M. A. M. Piah

Modeling leakage current and electric field behavior of wet contaminated insulators

The behavior of leakage current and electric field of insulators primarily depends on the environmental stresses. A mathematical analysis based on dimensional analysis technique is applied to develop the correlation of leakage current (LC) and electric field with the physical variables of the environmental stresses. The final model is established by relating the analytical results with the experimental results.

Effect of nanofillers on the polarization and depolarization current characteristics of new LLDPE-NR compound for high voltage application

Polymeric nanocomposites in which the nanosize fillers are evenly distributed in the polymer material attract attention as an insulating material due to their ability to enhance the materials performance properties of electrical and mechanical. For high voltage (HV) insulation application, one of the targets is to obtain new insulators with improved dielectric properties. This paper presents the outcome of an experimental study to determine the conductivity level of the linear low-density polyethylene- (LLDPE-)natural rubber (NR) compound, filled with different amount of SiO2 and TiO2 nanofiller by using the polarization and depolarization current (PDC) measurement technique. linear low-density polyethylene (LLDPE) and natural rubber (NR) with the ratio composition of 80 : 20 are selected as a base polymer. The experiment was conducted to find PDC pattern and conductivity variations of each of the LLDPE-NR/SiO2 and LLDPE-NR/TiO2 samples. The results show that the addition of SiO2 filler exhibited less conductivity compared to TiO2 filler with certain percentage. From the study, it can be concluded that LLDPE-NR/SiO2 is a better insulator compared with LLDPE-NR/TiO2.

Temperature effect on electrical treeing and partial discharge characteristics of silicone rubber-based nanocomposites

This study investigated electrical treeing and its associated phase-resolved partial discharge (PD) activities in room-temperature, vulcanized silicone rubber/organomontmorillonite nanocomposite sample materials over a range of temperatures in order to assess the effect of temperature on different filler concentrations under AC voltage. The samples were prepared with three levels of nanofiller content: 0% by weight (wt), 1% by wt, and 3% by wt. The electrical treeing and PD activities of these samples were investigated at temperatures of 20°C, 40°C, and 60°C. The results show that the characteristics of the electrical tree changed with increasing temperature. The tree inception times decreased at 20°C due to space charge dynamics, and the tree growth time increased at 40°C due to the increase in the number of cross-link network structures caused by the vulcanization process. At 60°C, more enhanced and reinforced properties of the silicone rubber-based nanocomposite samples occurred. This led to an increase in electrical tree inception time and electrical tree growth time. However, the PD characteristics, particularly the mean phase angle of occurrence of the positive and negative discharge distributions, were insensitive to variations in temperature. This reflects an enhanced stability in the nanocomposite electrical properties compared with the base polymer.

Comparative study on conductivity using Polarization and Depolarization Current (PDC) test for HV insulation

Polarization and Depolarization Current ( PDC) testing is a non-destructive dielectric testing method to determine the conductivity of insulations. It is one of the dielectric diagnostic techniques based on time domain measurement. PDC measurement technique has gained immense popularity due to its ability to assess the condition of HV insulation. PDC measurement can provide information about the conductivity within the initial periods (seconds) after a DC step voltage application. This paper present the review and comparison results from several published papers on application of PDC method in finding the conductivity of the various types of insulators. The scope of the review covered solid and liquid insulations types. In this paper, for solid insulation the studied was focused one ables insulations, electric machine stator insulation and paper insulator in power transformer insulation. For liquid insulation, the review and comparison was done on the biodegradable and mineral transformer oils. The review results show that the PDC technique successfully give indication on level of conductivity of the HV insulation materials.

Leakage current and surface discharge phenomena: effect on tracking and morphological properties of LLDPE-natural rubber compounds

Polymeric insulators are widely used for high voltage outdoor insulating application due to their substantial advantages compared to the porcelain and glass insulators. Although polymer materials have been proven good, research on development of new polymer-based materials is still on going since the benefits of using polymeric materials are not yet utilised to their full potential. In this work, a new formulated thermoplastic elastomer materials that are composed of linear low-density polyethylene (LLDPE) and natural rubber (NR) filled with different loadings of alumina trihydrate (ATH) fillers is presented. A surface tracking and erosion test is conducted to investigate the characteristics of leakage current on the material surface under the influence of wet contaminated conditions. A computer-based leakage current monitoring system is developed to monitor the leakage current waveform pattern as well as its frequency spectrum. The scanning electron microscope is used to investigate the morphological properties of the materials before and after the tracking test.

Electrical treeing in silicone rubber/organo-montmorillonite

Electrical treeing is one of the main reasons for failure of polymeric materials used in high voltage applications. Treeing is observed to originate at points where impurities, voids, defects, or conducting projections cause excessive local electric field stress in the dielectric. It has been proposed that nanofillers could be employed as an electrical tree inhibitor in polymeric insulating materials. With development of nanotechnology, polymer nanocomposites have drawn much attention, because they are expected to have improved mechanical, thermal and electrical properties over the neat polymer. In this paper, modified nanoclay was used to examine the initiation and propagation of electrical treeing. Effects of electrical treeing on nanocomposites insulating material filled with 1 wt% and 3 wt% of Organo-Montmorillonite (OMMT) were used in this work. The results have shown that electrical tree growth was suppressed in silicone rubber nanocomposites compared with neat silicone rubber which allowed a faster growth of electrical treeing. However, more studies should be carried out with different nanofiller/silicone ratios to see in further enhancements in tree inhibition could be achieved.

Measurement of surface charge distribution on glass insulator using steel mesh

This paper studies the charge distribution on the transmission line glass insulator surfaces under two different ac voltages viz. 28 kV and 33 kV. A string of four insulator units under dry and clean conditions is taken as the main research object. An attempt to capture the accumulated charge has been made by using radially shaped stainless steel mesh placed axially at a distance of 2 cm from each glass insulator circumference. Results show that the distribution of charge across each glass of insulator in the string is uneven, and the value of surface charge increases with the increment of applied voltage.

Comparative Study on Conductivity and Moisture Content Using Polarization and Depolarization Current (PDC) Test for HV Insulation

The Polarization and Depolarization Current (PDC) measurement is an efficient and effective diagnostic technique based on time domain measurement, for evaluating the high voltage insulation condition. This paper presents a review and comparison results from several published papers on the application of the PDC method to finding the conductivity and moisture content of various types of insulators. For solid insulation, the study was focused on cable insulation, electric machine stator insulation, and paper insulator in transformer insulation with different conditions. For liquid insulation, the review and comparison was done on biodegradable and mineral transformer oils, with fresh oil condition, and aged condition. The results from previous researchers tests were complied, analyzed and discussed, to evaluate the application of the PDC method to monitor the conductivity and moisture of HV equipment insulation systems. From the review results, the PDC technique successfully gives an indication of the conductivity and moisture level of high voltage insulation.

Electrical tracking characterization of LLDPE-Natural Rubber blends filled with nanofillers

Electrical tracking is a process of formation of permanent conducting path across the insulating material due to the surface erosion under high voltage application. The existing of leakage current (LC) on the wet contaminated material surface causes the generation of surface discharges that resulted to the material degradation. Electrical tracking test can be indicated as failure when LC exceed 60 mA for more than two seconds or at least 25mm of formation of carbon track or erosion breaks through the thickness of the sample. In this paper, a new formulated thermoplastic elastomer material which composed of Linear Low-Density Polyethylene with Natural Rubber (LLDPE/NR) filled and unfilled with different percentage of silicone oxide (SiO2) or titanium oxide (TiO2) as nanofiller is presented. The compound was tested based on IEC 60587 inclined plane tracking test procedure. The analysis of LC and rate of carbon track development were also conducted. Surface morphology analysis was carried out for investigating the degraded surface structure of the materials. The formulation of pure LLDPE/NR has shown the highest average leakage current whereas the composition of LLDPE/NR-TiO2 with 1 % wt of nanofiller was found to be the best electrical tracking resistance due to the lowest average leakage current and no carbon track appeared. The blends of LLDPE/NR-SiO2 show that low average leakage current and no carbon track in less than 5 % wt nanofiller. The usage of 5% wt or more for both nanofiller had shown the worst in carbon track formation.

Statistical Analysis of Electrical Tree Inception Voltage, Breakdown Voltage and Tree Breakdown Time Data of Unsaturated Polyester Resin

This paper presents a statistical approach to analyze electrical tree inception voltage, electrical tree breakdown voltage and tree breakdown time of unsaturated polyester resin subjected to AC voltage. The aim of this work was to show that Weibull and lognormal distribution may not be the most suitable distributions for analysis of electrical treeing data. In this paper, an investigation of statistical distributions of electrical tree inception voltage, electrical tree breakdown voltage and breakdown time data was performed on 108 leaf-like specimen samples. Revelations from the test results showed that Johnson SB distribution is the best fit for electrical tree inception voltage and tree breakdown time data while electrical tree breakdown voltage data is best suited with Wakeby distribution. The fitting step was performed by means of Anderson-Darling (AD) Goodness-of-fit test (GOF). Based on the fitting results of tree inception voltage, tree breakdown time and tree breakdown voltage data, Johnson SB and Wakeby exhibit the lowest error value respectively compared to Weibull and lognormal.