1. Lecture 4 Power System Operation Professor Tom Overbye Department of Electrical and Computer Engineering ECE 476 POWER SYSTEM ANALYSIS

2. 1 Reading and Homework Moving 1 st Exam? Oct 11 or 13? For lectures 4 through 6 please be reading Chapter 4 – we will not be covering sections 4.7, 4.11, and 4.12 in detail though you should still at least skim those sections. HW 1 is 2.9, 22, 28, 32, 48; due Thursday 9/8 For Problem 2.32 you need to use the PowerWorld Software. You can download the software and cases at the below link; get version 15. http://www.powerworld.com/gloversarma.asp Direct PowerWorld download page is http://www.powerworld.com/DemoSoftware/GloverSarmaSimdwnl dv15.asp

3. 2 State Variation in Electric Rates

4. 3 The Goal: Customer Choice

5. 4 The Result for California in 2000/1 OFF

6. 5 The California-Enron Effect Source : http://www.eia.doe.gov/cneaf/electricity/chg_str/regmap.html 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

7. 6 Natural Gas Boom, Bust and Boom

8. 7 August 14 th, 2003 Blackout

9. 8 2007 Illinois Electricity Crisis Two main electric utilities in Illinois are ComEd and Ameren Restructuring law had frozen electricity prices for ten years, with rate decreases for many. Prices rose on January 1, 2007 as price freeze ended; price increases were especially high for electric heating customers who had previously enjoyed rates as low as 2.5 cents/kWh 2009 average residential rate (in cents/kWh) is 9.08 in IL, 7.62 IN, 9.38 WI, 7.37 IA, 15.52 NY, 6.60 WA, 13.20 in CA, 9.82 US average

10. 9 The Rise of Renewables Currently about 4% of our electric capacity is wind The up/downs in 2001/2 and 2003/4 were caused by expiring tax credits

11. 10 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

12. 11 Smart Grid Perceptions

13. 12 In the News: Local Electricity Suppliers On Monday (Aug 29) the News-Gazette had a story about alternative electricity suppliers finally entering the Ameren residential market For example, BlueStar Energy offers electricity at a fixed price of 5.175 cents/kWh versus Ameren at 5.646 cents/kWh. There are other rate options as well so consumers need to shop around for what works best You still pay some money to Ameren for the use of the wires, just not for energy Check out www.pluginillinois.org

14. 13 In the News: Illinois Smart Grid Bill On Monday (Aug 29) legislation to “modernize” the Illinois electric grid was sent to Governor Quinn. He has promised to veto the bill. If vetoed it could be overriden in the fall veto session Supporters of the ten year, $3 billion effort, say the savings to consumers due to the installation of smart meters will more than offset the increase in rates. Quinn and other argue it gives too much money to ComEd and Ameren.

15. 14 Power System Operations Overview Goal is to provide an intuitive feel for power system operation Emphasis will be on the impact of the transmission system Introduce basic power flow concepts through small system examples

16. 15 Power System Basics All power systems have three major components: Generation, Load and Transmission/Distribution. Generation: Creates electric power. Load: Consumes electric power. Transmission/Distribution: Transmits electric power from generation to load. – Lines/transformers operating at voltages above 100 kV are usually called the transmission system. The transmission system is usually networked. – Lines/transformers operating at voltages below 100 kV are usually called the distribution system (radial).

17. 16 Simulation of the Eastern Interconnect

18. 17 Small PowerWorld Simulator Case Load with green arrows indicating amount of MW flow Used to control output of generator Direction of arrow is used to indicate direction of real power (MW) flow Note the power balance at each bus

19. 18 Power Balance Constraints Power flow refers to how the power is moving through the system. At all times in the simulation the total power flowing into any bus MUST be zero! This is know as Kirchhoff’s law. And it can not be repealed or modified. Power is lost in the transmission system.

20. 19 Basic Power Control Opening a circuit breaker causes the power flow to instantaneously(nearly) change. No other way to directly control power flow in a transmission line. By changing generation we can indirectly change this flow.

21. 20 Transmission Line Limits Power flow in transmission line is limited by heating considerations. Losses (I 2 R) can heat up the line, causing it to sag. Each line has a limit; Simulator does not allow you to continually exceed this limit. Many utilities use winter/summer limits.

22. 21 Overloaded Transmission Line

23. 22 Interconnected Operation Power systems are interconnected across large distances. For example most of North America east of the Rockies is one system, with most of Texas and Quebec being major exceptions Individual utilities only own and operate a small portion of the system, which is referred to an operating area (or an area).

24. 23 Operating Areas Transmission lines that join two areas are known as tie-lines. The net power out of an area is the sum of the flow on its tie-lines. The flow out of an area is equal to total gen - total load - total losses = tie-flow

25. 24 Area Control Error (ACE) The area control error is the difference between the actual flow out of an area, and the scheduled flow. Ideally the ACE should always be zero. Because the load is constantly changing, each utility must constantly change its generation to “chase” the ACE.

26. 25 Automatic Generation Control Most utilities use automatic generation control (AGC) to automatically change their generation to keep their ACE close to zero. Usually the utility control center calculates ACE based upon tie-line flows; then the AGC module sends control signals out to the generators every couple seconds.

27. 26 Three Bus Case on AGC Net tie flow is close to zero Generation is automatically changed to match change in load

28. 27 Generator Costs There are many fixed and variable costs associated with power system operation. The major variable cost is associated with generation. Cost to generate a MWh can vary widely. For some types of units (such as hydro and nuclear) it is difficult to quantify. For thermal units it is much easier. These costs will be discussed later in the course.

29. 28 Economic Dispatch Economic dispatch (ED) determines the least cost dispatch of generation for an area. For a lossless system, the ED occurs when all the generators have equal marginal costs. IC 1 (P G,1 ) = IC 2 (P G,2 ) = … = IC m (P G,m )

30. 29 Power Transactions Power transactions are contracts between areas to do power transactions. Contracts can be for any amount of time at any price for any amount of power. Scheduled power transactions are implemented by modifying the area ACE: ACE = P actual,tie-flow - P sched

31. 30 100 MW Transaction Scheduled 100 MW Transaction from Left to Right Net tie-line flow is now 100 MW

32. 31 Security Constrained ED Transmission constraints often limit system economics. Such limits required a constrained dispatch in order to maintain system security. In three bus case the generation at bus 3 must be constrained to avoid overloading the line from bus 2 to bus 3.

33. 32 Security Constrained Dispatch Dispatch is no longer optimal due to need to keep line from bus 2 to bus 3 from overloading

34. 33 Multi-Area Operation If Areas have direct interconnections, then they may directly transact up to the capacity of their tie-lines. Actual power flows through the entire network according to the impedance of the transmission lines. Flow through other areas is known as “parallel path” or “loop flows.”

35. 34 Seven Bus Case: One-line System has three areas Area left has one bus Area right has one bus Area top has five buses

36. 35 Seven Bus Case: Area View System has 40 MW of “Loop Flow” Actual flow between areas Loop flow can result in higher losses Scheduled flow

37. 36 Seven Bus - Loop Flow? 100 MW Transaction between Left and Right Transaction has actually decreased the loop flow Note that Top’s Losses have increased from 7.09MW to 9.44 MW

38. 37 Pricing Electricity Cost to supply electricity to bus is called the locational marginal price (LMP) Presently some electric makets post LMPs on the web In an ideal electricity market with no transmission limitations the LMPs are equal Transmission constraints can segment a market, resulting in differing LMP Determination of LMPs requires the solution on an Optimal Power Flow (OPF)

39. 38 3 BUS LMPS - OVERLOAD IGNORED Line from Bus 1 to Bus 3 is over-loaded; all buses have same marginal cost Gen 1’s cost is $10 per MWh Gen 2’s cost is $12 per MWh

40. 39 LINE OVERLOAD ENFORCED Line from 1 to 3 is no longer overloaded, but now the marginal cost of electricity at 3 is $14 / MWh

41. 40 MISO and PJM MISO and PJM are the reliability coordinators covering the electric grid in Illinois. ComEd is in PJM, and Ameren is in MISO.

42. 41 MISO ACE Chart from Aug 31, 2011 https://www.midwestiso.org/MarketsOperations/RealTimeMarketData/Pages/ACECh art.aspx

43. 42 MISO LMPs 8/31/11 at 11:05 AM www.midwestmarket.org