March 27, 2015
Power Systems
Jaime De La Ree ECE Department
Early History
• The “first generator” was developed by Michael Faraday in 1831
• John Woolrich patents magneto-electric generator in 1842 (for electrotyping)
• California Electric Light Co. supplies power for arc lighting 1879
• First power stations in London and New York in 1882
• 1884 the Pearl Street station supplied 59,000 after starting with 2300 bulbs
Power System • Elements
• Generators - Input • Loads - Outputs • Lines – Ties Gens to Loads
• Operating Characteristics & Constraints • Power Balance – KVL & KCL • Line flows based on Impedances • No large-scale storage • Manufacture as “we need it”
Operation • Key ingredients: Economics and
Reliability
• Economics – Large Optimization • Generator Scheduling and Commitments • Cost minimization
• Reliability – No violations of voltage levels, Frequency excursions, power flows,……
• Continuous monitoring • Control
Blackouts • 1965 North East of the USA • 1977 New York City blackout • 1989 Geomagnetic storm affected Hydo-Quebec • 1996 High summer heat Western North America
and parts of Mexico • 2003 Northeast Blackout • 2003 Malaysia • 2003 Hurricane Isabel • 2003 Sweden and Denmark • 2003 Italy • ………
Blackouts • System studies • Many recommendations • EMS Centers – SCADA • Supervisory Control and Data
Acquisition • Power Flows and Power Injections (Real
and Reactive)
• State Estimators • Z = f(x) Z – Mediciones x - State
7
Static State Estimator
• System is static while “scan” is made • Technology Limitation
• Non-Linear • Iterative
• Bad Data rejection- important
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Static State Estimator
• State of the system – EMS
• Contingency Analysis
• Operator makes topological and/or operational changes to move the system to a more secure operating point
• Generation Dispatch
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Static State Estimator
• Field Sensors – IEDs, PMUs • SCADA • EMS • State Estimation • Applications
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Static State Estimator • Data Collection
• SCADA (Supervisory Control and Data Acquisition)
• State of the system – EMS
• Large and Complex Harware-Software Systems
• Operator makes topological and/or operational changes to move the system to a more secure operating point
• Generation Dispatch
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A New Paradigm: PMU
• Synchrophasor • Synchronized Phasor Measurement
• PMU • Phasor Measurement Unit
2 45°
GPS
Phasors
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Sampled data Phasors Relay
Logic
Digital filtering
Analog filters In
puts
• Current and voltage magnitudes for relaying require computation of phasors
• Want to respond to symmetrical rms quantities in the presence of harmonics and other noise • Impedance relaying requires complex phasors from which impedance can be calculated
Phasors - Definition
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θ
t=0
θ
Real
Imag
inar
y
• The starting time defines the phase angle of the phasor.
• This is arbitrary.
• However, differences between phase angles are independent of the starting time.
Sampling, Fourier
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t
Input signal
xn xn-1 . . x1
Dat
a sa
mpl
es
cosi
nes
sine
s
sin and cos functions
Phasor X = ---Σ xk(coskθ - j sinkθ)
√2 N
Non-Recursive Calc.
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t
θ1
θ1
θ2
θ2 = θ1 + kφ
The non-recursive phasor rotates in the forward direction, one sample angle per sample.
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t
θ1
θ1
The recursive phasor remains fixed if the input waveform is constant.
θ2= θ1
θ2 = θ1
Recursive Calculation
Why are they Important?
• Captures Voltage/Current magnitude and angle
• All units are referenced to a common time
• All information is time tagged • High Resolution data • 30 – 60 phasors per second
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PMU –A new view
PMU –A new view
WAMS
• Synchronous Measurements • GPS • Time error in Nano-Sec
• Time Tagged samples • Data Concentrators
21
Aplicaciones
• Monitoring • Information to Operators
• Control • Process and Equipment optimal
• Protection • …….
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What is it?
• An adaptive protection scheme is: • Settings • Alarms • Triggering/Threshold values • Security vs Dependability • Stress vs Capacity
• Becomes more attuned with he prevailing conditions of power system
23
Adaptive Protection
• I know…….. Most likely we are going to have arguments with field protection engineers.
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Why?
• Traditional protection schemes/systems are based on pre-determined studies: • “Fixed” Loads • “Static” topologies • “Known” contingencies • Hidden Failures are……
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How?
• Advances in Monitoring Systems: • Synchronous • Wide Area
• Microprocessor-Based IEDs • Store • Process • Communicate
• All in a common time
26
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Where?
• Possibly one of the most interesting questions • Criticality
• Generators • Lines • Loads
Generators
• Loss of Excitation protection
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LOF Relay
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Lines
30
Lines
31
LODF
32
Changes of Topology
• The problem here is “load”
33
34
Changes of Topology
35
Changes of Topology
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Changes of Topology
• Load-Flow Solution • The re-distribution is incorrect: The
“swing” bus will shoulder all the necessary change.
• Generation Loss • Associated Losses
• Inertial re-dispatch • Long-Term the solution may be
appropriate. Short-Term the solution neglects the electrical distances
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Loss of Generation
Where are you?
38
Where are you?
39
Loss of Generation
• Bus Admittance Matrix • Zero entry at “ij” indicates that
there is no connection between node i and node j
• Kron Reduction
40
IgIn
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Ygg YgnYng Ynn
!
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VgVn
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&&
Loss of Generation
• Let In=0
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Ig0
!
"##
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Ygg YgnYng Ynn
!
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Ig = Ygg −YgnYnn−1Yng"# $%Vg
IEEE – 39 Bus System
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Loss of Generation
43
Gen 32 Off
44
Gen 32 Off
45
Gen 7 Off
46
Gen 7 Fuera
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Gen 7 Fuera
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Vision
Deploymen
t Challenge
Oscilla3on Detec3on Voltage
Stability Monitoring
Model Valida3on
Transmission Pathway and Conges3on Management
Automated Controls Detec3on of Imminent Disturbance Cascading
High SGIG ac3vity (9-‐12 projects)
Source: DOE
DG and Renewables Integra3on
1-‐2 Years 2-‐5 Years >5 Years
Controlled System
Separa3on
Medium SGIG ac3vity (5-‐8 projects) Low SGIG ac3vity (1-‐4 projects) No SGIG ac3vity
Frequency Stability
Monitoring
State Es3ma3on
Islanding and Restora3on
Wide Area Monitoring and Visualiza3on
Post-‐event Analysis
Disturbance Detec3on and
Alarming
SGIG=smart grid investment grant
Next?
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