Gearbox condition monitoring in wind turbines: A review

https://spiral.imperial.ac.uk/bitstream/10044/1/55847/5/1-s2.0-S0043164817309535-main.pdf

Prediction of micropitting damage in gear teeth contacts considering the concurrent effects of surface fatigue and mild wear

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.

/pdf/multidimensional-tensor-based-inductive-thermography-with-o2jdjoy7ed.pdf

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

This paper investigates two non-destructive evaluation methods, magnetic flux leakage (MFL) and eddy current pulsed thermography (ECPT), for both artificial and natural multiple cracks (MC) detection and visualization. The detection capability and characteristics of MC visualization are verified and compared through simulations and experiments. Results show that, MFL testing reflects the surface shapes and orientations of MC by 3D magnetic field imaging. However, it is unable to evaluate the depth of artificial MC and detailed surface shapes of natural MC due to limitations of sensor array spatial resolution. ECPT shows more capability in MC visualization in detail from thermal images. The obtained thermal image sequences from ECPT demonstrate rich transient and pattern information to evaluate MC geometrical features. After discussion of the two methods with the probability of detection (POD) analysis, a promising new sensing structure which potentially combines both advantages of them is proposed to enhance the NDE performance for MC evaluation.

Multiple cracks detection and visualization using magnetic flux leakage and eddy current pulsed thermography

The paper describes results obtained from the micro-elastohydrodynamic lubrication (micro-EHL) modeling of the gear tooth contacts used in micropitting tests together with a contact fatigue and damage accumulation analysis of the surfaces involved. Tooth surface profiles were acquired from pairs of helical test gears and micro-EHL simulations were performed corresponding to surfaces that actually came into contact during the meshing cycle. Plane strain fatigue and damage accumulation analysis shows that the predicted damage is concentrated close to the tooth surfaces and this supports the view that micropitting arises from fatigue at the asperity contact level. A comparison of the micropitting performance of gears finish-ground by two alternative processes (generation-grinding and form-grinding) suggests that 3D “waviness” may be an important factor in explaining their different micropitting behavior.

Analysis of Micro-Elastohydrodynamic Lubrication and Prediction of Surface Fatigue Damage in Micropitting Tests on Helical Gears

Experimental and analytical study of gear micropitting initiation and propagation under varying loading conditions

The contact fatigue performance of two pairs of case carburised gears with either an as-ground or superfinished surface finish was studied. This comparison test was carried out using a back-to-back gear test rig. Test results showed that superfinished gears provided an enhanced contact fatigue resistance with only the development of minor scratches and light micropitting after running, while as-ground gears failed through a sequence of initial micropitting, progressive micropitting, macropitting and scuffing.

The Effect of Superfinishing on the Contact Fatigue of Case Carburised Gears

This study investigates the probabilistic risk of gear tooth flank micro-pitting in wind turbine (WT) gearboxes and shows how relatively slow rate of supervisory control and data acquisition (SCADA) data, recorded during operation, can be used to analyse the onset of gear surface damage. Field measured time series of SCADA signals, including wind speed, generator power and rotational speed, were used to obtain the statistical variation of gear shaft torque and rotational speed. From the SCADA data obtained over a 2.2 year period random number datasets of smaller sizes were selected. Based on these random number datasets the effect of gear shaft torque and rotational speed variations on the probabilistic risk of gear micro-pitting was investigated. Determinations of the gear tooth flank contact stress and lubricant film thickness were based on the technical report of gear micro-pitting, ISO/TR 15144-1 (2010). The study has shown that the considered pinion gear is subjected to high load conditions resulting in high contact stresses. The variation of rotational speed causes greater sliding between the gear teeth. The results of specific lubricant film thicknesses have shown that there is considerable risk of gear micro-pitting under the operational conditions recorded from the SCADA field data.

Probabilistic analysis of gear flank micro-pitting risk in wind turbine gearbox using supervisory control and data acquisition data

The pulsed eddy current (PEC) technique generates responses over a wide range of frequencies, containing more spectral coverage than traditional eddy current inspection. Eddy current pulsed thermography (ECPT), a newly developed non-destructive testing (NDT) technique, has advantages such as rapid inspection of a large area within a short time, high spatial resolution, high sensitivity and stand-off measurement distance. This paper investigates ECPT for the evaluation of gear fatigue tests. The paper proposes a statistical method based on single channel blind source separation to extract details of gear fatigue. The discussion of transient thermal distribution and patterns of fatigue contact surfaces as well as the non-contact surfaces have been reported. In addition, the measurement for gears with different cycles of fatigue tests by ECPTand the comparison results between ECPT with magnetic Barkhausen noise (MBN) have been evaluated. The comparison shows the competitive capability of ECPT in fatigue evaluation.

Jishan Zhang

Papers

Analysis of Micro-Elastohydrodynamic Lubrication and Prediction of Surface Fatigue Damage in Micropitting Tests on Helical Gears

Experimental and analytical study of gear micropitting initiation and propagation under varying loading conditions

The Effect of Superfinishing on the Contact Fatigue of Case Carburised Gears

Probabilistic analysis of gear flank micro-pitting risk in wind turbine gearbox using supervisory control and data acquisition data

Eddy current pulsed thermography for fatigue evaluation of gear