Supervision consists of commanding a process and supervising its working. To achieve this goal, the supervisory system of a process must collect, supervise and record important sources of data linked to the process, to detect the possible loss of functions and alert the human operator. The main objective of a supervisory system is to give the means to the human operator to control and to command a highly automated process. So, the supervision of industrial processes includes a set of tasks aimed at controlling a process and supervising its operation. Supervisory control and data acquisition systems (SCADA) are widely used in industry for supervisory control and data acquisition of industrial processes. The process can be industrial, infrastructure or facility. SCADA system is used to observe and supervise the shop floor equipment’s in various industrial automation applications. SCADA software, working on DOS and UNIX operating systems used in the 1980s, was an alarm-based program, which has a fairly simple visual interface.
The SCADA system usually consists of the following subsystems: (1) A Man-Machine Interface (MMI) is the apparatus which presents process data to a human operator, and through this, the human operator, monitors and controls the process. (2) A supervisory system, acquiring data on the process and sending commands to the process. (3) Remote Terminal Units (RTUs) connecting to sensors in the process, converting sensor signals to digital data and sending digital data to the supervisory system. (4) Communication infrastructure connecting the supervisory system to the RTUs. In fact, most control actions are performed automatically by RTU or by programmable logic controllers (PLC). Host control functions are usually restricted to basic overriding or supervisory level intervention. For example, a PLC may control the flow of cooling water through part of an industrial process, but the SCADA system may allow operators to change the set points for the flow, and enable alarm conditions, such as loss of flow and high temperature, to be displayed and recorded. The feedback control loop passes through the RTU or PLC, while the SCADA system monitors the overall performance of the loop. With the advances of electronic and software technologies, the SCADA systems are widely used in industrial plant automation. It provides an efficient tool to monitor and control equipment in manufacturing processes on-line. The SCADA automation system always includes several functions, e.g., signal sensing, control, human machine interface, management, and networking. The objective of this paper is to show interests of the use of a SCADA system for thermal power plants (TPPs). Some examples of the application of a SCADA system are presented. The different steps of the applications of the SCADA system are developed and the different instrumentations are presented.
Presentation of a SCADA system:
Figure 1: SCADA system of the TPP.
The SCADA term (supervisory control and data acquisition) refers to a system that collects data coming from different sensors of an industrial or other process, these sensors can beings installed in the same site or distant (several Km), the introverted data are treated by an unit called processor power station (CPU, PCU, PC...), results are sent in real time to the Men / Machine interfacing that can be a computer with its peripherals. The SCADA system of the TPP of Rades (in Tunisia) orders and classifies all data for * Instantaneous impression.
* Visualization on screen using data tables and tabular diagrams. * Registration of instantaneous exchanges of numeric and analogical data. * Instantaneous calculation for example corrections of gas debits, direct middle specific consumption, middle values. * Storage of the analogical information of the process.
* Calculation of outputs and losses of the process.
* Surveillance of...