L2_ElectricPowerSystem

8/3/2019 L2_ElectricPowerSystem

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Electric Power System

ECEN 2060


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2ECEN2060

Electric Power System

Generation, transmission and distribution of constant

frequency (600.1 Hz in the US) 3-phase AC Constant-frequency AC:

Simple voltage step-up or step-down using transformers

Efficient transmission and distribution

3-phase:

Constant instantaneous power

Efficient, reliable generators

Efficient transmission and distribution

Complex interconnected system (grid*) with manygenerators adding power to meet time-varying demands forelectricity

*There are 3 separate power grids in the US


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3ECEN2060

US Power Grids

986 GW total capacity (2006)

275,000 miles of transmission lines


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4ECEN2060

A more detailed view

High-

VoltageDC (HVDC) lineexample

(Pacific intertie),846 miles,500kV, 2 GW


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5ECEN2060

Energy conversions in electricity generation

Chemical(e.g. coal)

Nuclear heat mechanical electrical

Carnot efficiency limit of heat enginesh < 1-TC/TH < 70%

Water flow

Radiation

steam

flow

Betz efficiency limit:h < 60%

mechanical electrical

Air flow mechanical electrical

electrical

Material bandgap efficiency limit:h < 50%

Hydro and wind

Photovoltaic

(kinetic)


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Fuel-Fired Electric Power Plant

6ECEN2060

TH = 600oC

= 873oK

Steam temperature

TC = 30o

C= 303oK

Coolingwatertemperature

Theoretical Carnot efficiency limit: h < 1-TC/TH < 0.65 = 65%Actual average efficiency of fuel-fired power plants is about 30-40%

Coal-fired Rankine-cycle plants generate about 50% of electricity in the US

Rankine cycle thermal power plant:water and steam

TextbookSections

3.4 and 3.5


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US Electricity Flow

Energy Information Administration, http://www.eia.doe.gov/(excellent source of energy-related data)

1 quadrillion Btu = 1015 Btu = 1.055x1018 J = 2.93x1011 kWh = 293 TWh

Loss: 64.7%

35.3%

T&D (Transmission and Distribution) losses: 1.31/13.83 = 9.5%
http://www.eia.doe.gov/http://www.eia.doe.gov/


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Demand fluctuations

Types of power plants

Baseload plants (e.g. coal-fired ornuclear) Intermediate (e.g. hydro or

combined-cycle) Peaking (e.g. combustion gas

turbines)


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Energy Generation InColorado

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Electricity Generation in Colorado

11.2 GW total capacity Total electricity generated (2006): 50.7 TWh, 70% coal-fired Average retail price: 7.61 cents/kWh

Boulder Valmont power plant: coal-fired (186 MW), gas combustion (43 MW)


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San Luis Valley Solar Data (09/11/2010) Good Day [1]

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ermittent Wind Generation

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Generation, transmission and distribution

Typical residential wiring

One of the distributionphases (4 kV in theexample shown) dropped

to two 120V circuits usingtransformer with a center-tapped secondary

Available AC voltages:120Vrms and 240Vrms(single-phase)

Voltage levels in transmission and distribution are based on efficiency/cost trade-offs


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Grid-Connected Renewable Sources

Must interface to the existing 60 Hz utility grid and

comply to utility regulations Challenges and opportunities

Geographical availability of grid transmission/distributionlines

Intermittency of renewable sources such as wind or solar

Increased needs for energy storage

Distributed generation

Distributed synchronization and system controls Economics

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