10-04-2017, 08:41 PM
This paper presents the applications of a supervisory control and data acquisition (SCADA) system in
thermal power plants (TPPs). In fact, a supervisory system must take into account the physiological and
cognitive features of the supervisory operator. The paper briefly discusses on the one hand the
different steps of the application of a SCADA system and the difficulties to manage and on the other
hand it presents three examples of the application of a SCADA system in a TPP in Tunisia and the
instrumentations and the measurements used. The first application is related to a counting system of
the natural gas, the second one is related to the supervision of pumps vibrations and the third one is
related to the supervision of heavy fuel oil.
Key words: SCADA, supervision, control, data acquisition, thermal power plant.
INTRODUCTION
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 (Baily and Wright, 2003).
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 (Carke et al., 2003).
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 equipments 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 (Warcuse et al., 1997) (Wiles, 2008).
The SCADA system usually consists of the following
subsystems (Ozdemir and Karacor, 2006):
Abbreviations: TPP, thermal power plants; SCADA,
supervisory control and data acquisition.
(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 (Horng, 2002).
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.
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