Sisir Nayak

Indian Institute of Technology Guwahati | IIT Guwahati

The streamer characteristics and breakdown strength of liquid insulation under high voltage stresses are studied by product design engineers, scientists and researchers in industries to develop a reliable and efficient material for high voltage liquid filled power apparatus. The present invention generally relates to an apparatus for analyzing brea...

The invention presents a novel technique to extract the moisture from transformer oil through online as well as offline methods

The purpose of this present study is to prepare a stable mineral-oil (MO)-based nanofluid (NF) for usage as a coolant in a transformer. Nanoparticles (NPs) such as hexagonal boron nitride (h-BN) and titanium oxide (TiO2) have superior thermal and electrical characteristics. Their dispersion into MO is likely to elevate the electrothermal properties...

The insulation system in a transformer degrades over time and it needs periodic monitoring for uninterrupted operation of the power system network. Moisture content (MC), acid number, and dissolved gases are the important parameters that establish the aging and degradation status of the transformer liquid insulation. This work focuses on using high...

The insulating oil in medium, high, extra high, and ultra-high voltage equipment such as transformer carry an equivalent role as solid insulation in reliable operation of the equipment. The insulating oil ages with time due to multiple stresses. The electrical, thermal and chemical properties of the aged oil degrade and in turn result in failure of...

This article presents the design of a compact microstrip-fed triple-band slot antenna for WLAN/WiMAX/C-band downlink satellite communications. The newly designed proposed simple structure has a considerably high-center frequency ratio and can significantly suppress cross-polarization levels. This antenna consists of a double annular-ring slot (DARS...

This article presents the design and characterization of a dual-band, compact, and dual-circularly polarized (CP) traveling wave series-fed circular slit microstrip array (TWSCSMA) antenna operating in quad-band CP at 2.5/3.5/3.8 GHz WiMAX and 5.2 GHz WLAN applications. The radiating structure consists of an annular ring traveling wave series-fed c...

Nanofluids with their superior electrical and thermal properties are a promising alternate liquid dielectric in power transformers. Alongside the electric field, magnetic field is also an integral part of power transformers. It accounts for power transfer through flux linkages and due to the design constraints, flux leakages exist in every transfor...

A parabolic profile pyramidal horn antenna with flaring in both the E- and H-plane is presented in this study. The proposed structure having aperture dimensions of 518.10 × 408.36 mm2 is designed and fabricated for S-band (2.2–3.3 GHz). Due to increase in the flaring by 3.35° in the E-plane and 3.18° in the H- plane compared to the optimal typical...

The main focus of this chapter is the processing of the natural ester-based oils to be used as an insulating liquid in a transformer and other electrical apparatus. Natural esters are eco-friendly alternatives obtained from renewable resources such as plant seeds. These natural oils are composed of triglycerides, which react with alcohol to produce...

In this work, a non-edible natural ester oil (NEO) is considered for the study of its ageing characteristics by the frequency domain spectroscopy (FDS). The NEO considered is the Jatropha Curcas oil (JAT) because of its non-edible and biodegradable nature. The FDS method is a non-destructive measurement technique which is used to analyze the charac...

An important element of the power system network is the transformer. The conventional mineral oil (MO), which acts as an insulation and heat transfer agent in a transformer plays a major role in its steadfast operation. The insulation is highly stressed during its operational lifetime. Thus, alternative insulating liquids are being studied to enhan...

In the existing solar photovoltaic modules, cells are connected in series. The performance of the series-connected module degrades severely during partial shading condition. Further, the use of bypass diode causes multiple peak (local and global peaks) problem. Therefore, total cross tied (TCT) connection has been proposed in this paper to connect...

This paper presents an aperture matched parabolic pyramid horn antenna (APPHA) having flaring in the E‐ and H‐ plane. The proposed structure is designed and manufactured for S‐band (2.2–3.3 GHz) with a semicircular aperture matched section in both planes. The APPHA gives half power beam width (HPBW) less than 17° and 15° in the E‐ and H‐ planes, re...

Transformer is the most important equipment in a power system network. Thermal and electrical stresses are the major cause of concerns for failures in a power transformer. These stresses are sustained by mineral oil (MO) which provides insulation as well as acts as a coolant in the transformer. MO is extensively used in power transformers for insul...

A graded refractive index metamaterial (MM) exhibits a magnetic dipole designed and demonstrated experimentally for 2.45 GHz operating frequency. The system efficiency of the far-field wireless power transfer technique increased to 32.6% with MM. With 16° reduction in half power beamwidths, 9.78 dBm is received at 1 m with 30 dBm input when MM is p...

Wind power generation is observing a significant use of doubly-fed induction generator (DFIG) due to its improved efficiency, but the converter used in the configuration is sensitive to the presence of a fault in the grid. This paper presents a fault ride-through (FRT) configuration, which includes a thyristor-based bridge-type non-superconducting...

In this paper, the maximum power point (MPP) of a photovoltaic (PV) source is estimated using the proposed explicit current-voltage (I- V) expression. The conversion of implicit expression of current to explicit expression of I-V equation is carried out using Maclaurin series expansion. The explicit I-V function of the PV module is validated with t...

This article presents a structure of coplanar waveguide (CPW)-fed star-shaped monopole antenna (SSMA) with a pair of quarter-circular-slit (QCS) and partly-hexagonal-ring-slit (PHRS) defected ground structure. By inserting a pair of QCS and PHRS on the rectangular ground plane, an excellent impedance bandwidth is achieved i.e., 139 % (from 2.2--12....

Abstract The effective implementation of battery management system (BMS) in various applications such as electric vehicles (EVs), renewable energy sources (RES) integrated smart‐grids and micro‐grids, necessitates accurate estimation of the battery parameters and states. This paper primarily focuses on offering an improved solution to the state of...

An important element of the power system network is the transformer. The conventional mineral oil (MO), which acts as an insulation and heat transfer agent in a transformer plays a major role in its steadfast operation. The insulation is highly stressed during its operational lifetime. Thus, alternative insulating liquids are being studied to enhan...

To increase lifespan and optimize capacity utilization of lithium-ion (Li-ion) battery, it is imperative to predict its states accurately. This paper primarily focuses on offering an improved solution for estimating one of the most important battery states known as state of charge (SOC). After extensive analysis of the current state-of-the-art meth...

The application of nanofluids (NFs) in power apparatus is increasing in the recent years because of its higher dielectric strength, higher thermal conductivity, lower electrical conductivity and lower dissipation factor. The reason for increase in the dielectric strength of the NFs over base oil is due to the electron scavenging by the nanoparticle...

The presentation is about the use of metamaterial in space solar power projects.

This paper aims at investigating the dissolved gas analysis (DGA) and long-term performance of Environtemp (FR3) and Jatropha Curcas oil (JAT). Thermal stress is applied to both oils in a sealed setup at 150 o C for up to 2000 hours and samples are removed and tested at 500 hour intervals. It is observed that FR3 is more prone to stray gassing as c...

This paper investigates the unsteady aerodynamic performance due to oscillatory motion. The wind flows velocity is constant across the wind turbine rotor is applied, therefore, the attached flow on a 2-D airfoil and the aerodynamic critical damping of the large-scale horizontal axis wind turbine (LS-HAWT) blade structure are considered. The blade e...

A study has been performed to extract the unknown parameters of a photovoltaic (PV) module using mathematical model-driven analysis. Neglecting the less significant terms, the number of non-linear exponential terms are reduced to develop a simplified algorithm to estimate five unknown parameters such as diode ideality factor, series resistance, shu...

A parabolic dish reflector (PDR) is designed and fabricated to convert the plane wave to spherical wave at the focus. The performance of PDR made from aluminum and Polydimethylsiloxane (PDMS) coated with aluminum is carried out. It is observed that the performance of the PDR made from PDMS is same as that made from aluminum, thus the proposed PDR m...

Estimation of the output power of a solar photovoltaic (PV) system during partial shading condition (PSC) is an interest of PV installers. Owing to the inclusion of a bypass diode, the occurrence of local and global maximum peak creates more difficulty in the calculation of maximum power output from a PV array. In this study, a mathematical model i...

Nanofluids (NFs) are an emerging technology in the field of dielectrics. These oils are used in transformers and other power apparatus for the purpose of insulation and cooling. The vegetable oil (VO) proposed in this paper is the Pongamia pinnata oil (PPO), commonly known as karanji oil. The molecular structure of PPO is changed by the transesteri...

This article shows the frequency tuning using PIN diode of transmission type digital metasurface. Here, the S21 amplitude of the unit cell in ON and OFF condition of PIN diode is given the digital code of “0” when the S21 value is less than - 8 dB, and “1” when the amplitude is 0 dB. It is observed that when the diode is ON, the 10 x 18 array shows...

A square slotted patch antenna for far-field wireless power transfer applications is presented. The antenna has compact size equal to 0.416�0.236�0.013� which can be fit into most of the devices. It exhibits a total of 780 MHz of -10 dB impedance bandwidth in S-band with good directional characteristics. A maximum of 1.24 dB gain is observed with 1...

In this paper, the efficient modeling of DC-RF module of space solar power satellite (SSPS) with improved antenna design and metasurface is proposed. With the higher losses as one of the present problem in the DC-RF conversion, using single-phase full-bridge topology with a maximum power point tracking algorithm is proposed. The design parameters o...

Estimation of the output power of a solar photovoltaic (PV) system during partial shading condition (PSC) is an interest of PV installers. Due to the inclusion of a bypass diode, the occurrence of local and global maximum peak creates more difficulty in the calculation of maximum power output from a PV array. In this paper, a mathematical model is...

A parabolic profile pyramidal horn antenna with flaring in both the E- and H-plane is presented in this study. The proposed structure having aperture dimensions of 518.10 × 408.36 mm2 is designed and fabricated for S-band (2.2–3.3 GHz). Due to increase in the flaring by 3.35° in the E-plane and 3.18° 3.18° in the H- plane compared to the optimal ty...

This invention is about designing an aperture matched parabolic pyramidal horn antenna (APPHA) to achieve the higher values of gain, half power beam width, and front-to-back ratio than typical pyramidal horn antenna with equal aperture area. The parabolic tapering concentrates radiating field in the propagating direction to great extent to have hig...

This invention is about transferring/harvesting the power/energy to/at the receiver end by using metamaterials for manned/unmanned applications. The WPT/WEH techniques used nowadays are having less efficiency and small distance coverage. Furthermore, its performance degrades as the transmitting antennasradiated electromagnetic waves that carries po...

Vegetable oils (VOs) are based on natural ester oil that is considered as an alternative to mineral oil for transformer applications. The dispersion of nanofillers into the VO is expected to improve the physicochemical and electrical performances. Surface-modified insulating nanoparticle is dispersed into the VO to prepare the VO-based nanofluid (N...

Vegetable oil (VO) based liquid dielectric are gradually being implemented to improve the heat transfer in electrical appliances to enhance their life and improve efficiency. The conventional VO based insulating oil is being moderately researched to improve the understanding of the physical mechanisms involved in their enhanced performance compared...

A novel ultrathin linear to cross-polarization transmission metasurface (MS) converter with a periodicity of 8 mm ( $\lambda_0$ /4.26, where $\lambda_0$ is free space wavelength at 8.8 GHz) is proposed which gives perfect transmission. The proposed MS is a single layer with a thickness of 0.8 mm (0.0235 $\lambda_0$ ). The conversion efficiency...

In this letter, the far-field wireless power transfer up to 6-m distance from the transmitting horn antenna (Tx) aperture using a new design gradient refractive index lens metamaterial (GRIN MM) is proposed for the first time, which increases the efficiency of power transfer. Double-sided-S-shaped GRIN MM unit cell dimensions are optimized for the...

In this paper, a sparse-technique-based representation of the signal over a learned dictionary and random decrement technique are explored to extract the oscillatory mode from the ambient data. The main contribution of the present work is to design a dictionary and compute the coefficients that best represent the clean signal to estimate the modes....

This paper presents a novel approach for the conversion of an implicit current-voltage (I-V) expression of a double diode model (DDM) photovoltaic (PV) module to an explicit expression of current in terms of voltage. A new method is proposed for the estimation of maximum power point (MPP) of a DDM PV module using the explicit I-V expression of a PV...

The transformer is a long run device in a power system network. When transformer oil comes in contact with cellulosic insulation in the presence of heat, the solid insulation undergoes polymerization. As a result, dielectric, mechanical and chemical properties of the oil and kraft paper get affected. In this present study, electrical, mechanical an...

This paper presents a nonedible karanji base vegetable oil (VO) as an alternative transformer oil. The nature of biodegradability, environment friendly and easy availability makes this oil a suitable candidate for liquid insulation. The crude karanji oil (CKO) is not at all suitable for the transformer use because of the higher acid number and visc...

The proposed metasurface design help to increase the radiation efficiency at 2.9 GHz by reducing the side and back lobes by making the phase difference of the waves emerging from the phase center of the horn antenna same after passing through metasurface array. The unit cell of the meta surface is having concentric ring structure made of copper on...

In this study, the prediction of the breakdown probability of a new batch of nanofluid (NF), namely exfoliated hexagonal boron nitride based NF is performed. Weibull two-parameter model distribution function has been used to predict the AC breakdown voltage (ACBDV) probability percentage at 5, 10, 50 and 63.2% of failure. To verify the effect of ag...

The development of nanofluids is necessary to replace the conventional transformer oil used in power and distribution transformers. A stable nanofluid has been prepared to verify its insulating and heat transfer performance in oxidative ageing environment. Due to the superior thermal and electrical properties of a nanoparticle (NP), its dispersion...

The measure of oxidation stability in the transformer oil leads to explain the chemical degradation of it. It is very difficult to ascertain the quality of the used oil in the transformer unless continuous monitoring of chemical characteristic. Therefore, in this innovation, the inventors are aimed to predict, the oxidative life of the transformer...