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2006年 9月 第28回雷保護国際会議
ICLP 2006 KANAZAWA(金沢）発表論文
Reproduction and Test Method of FRP Blade
Failure for Wind Power Generators by
Lightning
Masahiro Hanai, Hiroshi Koyama, Toshiba Corporation,
Norio Kubo, Ishikawajima-Harima Heavy Industries Co. Ltd.,
Yoichi Hashimoto, JFE Engineering Corporation,
Isamu Suzuki, Daioh Construction Co. Ltd., Ueda Yoshinori, Mitsubishi Heavy Industries Co. Ltd.,
Haruo Sakamoto, Kochi University of Technology
Abstract -- In Japan, the lightning damage to the FRP
blade for wind power generators is increasing together with
the increase in wind power generator installation in recent
years. Since lightning of Japan looks severely than that of
Europe and the U.S., lightning damage is a big issue of
Japan. In Kochi (Japan), six grade generators which are 600
to 750 kW are installed. Moreover, some of them were
damaged by lightning several times. After investigating
literature, we got to know what the cause of serious damage
does not understand yet. Therefore, we are establishing a
test method, while clarifying destructive climate by this
lightning, and being able to be made to perform examination
of the prevention method of destruction.
In the high voltage test, it was shown clearly that
lightning penetrates easily FRP that does not perform
conductive processing. Moreover, the large current
examination showed reappearance of the blade damaged
there, and showed the conformity of the failure mechanism
and the test method. It turned out that the breakdown
situation of a real machine can be explained by the
mechanism. If a lightning passes inside a FRP blade, the
temperature of air inside a blade will rise. As a result,
pressure goes up and a blade is damaged. Moreover, it
turned out that breakdown of positive polarity (winter)
lightning can be performed by the large current examination
with a short circuit generator.
The experiment was conducted mainly in the Toshiba
Hamakawasaki High Voltage and High Power Testing
Laboratory. This testing laboratory is one of the biggest
testing laboratories for an experiment about the high voltage
and high power in the world.
Contact address :
Masahiro Hanai
Toshiba Corporation
2-1 Ukishima-cho, Kawasaki-ku, Kawasaki 201-0082, Japan.
E-mail: [email protected]
Index term -- Wind power generator, Lightening
protection, FRP blade, Short-circuit generator, Lightning
impulse generator, Test method, Pressure
I. INTRODUCTION
According to the latest global tendency of
consideration of maintainable ecology like renewable
energy technology, wind power became popular. In Japan,
although the power in 1999 was only 2.3x104 kW, the
wind power in the termination of the fiscal year in 2001
reached 3x105 kW. The increasing rate of the power
generation capacity in wind power is very large.
Moreover, the target of wind power generator installation
was changed by the Japanese government to 300 to 3000
MW by 2010 in 2001. However, lightning damage is
increasing with the increase in installation of an wind
power generator.
The business-related department of Kochi Prefecture
requested Kochi University of Technology in 2002 to
inquire by the lightning protection for a FRP blade. We
are going to establish protection technology, have
consulted literature and have investigated the present
knowledge which can be used then since then. However,
the acquired information was not essential about a FRP
blade lightning damage mechanism and the direct
information about protection.
A certain information about the lightning protection
for the airplane material of non-conductivity was
aluminum coating [1] [2]. We tried to check the validity
of aluminum coating from the experiment conducted on a
previous paper [3] and [4]. An experimental result to
aluminum coating is effective in protection of lightning
damage. However, aluminum coating will burn by
lightning or will melt. As a result, a color changes and it
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looks dirtily. For this reason, it is thought that aluminum
coating gives one of the methods leading new protection.
However, it seems that aluminum coating needs to be
improved to a slight degree.
Author have done various examinations, in order to
investigate the damage mechanism of a FRP blade. In a
paper, while explaining the mechanism of damage to a
FRP blade, reference is made about that measurement
method. In the present experiment, we are using 1/2 scale
size model that imitated actual blade composition.
Authors have so far done various examinations, in
order to investigate the damage mechanism of a FRP
blade. In a paper, while explaining the mechanism of
damage to a FRP blade, reference is made about that
measurement method. In the present experiment, we are
using 1/2 scale size model that imitated actual blade
composition. The prepared model was prepared three
kinds. They are a FRP plate, one half of the scale size test
models of a 250kW wind power generator blade, and the
250kW wind power generator full scale blade which
divided into four parts. The experiment carried out the
high-voltage examination, which verifies whether a
lightning penetrates a FRP blade easily, and the large
current examination, which verifies whether a FRP blade
explodes with the current of a lightning. The failure of
examinations showed reproduction for the actual blade
failure at site by a lightning almost correctly, and the
result proved the compatibility of the measurement
method.
II. THE FEATURE OF A LIGHTNING, AND ITS SIMULATION
The lightning has simultaneously a high voltage and
large current (energy). For this reason, we need to have
test equipment that generates the high voltage and large
current (energy) which a lightning has as shown in Figure
1 about a method, in order to conduct the experiment that
imitated the lightning. The high voltage determines the
root. Moreover, the amount of large current & electric
charges determines the damage that a lightning generates.
However, we cannot fulfill two conditions by existing test
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equipment simultaneously. Therefore, the experiment
examined with the equipment made to generate either the
high voltage or large current.
At the first step of the reappearance examination, even
if there was no conductive material behind FRP, we
checked whether a lightning would penetrate a FRP blade
easily by the high-voltage examination. At the second
step, when a lightning passed along the inside of a FRP
blade by large current examination, it was checked
whether a FRP blade would explode.
All of the high-voltage examination and large current
examination that simulated the lightning were performed
in Hamakawasaki high-voltage and large current testing
laboratory of Toshiba.
III. HIGH VOLTAGE EXPERIMENT
A. High-voltage impulse test
The rated capacity 6MV impulse voltage generator is
used in testing as shown in Figure 2. The size of a
specimen is a FRP board with a length of 2,500mm, a
width of 430mm, and a thickness of 4mm. The FRP board
fixed at the lower part, and as a test piece did not break, it
stood and installed it. The distance between a FRP board
and a high-voltage electrode is 500mm. Three kinds of
FRP materials are used for an experiment. They are two
kinds of FRP containing glass fiber, and FRP in which the
copper mesh is contained with glass fiber. And aluminum
coating was performed to each FRP test specimen again.
And a total of six kinds of test specimen were prepared.
As follows, the procedure of the experiment charged
the impulse voltage generator to 2MV, and applied it to
the high voltage rod electrode. The air gap between a
high-voltage electrode and a test piece generated electric
discharge in 400 to 1,000 kV, discharge current flowed
through the surface of FRP. The peak current at that time
was about 20kA. Ten electric discharge examinations
were carried out to each test specimen. The days when the
experiment was conducted were 74% of humidity, the
temperature of 4-degree Celsius, and the atmospheric
pressure of 1,015 hPa.
High Voltage
Electrode
Discharge
FRP Plate
Figure 1 Approach to Lightning with High Voltage
and High Power Equipment
Figure 2 6MV Impulse Voltage Generator and Set-up
of FRP Plate for High Voltage Experiment
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B. Result
Table 1 shows the result of each experiment. All
electric discharge of the lightning flowed through the
course of aluminum coating about the sample equipped
with aluminum coating. Although there were some points
that aluminum showed dissolution partially, there was no
penetration of FRP. FRP damaged area of two kinds of
FRP samples that do not carry out aluminum coating on
the other hand. In FRP of 45 degrees textile, electric
discharge penetrated FRP, and generated damage about
30mm in diameter through the same course with 10 times.
Also, electric discharge penetrated FRP of special textile,
also made the small hole in several places, and penetrated.
On the other hand, although FRP containing a copper
mesh did not carry out penetration. But the serious burn
happened along the internal copper mesh. As mentioned
above, in FRP that does not perform conductive
processing, it turned out that a lightning is penetrated
easily and it trespasses upon an inside.
For this reason, at the following step, it was
investigated whether a site accident could be reproduced
when large current would be sent inside a blade.
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Table 2 IEC Protection Level [5]
Protection
Level IEC
61024-1-1
I
II
III
Peak
current
(kA)
200
150
100
Specific
energy
(kJ/Ω)
10000
5600
2500
Average rate Total current
of current rise transfer
(kA/µs)
(C)
200
300
150
225
100
150
Table 3 Parametric Values in Experiments
by Short Circuit Generator
Protection
Level
I Equivalent
II Equivalent
III Equivalent
IV (Option)
Peak
current
(kA)
47.1
35.3
23.6
12.5
Specific
energy
(kJ/Ω)
11100
6230
2780
Average rate Total current
of current rise transfer
(kA/µs)
(C)
0.0109
300
0.0082
225
0.0055
150
80
1m
IV. LARGE CURRENT EXAMINATION
A. An experimental condition and a setup
According to the technical report of IEC-International
Electrotechnical Commission (TR61400-24) [5], the
experimental conditions were determined. Table 2 shows
the IEC values describing the lightning parameter. The
protection levels I is the highest total current transfer.
Using the short circuit generator to conduct the large
current & charge experiment, we set the protection level
shown in Table 3. Although the peak current and average
rate of current rise between Tables 2 and 3 are different,
the specific energy and total current transfer are almost
the same in two cases. We think that the total current
transfer is the most effective value. Since the lowest total
current transfer in Table 2 is 150 C, we add the 80 C as
our optional value in Table 3.
The test piece of the 1/2 size model is 1/2 width and
1/2 thickness of those for the 250 kW power generator.
However, the length was determined to be 1 m, although
the length of actual blade is 12.6 m. Figure 3 shows the
set-up of the 1/2 scale size model blade. The electricity to
the electrode shown at the upper side of the figure comes
from the short circuit generator shown in Figure 4. The
guidance of the electric was selected in two ways. One is
on the surface of the blade, being guided by a copper
Table 1 High Voltage Experiment Results
45 degree
GPRP
Special weave
GPRP
GFRP with
copper mesh
With aluminum
coating
Without aluminum
coating
Passed the aluminum
coating portion
Passed the aluminum
coating portion
Penetrated on the back
side of FRP
Penetrated on the back
side of FRP
Penetrated into the copper
mesh portion in FRP
Passed the aluminum
coating portion
Figure 3 Set up of 1/2 Scale Size Model Specimens
Figure 4 Short Circuit Generator for Large
Current Experiment
small wire. The other is in the inside of the blade, and the
wire is guided into the blade from the tip of the electrode.
For the 1/4 cut piece of the actual blade (The location
is 2/4 from the tip side), the same lightning experiment
was conducted. Figure 5 shows the set-up. The figure
shows that the 1/4 blade was put on the floor, and the
electrode is upper on the blade. The electricity guidance
to the inside of the blade is from the tip side face of the
test piece about 1m (left hand of the right figure) to the
artificial hole (right of the right figure)
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1m
Figure 5 Set-up of Full Scale 1/4 Cut Model
Specimens
B. Result
1) The experimental result by one half of size
specimens
A result is summarized to Table 4. The first three
experiments are the ones for the surface current. Table 4
also shows the number of the tests at the left hand. No. 13 are sides A-1 and A-2. Figures 6 shows the result of No.
3, that is one of blade burned. Although No.1 and 2 in
Table 4 is not shown in figures, bu the result is almost
same, and the blade was burned. Therefore, if the current
flows on the surface of the blade, the surface is burned,
and no explosion. There remains smoke and soot. It looks
that the function of the FRP blade is capable to be used
again.
However, when the lightning current once flows into
the blade, the blade explodes. Figure 7 shows the results
of Actual current and Arc voltage waveform for the No. 4
in Table 4 test, which is the one of the inside current case
using TP-1. The TP-1 was used after the tests No.1-3
were finished. The result was explosion of the blade as
shown in figure 8. As well as the case of No. 4, No. 5
using TP-2 exploded.
In the tests of 1-3, the lightning current flew on the
surface of the blade. The state of smoke and soot did not
depend on the total current transferred.
2) The experimental result by enough size specimens
The result of the full scale 1/4 cut model specimens is
shown in Figure 9. Size blade with a sufficient portion of
2/4 from the chip side also exploded. Since the power of
the burst was frightful, the blade was fixed with the rope,
Figure 6 Results for 1/2 Scale Size Model Specimens
(Surface Current of 281C)
10ms
Terminal Voltage
Current
Arc Voltage
1kV
Figure 7 Current and Arc Voltage Waveform of Large
Current Test (Inside Current of 146C)
Table 4 Conditions and Results of Large Current Test
Actual condition
Copper Planned Peak
Total
Wire
Level
Current Current
Location
(kA)
(C)
Surface
11.9
70.3
IV
Side A-1
1/2
21.4
129
III
Model
TP-1 Surface
45.6
281
I
Side A-2
No. Test
Piece
Result &
Figures
1
Surface Burned
2
3
4
Inside
5
1/2
Inside
TP-2
FULL Inside
-1(2/4)
6
Surface Burned
Surface Burned
IV
11.1
66.4
Exploded
III
22.9
146
Exploded
I
42.2
264
Exploded
Figure 8 Results for 1/2 Scale Size Model Specimens
(Inside Current of 66.4C)
but the blade was damaged at the place where this rope
was rolled. Immediately after conducting a lightning
experiment, as we needed to use the fire extinguisher,
smoke and fire arose.
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4m
Figure 9 Results for Full Scale 1/4 Cut Model
Specimens
V. DISCUTTION
A. The simulation of a positive polarity (winter) lightning
with a short circuit
This time, the large current examination that
determines the damage of a lightning was performed
using the waveform of the commercial frequency current
of 50Hz with the short circuit generator. On the other
hand, as shown in Tables 2 and 3, in the examination
using the current of the lightning parameter decided by
IEC TR-61400-24, and this commercial frequency,
current increasing rates differ greatly.
However, the lightning strike current of the positive
polarity (winter) lightning actually surveyed in Japan Sea
has a very small current increasing rate to Figure 10 [6]. It
turns out that especially the first peak current has rise time
with a frequency of about 50Hz. For this reason, even if
simulating current using a short circuit generator, it is
considered that the current of a positive polarity (winter)
lightning with such a low current increasing rate is
satisfactory.
Current (kA)
15
10ms: 1/2 cycle of 50Hz
10
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be occurred also at the total charges of 75C. The
following things can be considered as this cause.
First, the heat by current flowing occurs. For this
reason, air inside a blade expands and high pressure is
occurred. As a result, a blade explodes, without the ability
to bear high internal pressure.
As shown in Figure 8, it turned out that the arc in an
air is shared in the voltage of 1000 V/m at 23kA current
from this experimental result. As a result, the calorific
value (W) per 1 meter by an arc is following.
W=∫(V*I) dt
= V*∫ (I) dt
=V*Q
(1)
where W is the calorific value (J), V is the arc voltage (V),
I is the arc current (A) and Q is the total amounts of
electric charges (C).
When arc voltages are assumed to be 1000 V/m and
the total amount 75C of electric charges, the quantity of
heat of 90 kJ/m will occur inside a blade. We can
calculate the temperature rise of the air in the 1/2 Scale
Size Model Specimen using the specific heat and volume
of air. At total current is 146C, the temperature rise of the
air will become about 14000 degrees Celsius and air will
expand, if it calculates by making it a base, and it
contributes to the pressure increase of a blade altogether,
the pressure inside a blade will rise to about 50 atm.
Since it seems that it has still sufficiently high pressure
even if air by this expansion escapes through the hole of a
blade etc., it can explain that a blade explodes. Since an
actual blade is 4 times the volume of this 1/2 scale size
model, the almost same pressure increase occurs in 300C
whose amount of electric charges is 4 times of the 75C,
and it can explain that a blade explodes similarly. As
mentioned above, FRP blade failure of the wind power
generator by a lightning showed clearly that it is
reproducible with the high-voltage examination by
lightning impulse voltage generating equipment, and the
large current examination, which uses a short circuit
generator.
VI. CONCLUSION
5
0
0
10
20
30
Time (ms)
40
50
Figure 10 Observed Waveform of Positive Polarity
Lightning Current [6]
B. The mechanism of blade failure
From the result of a high-voltage examination, when
the blade has conductivity, a lightning does not invade the
inside of a blade. On the other hand, when the blade is
using FRP with high insulation performance, a lightning
penetrates FRP easily and can invade the inside of a blade.
From the result of a large current test examination, if a
lightning invades the inside of a blade, an explosion will
In order to solve the mechanism in which a lightning
does damage to the blade of a wind power generator and
to work on the measure, the high-voltage examination and
the large current examination were carried out. As a result,
the following things became clear.
1. By high-voltage examination, a lightning penetrates the
board made from FRP of an insulator easily.
2. At the blade model of 1/2 scale, in the large current
examination which uses a short circuit generator, when
the course of the lightning went into the inside of a blade,
the explosion was occurred at 66C. This value is below
the total amount 80C of electric charge transfers, which is
a 50% value of a positive polarity (winter) lightning.
3. When the course of a lightning was the blade surface, it
became damage only to a little burn of the surface also in
the total amount 281C of electric charge transfers
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equivalent to level I.
4. The survey current wave type of the positive polarity
(winter) lightning resembles well the half-wave of the
alternating voltage, which uses a short circuit generator.
5. The damage situation of the blade model in the large
current examination performed with alternating voltage
resembles damage to the blade of a real machine. And it
turned out that verification of the lightning strike damage
decided by IEC TR 61400-24 could be performed in the
large current examination, which used the short circuit
generator.
6. FRP blade failure of the wind power generator by a
lightning showed clearly that it is reproducible with the
high-voltage examination by lightning impulse voltage
generating equipment, and the large current examination
with a short circuit generator.
VII. RECOGNITION
The authors greatly acknowledge the support from the
Kochi prefecture government
VIII. REFERENCE
[1]
[2]
[3]
[4]
[5]
[6]
R.H. Golde, Lightning Volume 2, Lightning Protection, Academic
Press,1977
F.A. Fisher, J.A. Plumer, and et al, Lightning Protection of Aircraft,
Lightning Technology Inc., 1999
H. Sakamoto, et al, “Lightning Protection of FRP Blades for Wind
Power Generators”, World Renewable Energy Conference Denver,
Colorado, Sept. 2004
H. Sakamoto and M. Hanai, “Reproduction and Mechanism of
FRP Blades Failure for Wind Power Generators”, Journal, JSME,
to be submitted 2005.
Wind turbine generator systems-Part24: Lightning Protection, IEC
TR 61400-24
K. Yamashita, Y. Mizutani, D. Tanaka, M.Yoda and I.
Miyachi, ”Positive and Negative Current Wveform of RocketTriggered Lightning”, in Proc. 1999 Annual Meeting Record of
IEE of Japan , No.1639, pp.7-30
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