Wind Turbine Nacelle Research Articles

台風による南大隅 WF 風車ナセルカバー飛散・損傷事故について

台風による南大隅 WF 風車ナセルカバー飛散・損傷事故について

An experimental study on the fault diagnosis of wind turbines through a condition monitoring system

To detect wind turbine faults at an early stage, an investigation into a practical maintenance and repair approach was carried out on Jeju Island, South Korea. A condition monitoring system was installed in each wind turbine nacelle to detect the vibration signals from the gearbox and the generator. The vibration signals were measured by strain gauges on the gearbox and the generator for a period of approximately one to two years. A time domain analysis to detect the components’ faults was performed, and a frequency domain analysis was conducted to find the location of the faults that occurred. Using the criteria of acceptance level for the root mean square suggested in Verein Deutscher Ingenieure standard 3834, it was determined whether or not the gearbox and the generator were operated normally. After a fault was detected by root mean square analysis, the fast fourier transform spectrum was analyzed and then compared with that suggested by the International Organization for Standardization standard 10816–21 and 13373–1. Repair work was then conducted on the defective parts of the components. The root mean square and the acceleration value of the normal, the warning and the abnormal conditions were compared with one another. As a result, cavitation might occur in the gear oil pump attached to the gearbox due to the high acceleration values observed for frequencies ranging from 5000 Hz to 11000 Hz. Additionally, the generator bearing at the non drive end was found to be broken because the defect frequency of the bearing was 88 Hz, which was derived from envelope spectrum analysis. The root mean square and the acceleration values for the gearbox and the generator decreased to values indicating normal operating conditions after the damage repair. The annual energy production increased by 1.8 % after the generator bearing repair.

THE USE OF PLATE SPRINGS FOR PRELOADING OF A SYSTEM OF TAPERED ROLLER BEARINGS OF A WIND TURBINE GEARBOX

The use of preloaded tapered roller bearings in wind turbine drive systems allows a transfer of load in the case of high variations of axial forces. The examined bearing system, a modification of a current design, consists of a pair of different sized bearings. Previous study showed the high sensitivity of tapered roller bearings on the existing radial interference. Dimensional tolerances used in the original design do not allow obtaining precise values of preload required for slippage-free operation of bearings with varying wind turbine load conditions. With the aim of achieving expected preload values, the use of plate springs (Belleville springs) is proposed. The springs will allow creating an axial force, independently of real dimensions in a modernised unit. Furthermore, it is very important in the case of gearbox retrofits to be executed up in the wind turbine nacelle without dismantling the gearbox.

Effect of grid topology on numerical simulations of flow fields around wind turbine nacelle anemometer

Effect of grid topology on numerical simulations of flow fields around wind turbine nacelle anemometer

Effect of Grid Topology on Numerical Simulations of Flow Fields around Wind Turbine Nacelle Anemometer

Effect of Grid Topology on Numerical Simulations of Flow Fields around Wind Turbine Nacelle Anemometer

Overview of Wind Parameters Sensing Methods and Framework of a Novel MCSPV Recombination Sensing Method for Wind Turbines

The paper presents an overview of the traditional methods to obtain wind parameters such as wind speed, wind direction and air density. After analyzing wind turbines’ arrangements and communication characteristics and the correlation of operation data between wind turbines, the paper proposes a novel recombination-sensing method route of “measuring–correlating–sharing–predicting–verifying” (MCSPV) and explores its feasibility. The analysis undertaken in the paper shows that the wind speed and wind direction instrument fixed on the wind turbine nacelle is simple and economical. However, it performs in-process measurement, which restricts the control optimization of wind turbines. The light detection and ranging (LIDAR) technology which is accurate and fast, ensures an early and super short-time sensing of wind speed and wind direction but it is costly. The wind parameter predictive perception method can predict wind speed and wind power at multiple time scales statistically, but it has limited significance for the control of the action of wind turbines. None of the traditional wind parameter-sensing methods have ever succeeded in air density sensing. The MCSPV recombination sensing method is feasible, both theoretically and in engineering, for realizing the efficient and accurate sensing and obtaining of such parameters as wind speed, wind direction and air density aimed at the control of wind turbines.

Experimental Study of Wind Load acting on Wind Turbine Nacelles

The paper investigates wind-induced load on wind turbine nacelles through a series of wind tunnel experiments taking into account inflow turbulence and wind direction. First of all, pressure field data is collected using pressure taps distributed over the top, side and rear surfaces of the scaled nacelle model. It is observed that mean pressure distribution for nonturbulent uniform flow and turbulent shear flow cases were similar at lower yaw angle, but for higher yaw angle, pressure coefficient is smaller (more negative) close to the upstream edge when the inflow is turbulent. However, due to enhanced momentum entrainment, the streamwise extent of such strong negative pressure region is smaller. Force coefficient computed from the pressure data shows that the peak load for turbulent inflow case is significantly higher than for nonturbulent uniform inflow case. The measurement data are also used to propose models for peak factor and coefficient of variation, which can be used to estimate peak loads. The proposed models take into account both inflow turbulence and yaw misalignment, and predicted the peak force coefficients which showed satisfactory agreement with measurement. Finally, it was found that the magnitude of the load calculated by the GL guideline was satisfactory for DLC 6.1, but it was underestimated for DLC 6.2.

Flammability hazards of typical fuels used in wind turbine nacelle

SummaryThis study aims to develop a complete methodology for assessing flammability hazards of typical fuels (ie, transformer oil, hydraulic oil, gear oil, and lubricating grease) used in a wind turbine nacelle by combining different experimental techniques such as thermogravimetric analysis and cone calorimetry. Pyrolysis properties (onset temperature, temperature of maximum mass loss rate, and mass residue) and reaction‐to‐fire properties (ignition time, heat release rate, mass loss rate, and smoke release rate) were determined and used for a preliminary assessment of thermal stability and flammability hazards. Additional indices, for ignition and thermal behavior (effective heat of combustion, average smoke yield, and smoke point height, heat release capacity, fire hazard parameter, and smoke parameter, were calculated to provide a more advanced assessment of the hazards in a wind turbine. Results show that pyrolysis of transformer oil, lubricating grease, hydraulic oil, and gear oil occur in the range of 150°C to 550°C. Lubricating grease and transformer oil show the higher and lower thermal stabilities with maximum pyrolysis rate temperatures of 471°C and 282°C, respectively. The measured relation between ignition time and radiant heat flux agrees well with Janssens method (a power of 0.55). The aforementioned indices appear to provide a reasonable prediction of performance under real fire conditions according to a full‐scale fire test documented by Declercq and Van Schevensteen. The results of the study indicate that transformer oil is the easiest to ignite while lubricating grease is the most difficult to ignite but also has the highest smoke production rate; that transformer oil has the highest heat release rate while gear oil has the lowest; and that the fire hazard parameter is the highest for transformer oil and the smoke parameter is the highest for lubricating grease. The potential of this type of work to design safer wind turbines under performance‐based approaches is clearly clarified.

An experimental field study of the grounding system response of tall wind turbines to impulse surges

In this work, an experimental investigation of the grounding system behavior of tall wind turbines in both time and frequency domains is presented. Two scenarios were considered: in the first one, measurements were carried out on the grounding system embedded in the wind turbine foundation, before assembly of the wind turbine itself; in the second one, the complete wind turbine (tower, nacelle and blades) was included. The study also presents an enhanced signal processing technique for noise cancelation in a harsh electromagnetic environment. In the analysis, the frequency dependence of the grounding impedance was evaluated and a numerical simulation in steady state was performed. The simulation model leads to a satisfactory representation of the studied system. Preliminary results show that the evaluated grounding impedance is not significantly affected by the presence of the complete wind turbine at the evaluated frequencies.

Design-order, non-conformal low-Mach fluid algorithms using a hybrid CVFEM/DG approach

A hybrid, design-order sliding mesh algorithm, which uses a control volume finite element method (CVFEM), in conjunction with a discontinuous Galerkin (DG) approach at non-conformal interfaces, is outlined in the context of a low-Mach fluid dynamics equation set. This novel hybrid DG approach is also demonstrated to be compatible with a classic edge-based vertex centered (EBVC) scheme. For the CVFEM, element polynomial, P, promotion is used to extend the low-order P=1 CVFEM method to higher-order, i.e., P=2. An equal-order low-Mach pressure-stabilized methodology, with emphasis on the non-conformal interface boundary condition, is presented. A fully implicit matrix solver approach that accounts for the full stencil connectivity across the non-conformal interface is employed. A complete suite of formal verification studies using the method of manufactured solutions (MMS) is performed to verify the order of accuracy of the underlying methodology. The chosen suite of analytical verification cases range from a simple steady diffusion system to a traveling viscous vortex across mixed-order non-conformal interfaces. Results from all verification studies demonstrate either second- or third-order spatial accuracy and, for transient solutions, second-order temporal accuracy. Significant accuracy gains in manufactured solution error norms are noted even with modest promotion of the underlying polynomial order. The paper also demonstrates the CVFEM/DG methodology on two production-like simulation cases that include an inner block subjected to solid rotation, i.e., each of the simulations include a sliding mesh, non-conformal interface. The first production case presented is a turbulent flow past a high-rate-of-rotation cube (Re, 4000; RPM, 3600) on like and mixed-order polynomial interfaces. The final simulation case is a full-scale Vestas V27 225 kW wind turbine (tower and nacelle omitted) in which a hybrid topology, low-order mesh is used. Both production simulations provide confidence in the underlying capability and demonstrate the viability of this hybrid method for deployment towards high-fidelity wind energy validation and analysis.

Pyrolysis Properties and Kinetics of Typical Liquid Oils in Wind Turbine Nacelle

Abstract To evaluate fire risk of typical liquid oils applied in nacelle of wind turbine, pyrolysis properties prior to combustion should be known. Pyrolysis properties of three kinds of typical oils of hydraulic oil, gearbox oil and transformer oil were studied by using Thermogravimetry (TG)- Differential Scanning Calorimetry (DSC) technique. Pyrolysis kinetics was analyzed. Apparent activation energy and pre-exponential factor were calculated by using Kissinger method. Results show that according to the TG-DSC analysis, for all three oils, the pyrolysis processes can be divided into three stages. The first stage is evaporation from room temperature to 140.1 °C (gearbox oil), 123.4 °C (transformer oil), and 144.1 °C (hydraulic oil). The second stage is the primary mass loss stage, corresponding temperature is in the range of 140.1–542.0 °C (gearbox oil), 123.4–294.1 °C (transformer oil), and 144.1–329.5 °C (hydraulic oil), among which the temperature of maximum heat mass loss rate of gearbox oil, transformer oil and hydraulic oil is 402.6, 220.1 and 262.6 °C. The third stage is the end of char oxidation and mass of residual char is kept constant, the temperature is higher than 542.0, 294.1, and 329.5 °C. Activation energies and pre-exponential factors were obtained by kinetic analysis, according to the pyrolysis kinetics analysis, the hydraulic oil is more prone to be pyrolyzed than gearbox oil and transformer oil and this provides a basis for judging the combustion characteristics of oil products by pyrolysis kinetic parameters in the future.

Study on the Shape of Wind Turbine Tower and Nacelle

Study on the Shape of Wind Turbine Tower and Nacelle

Wavelet and Hilbert Huang transform based wind turbine imbalance fault classification model using <i>k</i>-nearest neighbour algorithm

Wind turbine (WT) is a key part in wind power generator system (WTGs). For proper operation, condition monitoring and fault diagnosis is a major part in WTGs. In this paper, three different types of nacelle yaw faults along with healthy condition are analysed using wavelet transform (WT) and Hilbert Huang transformed (HHT) based k-nearest neighbour (k-NN) algorithm. For decomposing the raw signals, discrete approximation of Meyer wavelet function (DMeyer/dmey) is used and to extract the feature, Hilbert Huang transform is used to find the amplitude and phase feature of decomposed signal. k-nearest neighbour algorithm based classifier is designed for classifying faults based on extracted features. Prepared feature matrix of twenty one attributes is used for wind turbine nacelle yaw imbalance fault classification. The proposed technique is being compared with other computational intelligence dependent techniques of artificial neural network (i.e., multilayer perceptron-MLP). Results and different comparisons of proposed technique could work as an essential tool for fault diagnosis of WTGs.

南大隅WF 風車ナセルカバー飛散・損傷事故の再発防止に向けた強度対策検討

南大隅WF 風車ナセルカバー飛散・損傷事故の再発防止に向けた強度対策検討

Numerical investigations of the thermal behavior of a HAWT nacelle using ANSYS FLUENT

The Algerian Sahara is characterized by severe climate conditions where temperature reaches high levels with large variations during day and season. Nacelles of horizontal axis wind turbines (HAWT) operating in this region are subjected to the overheating problem, in particular the electromechanical components becoming less effective as they heat up during use. In order to maintain an appropriate temperature of the air within the nacelle, an active cooling system has to be set up to reject the generated heat towards the external environment and the resulting heat transfer must be properly controlled. The present work investigates the thermal behavior of the nacelle of a typical commercial wind turbine. The impact of radiation and turbulent natural convection heat transfer within the nacelle has been investigated numerically using ANSYS FLUENT code, whereas the forced convection heat exchange with the surrounding environment has been modeled using a suitable correlation. Temperature and velocity profiles within the nacelle have been presented and discussed. Variations of the average temperature inside the nacelle and the required cooling capacity are determined and thoroughly discussed.

Numerical investigations of laminar buoyant heat transfer in a 2D-enclosure – Application to wind turbine nacelle operating in hot climate

The climate of the Algerian Sahara is characterized by extremethermal conditions. The wind turbines installed in theSahara, namely the electromechanical equipment located insidethe nacelle (e.g. electrical generator), are subjected to high andfluctuating temperature gradients during the day and the seasons.This reality might generate contradictory constraints of designand can lead to some difficulties of conception. In order to maintainan appropriate temperature of the air inside the nacelle (i.e.acceptable average temperature of the electromechanical equipment),the heat generated by the generator must be rejected towardsthe environment, and the resulting heat transfer must becontrolled properly. This work deals with heat transfer effectswithin a reduced scale nacelle, i.e. hypothetical nacelle. Forthis purpose, a small nacelle dimensions has been considered andrepresented as rectangular cavity. In this paper, the air flow fieldswithin the nacelle have been described using the Navier-Stokesequations. The energy equation has been used to account for heattransfer effects. ANSYS FLUENT code has been employed tosolve the resulting governing equations. The main object of thiswork is to determine the average temperature inside the nacelle,as well as to investigate its variation with the required coolingcapacity.DOI: http://dx.doi.org/10.5755/j01.mech.23.5.15815

Nacelle-based Lidar Measurements for the Calibration of a Wake Model at Different Offshore Operating Conditions

Commonly, wake models are calibrated in wind tunnels or using flow simulations with a wide degree of physical details. In general, it is assumed that these methods cannot fully reproduce the real operating conditions of wind turbines. This research aims at investigating the calibration of an analytical single wake model in relation to full-scale measurements. Within this scope, we fitted the wake model to wake measurements realised with a lidar installed on the nacelle of an offshore wind turbine. We studied the parameters returned by the fit separating cases at different levels of atmospheric turbulence and thrust on the wind turbine rotor. Comparing the results with a published calibration based on few LES wind fields representative for partial load conditions, we achieved good agreement when the considered wind turbines operated in similar conditions. For other situations, i.e. at full load, we found different calibrations of the model parameters. Our results show that and how nacelle-based lidar measurements can be complementary in the development of wake models.

Hybrid, Multi-Megawatt HVDC Transformer Topology Comparison for Future Offshore Wind Farms

With the wind industry moving further offshore, High Voltage Direct Current (HVDC) transmission is becoming increasingly popular. HVDC transformer substations are not optimized for the offshore industry though, increasing costs and reducing redundancy. A suggested medium frequency, modular hybrid HVDC transformer located within each wind turbine nacelle could mitigate these problems, but the overall design must be considered carefully to minimize losses. This paper’s contribution is a detailed analysis of the hybrid transformer, using practical design considerations including component library minimization. The configurations investigated include combinations of single phase H-Bridge and Modular Multilevel Converter topologies operating under minimum switching frequency control strategies. These were modelled in the MATLAB/Simulink environment. The impact of the minimum switching control strategy and converter topology on power transfer stability and overall efficiency is then investigated. It was found that the H-Bridge converter generated the lowest overall losses, but there was a trade off with power flow sensitivity due in part to the additional harmonics generated.

On the attachment of dart lightning leaders to wind turbines

Wind turbines are prone to damages due to lightning strikes and the blades are one of the most vulnerable components. Even though the blade tip is usually protected in standard designs, lightning damages several meters away from it have also been observed in some field studies. However, these damages inboard from the tip cannot be explained by the attachment of downward stepped leaders or the initiation of upward lightning alone. In this paper, the attachment of dart leaders in an upward lightning flash is investigated as a mechanism of strikes to inboard sections of the blade and the nacelle of large wind turbines. Dart leaders in an upward lightning flash use the channel previously ionized by the preceding stroke or the continuous current. The analysis is performed with the self-consistent leader inception and propagation model (SLIM). A commercial large wind turbine with 45m long blades and hub height of 80m is analysed as a case study. The impact of the prospective return stroke peak current, the rotation angle of the blade and the wind on the location of lightning strikes on this mechanism is analysed. The probability of lightning attachment of dart leaders along the blade for the case study is also calculated. It is shown that this damage mechanism could create a new strike point only when the blade of a wind turbine rotates sufficiently from its initial position (at the inception of the initial upward leader) until the start of the dart leader approach. Thus, dart leader attachment is a mechanism that can explain lightning strikes to the nacelle and to the inboard region several meters away from the blade tip in large wind turbines. However, dart leader attachment cannot explain the lightning strikes observed in the close vicinity of the blade tip (in the region between 1.5 and 6m from it).

Defect characterisation of tensile loaded CFRP and GFRP laminates used in energy applications by means of infrared thermography

The increased use of fibre reinforced plastic (FRP) composites for improved efficiency and reliability in energy related applications, e.g. wind and marine turbine blades, nacelles, oil and gas flexible risers, also increases the demand for innovative non-destructive testing technologies. In this contribution, results concerning the characterisation of CFRP and GFRP during and after quasi-static tensile loading are presented. It includes the measurement of optical properties in the infrared spectral range, tensile loading tests with the observation of the temperature distribution at one or both sides of the specimens using an infrared camera for the preparation and monitoring of intended natural defects, and active thermography inspections after tensile loading. It is shown that the defect preparation was successful. Thermographic monitoring during and active thermography testing after tensile loading enable the detection of the lateral extend of the generated defects. Differences between CFRP and GFRP materials are discussed.