ECE 476 Power System Analysis

Lecture 2: Power Industry History, Review of Phasors

Prof. Tom Overbye

Dept. of Electrical and Computer Engineering

University of Illinois at Urbana-Champaign

overbye@illinois.edu

Announcements

• Please read Chapters 1 and 2• HW 1 is 2.9, 22, 28, 32, 48; due Thursday 9/3

• Will be turned in (for other homework we may have an in-class quiz)

• For Problem 2.32 you need to use the PowerWorld Software. You can download the software and cases at the below link; get version 18 (August 20, 2015) http://www.powerworld.com/gloversarma.asp

History, cont’d

• 1896 – ac lines deliver electricity from hydro generation at Niagara Falls to Buffalo, 20 miles away; also 30kV line in Germany

• 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

3

History, cont’d

• 1935 – Congress passes Public Utility Holding Company Act to establish national regulation, breaking up large interstate utilities (repealed 2005)• This gave rise to electric utilities that only operated in one state

• 1935/6 – Rural Electrification Act brought electricity to rural areas

• 1930’s – Electric utilities established as vertical monopolies

• Frequency standardized in the 1930’s

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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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Midwest Electric Grid in About 2000

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Image Removed

History, cont’d -- 1970’s

• 1970’s brought inflation, increased fossil-fuel prices, calls for conservation and growing environmental concerns

• Increasing rates replaced decreasing ones• 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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PURPA and Renewables

• PURPA, through favorable contracts, caused the growth of a large amount of renewable energy in the 1980’s (about 12,000 MW of wind, geothermal, small scale hydro, biomass, and solar thermal)– These were known as “qualifying facilities” (QFs)– California added about 6000 MW of QF capacity during the

1980’s, including 1600 MW of wind, 2700 MW of geothermal, and 1200 MW of biomass

– By the 1990’s the ten-year QFs contracts written at rates of $60/MWh in 1980’s, and they were no longer profitable at the $30/MWh 1990 values so many sites were retired or abandoned

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Abandoned Wind Farm Need South Point in Hawaii

Source: Prof. Sanders10

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 • 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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Electricity Prices, 1960-2010

Source: EIA, Annual Energy Review, 2010, Figure 8.10

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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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The Rise of Natural Gas Generation

Source: US EIA, 201118

August 14th, 2003 Blackout

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My Favorite 8/14/2003 Blackout Cartoon!

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The Smart Grid

• The term “Smart Grid” dates officially to the 2007 “Energy Independence and Security Act”, Title 13 (“Smart Grid”)• Use of digital information and control techniques• Dynamic grid optimization with cyber-security• Deployment of distributed resources including • Customer participation and smart appliances• Integration of storage including PHEVs• Development of interoperability standards

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Smart Grid Perceptions (Some of Us Like the Term “Smarter”)

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Renewable Portfolio Standards (September 2012)

Source: http://www.dsireusa.org/23

Power System Modeling and Time Frames

• Much of class covers power system models. An important quote to keep in mind is – “Essentially, all models are wrong, but some are useful.

However, the approximate nature of the model must always be borne in mind.” G.E.P. Box, N.R. Draper, Empirical Model-Building and Response Surfaces, Wiley, 1987, p. 424.

• Power systems coversmany different timeframes, with essentiallyno models valid forall of them

Image: Sauer, P.W., M. A. Pai, Power System Dynamics and Stability, Stripes Publishing, 200724

Review of Phasors

Goal of phasor analysis is to simplify the analysis of constant frequency ac systems

v(t) = Vmax cos(wt + qv)

i(t) = Imax cos(wt + qI)

Root Mean Square (RMS) voltage of sinusoid

2 max

0

1( )

2

T Vv t dt

T

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Phasor Representation

j

( )

Euler's Identity: e cos sin

Phasor notation is developed by rewriting

using Euler's identity

( ) 2 cos( )

( ) 2 Re

(Note: is the RMS voltage)

V

V

j t

j

v t V t

v t V e

V

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Phasor Representation, cont’d

The RMS, cosine-referenced voltage phasor is:

( ) Re 2

cos sin

cos sin

V

V

jV

jj t

V V

I I

V V e V

v t Ve e

V V j V

I I j I

(Note: Some texts use “boldface” type for complex numbers, or “bars on the top”)

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Advantages of Phasor Analysis

0

2 2

Resistor ( ) ( )

( )Inductor ( )

1 1Capacitor ( ) (0)

C

Z = Impedance

R = Resistance

X = Reactance

XZ = =arctan( )

t

v t Ri t V RI

di tv t L V j LI

dt

i t dt v V Ij C

R jX Z

R XR

Device Time Analysis Phasor

(Note: Z is a complex number but not a phasor)

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RL Circuit Example

2 2

( ) 2 100cos( 30 )

60Hz

R 4 3

4 3 5 36.9

100 305 36.9

20 6.9 Amps

i(t) 20 2 cos( 6.9 )

V t t

f

X L

Z

VI

Z

t

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