Outdoor Insulators Research Articles

Silicone rubber insulators for polluted environments part 1: enhanced artificial pollution tests

The development of polymeric materials for outdoor insulation has been much aided by existing standard laboratory tests such as inclined-plane procedures. The position is less satisfactory in respect of the optimization of insulator profiles and the choice of the minimum unified specific creepage distance (USCD) for a given site pollution severity (SPS). Standard tests currently under revision are stated to be 'not directly applicable to polymeric insulators'. Such tests are, therefore, urgently needed to discriminate the pollution performance of silicone-rubber insulators of different housing materials and profiles, to quantify the inverse relationship of pollution severity and flashover voltage and to assess the influence of wetting rate. A suitable test strategy would also avoid housing damage from excessive flashovers. A new test procedure is presented here to achieve these objectives. This is not confined to flashover voltage measurements. A high-resolution data acquisition system is used to monitor and store the waveforms of the applied test voltage and leakage current throughout tests on 11kV silicone-rubber insulators. This enhancement provides a further basis for the quantitative comparison of insulators in artificial pollution testing, because the results corroborate the inverse relationship between flashover voltage and pre-flashover leakage current. Part 2 demonstrates the pollution performance of 11kV silicone-rubber insulators when surface texturing is used to increase USCD values.

Dielectric Properties of Polyvinyl Chloride with Wollastonite Filler for the Application of High-Voltage Outdoor Insulation Material

Even though polymer composite materials have been widely used as an outdoor insulation material, their life expectancy is still unknown. Thus, to develop a better insulation, it is important to determine the electrical properties of the polymeric materials. As mentioned in previous researches, adding filler to the polymer will help to increase the performance of insulating materials. In this paper, a new polymeric insulation material for high-voltage application, polyvinyl chloride (PVC) with the addition of Wollastonite CaSiO3 filler is presented. It was expected that the combination of filler with PVC would give better result when experiencing ageing process. The material would be put into tracking and erosion resistance test first and then analysed in accordance with BSEN 60587:2007. It would then be further tested through tan delta and dielectric strength test. The thermal heat transfer would be measured before, during and after the ageing process. Water absorption test was also conducted to observe the hydrophobicity characteristics of the insulation material. The water absorption test was based on ASTM D570-98. Comparison would then be made between the PVC with filler and PVC without filler based on the result obtained from the experiment. The results showed that based on the physical characteristics, the addition of filler to PVC gave better results in term of hydrophobicity performance, meanwhile based on the inclined plane test, all samples passed the satisfied condition. However, not all electrical testing showed satisfactory results and further testing should be conducted.

Outdoor Insulators Testing Using Artificial Neural Network-Based Near-Field Microwave Technique

This paper presents a novel artificial neural network (ANN)-based near-field microwave nondestructive testing technique for defect detection and classification in nonceramic insulators (NCI). In this paper, distribution class 33-kV NCI samples with no defects, air voids in silicone rubber and fiber glass core, cracks in the fiberglass core, and small metallic inclusion between the fiber core and shank were inspected. The microwave inspection system uses an open-ended rectangular waveguide sensor operating in the near-field at a frequency of 24 GHz. A data acquisition system was used to record the measured data. ANN was trained to classify the different types of defects. The results showed that all defects were detected and classified correctly with high recognition rates.

Calculation of Electric Field Characteristics of Insulator Under Sandstorm Condition

Sandstorm has influence on the the electrical properties of outdoor insulator, and the analysis of the electric field characteristics of insulator under sandstorm condition is very important. The electrostatic field finite element method (FEM) is used to calculate the electric field distribution along long rod insulator under sandstorm condition with FEM software after calculating the one under clean condition. The results of calculation show that the sand deposition decreases the electric field strength of insulator covered with sand, and increases the field strength of the corresponding shed key points. The electric field strength of the non-sand region will increase, when the non-sand region appears in sand layer on insulator. Suspended sand particles in the ambient air can distort the electric field distribution along insulator, and which is significantly affected by the size, the quantity, the charge-to-mass ratio and the charge polarity of sand particles. DOI : http://dx.doi.org/10.11591/telkomnika.v12i2.3902

Nanostructured hydrophobic DC sputtered inorganic oxide coating for outdoor glass insulators

We report the structural, optical and electrical properties of nanostructured hydrophobic inorganic hafnium oxide coating for outdoor glass insulator using DC sputtering technique to combat contamination problem. The properties were studied as a function of DC power. The characterization of the films was done using X-ray diffraction, EDS, surface profilometer, AFM, impedance analyser and water contact angle measurement system. The DC power was varied from 30 to 60W and found to have a great impact on the properties of hafnium oxide. All the deposited samples were polycrystalline with nanostructured hydrophobic surfaces. The intensity of crystallinity of the film was found to be dependent on sputtering power and hydrophobicity was correlated to the nanoscale roughness of the films. The optical property reveals 80% average transmission for all the samples. The refractive index was found in the range of 1.85–1.92, near to the bulk value. The band gap calculated from transmission data was >5.3eV for all deposited samples ensuring dielectric nature of the films. Surface energy calculated by two methods was found minimum for the film deposited at 50W sputtering power. The resistivity was also high enough (∼104Ωcm) to hinder the flow of leakage current through the film. The dielectric constant (ɛ) was found to be thickness dependent and also high enough (ɛmax=23.12) to bear the large electric field of outdoor insulators.

Trend of Research and Development in Dielectrics and Insulating Materials

This is a review of the 43rd Symposium on Electrical and Electronic Insulating Materials and Applications in Systems (SEEIMAS) hosted by Technical Committee on Dielectrics and Electrical Insulation (TC-DEI) in IEEJ in order to overview the research trend in this specific field. Application of various kinds of numerical simulation, functionalized thin materials, aging of insulating materials under various condition, insulation system under inverter surges, space charge assessment, asset management regarding to insulation performance, outdoor insulations, thin dielectric films and other topics are dealt with. The proceedings booklet in Japanese, with English abstract and figure captions for each presentation, will be available at the IEEJ office.

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.

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.

Artificial Neural Network Assisted Digital Image Processing to Determine the Hydrophobicity of Polymeric Materials

Hydrophobicity of polymeric insulators of high power transmission line is an important property because it is a good monitor of aging of polymeric outdoor insulator. An employee on the high-voltage transmission line makes this procedure during operation, which can lead to injuries and incorrect estimation of the insulator integrity. In this way, digital image processing is a promising and objective tool to analyze the polymer surface. In this study, two thousand pictures were taken from the wetted insulator surface and analyzed by artificial neural network assisted digital image processing. The neural network used is based on back-propagation method, and Haralicks descriptors were used to quantify the hydrophobic aspect of various polymeric aged surfaces.

RF-based monitoring and classification of partial discharge on wet silicone rubber surface

The main objective of this study is to investigate the feasibility of using an RF antenna to detect and classify partial discharges on polymer insulation surfaces. The detected discharges are identified based on their originating sources, employing a cascade of feature extraction, feature selection and the standard artificial neural network classifier. Both statistical and spectral analyses have been used for feature extraction. Feature extraction is followed by a feature selection stage with a novel implementation of stepwise regression method in order to derive representative feature vectors, yet with minimum dimensionality. Suppression of redundant features is therefore achieved, thereby enhancing the classification reliability. Finally, classification is performed using a standard feed forward neural network with back propagation training algorithm. The proposed method is found to be successful in classifying different types of partial discharge with recognition accuracy exceeding 96%. The proposed method can be an essential stage towards overhead line inspection to assess the status of outdoor polymer insulators, where partial discharges could be initiated from surface discharges due to pollution and/or from corona discharges from energized ends.

Investigation on Flashover Development Mechanism of Polymeric Insulators by Time Frequency Analysis

This paper deals with the analysis of leakage current characteristics of silicone rubber insulator in order to develop a new condition monitoring tool to identify the flashover of outdoor insulators. In this work, laboratory based pollution performance tests are carried out on silicone rubber insulator under ac voltage at different pollution levels and relative humidity conditions with sodium chloride (NaCl) as a contaminant. Min-Norm spectral analysis is adopted to calculate the higher order harmonics and Signal Noise Ratio (SNR). Choi-Williams Distribution (CWD) function is employed to understand the time frequency characteristics of the leakage current signal. Reported results on silicone rubber insulators show that the flashover development process of outdoor polymer insulators could be identified from the higher order harmonics and signal noise ratio values of leakage current signals.

Silicone Rubber MgO Nanocomposite for High Voltage Outdoor Insulation Application

This paper deals with the experimental studies of the Electrical properties of silicone rubber filled with Magnesium Oxide (MgO) nanofillers at low filler concentration by weight (1% - 3%). The silicone rubber nanocomposite samples are prepared by mastication process. The structure and morphology studies of the composites are studied using X – Ray Diffraction and scanning electron microscopy techniques. The thermogravimetric analysis shows that the thermal stability of the silicone rubber is enhanced on addition of the nanofillers. The frequency dependence of the dielectric properties like ac conductivity, relative permittivity and loss tangent are studied. The ac dielectric strength, the arc resistance properties and the mechanical properties are also studied as a function of filler concentration. The results show that even at low filler concentrations, the nanocomposite demonstrates a remarkable enhancement in dielectric constant, arc resistance and mechanical strength which can be applied for many existing electrical systems.

Call for papers - Cross-disciplines in outdoor insulation

Call for papers - Cross-disciplines in outdoor insulation

An Experimental Study on Surface Discharge Characteristics of Different Types of Polymeric Material under AC Voltage

Surface discharge is a common electrical discharge that normally occurs on the surface of outdoor insulators and also causes the failure in the electrical insulation system. One of the causes of surface discharge is the presence of high voltage stress. Experimental works had been carried out to examine the surface discharge characteristics on polymeric samples as insulation material. The IEC (b) electrode configuration had been used to investigate the surface discharges phenomena of different types of polymeric materials with controlled of air relative humidity (RH). In these experimental works, three types of polymeric sample were selected, namely high-density polyethylene (HDPE), ethylene-vinyl acetate (EVA), and polystyrene (PS), respectively. The characteristics of the discharge are critically depending on the types of polymer. Surface discharges intensity, number of discharge occurrence, and surface morphology of each polymeric material were also investigated. Comparisons of these electrical characteristics were conducted among the samples. Results from the experiment showed that the EVA samples experienced severe degradation as compared to HDPE and PS samples.

Electrical Characteristics of Polyvinyl Chloride with Wollastonite Filler for High Voltage Outdoor Insulation Material

Even though polymer composite materials have been widely used as an outdoor insulation material, their life expectancy is still unknown. Thus, to develop a better insulation, it is important to determine the electrical properties of the polymeric materials. As mentioned in previous researches, adding filler to the polymer will help to increase the performance of insulating materials. In this paper, a new polymeric insulation material for high voltage application, Polyvinyl Chloride (PVC) with the addition of Wollastonite CaSiO3 filler is presented. It was expected that the combination of filler with PVC would give better result when experiencing ageing process. The material would be put into tracking and erosion resistance test first and then analyzed in accordance with BSEN 60587:2007. It would then be further tested through tan delta and dielectric strength test. Comparison would then be made between the PVC with filler and PVC without filler based on the result obtained from the experiment. However, not all electrical testing showed satisfactory results and further testing should be conducted.

Intelligent Diagnosis and Calculation of Electrical Insulation Fault for Smart Power Grid

We make an approach to the intelligent diagnosis and calculation of electrical insulation fault for smart power grid. By the electric field calculation method and the online detecting method, the insulation diagnosis model is presented in this paper. This monitoring system can monitor the leakage current of outdoor insulators effectively, and this system can make use of modern computers and communication technology to deal with these real time signals. Therefore, we use the results to increase the ability and the condition of working for the smart grids.

Characterization of discharges on non-uniformly polluted glass surfaces using a wavelet transform approach

In this work, the electric discharges activity on non-uniformly polluted glass plane insulator model is investigated for increasing applied voltage levels up to flashover. The effect of pollution severity was simulated using pollution solution containing various kaolin concentrations. The polluted sample has a strip that is dry and clean which is parallel to the electrodes planes. Configurations with various widths (2 to 14 cm) and locations of this dry clean strip were tested, and both the leakage current and the accumulated charge were examined. Further in-depth examination of the leakage current waveforms was carried out using a wavelet analysis approach. The Discrete Wavelet Transform (DWT) is adopted for the leakage current decomposition in several time-frequency bands. The STD-MRA (Standard Deviation-Multi Resolution Analysis) representation is employed to specify the Detail components (frequency components). It is shown that these can be used to detect the presence or absence of partial arcs activity over the dry clean strips. The reported results show that the simultaneous increase in the standard deviation of the Details components D8 and D10 indicates the presence of the partial arcs. However, the increase only in the standard deviation of the Detail component D10 indicates no discharge activity. Such approach may have some useful application when analyzing the leakage current on its own to monitor discharge activity on polluted surface. Further work is on-going to apply this approach to full outdoor insulators.

Influence of sputtering pressure on the structural, optical and hydrophobic properties of sputtered deposited HfO2 coatings

The aim of this work is to develop hydrophobic coatings for outdoor insulators using sputtering technique. Hafnium oxide is characterized by high dielectric constant, large band gap (5.6eV), high refractive index (2.1) and good mechanical, thermal and chemical properties. Hence HfO2 is suitable as a protective coating for outdoor insulators used in the transmission line and transformers. Hafnium oxide coatings were deposited on glass substrates by DC magnetron sputtering technique at a sputtering pressure of 5mTorr, 10mTorr, 15mTorr, 20mTorr and 25mTorr. The deposited films were characterized by techniques like X-ray diffraction (XRD), atomic force microscopy (AFM), water contact angle goniometry and UV–vis-NIR spectrophotometer. The average crystallite size calculated from XRD peaks shows that it increases with increase in sputtering pressure up to 15mTorr and then it starts decreasing. The roughness calculated from AFM images shows the similar trend. The deposited films were found to be hydrophobic and transparent. The hydrophobicity of the films was correlated with the roughness calculated from AFM. The effect of sputtering pressure was also investigated on optical band gap and refractive index calculated from transmission and absorption data. The electrical resistivity was found to be high, thus ensuring insulating property of the deposited films.

Effect of sputtering gas on structural, optical and hydrophobic properties of DC-sputtered hafnium oxide thin films

The outdoor ceramic insulators of power transmission lines and transformers are suffering from the problem of contamination due to which surface flashover phenomenon is frequent. The main objective of this work was to prepare hydrophobic hafnium oxide (HfO2) thin films to mitigate contamination problem. The hafnium oxide coatings were deposited on glass substrates by DC reactive magnetron sputtering from a pure hafnium target. The depositions of HfO2 films were carried out in O2+Ar and O2+He atmosphere. The structural, optical and hydrophobic properties were examined by varying O2/Inert gas ratio. The prepared samples were characterized by X-ray diffraction, EDS, AFM, UV–vis-NIR spectrophotometer and contact angle goniometer. The coatings were found to be crystalline, transparent and hydrophobic for all samples. The deposition rate, hydrophobicity, transparency, band gap and particle size are better for the films deposited in argon atmosphere in comparison to helium. The hydrophobicity was found to be dependent on roughness of the film. The roughness (5.06nm) and the water contact angle (102.25°) were found maximum for the film deposited at O2/Ar ratio equals to 0.5. The transmittance was also found ~90% at this particular ratio. The band gap of the film deposited at above mentioned ratio was found to be 5.41eV ensuring insulating nature of the film.

Pollution flashover performance of full-scale ±800 kV converter station post insulators at high altitude area

On the background of the peculiar technology problems with the external insulation of UHV dc equipment in China, caused by high altitude and heavy pollution, this paper presents the pollution flashover performance of full-scale ±800 kV converter station post insulators at actual high altitude area. The tests were carried out according to the solid layer method, and the 50% withstand voltage (U50%) was determined by the up-and-down method. The artificial contamination test results indicated that the shed configuration and the rod diameter had a significant influence on the flashover voltages. Shed parameters of one big and one small alternating shed composite post insulator which had superior dc pollution flashover performance had been recommended. The relationship between U50% and insulation height was approximately linear at actual high altitude area for post insulators. It was found that partial discharges occurred at the top section firstly and partial arcs easily appeared at the parts nearby the connecting fittings during the flashover process. And arc floating phenomenon was significantly serious in actual high altitude area. Furthermore, comparison was made between the U50% values of composite post insulators in fog and in rain. The U50% values in fog of composite post insulators were generally higher than that in rain. Thus, the outdoor insulation design of composite post insulators should primarily consider the U50% value in fog. This work thus provides useful reference for the design, operation and maintenance of UHV dc converter stations outdoor insulators in China.