Sharin Ab Ghani

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.

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.

A Preliminary Study on Optimizing the In-Lab Reclamation Process Parameters of Used Transformer Oils Using the Taguchi Method

With the rapid growth of communications via the Internet, the need for an effective firewall system which has not badly affect the overall network performances has been increased. In this paper, a Field Programmable Gate Array (FPGA) -based firewall system with high performance has been implemented using Network FPGA (NetFPGA) with Xilinx Kintex-7 XC7K325T FPGA. Based on NetFPGA reference router project, a NetFPGA-based firewall system was implemented. The hardware module performs rule matching operation using content addressable memory (CAM) for higher speed data processing. To evaluate system performance, throughput, latency, and memory utilization were measured for different cases using different tools, also the number of rules that an incoming packet is subjected to was varied to get more readings using both software and hardware features. The results showed that the designed firewall system provides better performance than traditional firewalls. System throughput was doubled times of the one with Linux-Iptables firewalls.

Transformer Fault Classification from Polarization Current Measurement Results by Using Statistical Technique

In general, the presence of moisture and other impurities inside the insulator or oil can cause the breakdown of the power transformer. Polarization and Depolarization Current (PDC) is one of the technique to assess the condition of insulation oil in power transformer and can be applied in many electrical apparatus such as power cables and on load tap changer as well as to estimate conductive and moisture content of the insulation. Basically, it is a technique that is based on time domain measurement and has been used since 1990. For this research, the PDC data will be analyzed using graphical method and statistical technique to classify the transformer faults into a proper range. Lastly, it will be validated with the results from previous research. The output of the research work revealed that in term of the sequence, the results obtain in both graphical technique and the statistical technique is identical with the results presented in previous research. Hence, the range of the faults started with partial discharge, followed by arcing and lastly is the overheating.

Formation and Effect of Moisture Contents to Kraft Paper’s Life of In-Service Power Distribution Transformer

Examples of solid and liquid electrical insulations for power transformer are mineral oil and cellulose based paper. As transformers performed their function to step-up or step-down voltage level, its’ insulations will be degraded. Paper insulation is considered the most critical component in a transformer insulation system because it is not easily replaced if compared to oil where it is easily reconditioned in-order to remove water and contaminants. Studies show that temperature, moisture contents and oxygen contributed to paper insulation degradation. Moisture and furanic compound were produced from these deterioration processes. This paper is focused on the formation and effect of moisture to Kraft paper’s life. Levels of moisture contents were obtained from in-service power distribution transformers. These data then is used to assess the Kraft paper’s life by means of Weibull plot. This study shows that level of moisture contents can be used to assess the life of Kraft paper insulation.

Automated Calculation of Thermodynamic Potential Applied for Proton Exchange Membrane (PEM) Fuel Cell

Energy sources are the utility main important aspect in our daily basic life. However, their cost of operation, installation or maintenance is continuously growing to be highly expensive and to this, the solution is by encouraging the usages of recently famous renewable energy, Proton Exchange Membrane (PEM) Fuel Cell. However, this PEM Fuel Cell is not widespread and still new in Malaysia as well as the research is still in the initial stage. Therefore, the purpose of this research is to design the Automated Calculation of Thermodynamic Potential Applied for PEM Fuel Cell. In this project, two different steps will take place. First, the implementation of block parameters of PEM Fuel Cell via MATLAB simulink software (*.mdl) has been used to calculate the hydrogen pressure against Thermodynamic Potential (Enernst) value and temperature against Enernst. In order to ensure that the calculation is accurate, these two different values will be compared with the theoretical calculations. Next, the development of Graphical User Interface (GUI) by using Microsoft Visual Studio is implemented. This GUI is prepared in order to create the application of Automated Calculation of Thermodynamic Potential Applied for PEM Fuel Cell. As a result, the new developed application system is expected to automatically calculate the nominal efficiency and the thermodynamic potential value of PEM Fuel Cell.

Comparative Study of Worldwide Standards for Interpreting Frequency Response Analysis (FRA) Results of Distribution Transformers

Distribution transformer in Malaysian electricity network is categorized as major element on delivering electricity throughout the nation. Advanced diagnostic tools are used to monitor any technical problem of transformer to sustain its capability in the long run. One type of it which is currently being used in worldwide is Frequency Response Analysis (FRA). The reliability from this method is proven worldwide in diagnosing transformer condition especially a mechanical movement. FRA technique is done by comparing the response result in transformer initial condition to its current condition. The interpretation of transformer condition from the response is based on frequency sub-bands. Each frequency sub-bands are indicating any movement parts of transformer and electrical faults. Currently, there are three worldwide standards established for interpreting the FRA results but both of them are different in frequency sub-bands range. Up to now, there are no research papers comparing the fault detection capabilities from frequency sub-bands range for both standards. In this paper, comparative study is done to visualize and interpret the capabilities from three standards (IEEE Std C57.149 2012, DL/T911-2004 and Cigre WG A2/26); by focus on the frequency sub-bands range.

Study of magnetic fields produced by transmission line tower using finite element method (FEM)

Transmission line is a medium to transmit electric energy from one place to another for long distances. For instance, the aim is to reduce losses. Typically, in Malaysia the overhead transmission line was used because cost and maintenance can be handling easily. Despite, the transmission line also produced high strength of electric and magnetic field under the tower. Therefore, the tendency of magnetic field effected to the human and environment has to be identified wisely. However the real measurement under transmission line tower may give high risk. Therefore the best approach is to carry out the information by performing simulation study. In this project, Finite Element Method (FEM) via ANSYS Maxwell software was carried out. The transmission line modeling is focused on 132kV and 275kV specifications. Magnetic field analysis under the transmission tower is carrying out in this research work. Finally, it is a successful work in modeling the transmission line by validating the result with the actual on-site measurement especially on 132kV transmission line.

On-site OLTC monitoring using duval triangle and DWRM

Generally, the insulation degradation and contacts failure happened inside the On Load Tap Changer (OLTC). Besides, the OLTC performance can be dropped due to contact wear. Hence., the worn contact creates hotspots inside OLTC tank and affects the insulating oil. Due to this phenomenon, the insulating oil will degrade faster. Consequently, the whole unit of the transformer will be affected as well. Therefore, it is important to find new ways to detect the contacts wear inside the OLTC as it impacts the insulation oil and the age of the transformer. Thus, this paper demonstrates the application of Duval Triangle method during the diagnosis of OLTC to provide any significant indication related to the breakdown of OLTC. Besides, this paper introduced the advanced technique, Dynamic Winding Resistance Measurement (DWRM) to figure out the types and locations of faults occurred inside the OLTC. Finally, visual inspections will be carried out to validate the both results obtained from DGA and DWRM respectively. The analysis in this paper revealed that the findings from Duval Triangle method were similar to the outcomes carried out by DWRM.