Product Notes

What is the latest permanent
magnet technology development?

For high power permanent magnet (PM)
machines in the MW range the first wind
turbine applications have required
constructions with high pole numbers and
low speeds. With permanent magnet material
it is easy to design high pole number rotors.
In order to develop PM machines for higher
speeds, with 4 to 8 poles, the solutions and
constructions required are somewhat
different.

For higher speeds ABB has developed an
efficient rotor design that meets the
requirements of this application. It features
effective utilization of PM materials and
strong, robust and reliable construction. The
cooling arrangement has also been
developed to take advantage of the lower
losses, especially in the rotor.

In this solution the excitation is provided by
the permanent magnets. No windings are
therefore needed in the rotor, and excitation
losses in the rotor are also eliminated.

What are the main features?

frame size: 500 mm

nominal speed: 1500 rpm

typical speed range: 25...125 %

efficiency: > 98 %

power range: up to 3600 kW

What are the benefits for
customers?

The customer benefits are based on the
smaller size and higher efficiency of
permanent magnet generators. High
efficiency means better utilization of the wind
energy, i.e. more electrical power is produced
from the same amount of wind energy. The
compact size and reduced overall weight
provide benefits in the construction of the
nacelle.

There are also benefits in the machinery
design, as PM generators are easier to keep
cool. Low rotor losses with PM generators
mean the rotor can be kept at a lower
temperature, which in turn reduces the
bearing temperature.

What are permanent magnet
materials?

Ferromagnetic materials sustain their
magnetization after the external magnetic
field is removed. In commercial permanent
magnet materials this hysteresis effect
-which is controlled by the phase structure of
the material- is so strong that almost all of the
magnetic polarization generated by the
external field is retained after the field is
removed. When a piece of this material is
magnetized, it also generates a magnetic field
outside of itself. This property forms the basis
for the technical applications of permanent
magnets.

The most efficient materials available today
are so-called Neo or Nd-Fe-B magnets, these
are multiphase compounds, predominantly
manufactured using powder metallurgy. Their
main constituents are iron, neodymium and
boron. Some grades also contain dysprosium
and cobalt.

New Permanent Magnet Generator for
Wind Turbine Applications

PM304 RevA,Sep 03

Specifications subject to change without notice.

2.5 MW PM-generator

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1

Product Notes

Are permanent magnet

generators

high or low speed machines?

The generators can be built for either high or
low speed depending on the requirements of
the wind turbine machinery. The generator
speed can be selected to match the choice of
gear ratio. The generator size is minimized in
high speed installations.

How are the high efficiency levels
achieved?

The high efficiency of permanent magnet
generators is mainly based on
their operating principle, with
excitation provided by the
permanent magnets. No
windings are therefore needed
in the rotor, and excitation
losses in the rotor are also
eliminated. This results in a
substantial increase in
efficiency, as excitation
losses typically represent 20
to 30 percent of overall
generator losses.

ABB Oy
Electrical Machines
Finland
Tel:

[phone]

Fax:

[phone]

www.abb.com/motors&drives

Excitation losses are minimized in permanent
magnet generators, and this contributes to the
high efficiency of these generators over the whole
output range.

The development of magnetic
materials during the last
decade has led to significant
improvements in magnetic
properties. High remanence
(B) and high coersive force (H)
values have been achieved
with temperature ratings (up to
180 C) suitable for motor and
generator applications.

The graph shows how the
maximum magnetic energy of
permanent magnet materials
has developed.

0

100

200

300

400

500

1910

1930

1950

1970

1990

(BH)

ma

x

[k

J

m

³]

Steels

Ferrites

AlNiCo

SmCo

SmFeN

NdFeB

T ypical curves of a 2.5 M W PM G

0 ,9 8 2

0 ,9 5 9

0 ,9 2

0 ,9 4

0 ,9 6

0 ,9 8

1

0

0 ,2

0 ,4

0 ,6

0 ,8

1

1 ,2

sp eed (p u )

P, U, I

0

0,5

1

eff

e ta (p u)

U /un

P /p n

I/In

= 98,2 %

η

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