In this paper, the common-mode voltage (CMV) elimination is focused on five-phase induction motor (F-PIM) drive which is controlled by a direct torque control method. Since the motor is fed by ...inverter, the CMV is generated in the drive. The CMV allows common-mode current (CMC) to circulate in the bearing parts of the drive. The CMC may eventually damage the complete drive, if it is not controlled. Therefore, the proposed DTC strategy targets the elimination of the CMV. Since the F-PIM is fed by three-level five-phase inverter (T-LF-PI), there are 243 voltage vectors (VVs) available for the DTC operation. These VVs are distributed at different locations in
d-q
stator plane in the form of main and intermediate VVs. The 41 intermediate VVs are selected, due to their ability of eliminating the CMV, through seven-level torque and two-level flux comparators. By implementing a seven-level torque comparator (S-LTC) the torque ripple is reduced. For validating the proposed DTC method, simulation and experimental results are provided.
Polypropylene (PP) is being considered as a suitable alternative to the cross‐linked polyethylene (XLPE) insulation as the latter is prone to the space charge accumulation when subjected to the ...voltage polarity reversals in line‐commutated converter high voltage direct current transmission. This novel contribution correlates the space charge accumulation with the trap distribution inside XLPE and PP under the polarity reversal condition. The pulse electro‐acoustic and surface potential decay methods are used to measure the space charge and trap distributions, respectively. These measurements are carried at different poling durations (1 and 6 h at each polarity) and cycles of voltage polarity reversal (one and three cycles) at the electric field of 60 kV/mm. The XLPE shows more homo and hetero charge accumulation than PP. Dominant shallow traps in the XLPE are responsible for the space charge accumulation, whereas deep traps with higher trap density inhibit space charge accumulation within the PP. Furthermore, the positive and negative threshold fields for the space charge accumulation are measured. It is observed that the space charge can be easily accumulated under the negative electric field. Interestingly, the space charge decays rapidly inside the XLPE with the increased number of polarity reversal cycle. A valid theoretical model is developed to explain the space charge accumulation inside the XLPE and PP. The field‐assisted ionization plays a key role in the space charge accumulation inside the XLPE.
For high temperature superconducting (HTS) dc cables, one key issue is the necessity of using polymer dielectrics with higher dielectric strength at cryogenic temperature in liquid nitrogen. ...Nanocomposites have played an important role in improving the dielectric properties of epoxy resin (EP). This article investigates on the dc breakdown strength and the surface potential behavior of the epoxy/Al 2 O 3 nanocomposites (0, 1, 3, 5 wt%) at the room and cryogenic temperatures. Moreover, the trap distributions are analyzed from the surface potential decay (SPD) measurement. The possible effect of the trap distributions on the dc breakdown strength is discussed with the valid results. The measurements show that the dc breakdown strength and the initial surface potential continually increased with the nanoparticle addition up to 3 wt% at both room and cryogenic temperatures, and decreased thereafter. The enhancement of the breakdown strength and the initial potential is also found at cryogenic temperature. Besides, the addition of the nanoparticles decreased the rate of SPD compared with the pure epoxy. It is proposed that the higher trap density and trap level enhances the dc breakdown strength. Interestingly, under the cryogenic environment, the nanoparticles addition significantly affects the trap distributions, which further influences the dielectric strength. The enhanced dc breakdown strength is attributed to the reduced space charge formation, the charge carrier mobility and the energy of the charge carriers within the sample bulk.
This paper investigates partial discharge (PD) characteristics of crosslinked polyethylene (XLPE) nanocomposites for unmodified, agglomerated, and Octylsilane-modified silica nanofillers (nano 1, 2, ...3, 4, 5, 10 wt %) case. The surface modification of nanofiller helps to reduce the PD formation marginally. Octylsilane surface-modified XLPE/silica nano 3 wt % exhibits the lowest PD activity with highest discharge inception voltage and breakdown voltage. Also, the issue of change in the polymer structure due to the addition of nanofillers is reported here. The differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), fourier transform infrared (FTIR), and contact angle measurement study conducted suggests that the addition of nanosilica leads to the change in the melting point, thermal degradation temperature, heat of fusion, bonding structure and the contact angle of the polymer, respectively. These structural changes are explained with the supporting theory.
The potential of nanocomposites have been drawing the intention of the researchers from energy storage to electricalinsulation applications. Nanocomposites are known to improve dielectric properties, ...such as the increase in dielectricbreakdown strength, suppressing the partial discharge (PD) as well as space charge, and prolonging the treeing, etc. Inthis review, different theories have been established to explain the reactions at the interaction zone of polymer matrixand nanofiller; the characterization methods of nanocomposites are also presented. Furthermore, the remarkablefindings in the fields of epoxy, cross-linked polyethylene (XLPE), polypropylene and polyvinyl chloride (PVC)nanocomposites are reviewed. In this study, it was observed that there is lack of comparison between results of labscale specimens and actual field aged cables. Also, non-standardization of the preparation methods and processingparameters lead to changes in the polymer structure and its surface degradation. However, on the positive side, recentattempt of 250 kV XLPE nanocomposite HVDC cables in service may deliver a promising performance in the comingyears. Moreover, materials such as self-healing polymer nanocomposites may emerge as substitutes to traditionalinsulations. KCI Citation Count: 0
The application of polymer nanocomposites is limited to the laboratory scale, and prototype development is yet to be reported in major applications. This study pursues a systematic approach of ...fabricating winding insulation of the low-voltage alternator using the novel polyester resin/hexagonal boron nitride (hBN) nanocomposite through standardized preparation and manufacturing processes. The optimal content of hBN nanofillers for fabricating of stator and rotor windings is determined through various preliminary tests. After that, a total of 24 prototypes of wound stators and rotors for low-voltage alternators (output voltage: 240 V) with different ratings (15 kVA and 30 kVA) are fabricated. These prototypes consist of polyester resin/hBN nanocomposite-based stator and rotor windings and special polyester insulating enamel gray coating mixed with optimal nanofiller content. The insulation resistance and polarization index measurements of fabricated prototypes are carried out. Furthermore, the thermal ageing of these prototypes is carried out at 160 °C and 180 °C to simulate the effect of higher operating temperatures. The results show that degradation-resistant and durable insulation systems with longer life can be developed using polyester resin/hBN nanocomposites for any ratings of low voltage rotating machine that uses polyester resin insulation.
Mineral oil (MEO) is widely used in power transformers for insulation and cooling purposes. Recently, alternative insulating oils, such as natural ester and synthetic ester oils (NEO and SEO) etc., ...have also been considered due to their eco-friendly nature. However, the performance of these oils deteriorates with aging, adversely affecting their dielectric properties. This study proposes a novel framework employing Fourier transform infrared spectroscopy (FTIR) and a recurrence plot-based deep learning framework to identify the aging state of transformer insulation accurately. For this purpose, FTIR data representing different aging stages of MEO, SEO, and NEO insulations are measured and converted into 2D images using a recurrence plot (RP). Following this, image augmentation using deep convolutional generative adversarial network (DCGAN) technique has been implemented for image augmentation and finally, a convolutional neural network (CNN) model is developed to classify the aging stages of the three aforementioned insulating oils. The performance of the proposed CNN model is compared with Alexnet, Resnet-50, and VGGNet-16, respectively. It has been observed that the proposed model returned accuracies of 97.25%, 97.5%, and 97.00% for classification of ageing state of MEO, NEO, and SEO sample data. The performance of the proposed model was also validated on oil samples collected from real-life power transformer. The proposed model can be implemented for in-situ diagnosis of transformer insulation.
This paper presents the influence of Aluminum Nitride (AlN) nanoparticles on the electrical and material properties of epoxy resin (EP). The EP/AlN nanocomposites with different concentrations of ...nano-AlN fillers are prepared. The dispersion of the nano-AlN particles in the composites is analyzed by a field emission scanning electron microscope (FESEM). The electrical properties are investigated by the space charge and DC conductivity measurements, whereas the material properties are studied by Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively. The results show that the homo-charge accumulation appears near both electrodes during the polarization, but there are limited negative charges left near both electrodes in the depolarization for the pure EP sample. There is no space charge accumulation in the 1 wt% and 2 wt% EP/AlN nanocomposites. The electric field distortion of the pure EP sample is 20%. Moreover, the electric field distortion initially decreases with the increase of the nano-AlN content, but it increases for the 2 wt% nano-AlN sample. Temperature has a dominant influence on the DC conductivity of the EP/AlN nanocomposites comparing to the pure EP. However, the DC conductivity of the nanocomposites becomes stable at high temperatures. It is also found that the weight loss of the samples decreases with the addition of the nano-AlN and the 1 wt% nano-AlN sample has the highest glass transition temperature. It is elucidated that the high apparent mobility and activation energy facilitate the space charge transport and suppressing the space charge accumulation. Furthermore, the nano-AlN filler can increase the trap level and trap energy density of the deep traps in the sample. The dielectric loss of the EP at high frequency is reduced with the content of 1 wt% nano-AlN. Furthermore, the addition of the nano-AlN can improve the thermal stability of the EP. The 1 wt% nano-AlN sample has the superior electrical insulation and material performance amongst the tested materials.
•1. This paper presents the electrical and material properties of the epoxy resin based composites with the aluminum nitride.•2. Electrical properties of the nanocomposites are enhanced significantly with the addition of the nano-AlN.•3. The enhanced material properties are discussed with the valid explanation.•4. The addition of nano-AlN to improve the properties of the epoxy resin for packaging materials is promising.
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