Availability Of Wind Turbines Research Articles

Integration of Degradation Processes in a Strategic Offshore Wind Farm O&M Simulation Model

Decision support models for offshore wind farm operation and maintenance (O&M) are required to represent the failure behavior of wind turbine components. Detailed degradation modelling is already incorporated in models for specific components and applications. However, component degradation is only one of many effects that must be captured in high-level strategic decision support models that simulate entire wind farms. Thus, for practical applications, a trade-off is needed between detailed degradation modelling and the level of simplicity of input data representation. To this end, this paper discusses two alternative approaches for taking into account component degradation processes in strategic offshore wind farm O&M simulation models: (1) full integration of the degradation process in the O&M simulation model; and (2) loose integration where the degradation process is translated into simplified input to the O&M model. As a proof-of-concept, a Markov process for blade degradation has been considered. Simulations using the NOWIcob O&M model show that the difference between full and loose integration is small in terms of aggregated output parameters such as average wind turbine availability and O&M costs. Although loose integration models some effects less accurately than full integration, the former is more flexible and convenient, and the accuracy is for most purposes sufficient for such O&M models.

Multi-hazard response analysis of a 5MW offshore wind turbine

Wind energy has already dominant role on the scene of the clean energy production. Well-promising markets, like China, India, Korea and Latin America are the fields of expansion for new wind turbines mainly installed in offshore environment, where wind, wave and earthquake loads threat the structural integrity and reliability of these energy infrastructures. Along these lines, a multi-hazard environment was considered herein and the structural performance of a 5 MW offshore wind turbine was assessed through time domain analysis. A fully integrated model of the offshore structure consisting of the blades, the nacelle, the tower and the monopile was developed with the use of an aeroelastic code considering the interaction between the elastic and inertial forces, developed in the structure, as well as the generated aerodynamic and hydrodynamic forces. Based on the analysis results, the dynamic response of the turbine’s tower was found to be severely affected by the earthquake excitations. Moreover, fragility analysis based on acceleration capacity thresholds for the nacelle’s equipment corroborated that the earthquake excitations may adversely affect the reliability and availability of wind turbines.

Multidimensional Tensor-Based Inductive Thermography With Multiple Physical Fields for Offshore Wind Turbine Gear Inspection

Condition monitoring (CM), fault diagnosis (FD), and nondestructive testing (NDT) are currently considered crucial means to increase the reliability and availability of wind turbines. Many research works have focused on CM and FD for different components of wind turbine. Gear is typically used in a wind turbine. There is insufficient space to locate the sensors for long-term monitoring of fatigue state of gear, thus, offline inspection using NDT in both manufacturing and maintenance processes are critically important. This paper proposes an inductive thermography method for gear inspection. The ability to track the properties variation in gear such as electrical conductivity, magnetic permeability, and thermal conductivity has promising potential for the evaluation of material state undertaken by contact fatigue. Conventional thermography characterization methods are built based on single physical field analysis such as heat conduction or in-plane eddy current field. This study develops a physics-based multidimensional spatial-transient-stage tensor model to describe the thermo optical flow pattern for evaluating the contact fatigue damage. A helical gear with different cycles of contact fatigue tests was investigated and the proposed method was verified. It indicates that the proposed methods are effective tool for gear inspection and fatigue evaluation, which is important for early warning and condition-based maintenance.

Availability, operation and maintenance costs of offshore wind turbines with different drive train configurations

AbstractDifferent configurations of gearbox, generator and power converter exist for offshore wind turbines. This paper investigated the performance of four prominent drive train configurations over a range of sites distinguished by their distance to shore. Failure rate data from onshore and offshore wind turbine populations was used where available or systematically estimated where no data was available. This was inputted along with repair resource requirements to an offshore accessibility and operation and maintenance model to calculate availability and operation and maintenance costs for a baseline wind farm consisting of 100 turbines. The results predicted that turbines with a permanent magnet generator and a fully rated power converter will have a higher availability and lower operation and maintenance costs than turbines with doubly fed induction generators. This held true for all sites in this analysis. It was also predicted that in turbines with a permanent magnet generator, the direct drive configuration has the highest availability and lowest operation and maintenance costs followed by the turbines with two‐stage and three‐stage gearboxes. Copyright © 2016 John Wiley & Sons, Ltd.

Economic viability analysis for icing blades detection in wind turbines

Reliability, availability, maintainability and safety (RAMS) of wind turbines in cold climates are closely related to ice accretion. The deterioration of RAMS of the wind turbines involves costs such as Operation and Maintenance costs and energy losses. Systems to monitor the condition of the wind turbines play a key role in the wind energy industry to decrease the costs mentioned above and to improve the maintenance management. This research presents an economic study of the life cycle cost (LCC) for ice condition monitoring systems in wind turbines. In particular, the paper studies the economic feasibility of different commercial ice detection systems through a LCC model when wind turbines are exposed to different scenarios. To date, the scientific literature does not collect any study about the LCC for ice detection systems using different annual rates of return, and providing a map with numerical solution. The study is extended by including a bank loan for a real point of view. The findings of this study reveal the ice detection systems that are more profitable and the selection criteria to decide the use of a bank loan. Finally, it is shown that predictive costs are much smaller than corrective cost reaching a reduction of these corrective costs with the ice detection systems.

Economic evaluation of maintenance strategies for wind turbines: a stochastic analysis

The authors develop a stochastic model for assessing the life-cycle cost and availability of wind turbines resulting from different maintenance scenarios, with the objective to identify the most cost-effective maintenance strategy. Using field-data-based reliability models, the wind turbine – in terms of reliability – is modelled as a serial connection of the most critical components. Both direct cost for spare parts, labour and access to the turbine, as well as indirect cost from production losses are explicitly taken into account. The model is applied to the case of a Vestas V44–600 kW wind turbine. Results of a reliability-centred maintenance analysis of this wind turbine are used to select the most critical wind turbine components and to identify possible maintenance scenarios. This study reveals that corrective maintenance is the most cost-effective maintenance strategy for the gearbox and the generator of the V44 turbine, while the cost benefit of condition-based maintenance using online condition-monitoring systems increases with higher electricity price, turbine capacity and remoteness of sites.

Availability of Different Wind Power Plant Configurations Based on Components Performance Statistics

In this paper analysis of availability of different wind power plant configurations based on components performance statistics will be performed. Influence of different wind turbine components failures using four dominant wind turbine configuration concepts will be investigated. Wind turbine availability and expected energy not served will be presented.

Characteristics for wind energy and wind turbines by considering vertical wind shear

The probability distributions of wind speeds and the availability of wind turbines were investigated by considering the vertical wind shear. Based on the wind speed data at the standard height observed at a wind farm, the power-law process was used to simulate the wind speeds at a hub height of 60 m. The Weibull and Rayleigh distributions were chosen to express the wind speeds at two different heights. The parameters in the model were estimated via the least square (LS) method and the maximum likelihood estimation (MLE) method, respectively. An adjusted MLE approach was also presented for parameter estimation. The main indices of wind energy characteristics were calculated based on observational wind speed data. A case study based on the data of Hexi area, Gansu Province of China was given. The results show that MLE method generally outperforms LS method for parameter estimation, and Weibull distribution is more appropriate to describe the wind speed at the hub height.

Fault Diagnosis of a Wind Turbine Benchmark via Identified Fuzzy Models

In order to improve the availability of wind turbines and to avoid catastrophic consequences, the detection of faults in their earlier occurrence is fundamental. This paper proposes the development of a fault diagnosis scheme relying on identified fuzzy models. The fuzzy theory is exploited since it allows approximating uncertain models and managing noisy data. These fuzzy models, in the form of Takagi-Sugeno prototypes, represent the residual generators used for fault detection and isolation (FDI). A wind turbine benchmark is used to validate the achieved performances of the designed FDI scheme. Finally, extensive comparisons with different fault diagnosis methods highlight the features of the suggested solution.

Multiple Open-Circuit Faults Diagnosis in Back-to-Back Converters of PMSG Drives for Wind Turbine Systems

In order to increase the reliability and availability of wind turbines, condition monitoring and fault diagnosis are considered crucial means to achieve these goals. In this context, direct drives wind turbines based on permanent-magnet synchronous generators (PMSGs) with full-scale power converters are an emerging and promising technology. However, several statistical studies point out that power converters are a significant contributor to the overall failure rate of modern wind turbines. Accordingly, this paper presents a new algorithm for multiple open-circuit faults diagnosis in full-scale back-to-back converters, applied in PMSG drives used for wind turbine systems. The proposed method is based on a Luenberger observer and on an adaptive threshold, which can guarantee a reliable diagnosis independently of the drive operating conditions. Several simulation and experimental results using a PMSG drive with a full-scale converter are presented, showing the diagnostic algorithm effectiveness and robustness against false alarms for both generator- and grid-side converters.

Distribution system feeder reconfiguration considering different model of DG sources

Abstract This work presents a methodology for distribution system feeder reconfiguration considering different model of DGs with an objective of minimizing real power loss. The distributed generation availability of wind turbines, solar photovoltaic panels and fuel cell etc., are classified into different models according to their operation modes and control characteristics. Decimal coded quantum particle swarm optimization (DQPSO) has been applied to solve feeder reconfiguration of DGs. The method applies decimal encoding to quantum particle swarm optimization (QPSO), which can decrease the particle length, generate few infeasible solutions and have better search efficiency. Aiming to the problem that the reactive power output of PV model sometimes exceeds the limit, this paper researches the impact factors of the output reactive power during reconfigurations, such as rated active power and rated voltage magnitude. The method has been tested on IEEE 33-bus and PG&E 69-bus radial distribution systems to demonstrate the performance and effectiveness of the proposed method.

Gear-box fault detection using time-frequency based methods

Gear-box fault monitoring and detection is important for optimization of power generation and availability of wind turbines. The current industrial approach is to use condition monitoring systems, which runs in parallel with the wind turbine control system, using expensive additional sensors. An alternative would be to use the existing measurements which are normally available for the wind turbine control system. The usage of these sensors instead would cut down the cost of the wind turbine by not using additional sensors. One of these available measurements is the generator speed, in which changes in the gear-box resonance frequency can be detected. Two different time–frequency based approaches are presented in this paper. One is a filter based approach and the other is based on a Karhunen–Loeve basis. Both of them detect the gear-box fault with an acceptable detection delay of maximum 100s, which is neglectable compared with the fault developing time.

Active stall control for large offshore horizontal axis wind turbines; a conceptual study considering different actuation methods

The increasing size of Horizontal Axis Wind Turbines and the trend to install wind farms further offshore demand more robust design options. If the pitch system could be eliminated, the availability of Horizontal Axis Wind Turbines should increase. This research investigates the use of active stall control to regulate power production in replacement of the pitch system. A feasibility study is conducted using a blade element momentum code and taking the National Renewable Energy Laboratory 5 MW turbine as baseline case. Considering half of the blade span is equipped with actuators, the required change in the lift coefficient to regulate power was estimated in ΔCl = 0.7. Three actuation technologies are investigated, namely Boundary Layer Transpiration, Trailing Edge Jets and Dielectric Barrier Discharge actuators. Results indicate the authority of the actuators considered is not sufficient to regulate power, since the change in the lift coefficient is not large enough. Active stall control of Horizontal Axis Wind Turbines appears feasible only if the rotor is re-designed from the start to incorporate active-stall devices.

Residual Generator Fuzzy Identification for Wind TurbineBenchmark Fault Diagnosis

In order to improve the availability of wind turbines, thus improving theirefficiency, it is important to detect and isolate faults in their earlier occurrence. The mainproblem of model-based fault diagnosis applied to wind turbines is represented by thesystem complexity, as well as the reliability of the available measurements. In this work, adata-driven strategy relying on fuzzy models is presented, in order to build a fault diagnosissystem. Fuzzy theory jointly with the Frisch identification scheme for errors-in-variablemodels is exploited here, since it allows one to approximate unknown models and manageuncertain data. Moreover, the use of fuzzy models, which are directly identified from thewind turbine measurements, allows the design of the fault detection and isolation module.It is worth noting that, sometimes, the nonlinearity of a wind turbine system could lead toquite complex analytic solutions. However, IF-THEN fuzzy rules provide a simpler solution,important when on-line implementations have to be considered. The wind turbine benchmarkis used to validate the achieved performances of the suggested fault detection and isolationscheme. Finally, comparisons of the proposed methodology with respect to different faultdiagnosis methods serve to highlight the features of the suggested solution.

Side‐band algorithm for automatic wind turbine gearbox fault detection and diagnosis

Improving the availability of wind turbines is critical for minimising the cost of wind energy, especially offshore. The development of reliable and cost-effective gearbox condition monitoring systems (CMSs) is of concern to the wind industry, because the gearbox downtime has a significant effect on the wind turbine availabilities. Timely detection and diagnosis of developing gear defects is essential for minimising an unplanned downtime. One of the main limitations of most current CMSs is the time consuming and costly manual handling of large amounts of monitoring data, therefore automated algorithms would be welcome. This study presents a fault detection algorithm for incorporation into a commercial CMS for automatic gear fault detection and diagnosis. Based on the experimental evidence from the Durham Condition Monitoring Test Rig, a gear condition indicator was proposed to evaluate the gear damage during non-stationary load and speed operating conditions. The performance of the proposed technique was then successfully tested on signals from a full-size wind turbine gearbox that had sustained gear damage, and had been studied in a National Renewable Energy Laboratory's (NREL) programme. The results show that the proposed technique proves efficient and reliable for detecting gear damage. Once implemented into the wind turbine CMSs, this algorithm can automate the data interpretation, thus reducing the quantity of the information that the wind turbine operators must handle.

해상풍력단지 내부그리드의 전력손실비용에 관한 연구

The cross-section area of cable in the Offshore Wind Farm (OWF) is smaller than that in the onshore wind farm. Because the power loss in OWF is large relatively, the power loss is a key element for the economic evaluation of OWF design. The availability of wind turbine in OWF and the size of OWF are larger than those of onshore wind farm. If the economic evaluation of OWF ignores the availability of wind turbines, the power loss cost of OWF is overpriced. Since there are so many wind turbines, also, the calculation of power loss should be more accurate.<BR> In this paper, a method to calculate power loss is proposed for the design of big and complex inner-grid in OWF. The 99.5MW OWF is used for case study to see what effect the proposed method have on the power loss cost.

Extraction of the inherent nature of wind speed using wavelets and FFT

Due to technological advancement, availability of multi-megawatt wind turbines, ease of installation and maintenance, economic compatibility and commercial acceptance, wind power is being used globally for both grid-connected and off-grid applications. The wind power is intermittently available due to the fluctuating nature of the wind and hence needs to be understood well. Its variability was studied in this paper both in time and spatial domain. The present work utilized daily mean values of wind speed from different meteorological stations spread over the Kingdom of Saudi Arabia in conjunction with wavelet transform and fast Fourier transform power spectrum techniques to understand the dynamic nature of the wind at nine stations. The study found that wind speed changed by ±0.6 to ±1.6knots over a long period of about 10years depending on the locations. The long-term mean wind speed of 5.6, 8.9, 6.25, 8.1, 6.0, 7.1, 6.0, 8.6 and 7.3knots was obtained at Abha, Dhahran, Gizan, Guriat, Hail, Jeddah, Riyadh, Turaif and Yanbu, respectively.

The Importance of Control Monitoring Systems in Wind Parks Maintenance

The objective of every wind energy producer is to reduce operational costs associated to the production as a way to increase profits. One other issue that must be looked carefully is the equipment maintenance.Increase the availability of wind turbines by reducing the downtime associated to failures is a good strategy to achieve the main goal of increase profits. As a way to help in the definition of the best maintenance strategies, condition monitoring systems (CMS) have an important role to play. Informatics tools to make the condition monitoring of the wind turbines were developed and are now being installed as a way to help producers reducing the operational costs. There are a lot of developed systems to do the monitoring of a wind turbine or the whole wind park, in this paper will be made an overview of the most important systems.

Economic Evaluation of Maintenance Strategies for Wind Turbines: A Stochastic Analysis

We develop a stochastic model for assessing the life-cycle cost and availability of wind turbines resulting from different maintenance scenarios, with the objective to identify the most cost-effective maintenance strategy. Using field-data based reliability models, the wind turbine – in terms of reliability – is modeled as a serial connection of the most critical components. Both direct cost for spare parts, labor, and access to the turbine, as well as indirect cost from production losses are explicitly taken into account. The model is applied to the case of a Vestas V44–600kW wind turbine. Results of a Reliability-Centered Maintenance (RCM) analysis of this wind turbine are used to select the most critical wind turbine components and to identify possible maintenance scenarios.

Empirical correlation between hub height and local wind shear exponent for different sizes of wind turbines

Abstract The increasing rate of adverse environmental events has made people from all walks of life more aware of the utilization of clean and renewable sources of energy. Technological advancement and the availability of efficient wind turbines of a few tens of kilowatt to multi-megawatt sizes which cover all human applications have made the utilization of wind power the technology of choice. For its optimal utilization, the site-dependent analysis of the wind and its variation with height and the economics of increasing the tower height (hub height) have become necessary factors. This paper proposes a new correlation for the estimation of optimal hub height for harnessing the power of the wind on an economically competitive basis. The optimal hub heights for Dhahran, Dhulom, Gassim, Juaymah and Rawdat Ben Habbas were found to be 64, 66, 81, 70 and 82 m, respectively. Furthermore, seven empirical correlations were developed for seven sites for wind turbines of rated power of 600 to 5000 kW. Wind speed measurements made at 20, 30 and 40 m at seven sites were used in the present work.