idsession
code

196

D-3-1

Periodic Safety Management
Inspections

56

D-3-2

Prognostic Model to analyze theeffects of REWITEC® nano coating Mr., Dipl.-Ing. Stefan Bill
treatment of wind turbine gearboxes

REWITEC GmbH

74

D-3-3

Simulating O&M strategies foroffshore wind farms by O2M

DNV GL AS, Japan Branch

99

D-3-4

Vibration analysis on rolling bearing
Mr. Yizhou Yang
fault of wind turbine unit

Gas Turbine Institute, Departmentof Thermal Engineering, Tsinghua
University

95

D-3-5

Taikoyama Wind Farm Fatigue
Failure Accident Analysis Based on Dr. Yin Liu
Aerodynamic and FEM Modelling

the University of Tokyotitle

Presenter name

Mr. Takashi Matsunobu

Mr. Yukinobu Uchida

Affiliation

Hitachi Ltd.

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1-Nov. 10:45 - 12:15 [ Operation & maintenance (2) ]Periodic Safety Management Inspections
Takashi Matsunobu1, Tsutomu Ono1 and Nobuhiro Kaizu2
1Hitachi Ltd., 2Japan Wind Power Association

Abstract:
Wind power generation is different from another power generation method which burns a fossil fuel and is the safe electricalgenerating system which has no discharge of a greenhouse gas during the operation. It is promoted because its levelized cost ofenergy is relatively low among the natural energy sources. Wind power stations beyond 447 plants, 1,948 units, 2,715MW, aredriving in Japan at the end of March, 2014. In recent years a collapse of wind turbine and a fatal accident occur in several wind
power plants, and have raised a problem about keeping safety of wind turbine system. This paper explains the fact that windturbines have been designed, operated and maintained safely based upon standards and laws such as Electricity Business Act,
which is revised by the analysis of the recent wind turbine accidents.

Prognostic Model to analyze the effects of REWITEC®
nano coating treatment of wind turbine gearboxes
Stefan BillREWITEC GmbHAbstract:
REWITEC® is an independent, medium-sized business that develops innovative nano- and micro-particle-based lubricant additives andmarkets these in Wind Turbine applications around the world. When applying the products, treated machinery, gearboxes, bearings andinternal combustion engines can run with reduced friction, temperature and great reliability and durability due to reduced abrasion and wear.
1. REWITEC® - Examples of application Coating and analysis of a wind turbine gearbox GE 1.5 SL Before treatment with REWITEC: →Operational wear visible → In the foot area visible seizing and stray metallic particle run through marks Treatment with REWITEC after 6weeks: → Stray metallic particle run through and seizure are greatly smoothed out → Run through marks and pitting are greatly smoothed out•
Less stress for the tooth flank•
Reduction of the surface roughness and friction force•
Improved load carrying capacity
2. Project Prognostic Model
2.1 ProjectUsing the REWITEC® provided specific gear and bearing surface roughness measurements with and without treatment, Sentient Science
ran two cases for each of several critical components (intermediate pinion bearing, planetary bearing and intermediate pinion gear). Asidefrom the surface roughness differences Sentient Science assumed that all other model input parameters including bearing and gear loads,
metallurgical and material properties, and oil viscosity remained unchanged from Sentient Science´s Winergy 4410.2 prognostic model.
Sentient Science used its proprietary six-step prognostic modelling process to evaluate life of the two different surface finishes. REWITEC®
used these tests to provide Sentient Science with the surface finish data of the components with and without REWITEC® DuraGear® W100treatments.
2.2 Mixed – EHL Modell
To take the influence of microasperity into account for determination of probabilistic fatigue life, Sentient Science mixed EHL(elastrohydrodynamic) solver utilizes simulated surface roughness profiles in an explicit deterministic calculation of surface tractions.
Surface traction refers to the pressures transmitted between two surfaces through a lubricant.
Outcome: We can directly determine the performance of a given surface finish during the generation, sustainment, and/or failure of an EHL
film at the contact zone.
•Synthetic surface roughness profiles are generated for use in mixed-EHL•
Spatially and spectrally identical to measured surfaces•
Surface ‘lay’ is accounted for through autocorrelation function
2.3 Result
DigitalClone® predicts that a Winergy 4410.2 damaged gearbox treated with REWITEC® DuraGear® W100 has a significant
improvement in life than untreated gearbox and representative turbine operating conditions. Specifically, for bearings, REWITEC´sDuraGear® W100 treatment is expected to improve the overall contact fatigue life by a factor of 3.3. For gears, REWITEC´s DuraGear®
W100 treatment is expected to improve the overall fatigue life by a factor of 2.6.

For more information and contact, please visit our multi- lingual website www.rewitec.com
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1-Nov. 10:45 - 12:15 [ Operation & maintenance (2) ]Simulating O&M strategies for offshore wind farms by O2M
Yukinobu Uchida
DNV GL AS, Japan Branch

Abstract:
In the absence of many years of commercial experience, the offshore wind industry is faced with significant levels ofuncertainty when it comes to operational expectations. These risks are exacerbated by concerns over turbine reliability andaccessibility. It is widely anticipated that the cost of operation and maintenance (O&M) for offshore project will certainly behigher than equivalent onshore wind farms, although the extent of this increase is unclear. While warranties play a role here,
they are merely a mechanism for transferring responsibility and risk from owners and lenders to contractors.
In order to improve understanding of O&M risks and wind farm performance, a modelling tool has been developed which
simulates the operation of offshore wind farm projects. The approach is based on Monte Carlo analysis with turbine failuresoccurring on a stochastic basis. Delays associated with poor weather are simulated using a statistical wave module based on
spectral analysis. Wave heights are correlated with wind speeds such that the effect of poor accessibility during periods of highwind is captured in the calculation of lost production revenue.
This modelling approach has been used here to examine typical O&M strategies at three notional sites. The exercise
demonstrates the impact of metocean climate on lost energy production and the improvements that can be achieved by
optimising O&M resourcing and infrastructure on a site-specific basis.
A clearer perspective in O&M issues associated with offshore wind projects will allow improved distribution of operationalrisk between owners, lenders and contractors.

Vibration analysis on rolling bearing fault of wind turbine unit
Yizhou Yang and Dongxiang Jiang
Gas Turbine Institute, Department of Thermal Engineering, Tsinghua University

Abstract:
Bearing faults can cause intensification of vibration of wind turbine units, and even lead to their failures. The detection ofbearing faults before more serious problems happen becomes very crucial. For the vibration feature extraction of rolling bearing
faults, a method combining Intrinsic Time-scale Decomposition (ITD) and Teager-Kaiser Energy Operator is used. ITD candecomposes a signal into a sum of components (so called proper rotation components) and a monotonic trend. And energy
operator is a simple algorithm calculating the energy of a signal, which is very sensitive to periodic impact fault. This method istested on data acquired from the wind turbine vibration fault experimental system, with artificial cracks in the bearings. Whendealing with large amount data from actual wind turbine units, the efficiency of an algorithm turns to be an issue of more
importance. Thus amplitude parameter analysis is first used to find potential bearing faults, then the feature extraction method
to judge whether there is a bearing fault and which type the fault is. Analysis on the vibration signals of the non-drive end ofseveral actual wind turbine units finds out significant bearing faults and shows the practicability and efficiency of the methods
presented in this paper.

3/41-Nov. 10:45 - 12:15 [ Operation & maintenance (2) ]Taikoyama Wind Farm Fatigue Failure Accident Analysis Based on
Aerodynamic and FEM Modelling
Yin Liu and Takeshi Ishihara
The University of Tokyo

Abstract:
One of the wind turbines’ nacelle collapsed at Taikoyama wind farm in Mar. 2013. It collapsed 12 years after theconstruction, at a very early stage of its 20 years design life time. Moreover, the accident happened only three months after theperiodical inspection. There are more than 120 same type wind turbines in service across Japan. It is necessary and urgent tounderstand the cause of this accident.
Field measurement was conducted including wind characteristics, tower natural frequency and bending moment. By
observing the fracture section, the material strength was found strong enough. But evidence of fatigue crack propagation wasdetected at the top tower wall inner surface. A preliminary conclusion was that the fatigue failure was due to the highturbulence intensity on the site. In order to verify it, an aerodynamic model was built to understand the turbine dynamicperformance. With the purpose of find out the relationship between top tower wall and high tension bolts at the position offlange joint where the fracture occurred, a very detailed FEM model was also built based on engineering drawing and filed
measurement, including the nacelle real shape, generator weight, yaw generator weight and yaw brake. The fatigue analysis
shows a 27 years fatigue life of the tower top wall, which meet the required 20 years life time, and arrives at the conclusion thatthe fatigue failure is not due to the high turbulence intensity. Meanwhile, 17 bolts opposite to hub were suffered from pretension reduction up to 30%~100% through field investigation. The FEM analysis indicates when the bolt’s pre-tension force
decreases, the top tower wall stress range increases. Less the pre-tension force left, larger the stress range will be. When 17bolts are damaged, the tower top wall stress is three times larger than the stress when all the bolts are in good condition. Thisphenomenon accelerates the fatigue initiation and propagation, and decreases the fatigue life of the tower top wall dramaticallyto 1/200 its design life time, in no more than two months.
The root cause of the Taikoyama wind farm accident is considered not the matter of design or extreme environment, but due
to the fatigue failure originates from the high tension bolts’ pre-tension force reduction. Human error should be avoided as far
as possible otherwise it may result to devastating consequence.

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