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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. [ABSTRACT FROM AUTHOR]

In the original article Norhafiz Azis's last name is spelled incorrectly. It is correct as reflected here. [ABSTRACT FROM AUTHOR]

The convenient design of a maximum power point tracking (MPPT) controller is key to the success of photovoltaic (PV) system performance in order to maximize the extracted power, which is affected significantly by weather fluctuations, particularly partial shading condition (PSC). This paper proposes a novel hybrid MPPT approach based on a modified Perturb and Observe (P&O) assisted by the Extremum Seeking Control (ESC) strategy, combining the benefits of these simple algorithms and, meanwhile, eliminating their drawbacks. The proposed algorithm is able to track the maximum possible power under any level of weather fluctuation, with comprehensive enhancement on all aspects of high performance, boosting the PV array efficiency to 100%, reducing the convergence time to less than 100 ms, completely eradicating the oscillations around the achieved power, and maintaining the simplicity levels of both involved strategies. More importantly, this algorithm is applicable for any PV array configuration, which enhances the robustness and novelty of the algorithm. The performance is verified using MATLAB/Simulink. A boost converter is used for controlling DC to DC (direct current to direct current) power. The proposed algorithm's performance is compared with the conventional P&O and incremental conductance (IC) algorithms under four different cases of weather conditions. The shortcomings of these algorithms are illustrated and the analysis confirms the effectiveness of the proposed algorithm accordingly. [ABSTRACT FROM AUTHOR]

Sustainable materials, such as vegetable oils, have become an effective alternative for liquid dielectrics in power transformers. However, currently available vegetable oils for transformer application are extracted from edible products with a negative impact on food supply. So, it is proposed in this study to develop cottonseed oil (CSO) as an electrical insulating material and cooling medium in transformers. This development is performed in two stages. The first stage is to treat CSO with tertiary butylhydroquinone (TBHQ) antioxidants in order to enhance its oxidation stability. The second and most important stage is to use the promising graphene oxide (GO) nanosheets to enhance the dielectric and thermal properties of such oil through synthesizing GO-based CSO nanofluids. Sodium dodecyl sulfate (SDS) surfactant was used as surfactant for GO nanosheets. The nanofluid synthesis process followed the two-step method. Proper characterization of GO nanosheets and prepared nanofluids was performed using various techniques to validate the structure of GO nanosheets and their stability into the prepared nanofluids. The considered weight percentages of GO nanosheets into CSO are 0.01, 0.02, 0.03 and 0.05. Dielectric and thermal properties were comprehensively evaluated. Through these evaluations, the proper weight percentage of GO nanosheets was adopted and the corresponding physical mechanisms were discussed. [ABSTRACT FROM AUTHOR]

This paper presents an investigation on the resonant oscillations of an 11 kV layer-type winding transformer under standard and chopped lightning impulse overvoltage conditions based on calculated parameters. The resistances, inductances and capacitances were calculated in order to develop the transformer winding equivalent circuit. The impulse overvoltages were applied to the high voltage (HV) winding and the resonant oscillations were simulated for each of the layers based on different electrostatic shield placement configurations. It is found that the placement of grounded shields between layer 13 and layer 14 results in the highest resonant oscillation and non-linear initial voltage distribution. The oscillation and linear stress distributions are at the lowest for shield placement between the HV and low voltage (LV) windings. [ABSTRACT FROM AUTHOR]

The retrofilling process involves the substitution of mineral oil in an existing transformer with ester oil serves as an alternate method to prolong the transformer lifetime. This pertains to the excellent characteristics of ester oil, recognized for its moisture resilience which in turns imparts a unique advantage by extending the lifespan of insulation paper. Nevertheless, the retrofilling procedure involves mixing the new ester oil with the existing aged mineral oil (AMO) in the transformer oil, which ultimately impacts the performance of the new ester oil. Hence, it is crucial to evaluate the performance of mixed oil to identify any indications of oil deterioration due to retrofilling before energising the transformer. In evaluating the performance of aged mineral-synthetic ester (AMO/SE) retrofilled oil, this work presents the analysis of the total acid number (TAN) and Fourier Transform Infrared (FTIR) spectra. Prior to the retrofilling process using fresh-treated synthetic ester oil, four distinct amounts of aged mineral oil (AMO) were prepared, comprising 3 %, 5 %, 7 % and 9 %. This option provides the opportunity to simulate varying levels of remaining mineral oil present in the transformer. The AMO samples were prepared by subjecting the fresh mineral oil to thermal ageing in a vacuum oven at a temperature of 130 ℃ for two different durations, i.e. 75 and 150 hours. Throughout the collected data, the amount of acids in AMO/SE oil has exhibited a rising trend with a decreased in proportions of AMO in the fresh-treated synthetic ester oil for both AMO conditions. Meanwhile, the severity of AMO conditions give a significant effect to the acid growth in AMO/SE retrofilled oil. In conjunction with FTIR spectra, the rise in acid concentration in retrofilled AMO/SE oils was clearly observable in the C=O stretch in the region of 1710-1770 cm-1, which exhibited a significant association with the TAN value. [ABSTRACT FROM AUTHOR]

Faced with the increasingly serious energy crisis and environmental pollution problems, traditional internal combustion engine vehicles are receiving more and more resistance, which has rapidly promoted the development of new energy electric vehicles. Permanent magnet synchronous motors are widely used in new energy electric vehicles and in other fields because of their simple structure, light weight, small size, and high power density. With the continuous advancement of production technology, the requirements of accuracy, rapidity, and stability in permanent magnet synchronous motor systems have gradually increased. Among many advanced control technologies, this paper proposes an optimized model predictive torque control strategy based on voltage vector expansion. This strategy involves the construction of a reference stator flux linkage vector based on the analytical relationship between electromagnetic torque, reference stator flux linkage amplitude, and rotor flux linkage and the transfer of the separate control of electromagnetic torque and flux linkage amplitude into flux linkage vector control. At the same time, the optimal duty cycle corresponding to the two adjacent extended voltage vectors and the zero vector is calculated according to geometric relationships so as to realize the three voltage vector duty cycle optimization control. Experimental results show the effectiveness and superiority of the proposed strategy. [ABSTRACT FROM AUTHOR]

An oil-filled transformer should be able to operate for a long time with proper maintenance. One of the best diagnostic methods for oil-immersed transformer condition is dissolved gas analysis (DGA). However, there are times where the produce of stray gassing event might lead to fault indication in the transformer. Machine learning algorithms are used to classify the DGA data into normal condition and corresponding faults based on IEEE limits and Duval pentagon method. The algorithms that will be used include boosted trees, RUS boosted trees and subspace KNN, which belongs to the same ensemble group. Data resampling technique (SMOTETomek) is applied and shows further improvement on the accuracy of predictions by machine learning algorithms when deal with imbalance data. The algorithms are able to achieve the accuracy of 82.6% (boosted trees), 81.2% (RUS boosted trees) and 72.5% (subspace KNN), respectively, when validated with actual transformer condition. [ABSTRACT FROM AUTHOR]

In recent years, the imminent environmental problems and increasing attention to the global energy crisis have prompted the need for new opportunities and technologies to meet higher demands for clean and sustainable energy systems. As a result, new energy electric vehicles have been developed to replace fossil fuel cars. Therefore, this paper presents a three-phase interleaved parallel bidirectional buck–boost converter, which is the core factor of electrical energy flow regulation and management between the battery pack and motor drive inverter within the high voltage direct current bus and converts the voltage from two directions. Corresponding circuit topology, mathematical model, and control strategy are analyzed in three operation states: charge buck, discharge boost, and electric energy interaction modes. The digital implementation with double closed loop, power feedforward compensation, and bidirectional switching logic are realized by XDPTM Digital Power Controllers XDPP1100-Q040 of Infineon Technologies AG. Finally, the experimental results of the proposed converter clearly show that it achieves the objectives, namely, the feasibility and practicality of the system. [ABSTRACT FROM AUTHOR]

• A novel P&O GMPP tracking algorithm based on trapezoidal rule concept is proposed. • The proposed Trapezoidal rule based P&O algorithm is evaluated under PSCs and severe cases of weather fluctuation. • The feasibility and effectiveness of the proposed algorithm are validated by intensive simulation and experimental tests. • The proposed algorithm has the advantages of low oscillation, fast response, stability, array independency, and simplicity. This paper proposes a new version of the perturb and observe (P&O) algorithm which is able to recognize the global maximum power point (GMPP) among the multiple maximum peaks that exist in the P-V curve under the effect of the partial shading condition (PSC). For the first time, Trapezoidal rule concept is employed in P&O approach as a new consideration in the tracking process to calculate the best path for precisely tracking the GMPP. The new algorithm allows the search to continue until the extremum maximum is identified among numerous local maximums, rather than being imprisoned at one of the local maximums as is the case with the standard algorithm. Furthermore, the algorithm is able to achieve the MPP efficiently under the presence of rapid and abrupt changes in irradiation levels. The proposed Trapezoidal rule based P&O algorithm is evaluated under three conditions: (1) under uniform irradiance (2) under shading conditions and (3) under sudden and step changes in irradiation levels as well as the transition between shading patterns. The feasibility and effectiveness of the suggested algorithm, as well as the well-designed boost converter, are validated using two different methodologies: a simulation model in MATLAB/Simulink and hardware implementation by the (TMS320F28335) digital signal processing controller. Both simulation and hardware results confirm that the proposed algorithm provides excellent efficiency of 100% and 99.6% respectively. The GMPP is achieved within less than 100 ms, which is extremely advantageous tracking time, that avoids the power losses. In addition, the minimal steady-state oscillation is shown, with the desired level of simplicity without the need to complicated computations or random particles. [ABSTRACT FROM AUTHOR]

This research addresses the challenge of voltage rise on low voltage distribution networks with high photovoltaic penetration. The proliferation of distributed generators, particularly small-scale PV systems, has raised concerns about voltage stability and power quality in these networks. Existing reactive power control techniques, such as fixed power factor and voltage-based methods (Q(V)), have limitations in effectively mitigating voltage rise while considering load variations and network sensitivity. To overcome these limitations, an adaptive reactive power control technique is proposed in this research. The technique combines both PV active power injection and network voltage considerations in real-time to dynamically adjust reactive power output. Unlike traditional methods, which directly link reactive power reference to PV active power or voltage, the adaptive technique calculates the change in reactive power reference (ΔQ) based on both factors. This dynamic approach enables more responsive and accurate voltage regulation. The effectiveness of the adaptive technique is demonstrated through MATLAB simulations on a representative low voltage distribution network. The results show that the adaptive technique outperforms existing methods, providing better voltage regulation and reduced losses. The technique's adaptability to different scenarios and variations is also highlighted. However, it is noted that the adaptive technique may have a slightly slower response time compared to existing methods due to its dynamic nature. [Display omitted] • Fixed PF and PF (P) reactive control had high losses but high effectiveness. • Q (V) reactive power had low losses but poor voltage regulation. • Adaptive control had a novel iterative technique, making it more flexible. • Adaptive control was based on PV active power and network voltage simultaneously. • Adaptive control had better voltage regulation and lower losses. [ABSTRACT FROM AUTHOR]

• Introduces a novel multi-pulse test for GaN HEMTs in non-isolated DC-DC converters. • Enhances dynamic on-resistance characterization during unstable states. • Combines SPICE simulation with static device characterization for circuit validation. • Achieves a marginal deviation of 2.32 % from existing benchmarks. • Develops a test PCB integrating simulated and empirical findings. This study addresses the critical gap in dynamic on-resistance characterization for GaN HEMTs within the initial unstable state in a non-isolated DC-DC converter, where the output voltage and currents fluctuate and exhibit overshoots or undershoots before stabilizing to their steady-state values, a domain within solar photovoltaic (PV) Maximum Power Point Tracking (MPPT) implementations which is crucial yet insufficiently examined. The authors present a novel multi-pulse test circuit within a synchronous buck converter configuration, complemented by SPICE simulation. This combination allows for the accurate assessment of clamping circuits' performance during transient states, significantly improving the precision of R DS(ON) measurements in unsteady phases. The approach deviates from conventional methods by merging empirical data with simulation insights to validate the efficacy of clamping circuits. The experimental results affirm the methodology's precision, with the highlighted Circuit V showcasing a marginal deviation of 2.32 % from existing benchmarks. This finding substantiates the method's dependability and practicality contributing to the GaN power electronics field. In addition, this research provides a powerful analytical tool for R DS(ON) evaluation, culminating in the design of a test PCB that synergizes with both simulated and empirical evidence, contributing future research in GaN HEMT power converter applications. [ABSTRACT FROM AUTHOR]

Insulation systems of electrical apparatus (fluid and solid) include transformer oil, insulating paper, glass, ceramic, mica and rubber. Normally, they are designed well to be stable at high temperatures and provide excellent electrical insulating properties in different operating loads. There is an increasing demand to modify the effectiveness and capabilities of these insulation systems to overcome various issues (e.g., overheating, overloading and short circuits). Moreover, they should match the new high voltage insulation requirements, safety, ultra-high voltage, and being environmentally friendly are some of them. Nanoparticles (NPs) are promising compensator materials that can be used to develop insulation systems with good thermophysical and dielectric properties. The results of many studies show marvelous enhancements in electrical and thermal properties. In this paper, the authors present a review that focuses on different NPs that are used in several aspects of insulation systems to improve the dielectric as well as the heat transfer properties of high voltage insulation applications. The review covers NPs types, the preparation methods, analysis approaches, different properties, performances and results, challenges, and the limitation of the use of NPs. [ABSTRACT FROM AUTHOR]

Blending of palm-based ester can effectively increase the flash point and thermal-oxidative stability of mineral transformer oil especially in the event of high loading and high temperature. Inversely, owing to the excellent dielectric properties of mineral oil, the dielectric properties of the esters can also be improved. Thus, high oleic palm-based trimethylolpropane (TMP) ester was blended and homogenized with 20 to 50 % of mineral oil, and the physico-chemical and electrical properties of each base fluid was compared with that of pure TMP ester and pure mineral oil. The samples were also subjected to oxidative stability test conducted at 95°C for 500 hours, with the presence of water, oxygen and copper/steel catalyst. During ester and mineral oil degradations, the oxidized oils take on dark brown color with the increase in oxidation products concentration and the sludge formation due to the reaction between the oil and the metal catalyst. XRF measurements performed on the samples showed an increase in iron and sulfur contents, which can be explained by the formation of superficial surface layer of iron (II) sulfide or ferrous sulfide. From the investigations, it was found that the 80/20 of ester/mineral oil blending sample have properties near to the standard values for transformer liquid insulation; thus, it can potentially replace traditional mineral oil as an alternate liquid insulation. [ABSTRACT FROM AUTHOR]

• Revealed the physical processes and characteristics of lightning attachment on UHV power lines. • Proposed a new expression for calculating the striking distance based on the LPM. • The model based on FEM avoids the complexities of charge simulation configuration and time consuming computation. • Analyzed the effects of operating voltage, phase angle, and terrain. A numerical model for lightning attachment on UHV-AC double-circuit transmission lines was developed using the leader propagation method (LPM) and the finite element method (FEM). The striking distance (SD) of the ground wire (GW) was calculated based on this model. The effects of operating voltage, phase angle, and terrain on the electric field of the wires were also analyzed. The simulation results revealed that when the phase conductors were energized, upward leaders (ULs) simultaneously occurred on both the GW and the upper-phase conductor. The velocity of the GW UL was faster than that of the upper-phase UL, allowing it to successfully intercept the downward leader (DL) in the air, while the upper-phase UL aborted after propagating 1.8 m under the shielding effect of the GW UL. A new expression of r s = 7.2 I p 0.87 for calculating the SD on the GW was proposed based on the simulation results. This expression provided reasonable results that fell between those obtained from the electro-geometric models and the analytical model. Additionally, the simulation results demonstrated that extremely high voltage, phase angle, and terrain slope increased the surface electric field of the upper-phase conductor, thereby increasing the risk of shielding failure. [ABSTRACT FROM AUTHOR]

The escalating demands in energy conversion necessitate the evolution of efficient power electronic devices beyond the limitations of traditional silicon (Si) counterparts. This research delves into the intricacies of the Enhancement mode Gallium Nitride High Electron Mobility Transistor (E-mode GaN HEMT). A focus is placed on its static characterization, parameter analysis, and the influence of external parasitic inductances, particularly regarding oscillation challenges during its hard switching process. Forward and revise bias are conducted through comparison with Si-MOSFET and Cascade-GaN HEMT, along with its static on-resistance and transfer characteristics. Through rigorous half-bridge double pulse circuit LTSPICE simulations, this study deciphers the turn-on and turn-off dynamics of the E-mode GaN HEMT. By scrutinizing various parasitic inductances, the research elucidates mechanisms instigating high-frequency voltage and current oscillations. Significantly, the research presents a hierarchy of parasitic inductance influences, employing an energy loss comparison. This analysis underscores the prominent impact of the common source parasitic inductance, which exhibits energy loss increases of 23.6 % and 22.7 % at junction temperatures of 25 °C and 75 °C, respectively. Building on these insights, the study recommends strategies to mitigate the effects of external parasitic inductance, underscoring the pivotal role of oscillation suppression in advanced GaN Printed Circuit Board (PCB) and Integrated Circuit (IC) designs. This comprehensive inquiry provides a blueprint for enhancing GaN circuit designs, paving the way for their optimal application in the evolving realm of power electronics. • Provided an in-depth simulated characterization of the E-mode GaN HEMT. • Elucidated the root causes of voltage and current oscillations instigated by parasitic parameters. • Simulated half bridge double pulse test circuit through LTSPICE with parasitic inductances. • Laid out a clear hierarchy in the optimization of parasitic inductances by contrasting energy losses. • Proposed a GaN half-bridge PCB design that accentuates the reduction of parasitic inductance effects. [ABSTRACT FROM AUTHOR]

Methyl esters of coconut, palm kernel and palm oils were transesterified with 2-ethylhexanol, trimethylolpropane or neopentylglycol to produce monoester and polyol esters in this study. Experimental investigations were conducted to explore the thermal-oxidative characteristics and catalytic effects of copper/iron on monoester and polyol esters by using the turbine oil oxidation test. Thermogravimetric analysis and differential scanning calorimetry were also performed to evaluate the thermal and oxidation onset temperature. Among the structural trends that improved the oxidative stability include increasing carbon chain length and presence of monounsaturated as opposed to saturated fraction. The study revealed that the presence of copper accelerated the degradation of certain polyol esters. Also, polyol esters are found to be thermally more stable than mineral transformer oils. • The dissolved copper can be used to correlate the degradation of esters via oxidation. • ED-XRF spectrometer of the degradation products can be used to study the metal contents in the oxidized oils. • The onset oxidation temperature of commercial synthetic ester is lower than the synthesized TMPE C18. [ABSTRACT FROM AUTHOR]

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., Competing Interests: The authors have read the journal’s policy and have the following competing interests: MAT is an employee of TNB Research Sdn. Bhd. This does not alter our adherence to PLOS ONE policies on sharing data and materials. There are no patents, products in development or marketed products associated with this research to declare.

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., Competing Interests: NO authors have competing interests.

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 (Al 2 O 3 ) 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 Al 2 O 3 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 Al 2 O 3 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 Al 2 O 3 . SDS and OA could also further improve the lightning breakdown voltage of CO at certain volume concentration of Al 2 O 3 . On the other hand, the lightning breakdown voltage of RBDPOB based Al 2 O 3 nanofluid (2nd type of samples) does not further improve with the introduction of surfactants. At most of the volume concentration of Al 2 O 3 , 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 Al 2 O 3 nanofluid are inconsistent in the presence of all surfactants. It is found that RBDPO and CO based Al 2 O 3 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.