Unbalanced line currents cause unbalanced voltage drops on the three phases of the supply system. Consequently, the voltage system within the supply network will become unbalanced. Voltage unbalance has different detrimental effects in electrical power systems, such as the growth of losses in drive systems and adjustable speed drives, supplementary heating, line-current unbalance, derating, torque pulsation, mechanical stresses, etc. This paper makes an effort to have a comprehensive analysis of the effects of different connection types of three phase transformers on voltage unbalance propagation in distribution networks. The indices of voltage unbalance factor (VUF) and current unbalance factor (IUF) are used in this paper to evaluate the unbalance propagation. These indices are acquired utilizing symmetrical component theory on three phase voltages and currents earned through the system impedance matrix. © 2012 IEEE.
Precise speed control of a Linear Induction Motor (LIM) drive becomes a complex issue due to the end effect phenomena which results in the weakening of the airgap flux and thrust. The end effect becomes severe when the LIM drive operates at higher speeds. The main purpose of this paper is to present an accurate qd dynamic model of linear induction motor suitable for vector control and drive applications considering the end effects. In this model not only the magnetizing inductance is modified but also the series resistance reflecting the eddy current is considered in the series with the magnetizing branch in both q and d axes. Moreover, a corresponding indirect field oriented control (IFOC) scheme is suggested. The effectiveness of the proposed IFOC scheme based LIM drive is verified by simulation results at different operating conditions. In addition, a five-level Cascaded H-bridge (CHB) inverter with multiband hysteresis modulation has been successfully applied for drive performance improvements. The results prove that the proposed LIM model and its related IFOC scheme show more accurate and comprehensive resultants and are therefore closer to the reality. Furthermore, utilization of the multilevel CHB inverter guarantees high drive performance and perfect control characteristics. ©2013 IEEE.
Publication Date: 2014
Transport (16484142)29(1)pp. 28-35
The evaluation of railway line capacity is an important problem, which effects majority of problems in rail transportation planning. The railway capacity is dependent on infrastructure, traffic, and operating parameters. A key factor affecting railway line capacity is the impact of different train types. As the combination of different train types increases, more interference is generated. In this paper, for evaluation of train type interactions on railway line capacity, an integer-programming model for both line and line section is presented. The problem is formulated as a multicommodity network design model on a space-discrete time network. The railway capacity is calculated using data typically available to planners. The inputs of the model are the characteristic of each train type and railway line attributes. The model determines railway capacity based on train type mixes. In addition, this model considers impact of train types on capacity and waiting time. In order to show the features of the model, a case study is implemented in Iran Railways. The capacity tends to increase non-linearly with small incremental changes in parameters. The mixture of train types reduces the railway line capacity. The proposed model can help railway managers for long-term planning. © 2014 Copyright © 2014 Vilnius Gediminas Technical University (VGTU) Press.
Yaghini, M.,
Sarmadi, M.,
Nikoo, N.,
Momeni, M. Publication Date: 2014
Networks and Spatial Economics (1566113X)14(3-4)pp. 317-333
In this paper, a compressed timetable is generated to calculate capacity consumption for under construction railway routes using an optimization approach. Since the detailed timetable for under construction routes does not exist, the timetable is not required in the applied model. The model generates a compressed timetable based on UIC 406 method. The capacity consumption problem is formulated as a multicommodity network design model on a space-discrete time network. A local branching heuristic algorithm is proposed to solve the model. The main idea underlining the local branching algorithm is the utilization of a general mixed integer programming solver to explore neighborhoods and locally search around the best-known solution by employing tree search. The parameters of the algorithm are tuned by using design of experiments. The proposed method is implemented in Iran Railways and the results are reported. © 2014, Springer Science+Business Media New York.
Ziari, H.,
Farahani h., H.Z.,
Goli, A.,
Galooyak, S.S. Publication Date: 2014
Petroleum Science and Technology (15322459)32(17)pp. 2102-2108
With the increase of traffic and consequently, and the loads applied on the roads, the need for a more durable pavement has a special significance. Therefore, the researchers have been seeking to improve the functional properties of bitumen and asphalt. For this reason, different materials have been used to modify these properties. In this study, the carbon nano tube (CNT) has been used as the modifier of bitumen performance. The use of this additive has improved both the classic (softening point, penetration degree, and so on) and performance (complex modulus, phase angle, fatigue parameter, rutting factor) properties of bitumen in comparison to the standard bitumen. © Taylor & Francis Group, LLC.
