wind turbines technology

Wind Turbines Technology

Cataldo Pignatale

Product Support ManagerVestas Italia S.r.l.

Desire-Net Project

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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

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Agenda

• 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

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Wind turbines characteristics

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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)

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Main parts of a modern wind turbine

Nacelle

Foundation

Blade

Hub

Tower

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• 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;

Horizontal axis rotor Vertical axis rotor

Wind Turbines Characteristics

Upwind turbine Downwind turbineActive yaw mechanism Free yaw mechanism2 blades 1 blade3 blades Pitch controlWith gerabox Without gearbox

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Control of power

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Control of powerReducing the power at high windspeed

• Reducing the lift and over speeding called Pitch variable speed

• Reducing the lift by generating stall

Flow on upper and lower surface equal no lift

Wind attack point

Wind attack point

At high wind the power is reduced by pitching the blades. This can be done in two ways.

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Control of powerPitching

Low wind High wind Stop

Pitch variable speed and optislip

Active stall

Passive stall

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Control of powerWind Power and Power Curves

m/s

Power

‘A’ is area ‘v’ is velocity (wind speed)‘’ is air density ‘Cp’ power coefficient

Wind power

Max Power = ½ · A · v3 · · Cp

Rated power

Pitch variable speed

Active stall

Passive stall

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Control of powerIso-power map wind speed and pitch angle

― Pitch control

0 kW

500 kW

1000 kW

1500 kW

2000 kW

2500 kW

Win

d s

pe

ed m

/s

5

25

15

10

20

-10 0 +10 +20 +30

Pitch angle (deg)-20

72 m rotor 2MW turbine

― Stall control

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Control of powerPitching mechanism

Pinion

Blade turning gear

Battery bank

Electrical

Hydraulic

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Type of generators

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Type of generator

Synchronous Asynchronous

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Type of generatorFixed speed asynchronous generator

50 Hz

60 x frequencynumber of pole pairs

rpm =

Rotational speed6-poled stator

rpm1000

+ kW (generator)

- kW(motor)

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Type of generator Variable speed asynchronous generators

50 Hz

AC

DC AC

DC

Stator field = 1000 rpm

Rotor mechanically = 1100 rpm

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Connection to the grid

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Connection to grid Direct

Grid frequency AC

PCC

Grid frequency AC

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Connection to gridIndirect

Variable frequency AC

(e.g. from synchronous generator)DC

Irregular switched AC Grid frequency AC

Rectifier Inverter PCC

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Control systems

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Control systems Fixed speed

Get

rieb

e 1:

50

Parkingbrake

Rotorbearing

Bypasscontactor

Soft startequipment

WTGcontrol

Asynchronous generator

6 ... 33 kV, f = 50 Hz/6 ... 34,5 kV, f = 60 Hz

Step-uptransformer

HVswitchgear

ABB drawing Passive Stall

Gearbox

Generatorswitchgear

ACf = constantn = costant

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Control systems Fixed speed

Get

rieb

e 1:

50

Parkingbrake

Rotorbearing

Bypasscontactor

Soft startequipment

WTGcontrol

Asynchronous generator

Step-uptransformer

HVswitchgear

ABB drawing Active Stall, Pitch Control

Gearbox

Generatorswitchgear

ACf = constantn = costant

Pitchdrive

6 ... 33 kV, f = 50 Hz/6 ... 34,5 kV, f = 60 Hz

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Control systems Semi-variable speed

ABB drawing Variable slip, pitch control

Get

rieb

e 1:

50

Parkingbrake

Rotorbearing

Bypasscontactor

Soft startequipment

WTGcontrol

Asynchronous generator

Step-uptransformer

HVswitchgear

Gearbox

Generatorswitchgear

ACf = constantn = semi-variable

Pitchdrive

RCCunit

RCCcontrol

HEAT

6 ... 33 kV, f = 50 Hz/6 ... 34,5 kV, f = 60 Hz

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Control systemVariable speed

ABB drawing Variable speed control DFIG (doubly fed induction generator)

Get

rieb

e 1:

50

Parkingbrake

Rotorbearing

WTGcontrol

Doubly-fedasynchronous

generator Step-uptransformer

HVswitchgear

Gearbox

Generatorswitchgear

ACf = constantn = variable

Pitchdrive

Generatorside

converter

Gridside

converter

Converter control

6 ... 33 kV, f = 50 Hz/6 ... 34,5 kV, f = 60 Hz

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Control system Variable speed

ABB drawing Variable speed control with full scale converter

Get

rieb

e 1:

50

Parkingbrake

Rotorbearing

WTGcontrol

Step-uptransformer

HVswitchgear

Gearbox

Generatorswitchgear

ACf = variablen = variable

Pitchdrive

Converter control

6 ... 33 kV, f = 50 Hz/6 ... 34,5 kV, f = 60 Hz

Asynchronous or synchrounous generator

Converter

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Control system Generator layout

Pitch/Stall/Active stall

Variable speed (DFIG)

1-2% slip

Stator Rotor

Grid

1-10 % slip

IGBT

Grid

Capacitor battery

Stator Rotor

Grid

Grid

DC

DC

Ac

dc Ac

dc

Stator Rotor

Semi-variable speed

Grid

Stator RotorDC

DC

Ac

dc Ac

dc

Variable speed, full scale converter

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Grid integration of wind turbines

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Grid integration of wind turbines Electric power path to consumers

Transformer station

Power station

Transformer station Consumer

Transformerstation

20,000V

400,000V

150,000V

20,000V

400/ 230 V

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Grid integration of wind turbines Medium and high voltage components

Grid

G

Transformer

Main contactors

Generator

Switchgear

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2

1

3

45

6

7

8

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LEGENDA:1

PORTA DUE ANTE IN LAMIERA ZINCATA 120x215 cm.CON CHIUSURA A TRE PUNTI, BLOCCO AREL E RETE ANTINEVE

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3 QUADRO DI BASSA TENSIONE AUSILIARI

GOLFARI DI SOLLEVAMENTOEPORTA DUE ANTE IN LAMIERA ZINCATA 120x215 cm.CON CHIUSURA A TRE PUNTI E RETE ANTINEVE

4

6

7TRASFORMATORE 900 kVA

MODULI MT

5

8

GRIGLIA ALTA IN VTR 120x50 cm. CON RETE ANTINEVE

CHIUSINO IN LAMIERA PER PASSAGGIO AL BASAMENTO

GRIGLIA BASSA IN VTR 120x50 cm. CON RETE ANTINEVE

2000

4500

5000

2290

3000

2500

2360

E

E

E

E

470

1670

0 2690

3890

470

16700

1850

650

0

50300 1650 745 595

200

50510

200

600

510200

780

800

780

380

600

680

600

100

1860

200

300

100

1

2

2

13

1316

17

20

1919

750

A

B

C

D

Grid integration of wind turbines Step-up transformer location

External housingInside tower housingNacelle housing

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Grid integration of wind turbines Connection of wind turbines

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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 infrastructure2.Power quality assessment 3.Electrical system stability issues

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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

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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

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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.

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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

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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 numbers)e.g. 165 Hz, 2525 Hz etc.

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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

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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).

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Coonstruction tecnologies of a modern wind turbine

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Main parts of a modern wind turbine

Nacelle

Foundation

Blade

Hub

Tower

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Onshore foundation

•Gravity concrete foundation

•Rock anchor foundation

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Offshore foundation

•Monopile

•Tripod

•Gravity

•Floating

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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

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Blade concepts

• Supporting carbon spar and glass fiber airfoil shells

• Wood carbon strong shell technology

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Supporting carbon spar concept

• The supporting spar with a rectangular section

• The airfoil shells with sandwich construction at the rear

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Wood carbon concept

• Plywood and carbon rods are used where high strength is needed

• Balsa or foam is used where only stiffness is needed

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Main components in the nacelle

Pitch systemGearbox

Hub

Hydraulic station

Main bearings/Main shaft

Yaw systemDisc brakeGenerator Coupling

Anemometer

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