SUPERVISORY CONTROL AND DATA ACQUISITION FOR AUTOMATIC SUB-STATION CONTROL
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Good people all, of every sort, give ear unto my song , this was the cry
made by thousands of operator running to and fro to detect, analyze and report the fault to their
senior officials and wait for their instructions to be followed. Finally someone heard their cry and a
master system was born. The energy is generated, transmitted, distributed and finally utilized. At
every stage certain supervision, control and protection is neces sary. This paper deals with basic
SCADA system, its components, basic block diagram, functions, applications and advantages of
SCADA helps in monitoring the system and have alarm generation facility incase
of faults, which helps in real time analysis. This paper deals with the data logging ability of
SCADA enabling off line analysis . Thus remote control over power system is achieved by
SCADA, which is effectively depicted in this paper.
This paper is an attempt to highlight the features of SCADA, which is a revolutionary
development in automotive monitoring and control of process. The need for SCADA as well as its
hierarchical structure has also been mentioned in the paper. The component of SCADA, which is
divided into two parts hardware and software, has also been taken in detail. Features of the SCADA
such as simulation options, data import and export function has also been taken into account. A
criterion for economic operation of grid as well as states in which it operates has also been
considered. Security and reliability which is a prime factor for automated system as well as the
different level of redundancies which is required for various automated system has been explained
to us. Facilities provided by the SCADA have also been highlighted in the paper.
V.Srividya & Y.Swathi
These days sophisticated working environment has become a need of the hour.
Analysis of the following problem would make the need more specific. For example: Central
Railways cover a large and extensive area and e fficient operation of such large network is must.
Consider that circuit breaker near remote place has tripped and the supply has been cutoff. The
power supply has to be restored as early as possible so that the route is cleared for the other trains
and the smooth flow of trains is possible.
Hence the question of centralized monitoring and control arises. If the person back in
control room knows the position of circuit breakers and could control it from there itself, the power
is restored quickly and hence disruption of train route is avoided. To achieve this control data is to
be acquired precisely and accurately. Thus the above problem shows us that there is need of
centralized control and monitoring system, which in this age is achieved by using the SCADA
Automation eliminates human errors, while achieving better productivity and optimum
utilization of resources with lesser requirement of time. SCADA is a revolutionary development in
automatic monitoring and control of processes. SCADAâ„¢s powerful tools are being increasingly
used for centralized control of remote processes to optimize operation of really complex systems
such as automation of energy distribution systems, generation of electricity, customer information
system and engineering analysis.
WHAT IS SCADA AND ITS NEED
SUPERVISORY CONTROL AND DATA ACQUISITION â€œwe more frequently call it as
SCADA. As the name implies SCADA system supervises, acquires and control data received from
a distant data source from the control center. SCADA system is located in the control center and is
operated in the scanning mode, communicating between the CONTROL CENTER and the
REMOTE STATION by means of two-way communication channels. Such a supervisory control
and data acquisition system is intended to facilitate the work of operator by acquiring and
compiling information as well as locating, identifying and reporting faults. On the basis of
information received, the operator makes necessary decisions via the control system he can the
perform different control operations in power stations or influence the processing of the
Auxiliary memory console
RTU RTU RTU
Simple SCADA system with single computer
information acquired. The main task of a modern day power system is to ensure quality and reliable
power at an economic rate. Hence the system is to be updated at a very fast rate (real time
mode/management), which helps to control the complex system effectively without any loss of
FUNCTIONS OF SCADA
Â¢ DATA ACQUSITION- Furnishes status information & measurands data to operator
Â¢ CONTROL - Allows the operator to control the devices e.g. ckt breakers ,Xmer, tap
changer etc from a remote centralised location .
Â¢ DATA PROCESSING - Includes data quality & integrity check , limit check , analog value
Â¢ TAGGING - Operator identifies any specific device & subjects to specific operating
restrictions to prevent from unauthorized operation
Â¢ ALARMS - Alerts the operator of unplanned events & undesirable operating conditions in
the order their severity & criticality
Â¢ LOGGING- Logs all operator entries, alarms &selected entries
Â¢ TRENDING- Plots measurements on selected scale to give information on the trends e.g.
one minute, one hour etc.
Â¢ HISTORICAL REPORTING - To save & analyze the historical data for reporting,
typically for a period of 2 or more years & to archive.
FUNCTIONAL UNITS OF SCADA:
The figure shown below
represents the simplest SCADA
configuration employing single
Computer receives data from
RTUs via the communication
interface. Operators control base
1.Data collection equipment.
2.Data transmission / telemetric equipment.
3. Remote terminal unit.
4. Data loggers.
5. Data presentation equipments.
one or more CRT terminals for display. With this, terminal it is possible to execute supervisory
control commands and request the display of data in alpha numerical formats arranged by
geographical location and of type. The programming input/output is used for modifying the
supervisory software. In the basic SCADA system, all the programs and the data is stored in the
main memory. The more sophisticated version of SCADA has additional auxiliary memories in the
form of magnetic disc units.
AUTOMATIC SUB-STATION CONTROL
The electrical energy is transferred from large g enerating stations to distant load centres via
various sub-stations. In every sub-station certain supervision, control and protection functions are
necessary. Every substation has a control room. The relay and protection panels and control panels
are installed in the control room. The various circuit breakers, tap changers and other devices are
controlled by corresponding control-relay panels. In a small independent sub-station, the
supervision and operation for normal service can be carried out by the oper ator with the aid of
analogue and digital control systems in the plant. The breakers can be operated by remote control
from the control room. During faults and abnormal conditions, the breakers are operated by
protective relays automatically. Thus, the primary control in sub-station is of two categories.
1. Normal routine operation by operators command.
2. Automatic operation by action of protective relays and control systems.
SUB STATION CONTROL FUNCTION ARRANGED THROUGH SCADA SYSTEM
1. Alarm Functions
Â¢ To sound alarm/annunciation regarding dangerous, uncommon events such as abnormal
values of process parameters, fire, illegal entry in premises, over temperatures, low voltage
of auxiliary supply, unusual happening etc. Alarms are obtained from data logger and are
for alerting this operator in the control room.
2. Control and Indication
Â¢ Control of two position devices such as circuit -breakers, isolators, earthing-switches,
starters. Indication of ON/OFF state of the devices on control board/mimic diagrams.
Â¢ Control of position of devices having positions (closed, middle open) e.g. values, input
settings, indication of position on control panels.
Â¢ Control positions of multi-position device e.g. tap changer, indication of position on
Â¢ Indication without control.
Â¢ Control without indication : e.g. raise or lower control of generator load by automatic load
Â¢ Set-point control to provide set point to a controller located at remote sub -station.
3. Data collection, recording, display.
4. Sequential operation of devices with predetermined time and conditions for operation of
Â¢ Auto-reclosing of circuit-breakers operation O-CO-Time-CO
Â¢ Operation of circuit-breaker, isolator and earthing switch in a particular sequence
during opening of circuit and another sequence during closing of circuit.
5. By means of SCADA system, the operator in control centre can cause operations in a
remote sub-station. The possible remote operations include :
Â¢ Opening and closing of switching devices I
Â¢ Tap-changing of transformers (voltage control)
Â¢ Switching of capacitor banks (voltage control)
Â¢ Load shedding (load frequency control)
6. Some of the remote operations are made automatic by one -line computer based system
without human intervention e.g. Net work islanding, Backup protection. The automatic
control function are segregated into :
Â¢ Interconnection functions
Â¢ Transmission line automatic function
Â¢ Distribution system automatic functions
TWO-WAY COMMUNICATION CHANNELS BETWEEN THE MASTER CONTROL
CENTRE AND REMOTE CONTROL CENTRE
SCADA systems were
used for scanning mode,
providing data regarding
etc.Traditional hard wired
Stop - Start
Alarams & Status
SCADA systems were arranged to perform several functions to supplement Automatic Control and
Now a days protective relays, control relays and control systems are used for automatic
control of generating stations and transmission systems along with SCADA. Only initiating devices
may be different or omitted with fully automatic SCADA control. For example, tap changing may
be initiated either by the sub-section control room operator or by the automatic voltage control
relays connected in the protection panel of the transformer.
Controls systems were arranged to keep the values of controlled quantities within target
limits. Protection equipments were arranged for sounding alarms and for tripping circuit -breakers.
With the recent revolution in microprocessor technology, the size, performance and cost of digital
automation systems have become acceptable in commercial installation. SCADA provides
integrated approach to power system protection, operation control and monitoring, automatically
with least intervention of the control room operator.
The microprocessors located in the master station, generating stations, transmission sub -
stations and distribution sub-stations provide control and protection decisions locally where the data
is located. The action is reported to the operator "by excep tion". The operator retains the option of
taking intervening action of overriding or initiating of his own. All these microprocessor based
systems are connected through the GLOBAL POSITIONING SYSTEM. The functions and
architecture of SCADA system is selected in accordance with the functional requirements and size
of the power system.
FEATURES OF SCADA
Tracker Option: This feature provides collection and storage of variety pertaining to the
serialized items such as time stamps, quality measurements, tempera ture, humidity, pressure,
sub- assembly part number etc through various automated sensors and readers like bar code
readers, radio frequency tags, mechanical tag based system. This information is used for over
viewing the flow of serialized items and the l ocation of materials through the system which
helps in isolating the defective items from the perfect ones. For example boxes or containers
over a specified weight limit may be routed to different storage area
Data import/export function: This feature allows the transfer of all the point configuration
data via a Ëœcomma separated variableâ„¢ file. Points are the representation of actual field
parameters; these are the variables in which the actual incoming data is stored. Similarly point
configuration can be sent to other SCADA system for their use over their. This is made
possible through data import/export facility. Data management is possible using MS EXCEL,
MS ACCESS etc.
Flexibility: This feature provides tools by which an existing system could be tailored
according to the changes taking place. Thus the user can mould the system according to the
demands thus making it more flexible.
Forecasting: Forecasting is the ability to predict future state of the system by studying
previously collected data. Forecasting feature of SCADA system allows the operator to
visualize the state of the system well in advance, hence the operator has enough time to manage
the system properly. This feature of SCADA finds a huge application in Energy Management
Job Management: Using SCADA all the tasks can be properly sequenced and executed to
allow the most efficient task scheduling for proper utilization of man and machinery of plant.
Thus ensuring the most optimum utilization of the resources. And hence the conformance to
international standards of safety and security of the plant and personnel is also ensured.
SECURITY OF SYSTEM OFFERED BY SCADA
In the age of automated systems, security, reliability and availability of data is top priority
of any computer based automated system. Small loss of data in such system can cause havoc and
may bring a system to a standstill.
SCADA ensures a high degree of security. Security of any process may be defined as the
ability of the system to operate in normal state even with the occur rence of specified contingencies.
The system shall by all means remain in the state of normal operation by means of fast acting
control systems following a contingency and without having a system to go into an emergency
state. Continuous monitoring of security and appropriate corrective action for improving security is
called security control. System security analysis is generally broken down into following three
System monitoring: SCADA provides up to date information regarding the condition of the
Contingency analysis: Sometimes abnormalities give the operator very less time to react.
SCADA system provides contingency analysis, which consists of action to be taken by the
operator in advance. Thus it allows the system to operate defensively.
Corrective action analysis: It allows the operator to take appropriate corrective action in the
event of contingency in order to ensure the smooth functioning of the process.
Advantages of SCADA system:
1. Flexible, simple, reliable.
2. Efficient with less manpower.
4. Self-checking and readability.
5. Portable and cost efficient.
Applications of SCADA system:
1. Inside power plant.
2. On power plant.
3. Industrial establishment.
4. Load dispatch center.
From the above paper we can summarize that the SCADA supplements the control and
protection system to form an integrated system, which is compact, economical and versatileÂ¦. In
short we can say that it acts under the GLOBAL POSITIONING SYSTEM, so that whole system
works in same time domain.
Today the buzzword in any industry is Optimal Performance at Maximum Economy.
SCADA has provided the industry with the perfect Man Machine Interface which has solved
many or to be precise, most of the problems related to monitoring, supervision, dat a acquisition and
controlling. The most significant contribution of SCADA is probably having an easy -to-use
graphical interface, which has made the tedious job of operators very easy. SCADA has manifold
applications like Distribution Management, Energy Management, Power Plant Management & Oil
and Gas Distribution System. SCADA has also enabled Grid monitoring by virtue of which power
can by shared on national basis. So the bottom line is that SCADA is a boon to Indian power
1. Sunil S. Rao, Switchgear Protection and Power Systems
2. A.K. Sawhney, Electrical Measurements & Measuring Instruments
3. The Information Digest On Energy â€œ Vol -2 March1992.
4. Tery News Wire â€œVol â€œII Jan1996 - Dec1996.
5. Tery Energy Environment Monitor- Vol-I March-1996.