Transcript Power Systems

ECE 530 – Analysis Techniques for
Large-Scale Electrical Systems
Lecture 1: Power System Overview
Prof. Hao Zhu
Dept. of Electrical and Computer Engineering
University of Illinois at Urbana-Champaign
[email protected]
8/24/2015
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Course Overview
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Course presents the fundamental analytic, simulation,
and computation techniques for the analysis of largescale electrical systems.
The course stresses the importance of the structural
characteristics of power systems, with an aim towards
practical analysis and applications.
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Topics
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Power system modeling
Power flow analysis: Newton-Raphson; Gaussian
elimination; Conjugate gradient descent
Advanced power flow topics
Sparse matrix techniques
Sensitivity analysis
Least-squares and state estimation
Power system equivalencing
Numerical integration methods
Eigenanalysis methods
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References
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M. Crow, “Computational Methods for Electric Power
Systems,” 2002.
Y. Saad, “Iterative Methods for Sparse Linear Systems,” 1996.
(Free online)
A. R. Bergen, “Power Systems Analysis,” 1986
A. J. Wood, B. F. Wollenberg, and G. B. Sheble, “Power
Generation, Operation, & Control,” 3rd ed., 2014
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Other resources
http://matt.might.net/articles/phd-school-in-pictures/
– IEEEXplore, Google Scholar
– Peers, networking
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Simple Power System
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Every power system has three major
components
– generation: source of power, ideally with a
specified voltage and frequency
– load: consumes power; ideally with a constant
resistive value
– transmission system: transmits power; ideally as
a perfect conductor
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Complications
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No ideal voltage sources exist
Loads are seldom constant
Transmission system has resistance, inductance,
capacitance and flow limitations
Simple system has no redundancy so power system will
not work if any component fails
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Notation - Power
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Power: Instantaneous consumption of energy
Power Units
Watts = voltage x current for dc (W)
kW –
1 x 103 Watt
MW –
1 x 106 Watt
GW –
1 x 109 Watt
TW –
1 x 1012 Watt
Installed U.S. generation capacity is about
900 GW ( about 3 kW per person)
Maximum load of Champaign/Urbana about 300 MW
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Notation - Energy
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Energy: Integration of power over time; energy is what
people really want from a power system
Energy Units
Joule =
1 Watt-second (J)
kWh –
Kilowatthour (3.6 x 106 J)
MWh –
One MW for one hour
TWh –
One million MWh
Btu –
1055 J; 1 MBtu=0.292 MWh
U.S. electric energy consumption is about 4000 TWh
kWh (about 12,500 kWh per person, which means on
average we each use 1.4 kW of power continuously)
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Notation and Voltages
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The IEEE standard is to write ac and dc in smaller case,
but it is often written in upper case as AC and DC.
Three-phase is usually written with the dash, also as
3-phase.
In the US the standard household voltage is 120/240V,
+/- 5%. Edison actually started at 110V dc. Other
countries have other standards, with the European
Union recently standardizing at 230V. Japan’s voltage
is 100V.
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Power System Examples
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Electric utility: can range from quite small, such as an
island, to one covering half the continent
– there are four major interconnected ac power systems in
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North American, each operating at 60 Hz ac; 50 Hz is used in
some other countries.
Airplanes and Spaceships: reduction in weight is
primary consideration; frequency is 400 Hz.
Ships and submarines
Automobiles: dc with 12 volts standard
Battery operated portable systems
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North America Interconnections
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Electric Systems
in Energy Context
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Class focuses on electric power systems, but we first
need to put the electric system in context of the total
energy delivery system
Electricity is used primarily as a means for energy
transportation
– Use other sources of energy to create it, and it is usually
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converted into another form of energy when used
About 40% of US energy is transported in electric form
Concerns about need to reduce CO2 emissions and
fossil fuel depletion are becoming main drivers for
change in world energy infrastructure
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Sources of Energy - US
About 40% of our energy is
consumed in the form
of electricity, a percentage
that is gradually increasing.
The vast majority of the nonfossil fuel energy is electric!
About 84% Fossil Fuels
In 2012 we got about 1.4%
of our energy from wind and
0.04% from solar (PV and
solar thermal)
1 Quad = 293 billion kWh (actual), 1 Quad = 98
billion kWh (used, taking into account efficiency)
Source: EIA Annual Energy Outlook 2013, Electric Power Monthly, July 2013
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US Historical and Projected
Energy Usage
Projections say we will still be 79% fossil in 2040!
Source: EIA Annual Energy Outlook 2014
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Worldwide Energy Usage
Source: EIA International Energy Outlook, 2013
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Electric Energy Economics
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Electric generating technologies involve a tradeoff
between fixed costs (costs to build them) and operating
costs
– Nuclear and solar high fixed costs, but low operating costs
– Natural gas/oil have low fixed costs but high operating costs
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(dependent upon fuel prices)
– Coal, wind, hydro are in between
Also the units capacity factor is important to
determining ultimate cost of electricity
Potential carbon “tax” or regulation?
http://spectrum.ieee.org/energywise/energy/policy/carbon-emissions-tax-or-regulate
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Ball park Energy Costs
Nuclear:
$15/MWh
Coal:
$22/MWh
Wind:
$50/MWh
Hydro:
varies but usually water constrained
Solar:
$120 to 180/MWh
Natural Gas:8 to 10 times fuel cost in $/Mbtu (3-12)
Note, to get price in cents/kWh take price in $/MWh and
divide by 10.
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Natural Gas Prices 1990’s to 2013
Marginal cost for natural gas fired electricity price
in $/MWh is about 7-10 times gas price
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The Rise of Natural Gas
Generation
Source: US EIA, 2011
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The Rise of Renewables: Wind
Currently
about 6%
of our
electric
capacity
is wind
The up/downs
in 2001/2 and
2003/4 were
caused by
expiring tax
credits
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The Rise of Renewables: Solar
Total US PV Capacity Reached 5.3 GW in 2013
Source: http://solartribune.com/wp-content/uploads/2013/06/credited_SEIA_U.S.-PVinstallations-by-quarter.jpg
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Key Driver for Renewables:
Concerns about Global Warming
Value was
about 280
ppm in
1800; in
2013 it is
396 ppm
Source: http://www.esrl.noaa.gov/gmd/ccgg/trends/
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Worldwide Temperature Graph
Baseline is 1961 to 1990 mean
Source: http://www.cru.uea.ac.uk/cru/info/warming/
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Looking Back a Little Further
With a lot more uncertainty!
Source: http://www.econ.ohio-state.edu/jhm/AGW/Loehle/SupplementaryInfo.pdf
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Going Back Further it
Was Mostly Cold!
http://commons.wikimedia.org/wiki/File:Ice_Age_Temperature.png
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Compelling Evidence?
natural forcing only
natural (solar + volcanic)
forcing alone does not
account for warming in the
past 50 years
anthropogenic forcing
only
natural + anthropogenic
forcing
adding human influences (greenhouse
gases + sulfate aerosols) brings the models
and observations into pretty close
agreement
"With four parameters I can fit an elephant and
with five I can make him wiggle his trunk." —
John von Neumann
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Source: Prof. Gross Fall 2013 ECE 333 Notes
And Where Might Temps Go?
The models
show rate of
increase values
of between
0.18 to 0.4 C
per decade.
The rate from
1975 to 2005
was about
0.2 C per
decade.
Source: http://www.epa.gov/climatechange/science/future.html#Temperature
More on global warming controversy:
https://en.wikipedia.org/wiki/Global_warming_controversy
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Brief History of Electric Power
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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
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History, cont’d
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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
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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
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Within a particular geographic market, the electric
utility had an exclusive franchise
Generation
Transmission
Distribution
Customer Service
In return for this exclusive
franchise, the utility had the
obligation to serve all
existing and future customers
at rates determined jointly
by utility and regulators
It was a “cost plus” business
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Vertical Monopolies
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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
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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 competition
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History – 1990’s & 2000’s
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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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State Variation in Electric Rates
http://www.teslarati.com/installing-solarcitys-solar-panel-system-for-tesla/
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Utility Restructuring
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Driven by significant regional variations in electric
rates through the introduction of competition
Eventual goal is to allow consumers to choose their
electricity supplier
Two events affected the process of deregulation
– California electricity crisis 2000-01(Enron Crisis
Timeline by FERC)
– Northeast blackout of 2003 (Final report)
https://www.ferc.gov/industries/electric/indus-act/wec/chron/chronology.pdf
http://energy.gov/sites/prod/files/oeprod/DocumentsandMedia/BlackoutFinal-Web.pdf
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The California-Enron Effect
WA
MT
VT ME
ND
MN
OR
ID
SD
WY
NV
WI
CO
CA
PA
IL
KS
AZ
OK
NM
RI
IA
NE
UT
NY
MI
MO
IN
OH
W
VA VA
KY
CT
NJ
DE
DC
MD
NC
TN
AR
SC
MS AL
TX
NH
MA
GA
LA
AK
FL
HI
electricity
restructuring
delayed
restructuring
Source : http://www.eia.doe.gov/cneaf/electricity/chg_str/regmap.html
no activity
suspended
restructuring
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Interconnected Power System
Basic Characteristics
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Three–phase ac systems:
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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
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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
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The transmission network consists of following
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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
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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
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Electrical devices are joined
together at buses
The distribution system is
used to supply the electricity
to the consumers
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A Substation Bus
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
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Transmission to Distribution
Transformer
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Electricity Supply
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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
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Most forms of renewable energy are created in the form of
electricity; examples include hydro, wind and solar.
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Fundamental Requirements
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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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Operational Requirements
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Electric power delivery by the system must meet
minimum standards of power quality
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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
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Power System Operation Regimes
steady state operations
steady state contingencies
operator response
automatic system response
disturbance response
transients
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9
10
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5
3
10 10 10
1
time
10
minutes hours; days; months
seconds
planning horizon
operations horizon
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