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Power Systems Energy Resources Efficiency and CO2 Generation basics
Electricity Generation
Eduardo Campero-Littlewood
Universidad Autonoma Metropolitana
Azcapotzalco Campus
Energy Department
Power Systems Energy Resources Efficiency and CO2 Generation basics
Content
1 Power Systems
2 Energy resources used to generate electricity
3 Efficiency and CO2 emissions of generating plants
4 Generation basics
Power Systems Energy Resources Efficiency and CO2 Generation basics
Power systems network
Delivery network25-132 kV
Industrialclient
Generatingplant
Elevatingstation
Transformationsubstation
Distribution substation
Transport Network110-380 kV
3-36 kV
Residentialclient
125-220V
Power Systems Energy Resources Efficiency and CO2 Generation basics
Thermal power generation
Water feeding pump
Coolingtower
Condenser
Fuel
Combustion gases
G
Electric generator
ElectricityTurbine
Power Systems Energy Resources Efficiency and CO2 Generation basics
Combined-cycle generating plant
Heat recovery steam generator
Coolingtower
Fuel
Compressor Gas Turbine
Heat recovery unit
G
Steam turbine Generator
Steam
G
Gas turbinegenerator
Non-condensingsteam turbine
Combustion chamber
Fresh air
Exhaust gases
55 °C
80 °C
Exhaust
Cogen
Representative energy flows for a combined-cycle, cogeneration plant with
back-pressure steam turbine, delivering thermal energy to a heating system.
Power Systems Energy Resources Efficiency and CO2 Generation basics
Steam turbine for electricity generation
Power Systems Energy Resources Efficiency and CO2 Generation basics
Hydraulic turbine
Power Systems Energy Resources Efficiency and CO2 Generation basics
Solar generating system
11MW Sevilla, Spain
Power Systems Energy Resources Efficiency and CO2 Generation basics
Wind energy generation system
2.5MW from 8 turbines in Santa Catarina, N. L., Mexico
Transmission lines
Substation
Power Systems Energy Resources Efficiency and CO2 Generation basics
Typical efficiencies
Power plant technnology Electricalefficiency [%]
Coal-fired steam turbine 35Dual steam turbine 35Fuel oil & gas steam turbine 34Gas combined-cycle 44Diesel combustion engine 37Hydroelectric dam 35Geothermal steam turbine 35Wind turbine 35Solar panels 9-12Nuclear 32
Power Systems Energy Resources Efficiency and CO2 Generation basics
Life cycle of electricity generation
Mining
Extraction and
Processing
Extraction and
Processing
Agriculture/
Forest
Geothermal
Energy
Pipeline
Transport
Pipeline
Transport
Cultivation and
Harvesting/
Collection
Refining
Transport
Distribution
Transport
Coal Power
Plant
Gas Power
Plant
Oil Power Plant
Biomass Power
Plant
Geothermal
Power Plant
Coal
Gas
Oil
Biomass
Geothermal
ELECTRICITY
MIX TO THE
NATIONAL GRID
Carbon Capture
and StorageWaste Disposal
Power Systems Energy Resources Efficiency and CO2 Generation basics
Life cycle of electricity generation
Hydro Energy
Mining and
Milling
Wave Energy
Solar Energy
Wind Energy
Fuel Enrichment Fuel Fabrication
Hydro Energy
Mining and
Milling
Wave Energy
Solar Energy
Wind Energy
Hydro
Nuclear
Ocean
Solar
Wind
ELECTRICITY
MIX TO THE
NATIONAL GRID
Waste Disposal
Power Systems Energy Resources Efficiency and CO2 Generation basics
Elements considered in life cycle analysis
GWP Global warming potential (CO2)
ADP Abiotic depletion potential (Sb antimony)
AP Acidification potential (SO2)
EP Eutrophication potential (NOx and others)
FAETP Freshwater aquatic ecotoxicity potential (heavy metals to airand water)
HTP Human toxicity potential (nickel, vanadium y arsenic)
MAETP Marine aquatic ecotoxicity potential (hydrogen fluoride)
OLDP Ozone layer depletion potential
POCP Photochemical ozone creation potential (SO2 and NOx)
TETP Terrestrial ecotoxicity potential (Chromium, nickel, vanadiumand mercury)
Power Systems Energy Resources Efficiency and CO2 Generation basics
Environmental impact for each kWh, the case of Mexico
Santoyo-Castelazo, E., Gujba, H., Azapagic, A., “Life cycle assessment of electricity generation in
Mexico.” 2011. Energy 36 (3), 1488-1499.
Power Systems Energy Resources Efficiency and CO2 Generation basics
CO2 Emissions in Mexico
Emissions of greenhouse effect gases in Mexico in 2010, according to theFifth National Communication to the United Nations FrameworkConvention on Climate Change.
Percentage of total emissions
Waste 6%
Transport 22%
ElectricityGeneration 22%
Other 5%
Manufacture, Industryand Construction 8%
Fugitiveemissions 11%
Industrialprocesses 8%
Soil usage 6%
Agriculture 12%
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation from conventional sources
Electricity Generation for Conventional Sources (fossil fuel)
CombinedCicle 62%
ConventionalThermoelectric 16%
Carbon 14%
Turbogas 3%
Other 5%
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation from non conventional sources
Electricity Generation for Non Conventional Sources
Hydroelectric 5%
Wind %
Nuclear %
Other 2%
Power Systems Energy Resources Efficiency and CO2 Generation basics
Electricity Tariff
The tariff for electricity consumption depends mainly on the followingelements:
Type of installation and voltage level
Period of the year
Power Systems Energy Resources Efficiency and CO2 Generation basics
Electricity Tariff
The tariff for electricity consumption depends mainly on the followingelements:
Type of installation and voltage level
Period of the year
Hour of the day
Power Systems Energy Resources Efficiency and CO2 Generation basics
Electricity Tariff
The tariff for electricity consumption depends mainly on the followingelements:
Type of installation and voltage level
Period of the year
Hour of the day
Power factor
Power Systems Energy Resources Efficiency and CO2 Generation basics
Electricity Tariff
The tariff for electricity consumption depends mainly on the followingelements:
Type of installation and voltage level
Period of the year
Hour of the day
Power factor
Maximum measured power during a period of time
Power Systems Energy Resources Efficiency and CO2 Generation basics
Electricity Tariff
The tariff for electricity consumption depends mainly on the followingelements:
Type of installation and voltage level
Period of the year
Hour of the day
Power factor
Maximum measured power during a period of time
Power Systems Energy Resources Efficiency and CO2 Generation basics
Electricity Tariff in Mexico
First Sunday of April to last Saturday of October (DST)
Days Base Intermediate Peak
Monday toFriday
0:00-6:00 6:00-20:0022:00-24:00
20:00-22:00
Saturday 0:00-7:00 7:00-24:00Sunday and
non-working days0:00-19:00 19:00-24:00
Power Systems Energy Resources Efficiency and CO2 Generation basics
Electricity Tariff in Mexico
Last Sunday of October to Saturday before first Sunday of April
Days Base Intermediate Peak
Monday toFriday
0:00-6:00 6:00-18:0022:00-24:00
18:00-22:00
Saturday 0:00-8:00 8:00-19:0021:00-24:00
19:00-21:00
Sunday andnon-working days
0:00-18:00 18:00-24:00
Power Systems Energy Resources Efficiency and CO2 Generation basics
Typical demand in UAM Azcapotzalco
00 03 06 09 12 15 18 21 00
Hour [h]
0
200
400
600
800
1000
1200
Dem
anded
Pow
erP3φ
[kW
]
Jun-17-2015
Base Intermediate Peak
00 03 06 09 12 15 18 21 00
Hour [h]
0
200
400
600
800
1000
1200
Dem
anded
Pow
erP3φ
[kW
]
Dec-02-2015
Base Intermediate Peak
Power Systems Energy Resources Efficiency and CO2 Generation basics
Electricity Tariff in Mexico: Invoice Demand
2016 Demand⋆
($/kW)Peak
($/kWh)Intermediate($/kWh)
Base($/kWh)
June 10.79 0.0954 0.0406 0.0339
⋆D = DP + FRI ×max (DI −DP, 0) + FRB ×max (DB −DPI, 0)
where:
D = Invoice DemandDP = Peak demand in peak periodDI = Peak demand in intermediate periodDB = Peak demand in base periodDPI = Peak demand in intermediate and peak periodsFRI = 0.30FRB = 0.15
Power Systems Energy Resources Efficiency and CO2 Generation basics
CO2 emissions in every hour of a Wednesday in Mexican power plants.
2 4 6 8 10 12 14 16 18 20 22 24
Hour [hr]
500
550
600
650
700
CO
2[g/k
Wh]
Power Systems Energy Resources Efficiency and CO2 Generation basics
Typical electric demand during a Wednesday at UAM-A.
2 4 6 8 10 12 14 16 18 20 22 24
Hour [hr]
0
200
400
600
800
1000
1200
Dem
and[kW
h]
Power Systems Energy Resources Efficiency and CO2 Generation basics
CO2 equivalent emissions in every hour of a Wednesday at UAM-A.
2 4 6 8 10 12 14 16 18 20 22 24
Hour [hr]
0
100
200
300
400
500
600
CO
2[kg]
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation Basics: Magnetic circuits
The basic theory of electricity generation is available in Fitzgerald and
Kingsley’s Electric Machinery
Umans, S., Fitzgerald, A., & Kingsley, C. (2013). Electric machinery.McGraw-Hill Higher Education.
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation Basics: Magnetic circuits
Simplifying assumptions for engineering solutions:
Consider Ampere’s law!
C
H · dl =
"
SC
J · da
whereH = Magnetic field intensity dl = Line differentialJ = Current density da = Surface differential
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation Basics: Magnetic circuits
μ>>μ0
i
N
ϕ
g
Basic scheme of a magnetic circuit.
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation Basics: Magnetic circuits
Consider Gauss’ law!
S
B · da = 0
whereB = Magnetic field density da = Surface differential
the presence of a high-permeability (µ ≫ µ0) material tends to causemagnetic flux to be confined to the paths defined by the structure
for uniform cross-sectional areas φ = BcAc
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation Basics: Magnetic circuits
a three-dimensional magnetic circuit can be represented by aone-dimensional equivalent circuit similar to an electric circuit
Rc
Rg
F = Ni
ϕ
μ>>μ0
i
N
ϕ
g
then theF= Ni = φR
where:
R =lc
µAc, φ =
"
S
B · da
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation Basics: Flux linkage and inductance
Time-varying magnetic fields produce electric fields according toFaraday’s law:
!
C
E · ds = −d
dt
"
S
B · da
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation Basics: Flux linkage and inductance
A winding consists of N closed contours C, so
e = Ndφ
dt=
dλ
dt, λ = Nφ
for a magnetic circuit composed of magnetic material of constantmagnetic permeability or with a dominating air gap, the linear relationbetween flux and current is called inductance:
L =λ
i
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation Basics: Flux linkage and inductance
Assuming the magnetic flux is uniform through most of the core H ∝ F
B ∝ φ, and hence, B ∝ λ.
Hence, a plot of flux versus current is of the same shape as a B −H curve.
H, i
B, λ
µ, L
usually assumedlinear (air)
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation Basics: Synchronous Generator
Armature-winding
Magnetic axis
Field
winding
Flux
paths
Stator
Rotor
a
-a
N-turn
armature
winding
aa
The field-winding of this machine produces a single pair of magnetic poles(similar to that of a bar magnet), and hence this machine is referred to as atwo-pole machine.
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation Basics: Synchronous Generator
The rotating magnetic field generates a sinusoidal time-varying emf(electromotive force) in the stator windings.When currents circulate in both rotor and stator windings, magnetic flux iscreated in the air gap between. The electromagnetic torque is produced bythe tendency of both magnetic fields to align.
Fr
Fs
Armature-windingMagnetic axis
Field winding
Flux paths
Stator
Rotor
a
-a
N-turn armaturewinding
aa
(a)
Time t [s]0 π 2π radians
0
v(t)
(b)
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation Basics: Synchronous Generator
The rotating magnetic field generates a sinusoidal time-varying emf(electromotive force) in the stator windings.When currents circulate in both rotor and stator windings, magnetic flux iscreated in the air gap between. The electromagnetic torque is produced bythe tendency of both magnetic fields to align.
Fr
Fs
Armature-windingMagnetic axis
Field winding
Flux paths
Stator
Rotor
a
-a
N-turn armaturewinding
aa
Fs
srsr
rr
ss
Frsinδsr = Fsrsinδs
Fssinδsr = Fsrsinδr
T =π
2
#
poles2
$2
ΦsrFr sin δr
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation Basics: Synchronous Speed
As the rotor rotates, the flux-linkages of the armature winding change withtime. Under some assumptions, the resulting coil voltage will be sinusoidalin time.In a two-pole machine, the coil voltage passes through a complete cycle foreach revolution of the machine. Thus, its frequency in cycles per second(Hz) is the same as the speed of the rotor in revolutions per second:
the electric frequency of the generated voltage is synchronized
with the mechanical speed.
As seen in the equation:
fe =ωe
2π
where ωe is the electrical angular frequency.
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation Basics: Synchronous Speed
Generated armature voltage of a two pole machine (ωm = ωe):
Time t [s]
0
Variable
f(t)
t = 2πωe
f(t) = cos(ωet)
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation Basics: Synchronous Speed
When a machine has more than two poles, it is convenient to express anglesin electrical degrees.
-a1
a2-a2
a1
One pair of poles in a multipole machine or one cycle of flux distributionequals 360 electrical degrees or 2π electrical radians. Since there are poles/2complete wavelengths, or cycles, in one complete revolution, it follows that
ωe =
#
poles2
$
ωm
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation Basics: Synchronous Speed
Generated armature voltage for a 4-pole machine. The mechanicalfrequency is half the electrical frequency
0 π 2π 3π 4πTime t[s]
0
Electrical radians
0 π 2π
Mechanical radians
Power Systems Energy Resources Efficiency and CO2 Generation basics
Generation Basics: Synchronous Speed
To maintain a constant frequency, machines with more than 2 poles mustrotate at a lower speed than that of a 2 pole machine.
The typical frequency of operation in America is 60Hz, yielding an angularvelocity of 3600 rpm for a two pole machine.
The rotational speed of a synchronous generator, in revolutions per minute,as a function of the electrical frequency is:
n =120poles
fe
Power Systems Energy Resources Efficiency and CO2 Generation basics
Synchronous Generator: Example
A synchronous generator is to produce 50 Hz sinusoidal voltages. Whatmust be its speed if the machine has, a) 2 poles, b) 4 poles and c) 40 poles?
Power Systems Energy Resources Efficiency and CO2 Generation basics
Synchronous Generator One-Phase Equivalent Circuit
Vf
Ea
Rf
Ra
Vt
+
-+ -
ArmatureField
If
Ia
Xs
Vt, Ea, Vf = Terminal, generated and field voltageIa, If = Armature and field currents
Ra, Rf = Armature and field resistancesLf = Field inductanceXs = Synchronous reactance, Xs = ωLs
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