This document summarizes a paper presented at the 2nd IEEE International Conference on Power and Energy held in Johor Baharu, Malaysia from December 1-3, 2008. The paper discusses the development of a Supervisory Control and Data Acquisition (SCADA) based Remote Terminal Unit (RTU) for distribution automation systems. Specifically, it presents the system architecture, design requirements, RTU specifications, interface with the SCADA system, input/output modules, communication protocols, and results. The SCADA-based RTU was developed to provide fault isolation, monitoring, and control capabilities for low voltage distribution automation.

1. 2nd IEEE International Conference on Power and Energy (PECon 08), December 1-3, 2008, Johor Baharu, Malaysia
Supervisory Control and Data Acquisition
System (SCADA) Based Customized Remote
Terminal Unit (RTU) for Distribution
Automation System
* M. M. Ahmed, Member, IEEE and ** W. L. Soo
*
Universiti Teknikal Malaysia Melaka (UTeM), Melaka, Malaysia. Email: musse@utem.edu.my
** Universiti Teknikal Malaysia Melaka (UTeM), Melaka, Malaysia. invy2004@hotmail.com
Abstract—This paper presents the development of a
Supervisory Control and Data Acquisition (SCADA) based
Remote Terminal Unit (RTU) for customer side distribution
automation system (DAS). It is to apply automation
technique for operating and controlling low voltage (LV)
down stream of 415/240V. The SCADA system developed
provides fault isolation operation, monitoring and
controlling functions for the operators and data collection
for future analysis. An embedded Ethernet controller is
used as RTU to act as converter for Human Machine
Interface (HMI) and to interact with digital input and
output modules. RTU is the master and digital input and
output modules are the slaves. RTU will initiate the
transaction with the digital input and output modules. Two
proprietary software systems are used are to develop
algorithm for the controller and to develop HMI for
monitoring and controlling functions for the operator.
Index Terms-- SCADA system, RTU, RS-485, Serial
Modules, Mod-bus, TCP/IP, Master-Slave.
I.
INTRODUCTION
Control systems designed to monitor processes
are referred to as data acquisition systems. If the system
allows also remote control to function based upon the
acquired data, it is referred to as a SCADA system [1].
Modern SCADA provides proper monitoring of
equipment to maintain operations at an optimal level by
identifying and correcting problems before they turn into
significant system failures.
A SCADA system consists of a number of
remote terminal units (RTUs) collecting field data and
sending that data back to a master station via a
communications system. The RTU provides an interface
to the field analog and digital sensors situated at each
remote site. The master station displays the acquired data
and also
allows the operator to perform remote control tasks. The
RTU provides an interface to the field analog and digital
sensors situated at each remote site.
1-4244-2405-4/08/$20.00 ©2008 IEEE
In this paper, system architecture, system design
requirement, RTU specification, SCADA system
interface, I/O modules, panel block diagram,
communication device
setting, transaction using mod-bus protocol, read and
write to HMI and results are presented.
SYSTEM DESIGN REQUIREMENT
II.
TABLE 1 describes the system design
requirement in this research.
The RTU and I/O Modules are required to
operate in the range of 0VDC to 30VDC. However for
the loads in the customer panel which represent the loads
use 240VAC.
In the service substation panel, 11 channels of
DO module and 1 channel of DI module are required. In
the customer service substation panel, 8 channels of DO
module and 1 channel of DI module are required.
For the communication part, the RTU needs to
provide two ports of RS485 communication protocol and
one TCP/IP port with 10Mbps speed.
Equipment is needed to measure two parameters
which are the phase voltage and phase current. The RTU
communicates with personal computer that runs under
Windows XP operating system with minimum hard disk
space of 500MB.
TABLE 1
SYSTEM DESIGN REQUIREMENT
No.
Item
1
Operating Voltage
2
Digital
Channels
1655
Output
Parameters
Specification
30VDC (RTU & I/O
Modules), 240VAC
(Loads)
Service
Substation
Panel: 11 channels
Customer
Service

2. 2nd IEEE International Conference on Power and Energy (PECon 08), December 1-3, 2008, Johor Baharu, Malaysia
3
Digital
Channels
Input
4
equipped with a Self Tuner ASIC for all RS-485 ports.
The Self-Tuner ASIC will auto detects and controls the
send and receive directions of the RS485 network. The
general feature of the RTU is illustrated in Fig. 2.
This RTU provides one on-board 10BaseT port
that is equipped with a RJ-45 connector.
Substation Panel: 8
channels
Service
Substation
Panel: 1 channel
Customer
Service
Substation Panel: 1
channel
Communication
Interface
Communication
Ports: Com1, Com2,
Com3
Baud Rate:9600
RS485
TCP/IP
5
6
PC-based
SCADA
Controller-RTU
LAN Configuration
7
Sensor/Transducer
Devices
8
Measurement
Parameters
Personal Computer
9
III.
Speed: 10Mbps or
100Mbps
Power supply: 10 to
30VDC
Operating
System:
Window NT/XP/CE
Speed: 40MHz
Memory: 512Kbytes
Ethernet port: 10
BaseT
Serial Port: Com 1,
Com 2, Com 3
Protocol:Modbus
serial protocol,
Modbus TCP/IP
protocol
Hub: Four-port of
10Mbps or 100Mbps
Speed: 10 Mbps or
100Mbps
CT 60/5A
24VDC Relay
3-Phase Contactor
Phase Voltage
Phase Current
Operating
System:
Windows
NT/2000/XP/CE
Memory: Minimum
of 256MB
Hard disk space:
Minimum of 500MB
Processor:
Compatible with Intel
Pentium IV or higher
Fig. 2. General Controller Block Diagram
The communication between HMI and RTU is
using TCP/IP protocol. A socket is a combination of port
number and IP address. HMI will always listen for any
request from the RTU. RTU will request a connection to
the HMI and HMI will accept the connection before data
can be sent or received.
IV.
I/O MODULES
The series modules, including D/I, D/O, A/D,
D/A, Timer/Counter and MMI modules, will be directly
connected to RS-485. These series modules can connect a
maximum of 256 modules to the RS-485 network. The
module address can be changed from 00 to FF, a total of
256 maximum. The series modules can be programmed to
1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200, a
total of 8 different speeds.
The I/O modules used in this research are
DI/DO module which is an 8 channel digital output and 4
channel digital input module, DI module which is a 16
channel digital input and DO module which is a 13
channel digital output
These modules can be remotely controlled by a
set of commands. The PC will send out a command string
to the RTU either by TCP/IP protocol or RS232 protocol.
RTU converts this command into a RS-485 before it
sends to RS-485 network.
RTU SPECIFICATION
Embedded Ethernet RTU is used in this research
project. The RTU is designed as embedded RTU. This
RTU is powered by an 80188-40 processor with 512K
bytes of static RAM and 512K bytes of Flash memory.
The EEPROM is designed to store the data which is not
changed very frequently. The 2-wire RS-485 port is
designed to directly drive the series modules. The RTU is
1656

3. 2nd IEEE International Conference on Power and Energy (PECon 08), December 1-3, 2008, Johor Baharu, Malaysia
Fig. 5. : Communication Wiring Diagram Between the RTU & the
Slaves
Fig. 3. Service Substation System Block Diagram
V.
PANEL BLOCK DIAGRAM
In Fig.3, the service substation block diagram
consists of power line and control line. The power line
shows the electricity supply to all the components in the
service substation panel. The controller and I/O modules
are supplied with dc power supply. Relay module
receives power supply from the digital output module.
The control line shows the communication line between
the controller and I/O modules.
In Fig.4, the customer service substation block
diagram also consists of power line and control line. The
power line starts from MCCB1 from the service
substation panel. Digital input/output module is supplied
with direct current power supply. The contactor module is
connected to the ac power supply. Relay module receives
the power supply from the digital input/output module.
The control line shows that the digital input/output
module is connected with the controller in the service
substation panel.
Fig. 5 shows the communication wiring diagram
between RTU and the slaves.
VI.
Fig. 4. Service Substation System Block Diagram
TRANSACTIONS USING MOD-BUS PROTOCOL
Mod-bus is the protocol commonly used for
SCADA applications. The Mod-bus transmission
protocol was developed by Gould Modicon for process
control systems [2]. A recent survey in the well-known
American Control Engineering magazine indicated that
over 40% of industrial communication applications use
the Mod-bus protocol for interfacing. [3]
Mod-bus protocol can be broken down into five
sections which are message format, synchronization,
memory location, function codes and exception
responses.
A transaction consists of a single request from
the host to a specific secondary device and a single
response from that device back to the host. Both of these
messages are formatted as mod-bus message frames [4].
Each such message frame consists of a series of bytes
grouped into four fields as described in Fig. 6.
Fig. 6. Format of Mod-bus message frame
1657

4. 2nd IEEE International Conference on Power and Energy (PECon 08), December 1-3, 2008, Johor Baharu, Malaysia
VIII.
RESULTS
Fig. 7 shows an example of message frame used
in this research to read two words value of variable V1 by
using mod-bus function 3.
Fig. 7. Read long word by Modbus
Fig. 8 shows an example of message frame used
in this research to write two words value of variable V1
by using mod-bus function 16.
Fig. 9. HMI and SCADA Applications for Service Substation Panel
Fig. 8. Write long word by mod-bus
VII.
COMMAND FORMAT OF DI/DO MODULE
Command format can be used to send and
receive data from HMI to DI/DO modules. The command
format consists of leading, address, command and
checksum. The response format consists of leading,
address, data and checksum. For example to change
module address from 01 to 02 a command
“%0102400600” is written in the HMI. RTU will send
“!02” to HMI if the new configuration is successful.
Tables 3 elaborates the command and receive syntaxes.
Fig. 9 shows the HMI and SCADA applications
for service substation panel developed by using the
proprietary software. The operator can operate manually
the MCCBs by pressing the Manual Button.
Fig.10 shows the status of the Main MCCB,
other MCBs and the outputs. If fault occurs, the MCB
and the outputs will change to red colors pattern showing
that the MCB is off status. In this case, alarms will be
triggered and displayed on the screen. Fig. 11 shows the
alarm messages. In the alarm list, the blue color text
indicates that the output has changed to healthy status and
the red color text indicates that the output is still
remained unhealthy. Once the fault points have been
checked and repaired, the “Reset” button from the control
button in Fig. 13 is pressed to restore the power supply to
all the outputs.
TABLE 3
SET MODULE CONFIGURATION
Command Syntax
%AANNTTCCFF[CHK](cr)
Response Syntax
!AA[CHK](cr)
?AA[CHK](cr)
Description
%- a delimiter character
AA - address of setting
module (00 to FF)
NN – new address for
setting module (00 to FF)
TT – type 40 for DIO
module
CC – new baudrate for
setting module
FF- new data format for
setting module
Description
Valid Command
Invalid Command
Fig. 10. MCCBs - Service Substation
Fig. 11. Alarm Messages
1658

5. 2nd IEEE International Conference on Power and Energy (PECon 08), December 1-3, 2008, Johor Baharu, Malaysia
TABLE 4
RESTORATION TIME FOR CUSTOMER SERVICE SUBSTATION
Panel
Minimum Restoration Time
(Second)
0.7
Customer Service
Substation
Service Substation
50
BASED ON DELAY TIMER SETTING
TABLE 5
MINIMUM TOTAL OF RESTORATION TIME
Fig. 12. Phase Current Reading from Power Analyzer (Customer
Service Substation Panel)
Delay
Timer
(Second)
Duration
Time 1
(Second)
Duration
Time 2
(Second)
Outage
Time
(Second)
Reset
Time
(Second)
6
3
1
0.5
0.1
24
12
4
2
-
30
15
5
2.5
-
54
33
15
10.5
-
42
21
7
3.5
0.7
The readings from the power analyzer are
captured from both panels. Fig.12 shows the
example of the graph displayed in HMI application.
The reading from this graph is plotted again using Excel
as shown in Fig. 13 for details analysis.
Table 5 shows the minimum total restoration
time for the customer service substation panel and the
service substation panel. The ELCB minimum operation
time is fifty milliseconds. In this case, the delay timer has
to be set higher than fifty milliseconds. The minimum
delay timer for the customer service substation panel is
one hundred milliseconds. For the service substation, the
delay timer is set to 5 seconds for proper operation of
switching the MCBs to on and off. These figures can only
be applied for the MCCB and MCBs used in this
research.
The system developed in this research is
excellent to save the time needed to restore back the
electricity supply after fault occurs. The restoration time
definitely cannot be achieved by manual isolation done
by the technicians at the remote substation site.
Fig. 13. Phase Current Reading from Power Analyzer (Customer
Service Substation Panel)
Based on the graph in Fig.13, the outage time,
duration time 1, duration time 2 and reset time are
obtained. Table 4 shows the details of the duration time 1,
duration time 2, outage time and reset time when the
delay timer in the customer service substation is set to six
seconds, three seconds, one second, five hundred
milliseconds and one hundred milliseconds.
The duration time 1 is the time period that is
needed by the system to identify which load is the fault
load. In this experiment, fixed fault points were chosen.
Duration time 2 is the time period that is needed by the
system to isolate the faulted load and restore electricity
supply to the rest of the healthy loads. Outage time is the
duration time that the customer experiences electricity
supply disruption. Reset time is the total time needed to
restore electricity supply to all the loads including the
faulted load that has already been repaired.
IX.
CONCLUSIONS
In this research project, a Customized SCADA
based RTU for service substation and customer service
substation is developed by using the open loop concept
for the distribution networks. In this research, a
Customized SCADA is built to provide automatic fault
isolation for low voltage distribution system. The HMI
can be monitored at different sites as the controller
equipped with TCP/IP features. Whenever the system
detects fault, an alarm message will be displayed at the
HMI side to acknowledge the operator. The status of
communication between the controller, digital I/O
modules, power analyzer with the HMI helps to
acknowledge the operator if there is a communication
breakdown. The SCADA system provides GUI, alarm
system, data logging and report management facilities for
the operator to interact with the equipment in the service
substation and the customer service substation.
1659

6. 2nd IEEE International Conference on Power and Energy (PECon 08), December 1-3, 2008, Johor Baharu, Malaysia
REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
[7]
A.Daneels and W.Salter, “What is Scada?”, International
Conference on Accelerator and Large Experimental
Physics Control System, Trieste, Italy, 1999, pp.1
Hugh Jack, “Automating Manufacturing Systems with PLCs”,
Version 4.7, April 14,2005, pp.643
John
Uffenbeck,Microcomputers
and
Microprocessors,
2000,1991,1985 by Prentice Hall, ISBN 0-13-209198-4,pp 509
Gordon Clarke, Practical Modern SCADA protocols: DNP3,
60870.5 and Related Systems, 2004, ISBN 07506 7995, pp.45
ICP DAS, 7188E/843X/844X/883X/884X TCP/IP Library User’s
Manual, Ver. 1.0 Copyright 2002 [Online] Available:
www.icpdas.com
Customized Non-interruptible Distribution Automation System,
Short Term Project No. PJP/2006/FKE (1) , UTeM, 2005-2006
Intelligent Distribution Automation System: Customized SCADA
Based Rtu For Distribution Automation System, M.Sc. Research
Project, UTeM, 2005-2007.
Soo Wai Lian was born in Malacca, Malaysia, on
June 3, 1978. She received her B.S degree in electrical engineering from
the University Technology Malaysia. She is with Universiti Teknikal
Malaysia Melaka (UTeM) pursuing her PhD degree. She is specializing
in electrical power distribution system.
BIOGRAPHIES
Dr. Musse Mohamud Ahmed is a
associate professor at the Faculty of
electrical Engineering, UTeM. He
graduated from Universiti Teknologi
Malaysia (UTM) in 2000 and got his
Ph.D. He worked Multimedia University
(MMU), as lecturer at the Faculty of
Engineering & Technology in Malacca
campus from 2000 to 2002. He joined
UTeM in March 2002 as a lecturer. In
October 2002, he was appointed as
deputy dean, postgraduate, research & development at the Faculty of
Electrical Engineering, UTeM, a position he held till March 2007.
Since then he has been working in UTeM. Dr. Musse has been
IEEE-PES member for eleven years and Executive Committee
Member for the last five years. His research interests include:
Distribution Automation System, Power System Operation and
Control Simulation & Modeling of Large Scale Power Systems,
Intelligent Power Systems, Energy & Renewable Energy and
Risk Assessment of Electricity Supply
1660
I.