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Abstract The valve‐side bushing of the UHV converter transformer is the key equipment in the DC transmission project, and its running state directly affects the security and stability of the power system. This paper analyses the attributes of the physical entities, uses the digital twins to establish the state feature set and proposes a zero‐sample state evaluation algorithm for the valve‐side bushing. First, the geometric, materials and electrical characteristics are analyzed, and the detailed components of carrier current are obtained by empirical mode decomposition. Then, COMSOL is used to establish digital twins, verify the validity of twins with axial heat distribution of bushing, and establish a state feature set with the extreme temperature inside and outside bushing. Finally, the fuzzy clustering algorithm is used to classify the state feature set, and the similarity is used as the index to realize the zero‐sample state evaluation of the valve‐side bushing. Through the demonstration and analysis of examples, the evaluation model solves the problems of difficulty in extracting the internal features, fewer fault samples, and training difficulty, which is conducive to improving the operation and maintenance management level of power transmission equipment.

The valve‐side bushing of the UHV converter transformer is the key equipment in the DC transmission project, and its running state directly affects the security and stability of the power system. This paper analyses the attributes of the physical entities, uses the digital twins to establish the state feature set and proposes a zero‐sample state evaluation algorithm for the valve‐side bushing. First, the geometric, materials and electrical characteristics are analyzed, and the detailed components of carrier current are obtained by empirical mode decomposition. Then, COMSOL is used to establish digital twins, verify the validity of twins with axial heat distribution of bushing, and establish a state feature set with the extreme temperature inside and outside bushing. Finally, the fuzzy clustering algorithm is used to classify the state feature set, and the similarity is used as the index to realize the zero‐sample state evaluation of the valve‐side bushing. Through the demonstration and analysis of examples, the evaluation model solves the problems of difficulty in extracting the internal features, fewer fault samples, and training difficulty, which is conducive to improving the operation and maintenance management level of power transmission equipment. [ABSTRACT FROM AUTHOR]

• Polymer insulators are susceptible to damage and accelerated aging due to contaminants, impacting their performance and structural integrity. • This study conducts comprehensive investigations about discharge behaviors of polymer insulator when exposed to three distinct contaminants: fly ash, salt, and algae. • Measurements of inception and surface breakdown voltages, along with partial discharge patterns, reveal unique responses to each contaminant. Salt intensifies electrical stress under dry conditions, accelerating aging and increasing partial discharge compared to other contaminants. Fly ash alters Partial Discharge Inception Voltage and Surface Breakdown Voltage, enhancing surface discharge performance, while algae's biofouling process deteriorates insulator surfaces, decreasing PDIV and altering PD patterns. • The findings of this study contribute to the enrichment of references related to partial discharge (PD) phenomena caused by salt, fly ash, and algae contaminants. By identifying unique PD patterns associated with each contaminant, this research enhances the ability to diagnose and mitigate insulator degradation in diverse environmental conditions. The performance of polymer insulators can be significantly compromised by the presence of contaminants, resulting in damage, structural alterations, and accelerated aging. Hence, this research aimed to investigate the discharge behavior of polymer insulators when exposed to various types of contaminants. Three distinct contaminants, namely fly ash, salt, and algae, were prepared for the study. In order to assess the characteristics of these insulators, measurements of inception and surface breakdown voltages were conducted for each sample. Additionally, partial discharge measurements were performed at two different applied voltages to observe the patterns of partial discharge under different contaminants. To aid in distinguishing the characteristics of partial discharge, a statistical method based on graphical analysis was employed. Furthermore, visual inspection was carried out after the occurrence of partial discharge activity to provide an explanation for these phenomena. The findings of the study revealed that each contaminant produced a unique pattern, which was influenced by the specific elements present in the respective contaminant. It was observed that contaminants exhibit varying effects on partial discharge depending on their nature. Salt was found to induce faster stress propagation, fly ash inhibited stress propagation, and algae had a degrading effect on the surface of the polymer insulators. [ABSTRACT FROM AUTHOR]

Polyethylene based polymeric insulators, are being increasingly used in the power industry for their inherent advantages over conventional insulation materials. Specifically, modern power cables are almost made with these materials, replacing the mass-impregnated oil-paper cable technology. However, for ultra-high dc voltage applications, the use of these polymeric cables is hindered by ununderstood charge transport and accumulation. The conventional conduction mechanisms (Pool-Frenkel, Schottky, etc.) fail to track high-field charge transport in low density polyethylene, which is semi-crystalline in nature. Until now, attention was devoted mainly to the amorphous region of the material. In this paper, authors propose a novel mechanism for conduction in low density polyethylene, which could successfully track experimental results. As an implication, a novel, substantial relationship is established for electrical conductivity that could be effectively used for understanding conduction and breakdown in polyethylene, which is vital for successful development of ultra-high voltage dc cables. [ABSTRACT FROM AUTHOR]

Abstract Gas‐filled internal crack might appear in thermoset materials like epoxy resin during the equipment manufacturing, which would become a vulnerable local region to initiate the electrical tree, thus prone to cause insulation failure. The withstand voltage test was carried on epoxy samples with artificial cracks based on a rod‐plane electrode arrangement. Simultaneously, surface state variation and tree evolution with crack were observed by an optical microscope in conjunction with a charge‐coupled device camera. The changes in morphology and chemical status of the crack surface were characterized by scanning electron microscopy, laser Raman spectrometer and energy dispersive spectrometer, respectively. It was found that the erosion and tree started from the borderline of crack under a relatively low electric field strength; however, the area near the electrode had relatively little damage. The breaking of epoxy molecular chains coarsens the crack surface and further forms deep channels on a micro‐level, which is the forerunner of the electrical tree inception. Based on these, the initiation mechanisms of the crack‐induced electrical tree and the reasons for the erosion near the borderline have been revealed. This study provides a train thought for the polymer degradation opening up into the initial tree channel during tree evolution processes.

Surface tracking and erosion is an irreversible degradation occurring on the insulator surface, and this can ultimately lead to failure of the insulator. Polymeric materials such as silicone rubber have many advantages; including a superior hydrophobic surface. However, polymers are exposed to ageing and degradation resulting from electrical and environmental stresses. The rotating wheel dip test is adopted to conduct a comparative study of surface conduction on the two insulators. A conventional design has been selected and compared with insulators having textured surface. Monitoring of the shed surface and insulator trunk using an IR camera were carried out to assess the temperature distribution along insulator profiles. A spatial analysis was also performed to identify key features of the two designs. Localised surface conductance measurements are proposed in this study. This helps to understand and distinguish the trends of conductance and its distribution on each surface, helping to predict the future surface degradation associated to each design.

With an impetuous growth of DC links and future grids that will be often hybrid, providing AC and DC supply to nearby or the same customer, an important element is often neglected, that is, electrical insulation. There are no doubts that overhead lines will step back compared to insulated cables, for known reasons of environmental impact, right of way and reliability, especially in an urban or harsh environment. On the other hand, while AC insulation systems have been investigated and used for decades, there is no analogue experience for DC polymeric insulation, nor for insulation systems subjected to power electronics supply. This study aims at enhancing the attention on this topic, focusing on insulation ageing mechanisms and models of relevance for hybrid AC/DC assets and grids. Ageing and life models for AC, DC and power electronics supply are discussed and compared to experimental data, focusing on partial discharge and space charge. It is shown how these two phenomena affect lifetime for different AC, DC and transient operating conditions. The main drivers for insulation design and material selection are discussed, showing that insulation reliability can be achieved only if operating stresses, ageing mechanisms and life models are known and accounted for properly by insulation designers.

Charge accumulation has always been a problem for the safe operation of gas insulated switchgear (GIS)/gas insulated transmission line (GIL) both under AC and DC. It is of great significance to investigate the behaviour of surface charge under high voltage. In this study, the charge distribution characteristics and accumulation mechanism on insulator surface in air and heptafluorobutyronitrile/carbon dioxide (C(4)F(7)N/CO(2)) mixtures under AC voltage are studied via the means of surface potential measurement and inversion algorithm, combined with the improved method of controlling the truncated phase of AC voltage. The results show that under the needle–plate electrode structure, charge distribution on the insulator surface presents a three-tier concentric circle structure both in air and C(4)F(7)N/CO(2) gas mixtures, and the charge composition of the innermost circle is closely related to the truncated phase of AC voltage. Under the same amplitude of voltage, the range of charge distribution on insulator surface in C(4)F(7)N/CO(2) mixtures is smaller than that in air, with the negative charges domination. It is suggested that the characteristic of charge distribution in C(4)F(7)N/CO(2) mixtures is related to the larger electron attachment cross-section of C(4)F(7)N gas in a wide range of electron energy distribution.

Polymer is an insulating substance that has become increasingly popular in recent years due to its benefits. Light density, superior dielectric and thermal properties, and water-resistant or hydrophobic properties are only a few of the benefits. The presence of impurities or pollutants on the insulator’s surface lowers its dielectric capacity, which can lead to current leakage. The influence of seawater and fly ash pollutants on the distribution of the electric field and the current density of the insulator was simulated in this study. The finite element method was used to execute the simulation (FEM). Polymer insulators are subjected to testing in order to gather current leakage statistics. The tested insulator is exposed to seawater pollution, which varies depending on the equivalent salt density deposit value (ESDD). The pollutant insulator for fly ash varies depending on the value of non-soluble deposit density (NSDD). The existence of a layer of pollutants increased the value of the electric field and the value of the surface current density, according to the findings. Both in simulation and testing, the ESDD value of seawater pollutants and the NSDD value of fly ash contaminants influenced the value of the leakage current that flowed. The greater the ESDD and NSDD values are, the bigger the leakage current will be.

A better performance and consequently the widespread use of polymeric insulators in different parts of the power grid can increase their role in the grid reliability. The accumulation of contamination and housing‐erosion are the two most effective factors in undermining the performance of this type of insulators. Therefore, electric utilities need to identify contaminated insulators for washing and cracks in polymeric housing to replace them with healthy specimens. This paper discusses the impact of contamination layer and housing‐erosion of polymeric insulators on the partial discharges (PD) at the insulator surface, through RF‐PRPD (phase resolved partial discharge) patterns. The existence of different sources of PDs in a real environment (transmission line or station) makes it difficult to use the PRPD patterns to distinguish them from each other. Therefore, using a conical monopole antenna, the simultaneous PD signals and the related RF‐PRPD pattern of samples under test are captured. The grayscale image was obtained using the time‐frequency matrix of the PD signals transform, by wavelet. Then, features are extracted and selected from grayscale image. By clustering of the PD signals, the resulted RF‐PRPD sub‐patterns are well separated and provided the necessary means to distinguish among the status of different samples under test. [ABSTRACT FROM AUTHOR]

This research provides conclusions that can partially cover the lack of knowledge related to the effects of ambient atmospheric conditions on DC electric power transportation. Two polymer insulating materials are used for completing this research study. Inside a climate chamber, the relative humidity is controlled and adjusted from 20% to 80% RH. Then, the samples are charged with positive or negative charges by applying [inline-formula] to the corona-generating ring of needles. The surface potential is measured using an electrostatic voltmeter and is converted into surface charge density later by applying the probe response matrix method. The pre-charged samples are then stressed with high-voltage negative or positive DC values inside the climate chamber over a range of controlled values of the surrounding air humidity until flashover takes place. The space charges, which can drift in the air gap to reach the solid surface, are highly affected by the level of the relative humidity of the surrounding air. Also, increasing humidity results in a reduction of the DC flashover inception voltage and a shorter time to flashover regardless of the voltage polarity. Moreover, the positive or negative flashover inception voltage of both materials increases with pre-deposited negative charges while it decreases with pre-deposited positive charges.

Sixteen composite insulators with service time between 10 and 14 years were sampled to conduct the specified mechanical load (SML) verification test in order to investigate whether their mechanical strength meet the criterion for continued running. Test results show that 15 out of the 16 samples pass the SML verification test. They show their failing load exceeding 1.4 times of SML, conforming to the calculation according to the mechanical strength model in the IEC 61109 standard. However, the remaining one fails to pass the test and its failing load is only 70% of SML. There are four kinds of failing modes, namely socket pulled out, ball pulled out, ball fractured and rod fractured, where socket pulled out is the most common failure mode and rod fracture mode only happens on X08 sample. The fact that X08 does not pass the test should be paid much attention since fracture of any one in the transmission lines can lead to severe transmission line accidents. Moreover, its appearance has some characteristics similar to some decay‐like fracture insulators which is, inferred that the mechanical strength of composite insulators in service can be affected by the environmental stresses. In addition, it is suggested to conduct sampling test periodically for the composite insulators which have been in service more than 10 years. [ABSTRACT FROM AUTHOR]

This study presents two different methods under uniform and non‐uniform pollution layer in order to measure and calculate the leakage current (LC) of silicone rubber insulators. Experimental test for evaluating the LC analysis of polluted insulator have been done in a laboratory clean fog chamber. The electric field and potential distributions were obtained from finite element method software for 3D models. The mathematical background and circuit theory are described in details by a section of insulator and using the extended form factor formula. The surface conductivity used in the calculations was extracted from the measured LC after wetting rate. LC characteristics under 1 : 1, 1 : 2, 1 : 5 and 1 : 10 ratios of top to bottom surface salt deposit density on polymeric insulators are studied. To verify the proposed models of this study, the results of experimental data and two other approaches are compared with together before dry‐band formation. Moreover, a dynamic LC model under uniform pollution layer has been introduced and extended in order to calculate the LC when the formation of dry‐bands along the insulator surface occurs. The dynamic model is drawn from experimental data and measured surface conductivity. [ABSTRACT FROM AUTHOR]

Electric field analysis around high‐voltage insulators is with an extreme importance during the development of new polymeric insulators design. In this study, the authors combine the finite‐element method (FEM) with the design of experiment method to investigate and describe the behaviour of textured silicone rubber insulators. First, a 3D FEM model of different silicone textured surfaces is developed. The maximum electric field is calculated taking into account various available patterns of hemispherical protuberance having different diameters. Then the design of experiment methodology is adopted to reduce the number of simulations and to give more significance to the results. Various influencing factors were considered in this stage. Finally, the analysis of variance is used to evaluate the contribution of the studied factors and their interaction on the total variation of the studied responses. [ABSTRACT FROM AUTHOR]

Highlights • First report relating fire properties of construction products to the Grenfell fire. • Flammability increases by factors of 10 to 100 from best to worst products. • Smoke toxicity 15 times greater for polyisocyanurate insulation than mineral wool. • Novel fire growth mechanism shows flaming polyethene drips igniting insulation foam. • Simple models able to predict fire behaviour in BS8414 test costing 100 times more. Abstract The 2017 Grenfell Tower fire spread rapidly around the combustible façade system on the outside of the building, killing 72 people. We used a range of micro- and bench-scale methods to understand the fire behaviour of different types of façade product, including those used on the Tower, in order to explain the speed, ferocity and lethality of the fire. Compared to the least flammable panels, polyethylene-aluminium composites showed 55x greater peak heat release rates (pHRR) and 70x greater total heat release (THR), while widely-used high-pressure laminate panels showed 25x greater pHRR and 115x greater THR. Compared to the least combustible insulation products, polyisocyanurate foam showed 16x greater pHRR and 35x greater THR, while phenolic foam showed 9x greater pHRR and 48x greater THR. A few burning drips of polyethylene from the panelling are enough to ignite the foam insulation, providing a novel explanation for rapid flame-spread within the facade. Smoke from polyisocyanurates was 15x, and phenolics 5x more toxic than from mineral wool insulation. 1 kg of burning polyisocyanurate insulation is sufficient to fill a 50m3 room with an incapacitating and ultimately lethal effluent. Simple, additive models are proposed, which provide the same rank order as BS8414 large-scale regulatory tests. [ABSTRACT FROM AUTHOR]

Abstract In the operation of OFETs, the electrical properties are strongly dependent on the merits of the constituting layers and the formed interfaces. Here we study the trap states variations at the interface between the organic semiconductor pentacene and polymer insulators. With ZrO 2 dielectric modified by polymers and find a 10 × decrease in the density of trap states at the semiconductor/insulator interface, bring about the charge carrier mobility increase from 0.058 cm2/Vs to 0.335 cm2/Vs. In addition, when compare to the thicker films at the same applied gate voltage, the thinner film would lead to enhanced coupling capability and more charges cumulative cumulated at the channel region, which is pivotal for optimizing the performance of OFETs. The results prove that the property of the insulator layer could impact largely on the device performance. [ABSTRACT FROM AUTHOR]

Investigations aiming to evaluate cause of failure of polymeric insulators used in Brazilian distribution networks reveal that it is not the presence of internal voids in their bulk but the fissures formed in the vicinity of insulator pins during their installation that cause the failure. [ABSTRACT FROM AUTHOR]

Surface charging is a common occurrence during service for all HV insulators as well as live-line tools during live-line maintenance work. The main sources of non-uniform charging are corona discharges from nearby and/or direct contact with energized objects and cloth wiping by tribo-charging effect. This paper focuses on studying the DC charging characteristics of three different insulating materials and the flashover performance of such pre-charged insulating materials. The samples used are cylinders of 130 mm length with different diameters. Surface charging by cloth wiping is found to be much more than that of corona discharges from energized objects. Surface charges take more than four hours to decay by 80%. Moreover, surface charges can increase the positive and negative flashover voltages of pre-charged samples by up to 13%. Mitigation methods to improve the flashover performance of insulating materials are identified. The research on surface charging forms hypotheses and recommendations which may improve the live-line maintenance procedures in ways that protect live-line workers from accidents. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract 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. Highlights • This anti-microbial insulator could effectively prevent the formation of biofilm and biodegradation of silicone rubber. • 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 only in the initial period within insulation margins. • More importantly, the biofilm inhibition process was environmentally friendly. After application on-site for 1 year, the antibiotic-loaded polymeric insulators retained antibiological properties without algae spots upon their surfaces. [ABSTRACT FROM AUTHOR]

The effect of thermal aging on the charging phenomena in cross-linked polyethylene (XLPE) has been studied under electron beam irradiation in scanning electron microscope (SEM). The dynamic variation of trapped charge represents the trapping process of XLPE under electron beam irradiation. We have found that the trapped charge variation can be approximated by a first order exponential function. The amount of trapped charge presents enhanced values at the beginning of aging at lower temperatures (80 °C and 100 °C). This suggests the diffusion of cross-linking by-products to the surface of sample that acts as traps for injected electrons. The oxidation which is a very important form of XLPE degradation has an effect at the advanced stage of the aging process. For higher temperatures (120 °C and 140 °C), the taken part process in the evolution of the trapped charge is the crystallinity increase at the beginning of aging leading to the trapped charge decreasing, and the polar groups generated by thermo-oxidation process at the end of aging leading to the trapped charge increase. Variations of leakage current according to the aging time have quite similar trends with the dielectric losses factor and consequently some correlations must be made between charging mechanisms and the electrical behaviour of XLPE under thermal aging. [ABSTRACT FROM AUTHOR]

Surface charge accumulation of polymer insulating materials is harmful to the safe operation of electrical equipment, especially under DC electric field excitation. In order to ensure the safety and stable operation of HVDC power system such as Gas-insulated transmission line, it is necessary to understand the influence of the surface charge on the flashover and improve the surface charge dynamic characteristics. In this paper, Epoxy resin (EP) is deposited by SiOx thin films with different plasma treatment conditions. The flashover voltages are measured with and without surface charges. The results show that the flashover occurs at lower voltage due to the accumulated charges on the EP surface. In particular, the surface charge with the same polarity of flashover discharge can reduce the surface flashover voltage significantly. Moreover, the charge decay rate is increased up to 90% by plasma treatment of 3 min, corresponding flashover voltage is increased. In addition, the flashover voltages of samples during the surface charge dissipation are obtained. Both static impact index I and dynamic impact index S are introduced to estimate effect of surface charge on dielectric surface flashover. [ABSTRACT FROM AUTHOR]

The life expectancy of a transformer is largely depended on the service life of transformer polymer insulation materials. Nowadays, several papers have reported that the traditional system poles obtained from polarization and depolarization current (PDC) data can be used to assess the condition of transformer insulation systems. However, the traditional system poles technique only provides limited ageing information for transformer polymer insulation. In this paper, the modified system poles obtained from PDC data are proposed to assess the ageing condition of transformer polymer insulation. The aim of the work is to focus on reporting a comparative investigation on the performance of modified system poles and traditional system poles for assessing the ageing condition of a transformer polymer insulation system. In the present work, a series of experiments have been performed under controlled laboratory conditions. The PDC measurement data, degree of polymerization (DP) and moisture content of the oil-immersed polymer pressboard specimens were carefully monitored. It is observed that, compared to the relationships between traditional system poles and DP values, there are better correlations between the modified system poles and DP values, because the modified system poles can obtain much more ageing information on transformer polymer insulation. Therefore, the modified system poles proposed in the paper are more suitable for the diagnosis of the ageing condition of transformer polymer insulation. [ABSTRACT FROM AUTHOR]

Dielectric characterization and conduction modeling of polymers are considered important owing to increasing use of polymeric insulation worldwide in power cables for electric power distribution. Electric conduction in polymers is a complex phenomenon and differs considerably at high electric fields where phenomena like space charge formation and charge injection from the electrodes come into the picture. This paper investigates the charge injection during polarization and subsequent discharging of low density polyethylene (LDPE) films at high electric fields (> 10 kV/mm) and under different temperatures. An attempt was made to study the short term Debye-type exponential behavior and long term power law behavior. Apart from the variation in the power law exponent for absorption current with increasing field, anomalies were noted in both types of relaxation currents at high electric fields and temperatures. Evidence of the polarization current anomaly was correlated with space charge behavior of samples. Interestingly, the space charge evolution under step voltage application was observed to be oscillatory in some cases, wherein, the charge trapping inside the dielectric bulk showed an oscillatory profile. The experimental factors which could contribute to anomalous discharging currents have also been thoroughly investigated and reported, which seem to have not been paid attention until now. [ABSTRACT FROM AUTHOR]

A major disadvantage of polymeric insulation is space charge accumulation at high dc electric fields. Space charge is associated with degradation and premature failure of polymeric insulation through distortion of electric fields. Polymer nanocomposites or nanodielectrics have emerged as a class of novel dielectric materials with improved material properties. We are therefore, looking at an increased use of nanocomposites in the near future. Additionally, we expect nanocomposites to be used in conjunction with conventional insulating materials, thus giving rise to interfaces. Interfaces are important because they often cause accumulation of interfacial charge or space charge with its attendant issues. The present work studies space charge behavior in nanocomposites and its interfaces with other materials. The space charge distribution is mapped using a Pulsed Electro-Acoustic (PEA) system. Polarization-depolarization current measurements are also performed. Measurements are performed under different experimental conditions (electric field, aging etc.). Experimental data indicate that nanoparticles affect charge injection as well as charge transport through change in interfacial and bulk properties. Further, thermal aging causes significant increase in charge injection and charge transport through the material. Experiments with as-received and surface-treated nanoparticles indicate that surface treatment affects the interphase significantly. [ABSTRACT FROM AUTHOR]

SUMMARY The authors carried out an outdoor exposure test and the 5000 h multiple stress test to ethylene vinyl acetate (EVA) polymer composite insulator used for 22 kV distribution line and an attempt was made to estimate the acceleration factor of the 5000-h multiple stress test corresponding to the climate condition of the Kyushu area. By comparing dry band arc cumulative charge of leakage current at 5000-h multiple stress test with that in the outdoor exposure test, the authors estimated the acceleration factor of the 5000-h multiple stress test to be about 20 times. The acceleration factor was found to almost agree with the evaluation result of the absorption of hydroxyl group by FT-IR analysis and the surface roughness of the insulator, respectively. Finally, for the electrical property, the expected life of EVA insulator that the authors developed was confirmed to be more than 40 years. [ABSTRACT FROM AUTHOR]

Polymer insulation surface degradation is affected by various factors. Surface discharge is one of the factors, which occurs between an insulating material and a conductor subjected to high voltage stress, leading to quality reduction of the insulation surface. Thus, it is essential to monitor the insulation material quality. In this study, the effect of surface discharges on various polymer types was investigated, which include polypropylene (PP), low density polyethylene (LDPE) and high density polyethylene (HDPE). The characteristics of partial discharge (PD) patterns and tan delta values from each polymer type were analysed. Weibull distribution was plotted to determine the probability occurrence and to analyse PD inception voltage. A finite element model was also developed to deduce the connection between PD characteristics and the electric field distribution on each polymer type. From the simulation and measurement results in this work, a greater understanding on the effect of surface discharges on different polymer material types can be gained. [ABSTRACT FROM AUTHOR]

Currently there are no international standards for evaluating the tracking and erosion resistance of DC polymeric insulation under contaminated conditions. Researchers often modify the existing AC inclined plane test standards such as the IEC-60587 to accommodate DC voltage conditions but this has been reported to give various inconsistences. This paper presents comprehensive experimental results on inclined plane tests of silicone rubber (SiR) insulation at 3.5 and 4.5 kV AC and positive DC using intravenous (IV) system as the pollutant supply. The leakage currents (LC) were recorded throughout the entire tests. In addition, various physiochemical tests namely, Fourier Transform Infrared analysis, thermo-gravimetric analysis, scanning electron microscopy and energy dispersive spectroscopy were performed on the aged and unaged samples. Results show that DC LC is bigger (about three times) than that under AC for the same equivalent voltages. Furthermore, DC LC variations are less random and the average magnitudes increase with duration of voltage application compared with AC. The physiochemical analyses show that 3.5 kV(rms) AC and 3.5 kV DC aged samples have comparable chemical characteristics albeit with electrode corrosion elements detected on the DC aged samples. Under 4.5 kV DC the degradation becomes significantly more severe and unrepeatable. It is therefore concluded that at 0.3 ml/min, pollutant flow rate, 3.5 kV positive DC and 3.5 kV(rms) AC are comparable as test voltages for inclined plane accelerated ageing of SiR insulation.

Located near the equator, Malaysia is a country with one of the highest lightning densities in the world. Lightning contributes to 70% of the power outages in Malaysia and affects power equipment, automated network systems, causes data losses and monetary losses in the nation. Therefore, consideration of insulator evaluation under lightning impulses can be crucial to evaluate and attempt to overcome this issue. This paper presents a new approach to increase the electrical performance of polymer insulators using a Room Temperature Vulcanisation (RTV) coating. The evaluation involves three different settings of polymer insulator, namely uncoated, RTV type 1, and RTV type 2 upper surface coatings. All the insulators were tested under three different conditions as dry, clean wet and salty under different impulse polarities using the even-rising test method. The voltage breakdown for each test was recorded. From the experiment, it was found that the effectiveness of the RTV coating application became apparent when tested under salty or polluted conditions. It increased the voltage withstand capabilities of the polymer insulator up to 50% from the basic uncoated insulator. Under dry and clean conditions, the RTV coating provided just a slight increase of the breakdown voltage. The increase in voltage breakdown capability decreased the probability of surface discharge and dry band arcing that could cause degradation of the polymeric material housing. The RTV type 1 coating was found to be more effective when performing under a lightning impulse. The findings might help the utility companies improve the performance of their insulators in order to increase power system reliability. [ABSTRACT FROM AUTHOR]

Cross-bonded three-phase single-core Cross-linked Polyethylene (XLPE) cables are widely used in power transmission and distribution systems. A great deal has been published on on-line monitoring of HV cable systems to prevent failure. Relative Dielectric Losses (DL) monitoring reveals the general condition of the cable insulation. Generally, DL measurement relies on measuring operating voltage and insulation leakage current. The main challenge to on-line monitoring of DL in Cross-bonded High voltage (CB HV) cables is the interconnectedness of metal sheath. Measured sheath currents are a combination of the leakage currents of each section and the imbalanced circulating current. Differentiating the leakage current of each interconnected section from the measured data is complex. The second challenge is that co-axial cables are used to connect cable sheaths to cable link boxes, for ease of installation and protection against moisture. As a result, any measured value contains currents from the two sheaths connecting at a joint. The third challenge is that it is hard to obtain the reference voltage synchronously and with high accuracy. Consequently, this paper investigates separation of leakage current components and analysis of DL based on leakage currents without reference voltage. A circuit model is proposed to describe the leakage current separation method for CB HV cables to allow on-line monitoring of DL, and the criterion required for assessing relative change of DL among different phases or sections of the cable for insulation deterioration are presented. Operational measurements from a cable system are analyzed and discussed. Results show that there is no significant deterioration in this monitored major section of a CB HV cable system. [ABSTRACT FROM PUBLISHER]

The object of research is the process of producing electric cables with polymer insulation for ultrahigh voltages. One of the most problematic places is the presence in the contours of the regulation of the thickness of insulation layers, the noise of measuring the speeds of worms of extruders and the diameters of the insulation layers, and also the time delay. The noisiness of useful signals and the time delay adversely affect the accuracy of layer thickness control and the speed of regulation and can lead to loss of system stability. To solve this problem, a parametric identification method is proposed, which under real conditions of noisy measurements of control object variables gives an estimate close to the exact values of the parameters. A modified least squares method is used, which in the situation of noisy input and output signals provides an unbiased estimate parameters, and a smaller spread rating than conventional least squares method. This is due to the fact that the proposed method makes it possible to reduce the spread of the quadratic functional by additional averaging on the set of quasi-static independent functionals. In comparison with the analogous well-known least squares method, it provides an increase in the accuracy of identifying parameters in conditions of noiselessness of not only output but also input signals. The introduction of research results in systems of adaptive control of the thickness of polymer insulation layers in the production of cables for ultra-high voltage will improve product quality and improve production efficiency. [ABSTRACT FROM AUTHOR]

Accelerated aging experimental investigations are performed on polymeric insulators which are used for extra high voltage (EHV) and ultra high voltage (UHV) transmission. A newly developed rotating wheel and dip test facility as per std. IEC 62217 is used for the study. The experimental study is conducted with AC stress for 15000 cycles. The specimen insulators used are of 725 mm creepage and treated under different environmental stresses close to the real service life. The present study focuses on the effect of acidic environment during acid rain encountered by the polymeric insulators. The contaminants used for the study are as per standard and practically observed acid rain information. A comparative study is carried out for normal and acidic environmental conditions, some interesting results are observed. Leakage current monitoring and visual observation were conducted at regular intervals. Results show acid treatment is found to be comparatively more severe than the normal treatment. Further Physico-chemical investigation are carried out using Fourier Transform Infrared (FTIR) Spectroscopy and Scanning Electron Microscopy (SEM), Energy dispersive X-ray Analysis (EDAX) and Thermo-Gravimetric Analysis (TGA) which confirm the severity of material degradation of polymeric insulators and corrosion over metal end fittings under acidic environmental condition. [ABSTRACT FROM AUTHOR]

We herein demonstrate a method for reducing the surface energy in polymer insulators for high-performance organic thin-film transistors (OTFTs). The surface energy of the poly(4-vinyl phenol) (PVP) insulator was reduced from 45 mJ/m2 to 32 mJ/m2 by treatment with UV/Ozone and octadecyltrichlorosilane (ODTS). The pentacene growth was controlled by the surface energy. It caused the pentacene film deposited on the ODTS-treated PVP insulator to induce three-dimensional growth, leading to an increase in the field-effect mobility of approximately 109%. These results demonstrate that the method of adjusting the surface energy in polymer insulators is suitable for enhancing the performance of OTFTs. [ABSTRACT FROM PUBLISHER]

Self-normalizing multivariate (SNM) analysis method was proposed to reflect characteristics of leakage current for monitoring dynamic surface discharges to flashover on polymer insulator in severe fog-polluted conditions. Based on the observation of discharge phenomena and temporal measurement of leakage current, the process just prior to flashover was separated into four stages: dominated resistive current, partial discharge, stable dry-band discharge, and pre-flashover. With discharge propagation in these stages, the SNM map was obtained. With increasing the pollution level, the SNM map shows no obvious difference in the resistive current dominated stage, while it looses more symmetry in both stable dry-band discharge and pre-flashover stages, which indicates the highest probability of surface flashover occurrence under the most severe fog condition investigated. [ABSTRACT FROM PUBLISHER]

In order to prove the effectiveness of direct fluorination in improving dc flashover performance of epoxy insulators in SF6 gas and also to provide evidence for the importance of surface conductivity of solid insulators, sheet-shaped and truncated cone epoxy samples were prepared and were fluorinated in a laboratory stainless vessel using a F2/N2 mixture with 12.5% F2 by volume at 0.1 MPa and 85 ?C for 30 min. Physicochemical characteristics of the fluorinated surface layer were evaluated by ATR-FTIR and SEM techniques, and the results showed substantial chemical modification of the surface layer, which has a thickness of 0.89 ?m and a roughened surface. Further, as expected on the basis of previous studies, measurements of surface electrical properties of the surface fluorinated sample, compared to the unfluorinated one, revealed a four orders of magnitude higher surface conductivity and a much more rapid decay of surface potential after corona charging. Dc flashover tests were performed on the truncated cone samples in SF6 gas at 0.1 MPa with a stepwise increasing voltage before and after the fluorination. The flashover test results showed a definite improvement in dc flashover voltage. For example, the flashover voltage at 63.2% probability or the mean flashover voltage for 2 min duration of the voltage step increased by 13.8% or 13.6% after the fluorination. The performance improvement is mainly attributed to easy leakage and dispersion of the charge deposited on the surface fluorinated sample from the gas phase, due to high conductivity of the fluorinated layer. The flashover test results also showed the influences of the duration of the voltage step on the flashover voltage and on the increase rate of flashover voltage. This means that even the time constant of the fast gas phase charging should be larger than 2 min, and that there should be different influences of the inhomogeneous surface conduction between the virgin sample and the fluorinated sample. [ABSTRACT FROM PUBLISHER]

Protection of medium voltage (MV) overhead lines against the indirect effects of lightning is an important issue in Malaysia and other tropical countries. Protection of these lines against the indirect effects of lightning is a major concern and can be improved by several ways. The choice of insulator to be used for instance, between the glass, ceramic or polymer, can help to improve the line performance from the perspective of increasing the breakdown strength. In this paper, the electrical performance of a 10 kV polymer insulator under different conditions for impulse, weather and insulator angle with respect to a cross-arm were studied (both experimental and modelling) and the results were discussed accordingly. Results show that the weather and insulator angle (with respect to the cross-arm) are surprisingly influenced the values of breakdown voltage and leakage current for both negative and positive impulses. Therefore, in order to select a proper protection system for MV lines against lightning induced voltage, consideration of the local information concerning the weather and also the insulator angles with respect to the cross-arm are very useful for line stability and performance. [ABSTRACT FROM AUTHOR]

SUMMARY Nowadays, trials to use even higher frequencies are pursued to realize high-speed wireless communications. In order to respond to such a trend, dielectric properties of insulating polymers at high frequencies have to be clarified, although the importance of clarifying low-frequency properties is still very high, especially for use as high-voltage insulators. In this regard, complex permittivity spectra from 10 mHz to 4.0 THz were obtained for various insulating polymers. The spectra obtained in the very wide frequency range are important, because they can be a valuable database and they provide various pieces of important information on dielectric characteristics. [ABSTRACT FROM AUTHOR]

Due to the advantages of ease of fabrication, low cost, and potential high reliability, through-silicon-vias (TSVs) using low-resistivity silicon posts as conductors and circular polymer liners as insulators have been developed for 3-D integration of microelectromechanical systems and microsensors. However, the large coefficients of thermal expansion (CTEs) of polymers lead to significant thermal stresses, which may cause silicon cracks. This paper reports the fabrication, thermal stress simulation, and thermal tests of a silicon TSV using benzocyclobutene (BCB) as the insulator. Silicon TSVs with high-aspect-ratio BCB liners have been fabricated by developing a vacuum-assisted filling method to achieve void-free BCB insulators. Finite-element method (FEM) is employed to simulate the thermal stresses caused by the mismatch in the CTE between silicon and BCB. High-temperature curing experiments show that crack in silicon substrates and silicon posts occurs on TSVs with specific dimensions. By correlating the results of FEM simulations and crack tests, the critical stress that causes silicon cracks is revealed, and design guidelines are proposed to achieve crack-free silicon TSVs. [ABSTRACT FROM PUBLISHER]

A mathematical model that considers the source-insulator interaction is presented for modeling flashover of polymer and porcelain insulators under contaminated conditions. The model is shown to be capable of handling polymer insulators with varying degrees of surface wettability or hydrophobicity. While a powerful source such as a practical power system causes insulator flashover performance to be lower than what can be expected from standard laboratory test, the relative reduction is more significant for porcelain than for polymer insulators. Line post and suspension insulators up to 500 kV have been considered for this study. [ABSTRACT FROM AUTHOR]

Environmental stability is one of the most important parameters for high-performance organic field-effect transistors (OFETs). Hydrophobic insulators usually possess much better air stability than some conventional inorganic and hydrophilic organic insulators. However, fabrication of devices with high integration by photolithography method cannot be directly performed on hydrophobic insulators due to their photoresist-unwettable properties. In this work, a simple yet efficient metal-assisted photolithography method is developed to achieve large-scale fabrication of highly integrated organic electronic devices on photoresist-unwettable insulators. By using copper (Cu) as sacrificial layer, photolithography can be performed on these insulators with nearly the same resolution, uniformity, and reproducibility as the conventional photolithography. This method shows excellent flexibility and is capable of fabricating high-integrated devices on a variety of hydrophobic insulators including hydrophobic amorphous fluoropolymer (CYTOP), poly(dimethylsiloxane) (PDMS), and octadecyltrichlorosilane (OTS)-modified SiO 2 . OFETs based on 6,13-dichloropentacene (DCP) microwires (MWs) with CYTOP as the insulator layer were fabricated, which exhibited excellent device performance. Much improved device stability with very low mobility degradation (less than 9%) was observed after 24 days. While devices fabricated on hydrophilic insulators of poly-(vinyl phenol) (PVP) and bare SiO 2 experienced dramatic performances decay within 24 days. Furthermore, by using metal-assisted photolithography method, flexible OFETs arrays could be further fabricated on polyethylene naphthalate (PEN) substrate, which showed excellent mechanical bending flexibility and stability. This work unveils the great potential of metal-assisted photolithography method for long-term stable high-integration organic electronic devices. [ABSTRACT FROM AUTHOR]

This study deals with the investigation on the effect of mineral contaminant and microbiological pollutant on outdoor polymer insulator. An experimental setup using preconditioned salt fog test is used to accelerate the desired environmental condition required by the pollutant to grow. As result, the effect of mineral contaminant on the growth of microbiological pollutant in the polymer insulator can be analyzed in a faster manner. Chlorella vulgaris as microbiological pollutant was successfully cultivated on 24 kVpolymer insulators in a controlled environmental condition. The analysis is presented by comparing the performances between preconditioned and normal insulators. A scanning electron microscope (SEM) test is also performed to determine the growth of chlorella vulgaris. Some leakage current and breakdown voltage measurement tests were conducted to determine the insulation performance of insulators. SEM results show that chlorella vulgaris layer did not grow on the normal insulators. Meanwhile chlorella vulgaris layer was formed up to of 30.5 pm depth inside pre-conditioned insulator surface. The test at 40 kV ac voltage shows up to 0.23 mA leakage current was detected on preconditioned insulators. The degradation of breakdown voltage of 12.5 % was detected after 8 weeks treatment. [ABSTRACT FROM AUTHOR]

Polymeric insulators are used for high voltage transmission and distribution systems due to their advantages over traditional ceramic/glass insulators. However, these insulators encounter various stresses in the service condition. CIGRE working group D1.14 has identified twelve important parameters for the evaluation of polymeric outdoor insulation materials. Tracking/erosion is an important parameter for the evaluation for long term performance. In the present work, experiments on polymeric insulators to thermal erosion are conducted, fourier transform infra-red (FTIR), scanning electron microscopy (SEM) are used to study the surface chemical and morphological changes and surface roughness measurements are done using 2D profilometer. Results obtained from thermal erosion experiments show severe de-polymerization and loss of hydrophobicity. An attempt has been made to evaluate the polymeric insulating materials using recurrence plot (RP) analysis. Recurrence plot analysis of discharge current sequence confirms, a discharge process is prolonged as the number of drops containing contaminants is increased. Quantitative indicators of RP analysis, recurrence rate (RR) and Determinism (DET) are used to evaluate the performance of various polymeric insulating materials used in the study. [ABSTRACT FROM PUBLISHER]

Corona resulting from the metallic parts of the transmission line insulators and hardware has proven to be the potential factor in inducing the degradation of polymer insulators. Corona activity is found to increase substantially during the foul weather condition (rain, fog/mist, hoarfrost), which further promotes the ageing of polymer insulators. Present work investigates the possible corona activity under fog/moist condition and its effects on the long term performance of polymer insulators in service. The spread of corona generated plasma is observed to be different under fog condition than in normal air condition. The concentrated streamers that are originated from the corona electrode during fog condition are believed to damage the polymer shed material locally and more intensely. This was confirmed by the scanning electron microscopy and Fourier infrared spectroscopy analysis carried out on the treated polymer samples, which showed more damage on the corona treated under fog than on the samples treated under normal air condition. Further TGA and EDAX studies have shown that loss of ATH occurs on the sample due to intense corona activity. [ABSTRACT FROM PUBLISHER]

Polymer FETs generally have a wide subthreshold regime due to a lot of disorder, mainly originated from domain/grain boundaries. Deep state’s charge transport of polymer transistors has not been investigated due to the difficulty in determining the field-effect mobility in the subthreshold region. In this paper, the features of the charge transport in deep and shallow states of polymer transistors will be discussed in detail through an accurate modeling and an analysis of subthreshold behavior in transistors. Charge transport in shallow states can be described by multiple trap and release transport, while hopping transport models, such as variable range hopping or Gaussian disorder-based model, describe well the deeper state’s charge transport. In addition, the transition between the conduction regimes is a function of temperature and carrier density. [ABSTRACT FROM PUBLISHER]

SUMMARY In general, a polymer insulator subjected to high voltage reaches breakdown as a result of the development of electrical trees. Magnesium hydroxide, a metal hydroxide, has the property of releasing water of crystallization at high temperatures. If the energy of a partial discharge is used by the decomposition of magnesium hydroxide, the growth of electrical trees will be inhibited and the lifetime of the polymer insulator can be expected to improve. Therefore, we have studied the effects of magnesium hydroxide on treeing. We confirmed that the electrical breakdown time of epoxy resin with 30 parts per hundred (resin) of magnesium hydroxide was 100 times longer than that of epoxy resin without it. Magnesia was detected through electron beam diffraction analysis of the filler particles located near the electrical tree, and it was found that a dehydration reaction took place in the magnesium hydroxide. In other words, as an explanation of the effect of inhibiting an electrical tree, the effect of the energy dispersion of a partial discharge is suggested along with the barrier effect of the fillers. [ABSTRACT FROM AUTHOR]

Corona discharges resulting from the metal parts of insulators and the line hardware affect the long term performance of the polymeric insulators used for outdoor application and can lead to its eventual failure. The authors previous work, involved in developing a new methodology to evaluate the performance of polymeric shed materials subjected to corona stresses in the presence of natural fog condition, results revealed more surface hydroxylation thereby resulting in more loss of hydropobhicity. With the increase in industrialization, there is an increase in acidic component of the rain as well as the fog (moisture). The present work, reports the effect of acid fog on the corona performance of the polymeric insulators for both AC and DC excitation, interesting results are obtained. A comparison of the experimental investigations revealed that the acidic fog has more effect than that of the normal fog. This fact has been confirmed by physico-chemical analysis like the scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS) and contact angle measurement. The effect of DC corona is found to be lesser in comparison with the AC; however the hydroxylation induced by the DC corona under the presence of fog is similar with that of AC excitation. [ABSTRACT FROM PUBLISHER]

Long term reliability is one of the most important performance measures for high voltage insulators in the power transmission and distribution networks. To evaluate the long-term performance of insulators, properties such as hydrophobicity, surface roughness, images from Scanning Electron Microscopy and dielectric breakdown measurements are often studied. In this paper, a new evaluation method based on the oscillating period of water droplet, namely Oscillating Water Droplet (OWD) method is proposed. Using a high-speed camera, the full sequence of the water droplet making contact with the composite surface was recorded and analyzed. The OWD was performed on specimens of different ageing levels. Further investigation on hydrophobicity using the optical contact angle device is performed to study the relationship between the oscillating water droplet over the surface and the contact angle. To study the loss of hydrophobicity, surface roughness tests were conducted using BRUKER ContourGT Optical Profiler with eight different roughness spots per specimen. Our results show that more time is needed for the water droplet to settle over the surface when the hydrophobicity is decreased due to aging. Scanning Electron Microscopy (SEM) images showing the level of degradation on the surface of the specimens are included. The results obtained are closely correlated to the decrease in dielectric breakdown voltage over the insulator surface as the period of aging cycle increases. This work also indicates that the OWD method can be applied as a new method for evaluating the hydrophobicity of polymeric insulators. [ABSTRACT FROM PUBLISHER]

The authors have demonstrated that the estimation of the precise locations of points in cables aged thermally or mechanically or by the irradiation of gamma rays is possible by a combination of frequency domain reflectometry and inverse fast Fourier transform. This paper examines how this ability of fault location depends on the type, structure, and insulation material of the cable, using several kinds of polymer insulated cables such as a triple core cable insulated with flame-retardant ethylene propylene diene copolymer, a dual core cable insulated with silicone rubber, a dual core cable insulated with crosslinked polyolefin (XLPO), a coaxial cylindrical cable insulated with low density polyethylene, and a flat cord insulated by polyvinyl chloride (PVC). As a result, for cables with lengths from 16 to 72 m, the maximum sensitivity is attained when the highest frequency of the inputted electromagnetic waves is 1.0 GHz or higher for coaxial cables, but around 300 to 800 MHz for dual or triple core cables. For the location attempt of the position heated by a heater, cables insulated with PVC give higher signal intensities than those insulated with XLPO. [ABSTRACT FROM PUBLISHER]