Power Grid and Blackouts Professor Mohamed A ElSharkawi
Power Grid and Blackouts Professor Mohamed A. El-Sharkawi 1
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 (>500 MW) 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 Peta. Wh (19 1015 Wh) of electric energy worldwide and over 4. 25 Peta. Wh in the USA. 2
Net generation of electrical energy (British Petroleum Annual Report, 2007) Peta = 1015 3
Generation capacity in the USA (Source: US Energy Information Administration) Tera = 1012 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 Load 1 Line 1 G xfmg Line 2 Xfm 2 Load 2 7
Radial System xfm 1 Load 1 Line 1 G xfmg Xfm 2 Line 2 Load 2 8
Network System xfm 1 Load 1 Line 1 G xfmg Line 3 Line 2 Xfm 2 Load 2 9
Generation Redundancy G 2 Line 4 Line 5 Load 1 Line 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
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 13
Setting of Capacity Generation deficit System wide load Peak Load Generation Capacity Generation Surplus 9 AM Noon 6 PM Time 14
Example • The system load demand for a given day can be approximated by • t is the time of the day in hour using the 24 -hour clock. • Compute the following: – – The times of the peak demands The average demand Compute the power to be imported during the first peak. 15
Solution 16
Solution 17
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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(c) M. A. El-Sharkawi and Mark Damborg, 3. 24
(c) M. A. El-Sharkawi and Mark Damborg, 3. 25
(c) M. A. El-Sharkawi and Mark Damborg, 3. 26
Power Outage 27
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 28
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 29
Why Blackouts Happen? • Due to a severe contingency • System lacks the balance of power due to – Lack of generation – Lack of transmission lines. 30
Balance of Power Pm Mechanical Power Controlled at plant G P Electrical Power Controlled by customers Pm = P 31
Mechanical Power • Controlled at the plant • Increased or decreased by changing the amount of water (steam) flow • Slow action • Control valve is called governor 32
Electrical Power • Controlled by customer • Topology changes in system can affect the flow of power • Fast action 34
Steady state operation Pm G P Ploss Pm = P P = Pl + Ploss Pl 35
Loss of load Pm G Ploss P P=0 Pl = 0 Pm >> P 36
Loss of line Pm G P Ploss P=0 Pm >> P Pl 37
Anatomy of Blackouts 40
Rotating mass Pm G P Meq is inertia constant 41
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Frequencies G Synchronous speed 60 Hz Infinite Bus f=60 Hz 43
Xs Pm G Vt Ia Xs Vo Xl Xl Ia Ef Vt El-Sharkawi@University of Washington Vo 44
Rotating mass Actual rotor speed Rotor Ef Vo Infinite bus 45
Rotating mass Rotor Ef Vo Infinite bus 46
Machine Current At t 2 Assumptions: n > ns Ef 2 Ef is constant Ia keeps increasing Ia 2 Xs At t 1 Ef 1 Vo Ia 1 Xs 47
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 48
Power Pool Pg Tie line Pimport Power Pool Pl Pexport Tie line 49
Energy Deficit in Power Pool Assume Pimport = 0 • Options: – – Reduce Pexport. Increase Pg. Disconnecting some loads. This is called rolling blackouts. Find another utility that can transmit the needed power through other transmission routs. 50
Spinning Reserve Pg Power Pool Ps Pl Tie line Pimport Tie line Pexport 51
Pool Margin ( ) 52
Blackout Scenario External Pool 1 Pg 1 Pl 1 P 1 Our power Pool Pg Pl P 2 Ps Ps 1 Tie line 1 External Pool 2 Pg 2 Pl 2 Ps 2 Tie lines 2 Operating Condition: Operating Condition with Spinning Reserve: If Tie line 2 is lost and 53
(c) M. A. El. Sharkawi and Mark Damborg, University of Washington 54
(c) M. A. El. Sharkawi and Mark Damborg, University of Washington 55
Frequency Varies By Area as Grid Separates (c) M. A. El. Sharkawi and Mark Damborg, University of Washington 58
Blackout Statistics • Area of 50 million people in eight states and two provinces • Approximately 61, 800 Megawatts (MW) of load • PJM Interconnection – 4, 000 MW • Midwest – 18, 500 MW • Hydro Quebec – 100 MW • Ontario – 21, 000 MW • New England – 2, 500 MW • New York – 24, 400 MW • 34, 000 miles of transmission (out of 150, 000 miles in U. S. ) • More than 290 generating units • Thousands of substations, switching facilities, circuit-protection devices, etc.
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