Alarms: Informs operator of unplanned events and undesirable operating conditions. Alarms are sorted by criticality, area of responsibility, and chronology. Acknowledgment may be required. Logging: Logs all operator entry, all alarms, and selected information Load shed: Provides both automatic and operator-initiated tripping of load in response to system emergencies. Trending: Plots measurements on selected time scales Since the master station is critical to power system operations, its functions are generally distributed among several computer systems depending on specific design. A dual computer system configured in primary and standby modes is most common SCADA functions are listed below without stating which computer has specific Manage communication circuit configuration Downline load RTU files Maintain scan tables and Check and correct message errors Convert to engineering units Detect status and measurement changes Monitor abnormal and out-of-limit conditions Log and time-tag sequence of events Respond to operator request Display information Acknowledge alarms Transmit control action to rtus Inhibit unauthorized actions Maintain historical files Log events and prepare reports Perform load shedding 67.3 Automatic Generation Control Automatic generation control (AGC) consists of two major and several minor functions that operate on-line in real time to adjust the generation against load at minimum cost. The major functions are load frequency control and economic dispatch, each of which is described below. The minor functions are reserve monitoring, which assures enough reserve on the system, interchange scheduling, which initiates and completes scheduled inter hanges, and other similar monitoring and recording functions. Load Frequency Control Load frequency control (LFC)has to achieve three primary objectives which are stated below in priority order 1. To maintain frequency at the scheduled value 2. To maintain net power interchanges with neighboring control areas at the scheduled values 3. To maintain power allocation among units at economically desired values The first and second objectives are met by monitoring an error signal, called area control error (ACE), which is a combination of net interchange error and frequency error and represents the power imbalance between c 2000 by CRC Press LLC© 2000 by CRC Press LLC • Alarms: Informs operator of unplanned events and undesirable operating conditions. Alarms are sorted by criticality, area of responsibility, and chronology. Acknowledgment may be required. • Logging: Logs all operator entry, all alarms, and selected information. • Load shed: Provides both automatic and operator-initiated tripping of load in response to system emergencies. • Trending: Plots measurements on selected time scales. Since the master station is critical to power system operations, its functions are generally distributed among several computer systems depending on specific design. A dual computer system configured in primary and standby modes is most common. SCADA functions are listed below without stating which computer has specific responsibility. • Manage communication circuit configuration • Downline load RTU files • Maintain scan tables and perform polling • Check and correct message errors • Convert to engineering units • Detect status and measurement changes • Monitor abnormal and out-of-limit conditions • Log and time-tag sequence of events • Detect and annunciate alarms • Respond to operator requests to: Display information Enter data Execute control action Acknowledge alarms • Transmit control action to RTUs • Inhibit unauthorized actions • Maintain historical files • Log events and prepare reports • Perform load shedding 67.3 Automatic Generation Control Automatic generation control (AGC) consists of two major and several minor functions that operate on-line in real time to adjust the generation against load at minimum cost. The major functions are load frequency control and economic dispatch, each of which is described below. The minor functions are reserve monitoring, which assures enough reserve on the system, interchange scheduling, which initiates and completes scheduled inter￾changes, and other similar monitoring and recording functions. Load Frequency Control Load frequency control (LFC) has to achieve three primary objectives which are stated below in priority order: 1. To maintain frequency at the scheduled value 2. To maintain net power interchanges with neighboring control areas at the scheduled values 3. To maintain power allocation among units at economically desired values The first and second objectives are met by monitoring an error signal, called area control error (ACE), which is a combination of net interchange error and frequency error and represents the power imbalance between