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  • 1.
    Abid, Fahim
    et al.
    KTH.
    Ghorbani, Hossein
    Pourrahimi, Amir Masoud
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Edin, Hans Ezz
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Differences in morphology and polarization properties of heat-treated XLPE and LDPE insulation2016In: 2016 IEEE CONFERENCE ON ELECTRICAL INSULATION AND DIELECTRIC PHENOMENA (IEEE CEIDP), IEEE conference proceedings, 2016, p. 113-116Conference paper (Refereed)
    Abstract [en]

    Cross-linked polyethylene (XLPE) is the most commonly used insulating material for extruded high voltage cable applications. Degassing is a heat-treatment process that is performed to remove methane from XLPE insulation which is formed during the crosslinking reactions as a by-product. Apart from removing methane, heat-treatment influences the electrical properties through changing the morphology due to annealing and also removal of polar crosslinking by-products. Scanning electron microscopy (SEM) is generally used to observe the changes in crystalline structure of the polymer. Frequency domain spectroscopy (FDS) is widely used to study polarization properties of dielectric materials. In this study these two methods are used for a comparative analysis of XLPE and LDPE subjected to different heat-treatment time, with or without a diffusion barrier. Electrical measurements are performed at room temperature. From the SEM imaging conducted after permanganate acid etching, formation of spherulites due to heat-treatment is not obvious in neither LDPE nor in XLPE. However, distinctions between LDPE and XLPE in SEM micrographs are evident. From studies with dielectric polarization spectroscopy, it is found that the LDPE samples are less sensitive to heat-treatment in comparison to the XLPE samples while dissipation factor of XLPE samples are influenced by the choice of pressing film used during sample preparation.

  • 2.
    Mahidhar, G. D. P.
    et al.
    Indian Inst Technol Madras, Dept Elect Engn, Madras 600036, Tamil Nadu, India..
    Sarathi, R.
    Indian Inst Technol Madras, Dept Elect Engn, Madras 600036, Tamil Nadu, India..
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Edin, Hans Ezz
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Study on Performance of Silica Nanoparticle Dispersed Synthetic Ester Oil under AC and DC Voltages2018In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 25, no 5, p. 1958-1966Article in journal (Refereed)
    Abstract [en]

    Synthetic ester oil (SEO) is becoming a replacement for mineral oil in transformers due to its biodegradability and for its better insulation properties. Silica nanoparticles dispersed in SEO can increase its corona inception voltage (CIV) and breakdown voltage compared to pure SEO. Physico-chemical studies were carried out to understand the characteristics of nanoparticles and nanofluids. Methodical experimental studies were carried out to understand the corona discharge activity in SEO based nanofluid. A ultra-high frequency (UHF) sensor was used to identify corona activity and it is concluded that the UHF signal radiated from corona activity in SEO and nanoparticle dispersed SEO have a bandwidth in the range of 700 MHz to 2 GHz. A comparative study on the CIV of SEO and nanofluid under harmonic AC voltages has been carried out, which indicates a reduction in the CIV as the total harmonic distortion of the supply voltage increases. Phase resolved partial discharge analysis indicates that the magnitude of discharges formed in nanofluid is much lower than in the SEO. Comparative statistical analysis are made with the breakdown voltages of the synthetic ester oil and nanofluid. A comparative analysis on the energy of the UHF signal due to the corona discharges is performed.

  • 3. Nikjoo, Roya
    et al.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hollertz, Rebecca
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wåhlander, Martin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Malmström, Eva
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Comparison of Oil-impregnated Papers with SiO2 and ZnO Nanoparticles or High Lignin Content, for the Effect of Superimposed Impulse Voltage on AC Surface PD2017In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 24, no 3, p. 1726-1734Article in journal (Refereed)
    Abstract [en]

    Surface discharge behavior of modified oil-impregnated paper (OIP) with nanoparticles (NPs), has been investigated under AC voltage with superimposed impulses. Surface Partial Discharges (PD) can develop at an oil-paper interface and lead to its degradation. Modified paper, made from fibers with adsorbed nanoparticles, can affect the partial discharge behavior of a paper in combination with oil at the interface between oil and fibers. Papers with two different concentrations (2 wt% and 6 wt%) of silica (SiO2), and paper with silanized zinc oxide (ZnO) nanoparticles (1 wt%) have been studied. Papers with SiO2 NPs showed lower impulse-induced surface PD activity. However, thorough purification during the production of SiO2 filled papers was necessary to achieve a good performance. With less purification, paper with 2 wt% of SiO2 did not show such significant improvements. Paper with 6 wt% of SiO2 NPs showed a large number of AC surface PDs, but low influence of impulse voltage on subsequent PD. Papers containing 1 wt% of silanized ZnO showed reduced relative permittivity, but no significant difference in surface PD behavior. The effect of high lignin content in Kraft paper has also been studied. Paper with higher lignin content showed better surface PD characteristics under the impulse. Paper with low concentrations of pure SiO2 NPs, and paper with high lignin content thus appear good candidates for further studies to improve the surface PD behavior of OIP.

  • 4.
    Swati, Kumari
    et al.
    Indian Inst Technol Madras, Dept Elect Engn, Madras 600036, Tamil Nadu, India..
    Sarathi, R.
    Indian Inst Technol Madras, Dept Elect Engn, Madras 600036, Tamil Nadu, India..
    Yadav, Kandur Sahitya
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Edin, Hans Ezz
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Corona Discharge Activity in Nanoparticle Dispersed Transformer Oil under Composite Voltages2018In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 25, no 5, p. 1731-1738Article in journal (Refereed)
    Abstract [en]

    Titania (TiO2) nanoparticles with cetyl trimethyl ammonium bromide (CTAB) surfactant dispersed in transformer oil has higher corona inception voltage than the normal transformer oil, under AC, DC, and composite AC and DC voltages. It is observed that corona inception voltage is lower under composite voltages compared to AC and DC voltages. The corona activity radiates ultra high frequency (UHF) signals with its dominant frequency near 1 GHz. Operating a spectrum analyzer in zero span mode, the UHF signals generated from the corona activity, the number of discharges is observed to be more under composite voltages than under AC voltages, both at inception and at higher voltages. A reduction in interfacial tension and an improvement in flash point is observed in nano-titania with surfactant dispersed transformer oil. The addition of surfactant reduces the turbidity of the nanofluid. Phase Resolved Partial Discharge (PRPD) analysis with UHF signals measured, indicates that corona discharge activity occurs around the peak and the pre-peak rising portions of the supply voltage. It is observed that more discharges occur in the positive half cycle for AC superimposed with positive DC voltage and in the negative half cycle for AC superimposed with negative DC voltage. The magnitude of UHF signals formed due to corona activity is less with nanofluid, irrespective of voltage profiles.

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