Glass Insulators Research Articles

Proposal of a dynamic numerical approach in predicting flashover critical voltage

<span lang="EN-US">Glass insulators, due to its diverse characteristics, were used widely around the world for high voltage transmission lines. Surfaces of the insulators are exposed to high electrical, mechanical, and thermal stresses over the period of service. Accumulation of contamination distort stresses distribution along the insulators that may lead to flashover under severe condition. In this paper, Obenaus pollution model has been adopted to propose a dynamic mathematical modelling to determine flashover critical voltage with regard to parameters such as pollution conductivity, arc length, and width of layer of contamination on the surface of glass insulator. In addition, laboratory experimental works have been carried out according to IEC60305 to validate the results from numerical approach, which indicate a good agreement.</span>

Influence of pollution chemical components on AC flashover performance of various types of insulators

The pollution on insulators is composed of various chemical components, which threaten the stability of external insulation. However, the existing insulation designs have not taken this issue into consideration. This work aimed to study the influence of pollution chemical components on flashover performance of insulators with various materials. Flashover tests of porcelain, glass and silicone rubber insulators polluted by eight types of common contaminants were conducted. Based on the test data, the influence of chemical components and their solubility on equivalent salt deposit density (ESDD) and insulator flashover performance were analysed; and the electrical properties of different types of insulators were compared. Results show that the ESDD contribution rate changes with chemical components. The dissolution characteristic has a significant influence on the measurement of ESDD; slightly soluble contaminants need to be considered separately. The corresponding insulator flashover gradient for ions can be summarised as Cl− < NO3 − < SO4 2−, K+ < Na+, NH4 + < Ca2+. For a glass insulator, the flashover gradient is 4.9–17.0% higher than that of a porcelain insulator. For a silicone rubber insulator, this gap reaches 14.6–24.4 and 83.3–90% for freely soluble pollution and CaSO4, respectively, this phenomenon can be explained by the combined action of the slightly soluble character of CaSO4 and hydrophobicity transference of silicone rubber.

Effect of DC electric field on water droplets' movement and icing process on insulator

Icing has a great effect on insulation of power networks. In order to know the insulator icing properties under electric field and help simulating the icing process precisely, the effects caused by electric field are investigated in this research. Taking glass insulator LXY-120 as samples, the electric field were calculated, based on which, the movement of charged water droplets was analysed. The simulation results show that, the electric forces can change the trajectory of water droplets by different degree which is affected by the collided position, relative distance, wind velocity and the size of water droplet, and the biggest track shift happens under the insulator shed with a rate larger than 120%. As a result, the collision efficiency β1 can increase up to 23% while MVD and wind velocity are both small. Through a series of icing contrast experiments in an artificial climate chamber, it is proved that the electric field can promote the dry-growth icing process with more ice growing directions and a higher icing rate, meanwhile, it affects the wet-growth icing showing as bending icicles and a lower icicle growing rate.

Effects of structure and material of polluted insulators on the wetting characteristics

Umbrella-type structure, the material of insulators and surface positions influence the wetting process of polluted insulator surfaces tremendously. Using a custom-made phase-angle-difference (PAD) detection device, the PAD of the different positions of different polluted insulators is measured, and the PAD curves and partial pollution surface electrical conductivity γ 20 varying with time are plotted. The results show that there is a certain difference in the wetting characteristics of different positions. The saturated wetting time of different positions of LXAY-70 insulators is 12.5-15 min; that for LXHY5-70 insulators is 12-25 min; that for XWP2-70 insulators is 8-14 min; and that for FXBW-10/70 insulators is 18-26.5 min. The umbrella-type structure is shown to have a direct effect on the wetting process of polluted insulators. The complicated umbrella-type structure, especially the existence of umbrella ribs, causes an uneven degree of wetting between the upper and lower surfaces, and leads to the increase of the difference in wetting state between the different positions. Furthermore, there is a certain difference in the wetting speed of insulators comprised of different materials. Hydrophilic porcelain and glass insulators are more easily wetted than composite insulators, even though the hydrophobicity class of composite insulators is 7.

Self-Shattering Defect Detection of Glass Insulators Based on Spatial Features

During an automatic power transmission line inspection, a large number of images are collected by unmanned aerial vehicles (UAVs) to detect existing defects in transmission line components, especially insulators. However, with twin insulator strings in the inspection images, when the umbrella skirts of the rear string are obstructed by the front string, defect detection becomes difficult. To solve this problem, we propose a method to detect self-shattering defects of insulators based on spatial features contained in images. Firstly, the images are segmented according to the particular color features of glass insulators, and the main axes of insulator strings in the images are adjusted to the horizontal direction. Then, the connected regions of insulators in the images are marked. After that, the vertical lengths of the regions, the number of insulator pixels in the regions, as well as the horizontal distances between two adjacent connected regions are selected as spatial features, based on which defect discriminants are formulated. Finally, experiments are performed using the proposed formula to detect self-shattering defects in the insulators, using the spatial distribution of the connected regions to locate the defects. The experiment results indicate that the proposed method has good detection accuracy and localization precision.

An accurate and real-time self-blast glass insulator location method based on faster R-CNN and U-net with aerial images

This paper proposes a new deep learning framework for the location of broken insulators (in particular the self-blast glass insulator) in aerial images. We address the broken insulators location problem in a low signal-noise-ratio (SNR) setting. We deal with two modules: 1) object detection based on Faster R-CNN, and 2) classification of pixels based on U-net. For the first time, our paper combines the above two modules. This combination is motivated as follows: Faster R-CNN is used to improve SNR, while the U-net is used for classification of pixels. A diverse aerial image set measured by a power grid in China is tested to validate the proposed approach. Furthermore, a comparison is made among different methods and the result shows that our approach is accurate in real time.

Development and Application of Live Replacement of Insulator Suspension Tool Components for Transmission Lines

Transmission line insulators will reduce the insulation level and become low-value insulators because of lightning flashover. Toughened glass insulators are used in 500kV Tongfeng 1 and 2 lines in Tonghua area. Most umbrella skirts will break and fall off after lightning flashover, which greatly reduces the insulation performance. It needs to be replaced in time, but frequent blackouts will bring great losses and reduce the reliability of power supply. Aiming at the frequent lightning hazards and lightning strikes on transmission lines in Tonghua area, a tool assembly for live replacement of insulators for transmission lines is developed. Through the application of this tool, the live operation mode is adopted to eliminate such defects. The operation time can be arranged and implemented in a very timely manner, which avoids the threat of long-term defects, effectively reduces the outage time of equipment, enhances the stability of power grid, and greatly improves the reliability of power supply of lines. Finally, taking the live line insulator suspension tool as an example, the economic benefit analysis is given, and the feasibility and correctness of the tool are verified..

Research of biological contamination and its effect on the properties of RTV-coated insulators

Recently, to improve the anti-fouling flashover performance of porcelain and glass insulators, room temperature vulcanized (RTV) silicone rubber coatings have been widely applied to their surface. However, it was found that, in warm and humid areas in China, the presence of RTV silicone coating could facilitate the growth of biological contamination such as algae. This study firstly analyzed the biofouling regularity of algae growth on the surface of outdoor RTV-coated insulators, considering growth direction, distribution on sheds, substation equipment, insulating material and effect of corona discharge. The effects of algae on the surface micro morphology, functional groups and flashover voltage of field insulator were then studied. The effects of environmental factors on algae growth were studied in detail. Finally, the influence of algae on the hydrophobicity and flashover characteristics of the RTV coating was examined. Through research, the growth regularity of algae on insulator surface is presented and put forward some measures to prevent and control algae growth. The results also showed that the presence of algae could decrease flashover performance of the RTV-coated insulators. However, the effect of algae on the aging of materials was insignificant.

Influence of the insulator geometry on the streamer propagation characteristics in polymeric insulators under positive polarity lightning impulse voltages

Polymer composite insulators acquire the position of their counterpart ceramic and glass insulators in high voltage overhead transmission systems due to their remarkable pollution performance. They have different potential and electric field distributions compared to that of ceramic insulators and the absence of intermediate pin and cap metal fittings makes them compact in size by reducing the distance between energised and grounded ends. This study presents a simulation-based approach to compute the streamer propagation characteristics in polymer suspension insulators under positive polarity lightning impulse voltages. The streamer inception, propagation, and sustenance criteria are evaluated using finite element method-based electric field computations. The significance of insulator geometries on streamer inception and propagation phenomena is well established. The insulator geometries such as weather sheds, location of the first shed, and shed radius have shown a strong influence on streamer inception and propagation path, which govern the flashover characteristics of the insulator. The lightning impulse flashover voltages of different insulators were determined experimentally to validate the computed results. A good agreement is found between simulation and experimental results.

AC flashover performance of different shed configurations of composite insulators under fan‐shaped non‐uniform pollution

Currently, it is founded that under unidirectional wind and certain landform, composite insulators are always fan-shaped non-uniformly polluted. In this paper, artificial pollution tests on three types of composite insulators with different shed configurations and under various fan-shaped non-uniform pollution conditions were carried out. Then the flashover performances of composite insulators, porcelain insulators and glass insulators were compared. Results indicate that there is a big difference between ac flashover performance of composite insulators under non-uninform pollution and uninform pollution. The flashover voltage of composite insulator is largely influenced by salt deposit density (SDD), the ratio of SDD of windward side to leeward side (W/L), the occupation ratio of leeward side k and the shed configurations. The relationship between SDD and U 50 still meets negative power function when composite insulator is fan-shaped non-uninform polluted. There is a reduction of 17.8–27.6% in the flashover strength when the ratio W/L of SDD decreases from 1/1 to 1/15. The shed configurations of composite insulators have great effects on the flashover performance. Composite insulators always have better withstand property compared to glass and porcelain insulators under either uniform pollution or fan-shaped non-uniform pollution.

Electrostatic Shielding of Faraday’s Ring Made of Stainless Steel 304 in the Glass Insulators

Electrostatic Shielding of Faraday’s Ring Made of Stainless Steel 304 in the Glass Insulators

Durability and Stiffness Estimation for the Composite Overwrap Electromagnetic Rail Launcher Barrel

One of the ways to decrease electromagnetic rail launcher (EMRL) barrel mass is to utilize composite material overwrap. Design of novel light, stiff, and durable EMRLs requires accurate computational prediction of barrel strength. This paper presents numerical model and corresponding computer code for the calculation of stresses in composite overwrap EMRL barrel. The computer code named, NDSPDE, based on the finite-element method for stresses analysis in complex geometric shapes designs in a plane strain. The code allows carrying out numerical structural studies of EMRL barrels under various electromechanical loads accounting for the orthotropic properties of utilized constructive materials. Depending on the requirements for EMRL barrel stiffness and durability the results of numerical studies allow to select suitable construction materials to optimize both the barrel design and the barrel electromechanical loading conditions. The safety margin evaluation of the side insulators and the overwrap was carried out by classical criterion of maximum tensile stress. Note that in durability assessing of other launcher elements the above safety margin is not applicable, since the stress is not unixial in the most loaded parts of those elements. In case of nonuniaxial stress, evaluation of the launcher structural elements durability requires utilization of more complex criteria, which account for the type of the stress state arising in the launcher elements. This paper presents the numerical results of the EMRL barrel cross-sectional parameter estimation including the glass fiber overwrap, rails, and insulators. Estimations were carried out both for stresses and for durability of the EMRL barrel structural elements.

Flashover Performance Test with Lightning Impulse and Simulation Analysis of Different Insulators in a 110 kV Double-Circuit Transmission Tower

The flashover performance of insulators is the foundation of the calculation of precise lightning protection. The material and structure of an insulator affect its flashover performance but the research on the differences in the flashover performance of different insulators and the analysis of the reason for these differences have not been clear. In this paper, lightning impulse flashover tests of two types of insulators (composite and glass insulators) were carried out in the National Engineering Laboratory (Kunming) for Ultrahigh-voltage Engineering Technology. In these tests, the insulators were hung in a 110 kV double-circuit transmission tower and a standard lightning impulse (1.2/50 μs) was applied to the insulators. The discharge path and the 50% impulse flashover voltage of the insulators were recorded. At the same time, the electric fields in the vicinity of different insulators were calculated using the finite element method with COMSOL Multiphysics. The electric field distribution and the uneven coefficient were analyzed. Combined with the flashover test data and the electric field simulation, the relationship between the flashover performance (discharge path and 50% impulse flashover voltage) and the electric field (electric field distribution and uneven coefficient) is found. The simulation results are in accordance with the test data and the conclusions can provide useful references for the external insulation design of transmission lines and the optimization of insulators.

Icing Condition Assessment of In-Service Glass Insulators Based on Graphical Shed Spacing and Graphical Shed Overhang

Icing on transmission lines might lead to ice flashovers of insulators, collapse of towers, tripping faults of transmission lines, and other accidents. Shed spacing and shed overhang of insulators are clues for evaluating the probability of ice flashover. This paper researches image-processing methods for the natural icing of in-service glass insulators. Calculation methods of graphical shed spacing and graphical shed overhang are proposed via recognizing the convexity defects of the contours of an icing insulator string based on the GrabCut segmentation algorithm. The experiments are carried out with image data from our climatic chamber and the China Southern Power Grid Disaster (Icing) Warning System of Transmission Lines. The results show that the graphical shed overhang of insulators show evident change due to icing. This method can recognize the most serious icing conditions where the insulator sheds are completely bridged. Also, it can detect bridging positions including the left side, right side, or both sides of the insulator strings in the images.

Insulator Fault Detection Based on Spatial Morphological Features of Aerial Images

Because insulators provide electrical insulation and mechanical support for electric transmission lines, these components are of paramount importance to safe and reliable operations of power systems. However, insulators are often considered to be prone to different faults, e.g., bunch-drop, which demands a novel solution for accurate fault detection and fault location. Current research efforts have primarily focused on the bunch-drop fault of glass insulators, and the study of ceramic insulators has not been reported to date. To this end, this paper proposes an algorithmic solution for the bunch-drop fault detection for both glass and ceramic insulators based on spatial morphological features, which can be integrated into an unmanned aerial vehicle-based inspection system. Color models can be established based on the unique color features of both glass and ceramic insulators. Next, the target areas of the insulators can be identified according to the color determination combined with the insulator’s spatial features. The target area is morphologically processed to highlight the fault location, and the rules are established based on the spatial feature differences between the insulators with and without faults. Consequently, the fault location can be accurately identified, and the coordinates can be determined. The performance of the proposed solution is evaluated in comparison with existing solutions. The numerical results demonstrate that the proposed solution can detect the bunch-drop faults of insulators with a better than average detection rate. In addition, the performance is assessed and validated in terms of robustness and real-time performance.

Improvement of electric field distribution by integrating composite insulators in a 400 kV AC double circuit line in Algeria

Because of their advantages over glass and porcelain insulators, composite insulators are being used now in power transmission lines for different voltage rating levels. Recently, the 400 kV level is introduced by Societe Nationale de l'Electricite et du Gaz, SONELGAZ (Algerian Company of Electric Power and Gas) where glass insulators are installed. For better electrical performances, we propose in this paper to integrate composite insulators in a three phase 400 kV AC double circuit line situated in the northwest of Algeria. A comparison is done between the already existing glass insulators and the proposed composite insulator in terms of electric field distribution. The electric field is studied along the leakage paths of the insulators under different surface conditions (dry and clean, uniformly and non uniformly polluted, and in presence of water droplets). Three composite insulators with different shed configurations are proposed. From these three configurations, we selected the insulator presenting lower electric field magnitude in critical areas mainly on the triple point junction (air — HV end — housing material interface). On the double circuit line, we focused our study on the phase insulator that presents the highest electrical stress. Impact of hardware fittings, tower, phases and conductors on the electric field distribution has been analyzed. Effects of bundled conductors have been also studied. Simulations were carried out by employing 2D Finite Element Method (FEM) using COMSOL Multiphysics® 4.3 software. Results show that electric field is lower in the case of composite insulators. Furthermore, we found that the calculation model can be simplified by not considering all circuit phases. Note that appropriate corona rings are considered on both HV and ground ends for glass and composite insulators and their geometrical parameters (corona ring diameter, corona ring tube diameter and corona ring height) are kept constant throughout the whole study.

Potential and Electric Field Characteristics of Broken Porcelain Insulator

&lt;span lang="EN-GB"&gt;Overhead line insulators can be damaged for various reasons during their service life. Porcelain or glass insulators once damaged can affect the reliability of power system networks. This paper presents the study of voltage and electric characteristics along the surface of a broken porcelain insulator located in a string of 10 unit insulators. Three models of broken porcelain insulators were being proposed and the analysis results on voltage and electric characteristics were individually collected. The broken porcelain insulator with the most significant effect were then being investigated in the strings of 10 unit insulators. The finite element software of Quickfield was used to analyze the voltage and electric characteristics. Form the presented results, it is proven that the single porcelain insulators with broken shed at the nearest to the electrode terminal gave the most significant effect of voltage and electric field distribution pattern along the creepage distance. However, when this type of broken insulator was included in a string of 10 unit insulators, maximum average value of voltage achieved once the broken insulator was located at the HV terminal. Meanwhile, the highest electric field strength was recorded when the broken insulator was located in the middle of the string.&lt;/span&gt;

Effects of ring-shaped non-uniform pollution on outdoor insulation electrical property

The inner area close to cap and pin of insulator is sometimes heavier polluted than the outer area, causing the contamination pattern on insulator surface look like ring-shape. This kind of non-uniform pollution may affect insulator flashover voltage. In this paper, artificial pollution tests of 4 types of porcelain and glass insulators with ring-shaped non-uniform pollution were carried out. Experimental results indicate that the SDD (salt deposit density), the non-uniform pollution degree K (the SDD ratio of inner part to outer part), the heavily polluted area with radius r, and the insulator profile all have significant effects on insulator flashover performance. The effects of K and r on flashover performance can be reflected by the change of pollution layer conductivity during flashover. Under ring-shaped non-uniform pollution, the relationship between Uso and SDD can still be expressed by negative power function, while coefficient a varies obviously with pollution non-uniformity, but exponent n does not. Finally the correction coefficients of flashover voltage considering non-uniform pollution degree K were also calculated for outdoor insulation design.

Automatic identification and location technology of glass insulator self-shattering

The insulator of transmission lines is one of the most important infrastructures, which is vital to ensure the safe operation of transmission lines under complex and harsh operating conditions. The glass insulator often self-shatters but the available identification methods are inefficient and unreliable. Then, an automatic identification and localization technology of self-shattered glass insulators is proposed, which consists of the cameras installed on the tower video monitoring devices or the unmanned aerial vehicles, the 4G/OPGW network, and the monitoring center, where the identification and localization algorithm is embedded into the expert software. First, the images of insulators are captured by cameras, which are processed to identify the region of insulator string by the presented identification algorithm of insulator string. Second, according to the characteristics of the insulator string image, a mathematical model of the insulator string is established to estimate the direction and the length of the sliding blocks. Third, local binary pattern histograms of the template and the sliding block are extracted, by which the self-shattered insulator can be recognized and located. Finally, a series of experiments is fulfilled to verify the effectiveness of the algorithm. For single insulator images, Ac, Pr, and Rc of the algorithm are 94.5%, 92.38%, and 96.78%, respectively. For double insulator images, Ac, Pr, and Rc are 90.00%, 86.36%, and 93.23%, respectively.

Breakdown process experiments of cap‐and‐pin insulators and their EMT leader progression model implementation

Here, breakdown tests of cap-and-pin glass insulators with arcing horns, conducted at two different HV labs, are presented. Since only volt-time curves are measured, a curve-fitting approach to determine leader progression model parameters is taken, which involves modelling of the impulse generator in detail and inclusion of the Motoyama model to simulate the breakdown. Furthermore, a comparison of the breakdown simulation results with LPM parameters for a pure air gap and the measurements is accomplished. Finally, a curve-fitting procedure is developed to fit the resulting volt-time curves from simulations to the measurements.