Transcript The Power Distribution System

The Power Grid
ELEC 403
The Citadel
Mark McKinney
The Power Grid
 Number
one invention of
the 20th century is
electrification
 US has one of the most
extensive and reliable
networks in the world
The Power Grid
 US
and Canada are
divided into eight large
regions (RROs –
Regional Reliability
Organizations) overseen
by the North American
Electric Reliability Council
(NERC)
 South Carolina is in
SERC
Source: NERC
SERC
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Comprised of about 50
member companies, co-ops,
and municipalities that supply
energy within the region
Covers an area of
approximately 560,000
square miles in sixteen states
Supplies about
1,000,000GWh of energy
annually
Dominated (like the US) by
coal and nuclear generation
SERC Transmission Mileage
(161kV and above)
25,000
20,000
15,000
10,000
5,000
0
161kV
Source: SERC Information Study, July 2006
230kV
345kV
500kV
SERC

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Comprised of about 50
member companies, co-ops,
and municipalities that supply
energy within the region
Covers an area of
approximately 560,000
square miles in sixteen states
Pumped Storage
3%
Supplies about
1,000,000GWh of energy
annually
Dual Fuel (Gas/Oil)
12%
Dominated (like the US) by
coal and nuclear generation
Source: SERC Information Study, July 2006
Hydro
6%
Gas
14%
Net Internal
Purchases
9%
Nuclear
16%
Coal
38%
Oil
2%
US Energy Usage
Source: US Energy Information Administration
Power in SC

South Carolina’s four nuclear power
plants supply about half of the
State’s electricity demand.

South Carolina receives most of its
coal from Kentucky.

Industry is the State’s largest
energy-consuming sector,
accounting for roughly two-fifths of
total energy consumption.
Source: US Energy Information Administration
Power in SC

If licensing and construction go as
planned, two new nuclear reactors
could come online in South Carolina
by 2016.

Per capita electricity use in South
Carolina is higher than the
nationwide average due to high airconditioning demand during hot
summer months and the widespread
use of electricity for home heating
during generally mild winter months.
Source: US Energy Information Administration
The US Power System
The Generating Station
• Can be nuclear, coal, etc…
• Usually a steam turbine
• Generates 3-phase AC power
• Output usually in the 1030kV range
• Voltage must be increased to
high voltage for
“transmission”
The US Power System
The Transmission Substation
• Voltage stepped-up to
150-500kV
• Allows for transmissions up
to 300 miles.
The US Power System
Transmission Lines
• Overseen by NERC
• The transmission phase
covers long distances at high
voltages
• Connect power plant to
localities
• Towers are BIG
• Also connect the various
companies and even regions
Transmission Lines
Aluminum has replaced copper lines
because they have lower cost and are
lighter weight.
A shield wire is connected directly to
the top of transmission line towers to
protect the main conductors from a
direct lightning strike.
Transmission lines are connected to
the towers by porcelain insulators.
Source: American Transmission Company
Transmission Line Structures
Designs of transmission lines vary greatly to meet various needs
 Electrical Properties
Electrical Capacity (I)
 Transmission Distance (V)
 Efficiency (R, L, & C)

 Aesthetics
Wood or Steel Construction
 Physical Size

 Environmental
Impact
Transmission Line Structures
Designs of transmission lines vary greatly to meet various needs
 Accessibility
Constructability
 Maintainability

 Zoning
and land-use
 Right-of-way/Easement
Width and height restrictions
 Determine voltage
and height of tower

Transmission Line Structures
Double-circuit, 138-kilovolt
transmission line built on
wood structures.
Local electric distribution lines,
cable and telephone lines are
sometimes carried on the same
structures to make efficient use of
space. Taller poles are needed to
do this.
Source: American Transmission Company
Transmission Line Structures
Double-circuit, 138-kilovolt
line build on galvanized steel
poles.
This type of design is often used
when the line will carry heavy
electric loads. Higher voltage
lines require taller polessometime 100 feet or more.
Source: American Transmission Company
Transmission Line Structures
138-kilovolt single-circuit line
on weathering steel.
This type of maintenance-free
structure will weather (rust) over
time to give the appearance of
wood and is generally used in
wooded areas.
Source: American Transmission Company
Transmission Line Structures
H-frame wood structure.
This type of design allows for
shorter spans (the distance
between structures.) In general
the height of the structures is less
than single pole structures.
Source: American Transmission Company
Transmission Line Structures
138-kilovolt steel H-frame.
Require less height, but wider
right-of way.
Source: American Transmission Company
Transmission Line Structures
345-kilovolt, double-circuit on
single poles.
Higher voltage lines require taller
poles and wider rights-of-way.
Source: American Transmission Company
The Power Substation
Power Substation
• Steps-down the HV for the
“distribution” network
• Voltages <100kV
The Power Substation
Power Substation
Switch Tower and Main Transformer
Distribution Bus
The Distribution Network
 Smaller,
low-voltage
poles
 Simpler designs – usually
wooden Ts
 Typically 7.2kV
What’s on the poles?
 Capacitor
banks
What’s on the poles?
 Reclosers
What’s on the poles?
 Transformers
At your house
 Transformer
 Tap
off of one
(occasionally two) phase