Zulkarnain A. Noorden

Application of response surface methodology for optimizing the oxidative stability of natural ester oil using mixed antioxidants

Natural ester insulation (NEI) oils have been developed since the early 1990s due to the increasing environmental, health and safety concerns from the public. NEI oils are well-known for having high fire and flash points, great moisture tolerance, good biodegradability and non-toxicity. However, NEI oils also have several drawbacks compared to mineral insulation (MI) oils such as low oxidative stability, high viscosity, low pour point and low resistance towards lightning impulse. Previous researchers have discovered that the oxidative stability of NEI oils can be improved by the addition of mixed antioxidants. However, such studies are focused on only one criterion and they neglect the dielectric strength of the oils. On the other hand, the one-factor-at-a-time (OFAT) method is commonly used to determine the optimum concentration of mixed antioxidants and requires a large number of samples. In this study, response surface methodology (RSM) technique is used to determine the optimum concentration of mixed antioxidants which will enhance the oxidative stability of NEI oil. The dielectric strength of the NEI oil is evaluated based on the AC breakdown voltage (BdV). RSM is chosen in this study because it is capable of determining the optimum values of the parameters of interest, without the need for a large number of test runs which will incur high cost for experimentation. A regression model is developed in this study based on the AC breakdown voltage of the NEI oil, propyl gallate and citric acid antioxidant concentrations. The oxidative induction time (OIT) and partial discharge inception voltage (PDIV) are carried out to determine the effect of the oxidative stability and withstand voltage on the partial discharge, respectively. The results showed that there is enhancement in the oxidative stability and dielectric strength of NEI oil using the optimum concentrations of mixed antioxidants relative to the fresh NEI oil. It can be concluded that RSM is a feasible alternative to determine the optimum concentration of antioxidants for NEI oils, which in turn, helps improve the oxidative stability and dielectric strength of these oils.

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

Multi-response optimization of the properties of natural ester oil with mixed antioxidants using taguchi-based methodology

A Taguchi-based methodology is proposed in this study in order to determine the optimum concentration of antioxidants which will enhance the oxidative stability of natural ester insulation (NEI) oil while ensuring superior dielectric strength performance. Conventional experimental testing involves the procurement of materials and equipment, sample preparation, experimental set-up and testing the samples with a large number of test runs to determine the optimum design parameters, which is costly and time-consuming. In this regard, the Taguchi-based methodology is advantageous since it can predict the optimum design parameters with fewer test runs. This methodology can also be used for multi-response optimization by applying a desirability function. The number of test runs for the antioxidant mixtures is generated using the L9 orthogonal array with three levels and two factors. This methodology limits the need to deal with the uncertainties associated with the range of factors, unlike the one-factor-at-a-time (OFAT) method. The oxidative induction time (OIT) and AC breakdown voltage (AC BdV) are selected as the output responses in accordance with the ASTM E1858 and ASTM D1816 standard test method, respectively. Analysis of variance (ANOVA) is used to determine the percentage contribution of each factor as well as the significance level of the model developed from the Taguchi-based methodology. The desirability function is used to transform the two output responses and generate the optimum value which complements both of the responses. Repeated tests are conducted to verify the repeatability and reproducibility of the OIT and AC BdV results for the optimized NEI oil based on a 95% confidence interval. In general, there is a significant enhancement in the OIT and AC BdV for the optimized NEI oil compared to those for fresh NEI oil. Hence, it can be concluded that the Taguchi-based methodology is a feasible approach to determine the optimum concentrations of mixed antioxidants for NEI oils.

New carbon material derived from mixture with lubricating oil and sulfuric acid and its electric property for EDLC

This paper describes the electric properties of new carbon materials derived from the chemical synthesis mixed with insulation oil or lubricating oil and sulfuric acid. New carbon material as an activated carbon has higher capacitance expecting for large electric energy storage system. The capacitance and internal resistance were measured as a function of mixture ratio of the materials using the capacitor model. Experimental results show that the new carbon material has a high potentiality for large electric energy storage systems.

A Review on the Reclamation Technologies for Service-Aged Transformer Insulating Oils

Zarina Mohd Noh*, Abdul Rahman Ramli, Marsyita Hanafi, M Iqbal Saripan, Ridza Azri Ramlee 1,2,3,4 Department of Computer and Communication Systems Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia 1,5 Fakulti Kejuruteraan Elektronik dan Kejuruteraan Komputer, Universiti Teknikal Malaysia Melaka (UTeM), Hang Tuah Jaya, 75450 Durian Tunggal, Melaka, Malaysia

Electrochemical impedance behavior of glass wool-based supercapacitors with different concentration of sulfuric acid

The paper presents the electrochemical impedance behavior of recently introduced corrosive resistant material for supercapacitors separator; glass wool under four different concentration of 0.5, 1, 5 and 18 mol/dm3 sulfuric acid (H2SO4) electrolytes. Ultracapacitors with a pair of activated carbon sheets as the active electrodes and each electrolyte-containing glass wool as the separator were constructed in a custom-made two-electrode test cell. The electrochemical impedance was carried out within the frequency range of 1 mHz to 100 kHz. The impedance data were extracted into a typical Nyquist plot, complex capacitance and complex powers in order to thoroughly evaluate the supercapacitors performance in terms of their specific capacitance, associated resistances, relaxation time and power capacity. Appealingly, as compared to the lower concentrated electrolyte-based supercapacitor, the supercapacitor with 18 mol/dm3 H2SO4 electrolyte has outperformed others with 18% increment of specific capacitance, 57% enhancement of relaxation time and 63% reduction of internal series resistance. Overall, the electrochemical impedance behavior of the glass wool-based supercapacitors approach closely to an ideal capacitive characteristic under various H2SO4 concentration, indicating its high potential to be applied in higher performance supercapacitor construction.

Charge-discharge cyclability of ultracapacitor with glass wool separator under high concentrated sulfuric acid

The paper evaluates the charge-discharge cyclability of ultracapacitor with glass wool separator under various concentration of aqueous sulfuric acid (H2SO4) electrolytes. For lower concentrated electrolyte of 1 mol/dm3 H2SO4, the performance was compared to an ultracapacitor with conventional cellulose separator. Two-electrode ultracapacitors were constructed by sandwiching two activated carbon electrodes with each electrolyte-containing separator material. The cyclability test was performed with constant charge-discharge current of 10 mA for up to 300 cycles. Prior to the cyclability test, the constructed ultracapacitors were evaluated based on cyclic voltammetry and galvanostatic tests. The glass wool-based capacitor has performed comparably to the conventional cellulose-based capacitor in terms of its specific capacitance and internal resistance for up to 300 cycles. Interestingly, in a higher concentrated electrolyte of 18 mol/dm3 H2SO4, the specific capacitance of the glass wool-based ultracapacitor is 40% greater than of 1 mol/dm3 H2SO4 electrolyte. It is envisaged that by applying the glass wool as the separator coupled, with high concentration aqueous electrolyte may lead to higher rating ultracapacitor at relatively lower cost as compared to an organic electrolyte-based ultracapacitor.

Analysis of relationship between acceleration and battery state-of-charging in electric vehicle

Electric vehicle (EV) had the potential for helping to create a more sustainable future as it powered by green technology battery. Therefore, the investigation on battery performance has gained a lot of attention since it is one of advanced technology storage element. This paper reviews an analysis of the relationship between the acceleration of electric vehicles and state-of-charging (SOC) of battery in EV. The energy storage capacity reduction in the battery is inversely proportional to the acceleration rate. As the driving cycles and acceleration rate changing will influence the time taken for the battery to reach 0% of SOC. Several random driving cycles are created in order to identify its relationship with SOC. At the end of this paper, a mathematical equation is introduced to represent the relationship between acceleration rates versus SOC of EV.

Electrochemical Study of Hydrocarbon-Derived Electrolytes for Supercapacitors

In this paper, we evaluate the essential electrochemical properties – capacitive and resistive behaviors – of hydrocarbon-derived electrolytes for supercapacitor application using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrolytes were systematically prepared from three hydrocarbon-derived compounds, which have different molecular structures and functional groups, by treatment with high-concentration sulfuric acid (H2SO4) at room temperature. Two-electrode cells were assembled by sandwiching an electrolyte-containing glass wool separator with two active electrodes of activated carbon sheets. The dc electrical properties of the tested cells in terms of their capacitive behavior were investigated by CV, and in order to observe the frequency characteristics of the constructed cells, EIS was carried out. Compared with the tested cell with only high-concentration H2SO4 as the electrolyte, the cell with the derived electrolytes exhibit a capacitance as high as 135 F/g with an improved overall internal resistance of 2.5 Ω. Through the use of a simple preparation method and low-cost precursors, hydrocarbon-derived electrolytes could potentially find large-scale and higher-rating supercapacitor applications.

Comparison of terahertz and infrared spectroscopy for degraded hydrocarbon liquid

Terahertz (THz) spectroscopy has high sensitivity for the interaction between molecules and vibration of large molecules. Besides, it is well known that infrared (IR) spectroscopy can be used to detect the vibration of functional groups. Hence, the comparison of the conventional diagnosis method using IR spectroscopy and THz spectroscopy is expected for more potential diagnosis. In this study, the comparison between THz spectroscopy and IR spectroscopy for deteriorated hydrocarbon liquids has been conducted for the degraded insulating oils. The surveyed samples are pure dodecane and mineral oil. The degraded samples are made by heating in the oxygen atmosphere. In addition, we also measured the breakdown voltage and the volume resistivity to know the states of degraded insulating oil. The experimental results show that oxidation causes spectral changes in the both of THz and IR regions. The spectral change in the IR region is due to carbonyl group and hydroxyl group vibrations. Whereas, in the THz region, the spectral change originates from the modification of intermolecular interaction. The degradation phenomena of the insulating oil contribute to higher carbonyl/hydroxyl content and associated by stronger intermolecular interaction that leads to its lower breakdown voltage.