Mohd Hafizi Ahmad

Analytical calculation of sensing parameters on carbon nanotube based gas sensors

Carbon Nanotubes (CNTs) are generally nano-scale tubes comprising a network of carbon atoms in a cylindrical setting that compared with silicon counterparts present outstanding characteristics such as high mechanical strength, high sensing capability and large surface-to-volume ratio. These characteristics, in addition to the fact that CNTs experience changes in their electrical conductance when exposed to different gases, make them appropriate candidates for use in sensing/measuring applications such as gas detection devices. In this research, a model for a Field Effect Transistor (FET)-based structure has been developed as a platform for a gas detection sensor in which the CNT conductance change resulting from the chemical reaction between NH3 and CNT has been employed to model the sensing mechanism with proposed sensing parameters. The research implements the same FET-based structure as in the work of Peng et al. on nanotube-based NH3 gas detection. With respect to this conductance change, the I–V characteristic of the CNT is investigated. Finally, a comparative study shows satisfactory agreement between the proposed model and the experimental data from the mentioned research.

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.

Organo-montmorillonite as an electrical treeing retardant for polymeric insulating materials

This paper presents investigation on the propagation of electrical treeing in silicone rubber samples filled with Montmorillonite (MMT) and Organo-montmorillonite (OMMT) nanoclays as fillers for electrical tree inihibition. Treeing experiments were conducted by applying ac voltage with increasing rate of 0.5 kV per second at power frequency on pure silicone rubber, silicone rubber filled with 1% MMT and silicone rubber filled with 1% OMMT samples respectively and treeing propagation length and inception voltage within 30 minutes aging period were observed. Result from this study showed that the silicone rubber/OMMT sample exhibited the shortest tree length as well as highest tree inception voltage followed by the silicone/MMT sample with the pure silicone rubber having the least electrical performance. This finding suggests the OMMT can be used a filler in polymeric insulating materials for electrical tree inhibition.

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.

Electrical treeing initiation and propagation in silicone rubber nanocomposites

Electrical tree initiation voltage and tree propagation length for unfilled silicone rubber, silicone rubber nanocomposites filled with 1% and 3% of OMMT and SiO2 was presented in this paper. This study investigates the capabilities of OMMT and SiO2 in silicone rubber in order to inhibit the growth of electrical treeing. From the result of this study has indicated that in the filled nanocomposite sample, the OMMT acts as barrier to unfilled silicone rubber and silicone rubber filled with SiO2 because the capabilities to decreased the tree propagation length of electrical tree. This result revealed that OMMT could be used as filler in silicone rubber insulating material for the purpose of retarding electrical tree growth.

Statistical study on tree inception voltage of silicone rubber and epoxy resin

Weibull distribution has been used widely by many researches around the world especially in the analysis of high voltage experimental data. Unfortunately, most of the experimental data analysis was not following the accurate statistical technique. Thus in this paper, a statistical study on the tree inception voltage of silicone rubber and epoxy resin is presented. The tree inception voltage of silicone rubber and epoxy resin was measured via camera-equipped online monitoring system. The leaf-like specimen was used as test sample. The experiment was performed based on IEC 1072:1991 “Methods of Test for Evaluating the Resistance of Insulating Materials against the Initiation of Electrical Trees”. The obtained results were analysed statistically by using fitting method. Anderson-Darling goodness-of-fit test was performed in order to obtain the best fitting distribution. Comparison exercise was made between the fitted distribution and Weibull distribution. Based on Anderson-Darling tests, the tree inception voltage of silicone rubber and epoxy resin was best fitted with Johnson SB distribution. Based on this fitted distribution, the value of tree inception voltage for silicone rubber and epoxy resin was calculated and equalled to 3.1529 kV and 4.6528 kV respectively. Thus, it was found that, the fitting method by means of Anderson-Darling goodness-of-fit test was successful to recognize the best fitted distribution for the value of tree inception voltage for silicone rubber and epoxy resin.

A comparative study on the effect of electrical ageing on electrical properties of palm fatty acid ester (PFAE) and FR3 as dielectric materials

Transformer oil is commonly used in electrical insulation, cooling and lubrication of sliding components. There are many factors that negatively affect the electrical insulation properties of power transformers in its operation. Due to the increasing need to replace the petroleum-based mineral oil, there is an interest in replacing the oil with biodegradable vegetative-based oil. The properties of alternative oils that can be used to replace the existing mineral oil are described. Firstly, the vegetable oil was analyzed using computational simulation to investigate the dielectric characteristic and compared to the existing mineral oil. Then, a comparative experimental study concerning the ageing of vegetative-based oil, namely palm fatty acid ester (PFAE) and FR3 by comparing them with the commercially available mineral oil was conducted. Several important properties such as breakdown voltage, the dielectric dissipation factor (tan d) and the capacitance of PFAE and FR3 oils have been measured. Varying ageing time have been applied during experimental process. Based on the experimental results, both oils show higher breakdown voltage compared to the mineral oil. In addition, both of the vegetative-based oils have lower value of dielectric dissipation factor and higher value of capacitance. Therefore, both oils are good insulating oils for transformer applications.

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.

Short-Term Breakdown in Silicone Rubber Based Nanocomposites Caused by Electrical Treeing

This paper presents experimental study on short-term breakdown of silicone rubber based nanocomposites with different silicone dioxide (SiO2) nanofiller loading by focusing on the effect of electrical tree. The objective of this study was to investigate the ability of SiO2 nanofiller to inhibit the growth of electrical tree in silicone rubber until breakdown. Samples of silicone rubber based nanocomposites (three samples were filled with 1wt%, 2wt% and 3wt% of SiO2 respectively whereas the forth sample was unfilled silicone rubber), were used in this experimental study and two parameters such as electrical tree initiation voltage and breakdown time were measured. Based on the obtained results, the sample with the highest SiO2 loading has shown the highest tree initiation voltage and the longest breakdown time. Therefore, this makes SiO2 a promising material to be used as fillers in polymeric insulations for the purpose of retarding electrical tree growth.

Measurement of Dielectric Properties of Low-Density Polyethylene Nanocomposites Using “Sub-Hertz” Dielectric Spectroscopy

Recently, many studies have been conducted on the dielectric properties of Low-Density Polyethylene (LDPE) nanocomposites and produced different results. However, the composition of LDPE polymer and boron nitride (BN) as nanofiller has neither been well understood nor producing a convenient result. Similarly, the dielectric spectroscopy measured at “sub–hertz” frequency has been of little interest among researchers since it is often influenced by “conduction-like” effect. This research identified the dielectric properties of LDPE nanocomposites filled with hexagonal boron nitride (h-BN) nanofillers by using dielectric spectroscopy technique. The dielectric loss and relative permittivity for three different filler concentrations were investigated under “sub-hertz” frequency ranges at room temperature. The cylindrical electrode with guard ring configuration was used to conduct the experiment, in accordance to the ASTM D150 standard. The results revealed that 5 wt% filled polymer has lower loss tangent and permittivity compared to the unfilled polymer, due to the strong interaction between nano-particle and the polymer. This strong interaction is believed to limit the movement of the polymer chain. The decrease in loss tangent also indicates lower quasi-DC at low frequency. However, further increase in the filler loading has recorded an increment in the value of permittivity and loss tangent. This higher effective permittivity is mainly due to the influence of the filler permittivity