Need of computer control of power systems 1)The number of variables involved in a very large power System,the quantity of data to be processed and the complexity and variety of decisions that have to be taken keeping in the view the large number of constrains involved makes the instrument and controller more complecated . Note:The Controllers are replaced by a computer Or When a computer introduced into a loop,the process is said to be Computer Control. 2)Ability to perform operation at an unattended location from an attended station Or operating center. 3)Speed Reliability and accuracy. 4)Increase in unit size, growth of interconnected and the need to maintain the system in normal mode require sophisticated control, instrumentation and protectionconcept of energy control centers and functions— * The energy control centre (ECC) has traditionally been the decision-centre for the electric transmission and generation interconnected system. The ECC provides the functions necessary for monitoring and coordinating the minute-by-minute physical and economic operation of the power system. * There are 4 types of control centres. i) Local Control Centre ii) Area Load Dispatch Centre iii) State Load Dispatch Centre iv) Regional Control Centre.concept of energy control centers and functions— First Generating stations, Local Control Centre Substations Second ‘Sub transmission & Area Load Dispatch Centre ‘Transmission Network Third ‘Transmission System State Load Dispatch Centre Fourth Interconnected Power Regional Control Centre ‘Systems. + These are run in an off-line or via a remote terminal linked to a large computer centre. Local Control Centre : A number of control functions are performed locally at the power stations and substations. The typical controls carried in the local control centre are,concept of energy control centers and functions— Area Load Dispatch Centre : In this, groups of generating stations or substations control are carried out. This requires system data a network topology for control. State Load Dispatch Centre : In this centre, all the information is received from area load dispatch center and local centers. Then minute- to-minute operation of the power system at the state level is carried out. It may have the following functions (1)System Generation and Load Monitoring and Control for Demand Control. (2)System wide State Monitoring and Control (3)Circuit Breaker Condition Monitoring and Control (3) Load Shedding and Restoration (4) Supervisory Control for Transmission Lines and Equipments. 5)System Alarm Monitoring and Corrective Actions.6) Planning and Monitoring of Power System Operationconcept of energy control centers and functions— PMU Regional Control Centre ‘The Regional Load Dispatch Centre may be regarded as a coordinating and monitoring center for state level load dispatch center with covering main objectives: 1) Integrated Operation of State Level Dispatch centre 2)Operation and Maintenance Schedules for maximum capacity Utilization 3)Operation and Maintenance Schedules for Generating Plants 4)Monitor and Control of inter-state Power Transactions 5)Monitor and Control of inter-regional Power TransactionsPMU Function of PMU:(PMU-Phasor Measurement Unit) + Aphasor measurement unit (PMU) measures the phasor values of current and voltage. Note: Synchrophasors are time-synchronized numbers that represent both the magnitude and phase angle of the sine waves found in electricity, and are time-synchronized for accuracy. They are measured by high-speed monitors called Phasor Measurement Units (PMUs) that are 100 times faster than SCADA. * PMU measurements record grid conditions with great accuracy and offer insight into grid stability or stress. * Phasor measurement units (PMUs) and its measured synchrophasors make a valuable contribution to the dynamic monitoring of transient processes in energy supply systems.System Monitoring “© The prerequisite for security assessment of a power system is the knowledge of the system states. Monitoring the system is therefore the Ist step. Measurement devices dispersed throughout the system help in getting a picture of the current operating state. The measurements can be in the form of power injections, power flows, voltage, current, status of circuit breakers, switches, transformer taps, generator output etc., which are telemetered to the control centre, © Usually a state estimator is used in the control centre to process these telemetered data and compute the best estimates of the system states. 4 Remote control of the circuit breakers, disconnector switches, transformer taps ete. is generally possible. The entire measurement and control system is commonly known as supervisory control and data acquisition (SCADA) system.Data acquisition and controls + Data acquisition provides operators and computer control systems with status and measurement information needed to supervise overall operations. Security control analyses the consequences of faults to establish operating conditions. Data acquisition and remote control is performed by computer systems called supervisory control and data acquisition (SCADA) systems. * ASCADA system consists of a master station and remote terminal unit (RTU). * Master station communicates information to the RTU for observing and controlling plants.Data acquisition and controls RTUs are installed at generating station or transmission substation or distribution substation. RTUs transmitting status of the device and measurements to master station and receive control commands from the master station. The transients may be in the form of voltage or current fluctuations. Ina real power system, the transient may result in the failure of components and it is sometimes difficult to trace the origin of disturbance. Using a Data Acquisition System, the transients can be reduced and analyzedData acquisition and controls Atypical Energy Control Centre can perform the following functions: 1. Lond forecasting: Load should be estimated in advanee. 1H. Power system planning: > Forgeneration > Fortransmission and dstetbution (should aim a excess capacity than load), {i Unit Commitment: The constuns are ~ spinning reserve, minimum up time, minimum dow time, hydro constrains and fuel constraints. |v, Maintenance scheduling: The planned maintenance outage ofthe generation equipment over a given faure perio. Security monitoring: The on-line process using rea time data for analyzing the effects of ‘outages contingencies on the steady sate performance of the system. ML Stae estimation: It isthe process of estimating the tate. When based on system monitoring data, it produces best estimates ofthe power system sate, ‘il Reonomle dlspatch: Iie to distribute the load among the generating nis soa to minimize the total coat ofthe system,‘System hardware configurations- SCADA and EMS functions Supervisory control and data acquisition system(SCADA): * It consists of a master station and remote terminal unit (RTU) linked by ‘communication channel. The hardware components can be classified into: 1. Process computer and associated hardware at the Energy Control Centre 2. RTUs and the associated hardware atthe remote stations. 3. Communication equipment that links the RTUs and process computers at the master lation, System Hardware Configuration: ‘+ The supervisory control and data acquisition system(SCADA) allows afew operators to monitor the generation and HV transmission system, *+ Consistent with principles of high reliability and safe features, electric utes have almost universally applied a redundant set of dual digital computers forthe functions of remote data aequistion control, energy management and system security. + Both computers he devices sic asp Incr own core memory and drive an extensive numberof input-outpat fer, teletypes, magnetic tape dive, a disks ado on‘System hardware configurations- SCADA and EMS functions + Usually one computer, the on units, is monitoring and controlling the power system. + The backup computer may be executing off-line batch programs such as load forecasting to bhydro-thermal allocation, + The on-line computer periodically updates a is: niemory shared betwen the Ho competeSystem hardware configurations- SCADA and EMS functions The above figure gives a detailed block diagram of atypical digital computer control and monitoring for power systems. The information used by the on-line computer has a maximum age of update cycle. *+ Upon a fail over or switch-in status command, the stored information of the common disk is inserted in the memory of the on-line computer. + Allof the peripheral equipment is interfaced with the computer through input-output ‘microprocessors that have been programmed to communicate, as well as preprocess the analog information, check for limits, convert to another system of units and so on. Typically, the following categories are scanned every two seconds. > All status points such as switchgear position, substation loads and voltages, transformer tap positions and capacitor banks, > Ticcline flows and interchanges schedules > Generators loads, voltage, operating limits ad boiler capacity. > Telemetry verification to detect failures and errors in the remote bilateral communication links between the digital computer and the remote equipment.(Note:Telementry-May ba analog Or digital)System hardware configurations- SCADA and EMS functions Function of SCADA: Data acquisition Information display. . Supervisory Control (CBs:ON/OFF, Generator: stop/start, RAISE/LOWER command) |. Information storage and result display. 5. Sequence of events acquisition, Remote terminal unit processing, . General maintenance. 3. Runtime status verification. ). Economic modeling 10. Remote start/stop, 11, Load matching based on economics. 12. Load shedding.System hardware configurations- SCADA and EMS functions EMS(Energy Management System): + Energy management is the process of monitoring, coordinating and controlling the generation, transmission and distribution of electrical energy. * Itis performed at centres called ‘system control centres’, by a computer system called Energy Management System (EMS). + Data acquisition and remote control is performed by the computer system called SCADA, which forms the front end of EMS. * The EMS communicates with generating, transmission and distribution systems through SCADA systems.