2001 IEEE Porto Power Tech Proceedings (Cat. No.01EX502)

Corresponding to the increasing capacity utilization of power systems, a systematic use of the load-flow controlling capabilities of multifunctional FACTS devices can increase the available transfer capability (ATC) enabling additionally demanded power transits. For an effective power transit control, the aptitude of possible locations of FACTS devices is assessed by a sensitivity analysis based o... View full abstract»

In keeping with European Union Directives for promoting renewable based energy, a significant increase in installed wind and small-hydro power is expected in Portugal in ten years. A significant part of the identified renewable potential is located in the Northwest region, where a power generation surplus already exists. Therefore, expansion of the existing transmission grid is required, in order ... View full abstract»

Energy market opening, with higher net utilization, and increasing competition are urgently requiring a solution to strongly limit loop flows. This paper presents an approach to manage loop flow problem in liberalized power systems. This methodology, which involves implementation of FACTS devices, also applies network reduction models towards a solution of the problem in the real networks. A UPFC ... View full abstract»

With increasing focus on economical as well as environmentally friendly means for mass transit, rail transport is getting renewed momentum in many countries. This means investing in novel rail infrastructure as well as upgrading and electrifying of existing facilities. The feeding of heavy rolling stock from AC grids will in many cases cause unacceptable voltage drops as well as unsymmetry between... View full abstract»

A new computer model is presented for precise calculation of sag and tensions of composite conductors for overhead lines. All the effects known to increase the sag are accounted for: residual deformations, evolution of creep with time, compression in aluminum layer of ACSR conductors at high temperature, etc. This general model can also be applied for the simpler cases of one-material conductors a... View full abstract»

The legislation currently in force that affects the construction of overhead electricity transmission or distribution lines establishes an extensive number of conditioning factors as regards licences, public exposition of projects, rights regarding the presentation of allegations, etc. For that reason, the period that can elapse between the time the need for the installation of a new line is detec... View full abstract»

Changing the earthing system of medium voltage networks is a complex operation. It is necessary to take into account all the various technical aspects of the totality of the equipment involved in this process. Frequently, considerable additional economic investment is required as a result of this analysis of technical aspects. However, there are good reasons for reconsidering this possibility when... View full abstract»

There is a large bibliography in simulation models for linear induction motors (LIMs). However, most of them only consider steady state performance. LIMs working as linear drives generally operate under transient conditions. The aim of this paper is to investigate the suitability of different mathematical models to simulate LIMs as linear drives. A study of most major techniques of calculating lum... View full abstract»

The aim of this work is to present a mathematical model for the linear induction motor, this model allows estimation of its efficiency, considering the winding space harmonics. This work followed the strategy of research among rotary machines to find the one which could be the base of all the studies. The machine found, was the rotary three-phase asymmetrical induction motor. This is justified by ... View full abstract»

In order to investigate transient performance problems in isolated power systems an accurate system dynamic model is required. Real measurements, under specific system operational conditions, have been used for the identification of the conventional generator unknown parameters. Frequency and power variations, resulting from the formulation model using the estimated parameters, are compared with t... View full abstract»

This paper presents prime mover models suitable for island operation simulation. It deals with the design principles of a power station with gas unit from power station-network interaction point of view. View full abstract»

The paper describes some of the investigations made in order to evaluate the possibilities for defining a model valid for a class of distribution transformers (10/0.4 kV) covering the frequency range from the operational frequency to above the most dominating disturbing frequencies. The work reported covers both an analytical description of the semi-ideal /spl Delta/-Y/sub 0/ coupled transformer; ... View full abstract»

The brushless excitation of synchronous machines is an attractive solution for wound rotor machines, since no slip-rings are necessary. The paper investigates the rotating transformer method. For controlling the input voltage of the exciter AC chopper is proposed. Two kinds of the AC choppers are investigated, discussed and compared mainly considering the additional losses, which is important at t... View full abstract»

A twin polarimetric configuration based on the Faraday effect for the measurement of electric currents in high voltage environments is presented. Field test results are shown that indicate the device suitability for current metering and relaying applications. View full abstract»

This paper proposes an equation that provides an estimation for the number of forests (n/sub F/) that can be generated from another forest considering only one pair of changes with the number of nodes and edges maintained. This calculus is important for a variety of problems in distribution systems including planning, restoration, losses and voltage drop minimization. View full abstract»

An improved hybrid method is discussed, employing a finite-element method along with Faraday's law and standard circuit analysis, in order to predict the induced voltages and currents on a pipeline with defects on its coating, running parallel to a faulted line and remote earth. Such defects are a frequent situation especially when old pipelines are considered and are modeled as resistances, calle... View full abstract»

The protection of the environment requires compact EHV tower constructions. This trend results in decreasing the clearances and phase-to-phase distances. It is expected, that both the number of faults and the amplitude of the secondary arc current will grow in the future. All these make it necessary to improve the efficiency of single-phase reclosing. Secondary arc duration values gained at field ... View full abstract»

Transients resulting from switching of capacitor banks in electrical distribution systems affects power quality. The transient overvoltages can theoretically reach peak phase to earth values in the order of 2.0 p.u. High current transients can reach values to ten times the capacitor nominal current with duration of several milliseconds. Another severe operating condition is the switching on a seco... View full abstract»

Induction machines are mostly used as generators in wind power stations. Since induction machines also have a stability problem, it is important to analyze the transient stability of the power system including wind power stations. This paper presents simulation analyses of transient stability of a power system including an induction generator performed by PSCAD/EMTDC. View full abstract»

The KEPS Real Time Digital Simulator (RTDS/sup (R)/) is the largest real time power system simulator ever built. A power system which includes 320 (3-phase) buses and 90 generators has been modeled and run in real time. Since such large-scale systems were involved, it was not practical to validate them using nonreal time electromagnetic transient programs such as EMTDC/sup TM/ or EMTP. Instead, th... View full abstract»

This paper presents studies carried out on the Hellenic system in order to assess the effect of the existence of only one main interconnection with the rest Balkan system, the Bulgaria interconnection. The dynamic behavior is analyzed for selected disturbances and shows that for large generation loss in the Greek network there is isolation of the Greek system, due to the short activation time of t... View full abstract»

This work aims to develop a controller based on fuzzy logic to simulate a static voltage compensator in power system transient stability analysis. Performance comparisons are made between the developed controller and the SVC through transient stability analyses performed using an IEEE 14-bus system. View full abstract»

In this paper, a comprehensive analytical methodology for the analysis and study of subsynchronous torsional interactions (SSTI) between turbine-generators and static VAr compensators (SVCs) embedded in a series capacitive-compensated AC power network is presented. Emphasis is being placed upon the study of the effect of load characteristics on SSTI. The methodology is based on a flexible approach... View full abstract»

The distribution capability for additional DECS-power of the existing distribution network is an important criteria for the soon-coming increasing installation of e.g. fuel-cell-systems for house supplying. In this paper, a method is described which allows the calculation of the maximum cumulated DECS-power of individual distribution networks. The calculation is based on an optimization problem, a... View full abstract»