieved by the following technical scheme: A comprehensive weight reduction design method for power transformers suitable for low-frequency power transmission systems, comprising the following steps: S1. Determine the original technical data according to the design task book; S2. Determine the benchmark scheme for transformer design based on the original technical data; S3. Optimize the magnetic circuit design based on the benchmark solution; S4. Optimize the conductive design for the scheme after the magnetic circuit design optimization; S5. Optimize the insulation design based on the optimized conductive design to obtain the final design solution of the transformer.

[0007] Furthermore, the original technical data in step S1 include rated capacity, rated voltage, voltage regulation requirement, rated frequency, number of phases, winding connection group number, rated performance parameters, rated operating conditions, cooling method, temperature rise limit, insulation level, and noise level. The rated performance parameters include no-load loss, load loss, no-load current, and short-circuit impedance.

[0008] Furthermore, the step S2 specifically includes the following steps: S21, select the silicon steel sheet brand, core column working magnetic flux density and core structure; S22, calculate the core diameter and select the cross-section of the core column and the iron yoke; S23, perform winding and insulation design; S24. Calculate the impedance voltage.

[0009] Furthermore, the specific process of step S21 is: the minimum magnetic polarization intensity reached by the core under the alternating magnetic field with a peak value of 800A / m As the design saturation flux density, 1.82~1.91T; Considering that the transformer can output rated current at 105% of the rated voltage, for some special use cases, it is also required to operate at no more than 110% of the rated voltage. The design magnetic density of the transformer is controlled at And below, design The selection range is 1.55~1.74T, among which, for medium and small transformers, The selection range is 1.55~1.65T; for large transformers, The selection range is 1.7~1.74T; The transformer core serves as the channel for the main magnetic flux. For single-phase transformers, a single-phase three-column structure is adopted; for three-phase transformers, when the core diameter exceeds 1000mm, a three-phase five-column structure is selected.

[0010] Furthermore, the specific process of step S22 is as follows: Calculate the core diameter, that is: (mm); in, It is the empirical coefficient of core diameter, and the copper coil winding and cold-rolled silicon steel sheet are selected from 51 to 57; is the capacity of each column of the transformer; The core lamination coefficient is 0.96~0.97; For medium, large and extra-large transformers, the core column section selects a multi-stage rectangular section of the circumscribed circle, and a multi-stage elliptical section is used as the side yoke section.

[0011] Furthermore, the specific process of step S23 is as follows: For the structure of winding coil, including: Layered coils are suitable for small-capacity low-voltage coils, and multi-layered coils are suitable for small-capacity high-voltage coils; Spiral coils are suitable for low voltage, high current coils or voltage regulating coils; Tangled coil: high voltage coil suitable for high voltage; The tangled continuous coil is a partially compensated coil structure; Inner shielded coil, shielding wire is added to the line segment to increase its longitudinal capacitance and improve the impulse distribution. With this structure, the high-voltage winding of the high-voltage and large-capacity transformer can be wound with transposed wires; In order to reduce the load loss of the transformer, oxygen-free copper wire is used for winding. The winding of large power transformers uses transposed wires, which can greatly reduce the load loss, reduce the temperature rise of the winding hot spot, improve the mechanical strength of the winding, make the structure more compact, and make the coil processing easier; The current density of the coil conductor mainly depends on the load loss, the temperature rise of the coil and the dynamic and thermal stability when the secondary side of the transformer is suddenly short-circuited. The current density of the copper wire of the low-voltage coil is 4.5 And below, the current density of the copper wire of high and medium voltage coils is 3 ; The high-voltage coil turn insulation is 1.35mm, the medium-voltage is 0.6mm, and the low-voltage is 0.45mm; the high-pressure oil channel is 5mm, the medium-pressure oil channel is 4mm, and the low-pressure oil channel is 3.5mm; the phase distance is greater than 120mm, and the three-phase five-column core needs to increase the distance from the coil to the side column, which is greater than 100mm; Select Class A insulation system for power frequency transformer and calculate its stable temperature rise under rated load so that its value does not exceed the corresponding limit.

[0012] Furthermore, the specific process of step S24 is as follows: The impedance voltage consists of two components: resistance voltage drop and reactance voltage drop. For large transformers, the resistance voltage drop is negligible and the impedance voltage calculation formula is: ,in, f is the frequency, IW is the rated current × the total number of turns when the main tap is connected, is the potential per turn, H is the average reactance height of the coil, ∑D is the leakage width, ρ is the Rockwell coefficient, K is the additional reactance coefficient.

[0013] Furthermore, the step S3 is specifically based on the magnetization properties of ferromagnetic materials, adopting the idea of ​​improving the design magnetic density to reduce the cross-sectional area of ​​the core, and adopting Ultra-high magnetic induction oriented silicon steel sheet ≥1.93 T, considering that the transformer can output rated current at 105% of the rated voltage, the magnetic density is designed to be controlled at .

[0014] Furthermore, the step S4 specifically optimizes the conductive design by increasing the current density of the winding copper wire.

[0015] Furthermore, the step S5 specifically uses the synthetic ester MIDEL 7131 as the transformer insulating oil to reduce the insulation distance and optimize the insulation design.

[0016] Compared with the prior art, the present invention has the following advantages: The present invention first determines the original technical data according to the design task book; then determines the reference scheme of transformer design according to the original technical data; then optimizes the magnetic circuit design, the conductive design, and the insulation design in turn for the reference scheme to obtain the final design scheme of the transformer. Therefore, considering the core material, winding design, insulation design, heat dissipation system, and leakage magnetic design optimization, the comprehensive weight reduction of the transformer can be reliably achieved.

[0017] When optimizing the magnetic circuit, the present invention takes into account that the low-frequency design of the transformer increases the cross-sectional area of ​​the core and the number of winding turns, which in turn increases the overall volume and weight of the transformer. Therefore, based on the magnetization properties of ferromagnetic materials, the idea of ​​improving the design magnetic density is adopted to reduce the cross-sectional area of ​​the core: ≥1.93 T ultra-high magnetic induction oriented silicon steel sheet, considering that the transformer can output rated current at 105% of the rated voltage, the magnetic density is designed to be controlled at .

[0018] The present invention adopts a higher heat resistance grade when conducting the optimized design, improves the temperature rise limit of the transformer, allows the transformer winding to have a higher temperature rise limit, and adopts a higher current density for the winding copper wire. Both the high-voltage coil and the medium-voltage coil can increase the current density to 4.5 A smaller heat dissipation area can be achieved, thereby reducing the weight and volume of the transformer.

[0019] When performing insulation optimization design, the present invention considers that during the normal operation of the transformer, the transformer oil channel plays a very important role, mainly including heat dissipation and insulation. The design uses MIDEL 7131 as the transformer insulating oil, which can reduce the oil channel between turns of high and medium voltage winding coils to 3.5 mm, and can achieve lightweight and miniaturization of the low-frequency transformer itself. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the method flow of the present invention; Figure 2 Design a flow chart for the benchmark scenario; Figure 3 Schematic diagram of the magnetic circuit design optimization process; Figure 4 Schematic diagram of the optimization process for conductive design; Figure 5 Schematic diagram of the insulation design optimization process; Figure 6 This is a schematic diagram of the application framework of this solution. DETAILED DESCRIPTION

[0021] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] Example

[0023] like Figure 1 As shown, a comprehensive weight reduction design method for power transformers suitable for low-frequency power transmission systems includes the following steps: S1. Determine the original technical data according to the design task book; S2. Determine the benchmark scheme for transformer design based on the original technical data; S3. Optimize the magnetic circuit design based on the benchmark solution; S4. Optimize the conductive design for the scheme after the magnetic circuit design optimization; S5. Optimize the insulation design based on the optimized conductive design to obtain the final design solution of the transformer.

[0024] In step S1, before the formal electromagnetic calculation begins, the original conditions for transformer design must first be determined according to the design task book. The main items are: rated capacity, rated voltage, whether voltage regulation is required, rated frequency, number of phases, winding connection group number, rated performance parameters (no-load loss, load loss, no-load current, short-circuit impedance, etc.), rated operating conditions, cooling method, temperature rise limit, insulation level, noise level, etc.

[0025] In step S2, the benchmark solution refers to the transformer design solution with a power frequency of 50 Hz under the same conditions. This solution is an optimized transformation of the 50 Hz power frequency transformer to a low frequency and light weight. Figure 2 As shown, the main contents are: 1) Select the silicon steel sheet grade, core column working magnetic flux density and core structure When designing a transformer, the minimum magnetic polarization intensity of the core is usually 800A / m under the alternating magnetic field (peak value). As the design saturation flux density. For the most commonly used cold-rolled silicon steel sheets, generally It is 1.82~1.91T.

[0026] Considering that the transformer can output rated current at 105% of the rated voltage, for some special use cases, it is also required to operate at no more than 110% of the rated voltage. The design magnetic density of the transformer is generally controlled at And below. Currently under design The selection range is 1.55~1.74T. For medium and small transformers, it is generally 1.55~1.65T; for large transformers, it is generally 1.7~1.74T.

[0027] The transformer core is the channel for the main magnetic flux. For single-phase transformers, a single-phase three-column structure is generally adopted; for three-phase transformers, when the core diameter exceeds 1000mm, in order to enable the transformer to be transported within the transformer factory and transported by road outside the transformer factory, a three-phase five-column structure is selected during design.

[0028] 2) Calculate the core diameter and select the core column and yoke cross section At present, an empirical formula is used to calculate the core diameter during design, namely: (mm), where ——The empirical coefficient of core diameter, copper coil winding and cold-rolled silicon steel sheet should be 51~57; ——Capacity of each transformer column, kVA.

[0029] The core lamination coefficient is an important factor affecting the effective cross-sectional area of ​​the core column. At present, due to the continuous improvement of the quality of silicon steel sheets and the continuous improvement of core processing and binding technology, it can be achieved to 0.96~0.97.

[0030] For medium, large and extra-large transformers, the core column cross-section selects a multi-level rectangular cross-section of the circumscribed circle. In order to make the magnetic flux distribution uniform and simplify the process, transformer manufacturers often use a multi-level elliptical cross-section as the side yoke cross-section during design.

[0031] 3) Winding and insulation design The structural types of winding coils are usually the following: Layer coil: Generally suitable for small-capacity low-voltage coils, multi-layer layer coils are suitable for small-capacity high-voltage coils.

[0032] Spiral coil: suitable for low voltage, high current coils or voltage regulating coils.

[0033] Continuous coil: has a wide range of applications and high mechanical strength, but requires high winding technology.

[0034] Tangled coil: Since it increases the longitudinal capacitance, it improves the impact distribution and is suitable for high-voltage coils with high voltage.

[0035] Tangled continuous coil: a partially compensated coil structure.

[0036] Internally shielded coil: Shielding wire is added to the line segment to increase its longitudinal capacitance and improve the impact distribution. This structure allows the high-voltage winding of a high-voltage and large-capacity transformer to be wound with transposed wires.

[0037] In order to reduce the load loss of the transformer, oxygen-free copper wire is used for winding. The winding of large power transformers uses transposed wires, which can greatly reduce load loss, reduce the temperature rise of winding hot spots, improve the mechanical strength of the winding, make the structure more compact, and make the coil processing easier.

[0038] The current density of the coil conductor mainly depends on the load loss, the temperature rise of the coil and the dynamic and thermal stability when the secondary side of the transformer is suddenly short-circuited. Generally, the current density of the copper wire of the low-voltage coil is 4.5 And below, the current density of the copper wire of high and medium voltage coils is 3 about.

[0039] The high-voltage coil turn insulation uses 1.35mm, the medium-voltage uses 0.6mm, and the low-voltage uses 0.45mm. The high-pressure oil channel is 5mm, the medium-pressure oil channel is 4mm, and the low-pressure oil channel is 3.5mm. The phase distance needs to be greater than 120mm, and the three-phase five-column core needs to increase the distance from a coil to the side column, which is greater than 100mm. Power transformers are generally operated continuously for a long time. When designing, the power frequency transformer usually selects the A-class insulation system, and calculates its stable temperature rise under rated load so that its value does not exceed the limit in Table 1.

[0040] Table 1 Temperature rise limit table

[0041] 4) Impedance voltage Impedance voltage consists of two components: resistance voltage drop and reactance voltage drop. The resistance voltage drop is generally very small and can be ignored for large transformers. Impedance voltage calculation formula: ; Where: f ——frequency, Hz; IW ——Rated current × total number of turns when main tapping (data on the same side); ——Electric potential per turn, (V / turn); H ——Average reactance height of the coil; ∑D——Leakage magnetic width; ρ ——Rockwell coefficient; K ——Additional reactance coefficient.

[0042] The standard short-circuit impedance values ​​of double-winding and three-winding transformers and autotransformers are shown in Tables 2 and 3 (deviation ±10%).

[0043] Table 2 Standard short-circuit impedance of double-winding power transformer

[0044] Table 3 Standard short-circuit impedance values ​​for double-winding and autotransformers

[0045] The process of step S3 is as follows Figure 3 As shown in the figure, the low-frequency design of the transformer increases the cross-sectional area of ​​the core and the number of winding turns, which in turn increases the overall volume and weight of the transformer. Based on the magnetization properties of ferromagnetic materials, the idea of ​​increasing the design magnetic density is adopted to reduce the cross-sectional area of ​​the core. Ultra-high magnetic induction oriented silicon steel sheet ≥1.93 T, considering that the transformer can output rated current at 105% of the rated voltage, the designed magnetic flux density can be controlled within .

[0046] The process of step S4 is as follows Figure 4 As shown in the figure, using a higher heat resistance grade and increasing the temperature rise limit of the transformer can allow the transformer winding to have a higher temperature rise limit. The winding copper wire can use a higher current density, and the current density of both the high-voltage coil and the medium-voltage coil can be increased to 4.5 about.

[0047] The process of step S5 is as follows Figure 5 As shown in the figure, in the normal operation of the transformer, the transformer oil channel plays an important role, mainly including heat dissipation and insulation. Using MIDEL 7131 as the transformer insulating oil, the oil channel between the turns of high and medium voltage winding coils can be reduced to 3.5mm.

[0048] This scheme takes into account that flexible low-frequency power transmission is essentially still AC power transmission, and the voltage level can be adjusted through the AC transformer. The induced electromotive force of the transformer is shown as follows: Taking 20Hz as an example, when a 50Hz industrial frequency transformer works at a frequency of 20Hz, assuming that the core will not be saturated, in order to stimulate the same induced electromotive force as in the industrial frequency working state, the maximum working magnetic flux density in the transformer core needs to be increased to 2.5 times the original value. However, in the actual operation process, the core will be severely saturated, which will cause no-load losses and no-load current surges, and the core temperature rise will increase. In severe cases, the transformer will be burned. Therefore, it is necessary to increase the core cross-section and number of turns in the design to solve the problem, but this will increase the total volume and weight of the core, windings and even the transformer. Therefore, for the weight reduction of low-frequency transformers, this solution mainly starts from the optimization of core materials, winding design, insulation design, heat dissipation system and leakage magnetic design, such as Figure 6 shown.

[0049] 1. Core material 1) Design magnetic density selection At present, the core of large power transformer is made of high magnetic induction ( Considering the weight and volume issues of large-capacity and high-voltage offshore low-frequency main transformers, which have become the key issues in the application of offshore wind power low-frequency transmission projects, this solution uses ultra-high magnetic induction ( 1.93T) silicon steel sheet can further improve the design magnetic density. Considering that the transformer can output rated current at 105% of the rated voltage, the design magnetic density of the transformer can be selected as: .

[0050] 2) Cross-sectional area of ​​core column Taking the transformer designed under industrial frequency conditions as the benchmark (mainly the design of magnetic flux density, core column diameter and core column cross-sectional area), the core column cross-sectional area of ​​the low-frequency transformer is optimized by using ultra-high magnetic induction materials.

[0051] 2. Winding design In the transformer winding design, the number of coil turns and the structural height are mainly considered. For the nacelle transformer with limited installation environment, the number of transformer winding turns and the structural height are required to remain unchanged or decrease; for the step-up transformer without installation environment restrictions, the number of coil turns and the structural height of the winding can be appropriately increased.

[0052] 3. Insulation design The main functions of insulating oil in oil-immersed transformers are insulation and heat dissipation. According to the type of base oil, it can be divided into four categories, namely mineral oil, silicone oil, synthetic ester and natural ester (commonly known as vegetable oil). The technology of using mineral oil as transformer insulating oil is mature and has been widely used. Among them, #10, #25 and #45 oils are commonly used mineral insulating oils in the transformer industry. With the continuous development of the research and application technology of ester high-ignition point insulating oil, ester high-ignition point insulating oil transformers have been considered as a new type of safe and environmentally friendly transformer. This scheme uses synthetic ester (MIDEL 7131) as transformer insulating oil. MIDEL7131 insulating oil is specially developed for traditional oil-immersed transformers and is a safer alternative insulating oil. It has excellent high and low temperature resistance, better fire safety, more environmental protection, and excellent oxidation resistance and moisture resistance. Its breakdown voltage is higher than that of mineral oil. Using MIDEL 7131 insulating oil can reduce the insulation size and realize the lightweight and miniaturization of the low-frequency transformer itself.

[0053] 4. Cooling system Overall high heat resistance design Using insulating materials with higher heat resistance grades (B, F, H) and increasing the temperature rise limit of the transformer can allow the transformer core and winding to have higher temperature rise limits and smaller heat dissipation area, thereby reducing the weight and volume of the transformer.

[0054] Optimize heat dissipation layout When designing the core, calculate the core temperature rise. Under the condition that the insulation system allows temperature rise, the following are done: ① No oil channels are set in the core; ② Under the power frequency condition, reduce the number of oil channels in the core; ③ Reduce the thickness of the oil channels.

[0055] When designing the coil winding, reduce the thickness of the inter-turn oil channel.

[0056] As for the cabin change, the radiators are distributed throughout the cabin to balance the cabin weight.

[0057] Use efficient cooling to reduce size and weight The oil-immersed transformer adopts a forced oil circulation air cooling solution to speed up the oil flow rate in the transformer, improve the heat dissipation efficiency, and cool the hot oil through the heat exchanger and return it to the transformer, reducing the product volume.

[0058] 5. Leakage reactance and leakage magnetic flux design optimization Magnetic leakage refers to the magnetic flux generated by the escape of magnetic field due to incomplete magnetic circuit in transformer. This part of magnetic flux does not pass through the core or coil, so it cannot provide effective power to the load and only generates energy loss. The generation of magnetic leakage is related to the structure of the transformer. For example, the gap between the core and the coil, the change of the number of coil turns and other factors will affect the magnitude of magnetic leakage. In order to reduce the impact of magnetic leakage, the following measures need to be taken: Optimizing the structural design of transformers By rationally designing the transformer structure, reducing the gap between the core and the coil and the change in the number of coil turns, the generation of leakage magnetic flux can be reduced.

[0059] Use the right materials Selecting appropriate insulating materials can reduce the thickness of the insulating layer, thereby reducing the leakage magnetic path and reducing the occurrence of leakage reactance. To verify the effectiveness of this solution, this embodiment performs weight reduction design for single-phase transformers and three-phase transformers, where the product specifications and technical requirements of single-phase transformers are as follows:

[0060] After applying this solution for optimization design, the basic parameter comparison is as follows:

[0061] This solution is used to transform the single-phase transformer into a low-frequency and lightweight transformer. Compared with the power frequency transformer, the volume is increased by 44%; compared with the 20Hz low-frequency transformer designed in a conventional way, the weight is reduced by 15.04%, and the load loss is increased by 10.5%. Because of the high loss, a high-temperature insulation system is used to reduce the product size. The product specifications and technical requirements of the three-phase transformer are as follows:

[0062] After applying this solution for optimization design, the basic parameter comparison is as follows:

[0063] Through this solution, the three-phase transformer is transformed into a low-frequency and lightweight one. Compared with the industrial frequency transformer, the volume is increased by 49.23%; compared with the 20Hz low-frequency transformer designed in a conventional way, the weight is reduced by 18.67% and the load loss is increased by 8.69%.

Claims

1. A comprehensive weight reduction design method for power transformers suitable for low-frequency power transmission systems, It is characterized in that The following steps are involved: S1. Determine the original technical data according to the design task book; S2. Determine the benchmark design scheme of the transformer based on the original technical data; S3. Optimize the magnetic circuit design based on the benchmark solution; S4. Optimize the conductive design for the scheme after the magnetic circuit design optimization; S5. Optimize the insulation design based on the optimized conductive design to obtain the final design solution of the transformer.

2. According to claim 1, a comprehensive weight reduction design method for power transformers suitable for low-frequency power transmission systems, It is characterized in that The original technical data in step S1 include rated capacity, rated voltage, voltage regulation requirement, rated frequency, number of phases, winding connection group number, rated performance parameters, rated operating conditions, cooling method, temperature rise limit, insulation level, and noise level. The rated performance parameters include no-load loss, load loss, no-load current, and short-circuit impedance.

3. According to claim 1, a comprehensive weight reduction design method for power transformers suitable for low-frequency power transmission systems, It is characterized in that The step S2 specifically includes the following steps: S21, select the silicon steel sheet brand, core column working magnetic flux density and core structure; S22, calculate the core diameter and select the cross-section of the core column and the iron yoke; S23, perform winding and insulation design; S24. Calculate the impedance voltage.

4. According to claim 3, a comprehensive weight reduction design method for power transformers suitable for low-frequency power transmission systems, It is characterized in that The specific process of step S21 is: the minimum magnetic polarization intensity reached by the core under the alternating magnetic field with a peak value of 800A / m As the design saturation flux density, 1.82~1.91T; Considering that the transformer can output rated current at 105% of the rated voltage, for some special use cases, it is also required to operate at no more than 110% of the rated voltage. The design magnetic density of the transformer is controlled at And below, design The selection range is 1.55~1.74T, among which, for medium and small transformers, The selection range is 1.55~1.65T; for large transformers, The selection range is 1.7~1.74T; The transformer core serves as the channel for the main magnetic flux. For single-phase transformers, a single-phase three-column structure is adopted; for three-phase transformers, when the core diameter exceeds 1000mm, a three-phase five-column structure is selected.

5. According to claim 4, a comprehensive weight reduction design method for power transformers suitable for low-frequency power transmission systems, It is characterized in that The specific process of step S22 is as follows: Calculate the core diameter, that is: (mm); in, It is the empirical coefficient of core diameter, and the copper coil winding and cold-rolled silicon steel sheet are selected from 51 to 57; is the capacity of each column of the transformer; The core lamination coefficient is 0.96~0.97; For medium, large and extra-large transformers, the core column section selects a multi-stage rectangular section of the circumscribed circle, and a multi-stage elliptical section is used as the side yoke section.

6. A comprehensive weight reduction design method for power transformers suitable for low-frequency power transmission systems according to claim 5, It is characterized in that The specific process of step S23 is as follows: For the structure of winding coil, including: Layered coils are suitable for small-capacity low-voltage coils, and multi-layered coils are suitable for small-capacity high-voltage coils; Spiral coils are suitable for low voltage, high current coils or voltage regulating coils; Tangled coil: high voltage coil suitable for high voltage; The tangled continuous coil is a partially compensated coil structure; Inner shielded coil, shielding wire is added to the line segment to increase its longitudinal capacitance and improve the impulse distribution. With this structure, the high-voltage winding of the high-voltage and large-capacity transformer can be wound with transposed wires; In order to reduce the load loss of the transformer, oxygen-free copper wire is used for winding. The winding of large power transformers uses transposed wires, which can greatly reduce the load loss, reduce the temperature rise of the winding hot spots, improve the mechanical strength of the winding, make the structure more compact, and make the coil processing easier; The current density of the coil conductor mainly depends on the load loss, the temperature rise of the coil and the dynamic and thermal stability when the secondary side of the transformer is suddenly short-circuited. The current density of the copper wire of the low-voltage coil is 4.5 And below, the current density of the copper wire of high and medium voltage coils is 3 ; The high-voltage coil turn insulation is 1.35mm, the medium-voltage is 0.6mm, and the low-voltage is 0.45mm; the high-pressure oil channel is 5mm, the medium-pressure oil channel is 4mm, and the low-pressure oil channel is 3.5mm; the phase distance is greater than 120mm, and the three-phase five-column core needs to increase the distance from the coil to the side column, which is greater than 100mm; Select Class A insulation system for power frequency transformer and calculate its stable temperature rise under rated load so that its value does not exceed the corresponding limit.

7. A comprehensive weight reduction design method for power transformers suitable for low-frequency power transmission systems according to claim 6, It is characterized in that The specific process of step S24 is as follows: The impedance voltage consists of two components: resistance voltage drop and reactance voltage drop. For large transformers, the resistance voltage drop is negligible and the impedance voltage calculation formula is: ,in, f is the frequency, IW is the rated current × the total number of turns when the main tap is connected, is the potential per turn, H is the average reactance height of the coil, ∑D is the leakage width, ρ is the Rockwell coefficient, K is the additional reactance coefficient.

8. According to claim 1, a comprehensive weight reduction design method for power transformers suitable for low-frequency power transmission systems, It is characterized in that The step S3 is specifically based on the magnetization properties of ferromagnetic materials, and adopts the idea of ​​improving the design magnetic density to reduce the cross-sectional area of ​​the core. Ultra-high magnetic induction oriented silicon steel sheet ≥1.93 T, considering that the transformer can output rated current at 105% of the rated voltage, the magnetic density is designed to be controlled at .

9. The comprehensive weight reduction design method for power transformers suitable for low-frequency power transmission systems according to claim 1, It is characterized in that The step S4 specifically optimizes the conductive design by increasing the current density of the winding copper wire.

10. The comprehensive weight reduction design method for power transformers suitable for low-frequency power transmission systems according to claim 1, It is characterized in that The step S5 specifically uses the synthetic ester MIDEL 7131 as the transformer insulating oil to reduce the insulation distance and optimize the insulation design.

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