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

 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 25,000 20,000 15,000 10,000 5,000 0

Source: SERC Information Study, July 2006

SERC Transmission Mileage ( 161kV and above)

161kV 230kV 345kV 500kV 1,800 1,600 1,400 1,200 1,000 800 600 400 200 0 161kV 230kV 2006-2010 345kV 500kV 2011 - 2015

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 Supplies about 3% 1,000,000GWh of energy annually Dominated (like the US) by Dual Fuel (Gas/Oil) 12% coal and nuclear generation Hydro 6% Gas 14%

Source: SERC Information Study, July 2006

Net Internal Purchases 9% Oil 2% Nuclear 16% Coal 38%

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 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 System

The Generating Station

• Output usually in the 10 30kV range • Can be nuclear, coal, etc… • Usually a steam turbine • Generates 3-phase AC power • 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 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

 Reclosers

What’s on the poles?

What’s on the poles?

 Transformers

At your house

 Transformer  Tap off of one (occasionally two) phase