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U.S. Energy Information Administration, Annual Energy Review 2010. All energy input US average = 90.3 MWh per person, per year. Corresponds to 10.3 kW average energy input per person.

1 kWh = 3,412 BTU

How Much of the Total US Energy Above Flows Through the Grid?

We Depend on the Grid for Much of our Energy Needs

10.3 kW avg. input per person total energy, multiplied by 40% of total = 4.12 kW avg. electrical energy input per person.

4.12 kW avg. input, multiplied by 35% avg. power plant efficiency = 1.4 kW avg. electrical consumption per person.

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ERCOT Grid

Eastern GridWestern Grid

The U.S. Has Three Power Grids

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ERCOT

• 23 million customers

• 550 generating units

• 70,000 MW peak (about 3 kW per person)

• 40,000 miles of high voltage transmission lines

• 335 million MWhr annual energy (about 15 MWhr per person)

• Average annual load is 1.7 kW per person

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Generation Mix on Typical Winter Day

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Generation Mix on Typical Summer Day

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Basics of Grid Design and Operation• Planning number, 3 MW peak load per 1000 people

• Typical generator is about 500 MW, nuclear generator about 1000 MW

• Grid frequency is typically within 0.1 Hz of 60 Hz, and voltage is typically within 0.90 to 1.05 per unit of nominal.

ERCOT

Western Eastern

1-Minute Window

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Basics of Grid Design and Operation, cont.• The grid is low loss, lightly damped for oscillations, and very efficient (about

3% net losses in transmission, and 3% in distribution)

Unit Trip 2011/05/30 03:03:00 GMT. UT Pan Am Relative to U.T. Austin.

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Measured Total Curve Fit

Thump the grid (i.e., unit trip) and it rings

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Basics of Grid Design and Operation, cont.• The grid is designed so there is no load is lost and no lines/transformers are

overloaded when a contingency occurs (such as the loss of a transmission line or generator).

• The grid has inertia, but not as much as you might think. The rotating kinetic energy of a generator is about 6 seconds worth of rated power output.

• The sudden trip of a large generator causes the frequency to fall rapidly, until the governor response of the other generators halts the fall. The less grid inertia, the faster the frequency fall.

On 01/21/12, a sudden loss of generation occurred at 13:34 totaling 584 MW. Frequency declined to 59.752 HZ, ERCOT load was 31,275 MW.

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Minutes

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Grid Protection Must be Fast and Sure. But You Don’t Want False Trips!• Problems such as lightning-induced faults are isolated within 0.1 second

• Events such as faults cause generators to speed up because their power output drops but their mechanical power input is unchanged

• 0.2 seconds is a very long time in grids, in fact it is so long that generators can trip on overspeed and cause a blackout

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Grid Protection Must be Fast and Sure, cont.• Relays monitor voltages and currents, and when a grid problem

occurs, relays send trip signals to circuit breakers to isolate problems.

• Relays (i.e., computers) and their signal processing algorithms are no better than their sensing devices. Current transformers (CTs) isolate and scale transmission line currents down to the 0-5 Amp range. Voltage transformers (PTs) isolate and scale grid voltages down to the 120 Volt range.

• Today, most new relays are actually computers that use advanced signal processing techniques on voltage and current waveforms to quickly detect and deal with grid events while at the same time avoiding false trips

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Grid Protection Must be Fast and Sure, cont.• Directional relays communicate with their neighbors through fiber

optics, microwave, or low-frequency power line carrier signals, much like baseball players signal for the catch. Neighbors, one or two steps back, act in case the player drops the ball!

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High-Voltage Grid Transformers, 100’s of MW

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“Smart” Protection Uses Waveform AnalysisNormal Magnetizing Current

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Feds cite issues behind massive Southwest blackout (Source: www.ksl.com, May 1, 2012)

• Federal energy regulators blamed inadequate planning and lack of grid coordination for a massive blackout last year that started with the loss of a single transmission line at an Arizona substation and quickly affected millions of people in Southern California and Mexico's Baja California

• The outage knocked out traffic lights, causing gridlock on roads in the San Diego area. Two reactors at a nuclear power plant along the California coast went offline after losing electricity, and nearly 3.5 million gallons of sewage spilled into the ocean, closing beaches in San Diego.

• It was another reminder that U.S. transmission lines remain vulnerable to cascading power failures despite the safeguards that are in place.

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• Federal regulators found if the emergency settings had allowed for a higher level of power flows, it could have given operators time to mitigate the problem and the outage could have affected a much smaller area.

• Similar relay problems contributed to the 2003 blackout, said NERC Senior Vice President.

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Blackstart – The term used for grid recovery from a widespread or total blackout

Almost all generators require grid power to start. Few generators can start themselves. Hydro generators are sometimes capable of self-starting, and then energize the grid in sections so that other generators can start, and so on.

• FERC requires grids to have a blackstart plan, i.e., reestablishing the grid from a total blackout. ERCOT has a blackstart training school.

• Some questions from grid engineers are: Gas-fired generators have no local fuel, and depend on pipeline network. If gas pipeline compressors are not operational, gas-fired generators cannot start.

• Communications are essential for blackstart – will communications be functioning after a blackout?

• Recovery from a total blackout can take 1 week. No credit cards, no gas pumps, no ATM machines, …

• How much cash to you carry???