Method for calculating service life of oil paper insulating material based on harmonic current influence

Abstract

The invention relates to a method for calculating the service life of an oil-paper insulating material based on harmonic current influence, and the method achieves the precise calculation of the service life of the oil-paper insulating material under a complex harmonic current condition through a constructed thermal-mechanical multi-physics field coupling simulation model. And a temperature influence factor and a vibration influence factor are proposed, so that the influence of the harmonic current content and frequency on the oil paper insulation temperature and stress is quantified. And fusing the temperature influence factor and the vibration influence factor to obtain an oil paper insulation life improvement calculation model. The method can accurately evaluate the long-term influence of the harmonic current on the thermal-mechanical joint damage of the oil-paper insulation system, improves the operation stability of the transformer, and provides guarantee for the normal operation of a power system. Compared with the prior art, the method has the advantages of high accuracy, high reliability, adaptability to complex environments and the like.

Description

Technical Field

[0001] The invention relates to the field of transformer equipment life assessment, and in particular to a method for calculating the life of an oil-paper insulation material based on the influence of harmonic current. Background Art

[0002] With the widespread application of renewable energy and power electronic equipment in power systems, the generation and propagation of harmonic currents have become increasingly complex, seriously affecting the safe operation of transformers. Harmonic currents not only cause temperature rise and stress increase in oil-paper insulation materials, but also accelerate their aging and cause insulation failure, thus threatening the long-term stability of the equipment. In the actual operation of converter transformers, the harmonic current frequency generated by the 12-pulse converter is mainly concentrated at 12k±1, which further aggravates the thermal and mechanical stress on the oil-paper insulation materials. Therefore, in-depth research on the impact of harmonic currents on the life of oil-paper insulation and the exploration of effective evaluation methods are of great significance to ensure the safe and reliable operation of power systems.

[0003] Chinese patent CN109239546B discloses a method for transformer insulation life prediction and reliability assessment. Based on the correction factor algorithm, a transformer insulation life assessment model under the combined influence of aging, moisture and temperature is established. By establishing the relationship between the operating status and the expected life, the operating status score is introduced into the aging life assessment model, and a new model is proposed in which insulation aging and operating status jointly characterize the failure rate. The effectiveness of this method is preliminarily verified through field tests. However, the life assessment of this patent does not fully consider the long-term impact of harmonic currents on insulating materials, and cannot meet the accurate prediction of the life of oil-paper insulation materials under harmonic current conditions. Therefore, how to achieve a more accurate and comprehensive prediction of the calculation of the insulation life of oil-paper insulation paper under complex harmonic currents is 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 method for calculating the life of oil-paper insulation materials based on the influence of harmonic currents, quantifying the influence of harmonic current content and frequency on the temperature and stress of oil-paper insulation through temperature influence factors and vibration influence factors.

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

[0006] According to one aspect of the present invention, a method for calculating the life of an oil-paper insulation material based on the influence of harmonic current is provided, comprising the following steps:

[0007] S1. Construct an electromagnetic-thermal-mechanical multi-physics field coupling simulation model for the oil-paper insulation system and obtain an oil-paper insulation life calculation model;

[0008] S2. Obtaining temperature influence factors and vibration influence factors under different harmonic currents based on the simulation model;

[0009] S3. Input harmonic current parameters and obtain a predicted life value of the oil-paper insulation based on the calculation model.

[0010] Furthermore, the oil-paper insulation life calculation model of S1 quantifies the influence of harmonic current content and frequency on oil-paper insulation temperature and stress, and integrates temperature influence factor and vibration influence factor to calculate and predict the life of oil-paper insulation under complex harmonic current.

[0011] Furthermore, S2 fits the hot spot temperatures of the grid-side and valve-side windings under different harmonic current frequencies in the simulation model to obtain temperature influence factors and vibration influence factors under different harmonic currents.

[0012] The expression of the temperature influence factor under different harmonic currents is:

[0013]

[0014] Among them, T f is the hot spot temperature of the winding under different harmonic current frequencies; T0 is the initial hot spot temperature of the winding under different harmonic currents; τ is the response time of the hot spot temperature of the winding with the change of harmonic frequency; k f is the coefficient of change of the hot spot temperature of the winding under the action of different harmonic current frequencies; f is the frequency corresponding to the harmonic current.

[0015] The expression of the vibration influence factor under different harmonic currents is:

[0016]

[0017] Among them, σ f is the total stress of the winding; σ 50Hz is the stress value of the winding at 50Hz; Δσ f is the winding stress value under the action of high-frequency harmonic current; β is the content of different harmonic currents; f is the frequency corresponding to the harmonic current; a f is the influence coefficient of harmonic current of different frequencies on winding stress; b f I is the influence index of different frequency harmonic currents on winding stress; f is the harmonic current; I 50Hz is the harmonic current at 50Hz.

[0018] Furthermore, the oil-paper insulation life calculation model expression of S1 is:

[0019]

[0020] Among them, ω DPis the cumulative loss rate of the degree of polymerization of the insulation paper; DPt is the degree of aggregation at time t, i.e., λ DP0 is the initial degree of polymerization, λ DPend is the degree of polymerization at the end of life; α σ is the time-stress translation factor; α T is the temperature shift factor; β is the input harmonic current parameter; σ f is the total stress of the winding; R is the gas constant; T is the temperature; E a is the activation energy; T f is the temperature influence factor; ω DP is the cumulative loss rate of the degree of polymerization of the insulation paper; ω * DP Ability to save for insulation paper degradation; is the fitting value of the rate of decrease of polymerization degree under different mechanical stresses; is the aging time for the degree of polymerization to reach a certain state value under different temperatures and stresses; α σ，T is the stress-temperature translation factor; is the lifetime at temperature T.

[0021] When the ω DP When it is 0, it means that the insulation paper has not aged. DP When it is 1, it means that the insulation paper is completely degraded.

[0022] The oil-paper insulation life value is obtained by combining the calculation model with the temperature influence factor and the vibration influence factor obtained by S2. in, is the temperature shift factor under different harmonic currents; is the temperature T under different harmonic currents f The time of a point on the fitting curve; is the stress-temperature translation factor under different harmonic currents; K is the aging time for the degree of polymerization to reach a certain state value under different temperatures and mechanical stresses. DP represents the rate at which the degree of polymerization decreases, Non-reference temperature The time of a point on the fitted curve.

[0023] Furthermore, the simulation model of S1 is based on the refined geometric model of transformer windings, sets material properties and boundary conditions according to the type and parameters of the transformer, and obtains the simulation model through the electromagnetic-thermal-mechanical multi-physics coupling of the oil-paper insulation system. The harmonic current parameters of S1 include different harmonic current contents and the frequencies corresponding to the harmonic currents.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) Improve calculation accuracy: By integrating the temperature influencing factors and the vibration influencing factors, an improved calculation model for the oil-paper insulation life is proposed, which can realize the accurate calculation of the insulation life of oil-paper insulation under complex harmonic currents.

[0026] (2) Improve transformer reliability and stability: By calculating the insulation life, the long-term impact of harmonic current on the thermal-mechanical combined damage of the oil-paper insulation system is accurately evaluated, thereby improving the operating stability of the transformer.

[0027] (3) Adaptability to complex harmonic environments: The method of the present invention is suitable for calculating the life of oil-paper insulation under complex harmonic current conditions, and provides technical support for evaluating the operating stability of transformers in power systems containing a large amount of harmonic currents. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The flowchart of the calculation method of the life of oil-paper insulation material based on the influence of harmonic current;

[0029] Figure 2 This is a two-dimensional refined simulation model diagram of the winding;

[0030] Figure 3 This is the winding temperature distribution cloud diagram of the simulation model under rated load;

[0031] Figure 4 This is the temperature distribution cloud diagram of the winding under the action of 250Hz 5% harmonic current;

[0032] Figure 5 This is the temperature distribution cloud diagram of the winding under the action of 250Hz 10% harmonic current;

[0033] Figure 6 This is the temperature distribution cloud diagram of the winding under the action of 250Hz 15% harmonic current;

[0034] Figure 7 This is the temperature distribution cloud diagram of the winding under the action of 250Hz 20% harmonic current;

[0035] Figure 8 This is the temperature distribution cloud diagram of the winding under the action of 650Hz 5% harmonic current;

[0036] Fig. 9 This is the temperature distribution cloud diagram of the winding under the action of 650Hz 10% harmonic current;

[0037] Fig.10 This is the temperature distribution cloud diagram of the winding under the action of 650Hz 15% harmonic current;

[0038] Fig.11 This is the temperature distribution cloud diagram of the winding under the action of 650Hz 20% harmonic current;

[0039] Fig.12 It is the stress distribution cloud diagram of winding under rated current;

[0040] Fig.13 This is the stress distribution cloud diagram of the winding under the action of 250Hz 5% harmonic current;

[0041] Fig.14 This is the stress distribution cloud diagram of the winding under the action of 250Hz 10% harmonic current;

[0042] Fig.15 This is the stress distribution cloud diagram of the winding under the action of 250Hz 15% harmonic current;

[0043] Fig.16 This is a cloud diagram of winding stress distribution under the action of 250Hz 20% harmonic current. DETAILED DESCRIPTION

[0044] 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.

[0045] Example 1

[0046] The valve-side winding of the converter transformer is subjected to the combined effects of AC and DC voltages during operation, which will generate a large number of harmonic components with frequencies higher than the fundamental frequency. A large number of high-frequency harmonic currents will cause the winding temperature to rise and induce nonlinear electromagnetic forces. The temperature rise of the converter transformer winding is mainly caused by resistance loss and eddy current loss. The harmonic current content affects the DC resistance and eddy current loss of the winding by changing the current density of the conductor, thereby changing the temperature distribution of the winding. The harmonic current frequency changes the eddy current density distribution through the skin effect, affecting the equivalent resistance and eddy current loss, which in turn causes the temperature distribution of the winding to change; the electromagnetic stress on the converter transformer winding is mainly determined by the instantaneous harmonic current density and magnetic induction intensity, among which the mechanical stress depends on factors such as the geometric structure and the Young's modulus of the material, and the electromagnetic stress is affected by the content and frequency of different harmonic currents, resulting in uneven force on the winding.

[0047] In order to comprehensively consider the influence of various factors on the life of oil-paper insulation materials and more accurately calculate the life of oil-paper insulation materials, such as Figure 1 As shown, this embodiment discloses a method for calculating the life of oil-paper insulation material based on the influence of harmonic current, comprising the following steps:

[0048] S1. Construct an electromagnetic-thermal-mechanical multi-physics field coupling simulation model for the oil-paper insulation system and obtain an oil-paper insulation life calculation model;

[0049] S2. Obtaining temperature influence factors and vibration influence factors under different harmonic currents based on the simulation model;

[0050] S3. Input harmonic current parameters and obtain a predicted life value of the oil-paper insulation based on the calculation model.

[0051] The oil-paper insulation life calculation model of S1 quantifies the influence of harmonic current content and frequency on the temperature and stress of oil-paper insulation, integrates temperature influence factor and vibration influence factor to calculate and predict the life of oil-paper insulation under complex harmonic current. The simulation model is based on the refined geometric model of transformer windings. According to the type and parameters of the transformer, the material properties and boundary conditions are set, and the simulation model is obtained by integrating the electromagnetic-thermal flow-mechanical multi-physics field coupling of the oil-paper insulation system. Harmonic current parameters include different harmonic current contents and the corresponding frequencies of harmonic currents.

[0052] In the simulation model, S2 fits the hot spot temperatures of the grid-side and valve-side windings under different harmonic current frequencies to obtain the temperature influence factors and vibration influence factors under different harmonic currents.

[0053] The expression of temperature influence factor under different harmonic currents is:

[0054]

[0055] Among them, T f is the hot spot temperature of the winding under different harmonic current frequencies; T0 is the initial hot spot temperature of the winding under different harmonic currents; τ is the response time of the hot spot temperature of the winding with the change of harmonic frequency; k f is the coefficient of change of the hot spot temperature of the winding under the action of different harmonic current frequencies; f is the frequency corresponding to the harmonic current.

[0056] The expression of vibration influence factor under different harmonic currents is:

[0057]

[0058] Among them, σ f is the total stress of the winding; σ 50Hz is the stress value of the winding at 50Hz; Δσ f is the winding stress value under the action of high-frequency harmonic current; β is the content of different harmonic currents; f is the frequency corresponding to the harmonic current; a f is the influence coefficient of harmonic current of different frequencies on winding stress; b f I is the influence index of different frequency harmonic currents on winding stress; f is the harmonic current; I 50Hz is the harmonic current at 50Hz.

[0059] The traditional life calculation model expression at different aging temperatures is:

[0060]

[0061] Among them, ω DP is the cumulative loss rate of the degree of polymerization of the insulation paper, ω DP =0 means that the insulation paper has not aged, ω DP =1 means that the insulation paper is completely degraded, and the actual range is 0<ω DP <1;λ DPt is the degree of aggregation at time t, λ DP0 is the initial degree of polymerization; ω * DP The ability to save insulation paper degradation; k DP is the rate at which the degree of polymerization decreases; t ref E is the aging time for the degree of polymerization to reach a certain state value; a is the activation energy; R is the gas constant; α T is the temperature shift factor; t T is the time of a point on the fitting curve at the non-reference temperature T. When calculating the lifespan, The lifetime is determined to be the end, and the time taken for the degree of polymerization to decrease to the end of the lifetime is finally calculated to represent the lifetime L at temperature T. T .

[0062] Considering the change of the cumulative loss rate of polymerization degree under different mechanical stress intensities, the expression of the traditional thermal-mechanical combined stress effect on oil-paper insulation life calculation model under different mechanical stress intensities σ and temperatures T is obtained as follows:

[0063]

[0064] Among them, ω DP is the cumulative loss rate of the degree of polymerization of the insulation paper; DPt is the degree of aggregation at time t, λ DP0 is the initial degree of polymerization; α σ is the time-stress translation factor; β is a constant with volume dimension; σ is the intensity of the applied stress; R is the gas constant; T is the reaction temperature; α T is the temperature shift factor; t ref，σref is the aging time for the degree of polymerization to reach a certain state value under different temperatures and stresses; α σ，T is the stress-temperature translation factor; T ref，σref It is the aging time for the degree of polymerization to reach a certain state value under different temperatures and mechanical stresses; is the fitting value of the rate of decrease of polymerization degree under different mechanical stresses; t T，σ is the non-reference temperature T ref，σref The time of a point on the fitted curve.

[0065] Based on the temperature and stress variation law of oil-paper insulation under different harmonic currents, the fusion temperature influence factor T is proposed. f and vibration influence factor σ f The improved calculation model for oil-paper insulation life is expressed as follows:

[0066]

[0067] Among them, ω DP is the cumulative loss rate of the degree of polymerization of the insulation paper; DPt is the degree of aggregation at time t, i.e., λ DP0 is the initial degree of polymerization, λ DPend is the degree of polymerization at the end of life; α σ is the time-stress translation factor; α T is the temperature shift factor; β is the input harmonic current parameter; σ f is the total stress of the winding; R is the gas constant; T is the temperature; E a is the activation energy; T f is the temperature influence factor; ω DP is the cumulative loss rate of the degree of polymerization of the insulation paper; ω * DP Ability to save for insulation paper degradation; is the fitting value of the rate of decrease of polymerization degree under different mechanical stresses; is the aging time for the degree of polymerization to reach a certain state value under different temperatures and stresses; α σ，T is the stress-temperature translation factor; is the lifetime at temperature T.

[0068] The temperature influence factor and vibration influence factor obtained by S2 are used to obtain the oil-paper insulation life value and substitute it into the calculation model. in, is the temperature shift factor under different harmonic currents; is the temperature T under different harmonic currents f The time of a point on the fitting curve; is the stress-temperature translation factor under different harmonic currents; K is the aging time for the degree of polymerization to reach a certain state value under different temperatures and mechanical stresses. DP represents the rate at which the degree of polymerization decreases, Non-reference temperature The time of a point on the fitted curve.

[0069] The specific expression for calculating the life value is:

[0070]

[0071] like Figure 2 The figure shows a two-dimensional refined simulation model of the real converter transformer winding, including the valve side and the grid side. Electromagnetic-thermal-mechanical multi-physics field coupling simulation is carried out to obtain the temperature distribution and stress distribution of the converter transformer under different harmonic currents.

[0072] like Figure 3 The figure shows the winding temperature distribution cloud diagram under rated load. Figure 4 , Figure 5 , Figure 6 and Figure 7 These are the temperature distribution cloud diagrams of the windings under the action of 5% harmonic current, 10% harmonic current, 15% harmonic current and 20% harmonic current at 250Hz. Figure 8 , Fig. 9 , Fig.10 and Fig.11 They are the temperature distribution cloud diagrams of the windings under the action of 5% harmonic current, 10% harmonic current, 15% harmonic current and 20% harmonic current at 650Hz.

[0073] like Fig.12 The following is a cloud diagram showing the stress distribution of the winding under rated load. Fig.13 , Fig.14 , Fig.15 and Fig.16 These are the winding stress distribution cloud diagrams under the action of 5% harmonic current, 10% harmonic current, 15% harmonic current and 20% harmonic current at 250Hz.

[0074] Based on the distribution characteristics of winding temperature and stress under different harmonic currents, the calculation formulas of converter transformer winding temperature and stress under different harmonic currents are obtained through mathematical fitting. Taking the grid-side winding temperature and stress change characteristics as an example, the calculation results of the temperature influence factor and vibration influence factor are as follows:

[0075]

[0076] σ f =9.638×10 6 +1.424β 250Hz 1.104 .

[0077] By bringing the obtained temperature influence factor and vibration influence factor under the influence of harmonic current into the improved calculation model of oil-paper insulation life that integrates temperature influence factor and vibration influence factor, the calculation model of oil-paper insulation life containing harmonic current content and frequency can be obtained. The expression is:

[0078]

[0079] By inputting the harmonic current parameter β, that is, different harmonic current contents and the frequency f corresponding to the harmonic current, the predicted value of the oil-paper insulation life considering the influence of harmonic current on the thermal-mechanical combined stress is obtained.

[0080] Example 2

[0081] The calculation results of insulation life loss under different inlet oil temperatures, different hot spot temperatures and different mechanical stresses under different harmonic currents are shown in Table 1.

[0082] Table 1 Calculation results of insulation life loss under the combined influence of temperature and mechanical stress considering harmonic current

[0083]

[0084] 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 method for calculating the life of oil-paper insulation materials based on the influence of harmonic current, characterized in that: The steps include: S1. Construct an electromagnetic-thermal-mechanical multi-physics field coupling simulation model for the oil-paper insulation system and obtain an oil-paper insulation life calculation model; S2. Obtaining temperature influence factors and vibration influence factors under different harmonic currents based on the simulation model; S3. Input harmonic current parameters and obtain a predicted life value of the oil-paper insulation based on the calculation model.

2. The method for calculating the life of oil-paper insulation material based on the influence of harmonic current according to claim 1 is characterized in that: The oil-paper insulation life calculation model of S1 quantifies the influence of harmonic current content and frequency on the temperature and stress of oil-paper insulation, and integrates temperature influence factor and vibration influence factor to calculate and predict the life of oil-paper insulation under complex harmonic current.

3. The method for calculating the life of oil-paper insulation material based on the influence of harmonic current according to claim 1, characterized in that: The S2 fits the hot spot temperatures of the grid-side and valve-side windings under different harmonic current frequencies in the simulation model to obtain the temperature influence factors and vibration influence factors under different harmonic currents.

4. The method for calculating the life of oil-paper insulation material based on the influence of harmonic current according to claim 3 is characterized in that: The expression of the temperature influence factor under different harmonic currents is: Among them, T f is the hot spot temperature value of the winding under different harmonic current frequencies; T0 is the initial hot spot temperature value of the winding under different harmonic currents; τ is the response time of the hot spot temperature of the winding with the change of harmonic frequency; k f is the temperature variation coefficient of the hot spot of the winding under the action of different harmonic current frequencies; f is the frequency corresponding to the harmonic current.

5. The method for calculating the life of oil-paper insulation material based on the influence of harmonic current according to claim 3 is characterized in that: The expression of the vibration influence factor under different harmonic currents is: Among them, σ f is the total stress of the winding; σ 50Hz is the stress value of the winding at 50Hz; Δσ f is the winding stress value under the action of high-frequency harmonic current; β is the content of different harmonic currents; f is the frequency corresponding to the harmonic current; a f is the influence coefficient of harmonic current of different frequencies on winding stress; b f I is the influence index of different frequency harmonic currents on winding stress; f is the harmonic current; I 50Hz is the harmonic current at 50Hz.

6. The method for calculating the life of oil-paper insulation material based on the influence of harmonic current according to claim 1, characterized in that: The calculation model expression of the oil-paper insulation life of S1 is: Among them, ω DP is the cumulative loss rate of the degree of polymerization of the insulation paper; DPt is the degree of aggregation at time t, i.e., λ DP0 is the initial degree of polymerization, λ DPend is the degree of polymerization at the end of life; α σ is the time-stress translation factor; α T is the temperature shift factor; β is the input harmonic current parameter; σ f is the total stress of the winding; R is the gas constant; T is the temperature; E a is the activation energy; T f is the temperature influence factor; ω DP is the cumulative loss rate of the degree of polymerization of the insulation paper; ω * DP Ability to save for insulation paper degradation; is the fitting value of the rate of decrease of polymerization degree under different mechanical stresses; is the aging time for the degree of polymerization to reach a certain state value under different temperatures and stresses; α σ，T is the stress-temperature translation factor; is the lifetime at temperature T.

7. The method for calculating the life of oil-paper insulation material based on the influence of harmonic current according to claim 6, characterized in that: When the ω DP When it is 0, it means that the insulation paper has not aged. DP When it is 1, it means that the insulation paper is completely degraded.

8. The method for calculating the life of oil-paper insulation materials based on the influence of harmonic current according to claim 6, characterized in that: The oil-paper insulation life value is obtained by combining the calculation model with the temperature influence factor and the vibration influence factor obtained by S2. in, is the temperature shift factor under different harmonic currents; is the temperature T under different harmonic currents f The time of a point on the fitting curve; is the stress-temperature translation factor under different harmonic currents; K is the aging time for the degree of polymerization to reach a certain state value under different temperatures and mechanical stresses. DP represents the rate at which the degree of polymerization decreases, Non-reference temperature The time of a point on the fitted curve.

9. The method for calculating the life of oil-paper insulation materials based on the influence of harmonic current according to claim 1, characterized in that: The simulation model of S1 is based on the refined geometric model of the transformer winding. According to the type and parameters of the transformer, the material properties and boundary conditions are set, and the simulation model is obtained by integrating the electromagnetic-thermal flow-mechanical multi-physical field coupling of the oil-paper insulation system.

10. The method for calculating the life of oil-paper insulation materials based on the influence of harmonic current according to claim 1, characterized in that: The harmonic current parameters of S1 include different harmonic current contents and frequencies corresponding to the harmonic currents.

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