System of choice

Wide-area measurements have been an integral part of power system operations for over six decades. They have been used in economic dispatch and automatic generation control systems in electric utility control centers using real-time measurements of power flows on remote tie lines and generator output powers. In the late 1960s a new class of wide-area measurement systems came into use--supervisory control and data acquisition (SCADA) systems--in order to provide real-time state estimates of the power system in the electric utility energy management systems (EMSs). Over the years, the "real time" in these SCADA-based measurements came to imply measurements performed over a data window of several seconds without regard to the precise instant when the measurements were made.