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  1. Fulltext Top-oil temperature model for transformers based on nonlinear thermal resistance, lumped capacitance and thermal-electrical analogy
    Roslan, M.H., Azis, N., Jasni, J., Ibrahim, Z.
    Pertanika Journal of Science & Technology, 2017;25(102):151-160.
    MyJurnal
    Top-Oil Temperature (TOT) is one of the basic components to estimate the Hot-Spot temperature (HST) of the transformers. This paper presents an alternative TOT model based on the heat transfer theory that utilises Nonlinear Thermal Resistance (NTR) and Lumped Capacitance (LC) approaches. It is applied in a thermal-electrical analogy and the heat transfer equivalent equation is determined. This model is tested on a measured TOT of 250 MVA ONAF and 400 MVA ONAF transformers obtained from IEC 60076-7 and previous research. A comparison of TOT is carried out with the existing models IEC 60076-7 exponential and IEEE Loading Guide clause 7 methods. It is found that the thermal model based on the NTR and LC approach could determine the measured TOT closer than the existing methods available in the standards.
  2. Fulltext Assessment of transformer health index using different model
    Jasni, J., Azmi, A., Azis, N., Yahaya, M.S., Talib, M.A.
    Pertanika Journal of Science & Technology, 2017;25(102):143-150.
    MyJurnal
    Transformer failures lead to interruption of power supply. Therefore, asset management is important to monitor the efficient functioning of transformers. An important approach in asset management is condition assessment whereby the health status of the transformer is assessed via a health index. There are many methods in determining the final value of a health index. This paper examines how different assessment methods can be used in order to come up with the final health index and output of final health index. The output trend shapes are almost the same for Assessment Model A, B and C except for Assessment Model D. There is no strong correlation between the health index and age of the transformer. Generally, the value of health index of the transformer is reflected by its operation and loading history .This paper hence examines the assessment steps and results that will guide the development of a new approach to determine health index value.
  3. Investigation of Kenaf Paper in the Presence of PVA for Transformers Application
    Umair M, Azis N, Halis R, Jasni J
    Materials (Basel), 2020 Nov 06;13(21).
    PMID: 33171971 DOI: 10.3390/ma13215002
    This paper presents an investigation on the physio-mechanical properties and AC breakdown voltage of the Kenaf paper in the presence of Polyvinyl Alcohol (PVA) for transformers application. Kenaf bast fibers were used in order to produce the paper through the soda pulping process. The pulps were subjected to beating up to 12,000 revolutions, whereby the PVA was added to the pulps at a different weight percentage concentration up to 12%. Morphological study was carried out on the Kenaf paper based on Scanning Electron Microscopy (SEM). The apparent density, Tensile Index (TI), Burst Index (BI), Tear Index (TeI), and AC breakdown voltage of the Kenaf paper were measured. It is found that the TI and BI of Kenaf paper can be slightly improved through the introduction of PVA. On other hand, the TeI of the Kenaf paper decreases with the increment of the PVA. The AC breakdown voltage of the Kenaf paper slightly increases with the increment of PVA weight percentage concentration.
  4. Palm-Based Neopentyl Glycol Diester: A Potential Green Insulating Oil
    Raof NA, Yunus R, Rashid U, Azis N, Yaakub Z
    Protein Pept Lett, 2018;25(2):171-179.
    PMID: 29359647 DOI: 10.2174/0929866525666180122095056
    BACKGROUND: The transesterification of high oleic palm oil methyl ester (HOPME) with neopentyl glycol (NPG) has been investigated. The present study revealed the application of low-pressure technology as a new synthesis method to produce NPG diesters. Single variable optimization and response surface methodology (RSM) were implemented to optimize the experimental conditions to achieve the maximum composition (wt%) of NPG diesters.

    OBJECTIVE: The main objective of this study was to optimize the production of NPG diesters and to characterize the optimized esters with typical chemical, physical and electrical properties to study its potential as insulating oil.

    METHODS: The transesterification reaction between HOPME and NPG was conducted in a 1L three-neck flask reactor at specified temperature, pressure, molar ratio and catalyst concentration. For the optimization, four factors have been studied and the diester product was characterized by using gas chromatography (GC) analysis. The synthesized esters were then characterized with typical properties of transformer oil such as flash point, pour point, viscosity and breakdown voltage and were compared with mineral insulating oil and commercial NPG dioleate. For formulation, different samples of NPG diesters with different concentration of pour point depressant were prepared and each sample was tested for its pour point measurement.

    RESULTS: The optimum conditions inferred from the analyses were: molar ratio of HOPME to NPG of 2:1.3, temperature = 182°C, pressure = 0.6 mbar and catalyst concentration of 1.2%. The synthesized NPG diesters showed very important improvement in fire safety compared to mineral oil with flash point of 300°C and 155°C, respectively. NPG diesters also exhibit a relatively good viscosity of 21 cSt. The most striking observation to emerge from the data comparison with NPG diester was the breakdown voltage, which was higher than mineral oil and definitely in conformance to the IEC 61099 limit at 67.5 kV. The formulation of synthesized NPD diesters with VISCOPLEX® pour point depressant has successfully increased the pour point of NPG diester from -14°C to -48°C.

    CONCLUSION: The reaction time for the transesterification of HOPME with NPG to produce NPG diester was successfully reduced to 1 hour from the 14 hours required in the earlier synthesis method. The main highlight of this study was the excess reactant which is no longer methyl ester but the alcohol (NPG). The optimum reaction conditions for the synthesis were molar ratio of 2:1.13 for NPG:HOPME, 182°C, 0.6 mbar and catalyst concentration of 1.2 wt%. The maximum NPG diester yield of 87 wt% was consistent with the predicted yield of 87.7 wt% obtained from RSM. The synthesized diester exhibited better insulating properties than the commercial products especially with regards to the breakdown voltage, flash point and moisture content.

  5. Fulltext Effect of shield placement for transient voltage mitigation due to switching surges in a 33/11 kV transformer windings
    Srikanta Murthy A, Azis N, Jasni J, Othman ML, Mohd Yousof MF, Talib MA
    PLoS One, 2020;15(10):e0240368.
    PMID: 33035254 DOI: 10.1371/journal.pone.0240368
    This study presents an investigation on the effect of shield placement for mitigation of transient voltage in a 33/11 kV, 30 MVA transformer due to Standard Switching Impulse (SSI) and Oscillating Switching Impulse (OSI) surges. Generally, the winding and insulation in transformers could experience severe voltage stress due to the external impulses i.e. switching events. Hence, it is important to examine the voltage stress and identify the mitigation action i.e. shield placements in order to reduce the adverse effect to the transformer windings. First, the resistances, inductances, and capacitances (RLC) were calculated for disc type transformer in order to develop the winding RLC equivalent circuit. The SSI and OSI transient voltage waveforms were applied to the High Voltage (HV) winding whereby the transient voltages were simulated for each disc. The resulting voltage stresses were mitigated through different configurations of electrostatic shield placements. The resonant oscillations generated due to switching surges were analysed through initial voltage distribution. The analyses on the transient voltages of the transformer winding and standard error of the slope (SEb) reveal that the location of shield placement has a significant effect on the resonant switching voltages. The increment of the shield number in the windings does not guarantee optimize mitigation of the resonant switching transient voltages. It is found that the voltage stress along the windings is linear once a floating shield is placed between the HV and Low Voltage (LV) windings of the disc-type transformer under the SSI and OSI waveforms. These findings could assist the manufacturers with appropriate technical basis for mitigation of the transformer winding against the external transient switching overvoltage surges.
  6. Fulltext Experimental Study on the Partial Discharge Characteristics of Palm Oil and Coconut Oil Based Al2O3 Nanofluids in the Presence of Sodium Dodecyl Sulfate
    Mohamad NA, Azis N, Jasni J, Kadir MZAA, Yunus R, Yaakub Z
    Nanomaterials (Basel), 2021 Mar 19;11(3).
    PMID: 33808641 DOI: 10.3390/nano11030786
    This experimental study aims to examine the partial discharge (PD) properties of palm oil and coconut oil (CO) based aluminum oxide (Al2O3) nanofluids with and without surfactants. The type of surfactant used in this study was sodium dodecyl sulfate (SDS). The volume concentrations range of Al2O3 dispersed in oil samples was varied from 0.001% to 0.05%. The ratio of surfactants to nanoparticles was set to 1:2. In total, two different types of refined, bleached and deodorized palm oil (RBDPO) and one type of CO were measured for PD. Mineral oil (MO) was also examined for comparison purpose. PDIV measurements for all samples were carried out based on rising voltage method whereby a needle-sphere electrode configuration with a gap distance of 50 mm was chosen in this study. Al2O3 improves the PDIVs of RBDPO, CO and MO whereby the highest improvements of PDIVs are 34%, 39.3% and 27%. The PD amplitude and repetition rate of RBDPO improve by 38% and 81% while for CO, it can increase up to 65% and 80% respectively. The improvement of PD amplitude and repetition rate for MO are 18% and 95%, regardless with and without SDS. Without SDS, the presence of Al2O3 could cause 26%, 75% and 65% reductions of the average emission of light signals for RBDPOA, RBDPOB and CO with the improvement of PD characteristics but both events do not correlate at the same volume concentration of Al2O3. On the other hand, the average emission of light signal levels of the oils increases with the introduction of SDS. The emission of light signal in MO does not correlate with the PD characteristics improvement either with or without SDS.
  7. Fulltext Extraction of winding parameters for 33/11 kV, 30 MVA transformer based on finite element method for frequency response modelling
    Srikanta Murthy A, Azis N, Jasni J, Othman ML, Mohd Yousof MF, Talib MA
    PLoS One, 2020;15(8):e0236409.
    PMID: 32853253 DOI: 10.1371/journal.pone.0236409
    This paper proposes an alternative approach to extract transformer's winding parameters of resistance (R), inductance (L), capacitance (C) and conductance (G) based on Finite Element Method (FEM). The capacitance and conductance were computed based on Fast Multiple Method (FMM) and Method of Moment (MoM) through quasi-electrostatics approach. The AC resistances and inductances were computed based on MoM through quasi-magnetostatics approach. Maxwell's equations were used to compute the DC resistances and inductances. Based on the FEM computed parameters, the frequency response of the winding was obtained through the Bode plot function. The simulated frequency response by FEM model was compared with the simulated frequency response based on the Multi-conductor Transmission Line (MTL) model and the measured frequency response of a 33/11 kV, 30 MVA transformer. The statistical indices such as Root Mean Square Error (RMSE) and Absolute Sum of Logarithmic Error (ASLE) were used to analyze the performance of the proposed FEM model. It is found that the simulated frequency response by FEM model is quite close to measured frequency response at low and mid frequency regions as compared to simulated frequency response by MTL model based on RMSE and ASLE analysis.
  8. Fulltext Ageing Study of Palm Oil and Coconut Oil in the Presence of Insulation Paper for Transformers Application
    Mohamad NA, Azis N, Jasni J, Ab Kadir MZA, Yunus R, Yaakub Z
    Materials (Basel), 2018 Mar 30;11(4).
    PMID: 29601520 DOI: 10.3390/ma11040532
    This paper presents a sealed ageing study of palm oil (PO) and coconut oil (CO) in the presence of insulation paper. The type of PO under study is refined, bleached, and deodorized palm oil (RBDPO) olein. Three different variations of RBDPO and one sample of CO are aged at temperatures of 90 °C, 110 °C, and 130 °C. The properties of RBDPO and CO as well as paper under ageing are then analysed through dielectric and physicochemical measurements. It is found that the effect of ageing is not significant on the alternating current (AC) breakdown voltages and relative permittivities of RBDPO and CO. There is a slight increment trend of the resistivity for CO, while for all of the RBDPO, the resistivity slightly decreases as the ageing progresses. Only CO shows an apparent reduction of the dielectric dissipation factor. Throughout the ageing time, the acidities of all of the RBDPO and CO remain at low level, while the moisture in oils decreases. The tensile index (TI) of the papers for all of the RBDPO and CO retain more than 50% of the TI. A significant increment of the paper ageing rates of all of the RBDPO and CO is observed at an ageing temperature of 130 °C.
  9. Fulltext Zinc/Aluminium⁻Quinclorac Layered Nanocomposite Modified Multi-Walled Carbon Nanotube Paste Electrode for Electrochemical Determination of Bisphenol A
    Zainul R, Abd Azis N, Md Isa I, Hashim N, Ahmad MS, Saidin MI, et al.
    Sensors (Basel), 2019 Feb 22;19(4).
    PMID: 30813385 DOI: 10.3390/s19040941
    This paper presents the application of zinc/aluminium-layered double hydroxide-quinclorac (Zn/Al-LDH-QC) as a modifier of multiwalled carbon nanotubes (MWCNT) paste electrode for the determination of bisphenol A (BPA). The Zn/Al-LDH-QC/MWCNT morphology was examined by a transmission electron microscope and a scanning electron microscope. Electrochemical impedance spectroscopy was utilized to investigate the electrode interfacial properties. The electrochemical responses of the modified electrode towards BPA were thoroughly evaluated by using square-wave voltammetry technique. The electrode demonstrated three linear plots of BPA concentrations from 3.0 × 10-8⁻7.0 × 10-7 M (R² = 0.9876), 1.0 × 10-6⁻1.0 × 10-5 M (R² = 0.9836) and 3.0 × 10-5⁻3.0 × 10-4 M (R² = 0.9827) with a limit of detection of 4.4 × 10-9 M. The electrode also demonstrated good reproducibility and stability up to one month. The presence of several metal ions and organic did not affect the electrochemical response of BPA. The electrode is also applicable for BPA determination in baby bottle and mineral water samples with a range of recovery between 98.22% and 101.02%.
  10. Fulltext Effects of RTV coating on the electrical performance of polymer insulator under lightning impulse voltage condition
    Jamaludin FA, Ab-Kadir MZA, Izadi M, Azis N, Jasni J, Abd-Rahman MS
    PLoS One, 2017;12(11):e0187892.
    PMID: 29136025 DOI: 10.1371/journal.pone.0187892
    Located near the equator, Malaysia is a country with one of the highest lightning densities in the world. Lightning contributes to 70% of the power outages in Malaysia and affects power equipment, automated network systems, causes data losses and monetary losses in the nation. Therefore, consideration of insulator evaluation under lightning impulses can be crucial to evaluate and attempt to overcome this issue. This paper presents a new approach to increase the electrical performance of polymer insulators using a Room Temperature Vulcanisation (RTV) coating. The evaluation involves three different settings of polymer insulator, namely uncoated, RTV type 1, and RTV type 2 upper surface coatings. All the insulators were tested under three different conditions as dry, clean wet and salty under different impulse polarities using the even-rising test method. The voltage breakdown for each test was recorded. From the experiment, it was found that the effectiveness of the RTV coating application became apparent when tested under salty or polluted conditions. It increased the voltage withstand capabilities of the polymer insulator up to 50% from the basic uncoated insulator. Under dry and clean conditions, the RTV coating provided just a slight increase of the breakdown voltage. The increase in voltage breakdown capability decreased the probability of surface discharge and dry band arcing that could cause degradation of the polymeric material housing. The RTV type 1 coating was found to be more effective when performing under a lightning impulse. The findings might help the utility companies improve the performance of their insulators in order to increase power system reliability.
  11. Effect of surfactants on the lightning breakdown voltage of palm oil and coconut oil based Al2O3 nanofluids
    Mohamad NA, Azis N, Jasni J, Ab Kadir MZA, Yunus R, Yaakub Z
    Nanotechnology, 2020 Aug 04;31(42):425708.
    PMID: 32748802 DOI: 10.1088/1361-6528/aba1b9
    In this paper, the effect of different types of surfactants on the lightning breakdown voltages of palm oil (PO) and coconut oil (CO) based aluminium oxide (Al2O3) nanofluids is investigated. Three different types of surfactants were used in this study known as cationic (cetyl trimethyl ammonium bromide (CTAB)), anionic (sodium dodecyl sulfate (SDS)) and non-ionic (oleic acid (OA)). The volume percentage concentrations of Al2O3 dispersed into PO and CO were varied from 0.001% to 0.05%. The ratio of surfactant to the nanoparticles was set to 50% from the volume concentration of nanoparticles which equivalent to 1:2. In total, two types of refined, bleached and deodorized palm oil (RBDPO) and one type of CO were examined for lightning breakdown voltage. The test was carried out based on needle-sphere electrodes configuration with 25 mm gap distance. The presence of Al2O3 improves both positive and negative lightning breakdown voltages of RBDPO and CO. Under the positive and negative polarities, the CTAB does provide further improvements on the lightning breakdown voltages of RBDPOA (1st type of samples) and CO at most of the volume of concentration of Al2O3. SDS and OA could also further improve the lightning breakdown voltage of CO at certain volume concentration of Al2O3. On the other hand, the lightning breakdown voltage of RBDPOB based Al2O3 nanofluid (2nd type of samples) does not further improve with the introduction of surfactants. At most of the volume concentration of Al2O3, the introduction of CTAB further increases the times to breakdown and decrease the average streamer velocities of RBDPOA under both polarities. The same finding is observed for CO under positive polarity with CTAB and SDS as well as under negative polarity in the presence of all surfactants. The streamer velocities and times to breakdown patterns of RBDPOB based Al2O3 nanofluid are inconsistent in the presence of all surfactants. It is found that RBDPO and CO based Al2O3 nanofluids have second mode of streamer whereby the streamer velocities are from 1 km s-1 to 1.63 km s-1 regardless with or without surfactants.
  12. Fulltext A persistent antimicrobial resistance pattern and limited methicillin-resistance-associated genotype in a short-term Staphylococcus aureus carriage isolated from a student population
    Mat Azis N, Pung HP, Abdul Rachman AR, Amin Nordin S, Sarchio SNE, Suhaili Z, et al.
    J Infect Public Health, 2017 Mar-Apr;10(2):156-164.
    PMID: 27033676 DOI: 10.1016/j.jiph.2016.02.013
    The aim of the present study was to assess and compare the antimicrobial susceptibility pattern against a panel of antibiotics and molecular and methicillin resistance-associated genotypes of 120 carriage S. aureus isolates previously isolated from a student population at two isolation events within a one-month interval. The antibiotic susceptibility of isolates was determined using the Kirby-Bauer disc-diffusion method (cefoxitin by Etest). The MRSA was screened using polymerase chain reaction for the presence of the mecA gene. The mecA-positive isolates were subjected to staphylococcal cassette chromosome (SCC) mec typing, multilocus sequence typing (MLST) and eBURST analysis. All isolates were characterized for the presence of the Panton-Valentine leukocidin (PVL) gene, an enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) pattern and the spa type. For the two occasions where S. aureus was isolated, the highest frequency of resistance was observed for penicillin (70% and 65%, respectively), with a lower rate against erythromycin and tetracycline (<12%). All isolates were susceptible to ciprofloxacin and gentamycin. As for methicillin resistance, eight isolates had minimum inhibitory concentrations (MIC) of resistant categories, but 10 isolates (8.33%) were positive for the mecA gene. The mecA-positive isolates belonged to SCCmec types I (n=9) and V (n=1). MLST was resolved for only three MRSAs, ST508 (n=1), ST88 (n=1) and ST96 (n=1). The results of the eBURST analysis showed that the MRSA isolates analyzed in the present study were potentially related to MRSA identified in other countries. Approximately half of the persistent S. aureus carriers harbored S. aureus of a similar spa type in the respective individuals during both isolation events. A persistent antimicrobial pattern and limited distinct MRSAs were observed over the short study period. The latter frequently exhibited SCCmec type I, commonly associated with hospital-acquired (HA) characteristics, but further delineation is needed to justify the origins of these bacteria.
  13. Characterization of resistance to selected antibiotics and Panton-Valentine leukocidin-positiveStaphylococcus aureusin a healthy student population at a Malaysian University
    Suhaili Z, Rafee P', Mat Azis N, Yeo CC, Nordin SA, Abdul Rahim AR, et al.
    Germs, 2018 Mar;8(1):21-30.
    PMID: 29564245 DOI: 10.18683/germs.2018.1129
    Introduction: This study aims to assess the antimicrobial susceptibility profiles ofStaphylococcus aureusstrains isolated from university students and to determine the prevalence of constitutive and inducible clindamycin resistance, the latter being able to cause therapeutic failure due to false in vitro clindamycin susceptibility.

    Methods: S. aureus
    strains were isolated from the nasal swabs of 200 health sciences students of a Malaysian university. Twelve classes of antibiotics were used to evaluate the antimicrobial susceptibility profiles with the macrolide-lincosamide-streptogramin B (MLSB) phenotype for inducible clindamycin resistance determined by the double-diffusion test (D-test). Carriage of resistance and virulence genes was performed by PCR onS. aureusisolates that were methicillin resistant, erythromycin resistant and/or positive for the leukocidin gene,pvl(n=15).

    Results: Forty-nine isolates were viable and identified asS. aureuswith four of the isolates characterized as methicillin-resistantS. aureus(MRSA; 2.0%). All isolates were susceptible to the antibiotics tested except for penicillin (resistance rate of 49%), erythromycin (16%), oxacillin (8%), cefoxitin (8%) and clindamycin (4%). Of the eight erythromycin-resistant isolates, iMLSBwas identified in five isolates (three of which were also MRSA). The majority of the erythromycin-resistant isolates harbored themsrAgene (four iMLSB) with the remaining iMLSBisolate harboring theermCgene.

    Conclusion: The presence of MRSA isolates which are also iMLSBin healthy individuals suggests that nasal carriage may play a role as a potential reservoir for the transmission of these pathogens.

  14. A Nanocomposite Paste Electrode Sensor for Simultaneous Detection of Uric Acid and Bisphenol A Using Zinc Hydroxide Nitrate-Sodium Dodecylsulfate Bispyribac
    Yulkifli Y, Yandes WP, Isa IM, Hashim N, Ulianas A, Sharif SNM, et al.
    Sensors (Basel), 2023 Oct 10;23(20).
    PMID: 37896460 DOI: 10.3390/s23208366
    The fabrication of a zinc hydroxide nitrate-sodium dodecylsulfate bispyribac modified with multi-walled carbon nanotube (ZHN-SDS-BP/MWCNT) paste electrode for uric acid and bisphenol A detection was presented in this study. Electrochemical impedance spectroscopy, chronocoulometry, square-wave voltammetry, and cyclic voltammetry were all used to examine the electrocatalytic activities of modified paste electrodes. The modified electrode's sensitivity and selectivity have been considered in terms of the composition of the modifier in percentages, the types of supporting electrolytes used, the pH of the electrolyte, and square-wave voltammetry parameters like frequency, pulse size, and step increment. Square-wave voltammetry is performed by applying a small amplitude square-wave voltage to a scanning potential from -0.3 V to +1.0 V, demonstrating a quick response time and high sensitivity. The ZHN-SDS-BP/MWCNT sensor demonstrated a linear range for uric acid and bisphenol A from 5.0 µM to 0.7 mM, with a limit of detection of 0.4 µM and 0.8 µM, respectively, with good reproducibility, repeatability, and stability as well. The modified paste electrode was successfully used in the determination of uric acid and bisphenol A in samples of human urine and lake water.
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