Power Supplies, Harmonics

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ECE 333 (398RES)Renewable Energy Systems

• Lecture 6
• Power Supplies, Harmonics
• Professor Tom Overbye
• Department of Electrical andComputer Engineering

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Announcements

• Be reading Chapter 3
• Homework 2 is due now.
• Homework 3 is 1.4, 2.11, 2.12, 2.14, SP 2. Due
  date is Feb 12.
• Special Problem (SP) 2
• A 480/240 V, 4.8-kVA, 60-Hz, single-phase
  transformer is used to supply a 4.8 kVA load with
  a power factor of 0.8 lagging at rated voltage of
  240 V.
• a) If you assume the transformer is ideal, what
  would be the magnitude of the expected primary
  side (480 Volt side) current?
• b) Again, if you assume the transformer is ideal,
  what is the equivalent impedance of the load
  viewed from the primary side of the transformer?

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Power Supplies for AC to DC

• Two main types of power supplies linear
  (simpler) and switched-mode (more efficient)

Linear
Switched-mode
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Power System Harmonics

• So far class has talked about fundamental
  frequency analysis. Many traditional loads only
  consume power at the fundamental frequency.
  However, some loads, mostly electronic-based,
  tend to draw current in non-linear pulses, which
  gives rise to harmonics.
• If current has half-wave-symmetry (values are
  equal and opposite when separated by T/2) then
  there are no even harmonics

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Switched-Mode Power Supply Current
Source www.utterpower.com/commercial_grid.htm
6
Quick Review of Fourier Analysis
.
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Harmonic Current Specturm

• The below figure shows the harmonic current
  components for an 18-W, electronic-ballast
  compact fluorescent lamp.

Source Fig 2.34 of Renewable and Efficient
Electric Power Systems by Masters
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Current Waveform for CFL
Figure 2.35
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Total Harmonic Distortion (THD)
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Key Problems with Harmonics

• A key problem with the third harmonic is neutral
  current since the fundamental 120 degree phase
  shift becomes 360 degrees for the third harmonic
  so the third harmonic values do not cancel (also
  true for other triplen harmonics)
• Delta-grounded wye transformers prevent triplen
  harmonic currents from flowing into the power
  grid
• Harmonics cause transformer overheating since
  core losses are proportional to frequency
• Harmonic resonance, particularly with shunt
  capacitors (can be around 5th or 7th harmonic
  values)

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A Little Background on the Electric Utility
Industry

• First real practical uses of electricity began
  with the telegraph (around the civil war) and
  then arc lighting in the 1870s (Broadway, the
  Great White Way).
• Central stations for lighting began with Edison
  in 1882, using a dc system (safety was key), but
  transitioned to ac within several years. Chicago
  Worlds fair in 1893 was key demonstration of
  electricity
• High voltage ac started being used in the 1890s
  with the Niagara power plant transferring
  electricity to Buffalo also 30kV line in Germany
• Frequency standardized in the 1930s

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Regulation and Large Utilities

• Electric usage spread rapidly, particularly in
  urban areas. Samuel Insull (originally Edisons
  secretary, but later from Chicago) played a major
  role in the development of large electric
  utilities and their holding companies
• Insull was also instrumental in start of state
  regulation in 1890s
• Public Utilities Holding Company Act (PUHCA) of
  1935 essentially broke up inter-state holding
  companies
• This gave rise to electric utilities that only
  operated in one state
• PUHCA was repealed in 2005
• For most of the last century electric utilities
  operated as vertical monopolies

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Vertical Monopolies

• Within a particular geographic market, the
  electric utility had an exclusive franchise

In return for this exclusive franchise, the
utility had the obligation to serve all existing
and future customers at rates determined
jointly by utility and regulators It was a cost
plus business
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Vertical Monopolies

• Within its service territory each utility was the
  only game in town
• Neighboring utilities functioned more as
  colleagues than competitors
• Utilities gradually interconnected their systems
  so by 1970 transmission lines crisscrossed North
  America, with voltages up to 765 kV
• Economies of scale keep resulted in decreasing
  rates, so most every one was happy

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Current Midwest Electric Grid
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History, contd -- 1970s

• 1970s brought inflation, increased fossil-fuel
  prices, calls for conservation and growing
  environmental concerns
• Increasing rates replaced decreasing ones
• As a result, U.S. Congress passed Public
  Utilities Regulator Policies Act (PURPA) in 1978,
  which mandated utilities must purchase power from
  independent generators located in their service
  territory (modified 2005)
• PURPA introduced some competition, but its
  implementation varied greatly by state

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PURPA and Renewables

• PURPA, through favorable contracts, caused the
  growth of a large amount of renewable energy in
  the 1980s (about 12,000 MW of wind, geothermal,
  small scale hydro, biomass, and solar thermal)
• These were known as qualifying facilities (QFs)
• California added about 6000 MW of QF capacity
  during the 1980s, including 1600 MW of wind,
  2700 MW of geothermal, and 1200 MW of biomass
• By the 1990s the ten-year QFs contracts written
  at rates of 60/MWh in 1980s, and they were no
  longer profitable at the 30/MWh 1990 values so
  many sites were retired or abandoned

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Abandoned Wind Farm Need South Point in Hawaii
http//everything-everywhere.com/photos/abandoned_
wind_farm_hawaii.jpg
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Electricity Prices, 1990-2007
Total USA solar/pv energy production was
essentially flat from 1990 to 2005 (0.06 quad vs.
0.065) Total wind generation stayed flat during
1990s (around 0.03) but is now growing (0.32 in
2007 solar/pv is 0.08 in 2007)
Source EIA, annual energy review, 2007
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History, contd 1990s 2000s

• Major opening of industry to competition occurred
  as a result of National Energy Policy Act of 1992
• This act mandated that utilities provide
  nondiscriminatory access to the high voltage
  transmission
• Goal was to set up true competition in generation
  
• Result over the last few years has been a
  dramatic restructuring of electric utility
  industry (for better or worse!)
• Energy Bill 2005 repealed PUHCA modified PURPA

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State Variation in Electric Rates
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The Goal Customer Choice
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The Result for California in 2000/1
24
The California-Enron Effect
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August 14th, 2003 Blackout
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My Favorite Blackout Cartoon
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2007 Illinois Electricity Crisis

• Two main electric utilities in Illinois are ComEd
  and Ameren
• Restructuring law had frozen electricity prices
  for ten years, with rate decreases for many.
• Prices rose on January 1, 2007 as price freeze
  ended price increases were especially high for
  electric heating customers who had previously
  enjoyed rates as low as 2.5 cents/kWh
• Current average residential rate (in cents/kWh)
  is 10.4 in IL, 8.74 IN, 11.1 WI, 7.94 MO, 9.96
  IA, 19.56 CT, 6.09 ID, 14.03 in CA, 10.76 US
  average

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Renewable Portfolio Standards (Feb 2009)
ME 30 by 2000 10 by 2017 - new RE
MN 25 by 2025 (Xcel 30 by 2020)
VT (1) RE meets any increase in retail sales by
2012 (2) 20 RE CHP by 2017
WA 15 by 2020

• NH 23.8 in 2025

WI requirement varies by utility 10 by 2015
goal
ND 10 by 2015

• MA 15 by 2020 1 annual increase(Class I
  Renewables)

MT 15 by 2015
OR 25 by 2025 (large utilities) 5 - 10 by
2025 (smaller utilities)
MI 10 1,100 MW by 2015
RI 16 by 2020
SD 10 by 2015
CT 23 by 2020

• NV 20 by 2015

IA 105 MW
UT 20 by 2025

• NY 24 by 2013

• OH 25 by 2025

• NJ 22.5 by 2021

IL 25 by 2025
CA 20 by 2010

• CO 20 by 2020 (IOUs)
• 10 by 2020 (co-ops large munis)

• PA 18 by 2020

• MO 15 by 2021

• MD 20 by 2022

• NC 12.5 by 2021 (IOUs)
• 10 by 2018 (co-ops munis)

• AZ 15 by 2025

• DE 20 by 2019

• DC 20 by 2020

• NM 20 by 2020 (IOUs)
• 10 by 2020 (co-ops)

VA 12 by 2022
TX 5,880 MW by 2015
HI 20 by 2020
28 states have an RPS 5 states have an RE goal
State RPS

• Solar hot water eligible
• Minimum solar or customer-sited RE requirement
• Increased credit for solar or customer-sited
  RE
• Includes separate tier of non-renewable
  alternative energy resources

State Goal
Source http//www.dsireusa.org/
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Impact of 2009 Stimulus Bill on Renewable Energy
?
Stay tuned! Well know more soon!