Thesis Presentation_Pulok_v1

Real-time Voltage Stability Monitoring Tool for Power System Transmission Network Using Synchrophasor Data.

Master’s Thesis Defense Presentationby

Md Kamrul Hasan PulokMS degree candidate

Advisor : Dr. Omar Faruque

Research Objective

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

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.

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:

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

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

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

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

Ref: http://www.eia.gov/todayinenergy/detail.cfm?id=5630http://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

Application of PMUs

Power System Wide Area Monitoring Systems (WAMS)

Wide area control application

Power system protection

Intelligent Alarms

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

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

Power SystemPMU

PMU

PMU

PMU

Communication Network

Local PDC StationsPDC

PMU

PMU PMU

PMU


PDC

PMU

PMU

PMU


PDC


Centralized PDC

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

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

OpenPDC and SQL Server Database

Not Fully Observable

• 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

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

GFully Observable

According to observability criteria, for same minimum number of PMU, PMU can be positioned at different bus locations maintaining full observability.

Network Observability

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 LocationThis is a mathematical optimization problem

Formulation To Identify Optimum PMU Location

Proposed Algorithm

Developed GUI for Optimal PMU Placement Identifier

[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 IEEE 39 Bus system 13 13 13 284 sec 173 sec 0.079 sec IEEE 57 Bus system 17 17 17 658 sec 350 sec 0.567 sec

We developed our own tool using Integer linear programming (ILP) method.

Results

Comparison:

Results

Useful feature of the GUI toolProvides 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.

13 PMUs are used with observable branches of 52

IEEE 39 Bus : Installed PMU locations

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 measurem

ent 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.

Linear State Estimation (LSE)

System Topology Matrix [H]

Voltage measurement bus incidence matrix

[II]

Current measurement bus incidence matrix

[A]

Series Admittance Matrix [Y]Shunt Admittance

Matrix [Ys]

Linear State Estimation (LSE)For big power system, robust algorithm required to update system topology matrix

PMU Measurement

matrix [z]LSE States

[x]

Process diagram of Real-time SE

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.

Ref: 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

Key Reasons of Voltage InstabilityCritical 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

Algorithms To Analyze Voltage Stability

System Variable Based VSI

Voltage Collapse Proximity Index (VCPI)

Voltage Stability Index (VSI)

Voltage Stability Boundary

Many Algorithms are Available.

• Most Popular• Suitable for Real-time implementation

Comparative study is performed using Real-time

simulation

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.

Voltage Stability Index (VSI)Based on maximum transferrable power through transmission line


• Index Range : 0 to 1• Higher means more vulnerable• One Index.

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

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.

Simulation Results

Simulation ResultsVoltage Stability Boundary in P-Q Plane

Simulation Results

line ranking comparison by VSI and VCPI (at 140% load, case-1)

Weakest Line Ranking based on VSI and VCPI

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

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

Voltage Stability Monitoring (VSM) Tool

Key Contributions Of This Research

Developed real-time dynamic state estimator tool

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

Conclusion

The research objective is accomplished by developing a real-time voltage stability analysis

and visualization tool.

Video Demonstration

Thanks Questions/ Comments/ Suggestions are most welcome.

Appendix

Matrix Formulation Rules

• 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 ProtectionSlide 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

Ref: 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

“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

21Real-time

Presentation Stage1 : Project Introduction : Real-time

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_simulationhttp://spinoff.nasa.gov/spinoff1997/images/109.jpghttp://sine.ni.com/cms/images/casestudies/shanghaiphoto.png?sizehttp://www.engineering.com/Portals/0/BlogFiles/swasserman/bigstock-mechanical-technician-operativ-18987962.jpghttp://4.bp.blogspot.com/-1-vfGwW8maM/UCubVpBQhFI/AAAAAAAASXk/XdnuSxxRA0c/s523/mapsmania.gif

21Real-time

21

Presentation Stage1 : Project Introduction : Power System Transmission Network

• 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

• 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.

Research Phases:

Ref: Power System Analysis, Hadi Saadat, Page 58

Thesis Presentation_Pulok_v1

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