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ECE 530 – Analysis Techniques for Large-Scale Electrical Systems
Prof. Hao ZhuDept. of Electrical and Computer Engineering
University of Illinois at Urbana-Champaign
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Lecture 2: Power System Modeling
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Announcements
• Class will make extensive use of PowerWorld Simulator. If you do not have a copy of v18, the free 42 bus student version is available for download at
http://www.powerworld.com/gloversarmaoverbye
• Start getting familiar with this package. Free training material is available at
http://www.powerworld.com/training/online-training
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Brief History of Electric Power
• Early 1880’s – Edison introduced Pearl Street dc system in Manhattan supplying 59 customers within a one mile radius
• 1884 – Sprague produces practical dc motor• 1885 – invention of transformer• Mid 1880’s – Westinghouse/Tesla introduce rival
ac system• Late 1880’s – Tesla invents ac induction motor• 1893 – First 3-phase transmission line operating
at 2.3 kV, 12 km in Southern California 3
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History, cont’d
• 1896 – ac lines deliver electricity from hydro generation at Niagara Falls to Buffalo, 20 miles away
• Early 1900’s – Private utilities supply all customers in area (city); recognized as a natural monopoly; states step in to begin regulation
• By 1920’s – Large interstate holding companies control most electricity systems; highest voltages were 200 kV
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History, cont’d
• 1935 – Congress passes Public Utility Holding Company Act (PUHCA) to establish national regulation, breaking up large interstate utilities (repealed 2005)
• 1935/6 – Rural Electrification Act brought electricity to rural areas
• 1930’s – Electric utilities established as vertical monopolies
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Vertical Monopolies
• Within a particular geographic market, the electric utility had an exclusive franchise
Generation
Transmission
Distribution
Customer Service
In return for this exclusivefranchise, the utility had theobligation to serve all existing and future customersat rates determined jointlyby utility and regulators
It was a “cost plus” business
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Vertical Monopolies
• Within its service territory each utility was the only game in town
• Neighboring utilities functioned more as colleagues than competitors
• Utilities gradually interconnected their systems so by 1970 transmission lines crisscrossed North America, with voltages up to 765 kV
• Economies of scale keep resulted in decreasing rates, so most every one was happy
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345 kV+ Transmission Growth at a Glance (From Jay Caspary)
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345 kV+ Transmission Growth at a Glance (From Jay Caspary)
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345 kV+ Transmission Growth at a Glance (From Jay Caspary)
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345 kV+ Transmission Growth at a Glance (From Jay Caspary)
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History -- 1970’s
• 1970’s brought inflation, increased fossil-fuel prices, calls for conservation and growing environmental concerns
• Increasing rates • As a result, U.S. Congress passed Public
Utilities Regulator Policies Act (PURPA) in 1978, which mandated utilities must purchase power from independent generators located in their service territory (modified 2005)
• PURPA introduced some competition12
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History – 1990’s & 2000’s
• Major opening of industry to competition occurred as a result of National Energy Policy Act of 1992
• This act mandated that utilities provide “nondiscriminatory” access to the high voltage transmission
• Goal was to set up true competition in generation
• Result over the last few years has been a dramatic restructuring of electric utility industry (for better or worse!)
• Energy Bill 2005 repealed PUHCA; modified PURPA
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Utility Restructuring
• Driven by significant regional variations in electric rates
• Goal of competition is to reduce rates through the introduction of competition
• Eventual goal is to allow consumers to choose their electricity supplier
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State Variation in Electric Rates
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The Goal: Customer Choice
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The Result for California in 2000/1
OFF
OFF
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The California-Enron Effect
Source : http://www.eia.doe.gov/cneaf/electricity/chg_str/regmap.html
RI
AK
electricityrestructuring
delayedrestructuring
no activitysuspended
restructuring
WA
OR
NV
CA
ID
MT
WY
UT
AZ
CO
NM
TX
OK
KS
NE
SD
NDMN
IA
WI
MO
IL IN OH
KY
TN
MS
LA
AL GA
FL
SC
NC
WVA VA
PA
NY
VT ME
MI
NH
MA
CTNJ
DEMD
AR
HI
DC
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August 14th, 2003 Blackout
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The Rise of Natural Gas Generation
Source: US EIA, 201120
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The Rise of Renewables: Wind
Currentlyabout 6%of our electric capacityis wind
The up/downsin 2001/2 and2003/4 werecaused by expiring taxcredits
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Rise of Renewables: Solar
22Source: http://solartribune.com/wp-content/uploads/2013/06/credited_SEIA_U.S.-PV-installations-by-quarter.jpg
Total US PV Capacity Reached 5.3 GW in 2013
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Interconnected Power System Basic Characteristics
• Three – phase ac systems:– generation and transmission equipment is usually
three phase– industrial loads are three phase– residential and commercial loads are single phase
and distributed equally among the phases; consequently, a balanced three – phase system results
• Synchronous machines generate electricity– Exceptions: some wind is induction generators;
solar PV• Interconnection transmits power over a wider
region with subsystems operating at different voltage levels
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Power Systems: Basic Characteristics
• The transmission network consists of following– the high voltage transmission system;– frequently, the subtransmission system; – sometimes, even the distribution system
• The transmission system forms the backbone of the integrated power system and operates at the highest voltage levels; typically, above 150 kV
• Less losses at high voltages (S=VI* and I2R losses), but more difficult to insulate.
• The subtransmission levels are in the 69 to138 kV range
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Power Systems: Basic Characteristics
• The generator output voltages are typically in the 11kV to 35 kV range and step up transformers are used to transform the potentials to transmission system voltage levels–Wind turbines have voltages in 600V range
• Bulk power system, which includes the transmission system and generators, is networked
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Power Systems: Basic Characteristics
• Electrical devices are joined together at buses
• The distribution system is used to supply the electricity to the consumers– primary distribution voltages
are in the 4 kV to 34.5 kV range at which industrial customers obtain their electricity supply
– secondary distribution voltage is 120/240 V to the residential/commercial customers
– distribution system is usually radial, except in some urban areas
A Substation Bus
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Transmission to Distribution Transformer
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Electricity Supply
• The basic function of a power system is to convert energy from one source to the electrical form; a key characteristic is that energy is not consumed as electricity but converted into heat, light, sound, mechanical energy or information
• The widespread use of electricity is due to its ability to transport and control efficiently and reliably
• Electricity is, by and large, a relatively clean source of energy– Most forms of renewable energy are created in the
form of electricity; examples include hydro, wind and solar.
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Fundamental Power System Requirements
• System must be able to track load continuously: continuous balance of supply and demand
• System must provide reliable supply of electricity at least cost
• System must have least environmental impacts in providing electricity to meet its customers’ demands
Yearly Load Variation Daily Load Variation
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Fundamental Requirements of a Power System
• Electric power delivery by the system must meet minimum standards of power quality– constant frequency– constant voltage– adequate reliability
• System must be able to supply electricity even when subjected to a variety of unexpected contingencies, such as the loss of a transmission line or generator
• A key focus of this course is the control capability to meet these requirements
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Power Systems Operate on Many Time Scales
electromagnetic transients
machine-network interaction
first swing transient stability
10 - 6 10
- 5 10 - 4 10 - 3 10
- 2 0.1 1 10
time, sec
induction motor dynamics
generator/excitation dynamics
prime mover control
mechanically switched capacitors/reactors
SVC
generator inertial dynamics
DC
protective relaying
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load/power transfer increase
line/transformer overload
10 100 1,000 10,000time, sec
gas turbine start-up
boiler dynamics
OLTC transformer & distribution
voltage regulator
powerplant operator actions
generation change/AGC
excitation limiting
system operator actions
prime mover control
load diversity thermostat control
protective relaying including overload
protection
DC converter OLTC
Power Systems Operate on Many Time Scales
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Power System Operation Regimes
transients
disturbance response
automatic system response
operator response
steady state operationssteady state contingencies
time
minutesseconds 910 710 10
operations horizon planning horizonhours; days; months
510 310 110
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Generation Control and Scheduling Example
timescale
loadvariations function decision
seconds small &random
automatic generationcontrol
match the on-line generation with the load
minutes large economic dispatch allocate economically the load among the committed generating units
days
and
hours
wide
hydroscheduling
unit commitment
hydrothermalcoordination
transactionevaluation
water releases from reservoirs and hourly hydro generation
start-up and shutdown of units
integrated hydro schedule and unit commitment
interchange of power/energy with neighboring systems
weeks very wide swings
fuel, hydro and maintenance scheduling
meet load economically with the installed resource mix
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