Aging Of Composite Insulators Research Articles

Study on the Aging Characteristics of a ±500 kV Composite Dead-End Insulator in Longtime Service.

Composite insulators have been widely used in power grids due to their excellent electrical-external-insulation performance. Long-term operation at high voltage levels accelerates the aging of composite insulators; however, there is a scarcity of research on aged composite insulators operating at 500 kV for over ten years. In this paper, the mechanical, electrical, and microscopic properties were tested on different sheds along a 500 kV composite insulator that had been running for 18 years. Additionally, the results were compared with a new insulator and the standards for live insulator operation. The results showed that the aging of the high-voltage end of composite insulators was the most serious. The results of the physical properties test indicated that the insulator's hardness was compliant but its tensile strength and break elongation did not meet standards. Under wet conditions, the pollution flashover voltage decreases by about 50% compared to the new insulator. Combined with the microscopic test results, the shed skeleton structure could be damaged and the filler might be lost during the aging process of polydimethylsiloxane (PDMS). The hardness of the insulator would increase by the precipitation of inorganic silicon; however, inorganic silicon might destroy the hydrophobicity and other properties of insulator sheds. These results can provide theoretical references for insulator life prediction and operation protection.

Reproduction and Analysis of Decay-Like Aging Development Induced by Interfacial Discharge in Composite Insulators

In the last decade, the decay-like aging phenomena of fiber reinforced plastic (FRP) core rods in composite insulators appeared frequently, and have significantly affected the safety of power transmission lines. However, the mechanism of its occurrence and development is still unclear. In this work, a method based on rod-housing interfacial discharge is proposed to artificially reproduce the occurrence and development of decay-like aging in FRP core rods under laboratory conditions. The aging process is explored under a high-humidity environment, where high-acidity and high-temperature conditions are also provided by interfacial discharge. The micro- and macro-scopic structures, physicochemical properties and leakage currents of FRP samples are characterized during a 1000-hour aging process. The laboratory aged samples resemble the decay-like phenomena in on-site insulators, indicating the effectiveness of this method. Experimental results show that interfacial discharge can trigger the decomposition of epoxy resin in FRP core rods, leading to exposure of glass fibers. Electrical erosion slows down as aging time increases, and the erosion rate is positively related to the porosity of core rods. Further discussion indicates that erosion is impeded by glass fibers in the surface aging layer due to its high thermal and chemical stability, and a three-stage erosion process model is proposed. Finally, a semi-empirical model is proposed to describe this aging process, in which the influence of core rod porosity is taken into account. This work provides an effective laboratorial method to reproduce the decay-like aging of composite insulators, and reveals its erosion process and the underlying mechanism.

Optimized Unilateral Magnetic Resonance Sensor with Constant Gradient and Its Applications in Composite Insulators

In this study, an optimized unilateral magnetic resonance sensor with a three-magnet array is presented for assessing the aging of composite insulators in power grids. The sensor’s optimization involved enhancing the static magnetic field strength and the homogeneity of the RF field while maintaining a constant gradient in the direction of the vertical sensor surface and maximizing homogeneity in the horizontal direction. The center layer of the target area was positioned 4 mm from the coil’s upper surface, resulting in a magnetic field strength of 139.74 mT at the center point of the area, with a gradient of 2.318 T/m and a corresponding hydrogen atomic nuclear magnetic resonance frequency of 5.95 MHz. The magnetic field uniformity over a 10 mm × 10 mm range on the plane was 0.75%. The sensor measured 120 mm × 130.5 mm × 76 mm and weighed 7.5 kg. Employing the optimized sensor, magnetic resonance assessment experiments were conducted on composite insulator samples utilizing the CPMG (Carr–Purcell–Meiboom–Gill) pulse sequence. The T2 distribution provided visualizations of the T2 decay in insulator samples with different degrees of aging.

Evaluation Method for the UV Aging State of Composite Insulators Based on Hyperspectral Characteristic

Strong ultraviolet (UV) radiation is one of the main factors that lead to the aging of composite insulators of transmission lines in high altitude areas, which has brought security risks to the operation of power systems. The aging status information obtained by traditional insulation surface aging detection methods is indirect and limited, or time-consuming and labor-intensive. In this paper, a non-contact nondestructive testing evaluation method based on hyperspectral technology is proposed to quickly detect the UV aging state of composite insulator surface. Firstly, the hyperspectral imaging platform is used to image a number of continuous bands on the insulator surface. Combining the aging calibration data, a locally reserved projection-convolutional neural network (LPP-CNN) model is established to to extract the characteristic bands of aging surface and provide a way to accurately evaluate surface UV aging degree of insulators. The model has a high resolution of aging degree, which provides a new idea and theoretical basis for realizing non-contact non-destructive online detection of surface aging under ultraviolet light.

Effect of CeO2 on UV aging of composite insulators prepared by template‐spraying method

AbstractWhen the silicone rubber composite insulator is exposed outdoors for a long time, it will be affected by high‐temperature ultraviolet environments. In order to ensure the operation of silicone rubber composite insulators, a super‐hydrophobic composite insulator with antiaging characteristics was prepared by mixing cerium dioxide (CeO2) with silicone rubber and spraying CeO2 on the surface of silicone rubber. This article studied the aging characteristics of the base and surface of silicone rubber composite insulator by CeO2 in ultraviolet environment. The properties of silicone rubber composite insulators before and after aging were tested by mechanics, contact Angle, rolling Angle, bounce, and icing experiments. The aging mechanism of silicone rubber was analyzed by Fourier transform infrared spectroscopy and search engine marketing. This study prepared composite insulators with excellent mechanical, hydrophobic, and antiicing properties. The aging resistance of silicone rubber composite insulators is improved by adding CeO2 into silicone rubber matrix and spraying CeO2 on the surface, which also ensure the use of composite insulators in high‐temperature ultraviolet environment.

Calibrating Method of Aging Degree of Silicone Rubber for Composite Insulator in the Power Grid Operation

There are many factors that cause the aging of composite insulators, and the aging of the insulators will cause greater harm to the operation of the power grid and the quality of power consumption of users. This paper analyzes the mechanism of insulator aging caused by different factors, and uses optical microscope to study the microscopic morphology of insulators to determine the degree of insulator aging. The board-to-board partial discharge experimental device is used to further verify the accuracy of the calibration, and the partial discharge voltage is used as the characteristic quantity to judge the degree of aging. The results show that the partial discharge voltage changes with the aging degree of composite insulators, and presents a certain rule. This research provides a favorable reference for the aging calibration method of composite insulators.

Testing Method for Composite Insulators Interface Based on Nonlinear Ultrasonic

The interface is the weakness of composite insulators. As the interface bonding fails, the uniform distribution of electric field will be affected, which accelerates the aging of composite insulators and affects the safe operation of transmission lines. Because of the stress between the sheath and the rod, the air gap at the interface is generally less than 10 ţm and there is extrusion contact in some areas. Therefore, conventional nondestructive testing technology based on refraction and reflection principle cannot effectively identify the faulty insulators in the initial stage of bonding failure. Based on the constitutive model of the interface of composite insulators, the friction force of the interface after bonding failure introduces more nonlinearity in mechanical properties than hydrogen bond under well bonding condition. The numerical results show that under the influence of the nonlinear constitutive relation, the higher harmonic components in the spectrum will increase significantly. The experimental results of plate and insulator samples confirm the validity of numerical calculation. Based on the normalized nonlinearity coefficient, the interface state of composite insulators at the initial stage of bonding failure can be effectively identified.

Evaluation of aging process of silicone rubber composite insulators with photothermal radiometry

Silicone rubber composite insulators are increasingly used in high-voltage power transmission and distribution grids. However, the aging of composite insulators is a serious safety issue of power systems. Understanding the aging mechanism of composite insulators is therefore of great importance. In this paper, a 3D photothermal radiometry (PTR) is employed to determine the thermal and absorption properties of silicone rubber composite insulators aged in natural environment. A 3D PTR model was developed to extract precisely the thermal diffusivity and absorption coefficients of the composite insulators. In this PTR model both surface and bulk absorptions were accounted for by taking into consideration the fact that a surface absorption of aged composite insulators would be created and changed by surface crazing, chalking, and contamination during aging process. By multi-parameter fitting the measured modulation frequency dependences of PTR amplitude and phase to this 3D PTR model, the thermal diffusivity, surface absorption, as well as bulk absorption coefficient of the composite insulators were extracted simultaneously. The comparisons between the thermal diffusivities, absorption characteristics of fresh and aged composite insulators indicated that aging caused significant decrease of thermal diffusivity and substantial increase of absorption of composite insulators, and the thermal diffusivity and absorption changes were aging level dependent. These experimental results demonstrated that both thermal and absorption properties may be useful parameters for evaluating the aging level and understanding the aging mechanism of silicone rubber composite insulators.

Thermo-oxidative aging analysis of HTV silicone rubber used for outdoor insulation

In China high temperature vulcanized (HTV) silicone rubber has been applied to manufacture the sheds and sheath of composite insulators for decades. Being exposed to environmental stressors including sunlight, UV radiation, oxidization, electrical stress and moisture throughout the whole operation period, various aging phenomena could be observed, among which color fading and hardening are two important indexes which may be directly related to the performance of composite insulators. According to polymer aging theory, thermo-oxidative could be the main aging reaction leading to the hardening of HTV silicone rubber and in this paper, Thermogravimetric Analysis (TGA) combined with Differential Scanning Calorimetry (DSC), Infrared Spectroscopy (IR) and Mass Spectroscopy (MS) are applied to study the degradation and decomposition process of HTV silicone rubber in air (oxidizing atmosphere) and nitrogen (inert atmosphere) respectively. 18 composite insulator specimens have been collected and their color fading degree, hardness, crosslink density as well as thermal performance have been measured and calculated. A correlation analysis showed that physical crosslink density had a strong positive relation with hardness of specimens whereas chemical crosslink density showed negative relations with hardness. It is concluded that TGA is an effective method to simulate and study the thermo-oxidative aging process of HTV silicone rubber and the measurement results of crosslink density shows that decomposition and over crosslinking reactions have taken place simultaneously in HTV silicone rubber and led to the aging of composite insulators together.

Novel capacitive proximity sensors for assessing the aging of composite insulators

A novel electrode structure consisting of a variable spacing interdigital electrode (VS-IDE) was proposed for assessing of the aging of silicone rubber sheds with variable thickness. A series of numerical simulations and experiments have been carried out to investigate the influences of finger number, unit width, and metallization ratio on the signal strength and penetration depth of sensors with a traditional interdigital electrode structure. According to the relationship between the penetration depth and the unit width, the width of each finger that composed the VS-IDE structure sensor was optimized individually to confine the electric field line within the sheds under test. Experimental results showed that compared to the other sensors, the optimal sensor exhibited high amplitude, high sensitivity, and excellent stability against the effects of environmental humidity. The developed capacitive proximity sensors have been used for assessing of the aging of silicone rubber sheds in composite insulators, and the feasibility of assessing insulation degradation by quantitative capacitive techniques is demonstrated.

Simulation and Analysis for Composite Casing Aging Trend Based on ANSYS

According to the aging characteristics of composite casing, we have established the composite bushing model of different radius with the ANSYS finite element analysis software, and analyzed the defects in different forms and the action under different mechanical stress. At the same time, we have studied the aging trend of composite casing and compared with the similarities and differences between the aging of composite insulators. The result showed that under the mechanical stress the bigger than the smaller aging deformation was more serious, and the defect forms had no obvious influence on the development of aging. Thus, the composite casing artificial accelerated aging test should increase the role of mechanical force factor, while the composite insulator aging research methods and conclusions should also increase the qualification when applied to silicone rubber composite casing.

The FTIR Analysis of Field Aged Composite Insulators

With the increasing of the amount of composite insulators in power network, the transmission accidents caused by the fault of composite insulators are increased and the aging of composite insulators should be paying more attention. In the paper, fourier transform infrared spectroscopy (FTIR) is used to analysis the molecular structure of silicone rubber material of composite insulators. The results indicated that the higher the electric field of the insulator shed, the lower the peak of FTIR spectra. The heavier pollution the sample run, the lower the peak of FTIR spectra. So more attention should be pay to the samples which run in heavier pollution region or the high field part of the insulator.

Influences of Electric-Field Distribution Along the String on the Aging of Composite Insulators

This paper studies the uneven aging of the composite insulators along the string caused by the nonuniform electric-field distribution. Sheds along the string of two 110-kV composite insulators with varied operation time on transmission lines are analyzed systematically by means of hydrophobicity and thermally stimulated current (TSC) tests, and the aging characteristics of different part of the axial sheds are compared. This paper studies the influences of the electric-field distribution along the string on the aging of composite insulators, combined with the results of electric-field simulation and electric aging tests. Results show that the higher the electric-field strength is, the worse the hydrophobicity of composite insulators surface is and the larger the amount of trap charge is. The study suggests the nonuniform electric-field distribution is the main reason for the uneven aging of the sheds along the composite insulators string.

Aging of composite insulators: simulation by electrical tests

To assess the long term performance of 72 kV and 230 kV composite long rod insulators, different laboratory aging tests have been developed. Two principal diagnostic tests were used to measure the performance of the insulators, the quick flashover salt-fog (QFO SF), and the rapid flashover clean-fog (RFO CF) tests. The following aging processes were used: cement coating and clean-fog, salt fog, and cement coating and salt fog. Similar sets of insulators were also aged in the field for over three years, and all the insulators were evaluated in the laboratory. The cement/salt-fog aging process was found to be the most controllable and realistic after the results were assessed by means of the RFO CF test. >