ECE 530 – Analysis Techniques for Large-Scale Electrical Systems Prof. Hao Zhu Dept. of Electrical and Computer Engineering University of Illinois at Urbana-Champaign 8/24/ Lecture 1: Power System Overview

Course Overview Course presents the fundamental analytic, simulation, and computation techniques for the analysis of large- scale electrical systems. The course stresses the importance of the structural characteristics of power systems, with an aim towards practical analysis and applications. 2

Topics 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 3

References M. Crow, “Computational Methods for Electric Power Systems,” Y. Saad, “Iterative Methods for Sparse Linear Systems,” (Free online) A. R. Bergen, “Power Systems Analysis,” 1986 A. J. Wood, B. F. Wollenberg, and G. B. Sheble, “Power Generation, Operation, & Control,” 3 rd ed.,

Other resources – IEEEXplore, Google Scholar – Peers, networking 5

Simple Power System 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 6

Complications 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 7

Notation - Power Power: Instantaneous consumption of energy Power Units Watts = voltage x current for dc (W) kW –1 x 10 3 Watt MW – 1 x 10 6 Watt GW–1 x 10 9 Watt TW–1 x Watt Installed U.S. generation capacity is about 900 GW ( about 3 kW per person) Maximum load of Champaign/Urbana about 300 MW 8

Notation - Energy 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 10 6 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) 9

Notation and Voltages 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. 10

Power System Examples 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 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 11

North America Interconnections 12

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 sources of energy to create it, and it is usually 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 13

Sources of Energy - US About 84% Fossil Fuels Source: EIA Annual Energy Outlook 2013, Electric Power Monthly, July 2013 About 40% of our 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 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) 14

US Historical and Projected Energy Usage Projections say we will still be 79% fossil in 2040! Source: EIA Annual Energy Outlook

Worldwide Energy Usage 16 Source: EIA International Energy Outlook, 2013

Electric Energy Economics 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 (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? 17

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

Natural Gas Prices 1990’s to 2013 Marginal cost for natural gas fired electricity price in $/MWh is about 7-10 times gas price 19

The Rise of Natural Gas Generation Source: US EIA,

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 21

The Rise of Renewables: Solar 22 Source: installations-by-quarter.jpg Total US PV Capacity Reached 5.3 GW in 2013

Key Driver for Renewables: Concerns about Global Warming Source: Value was about 280 ppm in 1800; in 2013 it is 396 ppm 23

Worldwide Temperature Graph Source: / Baseline is 1961 to 1990 mean 24

Looking Back a Little Further 25 Source: With a lot more uncertainty!

Going Back Further it Was Mostly Cold! 26

Compelling Evidence? 27 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 Source: Prof. Gross Fall 2013 ECE 333 Notes "With four parameters I can fit an elephant and with five I can make him wiggle his trunk." — John von Neumann

And Where Might Temps Go? Source: 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. 28 More on global warming controversy:

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 29

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 30

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 31

Vertical Monopolies 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 32

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 33

345 kV+ Transmission Growth at a Glance (From Jay Caspary) 34

345 kV+ Transmission Growth at a Glance (From Jay Caspary) 35

345 kV+ Transmission Growth at a Glance (From Jay Caspary) 36

345 kV+ Transmission Growth at a Glance (From Jay Caspary) 37

History ’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 competition 38

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 39

State Variation in Electric Rates 40

Utility Restructuring 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 (Enron Crisis Timeline by FERC) – Northeast blackout of 2003 (Final report)

The California-Enron Effect Source : RI AK electricity restructuring delayed restructuring no activity suspended restructuring WA OR NV CA ID MT WY UT AZ CO NM TX OK KS NE SD ND MN IA WI MO IL IN OH KY TN MS LA AL GA FL SC NC W VA PA NY VT ME MI NH MA CT NJ DE MD AR HI DC 42

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 43

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 I 2 R losses), but more difficult to insulate. The subtransmission levels are in the 69 to138 kV range 44

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 45

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 46

Transmission to Distribution Transformer 47

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. 48

Fundamental 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 49

Operational Requirements 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 50

Power System Operation Regimes transients disturbance response automatic system response operator response steady state operations steady state contingencies time minutes seconds operations horizon planning horizon hours; days; months 51