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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 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 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