kth.sePublications
Change search
Refine search result
12 1 - 50 of 95
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Kane, Makarand
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Månsson, Daniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Investigations Into Conducted Emissions of A 10 kW Photovoltaic Plant2024In: IEEE Letters on Electromagnetic Compatibility Practice and Applications, E-ISSN 2637-6423Article in journal (Refereed)
    Abstract [en]

    Considering inverter as the source of electromagnetic emission signals in a photovoltaic (PV) plant, a comprehensive set of measurements of conducted emissions at the input and output of the inverter in a 10 kW PV plant are presented. These are particularly relevant on the backdrop of (a) ban of products in the EU market due to non-compliance and (b) the increased switching frequency in the inverters ( 100s of kHz) in near future. Specifically, the common mode (CM) and differential mode (DM) currents and voltages are measured, and their frequency domain behavior is studied. It is suggested that conducted emissions from PV can be classified into three zones: viz., extremely low frequency (ELF) zone, power frequency zone, and switching frequency zone. Important observations from this exercise are measurement of harmonic contents of current with total rated current distortion (TRD), imbalance in the output voltage and low frequency ripples in the DC voltage. Frequency domain behavior of the CM quantities is studied which throws light on important points like relation between input and output CM quantities, relation between CM voltage and CM current.

  • 2.
    Cheng, Jialu
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Yizhou, Zhang
    China Nuclear Power Operation Technology Co., Ltd., Minzu Road 1021, Wuhan 430073, China.
    Yun, Hao
    China Nuclear Power Operation Technology Co., Ltd., Minzu Road 1021, Wuhan 430073, China.
    Wang, Liang
    China Nuclear Power Operation Technology Co., Ltd., Minzu Road 1021, Wuhan 430073, China.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    A Study of Frequency Domain Reflectometry Technique for High-Voltage Rotating Machine Winding Condition Assessment2023In: Machines, E-ISSN 2075-1702, Vol. 11, no 883Article in journal (Refereed)
    Abstract [en]

    Detecting and locating local degradations at an incipient stage is very important for mission-critical high-voltage rotating machines. One particular challenge in the existing testing techniques is that the characteristic of a local incipient defect is not prominent due to various factors such as averaging with the healthy remainder, attenuation in signal propagation, interference, and varied operating conditions. This paper proposes and investigates the frequency domain reflectometry (FDR) technique based on the scattering parameter measurement. The FDR result presents the object length, wave impedance, and reflections due to impedance discontinuity along the measured windings. Experiments were performed on two commercial coils with artificially created defects. These defects include turn-to-turn short, surface creepage, loose coils, insufficient end-winding spacing, and local overheating, which are commonly seen in practice. Two practical water pumps in the field were also selected for investigation. The study outcome shows that FDR can identify and locate structural and insulation degradation in both shielded and unshielded objects with good sensitivity. This makes FDR a complementary technique for machine fault diagnosis and aging assessment.

    Download full text (pdf)
    Paper
  • 3.
    Habib, Md Zakaria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Duvnjak Zarkovic, Sanja
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Shayesteh, Ebrahim
    Swedish Natl Grid Svenska Kraftnät, Sundbyberg, Sweden..
    Distributed fault-passage indicators versus central fault location: Comparison for reliability centred planning of resonant-earthed distribution systems2023In: Energy Reports, E-ISSN 2352-4847, Vol. 9, p. 1731-1742Article in journal (Refereed)
    Abstract [en]

    Fault location methods are crucial for reducing fault restoration time, and thus improving a network's system average interruption duration index (SAIDI) and customer outage cost. Resonant-earthed systems pose problems for traditional fault location methods, leading to poor accuracy and a need for additional complexity. In this context, methods that detect fault direction (fault-passage indicators, FPI) at multiple points in the network may show advantages over a central distance-estimation method using fault locators (FL) of poor accuracy. This paper includes a comparative study of these two major fault location methods, comparing the reliability benefit from a varied number of FPIs or a central method. The optimal placement of the fault locating devices is found by formulating a mixed-integer linear programming (MILP) optimization approach that minimizes both outage and investment costs and assesses SAIDI. This approach has been tested on an example distribution system. However, to justify the universality of the algorithm, the RBTS reliability test system has also been analysed. The comparison of location methods and placement method of FPIs are useful for reliability centred planning of resonant-earthed distribution systems where fault location is to be used. Results show that a small number of FPIs that give accurate identification of direction may give more cost effective increase in reliability than a distance estimate by FL with typical levels of inaccuracy.

  • 4. Kane, Makarand
    et al.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Månsson, Daniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Experimental Investigations into Common Mode Impedance of PV Panels2023Conference paper (Refereed)
    Abstract [en]

    The nature of common mode (CM) parasitic impedance (ZPV) of photovoltaic (PV) panels is investigated by experimentation. Measurements are done by two methods: (a) time domain signal recording using a signal generator and an oscilloscope (b) frequency sweep using an LCR meter. It is shown that ZPV is not purely capacitive for the frequency range from 50 Hz to 1 MHz.  It is also shown that the total common mode impedance in a PV installation is affected by the nature of ZPV.  The frequency spectrum of CM current would be different if ZPV is not purely capacitive. This would affect the design of CM filters on the DC and AC side and also equipment like PV emulators, DC line impedance stabilization network, etc.

    Download full text (pdf)
    ZPV_Kane
  • 5.
    Habib, Md Zakaria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Incremental Phase-Current Based Fault Passage Indication for Earth Faults in Resonant Earthed Networks2023In: Electricity, E-ISSN 2673-4826, Vol. 4, no 2, p. 96-113Article in journal (Refereed)
    Abstract [en]

    We propose a method for the fault passage indication of earth faults in resonant-earthed networks, based on phase current measurements alone. This is particularly relevant for electricity distribution systems at medium-voltage levels. The method is based on the relative magnitudes of the phasor changes in the phase currents due to the fault. It is tested for various network types and operation configurations by simulating the network in pscad and using the simulated currents as the input for an implementation of the method in matlab. In over-compensated networks, the method shows reliable detection of the fault passage, with good selectivity and sensitivity for both homogeneous and mixed (cable and overhead line) feeders. However, for the less common under-compensated systems, it has limitations that are described further in this study. The method has good potential for being cost effective since it requires only current measurements, from a single location, at a moderate sampling rate.

  • 6.
    Amizhtan, S. K.
    et al.
    Indian Institute of Technology Madras, Department of Electrical Engineering, Chennai, India, 600036.
    Sarathi, R.
    Indian Institute of Technology Madras, Department of Electrical Engineering, Chennai, India, 600036.
    Vinu, R.
    Indian Institute of Technology Madras, Department of Chemical Engineering, Chennai, India, 600036.
    Edin, Hans Ezz
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Investigation on Carbon particle formation with Electro-Thermal ageing of Transformer oil2023In: ICDL 2023 - 22nd IEEE International Conference on Dielectric Liquids, Institute of Electrical and Electronics Engineers (IEEE) , 2023Conference paper (Refereed)
    Abstract [en]

    Present work deals with accelerated electrical and thermal stress on transformer oil and its characteristic variation on Fuller's earth (FE) reclamation. The influence of carbon particles in the fluid, its role on thermal ageing characteristics can be understood by electrical characterization. Reclamation of insulation fluid extends the lifetime and reliability of the transformer over the year of operation. The average particle size of carbon particles on electrical breakdown are in the range of 644 nm. Dielectric response spectroscopy (DRS) which identifies the conductivity and relative permittivity variation with the effect multi-stress ageing. Conduction mechanism with higher electric field is simulated by current-voltage (IV) characteristics using non-uniform field configuration to derive the ionic mobility of the liquid. Dissolved decayed products and turbidity showed drastic enhancement with multi-stress ageing than the thermally aged specimen. Reclamation with fuller earth treatment removes the carbon traces and ageing by-products in the fluid regaining its relative dielectric performances. Rheological aspects with viscosity indicates the ageing by-products build and also its characteristic variation on the reclamation process.

  • 7.
    Amizhtan, S. K.
    et al.
    Indian Inst Technol Madras IIT Madras, Dept Elect Engn, Chennai 600036, India..
    Sarathi, R.
    Indian Inst Technol Madras IIT Madras, Dept Elect Engn, Chennai 600036, India..
    Edin, Hans Ezz
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering and Fusion Science.
    Study on Conduction Mechanism in Corrosive Transformer Oil and its Reclamation Properties2023In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 30, no 5, p. 2232-2239Article in journal (Refereed)
    Abstract [en]

    This work deals with the effect of oil reclamation on the conduction mechanism and dielectric aspects of accelerated thermally aged transformer mineral oil. The reclamation is a treatment with Fuller's earth (FE) adsorbent to remove corrosive sulfur compounds and other contaminants formed during thermal aging. The properties of the oil are compared between different stages of the treatment. Corona (partial discharge) inception is identified by the optical fluorescent fiber technique. The results show an increased corona inception voltage after treatment. Dielectric response spectroscopy (DRS) showed a lower loss factor and electrical conductivity after treatment. The conduction mechanism is measured under uniform and nonuniform electric fields with variations in applied voltage magnitude. The conduction mechanism at a uniform electric field (low E) is studied using the polarity reversal technique to estimate the respective ionic motilities in the fluid. The apparent mobility of ions, conductivity, ionic radius, and concentration from the oil are found to reduce on reclamation. In addition, the conduction mechanism for a higher electric field is simulated by the current-voltage characteristic in nonuniform conditions and the slope determines the ionic mobility of the fluid.

  • 8.
    Hoq, Md Tanbhir
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Wang, Jianping
    Hitachi Energy Research, Hitachi Energy, Västerås, Sweden.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    An Incremental Quantity Based Protection with Capacitor Voltage Estimation for Mid-Line Series Compensation2022Conference paper (Refereed)
    Abstract [en]

    Series capacitors are installed in transmission lines to increase power transfer capacity. However, their addition creates challenges for the line protection. Security and speed of phasor based protection schemes that work with local measurements (communication independent) are severely affected in the presence of series capacitors. Therefore, time-domain based protection methods may be considered as a potential solution for communication independent protection of series compensated lines. In this paper, an incremental quantity based protection scheme is presented for series compensated lines with the capacitor in the middle of the line. The method involves estimating the voltage across the capacitor bank, based on the current in the capacitor bank and metal oxide varistor during faults. Then this capacitor voltage estimation is used to implement the incremental quantity protection. The incremental quantity method consists of fault detection, phase selection, directional discrimination and distance estimation. A PSCAD model of a 500 kV, 200 km transmission line is used to simulate fault cases for evaluating the method. The proposed method is tested with different compensation levels, fault types, fault positions, inception angles, fault resistances and source impedance ratios. The results show that the proposed method can meet the dependability and security demands for the protection of series compensated lines.

    Download full text (pdf)
    fulltext
  • 9.
    Kane, Makarand
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Månsson, Daniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Characterization of Parasitic Impedances of PV Panels from Common Mode Perspective2022In: 2022 International Symposium on Electromagnetic Compatibility – EMC Europe, 2022, Institute of Electrical and Electronics Engineers (IEEE), 2022Conference paper (Refereed)
    Abstract [en]

    Parasitic impedances of PV panels play an important role in the common mode circuit. This work has investigated parasitic impedance model including capacitances and inductances, against the one with only capacitances considered in the literature. Further, the effects of geometrical and environmental factors on the parasitic capacitances are analysed using Finite Element Method (FEM) and Design of Experiments (DoE). The analysis has revealed that the water layer above panels is significant for cell-to-frame capacitance and not for cell-to-ground capacitance. Frequency domain analysis of total parasitic impedances is presented which shows that the total impedance exhibits resonances and inductive behaviour in the MHz range. These features are not captured if only capacitive model is considered.

  • 10.
    Taylor, Nathaniel
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Hao, Jing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    DC-biased dielectric measurements using an existing frequency-domain spectroscopy (FDS) instrument and series battery2022In: Proceedings of the 27th Nordic Insulation Symposium, Trondheim: Norwegian University of Science and Technology (NTNU) Library , 2022, Vol. 27Conference paper (Refereed)
    Abstract [en]

    We present a simple method for adding DC bias to frequency-domain spectroscopy (FDS) measurements by inserting a battery in series in the `high' lead to the specimen. An instrument designed for FDS measurements with pure AC can be used in this way without modification, even for DC voltages above the instrument's AC range. Issues and limitations of the method are discussed, along with some alternative methods. Experimental results from FDS measurements on well defined linear specimens are compared with/without the DC bias, to check that the measurement is not disturbed by the DC source. The only detected difference was the expected effect of including the battery impedance in series with the specimen in the measurement. This effect was negligible for typical lab-specimen capacitances, around and below power frequency. The nature of battery impedance is further described, as multiple small batteries in series can strongly affect the results for large specimens and at high frequencies.

    Download full text (pdf)
    dc_biased_fds__Taylor_Hao__NORD-IS_2022.pdf
  • 11.
    Mahidhar, G. D. P.
    et al.
    Department of Electrical Engineering, Indian Institute of Technology Madras, Chennai, India.
    Sarathi, R.
    Department of Electrical Engineering, Indian Institute of Technology Madras, Chennai, India.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Edin, Hans Ezz
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Dielectric Properties of Silica‐Based Synthetic Ester Nanofluid2022In: Alternative Liquid Dielectrics for High Voltage Transformer Insulation Systems: Performance Analysis and Applications / [ed] U. Mohan Rao, I. Fofana, R. Sarathi, John Wiley & Sons, 2022, p. 273-303Chapter in book (Refereed)
    Abstract [en]

    In recent times, nanoparticles-dispersed ester fluids are reported to exhibit improved thermal and electrical properties for its application in insulation system. In the present study, insulating nanoparticles of silica were dispersed in synthetic ester fluid to improve electrical characteristics of the base fluid. A two-step process involving mechanical shear mixing and ultrasonication was adopted for producing nanofluids. Physical and chemical characterization of nanofluids were carried out to estimate stability of the nanofluid with optimum concentration of nanoparticles and surfactants. To substantiate the influence of nanoparticles and surfactant on the dielectric properties of the nanofluid, conductivity measurements were made at low and high electric field conditions. It was observed that in the presence of electric field, the motion of ions is inhibited due to its trapping by the surface of nanoparticle, leading to lower ionic mobility. To explore the governing mechanisms further, electrical insulating performance of the nanofluid and corona discharge activity were investigated under AC and DC voltages using ultrahigh frequency (UHF) technique. This study has also shown an increase of 30% improvement in the corona inception voltage (CIV) upon addition of nanoparticles. The discharge activity was also mitigated due to incorporation of nanofillers in the fluid. The energy of discharge was found to be lower in nanofluid as compared to base fluid. It was evident from the present studies that silica-based nanofluids have shown superior dielectric performance compared to the base synthetic ester fluid.  

  • 12.
    Amizhtan, S. K.
    et al.
    Indian Inst Technol Madras IIT Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Amalanathan, A. J.
    Indian Inst Technol Madras IIT Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Babu, Myneni Sukesh
    Indian Inst Technol Madras IIT Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Sarathi, R.
    Indian Inst Technol Madras IIT Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Kumar, Ganesh
    Indian Inst Technol Madras IIT Madras, Dept Ocean Engn, Chennai 600036, Tamil Nadu, India..
    Sangwai, Jitendra S.
    Edin, Hans Ezz
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Experimental Study and ANN Analysis of Rheological Behavior of Mineral Oil-Based SiO2 Nanofluids2022In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 29, no 3, p. 956-964Article in journal (Refereed)
    Abstract [en]

    This work reports an experimental and theoretical analysis of the rheological properties of mineral oil-based SiO2 nanofluid for their potential applications in transformer insulation. The flow electrification mechanism on the nanofluids with different surfactants such as cetyl trimethyl ammonium bromide (CTAB), oleic acid, and Span 80 is studied using a spinning disk technique. The results show a higher streaming current for the nanofluids with CTAB as a surfactant compared to oleic acid and Span 80. The rheological behavior of nanofluids is explored with the double gap concentric cylinder geometry. The variation of shear stress with shear rate follows a power law relationship along with a yield stress observed for all the nanofluids. A transition is seen from storage modulus to dominant loss modulus for the nanofluids during the frequency sweep analysis, whereas no transition is observed in the case of mineral oil. In addition, regression analysis using artificial neural network (ANN) algorithms are performed on the experimentally measured viscosity of the nanofluids in order to estimate theoretical parameters and provide insights into the streaming current formation. The desirable rheological characteristics of nanofluids are identified for achieving enhanced insulation performance in transformers.

  • 13.
    Hao, Jing
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Xie, Yiming
    Wuhan Univ, Sch Elect Engn & Automat, Wuhan 430072, Peoples R China..
    Frequency-Domain Spectroscopy of Oil and Oil-Impregnated Pressboard With DC Bias2022In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 29, no 2, p. 370-377Article in journal (Refereed)
    Abstract [en]

    Dielectric response measurement is widely used to characterize oil/oil-impregnated pressboards in order to evaluate the condition of transformer insulation. Insulation systems with oil can exhibit voltage dependence at low frequencies. This is due to the limited number of mobile charges in the liquid, rather than to the dielectric relaxation processes that may, in some cases, be of more interest to study. This work investigates the voltage-dependent properties of oil/oil-impregnated pressboards under ac voltages with regard to the complex permittivities. Frequency-domain spectroscopy (FDS) measurements are made with a dc voltage added to the ac voltage stimulus. Considered influences are the voltage amplitudes and polarity as well as the dependence on temperature. Properties of the space-charge polarization in the oil and oil-impregnated pressboard are calculated and discussed based on the dc-biased measurements. It is seen that using the dc bias in the FDS measurements of oil/oil-impregnated pressboard can significantly decrease the voltage dependence of the results that are caused by ion drift and consequent depletion of ions from the bulk liquid. Based on the dc-biased measurements, the complex permittivity due to the linear and nonlinear polarization can be separated.

  • 14.
    Cheng, Jialu
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Impact of Advanced Bushing Diagnostic Techniques on Operation Reliability and Maintenance Strategy2022In: Proceedings 2022 IEEE International Conference on High Voltage Engineering and Applications, ICHVE 2022, Institute of Electrical and Electronics Engineers (IEEE) , 2022Conference paper (Refereed)
    Abstract [en]

    The reliability of power transformers is crucial for the safety operation of the power system. Detection of incipient faults, as well as natural aging, is the key to reduce the failure risk, which gives the operators adequate margin to perform maintenance before reaching a critical failure. Routine maintenance consists of a few testing techniques to check whether mechanical and electrical components fulfill the minimum threshold requirement. In addition, there are various advanced diagnostic testings that are capable of giving more precise condition indications of a transformer in thermal, electrical, and mechanical aspects. The reliability of transformers can thus be enhanced with the help of advanced diagnostic testings. However, in practice, it is often costly to perform the advanced testings and the effectiveness is hard to verify due to the lack of relevant cases and case studies. According to the published statistics, the failure rate is only around 0.1% - 0.2% per year. In this project, a widely accepted insulation condition diagnostic method, Dielectric Frequency Response, DFR was investigated in aspects of cost and return. Testing objects were a group of transformer bushings in three HVDC substations. Reliability is enhanced by identifying incipient bushing defects that cannot be detected by other routine testing techniques. By analyzing the cost and return of the DFR testing, the transition of the current maintenance strategy towards reliability-centered is in position.

  • 15.
    Amizhtan, S. K.
    et al.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Amalanathan, A. J.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Sarathi, R.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Edin, Hans Ezz
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Impact of Magnetic Field on Corona Discharge Behavior of Mineral Oil Under AC Voltage2022In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 29, no 4, p. 1417-1424Article in journal (Refereed)
    Abstract [en]

    This article reports an experimental investigation of the impact of magnetic field on corona discharge activity in mineral oil, using both ultrahigh-frequency (UHF) and fluorescence techniques under ac voltage. The results show that corona inception voltage (CIV) increased under ac voltage with varying harmonic frequencies without considering any phase shift and reduced marginally under magnetic field. In addition, the impact of the magnetic field shifted the dominating frequency of the UHF signal (0.9 GHz) obtained under ac voltage toward lower frequencies (0.3 and 0.6 GHz). Under high magnetic fields, the parameters such as rise time, fall time, and pulsewidth of the fluorescence signal increased in its magnitude compared to its effect without a magnetic field. Also, using both the UHF sensor and the fluorescence sensor, there was no clear difference in the phase-resolved partial discharge (PRPD) pattern caused by corona discharge (with and without magnetic field). Furthermore, the number of discharges is observed to be high under the impact of harmonic ac voltages with third- and seventh-order containing total harmonic distortions (THDs) of 4% and 40%.

  • 16.
    Amizhtan, S. K.
    et al.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Amalanathan, A. J.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Sarathi, R.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Srinivasan, Balaji
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Gardas, Ramesh L.
    Indian Inst Technol Madras, Dept Chem, Chennai 600036, Tamil Nadu, India..
    Edin, Hans Ezz
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Impact of Surfactants on the Electrical and Rheological Aspects of Silica Based Synthetic Ester Nanofluids2022In: IEEE Access, E-ISSN 2169-3536, Vol. 10, p. 18192-18200Article in journal (Refereed)
    Abstract [en]

    This study reports experimental investigations of the effects of different surfactants (CTAB, Oleic acid and Span 80) on silica based synthetic ester nanofluids. The positive and negative potential observed for the ionic (CTAB) and non-ionic surfactant (Span 80) from zeta potential analysis indicates an improved stability. The optimization of nanofillers and surfactants is performed considering the corona inception voltage measured using ultra high frequency (UHF) technique and fluorescent fiber. Rheological analysis shows no significant variation of properties with shear rate, implying Newtonian behavior even with the addition of surfactant. In addition, the permittivity of the nanofluid is not much affected by adding surfactant but a marginal variation is noticed in the loss tangent with the effect of temperature. The fluorescence spectroscopy shows no change in the emission wavelength with the addition of silica nanofiller and surfactants. Flow electrification studies indicate an increase in the streaming current with the rotation speed and temperature, with a higher current magnitude observed in the case of nanofluids.

  • 17.
    Cheng, Jialu
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Werelius, Peter
    Megger Sweden AB, Engn Dept, S-18236 Danderyd, Sweden..
    Nonlinear Dielectric Properties of the Stator and Transformer Insulation Systems2022In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 29, no 1, p. 240-246Article in journal (Refereed)
    Abstract [en]

    Composite insulation systems usually exhibit nonlinear phenomena, such as voltage-dependent dielectric response and high-order current harmonics. In this article, a high-voltage system capable of performing both dielectric frequency response (DFR) and polarization/depolarization current (PDC) measurements up to 20 kV is devised. The nonlinear properties of the motor stator and power transformer insulation systems are studied. Experimental results show that the voltage-dependent effect becomes significant as the voltage magnitude approaches the nominal and frequency decreases. The third current harmonic component is found to be dominant over the other components and has a strong correlation with the decrease in the dissipation factor. By taking both the fundamental and third-harmonic components into account, more consistent voltage-dependent characteristics are revealed. These features are important indications of insulation defects that are often neglected in field diagnostic testings. The investigation of the nonlinear properties helps to enhance the condition diagnosis reliability.

  • 18.
    Hoq, Md Tanbhir
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Wang, Jianping
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    An Incremental Quantity Based Distance Protection with Capacitor Voltage Estimation for Series Compensated Transmission Lines2021In: IEEE Access, E-ISSN 2169-3536, Vol. 9, p. 164493-164502Article in journal (Refereed)
    Abstract [en]

    Series capacitors increase the power transfer limit of transmission lines. However, the protection of series compensated lines using only local measurement is challenging. Phasor based distance protection experiences delay and directional problems in the presence of a series capacitor. This paper presents an incremental quantity based distance protection algorithm for series compensated lines. The algorithm uses instantaneous voltage and current measurement from the local bus. It consists of capacitor voltage estimation, fault detection, phase selection, directional discrimination and distance estimation. The algorithm is extensively tested based on simulations with a line-end series capacitor, considering different source impedance ratios, fault inception angle, compensation levels, and fault resistance, location and type. This time-domain method is shown to work well, with fast decision time.

  • 19.
    Gomes Guerreiro, Gabriel Miguel
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS). Hitachi ABB Power Grids, Natverksgatan 3, S-72136 Västerås, Sweden..
    Gajic, Z.
    Hitachi ABB Power Grids, Natverksgatan 3, S-72136 Västerås, Sweden..
    Zubic, S.
    Hitachi ABB Power Grids, Natverksgatan 3, S-72136 Västerås, Sweden..
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Habib, Md Zakaria
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Cross-Country faults in resonant-grounded networks: Mathematical modelling, simulations and field recordings2021In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 196, article id 107240Article in journal (Refereed)
    Abstract [en]

    Cross-Country Faults (CCFs) are defined by the occurrence of two Single Phase-to-Ground faults taking place simultaneously in different phases and at different locations of the galvanically connected network. Few studies about these faults in MV systems have been done so far, particularly with real fault data and simulations. In this work, first a mathematical model is derived to understand basic properties of CCFs. Then, simulations in RSCAD/RTDS (R) using real data obtained from an utility in Scandinavia are discussed and validated with two real faults measured in the field for resonant-grounded networks in Sweden and Norway. The mathematical calculations proved to have a good accuracy and showed important properties of CCFs such as the dependency of both faults of each others fault resistance and location. Furthermore, it was observed that such faults can be very different from more common types of faults in the power system. Interesting behaviors can appear particularly when feeders are connected in ring, where an extra current with smaller magnitude and 180 degrees appears on the measurement point, as well as in lines with double infeed where a very large difference is detected depending on the fault location which influences directly both ends of the line.

  • 20.
    Hoq, Md Tanbhir
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Distance Protection of Series Capacitor Compensated Lines: Practical Considerations, Industrial Status and Development2021In: Electricity, E-ISSN 2673-4826, Vol. 2, no 2, p. 168-186Article in journal (Refereed)
    Abstract [en]

    The introduction of series capacitors in transmission lines causes problems in terms of reliability and the security of distance protection relays. As distance protection is widely used in the transmission network, the challenge of applying it to series compensated lines has been taken up by utilities and relay manufacturers in various ways. In the field of power system protection, developments are largely driven by relay manufacturers, and are often not published in the academic literature; the status and trend of the relay manufacturer’s development are better found in their product manuals and patent activity. Further insight into specific implementations by transmission utilities can be found from publications in industry-led forums and some academic journals. This article surveys the status and development of distance protection for series compensated lines, with a focus on industrial implementation and practical considerations. Factors that influence the protection of series compensated lines are presented. Implementation examples reported by utilities are summarized as examples of the different situations encountered and the methods used to deal with them. It is observed that many utilities use communication-aided protection in series compensated lines, and distance protection is used with reduced reach. Solutions described in relay manuals are presented to demonstrate the manufacturers’ approaches to problems associated with series capacitor protection. While there are methods to counter voltage inversion, current inversion seems to represent a more serious challenge. A patent overview indicates the trends in this domain to be moving towards time-domain-based faster protection methods.

  • 21.
    Hoq, Md Tanbhir
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Wang, Jianping
    ABB Power Grids Sweden AB, Power Grids Research, Västerås 722 26, Sweden.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Review of recent developments in distance protection of series capacitor compensated lines2021In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 190, article id 106831Article in journal (Refereed)
    Abstract [en]

    Introduction of series capacitors in transmission lines can cause problems with reliability and security of distance protection, due to problems such as current inversion, voltage inversion and sub-synchronous oscillation. Distance protection is widely used for transmission lines and has desirable features not available from traditional alternatives, which has motivated attempts to adapt it to work better with series capacitors. Research and development in overcoming the challenges using distance protection in series compensated lines have also been actively pursued during this period. Thus there is a need to summarize and systematically categorize developments, to show recent trends and highlight further research opportunities. This paper aims to fill that gap by a thorough literature survey of distance protection of series compensated lines, including a clear background of the problems that need to be solved. The scope of this work is limited to distance protection schemes that work with local measurements only. It is observed that the developments in this domain are largely concentrated on voltage drop estimation across capacitor bank, phasor estimation and adaptive protection schemes. This work will provide an overview of the latest developments for experienced researchers and will be a reference for new researchers interested in this domain.

  • 22.
    Mahidhar, G. D. P.
    et al.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Kumar, B. Aneesh
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Sarathi, R.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Edin, Hans Ezz
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Desai, B. M. Ashwin
    Khalifa Univ, Dept Elect & Comp Engn, Abu Dhabi, U Arab Emirates..
    Understanding of Incipient discharges in Transformer Insulation by reconstruction of Digital Twins for the discharges using Generative Adversarial Networks2021In: 2021 Ieee Electrical Insulation Conference (Eic), Institute of Electrical and Electronics Engineers (IEEE) , 2021, p. 631-634Conference paper (Refereed)
    Abstract [en]

    Partial discharge (PD) monitoring is one of the diagnostic technique adopted for identifying the variety of defects in transformer insulation. Ultra high frequency (UHF) technique is gaining importance in PD monitoring applications of transformer due to various advantages. Different type of incipient discharges arose from defects in transformer insulation that needs to be identified. In an actual test site there can be noises that can hinder data acquisition and defect identification can become difficult. By using artificially reconstructed signals of known practically occurring defect models, the loss in data can be overcome. In the present study, Deep Convolutional Generative Adversarial Networks (DCGAN) technique is adopted to reconstruct the UHF partial discharge signals with high fidelity. Time-Frequency characteristics of the signals were used to build the DCGAN network and the reconstructed UHF signals are evaluated by studying the frequency characteristics of the generated signal.

  • 23.
    Habib, Md Zakaria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    F. Abdel-Fattah, Mohamed
    Reykjavik University, Iceland.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    A Current-based Solution for Earth-fault Location in Resonant-earthed Medium-voltage Distribution Systems2020In: IET Conference Publications, Liverpool, United Kingdom, 2020Conference paper (Refereed)
    Abstract [en]

    This paper proposes a novel approach to locate earth-faults in resonant-earthed distribution systems. It uses the fundamental-frequency current measurements to determine the direction of the fault current and thereby to locate the faulted section. It sets the current-angle of the faulty phase as the reference for measuring the angles of the remaining two phase-currents. These three phasor quantities are then processed to determine the direction of the fault from the measurement point. The proposed method requires an adequate resistive current from the neutral for successfully determining the faulted section. The validity of the method has been tested by PSCAD simulations for a small-scale overhead distribution system.

  • 24.
    Mahidhar, Gorla Durga Pawan
    et al.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, TN, India..
    Somasundaram Karthikeyan, Amizhtan
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, TN, India..
    Sarathi, Ramanujam
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, TN, India..
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Edin, Hans Ezz
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Dielectric properties of mixed mineral and synthetic ester oil2020In: IET Science, Measurement & Technology, ISSN 1751-8822, E-ISSN 1751-8830, Vol. 14, no 9, p. 704-714Article in journal (Refereed)
    Abstract [en]

    The dielectric properties of 20% synthetic ester oil mixed with mineral oil were studied for its potential applications as an insulator in transformers. The corona inception voltage of mixed oil under AC and DC voltages was measured by the ultra-high frequency (UHF) technique. A statistical study of the breakdown voltage of mixed oil under AC, DC and standard lightning impulse voltages was carried out to obtain a database which would be useful for designing transformer insulation. Further, the mixture was subjected to continuous breakdown studies under AC voltage with lightning impulse voltages, at regular intervals and characterised through measurement of interfacial tension, flash point, ionic mobility as well as UV-vis spectroscopy and frequency-domain spectroscopy studies to understand the liquid's chemical stability. The results of the study have shown that the mixture was stable even after several breakdowns. The ionic mobility and polarisation current have increased, indicating higher losses in the oil. UHF signal energy analysis and phase-resolved partial discharge analysis have revealed a reduction in discharge activity with mixed oils.

  • 25.
    Mahidhar, G. D. P.
    et al.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Sarathi, R.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Edin, Hans
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Dielectric Properties of Silica based Synthetic Ester Nanofluid2020In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 27, no 5, p. 1508-1515Article in journal (Refereed)
    Abstract [en]

    This work studies the impact of silica nanoparticles on the dielectric properties of synthetic ester oil. A stable nanofluid is prepared by addition of surfactant. With addition of nanoparticles there is an increment in dielectric constant and decrement in dielectric loss constant. An attempt is made to understand the conduction mechanisms in uniform field and non-uniform electric field configuration by means of analysing the mobility of ions. Under uniform electric field stress (<0.1 kV/mm), by means of conduction current measurement with polarity reversal, the ionic mobility, conductivity, ionic concentration and ionic radius are deduced. There is a reduction in ionic mobility by addition of nanoparticle and surfactant. To understand the conduction mechanisms in high electric field condition, the current-voltage characteristics of the nanofluid are measured. Using this data, apparent mobility due to electrohydrodynamic motion is estimated, giving a lower mobility in the case of nanofluid, which could be the cause of the increased corona inception voltage.

  • 26.
    Hoq, Md Tanbhir
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Wang, Jianping
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Impact of High Levels of Series Compensation on Line Distance Protection2020In: IET Conference Publications, 2020Conference paper (Refereed)
    Abstract [en]

    Series compensation of transmission lines creates several challenges for distance protection, particularly at the high compensation levels that have recently become more common. In this paper, the effect of high levels of series compensation on distance protection is evaluated, using a PSCAD simulation model of a 500 kV, 200 km transmission line with a series capacitor bank. The capacitor bank model includes overvoltage protection using a metal oxide varistor (MOV) and bypass circuit breaker. Compensation levels of 70%, 100% and 140% are simulated and phase to ground faults are simulated at several positions along the line, with fault resistance of 0 Ω and 30 Ω and fault inception angle of 0 ° and 90 °. It is observed from the simulation results that traditional distance protection experiences severe challenges at high levels of series compensation. With increasing compensation level, an increased length of line experiences voltage inversion and current inversion during a fault. The fault trajectories in the R-X plane show that voltage and current inversion during a fault can cause directional problems and delay for the distance relay. Sub-synchronous oscillation (SSO) is observed for faults in series compensated lines, causing over-reach and under-reach problems as well as delayed relay operation.

    Download full text (pdf)
    Impact of High Levels of Series Compensation on Line Distance Protection
  • 27.
    Habib, Md Zakaria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Hoq, Md Tanbhir
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Duvnjak Zarkovic, Sanja
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Impact of the fault location methods on SAIDI of a resonant-earthed distribution system2020In: 2020 IEEE International Conference on Power Systems Technology, POWERCON 2020, Institute of Electrical and Electronics Engineers Inc. , 2020Conference paper (Refereed)
    Abstract [en]

    Reliability indices of a distribution system can be improved by reducing failure rate and restoration time. A resonant-earthed distribution system has a low failure rate because numerous transient faults become self-extinguishing. However, in such networks, it can be difficult and time-consuming to locate nontransient faults resulting in aggravating the restoration time. This paper analyzes how different fault location methods affect the restoration time and SAIDI. Two major fault location methods are modeled for the calculation of the reliability indices and then applied to a radial feeder of a medium-voltage distribution system. The results show that SAIDI varies depending on the applied fault location method and its accuracy. The influence of fault location methods on labour costs is also discussed.

  • 28.
    Cheng, Jialu
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Werelius, Peter
    Abideen, Amar
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Hao, Jing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Influence of Nonlinear Stress Grading Material on Dielectric Frequency Response of Stator Insulation2020In: 7th IEEE International Conference on High Voltage Engineering and Application, ICHVE 2020 - Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2020Conference paper (Refereed)
    Abstract [en]

    Aging of high voltage generators and motors lead to changes in the dielectric properties of the stator winding insulation system. Research on the relation between aging and dielectric response has been going on for decades. A particular challenge is that the coil insulation consists of several materials: two that strongly affect the dielectric response are the ground-wall insulation and the stress grading shield (end-corona protection, ECP), which exhibit quite different properties. The influence of the ECP on the overall dielectric response of the insulation system might dwarf the condition change of the ground-wall insulation. In this paper, we introduce a test system that can measure the dielectric response in both time and frequency domain from low to rated voltage. Measurement results of two types of custom-designed, commercial standard stator winding coils are presented, and the influence of the ECP can be observed. The validity of time-frequency domain transformation of this nonlinear system is discussed. This paper acts as a basis for the application of dielectric diagnostic testing in the field.

  • 29.
    Somasundaram Karthikeyan, Amizhtan
    et al.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Mahidhar, Gorla Durga Pawan
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Sarathi, Ramanujam
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Edin, Hans Ezz
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Investigation on electrical, thermal and mechanical properties of thermally aged pressboard impregnated with mixed mineral oil and synthetic ester fluid2020In: IET Science, Measurement & Technology, ISSN 1751-8822, E-ISSN 1751-8830, Vol. 14, no 10, p. 1029-1036Article in journal (Refereed)
    Abstract [en]

    The proposed study compares the electrical, thermal and mechanical performances of thermally aged cellulose pressboard material impregnated in mineral oil, synthetic ester fluid and mixed oil. The electrical insulation characteristics of oil-impregnated pressboard (OIP) are studied by means of surface discharge inception voltage (SDIV) using an ultra-high frequency technique and surface potential measurement analysis. It indicates that OIP aged in mineral oil has higher surface potential due to higher charge trap density compared to that of the mixed oil and synthetic ester fluid. Mechanical and thermal characteristics of the aged OIP are studied by means of tensile strength measurement and thermo-gravimetric analysis, respectively. The change in the chemical composition of OIP is studied by means of laser-induced breakdown spectroscopy, which indicates lower plasma temperature with mineral oil-based OIP indicating higher degradation state. To further understand the microscopic structure of the thermally aged OIP in different oils, scanning electron microscopy and X-ray diffraction studies have been performed. The pressboard thermally aged in synthetic ester fluid and the mixed oil has better electrical, thermal and mechanical properties as compared with the pressboard aged in mineral oil.

  • 30.
    Hao, Jing
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Xu, X.
    Cheng, Jialu
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Non-contact Method for Dielectric Response Measurements2020In: 7th IEEE International Conference on High Voltage Engineering and Application, ICHVE 2020 - Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2020Conference paper (Refereed)
    Abstract [en]

    The dielectric response measurement is an important technique to assess the properties of insulation materials. However, the widely used approach with contact between samples and electrodes can in some cases limit the accuracy of the measurement. In this paper, an easily fabricated design is introduced and used to perform non-contact measurements. Air-reference measurements, comparing the sample to an air-gap for improved calibration, are used for all measurements. Results obtained by contact and non-contact methods, and with the feedback of electrometer locked and unlocked are compared. The effect of the pressure applied by the electrode is also investigated for both non-contact and contact measurements. Results show that the non-contact method can be an alternative to reduce contact problems between the sample and electrodes. For air-reference measurements, the impedance measurement instrument should be forced to use the same reference component for the air and sample measurements. Results obtained by the non-contact measurements are less sensitive to the pressure compared to that by contact measurements. 

  • 31.
    Hao, Jing
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Xiangdong, Xu
    Chalmers Univ Technol, Elect Power Engn, S-41296 Gothenburg, Sweden.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Non-contact method to reduce contact problems between sample and electrode in dielectric measurements2020In: High Voltage, ISSN 2397-7264, Vol. 5, no 6, p. 753-761Article in journal (Refereed)
    Abstract [en]

    Dielectric response measurement is a widely used technique for characterising dielectric materials in terms of theircapacitance and dielectric loss. However, the widely used approach with contact between samples and electrodes can in somecases limit the accuracy of the measurement. The authors introduce an easily realised electrode arrangement for non-contactmeasurements, which avoids these contact problems. The performance of the electrode arrangement in terms of the edge effectis assessed. The non-contact and contact methods are compared based on error-sensitivity analysis and experimental results.Differences are studied further, with attention to contact pressure. The non-contact method is also compared experimentally withthe one-sided non-contact method. Air-reference measurements, comparing the sample to an air-gap for improved calibration,are used for all measurements. The results show that the non-contact method can be an alternative to reduce contact problemsbetween the sample and electrodes, although error sensitivity can be higher when the non-contact method is used. The non-contact method can decrease the influence of the pressure applied to the sample compared to the contact method, and can alsoreduce the problem of poor contact that can arise from the absence of pressure in the one-sided non-contact method

    Download full text (pdf)
    fulltext
  • 32.
    Hao, Jing
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Xiangdong, Xu
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    An Electrode Setup for Non-contact Dielectric Response Measurement2019In: Proceedings of the 26th Nordic Insulation Symposium, Tampere, June 2019, Norwegian University of Science and Technology (NTNU) Library , 2019Conference paper (Refereed)
    Abstract [en]

    The dielectric response measurement is a widely used technique for characterizing dielectric materials. However, the contact problems between samples and electrodes existing in the use of conventional electrode setup limit the accuracy of the measurement. In this paper, a type of electrode arrangement is introduced for avoiding direct contacts of the sample with both the bottom and the top electrode. The edge effect of this arrangement is calculated by the FEM model. The equations to derive the complex permittivity is presented. The measurement instrument is described and the influence of the potential difference between two terminals of the IDAX input is analyzed. Furthermore, the error sensitivities are compared between the non-contact and contact methods. The results show that this electrode arrangement can be used to perform non-contact measurements, and the edge effect of it is not significant. The potential between the two terminals of the IDAX is not an obstacle to obtain results with high accuracy. Overall, the non-contact electrode arrangement combined with the IDAX 300 can potentially improve the accuracy of dielectric response measurements although the non-contact methods can increase the sensitivities to errors.

    Download full text (pdf)
    fulltext
  • 33.
    Hoq, Md Tanbhir
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Habib, Md Zakaria
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Reliability Assessment of Protection Schemes for Series Compensated Transmission Lines2019In: 4th International Conference on System Reliability and Safety (ICSRS), Rome, Italy, Institute of Electrical and Electronics Engineers (IEEE) , 2019Conference paper (Refereed)
    Abstract [en]

    Series capacitors are used in transmission lines for enhancing power transmission limit. However, they complicate the line’s protection due to impedance change of the line, voltage inversion, current inversion and sub-synchronous oscillation. Distance and differential protections are used in different arrangements in transmission line protection. Often they are used together as main and backup protection. In this paper, the fault tree method is used to compare the reliability of three common transmission line protection schemes. The schemes considered here are distance (main)-distance (backup)(Z; Z), differential (main)-distance (backup) (delta;Z) and differential (main)-differential (backup) (delta;delta). Fault trees are used to calculate the reliability of protection schemes in terms of both unavailability and failure rate. The analyses show that, for series compensated lines, using distance protection reduces protection system reliability. Differential protection performs best in terms of reliability despite depending entirely on communication.

    Download full text (pdf)
    Reliability Assessment of Protection Schemes for Series Compensated Transmission Lines
  • 34.
    Cheng, Jialu
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Werelius, Peter
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Temperature Influence on Dielectric Response of Rotating Machine Insulation and Its Correction2019In: Proceedings of the 26th Nordic Insulation Symposium, 2019, p. 145-149Conference paper (Refereed)
    Abstract [en]

    Insulation condition is an essential aspect for the operational reliability of high voltage rotating machines in power plants and industrial applications. Insulation resistance (IR) and line-frequency dissipation-factor / power-factor (tanδ) measurement are often performed for the assessment of stator insulation condition. These measured values need to be normalized to a reference temperature (e.g. 40 °C) for comparison and trending and this is traditionally achieved by multiplying the results with a certain factor. However, this correction could be subject to error for an individual devicesince the correction factors recommended by various standards are average values of a certain number of machines at different conditions. In addition to that, insulation condition also has some influence on the temperature dependent property. With the introduction of Dielectric Frequency Response, DFR and Polarization/Depolarization Current, PDC as more advanced insulation diagnostic methods, with proper modelling, temperature correction can be done based on the insulation condition of an individual device and thus accuracy is considerably improved. In this paper, the background of DFR and its superiority in temperature correction are introduced. After that, the numerical Fourier and Inverse Fourier Transformation algorithm is applied to correct the time domain measurement (IR and PDC).

    Download full text (pdf)
    fulltext
  • 35.
    Hoq, Md Tanbhir
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Wang, Jianping
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    The Impact of Current Inversion on Line Protection in High Voltage Transmission Lines with Series Compensation2019Conference paper (Refereed)
    Abstract [en]

    Series capacitors are used in some transmission lines to raise the power transfer limit. If a fault occurs at a location behind which the total reactance is capacitive, the result is current inversion, also known as current reversal. In a current inversion, current leads the voltage instead of lagging it. The probability of current inversion increases with higher levels of compensation. In this paper, the effect of current inversion is studied in distance and differential protection of transmission lines. A 500 kV transmission line is modelled, with compensation levels of 70%, 100% and 140%. Phase to ground faults are applied with fault inception angles of 0, 60 and 90. It is shown that current inversion can cause serious problems with distance protection. Differential protection is not severely affected by current inversion. The protection schemes are significantly influenced by parameters of the capacitor bank overvoltage protection components, particularly the metal-oxide varistor.

    Download full text (pdf)
    The Impact of Current Inversion on Line Protection in High Voltage Transmission Lines with Series Compensation
  • 36. Kande, M.
    et al.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Automation system generic security key manager2018In: Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society, Institute of Electrical and Electronics Engineers Inc. , 2018, p. 2867-2871Conference paper (Refereed)
    Abstract [en]

    The security research interest in industrial automation domain has gained importance due to the increased severity of cyber threats towards existing and future industrial systems. Secure communication between the devices is vital for creating a secure environment in the industrial plant. The keys used for secure communication must be protected against unauthorized disclosure, misuse, alteration or loss. In addition to that, industrial automation deployment has unique and strict demands on Quality Of Service (QOS). Conventional security architectures may not meet these requirements without substantial addition of cost and complexity. From a system level perspective, a flexible, easy to integrate and scalable key management architecture is essential for successful security deployment. This paper addresses interoperability and ease of integration using a centralized generic key management infrastructure designed for industrial automation systems. 

  • 37.
    Rabuzin, Tin
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Lavenius, Jan
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electric Power and Energy Systems.
    Bayesian Detection of Islanding Events Using Voltage Angle Measurements2018In: 2018 IEEE International Conference on Communications, Control, and Computing Technologies for Smart Grids, SmartGridComm 2018, IEEE, 2018, article id 8587561Conference paper (Refereed)
    Abstract [en]

    The growing presence of distributed generation in power systems increases the risk for the unintentional creation of electrical islands. It is important to apply reliable and quick is landing protection methods. At the same time, the deployment of phasor measurement units facilitates the usage of data-oriented techniques for the development of new wide-area protection applications, one of which is islanding protection. This paper presents a Bayesian approach to detecting an islanding event, which utilizes measurements of voltage angles at the system's buses. A model of mixtures of probabilistic principal component analysers has been fitted to the data using a variational inference algorithm and subsequently used for islanding detection. The proposed approach removes the need for setting parameters of the probabilistic model. The performance of the method is demonstrated on synthetic power system measurements.

  • 38.
    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), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Edin, Hans Ezz
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, 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.

  • 39.
    Habib, Md Zakaria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Wang, Jianping
    Li, YouYi
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Phase Shift Compensation Method for the Line Differential Protection on UHV-AC Transmission Lines2018Conference paper (Refereed)
    Abstract [en]

    Line differential protection is popular for its good selectivity and simplicity as long as there is a dependable communication system between the two ends of the line. However, the sensitivity needs to be compromised when traditional line differential scheme is applied for UHV-AC lines because of the large charging current. This paper presents a study of the impact of UHV transmission line characteristics on line differential protection and a proposed solution based on compensation of the phase shift that exists between the sending and receiving end currents.

  • 40.
    Mahidhar, Gorla Durga Pawan
    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), Electrical Engineering, Electromagnetic Engineering.
    Edin, Hans Ezz
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, 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.

  • 41. 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.

  • 42.
    Nikjoo, Roya
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Dielectric response measurement by impulse stimulus on AC: Measurement considerations, and laboratory testing on a bushing2017In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 24, no 1, p. 511-518, article id 7873509Article in journal (Refereed)
    Abstract [en]

    Dielectric response (DR) measurement is commonly used for condition assessment of insulation systems of power components. A method for measurement of dielectric response using the stimulus of natural transients such as lightning and switching impulses was proposed in earlier work. Its desirable features include the ability to make measurements online over a range of frequencies, without requiring a voltage source. This article presents a laboratory demonstration of the method on a 150 kV service-aged transformer bushing, where the stimulus was a standard lightning impulse voltage superimposed on an AC voltage. Several aspects of the measurement and data processing that affect the results are studied experimentally and numerically. The results are compared with low-voltage frequency domain spectroscopy (FDS). Reasonable accuracy for monitoring changes in DR can be achieved by suitable choice of measurement circuit and data acquisition. The study suggests an approach for online monitoring of dielectric properties of power transformer bushings, and diagnostics of defects that affect the high frequency region of DR, such as moisture content.

  • 43.
    Chen, Feng
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Balieu, Romain
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Kringos, Niki
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Dynamic application of the Inductive Power Transfer (IPT) systems in an electrified road: Dielectric power loss due to pavement materials2017In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 147, p. 9-16Article in journal (Refereed)
    Abstract [en]

    Inductive Power Transfer (IPT) technology is seen as a promising solution to be applied in an electrified road (eRoad) to charge Electric Vehicles (EVs) dynamically, i.e. while they are in motion. Focus in this study was placed on the dielectric loss effect of pavement surfacing materials on the inductive power transfer efficiency, induced after the integration of the technology into the physical road structure. A combined experimental and model prediction analysis was carried out to calculate this dielectric loss magnitude, based on which some preliminary conclusions as well as a prioritization of future focus needs were summarized in detail.

  • 44.
    Kande, Mallikarjun
    et al.
    KTH, School of Electrical Engineering (EES). ABB .
    Isaksson, Alf J.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Rotating Electrical Machine Condition Monitoring Automation-A Review2017In: Machines, E-ISSN 2075-1702, Vol. 5, no 4, article id 24Article, review/survey (Refereed)
    Abstract [en]

    We review existing machine condition monitoring techniques and industrial automation for plant-wide condition monitoring of rotating electrical machines. Cost and complexity of a condition monitoring system increase with the number of measurements, so extensive condition monitoring is currently mainly restricted to the situations where the consequences of poor availability, yield or quality are so severe that they clearly justify the investment in monitoring. There are challenges to obtaining plant-wide monitoring that includes even small machines and non-critical applications. One of the major inhibiting factors is the ratio of condition monitoring cost to equipment cost, which is crucial to the acceptance of using monitoring to guide maintenance for a large fleet of electrical machinery. Ongoing developments in sensing, communication and computation for industrial automation may greatly extend the set of machines for which extensive monitoring is viable.

  • 45.
    Wåhlander, Martin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Nilsson, Fritjof
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Andersson, Richard L.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Cobo Sanchez, Carmen
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Carlmark, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Hillborg, Henrik
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials. ABB AB.
    Malmström, Eva
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Tailoring Dielectric Properties using Designed Polymer-Grafted ZnO Nanoparticles in Silicone Rubber2017In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, p. 14241-14258, article id C6TA11237DArticle in journal (Refereed)
    Abstract [en]

    Polymer grafts were used to tailor the interphases between ZnO nanoparticles (NPs) and silicone matrices. The final electrical properties of the nanocomposites were tuned by the grafted interphases, by controlling the inter-particle distance and the NP-morphology. The nanocomposites can be used in electrical applications where control of the resistivity is desired. Hansen's solubility parameters were used to select a semi-compatible polymer for grafting to obtain anisotropic NP morphologies in silicone, and the grafted NPs self-assembled into various morphologies inside the silicone matrices. The morphologies in the semi-compatible nanocomposites could be tuned by steering the graft length of poly(n-butyl methacrylate) via entropic matrix-graft wetting using surface-initiated atom-transfer radical polymerization. Image analysis models were developed to calculate the radius of primary NPs, the fraction of aggregates, the dispersion, and the face-to-face distance of NPs. The dielectric properties of the nanocomposites were related to the morphology and the face-to-face distance of the NPs. The dielectric losses, above 100 Hz, for nanocomposites with grafted NPs were approximately one decade lower than those of pristine NPs. The isotropic nanocomposites increased the resistivity up to 100 times compared to that of neat silicone rubber, due to the trapping of charge carriers by the interphase of dispersed NPs and nanoclusters. On the other hand, the resistivity of anisotropic nanocomposites decreased 10–100 times when the inter-particle distance in continuous agglomerates was close to the hopping distance of charge carriers. The electrical breakdown strength increased for compatible isotropic nanocomposites, and the temperature dependence of the resistivity and the activation energy were ∼50% lower in the nanocomposites with grafted NPs. These flexible dielectric nanocomposites are promising candidates for low-loss high-voltage transmission cable accessories, mobile electronic devices, wearables and sensors.

    Download full text (pdf)
    fulltext
  • 46.
    Niasar, M. Ghaffarian
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Kiiza, Respicius Clemence
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Dielectric Frequency Response of Oil-impregnated Paper: the Effect of Partial Discharges Compared to other Influences2016In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 23, no 3, p. 1769-1777Article in journal (Refereed)
    Abstract [en]

    In this paper, the influence of partial discharges (PD) on the subsequent dielectric properties of oil-impregnated paper (OIP) is investigated. Dielectric frequency response (DFR) of OIP is investigated at varied levels of moisture, thermal aging, temperature, oil conductivity and electrode material, to allow comparison of these influences. It is shown that PD activity inside OIP can significantly change the real and imaginary parts of permittivity of the paper layers, especially in the frequency range below 100 Hz. It is shown that even if the PD activity is concentrated on a few percent of the test sample, the real part of permittivity measured on the entire sample after a few tens of hours of PD activity can increase up to 10 times at very low frequencies (similar to 1 mHz) and the imaginary part of the permittivity can increase up to 100 times at low frequencies (similar to 1 Hz). The change of the real and imaginary parts of permittivity due to PD activity is permanent. It is very similar to the change caused by thermal aging, and somewhat similar to the change caused by moisture and higher oil conductivity. It is also shown that the dissipation factor of OIP in contact with copper and brass increases, even in the absence of PD, but contact with aluminum and stainless steel has no influence on DFR of OIP. The results suggest that the influence of PD can be significant when estimating the moisture content or the level of thermal aging of OIP with DFR method.

  • 47.
    Chen, Feng
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Dynamic application of the Inductive Power Transfer (IPT) systems in an electrified road: Dielectric power loss due to pavement materials2016In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526Article in journal (Other academic)
    Abstract [en]

    It is well-known that the high cost and limited performance of existing energy storage systems have significantly constrained the commercialization of the Electric Vehicle (EV) at large scale. In recent years, attention has been given not only to the improved energy storage systems but also to develop appropriate charging infrastructures that would allow the EVs to be powered in an easier way. Inductive Power Transfer (IPT) technology, also known as a near-field wireless power transfer technology, is capable of delivering electricity wirelessly with large power and high efficiency at a given gap distance. It is therefore seen as a promising solution to be applied in an electrified road (eRoad) to charge EVs dynamically, i.e. while they are moving. Various technical aspects of this contactless charging solution have been studied actively by system developers, such as the charging power, its efficiency, the optimum gap distance as well safety issues. Focus in this study is placed on the effect of pavement surfacing materials on the wireless power transfer efficiency, after the integration of the technology into the physical road structures. Specifically, a combined experimental and model prediction analysis has been carried out to investigate this potential energy loss in a quantitative way, based on which some preliminary conclusions as well as a prioritization of future focus needs are summarized in detail. This work provides thus an important beginning for understanding the pavement materials’ influence on the IPT systems that may be used for dynamic applications in an eRoad.

  • 48.