Space electric field detection method based on influence of harmonic current temperature rise on dielectric constant

Abstract

The invention relates to a space electric field detection method based on the influence of harmonic current temperature rise on dielectric constants, which analyzes the influence of dynamic change of oil paper insulation dielectric parameters along with temperature on a winding and an oil paper electric field under the harmonic action through the change rule of relative dielectric constants of transformer oil and an oil-immersed paperboard at different temperatures. The influence rule of different temperatures on oil paper insulation dielectric constants is quantified, a calculation model of the dielectric constants is obtained, when a converter transformer model is constructed, a harmonic source is applied to serve as an excitation source, the interaction effect of an electromagnetic field and a temperature field under electric-heat combined stress is accurately simulated, and therefore detection of a space electric field better conforms to the actual working condition. Compared with the prior art, the method has the advantages of being accurate in detection, high in applicability, high in safety and the like.

Description

Technical Field

[0001] The invention relates to the technical field of transformer fault diagnosis and status assessment, and in particular to a spatial electric field detection method based on the influence of harmonic current temperature rise on dielectric constant. Background Art

[0002] In recent years, with the application of power electronic equipment in DC transmission projects, the switching operation and nonlinear characteristics of UHV DC transmission systems have caused a large number of harmonics to be generated, which have adverse effects on equipment. The operating environment of converter transformers is complex, in which the oil-paper insulation system must not only withstand the mixed voltage of AC and DC, but also directly withstand the large number of harmonic components generated by commutation, which promotes the generation of partial discharge and increases the risk of equipment insulation failure. Therefore, it is very important to study the spatial electric field of the converter transformer insulation system under complex harmonic conditions.

[0003] Chinese patent application CN117574795A considers the mutual influence of electromagnetic field, temperature field and flow field, establishes the electromagnetic model inside the transformer, improves the accuracy and reliability of transformer temperature monitoring, and avoids damaging the transformer casing and being affected by electromagnetic interference. However, the application does not consider the influence of temperature on the dielectric parameters of oil-paper insulation materials, and does not use harmonics as an excitation source, which lacks the accuracy of the spatial electric field calculation results. Therefore, how to more accurately detect the spatial electric field of the converter transformer in a more realistic and complex working condition has become a technical problem that needs to be solved. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a spatial electric field detection method based on the influence of harmonic current temperature rise on the dielectric constant. Through the calculation model of the dynamic change of temperature on the dielectric parameters of oil-paper insulation, the influence of different temperatures on the dielectric parameters of oil-paper insulation is quantitatively described, and harmonics are used as excitation sources to accurately simulate the interaction between the electromagnetic field and the temperature field under electric and thermal combined stress.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] According to one aspect of the present invention, there is provided a spatial electric field detection method based on the influence of harmonic current temperature rise on dielectric constant, comprising the following steps:

[0007] S1. Construct an electric-magnetic-thermal-flux multi-field coupled converter transformer model and set harmonic excitation through the field-circuit coupling module;

[0008] S2. Using the field-circuit coupling method to perform finite element analysis on the temperature field of the converter transformer to obtain the temperature distribution;

[0009] S3, obtaining the dielectric constant distribution of insulating oil and insulating paperboard by using the dielectric constant fitting formula of oil-paper insulation through the temperature distribution;

[0010] S4. Based on the dielectric constant distribution, finite element analysis is performed on the commutation transformer electric field to obtain the spatial electric field distribution.

[0011] Furthermore, the model of S1 includes the iron core, winding, insulating oil, insulating paper and end insulating angle ring of the converter transformer, and its external structure is ignored. The relevant material parameters of the converter transformer iron core, winding, insulating oil and insulating paper are fixed values, and the relative dielectric constants of the insulating oil and insulating paper are variables that change with temperature.

[0012] Furthermore, the harmonic excitation of S1 includes the rated current excitation and rated voltage excitation added at both ends of the winding, and the harmonic current is superimposed on the fundamental current, and the harmonic voltage is superimposed on the fundamental voltage in the form of applying an external current source. The 5th, 7th, 11th and 13th harmonics are used, accounting for 20%, 14.3%, 9.1% and 7.7% of the fundamental respectively, and the remaining higher harmonics are ignored.

[0013] The rated current excitation expression is:

[0014] I A =I N sin(2πf1·t)+βI N sin(2πf n ·t)

[0015]

[0016]

[0017] Among them, I A ,I B ,I C are the current excitations applied to the three phases A, B, and C, f1 is the fundamental frequency, I N is the rated current, β is the harmonic current content, f n is the harmonic frequency;

[0018] The rated voltage excitation expression is:

[0019] U A =U N sin(2πf1·t)+βU N sin(2πf n ·t)

[0020]

[0021]

[0022] Among them, UA , U B , U C are the voltage excitations applied to the three phases A, B, and C, f1 is the fundamental frequency, U N is the rated value of applied voltage, β is the harmonic current content, f n is the harmonic frequency.

[0023] Furthermore, the temperature field finite element analysis of S2 is performed by setting the heat conduction mode generated by the transformer winding, that is, the heat is transferred to the surface of the winding by heat conduction, heat convection and heat radiation modules. The energy conservation law of the heat transfer process in the solid domain of the winding is set to calculate the temperature distribution of the converter transformer.

[0024] Furthermore, the fitting expression of the relative dielectric constant distribution of the insulating oil obtained in S3 with the temperature distribution is:

[0025] ε r_oil (T) = 2.334-0.00125T,

[0026] Where T is the temperature of the insulating oil at that location, in Kelvin (K).

[0027] The fitting expression of the relative dielectric constant distribution of the insulating paperboard obtained in S3 with the temperature distribution is:

[0028] ε r_paper (T)=-8.62297+0.09714T-0.00025084T 2 +0.000000212298T 3 ,

[0029] Where T is the temperature of the insulating paperboard at that location, in Kelvin (K).

[0030] Furthermore, the S4 space electric field calculation is simulated by Maxwell's equations and electric field potential relationship to obtain the commutation transformer space electric field distribution.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) Improving the accuracy and reliability of electric field distribution detection: By comprehensively considering the dynamic relationship between harmonic current, temperature and dielectric constant, the electric field in the converter transformer internal space can be accurately calculated, thereby improving the accuracy and reliability of electric field calculation.

[0033] (2) Enhanced practicality and applicability: A calculation model for the dynamic change of temperature on the dielectric parameters of oil-paper insulation is introduced, which can quantitatively describe the influence of different temperatures on the dielectric parameters of oil-paper insulation. Harmonic excitation is added according to actual working conditions, making the electric field calculation closer to the actual working conditions, expanding the scope of application and enhancing practicality.

[0034] (3) Improve the operational stability and safety of power equipment: By analyzing the impact of harmonic current and temperature on the internal electric field of the transformer, the electric field distribution can be accurately detected, thereby improving the operational stability and safety of power equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flow chart of a spatial electric field detection method based on the influence of harmonic current temperature rise on dielectric constant;

[0036] Figure 2 It is the structural diagram of the two-dimensional geometric model of the converter transformer;

[0037] Figure 3 It is the temperature distribution cloud diagram of the converter transformer model;

[0038] Figure 4 is the distribution diagram of relative dielectric constant of insulating oil with temperature;

[0039] Figure 5 The distribution diagram of relative dielectric constant of insulating paperboard with temperature;

[0040] Figure 6 It is the spatial electric field intensity diagram when the harmonic voltage and current frequency is 50HZ;

[0041] Figure 7 It is the spatial electric field intensity diagram when the harmonic voltage and current frequency is 250HZ;

[0042] Figure 8 It is the spatial electric field intensity diagram when the harmonic voltage and current frequency is 350HZ;

[0043] Fig. 9 It is the spatial electric field intensity diagram when the harmonic voltage and current frequency is 550HZ;

[0044] Fig.10 It is the spatial electric field intensity diagram when the harmonic voltage and current frequency is 650HZ;

[0045] Fig.11 This is a diagram showing the influence of harmonic frequency on the maximum field strength under the action of 5% harmonic current and 5% harmonic voltage. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0047] Example 1

[0048] like Figure 1 As shown, a spatial electric field detection method based on the influence of harmonic current temperature rise on dielectric constant includes the following steps:

[0049] S1. Construct an electric-magnetic-thermal-flux multi-field coupled converter transformer model and set harmonic excitation through the field-circuit coupling module;

[0050] S2. Using the field-circuit coupling method to perform finite element analysis on the temperature field of the converter transformer to obtain the temperature distribution;

[0051] S3, obtaining the dielectric constant distribution of insulating oil and insulating paperboard by using the dielectric constant fitting formula of oil-paper insulation through the temperature distribution;

[0052] S4. Based on the dielectric constant distribution, finite element analysis is performed on the commutation transformer electric field to obtain the spatial electric field distribution.

[0053] like Figure 2 As shown in Figure 1, it is a multi-field coupled converter transformer model, including the core, winding, insulating oil, insulating paper and end insulating angle ring of the converter transformer, ignoring its external structure. The relevant material parameters of the converter transformer core, winding, insulating oil and insulating paper are fixed values, as shown in Table 1. The relative dielectric constants of insulating oil and insulating paper are variables that change with temperature.

[0054] Table 1 Basic parameters of converter transformer materials

[0055] Parameter name Iron Core Winding Insulation Paper Insulating oil density 7870 8923.3 1661 900 Poisson's ratio 0.29 0.35 0.3 0.4 Relative magnetic permeability BH 1 1 1 Conductivity <![CDATA[2×10 7 ]]> <![CDATA[4.68×10 7 ]]> <![CDATA[10 -15 ]]> <![CDATA[10 -12 ]]> Young's modulus <![CDATA[6×10 10 ]]> <![CDATA[5.3×10 10 ]]> 5000 800

[0056] The harmonic excitation of S1 includes the rated current excitation and rated voltage excitation added at both ends of the winding, and the harmonic current is superimposed on the fundamental current, and the harmonic voltage is superimposed on the fundamental voltage in the form of applying an external current source. The 5th, 7th, 11th and 13th harmonics are used, accounting for 20%, 14.3%, 9.1% and 7.7% of the fundamental respectively, and the remaining higher harmonics are ignored.

[0057] The rated current excitation expression is:

[0058] I A =I N sin(2πf1·t)+βI N sin(2πf n·t)

[0059]

[0060]

[0061] Among them, I A ,I B ,I C are the current excitations applied to the three phases A, B, and C, f1 is the fundamental frequency, I N is the rated current, β is the harmonic current content, f n is the harmonic frequency;

[0062] The rated voltage excitation expression is:

[0063] U A =U N sin(2πf1·t)+βU N sin(2πf n ·t)

[0064]

[0065]

[0066] Among them, U A , U B , U C are the voltage excitations applied to the three phases A, B, and C, f1 is the fundamental frequency, U N is the rated value of applied voltage, β is the harmonic current content, f n is the harmonic frequency.

[0067] The expression for superposition of 5th, 7th, 11th and 13th harmonics is:

[0068]

[0069] Among them, I d is the fundamental current amplitude; ω is the fundamental angular frequency.

[0070] The temperature field finite element analysis of S2 is performed by setting the heat conduction mode generated by the transformer winding, that is, the heat is transferred to the surface of the winding by heat conduction, heat convection and heat radiation modules. The energy conservation law of the heat transfer process in the solid domain of the winding is set to calculate the temperature distribution of the converter transformer.

[0071] By combining Maxwell's equations and the electric field potential relationship, the expression is:

[0072]

[0073] E=ε0εr (T)D;

[0074]

[0075] Where D is the electric flux density; ρ is the volume charge density in space; E is the electric field strength; ε0 is the vacuum dielectric constant; ε r (T) is the relative dielectric constant of oil-paper insulation material considering the temperature effect under the action of harmonic current; is the potential; ▽ is the Hamiltonian operator, we get:

[0076]

[0077] That is, based on the potential distribution of the influence of harmonic current temperature rise on the relative dielectric constant, and then substituted into Get the distribution of the electric field.

[0078] The fitting expression of the relative dielectric constant distribution of insulating oil with temperature distribution is:

[0079] ε r_oil (T) = 2.334-0.00125T,

[0080] Where T is the temperature of the insulating oil at that location, in Kelvin (K).

[0081] The fitting expression of the relative dielectric constant distribution of insulating paperboard with temperature distribution is:

[0082] ε r_paper (T)=-8.62297+0.09714T-0.00025084T 2 +0.000000212298T 3 ,

[0083] Where T is the temperature of the insulating paperboard at that location, in Kelvin (K).

[0084] Example 2

[0085] This embodiment takes ZZDFPZ-405000 / 500-400 UHV converter transformer as an example, applies power frequency current, and the calculated temperature distribution is as follows: Figure 3 As shown, Figure 3 The obtained temperature distribution data is calculated using the fitting formula, and the relative dielectric constant distribution of the insulating oil and insulator is obtained as follows: Figure 4 and Figure 5 shown.

[0086] Based on the relative parameter distribution characteristics of oil-paper insulation obtained under various conditions, the electric field distribution of the grid-side winding and valve-side winding of the converter transformer under the influence of 5% harmonic current and 5% harmonic voltage is simulated, and the electric field distribution results of the converter transformer winding at the moment of maximum electric field intensity under different harmonic frequencies (harmonic voltage and current frequencies are 250Hz, 350Hz, 550Hz, and 650Hz, respectively) are obtained, as shown in Figure 2. Figure 6 , Figure 7 , Figure 8 , Fig. 9 and Fig.10 The influence of harmonic frequency on the maximum field strength under the action of 5% harmonic current and 5% harmonic voltage is summarized as follows: Fig.11 As shown in the figure, under the action of 50Hz fundamental wave, the maximum value of electric field strength is 5.0534kV / mm, and under the action of 250Hz harmonic, the maximum value of electric field strength is 5.1099kV / mm, which increases to a certain extent; when the harmonic voltage frequency increases to 350Hz and 550Hz, the maximum value of electric field strength is 4.6055kV / mm and 4.6092kV / mm respectively, both of which show a significant decrease; but under the action of 650Hz harmonic, the maximum value of electric field strength rises back to 5.1192kV / mm, which is higher than the value under the power frequency. Compared with the effect of pure harmonic voltage frequency on the electric field strength of the winding, the electric field strength of the winding increases under the combined action of harmonic current and harmonic voltage, especially under the action of 650Hz frequency harmonic, the electric field strength of the winding is 0.0658kV / mm higher than the electric field strength under the power frequency, that is, the harmonic current has an enhancing effect on the electric field strength of the UHV converter transformer winding.

[0087] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A spatial electric field detection method based on the influence of harmonic current temperature rise on dielectric constant, characterized in that: The following steps are involved: S1. Construct an electric-magnetic-thermal-flux multi-field coupled converter transformer model and set harmonic excitation through the field-circuit coupling module; S2. Using the field-circuit coupling method to perform finite element analysis on the temperature field of the converter transformer to obtain the temperature distribution; S3, obtaining the dielectric constant distribution of insulating oil and insulating paperboard by using the dielectric constant fitting formula of oil-paper insulation through the temperature distribution; S4. Based on the dielectric constant distribution, finite element analysis is performed on the commutation transformer electric field to obtain the spatial electric field distribution.

2. A spatial electric field detection method based on the influence of harmonic current temperature rise on dielectric constant according to claim 1, characterized in that: The model of S1 includes the core, winding, insulating oil, insulating paper and end insulating angle rings of the converter transformer, and its external structure is ignored.

3. The spatial electric field detection method based on the influence of harmonic current temperature rise on dielectric constant according to claim 2 is characterized in that: The relevant material parameters of the commutation transformer core, winding, insulating oil and insulating paper are fixed values, and the relative dielectric constants of the insulating oil and insulating paper are variables that change with temperature.

4. The spatial electric field detection method based on the influence of harmonic current temperature rise on dielectric constant according to claim 1 is characterized in that: The harmonic excitation of S1 includes rated current excitation and rated voltage excitation added at both ends of the winding, so as to superimpose the harmonic current and fundamental current, and the harmonic voltage and fundamental voltage in the form of applying an external current source.

5. The method for detecting a spatial electric field based on the influence of temperature rise of harmonic current on dielectric constant according to claim 4, characterized in that: The rated current excitation expression is: I A =I N sin(2πf1·t)+βI N sin(2πf n ·t) Among them, I A ,I B ,I C are the current excitations applied to the three phases A, B, and C, f1 is the fundamental frequency, I N is the rated current, β is the harmonic current content, f n is the harmonic frequency; The rated voltage excitation expression is: U A =U N sin(2πf1·t)+βU N sin(2πf n ·t) Among them, U A , U B , U C are the voltage excitations applied to the three phases A, B, and C, f1 is the fundamental frequency, U N is the rated value of applied voltage, β is the harmonic current content, f n is the harmonic frequency.

6. A spatial electric field detection method based on the influence of harmonic current temperature rise on dielectric constant according to claim 5, characterized in that: The 5th, 7th, 11th and 13th harmonics are used, accounting for 20%, 14.3%, 9.1% and 7.7% of the fundamental wave respectively, and the remaining higher harmonics are ignored.

7. The spatial electric field detection method based on the influence of harmonic current temperature rise on dielectric constant according to claim 1 is characterized in that: The temperature field finite element analysis of S2 calculates the temperature distribution of the converter transformer by setting the heat conduction mode generated by the transformer winding and the energy conservation law of the heat transfer process in the solid domain of the winding.

8. The spatial electric field detection method based on the influence of harmonic current temperature rise on dielectric constant according to claim 1 is characterized in that: The fitting expression of the relative dielectric constant distribution of the insulating oil obtained in S3 with the temperature distribution is: e r_oil (T)=2.334-0.00125T, Where T is the temperature of the insulating oil at that location, in Kelvin (K).

9. The spatial electric field detection method based on the influence of harmonic current temperature rise on dielectric constant according to claim 1 is characterized in that: The expression for fitting the relative dielectric constant distribution of the insulating paperboard obtained in S3 with the temperature distribution is: e r_paper (T)=-8.62297+0.09714T-0.00025084T 2 +0.000000212298T 3 , Where T is the temperature of the insulating paperboard at that location, in Kelvin (K).

10. The spatial electric field detection method based on the influence of harmonic current temperature rise on dielectric constant according to claim 1, characterized in that: The spatial electric field calculation of S4 is simulated by Maxwell's equations and electric field potential relationship to obtain the spatial electric field distribution of the commutation transformer.

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