Thesis Presentation_Pulok_v1

Real-time Voltage Stability MonitoringTool for Power System
TransmissionNetwork Using SynchrophasorData.
Master’s Thesis Defense Presentation
by
Md Kamrul Hasan Pulok
MS degree candidate
Advisor : Dr. Omar Faruque

2
Research Objective
To Develop A Real-time Voltage Stability Analysis
And Visualization Tool.

3
Research Motivation
Power system infrastructure tend to have high utilization
Higher utilization means higher vulnerability to system collapse
Big challenge for monitoring and predicting voltage collapses
Traditional SCADA measurements are unsuitable for real-time
voltage stability analysis
The motivation of this research is to use available advanced
technologies for real-time voltage stability analysis with the
goal of achieving smart grid.

4
Challenges and Solution
For real-time application, measurement device with
high sampling rate required
PMU Devices are expensive
Real-time metered data storage and retrieval
Real-time dynamic state estimation
Real-time interfacing with developed GUI tool and
database server
Synchrophasor Technology
(PMU)
Optimal PMU Placement
algorithm
OpenPDC (Phasor data
concentrator)
Microsoft SQL Database
server 2012
Linear state estimation
method (LSE)
Challenges Solution

Technology Used/Developed:
5
Real-time Digital Simulation (RTDS®)
Technology
Synchrophasor (PMU) Technology
Novel Algorithm for Optimal PMU
Placement
Real-time Dynamic State Estimation
Real-time Voltage Stability Visualization

6
RTDS Power
system Model
Phasor data
streaming
through IEEE
C37.118 Protocol
Internet
Phasor Data
Concentrator
Microsoft SQL
server
Control CenterRemote Power System
Communication System
Dynamic
State
Estimation
VSI
Calculatio
n
Visualization
VSM Tool
PMU
measurements
Block diagram of Real-time VSM Tool
VSM : Voltage Stability Monitoring

7
Power System : IEEE 39 Bus test System
No. of Generators : 10 (Total Generation around 6 GW)
Bus Voltage : 345 kV
Simulation Tool : Real-time Digital Simulator (RTDS®)
Racks Used : 2
Simulation time-steps : 50 micro-seconds
RSCAD Model
(User Interface)
Real time digital simulator
(with multi core
processor)
RSCAD Run-time view
RTDS Model of Power system

8
Technology
Placement

9
 Synchronized Phasor Measurement Unit, also known as PMU.
 Synchronized with common time source like GPS
 Calculates voltage and current Phasors, frequency & Rate of change of frequency
 Reports measurement over the Internet.
Ref: http://www.qualitrolcorp.com/Products/Fault_Recording_and_Fault_Location/Phasor_Measurement_Units/
Definition of Synchrophasor

10
Ref: http://www.eia.gov/todayinenergy/detail.cfm?id=5630
http://www.phasor-rtdms.com/phaserconcepts/phasor_adv_faq.html
Why Synchrophasor (PMU)?
SCADA Measurements
• Slow (time resolution in the range of 2sec to 10sec)
• Unsynchronized with other measurements
• Considered as X-ray quality measurements
PMU Measurements
• Fast (time resolution in the range of milliseconds)
• Time Synchronized with other measurements.
• Considered as MRI quality measurements

11
Application of PMUs
Power System Wide Area Monitoring Systems (WAMS)
Wide area control application
Power system protection
Intelligent Alarms

12
P-Class PMU:
“P class is intended for applications requiring fast response and mandates no explicit
filtering. The letter P is used since protection applications require fast response.”—IEEE Std.
Key Characteristics:
 Protection Class
 Gives fast response
 Used in protection applications.
Ref: IEEE Standard C37.118.1-2011
M-Class PMU:
“M class is intended for applications that could be adversely effected by aliased signals and
do not require the fastest reporting speed. The letter M is used since analytic measurements
often require greater precision but do not require minimal reporting delay”---IEEE Std.
Key Characteristics:
 Measurement Class
 Gives precise response
 Used in measurement applications.
IEEE Std C37.118.1-2011 : IEEE Standard for Synchrophasor Measurements for Power Systems
P-class Used
IEEE Standard for PMU

13
RTDS PMU Model : Used GTNET Card
GTNET Card
PMU model Settings:
• Protocol : IEEE C37.118.2011
• PMU Class : P
• Sampling Rate : 10Hz
• Streaming phasor data through internet using TCP protocol.
RTDS Model of PMU

PDC Network
14
Power System
PMU
PMU
PMU
PMU
Communicati
on Network
Local PDC Stations
PDC
PMU
PMU
PMU
PMU
Communicati
on Network
PDC
PMU
PMU
PMU
Communicati
on Network
PDC
Communication Network
Centralized PDC

15
RTDS Power
system Model
PMU
measurements
Phasor data streaming
through IEEE C37.118
Protocol
Internet
Phasor Data
Concentrator
Microsoft SQL
server
Control CenterRemote Power System
Communication System
Block Diagram of PDC Network

16
Functions of PDC
To synchronize phasor measurements by aligning the time- tag of the measurements
Create a system wide time-series measurement set
Flag measurements based on the results of various quality inspection
Monitor PMUs performance : Latency, frame rate, quality & connection status etc.
Functional Elements of PDC
Phasor Data handler and
processor
OpenPDC
Storage of data in a database
server
SQL Server 2012

17
OpenPDC and SQL Server Database

18
Technology
Placement

Not Fully Observable
19
• PMU Devices are expensive. So we cannot use PMU devices at every bus for measurement.
• So we need to find out minimum number of PMU requirement and Bus locations.
• To do this, we need to perform observability analysis.
• Observability of Network: A network is fully observable if states of the bus can be either
measured or estimated.
G
m
mm
Fully Observable
Optimal PMU Placement

20
To identify minimum PMU bus locations, we need to perform observability analysis.
Observability analysis criteria:
1. For a bus selected for PMU placement, bus voltage phasor and current phasor of all incident
branches are known.
2. For known voltage phasor and current of an incident branch at a bus, voltage phasor at
other bus of this branch can be evaluated.
3. For known voltage phasor at both ends of a branch, current phasor of this branch can be
calculated.
G
e
P
e
v
i i
G
Fully Observable
According to observability criteria, for same minimum number of PMU, PMU can be positioned
at different bus locations maintaining full observability.
Network Observability

21
9 Bus
System 1
9 Bus
System 2
Total Bus 9 9
PMU Bus 3 2
PMU Channel 7 9
Total Branch 9 14
PMU Location % 33.3% 22.2%
Minimum Number of PMU depends
on network structure
We need the help of computer to identify optimum PMU locations. So we developed our own.
Minimum PMU usage
7 6 5
8
1
9
2
4
3

Formulation To Identify Optimum PMU Location
This is a mathematical optimization problem

Formulation To Identify Optimum PMU Location

25
Developed GUI for Optimal PMU Placement Identifier

26
[1] Greedy Algorithm, Breadth-first algorithm
[2] Particle swarm optimization method
[3] 3 stage optimal PMU Placement
There are many algorithms are available for PMU placement optimization. Some are like:
Ref: [1] Jiangxia Zhong, Phasor Measurement Unit (PMU) Placement Optimisation in Power Transmission Network based on Hybrid Approach;
[2] Rather, Z.H.; Chengxi Liu; Zhe Chen; Thogersen, P., ”Optimal PMU Placement by improved particle swarm optimization,”
[3] B.K. Saha Roy, A.K. Sinha, A.K. Pradhan, An optimal PMU placement technique for power system observability, International Journal of Electrical Power & Energy Systems,
No. of PMU required Execution Time required
Test System BPSO IBPSO Our Tool BPSO IBPSO Our Tool
IEEE 24 Bus system 7 7 7 22.3 sec 15.4 sec 0.019 sec
IEEE 30 Bus system 10 10 10 144 sec 82 sec 0.041 sec
We developed our own tool using Integer linear programming (ILP) method.
Results
Comparison:

28
Useful feature of the GUI tool
Provides Alternative bus locations for same minimum number of PMU
• Higher observable branches give redundant measurement, so robust State
estimation possible
• Lower observable branches require lower usage of C.T. transformer. So low cost.

29
13 PMUs are used with observable branches of 52
IEEE 39 Bus : Installed PMU locations

30
Technology
Placement

31
State Estimation (SE)
High Cost of
PMU
Limited
Number of
PMU
Limited
Number of
direct
measurement
of bus voltages
Need State
Estimation to
get indirect
measurement
of remaining
buses
Traditional SCADA measurement based SE:
• Based on P, Q, V and I measurements
• Thus all SE algorithms are solution of non-linear equations in iterative process.
• Unsuitable for real-time state estimation.
PMU based SE:
• Based on V and I measurements
• Thus linear state estimation (LSE) possible which can solve in one iteration.
• Suitable for real-time state estimation.

32
Linear State Estimation (LSE)

33

System
Topology
Matrix [H]
Voltage
measurement
bus incidence
matrix [II]
Current
measurement
bus incidence
matrix [A]
Series
Admittance
Matrix [Y]
Shunt
Admittance
Matrix [Ys]
34
For big power system, robust algorithm required to update system topology matrix
PMU
Measurement
matrix [z]
LSE States
[x]

35
Process diagram of Real-time SE

36
State Estimation Results
• We found Maximum State estimation error at normal load settings around 4%.
• Most of the Bus have SE error less then 1%.
• It can be reduced if we install more PMUs in the network.

37
Technology
Placement

38Ref: IEEE/CIGRE Joint Task Force on Stability Terms and Definitions; "Definition and Classification of Power System Stability".
“Power system stability is the ability of an electric power system, for a given initial
operating condition, to regain a state of operating equilibrium after being subjected
to a physical disturbance, with most system variables bounded so that practically the
entire system remains intact.” -- IEEE/CIGRE Joint Task Force
Voltage Stability:
• It refers to the ability of a power system to maintain steady voltages at all buses in
the system after being subjected to a disturbance.
• It depends on the ability to maintain equilibrium between load demand and load
supply from the power system.
Voltage Stability

39
Key Reasons of Voltage Instability
Critical Load increase
(Beyond System
Capacity)
Increased reactive
power consumption
Inability to meet
reactive power demand
Unable to maintain
transmission of power
Unable to maintain
Generation
Voltage drop
Voltage Collapse

40
Algorithms To Analyze Voltage Stability
System Variable
Based VSI
Voltage Collapse
Proximity Index
(VCPI)
Voltage Stability
Index (VSI)
Voltage Stability
Boundary
Jacobian Matrix
Based VSI
Many Algorithms are Available.
• Most Popular
• Suitable for Real-time
implementation
Comparative study is
performed using Real-time
simulation

41
Voltage Collapse Proximity Indicator (VCPI)
Based on maximum transferrable power through transmission line
• Index Range : 0 to 1
• Higher means more vulnerable
• 4 Separate Index.

42
Voltage Stability Index (VSI)
Based on maximum transferrable power through transmission line
• Index Range : 0 to 1
• Higher means more vulnerable
• One Index.

43
The coefficients a, b, c are determined by points A, B and C in P-Q plane
Voltage Stability Boundary in P-Q Plane
Parabolic Equation:
• Stable Condition : Operating
point inside Boundary
• Unstable Condition : Outside
boundary

44
Simulation
• Real-time simulations are performed to compare voltage stability analysis
algorithms.
• IEEE 39 Bus RTDS model with installed PMUS are USED.
• To simulate voltage instability condition, loads are increased by 1% after
each 10sec.
• Two case study:
• Case-1 with Infinite source representing strong grid
• Case-2 without Infinite source.

46
Simulation Results
Voltage Stability Boundary in P-Q Plane

47
Simulation Results
line ranking comparison by VSI and VCPI (at 140% load, case-1)
Weakest Line Ranking based on VSI and VCPI

48
Key take-away
Both VSI and VCPI can effectively index voltage stability Margin
Also they can predict voltage instability based on system structure
By using VSI, ranking of weakest line is possible
VSI has only one index. So it is more suitable for the VSM tool.
Voltage stability boundary is suitable for visualization
Voltage stability boundary is useful to understand for which power
(P/Q) instability is more prominent
VSI and Voltage stability boundary are implemented in the tool

49
Voltage Stability Monitoring (VSM) Tool : Features
VSM
Ultra-fast data
communication
with SQL Sever
Real-time
phasor data
processor
Real-time
dynamic
estimator
Real-time VSI
Calculation
Real-time
weakest line
ranking
Intuitive
Visualization

50
Voltage Stability Monitoring (VSM) Tool

51

Key Contributions Of This Research
Developed a novel algorithm to identify optimum PMU
placement
Developed a Optimum PMU Placement Identifier tool
with intuitive GUI
Setup a PDC server in the CAPS Lab. Developed an
algorithm for real-time data communication
Developed real-time dynamic state estimator tool
Developed real-time Voltage stability monitoring tool
which is usable for WAMS

54
Possible Future Work
Real-time application of PMU data can be explored and implemented
Power
Oscillation
Monitoring
Automatic
Generator
Shedding
Power Swing
Detection and
Protection
Load Shedding
under Remedial
Action Schemes
(RAS)
Fault Location
Identification

55
Conclusion
The research objective is accomplished by
developing a real-time voltage stability analysis
and visualization tool.

57
Thanks
Questions/ Comments/ Suggestions are most welcome.

• Power swing detection and protection
• Load shedding under Remedial Action Schemes (RAS).
• Synchrophasor assisted Black Start
• Automatic Generator Shedding
• Fault location identification
• Bus deferential relaying
• Line deferential protection
• Fine tuning of line parameters
• Synchrophasor application to controlled islanding
• Detection of power system inter-area oscillations
• Synchrophasor-based Line Backup Protection
Slide 61
Application of PMUs in Protection Technology

• Voltage stability index monitoring and prediction
• Line thermal monitoring
• Ambient and transient power oscillation monitoring
• Power oscillation monitoring
• Power damping monitoring
• Phase angle monitoring
• Wide area frequency monitoring
Application of PMUs in WAMS

63Ref: IEEE/CIGRE Joint Task Force on Stability Terms and Definitions; "Definition and Classification of Power System Stability“
http://rochistory.com/blog/wp-content/uploads/2013/08/blackout2003.jpg.
• Possible outcomes of this instability :
– Loss of load in an area
– Tripping of lines and other elements leading to cascading outages
– Loss of synchronism of some generators may result from these outages.
– Voltage Collapse
– voltage instability leads to a blackout or abnormally low
voltages in a significant part of the power system
Outcomes of Voltage Stability

Presentation Stage1 : Project Introduction : Real-time
64
“Real-time is a term often used to distinguish reporting or depicting events at the same rate and
sometimes at the same time as they unfold, rather than compressing a depiction or delaying a
report.”
- Wikipedia
“Real-time simulation refers to a computer model of a physical system that can execute at the
same rate as actual "wall clock" time. “
In other words, the computer model runs at the same rate as the actual physical system.
For example if a tank takes 10 minutes to fill in the real-world, the simulation would take 10
minutes as well.
- Wikipedia
Ref: http://en.wikipedia.org/wiki/Real-time
21
Real-time

Presentation Stage1 : Project Introduction : Real-time
65
Usage of Real-time simulation:
• In the industrial market for operator training and off-line controller tuning
• Statistical power grid protection tests
• Aircraft design and simulation
• Motor drive controller design
• Space robot integration
• Power System simulation
• Hardware in the loop testing
• and so on…
Ref: http://en.wikipedia.org/wiki/Real-time_simulation
http://spinoff.nasa.gov/spinoff1997/images/109.jpg
http://sine.ni.com/cms/images/casestudies/shanghaiphoto.png?size
http://www.engineering.com/Portals/0/BlogFiles/swasserman/bigstock-mechanical-technician-operativ-18987962.jpg
http://4.bp.blogspot.com/-1-vfGwW8maM/UCubVpBQhFI/AAAAAAAASXk/XdnuSxxRA0c/s523/mapsmania.gif
21
Real-time

21
Presentation Stage1 : Project Introduction : Power System Transmission Network
66
• Used for bulk transfer of electrical energy from generating power plants to substations.
• Transmission lines, when interconnected with each other, become transmission networks.
• Electricity is transmitted at high voltages (120 kV or above) to reduce the energy losses in long-
distance transmission.
http://en.wikipedia.org/wiki/Electric_power_transmission
Power System Transmission Network

Presentation Stage1 : Project Introduction : Power System Transmission Network
67
• Transmission lines, when interconnected with each other, become transmission networks.
•The Continental U.S. power transmission : 300,000 km of lines
•operated by approximately 500 companies.
Ref: http://upload.wikimedia.org/wikipedia/commons/d/d4/UnitedStatesPowerGrid.jpg
Why Transmission line in Network form required?
• There should be always a balance between power supply and load demand.
• If load demand significantly exceeds > possible generation plant and transmission equipment
outage > possible regional blackout.
• To avoid this scenario, multiple redundant alternative routes for power flow arranged by
transmission network.
21
Power System Transmission Network

Appendix-1
PMU Method of Operation:
• A PMU can measure 50/60 Hz AC waveforms (voltages and currents) typically at a rate of 48
samples per cycle (2880 samples per second).
• The analog AC waveforms are digitized by an Analog to Digital converter for each phase.
• A phase-lock oscillator along with a Global Positioning System (GPS) reference source
provides the needed high-speed synchronized sampling with 1 microsecond accuracy.
• The resultant time tagged Phasors can be transmitted to a local or remote receiver at rates
up to 60 samples per second.
• The Phasor data is collected either on-site or at centralized locations using Phasor Data
Concentrator (PDC) technologies.
68

Ref: Power System Analysis, Hadi Saadat, Page 58

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