the power grid
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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. - PowerPoint PPT PresentationTRANSCRIPT
Power Systems Introduction
ELEC 403/605The Citadel
Mark McKinney
Every power system has three major components
generation: source of power, ideally with a specified voltage and frequency
load: consumes power; ideally with a constant resistive value
transmission system: transmits power; ideally as a perfect conductor
Basics
BasicsComplications
No ideal voltage sources existLoads are seldom constantTransmission system has resistance, inductance,
capacitance and flow limitationsSimple system has no redundancy so power
system will not work if any component fails
BasicsPower: Instantaneous consumption of energyInstalled U.S. generation capacity is about
900 GW ( about 3 kW per person) Energy: Integration of power over time; energy is
what people really want from a power systemJoule = 1 Watt-second (J)kWh = Kilowatt-hour (3.6 x 106 J)Btu = 1055 J; 1 MBtu =0.292 MWh
U.S. electric energy consumption is about 3600 billion kWh (about 13,000 kWh per person, which means on average we each use 1.5 kW of power continuously)
The Power GridNumber one invention of
the 20th century is electrification
US has one of the most extensive and reliable networks in the world
The 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
SERCSERC 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
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
Nuclear16%
Dual Fuel (Gas/Oil)12%
Gas14% Oil
2%
Net Internal Purchases
9%
Coal38%
Pumped Storage3%
Hydro6%
Source: SERC Information Study, July 2006
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 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.
If licensing and construction go as planned, two new nuclear reactors could come online in South Carolina by 2020.
Source: US Energy Information Administration
VC Summer Plant Unit 1 is a Westinghouse 3-loop 1GW reactor that went online in 1984.
Construction began in 1974. Units 2 & 3 are Westinghouse AP1000 1.25GW reactors.
Simpler design than previous reactors. According to NRC, orders of magnitude safer than previous designs. Better passive protection than nearly any other reactor design.
Unit 2 was the first nuclear reactor to begin construction in the US in 30 years. New reactors co-owned by SCE&G (60%) and Santee Cooper (40%) Being built in parallel with two identical reactors at Vogtle Plant in Georgia Original estimates called for completion in 2016, later estimates indicated that
Units 2 and 3 could go online in 2019 and 2020, but recent financial difficulties have put the entire project in jeopardy. Construction began in 2013.
VC Summer Nuclear Plant
The 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 Transmission Substation• Voltage stepped-up to
150-500kV• Allows for transmissions up
to 300 miles.
The 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 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
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-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
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 SubstationPower Substation• Steps-down the HV for the
“distribution” network• Voltages <100kV
The Power SubstationPower Substation
Switch Tower and Main Transformer
Distribution Bus
The Distribution NetworkSmaller, low-voltage
polesSimpler designs –
usually wooden TsTypically 7.2kV
What’s on the poles?Capacitor banks
What’s on the poles?Reclosers
What’s on the poles?Transformers
At your houseTransformerTap off of one
(occasionally two) phase