Second International Conference on Electrical and Computer Engineering
ICECE 2002, 26-28 December 2002, Dhaka, Bangladesh
Supervisory Control and Data Acquisition (SCADA) Through
Internet
M. Mahmud, M. R. Karim, M. M. Islam and K. M. Rahman
Department of Electrical and Electronic Engineering
Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh
Email: kmr@eee.buet.ac.bd
Abstract - An Internet based SCADA (Supervisory
Control And Data Acquisition) system is presented in
this paper. Primary data, i.e. the real time data of the
power system, is acquired at every node of outward
power/energy flow with the help of a client PC
equipped with high-resolution multi-channel data
acquisition card. The data thus acquired are sent to a
central monitoring station, which may also be used as
a server PC. The program used in the server PC
performs the necessary analysis and display (both
numerically and graphically) the data received from
the client. With preset values of control parameters,
when analyzed data finds the parameters exceeding
the preset values, it sends a trip signal to the client PC
that disconnects that node of outward power flow
from the sub regional power system. The server side
program also keeps a record of the incoming data of
the client in a database for further use. This server PC
is connected to the World Wide Web via Internet. In
the web, there is a SCADA website, where with
proper authentication a supervisor can visualize the
real time data of the sub-regional power system and if
necessary, can control too.
gives some visual controls to the user whether in the
central unit or in the web page in Internet.
RTU-1
(Remote
Terminal Unit)
INTRODUCTION
LAN
World Wide
Web
Web Server
Dial Up Network
Fig. 1 Functional block diagram of the proposed
INTERNET SCADA.
The
proposed
INTERNET
SCADA
incorporates the following features:
SCADA is a technology that enables users to
access, monitor information and data of their
equipment and processes, and control large, complex
and mission critical installations like power stations,
oil/gas pipelines (for measurement and control of
outward flow power/energy and oil, gas respectively).
E-SCADA, on the other hand is an Internet-based
SCADA (also known as Web-based SCADA), which
utilizes the public Internet infrastructure as a
communication medium, which facilitates with the
versatile supervision and control, not necessarily from
a remote control center, but from any part of the world
with facilities of World Wide Web. It is a low-cost
solution that brings SCADA-like functionality to the
masses.
i)
system
It uses server, based on the latest technology
available from Microsoft and incorporates the
relevant standards for maintaining security and
privacy
ii) The scheme provides total turnkey solutions
and does not need expert maintenance and
analysis.
iii) With the help of IP address, any site can be
selected or a new site can be added to the
system.
iv) Real time client data from different channels
are shown simultaneously in client, SCADA
central or in web pages.
v) Any type of message can be sent from any
where of the total scheme for protection and
maintenance purpose.
vi) Relays can be tripped physically from
anywhere of the total system.
This paper presents a new method of data acquisition
and control through Internet. Full system provides
online display of the status of the system and thus
ISBN 984-32-0328-3
RTU-1
(Remote
Terminal Unit)
SCU
(SCADA Central
Unit)
Keywords – E-SCADA, Real Time Data Monitoring,
Web-Control, Remote Controlling.
1.
RTU-1
(Remote
Terminal Unit)
56
2.
E-SCADA
E-SCADA’s architecture is similar to the client/server
architecture where clients are slim clients with little or
no software other than a standard browser (e.g. MS
Internet Explorer, Netscape Navigator, etc.) ESCADA’s architecture also uses web servers, which
can act as database management servers as well as
applications servers. In brief, E-SCADA is the system
that interfaces between traditional SCADA with
Internet with the addition of new features.
Exchange of real time and semi real time data between
client and server has got an extensive use to make the
system more flexible over closed control systems.
This ensures improved service, reliability, and
information An Internet-based architecture is an ideal
and flexible platform for this constantly changing
business.
Internet-based architecture would allow utilities to
offer control and monitoring services to their lower
tier systems or offer control to geographically
disjointed power generation entities, or take on
additional revenue generating ventures such as
regulation, load management, energy accounting,
meter reading, and billing. In addition to deregulated
power market forces that require a dynamic control
system platform, other variables also dictate the need
for an Internet-based Supervisory Control and Data
Acquisition System.
An Internet-based SCADA system i.e. an E-SCADA
will provide a technology alternative to companies
who cannot deal with large, complex, traditional
SCADA systems.
3.
SOFTWARE DEVELOPMENT
separately for three channels. Power is calculated for
channel-1 and displayed simultaneously. These data
are sent to the SCADA Central Unit, which is
connected to the RTU through LAN. For this
operation first a connection request is sent to SCU
using ‘Connect To Server” button. Depending upon
the reply of the SCU if a connection is established and
SCU is ready to listen, these Data are sent to the SCU.
All the data at a particular instant are used to make a
composite one which is sent to the SCU.
iii. Communicating with the SCU user
The RTU operator can communicate with the SCU
operator and also with the user who connects to the
scheme through web page and Internet using chat box.
iv. Controlling the circuit to run
The circuit under can be disabled to run at adverse
situations using the “Stop” command, which sends a
signal to trip a circuit breaker. This condition of the
circuit is updated everywhere in RTU, SCU, web
page. When “Stop” command is sent the “Stop” button
is changed to “Restart” button which enables the RTU
user to again reconnect the circuit to power supply.
This “Restart” facility is available only in the RTU
window.
B. SCU (SCADA Central Unit)
A Windows based PC is used as an SCU. Ethernet
Card (100 Base T) is used for communicating with
RTUs through TCP/IP LAN. SCU is equipped with
necessary GUI based software for controlling and
monitoring the system.
SITE CONTROLLER
This site controller has four different options:
The whole system consists of three different parts.
They are:
i)
Open Site: This option dynamically generates
the list of all the client sites stored in the
database from which any of the sites can be
opened.
ii)
Define New Site: By this option a new site can
be opened with different option.
A. Remote Terminal Unit (RTU)
B. SCADA Central Unit (SCU)
C. Web Site.
A. RTU (Remote Terminal Unit)
In each RTU, a Windows based PC is equipped with
Ethernet card and hardware interfacing circuits, which
interact with its local instruments for data acquisition.
It is also equipped with GUI based software for data
acquisition, messaging and interfacing with local
instruments.
iii) Global Setting: Set some global settings in the
SCADA central unit.
iv)
DATA FROM RTU
Communication Protocol
i. Data Acquisition
The data acquisition is performed by Data Acquisition
Card (DAC) PCL 812PG. It has 16 bipolar channels
and the individual channels can be programmed for
gains upto 16 times.
ii. Visualization
This GUI shows that three list boxes shows current
that were acquisitioned by DAC are displayed
Edit/ Delete Site: By this option any site in the
database can be edited or deleted.
1.
Dedicated wires and custom signaling
2.
Wireless with custom signaling.
3.
Using a standard network protocol wired
or wireless.
With any form of custom signaling, system would be
bound with the specific physical media used. But by
using a standard network protocol, the system would
57
be independent of the physical media. This would
make the system tremendously flexible, as it allows us
to choose the most appropriate physical media when
the system is deployed. Also, it means the system can
be deployed in a variety of environments. So the third
alternative is chosen.
COMMUNICATION
USERS
BETWEEN
DIFFERENT
A list box is used as for chat console for doing the
purpose of communication between different users.
TREND ANALYSIS
An analysis by which, the SCU can predict the future
data of the specific RTU. The database is used here.
The linear-regression curve fitting technique in
equation form is used in this analysis.
AUTO-TRIPPING CAPABILITY
In SCU, there is a program, which after proper
analysis can decide itself whether it is necessary to trip
a relay to disconnect a circuit. If necessary it
automatically sends trip signal. An inverse time
characteristic curve, defined by three parameters, is
used to make such a decision. The time of operation is
calculated by,
 I

t op = K /  
  I set
Fig. 2 Site controller of the SCU.




α


− 1

Where, top is the time after which relay should operate.
I is RMS of line current. K, α, and Iset have predefined
values.
VISUALIZATION AND CONTROL
C. WEB-SITE
This program receives the data and draws a visual
representation of it. Three list boxes show three
currents from the three channel of the remote client. In
the fourth list box, power of the first channel is shown
which is calculated in the server. The graphics
interface of this part shows a current vs. time graph as
shown in Fig. 3.
Security is an important fact in control
applications. To prevent unauthorized access to
the server, Username and authentication password
along with encryption is used. The authentic user
can see:
DATA FRAME
In this frame, three different current from different
channel is shown with the time of data taken. The web
server fetches the data from the database stored in the
server.
COMMUNICATION AND CONTROL FRAME
This frame gives the user the facility to directly
communicate with the operator in the SCADA central
unit and also to the remote site that is connected.
Through the chat console, user can communicate with
them.
Fig. 3 Graphical representation of data.
Also in this frame, there is trip button. By pressing
this button, user can send a trip signal to the specific
site connected to the SCDA central. Thus a user can
control any site from utmost remote corner of the
world through Internet.
In the control part, a trip button is used by which the
operator can send a trip signal to a specific RTU. The
signal makes the RTU to trip the attached system.
The web page refreshes always. As a result, user can
see the most possible updated data stored in the
database.
DATABASE
4.
A database is also stored in the SCU server, which
store a predefined amount of data.
The full system is established in the laboratory for
experimental basis. Two windows based pc with
58
PROGRAM OUTPUT
necessary equipment is connected through a LAN
network. One pc is used as SCADA central unit and
also as web server. The whole system gives a very
satisfactory response. The RTU window with data is
shown in Fig. 4, the MTU window of SCU with data
is shown in Fig. 5 and the Web page with data is
shown in Fig. 6.
independent. It runs over any machine having
windows platform and visual studio. As the program
run through Internet, a delay may occur during the
communication, which severely depends on the
quality of the communication line. The scheme is
tested in the lab and found to work satisfactorily. This
proposed scheme may be extended for use in water
distribution control, radio site monitoring, building or
factory automation, engine/ generator set monitoring,
remote energy metering, flow metering and valve
control systems.
REFERENCES
Fig. 4 Data shown in the RTU.
[1]
S. Meddida, N. Srekumar and K. V Prasad,
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[2]
Hal Burch and Bill Cheswick, "Mapping the
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[5]
B Doug Seven, Donny Mack, “Programming
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Fig. 5 Data shown in the MTU.
WEB REFERENCE
Fig. 6 Data shown in web page.
5.
CONCLUSION
This paper presents an improved scheme incorporating
data acquisition, controlling real time data as well as
communicating through Internet. The scheme is
designed on windows platform using two languages:
Visual Basic and Active Server Pages (ASP). As it is
developed in windows platform, it is not platform
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