25 research outputs found
Investigation of loss of synchronism phenomenon in synchronous machines and protection using trajectory of relative speed
No full textThe "loss of synchronism" condition in a synchronous machine is a critical state where the rotor fails to stay synchronized with the stator magnetic field. This can be caused by various factors, including system disturbances and power system instabilities. A machine undergoing a loss of synchronism may experiences torsional stresses, increased rotor iron currents and winding stresses in their mechanical systems. Synchronous machine loss of synchronism protection is employed to promptly disconnect a machine operating asynchronously to avoid damage or degradation.
This thesis explores the loss of synchronism phenomenon in synchronous generators and introduces a novel loss of synchronism detection method based on the estimated relative speed of the rotor. The proposed algorithm utilizes readily available terminal voltage, current and machine parameters to estimate the rotor speed following a disturbance. It identifies loss of synchronism condition if the estimated relative speed tends to increase during a swing cycle. This method is computationally simple, easy to implement, and faster than impedance-based techniques under certain conditions. The sensitivity and security of this method is evaluated through time-domain simulations under various power system conditions. The performance of the proposed method is also compared against well established loss of synchronism protection schemes.
The occurrence of loss of synchronism in synchronous condensers has not been extensively studied, primarily due to its rarity in traditional power systems. However, with the increasing integration of inverter-based resources and associated grid issues, synchronous condensers have become more common. The literature indicates a considerable gap in understanding the loss of synchronism phenomenon in synchronous condensers, particularly under conditions where inverter-based resources dominate the power grid. This thesis examines the loss of synchronism phenomenon in synchronous condensers, including theoretical analysis using phasor diagrams of realistic scenarios. It also investigates the distinction between loss of synchronism and the pole slipping phenomenon, which has led to failures in traditional impedance-based schemes. The proposed relative speed-based method is applied to synchronous condensers and its effectiveness is demonstrated in situations where traditional schemes have failed.
Additionally, effectiveness of the proposed method in weak grids with a high penetration of inverter-based resources is analysed using a modified IEEE 39 bus system.February 202
Critical factors affecting efficient yard planning in a seaport container terminal
No full textOperations at a container yard within a port terminal represent one of the most complex aspects of terminal operations, as both inbound and outbound container flows must be handled simultaneously. Yard planning involves allocating appropriate storage locations for these containers in order to integrate all activities within the terminal area into a seamless operation. Consequently, yard planning directly influences port efficiency by addressing the storage allocation of inbound containers, the utilisation of yard equipment, and the retrieval sequence of outbound containers. Several factors determine the efficiency of the yard planning process. The main objective of this paper is to explore and identify the factors affecting yard planning and its efficiency from the perspective of port terminal executives. A questionnaire survey was conducted with the participation of 30 port industry professionals representing the three port terminals operating at the Port of Colombo in Sri Lanka. The study employs the Analytic Hierarchy Process (AHP) method to identify the critical factors influencing yard planning efficiency and to determine the relative weight of each factor. The paper further offers managerial and technical implications for improving yard planning in port terminal management
The impacts of 3D radiative transfer effects on cloud radiative property simulations and retrievals
No full textThis paper presents a new method for representing the important effects of horizontal radiation transport through cloud sides in two-stream radiation schemes. Ordinarily, the radiative transfer equations are discretized separately for the clear and cloudy regions within each model level, but here terms are introduced that represent the exchange of radiation laterally between regions and the resulting coupled equations are solved for each layer. This approach may be taken with both the direct incoming shortwave radiation, which is governed by Beer’s law, and the diffuse shortwave and longwave radiation, governed by the two-stream equations. The rate of lateral exchange is determined by the area of cloud “edge.” The validity of the method is demonstrated by comparing with rigorous 3D radiative transfer calculations in the literature for two cloud types in which the 3D effect is strong, specifically cumulus and aircraft contrails. The 3D effect on shortwave cloud radiative forcing varies between around −25% and around +100%, depending on solar zenith angle. Even with an otherwise very simplistic representation of the cloud, the new scheme exhibits good agreement with the rigorous calculations in the shortwave, opening the way for efficient yet accurate representation of this important effect in climate models.This work is supported by the grant CyberTraining: DSE: Cross-Training of Researchers in Computing, Applied Mathematics and Atmospheric Sciences using Advanced Cyberinfrastructure Resources from the National Science Foundation (grant no. OAC–1730250). This grant also supported co-author Chamara Rajapakshe as graduate assistant. The hardware in the UMBC High Performance Computing Facility (HPCF) is supported by the U.S. National Science Foundation through the MRI program (grant nos. CNS– 0821258, CNS–1228778 , and OAC–1726023) and the SCREMS program (grant no. DMS–
0821311), with additional substantial support from the University of Maryland, Baltimore County (UMBC). See hpcf.umbc.edu for more information on HPCF and the projects using its resources.https://userpages.umbc.edu/~gobbert/papers/CT2018Team5.pd
The Pearly Gates: A collection of science fiction short stories
No full textWhen Saint Peter passes through the pearly gates, he is confronted with a profound dilemma. By the year 2100, Earth stands on the brink of extinction, and humanity as a whole seeks admission to heaven. However, in accordance with the admission criteria of heaven, every individual is entitled to enter, potentially overwhelming the heavenly supply chain. Can Saint Peter find a solution?To discover the answer and enjoy an additional 14 captivating short stories, delve into this book. While it falls under the umbrella of science fiction, it offers a unique twist. The author delves deep into the realm of science itself, moving beyond the familiar territories of aliens and time travel. This book is crafted to cater to both science enthusiasts and those less versed in scientific matters.Chamara Panakaduwa, a proud product of the University of Salford, the University of Bedfordshire, and Birmingham City University, presents this distinct creation for aficionados of science fiction as well as casual readers. The book's distinctive flavour is its infusion of the concept of sustainability, a personal favourite of the author
A molecular dynamics study of thermal conductivity and viscosity in colloidal suspensions: From well-dispersed nanoparticles to nanoparticle aggregates
No full textSpatial Feature Reduction in Long-term EEG for Patient-specific Epileptic Seizure Event Detection
No full textAPPJ
No full textLack of knowledge and cultural or personal objections prevent women from using contraceptives even if they want to space or limit their pregnancies, thus leading to an unmet need for contraception. Utilizing secondary data from 4,129 ever-married women included in the 2000 Reproductive Health (RH) Baseline Surveys,
this article examines the relationship between selected psychosocial factors and unmet need. After controlling for the effects of attitude, a low level of knowledge was significantly associated with either unmet need for spacing (p<0.001) or limiting (p<0.001). By contrast, after controlling for the effects of age, the number of living children, knowledge and access to family planning services, the association of
negative attitude with unmet need was modified by educational level. In comparing women with a negative attitude to those with a positive one, the adjusted odds ratio of having unmet need for spacing (OR=3.8, 90 per cent CI=2.0-7.3) and unmet need for limiting (OR=2.2, 90 per cent CI=1.2-4.0) was found to be highest among those with low levels education. Meanwhile, no association existed between attitude and unmet need among women with tertiary
education.Abstracts ... 1
Articles
Addressing Unmet Need: Potential for Increasing Contraceptive Prevalence in the Philippines - By Paulyn Jean B. Acacio-Claro and Maridel P. Borja ... 5
Below to above Replacement: Dramatic Increase in Fertility and its Determinants in Sri Lanka - By W. Indralal De Silva, B. Nishanthi Perera and K. Chamara Anuranga ... 27
The Effect of Remittances on Return Migration and its Relation to Household Wealth: The Case of Rural Thailand - By Yuying Tong and Martin Piotrowski ... 53
Determinants of Living Arrangements of Elderly in Orissa, India: An Analysis - By A.K. Panigrahi ... 9
