FIGURE 67.1 Central dispatch operation arena of Entergy Corporation's Beaumont Control Center(Beaumont, Texas) OPERATING SYSTEM DATAbASE UTILITIES, SERVICES APPLICATIONS Operations Training AUTOMATIC ERATION Supervisory CONTROL POWER SYSTEM Contro SECURITY ONTROL FIGURE 67.2 Layers of a modern EMS. 67.2 Power System Data acquisition and Control A SCADA system consists of a master station that communicates with remote terminal units(rTUs) for the purpose of allowing operators to observe and control physical plants. Generating plants and transmission substations certainly justify RTUs, and their installation is becoming more common in distribution substations as costs decrease. RTUs transmit device status and measurements to, and receive control commands and setpoint data from, the master station. Communication is generally via dedicated circuits operating in the range of 600 to 4800 bits/s with the RTU responding to periodic requests initiated from the master station(polling)every 2 to 10 s, depending on the criticality of the data The traditional functions of SCADA systems are summarized Data acquisition: Provides telemetered measurements and status information to operator Supervisory control: Allows operator to remotely control devices, e.g., open and close circuit breakers A"select before operate" procedure is used for greater safety Tagging: Identifies a device as subject to specific operating restrictions and prevents unauthorized operation. c2000 by CRC Press LLC© 2000 by CRC Press LLC 67.2 Power System Data Acquisition and Control A SCADA system consists of a master station that communicates with remote terminal units (RTUs) for the purpose of allowing operators to observe and control physical plants. Generating plants and transmission substations certainly justify RTUs, and their installation is becoming more common in distribution substations as costs decrease. RTUs transmit device status and measurements to, and receive control commands and setpoint data from, the master station. Communication is generally via dedicated circuits operating in the range of 600 to 4800 bits/s with the RTU responding to periodic requests initiated from the master station (polling) every 2 to 10 s, depending on the criticality of the data. The traditional functions of SCADA systems are summarized: • Data acquisition: Provides telemetered measurements and status information to operator. • Supervisory control: Allows operator to remotely control devices, e.g., open and close circuit breakers. A “select before operate” procedure is used for greater safety. • Tagging: Identifies a device as subject to specific operating restrictions and prevents unauthorized operation. FIGURE 67.1 Central dispatch operation arena of Entergy Corporation’s Beaumont Control Center (Beaumont, Texas) which includes a modern EMS. FIGURE 67.2 Layers of a modern EMS