Abstract
The objective of this paper is to analyse the steady state and dynamic behaviour of a MicroGrid system containing one microturbine generating Combined Heat and Power feeding some small local loads in islanded mode of operation. Future operating scenarios were also analysed and simulated, namely considering the installation of photovoltaic panels near consumers.

Abstract
In this paper it is proposed a probabilistic stead-state security assessment of an electric power system using a Monte Carlo method. This approach evaluates a probabilistic measure of the system security, instead of just a particular response to a specified contingency. Performance indices are used to assess the impact of the contingencies in the power system security. These indices allow to accurately evaluate the influence of the overloads, voltage limit violations and voltage stability problems in the power network. A probabilistic version the SECURsySTEM software package developed by the authors was applied to the IEEE 118 busbars test power system. During the simulation time, the occurrence of contingencies and the subsequent protective actions are assumed as a stochastic process. Finally, some conclusions that provide a valuable contribution to the understanding of the power system security analysis are pointed out.

Abstract
With the development of electric power systems and their increase of complexity, basically due to the interconnection to other production centres, impose the necessity of introduction of new control system techniques. The efficiency of these control centres is only possible if data received from network arrives quickly and with accuracy. The basic task of a system operation is to get a reliable and accurate real time network model. In the past and even in the present, the real time network model is obtained by the use of System Control and Data Acquisition (SCADA) and processing of the SCADA data via state estimator algorithms. Today's reality is different, intelligent electronic devices (IEDs), digital fault recorders (DFRs), phase measurement units (PMUs) and relays, collects an enormous amount of data that arrives to control centres through SCADA system. So, other ways to validate and utilize this data are needed.

Abstract
In recent years, the electricity sector undergoes a restructuring process, operationally and commercially, moving from a vertical integrated model to a market oriented model. With past and current difficulties in building new transmission lines and the significant increase in power transactions associated with competitive electricity markets, maintaining system security, with special regard to voltage instability/collapse issues, is more than ever one of the main concerns for market and system operators. Voltage is most readily controlled by adjustments to reactive power injections in power system. Reactive power can be produced and absorbed by both generation and transmission equipment. System operators, transmission owners, generators, customers, power marketers and government regulators need to pay close attention to voltage control. This paper is devoted to the study of the reactive power support for dynamic voltage stability of a restructured electric power system. A severe contingency situation was simulated. The automatic voltage regulators of the generating units and the mechanically switched shunt capacitors were modelled. The simulation results were obtained using the commercial transient software package EUROSTAG. Finally, some conclusions that provide a better understanding of the voltage collapse phenomena are pointed out.

Abstract
Actually, the electric energy has a high importance in all activities, namely, the economic activity and on its development. Sectors of activity like, communications, transports, illumination and many others industrial processes are sustained. With the increase of the global energy needs, and considering the Kyoto's protocol, the importance of green power as been increased. Based in that scenario, it's easy to understand the appearance of new low capacity producers, which should satisfy certain operation parameters to be connected to the network. Connections of small electric energy producers lead to some problems related with the voltage stability on transport and distribution systems, being crucial the satisfaction of several parameters with the objective to guarantee the electric system stability. In this article, the state of the art for the stability problems in power systems is made, being specially analyzed the Portuguese case. It's also analyzed lower producers response on voltage collapse and the parameters that they should satisfy in those situations.

Abstract
Nowadays when utilities are faced with increasing requirements regarding Quality of Service, it is important to be aware that severe contingencies can happen, in an unpredictable way which far exceeds all the security principles used for planning and system operation. In any electricity transmission system, a security condition must be assured - either in steady or in transient state - otherwise the essential service provided to costumers could be severely jeopardized. Present day Quality of Service requirements that are imposed on the electrical utility companies force them to develop efficient processes to analyze and react to incidents that can happen in an unpredictable way and far exceed all the security principles used. The simulation and analysis of these scenarios allow us to minimize the risk of system unbalance and voltage collapse. The steady state simulations of the Portuguese Transmission System were made in PSS/E software from Siemens Power Transmission Distribution, Inc., using savecases that represent pictures of the real system. The simulation results presented focus on aspects like energy not supplied, generation lost and topological changes resulting from an incident, which will affect mainly the power flow distribution within the grid elements that will remain in service (connected) and the voltage level in the system bus-bars. These results allow us to be better prepared to face these severe disturbances, defining procedures for emergency situation and training the control room operators.