TThe inTeresT in phasor measuremenT Technology has reached a peak in recent years, as the need for the best estimate of the power system's state is recognized to be a crucial element in improving its performance and its resilience in the face of catastrophic failures. in most countries installing the phasor measurement units (pmus) and getting to know the pmu system behavior through continuous observations of system events has been the first step. all installations are reaching for a hierarchical wide-area measurement system (Wams) so that the measurements obtained from various substations on the system can be collected at central locations from which various monitoring, protection, and control applications can be developed. in this article, experts from several countries summarize their Wams-related activities in some detail. it is of course not possible to claim that this is a complete list of countries pursuing this technology. To the best of our knowledge similar activities are also progressing in south africa, Taiwan, Japan, and several other countries. however, the contributions here provide an account of the most advanced stages in Wams development in major world economies.-A.G. Phadke The Brazilian national interconnect power system (sin) is characterized with a dominant hydroelectric power generation and long-distance power transfers from generation parks to load centers (Figure 1). studies for phasor measurement applications in Brazil were started in the early 1990s by the study committee of the interconnected operation coordination group (gcoi), prior to the deregulation of the Brazil energy sector. difficulties faced by the Brazilian economy during that decade and the restructuring process of the electric energy sector delayed the project.

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Monitoring of events in the power system provides a great deal of insight into the behavior of the system. Events with impact on the entire power system typically occur in or near the transmission network and are therefore best monitored at transmission system substations. This puts great demands on the equipment and in general restricts the use of the data since it becomes property of the transmission system operator. An alternative is to measure at lower voltage levels. This paper documents the close agreement between voltage and frequency at low and high voltage levels during a remote and a nearby fault in the transmission network. The very high quality of the data suggests that valuable information about the transmission system can be obtained at lower voltages.Index Terms-Power system dynamic stability, power system faults, power system monitoring.

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Distributed energy resources, such as wind turbine generators, often employ induction generators. When such a generator is subjected to a nearby fault, its rotor may accelerate and reach high steady-state speed far from that corresponding to the frequency of the system. This is the generator counterpart to induction motor stalling, which is classified as voltage stability. The phenomenon is a matter of stability, but it is not covered by current definitions of power system stability. We denote this type of stability as speed stability and propose a definition, which also includes induction motor stalling.