Shiv Nadar University is a comprehensive, multidisciplinary, research-focused, and student-centric University offering a full range of academic programs at the undergraduate, postgraduate and doctoral level. With state-of-the-art infrastructure, the University comprises of academic wings, sophisticated labs, international standard sports facilities, amphitheaters, auditorium, conference rooms and smart classrooms. The University&rsquo;s goal is to become internationally recognized for the quality of its research and creative endeavors and their applicability to improving quality of life, generating new insights and expanding the boundaries of human knowledge creativity. Committed to excellence in teaching, research and service, the University aims to serve the higher education needs of India and the world beyond.

Shiv Nadar University

The inner winding of transformers may get buckled under the short-circuit condition. To avoid the buckling of the inner winding, the critical stress at which buckling occurs should be more than the applied stress during a short-circuit event. The important parameters on which the critical buckling stress depends are the inner winding radial dimension, number and dimension of strands, distance between the two adjacent axial sticks, dimension of the axial sticks, proof stress of the conductor material, etc. In literature, for the given geometrical details of the inner winding, the variation of critical stress with the number of axial sticks and the value of proof stress of the conductor material are not reported. In this letter, the effects of varying the number of axial sticks and the proof stress of the conductor material on the value of critical stress of the inner winding have been investigated. © 1986-2012 IEEE.

World University root node

Electrical Engineering

(SoE) School of Engineering

IEEE Transactions on Power Delivery

Effects of Axial Sticks and Proof Stress of Conductor Material on the Buckling Strength of Transformer Inner Winding

Phubbing is defined as ignoring people with whom you have a face-to-face relationship to attend to smartphones. The phenomenon of phubbing particularly affects the teenage and young segments of the population. The main problem lies in the impact it has on individuals’ social relationship. A lack of validated instruments to diagnose this phenomenon has been observed amongst the Spanish-speaking youth. The objective pursued with this research was to analyse the structural validity and reliability of the Spanish scale in a sample of 454 Peruvian university students. A reliability study was carried out following Cronbach and McDonald, complemented with an exploratory and confirmatory factor analysis. The results show good reliability and validity values. Finally, some aspects associated with users’ profiles in relation to the scale were discussed too. A need exists to have adapted instruments which permit to measure emerging social threats such as phubbing, so that risk profiles can be identified and for us to be able to act in time. Most of the students surveyed regularly engaged in phubbing, and a significant percentage of them had personal and social problems because of this, including lack of sleep hours or arguments with friends and relatives, to quote but two. &nbsp;

Fulltext

NAER

<a href="https://naerjournal.ua.es/article/view/v10n2-1">Scale for Measuring Phubbing in Peruvian University Students: Adaptation, Validation and Results of Its Application</a>

During a short circuit, the transformer's inner winding, which is supported by the inner support structure, may fail due to the buckling phenomenon. This occurs due to the generation of large radially inward electromagnetic force on the inner winding. In the literature, the effect of the number of axial supporting spacers on the critical buckling stress is reported, but there is no investigation about the effect of their circumferential width on the value of the critical buckling stress. In this letter, the effect of the circumferential width of the axial supporting spacers on the value of critical buckling stress of the transformer inner winding has been investigated. An algorithm has been given to calculate the critical buckling stress of the inner winding. A case study has been taken from the published work, and by varying the width of the spacers, the factor of safety against buckling has been determined. © 1986-2012 IEEE.

Effect of Width of Axial Supporting Spacers on the Buckling Strength of Transformer Inner Winding

During the winding process of a transformer, a residual strain is induced in its windings conductors. In this paper, the effect of the strain on the mechanical strength of transformer windings under the worst case condition of the short circuit has been investigated. The distribution of the residual strain in the conductors during its winding process has been determined analytically. The strain induced in the conductors under the action of radial short-circuit forces has been computed. The two strains are then added to obtain a resulting strain. By using the Ramberg-Osgood stress-strain relation of the conductor (copper) material, resulting stress is determined. A case study has been given where the presence of residual strain in the conductors of a power transformer has been taken into account for determining its mechanical strength under the worst case condition of short circuit. © 2015 IEEE.

An investigation of winding curvature effect on the mechanical strength of transformer windings

The buckling of conductors of inner windings in transformers is one of the major causes of their failures. It can occur when a large magnitude of radial short-circuit electromagnetic force acts on them. In this paper, initially, mechanical strains developed during winding processes and due to radial short-circuit forces have been determined. The two mechanical strains viz. the short-circuit induced strain and the winding process-induced strain are algebraically added to obtain their resulting strain. The stress corresponding to the resulting strain has been determined by using the Ramberg-Osgood stress-strain relation. The critical buckling stress has been calculated and compared with the resulting stress. The analytically obtained result of the strain induced in the winding conductor during its winding process has been verified using the finite-element method. A case study has been described in which the factor of safety against the buckling strength is determined. © 1986-2012 IEEE.

Analysis of buckling strength of inner windings in transformers under radial short-circuit forces

Spiraling of conductors in a helical winding of a transformer may lead to a catastrophic failure under the action of torsional short-circuit electromagnetic forces. Torsional forces are produced by the interaction of the axial component of the short-circuit current and the radial component of the leakage magnetic flux density. In this paper, 3-D magnetostatic analysis has been performed to determine the leakage magnetic-field distribution in a 130-MVA power transformer. Torsional electromagnetic forces are calculated from the analysis to determine circumferential displacements of conductors of its low-voltage helical winding. Furthermore, mechanical stress components are computed and a factor of safety is defined, which gives an indication as to whether the winding conductors are in the elastic or plastic zone. The numerical results thus obtained by the finite-element method are verified using the first principles from mechanics. The effect of looseness in the inner support structure on the von-Mises equivalent stress and, hence, on the factor of safety has been studied. © 1986-2012 IEEE.

Coupled electromagnetic-structural analysis of the spiraling phenomenon in a helical winding of a power transformer

Purpose - The purpose of this paper is to give a comprehensive description of various safety factors that need to be determined while assessing the short-circuit strength of transformers. Design/methodology/approach - Factors of safety are divided into two categories: radial and axial. Some of the latest approaches in assessing the strength are elaborated. Findings - Six major sets of calculations are identified: three each for radial and axial electromagnetic forces. Corresponding factors of safety are defined and calculated for practical transformers. These factors are related to the strength and stability aspects of windings. Research limitations/implications - The work gives pointers for further research at appropriate places while highlighting the challenges involved in the assessment of the short-circuit strength. Practical implications - The presented overview of the factors of safety can be a useful guide for the practicing transformer engineers. Originality/value - The main contribution of the reported work is in highlighting the intricacies associated with the subject of short-circuit strength of power transformers. It can serve as a reference document for future research works in the area since the procedures are outlined for calculating the factors of safety through six case studies. © 2012 Emerald Group Publishing Limited. All rights reserved.

COMPEL - The International Journal for Computation and Mathematics in Electrical and Electronic Engineering

Towards short-circuit proof design of power transformers

The tilting phenomenon may lead to a catastrophic failure, such as an interturn fault in transformers, under the action of axial short-circuit electromagnetic forces. In this paper, first, a state-space approach has been used to determine the eigenvalues of various winding configurations used in practice by assuming a small value of tilt angle up to 10°. These eigenvalues decide the critical tilting forces and the natural frequencies of windings. The four cases involving disk, layer, helical windings (all these with strip conductor), and layer winding with continuously transposed cable conductor have been analyzed. Further, initial critical tilt angles are determined for various magnitudes of the axial force in a typical 5-MVA transformer. © 2011 IEEE.

Eigenvalue analysis for investigation of tilting of transformer winding conductors under axial short-circuit forces

Dynamic axial displacement of high voltage (HV) winding disk of a power transformer has been calculated by Green's function approach, when time varying axial electromagnetic forces corresponding to worst case of short circuit condition, are applied. An elaborate analysis of the axial electromagnetic forces and corresponding axial displacement of a top-end disk of HV winding is carried out. Under the action of these time varying forces, the winding moves in the axial direction as a function of time between radially placed insulation spacers. Between the spacer supports the winding sections can be considered as clamped-clamped (C-C) beams. Static Green's function of such a beam structure is determined first, and convolving it with axial electromagnetic force determines the axial displacement (bending) at any point on the beam for the purpose of verification of the methodology. Dynamic Green's function of the same winding sector is subsequently derived, which is used to obtain displacement of the winding section by convolving it with an applied time varying axial electromagnetic force. The results are verified with commercial FEM software. © 2010 - IOS Press and the authors.