Renewable Energy(Wind)
Transcript of Renewable Energy(Wind)
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RENEWABLE
ENERGY(WIND)
Dr. Biswajit Basu
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Topics
1. Introduction Wind Turbine2. Wind Characteristics and Resources
General, Atmospheric Boundary Layer, Wind data
analysis, resource estimation, statistical techniques,measurement and instrumentation
3. Aerodynamics
1-D momentum and Betz limit, Ideal HAWT, Bladeelement theory, Blade shape, rotor design simplifiesHAWT rotor performance calculation, Drag, advancedtopics
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Introduction
Important factors for re-emergence of windenergy
NeedNeed; finiteness of fossil fuel
Potential; wind exists everywhere in the world TechnologyTechnology; other fields applied to wind turbine
VisionVision; a new way to use
Political willPolitical will; support research, testing, provideregulatory reform, interconnection withnetworks, incentive
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Modern Wind Turbines
Difference between wind mill are wind turbine capacity
small ~ 10 kW to ~ 50 kW to 2 MW
Aerodynamic force of lift => net positive torque on rotating
shaft => mechanical power => electricity in a generator
Not possible to store ~responds to wind immediately
available
Variability/Fluctuation
Not transportable
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Modern Wind Turbine
Horizontal Axis Wind Turbine ( HAWT)
HAWT ROTOR CONFIURATION
OptionsOptions
Number of Blades ( 2 or 3)
Rotor Orientation
Blade material, Profile
Hub Design Power Control =>Aerodynamic control ( STALL)
=> Variable Pitch Blade ( Pitch Control)
Fixed or Variable Rotor Speed Orientation by self aligning ( Free Yaw) or direct control
(Active Yaw)
Gearbox or Direct drive Generator
Synchronous or Induction Generator
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Rotor
Hub and Blades (important from performance
and cost)
Most turbines up wind with 3 blades
Fixed blade pitch with stall control ( intermediate
size), Increased pitch control ( larger size)
Materials; composites- fiber glass reinforcedplastics (GRP), wood/epoxy laminates
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Drive Train
Rotating parts
Low speed shaft (rotor side), gear box, high speed shaft
(generator side)
Supporting bearings, couplings, brakes, rotating parts ofgenerator
Types of gearbox: parallel shaft, planetary larger
machines (planetary gearbox) Unique loading: fluctuating wind and dynamics of large
rotors
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Generator
Induction or Synchronous
Induction more popular (50 Hz, 1500 rpm)
Induction: more rugged, inexpensive, easy toconnect to network
Variable speed wind turbine( less wear andtear, more efficiency)
Hardware: variable speed; power electronicscomponent; suitable power electronicconverters
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Nacelle and Yaw System Wind turbine housing, machine bed plate or maintenance
and yaw orientation system Mainframe: mounting and alignment
Nacelle: Protection from weather
Yaw system : align rotor with wind direction (bearingconnecting mainframe to tower)
Active: Contain motors which drive pinion gear against a bullgear attached to the yaw bearing
Sensor: On Nacelle
Yaw Brakes
Free yaw in down wind machine
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Tower and Foundation
Tower structure and foundation
Free standing; stand tubes; lattice or concrete
For smaller turbines, guyed towers
Tower height is typically 1 to 1.5 times rotordiameter
Possibility of coupled tower/rotor vibration
For down wind rotors, effect of tower shadow
causes complex tower dynamics, power
fluctuations, noise generation
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Controls
Sensor speed, position, temperature,flow, current
Controller mechanical, electrical,
computer Power amplifiers switches, electrical
amplifiers, hydraulic pumps, valves
Actuators motors, pistons, magnetsand solinoids
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Aim:
Upper bound on torque and power
experienced by drive train
Maximizing fatigue life of rotor drive train
and structural components
Maximize energy production
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Balance of Electrical Systems
Cables, switchgear, transformer
Power electronic converters, power
factor correction capacitors
Yaw, pitch motors
Interconnection with network
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Wind Characteristics
Mechanics of wind motion
Spatial variation in heat transfer to the earths atmosphere
create variations in the atmospheric pressure field
Cause: Air movement from high to low pressureFour atmospheric forces
1. Pressure forces
2. Coriolis force (rotation)
3. Inertial forces (large scale circular motion)
4. Frictional forces
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Wind Characteristics (contd)
Pressure force 1p
p
F n
=
= density of air, p = pressure ( n is the direction
normal to the lines of constant pressure)
Coriolis Force Fc= fu, u = wind speed,
f = Coriolis parameter = 2 sinw
= Latitude, = angular rotation of earthw
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Variation in time
Inter-annual:> 1 year, long term
30 years data required, average (annual) over 5years
Prediction at 90% confidence levelAnnual: Significant seasoned variations;
monthly average wind speeds
Diurnal: Large wind variations on a daily scaledue to differential heating of earths surfaceduring the daily radiation cycle
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Short-term:
Short term wind speed variation induce
turbulence and gust over mean
Usually mean variation over 10 min or
less sampled at 1 sec. Stochastic character represent
turbulence Gust is a discrete event
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Atmospheric boundary layer
Lapse rate dp = -gdzp = pressure, = density,z = elevation measured positive upward
1st Law of ThermodynamicsHeat transferred, dq = du + pdv
= dh dp
=CpdT 1/ dpT = temperature, u = internal energy, h = enthalpy,= Specific heat, Cp =constant pressure specific heat
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Atmospheric boundary layer
(contd)
For adiabatic pressure, dq = 0
Therefore, CpdT = 1/ dp = -g/Cpwhich gives
g = 9.81 m/s2; Cp= 1.005 KJ/kgKThis is important for atmospheric stability and generation of
turbulence
0 . 0 0 9 8
a d i a b a t i c
d T K
d z m
=
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Turbulence
Turbulence Intensity ( TI)
Velocity,_
u U U= +
0
1, 10min
t
U udt t
t
= =
_
U=mean, U =fluctuating
Sampled form,1
1i
is
U uN =
= sN
, . ,s st N t N No of samples t Sampling time = = =
uTI
U
=
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Turbulence (contd)
where, standard deviation
( )2
1
1
1
sN
u i
is
u UN
=
=
Normally, TI = 0.1 to 0.4, depends on site terrain
features and surface conditions
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Wind Velocity Profile
Log law
( )*
0
lnU zU zk z
=
z0= Surface roughness, K = Von Karman constant = 0.4U*=friction velocity
0*ln( ) ( ) ln( )
K
z U z zU
= + Also,
Z0 is a function of terrain
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Wind Velocity Profile (contd)
Power law (simple)0
0
ln
( )( ) ln rr
z
zU zzU z
z
=
( )( )r r
U z zU z z
=
= function of elevation, time of day, season, terrain, temperature
( )( )
0.37 0.088ln,
1 0.088 ln 10
ref
ref
Uvelocity height
z
=
( )2
10 0 10 00.096log 0.016 log 0.24z z= + +(surface
roughness)
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Wind Speed Measurement
Cup anemometers: Based on rotation
Propeller anemometers: Three
dimensional measurement of velocity
components Kite anemometers: At heights greater
than towers; at areas of high turbulenceAcoustic Doppler sensors (SODAR)
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Advanced Topics
Application of stochastic processes
Fatigue Model field data with historical datae
Turbulence
Load Structured excitation
Fatigue
Control Power Quality
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Advanced Topics (contd)
CFD for flow characterization
Numerical modelling of complex flow Micrositing
Resource assessment tool to determine exactposition
CFD models or micrositing models
Statistically based resource assessment Alternative of physical models
MCP approach (Measure-Correlate-Predict)
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1-D Momentum Theory and Betz
Limit
Idealized rotor turbine
Actuator disk model of WT
Assumptions: Homogeneous, incompressible, steady state flow
No frictional drag
Infinite number of blades
Uniform thrust over disk
A non rotating wake
Static pressure for upstream and for downstream of the
rotor is equal to the undisturbed air pressure
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