Transmission Line Insulators Research Articles

Prediction of surface leakage current of overhead insulators under environmental and electrical stresses

Leakage current is one of the critical aspects to consider for overhead transmission line insulator’s condition and performance assessment. As the leakage current increase, the size of the dry band also will increase leads to the dry band arcing, deteriorate the insulator performance and contribute to the development of insulator flashover. Based on the literature study, other than the existence of contaminations on the surface of insulator combined with moisture, the variation in leakage current is also affected by the environmental and electrical stresses. Previous researches have shown the effect of environmental and electrical stresses on surface leakage current based on experimental and simulation results. This paper outlines an analytical approach based on dimensional analysis to propose a new mathematical model of leakage current under environmental and electrical stresses. To justify the applicability of the derived dimensional model, the new model has been validated using previous researcher’s experimental results. The validation indicated that the proposed model had shown a good agreement with the previous experimental results. The proposed dimensional equation for this research work can be potentially used as a predictive performance model to evaluate and monitor the leakage current and insulator’s performance

Analysis and detection of electric field distribution characteristics of degraded insulators

Abstract After long-term operation, the electrical performance of UHV transmission line insulator string decreases and zero-value insulators are prone to occur. The existence of zero-value insulators leads to the flashover of insulator strings, which causes large-scale power outages in serious cases. In order to improve the power quality and detect the zero-value insulators of transmission lines more timely and efficiently, the influence of zero-value insulators on the electric field distribution of insulator strings is simulated and calculated by finite element method. At the same time, taking the grounding current of insulator string as the cut-in point, the principal component analysis method is used to screen the effective characteristic quantities, and then as the input of artificial neural network, and the fault area of insulator string is determined by the neural network. The simulation results show that the recognition accuracy of artificial neural network based on insulator string grounding current is high, and it has certain engineering application value.

Review on RTV Silicone Rubber Coatings Insulator for Transmission Lines

Nowadays, the usage of RTV Silicone Rubber as Insulator coatings are increased due to its advantages to avoid pollution flashover of contaminated insulator. Besides, the coatings can reduce the maintenance cost and scheduled routine. This paper had introduced the advantage of RTV Silicone Rubber coatings on insulator, such as good adhesion, nominal thickness range and good hydrophobicity. There are three method of coatings application, such as brushing, spraying and dipping. Suitable method is used to specific insulator application. Meanwhile, this paper also explained about installation of coated insulator in the field.

Dust contamination on surface of transmission line insulators in air-polluted regions in China: statistical characteristics, adhesion mechanism, and environmental impact factors.

Dust particles suspended in the atmosphere have been a big headache for electric power transmission industry in China. As transmission lines pass through dusty or air-polluted areas, dust contaminants are likely to deposit and accumulate on line insulators, which is one of the greatest causes of flashover and failure of power transmission. To study the statistical characteristics of this type of contamination, dust samples were collected and measured, and a physical model was set up to explain the deposition and accumulation mechanism of the particles. The trajectories of particles were tracked using fluid mechanics and contact mechanics, and an adhesion criterion was proposed. Simulation software was then applied to validate the model; further different environmental factors were studied that would affect the particle size distribution. The results show that under natural contamination conditions, the particle size distribution on the surface of the insulator shows a certain concentration at size ranges 1~100μm and basically obeys a log-normal distribution. In addition, relative humidity, air velocity, and the charge accumulated on the surface all have significant influences on particle size distribution characteristics, while the effect of the electric field is mainly reflected in the difference in the number concentration of particle adhesion.

Analysis of Salt Mixture Contamination on Insulators via Laser-Induced Breakdown Spectroscopy

The composition of contamination deposited on transmission line insulators can affect their surface flashover voltage. Currently, there is no rapid on-line method to detect this contamination composition in power grids. In this paper, we applied laser-induced breakdown spectroscopy (LIBS) to analyze contamination on insulator surfaces. Usually, Na and Ca salts are found in contamination along with various sulfate, carbonate, and chloride compounds. As an element’s detection method, LIBS can only measure a certain element content, for example, Ca. The mixture of various compounds with the same cations can influence the LIBS signal. The influence of mixing ratios on the calibration curves and relative spectral intensity was studied via LIBS. Na2CO3, NaHCO3, CaSO4, and CaCO3 samples containing different proportions of Na and Ca were prepared. The linear correlation coefficients (R2) for the Na and Ca calibration curves generated using various mixing ratios were analyzed. The results showed that the mixture ratio did not dramatically affect the linear calibration curves for mixtures containing the same cations. This finding may significantly reduce the difficulty of applying LIBS analysis for complex contamination on insulators. The laser energy density had effects on the spectral characteristics of the measured elements. The partial least-square regression (PLSR) model can improve the accuracy of Na and Ca prediction.

Experimental Study on Glaze Icing Detection of 110 kV Composite Insulators Using Fiber Bragg Gratings.

Icing detection of composite insulators is essential for the security and stability of power grids. As conventional methods have met difficulties in harsh weather, a 110 kV composite insulator with embedded Fiber Bragg Gratings (FBGs) was proposed for detecting glaze icing in this paper. FBG temperature compensation sensors in ceramic tubes were adopted for simultaneous measurement of icicle loads and temperature. Then, temperature calibration experiments and simulated icicle load experiments were carried out to obtain temperature and icicle load characteristics of FBGs. The results showed that temperature sensitivities of FBG strain sensors and FBG temperature compensation sensors were 18.16 pm/°C, and 13.18 pm/°C, respectively. Besides, wavelength shifts were linearly related to icicle loads within the polar angle range of −60° to 60°, and the load coefficient of FBG facing the icicle was -34.6 pm/N. In addition, the wavelength shift generated by several icicles was equal to the sum of wavelength shifts generated by each icicle within the polar angle range of −15° to 15°. Finally, icicles can cause wavelength shifts of FBGs within a big shed spacing. The paper provides a novel icing detection technology for composite insulators in transmission lines.

Contamination Characteristics of Typical Transmission Line Insulators by Wind Tunnel Simulation

In this paper, contamination distribution results on 4 insulators surface as well as NSDD (non-soluble deposit density) in different test conditions were obtained. Further, contamination performances of 4 insulators were compared. Finally, contamination process was simulated by the Eulerian multiphase model based on computational fluid dynamics. Research results showed that: contamination performances of insulators were obviously affected by insulator structures, wind speed and RH (relative humidity). Contamination distribution is non-uniform on 4 insulators. Contamination degree of 4 insulators on leeward surface is greater than that of windward surface. NSDDB (NSDD of bottom surface) of disc shaped insulators is higher than NSDDT (NSDD of top surface), the opposite is true for shed shaped insulators. Besides, the saturated contamination characteristics of 4 insulators are different in saturated NSDD and saturated time. Wind speed and RH both have great influence on the insulators contamination. The increase of wind speed and RH will lead to higher NSDD. However, it is noteworthy that RH has little impact on NSDD of composite insulators. In addition, the numerical simulation based on computational fluid dynamics and experimental results in wind tunnel are in good agreement. So it is suggested that numerical simulation can be used to test the anti-pollution performance of insulators with different structures in different environments.

Studying AC Flashover Performance of Suspension Insulators Under Natural Cold Fog and Wet Deposition Conditions

The electrical performance of insulators under comprehensive conditions including low air pressure, pollution and icing, is an important basis for the selection of external insulation. However, the problem of cold wet deposition has not attracted extensive and considerable interest in research. Based on flashover tests of suspension insulators in field test station, the AC flashover performance of insulators was studied. The results show that the duration of existence of the arc throughout the composite insulator surface in case of condensation was significantly lower than that in case of freezing fog flashover because of a change of the sheds surface roughness, which leads the arc melt the frozen fog droplets on the sheds surface and extends its flashover time. Compared with the flashover characteristics of the hydrophilic insulators in frost fog, the composite insulators exhibited clear arc extinguishing and arc starting phenomena. Moreover, the wind velocity has affected the flashover performance of suspension insulators in cold fog. Studying flashover characteristics of suspension insulators can contribute to the design of the external insulation of transmission lines and substations under natural cold fog and wet deposition regions.

Insulator Segmentation for Power Line Inspection Based on Modified Conditional Generative Adversarial Network

There are a large number of insulators on the transmission line, and insulator damage will have a major impact on power supply security. Image-based segmentation of the insulators in the power transmission lines is a premise and also a critical task for power line inspection. In this paper, a modified conditional generative adversarial network for insulator pixel-level segmentation is proposed. The generator is reconstructed by encoder-decoder layers with asymmetric convolution kernel which can simplify the network complexity and extract more kinds of feature information. The discriminator is composed of a fully convolutional network based on patchGAN and learns the loss to train the generator. It is verified in experiments that the proposed method has better performances on mIoU and computational efficiency than Pix2pix, SegNet, and other state-of-the-art networks.

Infrared Evaluation Classification Method for Deteriorated Insulator Based on Bayesian Algorithm

The insulation state detection of transmission line insulators in power systems is essential to ensure the reliability of transmission power supply. Aiming at the low accuracy of the infrared diagnostic fault diagnosis method for porcelain insulators in transmission lines, this paper proposes a classification method based on Bayesian algorithm for the classification of infrared map degradation degree of insulators. Bayesian algorithm is used to mine the correspondence between the characteristic parameters of the insulator infrared inspection map and the insulator state represented by the map, so as to improve the Bayesian network structure and finally classify the map. The results show that the method can effectively classify the operating state of insulators. The accuracy of the power insulator state classification model based on Bayesian algorithm reaches 94.2%.A new method of intelligent detection and diagnosis for evaluating the deterioration of insulators is proposed. This method has the advantage of high stability and accuracy.

Influence of pollution on potential and electric field distribution of porcelain insulator in 110kV transmission line

The spatial potential and electric field distribution of clean insulator and insulator with different degrees of pollution in 110kV transmission lines are analyzed with Comsol Multiphysics software. The results show that: The curve connected by the voltage borne by the single piece insulator in the clean insulator string is saddle-shaped. The voltage borne by the high-voltage end and the low-voltage end is large, while the voltage borne by the middle part of the insulator string is small. With the increase of pollution degree, the overall trend of potential distribution remains unchanged, but the higher the pollution degree is, the greater the maximum voltage on the high-voltage side of the insulator will be, and the smaller the minimum voltage on the low-voltage side will be. With the increase of pollution degree, the general trend of electric field distribution around insulator string remains unchanged, but the maximum value of electric field increases.

Porcelain suspension insulator for OHTL: A comparative study of new and used insulators using 3D-CT

The 3D-CT technique, which is a non-destructive method, is used to verify the use of porcelain insulators for overhead transmission lines (OHTL). 3D-CT techniques are often used to detect defects such as cracks in automotive parts or in the medical field. The results of the 3D-CT technique applied to porcelain insulators indicate a clear difference in the size and distribution of pores between new and used porcelain insulators. The most significant difference is the degradation rate of the porcelain insulator. In the case of the used product, the largest pore size of 24 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> was found in the cement part exposed to the external environment; however, no pore was found in the new product. In addition, for the used porcelain insulator, 18 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> pores were found in the pin head part, which is a part where stress is concentrated; however, few small pores were found at the same position in the new porcelain insulator. Based on the size and distribution of the pores, the areas where the deterioration was the most rapid were identified. The pore area of the cement at the bottom of the cap was five times larger than that at the top when compared to the total area of the cement. This study confirms the size and distribution of defects occurring in the insulator based on aging and provides insight into the long-term reliability and life prediction of insulators.

Stress Simulation Study on a Novel Combination String of Transmission Line Insulators

The insulator string mainly plays a role of fixing wire and preventing the current from returning to the ground in the power transmission and transformation project. In order to compress the corridor width of the transmission line and make it convenient for breaking line, we proposed a novel structure in which the V-type fittings and the tensile insulator string are optimally combined. In this paper, the mathematical model of mechanical analysis for the structure is established. According to the equilibrium conditions of space force system, the factors affecting the stress of the structure are analysed. In addition, a simulation model is built in the finite element analysis software. The stress distributions of the new structure by setting two installation angles are calculated and the special parts with weak mechanical properties in the new structure are explored based on the generated stress cloud diagram. We compare the maximum value of the von Mises equivalent stress in the two arrangements. A conclusion of better than 45° at a mounting arrangement angle of 50° was obtained. The research results provide a theoretical reference for further optimization design and installation of the combined structure in the future.

Effects of Lightning Channel Equivalent Impedance on Lightning Performance of Overhead Transmission Lines

Modeling of lightning return-stroke channel affects significantly the estimation of fast-front overvoltages arising across overhead line insulators, thus, also the lightning performance of power lines. This paper introduces a simplified method for estimating the minimum lightning currents causing shielding failure flashover and backflashover of overhead transmission line insulation, as affected by lightning channel equivalent impedance. The validity of the proposed methodology is demonstrated through ATP-EMTP simulations of typical 66 up to 765-kV overhead transmission lines with variable tower ground resistance. An assessment is made of the effects of lightning channel equivalent impedance on the lightning performance of overhead lines, that is, shielding failure flashover and backflashover rates. Lightning channel equivalent impedance values of 1000 and 400 Ω are suggested, respectively, for shielding failure and backflashover studies, based on the results obtained in this paper together with a discussion on the literature data regarding channel impedance.

Synergistic effects of mechanical and environmental loading in stress corrosion cracking of glass/polymer composites

Polymer matrix composites have become one of the most popular advanced materials in various industries due to their outstanding properties, appropriate cost, and various and easy manufacturing methods. Unidirectional glass fiber reinforced polymer composites were investigated in this study for use as insulators in power transmission lines. Synergistic effects of nitric acid exposure, applied tensile stress, and time were examined. Physical and electrical properties of composites including acid/water absorption and current leakage were evaluated. Regarding high voltage tests, a direct correlation was found between the amount of absorbed moisture and the leakage current. Mechanical tests, including tensile, flexural, and compressive strength were performed on glass fiber reinforced polymer composites. The composites were degraded because of the stress corrosion cracking as verified by scanning electron microscopy. Stress corrosion cracking damage affected the composites differently depending on their composition; it was measured by the number of fiber cracks, amount of metallic ion leaching from the fibers, and the reduction in mechanical properties of the composites.

Effects of asymmetrical algal distribution on the AC flashover characteristics of bio-contaminated silicone rubber insulators

Polymer insulators are reported to be contaminated by algae in tropical and subtropical climates around the world. Here, the biological contaminates were sectorial distributed on the insulator surface, stretching from the edge of the shed to the interior section near the core. The radial growth ratio and axial length of the algal column was varying under different environmental conditions. To explore the flashover characteristics under these conditions, the triangle plate model was established, in which algal colonization varied in radial growth ratio and algal column length quantitatively, and the inorganic pollutants were divided into three pollution degrees. The results showed that the increasing algal distribution gradually decreased the flashover voltage, whereas when the algal column was too slender, the flashover voltage increased. Meanwhile, the arc tended to elongate within the bio-contaminated area, and the flashover voltage significantly decreased when the algal column nearly covered the full specimen. Furthermore, surface conductivity and pollutant resistance were theoretically deduced from the Obenaus model, the results of which coincided with the calculated value from the flashover measurements. The change in discharge characteristics was attributed to the loss of hydrophobicity. This research could provide valuable information for the maintenance of bio-contaminated insulators in transmission lines of power systems.

Transmission line insulator fault detection based on ultrasonic technology

With the continuous development of modern society, the construction of transmission network has been rapidly advanced, and the reliability of power supply has been fundamentally improved, but the workload of detecting insulators has also increased. In order to further reduce the tripping rate of the transmission line, the insulator fault detection work cannot be delayed. However, the traditional detection method has low efficiency, poor safety and high cost, which cannot meet the requirements. This paper proposes a method of applying ultrasonic technology to line insulator detection by referring to the application of ultrasonic technology in the United States and South Korea. The method realizes fault detection of the insulator by collecting, processing and amplifying the ultrasonic signal.

Experimental Study of Multiple-Reignition Features of Secondary Arcs on EHV/UHV Transmission Lines

When a single-phase-to-ground fault occurs in a power system, a secondary arc will normally be generated at the fault position after the fault phase has been interrupted. A detailed investigation of multiple-reignition features of secondary arcs on extra-high-voltage/ultra-high-voltage transmission lines is, therefore, very important. In this paper, an experimental setup for generating a secondary arc across a transmission-line insulator string is presented, and both the discharge waveforms and images are synchronously recorded. According to the properties of the discharge waveforms, the discharge process is divided into two stages and each stage is analyzed. The evolution of the volt–ampere characteristic and the resistance–current curve of the secondary arc is found to exhibit hysteresis during the discharge process. Multiple-reignition images of the secondary arcs are converted into binary images using image threshold processing. The arc length and breakdown voltage are discussed in association with the discharge images. Morphological changes in the secondary arc during a single discharge process are analyzed in terms of self-magnetic compression theory, and the extinction mechanism of the arc discharge is discussed on the basis of two theoretical approaches.

The Reasearch development of the Filthy detection technology for Transmission line Insulators

According to the testing methods, filthy degree measurement can be divided into direct detection and indirect detection. This paper reviewed the development history of impurity detection and the current status quo at home and abroad. On the basis of existing research, impurity detection technology application situation, analysis their respective advantages and disadvantages, summarized power system layout is structured and disadvantages. Impurity detection to seek new breakthroughs to integrated a variety of integrated pollution direct detection methods, build a real-time monitoring system, realize the insulator filth adherent state of timely, accurate, in order to reduce the pollution flashover accident and provide support for power grid external insulation protection.

ECONOMIC CORRECTION OF CURRENT DENSITIES IN THE WIRES OF THE EXISTING OVERHEAD LINES OF 110-220 KV

In this article, we present the methods used to date, the choice of the cross-sections of the wires of overhead transmission lines, taking into account not only the losses from the load currents, but also the corona losses and linear insulation of overhead transmission lines. The method of economic optimization of electrical loads and current density in operating air lines is considered, where the target functions are the specific discounted costs for transmission of 1 kW. h of electric power.