ECE 333 Renewable Energy Systems

Lecture 6: Power System Operations

Prof. Tom Overbye

Dept. of Electrical and Computer Engineering

University of Illinois at Urbana-Champaign

overbye@illinois.edu

Announcements

• Be reading Chapter 3; also read Prof. Sauer's article on course website explaining reactive power

• Quiz today on HW 2• HW 3 is posted; it will be covered by an in-class quiz on

Thursday Feb 12– Material from Power Systems history and operations will be

covered on exams (such as true/false)

• Talk by Jana Sebestik, "SparkingInterest in Smart Grid Stuff", Friday Feb 6 at 1pm in NCSA Auditorium

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In the News: Pakistan Blackout

• On Sunday Jan 25, 2015 Pakistan had a nationwide blackout, the worst in their history, with 80% of the country out– Service was restored to major

cities later in the day– Blackout was tied to rebels

blowing up two 220 kV transmission lines betweenGuddu-Quetta

– Caused a cascade that took outmost of the rest of their grid

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Sources: http://www.nytimes.com/2015/01/26/world/asia/widespread-blackout-in-pakistan-deals-another-blow-to-government.html?_r=0; http://www.geni.org/globalenergy/library/national_energy_grid/pakistan/pakistaninationalelectricitygrid.shtml

Natural Gas Boom, Bust and Boom

Source: EIA4

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

• 2014 average residential rate (in cents/kWh) is 11.42 in IL, 11.27 IN, 13.94 WI, 20.13 NY, 8.77 WA, 16.22 in CA, 37.59 in HI, 12.53 US average

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The Rise of Renewables: Wind

Source: AWEA Wind Power Outlook 4th Qtr, 2014 (released 1/28/15)

While2014 additionswere a jump from,2013 they were still muchbelow 2012 values

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Recent Growth in Solar

• Solar is growing rapidly in the US,but its growth if being fueled bylow cost imported panels primarilyfrom China.

Source: Wall Street Journal, Sept 10, 2012 7

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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Illinois 2012: Municipal Aggregation

• Urbana and Champaign residents started seeing substantially lower electric bills as a result of municipal aggregation• This was approved by a 2-1 margin in 3/2012 referendum

• Municipal aggregation means all residents of a community get their electricity from a third party supplier chosen by the city (as opposed to the local utility) unless they specifically opt out. .

• They still get bills from Ameren, and do pay an electricity delivery charge (about 30 to 40% of total bill)

• Recently Ameren rates have dropped, making third party options less attractive 10

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

Renewable Portfolio Standards Set by States

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Power System Operations:One-line Diagrams

• Most power systems are balanced three phase systems.

• A balanced three phase system can be modeled as a single (or one) line.

• One-lines show the major power system components, such as generators, loads, transmission lines.

• Components join together at a bus.

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Substation Bus

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Power System Time Frames

14Image source: P.W. Sauer, M.A. Pai, Power System Dynamics and Stability, 1997, Fig 1.2, modified

Next few slides will consider the power flow (quasi-steady)time frame

PowerWorld Simulator Three Bus System

Bus 2 Bus 1

Bus 3Home Area

204 MW

102 MVR

150 MW

150 MW 37 MVR

116 MVR

102 MW 51 MVR

1.00 PU

-20 MW 4 MVR

20 MW -4 MVR

-34 MW 10 MVR

34 MW-10 MVR

14 MW -4 MVR

-14 MW

4 MVR

1.00 PU

1.00 PU

106 MW 0 MVR

100 MWAGC ONAVR ON

AGC ONAVR ON

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

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Power Flow

• A common power system analysis tool is the power flow – It shows how real and reactive power flows through a network,

from generators to loads

• Solves sets of non-linear equations enforcing "conservation of power" at each bus in the system (a consequence of KCL)– Loads are usually assumed to be constant power – Used to determine if any transmission lines or transformers are

overloaded and system voltages

• Educational version PowerWorld tool available at– http://www.powerworld.com/gloversarmaoverbye

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Metro Chicago Electric Network

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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.

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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.

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Basic Power Flow 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.

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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.

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Overloaded Transmission Line

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Interconnected Operation

• Power systems are interconnected. Most of North America east of the Rockies is one system, with most of Texas and Quebec being exceptions

• Interconnections are divided into smaller portions, called balancing authority areas (previously called control areas)

• Balancing authorities sometimes correspond to a single utility, but increasingly they include a large number of utilities.

• NERC Reliability Coordinators are charged with overseeing the reliable operation of the grid

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NORTH AMERICAN INTERCONNECTIONS

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NERC Reliability Coordinators

Illinois issplit, withthe ComEdpart in PJM,with the rest of the state in MISO

Source: http://www.nerc.com/page.php?cid=5%7C67%7C20625

Balancing Authority (BA) 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

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North American Balancing Authorities

Source: http://www.nerc.com/AboutNERC/keyplayers/Pages/default.aspx 27

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.

https://www.misoenergy.org/MarketsOperations/RealTimeMarketData/Pages/ACEChart.aspx

MISO ACE|(in MW) from 9/19/12. Atthe time the MISO loadwas about 65GW

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Automatic Generation Control

• BAs use automatic generation control (AGC) to automatically change their generation to keep their ACE close to zero.

• Usually the BA control center calculates ACE based upon tie-line flows; then the AGC module sends control signals out to the generators every couple seconds.

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Three Bus Case on AGC

Bus 2 Bus 1

Bus 3Home Area

266 MW

133 MVR

150 MW

250 MW 34 MVR

166 MVR

133 MW 67 MVR

1.00 PU

-40 MW 8 MVR

40 MW -8 MVR

-77 MW 25 MVR

78 MW-21 MVR

39 MW-11 MVR

-39 MW

12 MVR

1.00 PU

1.00 PU

101 MW 5 MVR

100 MWAGC ONAVR ON

AGC ONAVR ON

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