The Electricity
Delivery System
Electricity is the flow of electrical power or charge. It is a secondary energy source, which means that we get it from the conversion of other sources of energy, including:
x
x
x
x
x
Coal
Natural gas
Petroleum
Nuclear energy
Hydro energy
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x
Electricity Basics
Geothermal energy
Solar energy
Wind energy
Biomass
The energy sources used to make electricity can be renewable
or non-renewable, but electricity itself is neither renewable or
non-renewable.1
1. EIA. “What is Electricity?” http://www.eia.doe.gov/kids/energyfacts/sources/
electricity.html#SecondarySource (Accessed December 14, 2005).
Source: EIA. “Electricity Basics 101.” http://www.eia.doe.gov/basics/
electricity_basics.html (Accessed December 13, 2005).
Generation
An electric utility power station uses either a turbine, engine,
water wheel, or other similar machine to drive an electric
generator or a device that converts mechanical or chemical
energy to generate electricity.
Steam turbines, internalcombustion engines, gas
combustion turbines, water
turbines, and wind turbines are the
most common methods to generate
electricity. Most power plants are
about 35 percent efficient. That
means that for every 100 units of
energy that go into a plant, only 35
units are converted to usable
electrical energy.2
Most of the electricity in the United
States is produced in steam
turbines. A turbine converts the
kinetic energy of a moving fluid
(liquid or gas) to mechanical
energy. Steam turbines have a
series of blades mounted on a shaft
against which steam is forced, thus rotating the shaft connected
to the generator. In a fossil-fueled steam turbine, the fuel is
burned in a furnace to heat water in a boiler to produce steam.2
2. EIA. “Electricity—A Secondary Energy Source.” http://www.eia.doe.gov/kids/
energyfacts/sources/electricity.html#Generation (Accessed December 14, 2005)
www.electricity.doe.gov
Did you know?
According to the EIA, 281 gigawatts of new generating
capacity will be needed by
2025 to meet the growing demand for electricity. This is
equivalent to 937 new 300megawatt power plants.
Electricity Generation by Fuel Source in the
United States, 2003
Petroleum
3%
Natural Gas
17%
Nuclear
20%
Coal
51%
Other
0%
Hydroelectric
7%
Other
Renew ables
2%
Source: EIA. Electric Power Annual. 2003 data.
February 2006
Generation
Transmission
Distribution
Substations
A substation is a high-voltage electric system facility. It is
used to switch generators, equipment, and circuits or lines in
and out of a system. It also is used to change AC voltages
from one level to another, and/or change alternating current
to direct current or direct current to alternating current. Some
substations are small with little more than a transformer and
associated switches. Others are very large with several
transformers and dozens of switches and other equipment.5
In the U.S., there are 10,287 transmission substations and 2,179
distribution substations.7 Transmission substations use transformers to convert a generator’s voltage up to 155,000 to
765,000 volts for long distance transmission in order to reduce
transmission line losses. The distribution substation steps
power down the voltage to distribution levels and splits it into
many directions.
Substations are critical component of our distribution system,
and a loss of only 4% of transmission substations would result
in a 60% loss of connectivity.8
7. “Structural Vulnerability of the North American Power Grid.” http://arxiv.org/
PS_cache/cond-mat/pdf/0401/0401084.pdf.
8. Midwest Research Institute. “Research Team Finds US Power Grids Vulnerable.” http://
www.trackingterrorism.com/default.asp?dismode=article&foobar=1029&artid=99.
Type and Number of Equipment Installed at All U.S.
Substations
There are four main types of substations: 6
x
x
x
x
Step-up transmission substations—receive electric
power from a nearby generating facility and use a large
power transformer to increase the voltage for
transmission to distant locations.
Step-down transmission substations—are located at
switching points in an electrical grid. They connect
different parts of a grid and are a source for
subtransmission lines or distribution lines. This
substation can change a transmission voltage to a
subtransmission voltage, usually 69 kV.
Distribution substations—are located near to the endusers. Distribution substation transformers change the
transmission or subtransmission voltage to lower levels
for use by end-users. Typical distribution voltages vary
from 34,500Y/19,920 volts to 4,160Y/2400 volts.
Underground distribution substations—are also
located near to
the end-users.
Distribution
substation
transformers
change the
subtransmission
voltage to lower
levels for use
by end-users.
5. OSHA. www.osha.gov (Accessed 11/23/05).
6. ibid.
www.electricity.doe.gov
Equipment
Autotransformer
Oil Circuit Breaker
Oil Circuit Recloser
Reactor
Transformer
Vacuum Circuit
Breaker
Vacuum Circuit
Recloser
Voltage Regulator
Total Number Installed
12,151
193,586
7,004
422
63,797
338
169
25,443
Note: Totals for all substations within the utility industry based
on the assumption of 50,000 total and extrapolated from
Entergy data.
Source: EPA, “Data on Oil Filled and Process Equipment,” Sept. 2004.
Operational Electrical Equipment Device Breakdown for
Substations by Volume of Oil Contained in In-service
Equipment
Device Volume Range
(gallons)
< 54
55-100
101-500
501-1,500
1,501 – 5,000
5,001 - 10,000
10,001 – 15,000
15,001 – 20,000
> 20,000
Number of Pieces of
Electrical Equipment
46,245
60,253
55,401
36,709
61,097
32,869
6,878
3,333
1,435
Note: Totals for substations within the utility industry based on the
assumption of 50,000 total and extrapolated from Entergy data.
Source: EPA, “Data on Oil Filled and Process Equipment,” Sept. 2004.
February 2006
Generation
Transmission
Distribution
Transmission
Transmission lines carry
electric energy from one point
to another in an electric power
system. They can carry
alternating current (AC) or
direct current (DC) or a system
can be a combination of both.3
distinguish transmission lines
from distribution lines are that
they are operated at relatively
high voltages, they transmit
large quantities of power, and
they transmit the power over
large distances.4
Also, electric current can be carried by either overhead
or underground lines. The main characteristics that
3. OSHA. www.osha.gov (Accessed
December 13, 2005).
4. ibid.
Ownership of High-Voltage Transmission Lines in the U.S.,
1994
Miles of AC and DC Transmission Lines in the U.S. in 2002
Voltage (kV)
AC
230
345
500
765
Total AC
Miles
76,762
49,250
26,038
2,453
154,503
Total AC/DC
Voltage (kV)
DC
250-300
400
450
500
Total DC
157,810
Miles
930
852
192
1,333
3,307
Source: DOE “National Transmission Grid Study,” May 2002.
Source: EIA “The Changing Structure of the Electric Power Industry 2000: An
Update,” October 2000.
Circuit Miles of Electric Transmission Lines in Service by Division and Voltage Level
(Preliminary 2003 data)
Circuit Miles – Voltage Level (Kilovolts)
Division
New England
(ME, NH, VT, MA, RI, CT)
Middle Atlantic
(NY, NJ, PA)
East North Central
(OH, IN, IL, MI, WI)
West North Central
(MN, IA, MO, ND, SD, NE, KS)
South Atlantic
(DE, MD, DC, VA, WV, NC, SC,
GA, FL)
East South Central
(KY, TN, AL, MS)
West South Central
(AR, LA, OK, TX)
Mountain
(MT, ID, WY, CO, NM, AZ, UT,
NV)
Pacific
(WA, OR, CA)
Alaska and Hawaii
(AK, HI)
Total by Voltage Level
Total
Per
Division
% that is
Shareholder
-Owned
<132
132-143
144-188
189-253
254-400
401-600
>600
13,092
271
--
342
1,904
536
--
16,145
97.4
23,888
3,948
--
5,581
3,940
2,264
351
39,972
90.8
42,781
24,991
2,461
1,548
16,338
--
1,218
89,336
72.7
69,464
1,998
9,560
8,642
8,990
1,124
--
99,778
45.1
48,587
8,505
491
23,167
411
5,948
644
87,753
80.5
29,117
2,237
14,014
3,445
1,003
3,270
258
53,343
42.1
34,384
32,482
3,105
3,787
13,764
1,869
--
89,392
71.8
41,195
5,008
2,002
14,651
10,332
7,056
1,687
81,930
58.6
39,511
588
571
22,687
2,876
10,803
557
77,593
61.0
1,749
505
--
198
209
--
--
2,660
44.1
343,768
80,533
32,204
84,048
59,767
32,870
4,715
637,902
65.2
Source: Edison Electric Institute. EEI Statistical Yearbook Based on 2004 Data. Aug. 2005.
www.electricity.doe.gov
February 2006
Generation
Transmission
Distribution
Overhead Transmission
Long distance transmission is typically
done with overhead lines at voltages of 110
to 765 kV. Many of American Transmission Company’s existing overhead transmission lines were built during the 1950s
and 1960s, when the common structure
design was self-supporting steel lattice towers.9 However, over 9,500 miles of new
high-voltage transmission lines (mainly 230
kV) were built during the 1990s, many of
which used other structural designs.10 The
width of the transmission line right-of-way
needed for these structures depends on their
voltage and height, and is often 75-150 feet
or more. Structures managed by utilities
include: 11
Source: OSHA. www.osha.gov (Accessed 12/1/05).
Wood poles (to handle double-circuit,
138kV lines) Local electric distribution
lines, cable, and telephone lines can be
carried on the same structures to make
efficient use of space. Taller poles are
needed to do this.
Steel poles (to handle double-circuit,
138kV lines) This type of design is of-
ten used when the line will carry heavy
electric loads. Higher voltage lines require taller poles-sometime 100 feet or more.
138-kilovolt single-circuit line on weathering steel This
type of maintenance-free structure will weather over time to
give the appearance of wood.
H-frame wood structure This type of design allows for
shorter spans. Typically, the height of the structures is less
than single pole structures.
Double-circuit 138-kilovolt steel lattice tower Transmission structures of this design are no longer used for new construction.
138-kilovolt steel H-frame
345-kilovolt, double-circuit on single poles Higher voltage lines require taller poles and wider rights-of-way.
While the average life expectancy of conductors varies, those
with polymer insulators have a life expectancy of greater than
50 years.12
9. American Transmission Company. http://www.atcllc.com/IT10.shtml .
10. Energy Information Administration. “Electricity Transmission Fact Sheet.” http://
www.eia.doe.gov/cneaf/electricity/page/fact_sheets/transmission.html.
11. American Transmission Company. http://www.atcllc.com/IT10.shtml .
12. Hubbell Power Systems. www.hubbellpowersystems.com.
www.electricity.doe.gov
Miles of Planned Transmission Lines (230 kV or greater) in
Various NERC Regions, 2004-2013
Region
Eastern Interconnection
NPCC
MACC
FRCC
SERC
MAIN
MAPP
ECAR
SPP
Western Interconnection
AZ-NM
CA-NV
NPP
RMPP
ERCOT Interconnection
Total Planned Miles
Miles
>4,000
119 (59 miles are underground)
134
440
1,846 (2 miles are
underground)
519 (6 miles are underground)
696
109
211
>3,100
1,231
408
1,201
277
>350
>7,100
Source: EEI “Meeting U.S. Transmission Needs,” July 2005.
February 2006
Generation
Transmission
Underground Transmission
Underground transmission lines account for only 0.2% of the
total transmission lines installed in the U.S. in 2001. At the
same time, almost half
(49%) of the capital expenditures for new transmission and distribution wires
between 1993 and 2002 has
been invested in underground wires.13
Underground transmission
lines have a safe life of 2535 years, but can become
unreliable after 15-20
years. Underground lines
cost approximately $1 million per mile; 10 times
more than an overhead
transmission line.14
There are four main types of underground transmission lines,
which include:15
x
High pressure, fluidfilled pipe (HPFF)HPFF pipes are the
most common in the
U.S. Each pipe consists of a single steel
pipe with three, highvoltage, aluminum or
copper conductors
inside surrounded by dielectric oil at 200 psi. Each conductor is insulated with oil impregnated paper, and covered in a metal shielding.
Miles of Installed Overhead and Underground Line
as of 2001
Over Head Distribution,
67%
Under Ground
Distribution, 20.8%
Over Head Transmission,
12%
Under Ground
Transmission, 0.2%
Source: EEI. “Out of Sight, Out of Mind?” A Study on the Costs and Benefits of
Undergrounding Overhead Power Lines.” Jan. 2004.
www.electricity.doe.gov
Distribution
x
High pressure, gas-filled pipe (HPGF)- A HPGF pipe
is similar to the fluid-filled pipe with the exception of the
dielectric oil, which has been
replaced with nitrogen.
x
Self contained fluid-filled
(SCFF)- SCFF pipes are
often the choice for underwater installations. These hollow conductors are filled
with an insulating fluid,
wrapped with an insulating paper, followed by a metal
sheath and plastic coating. These are not placed together
in a pipe for installation, and remain independent.
x
Cross-linked polyethylene
(XLPE)- In the XLPE, also
called a “solid dielectric”
transmission line, a solid
dielectric material replaces
the pressurized liquid or
gas described in the previously. These are not
installed in a bundle,
rather each conductor;
surrounded by a semiconductive shield,
cross-linked polyethylene insulation, and a
metallic shield and
plastic coating; is set
individually in a concrete track.
13. Edison Electric Institute. “Out of Sight, Out of Mind?” A Study on the Costs and
Benefits of Undergrounding Overhead Power Lines.” Jan. 2004.
14. ibid.
15. Wise, Kristi. “Going Underground: A Growing Reality for Transmission Line
Routing?” http://www.eei.org/meetings/nonav_meeting_files/nonav_2003-03-30km/index.htm. Mar. 2003.
Typical Capital Costs for Electric Transmission Lines,
by Voltage
Capital Cost
Transmission Facility
($ per mile)
New 345 kV single circuit line
915,000
New 345 kV double circuit line
1,710,000
New 138 kV single circuit line
390,000
New 138 kV double circuit line
540,000
Approximately 4
times the cost of
Single circuit underground lines
single circuit lines
Upgrade 69 kV to 138 kV line
400,000
Source: National Council on Electricity Policy, “Electricity Transmission: A Primer,”
June 2004.
February 2006
Generation
Transmission
Distribution
Electric Utility Cost Trends
The Handy-Whitman Indexes
show the level of costs for
different types of utility
construction. The index is
maintained for general items of
construction, such as reinforced
concrete, and specific items of
material or equipment, such as
pipe or turbo-generators.
Based on data from this index,
electric utility construction costs
are typically higher for
transmission plants than they are
for distribution plants. Over the
past decade, the cost trends for
transmission plants have
increased 23 percent and those
for distribution plants have
increased 21 percent.16
16. Edison Electric Institute. EEI Statistical
Yearbook Based on 2004 Data. Aug. 2005.
The Office of Electricity Delivery and Energy Reliability (OE)
The Office maintains the following three divisions:
x
x
x
OE Research and Development
Division—researches and develops the
next generation of electricity
transmission and delivery
technologies to make America’s
energy system less vulnerable and
more productive in the future.
OE Permitting, Siting and Analysis Division—works to
expand energy transmission and
delivery capacity in the United States
and between the United States and
our neighbors. We study today’s
markets and regulations to identify
better ways of managing and
operating our energy systems in the future.
OE Infrastructure Security and
Energy Restoration Division—helps
protect America’s critical
infrastructure from disruption and
restore it as quickly as possible in
emergencies.
www.electricity.doe.gov
Mission:
The mission of the Office of Electricity
Delivery and Energy Reliability is to lead
national efforts to modernize the electric
grid; enhance security and reliability of
the energy infrastructure, and facilitate
recovery from disruptions to energy
supply.
Director:
Kevin Kolevar
Communications:
Vernellia Johnson
vernellia.Johnson@hq.doe.gov
U.S. Department of Energy
Office of Electricity Delivery and Energy Reliability
1000 Independence Avenue, SW
Washington, DC 20585
(202) 586-7701
(202) 586-1472
Produced for:
The U.S. Department of Energy
by Energetics, Incorporated
February 2006