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This study examines the effect of low molecular weight acid (LMA), moisture and oxygen on the thermal ageing characteristics of refined, bleached, and deodorised palm oil (RBDPO). The paper moisture was varied between 0.5 and 3.5. The oil was initially subjected to 0.2 g of LMA and 20 mbar of oxygen pressure. The thermal ageing experiment was performed at 120 °C and 140 °C for 28 days. Several dielectric and physiochemical parameters were measured which included dielectric dissipation factor, relative permittivity, resistivity, moisture in oil, acidity, and thermogravimetric analysis (TGA). It is found that LMA and moisture in paper do not affect the relative permittivity of RBDPO and mineral oil (MO). The dielectric dissipation factor of RBDPO and MO reveals slight increment trends within the ageing time. The decrements of resistivities occur after 7 days of ageing for both RBDPO and MO while only RBDPO shows decrement trend of moisture in oil. The ageing patterns of relative permittivities, dielectric dissipation factors and resistivities for RBDPO are similar to MO. The increment of acidity for RBDPO is more apparent that MO throughout the ageing time. All RBDPOs are more resistant to ageing than MO based on the TGA.

Researchers have worked on positive leader propagation models and proposed different theoretical and numerical approaches. The charge simulation method (CSM) has traditionally been chosen to model the quasi-static electric field of each stage of leader propagation. The biggest drawback of the CSM is that the calculation is complicated and time-consuming when dealing with asymmetric electric field structures. On the contrary, the finite element method (FEM) is more suitable and reliable for solving electrostatic field problems with asymmetric and complex boundary conditions, avoiding the difficulties of virtual charge configuration and electric field calculation under complex boundary conditions. This paper modeled a self-consistent streamer-leader propagation model in an inverted rod-plane air gap based on FEM and the voltage distortion method (VDM). The voltage distortion coefficient was analyzed to calculate the streamer length and space charge. The physical dynamic process of the discharge was simulated with the help of COMSOL Multiphysics and MATLAB co-simulation technology. The results show that the initial voltage of the first corona is -1036 kV, close to the experiment value of -1052 kV. The breakdown voltage of -1369 kV is highly consistent with the experimental value of -1365 kV. The largest streamer length is 2.72 m, slightly higher than the experimental value of 2.3 m. The leader velocity is 2.43×104 m/s, close to the experiment value of 2.2×104 m/s. This model has simple calculations and can be used in complex electrode configurations and arbitrary boundary conditions without simplifying the model structure, making the model more flexible.

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.

This work examines the physical and electrical breakdown characteristics of kenaf paper coated with Polyvinyl Alcohol (PVA) for application in power transformers. The paper was made from kenaf bast fibers using the soda pulping method, whereby the pulps were subjected to 12,000 beating revolutions. PVA with weight percentage concentration up to 6% was introduced to the beaten kenaf through a spin coating approach. The structure of the kenaf paper was examined through Scanning Electron Microscopy (SEM). The physical properties examined were apparent density, Tensile Index (TI), Burst Index (BI), and Tear Index (TeI), while AC breakdown voltage and strength were analyzed for the electrical property. It is found that the beating and external PVA improve the kenaf paper’s apparent density, TI, BI, and AC breakdown strength while the TeI decreases.

This research paper presents the experimental results of the lightning pre-breakdown and breakdown voltages of Palm Oil (PO) and Mineral Oil (MO) in the presence of Al2O3 under positive voltage polarity. The experiments were conducted using a needle-plane electrode configuration as a non-uniform field. The positive lightning breakdown voltages of two types of refined, bleached, and deodorized PO with various concentrations of nanofluids were determined. The lightning pre-breakdown was monitored through light signal recordings. The light signal emission increased with the applied voltage for all samples. The presence of Al2O3 in both PO and MO increases the positive lightning breakdown voltages.

Developing a numerical simulation model for shielding failure evaluation of UHV transmission lines is an urgent task. In this article, a dynamic leader propagation model of lightning attachment to UHV transmission lines was developed based on FEM. The lightning downward leader descending vertically at a speed of 2×105m/s from a distance of 50 m from the side of the UHV transmission line was considered as a lossy conductor. Peek’s formula was used for initial corona inception criterion. The streamer space charge and the leader length were calculated by using the voltage distortion method. The upward leader was assumed to propagate in the direction of the maximum field strength. The final jump was considered to occur once the average electric field strength of the remaining gap reaches 450 kV/m. Without considering the operating voltage, the simulation result shows that the striking distance of the ground wire under the return stroke current of 10 kA, 20 kA, 30 kA, 40 kA and 50 kA is 54 m, 94 m, 143 m, 157 m, and 234m respectively. A new expression of rs=7.2I0.87p for the striking distance calculation based on LPM was proposed. The striking distance calculated by this new model is between the EGM empirical model and theoretical model, which proves that the model is reasonable.

This paper examines the performance of partial discharge localization refined bleach deodorized palm oil (RBDPO) based on acoustic emission (AE) partial discharge (PD) method. The PD was initiated through a needle-plane electrodes configuration. The electrical PD was measured through Impedance Matching Circuit (IMC) whereby the AE PD signal was measured using AE sensor placed on the surface of the test tank. The time of arrival (TOA) was computed based on the electrical and AE PD signals. It is found that the PD count and maximum amplitude for RBDPO are lower than mineral oil. The PD in RBDPO can be located through TOA whereby the location error is lower than MO.

This paper presents an examination on acoustic emission (AE) partial discharge (PD) signal characteristic in oil in the presence of pressboard. First, a test tank was fabricated whereby the PD was generated through needle-plane electrode configuration. Next, the pressboard was placed at the PD source. The electrical PD was measured through Impedance Matching Circuit (IMC) whereby the AE PD signal was measured using AE sensor. Based on the measured AE PD signal, the time of arrival (TOA), amplitude, duration, and distance between PD location and AE sensor was examined. Location error and root mean square error (RMSE) was used to evaluate the PD localization error rate. It is found that the presence of pressboard has an impact on PD localization location error rate and RMSE.

This manuscript discusses the computation of electromagnetic forces on a disc-type winding due to a standard switching impulse (SSI). First, the resistances, inductances and capacitances (RLC) of a 30 MVA, 33/11 kV disctype distribution transformer were estimated to obtain the winding equivalent circuit. The transient voltage waveforms for each of the disc layers and corresponding resonances of the windings under the SSI were then obtained in time domains. Next, the axial and radial force distributions in the disc winding due to the SSI were computed. The forces on each disc layer and along the disc windings due to the SSI were computed based on the analytical and numerical methods via the finite element method (FEM) respectively. The non-uniform switching impulse voltage distribution results in non-uniform force distribution along the disc winding. The magnitude of the axially directed force on the disc winding is found to be higher as compared to the radially directed force.

This paper investigates the behaviour of partial discharge (PD) in transformer insulation paper based on the Finite Element Method (FEM). The three-dimensional (3D) FEM model consists of conductor and insulation paper, representing part of a transformer’s high voltage winding. The conductor’s width, height, and length used in this study were 2.4 mm, 11.5 mm, and 16 mm. An insulation paper thickness of 1 mm was modelled around the conductor. An internal cavity with a diameter of 0.5 mm cavity was introduced within the insulation paper. This study introduced two locations of the spherical cavities at the centre and left corner of the insulation paper: Location 1 (L1) and Location 2 (L2). An AC voltage of 33 kV, 50 Hz, was applied to the conductor while the bottom of the insulation paper was grounded. The model was used to study the electric field distribution within the insulation paper and its effect on PD current and charge magnitude. The influence of cavity location on the charge magnitude was also examined. It is found that the electric field distribution is influenced by the conductor configuration as well as the location of the cavity. The electric field in the cavity is the highest at L1 compared to L2. The first PD occurs faster for the cavity with a high electric field. Due to the PD occurrence at the same inception field, the real PD current and charge magnitude is similar at different locations. The apparent PD current and charge magnitude induced at the ground electrode is slightly higher at L1 than at L2.