SDIV of OIP material gets altered with thermal ageing temperature of OIP material, supply voltage frequency and the harmonic content in the supply voltage. The UHF signal radiated due to surface discharges formed under AC voltage, high frequency AC voltages and with harmonic voltages, have dominant frequency at about 0.9 GHz. Surface charge accumulation studies indicate that thermal ageing have high impact on amount of charge accumulation. Also number of layers of insulation have high charge trap density, which is ascertained through tdv/dt plot. The amount of charge accumulated is high with pressboard impregnated in titania nanoparticle dispersed transformer oil. The SD activity occurs at the rising portion of AC voltage and at high dv/dt’s with harmonic AC voltages. More number of discharges occur with OIPs thermally aged at higher temperature. Physico-chemical changes clearly indicate not much of a change occurs with transformer insulation due to thermal ageing. © 2017, School of Electrical Engineering and Informatics. All rights reserved.

Ramanujam Sarathi

Department of Electrical Engineering

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IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

International Journal on Electrical Engineering and Informatics

This paper proposes a combined adaptive droop based load sharing, MPP tracking and energy management of photovoltaic (PV) based DC microgrid system. A proportional droop index (PDI) algorithm is introduced, which is a function of normalized current sharing difference and voltage deviation in the output side of the converter. The proposed method calculates adaptive virtual resistance Rdroop, which allows the PV converter to operate at MPP or load sharing mode. By fine-tuning Rdroop values, the proposed method eliminates poor voltage regulation issues of the conventional droop method. The control of hybrid energy storage system (HESS) with battery and super-capacitor (SC) is also discussed to stabilize the DC grid voltage and energy management of the DC microgrid. The detailed analysis and design procedure of low voltage (LV) DC microgrid systems are explained and the effectiveness of the proposed method is verified by simulation and experimental studies. IEEE

IEEE Journal of Emerging and Selected Topics in Power Electronics

A Unified Control Scheme for a Standalone Solar-PV LVDC Microgrid System with HESS

The levitation voltage of the conducting/non conducting particle in the SF6 gas filled electrode gap is high under DC voltage compared with the AC voltage. The levitation voltage increases with frequency of the supply voltage. Particle levitation voltage marginally increases with increase in THD of the harmonic AC voltage. The levitation voltage of the particle increases as and when the barrier is moved towards the high voltage electrode. No polarity dependency is observed on levitation voltage under DC voltages. Percentage of filler content in epoxy nanocomposites has high impact on levitation voltage of the particle. The analysis of levitation voltage with epoxy nanocomposites indicates that up to 3 wt% of MgO added specimen, the levitation voltage is high and above which a marginal reduction in levitation voltage of particle in SF6 gas medium is observed. The UHF signal magnitude caused by the particle movement process increases with the applied voltage. Also, the extinction voltage of particle movement is lower than the levitation voltage. Also, with increase of applied voltage, on levitation, the magnitude of UHF signal increases. However, on reducing the applied voltage, the UHF signal magnitude is much higher than onward application of voltage. This characteristics is almost the same under AC and DC voltages. The FFT analysis of UHF signal formed due to particle under AC and DC voltages, at the point of inception has dominant frequency at around 1 GHz. When the applied voltage is increased, especially under DC voltages, the FFT analysis of UHF signal formed indicates energy content in the band 2-3 GHz is increased, indicating indirectly, the rate of charge transfer due to particle movement with opposite electrode is high under DC voltages. The FFT analysis of UHF signal formed by non-conducting particle under high frequencies have the energy content increased in the range 2-5 GHz. PRPD analysis indicates that PD activity is observed in the entire phase of the applied AC voltage, irrespective of harmonics and THDs. The number of PD occurrence is high where the rate of rise of supply voltage is high. © 1994-2012 IEEE.

IEEE Transactions on Dielectrics and Electrical Insulation

Partial discharge activity due to particle movement in SF6 gas filled electrode gap under different voltage profiles

We study FAST TCP, a new transmission control protocol that uses queueing delay as its feedback measure. We highlight two continuous-time models proposed for FAST that represent two operating regimes: (i) queueing delay forms a large component of the end-to-end delay, (ii) propagation delay is the dominant component of the end-to-end delay. These models when coupled with the integrator model for the queue, are shown to yield qualitatively similar results. We then study one of these models in different queueing regimes. In the scenario where the queue can be modelled as an integrator, we conduct a detailed local stability analysis. This yields strict bounds, on the system parameters and round-trip time, to ensure local stability. We show that the system undergoes a Hopf bifurcation, when these bounds are violated, leading to the emergence of limit cycles in the system dynamics. As limit cycles could be detrimental to network performance, we conduct a detailed Hopf bifurcation analysis using Poincaré normal forms and center manifold theory. This enables us to characterise the type of the Hopf bifurcation and determine the orbital stability of the limit cycles. We then consider a regime with smaller queues, where end systems react primarily to packet loss. In this regime, larger thresholds could lead to instability. Packet-level simulations corroborate our analytical insights; non-linear oscillations are indeed observed in the queue size. © 2017 Elsevier B.V.

Performance Evaluation

FAST TCP: Some fluid models, stability and Hopf bifurcation

Molybdenum carbide (MoC) nanoparticles were generated by exploding molybdenum conductor in methane gas ambience at different pressures. To enhance the level of carburization, exploding conductor was coated with graphite and paraffin mixtures. Various physico-chemical studies were employed to characterize the produced nano-carbide particles, viz., X-ray diffraction, optical emission spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. It was deduced from these investigations that the nano-MoC particles produced by a wire explosion process (WEP) are spherical in shape. The size of the particles formed by WEP can be controlled by varying the operating ambience pressure of the methane gas. The particle size produced follows a log-normal distribution. Optical emission results clearly indicates the presence of Mo-I, C-I, and C-II components during WEP. X-ray photoelectron spectroscopy confirms the formation of MoC. © 1973-2012 IEEE.

IEEE Transactions on Plasma Science

Investigation of Nano-Molybdenum Carbide Particle Produced by Wire-Explosion Process

This paper presents a predictive voltage control scheme for the effective control of a transformerless dynamic voltage restorer (TDVR). This control scheme utilizes the discrete model of a voltage source inverter and an interfacing filter for the generation of the switching strategy of inverter switches. Predictive voltage control algorithm-based TDVR tracks the reference voltage effectively and maintains load voltages sinusoidal during various voltage disturbances as well as load conditions. Moreover, this scheme does not require any linear controller or modulation technique. Simulation and experimental results are presented to verify the performance of the proposed scheme. © 1982-2012 IEEE.

Journal	International Journal on Electrical Engineering and Informatics
Publisher	School of Electrical Engineering and Informatics
ISSN	20856830
Open Access	Yes