Performance Of Outdoor Insulators Research Articles

Environmental Effects on Parameters of Leakage Current Equivalent Circuits of Outdoor Insulators

The performance of outdoor insulators in transmission lines may deteriorate due to aging and can even be enhanced by the presence of pollutants. Leakage current (LC) measurement is one of the most effective methods to diagnose the insulator condition, utilizing LC parameters such as magnitude and total harmonic distortion (THD). However, research on the interpretation of these parameters is still limited. This paper discusses the diagnostic method by simulation, employing the LC equivalent circuits of different types of insulators and examining the influence of environmental factors, such as humidity and pollutant levels. LC waveforms are first obtained through experiments on various insulator types, including traditional ceramic and glass insulators, advanced composite insulators, or the hybrid type of RTV silicone rubber-coated and conducting glazed insulators. Subsequently, simulations on the LC circuits of Suwarno’s and Kizilcay’s models are performed to obtain similar LC waveforms and properties. The values of the equivalent circuit parameters are then used to diagnose each insulator’s characteristics and environmental effects. The results indicate that composite insulators of epoxy resin or SiR have a larger intrinsic resistance of ~40 GΩ and nonlinear resistance (a few MΩ to tens of GΩ), representing high surface resistance of the insulators against water and pollutants. A comparison of these parameters is expected to indicate the severity levels of insulator condition. Doi: 10.28991/ESJ-2024-08-01-022 Full Text: PDF

Improvement of the Electrical Performance of Outdoor Porcelain Insulators by Utilization of a Novel Nano-TiO2 Coating for Application in Railway Electrification Systems

The present study aimed to develop the electrical performance of outdoor insulators using a nano-TiO2 coating for railway electrification systems. The prototype design of porcelain insulators with normal coatings and using a nano-TiO2 coating is based on IEC 60815-1. The first test was performed to measure the low-frequency flashover AC voltage under both dry and wet conditions. In addition, the other test was conducted to measure the lightning impulse critical-flashover voltage at positive and negative polarity under dry-normal and wet-contaminated conditions. X-ray diffraction (X-RD) and Scanning electron microscopy (SEM) were used to examine the micro surface and show that the nano-TiO2 coating was adhered to the surface of the outdoor porcelain insulator and exists in an amorphous state. Additionally, it was observed and discovered that scattered nano-TiO2 strengthens the glassy matrix and creates a sturdy barrier that causes flashover voltage to be reduced under conditions of high dielectric strength. Nanostructured ceramic formulations outperform ordinary porcelain in terms of breakdown voltage strength, particularly for the insulators’ low-frequency flashover performances under dry and wet test conditions. However, a significant change in the lightning impulse critical-flashover voltage characteristics is observed and is not much better when adding the nano-TiO2 coating to the porcelain insulators.

Predicting the DC pollution flashover voltage on the insulation surfaces with superhydrophobicity

Cleanliness and desiccative are necessary for outdoor insulation surfaces to maintain the voltage withstand capability especially in humid and polluted operation conditions. Once the voltage withstanding capability of insulation coatings is reduced by contaminant electrolyte, flashover accidents would be easier to happen, causing tremendous economy and energy losses. Superhydrophobic coatings, due to their self-cleaning property, are deemed to have great application potential in maintaining outdoor insulation performance, especially in humid and polluted environments. The water patterns on superhydrophobic coating in humid and polluted conditions are obviously different from those on traditional insulation coatings. Flashover voltage is one of the indices for quantifying insulation strength, while to date it is still unclear whether the commonly-used flashover voltage prediction models based on Obenaus’s theory are still suitable to be applied in the cases with superhydrophobic surface. Here we proposed a facile and low-cost preparation method of superhydrophobic coating. By analyzing the specific surface condition under humid and polluted conditions, and considering the development of arc path, a novel theoretical model for predicting flashover voltage of superhydrophobic coatings is established from the perspective of electric field. The flashover voltage of the synthesized coating as well as Room Temperature Vulcanized (RTV) silicone rubber coating are tested and compared, for investigating the insulation strength on the synthesized superhydrophobic coating, and verifying the accuracy of the proposed prediction model. It is found the synthesized superhydrophobic coating shows self-cleaning property during the wetting and voltage applying process, the flashover voltage of superhydrophobic coating is higher than that of RTV coating, and is affected less obviously by the change in pollution degree, compared with RTV coating. The established model shows better accuracy in predicting the flashover voltage of superhydrophobic coating than the traditional one, with errors of less than 6%. Based on the proposed model, the flashover voltage of polluted superhydrophobic coating surface is positively and negatively related to the volume and the contact angle of the polluted electrolyte droplet, respectively.

Laboratory investigation of the impact of air pollution on partial discharge inception voltage of insulators in a specific region

<span lang="EN-US">Studying the discharge characteristics of transmission line insulators in the presence of pollution, particularly when the contaminated layer is wet by rain, fog or condensation, is necessary for selecting the proper insulation. Therefore, identifying the major air pollutants as well as the most effective ones on the discharge performance of outdoor insulators is mandatory. A systematic approach has been proposed to evaluate the impact of dominant air pollutants of an area on partial discharge (P.D) inception voltage of specimen insulators. Based on the suggested method, determining the pollution constituents, defining the dominant pollutant of the area, finding the most commonly used insulators for medium and above distribution voltages within the geographical boundaries of the Central Province of Iran, as well as examining the effect of dominant air pollutant of the region on partial discharge inception voltage of designated insulators by laboratory measurements, are the necessary steps toward a comprehensive study of the subject.</span>

Condition Monitoring of Outdoor High Voltage Insulators, Online and Offline Techniques: A review

Outdoor insulator plays a vital role in high voltage transmission and distribution system. The performance and properties of outdoor insulator may severely affect due to various types of pollutants. The failure of insulation in high voltage system results in loss of supply and a huge loss of electrical energy to distribution utilities. In order to reduce power losses and provide a reliable power transmission, selection and design of insulators is very important. To monitor the condition and performance of outdoor insulator in contaminated conditions an appropriate diagnostic technique is required. In this paper various online and offline techniques for conditioning monitoring of outdoor insulators are reviewed under different contaminated conditions. To maintain the healthy environment, the condition monitoring of power line insulators is an important requirement. There are number of techniques that have been introduced to fulfil this requirement. Each technique used at different contaminated condition have their own pros and cons. The findings indicate that the most important effect on the surface of the insulators based on the contamination on the surface leakage current and the flashover voltage. This paper will help in the selection and design of condition monitoring techniques for high voltage outdoor insulator.

Discharge Behavior and Morphological Characteristics of Suspended Water-Drop on Shed Edge during Rain Flashover of Polluted Large-Diameter Post Insulator

Rain is one of the dominant meteorological factors threatening the outdoor insulation performance of ultra-high voltage (UHV) power stations. Discharge occurring on the polluted surface of post insulators in rain has always been a major concern of power stations. Previous studies have shown that suspended water droplets on the shed edge play an important role in the rain flashover process. In this work, artificial contamination rain flashover tests were carried out in a laboratory on a UHV DC (Ultra-High Voltage Direct Current) large-diameter composite post insulator, which had a rod diameter of 625 mm and alternating sheds (105 mm and 75 mm for larger and smaller shed overhang, respectively). The discharge mechanism was analyzed base on the observation of discharge phenomenon of suspended water-drops on the shed edge. Moreover, simulation models by COMSOL Multiphysics were established to investigate the electric field around sheds and suspended water-drops, as well as the shape change of water droplets on the insulation surface, especially at the edge of the shed. Results show that the shape parameters of water-droplets changed continuously under the combined action of gravity, surface tension, and capillary tension. Suspended water-droplets on the shed edge showed a great influence on the electric field distribution, and the resulting discharge lead to the bridging between sheds. This work paves a new way to revealing the contamination rain flashover mechanism on post insulators and provides critical knowledge for power stations on preventing flashover accidents.

Improving the outdoor insulation performance of Chinese EHV and UHV AC and DC overhead transmission lines

Power girds in different countries face different types of threats and in China the threats severely affecting grid reliability were in the past large power outage accidents caused by pollution flashovers. First records of pollution flashover accidents in China can be traced back to 1950s in industrial areas in Northeast and East China. Thereafter, such accidents occurred occasionally, but after 1970s they started to expand and were recorded in most of the country's provinces. The very first large area outage accident caused by pollution flashover happened in early 1974 in Northeast China around the local largest cities Shenyang and Fushun. Between 1971 and 1994, 3542 pollution-caused line trip-outs (several trip-outs on one overhead line (OHL) happening the same day is counted in China as a single event) were recorded on 35-500 kV OHLs and 1768 substation trip-outs. A total of 44 large area outage accidents caused by pollution flashovers took place during the 30 year period before 2007, as shown in Figure 1, while the outages recorded between 1981 and 2001 accounted for 43% of the total number. Among them, outages of super large character occurred every 5-6 years, e.g., in 1990 in North China and Northeast China, in 1996-1997 in East China and Central China, 2001 in North China and Northeast China [1-3]. Here we refer to the large area outage accidents as flashover events on several main transmission overhead lines and substations, appearing during one or several consequent severe meteorological events and continuing for several days. They affect several big cities within one province and stretch over an area of less than 100 thousand km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . For super large area outage accident, we refer to the accidents stretching across several provinces over the area of 200-300 thousand km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and resulting in hundreds of pollution flashover events.

Performance of outdoor insulators in tropical conditions of Sri Lanka

Ceramic insulators, specifically porcelain and glass insulators, have widely been used all over the world since the 19th century [1,2]. However, when such insulators are energized and exposed to different pollution environments under different climatic and weather conditions, leakage current (LC) develops along their surfaces [3-7] and eventually cause flashovers. Various remedial measures have been adopted by power utilities to mitigate this problem. Among the common methods are: (a) increasing insulator creepage (leakage) distance, (b) reducing supply voltage, (c) insulator washing (cleaning), (d) oiling or greasing (silicone) the insulator surface, and (e) insulator replacement. Composite insulators, also referred to as non-ceramic or polymeric insulators, have also been used during the last six decades as an alternative to the ceramic insulators [8-10]. The housing materials most often used have been silicone rubber (SIR) [11] and ethylene-propylene-diene-monomer based rubber (EPDM) [12]. Water repellent (hydrophobic) properties of composite insulators, light weight, resistance to vandalism are among the main reasons for their usage. This has been proven by positive outcomes of numerous studies performed in laboratory and field conditions [8,9,13-16]. However, due to exposure to harsh service stresses such as corona discharges, UV radiation and chemical attacks etc., the housing materials may lose hydrophobic properties and develop surface degradation (tracking, erosion). In addition to the ever-increasing use of composite insulators, polymeric coatings (mainly RTV silicone rubber) [17] and semi-conducting glazes [18] have also been adopted for improving performance of ceramic and glass insulators [19].

Power utility perspective on natural ageing and pollution performance of outdoor insulators

For many years Eskom has followed international guidelines in selecting transmission and distribution insulator products for use in polluted environments.

Online Condition Monitoring and Leakage Current Effect Based on Local Area Environment

High voltage outdoor insulator plays a pivotal role in safety and reliability of power transmission system.Contamination severely influences the performance of outdoor insulator. To asses contamination severity on insulator surface and to predict flashovers, leakage current monitoring is required. The amount of leakage current flowing on the surface of insulator indicates insulation safety. Increase in leakage current generates high voltage peaks at insulator dead ends. The voltage may be as high as 1000–5000 volts, mainly depends on certain weather conditions, results in enormous amount of power losses and threat to public safety. The insulator performance depends on amount and type of pollution and wetting mechanism. Leakage current is important tool to investigate insulator electrical surface activity. The scope of this paper is to review leakage current effect based on local area conditions. Leakage current importance for insulators and different techniques used to measure leakage current in lab and at field, special focus on online leakage current monitoring.

Fixed least squares support vector machines for flashover modelling of outdoor insulators

Many theoretical and experimental studies have been performed to optimize the maintenance times of outdoor insulators. But most of the proposed methods are both time consuming and difficult to apply in practice and also they rely mainly on pollution charts and they are not reliable to weather variations. Artificial intelligence has been extensively applied to solve a large number of electrical and high voltage engineering modeling and optimization problems. In this paper, a methodology based on modified LS-SVM strategy using a fixed set of support vectors is proposed to evaluate the flashover performance of outdoor insulators under contaminated conditions, where the candidate support vectors are selected from the training set according to a quadratic Renyi criterion. The obtained results are promising and ensure that the presented technique can help high voltage engineers to assess insulator performance including such important factors as the flashover behavior, the insulator geometrical parameters, aging, and contamination accumulation. Further comparative analysis of the estimated results with the measured data collected from the site measurement demonstrate the effectiveness of the use of fixed-size LS-SVMs models for flashover prediction.

Inhibition of algae growth on HVDC polymeric insulators using antibiotic-loaded silica aerogel nanocomposites

Algae contamination has been observed on high-voltage direct current transmission (HVDC) polymeric insulators in tropical and subtropical areas, and this has an impact on the outdoor insulation performance. In this paper, the antibiotic 4,5-dicholoro-2-octyl-2H-isothiazolone-one (DCOIT) was chosen to be loaded onto the porous silica aerogel through sol-gel and dip-molding methods; the nanocomposites were mixed with base silicone rubber to prepare the antibiotic polymeric insulator. The algae inhibition properties of the insulators were characterized by the damaged membrane rate, photosynthesis rate (SAT) and chlorophyll-a density (Chl) of the algae cells. The results showed that the antibiotic insulators were free from algae colonization and that the extermination process could be completed within 21 days. During the antibiotic treatment process, the specimen surface stayed hydrophobic because of the water repellent property of nano silica. Meanwhile, due to its excellent dispersibility and electrical resistivity, the volume conductivity and surface conductivity were slightly increased in the initial period within insulation margins. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) of antibiotic-containing insulators was carried out, and the intermediate products in the treatment process were verified. After algae apoptosis, the functional group on the silicone rubber was returned to its initial condition before algae colonization. After application on-site for 1 year, the antibiotic-loaded insulators retained antibiological properties without algae spots upon their surfaces.

Properties and applications of superhydrophobic coatings in high voltage outdoor insulation: A review

The deposition of ice, snow, pollution or their mixtures on the surface of outdoor insulators may severely affect their performance, resulting in electrical and or mechanical failures. Various preventative methods are used to minimize the problems of ice and pollution build up on the surface of outdoor insulators. In the last few decades, advanced coatings have been developed for better performance of outdoor insulators in contaminated and freezing environments. These advanced coatings offer the advantage of low wettability, high thermal and ultraviolet resistance, self-cleaning, self-healing, low ice adhesion strength and delayed freezing time. It is believed that these benefits will not only increase the reliability of transmission systems but may also reduce the capital cost of transmission infrastructure. This paper presents a detailed review on the properties and applications of superhydrophobic coatings in outdoor high voltage insulation. This review can be beneficial to scientists and engineers in evaluating the performance and durability of superhydrophobic coatings in polluted and freezing conditions. It also highlights the need for standardized tests and procedures for better understanding the behavior of superhydrophobic coatings in different environments and their long-term durability.

Comparative investigation of silicone rubber composite and room temperature vulcanized coated glass insulators installed in coastal overhead transmission lines

The fault-free performance of outdoor insulators is a matter of great importance for power utilities as a single insulator fault may lead to an extended outage. Several factors related to operation conditions affect the performance of outdoor insulators, with pollution being probably the most significant one [1]-[3]. Coastal areas are considered heavily polluted due to the deposition of sea salt on the insulators. When the deposited salt is diluted in water through humidity, drizzle, fog, or light rain, a conductive solution is created and leakage current flows on the surface. The activity may advance, under favorable conditions, to flashover. Therefore, the local weather and climate is an important factor for the determination of pollution severity as strong winds carry more salt and frequent rains may provide natural cleaning.

Experimental study using design of experiment of pollution layer effect on insulator performance taking into account the presence of dry bands

Performance of outdoor insulator under polluted conditions depends specially in the contamination layer configuration and conductivity, which makes important to take them into account during the conception and the design of new insulator. This paper presents an experimental study of the flashover voltage of polluted insulator as a function of pollution layer parameters such as; conductivity, layer length, position, number and width of dry bands. Many configurations of pollution distribution are studied using design of experiment methodology. Parameters effects and their interactions have been investigated and evaluated using ANOVA variance analysis statistical technique. The relationship between pollution parameters and the flashover voltage are modeled and analyzed using response surface methodology. Results show how much the flashover voltage of non-uniformly polluted surface is mainly influenced by length of contamination layer and conductivity. Moreover, the obtained statistical models of flashover voltage are adequate with experimentation results. Such information can be exploited to optimize the design of glass insulator used in polluted areas, by making suitable design to create much and wider dry bands in the middle of the insulator surface.

Coupled field finite element analysis of pin-and-cap disk type insulator assembly

Extensive research has been done throughout the world on the performance of outdoor insulators and insulator assembly, in the area of structural, thermal and electrical analysis. These effects, i.e., structural, thermal and electric have been studied on individual basis only. That is only one effect is considered, however in the real field these effects should be considered simultaneously for the complete analysis of insulator and insulator assembly since these three effects are present at the same time. In this paper, coupled field structural-thermal-electrical finite element simulations are carried out by using a commercially available software package, which allow quantifying the effects of insulator assembly on when structural, thermal and electrical load distribution are considered simultaneously. The structural, thermal and electrical results are obtained for a single 11 kV cap-and-pin type ceramic disc type insulator assembly are analysed and presented. It is observed that under normal working conditions of an insulator assembly the structural, thermal and electrical loads are found mutually coupled, but not going to affect the structural, thermal and electrical characteristics of an insulator assembly and its components.

50 years in icing performance of outdoor insulators

During the last 50 years a significant technical advance, namely in our understanding and control of switching-surge overvoltages, has had some unintended and adverse consequences when designers took full advantage of the possibility of reduced insulator dimensions. Glaze ice accretion can produce harmful effects, especially on closely spaced or large-diameter station post insulators and bushings. Partial or full bridging of the leakage distance occurs for moderate ice-accretion levels and reduces insulator reliability during melting in saturated conditions. Colocation of HV or EHV substations with roads or expressways on which deicing salt is spread has proved particularly problematic. The DEIS has played an important role as a forum for exploring icing flashover physics and as a sponsor of improved test methods and applications guidance.

Measurement of leakage current for monitoring the performance of outdoor insulators in polluted environments

Monitoring of leakage currents on various types of insulators, in the field and in laboratory tests, has provided a much broader perspective on the performance of outdoor insulators in various pollution zones. The technique can be effective for corrective maintenance of transmission lines, provided the type of pollutant and the critical leakage currents are analyzed periodically. A leakage current that is continuous, periodic, or increasing with time is one consideration in the performance of insulators in pollution zones, whereas the maximum permissible levels of leakage current at flashover, which is considerably different for each insulator profile, is another consideration. What this means is that insulators showing lower leakage currents will not necessarily have the best operating performance. The insulator profile affects the accumulation of pollutants, which defines their pollution performance, and control of the leakage current by the insulator design depends largely on the type of pollutant. As a result, there is no unique solution, and leakage current values with flashover risk from laboratory tests for various types of insulators must be determined by using the type of pollutant in the field. This combination of strategies will provide an effective means of ensuring reliable transmission line operation in pollution zones.

Installing insulation jacket to improve outdoor insulation performance of composite insulator

In the paper, a new approach is proposed to improve the outdoor insulation properties of transmission lines. It is achieved by installing the insulation jackets and additional grading rings onto transmission line conductors. The impact of insulation jacket parameters on the electrical field distribution along a 220 kV composite insulator was simulated by a finite element program assuming dry surface contamination. The corona inception voltage was measured on real composite insulators and the measurement results verified the conclusion from the simulation. Furthermore, the correlation between the insulation jackets' length and the contamination flashover voltage of composite insulators was studied. Based on the measurement and simulation results, the optimal insulation jacket parameters are suggested. In the last part of this paper, insulation jackets manufactured according to the optimal parameters are installed onto the transmission line conductor in the field. During one year of operation, the positive effect on the electric field distribution and the reliability of the installed insulation jackets have been confirmed.

Investigation of Leakage Current Waveforms Recorded in a Coastal High Voltage Substation

Leakage current monitoring is a widely employed technique to monitor the performance of outdoor insulation. The evaluation of leakage current waveforms recorded in the field, offers significant information since insulation’s performance is strongly linked with local conditions, and the waveforms’ shape correlate to different types of surface activity. In this paper, an investigation of leakage current waveforms recorded in a 150 kV coastal Substations suffering which suffers intense marine pollution is presented. Investigation of the recorded waveforms verified the basic waveform shapes described in the literature. Further, several variations of the basic types and complex waveforms, as well as field related waveforms, are presented. The need for added categorization criteria in the case of field measurements is discussed.