         DISTRIBUTED HUNTING SYSTEM OF VOLTAGE SAG EVENTS   Tiberiu Letia, Adina Astilean, Camelia Avram, Mircea Chindris, Andrei Cziker, Mihai Hulea   Technical University of Cluj Napoca, Cluj Napoca, Romania    Abstract: A new distributed approach for monitoring the voltage events (sags and overvoltage) in electric power system is proposed. The distributed monitoring system is implemented on a set of microcontrollers connected to personal computers that are linked through Internet. The microcontrollers endowed with voltage transducers implement information agents that communicate to a software multiagent-agent system when voltage events occur. The users of the power system can get information about events occurred during a period of time. Copyright © 2007 IFAC  Keywords: electric power systems, monitoring elements, discrete event systems, real-time systems, information systems.      1. INTRODUCTION  Modern power systems are subjected to important changes from a centralized architecture to a distributed one; this process is driven by the requirements set due to (i) the liberalization of electricity markets, and (ii) the trends towards renewable energy. As there are many players at different levels and there is not always a single controlling body, there is a large amount of information exchanged among different actors in such a distributed environment. Both energy and information flow need to be dependable: reliability, availability and integrity requirements are to be fulfilled (Van de Veyver, 2003). In these conditions, the problems related to power quality (PQ) have become very important, due to the extended use of power electronic based systems both by users and suppliers. The overall level of disturbances on the power system has increased, while many more sensitive devices, especially information and communication equipment, are connected to it. Unfortunately, some information indicates that reliability and quality of the supply are expected to decrease following deregulation of energy market. Indeed, a possible effect of deregulation is the reduction of investment in new infrastructure and the maintenance of the existing power system. Therefore, the deregulation of the electrical market is expected to have consistent effects on power quality, both from technical and legal/economical point of view, as these new conditions will lead to a raise of different incidents. Deregulation of energy market and the distributed architecture of the power system also play an important role as far as responsibilities for bad power quality are concerned. In these conditions it is more difficult to solve responsibility issues connected to damage of processes or machinery due to low supply quality, or simply to customer dissatisfaction. There are many types of power quality problems that could occur in a public electricity-supply system. A considerable number of events that occur on the utility grid are voltage sags. The voltage sag, according to EPRI (Electric Power Research Institute), is the most significant power quality problem. It affects service and IFAC Workshop ICPS'07 2007, July 09-11 Cluj-Napoca, Romania -240-