LMEN
SIE
2005
5TH INTERNATIONAL CONFERENCE ON ELECTROMECHANICAL AND POWER SYSTEMS
IS
CH
IN
AU
IO
VA
October 6-8, 2005 - Chisinau, Rep.Moldova
A
IASI CR
PERMANENT MAGNET GENERATOR FOR SMALL
WIND TURBINE
Ion Sobor, Nucolai Kobileatkii
Technical University of Moldova
Abstract – For direct driven small wind turbine (2-50 kW)
it is necessary to use permanent magnet generators with
rotational rated speed respectively 500 – 100 rev/min. For
Moldova Republic, at the first phase of the wind power
utilisation, it is reasonable to remanufacture standard
electrical machines into low speed permanent magnet
generators. The technical characteristics of two redesign and
build permanent magnet generators are presented.
1.
INTRODUCTION
The year of 1993 was marked as the starting of a new
wind boom, being characterised by annual increase
over 20% of installed power capacity. Thus, in 1999
the world capacity has increased with 3695 MW being
a record for wind sector and for the first time has
exceeded the installed nuclear capacity in the world in
the same year [1-3]. In 2003 has been registered a new
record–the world capacity has increased with 7950
MW. On the wind energy market appear new players–
our neighbours Ukraine with 57 MW and Romania
with 1 MW installed wind power [4].
Republic of Moldova (RM) is at the initial phase of
wind energy utilization. It is very important to identify
the most modern technologies in this field and through
the technological transfer or trough local elaborations,
speeding up the wind potential utilization.
This study is an attempt to identify what kind of
generator is rational to be used for wind turbine with
the power of 2-50 kW. Moreover, are presented the
studies results of two samples generators with
permanent magnets with power of 1,0 and 3,0 kW,
rotational speed 500 rev/min designed and built at
Electromechanical department of Technical University
of Moldova (TUM).
2. WHAT TYPE OF GENERATOR IS
RATIONAL TO BE USED FOR SMALL POWER
WIND TURBINE?
To answer this question we’ll appeal to European and
world statistics presented in [3]. The typical scheme of
the power generating unit consists of three main
elements: turbine, gearbox and electric generator.
Rotational speed of electric generator is usually 1000
or 1500 rev/min, but turbine speed rotation with a
power of 500 kW – has only 30 rev/min. Thus, the
gearbox should have the transmission coefficient 1:33
or 1:50. An alternative variant consists in utilisation of
a low-speed generator the rotor of which rotates at the
same speed as the rotor of the turbine. For the medium
size and megawatt turbines this scheme started to be
used in the 90s of the XXth century [5,6] and is called
Direct Driven Wind Turbine (DDWT). The main
advantages of the DDWT are following:
• It is decreased the transmission costs, noise and the
vibration.
• Increases the wind energy conversion efficiency.
• Increases the availability and reliability.
• Decreases the nacelle mass weight and dimensions
• Decreases the maintenance costs.
• The power characteristics P(V) moves in moderate
speed zone.
A specific characteristic of electric generators directly
coupled with wind turbine consists of small rotational
speed. In this case, to obtain the standard frequency 50
Hz, is necessary to place on the rotor a great number of
magnetic poles. As a result increases the diameter and
the generator mass.
In addition, rotational speeds which are the small
power wind turbine, will be determined as function of
rated power. These speeds will determine the rotation
speed scale for the generators direct coupled with
respective turbines.
The variations of the rotational speed and wind turbine
diameter as a power function are presented in figure 1.
The data were obtained from the publications
concerning turbines technical characteristics with three
blades, tip speed ratio 6 and wind speed 12 m/s [3, 7].
For the rated power scale 2-50 kW, the rotational
speed varies from 500 to 100 rev/min, turbine diameter
increases from 2.8 to 14 m. Poles number of the direct
driven generators must correspond to those indicated in
the Table 1.
Table 1- Rated power, diameter and rotational speed of
small wind turbine. Generator number of poles
P
D
n
2p
KW
M
rev/min
-
2
2,8
500
12
5
4,5
300
20
10
6,4
200
30
25
10,0
150
40
50
14,0
100
60
All direct driven generators may be divided in two
groups: with electromagnetic excitation and exited by
permanent magnets (PMG). The first group includes:
600
14
Rotational speed, Rev/mi
500
12
400
10
300
8
Rotor deameter, m
16
6
200
4
100
2
0
0
2
3
5
10
25
50
R a te d p o w e r . k W
Fig. 2 – The PMG redesigned from the
induction motor
R o ta tio n a l s p e e d
R o to r d ia m e te r
Fig. 1 – Rotational speed and rotor
diameter of the small wind turbine
1.
2.
Induction generator with arc stator;
Synchronous generator excited by a traditional
field winding;
3. A variable-reluctance generator.
The second group includes:
1. Radial-Flux permanent –magnet generator;
2. Axial –Flux permanent –magnet generator;
3. Transverse-Flux permanent –magnet generator;
Accordingly to [3] about 100 % of wind turbines at
ratings up to 50 kW have direct drive generators with
permanent magnets. There is of course an exception,
for example, manufacturer Atlantic Orient Corporation
designed a 20 kW variable-reluctance generator. The
variable-reluctance generator is the simplest generator
of all with only laminated iron on the rotor.
It is necessary to mention that the price of low-speed
generator with permanent magnet is 1200 - 1500
$US/kW [8,9]. This price is not acceptable for RM. In
this situation it is timely to remanufacture the standard
electrical machines, in particularly, induction motors or
synchronous generators excited by field winding, into
generators with permanent magnets. Of course, such
generator doesn’t have an optimal design, but the cost
is 2-3 time smaller.
In addition, the characteristics of two redesigned on
standard electrical machines base PMG, will be done.
3. REMANUFACTURED PERMANENT
MAGNET GENERATORS
In Figure 2 and 3 are presented the two PMG. For the
first was used the standard induction motor, type
4A100L6 and for the second – standard synchronous
generator with electromagnetic excitation, type БМ34,5/4. The main data of these standard machines are
given in Table 2. In Figure 4 and 5, for the first PMG,
are presented graphical illustration of the rectified
Fig. 3 – The PMG redesigned from the
synchronous generator with excited coil
tension Ud and efficiency as functions of power output.
The characteristics of the second PMG are given in
Figure 6 and 7.
Table 2 – Dimensions of standard electrical machines
Technical date &
Machine type
4A100L6
БМ3-4,5/4
dimensions
Rated power, kW or kVA
2,2
4,5
Rotational synchronous
1000
1500
speed, rev/min
Efficiency, %
81
76
Power factor
0,73
0,8
Active length, mm
120
60
Stator outer diameter, mm
168
313
Stator inner diameter, mm
113
220
Air gap length, mm
0,3
1,0
Number of poles
6
4
Number of stator slots
48
36
Slot opening width, mm
3,0
3,5
Excitation
Field coil
In both remanufactured generators were used NdFeB
permanent magnets: for first – arcs shape magnets and
for second – 4 block shape magnets per one pole. The
main PMG characteristics resulted from test data are
presented in Table 3.
Ud, V
280
350
240
300
200
250
Tension, V
160
120
80
200
150
100
40
50
0
0
200 400 600 800 1000 1200 1400 160
P, W
800 Rev/mun
600 Rev/min
500 Rev/min
400 Rev/min
300 Rev/min
200 tur/min
0
0
2
600 Rev/min
400 Rev/min
Fig.4 – The characteristics Ud (P) for PMG
redesigned from induction motor
Efficiency, %
1
3
4
5
Current, A
6
500 Rev/min
300 Rev/min
Fig.6- Volt – ampere characteristics of PMG
redesigned from generator with excited coil
90
80
100
70
90
60
80
Efficiency, %
50
40
30
20
10
0
0
250
800 Rev/min
400 Rev/min
500
750
1000 1250 1500 1750
Output power, W
600 Rev/min
500 Rev/min
200 Rev/min
Fig. 5- Efficiency of PMG redesigned from
induction motor
Table 3- Remanufactured PMG characteristics
Main characteristics
Generator type
PMG/4A
70
60
50
40
30
20
10
0
0
500 1000 1500 2000 2500 3000 3500 4000
600 Rev/min
400 Rev/min
Output power, W
500 Rev/min
300 Rev/min
Fig.7 – Efficiency of PMG redesigned
from generator with excited coil
PMG/БМ3
Rated rotational speed,
600
500
rev/min
Rated power, kW
1.0
3,0
Efficiency, %
80*
90
Number of poles
1
12
Air gap length, mm
1,0
1,0
Phase number
2
3
Slots number per pole and
2
1
phase
*
- Including the losses in the two phase rectifiers.
8. CONCLUSIONS
1. The rotational speed of the direct driven PMG for
the small wind turbines (2 - 50 kW) must be
between 500 and 100 rev/min. This means that the
rotor must have respectively 12 – 60 numbers of
poles.
2. At the initial phase of small wind implementation
in Moldova Republic it is reasonable to
remanufacture the standard electrical machines in
to low speed permanent magnet generators. In this
case the costs decrease 2-3 time.
3. The redesigned and build PMG have satisfactory
technical characteristics: efficiency – more than 80
% for rated output 1,0 kW and 90 % for rated
output 3,0 kW. For the rotational range speed about
2,0 the maximal efficiency remain the same.
4. It is recommended to choose for remanufacturing
the standard induction motor with small rated
rotational speed, for instance 750 or 600 rev/min.
In this case we can redesign it into PMG with rated
rotational speed with 375 or 300 rev/min. The slots
number per pole and phase qin this case is equal to
1. For obtaining rotational speed less than 300
rev/min it is necessary to design the generator with
q<1.
ACKNOWLEDGMENTS
The project has been performed with the financial support of
the Supreme Council for Science and Technological
Development, contract number 5/1-11.
REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
Le baromètre de l’énergie éolienne. Systèmes solaires – Le
jourmal des énergies renouvelables, nr. 141, Janvier – Février
2001, pag. 21 – 29.
Le baromètre de l’éolien. Systèmes solaires – Le jourmal des
énergies renouvelables, nr. 135, Janvier – Février 2000, pag. 29
– 36.
Wind Energy. The facts. European Wind Energy Association.
Luxembourg, 1999.
Baromètre de l’éolien. Systèmes solaires – L’observateur des
énergies renouvelables, nr. 159, Janvier–Février 2004, pag. 55
– 71.
Andreas Grauers. Design of Direct-diven Permanent-magnet
Generators for Wind Turbines. Technical Report nr. 292.
Chalmers University of Technology. Sweden, Goteborg.-1996,
133 p.
Petri Lampola. Directly Driven, Low-Speed Permanent-Magnet
Generators for Wind Power Applications. Acta Polytechnica
Scandinavica, Electrical Engineering Series, nr. 101, Espoo.2000, 62 p.
Дж. Твайделл,
А. Уэйр, Возобновляемые источники
энергии, Пер. с англ. – М.: Энергоатомиздат. 1990. – 392 с.
www.windstreampower.com/generators/PMA.html
http://www.solardyne.com
Ion Sobor was born in Mereşeni, R. Moldova,
on 17 January 1947.
Graduate in Electrical Machines and
Apparatuses in 1970 (Polytechnic Institute of
Chisinau); Ph.D. in Electrical Machines in
1979 (Harkov Polytechnic Institute, Ukraine).
From 1972 working, first assistant, lector now
associate professor, in Technical University of
Moldova. Major field of study: permanent
magnet electrical machines, electromagnetic devices, wind potential
assessment, solar pumping.
Nicolai Kobileatkii was born in Cigizin,
Cercasi, Ukraine, on 18 may 1939. Graduate
in Electrical Engineering in 1962 (Harkov
Institute for Agricultural Mechanisation and
Electrification, Ukraine); Ph.D. in Electrical
Machines in 1971 (Harkov Polytechnic
Institute, Ukraine). From 1965 working, first
assistant, lector, now associate professor, in
Technical University of Moldova. Major field
of study: electromagnetic drives, ferromagnetic converter, permanent
magnet electrical machines, solar pumping.