Disc Insulator Research Articles

Performance analysis of high voltage disc insulators with different profiles in clean and polluted environments using flashover, withstand voltage tests and finite element analysis

Severe pollution-induced flashovers on insulators present a pressing challenge to power system safety. The frequent failure of high-voltage insulators, particularly in the polluted environments of Pakistan, poses a critical concern. This paper investigates the impact of insulator profile on reducing pollution flashovers, testing two designs as per IEC standard 60383 and simulated using the Finite Element Method in COMSOL Multiphysics®. The test results revealed that deep under-ribs insulators exhibited a 5.008% reduction in flashover voltage, while alternating shed insulators experienced a 3.233% decrease in polluted conditions compared to clean conditions. Notably, under both clean and polluted conditions, alternating shed insulators consistently outperformed deep under-ribs insulators, with a 25.377% higher flashover voltage in clean conditions and a 27.400% superiority in polluted conditions. Computational analysis through the Finite Element Method in COMSOL Multiphysics shows a consistent pattern in potential distribution with increasing insulator count, but the presence of a pollution layer introduces spikes in the electric field distribution, validating experimental results. These findings highlight the superior performance of alternating shed insulators, especially in polluted environments.

A critical study on detection of pollution level of overhead insulators by measuring pH and conductivity of the contaminants

The flow of electric power requires overhead insulators to maintain a safe distance between charged conductors and supporting structures. These insulators are installed in outdoor locations and are hence subjected to a variety of adverse environmental conditions, such as airborne dust and other contaminants. In moist conditions, these pollution factors can cause flashover, resulting in the loss of energy in the form of heat and light. Therefore, it is crucial to determine various types of contaminants based on geographical conditions and analyze their effects on the insulation capabilities of these insulators. This research work analyzes the accumulation of certain contaminants on the insulators installed at various geographical locations. Experimental approaches for detecting the level of contamination of insulators have also been examined, along with their limitations. Moreover, the findings of pollution tests performed in industrial, coastal, desert, inland, agricultural, and biological areas are presented as well. The flash-over voltage (FOV) of disc insulators made of porcelain for various pH and conductivity values has been observed to correlate FOV with pH and conductivity values of the pollutants. The pH and conductivity of contaminants are crucial factors impacting the insulator's flashover voltage, which is influenced by surrounding atmospheric conditions. Understanding the composition and monitoring these parameters can aid in developing preventive maintenance programs based on specified pH values, ensuring the reliability and performance of overhead insulators.

Vibration Triggered Leakage of Surface Charge on Epoxy Insulator Under DC Voltage

Surface charge accumulation is considered a critical threat to the safe operation of epoxy insulators installed in gas-insulated switchgear (GIS). This paper reports on the charge leakage phenomenon of the insulator with the occurrence of impact vibration under DC voltage. A full-sized disc insulator with a multi-arc surface profile was employed as the test sample. A vibration system was established to output vibration to the insulator in two Modes. In Mode I, the maximum acceleration was 338.9 m/s2 and the impact frequency was 1.1 Hz. In Mode II, the maximum acceleration decreased to 4.6 m/s2 but the impact frequency increased to 107.5 Hz. The charge densities on the insulator surface were measured before and after the vibrations. The results indicated that the vibration led to the obvious leakage of homo-charges during the DC stressing process, especially in the non-planar region. The leakage of homo-charges under positive stressing was more remarkable than that under negative stressing. The reduction of homo-charge quantity was more serious in Mode I than in Mode II. It is suggested that the vibration-triggered charge leakage is mainly due to charge de-trapping caused by micro-displacement of molecular chain occurring in the insulator with the vibration and subsequent charge release to the gas phase under the normal electric field, by which the surface charge accumulation quantity is remarkably reduced.

Optimization of insulators in ±550 kV HVDC GIS for offshore wind platform considering charge accumulation

High voltage direct current (HVDC) gas-insulated switchgear (GIS) plays a crucial role in developing far offshore wind power and attaining renewable energy and interconnection objectives. However, surface charge accumulation reduces the surface flashover voltage and restricts the development of DC GIS at the higher voltage. In this paper, the design criteria for a ± 550 kV DC insulator were proposed based on DC insulation testing. The influence of geometry on electric field and charge distribution of obtuse conical insulators, disk insulators, and conical insulators was systematically investigated. The results show that the threshold of the tangential electric field under the DC superimposed lighting impulse test for the ±550 kV DC insulator is 11.1 kV/mm. The simulation results indicate that the increasing inclination of the insulator enhances the normal electric field and surface charge density, while the increase in insulator size diminishes the tangential electric field dramatically. The obtuse conical insulator with an upper surface inclination angle of 30°, a lower surface included angle of 140°, and a diameter of 812.5 mm is ideal for ±550 kV DC GIS. The obtained results may provide guidance for the compact design of insulators and the development of DC GIS.

Influence of contamination distribution in characterizing the flashover phenomenon on outdoor insulator

The aim of this work is to model the influence of uneven contamination distribution under various humidity on the pollution flashover voltage of 11 kV porcelain insulator disc. Four scenarios of contamination distribution were proposed to test the sample under various severities of contamination simulated by salt deposit density (SDD). Seriesflashover experiments on contaminated insulators were performed under various conditions. The voltage of flashover under clean condition was appointed as a reference value for analyzing the effect of pollution. Based on the percentage value of breakdown voltage of the contaminated insulator to the clean insulator, the conditions of the tested sample are classified into three categories namely normal (55–60%), caution (45–54 %) and severe (35–44%). In the experimental tests, the uneven contamination area dimension was taken into consideration. An artificial neural network (ANN), derived from experiment results was used as a tool to predict the flashover voltage. The ANN method is built with five inputs related to the geometry of the sample and pollution factors while the flashover voltage was set as the model's output. The results showed that the distribution of pollutants according to the presented scenario has a significant impact on the performance of the flashover voltage. In addition, the error value between the experiment outcomes and the prediction system appeared to be less than 6%. This suggests that the proposed ANN model can be an effective tool in forecasting the insulators’ flashover voltage under test.

Study on Steep Front Impulse Test Voltage Value of Disc Insulators with Variation in the Number of Units of Insulator String

The insulators used in power transmission and distribution networks should withstand abnormal system-generated switching impulses and natural lightning impulses. To avoid the failure of insulators in the field, the impulse puncture strength evaluation of the ceramic insulators is important. IEC 61211 standard stipulates the procedure to evaluate the ceramic disc insulators’ strength to withstand steep front impulses. In this test, the test voltage is determined by using a short standard string of five insulators. This paper presents the variation in the impulse stresses across the disc insulator units in the string due to non-linear voltage distribution under impulse flashover. This paper also correlates the test voltage values defined by the IEC standard with the highest stress on insulator units under impulse flashover of string insulators by using voltage distribution. The correlation study has been carried out with insulator strings having different arcing distances by using a different number of units.

External UHF Sensor for GIS PD Insulation Defect from Resin Hole

In view of the effective perception demand of PD (Partial Discharge) insulation defect of in-service GIS (Gas Insulated Switchgear), the external UHF (Ultra High Frequency, 0.3−3 GHz) sensing technology for GIS PD insulation defect from resin hole is studied in this paper. Firstly, rectangular waveguide theory is used to analyze the electromagnetic wave propagation characteristics from rectangular resin hole in GIS disc insulator. It is found that the energy of leaked electromagnetic wave mainly concentrates in the frequency band above 1 GHz. Then based on this frequency band characteristics, a cavity-backed bowtie sensor for GIS PD external detection is designed optimized by HFSS finite element software, in band of 1–3 GHz, its maximum VSWR is 7, the minimum is 1.1, the average is 2.9, and in band of 0.3–1 GHz, the maximum and minimum VSWR is 42.8 and 7, the average is 20.6. Finally, a sensor prototype is made, its sensitivity experiment is carried out on 220 kV GIS, experimental results show that the designed sensor can stably detect the PD electromagnetic wave signal leaked from the resin hole, and the signal energy in frequency band range is consistent with the theoretical analysis results.

Accurate Sensing of Insulator Surface Contamination Using Customized Convolutional Neural Network

Accurate sensing of contamination on the insulator surface is vital for the reliable operation of transmission lines. Hence, the present work aims to develop a deep learning framework for remote and accurate contamination sensing on the surface of outdoor insulators. The experiment is conducted on an 11-kV porcelain disc insulator to generate an extensive database of images representing different insulator surface conditions, i.e., clean surface and surface with sand, mud, and ash contaminations. The captured images were fed to a customized convolutional neural network (CNN) architecture for automated feature extraction and recognition. The proposed CNN model delivers appreciably high recognition accuracy at significantly reduced training time for sensing various insulator contaminations compared with other benchmark CNN models (AlexNet, VGGNet16, and ResNet50). Moreover, the proposed framework delivers an excellent recognition performance in sensing surface contamination under different lighting conditions. Therefore, the proposed methodology can be implemented for the condition monitoring of real-life insulators.

The Effect of a Metal Particle on Surface Charge Accumulation Behavior of Epoxy Insulator with Zoning Coating

Epoxy insulators are widely used in Gas-Insulated Transmission Lines (GILs), playing a significant role in electrical insulation and mechanical support. The metal particles generated during the production and operation of the equipment aggravate surface charge accumulation on the insulator, causing surface flashover. Therefore, it is necessary to study the suppression strategy of charge accumulation. In this paper, a downsized disc insulator was taken as the research object to investigate the effect of zoning coating on charge suppression with the presence of a linear aluminum metal particle under negative DC voltage. The zoning coating method was achieved by painting coatings with different conductivities in three areas on the insulator surface to regulate the charge. The inhibition mechanism of zoning coating on the charge accumulation in the presence of a linear metal particle was analyzed with the assistance of numerical simulation. The results showed that negative charges were accumulated in the nonplanar region as there was no metal particle, and the existence of metal particles led to the significant accumulation of positive charge speckles in the nonplanar region. The application of zoning coating could significantly inhibit the charge accumulation in the nonplanar area of the insulator and the charge injection from the grounded electrode to reduce the charge density. Under −25 kV, the maximum charge density on the insulator with the zoning coating was 48.1% lower than that without the coating, and the inhibition effect increased by 57.9% when the metal particle was introduced. This paper provides a new way to suppress the charge accumulation on the insulator surface.

A Method for Measuring Electric Field Distribution Along Insulator Surfaces Based on Electroluminescence Effect and Its Image Processing Algorithm

The measurement of electric field distribution along insulator surfaces plays a vital role in the design of insulators. This article proposes a measuring method of electric field distribution and its image processing algorithm based on electroluminescent effect. Unlike traditional electric field probes, this method is a noncontact measuring method that could reduce electric field distortion along insulator surfaces. There are three main steps: spraying epoxy coating mixed with ZnS:Cu electroluminescent powder on insulator surfaces, photoing luminescence images under different voltages, and deducing the electric field distribution by the proposed image processing algorithm. The surface electric field distributions of three typical insulators used in gas-insulated switchgear/gas-insulated transmission line (GIS/GIL) are measured. Compared with simulation results, the measurement errors of the disk insulator, the basin-type insulator, and the tri-post insulator are less than 2%, 4%, and 2.5%. This method provides a new way of measuring electric field distribution along insulator surfaces.

Statistical Reliability Analysis on Flashover Characteristics of Ceramic Disc Insulator and Polymeric Insulators

Statistical Reliability Analysis on Flashover Characteristics of Ceramic Disc Insulator and Polymeric Insulators

Dielectric withstand capability of functionally graded material disc insulator in single phase - gas insulated busduct

Regardless of the environment, electrical substations must be secure and efficient, and they must also be able to recover rapidly from any damage they suffer. Metal inserts at the conductor end of a single-phase gas insulated busduct (GIB) are shown to minimise stress in FGM insulator and to assess stress on a Triple Junction. Functionally graded materials are spatially scattered with several filler materials and doped with varying permittivity values in order to create homogeneous electrical field stress.Various voltages and grades of FGM are used in the simulation, as well as the insulator. The effect of grading on electrical field stress is further decreased by inserting the Metal Insert into the FGM insulator. The suggested insulator's efficiency is demonstrated by the findings gathered and examined.

Improved DC surface insulation performance of epoxy resin by gradient plasma fluorination

In order to improve the flashover voltage of the disc insulator in gas insulated transmission line under DC voltage, this paper considers reducing the electric field intensity on the surface by adjusting the surface conductivity distribution. Based on the joint simulation of improved particle swarm optimization algorithm and finite element, the surface conductivity gradient partition optimization model is constructed to obtain the optimal surface conductivity distribution sequence. The relationship between conductivity and treatment time is obtained by plasma fluorination, and the gradient distribution of the surface conductivity of the sample is realized by adding different ring polytetrafluoroethylene baffles. Microscopic tests are used to characterize the differences between different regions of the sample surface. The two-dimensional (2D) electric potential distribution, 2D charge density distribution, electric field intensity distribution and flashover voltage on the sample surface under pre-charging conditions are studied and compared with the simulation results. The results show that the maximum field strength of the sample with gradient treatment can be reduced by 71% and the flashover voltage can be increased by 45%. The research in this paper provides a good reference and theoretical support for the surface modification of disc insulators, such as the surface parameters with gradient distribution.

Study on the Propagation Characteristics of Partial Discharge Electromagnetic Waves in Gas Insulated Line

Defects in the gas insulated line can cause partial discharge, and the electromagnetic wave is generated. The finite difference time domain method is used to research the propagation of electromagnetic wave in gas insulated line structures. The electric field strength of time-domain waveform is selected as characteristic factor for analysis. By changing the gas insulated line model, the attenuation of electromagnetic wave through double insulator, L-type corner, T-type corner, straight tube and different GIL sizes is studied. In the straight tube structure, the amplitude attenuation of electromagnetic wave is linear and the attenuation band is between 1 GHz and 1.7 GHz. In the insulator, basin insulator has more serious influence on signal isolation than disc insulator. After passing through the insulator, the signal attenuation is obvious in the frequency band above 1 GHz. The amplitude of electromagnetic wave decreases more seriously through the corner structure, and the attenuation is at the whole frequency band. In different sizes of gas insulated line, the larger diameters of shell and conductor, the larger electromagnetic wave will be, and the faster attenuation will be; the length of gas insulated line cavity has little effect on electromagnetic wave. The theoretical research is expected to help to arrange the position of ultra-high frequency sensor reasonably.

Experimental study of porcelain and toughened glass suspension insulators under desert contamination

In this paper, the performance of porcelain and toughened glass suspension insulators artificially polluted with desert contamination is investigated experimentally. The withstand flashover voltage (FOV), and equivalent salt deposit density (ESDD) of desert contaminated insulators have been studied and reported. Artificial pollution testing was carried out, and desert contaminations were prepared in advance for four solutions (NaCl, CaSO4, KCl, and CaO) of different concentration levels to investigate the influence of desert contamination on the insulators of transmission lines. The flashover analyses are completed on 11 kV insulators with artificial pollution coatings. The contaminations materials are (a) Desert Salt Pollution-Dry pollution (b) Natural Fog Condition. Results have proven that flashover voltage decreased with the increase in the dry dessert pollution level at constant pressure and temperature condition. However, the study has also revealed that in the case of natural fog conditions, the flashover voltage of porcelain and toughened glass disc insulator became much lower than the dry test. From the results, it can be detected that engineers can predict and plan for the maintenance schedule of the poor performance of the insulators under different effluence environmental conditions. The study tested the effect of AC voltage flashover on the suspension insulators. However, the DC voltage is suggested to be used and results to be compared with the current study.

Mechanical defects diagnosis for gas insulated switchgear using acoustic imaging approach

Mechanical faults are major fault types in gas insulated switchgear (GIS). The vibration and acoustic signature provide valuable health indicator for GIS. This paper proposes a novel mechanical defect detection and identification approach for GIS using acoustic imaging. The vibration modals of a three-phase-in-one-tank GIS bus tube under different natural frequencies are investigated. An acoustic pressure sensor matrix is designed to obtain the acoustic intensity nephogram of the GIS. The gray-level co-occurrence matrix (GLCM) is used to extract the characteristics of the nephogram. Five eigenvalues, including angular second moment, contrast, entropy, correlation, and inverse different moment, are analyzed for three types of mechanical defects (i.e., loose anchor bolts, loose disc insulator bolts, and poor switchgear contact). A mechanical defect diagnostic approach for GIS is developed using the variation percentage of the averaged values of contrast as the key indicator. The effectiveness of the approach is validated using experimental data.

A method for measuring surface electric field intensity of insulators based on electroluminescent effect

The measurement for the surface electric field intensity of insulators based on electroluminescent effect is a non-contact measurement. By spraying a coating of epoxy paint mixed with ZnS:Cu electroluminescence powder on the surface of insulators, the part with high surface electric field intensity would be the first to glow. As the applied voltage increases, the area of luminous and the brightness increase. Therefore, the surface electric field distribution can be deduced by photographing and analyzing the luminescence of insulator surface coating. This method has successfully measured the surface electric field intensity distribution of disc insulators in GIL. Without the use of electric field probe, this method eliminates the electric field distortion caused by the probe completely. Besides, the permittivity of the coating can be decided according to the permittivity of the insulator material, and so eliminate the electric field distortion caused by the coating. The measure results of this method are in good agreement with reality.

Experimental, analytical and numerical analysis of voltage distribution along the cap-and-pin insulators

This paper deals with the experimental, analytical and numerical analysis of voltage distribution along the cap-and-pin insulators. Five different insulators strings are analyzed, consisting of two, three, four, five and six cap-and-pin U40BL glass disc insulators. Experimental measurements are performed in the high voltage laboratory at the Faculty of Electrical Engineering East Sarajevo. Measurement of the voltage distribution along the disc insulators is performed by using measuring sphere gap. Analytical calculations are performed by using mathematical model which considers parasite self-capacitances of disc insulators, as well as their parasite capacitances to the earth and to the phase conductor. Calculations of the parasite capacitances values are performed and optimum values which lead to the minimum difference between measured and calculated results are suggested. Numerical analyses of the non-linear voltage distribution are performed by using electrostatic field model in software Comsol Multyphisics. 2D axisymmetric models of the cap-and-pin insulators are developed. Despite the measuring configuration is not suitable for numerical analysis, relatively good agreement between the measured results and results calculated by using specialized software are achieved.

Improving tower grounding vs. insulation level to obtain the desired back-flashover rate for HV transmission lines

This paper aims to present a novel proposed formula, along with technical viewpoints, to solve the problem of transmission lines outage rate due to back-flashover phenomena in terms of soil resistivity, the number of disc insulator units in the string, and tower grounding system structure. Improving the tower grounding system (reducing the impedance) and developing the insulation level are appropriate solutions to prevent the occurrence of the back-flashover, dependent on many factors. To the best of our knowledge, the trade-offs between these two parameters, in respect of soil resistivity, to obtain the desired back-flashover rate (BFR) has not been presented via a compact formula yet. In this paper, it will be shown that in a specific soil resistivity and grounding structure, there is a minimum required insulator unit number and grounding conductor length to achieve the desired BFR, which could be calculated by the proposed formula, straightforwardly. Also, the economic selection between increasing the insulator unit number and developing the tower grounding system in terms of soil resistivity and BFR is investigated. The simulation procedure is coded with Matlab and linked to EMTP/ATP program to analysis the BFR. This method is done for a typical 150 kV overhead transmission line, however, it can be applied to any voltage level of transmission line and significantly facilitate the cost effective design of them.

Insulator Recognition and Fault Detection Using Deep Learning Approach

Uninterrupted power supply to electric power consumers has increasingly become a global necessity. Monitoring the health of distribution network is crucial to provide quality service. Traditional monitoring methods based on on-site patrols to detect faults have increasingly become labor-intensive and time-consuming, raising demand for new and more efficient techniques. To address this issue, we propose faster-RCNN by MXNet for both detection and classification tasks. We utilize convolutional neural network (CNN) for detecting and classifying both insulator components and faulty insulator discs from images captured on overhead electric power transmission systems. Using a dataset of images acquired through UAV (unmanned aerial vehicle) captures, detection and classification is dealt with by dividing the picture content of the training set into three classes: background, insulator and the defective part of insulator. We achieve target insulator recognition and positioning with impressive precision compared to other traditional technologies. Our work could have practical integrated implementation solutions for automated inspection of overhead transmission power line insulators. The code used can be found at https://github.com/QgZhan/Insulator-Defect-Detection.