Power Grid & Blackouts Prof. Ramzy R. Obaid
With many thanks and appreciation to Professor Mohamed A. El Sharkawi
Power System The electric power systems in the North America and Europe are probably the most complex systems ever built by human. In the USA, the power system contains: Several thousands of major generating units (>500MW) Tens of thousands of transmission lines (Millions of miles) Millions of transformers Hundreds of millions of protection and control devices. The power systems in 2006 produced over 19 PetaWh (19 10 15 Wh) of electric energy worldwide and over 4.25 PetaWh in the USA. 3
Net generation of electrical energy (British Petroleum Annual Report, 2007) USA TOTAL WORLD PWh 20 18 16 14 12 10 8 6 4 2 0 1990 1992 1994 1996 1998 2000 2002 2004 2006 Peta = 10 15 Year 4
Power Grid Electric power grid is considered a national security matter. Failures of power systems can have severe economic and safety consequences. Reliability concerns for utility systems are amplified by the deregulation activities, which increases the system s openness while simultaneously decreasing the applied degree of control. 5
Topology of Power Grid Transmission Line Redundancy Radial Network Generation Redundancy 6
Radial System xfm 1 Line 1 Load 1 G xfm g Line 2 Xfm 2 Load 2 7
Radial System xfm 1 Line 1 Load 1 G xfm g Xfm 2 Line 2 Load 2 8
Network System xfm 1 Line 1 Load 1 G xfm g Line 3 Xfm 2 Line 2 Load 2 9
Generation Redundancy G 2 Line 4 Line 5 Line 1 Load 1 G 1 Line 3 Line 2 Load 2 10
Energy Demand System wide load Peak Load 9 AM Noon 6 PM Time 11
Challenge Every utility must be able to meet the daily peak demands. High energy demand occurs for a few hours every day it is uneconomical to build generating plants to be used only during the peak loads. It is more economical to build generation to meet the average daily demand. 12
Setting of Capacity Generation deficit Peak Load System wide load Generation Capacity Generation Surplus 9 AM Noon 6 PM Time 13
Solution Trade electricity with neighboring utilities. When a utility has surplus, it sells the excess power to another utility that needs it. When it has a deficit, the utility buys the extra power from another utility with surplus. This arrangement requires all utilities to be interconnected through a mesh of transmission lines 14
Electric Energy Trade for Different Time Zones Power flow at 9 AM ET West Utility Tie line East Utility Power flow at noon ET 18
Electric Energy Trade for Different Seasons North Utility Summer power flow Winter power flow South Utility 19
World Wide Web of Power 20
WWW of Power Advantages: Operates the system economically. Equipment are shared between utilities Drawbacks: The power grid becomes incredibly complex. Enormous challenges for monitoring, operation and control of the system. Major failures in one area could affect other areas, thus creating wider blackouts. 21
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Power Outage 25
Power Outage Blackout: most or all loads in a given region are left without power. Outage: a portion of the system in a given region is left without power. Brownout: Drop in system voltage 26
What triggers Blackouts Faults Equipment damage Unauthorized tripping of transmission lines Human errors Natural calamities Breaks in communication links Sabotage Intrusion by external agents Gaming in the market 27
Why Blackouts Happen? Due to a severe contingency System lacks the balance of power due to Lack of generation Lack of transmission lines. 28
P m Mechanical Power Controlled at plant Balance of Power G P m = P P Electrical Power Controlled by customers 29
Mechanical Power Controlled at the plant Example: Hydropower plant: Increased or decreased by changing the amount of water (steam) flow Slow action Control valve is called governor 30
Governor Flow of water/steam Penstock 31
Electrical Power Controlled by customer Topology changes in system can affect the flow of power Fast action 32
Steady state operation P m G P P loss P m = P P l P = P l + P loss 33
Loss of load P m G P P loss P = 0 P l = 0 P m >> P 34
Loss of line P m G P P loss P = 0 P l P m >> P 35
Anatomy of Blackouts 38
A Blackout scenario Load power is lost Mechanical power is larger than electric power Mechanical power is not rapidly reduced Speed of generator increases. Machine is pulled out of synchronism Current increases Generator is tripped off to protect generator from overcurrent damage Loss of generation may result in blackout 44
Power Pool Power Pool P g P l Tie line P import Tie line P export P g P import P l P exp ort 45
Energy Deficit in Power Pool P g Options: P Reduce P export. Increase P g. import Assume P import = 0 P Disconnecting some loads. This is called rolling blackouts. Find another utility that can transmit the needed power through other transmission routs. l P g P export P l P export 46
Spinning Reserve P g Power Pool P s P l Tie line P import P export Tie line P P P P P g 47 import s l exp ort
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Blackout 2003 This blackout is the worst in history, so far. About 50 million people were affected by the blackout The power was out for several days. 51
Blackout 2003 On the hot summer day of August 14, 2003, the systems in the east and Midwest USA as well as Ontario, Canada were heavily loaded and the blackout started in the following sequence: A 680 MW coal generation plant in Eastlake, Ohio, tripped. An hour later, a transmission line in northeastern Ohio tripped because it was overloaded. The outage put extra strain on other transmission line, and the lines sagged and touches trees causing short circuits that trip the lines. In less than 3 minutes, 21 power plants were shut down including 7 nuclear power plants. 52