The Power Grid ELEC 403 The Citadel Mark McKinney

The Power Grid  Number one invention of the 20 th 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 SERC Transmission Mileage ( 161kV and above)  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

SERC  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

US Energy Usage Source: US Energy Information AdministrationUS 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 AdministrationUS Energy Information Administration

Power in SC  If licensing and construction go as planned, two new nuclear reactors could come online in South Carolina by  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 AdministrationUS 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 kV range Voltage must be increased to high voltage for “transmission”

The US Power System The Transmission Substation Voltage stepped-up to kV Allows for transmissions up to 300 miles.

The US Power System Transmission 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 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  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  Accessibility  Constructability  Maintainability  Zoning and land-use  Right-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 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 poles- sometime 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