Insulation Of Overhead Transmission Lines Research Articles

Ensemble Pretrained Convolutional Neural Networks for the Classification of Insulator Surface Conditions

Overhead transmission line insulators are non-conductive materials that separate conductors from grounded transmission towers. Once in operation, they frequently experience environmental pollution and electrical or mechanical stress. Since adverse operational conditions can lead to insulation failure, regular inspections are essential to prevent power outages. To this end, this paper proposes a novel technique based on deep convolutional neural networks (CNNs) to classify high-voltage insulator surface conditions based on their image. Successful applications of CNNs in computer vision have led to several pretrained architectures for image classification. To use these pretrained models, a practitioner typically fine-tunes and selects one final model via a model selection stage and discards all other models. In contrast with many existing studies that use such a “winner-takes-all” approach, here, we identify the best subset of seven popular pretrained CNN architectures that are combined by soft voting to form an ensemble classifier. From a machine learning (ML) perspective, this focus is warranted because the convolutional base of each pretrained architecture operates as a feature extractor and an ensemble of them works as a combination of various feature extraction rules. Our numerical experiments demonstrate the advantage of the identified ensemble model to individual pretrained architectures.

Detection of overhead line glass insulator condition using dual function device and deep learning approach

This paper presents a design of a multifunction smart wireless device for online condition monitoring of transmission line insulators. The proposed device can measure the insulator leakage current and take images of the high-voltage insulation. Yolov5-based models and deep convolutional neural networks (DCCN) are developed to analyze and classify the measured data and estimate the insulator's health condition. We have developed and tested a prototype of the proposed device. The device can issue a real-time warning message when a sudden change takes place in the leakage current value. The control center or smartphones receive the collected data wirelessly. We analyze the transmitted data using the developed methods to detect any anomalies and take appropriate remedial action. The performance and feasibility of the developed device are assessed through extensive experimental analysis. Results attest to the robustness of the proposed device, which is easy to install for existing and future overhead transmission line insulators.

Technique for Order Preference by Similarity to an Ideal Solution‐based comprehensive health assessment of composite insulators for overhead transmission lines

Technique for Order Preference by Similarity to an Ideal Solution‐based comprehensive health assessment of composite insulators for overhead transmission lines

Understanding Failure analysis using harmonic analysis and empirical mode decomposition techniques

The investigation pertains to the failure analysis of Fibre Reinforced Plastic rods used in overhead transmission line insulators using appropriate data acquisition and analysis. The leakage current data, over an experimental period is captured and time–frequency analysis is implemented for determining the in-service condition of the overhead transmission insulators. It is observed from the investigation that the signal displays various events like dry-band arcing, partial surface arcs and triple-point discharges at the electrodes. The study presents a simple time–frequency analysis used for presenting the phenomena, an algorithm is developed for the harmonic analysis, also Empirical Mode Decomposition is conducted to reinforce the analysis. The main focus of the study is to estimate the early failures with minimal time and with available data.

Tensile properties of hybrid kenaf/glass fiber reinforced epoxy composites with different stacking sequence using experimental and FEA simulation method

The conventional overhead transmission line insulators are usually made of glass and ceramics, but the materials are heavy and bulky. Therefore, kenaf fibre was chosen as partial replacement material to be reinforced with Glass/epoxy composite to reduce the weight and bulkiness of the composite structures. This study used Epoxy as matrix and kenaf/glass fibres to reinforce fillers to fabricate the composites in various stacking sequences. Finite Element Analysis (FEA) was carried out using LS-DYNA software to investigate the tensile properties of the hybrid composite. The results showed a significant improvement in tensile values of the modelled composite exhibited by the kenaf/glass fibre. The tensile strength of the hybrid composites was comparable with the Glass/Kenaf/Epoxy hybrid composites’ experimental results. About 200% tensile strength improvement can be observed for both experimental and numerical for G/K/G/E sample than pure epoxy samples, thus making the new composite a potential substitute for insulator applications.

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.

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.

Evaluation of flashover voltage property of snow accreted insulators for overhead transmission lines, part III - 154 kv full-scale flashover voltage test of snow accreted insulators -

In December 2005, Japan experienced a major outage in Niigata Kaetsu area due to a large amount of wet snow mixed with sea-salt accreted on several transmission line insulators. To clarify the causes of the snow-induced outage and increase reliability of the networks, a 154 kV class full-scale snow test procedure to evaluate various insulator designs was developed, and artificial flashover voltage tests of snow accreted insulators were carried out. High voltage flashover tests showed that the flashover voltage of both long-rod and cap & pin insulators was decreased with the increase of snow conductivity. Also, cap & pin insulators showed significantly higher flashover voltage than long-rod insulators. Thus substitution of long-rod insulators with cap & pin insulators appears to be reasonable as a countermeasure against snow induced flashovers.

Evaluation on flashover voltage property of snow accreted insulators for overhead transmission lines, part I - field observations and laboratory tests to evaluate snow accretion properties

This paper presents evaluation of snow accretion properties of long-rod and cap & pin insulators focusing on the phenomena found in the snowstorm in 2005, which related to wet snow accretion packed with sea-salt. Field observations at severe natural environment and laboratory tests under defined conditions were parallelly carried out in order to clarify wet snow accretion process under various conditions. In field observations, it was confirmed that snow easily accreted on insulators at temperature range especially between 0 and +1.0°C. The long-rod insulator's sheds were bridged more easily than that of cap & pin type because of its narrower shed spacing. In laboratory tests, cylindrical snow accretion, which was found in the snowstorm in 2005, was achieved. The mechanisms on explaining snow accretion on long-rod insulators were found to be similar to those confirmed for wires. The laboratory simulations agree well with the field observations. In order to estimate the amount of snow flux on insulators caused by a snow event for given climatic conditions, an index called the snow accretion potential ability (SAP) was proposed. SAP is defined by using the snow flux and associated with the weight term in the index for the snow stress product (SSP). SAP was adopted to evaluate snow accretion characteristics by field observations and laboratory tests, and the snow accretion phenomenon during a snowstorm in 2005 was discussed.

Evaluation on flashover voltage property of snow accreted insulators for overhead transmission lines, part II - flashover characteristics under salt contaminated snowstorm

This paper presents the flashover characteristics of snow-bridged insulators, and the related discharge propagation phenomena in the presence of salt contaminated snowstorms. Two types of flashover tests, a) Snow accretion without voltage application, then apply the voltage after snow accretion, b) Snow accretion during voltage application, were carried out on a 33 kV long rod insulator with the snow conductivity controlled between 180 and 980 μS/cm. Method a simulates the cold switch-on situations. In this case, the flashover voltage is found to be inversely proportional to the fifth root of the snow conductivity. Further, the flashover voltage showed a relation to the leakage resistance of snow-bridged insulators. Method b simulates energized situations during a snowstorm. The concept of Method b is equivalent to the “Ice Progressive Stress (IPS)” method described in the IEEE Std. 1783-2009. In this case, partial arc discharges gradually increase owing to the development of snow accretion. Flashovers are mostly induced during the period of snowstorm suspension, because the arc discharge can develop into a flashover without the cooling effect of the blizzard. Melting snow by heating of electric power does affect flashover characteristics. The minimum flashover stress by Method b is lower than that by Method a. However, in particular case of Method b with higher snow conductivity, too much discharge activities prevent snow accretion on the insulator. This leads to snow melting or snow shedding.

Comparison of External Insulation Level between AC and DC Overhead Transmission Lines

It is important to choose suitable insulator strings that matching the voltage level when trying to change an AC transmission line into a DC one. Historically based, most published works discuss the way of determining the number or the length of insulators for overhead transmission lines, which mainly consider about voltage levels, pollution classes, insulator types and their pollution performances. It calls for too much work for a line restructuring project. In order to simplify the work, a comparison of the choosing of insulator strings between AC and DC overhead transmission line is made in this paper. Two main results are obtained. One is that the ratio, which defined as α, of the number of insulator on DC transmission line and that on AC transmission line ranges from 1 to 2.5 with the decreasing of voltage level under the same pollution class, the other is that the value α remains substantially constant under the same voltage level, and it will decrease slightly as the pollution class increases. The results provide theoretical basis for the choosing of insulator strings in line restructuring projects.

Simulation of overhead transmission line insulators under desert environments

Till today, flashover because of pollution of insulators of overhead transmission lines (OHTL) is a major source of trouble in the electrical power transmission system. The importance of this problem can be assessed from fault statistics of high-voltage transmission lines. In Egypt, for example, about 82% of the total faults of transmission and distribution OHTL are because of pollution. This study deals with laboratory tests, which have been carried out on polluted insulators of the OHTL that simulate desert environments. In this study, the effect of the variation of conductivity of the polluted layer by means of equivalent salt deposit density on flashover voltage (FOV) is investigated. The effect of variation of conductivity of the polluted, layer along the time required by the procedure needed to form dew, on FOV is also studied. This study is useful for indicating the worst period after the formation of dew, where the probability of flashover is increased.

Snow accretion on overhead wires

Although snow accretion on overhead wires is a serious problem, recognized physical models have not yet been established. In this paper, attempts directed at understanding the mechanism of snow accretion on wires are reviewed. Fundamentals of the meteorological conditions under which snow accretes on wires, inferred mechanisms, mechanics and heat balance of snow accretion are briefly reviewed. A short historical review of research works throughout the world is given. Wind–tunnel tests aiming at examining the dependence of various parameters on the characteristics of accreted snow on wires are introduced and defects of such tests are discussed. Finally, attempts to establish snow–load design on power lines, with some results of observations under natural conditions, are briefly discussed. It should be emphasized that the present paper is characteristic of an interim report and summary about snow accretion on overhead wires, with the purpose of avoiding repetition of the same kind of research efforts and therefore accelerating further progress.

Interfacial breakdown on contaminated electrolytic surfaces

The insulation of overhead transmission lines and substations is subjected to several basic types of abnormal conditions that can cause flashovers and outages of long duration. One of these types is the abnormal voltage gradients in the insulation system caused by the contamination of solid insulator surfaces. The number of insulators needed to protect against contamination is uncertain, because there is a wide range in the severity of contamination, and there is considerable uncertainty as to the basic mechanisms by which contamination affects the insulation level of a given configuration. This paper outlines the results of investigations of interfacial breakdown on electrolytic surfaces. Models are used to simulate such polluted insulator problems. Effects of chemical nature of the contaminants and contamination levels on the critical flasher voltage are studied. In order to study such effects, different salts and salt combinations were used on the laboratory model. Single-arc and multiple-arc models are introduced where the phenomena of multiple discharges existing simultaneously on an electrolytic surface is also investigated. Mathematical models are suggested which include the successive formation of multiple arcs. The results obtained based on the new model agree quite well with the experimental values.

Development of a new apparatus for contamination measurement of overhead transmission line insulators

The authors have developed new apparatus capable of detecting contamination on the insulators of overhead power transmission lines. The apparatus consists of multiple leakage current detectors with Peltier modules and features very compact size and light weight. Accumulated contaminants can be measured automatically and continuously without wiping them. The apparatus has demonstrated excellent performance in both laboratory and field tests.