A method for calculating stress and predicting service life of a basin type insulator in service

Abstract

The application discloses a kind of in-service basin type insulator stress calculation and life prediction method.The calculation method includes: first, the structure parameters and operating parameters of in-service basin type insulator are obtained, and the in-service basin type insulator calculation model is constructed;Then the finite element method is used to solve the temperature and stress distribution of in-service basin type insulator;Finally, the stress of in-service insulator during operation is predicted according to the calculated stress to predict its life.The application adopts multi-physical field coupling method, and fully considers the influence of temperature on the conductivity of conductor and shell, as well as the influence on the dielectric constant of basin type insulator, which can accurately and effectively obtain the temperature and stress distribution of in-service basin type insulator, and improve the prediction accuracy of in-service basin type insulator life.

Description

Technical Field

[0001] This invention relates to the electrical field, and in particular to a method for stress calculation and life prediction of in-service basin insulators. Background Technology

[0002] Pot-type insulators are essential insulating components in GIS / GIL systems. Besides their insulating function, they also play a crucial role in supporting and isolating other structures, requiring them to possess sufficient mechanical strength. In actual operation, the busbar is constantly filled with high-voltage insulating gas and is subjected to varying thermal stresses, placing even higher demands on the mechanical strength of the pot-type insulators. Under external stress loads, significant internal stress concentration may occur within the pot-type insulator, leading to material aging. Areas of stress concentration are weak points in the pot-type insulator, both during operation and reliability testing. Discharge accidents in GIS caused by pot-type insulators often result in cracking of the insulators, leading to more serious consequences, all related to stress concentration. Therefore, it is necessary to understand the stress distribution of pot-type insulators.

[0003] Molecular-level changes in solid insulating materials under gas pressure and thermal stress are one of the main causes of insulator aging. As GIS / GIL equipment ages, pot-type insulators gradually age and deteriorate, requiring timely maintenance or replacement. However, blindly replacing equipment leads to economic waste. Therefore, understanding the stress field distribution of in-service insulators and predicting their expected lifespan is crucial. To avoid unnecessary equipment replacement and prevent power accidents caused by insulation failure, predicting the lifespan of in-service insulators has always been a closely watched and urgent issue for power grid operators. Published patents and literature primarily focus on hydrostatic testing at the factory, with little analysis of in-service insulator stress. Traditional methods use analytical methods to calculate the temperature field of the insulator and the service life at a specific voltage or temperature value to predict its lifespan, but the results are often inaccurate. Therefore, an accurate and reliable method for calculating the stress and predicting the lifespan of pot-type insulators is urgently needed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for calculating the stress and predicting the life of in-service basin insulators. This method aims to accurately calculate the stress of in-service basin insulators and subsequently predict their lifespan, preventing power accidents caused by insulator failure and ensuring the safe operation of equipment. This invention is based on a multi-physics coupling method involving electromagnetic, thermal, fluid, and force fields. By calculating the stress distribution of in-service insulators, it predicts the lifespan of basin insulators.

[0005] The technical solution adopted in this invention is as follows:

[0006] A method for stress calculation and life prediction of in-service basin insulators includes the following steps:

[0007] Step 1: Obtain the structural and operational parameters of the in-service basin insulator, including the insulator's geometric dimensions, material properties, operating current, voltage, and ambient temperature. Step 2: Construct a calculation model of the in-service basin insulator. The geometric model includes the conductor, basin insulator, shell, and insulating gas. The electromagnetic-thermal-fluid-force multi-physics coupling method is used to simulate and calculate the stress of the basin insulator, including (1) realizing bidirectional coupling of electromagnetic-thermal-fluid by considering the influence of temperature on the conductivity of the conductor and shell, and the influence of temperature on the dielectric constant of the basin insulator; (2) realizing thermal-force coupling by generating thermal strain through the thermal expansion and contraction effect of the material. Step 3: Statistically calculate the ambient temperature and the probability of occurrence throughout the year, and calculate the stress (τ) of the basin insulator at the corresponding ambient temperature according to Step 2. i Step 4: Calculate the lifespan of the basin insulator under different stresses through aging tests; based on the basin insulator stress (τ) obtained in Step 3... i Calculate the expected lifespan of the insulator.

[0008] The heat sources in step 2 include the electromagnetic losses of the conductor and the outer shell, and the dielectric losses of the basin insulator. The dielectric losses are calculated as follows:

[0009] Q d =∫E 2 ωεtanδdV

[0010] Where E is the electric field strength, ω is the phase angle, ε is the dielectric constant of the insulator, and Q is the electric field strength. d denoted as tanδ, where tanδ is the dielectric heating power and tanδ is the dielectric loss tangent.

[0011] In step 2, the mechanical boundary conditions of the basin insulator are as follows: the concave and convex surfaces of the insulator are subjected to pressure loads from the insulating gas, the contact surface between the insulator and the shell is a fixed constraint, and the remaining surfaces are free boundaries.

[0012] The annual ambient temperature and the probability of occurrence in step 3 are determined according to the following rules: Let the highest ambient temperature of the year be T. max Starting from the highest temperature, the ambient temperature is divided into several intervals with a tolerance of -5, such as [T max -5,T max ), [T max -10,T max -5), the probability of each temperature interval occurring is P. i The average temperature over the interval, such as (T) max -2.5),(T max -7.5) was used as the representative temperature for stress calculation in this range.

[0013] In step 4, the formula for calculating the expected life of the in-service basin insulator is as follows:

[0014]

[0015] Where L is the expected lifespan of the insulator; L i For an insulator material under a certain stress (τ) i Lifespan under the influence of ); L p This refers to the service life of the insulator.

[0016] The beneficial effects of this invention are: by employing a multi-physics field coupling method involving electromagnetic, thermal, fluid, and force to simulate and calculate the stress of in-service basin-type insulators, the temperature and stress field distributions of in-service basin-type insulators can be accurately calculated, achieving strong coupling of electromagnetic, thermal, fluid, and force fields. Furthermore, by predicting the lifespan of in-service basin-type insulators, this can effectively prevent power accidents caused by insulator insulation failure and ensure the safe operation of equipment.

[0017] Based on the above technical solution, the present invention can be further improved as follows:

[0018] Further: In step 2, the axial length of the geometric model of the basin insulator should be greater than 1.5 times the diameter of the basin insulator.

[0019] Further: In step 2, after calculating the temperature field distribution of the basin insulator, it is verified against the actual measured temperature of the insulator. If the difference between the simulation data and the actual measured data is less than 1%, the calculation model is considered accurate and reliable. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the steps of the method for stress calculation and life prediction of basin-type insulators provided in this embodiment of the invention.

[0021] Figure 2 This is a schematic diagram of the geometric model of the basin-type insulator provided in an embodiment of the present invention.

[0022] Wherein: 1-shell; 2-conductor; 3-pot-type insulator.

[0023] Figure 3 This is a schematic diagram of the electromagnetic-thermal-fluid-force multiphysics coupling of the basin-type insulator provided in an embodiment of the present invention.

[0024] Figure 4 This is a schematic diagram of the mechanical boundary of the basin-type insulator provided in an embodiment of the present invention. Detailed Implementation

[0025] To make the application, technical solution, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the following embodiments. The embodiments described herein are merely illustrative and are not intended to limit the present invention. The application principle of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0026] like Figure 1 As shown, the method for stress calculation and life prediction of in-service basin insulators according to an embodiment of the present invention includes the following steps:

[0027] Step 1: Obtain the structural and operational parameters of the in-service basin insulator, including (1) measuring the geometric dimensions and material properties of components such as insulators, conductors and shells, including electrical conductivity, thermal conductivity, coefficient of thermal expansion, etc.; (2) determining the operating current, voltage and ambient temperature of the equipment.

[0028] Step 2: Based on the structural and operational parameters of the pot-type insulator obtained in Step 1, construct a calculation model for the in-service pot-type insulator. For example... Figure 2 As shown, the geometric model includes the conductor, basin insulator, shell, insulating gas, etc., ignoring small components such as threads. Using numerical software, according to... Figure 3 The simulation calculation of the stress of the basin insulator is carried out by multi-physics coupling of electromagnetism, heat, fluid and force. It includes (1) realizing the bidirectional coupling of electromagnetism, heat and fluid by considering the influence of temperature on the conductivity of conductor and shell, and the influence of temperature on the dielectric constant of basin insulator; (2) realizing the coupling of heat and force by generating thermal strain through the thermal expansion and contraction effect of materials. The calculation process includes: first, constructing a computational geometric model, then performing mesh generation and mesh independence verification; finally, comparing the calculation results with actual measurement data to verify the accuracy of the calculation model.

[0029] In this step, the heat sources include the electromagnetic losses of the conductor and the outer shell, and the dielectric losses of the basin insulator. To solve for the dielectric losses, an electrostatic field calculation of the basin insulator is required to obtain its field strength distribution.

[0030] Step 3: Calculate the annual ambient temperature and its probability of occurrence, and then calculate the stress (τ) of the basin insulator at the corresponding ambient temperature as in Step 2. iThe annual ambient temperature and its probability of occurrence are determined according to the following rules: If the highest ambient temperature in a certain region is 315K and the lowest is 270K, then the ambient temperature is divided into several intervals with a tolerance of -5, starting from the highest temperature, such as [315, 310), [310, 305), ..., [275, 270). If the probability of the annual temperature occurring in the interval [310, 305) is 0.04, then the average temperature of the interval, 307.5K, is taken as the representative temperature of that interval for stress calculation. The probability of 307.5K occurring in the annual temperature range is considered to be 0.04. The same logic applies to other intervals.

[0031] Step 4: Calculate the stress (τ) of the basin insulator at different temperatures based on steps 2 and 3. i Aging tests were conducted on the materials of basin-type insulators to obtain their properties under different stresses (τ). i The insulator's lifespan under the given conditions is calculated, along with its expected lifespan. The formula for calculating the expected lifespan is:

[0032]

[0033] Where L is the expected lifespan of the insulator; L i For an insulator material under a certain stress (τ) i Lifespan under the influence of ); L p P represents the service life of the insulator. i For a certain stress (τ) i The probability of ) occurring.

[0034] For example: Aging tests show that the lifespan of a basin-type insulator under stresses of 1.0 MPa, 5.0 MPa, 10.0 MPa, and 15.0 MPa are 100 years, 40 years, 15 years, and 8 years, respectively. The annual probabilities of these stresses being 1.0 MPa, 5.0 MPa, 10.0 MPa, and 15.0 MPa are 0.5, 0.3, 0.15, and 0.05, respectively. The insulator has been in use for 10 years. Therefore, the remaining lifespan L of the insulator is:

[0035] 100×0.5+40×0.3+15×0.15+8×0.05-10=54.65 years.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications or additions made within the spirit and principles of the invention are subject to further clarification.

[0037] Any modifications, equivalent substitutions, and improvements made within this scope should be included within the protection scope of this invention.

Claims

1. A method for stress calculation and life prediction of in-service basin insulators, characterized in that, Includes the following steps: Step 1: Obtain the structural and operational parameters of the in-service basin insulators; Step 2: Construct a calculation model of the in-service basin insulator, and use the electromagnetic-thermal-fluid-force multiphysics coupling method to simulate and calculate the stress of the basin insulator to obtain the stress distribution of the basin insulator; This includes: 1) Achieving bidirectional electromagnetic-thermal-current coupling by considering the effects of temperature on the conductivity of the conductor and the outer shell, as well as the effects of temperature on the dielectric constant of the basin insulator; the effects of temperature on the conductivity of the conductor and the outer shell are as follows: Where σ0 is the material in T conductivity at 0 k The temperature coefficient of resistivity is measured experimentally. The thermal stress is calculated as follows: in, α th , T and T ref These are the coefficient of thermal expansion, material temperature, and initial temperature of the material, respectively. When performing electromagnetic-thermal-fluid-mechanical coupling simulation calculations, the heat sources in the model include not only the electromagnetic losses of the conductor and the shell, but also the dielectric losses of the basin insulator, as calculated in the following formula: in, E For field strength, ω The phase angle, ɛ The dielectric constant of the insulator is . Q d The heating power of the medium is tan. δ This is the tangent of the dielectric loss angle; The mechanical boundary conditions for a pot-type insulator are: the concave and convex surfaces of the insulator are subjected to pressure loads from the insulating gas, the contact surface between the insulator and the shell is a fixed constraint, and the other surfaces are free boundaries. 2) Thermo-mechanical coupling is achieved by generating thermal strain through the thermal expansion and contraction of materials; Step 3: Calculate the probability of the annual ambient temperature and, following Step 2, calculate the stress of the basin insulator at the corresponding ambient temperature. τ i The probability of the annual ambient temperature being the highest is determined according to the following rule: Let the highest ambient temperature of the year be... T max Starting from the highest temperature, the ambient temperature is divided into several intervals with a tolerance of -5. The probability of each interval's temperature occurring is... P i The average temperature of the interval is used as the representative temperature of that interval for stress analysis. τ i calculate; Step 4: Calculate the lifespan of the basin-type insulator under different stresses through aging tests; based on the basin-type insulator stress obtained in Step 3... τ i Calculate the expected life of the insulator. L Calculate as follows: in, L This refers to the expected lifespan of the insulator. L i For insulator material under a certain stress τ i Lifespan under action; L p This refers to the service life of the insulator.

2. The method for stress calculation and life prediction of in-service basin insulators as described in claim 1, characterized in that, In step 1, the structural parameters of the basin-type insulator include the insulator's geometric dimensions and material properties; the operating parameters include operating current, voltage, and ambient temperature.

3. The method for stress calculation and life prediction of in-service basin insulators as described in claim 1, characterized in that, The geometric model of a basin insulator includes a conductor, a basin insulator, a shell, and an insulating gas, and the axial length of the insulator geometric model is greater than 1.5 times the diameter of the insulator.

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