Method for monitoring spalling possibility of porcelain insulator

Abstract

The invention relates to a method for monitoring the spalling possibility of a porcelain insulator, which comprises the following steps of: establishing a porcelain insulator sleeve 1: 1 three-dimensional model by using finite element analysis software, applying pre-tightening force to two ends of the porcelain insulator sleeve, inputting performance parameters of a porcelain insulator sleeve wiring terminal, the porcelain insulator, cementing cement, an iron piece and an aluminum pad, setting boundary conditions, and calculating the spalling possibility of the porcelain insulator. Based on a force-temperature-structure coupling field theory, performing simulation calculation of the maximum stress to obtain the maximum stress of the porcelain insulator with different temperature fields and pretightening forces, and fitting data to obtain an empirical formula; substituting the tension strength into an empirical formula to obtain a critical value of the maximum pre-tightening force of the porcelain insulator sleeve assembly; the porcelain insulator sleeve is provided with a stress sensor and a temperature sensor, and actual stress and real-time temperature are collected. The beneficial effects of the invention are that whether the porcelain insulator is likely to be broken and whether the porcelain insulator needs to be checked by people can be known by comparing the stress measured by the stress sensor with the tensile strength, the processed data volume is small, and the health condition of the porcelain insulator can be rapidly obtained.

Description

Technical Field

[0001] The invention relates to a quality monitoring technology for the use status of a porcelain insulator of a high-voltage switch cabinet, and relates to monitoring whether the porcelain insulator has expansion and cracking. Background Art

[0002] The 10kV switchgear is a high-voltage switchgear used in power systems. It plays multiple roles in power systems, including receiving, distributing, controlling, protecting, switching, communicating, measuring, monitoring, isolating, and grounding. It is an important part of power system operation.

[0003] Porcelain insulators play a vital role in 10kV switchgear. Their main functions are as follows: 1. Supporting wires and cables: Insulators are used to support and fix wires and cables, ensuring that they remain in the correct position, withstand mechanical stress, and prevent damage due to mechanical vibration.

[0004] 2. Electrical insulation: Insulators provide electrical insulation between electrodes, preventing current from flowing directly through air or other media with weaker insulation capabilities. This ensures safe isolation between high-voltage components and ground or low-voltage components, preventing electrical faults and arc faults.

[0005] 3. Prevent corona discharge: In high voltage applications, insulators help reduce the phenomenon of corona discharge, which is a discharge of ionized gas that produces light and sound on the surface of the insulator, which can cause insulator damage over time.

[0006] 4. Prevent flashover: Insulators are also used to prevent flashover, which is when the electric field strength is high enough, the gas on the surface of the insulator or near it is ionized and an arc discharge is formed. Flashover can not only cause damage to the equipment, but also cause fire and explosion.

[0007] Therefore, in 10kV switchgear, the performance of insulators is directly related to the reliability and safety of the system, and their selection, installation and maintenance are very important.

[0008] At present, all 110kV substations are unmanned substations. Maintenance personnel can only inspect the equipment in accordance with the power outage plan. Usually, the equipment in the switch cabinet, including the insulators, has only a small observation window, and the overall status of the equipment cannot be seen. It is impossible to timely discover the quality of the porcelain insulating bushings in the switch cabinet, let alone the internal stress conditions of the porcelain insulating bushings, and the quality of the porcelain insulators cannot be monitored.

[0009] At present, the inspection of porcelain insulator bushings mainly relies on visual inspection by people. At present, the research on the failure of insulator bushings focuses on the failure analysis after the insulator is broken. Secondly, the current online inspection is mainly through placing temperature wax on the wiring terminal on the upper part of the porcelain insulator bushing. The three colors of yellow, green and red temperature wax represent the temperature of the insulator as 60℃, 70℃ and 80℃ respectively. Another detection method is to measure the temperature of the wiring terminal on the top of the porcelain insulator bushing through infrared temperature measurement. The above two methods cannot monitor the temperature of the porcelain insulator in real time. At the same time, since the end of the porcelain insulator is far away from the heat-prone part, the temperature of the upper end is rarely studied due to the stress concentration or breakage of the insulator caused by the preload. Summary of the invention

[0010] The purpose of the invention is to provide a method for monitoring whether a porcelain insulator has expansion cracks.

[0011] The technical solution of the present invention is: a method for monitoring the possibility of expansion and cracking of porcelain insulators, (1) using finite element analysis software to establish a 1:1 three-dimensional model of a porcelain insulator bushing, and then applying a preload force to both ends of the porcelain insulator bushing according to the actual installation situation, inputting the performance parameters of the porcelain insulator bushing terminal, porcelain insulator, cement, iron parts, and aluminum pads, setting boundary conditions, and based on the force-temperature-structure coupling field theory, performing simulation calculations on the maximum stress generated on the porcelain insulator under different temperature fields and different preload forces, obtaining the maximum stress borne by the porcelain insulator under different temperature fields and different preload forces, fitting the data, and obtaining an empirical formula; (2) Substituting the tensile strength that the porcelain insulator can withstand into the empirical formula, the critical value of the maximum preload that the porcelain insulator bushing assembly with different strengths can withstand is obtained; (3) According to the structure of the porcelain insulator bushing, stress and temperature sensors are installed in the gap between the aluminum pad and the porcelain insulator to collect the actual stress on the porcelain insulator and the real-time temperature of the porcelain insulator.

[0012] (4) When the equipment generates heat, the temperature and stress sensors immediately collect the temperature and stress of the porcelain insulator. If the preload force is fixed and the temperature of the insulator is constant, when the maximum stress on the insulator is greater than the design value of the tensile strength of the porcelain insulator, the porcelain insulator will break. Therefore, when the stress measured by the stress sensor is lower than the design value of the tensile strength by a certain range, an alarm is issued to remind the operation and maintenance personnel to check and verify the appearance quality of the porcelain insulator and take measures in advance to avoid the porcelain insulator from breaking.

[0013] The fitting empirical formula is: Where p is the preload force at both ends of the porcelain insulator bushing assembly, is the maximum stress that the porcelain insulator bushing bears at 50°C, is the maximum stress that the porcelain insulator bushing bears at 60°C, It is the maximum stress that the porcelain insulator bushing can withstand at 70℃.

[0014] The beneficial effects of the present invention are as follows: it is possible to know whether the applied preload is within the safety range of the porcelain insulator, and it is also possible to monitor in real time whether the temperature of the insulator is within the safety range. At the same time, it is possible to evaluate whether the insulator can be broken under the simultaneous action of the preload and temperature, and predict the life of the porcelain insulator. Because the preload of the insulator porcelain sleeve assembly is known, it is known that when the insulator temperature reaches a certain temperature, the maximum stress to which the insulator is subjected is known. If the maximum stress is greater than the tensile strength of a certain porcelain insulator, the porcelain insulator will break. By comparing the stress measured by the stress sensor with the tensile strength, it is possible to know whether the porcelain insulator is likely to break and whether someone needs to be sent for inspection. The amount of data to be processed is small, which is convenient for quickly and in real time to obtain the health status of the porcelain insulator, and avoid uncontrollable power grid accidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a structural diagram of the porcelain insulator bushing assembly; Figure 2 It is the mesh division diagram of the porcelain insulator bushing assembly; Figure 3 This is the simulation result diagram of the maximum stress on the porcelain insulator when the temperature is 50℃ and the preload is 50 N·m and 220 N·m; Figure 4 This is the simulation result diagram of the maximum stress on the porcelain insulator when the temperature is 60℃ and the preload is 50 N·m and 220 N·m; Figure 5 This is the simulation result diagram of the maximum stress on the porcelain insulator when the temperature is 70℃ and the preload is 50 N·m and 220 N·m; Figure 6 It is the fitting function curve of preload force and maximum stress when the temperature is 50℃; Figure 7 It is the fitting function curve of preload force and maximum stress when the temperature is 60℃; Figure 8 It is the fitting function curve of preload force and maximum stress when the temperature is 70℃; DETAILED DESCRIPTION

[0016] The steps of the invention scheme are: 1. First, use SolidWorks to establish a 1:1 three-dimensional model of the porcelain insulator bushing. Then, according to the actual installation situation, apply preload force at both ends of the porcelain insulator bushing, input the performance parameters of the porcelain insulator bushing terminal, porcelain insulator, cement, iron parts, and aluminum pads, set boundary conditions, and based on the force-temperature-structure coupling field theory, perform simulation calculations on the maximum stress generated on the porcelain insulator under different temperature fields and different preload forces. The maximum stress borne by the porcelain insulator under different temperature fields and different preload forces is obtained, and the data is fitted to obtain the empirical formula; 2. Substitute the tensile strength that the porcelain insulator can withstand into the empirical formula to obtain the critical value of the maximum preload that the porcelain insulator bushing assembly of different strengths can withstand. When replacing or repairing porcelain insulators, a preload lower than the critical value can be applied to the bolts at the connection between the terminal and the terminal block.

[0017] 3. According to the structure of the porcelain insulator bushing, stress and temperature sensors are installed in the gap between the aluminum pad and the porcelain insulator assembly to collect the actual stress on the porcelain insulator and the real-time temperature of the porcelain insulator.

[0018] 4. When the equipment fails or the bolt tightening force is insufficient, gaps will appear at the connection between the terminal and the terminal board, and poor contact will occur between the conductors. Therefore, different preload forces under different temperature conditions will cause the porcelain insulator to bear different maximum stresses. When the equipment is heated, the temperature and stress sensors will collect the temperature and stress of the porcelain insulator as soon as possible. At the same time, insulators of different qualities will have different tension strength design values. If the preload force is fixed and the temperature of the insulator is constant, when the maximum stress on the insulator is greater than the tension strength of the porcelain insulator, the porcelain insulator will break. Therefore, when the stress measured by the stress sensor is lower than a certain range of the tension strength design value, an alarm will be issued to remind the operation and maintenance personnel to check and verify the appearance quality of the porcelain insulator and take measures in advance to avoid the expansion of the accident.

[0019] Table 1 Performance parameters of a porcelain insulator bushing assembly material Table 2 Maximum stress values ​​corresponding to different temperatures and different preloads Figure 3 , 4, 5 are the simulation result diagrams of the maximum stress on the selected porcelain insulator. Multiple preload simulations were performed at 50 degrees, 60 degrees, and 70 degrees, which are 50 N·m, 60 N·m, 70 N·m, 80 N·m, 100 N·m, 120 N·m, 140N·m, 160 N·m, 170 N·m, 180 N·m, 190 N·m, 200 N·m, and 220 N·m respectively. The attached diagrams show the simulation result diagrams of the maximum stress of 50 N·m and 220 N·m.

[0020] Figure 6 , Figure 7 , Figure 8 It is the fitting function curve of preload and maximum stress at 50 degrees, 60 degrees and 70 degrees. When the preload is applied to the porcelain insulating bushing assembly, the fitting formula of preload and maximum stress borne by the porcelain insulator is: (1) (2) (3) Where p is the preload force at both ends of the porcelain insulator bushing assembly, is the maximum stress that the porcelain insulator bushing bears at 50°C, is the maximum stress that the porcelain insulator bushing bears at 60°C, It is the maximum stress that the porcelain insulator bushing can withstand at 70℃.

[0021] Example 1: In the operation and maintenance phase, in the later operation, if the temperature sensor detects that the temperature of the porcelain insulator is 50°C, and the preload force is 50 N·m during installation, then according to formula (1), the maximum stress received by the porcelain insulator is 122.7 MPa. Assuming that the tensile strength of the porcelain insulator is 200 MPa, the maximum stress received by the porcelain insulator is less than the tensile strength of the porcelain insulator, 200 MPa. At this time, the insulator is safe and does not need to be processed.

[0022] Example 2: If the temperature sensor detects that the temperature of the porcelain insulator is 70°C, and the preload force is 50 N·m during installation, then according to formula (3), the maximum stress received by the porcelain insulator is 203.4 MPa. Assuming that the tensile strength of the porcelain insulator is 200 MPa, the maximum stress received by the porcelain insulator is greater than the tensile strength of the porcelain insulator, which is 200 MPa. If the stress is greater than the tensile strength of the porcelain insulator, the porcelain insulator will break. Therefore, the operation and maintenance personnel should be asked to check and verify, and the focus should be on strengthening supervision and taking measures to avoid the expansion of the accident.

Claims

1. A method for monitoring the possibility of expansion and cracking of porcelain insulators, characterized in that: (1) Use finite element analysis software to establish a 1:1 three-dimensional model of the porcelain insulator bushing. Then, according to the actual installation situation, apply preload force at both ends of the porcelain insulator bushing, input the performance parameters of the porcelain insulator bushing terminal, porcelain insulator, cement, iron parts, and aluminum pads, set boundary conditions, and based on the force-temperature-structure coupling field theory, perform simulation calculations on the maximum stress generated on the porcelain insulator under different temperature fields and different preload forces. The maximum stress borne by the porcelain insulator under different temperature fields and different preload forces is obtained, and the data is fitted to obtain an empirical formula; (2) Substituting the tensile strength that the porcelain insulator can withstand into the empirical formula, the critical value of the maximum preload that the porcelain insulator bushing assembly with different strengths can withstand is obtained; (3) According to the structure of the porcelain insulator bushing, stress and temperature sensors are installed in the gap between the aluminum pad and the porcelain insulator to collect the actual stress and real-time temperature of the porcelain insulator; (4) When the equipment generates heat, the temperature and stress sensors immediately collect the temperature and stress of the porcelain insulator. If the preload force is fixed and the temperature of the insulator is constant, when the maximum stress on the insulator is greater than the design value of the tensile strength of the porcelain insulator, the porcelain insulator will break. Therefore, when the stress measured by the stress sensor is lower than the design value of the tensile strength by a certain range, an alarm is issued to remind the operation and maintenance personnel to check and verify the appearance quality of the porcelain insulator and take measures in advance to avoid the porcelain insulator from breaking.

2. A method for monitoring the possibility of expansion and cracking of porcelain insulators according to claim 1, characterized in that: The fitting empirical formula is: Where p is the preload force at both ends of the porcelain insulator bushing assembly, is the maximum stress that the porcelain insulator bushing bears at 50°C, is the maximum stress that the porcelain insulator bushing bears at 60°C, It is the maximum stress that the porcelain insulator bushing can withstand at 70℃.

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