A design method for low-frequency power transformers

Abstract

This invention provides a design method for low-frequency power transformers. The method first obtains the relative permittivity and dielectric loss factor test values ​​of transformer oil and oil-impregnated paperboard at low frequencies. Then, it obtains the magnetization curve, permeability curve, excitation power curve, and iron loss curve of the transformer's silicon steel sheets at low frequencies, thereby determining the selection of silicon steel sheets for the low-frequency transformer. Next, it calculates the transformer core diameter, coil structure, insulation radius, and short-circuit impedance. Furthermore, it includes anti-collapse pads under the transformer tank cover to support the mechanical strength of the tank cover and reduce transformer temperature rise. Finally, it analyzes the transformer's short-circuit withstand capability, calculating the axial overturning, radial buckling, and axial force of the windings to ensure the safe and reliable operation of the transformer. This invention enables the miniaturization, lightweighting, and high reliability design of low-frequency power transformers, solving the problem of a significant increase in the size and weight of power transformers due to frequency reduction.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power transformer, in particular to a design method of low-frequency power transformer. BACKGROUND

[0002] At present, the related research of low-frequency power transmission is basically only concentrated in the field of power generation and transmission, and there is little in-depth research in the field of low-frequency power transformer, which is the key equipment of power transmission. The power transformer is used to realize the power transmission according to the principle of electromagnetic induction. Frequency is a very important technical parameter in the design process of power transformer. The reduction of frequency will affect the insulation performance of power transformer, resulting in that the volume and weight of low-frequency power transformer are greatly increased compared with the power transformer with the same capacity and voltage level. SUMMARY

[0003] In view of the defects of the prior art, the present application provides a design method of low-frequency power transformer, which can realize the miniaturization, lightweight and high reliability design of low-frequency power transformer, and solve the problem of large volume and weight of power transformer caused by the reduction of frequency.

[0004] In order to solve the technical problem, the technical scheme adopted by the present application is as follows: a design method of low-frequency power transformer, comprising the following steps:

[0005] S01), repeatedly test the dielectric properties of different types of transformer oil and oil-impregnated paper under low-frequency environment, and obtain the relative dielectric constant and dielectric loss factor test values of transformer oil and oil-impregnated paper under low frequency;

[0006] S02), repeatedly test the performance parameters of different types of transformer silicon steel sheets under low-frequency environment, and obtain the magnetization curve, permeability curve, excitation power curve and iron loss curve of transformer silicon steel sheet under low frequency, and then determine the type selection of low-frequency transformer silicon steel sheet;

[0007] S03), according to the principle of Faraday electromagnetic induction, the diameter of low-frequency transformer core, the structure of coil, the insulation radius and the short-circuit impedance are calculated, and the anti-collapse pad is arranged below the tank cover of transformer oil tank to support the mechanical strength of tank cover and reduce the temperature rise of transformer;

[0008] S04), the anti-short-circuit strength of transformer is analyzed, the axial overturning and radial buckling of winding and axial force are calculated, and the weak parts of winding in the electromagnetic calculation scheme are optimized and adjusted according to the simulation results, so as to ensure the safety and reliability of the actual operation of transformer;

[0009] S05), according to the optimized electromagnetic calculation scheme, the drawing design of low-frequency transformer is carried out;

[0010] S06), according to the design drawings, low-frequency transformer production, assembly and test.

[0011] Further, the dielectric property test method of transformer oil and oil-impregnated paper at low frequency includes the following steps:

[0012] S11), process treatment is performed on the tested dielectric, i.e., transformer oil or oil-impregnated paper, wherein the transformer oil is subjected to 2h, 60℃ oil filtration treatment, and the oil-impregnated paper is subjected to 48h drying treatment at a temperature of 100℃ and a vacuum degree of 0.1kPa, and then the oil-impregnated paper is placed in an iron container for vacuuming to 0.1kPa and standing for 24h, and finally the transformer oil is injected into the iron container containing the insulation paper according to an oil-paper mass ratio of 15:1, and vacuum oil-impregnation treatment is performed for 24h;

[0013] S12), the treated tested dielectric is fixed on a sample holder;

[0014] S13), the temperature control system in the Novocontrol type broadband dielectric test system is started, and after the set temperature is reached and maintained for 1h, the dielectric property test of the tested dielectric is performed;

[0015] S14), the relative dielectric constant and dielectric loss factor of the tested dielectric are measured through the setting control software, and the test data are extracted and analyzed.

[0016] Further, the Novocontrol type broadband dielectric test system includes a measurement unit, a temperature control system, a sample holder and control software, the temperature range of the test is set to 20-100℃, and the frequency range is set to 1-10000Hz.

[0017] Further, the anti-collapse pad is in the shape of a convex character, an oil guide groove is formed in the center of the upper surface of the anti-collapse pad, and fixing holes for fixing the anti-collapse pad on the top of the upper beam of the iron core are formed at both ends of the anti-collapse pad.

[0018] Further, the anti-collapse pad is located between the tank cover of the transformer oil tank and the upper beam of the iron core, and a plurality of adjusting shims are arranged between the anti-collapse pad and the upper beam of the iron core.

[0019] Further, the REST software of VEI is applied to analyze the short-circuit resistance of the transformer, and the temperature distribution in the winding is analyzed, a global analysis model of the winding part is established through an electromagnetic calculation scheme, and the feasibility of the electromagnetic calculation scheme is verified.

[0020] The beneficial effects of this invention are as follows: This invention provides a design method for low-frequency power transformers, achieving miniaturization and lightweight design, reducing the production and manufacturing costs of low-frequency power transformers, solving the problem of a significant increase in the size and weight of power transformers due to frequency reduction, and improving the economic efficiency of low-frequency power transformers. This invention adds an anti-collapse pad under the transformer tank cover, which strengthens the mechanical strength of the tank cover, ensures smooth internal flow of transformer oil, improves the oil flow direction within the transformer body, increases the oil circulation speed, reduces internal temperature rise, and ensures the effective implementation of the miniaturized, lightweight, and highly reliable design of low-frequency power transformers. Attached Figure Description

[0021] Figure 1 This is a flowchart of the present invention;

[0022] Figure 2 A flowchart illustrating the method for testing the dielectric properties of transformer oil and oil-impregnated paperboard at low frequencies;

[0023] Figure 3 A schematic diagram of the main structure of the anti-collapse pad block for the core of a low-frequency transformer.

[0024] Figure 4 This is a side view of the anti-collapse pad block for the core of a low-frequency transformer.

[0025] Figure 5 A schematic diagram showing the installation location of the anti-collapse pads for the core of a low-frequency transformer.

[0026] In the diagram: 1. Anti-collapse pad block, 2. Iron core upper beam, 3. Oil guide groove, 4. Fixing hole. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0028] Example 1

[0029] This embodiment discloses a design method for a low-frequency power transformer, such as... Figure 1 As shown, it includes the following steps:

[0030] S01) The dielectric properties of different types of transformer oil and oil-impregnated paperboard under low-frequency environment were repeatedly tested using a broadband dielectric testing system. The test data were recorded and the fitting curve was plotted to obtain the relative dielectric constant and dielectric loss factor test values ​​of transformer oil and oil-impregnated paperboard under low frequency.

[0031] S02), using 25 cm Epstein square method principle for low frequency under different grade transformer silicon steel sheet performance parameters of repeated test, record test data and draw low frequency under transformer silicon steel sheet magnetization curve, permeability curve, excitation power curve, iron loss curve, comprehensive consideration cost, silicon steel sheet performance, weight and other factors, finally determine the low frequency transformer silicon steel sheet selection;

[0032] S03), according to Faraday electromagnetic induction principle E = 4.44N f Phi m = 4.44N f B S, Formula, low frequency transformer core diameter selection, coil structure, insulation radius, short circuit impedance electromagnetic calculation scheme design, wherein, E is the induced electromotive force of the coil, N is the number of turns, f is the frequency, Phi m The main magnetic flux amplitude of transformer core, B is the magnetic induction intensity, S is the cross section area of the core, u x The short circuit impedance voltage of transformer, IW is the ampere turns of transformer coil, Sigma D is the equivalent total area of transformer leakage magnetic, e z The potential of each turn, H x The average reactance height;

[0033] In order to realize the miniaturization design of low frequency power transformer, improve the strength of oil tank and reduce the top oil surface temperature, a kind of low frequency power transformer core anti collapse pad structure is proposed, which is located below the cover of transformer oil tank.

[0034] S04), through the application of VEI's REST software to analyze the short circuit strength of transformer, the axial overturning and radial buckling of winding and axial force are calculated, and the weak parts of winding in electromagnetic calculation scheme are optimized and adjusted according to the simulation results, so as to ensure the safety and reliability of transformer actual operation; through the application of WHC (Wingding Heat Calculation) in Trancalc integrated software of American SoftTeam company, the temperature distribution of winding is analyzed, and the feasibility of electromagnetic calculation scheme is verified according to the winding temperature distribution results.

[0035] S05), according to the optimized electromagnetic calculation scheme, the low frequency transformer drawing design is carried out.

[0036] S06), according to the design drawing, the low frequency transformer production, assembly and test are carried out.

[0037] As Figure 2 shown, the dielectric property test method of transformer oil and oil immersed paper under low frequency includes the following steps:

[0038] S01), special process treatment is performed on the tested dielectric (transformer oil or oil-impregnated paperboard). The transformer oil is subjected to 2h, 60℃ oil filtration treatment to reduce the water and impurity content in the oil; the insulation paperboard is first subjected to 48h drying treatment at a temperature of 100℃ and a vacuum degree of 0.1kPa, the insulation paperboard is placed in an iron container, vacuumed to 0.1kPa, and then left for 24h, and finally the transformer oil is injected into the iron container containing the insulation paperboard at an oil-paper mass ratio of 15:1, and subjected to 24h vacuum oil-impregnation treatment.

[0039] S02), the treated tested dielectric is fixed on a sample holder;

[0040] S03), the temperature control system in the Novocontrol broadband dielectric test system is started, and after the set temperature is reached and maintained for 1h, the dielectric property test of the tested dielectric is performed;

[0041] S04), the relative dielectric constant and dielectric loss factor of the tested dielectric are measured by setting the control software, and the test data are extracted and analyzed.

[0042] The Novocontrol broadband dielectric test system includes a measurement unit, a temperature control system, a sample holder and control software, the test temperature range is set to 20-100℃, and the frequency range is set to 1-10000Hz.

[0043] As shown in Figure 3 , 4 , 5, the low-frequency power transformer core anti-collapse pad structure is shown in Figure 3 , which is designed as a "convex" structure, an oil guide groove 3 with a width same as that of the anti-collapse pad 1 is opened in the center of the upper surface of the anti-collapse pad 1, and the width of the anti-collapse pad 1 is same as that of the core upper beam 2. Two fixing holes 4 are designed, one of which is a 18mm diameter circular hole, and the other is a long circular hole with a size of 18mm*28mm, which are fastened on the top of the core upper beam 2 through insulation screws. The gap between the upper surface of the anti-collapse pad 1 and the inner wall of the oil tank cover is about 20mm, and during the core assembly process, a plurality of adjusting pads are placed between each anti-collapse pad 1 and the core upper beam 2, the width and length of the adjusting pad are same as those of the anti-collapse pad, and the thickness is 3mm. The number of adjusting pads is appropriately adjusted according to the actual situation to ensure that the anti-collapse pad plays a role in supporting the mechanical strength of the oil tank cover and reducing the temperature rise of the transformer without affecting the oil tank cover, and realizes the design of miniaturization, light weight and high reliability of the low-frequency power transformer.

[0044] The above is only for the preferred embodiment of the present application, not to limit the scope of the present application, should be noted that for those skilled in the art, without departing from the principles of the present patent technology, can also make a number of improvements and replacements, these improvements and replacements should also be considered the scope of the present patent protection.

Claims

1. A method of designing a low frequency power transformer, characterized by: It comprises the following steps: S01), repeatedly test the dielectric properties of different types of transformer oil and oil-impregnated paper under low frequency environment, and obtain the relative dielectric constant and dielectric loss factor of transformer oil and oil-impregnated paper under low frequency; The dielectric property test of transformer oil and oil-impregnated paper under low frequency comprises the following steps: S11), process the tested dielectric, i.e. transformer oil or oil-impregnated paper, wherein the transformer oil is subjected to 2h, 60℃ oil filtration treatment, the oil-impregnated paper is subjected to 48h drying treatment at a temperature of 100℃ and a vacuum degree of 0.1kPa, the oil-impregnated paper is placed in an iron container and vacuumed to 0.1kPa, and then is left for 24h, and finally the transformer oil is injected into the iron container containing the insulation paper according to the oil-paper mass ratio of 15:1, and is subjected to 24h vacuum oil-impregnation treatment; S12), fix the processed tested dielectric on a sample holder; S13), start the temperature control system in the Novocontrol wideband dielectric test system, and after reaching the set temperature and keeping for 1h, test the dielectric property of the tested dielectric; S14), realize the measurement of the relative dielectric constant and dielectric loss factor of the tested dielectric by setting the control software, and realize the extraction and analysis of the test data; S02), repeatedly test the performance parameters of different types of transformer silicon steel sheets under low frequency environment, and obtain the magnetization curve, permeability curve, excitation power curve and iron loss curve of the transformer silicon steel sheet under low frequency, and then determine the selection of the silicon steel sheet for low frequency transformer; S03), select the diameter of the low frequency transformer core, calculate the coil structure, insulation radius and short circuit impedance according to the Faraday electromagnetic induction principle; and the anti-collapse pad is arranged below the transformer tank cover to support the mechanical strength of the tank cover and reduce the temperature rise of the transformer; S04), analyze the short circuit strength of the transformer by applying the REST software of VEI, calculate the axial overturning and radial buckling of the winding and the axial force, optimize and adjust the weak part of the winding in the electromagnetic calculation scheme according to the simulation result, ensure the safety and reliability of the actual operation of the transformer, and analyze the temperature distribution in the winding, establish the global analysis model of the winding part through the electromagnetic calculation scheme, and verify the feasibility of the electromagnetic calculation scheme; S05), design the drawing of the low frequency transformer according to the optimized electromagnetic calculation scheme; S06), produce, assemble and test the low frequency transformer according to the design drawing.

2. The design method of a low frequency power transformer according to claim 1, characterized in that: The Novocontrol wideband dielectric test system comprises a measurement unit, a temperature control system, a sample holder and control software, the temperature range of the test is set to 20-100℃, and the frequency range is set to 1-10000Hz.

3. The method of designing a low frequency power transformer according to claim 1, characterized in that: The anti-collapse pad is in the shape of a Chinese character, an oil guide groove is formed in the center of the upper surface of the anti-collapse pad, and fixing holes are formed at both ends of the anti-collapse pad for fixing the anti-collapse pad on the top of the upper beam of the core.

4. The method of designing a low frequency power transformer according to claim 1, characterized in that: The anti-collapse pad is located between the transformer tank cover and the upper beam of the core, and a plurality of adjusting shims are arranged between the anti-collapse pad and the upper beam of the core.

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