The Power GridThe Power Grid
ELEC 403The Citadel
Mark McKinney
The Power GridThe 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 GridThe Power GridUS 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
SERCSERCSERC Transmission Mileage
(161kV and above)
0
5,000
10,000
15,000
20,000
25,000
161kV 230kV 345kV 500kV0
200
400
600
800
1,000
1,200
1,400
1,600
1,800
161kV 230kV 345kV 500kV
2006-2010 2011 - 2015
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
Source: SERC Information Study, July 2006
SERCSERC 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
Nuclear16%
Dual Fuel (Gas/Oil)12%
Gas14% Oil
2%
Net Internal Purchases
9%
Coal38%
Pumped Storage3%
Hydro6%
Source: SERC Information Study, July 2006
US Energy UsageUS Energy Usage
Source: US Energy Information Administration
Power in SCPower 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 SCPower 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 air-conditioning 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 SystemThe US Power SystemThe Generating Station
• Can be nuclear, coal, etc…
• Usually a steam turbine
• Generates 3-phase AC power
• Output usually in the 10-30kV range
• Voltage must be increased to high voltage for “transmission”
The US Power SystemThe US Power SystemThe Transmission Substation
• Voltage stepped-up to 150-500kV
• Allows for transmissions up to 300 miles.
The US Power SystemThe US Power SystemTransmission Lines
• The transmission phase covers long distances at high voltages
• Towers are BIG
• Overseen by NERC
• Connect power plant to localities
• Also connect the various companies and even regions
Transmission LinesTransmission LinesAluminum 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
Transmission Line Structures
Electrical Properties Electrical Capacity (I) Transmission Distance (V) Efficiency (R, L, & C)
Aesthetics Wood or Steel Construction Physical Size
Environmental Impact
Designs of transmission lines vary greatly to meet various needs
Transmission Line Structures
Transmission Line Structures
Accessibility Constructability Maintainability
Zoning and land-useRight-of-way/Easement
Width and height restrictions Determine voltage
and height of tower
Designs of transmission lines vary greatly to meet various needs
Transmission Line Structures
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
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 poles-sometime 100 feet or more.
Source: American Transmission Company
Transmission Line Structures
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
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
Transmission Line Structures
138-kilovolt steel H-frame. Require less height, but wider right-of way.
Source: American Transmission Company
Transmission Line Structures
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 SubstationThe Power SubstationPower Substation
• Steps-down the HV for the “distribution” network
• Voltages <100kV
The Power SubstationThe Power SubstationPower Substation
Switch Tower and Main Transformer
Distribution Bus
The Distribution NetworkThe Distribution Network
Smaller, low-voltage poles
Simpler designs – usually wooden Ts
Typically 7.2kV
What’s on the poles?What’s on the poles?
Capacitor banks
What’s on the poles?What’s on the poles?
Reclosers
What’s on the poles?What’s on the poles?
Transformers
At your houseAt your house
TransformerTap off of one
(occasionally two) phase
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