EE 369Power Systems Engineering

Lecture 1Introduction

Slides by: Tom Overbye, University of IllinoisWith additions by Ross Baldick, University of Texas

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Simple Power System• Every power system has three major

components:– generation: source of power, ideally with a specified

voltage and frequency– load or demand: consumes power; ideally with a

constant resistive value– transmission system: transmits power; ideally as a

perfect conductor

• Additional components include:– distribution system: local reticulation of power,– control equipment: coordinate supply with load.

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Complications

• No ideal voltage sources exist.• Loads are seldom constant and are typically

not entirely resistive.• 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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Power• Power:

– Instantaneous rate of consumption of energy,– How hard you work!

• Power = voltage x current for dc • Power Units:

Watts = amps times volts (W)kW – 1 x 103 WattMW – 1 x 106 WattGW – 1 x 109 Watt

• Installed U.S. generation capacity is about 1000 GW ( about 3 kW per person)

• Maximum load of Austin about 2500 MW.• Maximum load of UT campus about 50 MW.

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Energy• Energy:

– Integration of power over time,– Energy is what people really want from a power

system,– How much work you accomplish over time.

• Energy Units:

Joule = 1 watt-second (J)

kWh – kilowatthour (3.6 x 106 J)

Btu – 1055 J; 1 MBtu=0.292 MWh• U.S. annual electric energy consumption is about 3600

billion kWh (about 13,333 kWh per person, which means on average we each use 1.5 kW of power continuously).

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Power System Examples• Interconnection: can range from quite small, such

as an island, to one covering half the continent:– there are four major interconnected ac power

systems in North America (five, if you count Alaska), 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 and

higher voltages used in electric vehicles.• Battery operated portable systems.

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North America Interconnections

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Electric Systems in Energy Context• 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 (“primary”) sources of energy to create

electricity, and electricity is usually converted into another form of energy when used.

– Electricity is used by transforming into another form of energy.

• About 40% of US energy is transported in electric form.

Energy sources in USTotal primary energy in 2014:About 81% Fossil Fuels

Source: EIA Annual Energy Outlook 2014

• About 40% of our total energy is consumed in the form of electricity, a percentage that is gradually increasing.• The vast majority of the non-fossil fuel energy is electric!• In 2013 we got about 3% of our electric energy from wind and < 1% from solar (PV and solar thermal): increasing over time, but still small.

Electricity Generation Sources in US 2012

by energy

Coal

Natural gas

Nuclear

Hydroelectric

Wind

Source: EIA 2013

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Generation Sources in California 2010

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Generation Sources in Texas 2010: (wind grown to around 10% by 2014)

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Generation Sources in Illinois 2010

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Energy Economics• Electric generating technologies involve a

tradeoff between fixed costs (primarily capital costs to build them) and operating costs:– Nuclear, wind, and solar high fixed costs, but low

operating costs,– Natural gas has low fixed costs but relatively high

operating costs (dependent upon fuel prices)– Coal in between (although recent low natural gas

prices has meant that some coal plants have higher operating costs than some natural gas).

• Total average costs depend on fixed costs, operating costs, and capacity factor (ratio of average power production to capacity).

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Ball park operating CostsNuclear: $10/MWhCoal: $40/MWh (some coal considerably lower)Wind: couple $/MWh (maintenance and

operating)Hydro: few $/MWh (maintenance and operating)Solar: $0/MWhNatural Gas:

cost in $/MWh is 7 to 20 times fuel cost in $/MBtu; for example, with $8/MBtu gas, cost is $56/MWh to $160/MWh; with $5/Mbtu gas, cost is $35/MWh to $100/MWh.

Note, to get price in cents/kWh take price in $/MWh and divide by 10.

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Natural Gas Prices – to 2013

Natural Gas Prices

Source: Energy Information Administration, http://www.eia.gov/todayinenergy/detail.cfm?id=7710

Future mix of sources. • Likely long-term low costs of gas and advent of

greatly increased renewables has already changed the mix in Texas away from coal and towards gas and wind:– Wind already around 10% of electrical energy in

Texas,– Coal traditionally in service throughout year, but

Texas asset owners may only run some coal in Summer.

• Expect the trend to continue, especially if the US (eventually) enacts climate change legislation.

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Goals of Power System Operation

• Supply load (users) with electricity at– specified voltage (110 ac volts common for

residential),– specified frequency,– at minimum cost consistent with operating

constraints, safety, etc.

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Major Impediments• Load is constantly changing:

• Electricity is not storable (stored by conversion to other forms of energy),

• Power system is subject to disturbances, such as lightning strikes.

• Engineering tradeoffs between reliability and cost.

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Example Yearly Electric Load

0

5000

10000

15000

20000

250001

518

1035

1552

2069

2586

3103

3620

4137

4654

5171

5688

6205

6722

7239

7756

8273

Hour of Year

MW

Lo

ad

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Course Syllabus (chapters 1 to 7 and 11)

• Introduction and review of complex power, phasors & three phase (chapter 2),

• Transformers and per-unit system (chapter 3),• Transmission line parameters (chapter 4),• Power flow analysis (chapter 6),• Symmetrical faults (chapter 7),• Power system controls (chapter 11),• Economic system operation (chapter 11), • Optimal power flow (chapter 11),• Deregulation and restructuring (throughout semester).

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Brief History of Electric Power

• Early 1880’s – Edison introduced Pearl Street dc system in Manhattan supplying 59 customers.

• 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.

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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” (cheapest for one firm to produce everything because of “economies of scale”); states step in to begin regulation.

• By 1920’s – Large interstate holding companies control most electricity systems.

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History, cont’d

• 1935 – Congress passes Public Utility Holding Company Act 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:Charge to retail customers set byregulatory authority to be cost of investment and operations plusregulated return on investment.

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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 (bigger is cheaper per unit capacity) coupled with growth in demand resulted in decreasing average costs.

• Decreasing average costs together with strongly increasing demand implied decreasing real prices to end-use customers over time.

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History, cont’d -- 1970’s

• 1970’s brought inflation, stagnation of demand growth, increased fossil-fuel prices, calls for conservation and growing environmental concerns.

• Increasing prices replaced decreasing ones.• In that context, U.S. Congress passed Public

Utilities Regulatory 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, cont’d – 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.• Texas followed suit in 1996 and 1999.• 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, reflecting variations in generation stock and endowments of natural resources.

• Goal of competition is to reduce prices and increase efficiency:– (in short term) through the introduction of

competition, and – (in long term) competition’s incentives for

technological innovation.

• Allow consumers to choose their electricity supplier.

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State Variation in Retail Electricity Prices

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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