Wind Turbines Technology
Cataldo Pignatale
Product Support Manager
Vestas Italia S.r.l.
Desire-Net Project
Session Contents
• Aim: at the end of this session participants will
have an overview of the wind turbine generators
technologies developed over the years and
implemented on the modern wind turbines
• Duration: 35-40min
2
Agenda
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Wind turbines characteristics
Control of power
Type of generators
Connection to grid
Control systems
Grid integration of wind trubines
Construction technologies of a modern wind turbine
3
Wind turbines characteristics
4
Wind Turbine Generator
Definition: Machine capable to convert the kinetic
energy of a wind tube into electrical energy.
“Betz' law’’’: less than 16/27 (or 59%) of the
kinetic energy in the wind can be converted to
mechanical energy using a wind turbine.
(Betz' law was first formulated by the German Physicist Albert Betz in 1919)
5
Main parts of a modern wind turbine
Blade
Nacelle
Hub
Tower
Foundation
6
Wind Turbines Characteristics
• Rotor axis: horizontal, vertical;
• Alignment to the wind: upwind, downwind;
• Alignment to the wind: active (forced) or passive
(free) yawing system;
• Number of blades: even, odd; 3, 2, 1;
• Control of power: pitch, stall, active stall, yaw;
• Rotation transmission: with or without gearbox;
• Type of generator: synchronous, asynchronous;
• Grid connection: direct, indirect;
3
blades
Horizontal
axis
rotor
Upwind
turbine
With gerabox Active
yaw
mechanism
1 blade
Pitch
control Free
Vertical
axis
rotor
2 blades
Downwind
turbine
yaw mechanism
Without gearbox
7
Control of power
8
Control of power
Reducing the power at high windspeed
At high wind the power is reduced by
pitching the blades. This can be done in
two ways.
• Reducing the lift
and over speeding
called Pitch
variable speed
Flow on upper and lower
surface equal  no lift
• Reducing the lift by
generating stall
9
Control of power
Pitching
Low wind
High wind
Stop
Pitch variable
speed and
optislip
Passive stall
Active stall
10
Control of power
Wind Power and Power Curves
Wind power
Power
Pitch variable speed
Active stall
Rated power
Passive stall
Max Power = ½ · A · v3 ·  · Cp
‘A’ is area
‘v’ is velocity (wind speed)
‘’ is air density
‘Cp’ power coefficient
m/s
11
Control of power
Iso-power map wind speed and pitch angle
25
2500 kW
― Stall control
2000 kW
― Pitch control
20
1500 kW
1000 kW
15
500 kW
0 kW
10
5
-20
-10
0
+10
+20
Pitch angle (deg)
+30
72 m rotor 2MW turbine
12
Control of power
Pitching mechanism
Electrical
Blade turning gear
Pinion
Battery bank
Hydraulic
13
Type of generators
14
Type of generator
Synchronous
Asynchronous
15
Type of generator
Fixed speed asynchronous generator
50 Hz
+ kW
(generator)
1000 rpm
- kW
(motor)
6-poled stator
Rotational speed
rpm =
60 x frequency
number of pole pairs
16
Type of generator
Variable speed asynchronous generators
50 Hz
Stator field = 1000 rpm
Rotor mechanically = 1100 rpm
DC
AC
AC
DC
17
Connection to the grid
18
Connection to grid
Direct
PCC
Grid frequency AC
Grid frequency AC
19
Connection to grid
Indirect
Rectifier
Variable frequency AC
(e.g. from synchronous generator)
Inverter
DC
Irregular switched AC
PCC
Grid frequency AC
20
Control systems
21
Control systems
Fixed speed
AC
f = constant
n = costant
Gearbox
Bypass
contactor
Generator
switchgear
Parking
brake
HV
switchgear
Rotor
bearing
Asynchronous generator
Soft start
equipment
Step-up
transformer
WTG
control
ABB drawing
6 ... 33 kV, f = 50 Hz/
6 ... 34,5 kV, f = 60 Hz
Passive Stall
22
Control systems
Fixed speed
AC
f = constant
n = costant
Gearbox
Bypass
contactor
Generator
switchgear
Parking
brake
HV
switchgear
Rotor
bearing
Asynchronous generator
Soft start
equipment
Step-up
transformer
Pitch
drive
ABB drawing
WTG
control
6 ... 33 kV, f = 50 Hz/
6 ... 34,5 kV, f = 60 Hz
Active Stall, Pitch Control
23
Control systems
Semi-variable speed
AC
f = constant
n = semi-variable
Bypass
contactor
Generator
switchgear
Parking
Gearbox brake
HV
switchgear
Rotor
bearing
Asynchronous
generator
RCC
unit
Soft start
equipment
HEAT
Step-up
transformer
6 ... 33 kV, f = 50 Hz/
6 ... 34,5 kV, f = 60 Hz
RCC
control
Pitch
drive
WTG
control
ABB drawing
Variable slip, pitch control
24
Control system
Variable speed
Generator
switchgear
AC
f = constant
n = variable
Parking
Gearbox brake
HV
switchgear
Rotor
bearing
Doubly-fed
asynchronous
generator
Generator
side
converter
Grid
side
converter
Step-up
transformer
6 ... 33 kV, f = 50 Hz/
6 ... 34,5 kV, f = 60 Hz
Pitch
drive
Converter
control
WTG
control
ABB drawing
Variable speed control DFIG (doubly fed induction generator)
25
Control system
Variable speed
AC
f = variable
n = variable
Generator
switchgear
Converter
Parking
Gearbox brake
HV
switchgear
Converter
control
Rotor
bearing
Asynchronous or
synchrounous generator
Step-up
transformer
6 ... 33 kV, f = 50 Hz/
6 ... 34,5 kV, f = 60 Hz
Pitch
drive
WTG
control
ABB drawing
Variable speed control with full scale converter
26
Control system
Generator layout
Pitch/Stall/Active stall
Semi-variable speed
Stator
Rotor
Stator Rotor
Grid
Grid
IGBT
Capacitor battery
1-10 % slip
1-2% slip
Variable speed, full scale converter
Variable speed (DFIG)
Grid
Stator
Rotor
Ac
dc
Grid
Ac
dc
DC
Stator
DC
DC
Ac
dc
Grid
Rotor
Ac
dc
DC
27
Grid integration of wind turbines
28
Grid integration of wind turbines
Electric power path to consumers
Power station
400,000V
20,000V
Transformer
station
Transformer
station
400/ 230 V
Consumer
150,000V
Transformer
station
20,000V
29
Grid integration of wind turbines
Medium and high voltage components
G
Generator
Main contactors
Transformer
Switchgear
Grid
30
Grid integration of wind turbines
Step-up transformer location
100
C
50
4
E
13
8
19
19
600
1
780
100
5
200
595
200
2690
1670
E
470
0
510
600
300
745
200
1650
3890
50
300
1850
600
1
16
650
780
2
17
1860
D
13
380
7
800
2
680
3
750
6
6
7
1670
E
470
0
0
2360
2500
3000
20
2
B
E
A
510
200
Nacelle
housing
Inside
tower
housing
External
housing
2000
2290
4500
5000
31
Grid integration of wind turbines
Connection of wind turbines
32
Grid integration of wind turbines
The wind turbines operate as a part of an integrated
power system with other production sources and
consumers. Therefore there is a mutual influence
between the wind turbines and the grid.
The following issues have to be considered:
1.Layout of grid-connecting infrastructure
2.Power quality assessment
3.Electrical system stability issues
33
Grid integration of wind turbines
Power quality assessment
Operation of wind turbine can be disturbed if following
grid parameter are not within defined limits:
•Voltage
•Frequency
•Voltage unbalance
•Harmonics level
Wind turbine connection shall not reduce existing power
quality on the grid
34
Grid integration of wind turbines
Parameters relevant for correct operation of wind turbines
• Voltage limits:
• Regime limits
• Slow transient limits
• Frequency limits:
• Normal operation limits
• Admitted transient limits
• Voltage unbalance:
• Admitted operational limits
• Harmonics level:
• Recommended maximum value: As defined in EN 50160
35
Grid integration of wind turbines
Possible negative impacts of WT to the power quality on electrical grid
Wind turbines can cause the following negative impact on the
grid:
•Stationary voltage increase
•High in-rush current
•Flicker
•Harmonics and inter-harmonics
Generally, the wind turbines´ impact on the grid depends on:
•Wind turbines characteristics
•The grid characteristics at the connection point (PCC)
Strong grids can accept more wind turbine without negative
consequences on power quality.
Weak grids can accept limited number of wind turbines, or the
grid has to be reinforced.
36
Grid integration of wind turbines
Flicker
Flicker describes the effects of rapid voltage
variations on electrical light. The flicker level can be
measured with an instrument called flicker-meter.
•Flicker during continuous operation
•Flicker due to generator switching
Limits are defined at PCC and global effect has to be
calculated as aggregated contribution of all the
installed wind turbines.
Wind turbine´s performances concerning flicker
emission are characterised by:
•flicker coeficient cf
•flicker step factor kf
37
Grid integration of wind turbines
Harmonics and inter-harmonics
Voltage deviations from the perfect sinus shaped 50 Hz curve
result in harmonics.
Harmonics are not wanted on the grid because they cause
increased losses and in serious cases it may lead to an
overloading of the capacitors, trans-formers and electrical
appliances as well as disturbances of communication systems
and control equipment.
It is differed between:
•Even harmonics e.g. 100, 200, 300… Hz
•Odd harmonics e.g. 150, 250, 350,550 … Hz
•Inter-armonics (50 multiplied with decimal
e.g. 165 Hz, 2525 Hz etc.
numbers)
38
Grid integration of wind turbines
Standards and recommendations
All units that deliver electrical power to electrical
system shall respect relevant power quality
standards.
The most relevant documents for wind turbines
are:
•IEC 61400-21 standard:
•“Power quality requirements for grid connected wind
turbines”
•IEC 61400-3 standard:
•“ EMC limits. Limitation of emissions of harmonic currents
for equipment connected to medium and high voltage power
supply systems”
•Local requirements
39
Grid integration of wind turbines
System stability issue
Large wind farms can influence not only locally grid but also a
large part of whole power supply system
•Dynamic grid stability may be a limiting factor to the grid
connection of large wind farms
•Grid stability analyses are needed
•Data for modeling or models of Wind Turbines may be
requested
Each country can issue local grid code requirements that have
to be duly considered in designing wind parks.
Fulfilment of grid code requirements might require installation
of additional equipments (capacitor banks, static VAR
compensators, dynamic VAR compensators).
40
Coonstruction tecnologies of a modern wind turbine
41
Main parts of a modern wind turbine
Blade
Nacelle
Hub
Tower
Foundation
42
Onshore foundation
•Gravity concrete foundation
•Rock anchor foundation
43
Offshore foundation
•Monopile
•Tripod
•Gravity
•Floating
44
The tower
Tubular
• Steel plates are rolled and welded
• Flanges at each section
• Shot blasted and coated with paint
Lattice
• Bars are prepared in factory and
assembled on site
• Bolted junctions
• Hot galvanized steel
45
Blade concepts
• Supporting carbon spar
and glass fiber airfoil
shells
• Wood carbon strong
shell technology
46
Supporting carbon spar concept
• The supporting spar with a
rectangular section
• The airfoil shells with sandwich
construction at the rear
47
Wood carbon concept
• Plywood and carbon rods are
used where high strength is
needed
• Balsa or foam is used where
only stiffness is needed
48
Main components in the nacelle
Anemometer
Main bearings/Main shaft
Hub
Pitch system
Gearbox
Hydraulic station
Generator
Coupling
Disc brake
Yaw system
49
50