Wind Turbine Main Shaft Research Articles

Compensation Algorithm for Wind Turbine Main Shaft Loads Based on LSTM

Abstract For wind turbine development, load size is the core and critical factor. Currently, most companies employ Bladed software for load calculations, which enjoys widespread use in engineering applications due to its efficiency and ease of use. However, constrained by the limitations of blade element theory and momentum theory, there still exist discrepancies between the simulation results and actual conditions. This paper aims to combine simulation algorithms with the application of an LSTM (Long Short-Term Memory) neural network to develop a compensation algorithm for the main shaft loads of wind turbines. By doing so, it endeavors to realize real-time monitoring of the main shaft loads, thereby providing a foundation for achieving high-precision control in wind turbine systems.

Influence of axial clearance on load distribution in double supported tapered roller bearings of wind turbine main shaft

The operational safety and stability of wind turbines are highly determined by the characteristics of main bearings, which are influenced by the axial clearance. In this paper, for the arrangement type of double-supported tapered roller bearings on the wind turbine main shaft, the actual clearance distribution assumption is established, and a new method of calculating the internal load distribution taking into account the axial clearance is proposed. Firstly, the mathematical relationship between the clearance of tapered roller bearings and ring displacement, contact deformation, and load interval is described. Secondly, the load components of main bearings are calculated by force balance equation and load-displacement condition. Finally, a mathematical model of main bearings including axial clearance is established, and it is numerically solved to obtain the internal load distribution of the bearings. The calculation results of a large megawatt wind turbine example show that: the axial load of both main bearings is negatively correlated with the sum of axial clearances; the number of loaded rolling elements is negatively correlated with the sum of axial clearances; and there exists an optimal value of the sum of axial clearances for main bearings to reach the optimal load carrying state.

Wind turbine main shaft crack detection with SCADA generator speed measurement

Preventing failure of structural components is a necessity for safe and economic operation of wind farms. This paper presents a novel detection method of wind turbine main shaft fractures based on data from the turbine SCADA system thus not needing retrofit sensors. The authors developed the crack detection method in the wake of a catastrophic failure on an offshore 3.6 MW wind turbine and applied it across multiple wind farms totalling more than a thousand turbines of the same type, minimising any further risk of failure. The novel method consists of tracking the amplitude of the 2P rotor harmonic in the generator speed and is found to outperform the most common metrics proposed in shaft crack detection literature: Rotor harmonics measured in fore-aft and side-side accelerations and estimates of the drivetrain torsional eigenfrequencies. The generator speed 2P amplitude of the cracked shaft turbine was significantly elevated 16 months before failure while all other benchmark metrics failed to detect the crack. The analysis showed that no other turbine in the fleet were exhibiting similar indications of main shaft cracks and indicated that any such failure would have a long lead time.

Extreme-Low-Speed Heavy Load Bearing Fault Diagnosis by Using Improved RepVGG and Acoustic Emission Signals.

With the worldwide carbon neutralization boom, low-speed heavy load bearings have been widely used in the field of wind power. Bearing failure generates impulses when the rolling element passes the cracked surface of the bearing. Over the past decade, acoustic emission (AE) techniques have been used to detect failure signals. However, the high sampling rates of AE signals make it difficult to design and extract fault features; thus, deep neural network-based approaches have been proposed. In this paper, we proposed an improved RepVGG bearing fault diagnosis technique. The normalized and noise-reduced bearing signals were first converted into Mel frequency cepstrum coefficients (MFCCs) and then inputted into the model. In addition, the exponential moving average method was used to optimize the model and improve its accuracy. Data were extracted from the test bench and wind turbine main shaft bearing. Four damage classes were studied experimentally. The experimental results demonstrated that the improved RepVGG model could be employed for classifying low-speed heavy load bearing states by using MFCCs. Furthermore, the effectiveness of the proposed model was assessed by performing comparisons with existing models.

Compound faults diagnosis method for wind turbine mainshaft bearing with Teager and second-order stochastic resonance

Low rotational speed and heavy load lead to the weak vibration energy and complexity of signals captured on wind turbine mainshaft bearing. Compared with single fault diagnosis, compound faults diagnosis is a challengeable task for the wind turbine mainshaft bearing. To extract fault features accurately, one fault diagnosis method based on Teager energy operator and second-order stochastic resonance (TSSR) is proposed. Firstly, Teager energy operator (TEO) is employed to achieve the purpose of enhancing impact energy in vibration signal. Then, under the assistance of residual noises, second-order stochastic resonance (SSR) is utilized for processed signal to enhance the fault features. Meanwhile, the modified signal-to-ratio (MSNR) index is carried out to select optimal parameters of SSR system automatically. Finally, the fault characteristic frequencies are identified by fast Fourier transform (FFT) spectrums of the SSR output. The test-rig artificial faulty bearing signal and wind turbine mainshaft bearing signal from wind farm are employed to illustrate the superiority and effectiveness of the proposed method. The contribution of the method provides a certain reference for the heavy-load and low-speed bearings fault diagnosis in other fields.

A new method for contact characteristic analysis of the tapered roller bearing in wind turbine main shaft

Premature failures of TRB in wind turbine remain a significant contributor to high operation and maintenance costs. The analysis of contact characteristics is the premise of the TRB failure investigation. In this paper, a novel five degrees of freedom (5DOF) TRB model which considers bearing clearance and preload, is established. Instead of the Newton-Raphson method, the meta-heuristic optimization is adopted to solve the nonlinear system by the L2-norm minimization control. This improvement can intelligently judge the load region of TRB, avoid the selection of initial values and improve the convergence speed. The load distribution results are compared to the simulation results of the finite element model, Romax model and Harris model to verify the effectiveness of the proposed model. Besides, the proposed method has a higher efficiency than the existing methods. Finally, the influences of bearing clearance and preload on the contact characteristic and fatigue life are discussed.

Identification of wind turbine main-shaft torsional loads from high-frequency SCADA (supervisory control and data acquisition) measurements using an inverse-problem approach

Abstract. To assess the structural health and remaining useful life of wind turbines within wind farms, the site-specific structural response and modal parameters of the primary structures are required. In this regard, a novel inverse-problem-based methodology is proposed here to identify the dynamic quantities of the drivetrain main shaft, i.e. torsional displacement and coupled stiffness. As a model-based approach, an inverse problem of a mathematical model concerning the coupled-shaft torsional dynamics with high-frequency SCADA (supervisory control and data acquisition) measurements as input is solved. It involves Tikhonov regularisation to minimise the measurement noise and irregularities on the shaft torsional displacement obtained from measured rotor and generator speed. Subsequently, the regularised torsional displacement along with necessary SCADA measurements is used as an input to the mathematical model, and a model-based system identification method called the collage method is employed to estimate the coupled torsional stiffness. It is also demonstrated that the estimated shaft torsional displacement and coupled stiffness can be used to identify the site-specific main-shaft torsional loads. It is shown that the torsional loads estimated by the proposed methodology is in good agreement with the aeroelastic simulations of the Vestas V52 wind turbine. Upon successful verification, the proposed methodology is applied to the V52 turbine to identify the site-specific main-shaft torsional loads and damage-equivalent load. Since the proposed methodology does not require a design basis or additional measurement sensors, it can be directly applied to wind turbines within a wind farm that possess high-frequency SCADA measurements.

Electromagnetic acoustic transducer for receiving longitudinal wave in the central hole of the wind turbine main shaft

For an operating wind turbine, the main shaft suffers severe structural damage. The surface breaking transverse crack threatens the safety of drive-train system directly. The crack examination method is available by diffracted waves in the central hole. In this research, an electromagnetic acoustic transducer (EMAT) for receiving diffracted longitudinal waves is proposed. Firstly, the converse piezomagnetic stress coefficients and magnetostriction coefficient were derived from the measured magnetic characteristic curve. The measured parameters were provided for sensor simulation. Considering the two coupling mechanisms, a receiving EMAT model was established for coil optimization. Secondly, the influence of materials, lift-off distance and cable type on sensor impedance would be analyzed in detail. Multiple factors were taken into account for impedance matching, and the signal amplitude was improved significantly. The angle divergence of the EMAT was also measured, showing the main lobe with 24°. The crack detection experiments were carried out on a shaft sample. The results show that the developed EMAT can achieve the reception of diffracted longitudinal waves, and the signals are distinguishable. The crack was evaluated simultaneously by the received diffracted waves, and the errors showed less than 3 mm.

Modal analysis and influence law of a wind turbine main shaft

A finite element model was established and modal analysis was performed on a wind turbine main shaft. By adjusting the length of the expansion sleeve, the effect of the length of the expansion sleeve on the natural frequency of the wind turbine shaft was summarized. The results show that the greater the length of the expansion sleeve, the greater the natural frequency of the wind turbine shaft.

Simulation Verification of Phased Array Ultrasonic Detection Scheme for Wind Turbine Main Shaft in Service

The main shaft is the key link in the wind turbine drive. Based on the previous scheme design of phased array ultrasonic testing of wind turbine and the results of transducer parameter range determined, simulation verification is carried out in this study. It is verified that the preliminary theoretical design scheme can effectively detect the early defects of the main shaft shoulder position of the wind turbine, which lays a good foundation for the field implementation in the future.

Transducer and Testing Scheme Design of Phased Array Ultrasonic Detection for Wind Turbine Main Shaft in Service

The wind main shaft is the important component for connecting the hub and gearbox, transmitting axial thrust and rotating torque in a high-power wind turbine. Defects of structural damage occur more often in the main shaft bearing constraints front end surface based on the previous study. New type of phased array ultrasonic testing technology is used for the first time, and the theoretical design is dedicated to the wind main shaft detection of phased array ultrasonic testing customized transducer and scheme. A suitable transducer parameter range and detection scheme are determined well.

Method for evaluation of surface crack size of wind turbine main shaft by using ultrasonic diffracted waves

The structural damage in the main shaft threatens the service safety of the wind turbine directly. The mechanical properties of the in-service main shaft tend to degrade severely due to the transverse cracks extending from the outer circumference. In the health monitoring of the shaft, it is of great importance not only to identify the cracks, but also to accurately evaluate the crack size. In this research, a novel quantitative method is proposed for the transverse crack characterization. The diffracted waves from the crack tip received in the central hole of the shaft are used to construct elliptic trajectories of beam path. The crack position and its depth can be determined by the intersection of the trajectories. Furthermore, a crack size quantification model is established, and the numerical demonstration is given for evaluation of crack position and depth. Meanwhile, an acoustic finite element model is developed, in which the path of the acoustic waves radiated from the end face of the shaft is analyzed in detail. The quantitative method is well confirmed by the simulation of cracks at different locations with different depths. Considering the accuracy of crack evaluation from a large size zone, the time of diffracted echo is calibrated by measuring the time shift of the transducers. A shaft sample with a transverse crack was used to implement the experimental verification. Totally, the sizing error is less than 5 mm, which indicates that this proposed method is effective for the evaluation of surface cracks in the main shaft.

Optimisation design for wind turbine mainshaft bearing based on lubrication reliability

The lubrication of the mainshaft bearing has a great influence on the safe operation of wind turbines. In this paper, an optimal design model of the mainshaft bearing of a wind turbine is established on the lubrication reliability analysis. The maximum rated dynamic load is set as the design objective. The roller number, roller diameter, roller length and wall thicknesses are design parameters. Constraints are formulated mainly based on lubrication reliability and structure consideration. In the lubrication reliability constraint model, the lubrication reliability criterion was determined by solving the minimum film thickness of numerical calculation model of grease EHL. The reliability of bearing lubrication is calculated by Monte Carlo Simulation, and uncertain variables based on sensitivity analysis are selected to improve calculation precision. In the structure constraints, range for the design variables is determined in terms of requirements of geometric structure and strength. Finally, the mainshaft bearing was optimised and analysed by genetic algorithms. The analysis results show that the rated dynamic load of bearing is improved from 1.3e6 N to 2e6 N. Meanwhile the lubrication reliability is improved about 10%. The model presented shows great advantages and practical usefulness in the mainshaft bearing research of wind turbines.

Optimisation design for wind turbine mainshaft bearing based on lubrication reliability

The lubrication of the mainshaft bearing has a great influence on the safe operation of wind turbines. In this paper, an optimal design model of the mainshaft bearing of a wind turbine is established on the lubrication reliability analysis. The maximum rated dynamic load is set as the design objective. The roller number, roller diameter, roller length and wall thicknesses are design parameters. Constraints are formulated mainly based on lubrication reliability and structure consideration. In the lubrication reliability constraint model, the lubrication reliability criterion was determined by solving the minimum film thickness of numerical calculation model of grease EHL. The reliability of bearing lubrication is calculated by Monte Carlo Simulation, and uncertain variables based on sensitivity analysis are selected to improve calculation precision. In the structure constraints, range for the design variables is determined in terms of requirements of geometric structure and strength. Finally, the mainshaft bearing was optimised and analysed by genetic algorithms. The analysis results show that the rated dynamic load of bearing is improved from 1.3e6 N to 2e6 N. Meanwhile the lubrication reliability is improved about 10%. The model presented shows great advantages and practical usefulness in the mainshaft bearing research of wind turbines.

Effect of Rare Earth Ce on the Microstructure and Mechanical Properties of 34CrNiMo6 Steel for Wind Turbine Main Shaft

The effect of rare earth Ce on mechanical properties is studied by investigating the precipitates evolution during heat treatment of 34CrNiMo6 steel. Five different rare earth Ce contents are carried out with the same holding time 3 hours. Then, the mechanical properties of 34CrNiMo6 steel are obtained under steady state conditions and impact conditions, respectively. The strength decreases while the elongation after breakage increases with the rare earth Ce content increasing. The impact absorbing energy at 20°C and −40°C increases with the rare earth Ce content increasing. Based on the experimental results, the recommended rare earth Ce content is 0.05 wt.%. The differences in mechanical properties among the different rare earth Ce contents may be the nucleation rate and growth of precipitates under different conditions. The spherification degree of cementite is more complete with rare earth Ce content, resulting in the decrease of mechanical properties and improvement of ductility.

Influence of Microalloying Element on the Microstructure and Mechanical Properties of 34CrNiMo6 Steel for Wind Turbine Main Shaft

The influence of the microalloying elements of 34CrNiMo6 steel on the microstructure and mechanical properties is investigated in this paper, especially Al and N. Then, the testing of the tensile strength, yield strength, elongation after breakage, and impact absorbing energy under the different conditions is carried out to compare the mechanical properties of materials. Based on the experimental results, the evolutions of mechanical properties with the content of aluminum are obtained. The average grain size test and scanning electron microscope results illustrate that the strengthening mechanism is the pinning effect of aluminum nitride.

Metallurgical quality evaluation of the wind turbine main shaft 42CrMo4 steel: microscopic and Mössbauer studies

Abstract In this paper, the results of the complex examination of the 42CrMo4 steel samples are presented. The samples were taken from the metallurgical forging prepared for the production of the wind turbine main shaft. The samples underwent Mössbauer spectroscopic analysis, as well as the measurement of its mechanical characteristics such as hardness and strength are analysed. Conversion electron Mössbauer spectrometry confirmed phase purity and isotropy of the investigated 42CrMo4 steel. The method provided accurate results, proving Mössbauer spectrometry to be an effective tool for the wind turbine main shaft analysis.

Fracture analysis of wind turbine main shaft

Shaft fracture at an early stage of operation is a common problem for a certain type of wind turbine. To determine the cause of shaft failure a series of experimental tests were conducted to evaluate the chemical composition and mechanical properties. A detail analysis involving macroscopic feature and microstructure analysis of the material of the shaft was also performed to have an in depth knowledge of the cause of fracture. The experimental tests and analysis results show that there are no significant differences in the material property of the main shaft when comparing it with the Standard, EN10083-3:2006. The results show that stress concentration on the shaft surface close to the critical section of the shaft due to rubbing of the annular ring and coupled with high stress concentration caused by the change of inner diameter of the main shaft are the main reasons that result in fracture of the main shaft. In addition, inhomogeneity of the main shaft micro-structure also accelerates up the fracture process of the main shaft. In addition, the theoretical calculation of equivalent stress at the end of the shaft was performed, which demonstrate that cracks can easily occur under the action of impact loads. The contribution of this paper is to provide a reference in fracture analysis of similar main shaft of wind turbines.

Analysis and Calculation of 3MW Wind-Turbine Main Shaft

To find the changing regularity of stress and displacement, a 3MW wind-turbine main shaft was modeled and analyzed at startup time of operation. The results were verified by theoretical calculation. Parametric design of the shaft was used through orthogonal experiment method in which parameters were consisted of structural and load ones. The optimal regression equation, which indicated the relationship between the shaft stress or displacement and the parameters, was given by using polynomial regression with the test results.

Models of Wind-Turbine Main-Shaft Bearings for the Development of Specific Lightning Protection Systems

One of the main cause of damages for wind turbine power plants is certainly constituted by lightning. Direct and indirect events can indeed produce damages and malfunctions of electrical and mechanical components. Concerning mechanical components, blades and bearings are the most involved parts. In particular, lightning-damages produced at bearings positioned at the mechanical interface between rotating parts of the wind turbine, can result in high costs, considering the difficulties involved in the replacement of such components. The paper presents a numerical and an analytical model of wind turbine main shaft bearings aimed at calculate their electrical impedance along with their experimental validation. These models provide useful criteria for the design of wind turbines lightning protection systems (LPS). In this respect, the paper presents also the development of a specific LPS for the protection of wind turbine bearings and the relevant effectiveness analysis obtained by means of experimental tests.