Wind Turbine Condition Research Articles

Modifying the aggregated wind farm model with a controller

A large wind farm can be simplified by the aggregated wind farm models for load flow, steady and transient stability studies. When a fault (such as a short circuit) happens in a large wind farm, some of wind turbines trip while others do not. This paper is to design a controller to modify the aggregated wind farm model in the case of one or more unit removed or added from the complete model. This is without stopping the simulation process during performing the steady state and transient analysis of the whole system. This controller can modulate the status of the wind turbines in the aggregated model in a given farm according to any change in this farm. By this controller, we save effort and time to change the status of wind turbines in the aggregated model. The proposed wind farm is composed of some smaller farms of permanent magnet synchronous generators (PMSGs) and others of squirrel cage induction generators (SCIGs).

Loss Analysis and Comparison of High Power Semiconductor Devices in 5MW PMSG MV Wind Turbine Systems

This paper provides a loss analysis and comparison of high power semiconductor devices in 5MW Permanent Magnet Synchronous Generator (PMSG) Medium Voltage (MV) Wind Turbine Systems (WTSs). High power semiconductor devices of the press-pack type IGCT, module type IGBT, press-pack type IGBT, and press-pack type IEGT of both 4.5kV and 6.5kV are considered in this paper. Benchmarking is performed based on the back-to-back type 3-level Neutral Point Clamped Voltage Source Converters (3L-NPC VSCs) supplied from a grid voltage of 4160V. The feasible number of semiconductor devices in parallel is designed through a loss analysis considering both the conduction and switching losses under the operating conditions of 5MW PMSG wind turbines, particularly for application in offshore wind farms. This paper investigates the loss analysis and thermal performance of 5MW 3L-NPC wind power inverters under the operating conditions of various power factors. The loss analysis and thermal analysis are confirmed through PLECS Blockset simulations with Matlab Simulink. The comparison results show that the press-pack type IGCT has the highest efficiency including the snubber loss factor.

Prediction of dynamic strains on a monopile offshore wind turbine using virtual sensors

The monitoring of the condition of the offshore wind turbine during its operational states offers the possibility of performing accurate assessments of the remaining life-time as well as supporting maintenance decisions during its entire life. The efficacy of structural monitoring in the case of the offshore wind turbine, though, is undermined by the practical limitations connected to the measurement system in terms of cost, weight and feasibility of sensor mounting (e.g. at muddline level 30m below the water level). This limitation is overcome by reconstructing the full-field response of the structure based on the limited number of measured accelerations and a calibrated Finite Element Model of the system. A modal decomposition and expansion approach is used for reconstructing the responses at all degrees of freedom of the finite element model. The paper will demonstrate the possibility to predict dynamic strains from acceleration measurements based on the aforementioned methodology. These virtual dynamic strains will then be evaluated and validated based on actual strain measurements obtained from a monitoring campaign on an offshore Vestas V90 3 MW wind turbine on a monopile foundation.

Modelling the drained response of bucket foundations for offshore wind turbines under general monotonic and cyclic loading

The response of bucket foundations on sand subjected to planar monotonic and cyclic loading is investigated in the paper. Thirteen monotonic and cyclic laboratory tests on a skirted footing model having a 0.3m diameter and embedment ratio equal to 1 are presented. The loading regime reproduces the typical conditions of offshore wind turbines: very large cyclic overturning moment, large cyclic horizontal load and comparatively little, self-weight induced, vertical load. The experimental soil-foundation response is interpreted within the macro-element approach, using an existing analytical model, suitably modified to accommodate the footing embedment and the application of cyclic load. Details of the proposed model are provided together with evidences of its ability to reproduce the essential features of the experimentally observed behaviour. The results of the study aim at increasing the confidence in the use of the macro-element approach to predict the response of bucket foundations for offshore wind turbines, notably as the long-term accumulated displacements are concerned.

Dynamic response sensitivity of an offshore wind turbine for varying subsoil conditions

In this paper, a comprehensive study is performed on the dynamic response of an offshore wind turbine installed on a monopile. The aim is to evaluate to what extent a change of the soil properties affects the fatigue loads for parked conditions. Based on consistent lumped-parameter models calibrated to semi-analytical impedance functions of a monopile embedded in a linear viscoelastic soil layer, fully coupled aero-hydro-elastic simulations are conducted in the nonlinear multi-body code Hawc2. Correlation of wind speeds and waves is derived on basis of wind–wave scatter diagrams from the North Sea. Changes of the soil stiffness, the soil damping and the presence of sediment transportation at seabed are shown to be critical for the fatigue damage equivalent moment at mudline that may change with more than 30% for parked wind turbine conditions.

An SVM-based solution for fault detection in wind turbines.

Research into fault diagnosis in machines with a wide range of variable loads and speeds, such as wind turbines, is of great industrial interest. Analysis of the power signals emitted by wind turbines for the diagnosis of mechanical faults in their mechanical transmission chain is insufficient. A successful diagnosis requires the inclusion of accelerometers to evaluate vibrations. This work presents a multi-sensory system for fault diagnosis in wind turbines, combined with a data-mining solution for the classification of the operational state of the turbine. The selected sensors are accelerometers, in which vibration signals are processed using angular resampling techniques and electrical, torque and speed measurements. Support vector machines (SVMs) are selected for the classification task, including two traditional and two promising new kernels. This multi-sensory system has been validated on a test-bed that simulates the real conditions of wind turbines with two fault typologies: misalignment and imbalance. Comparison of SVM performance with the results of artificial neural networks (ANNs) shows that linear kernel SVM outperforms other kernels and ANNs in terms of accuracy, training and tuning times. The suitability and superior performance of linear SVM is also experimentally analyzed, to conclude that this data acquisition technique generates linearly separable datasets.

Study on Unified Chaotic System-Based Wind Turbine Blade Fault Diagnostic System

At present, vibration signals are processed and analyzed mostly in the frequency domain. The spectrum clearly shows the signal structure and the specific characteristic frequency band is analyzed, but the number of calculations required is huge, resulting in delays. Therefore, this study uses the characteristics of a nonlinear system to load the complete vibration signal to the unified chaotic system, applying the dynamic error to analyze the wind turbine vibration signal, and adopting extenics theory for artificial intelligent fault diagnosis of the analysis signal. Hence, a fault diagnostor has been developed for wind turbine rotating blades. This study simulates three wind turbine blade states, namely stress rupture, screw loosening and blade loss, and validates the methods. The experimental results prove that the unified chaotic system used in this paper has a significant effect on vibration signal analysis. Thus, the operating conditions of wind turbines can be quickly known from this fault diagnostic system, and the maintenance schedule can be arranged before the faults worsen, making the management and implementation of wind turbines smoother, so as to reduce many unnecessary costs.

Analysis of throw distances of detached objects from horizontal-axis wind turbines

This paper aims at predicting trajectories of the detached fragments from wind turbines, in order to better quantify consequences of wind turbine failures. The trajectories of thrown objects are attained using the solution to equations of motion and rotation, with the external loads and moments obtained using blade element approach. We have extended an earlier work by taking into account dynamic stall and wind variations due to shear, and investigated different scenarios of throw including throw of the entire or a part of blade, as well as throw of accumulated ice on the blade. Trajectories are simulated for modern wind turbines ranging in size from 2 to 20 MW using upscaling laws. Extensive parametric analyses are performed against initial release angle, tip speed ratio, detachment geometry, and blade pitch setting. It is found that, while at tip speeds of about 70 m/s (normal operating conditions), pieces of blade (with weights in the range of approximately 7-16 ton) would be thrown out less than 700 m for the entire range of wind turbines, and turbines operating at the extreme tip speed of 150 m/s may be subject to blade throw of up to 2 km from the turbine. For the ice throw cases, maximum distances of approximately 100 and 600 m are obtained for standstill and normal operating conditions of the wind turbine, respectively, with the ice pieces weighting from 0.4 to 6.5 kg. The simulations can be useful for revision of wind turbine setback standards, especially when combined with risk assessment studies. Copyright © 2015 John Wiley & Sons, Ltd.

Ultimate and accidental limit state design for mooring systems of floating offshore wind turbines

The paper deals with the catenary mooring system design for tri-floater floating offshore wind turbines. Both ultimate (ULS) and accidental (ALS) limit states are examined, under 50 and 1 year return period environmental loads. Both power production and parked wind turbine conditions are analysed; for the former the ULS is applied, for the latter both ULS and ALS are considered. The platform static demand is assessed in terms of turbine thrust, wind, current and wave steady drift forces. The dynamic offset is determined considering both wave and low-frequency motions. Mooring patterns with 6, 9 and 12 chain cable and steel wire rope lines are considered. Water depth incidence is examined in the range between 50 and 300m and the mooring system is dimensioned so that the relevant weight is determined. The Dutch tri-floater is assumed as reference structure and three candidate sites in the Southern Mediterranean Sea are considered. It is found that platform admissible offset and line pattern significantly influence the mooring system weight; obtained results show that 9 and 12 line configurations are the necessary choice and the mooring line weight is independent of water depth between 100 and 200m, while increases out of this range.

Research on a power quality monitoring technique for individual wind turbines

The extensive deployment of megawatt-scale wind turbines is bringing more challenges to the safety and stability of electric grid than ever before. This is not only because of the unstable wind over time but the increased risk of power quality pollution by defective wind turbines particularly when the turbines today are still experiencing various reliability issues. To prevent the power quality pollution by defective turbines, a new power quality monitoring technique dedicated for individual wind turbines is developed in this paper, so that the quality of the power generated by an individual turbine can be monitored by the wind turbine condition monitoring system. Through simulated and physical experiments on a specially designed test rig, some encouraging results have been achieved. It has been shown that the proposed technique is not only valid for monitoring the power quality of an individual wind turbine, but helpful in detecting the mechanical and electrical faults occurring in the wind turbines.

Wind Turbine Seismic Load Analysis Based on Numerical Calculation

Large-scale wind turbines have come into common use in Europe. Because violent earthquakes are relatively rare there, insufficient consideration has been given to the seismic impact on the wind turbine specifications; however, at present, there are many wind farms being constructed in earthquake-prone regions, and the seismic impact cannot be ignored in wind turbine designs. Based on the multi-body system dynamic theory and taking into consideration the soil-structure interaction, this paper proposes a blade-cabin-tower-foundation coupled model in order to study the load-bearing conditions of wind turbines under seismic impact. According to the basic theory of multi-body system dynamics, the wind turbine blade and tower system comprises a series of continuous discrete units, while soil-structure interaction in the tower system is realized through the spring and damping set on the interface between the foundation and the soil body; the cabin is simplified as a rigid model. Based on the Eurocode 8 earthquake load spectrum, the dynamic response of a wind turbine working under seismic impact is analysed, and the seismic load is compared. Results of the study can serve as references for designing key parts and control strategies of wind turbines for earthquake-prone regions.

Effect of the Rudder on the Vibration Frequency of Wind Turbine

Based on the finite element theory, an analysis about the changing of rotor vibration mode of the wind turbine with and without rudder at static state, and a research was carried out to study the impact of the rudder on wind turbine vibration frequency during operation condition of a small horizontal axis wind turbine by using Ansys Workbench. The result showed that, rudder vibration mode was the coupling of rudder vibration mode and first order anti-symmetric vibration mode of rotor. With the increasing of rotating speed, wind turbine vibration frequency increased because of the stiffening effect caused by centrifugal force, and the difference of first order anti-symmetric vibration frequency and symmetric vibration frequency was decrease which was caused by the aerodynamic force. At the same time, the changing of the external load had no effect on the vibration frequency of rudder, the reason of that was counterweight of the rudder. When the rotor speed was in the resonance region, rudder vibration frequency was equal to first order anti-symmetric vibration frequency at the rotating speed n=10.91Hz, an obviously resonance phenomenon occurred. The related research could provide some theoretical guidance for the design of small wind turbine rudder.

Fault Diagnosis Approach for Incipient Bearing Fault in Wind Turbine under Variable Conditions

For the extreme operating environment and variable working conditions of wind turbine and difficulty in finding fault feature accurately and promptly, a new incipient bearing fault method based on selecting optimal IMF (Intrinsic Mode Function) and Hilbert spectrum was proposed. Firstly, non-stationary time-domain signals are converted to stationary or quasi-stationary angle-domain signals; secondly, the EMD (Empirical Mode decomposition) method is used to decompose modal for angular waveform signal and obtain the IMF, and optimal IMF components are selected by cross-correlation criteria and kurtosis criteria to reconstructing signal. Finally, the reconstruction signal is processed by using Hilbert transformation to obtain the marginal spectrum. The paper finally verifies the effectiveness of the proposed method through experiment.

Modeling turbine wakes and power losses within a wind farm using LES: An application to the Horns Rev offshore wind farm

A modeling framework is proposed and validated to simulate turbine wakes and associated power losses in wind farms. It combines the large-eddy simulation (LES) technique with blade element theory and a turbine-model-specific relationship between shaft torque and rotational speed. In the LES, the turbulent subgrid-scale stresses are parameterized with a tuning-free Lagrangian scale-dependent dynamic model. The turbine-induced forces and turbine-generated power are modeled using a recently developed actuator-disk model with rotation (ADM-R), which adopts blade element theory to calculate the lift and drag forces (that produce thrust, rotor shaft torque and power) based on the local simulated flow and the blade characteristics. In order to predict simultaneously the turbine angular velocity and the turbine-induced forces (and thus the power output), a new iterative dynamic procedure is developed to couple the ADM-R turbine model with a relationship between shaft torque and rotational speed. This relationship, which is unique for a given turbine model and independent of the inflow condition, is derived from simulations of a stand-alone wind turbine in conditions for which the thrust coefficient can be validated. Comparison with observed power data from the Horns Rev wind farm shows that better power predictions are obtained with the dynamic ADM-R than with the standard ADM, which assumes a uniform thrust distribution and ignores the torque effect on the turbine wakes and rotor power. The results are also compared with the power predictions obtained using two commercial wind-farm design tools (WindSim and WAsP). These models are found to underestimate the power output compared with the results from the proposed LES framework.

Development and application of a dynamic stall model for rotating wind turbine blades

In unsteady conditions of wind turbines, both the dynamic stall phenomenon and the three-dimensional (3D) rotational effect affect the rotor aerodynamics. The dynamic stall mechanism for rotating wind turbine blades is first investigated. Through the comparison of the aerodynamic data between the rotating blade and the two-dimensional (2D) airfoil, the normal force slope in the attached flow and the separation point expression in the separated flow are modified in the Beddoes-Leishman (B-L) dynamic stall model for rotating NREL wind turbine blades. The modified model is validated by the comparison between the calculation results and the experimental results of the lift and drag coefficients at different radial positions. Both the hysteresis loop shapes and the calculation values are closer to the experiment than the 2D dynamic stall model. The present dynamic stall model is then coupled to a free vortex wake model. The coupled model is used to calculate the unsteady blade aerodynamic loads and the low speed shaft torque of the NREL wind turbine in a yawed condition. The accuracy is greatly improved by the corrections presented in the paper.

Modeling and Stability Analysis of a Direct-Drive Direct-Grid Slip–Synchronous Permanent-Magnet Wind Generator

In order to simplify and increase the reliability of wind generators, a new type of a direct-drive directly grid-connected wind generator known as a slip–synchronous permanent-magnet generator (SS-PMG) is proposed. It consists of two integrated generating units, i.e., a directly turbine-connected slip PMG unit and a directly grid-connected PM synchronous generator unit. The main aim of this paper is to determine if this generator is stable under transient wind turbine and grid conditions. A transfer function model is developed to evaluate the dynamic performance of the wind generator system. The transient response of a single 15-kW grid-connected system is evaluated. It is shown that the generator is very stable under transient turbine torque conditions. Furthermore, it acts as a filter to prevent voltage flickering due to oscillatory turbine pulsations. A very important design aspect to take into account is the torque ripple characteristics of the slip PM generator as torque ripple can be transferred to the grid current under certain conditions. Simulated and dynamically measured results are shown for a series of 15-kW SS-PMG prototypes.

Comparison of methods for wind turbine condition monitoring with SCADA data

Wind turbine operational costs can be reduced by monitoring the condition of major components in the drivetrain. SCADA-based condition monitoring is attractive because the data are already collected, resulting in rapid deployment and modest set-up cost. Three SCADA-based monitoring methods were reviewed: signal trending; self-organising maps and physical model. The physical model was identified as being the most reliable at predicting impending component failures. A validation study on this method using five operational wind farms showed that it is possible to achieve a high detection rate and good detection accuracy. An advance detection period of between 1 month and 2 years was achieved by the method. The study has also highlighted limitations and areas for further development.

Wind Turbine Condition Monitoring: State-of-the-Art Review, New Trends, and Future Challenges

As the demand for wind energy continues to grow at exponential rates, reducing operation and maintenance (OM) costs and improving reliability have become top priorities in wind turbine (WT) maintenance strategies. In addition to the development of more highly evolved WT designs intended to improve availability, the application of reliable and cost-effective condition-monitoring (CM) techniques offers an efficient approach to achieve this goal. This paper provides a general review and classification of wind turbine condition monitoring (WTCM) methods and techniques with a focus on trends and future challenges. After highlighting the relevant CM, diagnosis, and maintenance analysis, this work outlines the relationship between these concepts and related theories, and examines new trends and future challenges in the WTCM industry. Interesting insights from this research are used to point out strengths and weaknesses in today’s WTCM industry and define research priorities needed for the industry to meet the challenges in wind industry technological evolution and market growth.

Wind turbine condition monitoring

Wind turbine condition monitoring

Editorial Special Issue on Wind Applications–Part 2

The topics of interest for this Special Issue include: wind energy harvesting, modeling and simulation of wind power converters, power electronic converter topologies for wind turbine generator systems, control of power electronic converters for wind turbine generators, condition monitoring, fault diagnosis, and protection for power electronic converters and machines in wind turbine generator systems, power electronics and control for small wind turbine systems in residential applications, synchrophasor applications in wind power generation, wind power grid connection issues, offshore wind power generation, FACTS applications for wind power, power electronics and control for energy storage in wind applications. This Special Issue is organized into two parts. Part 1 was published in the December 2013 issue. Part 2 is in this March 2014 issue.