Real Time Test Bed Development for Power System Operation

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Real Time Test Bed Development for Power
System Operation, Control and Cyber Security
Ram Mohan Reddi, Student Member, IEEE, and Anurag K Srivastava, Senior Member, IEEE
Abstract--With ongoing smart grid initiative, there is a
considerable need for developing new algorithmic solutions and
validating at laboratory level before they can be successfully
applied in the power grid. This research work addresses the
development of a real time test bed by integrating several
hardware’s including the Allen Bradley Programmable Logic
Controllers (PLC), National Instruments PXI (NI-PXI)
controller, Real Time Digital Simulator (RTDS), and Schweitzer
Engineering Lab (SEL) devices. This work also integrates the
OSIsoft PI Server system and the establishment of data channel
over Ethernet/IP for communication and control. The developed
test bed is evaluated by simulating a simple test case in RTDS
and executing the control logic in PLC. The test bed provides a
user friendly Human Machine Interface (HMI) for monitoring
and control at different levels of the system along with
capabilities for storing the power system data which includes
Synchrophasor data for forensic analysis. This test bed will be
essentially used for modeling and study of different power system
operation control algorithms as well as to investigate cyber
vulnerability and mitigation.
Index Terms— LabVIEW, NI-PXI, PI Server, PLC, Real Time
Test Bed, RTDS, HMI
I. INTRODUCTION
A
S the electric power system is moving towards the Smart
Grid (SG) development for improved reliable, secure, and
economic operation, implementation of such a system
requires enhanced testing and validation [1], [2]. Most of the
control action schemes mainly rely on extensive offline
studies using hypothetical scenarios and models that possibly
include errors [3]. Current developments in control schemes
are also more often theoretical and non-real time model based
scenarios which are rarely evaluated. There is a need for
testing and validating these ‘Real Time Monitoring and
Control’ techniques involving different hardware equipments
to achieve flexibility, ease of operation, interoperability,
control validation, and more importantly redundancy of the
control schemes [4]. Research works in the field of real time
control and data acquisition for power systems have been
reported in [5], [6] and [7], but either it depends on software
based analysis or limited hardware tests. Requirement for
modern power system automation has been reported and
Ram Mohan Reddi is with Department of Electrical and Computer
Engineering, Mississippi State University, Mississippi State, MS 39762.
([email protected], 662-312-0232).
Anurag K. Srivastava is with Department of Electrical and Computer
Engineering, Mississippi State University, Mississippi State, MS 39762.
([email protected], 662-325-5838).
existing from long time [8].The test bed developed here is
one-of-a-kind platform including simulated power grid
interfacing with sensor network and control center type setup
with data storage and different level of control. Developed test
bed provides a good working platform to test and validate
different protection and control schemes on several hardware
equipments varying from simple relays to PLC applications
and complex algorithms in the power system. The
interoperability of different hardware devices for power
system automation can be also tested.
This research work mainly focuses on key aspects of real
time modeling, simulation, remote monitoring, cyber security,
and control of power system operation by employing different
hardware features and software algorithms. The Developed
power system test bed utilizes the RTDS, PLC, NI-PXI
controller, and SEL devices. Corresponding software suites
are employed to model, monitor, and control the system in real
time.
II. OVERVIEW OF HARDWARE AND SOFTWARE EMPLOYED
This section discusses some basic details about the
hardware and software employed in the development of the
test bed for real time studies.
A. Real Time Digital Simulator
Real time digital simulator (RTDS) is a power system
simulator which simulates power system programs in real
time. This is unique in the sense that it works on the parallel
processing technique of digital signal processors and executes
the program developed on its processors and produces output
both graphically and through the output interface cards
incorporated into the system. The power system programs are
developed using RSCAD user interface which is specially
designed for RTDS and is used for both development of the
different power system scenarios and also for viewing and
studying the results graphically [9].
The RTDS present in the research lab at Mississippi state
university consists of two racks with eight triple processor
cards and two Giga processor cards, and additionally it
contains several input and output interface cards for sending
and receiving analog and digital signals. One of the important
interface cards used in this work is Digital to Analog
Converter Card (DDAC) from which 12 signals can be sent
out of the RTDS, and also the front panel inputs are used to
send the digital control signals into the RTDS to control the
elements in the simulated power system. Figure 1 shows the
Real Time Digital Simulator at MSU.
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time will vary based on the complexity and the length of the
Ladder Logic program.
The PLC (Fig 2.) present in the research lab at MSU is
supplied by Rockwell Automation, and it belongs to Compact
Logix family of systems and consists of an L35E processor
with 128 I/O [10].
Fig. 1. Real Time Digital Simulator (RTDS)
B. Programmable Logic Controller
A Programmable Logic Controller (PLC) is a standalone
system which is capable of continuously executing logic and
making decisions though the program written into it using the
real world analog and digital signals as inputs. These devices
are remote terminal units employed in many industries and in
a power system infrastructure for controlling the elements of
the corresponding systems. In this work, an Allen Bradley
manufactured Control Logix PLC is used in the test bed for
controlling a simulated breaker in the power system running
on the RTDS.
C. NI-PXI System
National Instruments PCI eXtension Interface system (NIPXI) is a real time embedded controller from National
Instruments used for real time testing purposes. Built on PXI
architecture which is an open PC based platform for test
measurement and control [11], this system is a low cost high
performance model used in various technologies. The NI-PXI
system at the MSU research lab (Fig 3.) is a standard 8 slot
chassis consisting of a 1084Q Embedded Controller and two
I/O cards 6608 and 6251 responsible for sending and receiving
analog and digital signals in and out of the controller. The
controller is a stand-alone system running a program written in
LabVIEW software.
Fig. 3. NI-PXI 8 slot system at MSU
Fig. 2. Programmable Logic Controller (PLC)
This PLC is capable of Ethernet communication, and an
identical PLC is also used in the test bed for testing the remote
control center operation and cyber security analysis. The
control logic is written by the RSLogix 5000 programming
software suite provided by Rockwell Automation for the
operation of the Compact Logix PLC and is a very flexible
and powerful tool for writing the programs into the PLC. The
current logic is developed in Ladder Logic (LL) using
RSLogix and runs continuously in the PLC. The PLC executes
the program through a procedure called scan cycle, where
ladder logic is scanned step by step by reading the inputs
variables and making the corresponding changes in the output
elements. This is repeated continuously and the simulation
D. LabVIEW
LabVIEW is a graphical programming tool for test,
measurement, and automation and is widely used as a virtual
instrumentation tool. It allows user to develop sophisticated
measurement, test, and control systems using intuitive
graphical icons and wires that resemble a flowchart [11]. This
tool is increasingly being used in development of laboratory
test applications as well as industry standard working
applications which are user friendly, and the test output can be
checked instantly. One of the major advantages of LabVIEW,
apart from being simple to use, is the ability to work with a
number of hardware interfaces using real world analog and
digital signals. LabVIEW programs work as simulation or data
acquisition applications depending on the requirement using
custom built hardware from National Instruments. This
consists of two windows, a block diagram window where the
actual graphical code is written and the front panel where the
output can be visualized. In the current research, LabVIEW is
used to develop a program which will acquire data from
RTDS and runs custom built programs as well as to send and
receive signals from the PLC. The LabVIEW program
developed runs in real time on the NI-PXI embedded
controller through Ethernet communication and displays the
results in the front panel of the LabVIEW program.
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E. PI System
The PI system or Plant Information system, delivered by
OSIsoft is one of the highly scalable and secure infrastructure
for the management of real time data and events [12]. It
includes several software interfaces for real time management
and data base creation and investigative studies. The PI system
is widely used among the industries, including power systems
for real time data management and visualization. The PI
system installed at MSU consists of a PI sever system and a PI
process book along with OPC and C37.118 interfaces.
The PI server system is a software tool which acquires,
analyzes, stores, and routes data in real time and is the core of
the PI system [12]. The PI server acquires the data from the
developed test bed and stores the data over a custom time
period in real time along with time stamping at flexible
scanning cycles. The acquired data is visualized in the PI
process book interface where the data is displayed as plots
relative to time and also is capable of alerting the operator
through alarms which act on the real time data. The data
acquisition is done through the OPC, and C37.118 interfaces
provided by OSIsoft and are capable of acquiring data from
third party devices. The overall system described above is
managed by the PI system manager in secure environment, as
only a selected group will have rights to view or modify the
real time data.
F. Ethernet/IP communication
Ethernet/IP is one of the commonly used communication
protocol, due to its simple operation and the ability to
incorporate number of devices by providing a fast
communication medium. Ethernet communication has the
advantages of higher transfer speeds, full duplex and collision
free operation, fiber optic interface, remote monitoring and
diagnostic support which make it viable for power system
operation and control [13]. A 100 Mbps Ethernet network is
used in this work with devices connected through a switch on
private IP configuration. The only exception is a second PLC
employed in the remote control center which communicates
through wireless Ethernet over radio using antennas. This is
specifically employed for testing the security standards of the
developed system.
III. TEST BED ARCHITECTURE AND OPERATION
The integration of various hardware devices is done
through Ethernet or hard wired connection. A simple power
system test case is developed in RSCAD and is executed on
the RTDS; the scaled signals from the simulated system are
sent to the PLC which is integrated with RTDS using the NIPXI system. The NI-PXI system is used here as there is no
direct connection procedure devised to connect Allen Bradley
compact logix PLC with RTDS, and moreover the NI system
provides an intermediate level for monitoring the data. The
block diagram of the developed test bed architecture is shown
in fig 4.
Fig. 4. Test Bed Communication Architecture
As seen from the figure, a remote control center is installed
with compact logix PLC and HMI for remotely monitoring the
data and to sending the control commands over the wireless
Ethernet. RTDS signals are hardwired to the SEL devices such
as SEL-421 relay for monitoring the system and fault
protection. In similar manner, it is connected to the NI- PXI
through the DDAC cards on the RTDS and the DAQ cards on
the PXI system. The control logic is written using, the
RSLogix 5000 tool for both the local and remote PLC’s. The
NI-PXI uses Ethernet/IP suite available in LabVIEW to write
and read data from the PLC data tags by directing the system
to PLC IP address. The HMI shown in fig. 4 are the
corresponding software suites needed for the hardware
operation. One more important part of the test bed is the PI
server system which is connected to the same Ethernet switch
and acquires the system data in real time. The data acquisition
is done by the OPC interface where the RTDS data is accessed
from the LabVIEW using OPC protocol, and the PMU (fig. 4)
data can be accessed by C37.118 interface installed on one of
the systems.
The operation of the test bed is as follows: firstly, the
power system developed using RSCAD is simulated in RTDS
and the required signals are sent out using the DDAC interface
to the NI-PXI system which is running a real time LabVIEW
program, which acquires the signals from RTDS. The program
displays the data graphically in the front panel and also writes
the data to local PLC tags. The PLC has a control logic which
tests for the component outage caused by faults and generates
digital control signals for possible remedial scheme, which are
read back by the LabVIEW program and sent to the RTDS.
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Fig. 5. RSCAD power system model
The SEL-421 device is also hardwired to the RTDS which
continuously monitors the power system data for faults. The
local PLC is connected to the PLC in the remote control center
which is also capable of running the control logic and
monitoring operations. Since all the communication
architecture is on Ethernet, the PI system is also incorporated
into the system which continuously acquires the power system
data from LabVIEW using OPC interface and acts as a data
repository and monitoring client. The real time data can be
collected over any period ranging from minutes to days or
more, only limited by the amount of space allocated for the
data storage. Thus, all the devices operate in real time making
it possible to run several tests on a smaller power system
network at laboratory level.
provision to manual induce a fault into the system causing
opening of one, or all breaker operations by relay leading to
possible unbalanced operation.
B. Test case scenario
The test case scenario comprises of inducing a fault
manually leading to generator outage. Corresponding
corrective action has to be taken by the monitoring and control
devices such that they shed one of the loads to balance the
system.
IV. TEST CASE AND NORMAL OPERATION
This section describes the small basic power system test
case employed in the research work and its results. Note that
there are several other applications are possible, and has been
completed but the simple one is presented here to have focus
on development of test bed instead of the application.
A. RSCAD power system model
The sample power system developed in RSCAD is a 3
phase four bus system with two 250 MW generators supplying
the power to two dynamic loads balancing the system. The
rms values of the currents are taken into account as the
monitoring parameters which are monitored at the generator
bus. The program also includes a DDAC block for sending the
analog signals from RTDS (fig. 5) for the complete power
system model monitoring. The model also includes a digital
input block to receive signals into the RTDS to operate on the
breakers or relays in the model. The run time window of the
program displays the monitoring currents and corresponding
changes along with the load breaker status. It also has a
Fig. 6. RSCAD front panel for no fault condition of the power system
The system should also monitor the failed generator status
since it has to bring the load back into the system if the fault
with generator is rectified. All the above operation should be
done in real time, and the PI system, LabVIEW, and the PLC
should be monitoring the system in order for the system to
operate successfully. Figure 6 shows the normal condition of
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the sample power system being monitored through the
RSCAD front panel. This includes the three phase currents
and voltages of the two generators and the breaker status
indicators for the generators and the manual breaker controls.
As shown in figure 6, all breakers are closed and voltage/
currents are balanced. When the system is operating normally
the current drawn by the loads are 1.05 kA each, and the rms
value being monitored at 0.761 kA.
V.
SIMULATION RESULTS
The first possible option to observe the system signals is
the RSCAD monitoring interface, to identify the fault
condition, as shown in fig. 7. It can be seen that one of the
phases of the generator, the phase 3 of generator one, has a
fault which is manually operated (can also be operated by
relay) and the breaker status is indicating the fault. It can be
seen from the other plots in fig. 7, that the system is
unbalanced as the current imbalances can be observed with the
generator one phase currents being dropped to 0.659 kA rms
with phase B being zero. At generator two, the corresponding
phase B current increased to 2.12 kA rms with others being
increased to 1.4 kA which clearly indicate the unbalanced
state of the system.
Fig. 8. LabVIEW front panel with indicators
System control will keep on sensing the status change
and should immediately bring the load back when generator
comes back in service for normal operation of the power
system. System control will work regardless of the number
of times the fault occurs and is cleared; the system senses
the change in real time and will take the necessary control
actions. Figure 9 shows the status of the system when it is
recovered from the fault. This can be concluded from the
fact that the monitoring parameter values observed in here
coincide with previous value of 0.7614 kA rms phase
currents for normal operation of the system.
Fig 7. Simulated system with fault on phase C generator 1
The LabVIEW program also recognizes this fault and
breaker opening and sends the same signal to the local PLC.
It also indicates the generator status using the LED
indicators, thus alerting the operator of failure. This also
acts as an additional medium to monitor and record the data,
and the graphs provided will show the real time variation of
the monitoring signals. This program will send the data to
the OPC server from where the PI system will pick up the
data for recording and storage. An immediate action is
taken here such that load one shed from the system so as to
balance the system with only one generator in operation.
This load shedding is indicated by the LED load status
indicators present in RSCAD as well LabVIEW front panel.
Figure 8 shows status of the LabVIEW front panel which
is monitoring the real time rms three phase currents which
are of the same magnitude as observed in the RSCAD
interface and any change in the system operation is reflected
here, and when the fault occurs, also can be seen is the
change in indicator color.
Fig. 9. Recovered system from the fault
Fig. 10. PI process book interface
The PI system also simultaneously monitors the changes
taking place in the system, and the PI server tracks these
changes in real time and stores the data and is capable of
sending it to the third party clients for further calculations, if
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needed. The PI process book is very useful in monitoring and
displaying the data, and also it is capable of indicating faults
with alarms, and the data plots are drawn over time by which
the system changes can be tracked over for longer periods.
The PI process book interface is shown in figure 10.
The interface developed in fig. 10 consists of six different
plots updating in real time over Ethernet the status of the
generator currents over time. Real time data update the plots
as well as store the three phase rms current data and interface
also consist of visual indicators for alerting the operator of any
faults. Here, the plots are monitoring the data for 3 hrs but are
modified to show data plots for 60 min to observe the changes
clearly.
The results explained above indicate the successful
integration of different hardware at laboratory level for testing
and validation of a power system network. The current
activities of this research also focus on PMU and PDC testing
by including them in the test bed developed for further
research activities.
VI. SUMMARY
The objective of this work is to develop a real time
automated power system network and control test bed at the
laboratory level to enhance the power system testing and
validation schemes. This is achieved by integrating different
hardware devices and developing communication interface
between those devices. Test case was developed and validated
for fault detection, breaker control, outage sensing, and
automated corrective action. A simple power system test case
is developed in RSCAD and simulated using RTDS to imitate
virtual power system. The NI-PXI system and the PLC work
on the monitoring and controlling part of the system. The
remote control center also provides added advantages and
opportunity for identifying cyber security vulnerabilities. The
PI system brings the added advantage of data repository,
monitoring and event analysis features for the overall system.
Simulating a larger power system and incorporating the
additional devices like Phasor Measurement Units (PMU) and
the Phasor data to the PI system are some of the future goals
of this research work.
VII. ACKNOWLEDGMENT
The authors gratefully acknowledge the continuous support
of the National Instruments, OSI Soft, RTDS Technologies
Inc, SEL Inc, and Control Systems Inc for their valuable
suggestions on the device installation and operation. We
would also like to thank the Department of Energy and Pacific
Gas and Electric Company for their financial support. A
special thanks to MSU Computer Science Engineering
department for providing us with valuable hardware and
additional expertise.
VIII. REFERENCES
[1]
U.S Department of Energy, “The Smart Grid: An Introduction”, Office
of Electricity Delivery and Energy Reliability, 2008, [Online]. Available
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http://www.rockwellautomation.com/
http://www.ni.com/
http://www.osisoft.com/
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IX. BIOGRAPHIES
Ram Mohan, Reddi is pursuing his master’s degree in Electrical and
Computer Engineering at Mississippi State University (MSU). He received
B.Tech. Degree from Regency Institute of Technology (RIT) affiliated to
Pondicherry University, Pondicherry, India in 2007. He is an active member
of IEEE and Power and Energy Society. He is the recipient of Outstanding
Academic Achievement award for 2003-2007 at RIT. His fields of interest
include Power System Automation, Measurement and Instrumentation, and
Control systems.
Anurag K. Srivastava received his Ph.D. degree from Illinois Institute of
Technology (IIT), Chicago, in 2005, M. Tech. from Institute of Technology,
India in 1999 and B. Tech. in Electrical Engineering from Harcourt Butler
Technological Institute, India in 1997. He is working as Assistant Research
Professor at Mississippi State University since September 2005. Before that,
he worked as research assistant and teaching assistant at IIT, Chicago, USA
and as Senior Research Associate at Electrical Engineering Department at the
Indian Institute of Technology, Kanpur, India as well as Research Fellow at
Asian Institute of Technology, Bangkok, Thailand. His research interest
includes real time simulation, power system modeling, power system security,
power system deregulation and artificial intelligent application in power
system. Dr. Srivastava is senior member of IEEE, and member of IET, Power
and Energy Society, Sigma Xi and Eta Kappa Nu. He serves as vice-chair of
IEEE PES career promotion committee and secretary of IEEE PES student
activities committee. He is recipient of several awards and serves as reviewer
for IEEE Transactions, international journals and conferences
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