Electricity Infrastructure: Overview and Issues (1)

H. Scott Matthews

February 13, 2003

Recap of Last LectureCurrent trans. system a 50-year project

with significant govt funding Generally paid for with gas (user) taxes

System of highways is ubiquitous, with most mileage and jurisdiction at the local level But most use/miles traveled arterial

Energy Use in the US Fuelwood dominant energy source from

founding of colonies to late 19th cent. (farms) Total work from all types of engines did not

exceed animals until mid-late 19th century. Coal (early 19th century) surpassed fuelwood

as dominant energy source 1885. Petroleum and natural gas surpassed coal as dominant (total) energy source around 1947. Consumption of these resources quadrupled in

a single generation (urbanization too)

More Energy in US Hydro & nuclear appeared around 1890 and 1957

respectively, yet have never gained dominance. Recent developments include solar, geothermal,

wind, ocean wave power For much of history, US self-sufficient in energy for

the most part (small coal imports from Britain during colonial times)

 Production / consumption rates essentially balanced in US until ~ late 1950s, at which time production fell behind consumption.

During 1970s the gap widened greatly

History of Electricity/Grid Electricity ‘system’ created in US 1881

Purpose was electricity for lights Edison had first central generation plant with small local

distribution system (DC only) 1881 cost: 24 cents/kWh! (now ~10 cents) Early 1900’s - intercity transmission lines

As utilities crossed state lines, had state PUCs, federal oversight, regulation

1930s-1950s: rural electrification, federally-run electric generating plants (hydro)

1950s- now: nuclear power, environ. Controls, fuel costs, Three Mile Island

What is Electric Power Grid?System of:

Generators (power plants) Transmission Lines (wires) Substations Distribution Lines Transformers Control Devices Users

Energy Used for GenerationPredominantly fossil fuels in USRequires transport of fuel from source

to power plant (recall transmission versus rail example last week) Separate infrastructure problem

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Generators Generally something spinning an electrical

generator (usually steam turbine) creating 3-phase AC power Everyone knows what DC (direct current) is - e.g.

batteries, fixed sources Houses use single-phase AC (alternating current), 60

cycles/second (Hz), max 170V, min -170V, root-mean-square = 120V

Why AC grids? Generators making AC! Converting AC->DC easier than DC->AC Transformers need AC (coming next)

Power Systems - Transmission Instead of a ‘ground wire’,

power systems use the ground (literally)

From generator, to substation to ‘step up’ voltage for trans. lines 155 to 765 kV! Can be sent hundreds (thous?)

of miles Trans. Lines : 3 wires (one

per phase)

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Power Systems - Distribution From trans. Line to power substation

Steps voltage down (resid: 7200V) Splits power into a bus to feed off Has circuit breakers for protection Then to distribution bus(es)

Each distribution bus carries 3-phase lines closer to users

Users only need 1 phase, so the distribution bus keeps getting split until only 1 phase carried on poles And another (small) transformer used on pole outside of

house to step down to 240V

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Other Issues Its generally easy to site the distribution part

of the grid If you want electricity, you need to allow it

Its much harder to get power plants and transmission lines sited Local/affected population may or may not be

‘served’ by them - no incentive Transmission is probably most critical

‘systems engineering problem’ in grid Electrification also led to ‘sprawl’ as it allowed

firms to locate away from energy sources

Blackout of November 9, 1965 By 1965, electricity part of everyday life Most of NE US (and Canada!) dark Sign that we were not managing well

Six days to realize source of problem 1 relay failed at station in Canada (Niagara Falls) Caused transmission line to go ‘open’ Caused series of cascading failures all the way back to New

York City Took only 15 minutes to blackout NE US

Caused people to rethink dependence Until then, power systems design geared around

‘isolation’ to prevent damage