Abstract
Voltage stability is an important concern of power system managers not only in the net planning phase but also in operation. This issue has become especially critical in recent years due to the deregulation phenomenon because of new exploration policies complying a system operation closer to its security limits. In particular, voltage collapse distance may approach emergency values or, in the worst case, make the system collapse. As voltage profile is extremely dependent on reactive power compensation, most common approaches integrate both objectives in the operation setting phase, trying to optimize reactive power production taking voltage profile into consideration. In this paper, authors propose an evolutionary approach application to the same problem but in the planning phase. It is shown that the cooperative procedure of planning and preventive control provides better solutions that if one deals with these issues one at a time. © 2001 IEEE.

Abstract
This paper deals with a problem of identification of the best subset of variables that should be used for dynamic security assessment of a power system, when this task is pro-vided by artificial neural networks (ANN)- The approach de-scribed here exploits ANN output sensitivities relatively to the inputs and correlation degrees, to identify the most relevant system variables to be used for an effective security assessment task. The ANNs are initially trained with all low-correlated candidate features, which enables the sensitivity analyses for the initial set of system features. Derivatives of the ANN output relatively to each input are obtained by exploiting the chain rule, similar to the one used for weights adaptation on Back-propagation Algorithm. A description of the application of this approach in a real system is present in the paper. Results obtained in the dynamic security assessment problem of the network of the island of Crete were quite successful. © 2001 IEEE.

Abstract
Feature subset selection is a central issue in a vast diversity of problems including classification, function approximation, machine learning and adaptive control. On a wide variety of applications, especially when using real data, input features may be not independent and output variable depends on the relationship among inputs rather than on input values themselves. Feature selection methods that assume independence of attributes will fail on these cases. On the other side, most of alternative approaches are quasi-exhaustive, requiring large CPU processing time. In this paper, an alternative methodology based on sensitivity analysis of trained artificial neural networks (ANN) is analyzed. Results so far attained on illustrative toy examples and on real data support the validity of the developed approach.

Abstract

Abstract
In this paper, we present a prototype of a DMS -Distribution Management System - using Object Oriented technology and a modular distributed multitask client-server architecture. The DMS is supported by an Object Oriented model in which the power system components are considered objects grouped in several classes according to their characteristics. The power system applications are software modules within this base platform that is physically located in a WEB server and are implemented in Java or C++. The users should connect to an HTML page in the server, download the desired applet to the client's machine establishing communication, interfaces and requesting services to the main system. The paper gives a global overview of the system, describes its architecture, gives details about the Database organization and describes the main characteristics and features of some power system applications as Topology Processor, Single Phase Power Flow and Symmetric Short Circuit. © 2001 IEEE.

Abstract
In the scope of a consultancy study conducted by the Power Systems Unit of INESC Porto, the yearly regulated remuneration of the Portuguese transmission provider was allocated to the network users considering an approach based on power-flow embedded methods. The tested cost allocation methods were the MW.mile, the Modulus and the Zero Counterflow. The application of that approach lead to geographically discriminated Tariffs for Use of Transmission Networks. This study must be considered as a contribution to the revision process of the current regulations when the first regulatory period is about to end. It should be emphasized that it was not the purpose of this study to question the current Cost of Service/Rate of Return strategy in force in the Portuguese transmission sector and to calculate the adequate yearly remuneration of the transmission provider. The only objective of this study was to simulate the application of alternative cost allocation approaches, given that the whole amount to allocate is fixed by current rules. In this way, we think it is possible to contribute to a more technically sounded discussion about the advantages and drawbacks of several approaches. © 2001 IEEE.