Fatigue Failure Accident of Wind Turbine Tower in Taikoyama Wind Farm Yin LIU 1 , Takeshi ISHIHARA 2 1,2 Department of Civil Engineering, School of Engineering, the University of Tokyo, Tokyo, Japan Abstract One of the wind turbine nacelles at Taikoyama wind farm collapsed due to the fatigue failure of high tension bolts. Strain gauges and accelerometers were installed on the wind turbine to verify the aerodynamic model. Furthermore a FEM model was built in order to find out the relationship between tower tube and high tension bolts at the position of flange joint, where the fracture occurred. When the bolt’s pre-tension force decreases, its stress range increases. Less the pretension force left, the larger the stress range will be. Hence when pre- tension force is 0%, the fatigue life is left for only a few days. On the other hand when 17 bolts are damaged, the turbine tube stress is three times larger than the stress when all the bolts are in good condition. Hence the fatigue evaluation shows that the life time rapidly decreases to less than two months compared with that of the normal life time which is 20 years. Key Words: Fatigue failure, pre-tension force, high tension bolt, nacelle collapse. 1. Introduction The Taikoyama wind farm is located at the top of Taikoyama Mountain, Kyoto Prefecture, Japan, which is surrounded by the Tango peninsular and faces north to the Sea of Japan. The construction cost is approximately 12.5 million dollars and it reduces nearly 5900 tons of carbon dioxide every year. The wind farm information is summarized in Table 1. In March 2013 the nacelle of No.3 wind turbine collapsed[1] and the accident scene and schematic diagram of the wind turbine is shown in Fig. 1. 1 Presenting and corresponding author, PhD candidate, E-mail: [email protected]Table 1 Summary of Taikoyama wind farm Name Operating time Manufacturer Unit Max power output Taikoyama Wind Farm 15th, November, 2001 Lagerwey 6×750kW 4500kW Performance Cut-in wind speed Rated wind speed Cut-out wind speed Resistant wind speed 3m/s 12m/s 25m/s 60m/s Rotor Diameter Generation rotor speed Number of blades Hub height 50.5m 13~33rpm 3 50m Tower Height Material 46m SM400 (steel) Flange connection high-tension bolts F10T M24 Nacelle Dimensions Material W5.6×L3.3×H6.5m SS400, GFRE Wind direction control Control method Active yaw control Rated power output control Control method Pitch control
9
Embed
Fatigue Failure Accident of Wind Turbine Tower in …windeng.t.u-tokyo.ac.jp/ishihara/proceedings/2015-9... · 2016-03-08 · Fatigue Failure Accident of Wind Turbine Tower in Taikoyama
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Fatigue Failure Accident of Wind Turbine Tower in
Taikoyama Wind Farm
Yin LIU1, Takeshi ISHIHARA2
1,2Department of Civil Engineering, School of Engineering, the University of Tokyo, Tokyo, Japan
Abstract
One of the wind turbine nacelles at Taikoyama wind farm collapsed due to the fatigue failure of high tension
bolts. Strain gauges and accelerometers were installed on the wind turbine to verify the aerodynamic model.
Furthermore a FEM model was built in order to find out the relationship between tower tube and high tension
bolts at the position of flange joint, where the fracture occurred. When the bolt’s pre-tension force decreases,
its stress range increases. Less the pretension force left, the larger the stress range will be. Hence when pre-
tension force is 0%, the fatigue life is left for only a few days. On the other hand when 17 bolts are damaged,
the turbine tube stress is three times larger than the stress when all the bolts are in good condition. Hence the
fatigue evaluation shows that the life time rapidly decreases to less than two months compared with that of the
Fig.21 shows one example of the time history of the
bolt pre-tension stress at the wind speed of 14m/s. It
is clear that when the pre-tension force drops the
stress range increases significantly.
The fatigue life investigation follows the rules
mentioned in Section 3.4. The ultimate tensile
strength of FT10 bolts is1000Mpa and the detail
category is 36.
The bolts fatigue life is shown in Fig. 22.
0
0.001
0.01
0.1
1
10
100
1000
020406080100
Bo
lts f
atig
ue
life
(Y
)
Bolt pre-tension force(%)
20 years
0.22 days
6.95 years
318.25 years
Fig. 22 Bolts fatigue life vs. bolt pre-tension percentage
As we can see that when the pre-tension force is
over 40%, the life time does not decrease. However
when the pre-tension force is below 40% the fatigue
life time drops dramatically as only a few days left,
when the pre-tension force is 0%.
4. Conclusions
This research is based on the collapse accident of
Taikoyama wind farm No.3 turbine. The field
measurement of tower model frequency, SCADA
data and strain gauge data were measured. At the
same time the aerodynamic model was built. In
addition, the tower top FEM model was built to
evaluate the high-tension bolts and tower tube
fatigue life.
The cause of the collapse of the wind turbine is
discussed and the following conclusions were drawn:
1) Due to high turbulence intensity at site, the control
of the wind turbine was modified by manufacturer.
Power output and maximum rotor speed were
adjusted according to measurement data, and a five
degree of pitch error was applied. With this control
method the simulation results show good agreement
with measurement results;
2) For the high tension bolts, by considering the
nonlinear phenomenon and stress concentration
closed to welding zone, when the pre-tension force
decreases, the stress range increases, especially
when pre-tension force is 0% it is 30 times larger. The
less the pre-tension force left, the larger its range is.
As a result, when the pre-tension force is below 40%
the fatigue life time drops drastically and it is only a
few days when the pre-tension force is 0%;
3) Similarly, the FEM model shows that with 17 bolts
broken the local stress at fracture section increases
more than three times compared with the case of
bolts at normal condition. This phenomenon
accelerated the fatigue initiation and propagation
and the fatigue life of the fracture section decreases
dramatically to 1/200 of its life time.
4) The reason for the Taikoyama wind farm accident
is now clearly understood in a detailed manner. It is
not the matter of design or material, but was due to
the fatigue failure caused by the reduction of high
tension bolts’ pre-tension force.
For the Taikoyama wind turbines’ high tension bolts,
according to the service manual the temporary
torqueing and final torqueing was applied. And at the
time of 500 hours after bolt changing, the re-
torqueing must be applied. However at the time of
periodical bolt changing operation, the re-torqueing
was not applied. The wind turbine is a rotating
machine system, in which the contact surface and
the bolt itself plasticity deforms accompany with the
wind turbine operation, and therefore the pre-tension
force reduces.
Moreover, according to the service manual, 5% of the
bolts should be inspected per year, which means
only three bolts were inspected. We should check at
least 16 bolts per year in order to cover the bolts in
all wind direction.
Besides, during the year from 2005 to2008, the
workers only conducted the method of counter mark
inspection to make sure the torque was enough.
It is a serious problem between manufacturer and
operator that expertise technique is not transferred
accurately and efficiently. Clear rules must be made
even after guarantee periods, or it may lead to
devastating accident.
Reference
[1] Kyoto fu, Report of the accident in Taikoyama wind farm No.3 wind turbine, Kyoto, 2013.
[2] International Electrotechnical Commission, (2005). IEC 61400-1, 3rd edition, Part 1: Design requirements. Geneva.
[3] Ishizaki, H.(1983) Wind profiles, turbulence intensities and gust factors for design in typhoon-prone regions. Journal of Wind engineering & Industrial Aerodynamics, 13: 55-66.
[4] T. Ishihara, P.V. phuc, Yozo Fujino. A Field Test and Full Dynamic Simulation on a Stall Regulated Wind Turbine. The sixth Asia-Pacific Conference on Wind Engineering, Seoul, September 2005: 599-612.
[5] Garrad Hassan Bladed, version 4.4, DNV-GL, 2013.
[6] Tony Burton, David Sharpe, Nick Jenkins. Wind Energy Handbook. John Wiley & Sons Ltd, Chichester, 2001.
[7] Japan Society of Civil Engineers, (2010). Guidelines for Design of Wind Turbine Support Structures and Foundations. Task Committee on Dynamic Analysis and Structural Design of Wind Turbine Committee of Structural Engineering, Tokyo.
[8] V. Caccese, P.A. Blomquist, K.A. Berube. Effect of weld geometric profile on fatigue life of cruciform welds mad by laser/GMAW processes. Marine Structures, 2006, 19: 1-22.
[9] Germanischer Lloyd WindEnergie GmbH (2005), Guideline for the Certification of Offshore Wind Turbines. Germanischer Lloyd WindEnergie, Hamburg.