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Overview of lectures in this series
Introduction and motors (Oct. 3)
2.  Motors and generators (Oct. 10)
3.  Distribution and use of electricity (Oct. 17)
4.  Wind power and dissipation (Oct. 24)
5.  Heat engines 1 (Oct. 31)
6.  Heat engines 2 (Nov. 7)
7.  Nuclear generation (Nov. 14)
8.  Solar power – thermal and electric (Nov. 21)
9.  Fuel cells (Dec. 5)
10.  Summary, Consumption and the future (Dec. 12)
1. 
http://kicp.uchicago.edu/~switzer/
Distribution and use of
electricity
COMPTON LECTURE 3: OCTOBER 17, 2009
ERIC SWITZER
“I shall make electricity so cheap that only the rich can
afford to burn candles.” – Thomas A. Edison
“Conspicuous consumption of valuable goods is a
means of reputability to the gentleman of leisure.” –
Thorstein Veblen
Lec. 1 and 2: Generators and motors
Flux = area*magnetic field (B)*cos(angle)
The start of an age
Paris, 1878
Zenobe Gramme’s AC
dynamos powered
Yablochkov arc lamps
along Avenue de l’Opera
and the Place de l’Opera for
the 1878 Paris Expo.
Image: wikipedia
Early use
  Early systems were
heterogeneous: different
voltages, AC, DC,
standards
  First uses: street cars
(several hundred volts),
arc street lamps (several
thousand volts), Edison
bulbs (100 volts).
  Low voltage generators
close to consumers
(distributed generation)
Arc lamps in Berlin by Carl Saltzmann, 1884
Image: wikipedia
The utility
  The first large low-voltage
public utility was Edison’s
Pearl Street Station in New
York City, which, in 1882
served 110 volts and 400
amps DC to 85 customers
in a one mile radius.
  The first large high-voltage
public utility was the
California Electric
Company (PG&E) in San
Francisco in 1879, which
sold DC power for arc
lights.
San Jose’s Eiffel tower: a flood light (reproduced in Low Tech magazine)
DC vs. AC
AC-DC schism
  Tesla was the strongest early
advocate of AC power and had a
falling-out with Edison and
joined Westinghouse. Thus
began the war of currents.
  The war of currents was brutal,
and Edison even sought to
demonstrate the dangers of AC
by electrocuting animals, coining
a new term for electrocution,
“Westinghoused”.
  It was not until 2007 that ComEd
stopped its NYC DC service.
  Today DC is used in transmission
applications where reactance
(line inductance and capacitance)
or power transmission between
synchronous AC grids is a
consideration.
Images: wikipedia, U.S. DoI, NPS, Edison National Historic Site
AC-DC schism
Chicago, Jackson Park, 1893
Images: wikipedia
  A decisive moment for AC
versus DC power occurred
at the World’s Columbian
Exposition in Hyde Park’s
Midway and Jackson Park
in 1893.
  General Electric (backed by
Edison and J. P. Morgan)
bid for DC power, while
Westinghouse (through
Tesla) bid for AC power.
Westinghouse won the bid,
but in retaliation, Edison
and GE banned Edison’s
patented bulbs.
Gulliver’s AC vs. DC?
  Lilliput: crack eggs from small end
  Blefuscu: crack eggs on the big end
  AC vs. DC, the same? An emphatic NO!
Why we have AC
2
P=IV=V /R
Joule power and Ohm’s law
Faraday’s law of induction
Why we have AC
  Let’s unpack this…
Pressure
  A pressure difference drives a flow
Image: wikipedia
Ohm’s law
Another way to say this: the drop in pressure/voltage is the flow/
current times the resistance:
ΔV = IR
Images: wikipedia, hyperphysics
Currents and pipes
Resistors do not eat electrons!
Current, flow are conserved (there are no leaks).
Voltage, pressure can change.
Loads in a circuit drop the voltage.
Images: hyperphysics
Power
  Voltage (V): energy per unit charge
  Current (I): charge per unit time
  Voltage times current is energy per unit time
  Energy per unit time is power (P)! (Watts)
P=I(ΔV)
Joule loss
P=I(ΔV)=(ΔV)2/R
Using: ΔV = IR
Net power into lattice vibrations = heating the wire
Image: wikipedia
sunburn
visible
Aside: Why not to use incandescent bulbs
Image: wikipedia
heat
AC vs. DC
  Back to the problem at hand: why AC?
Power delivered: a simple example
  500 kV wire carries 1 kA of current and has 25 Ω
resistance. The total power transmitted at the
generating end is P = I V = 500 MW. The voltage
drop across the transmission line is 25 kV, so at the
receiving end one has 475 kV. The total power lost is
25 MW. (a 5% loss).
  Suppose same generator power, but 125 kV. In this
case, the current must be 4 times larger to produce
the same power. The Joule loss is then 400 MW, or
(400 MW)/(500 MW) = 80%. Only 20% of the
power reaches the consumer!
How high a voltage: very high!
  154,000 miles of AC transmission lines in the US,
roughly half of which carry 230 kV, while the other
half carry 345 kV, 500 kV, 765 kV.
  Roughly 6 times that length is found in overhead
distribution lines.
The Eastern
interconnection has been
dubbed, “the largest
machine in the world”.
DC “interties”
Steel-reinforced,
uninsulated aluminum.
IEEE Electripedia
Superconductors
574 MW, 138 kV, 2000 ft
Holbrook, Long Island
bismuth-calcium-copper-oxygen/silver
(1st generation)
Transmission in high density, urban
areas.
American superconductor and BNL
BNL superconducting cable researchers:
Vyacheslav Solovyov, Tom Muller, and
Masaki Suenega.
230 kV >> 120 V: Enter the transformer
AC!
2 V in to 1 V out
Images: wikipedia
The transformer equation
•  Note: we increase the voltage, but decrease the current so that P=IV
is constant. Someone always has to pay!
•  Transmission generators can be 98-99% efficient, but this still
requires significant heat dissipation.
Ode to a toothbrush
Technology that drove AC power
  Needs: 1) a compact way to
Parson's 1MW (4 kV, single)
turbogenerator in Elberfeld, Germany.
(1899)
Images: wikipedia
produce the power for a large
network, and 2) an efficient
method to step voltages up
and down for trans- mission
and consumption.
  1) Charles Parsons’ MW-scale
generators
  2) mid 1880’s, by the
engineers Zipernowsky,
Blathy and Deri “ZBD” closed
core transformer; developed
further by Tesla,
Westinghouse, Stanley and
Franklin Leonard Pope
Birth of the grid
  Initially, power was provided by local generators.
  The first power pool in the US was in Connecticut in
1925.
  The pools subsumed local generators until, today,
North America is split into four synchronous
systems, the Eastern, Quebec, Texas, and Western
interconnections. Similar synchronous groups of
generators exist around the world.
  Advantages of a grid: N-1 (1-1=0), more predictable
(=cheaper) demand, diversity of supply
Net energy flows
32% eff.
25%
eff.
Fertilizers!
Units
  1 Btu = British thermal unit, the heat to raise the
temperature of 1 pound of water by 1 degree
Fahrenheit. 1 quad = 1 quadrillion Btu = 1015 Btu.
  1 Btu is also equal to 1054 joules
  1 Joule = lifting an apple one meter
  Rule of thumb: 1/3 of heat energy reaches consumers
as electrical energy.
  Lecture 5 and 6 – a fundamental efficiency limit
  7-9% loss in transmission is typical.
34% o
f tota
l
41% of total
Primary energy sources
Schematic of a nuclear power plant
Pressurized Water Reactor
Images: derived from wikipedia
Schematic of a coal power plant
Image: derived from wikipedia
Storage, fluctuation, intermittency
  Fluctuations in supply (intermittency), demand
  Consideration: renewable storage is useful for
intermittent sources like wind and solar.
  Demand depends on strange human factors: 2.8 GW
surge in England for people watching England's 1990
World Cup penalty shoot-out against Germany.
Gas turbines
GE H-series 480 MW generation gas
turbine.
In combined cycle: 60% efficiency possible.
Can spin up quickly, but fuels often cost more than coal or nuclear baseload.
Images: wikipedia
Storage – pumped water
  Pumped water – 75% (needs hydro. stations, capital)
  Nearest pumped storage is Luddington, MI (max
output=1.9 GW
  Need area, topography, capital
  ~20 GW capacity in US, 2-3% power
Images: wikipedia and http://www.consumersenergy.com/content/hiermenugrid.aspx?id=31
Consumption by sector
At home: insulation
At work: lights
Unit Physics Summary
  Currents in a magnetic field feel a force
  Currents produce magnetic fields
  Voltage is the energy per unit charge in a circuit
  Induction: the basis of electrical generation
  We need high voltages because of Joule loss
  Transformers produce the high voltage
  Energy is conserved
Overview of lectures in this series
Introduction and motors (Oct. 3)
2.  Motors and generators (Oct. 10)
3.  Distribution and use of electricity (Oct. 17)
4.  Wind power and dissipation (Oct. 24)
5.  Heat engines 1 (Oct. 31)
6.  Heat engines 2 (Nov. 7)
7.  Nuclear generation (Nov. 14)
8.  Solar power – thermal and electric (Nov. 21)
9.  Fuel cells (Dec. 5)
10.  Summary, Consumption and the future (Dec. 12)
1. 
http://kicp.uchicago.edu/~switzer/