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Power Supplies, Harmonics

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Title: Power Supplies, Harmonics

1
ECE 333 (398RES)Renewable Energy Systems

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

2
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?

3
Power Supplies for AC to DC

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

Linear
Switched-mode
4
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

5
Switched-Mode Power Supply Current
Source www.utterpower.com/commercial_grid.htm
6
Quick Review of Fourier Analysis
.
7
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
8
Current Waveform for CFL
Figure 2.35
9
Total Harmonic Distortion (THD)
10
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)

11
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

12
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

13
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
14
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

15
Current Midwest Electric Grid
16
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

17
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

18
Abandoned Wind Farm Need South Point in Hawaii
http//everything-everywhere.com/photos/abandoned_
wind_farm_hawaii.jpg
19
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
20
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

21
State Variation in Electric Rates
22
The Goal Customer Choice
23
The Result for California in 2000/1
24
The California-Enron Effect
25
August 14th, 2003 Blackout
26
My Favorite Blackout Cartoon
27
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

28
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