An Overview of the U.S. Electric Power Grid Generation Choices, Reliability, Challenges Tom Ferguson, P.E. Adjunct Instructor Dept. of Electrical Engineering University of Minnesota, Duluth Presentation to EE 1001 September 17, 2015

Where Electricity Comes From

What Do We Know About This? 1.We plug LOADS into it 2.It has THREE prongs in standard layout 3.The VOLTAGE is ~115 VAC 4.The WAVEFORM is sinusoidal 5.Only 60 Hz (cycles per second) is present 6.ELECTRONS come from somewhere 7.It’s almost always “ON” BUT! 1.Limited to 15 AMPS 2.Europe uses different plug 3.Voltage varies + 5% 4.Waveform is usually not “clean” 5.Harmonics may be present 6.Electrons come from THOUSANDS of generators 7.It’s 99.99% reliable (off for 53 minutes/yr)

Nuggets of Knowledge Nugget #1 Nugget #1: Electricity in the U.S. is an ELECTROMAGNETIC WAVE with a FREQUENCY OF 60 CYCLES PER SECOND, or 60 hertz (abbreviated 60 Hz)

Nuggets of Knowledge Nugget #2 (3000 miles)

Basic Electric Power System

Nuggets of Knowledge Nugget # 3 A simple TRANSFORMER has TWO WINDINGS wrapped around an IRON CORE VOLTAGES are TRANSFORMED according to the TURNS RATIO:

High Voltage Transmission –Long distance carrier of electricity –Connects generators with loads –High voltage reduces current flow (P=V x I) –Reduced current reduces losses (P loss =I 2 R) –Transmits energy at essentially speed of light

The Grid Powers Society Human behavior repeats itself daily –Morning routine: lights, hot water, electronics –Stores open: lights, heating/cooling –Industry starts: pumps, motors, arc furnaces The grid must respond to these loads –generators must be ready and reliable –generators must be controllable to match load The grid is very dynamic

A Typical Day on the California Grid 4 a.m. 2 p.m. 1 Megawatt can power about 500 homes Ramps up by 4500 MW in 80 minutes

Nuggets of Knowledge Nugget #4 POWER is the product of VOLTAGE and CURRENT or Power (W, watts) = Voltage (V, volts) X Current (I, Amperes) or P = V * I One MEGAWATT can supply about 500 homes

Generating Choices What types of generation are used? Varies across U.S. according to –availability of fossil fuels –availability of renewable energy sources –water availability –environmental limitations –state policies on renewables and nonrenewable generation

Power Generation Technologies

Includes Hydro Biomass Wind Solid Waste Geothermal Solar PV Solar Thermal Source: U.S. Energy Information Administration, Electric Power Monthly (June 2015). Percentages based on Table 1.1 for 2014 Calender Year. Updated 9/2015. Percentages on an ENERGY basis, not capacity. Coal 39% Natural Gas 27% Nuclear 20% Renewables 13% 2014

Challenges with Wind No mechanical energy storage (no inertia) 1 MW of nuclear = 8 to 12 MW of wind Not dispatchable Negative correlation with loads When loads are greatest during the mid-day, wind generation is lowest. Conversely, wind is highest when least needed (night).

Nuggets of Knowledge Nugget #5 Three Synchronized Regions in U.S. –Eastern U.S. (east of Rockies) –Western U.S. –Texas Nugget #5: All generators in each region are synchronized

Putting It All Together “The Grid” = Generators (about 18,000) + HV Transmission Network

Why Do the Lights Go Out? –Lightning and high winds –Animals (squirrels, rodents, snakes) –Car and train accidents –Power plant outages –Transmission line failures –Solar storms The high-voltage transmission system is already very “smart” The low-voltage distribution system has MANY OPPORTUNITIES FOR IMPROVEMENT The “smart grid” technologies are best suited to the low-voltage system

Good Luck!