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Generators for geared and direct drives,

and other electrical components

Professor Robert Nilssen, Electrical power, NTNU

INT MARE WINT 2013

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Magnetic fields and currents - induce voltages in windings

- produce forces in the generator

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P M

S M

isul

il

id,mach

us

Electric energy conversion - Variable power into the stable grid

- Variable speed, variable frequency

- Need for control

AC til DC DC til AC MtE EtE EtE

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Converters more functionality but higher costs

Induction generator

– doubly fed

PM generator

– full converter

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A look at the «system»

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Norwegian wind vision

To support our oil industry??

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Very large power units offshore !!

10-12MW? 3-5??MW 6-8 MW ??

Our goal: • 12 MW • Nacelle weight 350t!!? • Generator for less

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Some experiments in the North sea

allready

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A total technology optimization is

needed

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Huge investments in infra stucture

are needed

Energy storage

How do we control power flow and handle fault situations??

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Huge investments in subsea cables

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Back to the generator technology

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Wind turbine

with gear

Gear

Shaft

Small generator

(high speed)

Transformer, power

electronics

Large torque

Low torque generator

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What are the alternatives?

With gear – not roboust

Garles - durable - expensive

Hydraulic pump

Hydraulic gear - Low top weight - New - exciting - To be verified

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Direct driven Generators

• Low speed requires synchronous machines with high pole numbers

• With high pole numbers

-Field winding in Rotor, large diamter, High cost -PM magnetization, Less cost

• Why direct drive: - gear problems above 4 MW - less maintenance

• Why not:

- High Investment costs and weight

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New technology is needed to

keep offshore wind cost down!!

Cost

Power per unit

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Modular design

Rotor

Shaft

Stator

Converter

/Transformer

Flexible mounting

Framewok/Infrastructure

•Is it smart to use modular building blocks? •Should we integrate more? •ScanWind design -3.5MW

Bearing

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Scanwind an early

Norwegian Permanent

Magnet

Direct Drive

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Synchronous PM generator

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Gearless: Less speed – higher torque – larger and more expensiv generator

07.09.2013

Large generator – increased weight

P=wT T= k D2L

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The Enercon generator - Direct drive

- Without magnets

- Good

- Expensive

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Replacing the rotor winding with

permanent magnets

High pole numbers forces the rotor to be big.

Permanent magnets make the rotor and overall stator smaller.

Rotor with windings Rotor with Permanent Magnets

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Small magnetic poles gives normally a

very large slot number

-Insulation and fill factor in the slots become a problem. -Large number of components to assemble

Slots

Magnets

– why so small??

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Expensive distributed

windings for high pole

number radial flux

machines

Unique mobility

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Concentrated and fractional slot

winding

SmartMotor Design – verified at NTNU

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Motor, Gear and generator

– PhD study at NTNU

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RFPM-machine with

plastic cover

• Machine ready for testing

• Built by a PhD student

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The switch

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More integration

Converter/

Shaft

Fixed shaft Less bearings Simple frame Enercon – design

Shaft Rotor

Shaft

Framework/Infrastructure

Stator

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This technology is here 2010

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Secret design from Siemens

Januar 2010

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More integration

Con-

verter

Trafo

Inner stator Simple frames Large diameters

Rotor

Framework/Infrastruktur

Shaft

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Expectations for new technologies

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Aksial flux generators – often called disc

machines

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AFPM

Design drawing

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Axial flux machine

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Bygget!

AFPM – Built and tested

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The Sway turbine – generator – the biggest axial

flux machine in the world – 10- 12 MW

First on the sea bed

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Composite air cooled axial

flux stator

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